Synthesis and Characterization of Nanocrystalline NiO-GDC via sodium alginate-

mediated ionic sol gel method

Shaghayegh Pezeshkpour1 Babak Salamatinia1 Bahman Horri Amini12

1Discipline of Chemical Engineering School of Engineering Monash University Malaysia

Jalan Lagoon Selatan Bandar Sunway 47500 Subang Jaya Selangor Malaysia

2 Department of Chemical amp Process Engineering Faculty of Engineering and Physical

Sciences University of Surrey Surrey GU2 7XH United Kingdom

Corresponding Authors

Tel +60355146249 Fax _60355146207 (B Salamatinia)

Email babaksalamatiniamonashedu

Tel 01483 68 9846 (B Amini Horri)

Email baminihorrisurreyacuk

ABSTRACT

In this study nanocrystalline nickel oxide gadolinium-doped ceria (NiO-GDC) powder was

synthesized using an ionic sol-gel method The effects of calcination time and temperature on

the particle size and the physiochemical properties of nanocrystalline NiO-GDC are

presented in this paper Using this method gel beads were formed by contacting sodium

alginate solution as the gelling template and metal (gadoliniumceriumNi) nitrates as the

precursor The obtained nanocrystallites were characterized using Field Emission Scanning

Electron Microscopy powder X-ray diffraction energy dispersive X-ray spectroscopy

thermo gravimetric analysis nitrogen adsorptiondesorption analysis and Fourier transform

infrared spectroscopy It was observed that the increasing calcination temperature had

affected both the particle size and the surface area of the NiO-GDC whereas the increasing

calcination time had only impacted the size of the particles The smallest mesoporous

nanocrystalline NiO-GDC powder (121225 plusmn 0005 m2g surface area) composed of cubic

GDC (518 nm crystallite size) and cubic NiO (799 nm crystallite size) were synthesized at a

calcination temperature of 500 degC for 2 hours This study hopes to inspire more researches on

the ionic-gelation method for synthesizing other metal nanostructures as well as other

reaction parameters

Key words Sol-gel Nanocrystals Ion-exchange NiO-GDC

1 Introduction

The development of synthesing methods of nanocrystalline metal oxides has got

attention because of their properties such as porosity morphology crystallinity and doping

[1] Also their applications in different fields such as catalyst separation technology solid

oxide fuel cells as well as electrochemical devices and sensors make them high demand in

industry and high-tech usage [2-6] Between different nanocrystalline matal oxides the

intrest in synthesing NiO particles and its compounds is more because of their high physico-

chemical activity in different applications such as magnetic mateials [7] catalyst [8] ceramet

anod for solid oxid fuel cell [9] and gas sensors [10] Also another advantage of NiO

nanocrystals is the ability of sintering at low temperature to high density due to high surface

area and show high fracture toughness [11] Recently usage of nanocrystalline ceramic

materials such as NiO-GDC for anode of SOFCs have received more attention because of

presenting better returns or possess unique properties compared to the traditional ceramic

materials [12] So it is very important to synthesiz nanocrystals of NiO-GDC in an

enviromentaly friendly way A novel sol gel method has been used to synthesized

nanocrystals of NiO-GDC metal oxides using sodium alginate as templing agents for the first

time in current study

To date numerous methods have been proposed for synthesizing nanocrystalline NiO-

GDC powders such as using the polymeric organic complex solution method [13]

combustion method [14] mechanical mixing method [15] co-precipitation [16 17] glycine

nitrate process [18] and the physical mixing of metallic-ceramic constituents with ball

milling [19] The mechanical mixing of different constituent phases is a common technique

for producing NiO-GDC anode powders However the non-uniformity in the distribution of

elements is the main drawback of this method which often results in nonhomogeneous

structures and poor electrical performance of the SOFC anode Polymeric organic complex

solution method comprises of four heat treatment steps which is complicated and would

produce larger sized NiO-GDC nanocrystals [16] Combustion method is one of the simplest

ways to synthesize nanocrystalline NiO-GDC powders but particle agglomeration and phase

impurities are the main limitations of this method [20 21] Another popular but lengthy

technique for synthesizing NiO-GDC is via co-precipitation with several consecutive steps

using basic or acidic precipitating agents such as sodium hydroxide ammonium hydroxide

and oxalic acid [22] Nonetheless more work are needed to develop a simple efficient

environmentally-friendly and low cost method that would be able to produce homogeneous

mixed constituent phases that support the improved sintering properties for longer operational

durability and less degradation [23-25]

Recently biopolymers such as polysaccharides have been widely used as templating

agents for synthesizing nanocomposite powders due to their ability to control the size and

shape of particles with minimum hazardous wastes [26 27] Sodium alginate is a water

soluble non-toxic and biodegradable ldquogreenrdquo polysaccharide with (1-4)-linked β-D-

mannuronate (M) and C-5 epimer α-L-guluronate (G) blocks covalently linked together

which can be jellified when in contact with a solution containing transitional metal ions

Gelation of sodium alginate in an aqueous solution occurs because of the interaction between

the carboxylate groups in the sodium alginate structure and the multivalent metal cations

through a mechanism known as the ldquoegg boxrdquo model [11 28] The alginate gel structure

prevents the metal ions from getting close to each other which would result in a controlled

structural growth and consequently increases the likelihood of creating smaller sized

nanocomposite powders [29] In the last few years there has been a growing interest in the

application of sodium alginate to synthesize different nanoparticles such as Co Ni Ag NiO

and CoNi [11 29-31] An extensive study has been done on GDC nanocomposites as the

electrolyte part for low-temperature SOFCs [6] The same research team had also conducted a

preliminary study on synthesizing NiO-GDC which showed the potential of using this

method to produce nanocomposites of these metals [32] However the conditions were not

fully elaborated and there is still a lack of comprehensive study on this method and the

characterization of the synthesized material

This current study was focused on elaborating the effect of calcination temperature and

time on the synthesis of a high-purity nanocrystalline NiO-GDC (NiOCe08Gd02O190) powder

via the ionic-gelation of sodium alginate The nanocrystalline NiO-GDC obtained in this

study was characterized using thermal analysis (TGADSC) X-ray diffraction (XRD) Field

Emission Scanning Electron Microscopy (FESEM) Energy-dispersive x-ray spectroscopy

(EDX) Fourier transform infrared spectroscopy (FTIR) and nitrogen adsorption-desorption

(BET) This research investigated a new environmentally friendly method for synthesizing

pure NiO-GDC Detailed findings regarding the influence of dominant synthesizing variables

on the physiochemical properties of the nanocrystalline NiO-GDC powders are reported in

the following sections

2 Materials and Methods

21 Materials

Cerium (III) nitrate hexahydrate (Ce (NO3)36H2O 99 purity) and gadolinium (III)

nitrate hexahydrate (Gd(NO3)36H2O 999 purity) from Sigma Aldrich USA and

nickel(II) nitrate hexahydrate (Ni(NO3)26H2O 99 purity) from Merck Germany were used

as the starting materials without any further purification in this study Additionally Manugel

GHB sodium alginate powder ((C6H7NaO6)n MW 264 kDa) with an MG ratio of 059

obtained from BioPolymer UK was used as the gelling template

22 Synthesis of nanocrystalline NiO-GDC powders

A cationic solution with a total concentration of 30 gL was prepared by dissolving the

calculated amounts of each metal nitrate salt (Ce(NO3)36H2O) (Gd(NO3)36H2O) and

(Ni(NO3)26H2O) into ultra-pure water Sodium alginate solution at 3 wt was prepared by

dissolving the appropriate amount of sodium alginate (Na-Alg) powder into ultra-pure water

using a water-bath at 80 degC

Alginate beads with a diameter of approximately 2 mm before drying (Figure 1a) and 1

mm after drying (Figure 1b) were produced by dripping the Na-Alg solution into a

homogeneous metal nitrate solution using a 06 mm needle with a 20 mm internal diameter

syringe at a rate of 07 mLmin The alginate solution that dripped into the nitrate solution

had rapidly formed beads

Then the as-prepared beads were gently stirred in the nitrate solution for 24 h at a

stirring rate of 100 rpm to increase the ion-exchange reaction between Na+ (in the alginate

structure) and Ce3+ Gd3+ and Ni2+ (in the salt solution) at room temperature After 24 h the

beads were filtered and washed with 45 mL of ultra-pure water to remove any sodium nitrate

trapped in the gel structure Next the beads were dried in a Memmert oven (model UF110)

for 24 h at 50 ordmC All dropped beads were well distributed without any agglomeration (Figure

1a) Figure 1b shows the greenish coloured beads after drying at 50 degC in the oven for 24

hours which were approximately 1 mm in size Finally the dried bead sample underwent

calcination at different temperatures (500 degC 600 degC and 700 degC) for different durations (2

h 6 h and 10 h) with a fixed ramp rate of 2 degCmin Table 1 presents the combinations of

calcination times and calcination temperatures used in each experimental run The calcined

powders were ground with mortar and pestle to break the agglomerated particles

23 Characterization

Thermogravimetric analysis (TGA Q50 from TA Instruments USA) was used to

study the thermal decomposition behaviour of the dried gels and the calcined samples in air

between 25 degC and 800 degC with an increasing ramp rate of 5 degC minute X-ray powder

diffraction was performed using an XRD diffractometer (D8 Discover from Bruker

Germany) with CuKα1 radiation (λ = 154060Aring) in the 2θ range between 10deg and 90deg and a

scanning rate of 002 degs using the Bragg-Brentano beam method at 40 kV and 40 mA All

XRD patterns were indexed using ICDD file no 00-50-0201 and 00-002101216 for GDC and

NiO crystals respectively The crystallite sizes of the NiO and GDC nanocrystallites were

calculated using Scherrer equation D=09 λ βcosθ where D is the crystallite size (nm) λ is

the wavelength of the source (nm) β is the full width at half maximum (FWHM) of the peak

and θ is the Bragg angle (radians) The morphology of NiO-GDC nanocrystallite was

analysed using the micrograph images obtained from a Field Emission Scanning Electron

Microscopy (FESEM SU8010 Hitachi Japan) All FESEM specimens were coated with

platinum for 120 seconds with a sputter current at 30 mA using a coater (Quarum Q150R S)

prior to the analysis Energy-dispersive x-ray (Oxford Horiba Inca XMax50 EDX) analysis

was performed to confirm the presence of cerium gadolinium and oxygen atoms in all

samples The FTIR spectra of the calcined and the dried powders were obtained using a

Fourier transform infrared spectrometer (FTIR NICOLET 1810 USA) over the

wavenumber range of 650ndash4000 cm-1 The surface area of the calcined samples was measured

by a BET analyser (Micromeritics ASAP 2020 USA)

3 Results and Discussion

The results for the thermogravimetric analysis (TGADTA) of the dried and calcined

sample at 700 degC for 2 h are shown as the representative sample in Figure 2 Four weight loss

steps corresponding to room temperature 25 degC plusmn1 degC to 186 degC 186 degC to 301 degC 301 degC to

380 degC and 380 degC to 500 degC were observed for the dried sample (Figure 2a) The

decomposition steps in the TGA curves were found to be in good agreement with the DTA

curves represented in Figure 2a A weight loss of 1146 plusmn 010 was observed during the

first step (25 degC ndash 186 degC) that corresponded to the evaporation of water in the alginate

structure during heat treatment In the second step (186 degC - 301 degC) a weight loss of 3641plusmn

015 was detected that could be due to the cleavage of G-G G-M and M-M weaker

linkages in the alginate molecule causing considerable oxygen evolution Wang et al[11]

also reported similar results for the weight loss of alginate in the same temperature range for

the dried sample of NiO nanopowders with sodium alginate When the operational

temperature was increased from 301 to 380 degC during the third step further decomposition

occurred which resulted in approximately 57 plusmn 0075 of weight loss in the TGA profile

This can be attributed to the decomposition of metastable-NiO2 to thermodynamically more

stable NiO phase which is demonstrated as a small exothermic peak [11] During the fourth

step the temperature was further increased from 380 degC to around 500 degC The residues of b-

D-mannuronic acid (M) and a-L-guluronic acid (G) in the alginate structure were completely

oxidised as observed from the 1924 plusmn 0075 weight loss that resulted in an exothermic

decomposition peak Previous studies offered similar reasoning for the final decomposition

step [27] No further weight loss was observed at temperatures of higher than 500 degC Figure

2a shows that the decomposition process could be completed at 500 degC

The TGADTA plot for the sample that was calcined at 700 degC for 2 hours is shown in

Figure 2b Three major weight losses were visible in the plot The first weight loss of 018 plusmn

001 occurred between room temperature and approximately 48 degC and was due to water

evaporation which was confirmed by the small endothermic peak in the DTA curve During

the second step (75-91 degC) a weight loss of 194 plusmn 001 was observed due to organic

components that still remained after calcination [33] The third weight loss of 177plusmn 001

was observed between 93-406 degC which corresponded to the decomposition of Ni(OH)2 to

NiO Ce(OH)3 to CeO2 and Gd(OH)3 to Gd2O3 [33] No further weight loss was observed at

temperature of higher than 400 degC which indicated the absence of carbonaceous bonds or

any other undecomposed residue in the sample

The FESEM images for the NiO-GDC nanocrystallites synthesized with 3 loading

fractions of sodium alginate at 500 degC 600 degC and 700 degC calcination temperature with

different calcination time are displayed in Figures 3 4 and 5 respectively ImageJ software

was used to quantitatively analyse the FESEM images [34 35] First a binary image was

extracted by carefully performing intensity-thresholding on the original FESEM image

Using erosion and dilation irregular shapes were removed The remaining particles were

morphologically closed and smoothened by applying a Gaussian blur The resultant binary

images which contained particles in the form of blobs were passed to the analysis module

for an automatic measurement of the particle size The particle size distribution for each

image has been embedded at its top-right corner where micro denotes the average particle size

with the standard deviation and Ɲ denotes the number of particles utilized in the analysis

As seen in Figures 3 4 and 5 the particle size had slowly increased when the

calcination temperature was increased from 500 to 700 degC at a constant calcination time

These results could be linked to the agglomeration of the particles caused by several

phenomena such as lsquouncontrolled build-uprsquo lsquobridgingrsquo or lsquolumpingrsquo during the thermal

treatment process (refer Figures 3a 4a and 5a) [36] It was also observed that at a constant

calcination temperature the size of the nanocrystallites had increased due to the

agglomeration of smaller particles when the calcination time was increased from 2 h to 10 h

(refer Figures 4a 4b and 4c) Thus the agglomeration of smaller particles can be

manipulated by determining the optimum calcination temperature and duration to obtain

specific particle sizes In each series of images 3a 3b and 3c 4a 4b and 4c and 5a

5b and5c this trend can be seen for all calcination times and calcination temperatures

The results showed that the smallest particle size (641 nm) was obtained with

calcination conditions of 500 degC for 2 h (641 nm) The largest particle size of 2125 nm was

obtained at 700 degC after 10 h of calcination These results were in agreement with the

previous discussion In conclusion for synthesizing smaller nanocrystalline NiO-GDC lower

calcination temperature (500 degC) and shorter calcination time (2 h) is needed

The EDX elemental analysis and mapping is shown in Figure 6 for nancrystalline NiO-

GDC synthesized at 500 degC for 6 h which confirmed the presence of cerium gadolinium

oxygen and nickel atoms The sample shown in Figure 6 was chosen as an example to

represent all the samples that were elaborated in this study

X-ray diffraction (XRD) patterns of the nanocrystalline NiO-GDC powders synthesized

at different calcination times and temperatures are shown in Figure 7 The peaks for all

samples were well matched with the cubic Ce08Gd02O19 (Fm-3m ICDD00-50-0201) and

cubic NiO (Fm-3m ICDD 00-002101216) The average crystallite sizes of these particles

were determined using the Scherrer equation as listed in Table 2 The crystallite sizes of NiO

and GDC in NiO-GDC have been reported by several studies that used different methods

such as polymeric sol-gel (with NiO at 24 nm and GDC at 18 nm) [37] hydroxide co-

precipitation method (NiO at 305 nm and GDC at 273 nm) [17] solution combustion

synthesis (NiO at 30-58 nm and GDC at 40-50 nm) [38] micro emulsion method (NiO at

132 148 and 134 nm and GDC at 117 137 and 106 nm) as well as microemulsion-

mediated solvothermal process (NiO at 22 plusmn 2 nm and GDC at 20 plusmn 2 nm) These studies

have shown that ion-gelation synthesis can successfully synthesize smaller sized NiO-GDC

nanocomposites

The XRD patterns have shown that the diffraction peaks for GDC and NiO crystal

phases became sharper when calcination temperature was increased from 500 to 700 degC at

constant calcination time as well as when calcination time was increased from 2 h to 10 h at a

constant calcination temperature which indicated the growth in the crystallite size (Table 1)

due to particle agglomeration [36] At lower calcination temperature (500 degC) with different

calcination times (2 6 and 10 h) the broader peaks in an XRD pattern show the existence of

smaller-sized NiO and GDC crystallites for all samples [39] In this study the XRD pattern

(Figure 7) was in agreement with crystallite size tabulated in Table 2

The calculated crystallite sizes using the Scherrer equation (Table 2) supported the

results from the XRD patterns which indicated that by increasing the calcination time and

temperature the crystallite sizes of NiO and GDC were increased as well The calculated

crystallite sizes of NiO and GDC in Table 2 were in good agreement with the results attained

from the quantitative image analysis reported in Figure 3 Figure 4 and Figure 5 which

confirmed the influences of both the calcination temperature and calcination time on the size

of the powder particles

Figure 8 shows the FTIR spectra for the dried gel and the calcined samples at different

calcination temperatures and times The FTIR spectrum for the dried sample showed

numerous adsorption bands in the 800-1610 cm-1 region The peaks at 884 cm-1 could be

attributed to the C-C band for sodium alginate [40] Meanwhile the band at 1026 cm-1 (C-O-

C stretching) corresponded to sodium alginate glycosidic linkage [41] Additionally the

stretch at 3355 cm-1 and the absorption peaks at 1600 to 1414 cm-1 corresponded to O-H band

and the asymmetric and symmetric stretching vibration of the carboxylate group respectively

[42] After the dried sample had undergone thermal treatment at different calcination times

and temperatures a reduction in the intensity of carbon bands was observed which

confirmed the effectiveness of the calcination process in completing the thermal

decomposition of the biopolymer compound However further increase in the calcination

temperature and calcination time had led to a reduction in the intensity of the peaks This

condition showed that these samples had attained more purity in their metal oxide

compositions The absorption band for metal-oxygen has been reported by various studies

such as (Ce-OGd-ONi-O) was detected at approximately 635 cm-1 [33] (Ce-O) was

observed at 564 cm-1 while the 550-700 cm-1 region was assigned to NiO stretching vibration

[43-45] However due to the presence of noise at lower than 650 cm -1 the measuring range

utilized in these current experiments was between 650 cm-1 to 4000 cm-1

The BET analysis was conducted by applying the Barrett-Joyner-Halenda (BJH)

method to study the physicochemical properties of the calcined NiO-GDC at different

calcination times and temperatures Based on literature review there is a lack of information

on BET analysis of NiO-GDC and thus more in-depth studies are needed in this area The

nitrogen adsorption-desorption isotherms (hysteresis loops) of the NiO-GDC are given in

Figure 9 with the pore size distribution of the different samples in the inset The nitrogen

adsorption-desorption isotherms (Figure 9) indicated the presence of mesopores in the

samples based on the type IV isotherm as per IUPAC classification The mesopores were

formed due to the capillary condensation of the mesoporous materials thus confirming the

mesoporosity of the synthesized NiO-GDC nanocrystallites [46] The hysteresis loops of the

samples in the pp0 range of 04-10 illustrated the absence of micropores and that the pores

had changed into the mesoporous reign [46] The pore size distributions of the samples are

given in the inset of Figure 9 The majority of the NiO-GDC samples were in the mesoporous

region (10 nm) as determined by the BJH method which supported the N2 adsorption-

desorption isotherms

It can be observed from Figure 9 that for samples calcined at 500 degC for 2 h 6 h and 10 h the

relative pressure (corresponding to the onset of capillary condensation) has a higher value

which indicated the presence of the smaller pore size distribution for that sample [47]

The BET surface areas for all samples are summarized in Table 3 It can be seen that

at a specific calcination temperature increasing the calcination time from 2 h to 10 h had

caused the surface area of the sample to decrease due to the increasing particle size

Similarly by increasing the calcination temperature from 500 degC to 700 degC the surface areas

of the samples had decreased due to the increasing particle sizes The largest surface areas

corresponded to the nanocrystallite samples calcined at 500 degC for 2 h However these values

had reduced when the calcination temperature and time were gradually increased to 700 degC

and 10 h respectively These results are in good agreement with the particle sizes obtained

from the FESEM and XRD results

4 Conclusion

Nanocrytalline NiO-GDC powders were synthesized using an environmentally

friendly ionic gelation method with sodium alginate as the precursor The effects of the

synthesis parameters such as calcination temperature and calcination time on the properties

of the produced nanocrystalline NiO-GDC powders were studied using various

characterization techniques It was found that at a fixed calcination temperature the size of

the nanocrystals would increase with increasing calcination time Similarly at a fixed

calcination time and increasing calcination temperature larger nanocrystals were produced

Therefore for synthesizing smaller nanocrystals lower calcination temperature (500 degC) and

shorter calcination time (2 h) are recommended It was also observed that calcination

temperature has more effect on the BET surface compared to calcination time which showed

that the pore size of the nanocrystalline powders was more dependent on the calcination

temperature

5 Acknowledgement

The authors would like to acknowledge the Ministry of Science Education and Innovation

(MOSTI) of Malaysia for providing research funding under the e-science scheme grant

number 03-02-10-SF0259

References

1 Boury B and S Plumejeau Metal oxides and polysaccharides an efficient hybrid association for materials chemistry Green Chemistry 2015 17(1) p 72-88

2 Bell AT The impact of nanoscience on heterogeneous catalysis Science 2003 299(5613) p 1688-1691

3 Zhao X et al The role of nanomaterials in redox-based supercapacitors for next generation energy storage devices Nanoscale 2011 3(3) p 839-855

4 Sun Y-F et al Metal oxide nanostructures and their gas sensing properties a review Sensors 2012 12(3) p 2610-2631

5 Jia J et al Heterogeneous catalytic hydrogenation of CO 2 by metal oxides defect engineeringndashperfecting imperfection Chemical Society Reviews 2017 46(15) p 4631-4644

6 Pezeshkpour S et al Ionicndashgelation synthesis of gadolinium doped ceria (Ce 08 Gd 02 O 190) nanocomposite powder using sodium-alginate Ceramics International 2017 43(9) p 7123-7135

7 Atif M et al Studies on the magnetic magnetostrictive and electrical properties of solndashgel synthesized Zn doped nickel ferrite Journal of Alloys and Compounds 2011 509(18) p 5720-5724

8 Krstajić N et al Non-noble metal composite cathodes for hydrogen evolution Part I the NindashMoO x coatings electrodeposited from Wattrsquos type bath containing MoO 3 powder particles international journal of hydrogen energy 2011 36(11) p 6441-6449

9 Macedo DA et al NindashCGO cermet anodes from nanocomposite powders Microstructural and electrochemical assessment Ceramics International 2014 40(8) p 13105-13113

10 Gao H et al The design of excellent xylene gas sensor using Sn-doped NiO hierarchical nanostructure Sensors and Actuators B Chemical 2017 253 p 1152-1162

11 Wang Z GM Kale and M Ghadiri Novel Ion‐Exchange Process for the Preparation of Metal Oxide Nanopowders from Sodium Alginate Journal of the American Ceramic Society 2012 95(10) p 3124-3129

12 Galeano MAacuteN et al Studies on the structural quantitative and semi-quantitative analyses of NiOndashGDC nanocomposites RSC Advances 2016 6(77) p 72865-72876

13 Gil V C Moure and J Tartaj Sinterability microstructures and electrical properties of NiGd-doped ceria cermets used as anode materials for SOFCs Journal of the European Ceramic Society 2007 27(13) p 4205-4209

14 Akbari-Fakhrabadi A et al Combustion synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite anode and its electrical characteristics of semi-cell configured SOFC assembly Journal of Alloys and Compounds 2012 541 p 1-5

15 Ishihara T et al NickelndashGd-doped CeO 2 cermet anode for intermediate temperature operating solid oxide fuel cells using LaGaO 3-based perovskite electrolyte Solid State Ionics 2000 132(3) p 209-216

16 Ding C et al A comparative study of NiOndashCe 09 Gd 01 O 195 nanocomposite powders synthesized by hydroxide and oxalate co-precipitation methods Ceramics International 2012 38(1) p 85-92

17 Ding C et al Synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite powders for low-temperature solid oxide fuel cell anodes by co-precipitation Scripta Materialia 2009 60(4) p 254-256

18 Park S-Y et al Preparation of highly porous NiOndashgadolinium-doped ceria nano-composite powders by one-pot glycine nitrate process for anode-supported tubular solid oxide fuel cells Journal of Asian Ceramic Societies 2014 2(4) p 339-346

19 Zhu W and S Deevi A review on the status of anode materials for solid oxide fuel cells Materials Science and Engineering A 2003 362(1) p 228-239

20 Chick LA et al Glycine-nitrate combustion synthesis of oxide ceramic powders Materials Letters 1990 10(1-2) p 6-12

21 Basu RN et al Microstructure and electrical conductivity of LaNi 06 Fe 04 O 3 prepared by combustion synthesis routes Materials Research Bulletin 2004 39(9) p 1335-1345

22 SOFC ZS Microstructure development of the Ni-GDC anode material for IT-SOFC Materiali in tehnologije 2012 46(5) p 445-451

23 Aparicio M A Jitianu and LC Klein Sol-Gel Processing for Conventional and Alternative Energy 2012 Springer Science amp Business Media

24 Suciu C et al NiOYSZ nanoparticles obtained by new solndashgel route Chemical Engineering Journal 2008 140(1) p 586-592

25 Jiang SP and SH Chan A review of anode materials development in solid oxide fuel cells Journal of Materials Science 2004 39(14) p 4405-4439

26 Iyer A et al A Sucrose‐Mediated SolndashGel Technique for the Synthesis of MgOndashY2O3 Nanocomposites Journal of the American Ceramic Society 2013 96(2) p 346-350

27 Wang Z et al Ion-exchange kinetics and thermal decomposition characteristics of Fe2+-exchanged alginic acid membrane for the formation of iron oxide nanoparticles Journal of Materials Science 2014 49(20) p 7151-7155

28 Schnepp Z et al Alginate-mediated routes to the selective synthesis of complex metal oxide nanostructures CrystEngComm 2010 12(5) p 1410-1415

29 Wang Z GM Kale and M Ghadiri Synthesis and characterization of CexGd 1minus xO 2minus δ nanopowders employing an alginate mediated ion-exchange process Chemical Engineering Journal 2012 198 p 149-153

30 Brayner R et al Alginate-mediated growth of Co Ni and CoNi nanoparticles influence of the biopolymer structure Chemistry of Materials 2007 19(5) p 1190-1198

31 Balavandy SK K Shameli and ZZ Abidin Rapid and Green Synthesis of Silver Nanoparticles via Sodium Alginate Media Int J Electrochem Sci 2015 10 p 486-497

32 Choo CK BA Horri and B Salamatinia Synthesis and Characterization of Nickel (II) OxideGadolinium-Doped Ceria (NiOGDC) Nanocomposites As a Potential Material for Anode Supported LT-SOFCs in Proceedings of the World Congress on Engineering and Computer Science 2016

33 Rath MK M-J Lee and K-T Lee Preparation of nano-structured NindashCe 08 Gd 02 O 19 anode materials for solid oxide fuel cells via the water-in-oil (WO) micro-emulsion route Ceramics International 2014 40(1) p 1909-1917

34 Schneider CA WS Rasband and KW Eliceiri NIH Image to ImageJ 25 years of image analysis Nature methods 2012 9(7) p 671-675

35 Collins T ImageJ for Microscopy BioTechniques 43 S25-S30 httpdx doi org102144000112517 2007

36 Thierry R F Thierry and G Osenga Surface energy modified particles method of making and use thereof 2015 Google Patents

37 Macedo DA et al A versatile route for the preparation of NindashCGO cermets from nanocomposite powders Ceramics International 2013 39(4) p 4321-4328

38 Wandekar R et al Physicochemical studies of NiOndashGDC composites Materials Chemistry and Physics 2006 99(2) p 289-294

39 Prakash BS VW Grips and S Aruna A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes Journal of Power Sources 2012 214 p 358-364

40 Sartori C et al Determination of the cation content of alginate thin films by FTi r spectroscopy Polymer 1997 38(1) p 43-51

41 Lakouraj MM F Mojerlou and EN Zare Nanogel and superparamagnetic nanocomposite based on sodium alginate for sorption of heavy metal ions Carbohydrate polymers 2014 106 p 34-41

42 Srivastava M et al Synthesis of superparamagnetic bare Fe 3 O 4 nanostructures and coreshell (Fe 3 O 4alginate) nanocomposites Carbohydrate polymers 2012 89(3) p 821-829

43 Chavan A et al Effect of variation of NiO on properties of NiOGDC (gadolinium doped ceria) nano-composites Ceramics International 2012 38(4) p 3191-3196

44 Shen C and LL Shaw FTIR analysis of the hydrolysis rate in the solndashgel formation of gadolinia-doped ceria with acetylacetonate precursors Journal of sol-gel science and technology 2010 53(3) p 571-577

45 Wang T and D-C Sun Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method Materials Research Bulletin 2008 43(7) p 1754-1760

46 Sing KS Reporting physisorption data for gassolid systems with special reference to the determination of surface area and porosity (Recommendations 1984) Pure and applied chemistry 1985 57(4) p 603-619

47 Song X et al Synthesis and Characterization of Y-Doped Mesoporous CeO 2 Using A Chemical Precipitation Method Journal of Rare Earths 2007 25(4) p 428-433

calcination temperature of 500 degC for 2 hours This study hopes to inspire more researches on

the ionic-gelation method for synthesizing other metal nanostructures as well as other

reaction parameters

Key words Sol-gel Nanocrystals Ion-exchange NiO-GDC

1 Introduction

The development of synthesing methods of nanocrystalline metal oxides has got

attention because of their properties such as porosity morphology crystallinity and doping

[1] Also their applications in different fields such as catalyst separation technology solid

oxide fuel cells as well as electrochemical devices and sensors make them high demand in

industry and high-tech usage [2-6] Between different nanocrystalline matal oxides the

intrest in synthesing NiO particles and its compounds is more because of their high physico-

chemical activity in different applications such as magnetic mateials [7] catalyst [8] ceramet

anod for solid oxid fuel cell [9] and gas sensors [10] Also another advantage of NiO

nanocrystals is the ability of sintering at low temperature to high density due to high surface

area and show high fracture toughness [11] Recently usage of nanocrystalline ceramic

materials such as NiO-GDC for anode of SOFCs have received more attention because of

presenting better returns or possess unique properties compared to the traditional ceramic

materials [12] So it is very important to synthesiz nanocrystals of NiO-GDC in an

enviromentaly friendly way A novel sol gel method has been used to synthesized

nanocrystals of NiO-GDC metal oxides using sodium alginate as templing agents for the first

time in current study

To date numerous methods have been proposed for synthesizing nanocrystalline NiO-

GDC powders such as using the polymeric organic complex solution method [13]

combustion method [14] mechanical mixing method [15] co-precipitation [16 17] glycine

nitrate process [18] and the physical mixing of metallic-ceramic constituents with ball

milling [19] The mechanical mixing of different constituent phases is a common technique

for producing NiO-GDC anode powders However the non-uniformity in the distribution of

elements is the main drawback of this method which often results in nonhomogeneous

structures and poor electrical performance of the SOFC anode Polymeric organic complex

solution method comprises of four heat treatment steps which is complicated and would

produce larger sized NiO-GDC nanocrystals [16] Combustion method is one of the simplest

ways to synthesize nanocrystalline NiO-GDC powders but particle agglomeration and phase

impurities are the main limitations of this method [20 21] Another popular but lengthy

technique for synthesizing NiO-GDC is via co-precipitation with several consecutive steps

using basic or acidic precipitating agents such as sodium hydroxide ammonium hydroxide

and oxalic acid [22] Nonetheless more work are needed to develop a simple efficient

environmentally-friendly and low cost method that would be able to produce homogeneous

mixed constituent phases that support the improved sintering properties for longer operational

durability and less degradation [23-25]

Recently biopolymers such as polysaccharides have been widely used as templating

agents for synthesizing nanocomposite powders due to their ability to control the size and

shape of particles with minimum hazardous wastes [26 27] Sodium alginate is a water

soluble non-toxic and biodegradable ldquogreenrdquo polysaccharide with (1-4)-linked β-D-

mannuronate (M) and C-5 epimer α-L-guluronate (G) blocks covalently linked together

which can be jellified when in contact with a solution containing transitional metal ions

Gelation of sodium alginate in an aqueous solution occurs because of the interaction between

the carboxylate groups in the sodium alginate structure and the multivalent metal cations

through a mechanism known as the ldquoegg boxrdquo model [11 28] The alginate gel structure

prevents the metal ions from getting close to each other which would result in a controlled

structural growth and consequently increases the likelihood of creating smaller sized

nanocomposite powders [29] In the last few years there has been a growing interest in the

application of sodium alginate to synthesize different nanoparticles such as Co Ni Ag NiO

and CoNi [11 29-31] An extensive study has been done on GDC nanocomposites as the

electrolyte part for low-temperature SOFCs [6] The same research team had also conducted a

preliminary study on synthesizing NiO-GDC which showed the potential of using this

method to produce nanocomposites of these metals [32] However the conditions were not

fully elaborated and there is still a lack of comprehensive study on this method and the

characterization of the synthesized material

This current study was focused on elaborating the effect of calcination temperature and

time on the synthesis of a high-purity nanocrystalline NiO-GDC (NiOCe08Gd02O190) powder

via the ionic-gelation of sodium alginate The nanocrystalline NiO-GDC obtained in this

study was characterized using thermal analysis (TGADSC) X-ray diffraction (XRD) Field

Emission Scanning Electron Microscopy (FESEM) Energy-dispersive x-ray spectroscopy

(EDX) Fourier transform infrared spectroscopy (FTIR) and nitrogen adsorption-desorption

(BET) This research investigated a new environmentally friendly method for synthesizing

pure NiO-GDC Detailed findings regarding the influence of dominant synthesizing variables

on the physiochemical properties of the nanocrystalline NiO-GDC powders are reported in

the following sections

2 Materials and Methods

21 Materials

Cerium (III) nitrate hexahydrate (Ce (NO3)36H2O 99 purity) and gadolinium (III)

nitrate hexahydrate (Gd(NO3)36H2O 999 purity) from Sigma Aldrich USA and

nickel(II) nitrate hexahydrate (Ni(NO3)26H2O 99 purity) from Merck Germany were used

as the starting materials without any further purification in this study Additionally Manugel

GHB sodium alginate powder ((C6H7NaO6)n MW 264 kDa) with an MG ratio of 059

obtained from BioPolymer UK was used as the gelling template

22 Synthesis of nanocrystalline NiO-GDC powders

A cationic solution with a total concentration of 30 gL was prepared by dissolving the

calculated amounts of each metal nitrate salt (Ce(NO3)36H2O) (Gd(NO3)36H2O) and

(Ni(NO3)26H2O) into ultra-pure water Sodium alginate solution at 3 wt was prepared by

dissolving the appropriate amount of sodium alginate (Na-Alg) powder into ultra-pure water

using a water-bath at 80 degC

Alginate beads with a diameter of approximately 2 mm before drying (Figure 1a) and 1

mm after drying (Figure 1b) were produced by dripping the Na-Alg solution into a

homogeneous metal nitrate solution using a 06 mm needle with a 20 mm internal diameter

syringe at a rate of 07 mLmin The alginate solution that dripped into the nitrate solution

had rapidly formed beads

Then the as-prepared beads were gently stirred in the nitrate solution for 24 h at a

stirring rate of 100 rpm to increase the ion-exchange reaction between Na+ (in the alginate

structure) and Ce3+ Gd3+ and Ni2+ (in the salt solution) at room temperature After 24 h the

beads were filtered and washed with 45 mL of ultra-pure water to remove any sodium nitrate

trapped in the gel structure Next the beads were dried in a Memmert oven (model UF110)

for 24 h at 50 ordmC All dropped beads were well distributed without any agglomeration (Figure

1a) Figure 1b shows the greenish coloured beads after drying at 50 degC in the oven for 24

hours which were approximately 1 mm in size Finally the dried bead sample underwent

calcination at different temperatures (500 degC 600 degC and 700 degC) for different durations (2

h 6 h and 10 h) with a fixed ramp rate of 2 degCmin Table 1 presents the combinations of

calcination times and calcination temperatures used in each experimental run The calcined

powders were ground with mortar and pestle to break the agglomerated particles

23 Characterization

Thermogravimetric analysis (TGA Q50 from TA Instruments USA) was used to

study the thermal decomposition behaviour of the dried gels and the calcined samples in air

between 25 degC and 800 degC with an increasing ramp rate of 5 degC minute X-ray powder

diffraction was performed using an XRD diffractometer (D8 Discover from Bruker

Germany) with CuKα1 radiation (λ = 154060Aring) in the 2θ range between 10deg and 90deg and a

scanning rate of 002 degs using the Bragg-Brentano beam method at 40 kV and 40 mA All

XRD patterns were indexed using ICDD file no 00-50-0201 and 00-002101216 for GDC and

NiO crystals respectively The crystallite sizes of the NiO and GDC nanocrystallites were

calculated using Scherrer equation D=09 λ βcosθ where D is the crystallite size (nm) λ is

the wavelength of the source (nm) β is the full width at half maximum (FWHM) of the peak

and θ is the Bragg angle (radians) The morphology of NiO-GDC nanocrystallite was

analysed using the micrograph images obtained from a Field Emission Scanning Electron

Microscopy (FESEM SU8010 Hitachi Japan) All FESEM specimens were coated with

platinum for 120 seconds with a sputter current at 30 mA using a coater (Quarum Q150R S)

prior to the analysis Energy-dispersive x-ray (Oxford Horiba Inca XMax50 EDX) analysis

was performed to confirm the presence of cerium gadolinium and oxygen atoms in all

samples The FTIR spectra of the calcined and the dried powders were obtained using a

Fourier transform infrared spectrometer (FTIR NICOLET 1810 USA) over the

wavenumber range of 650ndash4000 cm-1 The surface area of the calcined samples was measured

by a BET analyser (Micromeritics ASAP 2020 USA)

3 Results and Discussion

The results for the thermogravimetric analysis (TGADTA) of the dried and calcined

sample at 700 degC for 2 h are shown as the representative sample in Figure 2 Four weight loss

steps corresponding to room temperature 25 degC plusmn1 degC to 186 degC 186 degC to 301 degC 301 degC to

380 degC and 380 degC to 500 degC were observed for the dried sample (Figure 2a) The

decomposition steps in the TGA curves were found to be in good agreement with the DTA

curves represented in Figure 2a A weight loss of 1146 plusmn 010 was observed during the

first step (25 degC ndash 186 degC) that corresponded to the evaporation of water in the alginate

structure during heat treatment In the second step (186 degC - 301 degC) a weight loss of 3641plusmn

015 was detected that could be due to the cleavage of G-G G-M and M-M weaker

linkages in the alginate molecule causing considerable oxygen evolution Wang et al[11]

also reported similar results for the weight loss of alginate in the same temperature range for

the dried sample of NiO nanopowders with sodium alginate When the operational

temperature was increased from 301 to 380 degC during the third step further decomposition

occurred which resulted in approximately 57 plusmn 0075 of weight loss in the TGA profile

This can be attributed to the decomposition of metastable-NiO2 to thermodynamically more

stable NiO phase which is demonstrated as a small exothermic peak [11] During the fourth

step the temperature was further increased from 380 degC to around 500 degC The residues of b-

D-mannuronic acid (M) and a-L-guluronic acid (G) in the alginate structure were completely

oxidised as observed from the 1924 plusmn 0075 weight loss that resulted in an exothermic

decomposition peak Previous studies offered similar reasoning for the final decomposition

step [27] No further weight loss was observed at temperatures of higher than 500 degC Figure

2a shows that the decomposition process could be completed at 500 degC

The TGADTA plot for the sample that was calcined at 700 degC for 2 hours is shown in

Figure 2b Three major weight losses were visible in the plot The first weight loss of 018 plusmn

001 occurred between room temperature and approximately 48 degC and was due to water

evaporation which was confirmed by the small endothermic peak in the DTA curve During

the second step (75-91 degC) a weight loss of 194 plusmn 001 was observed due to organic

components that still remained after calcination [33] The third weight loss of 177plusmn 001

was observed between 93-406 degC which corresponded to the decomposition of Ni(OH)2 to

NiO Ce(OH)3 to CeO2 and Gd(OH)3 to Gd2O3 [33] No further weight loss was observed at

temperature of higher than 400 degC which indicated the absence of carbonaceous bonds or

any other undecomposed residue in the sample

The FESEM images for the NiO-GDC nanocrystallites synthesized with 3 loading

fractions of sodium alginate at 500 degC 600 degC and 700 degC calcination temperature with

different calcination time are displayed in Figures 3 4 and 5 respectively ImageJ software

was used to quantitatively analyse the FESEM images [34 35] First a binary image was

extracted by carefully performing intensity-thresholding on the original FESEM image

Using erosion and dilation irregular shapes were removed The remaining particles were

morphologically closed and smoothened by applying a Gaussian blur The resultant binary

images which contained particles in the form of blobs were passed to the analysis module

for an automatic measurement of the particle size The particle size distribution for each

image has been embedded at its top-right corner where micro denotes the average particle size

with the standard deviation and Ɲ denotes the number of particles utilized in the analysis

As seen in Figures 3 4 and 5 the particle size had slowly increased when the

calcination temperature was increased from 500 to 700 degC at a constant calcination time

These results could be linked to the agglomeration of the particles caused by several

phenomena such as lsquouncontrolled build-uprsquo lsquobridgingrsquo or lsquolumpingrsquo during the thermal

treatment process (refer Figures 3a 4a and 5a) [36] It was also observed that at a constant

calcination temperature the size of the nanocrystallites had increased due to the

agglomeration of smaller particles when the calcination time was increased from 2 h to 10 h

(refer Figures 4a 4b and 4c) Thus the agglomeration of smaller particles can be

manipulated by determining the optimum calcination temperature and duration to obtain

specific particle sizes In each series of images 3a 3b and 3c 4a 4b and 4c and 5a

5b and5c this trend can be seen for all calcination times and calcination temperatures

The results showed that the smallest particle size (641 nm) was obtained with

calcination conditions of 500 degC for 2 h (641 nm) The largest particle size of 2125 nm was

obtained at 700 degC after 10 h of calcination These results were in agreement with the

previous discussion In conclusion for synthesizing smaller nanocrystalline NiO-GDC lower

calcination temperature (500 degC) and shorter calcination time (2 h) is needed

The EDX elemental analysis and mapping is shown in Figure 6 for nancrystalline NiO-

GDC synthesized at 500 degC for 6 h which confirmed the presence of cerium gadolinium

oxygen and nickel atoms The sample shown in Figure 6 was chosen as an example to

represent all the samples that were elaborated in this study

X-ray diffraction (XRD) patterns of the nanocrystalline NiO-GDC powders synthesized

at different calcination times and temperatures are shown in Figure 7 The peaks for all

samples were well matched with the cubic Ce08Gd02O19 (Fm-3m ICDD00-50-0201) and

cubic NiO (Fm-3m ICDD 00-002101216) The average crystallite sizes of these particles

were determined using the Scherrer equation as listed in Table 2 The crystallite sizes of NiO

and GDC in NiO-GDC have been reported by several studies that used different methods

such as polymeric sol-gel (with NiO at 24 nm and GDC at 18 nm) [37] hydroxide co-

precipitation method (NiO at 305 nm and GDC at 273 nm) [17] solution combustion

synthesis (NiO at 30-58 nm and GDC at 40-50 nm) [38] micro emulsion method (NiO at

132 148 and 134 nm and GDC at 117 137 and 106 nm) as well as microemulsion-

mediated solvothermal process (NiO at 22 plusmn 2 nm and GDC at 20 plusmn 2 nm) These studies

have shown that ion-gelation synthesis can successfully synthesize smaller sized NiO-GDC

nanocomposites

The XRD patterns have shown that the diffraction peaks for GDC and NiO crystal

phases became sharper when calcination temperature was increased from 500 to 700 degC at

constant calcination time as well as when calcination time was increased from 2 h to 10 h at a

constant calcination temperature which indicated the growth in the crystallite size (Table 1)

due to particle agglomeration [36] At lower calcination temperature (500 degC) with different

calcination times (2 6 and 10 h) the broader peaks in an XRD pattern show the existence of

smaller-sized NiO and GDC crystallites for all samples [39] In this study the XRD pattern

(Figure 7) was in agreement with crystallite size tabulated in Table 2

The calculated crystallite sizes using the Scherrer equation (Table 2) supported the

results from the XRD patterns which indicated that by increasing the calcination time and

temperature the crystallite sizes of NiO and GDC were increased as well The calculated

crystallite sizes of NiO and GDC in Table 2 were in good agreement with the results attained

from the quantitative image analysis reported in Figure 3 Figure 4 and Figure 5 which

confirmed the influences of both the calcination temperature and calcination time on the size

of the powder particles

Figure 8 shows the FTIR spectra for the dried gel and the calcined samples at different

calcination temperatures and times The FTIR spectrum for the dried sample showed

numerous adsorption bands in the 800-1610 cm-1 region The peaks at 884 cm-1 could be

attributed to the C-C band for sodium alginate [40] Meanwhile the band at 1026 cm-1 (C-O-

C stretching) corresponded to sodium alginate glycosidic linkage [41] Additionally the

stretch at 3355 cm-1 and the absorption peaks at 1600 to 1414 cm-1 corresponded to O-H band

and the asymmetric and symmetric stretching vibration of the carboxylate group respectively

[42] After the dried sample had undergone thermal treatment at different calcination times

and temperatures a reduction in the intensity of carbon bands was observed which

confirmed the effectiveness of the calcination process in completing the thermal

decomposition of the biopolymer compound However further increase in the calcination

temperature and calcination time had led to a reduction in the intensity of the peaks This

condition showed that these samples had attained more purity in their metal oxide

compositions The absorption band for metal-oxygen has been reported by various studies

such as (Ce-OGd-ONi-O) was detected at approximately 635 cm-1 [33] (Ce-O) was

observed at 564 cm-1 while the 550-700 cm-1 region was assigned to NiO stretching vibration

[43-45] However due to the presence of noise at lower than 650 cm -1 the measuring range

utilized in these current experiments was between 650 cm-1 to 4000 cm-1

The BET analysis was conducted by applying the Barrett-Joyner-Halenda (BJH)

method to study the physicochemical properties of the calcined NiO-GDC at different

calcination times and temperatures Based on literature review there is a lack of information

on BET analysis of NiO-GDC and thus more in-depth studies are needed in this area The

nitrogen adsorption-desorption isotherms (hysteresis loops) of the NiO-GDC are given in

Figure 9 with the pore size distribution of the different samples in the inset The nitrogen

adsorption-desorption isotherms (Figure 9) indicated the presence of mesopores in the

samples based on the type IV isotherm as per IUPAC classification The mesopores were

formed due to the capillary condensation of the mesoporous materials thus confirming the

mesoporosity of the synthesized NiO-GDC nanocrystallites [46] The hysteresis loops of the

samples in the pp0 range of 04-10 illustrated the absence of micropores and that the pores

had changed into the mesoporous reign [46] The pore size distributions of the samples are

given in the inset of Figure 9 The majority of the NiO-GDC samples were in the mesoporous

region (10 nm) as determined by the BJH method which supported the N2 adsorption-

desorption isotherms

It can be observed from Figure 9 that for samples calcined at 500 degC for 2 h 6 h and 10 h the

relative pressure (corresponding to the onset of capillary condensation) has a higher value

which indicated the presence of the smaller pore size distribution for that sample [47]

The BET surface areas for all samples are summarized in Table 3 It can be seen that

at a specific calcination temperature increasing the calcination time from 2 h to 10 h had

caused the surface area of the sample to decrease due to the increasing particle size

Similarly by increasing the calcination temperature from 500 degC to 700 degC the surface areas

of the samples had decreased due to the increasing particle sizes The largest surface areas

corresponded to the nanocrystallite samples calcined at 500 degC for 2 h However these values

had reduced when the calcination temperature and time were gradually increased to 700 degC

and 10 h respectively These results are in good agreement with the particle sizes obtained

from the FESEM and XRD results

4 Conclusion

Nanocrytalline NiO-GDC powders were synthesized using an environmentally

friendly ionic gelation method with sodium alginate as the precursor The effects of the

synthesis parameters such as calcination temperature and calcination time on the properties

of the produced nanocrystalline NiO-GDC powders were studied using various

characterization techniques It was found that at a fixed calcination temperature the size of

the nanocrystals would increase with increasing calcination time Similarly at a fixed

calcination time and increasing calcination temperature larger nanocrystals were produced

Therefore for synthesizing smaller nanocrystals lower calcination temperature (500 degC) and

shorter calcination time (2 h) are recommended It was also observed that calcination

temperature has more effect on the BET surface compared to calcination time which showed

that the pore size of the nanocrystalline powders was more dependent on the calcination

temperature

5 Acknowledgement

The authors would like to acknowledge the Ministry of Science Education and Innovation

(MOSTI) of Malaysia for providing research funding under the e-science scheme grant

number 03-02-10-SF0259

References

1 Boury B and S Plumejeau Metal oxides and polysaccharides an efficient hybrid association for materials chemistry Green Chemistry 2015 17(1) p 72-88

2 Bell AT The impact of nanoscience on heterogeneous catalysis Science 2003 299(5613) p 1688-1691

3 Zhao X et al The role of nanomaterials in redox-based supercapacitors for next generation energy storage devices Nanoscale 2011 3(3) p 839-855

4 Sun Y-F et al Metal oxide nanostructures and their gas sensing properties a review Sensors 2012 12(3) p 2610-2631

5 Jia J et al Heterogeneous catalytic hydrogenation of CO 2 by metal oxides defect engineeringndashperfecting imperfection Chemical Society Reviews 2017 46(15) p 4631-4644

6 Pezeshkpour S et al Ionicndashgelation synthesis of gadolinium doped ceria (Ce 08 Gd 02 O 190) nanocomposite powder using sodium-alginate Ceramics International 2017 43(9) p 7123-7135

7 Atif M et al Studies on the magnetic magnetostrictive and electrical properties of solndashgel synthesized Zn doped nickel ferrite Journal of Alloys and Compounds 2011 509(18) p 5720-5724

8 Krstajić N et al Non-noble metal composite cathodes for hydrogen evolution Part I the NindashMoO x coatings electrodeposited from Wattrsquos type bath containing MoO 3 powder particles international journal of hydrogen energy 2011 36(11) p 6441-6449

9 Macedo DA et al NindashCGO cermet anodes from nanocomposite powders Microstructural and electrochemical assessment Ceramics International 2014 40(8) p 13105-13113

10 Gao H et al The design of excellent xylene gas sensor using Sn-doped NiO hierarchical nanostructure Sensors and Actuators B Chemical 2017 253 p 1152-1162

11 Wang Z GM Kale and M Ghadiri Novel Ion‐Exchange Process for the Preparation of Metal Oxide Nanopowders from Sodium Alginate Journal of the American Ceramic Society 2012 95(10) p 3124-3129

12 Galeano MAacuteN et al Studies on the structural quantitative and semi-quantitative analyses of NiOndashGDC nanocomposites RSC Advances 2016 6(77) p 72865-72876

13 Gil V C Moure and J Tartaj Sinterability microstructures and electrical properties of NiGd-doped ceria cermets used as anode materials for SOFCs Journal of the European Ceramic Society 2007 27(13) p 4205-4209

14 Akbari-Fakhrabadi A et al Combustion synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite anode and its electrical characteristics of semi-cell configured SOFC assembly Journal of Alloys and Compounds 2012 541 p 1-5

15 Ishihara T et al NickelndashGd-doped CeO 2 cermet anode for intermediate temperature operating solid oxide fuel cells using LaGaO 3-based perovskite electrolyte Solid State Ionics 2000 132(3) p 209-216

16 Ding C et al A comparative study of NiOndashCe 09 Gd 01 O 195 nanocomposite powders synthesized by hydroxide and oxalate co-precipitation methods Ceramics International 2012 38(1) p 85-92

17 Ding C et al Synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite powders for low-temperature solid oxide fuel cell anodes by co-precipitation Scripta Materialia 2009 60(4) p 254-256

18 Park S-Y et al Preparation of highly porous NiOndashgadolinium-doped ceria nano-composite powders by one-pot glycine nitrate process for anode-supported tubular solid oxide fuel cells Journal of Asian Ceramic Societies 2014 2(4) p 339-346

19 Zhu W and S Deevi A review on the status of anode materials for solid oxide fuel cells Materials Science and Engineering A 2003 362(1) p 228-239

20 Chick LA et al Glycine-nitrate combustion synthesis of oxide ceramic powders Materials Letters 1990 10(1-2) p 6-12

21 Basu RN et al Microstructure and electrical conductivity of LaNi 06 Fe 04 O 3 prepared by combustion synthesis routes Materials Research Bulletin 2004 39(9) p 1335-1345

22 SOFC ZS Microstructure development of the Ni-GDC anode material for IT-SOFC Materiali in tehnologije 2012 46(5) p 445-451

23 Aparicio M A Jitianu and LC Klein Sol-Gel Processing for Conventional and Alternative Energy 2012 Springer Science amp Business Media

24 Suciu C et al NiOYSZ nanoparticles obtained by new solndashgel route Chemical Engineering Journal 2008 140(1) p 586-592

25 Jiang SP and SH Chan A review of anode materials development in solid oxide fuel cells Journal of Materials Science 2004 39(14) p 4405-4439

26 Iyer A et al A Sucrose‐Mediated SolndashGel Technique for the Synthesis of MgOndashY2O3 Nanocomposites Journal of the American Ceramic Society 2013 96(2) p 346-350

27 Wang Z et al Ion-exchange kinetics and thermal decomposition characteristics of Fe2+-exchanged alginic acid membrane for the formation of iron oxide nanoparticles Journal of Materials Science 2014 49(20) p 7151-7155

28 Schnepp Z et al Alginate-mediated routes to the selective synthesis of complex metal oxide nanostructures CrystEngComm 2010 12(5) p 1410-1415

29 Wang Z GM Kale and M Ghadiri Synthesis and characterization of CexGd 1minus xO 2minus δ nanopowders employing an alginate mediated ion-exchange process Chemical Engineering Journal 2012 198 p 149-153

30 Brayner R et al Alginate-mediated growth of Co Ni and CoNi nanoparticles influence of the biopolymer structure Chemistry of Materials 2007 19(5) p 1190-1198

31 Balavandy SK K Shameli and ZZ Abidin Rapid and Green Synthesis of Silver Nanoparticles via Sodium Alginate Media Int J Electrochem Sci 2015 10 p 486-497

32 Choo CK BA Horri and B Salamatinia Synthesis and Characterization of Nickel (II) OxideGadolinium-Doped Ceria (NiOGDC) Nanocomposites As a Potential Material for Anode Supported LT-SOFCs in Proceedings of the World Congress on Engineering and Computer Science 2016

33 Rath MK M-J Lee and K-T Lee Preparation of nano-structured NindashCe 08 Gd 02 O 19 anode materials for solid oxide fuel cells via the water-in-oil (WO) micro-emulsion route Ceramics International 2014 40(1) p 1909-1917

34 Schneider CA WS Rasband and KW Eliceiri NIH Image to ImageJ 25 years of image analysis Nature methods 2012 9(7) p 671-675

35 Collins T ImageJ for Microscopy BioTechniques 43 S25-S30 httpdx doi org102144000112517 2007

36 Thierry R F Thierry and G Osenga Surface energy modified particles method of making and use thereof 2015 Google Patents

37 Macedo DA et al A versatile route for the preparation of NindashCGO cermets from nanocomposite powders Ceramics International 2013 39(4) p 4321-4328

38 Wandekar R et al Physicochemical studies of NiOndashGDC composites Materials Chemistry and Physics 2006 99(2) p 289-294

39 Prakash BS VW Grips and S Aruna A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes Journal of Power Sources 2012 214 p 358-364

40 Sartori C et al Determination of the cation content of alginate thin films by FTi r spectroscopy Polymer 1997 38(1) p 43-51

41 Lakouraj MM F Mojerlou and EN Zare Nanogel and superparamagnetic nanocomposite based on sodium alginate for sorption of heavy metal ions Carbohydrate polymers 2014 106 p 34-41

42 Srivastava M et al Synthesis of superparamagnetic bare Fe 3 O 4 nanostructures and coreshell (Fe 3 O 4alginate) nanocomposites Carbohydrate polymers 2012 89(3) p 821-829

43 Chavan A et al Effect of variation of NiO on properties of NiOGDC (gadolinium doped ceria) nano-composites Ceramics International 2012 38(4) p 3191-3196

44 Shen C and LL Shaw FTIR analysis of the hydrolysis rate in the solndashgel formation of gadolinia-doped ceria with acetylacetonate precursors Journal of sol-gel science and technology 2010 53(3) p 571-577

45 Wang T and D-C Sun Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method Materials Research Bulletin 2008 43(7) p 1754-1760

46 Sing KS Reporting physisorption data for gassolid systems with special reference to the determination of surface area and porosity (Recommendations 1984) Pure and applied chemistry 1985 57(4) p 603-619

47 Song X et al Synthesis and Characterization of Y-Doped Mesoporous CeO 2 Using A Chemical Precipitation Method Journal of Rare Earths 2007 25(4) p 428-433

milling [19] The mechanical mixing of different constituent phases is a common technique

for producing NiO-GDC anode powders However the non-uniformity in the distribution of

elements is the main drawback of this method which often results in nonhomogeneous

structures and poor electrical performance of the SOFC anode Polymeric organic complex

solution method comprises of four heat treatment steps which is complicated and would

produce larger sized NiO-GDC nanocrystals [16] Combustion method is one of the simplest

ways to synthesize nanocrystalline NiO-GDC powders but particle agglomeration and phase

impurities are the main limitations of this method [20 21] Another popular but lengthy

technique for synthesizing NiO-GDC is via co-precipitation with several consecutive steps

using basic or acidic precipitating agents such as sodium hydroxide ammonium hydroxide

and oxalic acid [22] Nonetheless more work are needed to develop a simple efficient

environmentally-friendly and low cost method that would be able to produce homogeneous

mixed constituent phases that support the improved sintering properties for longer operational

durability and less degradation [23-25]

Recently biopolymers such as polysaccharides have been widely used as templating

agents for synthesizing nanocomposite powders due to their ability to control the size and

shape of particles with minimum hazardous wastes [26 27] Sodium alginate is a water

soluble non-toxic and biodegradable ldquogreenrdquo polysaccharide with (1-4)-linked β-D-

mannuronate (M) and C-5 epimer α-L-guluronate (G) blocks covalently linked together

which can be jellified when in contact with a solution containing transitional metal ions

Gelation of sodium alginate in an aqueous solution occurs because of the interaction between

the carboxylate groups in the sodium alginate structure and the multivalent metal cations

through a mechanism known as the ldquoegg boxrdquo model [11 28] The alginate gel structure

prevents the metal ions from getting close to each other which would result in a controlled

structural growth and consequently increases the likelihood of creating smaller sized

nanocomposite powders [29] In the last few years there has been a growing interest in the

application of sodium alginate to synthesize different nanoparticles such as Co Ni Ag NiO

and CoNi [11 29-31] An extensive study has been done on GDC nanocomposites as the

electrolyte part for low-temperature SOFCs [6] The same research team had also conducted a

preliminary study on synthesizing NiO-GDC which showed the potential of using this

method to produce nanocomposites of these metals [32] However the conditions were not

fully elaborated and there is still a lack of comprehensive study on this method and the

characterization of the synthesized material

This current study was focused on elaborating the effect of calcination temperature and

time on the synthesis of a high-purity nanocrystalline NiO-GDC (NiOCe08Gd02O190) powder

via the ionic-gelation of sodium alginate The nanocrystalline NiO-GDC obtained in this

study was characterized using thermal analysis (TGADSC) X-ray diffraction (XRD) Field

Emission Scanning Electron Microscopy (FESEM) Energy-dispersive x-ray spectroscopy

(EDX) Fourier transform infrared spectroscopy (FTIR) and nitrogen adsorption-desorption

(BET) This research investigated a new environmentally friendly method for synthesizing

pure NiO-GDC Detailed findings regarding the influence of dominant synthesizing variables

on the physiochemical properties of the nanocrystalline NiO-GDC powders are reported in

the following sections

2 Materials and Methods

21 Materials

Cerium (III) nitrate hexahydrate (Ce (NO3)36H2O 99 purity) and gadolinium (III)

nitrate hexahydrate (Gd(NO3)36H2O 999 purity) from Sigma Aldrich USA and

nickel(II) nitrate hexahydrate (Ni(NO3)26H2O 99 purity) from Merck Germany were used

as the starting materials without any further purification in this study Additionally Manugel

GHB sodium alginate powder ((C6H7NaO6)n MW 264 kDa) with an MG ratio of 059

obtained from BioPolymer UK was used as the gelling template

22 Synthesis of nanocrystalline NiO-GDC powders

A cationic solution with a total concentration of 30 gL was prepared by dissolving the

calculated amounts of each metal nitrate salt (Ce(NO3)36H2O) (Gd(NO3)36H2O) and

(Ni(NO3)26H2O) into ultra-pure water Sodium alginate solution at 3 wt was prepared by

dissolving the appropriate amount of sodium alginate (Na-Alg) powder into ultra-pure water

using a water-bath at 80 degC

Alginate beads with a diameter of approximately 2 mm before drying (Figure 1a) and 1

mm after drying (Figure 1b) were produced by dripping the Na-Alg solution into a

homogeneous metal nitrate solution using a 06 mm needle with a 20 mm internal diameter

syringe at a rate of 07 mLmin The alginate solution that dripped into the nitrate solution

had rapidly formed beads

Then the as-prepared beads were gently stirred in the nitrate solution for 24 h at a

stirring rate of 100 rpm to increase the ion-exchange reaction between Na+ (in the alginate

structure) and Ce3+ Gd3+ and Ni2+ (in the salt solution) at room temperature After 24 h the

beads were filtered and washed with 45 mL of ultra-pure water to remove any sodium nitrate

trapped in the gel structure Next the beads were dried in a Memmert oven (model UF110)

for 24 h at 50 ordmC All dropped beads were well distributed without any agglomeration (Figure

1a) Figure 1b shows the greenish coloured beads after drying at 50 degC in the oven for 24

hours which were approximately 1 mm in size Finally the dried bead sample underwent

calcination at different temperatures (500 degC 600 degC and 700 degC) for different durations (2

h 6 h and 10 h) with a fixed ramp rate of 2 degCmin Table 1 presents the combinations of

calcination times and calcination temperatures used in each experimental run The calcined

powders were ground with mortar and pestle to break the agglomerated particles

23 Characterization

Thermogravimetric analysis (TGA Q50 from TA Instruments USA) was used to

study the thermal decomposition behaviour of the dried gels and the calcined samples in air

between 25 degC and 800 degC with an increasing ramp rate of 5 degC minute X-ray powder

diffraction was performed using an XRD diffractometer (D8 Discover from Bruker

Germany) with CuKα1 radiation (λ = 154060Aring) in the 2θ range between 10deg and 90deg and a

scanning rate of 002 degs using the Bragg-Brentano beam method at 40 kV and 40 mA All

XRD patterns were indexed using ICDD file no 00-50-0201 and 00-002101216 for GDC and

NiO crystals respectively The crystallite sizes of the NiO and GDC nanocrystallites were

calculated using Scherrer equation D=09 λ βcosθ where D is the crystallite size (nm) λ is

the wavelength of the source (nm) β is the full width at half maximum (FWHM) of the peak

and θ is the Bragg angle (radians) The morphology of NiO-GDC nanocrystallite was

analysed using the micrograph images obtained from a Field Emission Scanning Electron

Microscopy (FESEM SU8010 Hitachi Japan) All FESEM specimens were coated with

platinum for 120 seconds with a sputter current at 30 mA using a coater (Quarum Q150R S)

prior to the analysis Energy-dispersive x-ray (Oxford Horiba Inca XMax50 EDX) analysis

was performed to confirm the presence of cerium gadolinium and oxygen atoms in all

samples The FTIR spectra of the calcined and the dried powders were obtained using a

Fourier transform infrared spectrometer (FTIR NICOLET 1810 USA) over the

wavenumber range of 650ndash4000 cm-1 The surface area of the calcined samples was measured

by a BET analyser (Micromeritics ASAP 2020 USA)

3 Results and Discussion

The results for the thermogravimetric analysis (TGADTA) of the dried and calcined

sample at 700 degC for 2 h are shown as the representative sample in Figure 2 Four weight loss

steps corresponding to room temperature 25 degC plusmn1 degC to 186 degC 186 degC to 301 degC 301 degC to

380 degC and 380 degC to 500 degC were observed for the dried sample (Figure 2a) The

decomposition steps in the TGA curves were found to be in good agreement with the DTA

curves represented in Figure 2a A weight loss of 1146 plusmn 010 was observed during the

first step (25 degC ndash 186 degC) that corresponded to the evaporation of water in the alginate

structure during heat treatment In the second step (186 degC - 301 degC) a weight loss of 3641plusmn

015 was detected that could be due to the cleavage of G-G G-M and M-M weaker

linkages in the alginate molecule causing considerable oxygen evolution Wang et al[11]

also reported similar results for the weight loss of alginate in the same temperature range for

the dried sample of NiO nanopowders with sodium alginate When the operational

temperature was increased from 301 to 380 degC during the third step further decomposition

occurred which resulted in approximately 57 plusmn 0075 of weight loss in the TGA profile

This can be attributed to the decomposition of metastable-NiO2 to thermodynamically more

stable NiO phase which is demonstrated as a small exothermic peak [11] During the fourth

step the temperature was further increased from 380 degC to around 500 degC The residues of b-

D-mannuronic acid (M) and a-L-guluronic acid (G) in the alginate structure were completely

oxidised as observed from the 1924 plusmn 0075 weight loss that resulted in an exothermic

decomposition peak Previous studies offered similar reasoning for the final decomposition

step [27] No further weight loss was observed at temperatures of higher than 500 degC Figure

2a shows that the decomposition process could be completed at 500 degC

The TGADTA plot for the sample that was calcined at 700 degC for 2 hours is shown in

Figure 2b Three major weight losses were visible in the plot The first weight loss of 018 plusmn

001 occurred between room temperature and approximately 48 degC and was due to water

evaporation which was confirmed by the small endothermic peak in the DTA curve During

the second step (75-91 degC) a weight loss of 194 plusmn 001 was observed due to organic

components that still remained after calcination [33] The third weight loss of 177plusmn 001

was observed between 93-406 degC which corresponded to the decomposition of Ni(OH)2 to

NiO Ce(OH)3 to CeO2 and Gd(OH)3 to Gd2O3 [33] No further weight loss was observed at

temperature of higher than 400 degC which indicated the absence of carbonaceous bonds or

any other undecomposed residue in the sample

The FESEM images for the NiO-GDC nanocrystallites synthesized with 3 loading

fractions of sodium alginate at 500 degC 600 degC and 700 degC calcination temperature with

different calcination time are displayed in Figures 3 4 and 5 respectively ImageJ software

was used to quantitatively analyse the FESEM images [34 35] First a binary image was

extracted by carefully performing intensity-thresholding on the original FESEM image

Using erosion and dilation irregular shapes were removed The remaining particles were

morphologically closed and smoothened by applying a Gaussian blur The resultant binary

images which contained particles in the form of blobs were passed to the analysis module

for an automatic measurement of the particle size The particle size distribution for each

image has been embedded at its top-right corner where micro denotes the average particle size

with the standard deviation and Ɲ denotes the number of particles utilized in the analysis

As seen in Figures 3 4 and 5 the particle size had slowly increased when the

calcination temperature was increased from 500 to 700 degC at a constant calcination time

These results could be linked to the agglomeration of the particles caused by several

phenomena such as lsquouncontrolled build-uprsquo lsquobridgingrsquo or lsquolumpingrsquo during the thermal

treatment process (refer Figures 3a 4a and 5a) [36] It was also observed that at a constant

calcination temperature the size of the nanocrystallites had increased due to the

agglomeration of smaller particles when the calcination time was increased from 2 h to 10 h

(refer Figures 4a 4b and 4c) Thus the agglomeration of smaller particles can be

manipulated by determining the optimum calcination temperature and duration to obtain

specific particle sizes In each series of images 3a 3b and 3c 4a 4b and 4c and 5a

5b and5c this trend can be seen for all calcination times and calcination temperatures

The results showed that the smallest particle size (641 nm) was obtained with

calcination conditions of 500 degC for 2 h (641 nm) The largest particle size of 2125 nm was

obtained at 700 degC after 10 h of calcination These results were in agreement with the

previous discussion In conclusion for synthesizing smaller nanocrystalline NiO-GDC lower

calcination temperature (500 degC) and shorter calcination time (2 h) is needed

The EDX elemental analysis and mapping is shown in Figure 6 for nancrystalline NiO-

GDC synthesized at 500 degC for 6 h which confirmed the presence of cerium gadolinium

oxygen and nickel atoms The sample shown in Figure 6 was chosen as an example to

represent all the samples that were elaborated in this study

X-ray diffraction (XRD) patterns of the nanocrystalline NiO-GDC powders synthesized

at different calcination times and temperatures are shown in Figure 7 The peaks for all

samples were well matched with the cubic Ce08Gd02O19 (Fm-3m ICDD00-50-0201) and

cubic NiO (Fm-3m ICDD 00-002101216) The average crystallite sizes of these particles

were determined using the Scherrer equation as listed in Table 2 The crystallite sizes of NiO

and GDC in NiO-GDC have been reported by several studies that used different methods

such as polymeric sol-gel (with NiO at 24 nm and GDC at 18 nm) [37] hydroxide co-

precipitation method (NiO at 305 nm and GDC at 273 nm) [17] solution combustion

synthesis (NiO at 30-58 nm and GDC at 40-50 nm) [38] micro emulsion method (NiO at

132 148 and 134 nm and GDC at 117 137 and 106 nm) as well as microemulsion-

mediated solvothermal process (NiO at 22 plusmn 2 nm and GDC at 20 plusmn 2 nm) These studies

have shown that ion-gelation synthesis can successfully synthesize smaller sized NiO-GDC

nanocomposites

The XRD patterns have shown that the diffraction peaks for GDC and NiO crystal

phases became sharper when calcination temperature was increased from 500 to 700 degC at

constant calcination time as well as when calcination time was increased from 2 h to 10 h at a

constant calcination temperature which indicated the growth in the crystallite size (Table 1)

due to particle agglomeration [36] At lower calcination temperature (500 degC) with different

calcination times (2 6 and 10 h) the broader peaks in an XRD pattern show the existence of

smaller-sized NiO and GDC crystallites for all samples [39] In this study the XRD pattern

(Figure 7) was in agreement with crystallite size tabulated in Table 2

The calculated crystallite sizes using the Scherrer equation (Table 2) supported the

results from the XRD patterns which indicated that by increasing the calcination time and

temperature the crystallite sizes of NiO and GDC were increased as well The calculated

crystallite sizes of NiO and GDC in Table 2 were in good agreement with the results attained

from the quantitative image analysis reported in Figure 3 Figure 4 and Figure 5 which

confirmed the influences of both the calcination temperature and calcination time on the size

of the powder particles

Figure 8 shows the FTIR spectra for the dried gel and the calcined samples at different

calcination temperatures and times The FTIR spectrum for the dried sample showed

numerous adsorption bands in the 800-1610 cm-1 region The peaks at 884 cm-1 could be

attributed to the C-C band for sodium alginate [40] Meanwhile the band at 1026 cm-1 (C-O-

C stretching) corresponded to sodium alginate glycosidic linkage [41] Additionally the

stretch at 3355 cm-1 and the absorption peaks at 1600 to 1414 cm-1 corresponded to O-H band

and the asymmetric and symmetric stretching vibration of the carboxylate group respectively

[42] After the dried sample had undergone thermal treatment at different calcination times

and temperatures a reduction in the intensity of carbon bands was observed which

confirmed the effectiveness of the calcination process in completing the thermal

decomposition of the biopolymer compound However further increase in the calcination

temperature and calcination time had led to a reduction in the intensity of the peaks This

condition showed that these samples had attained more purity in their metal oxide

compositions The absorption band for metal-oxygen has been reported by various studies

such as (Ce-OGd-ONi-O) was detected at approximately 635 cm-1 [33] (Ce-O) was

observed at 564 cm-1 while the 550-700 cm-1 region was assigned to NiO stretching vibration

[43-45] However due to the presence of noise at lower than 650 cm -1 the measuring range

utilized in these current experiments was between 650 cm-1 to 4000 cm-1

The BET analysis was conducted by applying the Barrett-Joyner-Halenda (BJH)

method to study the physicochemical properties of the calcined NiO-GDC at different

calcination times and temperatures Based on literature review there is a lack of information

on BET analysis of NiO-GDC and thus more in-depth studies are needed in this area The

nitrogen adsorption-desorption isotherms (hysteresis loops) of the NiO-GDC are given in

Figure 9 with the pore size distribution of the different samples in the inset The nitrogen

adsorption-desorption isotherms (Figure 9) indicated the presence of mesopores in the

samples based on the type IV isotherm as per IUPAC classification The mesopores were

formed due to the capillary condensation of the mesoporous materials thus confirming the

mesoporosity of the synthesized NiO-GDC nanocrystallites [46] The hysteresis loops of the

samples in the pp0 range of 04-10 illustrated the absence of micropores and that the pores

had changed into the mesoporous reign [46] The pore size distributions of the samples are

given in the inset of Figure 9 The majority of the NiO-GDC samples were in the mesoporous

region (10 nm) as determined by the BJH method which supported the N2 adsorption-

desorption isotherms

It can be observed from Figure 9 that for samples calcined at 500 degC for 2 h 6 h and 10 h the

relative pressure (corresponding to the onset of capillary condensation) has a higher value

which indicated the presence of the smaller pore size distribution for that sample [47]

The BET surface areas for all samples are summarized in Table 3 It can be seen that

at a specific calcination temperature increasing the calcination time from 2 h to 10 h had

caused the surface area of the sample to decrease due to the increasing particle size

Similarly by increasing the calcination temperature from 500 degC to 700 degC the surface areas

of the samples had decreased due to the increasing particle sizes The largest surface areas

corresponded to the nanocrystallite samples calcined at 500 degC for 2 h However these values

had reduced when the calcination temperature and time were gradually increased to 700 degC

and 10 h respectively These results are in good agreement with the particle sizes obtained

from the FESEM and XRD results

4 Conclusion

Nanocrytalline NiO-GDC powders were synthesized using an environmentally

friendly ionic gelation method with sodium alginate as the precursor The effects of the

synthesis parameters such as calcination temperature and calcination time on the properties

of the produced nanocrystalline NiO-GDC powders were studied using various

characterization techniques It was found that at a fixed calcination temperature the size of

the nanocrystals would increase with increasing calcination time Similarly at a fixed

calcination time and increasing calcination temperature larger nanocrystals were produced

Therefore for synthesizing smaller nanocrystals lower calcination temperature (500 degC) and

shorter calcination time (2 h) are recommended It was also observed that calcination

temperature has more effect on the BET surface compared to calcination time which showed

that the pore size of the nanocrystalline powders was more dependent on the calcination

temperature

5 Acknowledgement

The authors would like to acknowledge the Ministry of Science Education and Innovation

(MOSTI) of Malaysia for providing research funding under the e-science scheme grant

number 03-02-10-SF0259

References

1 Boury B and S Plumejeau Metal oxides and polysaccharides an efficient hybrid association for materials chemistry Green Chemistry 2015 17(1) p 72-88

2 Bell AT The impact of nanoscience on heterogeneous catalysis Science 2003 299(5613) p 1688-1691

3 Zhao X et al The role of nanomaterials in redox-based supercapacitors for next generation energy storage devices Nanoscale 2011 3(3) p 839-855

4 Sun Y-F et al Metal oxide nanostructures and their gas sensing properties a review Sensors 2012 12(3) p 2610-2631

5 Jia J et al Heterogeneous catalytic hydrogenation of CO 2 by metal oxides defect engineeringndashperfecting imperfection Chemical Society Reviews 2017 46(15) p 4631-4644

6 Pezeshkpour S et al Ionicndashgelation synthesis of gadolinium doped ceria (Ce 08 Gd 02 O 190) nanocomposite powder using sodium-alginate Ceramics International 2017 43(9) p 7123-7135

7 Atif M et al Studies on the magnetic magnetostrictive and electrical properties of solndashgel synthesized Zn doped nickel ferrite Journal of Alloys and Compounds 2011 509(18) p 5720-5724

8 Krstajić N et al Non-noble metal composite cathodes for hydrogen evolution Part I the NindashMoO x coatings electrodeposited from Wattrsquos type bath containing MoO 3 powder particles international journal of hydrogen energy 2011 36(11) p 6441-6449

9 Macedo DA et al NindashCGO cermet anodes from nanocomposite powders Microstructural and electrochemical assessment Ceramics International 2014 40(8) p 13105-13113

10 Gao H et al The design of excellent xylene gas sensor using Sn-doped NiO hierarchical nanostructure Sensors and Actuators B Chemical 2017 253 p 1152-1162

11 Wang Z GM Kale and M Ghadiri Novel Ion‐Exchange Process for the Preparation of Metal Oxide Nanopowders from Sodium Alginate Journal of the American Ceramic Society 2012 95(10) p 3124-3129

12 Galeano MAacuteN et al Studies on the structural quantitative and semi-quantitative analyses of NiOndashGDC nanocomposites RSC Advances 2016 6(77) p 72865-72876

13 Gil V C Moure and J Tartaj Sinterability microstructures and electrical properties of NiGd-doped ceria cermets used as anode materials for SOFCs Journal of the European Ceramic Society 2007 27(13) p 4205-4209

14 Akbari-Fakhrabadi A et al Combustion synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite anode and its electrical characteristics of semi-cell configured SOFC assembly Journal of Alloys and Compounds 2012 541 p 1-5

15 Ishihara T et al NickelndashGd-doped CeO 2 cermet anode for intermediate temperature operating solid oxide fuel cells using LaGaO 3-based perovskite electrolyte Solid State Ionics 2000 132(3) p 209-216

16 Ding C et al A comparative study of NiOndashCe 09 Gd 01 O 195 nanocomposite powders synthesized by hydroxide and oxalate co-precipitation methods Ceramics International 2012 38(1) p 85-92

17 Ding C et al Synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite powders for low-temperature solid oxide fuel cell anodes by co-precipitation Scripta Materialia 2009 60(4) p 254-256

18 Park S-Y et al Preparation of highly porous NiOndashgadolinium-doped ceria nano-composite powders by one-pot glycine nitrate process for anode-supported tubular solid oxide fuel cells Journal of Asian Ceramic Societies 2014 2(4) p 339-346

19 Zhu W and S Deevi A review on the status of anode materials for solid oxide fuel cells Materials Science and Engineering A 2003 362(1) p 228-239

20 Chick LA et al Glycine-nitrate combustion synthesis of oxide ceramic powders Materials Letters 1990 10(1-2) p 6-12

21 Basu RN et al Microstructure and electrical conductivity of LaNi 06 Fe 04 O 3 prepared by combustion synthesis routes Materials Research Bulletin 2004 39(9) p 1335-1345

22 SOFC ZS Microstructure development of the Ni-GDC anode material for IT-SOFC Materiali in tehnologije 2012 46(5) p 445-451

23 Aparicio M A Jitianu and LC Klein Sol-Gel Processing for Conventional and Alternative Energy 2012 Springer Science amp Business Media

24 Suciu C et al NiOYSZ nanoparticles obtained by new solndashgel route Chemical Engineering Journal 2008 140(1) p 586-592

25 Jiang SP and SH Chan A review of anode materials development in solid oxide fuel cells Journal of Materials Science 2004 39(14) p 4405-4439

26 Iyer A et al A Sucrose‐Mediated SolndashGel Technique for the Synthesis of MgOndashY2O3 Nanocomposites Journal of the American Ceramic Society 2013 96(2) p 346-350

27 Wang Z et al Ion-exchange kinetics and thermal decomposition characteristics of Fe2+-exchanged alginic acid membrane for the formation of iron oxide nanoparticles Journal of Materials Science 2014 49(20) p 7151-7155

28 Schnepp Z et al Alginate-mediated routes to the selective synthesis of complex metal oxide nanostructures CrystEngComm 2010 12(5) p 1410-1415

29 Wang Z GM Kale and M Ghadiri Synthesis and characterization of CexGd 1minus xO 2minus δ nanopowders employing an alginate mediated ion-exchange process Chemical Engineering Journal 2012 198 p 149-153

30 Brayner R et al Alginate-mediated growth of Co Ni and CoNi nanoparticles influence of the biopolymer structure Chemistry of Materials 2007 19(5) p 1190-1198

31 Balavandy SK K Shameli and ZZ Abidin Rapid and Green Synthesis of Silver Nanoparticles via Sodium Alginate Media Int J Electrochem Sci 2015 10 p 486-497

32 Choo CK BA Horri and B Salamatinia Synthesis and Characterization of Nickel (II) OxideGadolinium-Doped Ceria (NiOGDC) Nanocomposites As a Potential Material for Anode Supported LT-SOFCs in Proceedings of the World Congress on Engineering and Computer Science 2016

33 Rath MK M-J Lee and K-T Lee Preparation of nano-structured NindashCe 08 Gd 02 O 19 anode materials for solid oxide fuel cells via the water-in-oil (WO) micro-emulsion route Ceramics International 2014 40(1) p 1909-1917

34 Schneider CA WS Rasband and KW Eliceiri NIH Image to ImageJ 25 years of image analysis Nature methods 2012 9(7) p 671-675

35 Collins T ImageJ for Microscopy BioTechniques 43 S25-S30 httpdx doi org102144000112517 2007

36 Thierry R F Thierry and G Osenga Surface energy modified particles method of making and use thereof 2015 Google Patents

37 Macedo DA et al A versatile route for the preparation of NindashCGO cermets from nanocomposite powders Ceramics International 2013 39(4) p 4321-4328

38 Wandekar R et al Physicochemical studies of NiOndashGDC composites Materials Chemistry and Physics 2006 99(2) p 289-294

39 Prakash BS VW Grips and S Aruna A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes Journal of Power Sources 2012 214 p 358-364

40 Sartori C et al Determination of the cation content of alginate thin films by FTi r spectroscopy Polymer 1997 38(1) p 43-51

41 Lakouraj MM F Mojerlou and EN Zare Nanogel and superparamagnetic nanocomposite based on sodium alginate for sorption of heavy metal ions Carbohydrate polymers 2014 106 p 34-41

42 Srivastava M et al Synthesis of superparamagnetic bare Fe 3 O 4 nanostructures and coreshell (Fe 3 O 4alginate) nanocomposites Carbohydrate polymers 2012 89(3) p 821-829

43 Chavan A et al Effect of variation of NiO on properties of NiOGDC (gadolinium doped ceria) nano-composites Ceramics International 2012 38(4) p 3191-3196

44 Shen C and LL Shaw FTIR analysis of the hydrolysis rate in the solndashgel formation of gadolinia-doped ceria with acetylacetonate precursors Journal of sol-gel science and technology 2010 53(3) p 571-577

45 Wang T and D-C Sun Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method Materials Research Bulletin 2008 43(7) p 1754-1760

46 Sing KS Reporting physisorption data for gassolid systems with special reference to the determination of surface area and porosity (Recommendations 1984) Pure and applied chemistry 1985 57(4) p 603-619

47 Song X et al Synthesis and Characterization of Y-Doped Mesoporous CeO 2 Using A Chemical Precipitation Method Journal of Rare Earths 2007 25(4) p 428-433

and CoNi [11 29-31] An extensive study has been done on GDC nanocomposites as the

electrolyte part for low-temperature SOFCs [6] The same research team had also conducted a

preliminary study on synthesizing NiO-GDC which showed the potential of using this

method to produce nanocomposites of these metals [32] However the conditions were not

fully elaborated and there is still a lack of comprehensive study on this method and the

characterization of the synthesized material

This current study was focused on elaborating the effect of calcination temperature and

time on the synthesis of a high-purity nanocrystalline NiO-GDC (NiOCe08Gd02O190) powder

via the ionic-gelation of sodium alginate The nanocrystalline NiO-GDC obtained in this

study was characterized using thermal analysis (TGADSC) X-ray diffraction (XRD) Field

Emission Scanning Electron Microscopy (FESEM) Energy-dispersive x-ray spectroscopy

(EDX) Fourier transform infrared spectroscopy (FTIR) and nitrogen adsorption-desorption

(BET) This research investigated a new environmentally friendly method for synthesizing

pure NiO-GDC Detailed findings regarding the influence of dominant synthesizing variables

on the physiochemical properties of the nanocrystalline NiO-GDC powders are reported in

the following sections

2 Materials and Methods

21 Materials

Cerium (III) nitrate hexahydrate (Ce (NO3)36H2O 99 purity) and gadolinium (III)

nitrate hexahydrate (Gd(NO3)36H2O 999 purity) from Sigma Aldrich USA and

nickel(II) nitrate hexahydrate (Ni(NO3)26H2O 99 purity) from Merck Germany were used

as the starting materials without any further purification in this study Additionally Manugel

GHB sodium alginate powder ((C6H7NaO6)n MW 264 kDa) with an MG ratio of 059

obtained from BioPolymer UK was used as the gelling template

22 Synthesis of nanocrystalline NiO-GDC powders

A cationic solution with a total concentration of 30 gL was prepared by dissolving the

calculated amounts of each metal nitrate salt (Ce(NO3)36H2O) (Gd(NO3)36H2O) and

(Ni(NO3)26H2O) into ultra-pure water Sodium alginate solution at 3 wt was prepared by

dissolving the appropriate amount of sodium alginate (Na-Alg) powder into ultra-pure water

using a water-bath at 80 degC

Alginate beads with a diameter of approximately 2 mm before drying (Figure 1a) and 1

mm after drying (Figure 1b) were produced by dripping the Na-Alg solution into a

homogeneous metal nitrate solution using a 06 mm needle with a 20 mm internal diameter

syringe at a rate of 07 mLmin The alginate solution that dripped into the nitrate solution

had rapidly formed beads

Then the as-prepared beads were gently stirred in the nitrate solution for 24 h at a

stirring rate of 100 rpm to increase the ion-exchange reaction between Na+ (in the alginate

structure) and Ce3+ Gd3+ and Ni2+ (in the salt solution) at room temperature After 24 h the

beads were filtered and washed with 45 mL of ultra-pure water to remove any sodium nitrate

trapped in the gel structure Next the beads were dried in a Memmert oven (model UF110)

for 24 h at 50 ordmC All dropped beads were well distributed without any agglomeration (Figure

1a) Figure 1b shows the greenish coloured beads after drying at 50 degC in the oven for 24

hours which were approximately 1 mm in size Finally the dried bead sample underwent

calcination at different temperatures (500 degC 600 degC and 700 degC) for different durations (2

h 6 h and 10 h) with a fixed ramp rate of 2 degCmin Table 1 presents the combinations of

calcination times and calcination temperatures used in each experimental run The calcined

powders were ground with mortar and pestle to break the agglomerated particles

23 Characterization

Thermogravimetric analysis (TGA Q50 from TA Instruments USA) was used to

study the thermal decomposition behaviour of the dried gels and the calcined samples in air

between 25 degC and 800 degC with an increasing ramp rate of 5 degC minute X-ray powder

diffraction was performed using an XRD diffractometer (D8 Discover from Bruker

Germany) with CuKα1 radiation (λ = 154060Aring) in the 2θ range between 10deg and 90deg and a

scanning rate of 002 degs using the Bragg-Brentano beam method at 40 kV and 40 mA All

XRD patterns were indexed using ICDD file no 00-50-0201 and 00-002101216 for GDC and

NiO crystals respectively The crystallite sizes of the NiO and GDC nanocrystallites were

calculated using Scherrer equation D=09 λ βcosθ where D is the crystallite size (nm) λ is

the wavelength of the source (nm) β is the full width at half maximum (FWHM) of the peak

and θ is the Bragg angle (radians) The morphology of NiO-GDC nanocrystallite was

analysed using the micrograph images obtained from a Field Emission Scanning Electron

Microscopy (FESEM SU8010 Hitachi Japan) All FESEM specimens were coated with

platinum for 120 seconds with a sputter current at 30 mA using a coater (Quarum Q150R S)

prior to the analysis Energy-dispersive x-ray (Oxford Horiba Inca XMax50 EDX) analysis

was performed to confirm the presence of cerium gadolinium and oxygen atoms in all

samples The FTIR spectra of the calcined and the dried powders were obtained using a

Fourier transform infrared spectrometer (FTIR NICOLET 1810 USA) over the

wavenumber range of 650ndash4000 cm-1 The surface area of the calcined samples was measured

by a BET analyser (Micromeritics ASAP 2020 USA)

3 Results and Discussion

The results for the thermogravimetric analysis (TGADTA) of the dried and calcined

sample at 700 degC for 2 h are shown as the representative sample in Figure 2 Four weight loss

steps corresponding to room temperature 25 degC plusmn1 degC to 186 degC 186 degC to 301 degC 301 degC to

380 degC and 380 degC to 500 degC were observed for the dried sample (Figure 2a) The

decomposition steps in the TGA curves were found to be in good agreement with the DTA

curves represented in Figure 2a A weight loss of 1146 plusmn 010 was observed during the

first step (25 degC ndash 186 degC) that corresponded to the evaporation of water in the alginate

structure during heat treatment In the second step (186 degC - 301 degC) a weight loss of 3641plusmn

015 was detected that could be due to the cleavage of G-G G-M and M-M weaker

linkages in the alginate molecule causing considerable oxygen evolution Wang et al[11]

also reported similar results for the weight loss of alginate in the same temperature range for

the dried sample of NiO nanopowders with sodium alginate When the operational

temperature was increased from 301 to 380 degC during the third step further decomposition

occurred which resulted in approximately 57 plusmn 0075 of weight loss in the TGA profile

This can be attributed to the decomposition of metastable-NiO2 to thermodynamically more

stable NiO phase which is demonstrated as a small exothermic peak [11] During the fourth

step the temperature was further increased from 380 degC to around 500 degC The residues of b-

D-mannuronic acid (M) and a-L-guluronic acid (G) in the alginate structure were completely

oxidised as observed from the 1924 plusmn 0075 weight loss that resulted in an exothermic

decomposition peak Previous studies offered similar reasoning for the final decomposition

step [27] No further weight loss was observed at temperatures of higher than 500 degC Figure

2a shows that the decomposition process could be completed at 500 degC

The TGADTA plot for the sample that was calcined at 700 degC for 2 hours is shown in

Figure 2b Three major weight losses were visible in the plot The first weight loss of 018 plusmn

001 occurred between room temperature and approximately 48 degC and was due to water

evaporation which was confirmed by the small endothermic peak in the DTA curve During

the second step (75-91 degC) a weight loss of 194 plusmn 001 was observed due to organic

components that still remained after calcination [33] The third weight loss of 177plusmn 001

was observed between 93-406 degC which corresponded to the decomposition of Ni(OH)2 to

NiO Ce(OH)3 to CeO2 and Gd(OH)3 to Gd2O3 [33] No further weight loss was observed at

temperature of higher than 400 degC which indicated the absence of carbonaceous bonds or

any other undecomposed residue in the sample

The FESEM images for the NiO-GDC nanocrystallites synthesized with 3 loading

fractions of sodium alginate at 500 degC 600 degC and 700 degC calcination temperature with

different calcination time are displayed in Figures 3 4 and 5 respectively ImageJ software

was used to quantitatively analyse the FESEM images [34 35] First a binary image was

extracted by carefully performing intensity-thresholding on the original FESEM image

Using erosion and dilation irregular shapes were removed The remaining particles were

morphologically closed and smoothened by applying a Gaussian blur The resultant binary

images which contained particles in the form of blobs were passed to the analysis module

for an automatic measurement of the particle size The particle size distribution for each

image has been embedded at its top-right corner where micro denotes the average particle size

with the standard deviation and Ɲ denotes the number of particles utilized in the analysis

As seen in Figures 3 4 and 5 the particle size had slowly increased when the

calcination temperature was increased from 500 to 700 degC at a constant calcination time

These results could be linked to the agglomeration of the particles caused by several

phenomena such as lsquouncontrolled build-uprsquo lsquobridgingrsquo or lsquolumpingrsquo during the thermal

treatment process (refer Figures 3a 4a and 5a) [36] It was also observed that at a constant

calcination temperature the size of the nanocrystallites had increased due to the

agglomeration of smaller particles when the calcination time was increased from 2 h to 10 h

(refer Figures 4a 4b and 4c) Thus the agglomeration of smaller particles can be

manipulated by determining the optimum calcination temperature and duration to obtain

specific particle sizes In each series of images 3a 3b and 3c 4a 4b and 4c and 5a

5b and5c this trend can be seen for all calcination times and calcination temperatures

The results showed that the smallest particle size (641 nm) was obtained with

calcination conditions of 500 degC for 2 h (641 nm) The largest particle size of 2125 nm was

obtained at 700 degC after 10 h of calcination These results were in agreement with the

previous discussion In conclusion for synthesizing smaller nanocrystalline NiO-GDC lower

calcination temperature (500 degC) and shorter calcination time (2 h) is needed

The EDX elemental analysis and mapping is shown in Figure 6 for nancrystalline NiO-

GDC synthesized at 500 degC for 6 h which confirmed the presence of cerium gadolinium

oxygen and nickel atoms The sample shown in Figure 6 was chosen as an example to

represent all the samples that were elaborated in this study

X-ray diffraction (XRD) patterns of the nanocrystalline NiO-GDC powders synthesized

at different calcination times and temperatures are shown in Figure 7 The peaks for all

samples were well matched with the cubic Ce08Gd02O19 (Fm-3m ICDD00-50-0201) and

cubic NiO (Fm-3m ICDD 00-002101216) The average crystallite sizes of these particles

were determined using the Scherrer equation as listed in Table 2 The crystallite sizes of NiO

and GDC in NiO-GDC have been reported by several studies that used different methods

such as polymeric sol-gel (with NiO at 24 nm and GDC at 18 nm) [37] hydroxide co-

precipitation method (NiO at 305 nm and GDC at 273 nm) [17] solution combustion

synthesis (NiO at 30-58 nm and GDC at 40-50 nm) [38] micro emulsion method (NiO at

132 148 and 134 nm and GDC at 117 137 and 106 nm) as well as microemulsion-

mediated solvothermal process (NiO at 22 plusmn 2 nm and GDC at 20 plusmn 2 nm) These studies

have shown that ion-gelation synthesis can successfully synthesize smaller sized NiO-GDC

nanocomposites

The XRD patterns have shown that the diffraction peaks for GDC and NiO crystal

phases became sharper when calcination temperature was increased from 500 to 700 degC at

constant calcination time as well as when calcination time was increased from 2 h to 10 h at a

constant calcination temperature which indicated the growth in the crystallite size (Table 1)

due to particle agglomeration [36] At lower calcination temperature (500 degC) with different

calcination times (2 6 and 10 h) the broader peaks in an XRD pattern show the existence of

smaller-sized NiO and GDC crystallites for all samples [39] In this study the XRD pattern

(Figure 7) was in agreement with crystallite size tabulated in Table 2

The calculated crystallite sizes using the Scherrer equation (Table 2) supported the

results from the XRD patterns which indicated that by increasing the calcination time and

temperature the crystallite sizes of NiO and GDC were increased as well The calculated

crystallite sizes of NiO and GDC in Table 2 were in good agreement with the results attained

from the quantitative image analysis reported in Figure 3 Figure 4 and Figure 5 which

confirmed the influences of both the calcination temperature and calcination time on the size

of the powder particles

Figure 8 shows the FTIR spectra for the dried gel and the calcined samples at different

calcination temperatures and times The FTIR spectrum for the dried sample showed

numerous adsorption bands in the 800-1610 cm-1 region The peaks at 884 cm-1 could be

attributed to the C-C band for sodium alginate [40] Meanwhile the band at 1026 cm-1 (C-O-

C stretching) corresponded to sodium alginate glycosidic linkage [41] Additionally the

stretch at 3355 cm-1 and the absorption peaks at 1600 to 1414 cm-1 corresponded to O-H band

and the asymmetric and symmetric stretching vibration of the carboxylate group respectively

[42] After the dried sample had undergone thermal treatment at different calcination times

and temperatures a reduction in the intensity of carbon bands was observed which

confirmed the effectiveness of the calcination process in completing the thermal

decomposition of the biopolymer compound However further increase in the calcination

temperature and calcination time had led to a reduction in the intensity of the peaks This

condition showed that these samples had attained more purity in their metal oxide

compositions The absorption band for metal-oxygen has been reported by various studies

such as (Ce-OGd-ONi-O) was detected at approximately 635 cm-1 [33] (Ce-O) was

observed at 564 cm-1 while the 550-700 cm-1 region was assigned to NiO stretching vibration

[43-45] However due to the presence of noise at lower than 650 cm -1 the measuring range

utilized in these current experiments was between 650 cm-1 to 4000 cm-1

The BET analysis was conducted by applying the Barrett-Joyner-Halenda (BJH)

method to study the physicochemical properties of the calcined NiO-GDC at different

calcination times and temperatures Based on literature review there is a lack of information

on BET analysis of NiO-GDC and thus more in-depth studies are needed in this area The

nitrogen adsorption-desorption isotherms (hysteresis loops) of the NiO-GDC are given in

Figure 9 with the pore size distribution of the different samples in the inset The nitrogen

adsorption-desorption isotherms (Figure 9) indicated the presence of mesopores in the

samples based on the type IV isotherm as per IUPAC classification The mesopores were

formed due to the capillary condensation of the mesoporous materials thus confirming the

mesoporosity of the synthesized NiO-GDC nanocrystallites [46] The hysteresis loops of the

samples in the pp0 range of 04-10 illustrated the absence of micropores and that the pores

had changed into the mesoporous reign [46] The pore size distributions of the samples are

given in the inset of Figure 9 The majority of the NiO-GDC samples were in the mesoporous

region (10 nm) as determined by the BJH method which supported the N2 adsorption-

desorption isotherms

It can be observed from Figure 9 that for samples calcined at 500 degC for 2 h 6 h and 10 h the

relative pressure (corresponding to the onset of capillary condensation) has a higher value

which indicated the presence of the smaller pore size distribution for that sample [47]

The BET surface areas for all samples are summarized in Table 3 It can be seen that

at a specific calcination temperature increasing the calcination time from 2 h to 10 h had

caused the surface area of the sample to decrease due to the increasing particle size

Similarly by increasing the calcination temperature from 500 degC to 700 degC the surface areas

of the samples had decreased due to the increasing particle sizes The largest surface areas

corresponded to the nanocrystallite samples calcined at 500 degC for 2 h However these values

had reduced when the calcination temperature and time were gradually increased to 700 degC

and 10 h respectively These results are in good agreement with the particle sizes obtained

from the FESEM and XRD results

4 Conclusion

Nanocrytalline NiO-GDC powders were synthesized using an environmentally

friendly ionic gelation method with sodium alginate as the precursor The effects of the

synthesis parameters such as calcination temperature and calcination time on the properties

of the produced nanocrystalline NiO-GDC powders were studied using various

characterization techniques It was found that at a fixed calcination temperature the size of

the nanocrystals would increase with increasing calcination time Similarly at a fixed

calcination time and increasing calcination temperature larger nanocrystals were produced

Therefore for synthesizing smaller nanocrystals lower calcination temperature (500 degC) and

shorter calcination time (2 h) are recommended It was also observed that calcination

temperature has more effect on the BET surface compared to calcination time which showed

that the pore size of the nanocrystalline powders was more dependent on the calcination

temperature

5 Acknowledgement

The authors would like to acknowledge the Ministry of Science Education and Innovation

(MOSTI) of Malaysia for providing research funding under the e-science scheme grant

number 03-02-10-SF0259

References

1 Boury B and S Plumejeau Metal oxides and polysaccharides an efficient hybrid association for materials chemistry Green Chemistry 2015 17(1) p 72-88

2 Bell AT The impact of nanoscience on heterogeneous catalysis Science 2003 299(5613) p 1688-1691

3 Zhao X et al The role of nanomaterials in redox-based supercapacitors for next generation energy storage devices Nanoscale 2011 3(3) p 839-855

4 Sun Y-F et al Metal oxide nanostructures and their gas sensing properties a review Sensors 2012 12(3) p 2610-2631

5 Jia J et al Heterogeneous catalytic hydrogenation of CO 2 by metal oxides defect engineeringndashperfecting imperfection Chemical Society Reviews 2017 46(15) p 4631-4644

6 Pezeshkpour S et al Ionicndashgelation synthesis of gadolinium doped ceria (Ce 08 Gd 02 O 190) nanocomposite powder using sodium-alginate Ceramics International 2017 43(9) p 7123-7135

7 Atif M et al Studies on the magnetic magnetostrictive and electrical properties of solndashgel synthesized Zn doped nickel ferrite Journal of Alloys and Compounds 2011 509(18) p 5720-5724

8 Krstajić N et al Non-noble metal composite cathodes for hydrogen evolution Part I the NindashMoO x coatings electrodeposited from Wattrsquos type bath containing MoO 3 powder particles international journal of hydrogen energy 2011 36(11) p 6441-6449

9 Macedo DA et al NindashCGO cermet anodes from nanocomposite powders Microstructural and electrochemical assessment Ceramics International 2014 40(8) p 13105-13113

10 Gao H et al The design of excellent xylene gas sensor using Sn-doped NiO hierarchical nanostructure Sensors and Actuators B Chemical 2017 253 p 1152-1162

11 Wang Z GM Kale and M Ghadiri Novel Ion‐Exchange Process for the Preparation of Metal Oxide Nanopowders from Sodium Alginate Journal of the American Ceramic Society 2012 95(10) p 3124-3129

12 Galeano MAacuteN et al Studies on the structural quantitative and semi-quantitative analyses of NiOndashGDC nanocomposites RSC Advances 2016 6(77) p 72865-72876

13 Gil V C Moure and J Tartaj Sinterability microstructures and electrical properties of NiGd-doped ceria cermets used as anode materials for SOFCs Journal of the European Ceramic Society 2007 27(13) p 4205-4209

14 Akbari-Fakhrabadi A et al Combustion synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite anode and its electrical characteristics of semi-cell configured SOFC assembly Journal of Alloys and Compounds 2012 541 p 1-5

15 Ishihara T et al NickelndashGd-doped CeO 2 cermet anode for intermediate temperature operating solid oxide fuel cells using LaGaO 3-based perovskite electrolyte Solid State Ionics 2000 132(3) p 209-216

16 Ding C et al A comparative study of NiOndashCe 09 Gd 01 O 195 nanocomposite powders synthesized by hydroxide and oxalate co-precipitation methods Ceramics International 2012 38(1) p 85-92

17 Ding C et al Synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite powders for low-temperature solid oxide fuel cell anodes by co-precipitation Scripta Materialia 2009 60(4) p 254-256

18 Park S-Y et al Preparation of highly porous NiOndashgadolinium-doped ceria nano-composite powders by one-pot glycine nitrate process for anode-supported tubular solid oxide fuel cells Journal of Asian Ceramic Societies 2014 2(4) p 339-346

19 Zhu W and S Deevi A review on the status of anode materials for solid oxide fuel cells Materials Science and Engineering A 2003 362(1) p 228-239

20 Chick LA et al Glycine-nitrate combustion synthesis of oxide ceramic powders Materials Letters 1990 10(1-2) p 6-12

21 Basu RN et al Microstructure and electrical conductivity of LaNi 06 Fe 04 O 3 prepared by combustion synthesis routes Materials Research Bulletin 2004 39(9) p 1335-1345

22 SOFC ZS Microstructure development of the Ni-GDC anode material for IT-SOFC Materiali in tehnologije 2012 46(5) p 445-451

23 Aparicio M A Jitianu and LC Klein Sol-Gel Processing for Conventional and Alternative Energy 2012 Springer Science amp Business Media

24 Suciu C et al NiOYSZ nanoparticles obtained by new solndashgel route Chemical Engineering Journal 2008 140(1) p 586-592

25 Jiang SP and SH Chan A review of anode materials development in solid oxide fuel cells Journal of Materials Science 2004 39(14) p 4405-4439

26 Iyer A et al A Sucrose‐Mediated SolndashGel Technique for the Synthesis of MgOndashY2O3 Nanocomposites Journal of the American Ceramic Society 2013 96(2) p 346-350

27 Wang Z et al Ion-exchange kinetics and thermal decomposition characteristics of Fe2+-exchanged alginic acid membrane for the formation of iron oxide nanoparticles Journal of Materials Science 2014 49(20) p 7151-7155

28 Schnepp Z et al Alginate-mediated routes to the selective synthesis of complex metal oxide nanostructures CrystEngComm 2010 12(5) p 1410-1415

29 Wang Z GM Kale and M Ghadiri Synthesis and characterization of CexGd 1minus xO 2minus δ nanopowders employing an alginate mediated ion-exchange process Chemical Engineering Journal 2012 198 p 149-153

30 Brayner R et al Alginate-mediated growth of Co Ni and CoNi nanoparticles influence of the biopolymer structure Chemistry of Materials 2007 19(5) p 1190-1198

31 Balavandy SK K Shameli and ZZ Abidin Rapid and Green Synthesis of Silver Nanoparticles via Sodium Alginate Media Int J Electrochem Sci 2015 10 p 486-497

32 Choo CK BA Horri and B Salamatinia Synthesis and Characterization of Nickel (II) OxideGadolinium-Doped Ceria (NiOGDC) Nanocomposites As a Potential Material for Anode Supported LT-SOFCs in Proceedings of the World Congress on Engineering and Computer Science 2016

33 Rath MK M-J Lee and K-T Lee Preparation of nano-structured NindashCe 08 Gd 02 O 19 anode materials for solid oxide fuel cells via the water-in-oil (WO) micro-emulsion route Ceramics International 2014 40(1) p 1909-1917

34 Schneider CA WS Rasband and KW Eliceiri NIH Image to ImageJ 25 years of image analysis Nature methods 2012 9(7) p 671-675

35 Collins T ImageJ for Microscopy BioTechniques 43 S25-S30 httpdx doi org102144000112517 2007

36 Thierry R F Thierry and G Osenga Surface energy modified particles method of making and use thereof 2015 Google Patents

37 Macedo DA et al A versatile route for the preparation of NindashCGO cermets from nanocomposite powders Ceramics International 2013 39(4) p 4321-4328

38 Wandekar R et al Physicochemical studies of NiOndashGDC composites Materials Chemistry and Physics 2006 99(2) p 289-294

39 Prakash BS VW Grips and S Aruna A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes Journal of Power Sources 2012 214 p 358-364

40 Sartori C et al Determination of the cation content of alginate thin films by FTi r spectroscopy Polymer 1997 38(1) p 43-51

41 Lakouraj MM F Mojerlou and EN Zare Nanogel and superparamagnetic nanocomposite based on sodium alginate for sorption of heavy metal ions Carbohydrate polymers 2014 106 p 34-41

42 Srivastava M et al Synthesis of superparamagnetic bare Fe 3 O 4 nanostructures and coreshell (Fe 3 O 4alginate) nanocomposites Carbohydrate polymers 2012 89(3) p 821-829

43 Chavan A et al Effect of variation of NiO on properties of NiOGDC (gadolinium doped ceria) nano-composites Ceramics International 2012 38(4) p 3191-3196

44 Shen C and LL Shaw FTIR analysis of the hydrolysis rate in the solndashgel formation of gadolinia-doped ceria with acetylacetonate precursors Journal of sol-gel science and technology 2010 53(3) p 571-577

45 Wang T and D-C Sun Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method Materials Research Bulletin 2008 43(7) p 1754-1760

46 Sing KS Reporting physisorption data for gassolid systems with special reference to the determination of surface area and porosity (Recommendations 1984) Pure and applied chemistry 1985 57(4) p 603-619

47 Song X et al Synthesis and Characterization of Y-Doped Mesoporous CeO 2 Using A Chemical Precipitation Method Journal of Rare Earths 2007 25(4) p 428-433

A cationic solution with a total concentration of 30 gL was prepared by dissolving the

calculated amounts of each metal nitrate salt (Ce(NO3)36H2O) (Gd(NO3)36H2O) and

(Ni(NO3)26H2O) into ultra-pure water Sodium alginate solution at 3 wt was prepared by

dissolving the appropriate amount of sodium alginate (Na-Alg) powder into ultra-pure water

using a water-bath at 80 degC

Alginate beads with a diameter of approximately 2 mm before drying (Figure 1a) and 1

mm after drying (Figure 1b) were produced by dripping the Na-Alg solution into a

homogeneous metal nitrate solution using a 06 mm needle with a 20 mm internal diameter

syringe at a rate of 07 mLmin The alginate solution that dripped into the nitrate solution

had rapidly formed beads

Then the as-prepared beads were gently stirred in the nitrate solution for 24 h at a

stirring rate of 100 rpm to increase the ion-exchange reaction between Na+ (in the alginate

structure) and Ce3+ Gd3+ and Ni2+ (in the salt solution) at room temperature After 24 h the

beads were filtered and washed with 45 mL of ultra-pure water to remove any sodium nitrate

trapped in the gel structure Next the beads were dried in a Memmert oven (model UF110)

for 24 h at 50 ordmC All dropped beads were well distributed without any agglomeration (Figure

1a) Figure 1b shows the greenish coloured beads after drying at 50 degC in the oven for 24

hours which were approximately 1 mm in size Finally the dried bead sample underwent

calcination at different temperatures (500 degC 600 degC and 700 degC) for different durations (2

h 6 h and 10 h) with a fixed ramp rate of 2 degCmin Table 1 presents the combinations of

calcination times and calcination temperatures used in each experimental run The calcined

powders were ground with mortar and pestle to break the agglomerated particles

23 Characterization

Thermogravimetric analysis (TGA Q50 from TA Instruments USA) was used to

study the thermal decomposition behaviour of the dried gels and the calcined samples in air

between 25 degC and 800 degC with an increasing ramp rate of 5 degC minute X-ray powder

diffraction was performed using an XRD diffractometer (D8 Discover from Bruker

Germany) with CuKα1 radiation (λ = 154060Aring) in the 2θ range between 10deg and 90deg and a

scanning rate of 002 degs using the Bragg-Brentano beam method at 40 kV and 40 mA All

XRD patterns were indexed using ICDD file no 00-50-0201 and 00-002101216 for GDC and

NiO crystals respectively The crystallite sizes of the NiO and GDC nanocrystallites were

calculated using Scherrer equation D=09 λ βcosθ where D is the crystallite size (nm) λ is

the wavelength of the source (nm) β is the full width at half maximum (FWHM) of the peak

and θ is the Bragg angle (radians) The morphology of NiO-GDC nanocrystallite was

analysed using the micrograph images obtained from a Field Emission Scanning Electron

Microscopy (FESEM SU8010 Hitachi Japan) All FESEM specimens were coated with

platinum for 120 seconds with a sputter current at 30 mA using a coater (Quarum Q150R S)

prior to the analysis Energy-dispersive x-ray (Oxford Horiba Inca XMax50 EDX) analysis

was performed to confirm the presence of cerium gadolinium and oxygen atoms in all

samples The FTIR spectra of the calcined and the dried powders were obtained using a

Fourier transform infrared spectrometer (FTIR NICOLET 1810 USA) over the

wavenumber range of 650ndash4000 cm-1 The surface area of the calcined samples was measured

by a BET analyser (Micromeritics ASAP 2020 USA)

3 Results and Discussion

The results for the thermogravimetric analysis (TGADTA) of the dried and calcined

sample at 700 degC for 2 h are shown as the representative sample in Figure 2 Four weight loss

steps corresponding to room temperature 25 degC plusmn1 degC to 186 degC 186 degC to 301 degC 301 degC to

380 degC and 380 degC to 500 degC were observed for the dried sample (Figure 2a) The

decomposition steps in the TGA curves were found to be in good agreement with the DTA

curves represented in Figure 2a A weight loss of 1146 plusmn 010 was observed during the

first step (25 degC ndash 186 degC) that corresponded to the evaporation of water in the alginate

structure during heat treatment In the second step (186 degC - 301 degC) a weight loss of 3641plusmn

015 was detected that could be due to the cleavage of G-G G-M and M-M weaker

linkages in the alginate molecule causing considerable oxygen evolution Wang et al[11]

also reported similar results for the weight loss of alginate in the same temperature range for

the dried sample of NiO nanopowders with sodium alginate When the operational

temperature was increased from 301 to 380 degC during the third step further decomposition

occurred which resulted in approximately 57 plusmn 0075 of weight loss in the TGA profile

This can be attributed to the decomposition of metastable-NiO2 to thermodynamically more

stable NiO phase which is demonstrated as a small exothermic peak [11] During the fourth

step the temperature was further increased from 380 degC to around 500 degC The residues of b-

D-mannuronic acid (M) and a-L-guluronic acid (G) in the alginate structure were completely

oxidised as observed from the 1924 plusmn 0075 weight loss that resulted in an exothermic

decomposition peak Previous studies offered similar reasoning for the final decomposition

step [27] No further weight loss was observed at temperatures of higher than 500 degC Figure

2a shows that the decomposition process could be completed at 500 degC

The TGADTA plot for the sample that was calcined at 700 degC for 2 hours is shown in

Figure 2b Three major weight losses were visible in the plot The first weight loss of 018 plusmn

001 occurred between room temperature and approximately 48 degC and was due to water

evaporation which was confirmed by the small endothermic peak in the DTA curve During

the second step (75-91 degC) a weight loss of 194 plusmn 001 was observed due to organic

components that still remained after calcination [33] The third weight loss of 177plusmn 001

was observed between 93-406 degC which corresponded to the decomposition of Ni(OH)2 to

NiO Ce(OH)3 to CeO2 and Gd(OH)3 to Gd2O3 [33] No further weight loss was observed at

temperature of higher than 400 degC which indicated the absence of carbonaceous bonds or

any other undecomposed residue in the sample

The FESEM images for the NiO-GDC nanocrystallites synthesized with 3 loading

fractions of sodium alginate at 500 degC 600 degC and 700 degC calcination temperature with

different calcination time are displayed in Figures 3 4 and 5 respectively ImageJ software

was used to quantitatively analyse the FESEM images [34 35] First a binary image was

extracted by carefully performing intensity-thresholding on the original FESEM image

Using erosion and dilation irregular shapes were removed The remaining particles were

morphologically closed and smoothened by applying a Gaussian blur The resultant binary

images which contained particles in the form of blobs were passed to the analysis module

for an automatic measurement of the particle size The particle size distribution for each

image has been embedded at its top-right corner where micro denotes the average particle size

with the standard deviation and Ɲ denotes the number of particles utilized in the analysis

As seen in Figures 3 4 and 5 the particle size had slowly increased when the

calcination temperature was increased from 500 to 700 degC at a constant calcination time

These results could be linked to the agglomeration of the particles caused by several

phenomena such as lsquouncontrolled build-uprsquo lsquobridgingrsquo or lsquolumpingrsquo during the thermal

treatment process (refer Figures 3a 4a and 5a) [36] It was also observed that at a constant

calcination temperature the size of the nanocrystallites had increased due to the

agglomeration of smaller particles when the calcination time was increased from 2 h to 10 h

(refer Figures 4a 4b and 4c) Thus the agglomeration of smaller particles can be

manipulated by determining the optimum calcination temperature and duration to obtain

specific particle sizes In each series of images 3a 3b and 3c 4a 4b and 4c and 5a

5b and5c this trend can be seen for all calcination times and calcination temperatures

The results showed that the smallest particle size (641 nm) was obtained with

calcination conditions of 500 degC for 2 h (641 nm) The largest particle size of 2125 nm was

obtained at 700 degC after 10 h of calcination These results were in agreement with the

previous discussion In conclusion for synthesizing smaller nanocrystalline NiO-GDC lower

calcination temperature (500 degC) and shorter calcination time (2 h) is needed

The EDX elemental analysis and mapping is shown in Figure 6 for nancrystalline NiO-

GDC synthesized at 500 degC for 6 h which confirmed the presence of cerium gadolinium

oxygen and nickel atoms The sample shown in Figure 6 was chosen as an example to

represent all the samples that were elaborated in this study

X-ray diffraction (XRD) patterns of the nanocrystalline NiO-GDC powders synthesized

at different calcination times and temperatures are shown in Figure 7 The peaks for all

samples were well matched with the cubic Ce08Gd02O19 (Fm-3m ICDD00-50-0201) and

cubic NiO (Fm-3m ICDD 00-002101216) The average crystallite sizes of these particles

were determined using the Scherrer equation as listed in Table 2 The crystallite sizes of NiO

and GDC in NiO-GDC have been reported by several studies that used different methods

such as polymeric sol-gel (with NiO at 24 nm and GDC at 18 nm) [37] hydroxide co-

precipitation method (NiO at 305 nm and GDC at 273 nm) [17] solution combustion

synthesis (NiO at 30-58 nm and GDC at 40-50 nm) [38] micro emulsion method (NiO at

132 148 and 134 nm and GDC at 117 137 and 106 nm) as well as microemulsion-

mediated solvothermal process (NiO at 22 plusmn 2 nm and GDC at 20 plusmn 2 nm) These studies

have shown that ion-gelation synthesis can successfully synthesize smaller sized NiO-GDC

nanocomposites

The XRD patterns have shown that the diffraction peaks for GDC and NiO crystal

phases became sharper when calcination temperature was increased from 500 to 700 degC at

constant calcination time as well as when calcination time was increased from 2 h to 10 h at a

constant calcination temperature which indicated the growth in the crystallite size (Table 1)

due to particle agglomeration [36] At lower calcination temperature (500 degC) with different

calcination times (2 6 and 10 h) the broader peaks in an XRD pattern show the existence of

smaller-sized NiO and GDC crystallites for all samples [39] In this study the XRD pattern

(Figure 7) was in agreement with crystallite size tabulated in Table 2

The calculated crystallite sizes using the Scherrer equation (Table 2) supported the

results from the XRD patterns which indicated that by increasing the calcination time and

temperature the crystallite sizes of NiO and GDC were increased as well The calculated

crystallite sizes of NiO and GDC in Table 2 were in good agreement with the results attained

from the quantitative image analysis reported in Figure 3 Figure 4 and Figure 5 which

confirmed the influences of both the calcination temperature and calcination time on the size

of the powder particles

Figure 8 shows the FTIR spectra for the dried gel and the calcined samples at different

calcination temperatures and times The FTIR spectrum for the dried sample showed

numerous adsorption bands in the 800-1610 cm-1 region The peaks at 884 cm-1 could be

attributed to the C-C band for sodium alginate [40] Meanwhile the band at 1026 cm-1 (C-O-

C stretching) corresponded to sodium alginate glycosidic linkage [41] Additionally the

stretch at 3355 cm-1 and the absorption peaks at 1600 to 1414 cm-1 corresponded to O-H band

and the asymmetric and symmetric stretching vibration of the carboxylate group respectively

[42] After the dried sample had undergone thermal treatment at different calcination times

and temperatures a reduction in the intensity of carbon bands was observed which

confirmed the effectiveness of the calcination process in completing the thermal

decomposition of the biopolymer compound However further increase in the calcination

temperature and calcination time had led to a reduction in the intensity of the peaks This

condition showed that these samples had attained more purity in their metal oxide

compositions The absorption band for metal-oxygen has been reported by various studies

such as (Ce-OGd-ONi-O) was detected at approximately 635 cm-1 [33] (Ce-O) was

observed at 564 cm-1 while the 550-700 cm-1 region was assigned to NiO stretching vibration

[43-45] However due to the presence of noise at lower than 650 cm -1 the measuring range

utilized in these current experiments was between 650 cm-1 to 4000 cm-1

The BET analysis was conducted by applying the Barrett-Joyner-Halenda (BJH)

method to study the physicochemical properties of the calcined NiO-GDC at different

calcination times and temperatures Based on literature review there is a lack of information

on BET analysis of NiO-GDC and thus more in-depth studies are needed in this area The

nitrogen adsorption-desorption isotherms (hysteresis loops) of the NiO-GDC are given in

Figure 9 with the pore size distribution of the different samples in the inset The nitrogen

adsorption-desorption isotherms (Figure 9) indicated the presence of mesopores in the

samples based on the type IV isotherm as per IUPAC classification The mesopores were

formed due to the capillary condensation of the mesoporous materials thus confirming the

mesoporosity of the synthesized NiO-GDC nanocrystallites [46] The hysteresis loops of the

samples in the pp0 range of 04-10 illustrated the absence of micropores and that the pores

had changed into the mesoporous reign [46] The pore size distributions of the samples are

given in the inset of Figure 9 The majority of the NiO-GDC samples were in the mesoporous

region (10 nm) as determined by the BJH method which supported the N2 adsorption-

desorption isotherms

It can be observed from Figure 9 that for samples calcined at 500 degC for 2 h 6 h and 10 h the

relative pressure (corresponding to the onset of capillary condensation) has a higher value

which indicated the presence of the smaller pore size distribution for that sample [47]

The BET surface areas for all samples are summarized in Table 3 It can be seen that

at a specific calcination temperature increasing the calcination time from 2 h to 10 h had

caused the surface area of the sample to decrease due to the increasing particle size

Similarly by increasing the calcination temperature from 500 degC to 700 degC the surface areas

of the samples had decreased due to the increasing particle sizes The largest surface areas

corresponded to the nanocrystallite samples calcined at 500 degC for 2 h However these values

had reduced when the calcination temperature and time were gradually increased to 700 degC

and 10 h respectively These results are in good agreement with the particle sizes obtained

from the FESEM and XRD results

4 Conclusion

Nanocrytalline NiO-GDC powders were synthesized using an environmentally

friendly ionic gelation method with sodium alginate as the precursor The effects of the

synthesis parameters such as calcination temperature and calcination time on the properties

of the produced nanocrystalline NiO-GDC powders were studied using various

characterization techniques It was found that at a fixed calcination temperature the size of

the nanocrystals would increase with increasing calcination time Similarly at a fixed

calcination time and increasing calcination temperature larger nanocrystals were produced

Therefore for synthesizing smaller nanocrystals lower calcination temperature (500 degC) and

shorter calcination time (2 h) are recommended It was also observed that calcination

temperature has more effect on the BET surface compared to calcination time which showed

that the pore size of the nanocrystalline powders was more dependent on the calcination

temperature

5 Acknowledgement

The authors would like to acknowledge the Ministry of Science Education and Innovation

(MOSTI) of Malaysia for providing research funding under the e-science scheme grant

number 03-02-10-SF0259

References

1 Boury B and S Plumejeau Metal oxides and polysaccharides an efficient hybrid association for materials chemistry Green Chemistry 2015 17(1) p 72-88

2 Bell AT The impact of nanoscience on heterogeneous catalysis Science 2003 299(5613) p 1688-1691

3 Zhao X et al The role of nanomaterials in redox-based supercapacitors for next generation energy storage devices Nanoscale 2011 3(3) p 839-855

4 Sun Y-F et al Metal oxide nanostructures and their gas sensing properties a review Sensors 2012 12(3) p 2610-2631

5 Jia J et al Heterogeneous catalytic hydrogenation of CO 2 by metal oxides defect engineeringndashperfecting imperfection Chemical Society Reviews 2017 46(15) p 4631-4644

6 Pezeshkpour S et al Ionicndashgelation synthesis of gadolinium doped ceria (Ce 08 Gd 02 O 190) nanocomposite powder using sodium-alginate Ceramics International 2017 43(9) p 7123-7135

7 Atif M et al Studies on the magnetic magnetostrictive and electrical properties of solndashgel synthesized Zn doped nickel ferrite Journal of Alloys and Compounds 2011 509(18) p 5720-5724

8 Krstajić N et al Non-noble metal composite cathodes for hydrogen evolution Part I the NindashMoO x coatings electrodeposited from Wattrsquos type bath containing MoO 3 powder particles international journal of hydrogen energy 2011 36(11) p 6441-6449

9 Macedo DA et al NindashCGO cermet anodes from nanocomposite powders Microstructural and electrochemical assessment Ceramics International 2014 40(8) p 13105-13113

10 Gao H et al The design of excellent xylene gas sensor using Sn-doped NiO hierarchical nanostructure Sensors and Actuators B Chemical 2017 253 p 1152-1162

11 Wang Z GM Kale and M Ghadiri Novel Ion‐Exchange Process for the Preparation of Metal Oxide Nanopowders from Sodium Alginate Journal of the American Ceramic Society 2012 95(10) p 3124-3129

12 Galeano MAacuteN et al Studies on the structural quantitative and semi-quantitative analyses of NiOndashGDC nanocomposites RSC Advances 2016 6(77) p 72865-72876

13 Gil V C Moure and J Tartaj Sinterability microstructures and electrical properties of NiGd-doped ceria cermets used as anode materials for SOFCs Journal of the European Ceramic Society 2007 27(13) p 4205-4209

14 Akbari-Fakhrabadi A et al Combustion synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite anode and its electrical characteristics of semi-cell configured SOFC assembly Journal of Alloys and Compounds 2012 541 p 1-5

15 Ishihara T et al NickelndashGd-doped CeO 2 cermet anode for intermediate temperature operating solid oxide fuel cells using LaGaO 3-based perovskite electrolyte Solid State Ionics 2000 132(3) p 209-216

16 Ding C et al A comparative study of NiOndashCe 09 Gd 01 O 195 nanocomposite powders synthesized by hydroxide and oxalate co-precipitation methods Ceramics International 2012 38(1) p 85-92

17 Ding C et al Synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite powders for low-temperature solid oxide fuel cell anodes by co-precipitation Scripta Materialia 2009 60(4) p 254-256

18 Park S-Y et al Preparation of highly porous NiOndashgadolinium-doped ceria nano-composite powders by one-pot glycine nitrate process for anode-supported tubular solid oxide fuel cells Journal of Asian Ceramic Societies 2014 2(4) p 339-346

19 Zhu W and S Deevi A review on the status of anode materials for solid oxide fuel cells Materials Science and Engineering A 2003 362(1) p 228-239

20 Chick LA et al Glycine-nitrate combustion synthesis of oxide ceramic powders Materials Letters 1990 10(1-2) p 6-12

21 Basu RN et al Microstructure and electrical conductivity of LaNi 06 Fe 04 O 3 prepared by combustion synthesis routes Materials Research Bulletin 2004 39(9) p 1335-1345

22 SOFC ZS Microstructure development of the Ni-GDC anode material for IT-SOFC Materiali in tehnologije 2012 46(5) p 445-451

23 Aparicio M A Jitianu and LC Klein Sol-Gel Processing for Conventional and Alternative Energy 2012 Springer Science amp Business Media

24 Suciu C et al NiOYSZ nanoparticles obtained by new solndashgel route Chemical Engineering Journal 2008 140(1) p 586-592

25 Jiang SP and SH Chan A review of anode materials development in solid oxide fuel cells Journal of Materials Science 2004 39(14) p 4405-4439

26 Iyer A et al A Sucrose‐Mediated SolndashGel Technique for the Synthesis of MgOndashY2O3 Nanocomposites Journal of the American Ceramic Society 2013 96(2) p 346-350

27 Wang Z et al Ion-exchange kinetics and thermal decomposition characteristics of Fe2+-exchanged alginic acid membrane for the formation of iron oxide nanoparticles Journal of Materials Science 2014 49(20) p 7151-7155

28 Schnepp Z et al Alginate-mediated routes to the selective synthesis of complex metal oxide nanostructures CrystEngComm 2010 12(5) p 1410-1415

29 Wang Z GM Kale and M Ghadiri Synthesis and characterization of CexGd 1minus xO 2minus δ nanopowders employing an alginate mediated ion-exchange process Chemical Engineering Journal 2012 198 p 149-153

30 Brayner R et al Alginate-mediated growth of Co Ni and CoNi nanoparticles influence of the biopolymer structure Chemistry of Materials 2007 19(5) p 1190-1198

31 Balavandy SK K Shameli and ZZ Abidin Rapid and Green Synthesis of Silver Nanoparticles via Sodium Alginate Media Int J Electrochem Sci 2015 10 p 486-497

32 Choo CK BA Horri and B Salamatinia Synthesis and Characterization of Nickel (II) OxideGadolinium-Doped Ceria (NiOGDC) Nanocomposites As a Potential Material for Anode Supported LT-SOFCs in Proceedings of the World Congress on Engineering and Computer Science 2016

33 Rath MK M-J Lee and K-T Lee Preparation of nano-structured NindashCe 08 Gd 02 O 19 anode materials for solid oxide fuel cells via the water-in-oil (WO) micro-emulsion route Ceramics International 2014 40(1) p 1909-1917

34 Schneider CA WS Rasband and KW Eliceiri NIH Image to ImageJ 25 years of image analysis Nature methods 2012 9(7) p 671-675

35 Collins T ImageJ for Microscopy BioTechniques 43 S25-S30 httpdx doi org102144000112517 2007

36 Thierry R F Thierry and G Osenga Surface energy modified particles method of making and use thereof 2015 Google Patents

37 Macedo DA et al A versatile route for the preparation of NindashCGO cermets from nanocomposite powders Ceramics International 2013 39(4) p 4321-4328

38 Wandekar R et al Physicochemical studies of NiOndashGDC composites Materials Chemistry and Physics 2006 99(2) p 289-294

39 Prakash BS VW Grips and S Aruna A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes Journal of Power Sources 2012 214 p 358-364

40 Sartori C et al Determination of the cation content of alginate thin films by FTi r spectroscopy Polymer 1997 38(1) p 43-51

41 Lakouraj MM F Mojerlou and EN Zare Nanogel and superparamagnetic nanocomposite based on sodium alginate for sorption of heavy metal ions Carbohydrate polymers 2014 106 p 34-41

42 Srivastava M et al Synthesis of superparamagnetic bare Fe 3 O 4 nanostructures and coreshell (Fe 3 O 4alginate) nanocomposites Carbohydrate polymers 2012 89(3) p 821-829

43 Chavan A et al Effect of variation of NiO on properties of NiOGDC (gadolinium doped ceria) nano-composites Ceramics International 2012 38(4) p 3191-3196

44 Shen C and LL Shaw FTIR analysis of the hydrolysis rate in the solndashgel formation of gadolinia-doped ceria with acetylacetonate precursors Journal of sol-gel science and technology 2010 53(3) p 571-577

45 Wang T and D-C Sun Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method Materials Research Bulletin 2008 43(7) p 1754-1760

46 Sing KS Reporting physisorption data for gassolid systems with special reference to the determination of surface area and porosity (Recommendations 1984) Pure and applied chemistry 1985 57(4) p 603-619

47 Song X et al Synthesis and Characterization of Y-Doped Mesoporous CeO 2 Using A Chemical Precipitation Method Journal of Rare Earths 2007 25(4) p 428-433

diffraction was performed using an XRD diffractometer (D8 Discover from Bruker

Germany) with CuKα1 radiation (λ = 154060Aring) in the 2θ range between 10deg and 90deg and a

scanning rate of 002 degs using the Bragg-Brentano beam method at 40 kV and 40 mA All

XRD patterns were indexed using ICDD file no 00-50-0201 and 00-002101216 for GDC and

NiO crystals respectively The crystallite sizes of the NiO and GDC nanocrystallites were

calculated using Scherrer equation D=09 λ βcosθ where D is the crystallite size (nm) λ is

the wavelength of the source (nm) β is the full width at half maximum (FWHM) of the peak

and θ is the Bragg angle (radians) The morphology of NiO-GDC nanocrystallite was

analysed using the micrograph images obtained from a Field Emission Scanning Electron

Microscopy (FESEM SU8010 Hitachi Japan) All FESEM specimens were coated with

platinum for 120 seconds with a sputter current at 30 mA using a coater (Quarum Q150R S)

prior to the analysis Energy-dispersive x-ray (Oxford Horiba Inca XMax50 EDX) analysis

was performed to confirm the presence of cerium gadolinium and oxygen atoms in all

samples The FTIR spectra of the calcined and the dried powders were obtained using a

Fourier transform infrared spectrometer (FTIR NICOLET 1810 USA) over the

wavenumber range of 650ndash4000 cm-1 The surface area of the calcined samples was measured

by a BET analyser (Micromeritics ASAP 2020 USA)

3 Results and Discussion

The results for the thermogravimetric analysis (TGADTA) of the dried and calcined

sample at 700 degC for 2 h are shown as the representative sample in Figure 2 Four weight loss

steps corresponding to room temperature 25 degC plusmn1 degC to 186 degC 186 degC to 301 degC 301 degC to

380 degC and 380 degC to 500 degC were observed for the dried sample (Figure 2a) The

decomposition steps in the TGA curves were found to be in good agreement with the DTA

curves represented in Figure 2a A weight loss of 1146 plusmn 010 was observed during the

first step (25 degC ndash 186 degC) that corresponded to the evaporation of water in the alginate

structure during heat treatment In the second step (186 degC - 301 degC) a weight loss of 3641plusmn

015 was detected that could be due to the cleavage of G-G G-M and M-M weaker

linkages in the alginate molecule causing considerable oxygen evolution Wang et al[11]

also reported similar results for the weight loss of alginate in the same temperature range for

the dried sample of NiO nanopowders with sodium alginate When the operational

temperature was increased from 301 to 380 degC during the third step further decomposition

occurred which resulted in approximately 57 plusmn 0075 of weight loss in the TGA profile

This can be attributed to the decomposition of metastable-NiO2 to thermodynamically more

stable NiO phase which is demonstrated as a small exothermic peak [11] During the fourth

step the temperature was further increased from 380 degC to around 500 degC The residues of b-

D-mannuronic acid (M) and a-L-guluronic acid (G) in the alginate structure were completely

oxidised as observed from the 1924 plusmn 0075 weight loss that resulted in an exothermic

decomposition peak Previous studies offered similar reasoning for the final decomposition

step [27] No further weight loss was observed at temperatures of higher than 500 degC Figure

2a shows that the decomposition process could be completed at 500 degC

The TGADTA plot for the sample that was calcined at 700 degC for 2 hours is shown in

Figure 2b Three major weight losses were visible in the plot The first weight loss of 018 plusmn

001 occurred between room temperature and approximately 48 degC and was due to water

evaporation which was confirmed by the small endothermic peak in the DTA curve During

the second step (75-91 degC) a weight loss of 194 plusmn 001 was observed due to organic

components that still remained after calcination [33] The third weight loss of 177plusmn 001

was observed between 93-406 degC which corresponded to the decomposition of Ni(OH)2 to

NiO Ce(OH)3 to CeO2 and Gd(OH)3 to Gd2O3 [33] No further weight loss was observed at

temperature of higher than 400 degC which indicated the absence of carbonaceous bonds or

any other undecomposed residue in the sample

The FESEM images for the NiO-GDC nanocrystallites synthesized with 3 loading

fractions of sodium alginate at 500 degC 600 degC and 700 degC calcination temperature with

different calcination time are displayed in Figures 3 4 and 5 respectively ImageJ software

was used to quantitatively analyse the FESEM images [34 35] First a binary image was

extracted by carefully performing intensity-thresholding on the original FESEM image

Using erosion and dilation irregular shapes were removed The remaining particles were

morphologically closed and smoothened by applying a Gaussian blur The resultant binary

images which contained particles in the form of blobs were passed to the analysis module

for an automatic measurement of the particle size The particle size distribution for each

image has been embedded at its top-right corner where micro denotes the average particle size

with the standard deviation and Ɲ denotes the number of particles utilized in the analysis

As seen in Figures 3 4 and 5 the particle size had slowly increased when the

calcination temperature was increased from 500 to 700 degC at a constant calcination time

These results could be linked to the agglomeration of the particles caused by several

phenomena such as lsquouncontrolled build-uprsquo lsquobridgingrsquo or lsquolumpingrsquo during the thermal

treatment process (refer Figures 3a 4a and 5a) [36] It was also observed that at a constant

calcination temperature the size of the nanocrystallites had increased due to the

agglomeration of smaller particles when the calcination time was increased from 2 h to 10 h

(refer Figures 4a 4b and 4c) Thus the agglomeration of smaller particles can be

manipulated by determining the optimum calcination temperature and duration to obtain

specific particle sizes In each series of images 3a 3b and 3c 4a 4b and 4c and 5a

5b and5c this trend can be seen for all calcination times and calcination temperatures

The results showed that the smallest particle size (641 nm) was obtained with

calcination conditions of 500 degC for 2 h (641 nm) The largest particle size of 2125 nm was

obtained at 700 degC after 10 h of calcination These results were in agreement with the

previous discussion In conclusion for synthesizing smaller nanocrystalline NiO-GDC lower

calcination temperature (500 degC) and shorter calcination time (2 h) is needed

The EDX elemental analysis and mapping is shown in Figure 6 for nancrystalline NiO-

GDC synthesized at 500 degC for 6 h which confirmed the presence of cerium gadolinium

oxygen and nickel atoms The sample shown in Figure 6 was chosen as an example to

represent all the samples that were elaborated in this study

X-ray diffraction (XRD) patterns of the nanocrystalline NiO-GDC powders synthesized

at different calcination times and temperatures are shown in Figure 7 The peaks for all

samples were well matched with the cubic Ce08Gd02O19 (Fm-3m ICDD00-50-0201) and

cubic NiO (Fm-3m ICDD 00-002101216) The average crystallite sizes of these particles

were determined using the Scherrer equation as listed in Table 2 The crystallite sizes of NiO

and GDC in NiO-GDC have been reported by several studies that used different methods

such as polymeric sol-gel (with NiO at 24 nm and GDC at 18 nm) [37] hydroxide co-

precipitation method (NiO at 305 nm and GDC at 273 nm) [17] solution combustion

synthesis (NiO at 30-58 nm and GDC at 40-50 nm) [38] micro emulsion method (NiO at

132 148 and 134 nm and GDC at 117 137 and 106 nm) as well as microemulsion-

mediated solvothermal process (NiO at 22 plusmn 2 nm and GDC at 20 plusmn 2 nm) These studies

have shown that ion-gelation synthesis can successfully synthesize smaller sized NiO-GDC

nanocomposites

The XRD patterns have shown that the diffraction peaks for GDC and NiO crystal

phases became sharper when calcination temperature was increased from 500 to 700 degC at

constant calcination time as well as when calcination time was increased from 2 h to 10 h at a

constant calcination temperature which indicated the growth in the crystallite size (Table 1)

due to particle agglomeration [36] At lower calcination temperature (500 degC) with different

calcination times (2 6 and 10 h) the broader peaks in an XRD pattern show the existence of

smaller-sized NiO and GDC crystallites for all samples [39] In this study the XRD pattern

(Figure 7) was in agreement with crystallite size tabulated in Table 2

The calculated crystallite sizes using the Scherrer equation (Table 2) supported the

results from the XRD patterns which indicated that by increasing the calcination time and

temperature the crystallite sizes of NiO and GDC were increased as well The calculated

crystallite sizes of NiO and GDC in Table 2 were in good agreement with the results attained

from the quantitative image analysis reported in Figure 3 Figure 4 and Figure 5 which

confirmed the influences of both the calcination temperature and calcination time on the size

of the powder particles

Figure 8 shows the FTIR spectra for the dried gel and the calcined samples at different

calcination temperatures and times The FTIR spectrum for the dried sample showed

numerous adsorption bands in the 800-1610 cm-1 region The peaks at 884 cm-1 could be

attributed to the C-C band for sodium alginate [40] Meanwhile the band at 1026 cm-1 (C-O-

C stretching) corresponded to sodium alginate glycosidic linkage [41] Additionally the

stretch at 3355 cm-1 and the absorption peaks at 1600 to 1414 cm-1 corresponded to O-H band

and the asymmetric and symmetric stretching vibration of the carboxylate group respectively

[42] After the dried sample had undergone thermal treatment at different calcination times

and temperatures a reduction in the intensity of carbon bands was observed which

confirmed the effectiveness of the calcination process in completing the thermal

decomposition of the biopolymer compound However further increase in the calcination

temperature and calcination time had led to a reduction in the intensity of the peaks This

condition showed that these samples had attained more purity in their metal oxide

compositions The absorption band for metal-oxygen has been reported by various studies

such as (Ce-OGd-ONi-O) was detected at approximately 635 cm-1 [33] (Ce-O) was

observed at 564 cm-1 while the 550-700 cm-1 region was assigned to NiO stretching vibration

[43-45] However due to the presence of noise at lower than 650 cm -1 the measuring range

utilized in these current experiments was between 650 cm-1 to 4000 cm-1

The BET analysis was conducted by applying the Barrett-Joyner-Halenda (BJH)

method to study the physicochemical properties of the calcined NiO-GDC at different

calcination times and temperatures Based on literature review there is a lack of information

on BET analysis of NiO-GDC and thus more in-depth studies are needed in this area The

nitrogen adsorption-desorption isotherms (hysteresis loops) of the NiO-GDC are given in

Figure 9 with the pore size distribution of the different samples in the inset The nitrogen

adsorption-desorption isotherms (Figure 9) indicated the presence of mesopores in the

samples based on the type IV isotherm as per IUPAC classification The mesopores were

formed due to the capillary condensation of the mesoporous materials thus confirming the

mesoporosity of the synthesized NiO-GDC nanocrystallites [46] The hysteresis loops of the

samples in the pp0 range of 04-10 illustrated the absence of micropores and that the pores

had changed into the mesoporous reign [46] The pore size distributions of the samples are

given in the inset of Figure 9 The majority of the NiO-GDC samples were in the mesoporous

region (10 nm) as determined by the BJH method which supported the N2 adsorption-

desorption isotherms

It can be observed from Figure 9 that for samples calcined at 500 degC for 2 h 6 h and 10 h the

relative pressure (corresponding to the onset of capillary condensation) has a higher value

which indicated the presence of the smaller pore size distribution for that sample [47]

The BET surface areas for all samples are summarized in Table 3 It can be seen that

at a specific calcination temperature increasing the calcination time from 2 h to 10 h had

caused the surface area of the sample to decrease due to the increasing particle size

Similarly by increasing the calcination temperature from 500 degC to 700 degC the surface areas

of the samples had decreased due to the increasing particle sizes The largest surface areas

corresponded to the nanocrystallite samples calcined at 500 degC for 2 h However these values

had reduced when the calcination temperature and time were gradually increased to 700 degC

and 10 h respectively These results are in good agreement with the particle sizes obtained

from the FESEM and XRD results

4 Conclusion

Nanocrytalline NiO-GDC powders were synthesized using an environmentally

friendly ionic gelation method with sodium alginate as the precursor The effects of the

synthesis parameters such as calcination temperature and calcination time on the properties

of the produced nanocrystalline NiO-GDC powders were studied using various

characterization techniques It was found that at a fixed calcination temperature the size of

the nanocrystals would increase with increasing calcination time Similarly at a fixed

calcination time and increasing calcination temperature larger nanocrystals were produced

Therefore for synthesizing smaller nanocrystals lower calcination temperature (500 degC) and

shorter calcination time (2 h) are recommended It was also observed that calcination

temperature has more effect on the BET surface compared to calcination time which showed

that the pore size of the nanocrystalline powders was more dependent on the calcination

temperature

5 Acknowledgement

The authors would like to acknowledge the Ministry of Science Education and Innovation

(MOSTI) of Malaysia for providing research funding under the e-science scheme grant

number 03-02-10-SF0259

References

1 Boury B and S Plumejeau Metal oxides and polysaccharides an efficient hybrid association for materials chemistry Green Chemistry 2015 17(1) p 72-88

2 Bell AT The impact of nanoscience on heterogeneous catalysis Science 2003 299(5613) p 1688-1691

3 Zhao X et al The role of nanomaterials in redox-based supercapacitors for next generation energy storage devices Nanoscale 2011 3(3) p 839-855

4 Sun Y-F et al Metal oxide nanostructures and their gas sensing properties a review Sensors 2012 12(3) p 2610-2631

5 Jia J et al Heterogeneous catalytic hydrogenation of CO 2 by metal oxides defect engineeringndashperfecting imperfection Chemical Society Reviews 2017 46(15) p 4631-4644

6 Pezeshkpour S et al Ionicndashgelation synthesis of gadolinium doped ceria (Ce 08 Gd 02 O 190) nanocomposite powder using sodium-alginate Ceramics International 2017 43(9) p 7123-7135

7 Atif M et al Studies on the magnetic magnetostrictive and electrical properties of solndashgel synthesized Zn doped nickel ferrite Journal of Alloys and Compounds 2011 509(18) p 5720-5724

8 Krstajić N et al Non-noble metal composite cathodes for hydrogen evolution Part I the NindashMoO x coatings electrodeposited from Wattrsquos type bath containing MoO 3 powder particles international journal of hydrogen energy 2011 36(11) p 6441-6449

9 Macedo DA et al NindashCGO cermet anodes from nanocomposite powders Microstructural and electrochemical assessment Ceramics International 2014 40(8) p 13105-13113

10 Gao H et al The design of excellent xylene gas sensor using Sn-doped NiO hierarchical nanostructure Sensors and Actuators B Chemical 2017 253 p 1152-1162

11 Wang Z GM Kale and M Ghadiri Novel Ion‐Exchange Process for the Preparation of Metal Oxide Nanopowders from Sodium Alginate Journal of the American Ceramic Society 2012 95(10) p 3124-3129

12 Galeano MAacuteN et al Studies on the structural quantitative and semi-quantitative analyses of NiOndashGDC nanocomposites RSC Advances 2016 6(77) p 72865-72876

13 Gil V C Moure and J Tartaj Sinterability microstructures and electrical properties of NiGd-doped ceria cermets used as anode materials for SOFCs Journal of the European Ceramic Society 2007 27(13) p 4205-4209

14 Akbari-Fakhrabadi A et al Combustion synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite anode and its electrical characteristics of semi-cell configured SOFC assembly Journal of Alloys and Compounds 2012 541 p 1-5

15 Ishihara T et al NickelndashGd-doped CeO 2 cermet anode for intermediate temperature operating solid oxide fuel cells using LaGaO 3-based perovskite electrolyte Solid State Ionics 2000 132(3) p 209-216

16 Ding C et al A comparative study of NiOndashCe 09 Gd 01 O 195 nanocomposite powders synthesized by hydroxide and oxalate co-precipitation methods Ceramics International 2012 38(1) p 85-92

17 Ding C et al Synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite powders for low-temperature solid oxide fuel cell anodes by co-precipitation Scripta Materialia 2009 60(4) p 254-256

18 Park S-Y et al Preparation of highly porous NiOndashgadolinium-doped ceria nano-composite powders by one-pot glycine nitrate process for anode-supported tubular solid oxide fuel cells Journal of Asian Ceramic Societies 2014 2(4) p 339-346

19 Zhu W and S Deevi A review on the status of anode materials for solid oxide fuel cells Materials Science and Engineering A 2003 362(1) p 228-239

20 Chick LA et al Glycine-nitrate combustion synthesis of oxide ceramic powders Materials Letters 1990 10(1-2) p 6-12

21 Basu RN et al Microstructure and electrical conductivity of LaNi 06 Fe 04 O 3 prepared by combustion synthesis routes Materials Research Bulletin 2004 39(9) p 1335-1345

22 SOFC ZS Microstructure development of the Ni-GDC anode material for IT-SOFC Materiali in tehnologije 2012 46(5) p 445-451

23 Aparicio M A Jitianu and LC Klein Sol-Gel Processing for Conventional and Alternative Energy 2012 Springer Science amp Business Media

24 Suciu C et al NiOYSZ nanoparticles obtained by new solndashgel route Chemical Engineering Journal 2008 140(1) p 586-592

25 Jiang SP and SH Chan A review of anode materials development in solid oxide fuel cells Journal of Materials Science 2004 39(14) p 4405-4439

26 Iyer A et al A Sucrose‐Mediated SolndashGel Technique for the Synthesis of MgOndashY2O3 Nanocomposites Journal of the American Ceramic Society 2013 96(2) p 346-350

27 Wang Z et al Ion-exchange kinetics and thermal decomposition characteristics of Fe2+-exchanged alginic acid membrane for the formation of iron oxide nanoparticles Journal of Materials Science 2014 49(20) p 7151-7155

28 Schnepp Z et al Alginate-mediated routes to the selective synthesis of complex metal oxide nanostructures CrystEngComm 2010 12(5) p 1410-1415

29 Wang Z GM Kale and M Ghadiri Synthesis and characterization of CexGd 1minus xO 2minus δ nanopowders employing an alginate mediated ion-exchange process Chemical Engineering Journal 2012 198 p 149-153

30 Brayner R et al Alginate-mediated growth of Co Ni and CoNi nanoparticles influence of the biopolymer structure Chemistry of Materials 2007 19(5) p 1190-1198

31 Balavandy SK K Shameli and ZZ Abidin Rapid and Green Synthesis of Silver Nanoparticles via Sodium Alginate Media Int J Electrochem Sci 2015 10 p 486-497

32 Choo CK BA Horri and B Salamatinia Synthesis and Characterization of Nickel (II) OxideGadolinium-Doped Ceria (NiOGDC) Nanocomposites As a Potential Material for Anode Supported LT-SOFCs in Proceedings of the World Congress on Engineering and Computer Science 2016

33 Rath MK M-J Lee and K-T Lee Preparation of nano-structured NindashCe 08 Gd 02 O 19 anode materials for solid oxide fuel cells via the water-in-oil (WO) micro-emulsion route Ceramics International 2014 40(1) p 1909-1917

34 Schneider CA WS Rasband and KW Eliceiri NIH Image to ImageJ 25 years of image analysis Nature methods 2012 9(7) p 671-675

35 Collins T ImageJ for Microscopy BioTechniques 43 S25-S30 httpdx doi org102144000112517 2007

36 Thierry R F Thierry and G Osenga Surface energy modified particles method of making and use thereof 2015 Google Patents

37 Macedo DA et al A versatile route for the preparation of NindashCGO cermets from nanocomposite powders Ceramics International 2013 39(4) p 4321-4328

38 Wandekar R et al Physicochemical studies of NiOndashGDC composites Materials Chemistry and Physics 2006 99(2) p 289-294

39 Prakash BS VW Grips and S Aruna A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes Journal of Power Sources 2012 214 p 358-364

40 Sartori C et al Determination of the cation content of alginate thin films by FTi r spectroscopy Polymer 1997 38(1) p 43-51

41 Lakouraj MM F Mojerlou and EN Zare Nanogel and superparamagnetic nanocomposite based on sodium alginate for sorption of heavy metal ions Carbohydrate polymers 2014 106 p 34-41

42 Srivastava M et al Synthesis of superparamagnetic bare Fe 3 O 4 nanostructures and coreshell (Fe 3 O 4alginate) nanocomposites Carbohydrate polymers 2012 89(3) p 821-829

43 Chavan A et al Effect of variation of NiO on properties of NiOGDC (gadolinium doped ceria) nano-composites Ceramics International 2012 38(4) p 3191-3196

44 Shen C and LL Shaw FTIR analysis of the hydrolysis rate in the solndashgel formation of gadolinia-doped ceria with acetylacetonate precursors Journal of sol-gel science and technology 2010 53(3) p 571-577

45 Wang T and D-C Sun Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method Materials Research Bulletin 2008 43(7) p 1754-1760

46 Sing KS Reporting physisorption data for gassolid systems with special reference to the determination of surface area and porosity (Recommendations 1984) Pure and applied chemistry 1985 57(4) p 603-619

47 Song X et al Synthesis and Characterization of Y-Doped Mesoporous CeO 2 Using A Chemical Precipitation Method Journal of Rare Earths 2007 25(4) p 428-433

015 was detected that could be due to the cleavage of G-G G-M and M-M weaker

linkages in the alginate molecule causing considerable oxygen evolution Wang et al[11]

also reported similar results for the weight loss of alginate in the same temperature range for

the dried sample of NiO nanopowders with sodium alginate When the operational

temperature was increased from 301 to 380 degC during the third step further decomposition

occurred which resulted in approximately 57 plusmn 0075 of weight loss in the TGA profile

This can be attributed to the decomposition of metastable-NiO2 to thermodynamically more

stable NiO phase which is demonstrated as a small exothermic peak [11] During the fourth

step the temperature was further increased from 380 degC to around 500 degC The residues of b-

D-mannuronic acid (M) and a-L-guluronic acid (G) in the alginate structure were completely

oxidised as observed from the 1924 plusmn 0075 weight loss that resulted in an exothermic

decomposition peak Previous studies offered similar reasoning for the final decomposition

step [27] No further weight loss was observed at temperatures of higher than 500 degC Figure

2a shows that the decomposition process could be completed at 500 degC

The TGADTA plot for the sample that was calcined at 700 degC for 2 hours is shown in

Figure 2b Three major weight losses were visible in the plot The first weight loss of 018 plusmn

001 occurred between room temperature and approximately 48 degC and was due to water

evaporation which was confirmed by the small endothermic peak in the DTA curve During

the second step (75-91 degC) a weight loss of 194 plusmn 001 was observed due to organic

components that still remained after calcination [33] The third weight loss of 177plusmn 001

was observed between 93-406 degC which corresponded to the decomposition of Ni(OH)2 to

NiO Ce(OH)3 to CeO2 and Gd(OH)3 to Gd2O3 [33] No further weight loss was observed at

temperature of higher than 400 degC which indicated the absence of carbonaceous bonds or

any other undecomposed residue in the sample

The FESEM images for the NiO-GDC nanocrystallites synthesized with 3 loading

fractions of sodium alginate at 500 degC 600 degC and 700 degC calcination temperature with

different calcination time are displayed in Figures 3 4 and 5 respectively ImageJ software

was used to quantitatively analyse the FESEM images [34 35] First a binary image was

extracted by carefully performing intensity-thresholding on the original FESEM image

Using erosion and dilation irregular shapes were removed The remaining particles were

morphologically closed and smoothened by applying a Gaussian blur The resultant binary

images which contained particles in the form of blobs were passed to the analysis module

for an automatic measurement of the particle size The particle size distribution for each

image has been embedded at its top-right corner where micro denotes the average particle size

with the standard deviation and Ɲ denotes the number of particles utilized in the analysis

As seen in Figures 3 4 and 5 the particle size had slowly increased when the

calcination temperature was increased from 500 to 700 degC at a constant calcination time

These results could be linked to the agglomeration of the particles caused by several

phenomena such as lsquouncontrolled build-uprsquo lsquobridgingrsquo or lsquolumpingrsquo during the thermal

treatment process (refer Figures 3a 4a and 5a) [36] It was also observed that at a constant

calcination temperature the size of the nanocrystallites had increased due to the

agglomeration of smaller particles when the calcination time was increased from 2 h to 10 h

(refer Figures 4a 4b and 4c) Thus the agglomeration of smaller particles can be

manipulated by determining the optimum calcination temperature and duration to obtain

specific particle sizes In each series of images 3a 3b and 3c 4a 4b and 4c and 5a

5b and5c this trend can be seen for all calcination times and calcination temperatures

The results showed that the smallest particle size (641 nm) was obtained with

calcination conditions of 500 degC for 2 h (641 nm) The largest particle size of 2125 nm was

obtained at 700 degC after 10 h of calcination These results were in agreement with the

previous discussion In conclusion for synthesizing smaller nanocrystalline NiO-GDC lower

calcination temperature (500 degC) and shorter calcination time (2 h) is needed

The EDX elemental analysis and mapping is shown in Figure 6 for nancrystalline NiO-

GDC synthesized at 500 degC for 6 h which confirmed the presence of cerium gadolinium

oxygen and nickel atoms The sample shown in Figure 6 was chosen as an example to

represent all the samples that were elaborated in this study

X-ray diffraction (XRD) patterns of the nanocrystalline NiO-GDC powders synthesized

at different calcination times and temperatures are shown in Figure 7 The peaks for all

samples were well matched with the cubic Ce08Gd02O19 (Fm-3m ICDD00-50-0201) and

cubic NiO (Fm-3m ICDD 00-002101216) The average crystallite sizes of these particles

were determined using the Scherrer equation as listed in Table 2 The crystallite sizes of NiO

and GDC in NiO-GDC have been reported by several studies that used different methods

such as polymeric sol-gel (with NiO at 24 nm and GDC at 18 nm) [37] hydroxide co-

precipitation method (NiO at 305 nm and GDC at 273 nm) [17] solution combustion

synthesis (NiO at 30-58 nm and GDC at 40-50 nm) [38] micro emulsion method (NiO at

132 148 and 134 nm and GDC at 117 137 and 106 nm) as well as microemulsion-

mediated solvothermal process (NiO at 22 plusmn 2 nm and GDC at 20 plusmn 2 nm) These studies

have shown that ion-gelation synthesis can successfully synthesize smaller sized NiO-GDC

nanocomposites

The XRD patterns have shown that the diffraction peaks for GDC and NiO crystal

phases became sharper when calcination temperature was increased from 500 to 700 degC at

constant calcination time as well as when calcination time was increased from 2 h to 10 h at a

constant calcination temperature which indicated the growth in the crystallite size (Table 1)

due to particle agglomeration [36] At lower calcination temperature (500 degC) with different

calcination times (2 6 and 10 h) the broader peaks in an XRD pattern show the existence of

smaller-sized NiO and GDC crystallites for all samples [39] In this study the XRD pattern

(Figure 7) was in agreement with crystallite size tabulated in Table 2

The calculated crystallite sizes using the Scherrer equation (Table 2) supported the

results from the XRD patterns which indicated that by increasing the calcination time and

temperature the crystallite sizes of NiO and GDC were increased as well The calculated

crystallite sizes of NiO and GDC in Table 2 were in good agreement with the results attained

from the quantitative image analysis reported in Figure 3 Figure 4 and Figure 5 which

confirmed the influences of both the calcination temperature and calcination time on the size

of the powder particles

Figure 8 shows the FTIR spectra for the dried gel and the calcined samples at different

calcination temperatures and times The FTIR spectrum for the dried sample showed

numerous adsorption bands in the 800-1610 cm-1 region The peaks at 884 cm-1 could be

attributed to the C-C band for sodium alginate [40] Meanwhile the band at 1026 cm-1 (C-O-

C stretching) corresponded to sodium alginate glycosidic linkage [41] Additionally the

stretch at 3355 cm-1 and the absorption peaks at 1600 to 1414 cm-1 corresponded to O-H band

and the asymmetric and symmetric stretching vibration of the carboxylate group respectively

[42] After the dried sample had undergone thermal treatment at different calcination times

and temperatures a reduction in the intensity of carbon bands was observed which

confirmed the effectiveness of the calcination process in completing the thermal

decomposition of the biopolymer compound However further increase in the calcination

temperature and calcination time had led to a reduction in the intensity of the peaks This

condition showed that these samples had attained more purity in their metal oxide

compositions The absorption band for metal-oxygen has been reported by various studies

such as (Ce-OGd-ONi-O) was detected at approximately 635 cm-1 [33] (Ce-O) was

observed at 564 cm-1 while the 550-700 cm-1 region was assigned to NiO stretching vibration

[43-45] However due to the presence of noise at lower than 650 cm -1 the measuring range

utilized in these current experiments was between 650 cm-1 to 4000 cm-1

The BET analysis was conducted by applying the Barrett-Joyner-Halenda (BJH)

method to study the physicochemical properties of the calcined NiO-GDC at different

calcination times and temperatures Based on literature review there is a lack of information

on BET analysis of NiO-GDC and thus more in-depth studies are needed in this area The

nitrogen adsorption-desorption isotherms (hysteresis loops) of the NiO-GDC are given in

Figure 9 with the pore size distribution of the different samples in the inset The nitrogen

adsorption-desorption isotherms (Figure 9) indicated the presence of mesopores in the

samples based on the type IV isotherm as per IUPAC classification The mesopores were

formed due to the capillary condensation of the mesoporous materials thus confirming the

mesoporosity of the synthesized NiO-GDC nanocrystallites [46] The hysteresis loops of the

samples in the pp0 range of 04-10 illustrated the absence of micropores and that the pores

had changed into the mesoporous reign [46] The pore size distributions of the samples are

given in the inset of Figure 9 The majority of the NiO-GDC samples were in the mesoporous

region (10 nm) as determined by the BJH method which supported the N2 adsorption-

desorption isotherms

It can be observed from Figure 9 that for samples calcined at 500 degC for 2 h 6 h and 10 h the

relative pressure (corresponding to the onset of capillary condensation) has a higher value

which indicated the presence of the smaller pore size distribution for that sample [47]

The BET surface areas for all samples are summarized in Table 3 It can be seen that

at a specific calcination temperature increasing the calcination time from 2 h to 10 h had

caused the surface area of the sample to decrease due to the increasing particle size

Similarly by increasing the calcination temperature from 500 degC to 700 degC the surface areas

of the samples had decreased due to the increasing particle sizes The largest surface areas

corresponded to the nanocrystallite samples calcined at 500 degC for 2 h However these values

had reduced when the calcination temperature and time were gradually increased to 700 degC

and 10 h respectively These results are in good agreement with the particle sizes obtained

from the FESEM and XRD results

4 Conclusion

Nanocrytalline NiO-GDC powders were synthesized using an environmentally

friendly ionic gelation method with sodium alginate as the precursor The effects of the

synthesis parameters such as calcination temperature and calcination time on the properties

of the produced nanocrystalline NiO-GDC powders were studied using various

characterization techniques It was found that at a fixed calcination temperature the size of

the nanocrystals would increase with increasing calcination time Similarly at a fixed

calcination time and increasing calcination temperature larger nanocrystals were produced

Therefore for synthesizing smaller nanocrystals lower calcination temperature (500 degC) and

shorter calcination time (2 h) are recommended It was also observed that calcination

temperature has more effect on the BET surface compared to calcination time which showed

that the pore size of the nanocrystalline powders was more dependent on the calcination

temperature

5 Acknowledgement

The authors would like to acknowledge the Ministry of Science Education and Innovation

(MOSTI) of Malaysia for providing research funding under the e-science scheme grant

number 03-02-10-SF0259

References

1 Boury B and S Plumejeau Metal oxides and polysaccharides an efficient hybrid association for materials chemistry Green Chemistry 2015 17(1) p 72-88

2 Bell AT The impact of nanoscience on heterogeneous catalysis Science 2003 299(5613) p 1688-1691

3 Zhao X et al The role of nanomaterials in redox-based supercapacitors for next generation energy storage devices Nanoscale 2011 3(3) p 839-855

4 Sun Y-F et al Metal oxide nanostructures and their gas sensing properties a review Sensors 2012 12(3) p 2610-2631

5 Jia J et al Heterogeneous catalytic hydrogenation of CO 2 by metal oxides defect engineeringndashperfecting imperfection Chemical Society Reviews 2017 46(15) p 4631-4644

6 Pezeshkpour S et al Ionicndashgelation synthesis of gadolinium doped ceria (Ce 08 Gd 02 O 190) nanocomposite powder using sodium-alginate Ceramics International 2017 43(9) p 7123-7135

7 Atif M et al Studies on the magnetic magnetostrictive and electrical properties of solndashgel synthesized Zn doped nickel ferrite Journal of Alloys and Compounds 2011 509(18) p 5720-5724

8 Krstajić N et al Non-noble metal composite cathodes for hydrogen evolution Part I the NindashMoO x coatings electrodeposited from Wattrsquos type bath containing MoO 3 powder particles international journal of hydrogen energy 2011 36(11) p 6441-6449

9 Macedo DA et al NindashCGO cermet anodes from nanocomposite powders Microstructural and electrochemical assessment Ceramics International 2014 40(8) p 13105-13113

10 Gao H et al The design of excellent xylene gas sensor using Sn-doped NiO hierarchical nanostructure Sensors and Actuators B Chemical 2017 253 p 1152-1162

11 Wang Z GM Kale and M Ghadiri Novel Ion‐Exchange Process for the Preparation of Metal Oxide Nanopowders from Sodium Alginate Journal of the American Ceramic Society 2012 95(10) p 3124-3129

12 Galeano MAacuteN et al Studies on the structural quantitative and semi-quantitative analyses of NiOndashGDC nanocomposites RSC Advances 2016 6(77) p 72865-72876

13 Gil V C Moure and J Tartaj Sinterability microstructures and electrical properties of NiGd-doped ceria cermets used as anode materials for SOFCs Journal of the European Ceramic Society 2007 27(13) p 4205-4209

14 Akbari-Fakhrabadi A et al Combustion synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite anode and its electrical characteristics of semi-cell configured SOFC assembly Journal of Alloys and Compounds 2012 541 p 1-5

15 Ishihara T et al NickelndashGd-doped CeO 2 cermet anode for intermediate temperature operating solid oxide fuel cells using LaGaO 3-based perovskite electrolyte Solid State Ionics 2000 132(3) p 209-216

16 Ding C et al A comparative study of NiOndashCe 09 Gd 01 O 195 nanocomposite powders synthesized by hydroxide and oxalate co-precipitation methods Ceramics International 2012 38(1) p 85-92

17 Ding C et al Synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite powders for low-temperature solid oxide fuel cell anodes by co-precipitation Scripta Materialia 2009 60(4) p 254-256

18 Park S-Y et al Preparation of highly porous NiOndashgadolinium-doped ceria nano-composite powders by one-pot glycine nitrate process for anode-supported tubular solid oxide fuel cells Journal of Asian Ceramic Societies 2014 2(4) p 339-346

19 Zhu W and S Deevi A review on the status of anode materials for solid oxide fuel cells Materials Science and Engineering A 2003 362(1) p 228-239

20 Chick LA et al Glycine-nitrate combustion synthesis of oxide ceramic powders Materials Letters 1990 10(1-2) p 6-12

21 Basu RN et al Microstructure and electrical conductivity of LaNi 06 Fe 04 O 3 prepared by combustion synthesis routes Materials Research Bulletin 2004 39(9) p 1335-1345

22 SOFC ZS Microstructure development of the Ni-GDC anode material for IT-SOFC Materiali in tehnologije 2012 46(5) p 445-451

23 Aparicio M A Jitianu and LC Klein Sol-Gel Processing for Conventional and Alternative Energy 2012 Springer Science amp Business Media

24 Suciu C et al NiOYSZ nanoparticles obtained by new solndashgel route Chemical Engineering Journal 2008 140(1) p 586-592

25 Jiang SP and SH Chan A review of anode materials development in solid oxide fuel cells Journal of Materials Science 2004 39(14) p 4405-4439

26 Iyer A et al A Sucrose‐Mediated SolndashGel Technique for the Synthesis of MgOndashY2O3 Nanocomposites Journal of the American Ceramic Society 2013 96(2) p 346-350

27 Wang Z et al Ion-exchange kinetics and thermal decomposition characteristics of Fe2+-exchanged alginic acid membrane for the formation of iron oxide nanoparticles Journal of Materials Science 2014 49(20) p 7151-7155

28 Schnepp Z et al Alginate-mediated routes to the selective synthesis of complex metal oxide nanostructures CrystEngComm 2010 12(5) p 1410-1415

29 Wang Z GM Kale and M Ghadiri Synthesis and characterization of CexGd 1minus xO 2minus δ nanopowders employing an alginate mediated ion-exchange process Chemical Engineering Journal 2012 198 p 149-153

30 Brayner R et al Alginate-mediated growth of Co Ni and CoNi nanoparticles influence of the biopolymer structure Chemistry of Materials 2007 19(5) p 1190-1198

31 Balavandy SK K Shameli and ZZ Abidin Rapid and Green Synthesis of Silver Nanoparticles via Sodium Alginate Media Int J Electrochem Sci 2015 10 p 486-497

32 Choo CK BA Horri and B Salamatinia Synthesis and Characterization of Nickel (II) OxideGadolinium-Doped Ceria (NiOGDC) Nanocomposites As a Potential Material for Anode Supported LT-SOFCs in Proceedings of the World Congress on Engineering and Computer Science 2016

33 Rath MK M-J Lee and K-T Lee Preparation of nano-structured NindashCe 08 Gd 02 O 19 anode materials for solid oxide fuel cells via the water-in-oil (WO) micro-emulsion route Ceramics International 2014 40(1) p 1909-1917

34 Schneider CA WS Rasband and KW Eliceiri NIH Image to ImageJ 25 years of image analysis Nature methods 2012 9(7) p 671-675

35 Collins T ImageJ for Microscopy BioTechniques 43 S25-S30 httpdx doi org102144000112517 2007

36 Thierry R F Thierry and G Osenga Surface energy modified particles method of making and use thereof 2015 Google Patents

37 Macedo DA et al A versatile route for the preparation of NindashCGO cermets from nanocomposite powders Ceramics International 2013 39(4) p 4321-4328

38 Wandekar R et al Physicochemical studies of NiOndashGDC composites Materials Chemistry and Physics 2006 99(2) p 289-294

39 Prakash BS VW Grips and S Aruna A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes Journal of Power Sources 2012 214 p 358-364

40 Sartori C et al Determination of the cation content of alginate thin films by FTi r spectroscopy Polymer 1997 38(1) p 43-51

41 Lakouraj MM F Mojerlou and EN Zare Nanogel and superparamagnetic nanocomposite based on sodium alginate for sorption of heavy metal ions Carbohydrate polymers 2014 106 p 34-41

42 Srivastava M et al Synthesis of superparamagnetic bare Fe 3 O 4 nanostructures and coreshell (Fe 3 O 4alginate) nanocomposites Carbohydrate polymers 2012 89(3) p 821-829

43 Chavan A et al Effect of variation of NiO on properties of NiOGDC (gadolinium doped ceria) nano-composites Ceramics International 2012 38(4) p 3191-3196

44 Shen C and LL Shaw FTIR analysis of the hydrolysis rate in the solndashgel formation of gadolinia-doped ceria with acetylacetonate precursors Journal of sol-gel science and technology 2010 53(3) p 571-577

45 Wang T and D-C Sun Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method Materials Research Bulletin 2008 43(7) p 1754-1760

46 Sing KS Reporting physisorption data for gassolid systems with special reference to the determination of surface area and porosity (Recommendations 1984) Pure and applied chemistry 1985 57(4) p 603-619

47 Song X et al Synthesis and Characterization of Y-Doped Mesoporous CeO 2 Using A Chemical Precipitation Method Journal of Rare Earths 2007 25(4) p 428-433

was used to quantitatively analyse the FESEM images [34 35] First a binary image was

extracted by carefully performing intensity-thresholding on the original FESEM image

Using erosion and dilation irregular shapes were removed The remaining particles were

morphologically closed and smoothened by applying a Gaussian blur The resultant binary

images which contained particles in the form of blobs were passed to the analysis module

for an automatic measurement of the particle size The particle size distribution for each

image has been embedded at its top-right corner where micro denotes the average particle size

with the standard deviation and Ɲ denotes the number of particles utilized in the analysis

As seen in Figures 3 4 and 5 the particle size had slowly increased when the

calcination temperature was increased from 500 to 700 degC at a constant calcination time

These results could be linked to the agglomeration of the particles caused by several

phenomena such as lsquouncontrolled build-uprsquo lsquobridgingrsquo or lsquolumpingrsquo during the thermal

treatment process (refer Figures 3a 4a and 5a) [36] It was also observed that at a constant

calcination temperature the size of the nanocrystallites had increased due to the

agglomeration of smaller particles when the calcination time was increased from 2 h to 10 h

(refer Figures 4a 4b and 4c) Thus the agglomeration of smaller particles can be

manipulated by determining the optimum calcination temperature and duration to obtain

specific particle sizes In each series of images 3a 3b and 3c 4a 4b and 4c and 5a

5b and5c this trend can be seen for all calcination times and calcination temperatures

The results showed that the smallest particle size (641 nm) was obtained with

calcination conditions of 500 degC for 2 h (641 nm) The largest particle size of 2125 nm was

obtained at 700 degC after 10 h of calcination These results were in agreement with the

previous discussion In conclusion for synthesizing smaller nanocrystalline NiO-GDC lower

calcination temperature (500 degC) and shorter calcination time (2 h) is needed

The EDX elemental analysis and mapping is shown in Figure 6 for nancrystalline NiO-

GDC synthesized at 500 degC for 6 h which confirmed the presence of cerium gadolinium

oxygen and nickel atoms The sample shown in Figure 6 was chosen as an example to

represent all the samples that were elaborated in this study

X-ray diffraction (XRD) patterns of the nanocrystalline NiO-GDC powders synthesized

at different calcination times and temperatures are shown in Figure 7 The peaks for all

samples were well matched with the cubic Ce08Gd02O19 (Fm-3m ICDD00-50-0201) and

cubic NiO (Fm-3m ICDD 00-002101216) The average crystallite sizes of these particles

were determined using the Scherrer equation as listed in Table 2 The crystallite sizes of NiO

and GDC in NiO-GDC have been reported by several studies that used different methods

such as polymeric sol-gel (with NiO at 24 nm and GDC at 18 nm) [37] hydroxide co-

precipitation method (NiO at 305 nm and GDC at 273 nm) [17] solution combustion

synthesis (NiO at 30-58 nm and GDC at 40-50 nm) [38] micro emulsion method (NiO at

132 148 and 134 nm and GDC at 117 137 and 106 nm) as well as microemulsion-

mediated solvothermal process (NiO at 22 plusmn 2 nm and GDC at 20 plusmn 2 nm) These studies

have shown that ion-gelation synthesis can successfully synthesize smaller sized NiO-GDC

nanocomposites

The XRD patterns have shown that the diffraction peaks for GDC and NiO crystal

phases became sharper when calcination temperature was increased from 500 to 700 degC at

constant calcination time as well as when calcination time was increased from 2 h to 10 h at a

constant calcination temperature which indicated the growth in the crystallite size (Table 1)

due to particle agglomeration [36] At lower calcination temperature (500 degC) with different

calcination times (2 6 and 10 h) the broader peaks in an XRD pattern show the existence of

smaller-sized NiO and GDC crystallites for all samples [39] In this study the XRD pattern

(Figure 7) was in agreement with crystallite size tabulated in Table 2

The calculated crystallite sizes using the Scherrer equation (Table 2) supported the

results from the XRD patterns which indicated that by increasing the calcination time and

temperature the crystallite sizes of NiO and GDC were increased as well The calculated

crystallite sizes of NiO and GDC in Table 2 were in good agreement with the results attained

from the quantitative image analysis reported in Figure 3 Figure 4 and Figure 5 which

confirmed the influences of both the calcination temperature and calcination time on the size

of the powder particles

Figure 8 shows the FTIR spectra for the dried gel and the calcined samples at different

calcination temperatures and times The FTIR spectrum for the dried sample showed

numerous adsorption bands in the 800-1610 cm-1 region The peaks at 884 cm-1 could be

attributed to the C-C band for sodium alginate [40] Meanwhile the band at 1026 cm-1 (C-O-

C stretching) corresponded to sodium alginate glycosidic linkage [41] Additionally the

stretch at 3355 cm-1 and the absorption peaks at 1600 to 1414 cm-1 corresponded to O-H band

and the asymmetric and symmetric stretching vibration of the carboxylate group respectively

[42] After the dried sample had undergone thermal treatment at different calcination times

and temperatures a reduction in the intensity of carbon bands was observed which

confirmed the effectiveness of the calcination process in completing the thermal

decomposition of the biopolymer compound However further increase in the calcination

temperature and calcination time had led to a reduction in the intensity of the peaks This

condition showed that these samples had attained more purity in their metal oxide

compositions The absorption band for metal-oxygen has been reported by various studies

such as (Ce-OGd-ONi-O) was detected at approximately 635 cm-1 [33] (Ce-O) was

observed at 564 cm-1 while the 550-700 cm-1 region was assigned to NiO stretching vibration

[43-45] However due to the presence of noise at lower than 650 cm -1 the measuring range

utilized in these current experiments was between 650 cm-1 to 4000 cm-1

The BET analysis was conducted by applying the Barrett-Joyner-Halenda (BJH)

method to study the physicochemical properties of the calcined NiO-GDC at different

calcination times and temperatures Based on literature review there is a lack of information

on BET analysis of NiO-GDC and thus more in-depth studies are needed in this area The

nitrogen adsorption-desorption isotherms (hysteresis loops) of the NiO-GDC are given in

Figure 9 with the pore size distribution of the different samples in the inset The nitrogen

adsorption-desorption isotherms (Figure 9) indicated the presence of mesopores in the

samples based on the type IV isotherm as per IUPAC classification The mesopores were

formed due to the capillary condensation of the mesoporous materials thus confirming the

mesoporosity of the synthesized NiO-GDC nanocrystallites [46] The hysteresis loops of the

samples in the pp0 range of 04-10 illustrated the absence of micropores and that the pores

had changed into the mesoporous reign [46] The pore size distributions of the samples are

given in the inset of Figure 9 The majority of the NiO-GDC samples were in the mesoporous

region (10 nm) as determined by the BJH method which supported the N2 adsorption-

desorption isotherms

It can be observed from Figure 9 that for samples calcined at 500 degC for 2 h 6 h and 10 h the

relative pressure (corresponding to the onset of capillary condensation) has a higher value

which indicated the presence of the smaller pore size distribution for that sample [47]

The BET surface areas for all samples are summarized in Table 3 It can be seen that

at a specific calcination temperature increasing the calcination time from 2 h to 10 h had

caused the surface area of the sample to decrease due to the increasing particle size

Similarly by increasing the calcination temperature from 500 degC to 700 degC the surface areas

of the samples had decreased due to the increasing particle sizes The largest surface areas

corresponded to the nanocrystallite samples calcined at 500 degC for 2 h However these values

had reduced when the calcination temperature and time were gradually increased to 700 degC

and 10 h respectively These results are in good agreement with the particle sizes obtained

from the FESEM and XRD results

4 Conclusion

Nanocrytalline NiO-GDC powders were synthesized using an environmentally

friendly ionic gelation method with sodium alginate as the precursor The effects of the

synthesis parameters such as calcination temperature and calcination time on the properties

of the produced nanocrystalline NiO-GDC powders were studied using various

characterization techniques It was found that at a fixed calcination temperature the size of

the nanocrystals would increase with increasing calcination time Similarly at a fixed

calcination time and increasing calcination temperature larger nanocrystals were produced

Therefore for synthesizing smaller nanocrystals lower calcination temperature (500 degC) and

shorter calcination time (2 h) are recommended It was also observed that calcination

temperature has more effect on the BET surface compared to calcination time which showed

that the pore size of the nanocrystalline powders was more dependent on the calcination

temperature

5 Acknowledgement

The authors would like to acknowledge the Ministry of Science Education and Innovation

(MOSTI) of Malaysia for providing research funding under the e-science scheme grant

number 03-02-10-SF0259

References

1 Boury B and S Plumejeau Metal oxides and polysaccharides an efficient hybrid association for materials chemistry Green Chemistry 2015 17(1) p 72-88

2 Bell AT The impact of nanoscience on heterogeneous catalysis Science 2003 299(5613) p 1688-1691

3 Zhao X et al The role of nanomaterials in redox-based supercapacitors for next generation energy storage devices Nanoscale 2011 3(3) p 839-855

4 Sun Y-F et al Metal oxide nanostructures and their gas sensing properties a review Sensors 2012 12(3) p 2610-2631

5 Jia J et al Heterogeneous catalytic hydrogenation of CO 2 by metal oxides defect engineeringndashperfecting imperfection Chemical Society Reviews 2017 46(15) p 4631-4644

6 Pezeshkpour S et al Ionicndashgelation synthesis of gadolinium doped ceria (Ce 08 Gd 02 O 190) nanocomposite powder using sodium-alginate Ceramics International 2017 43(9) p 7123-7135

7 Atif M et al Studies on the magnetic magnetostrictive and electrical properties of solndashgel synthesized Zn doped nickel ferrite Journal of Alloys and Compounds 2011 509(18) p 5720-5724

8 Krstajić N et al Non-noble metal composite cathodes for hydrogen evolution Part I the NindashMoO x coatings electrodeposited from Wattrsquos type bath containing MoO 3 powder particles international journal of hydrogen energy 2011 36(11) p 6441-6449

9 Macedo DA et al NindashCGO cermet anodes from nanocomposite powders Microstructural and electrochemical assessment Ceramics International 2014 40(8) p 13105-13113

10 Gao H et al The design of excellent xylene gas sensor using Sn-doped NiO hierarchical nanostructure Sensors and Actuators B Chemical 2017 253 p 1152-1162

11 Wang Z GM Kale and M Ghadiri Novel Ion‐Exchange Process for the Preparation of Metal Oxide Nanopowders from Sodium Alginate Journal of the American Ceramic Society 2012 95(10) p 3124-3129

12 Galeano MAacuteN et al Studies on the structural quantitative and semi-quantitative analyses of NiOndashGDC nanocomposites RSC Advances 2016 6(77) p 72865-72876

13 Gil V C Moure and J Tartaj Sinterability microstructures and electrical properties of NiGd-doped ceria cermets used as anode materials for SOFCs Journal of the European Ceramic Society 2007 27(13) p 4205-4209

14 Akbari-Fakhrabadi A et al Combustion synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite anode and its electrical characteristics of semi-cell configured SOFC assembly Journal of Alloys and Compounds 2012 541 p 1-5

15 Ishihara T et al NickelndashGd-doped CeO 2 cermet anode for intermediate temperature operating solid oxide fuel cells using LaGaO 3-based perovskite electrolyte Solid State Ionics 2000 132(3) p 209-216

16 Ding C et al A comparative study of NiOndashCe 09 Gd 01 O 195 nanocomposite powders synthesized by hydroxide and oxalate co-precipitation methods Ceramics International 2012 38(1) p 85-92

17 Ding C et al Synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite powders for low-temperature solid oxide fuel cell anodes by co-precipitation Scripta Materialia 2009 60(4) p 254-256

18 Park S-Y et al Preparation of highly porous NiOndashgadolinium-doped ceria nano-composite powders by one-pot glycine nitrate process for anode-supported tubular solid oxide fuel cells Journal of Asian Ceramic Societies 2014 2(4) p 339-346

19 Zhu W and S Deevi A review on the status of anode materials for solid oxide fuel cells Materials Science and Engineering A 2003 362(1) p 228-239

20 Chick LA et al Glycine-nitrate combustion synthesis of oxide ceramic powders Materials Letters 1990 10(1-2) p 6-12

21 Basu RN et al Microstructure and electrical conductivity of LaNi 06 Fe 04 O 3 prepared by combustion synthesis routes Materials Research Bulletin 2004 39(9) p 1335-1345

22 SOFC ZS Microstructure development of the Ni-GDC anode material for IT-SOFC Materiali in tehnologije 2012 46(5) p 445-451

23 Aparicio M A Jitianu and LC Klein Sol-Gel Processing for Conventional and Alternative Energy 2012 Springer Science amp Business Media

24 Suciu C et al NiOYSZ nanoparticles obtained by new solndashgel route Chemical Engineering Journal 2008 140(1) p 586-592

25 Jiang SP and SH Chan A review of anode materials development in solid oxide fuel cells Journal of Materials Science 2004 39(14) p 4405-4439

26 Iyer A et al A Sucrose‐Mediated SolndashGel Technique for the Synthesis of MgOndashY2O3 Nanocomposites Journal of the American Ceramic Society 2013 96(2) p 346-350

27 Wang Z et al Ion-exchange kinetics and thermal decomposition characteristics of Fe2+-exchanged alginic acid membrane for the formation of iron oxide nanoparticles Journal of Materials Science 2014 49(20) p 7151-7155

28 Schnepp Z et al Alginate-mediated routes to the selective synthesis of complex metal oxide nanostructures CrystEngComm 2010 12(5) p 1410-1415

29 Wang Z GM Kale and M Ghadiri Synthesis and characterization of CexGd 1minus xO 2minus δ nanopowders employing an alginate mediated ion-exchange process Chemical Engineering Journal 2012 198 p 149-153

30 Brayner R et al Alginate-mediated growth of Co Ni and CoNi nanoparticles influence of the biopolymer structure Chemistry of Materials 2007 19(5) p 1190-1198

31 Balavandy SK K Shameli and ZZ Abidin Rapid and Green Synthesis of Silver Nanoparticles via Sodium Alginate Media Int J Electrochem Sci 2015 10 p 486-497

32 Choo CK BA Horri and B Salamatinia Synthesis and Characterization of Nickel (II) OxideGadolinium-Doped Ceria (NiOGDC) Nanocomposites As a Potential Material for Anode Supported LT-SOFCs in Proceedings of the World Congress on Engineering and Computer Science 2016

33 Rath MK M-J Lee and K-T Lee Preparation of nano-structured NindashCe 08 Gd 02 O 19 anode materials for solid oxide fuel cells via the water-in-oil (WO) micro-emulsion route Ceramics International 2014 40(1) p 1909-1917

34 Schneider CA WS Rasband and KW Eliceiri NIH Image to ImageJ 25 years of image analysis Nature methods 2012 9(7) p 671-675

35 Collins T ImageJ for Microscopy BioTechniques 43 S25-S30 httpdx doi org102144000112517 2007

36 Thierry R F Thierry and G Osenga Surface energy modified particles method of making and use thereof 2015 Google Patents

37 Macedo DA et al A versatile route for the preparation of NindashCGO cermets from nanocomposite powders Ceramics International 2013 39(4) p 4321-4328

38 Wandekar R et al Physicochemical studies of NiOndashGDC composites Materials Chemistry and Physics 2006 99(2) p 289-294

39 Prakash BS VW Grips and S Aruna A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes Journal of Power Sources 2012 214 p 358-364

40 Sartori C et al Determination of the cation content of alginate thin films by FTi r spectroscopy Polymer 1997 38(1) p 43-51

41 Lakouraj MM F Mojerlou and EN Zare Nanogel and superparamagnetic nanocomposite based on sodium alginate for sorption of heavy metal ions Carbohydrate polymers 2014 106 p 34-41

42 Srivastava M et al Synthesis of superparamagnetic bare Fe 3 O 4 nanostructures and coreshell (Fe 3 O 4alginate) nanocomposites Carbohydrate polymers 2012 89(3) p 821-829

43 Chavan A et al Effect of variation of NiO on properties of NiOGDC (gadolinium doped ceria) nano-composites Ceramics International 2012 38(4) p 3191-3196

44 Shen C and LL Shaw FTIR analysis of the hydrolysis rate in the solndashgel formation of gadolinia-doped ceria with acetylacetonate precursors Journal of sol-gel science and technology 2010 53(3) p 571-577

45 Wang T and D-C Sun Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method Materials Research Bulletin 2008 43(7) p 1754-1760

46 Sing KS Reporting physisorption data for gassolid systems with special reference to the determination of surface area and porosity (Recommendations 1984) Pure and applied chemistry 1985 57(4) p 603-619

47 Song X et al Synthesis and Characterization of Y-Doped Mesoporous CeO 2 Using A Chemical Precipitation Method Journal of Rare Earths 2007 25(4) p 428-433

oxygen and nickel atoms The sample shown in Figure 6 was chosen as an example to

represent all the samples that were elaborated in this study

X-ray diffraction (XRD) patterns of the nanocrystalline NiO-GDC powders synthesized

at different calcination times and temperatures are shown in Figure 7 The peaks for all

samples were well matched with the cubic Ce08Gd02O19 (Fm-3m ICDD00-50-0201) and

cubic NiO (Fm-3m ICDD 00-002101216) The average crystallite sizes of these particles

were determined using the Scherrer equation as listed in Table 2 The crystallite sizes of NiO

and GDC in NiO-GDC have been reported by several studies that used different methods

such as polymeric sol-gel (with NiO at 24 nm and GDC at 18 nm) [37] hydroxide co-

precipitation method (NiO at 305 nm and GDC at 273 nm) [17] solution combustion

synthesis (NiO at 30-58 nm and GDC at 40-50 nm) [38] micro emulsion method (NiO at

132 148 and 134 nm and GDC at 117 137 and 106 nm) as well as microemulsion-

mediated solvothermal process (NiO at 22 plusmn 2 nm and GDC at 20 plusmn 2 nm) These studies

have shown that ion-gelation synthesis can successfully synthesize smaller sized NiO-GDC

nanocomposites

The XRD patterns have shown that the diffraction peaks for GDC and NiO crystal

phases became sharper when calcination temperature was increased from 500 to 700 degC at

constant calcination time as well as when calcination time was increased from 2 h to 10 h at a

constant calcination temperature which indicated the growth in the crystallite size (Table 1)

due to particle agglomeration [36] At lower calcination temperature (500 degC) with different

calcination times (2 6 and 10 h) the broader peaks in an XRD pattern show the existence of

smaller-sized NiO and GDC crystallites for all samples [39] In this study the XRD pattern

(Figure 7) was in agreement with crystallite size tabulated in Table 2

The calculated crystallite sizes using the Scherrer equation (Table 2) supported the

results from the XRD patterns which indicated that by increasing the calcination time and

temperature the crystallite sizes of NiO and GDC were increased as well The calculated

crystallite sizes of NiO and GDC in Table 2 were in good agreement with the results attained

from the quantitative image analysis reported in Figure 3 Figure 4 and Figure 5 which

confirmed the influences of both the calcination temperature and calcination time on the size

of the powder particles

Figure 8 shows the FTIR spectra for the dried gel and the calcined samples at different

calcination temperatures and times The FTIR spectrum for the dried sample showed

numerous adsorption bands in the 800-1610 cm-1 region The peaks at 884 cm-1 could be

attributed to the C-C band for sodium alginate [40] Meanwhile the band at 1026 cm-1 (C-O-

C stretching) corresponded to sodium alginate glycosidic linkage [41] Additionally the

stretch at 3355 cm-1 and the absorption peaks at 1600 to 1414 cm-1 corresponded to O-H band

and the asymmetric and symmetric stretching vibration of the carboxylate group respectively

[42] After the dried sample had undergone thermal treatment at different calcination times

and temperatures a reduction in the intensity of carbon bands was observed which

confirmed the effectiveness of the calcination process in completing the thermal

decomposition of the biopolymer compound However further increase in the calcination

temperature and calcination time had led to a reduction in the intensity of the peaks This

condition showed that these samples had attained more purity in their metal oxide

compositions The absorption band for metal-oxygen has been reported by various studies

such as (Ce-OGd-ONi-O) was detected at approximately 635 cm-1 [33] (Ce-O) was

observed at 564 cm-1 while the 550-700 cm-1 region was assigned to NiO stretching vibration

[43-45] However due to the presence of noise at lower than 650 cm -1 the measuring range

utilized in these current experiments was between 650 cm-1 to 4000 cm-1

The BET analysis was conducted by applying the Barrett-Joyner-Halenda (BJH)

method to study the physicochemical properties of the calcined NiO-GDC at different

calcination times and temperatures Based on literature review there is a lack of information

on BET analysis of NiO-GDC and thus more in-depth studies are needed in this area The

nitrogen adsorption-desorption isotherms (hysteresis loops) of the NiO-GDC are given in

Figure 9 with the pore size distribution of the different samples in the inset The nitrogen

adsorption-desorption isotherms (Figure 9) indicated the presence of mesopores in the

samples based on the type IV isotherm as per IUPAC classification The mesopores were

formed due to the capillary condensation of the mesoporous materials thus confirming the

mesoporosity of the synthesized NiO-GDC nanocrystallites [46] The hysteresis loops of the

samples in the pp0 range of 04-10 illustrated the absence of micropores and that the pores

had changed into the mesoporous reign [46] The pore size distributions of the samples are

given in the inset of Figure 9 The majority of the NiO-GDC samples were in the mesoporous

region (10 nm) as determined by the BJH method which supported the N2 adsorption-

desorption isotherms

It can be observed from Figure 9 that for samples calcined at 500 degC for 2 h 6 h and 10 h the

relative pressure (corresponding to the onset of capillary condensation) has a higher value

which indicated the presence of the smaller pore size distribution for that sample [47]

The BET surface areas for all samples are summarized in Table 3 It can be seen that

at a specific calcination temperature increasing the calcination time from 2 h to 10 h had

caused the surface area of the sample to decrease due to the increasing particle size

Similarly by increasing the calcination temperature from 500 degC to 700 degC the surface areas

of the samples had decreased due to the increasing particle sizes The largest surface areas

corresponded to the nanocrystallite samples calcined at 500 degC for 2 h However these values

had reduced when the calcination temperature and time were gradually increased to 700 degC

and 10 h respectively These results are in good agreement with the particle sizes obtained

from the FESEM and XRD results

4 Conclusion

Nanocrytalline NiO-GDC powders were synthesized using an environmentally

friendly ionic gelation method with sodium alginate as the precursor The effects of the

synthesis parameters such as calcination temperature and calcination time on the properties

of the produced nanocrystalline NiO-GDC powders were studied using various

characterization techniques It was found that at a fixed calcination temperature the size of

the nanocrystals would increase with increasing calcination time Similarly at a fixed

calcination time and increasing calcination temperature larger nanocrystals were produced

Therefore for synthesizing smaller nanocrystals lower calcination temperature (500 degC) and

shorter calcination time (2 h) are recommended It was also observed that calcination

temperature has more effect on the BET surface compared to calcination time which showed

that the pore size of the nanocrystalline powders was more dependent on the calcination

temperature

5 Acknowledgement

The authors would like to acknowledge the Ministry of Science Education and Innovation

(MOSTI) of Malaysia for providing research funding under the e-science scheme grant

number 03-02-10-SF0259

References

1 Boury B and S Plumejeau Metal oxides and polysaccharides an efficient hybrid association for materials chemistry Green Chemistry 2015 17(1) p 72-88

2 Bell AT The impact of nanoscience on heterogeneous catalysis Science 2003 299(5613) p 1688-1691

3 Zhao X et al The role of nanomaterials in redox-based supercapacitors for next generation energy storage devices Nanoscale 2011 3(3) p 839-855

4 Sun Y-F et al Metal oxide nanostructures and their gas sensing properties a review Sensors 2012 12(3) p 2610-2631

5 Jia J et al Heterogeneous catalytic hydrogenation of CO 2 by metal oxides defect engineeringndashperfecting imperfection Chemical Society Reviews 2017 46(15) p 4631-4644

6 Pezeshkpour S et al Ionicndashgelation synthesis of gadolinium doped ceria (Ce 08 Gd 02 O 190) nanocomposite powder using sodium-alginate Ceramics International 2017 43(9) p 7123-7135

7 Atif M et al Studies on the magnetic magnetostrictive and electrical properties of solndashgel synthesized Zn doped nickel ferrite Journal of Alloys and Compounds 2011 509(18) p 5720-5724

8 Krstajić N et al Non-noble metal composite cathodes for hydrogen evolution Part I the NindashMoO x coatings electrodeposited from Wattrsquos type bath containing MoO 3 powder particles international journal of hydrogen energy 2011 36(11) p 6441-6449

9 Macedo DA et al NindashCGO cermet anodes from nanocomposite powders Microstructural and electrochemical assessment Ceramics International 2014 40(8) p 13105-13113

10 Gao H et al The design of excellent xylene gas sensor using Sn-doped NiO hierarchical nanostructure Sensors and Actuators B Chemical 2017 253 p 1152-1162

11 Wang Z GM Kale and M Ghadiri Novel Ion‐Exchange Process for the Preparation of Metal Oxide Nanopowders from Sodium Alginate Journal of the American Ceramic Society 2012 95(10) p 3124-3129

12 Galeano MAacuteN et al Studies on the structural quantitative and semi-quantitative analyses of NiOndashGDC nanocomposites RSC Advances 2016 6(77) p 72865-72876

13 Gil V C Moure and J Tartaj Sinterability microstructures and electrical properties of NiGd-doped ceria cermets used as anode materials for SOFCs Journal of the European Ceramic Society 2007 27(13) p 4205-4209

14 Akbari-Fakhrabadi A et al Combustion synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite anode and its electrical characteristics of semi-cell configured SOFC assembly Journal of Alloys and Compounds 2012 541 p 1-5

15 Ishihara T et al NickelndashGd-doped CeO 2 cermet anode for intermediate temperature operating solid oxide fuel cells using LaGaO 3-based perovskite electrolyte Solid State Ionics 2000 132(3) p 209-216

16 Ding C et al A comparative study of NiOndashCe 09 Gd 01 O 195 nanocomposite powders synthesized by hydroxide and oxalate co-precipitation methods Ceramics International 2012 38(1) p 85-92

17 Ding C et al Synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite powders for low-temperature solid oxide fuel cell anodes by co-precipitation Scripta Materialia 2009 60(4) p 254-256

18 Park S-Y et al Preparation of highly porous NiOndashgadolinium-doped ceria nano-composite powders by one-pot glycine nitrate process for anode-supported tubular solid oxide fuel cells Journal of Asian Ceramic Societies 2014 2(4) p 339-346

19 Zhu W and S Deevi A review on the status of anode materials for solid oxide fuel cells Materials Science and Engineering A 2003 362(1) p 228-239

20 Chick LA et al Glycine-nitrate combustion synthesis of oxide ceramic powders Materials Letters 1990 10(1-2) p 6-12

21 Basu RN et al Microstructure and electrical conductivity of LaNi 06 Fe 04 O 3 prepared by combustion synthesis routes Materials Research Bulletin 2004 39(9) p 1335-1345

22 SOFC ZS Microstructure development of the Ni-GDC anode material for IT-SOFC Materiali in tehnologije 2012 46(5) p 445-451

23 Aparicio M A Jitianu and LC Klein Sol-Gel Processing for Conventional and Alternative Energy 2012 Springer Science amp Business Media

24 Suciu C et al NiOYSZ nanoparticles obtained by new solndashgel route Chemical Engineering Journal 2008 140(1) p 586-592

25 Jiang SP and SH Chan A review of anode materials development in solid oxide fuel cells Journal of Materials Science 2004 39(14) p 4405-4439

26 Iyer A et al A Sucrose‐Mediated SolndashGel Technique for the Synthesis of MgOndashY2O3 Nanocomposites Journal of the American Ceramic Society 2013 96(2) p 346-350

27 Wang Z et al Ion-exchange kinetics and thermal decomposition characteristics of Fe2+-exchanged alginic acid membrane for the formation of iron oxide nanoparticles Journal of Materials Science 2014 49(20) p 7151-7155

28 Schnepp Z et al Alginate-mediated routes to the selective synthesis of complex metal oxide nanostructures CrystEngComm 2010 12(5) p 1410-1415

29 Wang Z GM Kale and M Ghadiri Synthesis and characterization of CexGd 1minus xO 2minus δ nanopowders employing an alginate mediated ion-exchange process Chemical Engineering Journal 2012 198 p 149-153

30 Brayner R et al Alginate-mediated growth of Co Ni and CoNi nanoparticles influence of the biopolymer structure Chemistry of Materials 2007 19(5) p 1190-1198

31 Balavandy SK K Shameli and ZZ Abidin Rapid and Green Synthesis of Silver Nanoparticles via Sodium Alginate Media Int J Electrochem Sci 2015 10 p 486-497

32 Choo CK BA Horri and B Salamatinia Synthesis and Characterization of Nickel (II) OxideGadolinium-Doped Ceria (NiOGDC) Nanocomposites As a Potential Material for Anode Supported LT-SOFCs in Proceedings of the World Congress on Engineering and Computer Science 2016

33 Rath MK M-J Lee and K-T Lee Preparation of nano-structured NindashCe 08 Gd 02 O 19 anode materials for solid oxide fuel cells via the water-in-oil (WO) micro-emulsion route Ceramics International 2014 40(1) p 1909-1917

34 Schneider CA WS Rasband and KW Eliceiri NIH Image to ImageJ 25 years of image analysis Nature methods 2012 9(7) p 671-675

35 Collins T ImageJ for Microscopy BioTechniques 43 S25-S30 httpdx doi org102144000112517 2007

36 Thierry R F Thierry and G Osenga Surface energy modified particles method of making and use thereof 2015 Google Patents

37 Macedo DA et al A versatile route for the preparation of NindashCGO cermets from nanocomposite powders Ceramics International 2013 39(4) p 4321-4328

38 Wandekar R et al Physicochemical studies of NiOndashGDC composites Materials Chemistry and Physics 2006 99(2) p 289-294

39 Prakash BS VW Grips and S Aruna A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes Journal of Power Sources 2012 214 p 358-364

40 Sartori C et al Determination of the cation content of alginate thin films by FTi r spectroscopy Polymer 1997 38(1) p 43-51

41 Lakouraj MM F Mojerlou and EN Zare Nanogel and superparamagnetic nanocomposite based on sodium alginate for sorption of heavy metal ions Carbohydrate polymers 2014 106 p 34-41

42 Srivastava M et al Synthesis of superparamagnetic bare Fe 3 O 4 nanostructures and coreshell (Fe 3 O 4alginate) nanocomposites Carbohydrate polymers 2012 89(3) p 821-829

43 Chavan A et al Effect of variation of NiO on properties of NiOGDC (gadolinium doped ceria) nano-composites Ceramics International 2012 38(4) p 3191-3196

44 Shen C and LL Shaw FTIR analysis of the hydrolysis rate in the solndashgel formation of gadolinia-doped ceria with acetylacetonate precursors Journal of sol-gel science and technology 2010 53(3) p 571-577

45 Wang T and D-C Sun Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method Materials Research Bulletin 2008 43(7) p 1754-1760

46 Sing KS Reporting physisorption data for gassolid systems with special reference to the determination of surface area and porosity (Recommendations 1984) Pure and applied chemistry 1985 57(4) p 603-619

47 Song X et al Synthesis and Characterization of Y-Doped Mesoporous CeO 2 Using A Chemical Precipitation Method Journal of Rare Earths 2007 25(4) p 428-433

from the quantitative image analysis reported in Figure 3 Figure 4 and Figure 5 which

confirmed the influences of both the calcination temperature and calcination time on the size

of the powder particles

Figure 8 shows the FTIR spectra for the dried gel and the calcined samples at different

calcination temperatures and times The FTIR spectrum for the dried sample showed

numerous adsorption bands in the 800-1610 cm-1 region The peaks at 884 cm-1 could be

attributed to the C-C band for sodium alginate [40] Meanwhile the band at 1026 cm-1 (C-O-

C stretching) corresponded to sodium alginate glycosidic linkage [41] Additionally the

stretch at 3355 cm-1 and the absorption peaks at 1600 to 1414 cm-1 corresponded to O-H band

and the asymmetric and symmetric stretching vibration of the carboxylate group respectively

[42] After the dried sample had undergone thermal treatment at different calcination times

and temperatures a reduction in the intensity of carbon bands was observed which

confirmed the effectiveness of the calcination process in completing the thermal

decomposition of the biopolymer compound However further increase in the calcination

temperature and calcination time had led to a reduction in the intensity of the peaks This

condition showed that these samples had attained more purity in their metal oxide

compositions The absorption band for metal-oxygen has been reported by various studies

such as (Ce-OGd-ONi-O) was detected at approximately 635 cm-1 [33] (Ce-O) was

observed at 564 cm-1 while the 550-700 cm-1 region was assigned to NiO stretching vibration

[43-45] However due to the presence of noise at lower than 650 cm -1 the measuring range

utilized in these current experiments was between 650 cm-1 to 4000 cm-1

The BET analysis was conducted by applying the Barrett-Joyner-Halenda (BJH)

method to study the physicochemical properties of the calcined NiO-GDC at different

calcination times and temperatures Based on literature review there is a lack of information

on BET analysis of NiO-GDC and thus more in-depth studies are needed in this area The

nitrogen adsorption-desorption isotherms (hysteresis loops) of the NiO-GDC are given in

Figure 9 with the pore size distribution of the different samples in the inset The nitrogen

adsorption-desorption isotherms (Figure 9) indicated the presence of mesopores in the

samples based on the type IV isotherm as per IUPAC classification The mesopores were

formed due to the capillary condensation of the mesoporous materials thus confirming the

mesoporosity of the synthesized NiO-GDC nanocrystallites [46] The hysteresis loops of the

samples in the pp0 range of 04-10 illustrated the absence of micropores and that the pores

had changed into the mesoporous reign [46] The pore size distributions of the samples are

given in the inset of Figure 9 The majority of the NiO-GDC samples were in the mesoporous

region (10 nm) as determined by the BJH method which supported the N2 adsorption-

desorption isotherms

It can be observed from Figure 9 that for samples calcined at 500 degC for 2 h 6 h and 10 h the

relative pressure (corresponding to the onset of capillary condensation) has a higher value

which indicated the presence of the smaller pore size distribution for that sample [47]

The BET surface areas for all samples are summarized in Table 3 It can be seen that

at a specific calcination temperature increasing the calcination time from 2 h to 10 h had

caused the surface area of the sample to decrease due to the increasing particle size

Similarly by increasing the calcination temperature from 500 degC to 700 degC the surface areas

of the samples had decreased due to the increasing particle sizes The largest surface areas

corresponded to the nanocrystallite samples calcined at 500 degC for 2 h However these values

had reduced when the calcination temperature and time were gradually increased to 700 degC

and 10 h respectively These results are in good agreement with the particle sizes obtained

from the FESEM and XRD results

4 Conclusion

Nanocrytalline NiO-GDC powders were synthesized using an environmentally

friendly ionic gelation method with sodium alginate as the precursor The effects of the

synthesis parameters such as calcination temperature and calcination time on the properties

of the produced nanocrystalline NiO-GDC powders were studied using various

characterization techniques It was found that at a fixed calcination temperature the size of

the nanocrystals would increase with increasing calcination time Similarly at a fixed

calcination time and increasing calcination temperature larger nanocrystals were produced

Therefore for synthesizing smaller nanocrystals lower calcination temperature (500 degC) and

shorter calcination time (2 h) are recommended It was also observed that calcination

temperature has more effect on the BET surface compared to calcination time which showed

that the pore size of the nanocrystalline powders was more dependent on the calcination

temperature

5 Acknowledgement

The authors would like to acknowledge the Ministry of Science Education and Innovation

(MOSTI) of Malaysia for providing research funding under the e-science scheme grant

number 03-02-10-SF0259

References

1 Boury B and S Plumejeau Metal oxides and polysaccharides an efficient hybrid association for materials chemistry Green Chemistry 2015 17(1) p 72-88

2 Bell AT The impact of nanoscience on heterogeneous catalysis Science 2003 299(5613) p 1688-1691

3 Zhao X et al The role of nanomaterials in redox-based supercapacitors for next generation energy storage devices Nanoscale 2011 3(3) p 839-855

4 Sun Y-F et al Metal oxide nanostructures and their gas sensing properties a review Sensors 2012 12(3) p 2610-2631

5 Jia J et al Heterogeneous catalytic hydrogenation of CO 2 by metal oxides defect engineeringndashperfecting imperfection Chemical Society Reviews 2017 46(15) p 4631-4644

6 Pezeshkpour S et al Ionicndashgelation synthesis of gadolinium doped ceria (Ce 08 Gd 02 O 190) nanocomposite powder using sodium-alginate Ceramics International 2017 43(9) p 7123-7135

7 Atif M et al Studies on the magnetic magnetostrictive and electrical properties of solndashgel synthesized Zn doped nickel ferrite Journal of Alloys and Compounds 2011 509(18) p 5720-5724

8 Krstajić N et al Non-noble metal composite cathodes for hydrogen evolution Part I the NindashMoO x coatings electrodeposited from Wattrsquos type bath containing MoO 3 powder particles international journal of hydrogen energy 2011 36(11) p 6441-6449

9 Macedo DA et al NindashCGO cermet anodes from nanocomposite powders Microstructural and electrochemical assessment Ceramics International 2014 40(8) p 13105-13113

10 Gao H et al The design of excellent xylene gas sensor using Sn-doped NiO hierarchical nanostructure Sensors and Actuators B Chemical 2017 253 p 1152-1162

11 Wang Z GM Kale and M Ghadiri Novel Ion‐Exchange Process for the Preparation of Metal Oxide Nanopowders from Sodium Alginate Journal of the American Ceramic Society 2012 95(10) p 3124-3129

12 Galeano MAacuteN et al Studies on the structural quantitative and semi-quantitative analyses of NiOndashGDC nanocomposites RSC Advances 2016 6(77) p 72865-72876

13 Gil V C Moure and J Tartaj Sinterability microstructures and electrical properties of NiGd-doped ceria cermets used as anode materials for SOFCs Journal of the European Ceramic Society 2007 27(13) p 4205-4209

14 Akbari-Fakhrabadi A et al Combustion synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite anode and its electrical characteristics of semi-cell configured SOFC assembly Journal of Alloys and Compounds 2012 541 p 1-5

15 Ishihara T et al NickelndashGd-doped CeO 2 cermet anode for intermediate temperature operating solid oxide fuel cells using LaGaO 3-based perovskite electrolyte Solid State Ionics 2000 132(3) p 209-216

16 Ding C et al A comparative study of NiOndashCe 09 Gd 01 O 195 nanocomposite powders synthesized by hydroxide and oxalate co-precipitation methods Ceramics International 2012 38(1) p 85-92

17 Ding C et al Synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite powders for low-temperature solid oxide fuel cell anodes by co-precipitation Scripta Materialia 2009 60(4) p 254-256

18 Park S-Y et al Preparation of highly porous NiOndashgadolinium-doped ceria nano-composite powders by one-pot glycine nitrate process for anode-supported tubular solid oxide fuel cells Journal of Asian Ceramic Societies 2014 2(4) p 339-346

19 Zhu W and S Deevi A review on the status of anode materials for solid oxide fuel cells Materials Science and Engineering A 2003 362(1) p 228-239

20 Chick LA et al Glycine-nitrate combustion synthesis of oxide ceramic powders Materials Letters 1990 10(1-2) p 6-12

21 Basu RN et al Microstructure and electrical conductivity of LaNi 06 Fe 04 O 3 prepared by combustion synthesis routes Materials Research Bulletin 2004 39(9) p 1335-1345

22 SOFC ZS Microstructure development of the Ni-GDC anode material for IT-SOFC Materiali in tehnologije 2012 46(5) p 445-451

23 Aparicio M A Jitianu and LC Klein Sol-Gel Processing for Conventional and Alternative Energy 2012 Springer Science amp Business Media

24 Suciu C et al NiOYSZ nanoparticles obtained by new solndashgel route Chemical Engineering Journal 2008 140(1) p 586-592

25 Jiang SP and SH Chan A review of anode materials development in solid oxide fuel cells Journal of Materials Science 2004 39(14) p 4405-4439

26 Iyer A et al A Sucrose‐Mediated SolndashGel Technique for the Synthesis of MgOndashY2O3 Nanocomposites Journal of the American Ceramic Society 2013 96(2) p 346-350

27 Wang Z et al Ion-exchange kinetics and thermal decomposition characteristics of Fe2+-exchanged alginic acid membrane for the formation of iron oxide nanoparticles Journal of Materials Science 2014 49(20) p 7151-7155

28 Schnepp Z et al Alginate-mediated routes to the selective synthesis of complex metal oxide nanostructures CrystEngComm 2010 12(5) p 1410-1415

29 Wang Z GM Kale and M Ghadiri Synthesis and characterization of CexGd 1minus xO 2minus δ nanopowders employing an alginate mediated ion-exchange process Chemical Engineering Journal 2012 198 p 149-153

30 Brayner R et al Alginate-mediated growth of Co Ni and CoNi nanoparticles influence of the biopolymer structure Chemistry of Materials 2007 19(5) p 1190-1198

31 Balavandy SK K Shameli and ZZ Abidin Rapid and Green Synthesis of Silver Nanoparticles via Sodium Alginate Media Int J Electrochem Sci 2015 10 p 486-497

32 Choo CK BA Horri and B Salamatinia Synthesis and Characterization of Nickel (II) OxideGadolinium-Doped Ceria (NiOGDC) Nanocomposites As a Potential Material for Anode Supported LT-SOFCs in Proceedings of the World Congress on Engineering and Computer Science 2016

33 Rath MK M-J Lee and K-T Lee Preparation of nano-structured NindashCe 08 Gd 02 O 19 anode materials for solid oxide fuel cells via the water-in-oil (WO) micro-emulsion route Ceramics International 2014 40(1) p 1909-1917

34 Schneider CA WS Rasband and KW Eliceiri NIH Image to ImageJ 25 years of image analysis Nature methods 2012 9(7) p 671-675

35 Collins T ImageJ for Microscopy BioTechniques 43 S25-S30 httpdx doi org102144000112517 2007

36 Thierry R F Thierry and G Osenga Surface energy modified particles method of making and use thereof 2015 Google Patents

37 Macedo DA et al A versatile route for the preparation of NindashCGO cermets from nanocomposite powders Ceramics International 2013 39(4) p 4321-4328

38 Wandekar R et al Physicochemical studies of NiOndashGDC composites Materials Chemistry and Physics 2006 99(2) p 289-294

39 Prakash BS VW Grips and S Aruna A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes Journal of Power Sources 2012 214 p 358-364

40 Sartori C et al Determination of the cation content of alginate thin films by FTi r spectroscopy Polymer 1997 38(1) p 43-51

41 Lakouraj MM F Mojerlou and EN Zare Nanogel and superparamagnetic nanocomposite based on sodium alginate for sorption of heavy metal ions Carbohydrate polymers 2014 106 p 34-41

42 Srivastava M et al Synthesis of superparamagnetic bare Fe 3 O 4 nanostructures and coreshell (Fe 3 O 4alginate) nanocomposites Carbohydrate polymers 2012 89(3) p 821-829

43 Chavan A et al Effect of variation of NiO on properties of NiOGDC (gadolinium doped ceria) nano-composites Ceramics International 2012 38(4) p 3191-3196

44 Shen C and LL Shaw FTIR analysis of the hydrolysis rate in the solndashgel formation of gadolinia-doped ceria with acetylacetonate precursors Journal of sol-gel science and technology 2010 53(3) p 571-577

45 Wang T and D-C Sun Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method Materials Research Bulletin 2008 43(7) p 1754-1760

46 Sing KS Reporting physisorption data for gassolid systems with special reference to the determination of surface area and porosity (Recommendations 1984) Pure and applied chemistry 1985 57(4) p 603-619

47 Song X et al Synthesis and Characterization of Y-Doped Mesoporous CeO 2 Using A Chemical Precipitation Method Journal of Rare Earths 2007 25(4) p 428-433

adsorption-desorption isotherms (Figure 9) indicated the presence of mesopores in the

samples based on the type IV isotherm as per IUPAC classification The mesopores were

formed due to the capillary condensation of the mesoporous materials thus confirming the

mesoporosity of the synthesized NiO-GDC nanocrystallites [46] The hysteresis loops of the

samples in the pp0 range of 04-10 illustrated the absence of micropores and that the pores

had changed into the mesoporous reign [46] The pore size distributions of the samples are

given in the inset of Figure 9 The majority of the NiO-GDC samples were in the mesoporous

region (10 nm) as determined by the BJH method which supported the N2 adsorption-

desorption isotherms

It can be observed from Figure 9 that for samples calcined at 500 degC for 2 h 6 h and 10 h the

relative pressure (corresponding to the onset of capillary condensation) has a higher value

which indicated the presence of the smaller pore size distribution for that sample [47]

The BET surface areas for all samples are summarized in Table 3 It can be seen that

at a specific calcination temperature increasing the calcination time from 2 h to 10 h had

caused the surface area of the sample to decrease due to the increasing particle size

Similarly by increasing the calcination temperature from 500 degC to 700 degC the surface areas

of the samples had decreased due to the increasing particle sizes The largest surface areas

corresponded to the nanocrystallite samples calcined at 500 degC for 2 h However these values

had reduced when the calcination temperature and time were gradually increased to 700 degC

and 10 h respectively These results are in good agreement with the particle sizes obtained

from the FESEM and XRD results

4 Conclusion

Nanocrytalline NiO-GDC powders were synthesized using an environmentally

friendly ionic gelation method with sodium alginate as the precursor The effects of the

synthesis parameters such as calcination temperature and calcination time on the properties

of the produced nanocrystalline NiO-GDC powders were studied using various

characterization techniques It was found that at a fixed calcination temperature the size of

the nanocrystals would increase with increasing calcination time Similarly at a fixed

calcination time and increasing calcination temperature larger nanocrystals were produced

Therefore for synthesizing smaller nanocrystals lower calcination temperature (500 degC) and

shorter calcination time (2 h) are recommended It was also observed that calcination

temperature has more effect on the BET surface compared to calcination time which showed

that the pore size of the nanocrystalline powders was more dependent on the calcination

temperature

5 Acknowledgement

The authors would like to acknowledge the Ministry of Science Education and Innovation

(MOSTI) of Malaysia for providing research funding under the e-science scheme grant

number 03-02-10-SF0259

References

1 Boury B and S Plumejeau Metal oxides and polysaccharides an efficient hybrid association for materials chemistry Green Chemistry 2015 17(1) p 72-88

2 Bell AT The impact of nanoscience on heterogeneous catalysis Science 2003 299(5613) p 1688-1691

3 Zhao X et al The role of nanomaterials in redox-based supercapacitors for next generation energy storage devices Nanoscale 2011 3(3) p 839-855

4 Sun Y-F et al Metal oxide nanostructures and their gas sensing properties a review Sensors 2012 12(3) p 2610-2631

5 Jia J et al Heterogeneous catalytic hydrogenation of CO 2 by metal oxides defect engineeringndashperfecting imperfection Chemical Society Reviews 2017 46(15) p 4631-4644

6 Pezeshkpour S et al Ionicndashgelation synthesis of gadolinium doped ceria (Ce 08 Gd 02 O 190) nanocomposite powder using sodium-alginate Ceramics International 2017 43(9) p 7123-7135

7 Atif M et al Studies on the magnetic magnetostrictive and electrical properties of solndashgel synthesized Zn doped nickel ferrite Journal of Alloys and Compounds 2011 509(18) p 5720-5724

8 Krstajić N et al Non-noble metal composite cathodes for hydrogen evolution Part I the NindashMoO x coatings electrodeposited from Wattrsquos type bath containing MoO 3 powder particles international journal of hydrogen energy 2011 36(11) p 6441-6449

9 Macedo DA et al NindashCGO cermet anodes from nanocomposite powders Microstructural and electrochemical assessment Ceramics International 2014 40(8) p 13105-13113

10 Gao H et al The design of excellent xylene gas sensor using Sn-doped NiO hierarchical nanostructure Sensors and Actuators B Chemical 2017 253 p 1152-1162

11 Wang Z GM Kale and M Ghadiri Novel Ion‐Exchange Process for the Preparation of Metal Oxide Nanopowders from Sodium Alginate Journal of the American Ceramic Society 2012 95(10) p 3124-3129

12 Galeano MAacuteN et al Studies on the structural quantitative and semi-quantitative analyses of NiOndashGDC nanocomposites RSC Advances 2016 6(77) p 72865-72876

13 Gil V C Moure and J Tartaj Sinterability microstructures and electrical properties of NiGd-doped ceria cermets used as anode materials for SOFCs Journal of the European Ceramic Society 2007 27(13) p 4205-4209

14 Akbari-Fakhrabadi A et al Combustion synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite anode and its electrical characteristics of semi-cell configured SOFC assembly Journal of Alloys and Compounds 2012 541 p 1-5

15 Ishihara T et al NickelndashGd-doped CeO 2 cermet anode for intermediate temperature operating solid oxide fuel cells using LaGaO 3-based perovskite electrolyte Solid State Ionics 2000 132(3) p 209-216

16 Ding C et al A comparative study of NiOndashCe 09 Gd 01 O 195 nanocomposite powders synthesized by hydroxide and oxalate co-precipitation methods Ceramics International 2012 38(1) p 85-92

17 Ding C et al Synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite powders for low-temperature solid oxide fuel cell anodes by co-precipitation Scripta Materialia 2009 60(4) p 254-256

18 Park S-Y et al Preparation of highly porous NiOndashgadolinium-doped ceria nano-composite powders by one-pot glycine nitrate process for anode-supported tubular solid oxide fuel cells Journal of Asian Ceramic Societies 2014 2(4) p 339-346

19 Zhu W and S Deevi A review on the status of anode materials for solid oxide fuel cells Materials Science and Engineering A 2003 362(1) p 228-239

20 Chick LA et al Glycine-nitrate combustion synthesis of oxide ceramic powders Materials Letters 1990 10(1-2) p 6-12

21 Basu RN et al Microstructure and electrical conductivity of LaNi 06 Fe 04 O 3 prepared by combustion synthesis routes Materials Research Bulletin 2004 39(9) p 1335-1345

22 SOFC ZS Microstructure development of the Ni-GDC anode material for IT-SOFC Materiali in tehnologije 2012 46(5) p 445-451

23 Aparicio M A Jitianu and LC Klein Sol-Gel Processing for Conventional and Alternative Energy 2012 Springer Science amp Business Media

24 Suciu C et al NiOYSZ nanoparticles obtained by new solndashgel route Chemical Engineering Journal 2008 140(1) p 586-592

25 Jiang SP and SH Chan A review of anode materials development in solid oxide fuel cells Journal of Materials Science 2004 39(14) p 4405-4439

26 Iyer A et al A Sucrose‐Mediated SolndashGel Technique for the Synthesis of MgOndashY2O3 Nanocomposites Journal of the American Ceramic Society 2013 96(2) p 346-350

27 Wang Z et al Ion-exchange kinetics and thermal decomposition characteristics of Fe2+-exchanged alginic acid membrane for the formation of iron oxide nanoparticles Journal of Materials Science 2014 49(20) p 7151-7155

28 Schnepp Z et al Alginate-mediated routes to the selective synthesis of complex metal oxide nanostructures CrystEngComm 2010 12(5) p 1410-1415

29 Wang Z GM Kale and M Ghadiri Synthesis and characterization of CexGd 1minus xO 2minus δ nanopowders employing an alginate mediated ion-exchange process Chemical Engineering Journal 2012 198 p 149-153

30 Brayner R et al Alginate-mediated growth of Co Ni and CoNi nanoparticles influence of the biopolymer structure Chemistry of Materials 2007 19(5) p 1190-1198

31 Balavandy SK K Shameli and ZZ Abidin Rapid and Green Synthesis of Silver Nanoparticles via Sodium Alginate Media Int J Electrochem Sci 2015 10 p 486-497

32 Choo CK BA Horri and B Salamatinia Synthesis and Characterization of Nickel (II) OxideGadolinium-Doped Ceria (NiOGDC) Nanocomposites As a Potential Material for Anode Supported LT-SOFCs in Proceedings of the World Congress on Engineering and Computer Science 2016

33 Rath MK M-J Lee and K-T Lee Preparation of nano-structured NindashCe 08 Gd 02 O 19 anode materials for solid oxide fuel cells via the water-in-oil (WO) micro-emulsion route Ceramics International 2014 40(1) p 1909-1917

34 Schneider CA WS Rasband and KW Eliceiri NIH Image to ImageJ 25 years of image analysis Nature methods 2012 9(7) p 671-675

35 Collins T ImageJ for Microscopy BioTechniques 43 S25-S30 httpdx doi org102144000112517 2007

36 Thierry R F Thierry and G Osenga Surface energy modified particles method of making and use thereof 2015 Google Patents

37 Macedo DA et al A versatile route for the preparation of NindashCGO cermets from nanocomposite powders Ceramics International 2013 39(4) p 4321-4328

38 Wandekar R et al Physicochemical studies of NiOndashGDC composites Materials Chemistry and Physics 2006 99(2) p 289-294

39 Prakash BS VW Grips and S Aruna A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes Journal of Power Sources 2012 214 p 358-364

40 Sartori C et al Determination of the cation content of alginate thin films by FTi r spectroscopy Polymer 1997 38(1) p 43-51

41 Lakouraj MM F Mojerlou and EN Zare Nanogel and superparamagnetic nanocomposite based on sodium alginate for sorption of heavy metal ions Carbohydrate polymers 2014 106 p 34-41

42 Srivastava M et al Synthesis of superparamagnetic bare Fe 3 O 4 nanostructures and coreshell (Fe 3 O 4alginate) nanocomposites Carbohydrate polymers 2012 89(3) p 821-829

43 Chavan A et al Effect of variation of NiO on properties of NiOGDC (gadolinium doped ceria) nano-composites Ceramics International 2012 38(4) p 3191-3196

44 Shen C and LL Shaw FTIR analysis of the hydrolysis rate in the solndashgel formation of gadolinia-doped ceria with acetylacetonate precursors Journal of sol-gel science and technology 2010 53(3) p 571-577

45 Wang T and D-C Sun Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method Materials Research Bulletin 2008 43(7) p 1754-1760

46 Sing KS Reporting physisorption data for gassolid systems with special reference to the determination of surface area and porosity (Recommendations 1984) Pure and applied chemistry 1985 57(4) p 603-619

47 Song X et al Synthesis and Characterization of Y-Doped Mesoporous CeO 2 Using A Chemical Precipitation Method Journal of Rare Earths 2007 25(4) p 428-433

characterization techniques It was found that at a fixed calcination temperature the size of

the nanocrystals would increase with increasing calcination time Similarly at a fixed

calcination time and increasing calcination temperature larger nanocrystals were produced

Therefore for synthesizing smaller nanocrystals lower calcination temperature (500 degC) and

shorter calcination time (2 h) are recommended It was also observed that calcination

temperature has more effect on the BET surface compared to calcination time which showed

that the pore size of the nanocrystalline powders was more dependent on the calcination

temperature

5 Acknowledgement

The authors would like to acknowledge the Ministry of Science Education and Innovation

(MOSTI) of Malaysia for providing research funding under the e-science scheme grant

number 03-02-10-SF0259

References

1 Boury B and S Plumejeau Metal oxides and polysaccharides an efficient hybrid association for materials chemistry Green Chemistry 2015 17(1) p 72-88

2 Bell AT The impact of nanoscience on heterogeneous catalysis Science 2003 299(5613) p 1688-1691

3 Zhao X et al The role of nanomaterials in redox-based supercapacitors for next generation energy storage devices Nanoscale 2011 3(3) p 839-855

4 Sun Y-F et al Metal oxide nanostructures and their gas sensing properties a review Sensors 2012 12(3) p 2610-2631

5 Jia J et al Heterogeneous catalytic hydrogenation of CO 2 by metal oxides defect engineeringndashperfecting imperfection Chemical Society Reviews 2017 46(15) p 4631-4644

6 Pezeshkpour S et al Ionicndashgelation synthesis of gadolinium doped ceria (Ce 08 Gd 02 O 190) nanocomposite powder using sodium-alginate Ceramics International 2017 43(9) p 7123-7135

7 Atif M et al Studies on the magnetic magnetostrictive and electrical properties of solndashgel synthesized Zn doped nickel ferrite Journal of Alloys and Compounds 2011 509(18) p 5720-5724

8 Krstajić N et al Non-noble metal composite cathodes for hydrogen evolution Part I the NindashMoO x coatings electrodeposited from Wattrsquos type bath containing MoO 3 powder particles international journal of hydrogen energy 2011 36(11) p 6441-6449

9 Macedo DA et al NindashCGO cermet anodes from nanocomposite powders Microstructural and electrochemical assessment Ceramics International 2014 40(8) p 13105-13113

10 Gao H et al The design of excellent xylene gas sensor using Sn-doped NiO hierarchical nanostructure Sensors and Actuators B Chemical 2017 253 p 1152-1162

11 Wang Z GM Kale and M Ghadiri Novel Ion‐Exchange Process for the Preparation of Metal Oxide Nanopowders from Sodium Alginate Journal of the American Ceramic Society 2012 95(10) p 3124-3129

12 Galeano MAacuteN et al Studies on the structural quantitative and semi-quantitative analyses of NiOndashGDC nanocomposites RSC Advances 2016 6(77) p 72865-72876

13 Gil V C Moure and J Tartaj Sinterability microstructures and electrical properties of NiGd-doped ceria cermets used as anode materials for SOFCs Journal of the European Ceramic Society 2007 27(13) p 4205-4209

14 Akbari-Fakhrabadi A et al Combustion synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite anode and its electrical characteristics of semi-cell configured SOFC assembly Journal of Alloys and Compounds 2012 541 p 1-5

15 Ishihara T et al NickelndashGd-doped CeO 2 cermet anode for intermediate temperature operating solid oxide fuel cells using LaGaO 3-based perovskite electrolyte Solid State Ionics 2000 132(3) p 209-216

16 Ding C et al A comparative study of NiOndashCe 09 Gd 01 O 195 nanocomposite powders synthesized by hydroxide and oxalate co-precipitation methods Ceramics International 2012 38(1) p 85-92

17 Ding C et al Synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite powders for low-temperature solid oxide fuel cell anodes by co-precipitation Scripta Materialia 2009 60(4) p 254-256

18 Park S-Y et al Preparation of highly porous NiOndashgadolinium-doped ceria nano-composite powders by one-pot glycine nitrate process for anode-supported tubular solid oxide fuel cells Journal of Asian Ceramic Societies 2014 2(4) p 339-346

19 Zhu W and S Deevi A review on the status of anode materials for solid oxide fuel cells Materials Science and Engineering A 2003 362(1) p 228-239

20 Chick LA et al Glycine-nitrate combustion synthesis of oxide ceramic powders Materials Letters 1990 10(1-2) p 6-12

21 Basu RN et al Microstructure and electrical conductivity of LaNi 06 Fe 04 O 3 prepared by combustion synthesis routes Materials Research Bulletin 2004 39(9) p 1335-1345

22 SOFC ZS Microstructure development of the Ni-GDC anode material for IT-SOFC Materiali in tehnologije 2012 46(5) p 445-451

23 Aparicio M A Jitianu and LC Klein Sol-Gel Processing for Conventional and Alternative Energy 2012 Springer Science amp Business Media

24 Suciu C et al NiOYSZ nanoparticles obtained by new solndashgel route Chemical Engineering Journal 2008 140(1) p 586-592

25 Jiang SP and SH Chan A review of anode materials development in solid oxide fuel cells Journal of Materials Science 2004 39(14) p 4405-4439

26 Iyer A et al A Sucrose‐Mediated SolndashGel Technique for the Synthesis of MgOndashY2O3 Nanocomposites Journal of the American Ceramic Society 2013 96(2) p 346-350

27 Wang Z et al Ion-exchange kinetics and thermal decomposition characteristics of Fe2+-exchanged alginic acid membrane for the formation of iron oxide nanoparticles Journal of Materials Science 2014 49(20) p 7151-7155

28 Schnepp Z et al Alginate-mediated routes to the selective synthesis of complex metal oxide nanostructures CrystEngComm 2010 12(5) p 1410-1415

29 Wang Z GM Kale and M Ghadiri Synthesis and characterization of CexGd 1minus xO 2minus δ nanopowders employing an alginate mediated ion-exchange process Chemical Engineering Journal 2012 198 p 149-153

30 Brayner R et al Alginate-mediated growth of Co Ni and CoNi nanoparticles influence of the biopolymer structure Chemistry of Materials 2007 19(5) p 1190-1198

31 Balavandy SK K Shameli and ZZ Abidin Rapid and Green Synthesis of Silver Nanoparticles via Sodium Alginate Media Int J Electrochem Sci 2015 10 p 486-497

32 Choo CK BA Horri and B Salamatinia Synthesis and Characterization of Nickel (II) OxideGadolinium-Doped Ceria (NiOGDC) Nanocomposites As a Potential Material for Anode Supported LT-SOFCs in Proceedings of the World Congress on Engineering and Computer Science 2016

33 Rath MK M-J Lee and K-T Lee Preparation of nano-structured NindashCe 08 Gd 02 O 19 anode materials for solid oxide fuel cells via the water-in-oil (WO) micro-emulsion route Ceramics International 2014 40(1) p 1909-1917

34 Schneider CA WS Rasband and KW Eliceiri NIH Image to ImageJ 25 years of image analysis Nature methods 2012 9(7) p 671-675

35 Collins T ImageJ for Microscopy BioTechniques 43 S25-S30 httpdx doi org102144000112517 2007

36 Thierry R F Thierry and G Osenga Surface energy modified particles method of making and use thereof 2015 Google Patents

37 Macedo DA et al A versatile route for the preparation of NindashCGO cermets from nanocomposite powders Ceramics International 2013 39(4) p 4321-4328

38 Wandekar R et al Physicochemical studies of NiOndashGDC composites Materials Chemistry and Physics 2006 99(2) p 289-294

39 Prakash BS VW Grips and S Aruna A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes Journal of Power Sources 2012 214 p 358-364

40 Sartori C et al Determination of the cation content of alginate thin films by FTi r spectroscopy Polymer 1997 38(1) p 43-51

41 Lakouraj MM F Mojerlou and EN Zare Nanogel and superparamagnetic nanocomposite based on sodium alginate for sorption of heavy metal ions Carbohydrate polymers 2014 106 p 34-41

42 Srivastava M et al Synthesis of superparamagnetic bare Fe 3 O 4 nanostructures and coreshell (Fe 3 O 4alginate) nanocomposites Carbohydrate polymers 2012 89(3) p 821-829

43 Chavan A et al Effect of variation of NiO on properties of NiOGDC (gadolinium doped ceria) nano-composites Ceramics International 2012 38(4) p 3191-3196

44 Shen C and LL Shaw FTIR analysis of the hydrolysis rate in the solndashgel formation of gadolinia-doped ceria with acetylacetonate precursors Journal of sol-gel science and technology 2010 53(3) p 571-577

45 Wang T and D-C Sun Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method Materials Research Bulletin 2008 43(7) p 1754-1760

46 Sing KS Reporting physisorption data for gassolid systems with special reference to the determination of surface area and porosity (Recommendations 1984) Pure and applied chemistry 1985 57(4) p 603-619

47 Song X et al Synthesis and Characterization of Y-Doped Mesoporous CeO 2 Using A Chemical Precipitation Method Journal of Rare Earths 2007 25(4) p 428-433

9 Macedo DA et al NindashCGO cermet anodes from nanocomposite powders Microstructural and electrochemical assessment Ceramics International 2014 40(8) p 13105-13113

10 Gao H et al The design of excellent xylene gas sensor using Sn-doped NiO hierarchical nanostructure Sensors and Actuators B Chemical 2017 253 p 1152-1162

11 Wang Z GM Kale and M Ghadiri Novel Ion‐Exchange Process for the Preparation of Metal Oxide Nanopowders from Sodium Alginate Journal of the American Ceramic Society 2012 95(10) p 3124-3129

12 Galeano MAacuteN et al Studies on the structural quantitative and semi-quantitative analyses of NiOndashGDC nanocomposites RSC Advances 2016 6(77) p 72865-72876

13 Gil V C Moure and J Tartaj Sinterability microstructures and electrical properties of NiGd-doped ceria cermets used as anode materials for SOFCs Journal of the European Ceramic Society 2007 27(13) p 4205-4209

14 Akbari-Fakhrabadi A et al Combustion synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite anode and its electrical characteristics of semi-cell configured SOFC assembly Journal of Alloys and Compounds 2012 541 p 1-5

15 Ishihara T et al NickelndashGd-doped CeO 2 cermet anode for intermediate temperature operating solid oxide fuel cells using LaGaO 3-based perovskite electrolyte Solid State Ionics 2000 132(3) p 209-216

16 Ding C et al A comparative study of NiOndashCe 09 Gd 01 O 195 nanocomposite powders synthesized by hydroxide and oxalate co-precipitation methods Ceramics International 2012 38(1) p 85-92

17 Ding C et al Synthesis of NiOndashCe 09 Gd 01 O 195 nanocomposite powders for low-temperature solid oxide fuel cell anodes by co-precipitation Scripta Materialia 2009 60(4) p 254-256

18 Park S-Y et al Preparation of highly porous NiOndashgadolinium-doped ceria nano-composite powders by one-pot glycine nitrate process for anode-supported tubular solid oxide fuel cells Journal of Asian Ceramic Societies 2014 2(4) p 339-346

19 Zhu W and S Deevi A review on the status of anode materials for solid oxide fuel cells Materials Science and Engineering A 2003 362(1) p 228-239

20 Chick LA et al Glycine-nitrate combustion synthesis of oxide ceramic powders Materials Letters 1990 10(1-2) p 6-12

21 Basu RN et al Microstructure and electrical conductivity of LaNi 06 Fe 04 O 3 prepared by combustion synthesis routes Materials Research Bulletin 2004 39(9) p 1335-1345

22 SOFC ZS Microstructure development of the Ni-GDC anode material for IT-SOFC Materiali in tehnologije 2012 46(5) p 445-451

23 Aparicio M A Jitianu and LC Klein Sol-Gel Processing for Conventional and Alternative Energy 2012 Springer Science amp Business Media

24 Suciu C et al NiOYSZ nanoparticles obtained by new solndashgel route Chemical Engineering Journal 2008 140(1) p 586-592

25 Jiang SP and SH Chan A review of anode materials development in solid oxide fuel cells Journal of Materials Science 2004 39(14) p 4405-4439

26 Iyer A et al A Sucrose‐Mediated SolndashGel Technique for the Synthesis of MgOndashY2O3 Nanocomposites Journal of the American Ceramic Society 2013 96(2) p 346-350

27 Wang Z et al Ion-exchange kinetics and thermal decomposition characteristics of Fe2+-exchanged alginic acid membrane for the formation of iron oxide nanoparticles Journal of Materials Science 2014 49(20) p 7151-7155

28 Schnepp Z et al Alginate-mediated routes to the selective synthesis of complex metal oxide nanostructures CrystEngComm 2010 12(5) p 1410-1415

29 Wang Z GM Kale and M Ghadiri Synthesis and characterization of CexGd 1minus xO 2minus δ nanopowders employing an alginate mediated ion-exchange process Chemical Engineering Journal 2012 198 p 149-153

30 Brayner R et al Alginate-mediated growth of Co Ni and CoNi nanoparticles influence of the biopolymer structure Chemistry of Materials 2007 19(5) p 1190-1198

31 Balavandy SK K Shameli and ZZ Abidin Rapid and Green Synthesis of Silver Nanoparticles via Sodium Alginate Media Int J Electrochem Sci 2015 10 p 486-497

32 Choo CK BA Horri and B Salamatinia Synthesis and Characterization of Nickel (II) OxideGadolinium-Doped Ceria (NiOGDC) Nanocomposites As a Potential Material for Anode Supported LT-SOFCs in Proceedings of the World Congress on Engineering and Computer Science 2016

33 Rath MK M-J Lee and K-T Lee Preparation of nano-structured NindashCe 08 Gd 02 O 19 anode materials for solid oxide fuel cells via the water-in-oil (WO) micro-emulsion route Ceramics International 2014 40(1) p 1909-1917

34 Schneider CA WS Rasband and KW Eliceiri NIH Image to ImageJ 25 years of image analysis Nature methods 2012 9(7) p 671-675

35 Collins T ImageJ for Microscopy BioTechniques 43 S25-S30 httpdx doi org102144000112517 2007

36 Thierry R F Thierry and G Osenga Surface energy modified particles method of making and use thereof 2015 Google Patents

37 Macedo DA et al A versatile route for the preparation of NindashCGO cermets from nanocomposite powders Ceramics International 2013 39(4) p 4321-4328

38 Wandekar R et al Physicochemical studies of NiOndashGDC composites Materials Chemistry and Physics 2006 99(2) p 289-294

39 Prakash BS VW Grips and S Aruna A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes Journal of Power Sources 2012 214 p 358-364

40 Sartori C et al Determination of the cation content of alginate thin films by FTi r spectroscopy Polymer 1997 38(1) p 43-51

41 Lakouraj MM F Mojerlou and EN Zare Nanogel and superparamagnetic nanocomposite based on sodium alginate for sorption of heavy metal ions Carbohydrate polymers 2014 106 p 34-41

42 Srivastava M et al Synthesis of superparamagnetic bare Fe 3 O 4 nanostructures and coreshell (Fe 3 O 4alginate) nanocomposites Carbohydrate polymers 2012 89(3) p 821-829

43 Chavan A et al Effect of variation of NiO on properties of NiOGDC (gadolinium doped ceria) nano-composites Ceramics International 2012 38(4) p 3191-3196

44 Shen C and LL Shaw FTIR analysis of the hydrolysis rate in the solndashgel formation of gadolinia-doped ceria with acetylacetonate precursors Journal of sol-gel science and technology 2010 53(3) p 571-577

45 Wang T and D-C Sun Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method Materials Research Bulletin 2008 43(7) p 1754-1760

46 Sing KS Reporting physisorption data for gassolid systems with special reference to the determination of surface area and porosity (Recommendations 1984) Pure and applied chemistry 1985 57(4) p 603-619

47 Song X et al Synthesis and Characterization of Y-Doped Mesoporous CeO 2 Using A Chemical Precipitation Method Journal of Rare Earths 2007 25(4) p 428-433

29 Wang Z GM Kale and M Ghadiri Synthesis and characterization of CexGd 1minus xO 2minus δ nanopowders employing an alginate mediated ion-exchange process Chemical Engineering Journal 2012 198 p 149-153

30 Brayner R et al Alginate-mediated growth of Co Ni and CoNi nanoparticles influence of the biopolymer structure Chemistry of Materials 2007 19(5) p 1190-1198

31 Balavandy SK K Shameli and ZZ Abidin Rapid and Green Synthesis of Silver Nanoparticles via Sodium Alginate Media Int J Electrochem Sci 2015 10 p 486-497

32 Choo CK BA Horri and B Salamatinia Synthesis and Characterization of Nickel (II) OxideGadolinium-Doped Ceria (NiOGDC) Nanocomposites As a Potential Material for Anode Supported LT-SOFCs in Proceedings of the World Congress on Engineering and Computer Science 2016

33 Rath MK M-J Lee and K-T Lee Preparation of nano-structured NindashCe 08 Gd 02 O 19 anode materials for solid oxide fuel cells via the water-in-oil (WO) micro-emulsion route Ceramics International 2014 40(1) p 1909-1917

34 Schneider CA WS Rasband and KW Eliceiri NIH Image to ImageJ 25 years of image analysis Nature methods 2012 9(7) p 671-675

35 Collins T ImageJ for Microscopy BioTechniques 43 S25-S30 httpdx doi org102144000112517 2007

36 Thierry R F Thierry and G Osenga Surface energy modified particles method of making and use thereof 2015 Google Patents

37 Macedo DA et al A versatile route for the preparation of NindashCGO cermets from nanocomposite powders Ceramics International 2013 39(4) p 4321-4328

38 Wandekar R et al Physicochemical studies of NiOndashGDC composites Materials Chemistry and Physics 2006 99(2) p 289-294

39 Prakash BS VW Grips and S Aruna A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes Journal of Power Sources 2012 214 p 358-364

40 Sartori C et al Determination of the cation content of alginate thin films by FTi r spectroscopy Polymer 1997 38(1) p 43-51

41 Lakouraj MM F Mojerlou and EN Zare Nanogel and superparamagnetic nanocomposite based on sodium alginate for sorption of heavy metal ions Carbohydrate polymers 2014 106 p 34-41

42 Srivastava M et al Synthesis of superparamagnetic bare Fe 3 O 4 nanostructures and coreshell (Fe 3 O 4alginate) nanocomposites Carbohydrate polymers 2012 89(3) p 821-829

43 Chavan A et al Effect of variation of NiO on properties of NiOGDC (gadolinium doped ceria) nano-composites Ceramics International 2012 38(4) p 3191-3196

44 Shen C and LL Shaw FTIR analysis of the hydrolysis rate in the solndashgel formation of gadolinia-doped ceria with acetylacetonate precursors Journal of sol-gel science and technology 2010 53(3) p 571-577

45 Wang T and D-C Sun Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method Materials Research Bulletin 2008 43(7) p 1754-1760

46 Sing KS Reporting physisorption data for gassolid systems with special reference to the determination of surface area and porosity (Recommendations 1984) Pure and applied chemistry 1985 57(4) p 603-619

47 Song X et al Synthesis and Characterization of Y-Doped Mesoporous CeO 2 Using A Chemical Precipitation Method Journal of Rare Earths 2007 25(4) p 428-433

List of Figures

Figure 1 a) Beads formation before drying at (50degC) and b) after drying at (50 degC)

Figure 2 Thermal analysis of a) as-prepared NiO-GDC nanocrystallite and b) calcined sample at 700 degC for 2h

Figure 3 FESEM images for loading fraction of 3 at calcination temperatures of 500 degC for a) 2h b) 6 h c) 10 h

Figure 4 FESEM images for loading fraction of 3 at calcination temperatures of 600 degC for a) 2h b) 6 h c) 10 h

Figure 5 FESEM images for loading fraction of 3 at calcination temperatures of 700 degC for a) 2h b) 6 h c) 10 h

Figure 6 EDX analysis of NiO-GDC calcined at 500 degC for 2 hours

Figure 7 XRD pattern of NiO-GDC nanocrystalline based on constant calcination temperature at different calcination time a) 500 degC b) 600 degC and c) 700 degC

Figure 8 FT-IR spectra of dried and calcined samples at a) 500 degC b) 600 degC c) 700 degC for different calcination times

Figure 9 Nitrogen adsorptiondesorption isotherms of NiO-GDC nanocomposits samples calcined at a) 500 degC b) 600 degC and c) 700 degC for different calcination times The insets show the pore size distribution of the samples

a b

Figure 1 a) Beads formation before drying at (50 degC) and b) after drying at (50 degC)

a

b

Figure 2 Thermal analysis of a) as-prepared NiO-GDC nanocrystallite and b) calcined sample at 700 degC for 2h

a

b

c

Figure 3 FESEM images for loading fraction of 3 at calcination temperatures of 500 degC for a) 2h b) 6 h c) 10 h

a

b

c

Figure 1 FESEM images for loading fraction of 3 at calcination temperatures of 600 degC for a) 2h b) 6 h c) 10 h

a

b

c

Figure 2 FESEM images for loading fraction of 3 at calcination temperatures of 700 degC for a) 2h b) 6 h c) 10 h

Figure 3 EDX analysis of NiO-GDC calcined at 500 degC for 2 hours

a

b

c

Figure 4 XRD pattern of NiO-GDC nanocrystalline based on constant calcination temperature at different calcination time a) 500 degC b) 600 degC and c) 700 degC

a

b

c

Figure 5 FT-IR spectra of dried and calcined samples at a) 500 degC b) 600 degC c) 700 degC for different calcination times

a

b

c

Figure 6 Nitrogen adsorptiondesorption isotherms of NiO-GDC nanocomposits samples calcined at a) 500 degC b) 600 degC and c) 700 degC for different calcination times The insets show

the pore size distribution of the samples

List of Tables

Table 1 Calcination time and calcination temperature for different samplesTable 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formulaTable 3 BET surface are of samples at different calcination time and temperatures

Table 1 Calcination time and calcination temperature for different samples

Experiment ID Calcination time(hours)

Calcination temperature (degC)

12

5002 6003 7004

6500

5 6006 7007

10500

8 6009 700

Table 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formula

NiO GDC2h 6h 10h 2h 6h 10h

500degC 799 1257 1709 518 713 953

600degC 1473 1987 2442 964 1025 1171

700degC 1583 2084365 2513 1438 1781968 1782

Table 3 BET surface are of samples at different calcination time and temperatures

Calcination time

Calcination

temperature2h 6h 10h

500 degC 121225 m2g 78891 m2g 68923 m2g

600 degC 61579 m2g 60508 m2g 64342 m2g

700degC 48692 m2g 39753 m2g 32862 m2g

• 21 Materials
• 3 Results and Discussion

a b

Figure 1 a) Beads formation before drying at (50 degC) and b) after drying at (50 degC)

a

b

Figure 2 Thermal analysis of a) as-prepared NiO-GDC nanocrystallite and b) calcined sample at 700 degC for 2h

a

b

c

Figure 3 FESEM images for loading fraction of 3 at calcination temperatures of 500 degC for a) 2h b) 6 h c) 10 h

a

b

c

Figure 1 FESEM images for loading fraction of 3 at calcination temperatures of 600 degC for a) 2h b) 6 h c) 10 h

a

b

c

Figure 2 FESEM images for loading fraction of 3 at calcination temperatures of 700 degC for a) 2h b) 6 h c) 10 h

Figure 3 EDX analysis of NiO-GDC calcined at 500 degC for 2 hours

a

b

c

Figure 4 XRD pattern of NiO-GDC nanocrystalline based on constant calcination temperature at different calcination time a) 500 degC b) 600 degC and c) 700 degC

a

b

c

Figure 5 FT-IR spectra of dried and calcined samples at a) 500 degC b) 600 degC c) 700 degC for different calcination times

a

b

c

Figure 6 Nitrogen adsorptiondesorption isotherms of NiO-GDC nanocomposits samples calcined at a) 500 degC b) 600 degC and c) 700 degC for different calcination times The insets show

the pore size distribution of the samples

List of Tables

Table 1 Calcination time and calcination temperature for different samplesTable 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formulaTable 3 BET surface are of samples at different calcination time and temperatures

Table 1 Calcination time and calcination temperature for different samples

Experiment ID Calcination time(hours)

Calcination temperature (degC)

12

5002 6003 7004

6500

5 6006 7007

10500

8 6009 700

Table 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formula

NiO GDC2h 6h 10h 2h 6h 10h

500degC 799 1257 1709 518 713 953

600degC 1473 1987 2442 964 1025 1171

700degC 1583 2084365 2513 1438 1781968 1782

Table 3 BET surface are of samples at different calcination time and temperatures

Calcination time

Calcination

temperature2h 6h 10h

500 degC 121225 m2g 78891 m2g 68923 m2g

600 degC 61579 m2g 60508 m2g 64342 m2g

700degC 48692 m2g 39753 m2g 32862 m2g

• 21 Materials
• 3 Results and Discussion

a

b

Figure 2 Thermal analysis of a) as-prepared NiO-GDC nanocrystallite and b) calcined sample at 700 degC for 2h

a

b

c

Figure 3 FESEM images for loading fraction of 3 at calcination temperatures of 500 degC for a) 2h b) 6 h c) 10 h

a

b

c

Figure 1 FESEM images for loading fraction of 3 at calcination temperatures of 600 degC for a) 2h b) 6 h c) 10 h

a

b

c

Figure 2 FESEM images for loading fraction of 3 at calcination temperatures of 700 degC for a) 2h b) 6 h c) 10 h

Figure 3 EDX analysis of NiO-GDC calcined at 500 degC for 2 hours

a

b

c

Figure 4 XRD pattern of NiO-GDC nanocrystalline based on constant calcination temperature at different calcination time a) 500 degC b) 600 degC and c) 700 degC

a

b

c

Figure 5 FT-IR spectra of dried and calcined samples at a) 500 degC b) 600 degC c) 700 degC for different calcination times

a

b

c

Figure 6 Nitrogen adsorptiondesorption isotherms of NiO-GDC nanocomposits samples calcined at a) 500 degC b) 600 degC and c) 700 degC for different calcination times The insets show

the pore size distribution of the samples

List of Tables

Table 1 Calcination time and calcination temperature for different samplesTable 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formulaTable 3 BET surface are of samples at different calcination time and temperatures

Table 1 Calcination time and calcination temperature for different samples

Experiment ID Calcination time(hours)

Calcination temperature (degC)

12

5002 6003 7004

6500

5 6006 7007

10500

8 6009 700

Table 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formula

NiO GDC2h 6h 10h 2h 6h 10h

500degC 799 1257 1709 518 713 953

600degC 1473 1987 2442 964 1025 1171

700degC 1583 2084365 2513 1438 1781968 1782

Table 3 BET surface are of samples at different calcination time and temperatures

Calcination time

Calcination

temperature2h 6h 10h

500 degC 121225 m2g 78891 m2g 68923 m2g

600 degC 61579 m2g 60508 m2g 64342 m2g

700degC 48692 m2g 39753 m2g 32862 m2g

• 21 Materials
• 3 Results and Discussion

a

b

c

Figure 3 FESEM images for loading fraction of 3 at calcination temperatures of 500 degC for a) 2h b) 6 h c) 10 h

a

b

c

Figure 1 FESEM images for loading fraction of 3 at calcination temperatures of 600 degC for a) 2h b) 6 h c) 10 h

a

b

c

Figure 2 FESEM images for loading fraction of 3 at calcination temperatures of 700 degC for a) 2h b) 6 h c) 10 h

Figure 3 EDX analysis of NiO-GDC calcined at 500 degC for 2 hours

a

b

c

Figure 4 XRD pattern of NiO-GDC nanocrystalline based on constant calcination temperature at different calcination time a) 500 degC b) 600 degC and c) 700 degC

a

b

c

Figure 5 FT-IR spectra of dried and calcined samples at a) 500 degC b) 600 degC c) 700 degC for different calcination times

a

b

c

Figure 6 Nitrogen adsorptiondesorption isotherms of NiO-GDC nanocomposits samples calcined at a) 500 degC b) 600 degC and c) 700 degC for different calcination times The insets show

the pore size distribution of the samples

List of Tables

Table 1 Calcination time and calcination temperature for different samplesTable 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formulaTable 3 BET surface are of samples at different calcination time and temperatures

Table 1 Calcination time and calcination temperature for different samples

Experiment ID Calcination time(hours)

Calcination temperature (degC)

12

5002 6003 7004

6500

5 6006 7007

10500

8 6009 700

Table 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formula

NiO GDC2h 6h 10h 2h 6h 10h

500degC 799 1257 1709 518 713 953

600degC 1473 1987 2442 964 1025 1171

700degC 1583 2084365 2513 1438 1781968 1782

Table 3 BET surface are of samples at different calcination time and temperatures

Calcination time

Calcination

temperature2h 6h 10h

500 degC 121225 m2g 78891 m2g 68923 m2g

600 degC 61579 m2g 60508 m2g 64342 m2g

700degC 48692 m2g 39753 m2g 32862 m2g

• 21 Materials
• 3 Results and Discussion

a

b

c

Figure 1 FESEM images for loading fraction of 3 at calcination temperatures of 600 degC for a) 2h b) 6 h c) 10 h

a

b

c

Figure 2 FESEM images for loading fraction of 3 at calcination temperatures of 700 degC for a) 2h b) 6 h c) 10 h

Figure 3 EDX analysis of NiO-GDC calcined at 500 degC for 2 hours

a

b

c

Figure 4 XRD pattern of NiO-GDC nanocrystalline based on constant calcination temperature at different calcination time a) 500 degC b) 600 degC and c) 700 degC

a

b

c

Figure 5 FT-IR spectra of dried and calcined samples at a) 500 degC b) 600 degC c) 700 degC for different calcination times

a

b

c

Figure 6 Nitrogen adsorptiondesorption isotherms of NiO-GDC nanocomposits samples calcined at a) 500 degC b) 600 degC and c) 700 degC for different calcination times The insets show

the pore size distribution of the samples

List of Tables

Table 1 Calcination time and calcination temperature for different samplesTable 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formulaTable 3 BET surface are of samples at different calcination time and temperatures

Table 1 Calcination time and calcination temperature for different samples

Experiment ID Calcination time(hours)

Calcination temperature (degC)

12

5002 6003 7004

6500

5 6006 7007

10500

8 6009 700

Table 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formula

NiO GDC2h 6h 10h 2h 6h 10h

500degC 799 1257 1709 518 713 953

600degC 1473 1987 2442 964 1025 1171

700degC 1583 2084365 2513 1438 1781968 1782

Table 3 BET surface are of samples at different calcination time and temperatures

Calcination time

Calcination

temperature2h 6h 10h

500 degC 121225 m2g 78891 m2g 68923 m2g

600 degC 61579 m2g 60508 m2g 64342 m2g

700degC 48692 m2g 39753 m2g 32862 m2g

• 21 Materials
• 3 Results and Discussion

a

b

c

Figure 2 FESEM images for loading fraction of 3 at calcination temperatures of 700 degC for a) 2h b) 6 h c) 10 h

Figure 3 EDX analysis of NiO-GDC calcined at 500 degC for 2 hours

a

b

c

Figure 4 XRD pattern of NiO-GDC nanocrystalline based on constant calcination temperature at different calcination time a) 500 degC b) 600 degC and c) 700 degC

a

b

c

Figure 5 FT-IR spectra of dried and calcined samples at a) 500 degC b) 600 degC c) 700 degC for different calcination times

a

b

c

Figure 6 Nitrogen adsorptiondesorption isotherms of NiO-GDC nanocomposits samples calcined at a) 500 degC b) 600 degC and c) 700 degC for different calcination times The insets show

the pore size distribution of the samples

List of Tables

Table 1 Calcination time and calcination temperature for different samplesTable 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formulaTable 3 BET surface are of samples at different calcination time and temperatures

Table 1 Calcination time and calcination temperature for different samples

Experiment ID Calcination time(hours)

Calcination temperature (degC)

12

5002 6003 7004

6500

5 6006 7007

10500

8 6009 700

Table 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formula

NiO GDC2h 6h 10h 2h 6h 10h

500degC 799 1257 1709 518 713 953

600degC 1473 1987 2442 964 1025 1171

700degC 1583 2084365 2513 1438 1781968 1782

Table 3 BET surface are of samples at different calcination time and temperatures

Calcination time

Calcination

temperature2h 6h 10h

500 degC 121225 m2g 78891 m2g 68923 m2g

600 degC 61579 m2g 60508 m2g 64342 m2g

700degC 48692 m2g 39753 m2g 32862 m2g

• 21 Materials
• 3 Results and Discussion

Figure 3 EDX analysis of NiO-GDC calcined at 500 degC for 2 hours

a

b

c

Figure 4 XRD pattern of NiO-GDC nanocrystalline based on constant calcination temperature at different calcination time a) 500 degC b) 600 degC and c) 700 degC

a

b

c

Figure 5 FT-IR spectra of dried and calcined samples at a) 500 degC b) 600 degC c) 700 degC for different calcination times

a

b

c

Figure 6 Nitrogen adsorptiondesorption isotherms of NiO-GDC nanocomposits samples calcined at a) 500 degC b) 600 degC and c) 700 degC for different calcination times The insets show

the pore size distribution of the samples

List of Tables

Table 1 Calcination time and calcination temperature for different samplesTable 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formulaTable 3 BET surface are of samples at different calcination time and temperatures

Table 1 Calcination time and calcination temperature for different samples

Experiment ID Calcination time(hours)

Calcination temperature (degC)

12

5002 6003 7004

6500

5 6006 7007

10500

8 6009 700

Table 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formula

NiO GDC2h 6h 10h 2h 6h 10h

500degC 799 1257 1709 518 713 953

600degC 1473 1987 2442 964 1025 1171

700degC 1583 2084365 2513 1438 1781968 1782

Table 3 BET surface are of samples at different calcination time and temperatures

Calcination time

Calcination

temperature2h 6h 10h

500 degC 121225 m2g 78891 m2g 68923 m2g

600 degC 61579 m2g 60508 m2g 64342 m2g

700degC 48692 m2g 39753 m2g 32862 m2g

• 21 Materials
• 3 Results and Discussion

a

b

c

Figure 4 XRD pattern of NiO-GDC nanocrystalline based on constant calcination temperature at different calcination time a) 500 degC b) 600 degC and c) 700 degC

a

b

c

Figure 5 FT-IR spectra of dried and calcined samples at a) 500 degC b) 600 degC c) 700 degC for different calcination times

a

b

c

Figure 6 Nitrogen adsorptiondesorption isotherms of NiO-GDC nanocomposits samples calcined at a) 500 degC b) 600 degC and c) 700 degC for different calcination times The insets show

the pore size distribution of the samples

List of Tables

Table 1 Calcination time and calcination temperature for different samplesTable 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formulaTable 3 BET surface are of samples at different calcination time and temperatures

Table 1 Calcination time and calcination temperature for different samples

Experiment ID Calcination time(hours)

Calcination temperature (degC)

12

5002 6003 7004

6500

5 6006 7007

10500

8 6009 700

Table 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formula

NiO GDC2h 6h 10h 2h 6h 10h

500degC 799 1257 1709 518 713 953

600degC 1473 1987 2442 964 1025 1171

700degC 1583 2084365 2513 1438 1781968 1782

Table 3 BET surface are of samples at different calcination time and temperatures

Calcination time

Calcination

temperature2h 6h 10h

500 degC 121225 m2g 78891 m2g 68923 m2g

600 degC 61579 m2g 60508 m2g 64342 m2g

700degC 48692 m2g 39753 m2g 32862 m2g

• 21 Materials
• 3 Results and Discussion

a

b

c

Figure 5 FT-IR spectra of dried and calcined samples at a) 500 degC b) 600 degC c) 700 degC for different calcination times

a

b

c

Figure 6 Nitrogen adsorptiondesorption isotherms of NiO-GDC nanocomposits samples calcined at a) 500 degC b) 600 degC and c) 700 degC for different calcination times The insets show

the pore size distribution of the samples

List of Tables

Table 1 Calcination time and calcination temperature for different samplesTable 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formulaTable 3 BET surface are of samples at different calcination time and temperatures

Table 1 Calcination time and calcination temperature for different samples

Experiment ID Calcination time(hours)

Calcination temperature (degC)

12

5002 6003 7004

6500

5 6006 7007

10500

8 6009 700

Table 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formula

NiO GDC2h 6h 10h 2h 6h 10h

500degC 799 1257 1709 518 713 953

600degC 1473 1987 2442 964 1025 1171

700degC 1583 2084365 2513 1438 1781968 1782

Table 3 BET surface are of samples at different calcination time and temperatures

Calcination time

Calcination

temperature2h 6h 10h

500 degC 121225 m2g 78891 m2g 68923 m2g

600 degC 61579 m2g 60508 m2g 64342 m2g

700degC 48692 m2g 39753 m2g 32862 m2g

• 21 Materials
• 3 Results and Discussion

a

b

c

Figure 6 Nitrogen adsorptiondesorption isotherms of NiO-GDC nanocomposits samples calcined at a) 500 degC b) 600 degC and c) 700 degC for different calcination times The insets show

the pore size distribution of the samples

List of Tables

Table 1 Calcination time and calcination temperature for different samplesTable 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formulaTable 3 BET surface are of samples at different calcination time and temperatures

Table 1 Calcination time and calcination temperature for different samples

Experiment ID Calcination time(hours)

Calcination temperature (degC)

12

5002 6003 7004

6500

5 6006 7007

10500

8 6009 700

Table 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formula

NiO GDC2h 6h 10h 2h 6h 10h

500degC 799 1257 1709 518 713 953

600degC 1473 1987 2442 964 1025 1171

700degC 1583 2084365 2513 1438 1781968 1782

Table 3 BET surface are of samples at different calcination time and temperatures

Calcination time

Calcination

temperature2h 6h 10h

500 degC 121225 m2g 78891 m2g 68923 m2g

600 degC 61579 m2g 60508 m2g 64342 m2g

700degC 48692 m2g 39753 m2g 32862 m2g

• 21 Materials
• 3 Results and Discussion

List of Tables

Table 1 Calcination time and calcination temperature for different samplesTable 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formulaTable 3 BET surface are of samples at different calcination time and temperatures

Table 1 Calcination time and calcination temperature for different samples

Experiment ID Calcination time(hours)

Calcination temperature (degC)

12

5002 6003 7004

6500

5 6006 7007

10500

8 6009 700

Table 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formula

NiO GDC2h 6h 10h 2h 6h 10h

500degC 799 1257 1709 518 713 953

600degC 1473 1987 2442 964 1025 1171

700degC 1583 2084365 2513 1438 1781968 1782

Table 3 BET surface are of samples at different calcination time and temperatures

Calcination time

Calcination

temperature2h 6h 10h

500 degC 121225 m2g 78891 m2g 68923 m2g

600 degC 61579 m2g 60508 m2g 64342 m2g

700degC 48692 m2g 39753 m2g 32862 m2g

• 21 Materials
• 3 Results and Discussion

Table 1 Calcination time and calcination temperature for different samples

Experiment ID Calcination time(hours)

Calcination temperature (degC)

12

5002 6003 7004

6500

5 6006 7007

10500

8 6009 700

Table 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formula

NiO GDC2h 6h 10h 2h 6h 10h

500degC 799 1257 1709 518 713 953

600degC 1473 1987 2442 964 1025 1171

700degC 1583 2084365 2513 1438 1781968 1782

Table 3 BET surface are of samples at different calcination time and temperatures

Calcination time

Calcination

temperature2h 6h 10h

500 degC 121225 m2g 78891 m2g 68923 m2g

600 degC 61579 m2g 60508 m2g 64342 m2g

700degC 48692 m2g 39753 m2g 32862 m2g

• 21 Materials
• 3 Results and Discussion

Table 2 Crystalline size of synthesized NiO-GDC with Sherrerrsquos formula

NiO GDC2h 6h 10h 2h 6h 10h

500degC 799 1257 1709 518 713 953

600degC 1473 1987 2442 964 1025 1171

700degC 1583 2084365 2513 1438 1781968 1782

Table 3 BET surface are of samples at different calcination time and temperatures

Calcination time

Calcination

temperature2h 6h 10h

500 degC 121225 m2g 78891 m2g 68923 m2g

600 degC 61579 m2g 60508 m2g 64342 m2g

700degC 48692 m2g 39753 m2g 32862 m2g

• 21 Materials
• 3 Results and Discussion

Table 3 BET surface are of samples at different calcination time and temperatures

Calcination time

Calcination

temperature2h 6h 10h

500 degC 121225 m2g 78891 m2g 68923 m2g

600 degC 61579 m2g 60508 m2g 64342 m2g

700degC 48692 m2g 39753 m2g 32862 m2g

• 21 Materials
• 3 Results and Discussion