Journal of Hazardous Materials 203 204 (2012) 244 250

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Journal of Hazardous Materials

j our na l ho me p age: www.elsev ier .com

Titaniu alslm ca on methyl

AlagarsaCentre for Phot , India

a r t i c l

Article history:Received 22 JuReceived in reAccepted 5 DeAvailable onlin

Keywords:Aminosilicate TiO2Au nanoPhotocatalystChromium(VI)Methylene blue oxidationAdvanced oxidationreduction process

ium npreDAS/

undcavens invisperand o2 to Aps in

materials provided benecial role in the environmental remediation and purication process throughsynergistic photocatalytic activity by an advanced oxidationreduction processes.

2011 Elsevier B.V. All rights reserved.

1. Introdu

Titaniumgreater attelong time snium dioxidand tunablearea of phoelectrochrodye-sensitiz[1618]. Ndeposited oactivity tha(TiO2)nps sucarriers andminimize th

The hexathe environthe electropindustries. isms when In contrast,

CorresponE-mail add

0304-3894/$ doi:10.1016/j.ction

dioxidegold nanocomposite materials have receivedntion because of their interesting optical, electronic,tability and excellent catalytic activity [16]. The tita-egold nanomaterials ((TiO2Au)nps), due to their wide

band gap [7], nd wide range of applications in thetocatalysis [8], electrocatalysis [9], sonocatalysis [10],mic devices [11], photoelectrochemical cells [12,13],ed solar cells [14], biosensors [15] and gas sensors

oble metal nanoparticles such as Au, Ag, Pt and Irn the surface of the (TiO2)nps exhibit greater catalyticn that of the (TiO2)nps. The metal nanoparticles onrface act as an electron sink for the photoinduced charge

enhance the interfacial charge transfer process ande charge recombination [19,20].valent chromium (Cr(VI)) is a major pollutant added toment from the contaminated waters discharged fromlating industries, leather tanneries, paint and pigmentThe Cr(VI) is highly toxic to most of the living organ-the Cr(VI) concentration level is higher than 0.05 ppm.

the trivalent chromium (Cr(III)) is less toxic and one

ding author.ress: ramarajr@yahoo.com (R. Ramaraj).

of the essential nutrient for body function. Hence the reduction ofthe Cr(IV) ions into Cr(III) ions received great attention in the envi-ronment purication processes [2143]. Methylene blue (MB) is anorganic dye pollutant discharged from dyeing industries. The dyecontaminated water can affect the aquatic environments seriously.Removal of Cr(VI) and MB is a great challenge and several meth-ods were reported for the removal of these pollutants [38]. Amongthem, the photocatalytic purication is economically viable, facileand effective one.

In the past decade the photocatalytic removal of Cr(VI) was stud-ied by employing various photocatalysts, such as nano TiO2 [21,22],in the presence of phenolic compounds [23,24], oxalic acid andEDTA [25], formic acid [26], ammonium and formate ions [27], sal-icylic acid [28], AO7 and rhodamine B [29], di-n-butyl phthalate[30], rotating TiO2 mesh [31], sulphate modied TiO2 in the pres-ence of EDTA [32], TiO2BDD in the presence of RY15 [33], solgelderived TiO2 thin lm [34], ZnO in the presence of alizarin red-S [35]and methanol [36], polyoxomatalates in the presence of SA [37],rhodhamine B, metheylene blue and AO7 [38], neodymium-dopedTiO2 [39], Ag loaded TiO2 [40], iron doped TiO2 in the presence ofNO2[41], WO3 doped TiO2 nanotube in the presence of citric acid[42], organics acid modied TiO2 [43], and Aunps embedded TiO2framework in the presence of phenol [9].

In the present investigation, aminosilicate solgel supported(TiO2Au)nps were synthesized by depositionprecipitationmethod. The functionalized silicate solgel acts as a solid support

see front matter 2011 Elsevier B.V. All rights reserved.jhazmat.2011.12.019m dioxidegold nanocomposite materitalyst for simultaneous photodegradatiene blue

my Pandikumar, Ramasamy Ramaraj

oelectrochemistry, School of Chemistry, Madurai Kamaraj University, Madurai 625021

e i n f o

ne 2011vised form 2 December 2011cember 2011e 13 December 2011

solgelcomposite

reduction

a b s t r a c t

Aminosilicate solgel supported titanwere synthesized by simple depositiodation and reduction activity of the E(Cr(VI)) and methylene blue (MB) dyewas studied in the presence of hole sphotocatalytic degradation of MB waAunps on the (TiO2)nps surface and its dthe photocatalytic reduction of Cr(VI) from the conduction band of the TiOcompared to the TiO2 and (TiO2Au)n/ locate / jhazmat

embedded in silicate solgelof hexavalent chromium and

dioxidegold (EDAS/(TiO2Au)nps) nanocomposite materialscipitation method and characterized. The photocatalytic oxi-

(TiO2Au)nps lm was evaluated using hexavalent chromiumer irradiation. The photocatalytic reduction of Cr(VI) to Cr(III)gers such as oxalic acid (OA) and methylene blue (MB). Theestigated in the presence and absence of Cr(VI). Presence ofsion in the silicate sol-gel lm (EDAS/(TiO2Au)nps) improvedxidation of MB due to the effective interfacial electron transferunps by minimizing the charge recombination process whenthe absence of EDAS. The EDAS/(TiO2Au)nps nanocomposite

A. Pandikumar, R. Ramaraj / Journal of Hazardous Materials 203 204 (2012) 244 250 245

and provides stability to the embedded semiconductormetalnanocomposite materials and facilitates the preparation of thesolid phase photocatalyst in the lm form. The photoinduced Cr(VI)ions reduction process plays a signicant role in the synergistic andsimultaneoMB dye whshows one photocatalytively by Elm. Whenthe (TiO2AIf the redusome organis promotethe organiccharge recooxidationr

2. Experim

2.1. Chemic

TiO2 (hydrogen (trimethoxyblue (MB) (acid (OA) (Mused in this

2.2. Synthe

EDAS amby dispersiof ethanol, (25 wt.%), awas subjectperature fothe excess tion and redand dried usolgel (EDwas preparaqueous solowed by tcareful addwas dispersreadjusted orously stirnanomatericentrifugatiof double dsynthesizedfor 2 h in opreparationof 4.2 10of the EDASite materialnanoparticlnanocompophotocatalylead to the tion of browplasmon bawas not ob

.0

.2

.4

0.6

0.8TiO2 EDAS/TiO2

Diffusu)nps

ols w

aracal

sympo. Be

at a h for 4as a tomeoriesrecorn mn mscanscop

annincorderEing n (N2egassing the nanomaterials by owing N2 at 200 C for 2 h.

otocatalytic studies and analysis

photocatalyst lm was prepared by dispersing 750 mghesized EDAS/(TiO2Au)nps nanomaterials in 5 mL ethanolen sonicated for 5 min to ensure the homogeneous dis-n. The colloidal solution was coated as a lm on a glass1 cm2) by casting a known volume of the solution and wasd to dry in air at room temperature. Then the lm wased at 450 C for 30 min. For comparison, TiO2 (P-25) lmO2Au)nps in the absence of EDAS were also fabricated usinge procedure. The photocatalytic studies were carry out in

cell system at room temperature. The EDAS/(TiO2Au)nps2)nps or (TiO2Au)nps lm coated glass plate was immersedphotolysis cell containing a mixture of 0.4 mM K2Cr2O7 andMB and then irradiated with a light source. Before illumina-itrogen was purged into the reaction mixture for 30 min inhe reaction mixture was stirred at a constant speed duringus acceleration of decomposition and mineralization ofen EDAS/(TiO2Au)nps lm was used. The present studystep forward process to improve the efciency of thetic reduction and oxidation of Cr(VI) and MB, respec-DAS/(TiO2Au)nps embedded in aminosilicate solgel

the photoreduction of toxic Cr(VI) ions is carried out atu)nps system, the reduction of Cr(VI) proceeds slowly.ction is coupled with the photocatalytic oxidation ofic compounds (organic dye), the reduction of Cr(VI)

d signicantly in addition to the photodegradation of compounds leading to the effective decrease in thembination process at the (TiO2Au)nps, called advancededuction processes.

ental

als

Degussa P-25) (Evonik industries, Germany),tetrachloroaurate trihydrate (HAuCl4.3H2O), N-[3-silyl)propyl]ethylenediamine (EDAS) and methyleneAldrich), potassium dichromate (K2Cr2O7) and oxalicerck) were used as received and all the other chemicals

work were of analytical grade.

sis of EDAS/(TiO2Au)nps nanocomposite materials

inosilicate solgel functionalized TiO2 was preparedng 1 g of TiO2 (P-25) in a solution containing 30 mL1.3 g of water, 0.7 g of aqueous ammonium solutionnd 0.6 g of EDAS were added. The reaction mixtureed to sonication for 1 h and then stirred at room tem-r 12 h. Then the mixture was puried by removingEDAS and water or ammonia by repeated centrifuga-ispersion of the residue in absolute ethanol ve timesnder in vacuum at 80 C for 10 h. The aminosilicateAS) supported (TiO2Au)nps nanocomposite materialsed by depositionprecipitation method. Briey, 100 mLlution of 4.2 103 M HAuCl4 was heated to 80 C fol-he pH of the reaction mixture was adjusted to 7 byition of 1 M NaOH. Then 1 g of EDAS functionalized TiO2ed homogeneously into the solution and again pH wasto 7 using 1 M NaOH. The reaction mixture was vig-red for 2 h at 80 C. The EDAS supported (TiO2Au)npsals (EDAS/(TiO2Au)nps) were gathered by repeatedon (10,000 rpm for 15 min) and washed with 100 mListilled water under stirring for 10 min at 50 C. The

EDAS/(TiO2Au)nps was dried under vacuum at 100 Crder to remove the moisture completely. During the

of EDAS/(TiO2Au)nps), it was found that the addition3 M HAuCl4 to the EDAS/TiO2 lead the clear formation/(TiO2Au)nps) (1.08 wt.% of Au on TiO2) nanocompos-

and the surface plasmon band due the formation of Aues on TiO2 was observed (Fig. 1). The EDAS/(TiO2Au)npssite material with 1.08 wt.% Au on TiO2 was used for thesis studies. The change in HAuCl4 concentration did notclear formation of EDAS/(TiO2Au)nps and sedimenta-nish black color materials was observed. The surfacend due the formation of Au nanoparticles on TiO2served for these materials. For comparison, the same

0

0

0

Abs

orba

nce

Fig. 1. (TiO2A450 C.

protocEDAS.

2.3. Chmateri

Thenanoconiques250 C250 CBaSO4trophoaccesswere electroelectroZeiss spectro200 scwas reBrunauout usnitrogeafter d

2.4. Ph

Theof syntand thpersioplate (alloweannealand (Tithe sama glassor (TiOinto a 4 mM tion, ndark. T400 500 600 700

(TiO2-Au)nps EDAS/(TiO2-Au)npsd

c

ba

Wavelength (nm)

e reectance spectra of (TiO2)nps (P-25) (a), EDAS/(TiO2)nps (b),(c) and EDAS/(TiO2Au)nps (d) nanomaterials powders annealed at

as used to prepare bare (TiO2Au)nps in the absence of

terization of EDAS/(TiO2Au)nps nanocomposite

nthesized EDAS solgel supported (TiO2Au)npssite materials were characterized by various tech-

fore characterization, the sample were annealed ateating rate of 10 C per minute and then maintained at

h. The diffuse reectance spectra were recorded usingreference on Agilent 8453 diode array UVvisible spec-ter equipped with a Lab-Sphere diffuse reectance. Transmission electron microscopic (TEM) imagesded using JEOL 3010 high resolution transmissionicroscope with operating voltage of 300 kV. Scanningicroscopic (SEM) images were recorded using Carlning electron microscope. Energy-dispersive X-rayic (EDAX) analysis was carried out by FEI Quanta FEGg electron microscope. X-ray diffraction (XRD) pattern

ed on a Bruker AXS D8 Advance with Cu K radiation.mmettTeller (BET) surface area analysis were carried

Micrometrics Gemini 2375 surface area analyzer via) adsorptiondesorption, using a single-point method

246 A. Pandikumar, R. Ramaraj / Journal of Hazardous Materials 203 204 (2012) 244 250

illumination. A 450 W Xenon lamp was used as the light sourcewith a water lter cell (6 cm path length with pyrex glass windows)to cut off the far UV and IR radiations (Fig. S1). This water ltercell transmitted light from 340 nm onwards. The sample aliquotswere taken from the reaction sample at regular time intervals andwere tested for dye degradation using spectrophotometer [44]. TheCr(VI) ions were estimated by diphenylcarbazide method at 540 nmby analyzing the complex formed upon the addition of colorimetricreagent 1,5-diphenylcarbazide [45,46].

3. Results and discussion

3.1. Spectral characterization of (TiO2Au)nps nanocompositematerial

The present synthetic route for the preparation ofEDAS/(TiO2Au)nps nanocomposite material is a simple pro-cedure and, the afnity between the Aunps and the amine groupsin the EDAS plays a role in the formation of the (TiO2Au)npsnanocomposite material. The binding of silane on the surface of(TiO2)nps has been well understood [13]. The lone pair of electronspresent in the oxygen on the (TiO2)nps surfaces native hydroxylacts as a nucleophile towards the electron decient silicon in theEDAS and the silane is anchored on the TiO2 surface [13]. The Au(III)ions bind to those aminosilane molecules undergo reduction toform Aunps. The (NH2 Aunps) interaction is apparently sufcientto increase the local concentration of aminosilane around theAunps surface and to induce condensation and cross-linking ofadjacent silanols and thus creating stable EDAS/(TiO2Au)npsnanocomposite material.

The diffuse reectance spectra (DRS) of (TiO2)nps (P-25) (a),EDAS modied (TiO2)nps (b), (TiO2Au)nps (c) and EDAS sili-cate solgel supported (TiO2Au)nps (EDAS/(TiO2Au)nps) (d) wererecorded for powder samples annealed at 250 C and 450 C andare given in Fig. S2 and Fig. 1. The absorption spectral behavior ofthe samples annealed at 250 C (Fig. S2) and 450 C (Fig. 1) did notshow any observable change in the absorption band. The DRS ofthe EDAS/(TiO2Au)nps lms annealed at 250 C and 450 C wererecorded and are given in Fig. S3. The DRS spectra (Fig. S3) did notshow any change in the absorption band. The absorbance edge ofthe (TiO2Au)nps (Fig. 1) is signicantly enhanced the light absorp-tion in both UV and visible region. The absorption edge shiftedtowards longer wavelength when compared to the (TiO2)nps (P-25)and EDAS modied (TiO2)nps indicating a decrease in the band-gapof the EDAS/(TiO2Au)nps. The band-gap energy values of bare TiO2and EDAS/(TiO2Au)nps are calculated by using Taucs plot method[7]. The band-gap energy values of (TiO2)nps (P-25), EDAS/(TiO2)npsand EDAS/(TiO2Au)nps were calculated as 3.2, 3.32 and 3.19 eV,respectively. The measured band-gap energy of EDAS/(TiO2)nps(3.32 eV) showed a blue shift of 0.12 eV when compared to bare(TiO2)nps (P-25) (3.2 eV). This is mainly attributed to the interac-tion between the support material (aminosilicate matrix) and the(TiO2)nps [47]. For EDAS silicate solgel supported (TiO2Au)nps,the band gap energy was found to be 3.19 eV with a small redshift of 0.01 and 0.13 eV when compared to the bare (TiO2)npsand EDAS/(TiO2)nps. It clearly indicates the strong interaction andintragap formed between (TiO2)nps and Aunps [7]. The capping ofAunps on the surface of (TiO2)nps brings down the absorbance bandedge of (TiO2)nps near to the visible region [48]. It is expected thatthe Aunps, a good conductor, could facilitate the rapid transfer of

d EDAFig. 2. TEM images of (TiO2)nps (P-25) (A), (TiO2Au)nps (B) an S/(TiO2Au)nps (C) nanomaterials.

A. Pandikumar, R. Ramaraj / Journal of Hazardous Materials 203 204 (2012) 244 250 247

Fig. 3. SEM imannealed at 45

photogenerimizing thepair.

3.2. Morphmaterial

The TEDAS/(TiO2The TEM im(Fig. 2(A)). bution of laimage of thsmaller sizeTiO2. The prand dispersbetween Athe interfacundergo fecharge tran

The SEMsame magnmaterials sstructure mholes and The EDAX aposite mat

Table 1BET surface analysis of photocatalysts.

Photocataly

P-25) Au)np(TiO2

on ped aeaks ed a

EDAf eleu cot.%.

T su

surfps, (alys

le 1 a shoea an(TiO

matTiO2 ((TiO2EDAS/

emissiobservsion pobservfor theence oThe A1.08 w

3.3. BE

The(TiO2)narea anin TabTable 1face arof the sol-gelages of (TiO2)nps (P-25) (A) and EDAS/(TiO2Au)nps (B) nanomaterials0 C.

ated electrons from the (TiO2)nps to Aunps and thus min- charge recombination of photogenerated electron/hole

ology of EDAS supported (TiO2Au)nps nanocomposite

EM images of (TiO2)nps, (TiO2Au)nps andAu)nps at same magnications are given in Fig. 2.age of TiO2 nanoparticles shows spherical particles

The TEM image of the (TiO2Au)nps shows the distri-rger size Aunps on TiO2 surface (Fig. 2(B)). The TEM

e EDAS/(TiO2Au)nps (Fig. 2(C)) shows the formation of Aunps, which are highly dispersed on the surface of theesence of EDAS silicate on TiO2 facilitates the formationion of smaller Aunps on the TiO2. The ultimate contactunps and (TiO2)nps is more advantageous to increaseial electron transfer process. Both Aunps and (TiO2)npsrmi level equilibration and as a result the interfacialsfer process increases signicantly [49].

images of the (TiO2)nps and EDAS/(TiO2Au)nps withication are shown in Fig. 3. The nanocompositehow highly porous like structure and this porousay facilitates the diffusion of substrate into the pin-create the ultimate contact with the photocatalyst.nalysis of bare TiO2 and EDAS/(TiO2Au)nps nanocom-erials were recorded and are shown in Fig. S4. The

terials (Fig.and that thmesoporos

3.4. XRD pa

The XEDAS/(TiO2recorded ancrystallized(1 0 5), and (2 value), at 64.4 forbecome shAunps does the literatucan usuallyorganic pol39.2 and and (2 0 0) indicative oto rutile (3nanomaterand are shoany observas reportedthe XRD pa500 C revethe TiO2 wathe annealiof TiO2 in ((25 nm) calof (TiO2)npsusing the Sst BET surface area(m2 g1)

Average porediameter ()

Pore volume(cm3 g1)

43.7 54.30 0.065s 48.01 58.03 0.080Au)nps 48.12 67.29 0.083

eaks corresponding to the elements O and Ti weret 0.5 (O) and 4.5 (Ti), respectively for TiO2. The emis-corresponding to the elements O, Si, Au and Ti weret 0.5 (O), 1.8 (Si), 2.2 (Au) and 4.5 (Ti), respectivelyS/(TiO2Au)nps. The EDAX clearly conforms the pres-ments such as Si, Ti, O and Au in EDAS/(TiO2Au)nps.ntent in the EDAS/(TiO2Au)nps was calculated as

rface area analysis

ace area, pore size and pore volume were measured forTiO2Au)nps and EDAS/(TiO2Au)nps using BET surfaceis. The BET surface area analysis data are summarizednd their corresponding plots are presented in Fig. S5.ws that (TiO2Au)nps nanomaterial shows higher sur-d pore volume than that of the bare TiO2. The porosity

2Au)nps in the presence and absence of EDAS silicaterix are almost the same. The SEM images of the nanoma-

3) shows that the materials are obviously macroporouse N2-soprtion data prove the presence of micro andity (Fig. S5).

ttern of EDAS/(TiO2Au)nps

RD patterns of (TiO2)nps, (TiO2Au)nps andAu)nps nanomaterial lms annealed at 450 C wered are shown in Fig. S6. The XRD pattern showed highly

anatase TiO2 corresponding to (1 0 1), (0 0 4), (2 0 0),(2 1 1) diffractions at 25.3, 37.8, 48.1, 53.9, and 55.1

respectively (JCPDS No. 86-1156) and (310) diffraction rutile (Fig. S6). All the diffraction peaks of anatase TiO2arper and stronger indicating that the deposition ofnot alter the TiO2 crystalline nature. It is evident fromre [50,51] that an increase in the crystallinity of TiO2

lead to an improvement in the photodegradation oflutants [50,51]. It should be noted that the peaks around44.4 (2) are clearly observed due to the Au (1 1 1)diffractions (JCPDS No. 4-0784). The peak at 64.4 (2)f Au (2 2 0) was overlapped by the peak corresponding

1 0) [52,53]. The XRD pattern of EDAS/(TiO2Au)npsial lms annealed at 250 C and 450 C were recordedwn in Fig. S7. The XRD patterns (Fig. S7) did not showable change due to different annealed temperatures

in literature [52,53]. The previous reports show thattterns of TiO2(P-25) and TiO2Au recorded at 300 C toal the diffractions due to anatase and rutile TiO and2s found to stable when Au was deposited on TiO2 and

ng at 500 C did not change the content and particle sizeTiO2Au) samples [52,53]. The (TiO2)nps crystallite sizeculated from the full width at half-maximum (fwhm)(1 0 1) diffraction peak at the value of 25.3 (2) by

cherrer equation.

248 A. Pandikumar, R. Ramaraj / Journal of Hazardous Materials 203 204 (2012) 244 250

0 10 20 30 40 50 600.0

0.2

0.4

0.6

0.8

1.0

c

b

a

C/C

o

Irradia tio n Ti me ( min)

TiO2(P-25)

(TiO2-Au)nps

EDAS/(TiO2-Au)nps

Fig. 4. Photocatalytic reduction of Cr(VI) in the presence of oxalic acid at (TiO2)nps(P-25) (a), (TiO2Au)nps (b) and EDAS/(TiO2Au)nps (c) lms under irradiation. Con-centration of Cr(VI) = 0.4 mM and oxalic acid = 4 mM.

3.5. Photocatalytic activity of (TiO2Au)nps nanomaterials

The photocatalytic activity of the EDAS/(TiO2Au)nps nanocom-posite lm acid or MB dconcentratiused in thiwhich is sliratio of 1:3cial electron(Eq. (1)).

Cr2O72 + 1The changetime is shoite photocareduction oof (TiO2)npstocatalyst, tto Cr(III) w(Fig. 4). Thein the prese

0.4

0.5

0.6

0.7

0.8

0.9

1.0

C/C o

Fig. 5. Photoc(TiO2)nps (P-25diation. Conce

0.4

0.5

0.6

0.7

0.8

0.9

1.0

a

C/C

o

TiO2 (P-25)(TiO2-Au)nps

EDAS/(TiO -Au)

Fig. 6. Photoc(TiO2Au)nps (of methylene

change obsalyst lms observed at

I) ans on

(VI) tpreseduced 5AS/(Tcreasotod

ps on the nduc

the The r(VIutanDASnmen. 6 ant timTiO2crea

showwas studied using Cr(VI) ions in the presence of oxalicye as a sacricial electron donor under irradiation. The

on of the sacricial electron donor (SD) (oxalic acid)s study is based on the molar ratio of Cr(VI):SD = 1:5,ghtly higher than that of the theoretical requirement. In the present study, oxalic acid was used as a sacri-

donor to reduce the Cr(VI) to Cr(III) in aqueous solution

4 H+ + 6 e 2 Cr3+ + 7 H2O (1) in the concentration of Cr(VI) with respect to irradiationwn in Fig. 4. The EDAS/(TiO2Au)nps nanocompos-talyst lm exhibited signicantly faster photocatalyticf Cr(VI) to Cr(III) when compared to the catalytic activity(P-25) and (TiO2Au)nps (Fig. 5). Among the three pho-he EDAS/(TiO2Au)nps showed 91.5% of Cr(VI) reductionhen oxalic acid was used as SD with 1 h irradiation

photocatalytic reduction of Cr(VI) was also carried outnce of MB dye as SD. The time dependent concentration

TiO2 (P-25)

of Cr(Vdependand Crin the alytic rexhibitthe EDThe inand phof Aunsion inphotoiimizes[8,19].genic Cof pollsized Eenviro

FigsdiffereEDAS/(The declearly0 10 20 30 40 50 60

c

ba

Irradiation Time (min)

(TiO2-Au)nps EDAS/(TiO2-Au)nps

atalytic reduction of Cr(VI) in the presence of methylene blue at) (a), (TiO2Au)nps (b) and EDAS/(TiO2Au)nps (c) lms under irra-ntration of Cr(VI) = 0.4 mM and methylene blue = 4 mM.

tation of MBIt is known aromatic indye in the ponly 10 minthe absence60% photodCr(VI) at ththe concenvarying the

The decduring the Cr(VI) (Fig. (TiO2Au)nplotted agation of MB dthe EDAS/(Tmineralizat0 10 20 30 40 50 60

c

b

Irradiation Time (min)

2 nps

atalytic oxidation of MB in the absence of Cr(VI) at (TiO2)nps (P-25) (a),b) and EDAS/(TiO2Au)nps (c) lms under irradiation. Concentrationblue = 4 mM.

erved for Cr(VI) at different nanocomposite photocat-are shown in Fig. 5. A marked synergistic effect was

the EDAS/(TiO2Au)nps for the photocatalytic reductiond oxidation of methylene blue. The extend of synergy

the effective interfacial charge transfer between TiO2hrough Aunps. The smaller size Aunps deposited on TiO2ence of EDAS silicate solgel improves the photocat-tion and oxidation reactions. The bare (TiO2Au)nps lm4% decrease of Cr(VI) to Cr(III) after 1 h irradiation andiO2Au)nps showed the same decrease within 20 min.e in the photocatalytic reduction of Cr(VI) to Cr(III)egradation of MB dye are attributed to the presence

the surface of (TiO2)nps photocatalyst and its disper-functionalized EDAS silicate solgel lm. The effectiveed charge transfer process between TiO2 and Aunps min-recombination of the photogenerated charge carriersincrease in the photocatalytic conversion of carcino-) to nontoxic Cr(III) coupled with the photodegradationt MB dye shows the dual benets of the newly synthe-/(TiO2Au)nps in the lm state and its application in thetal remediation and purication processes.nd 7 show the photocatalytic degradation of MB ate under irradiation using (TiO2)nps, (TiO2Au)nps and

Au)nps lms both in the absence and presence of Cr(VI).se in the MB dye concentration with respect to times the degradation of MB molecules due to the fragmen- leading to the decoloration of dye under illumination.that the conjugated structure of MB is broken into smalltermediates [54,55]. The 49% photodegradation of MBresence of Cr(VI) at the EDAS/(TiO2Au)nps lm required

when compared to (TiO2)nps and (TiO2Au)nps lms in of EDAS (Fig. 7). Under similar experimental condition,egradation of MB dye required 1 h in the absence of

e bare (TiO2)nps and (TiO2Au)nps lms (Fig. 6). Varyingtration of Cr(VI) did not affect the MB degradation and

concentration of MB affected the Cr(VI) reduction.rease in total organic carbon (TOC) content observedphotocatalytic degradation of MB in the absence of8) and in the presence of Cr(VI) (Fig. 9) using (TiO2)nps,ps and EDAS/(TiO2Au)nps lms under irradiation isinst the time. In the absence of Cr(VI), the mineraliza-ye reached the highest value in 20 min of irradiation atiO2Au)nps lm. However, in the presence of Cr(VI) theion of MB dye reached the highest value in about 10 min

A. Pandikumar, R. Ramaraj / Journal of Hazardous Materials 203 204 (2012) 244 250 249

0 10 20 30 40 50 60

0.4

0.5

0.6

0.7

0.8

0.9

1.0

c

b

a

C/C

o

Irradiatio n Time (min)

TiO2 (P-25)(TiO2-Au)nps

EDAS/(TiO2-Au)nps

Fig. 7. Photocatalytic oxidation of MB in the presence of Cr(VI) at (TiO2)nps (P-25) (a),(TiO2Au)nps (b) and EDAS/(TiO2Au)nps (c) lms under irradiation. Concentrationof Cr(VI) = 0.4 mM and methylene blue = 4 mM.

at the EDAS/(TiO2Au)nps. The photocatalytic mineralization of MBdye was found to be higher at the EDAS/(TiO2Au)nps lm whencompared to (TiO2)nps (P-25) and (TiO2Au)nps lm (Figs. 8 and 9).This is mainly attributed to the effective simultaneous utilizationof photoindThe increasthe presencas an electmizes the cknown elecerated electthrough thedize the sac(TiO2)nps alto the absor

The scsimultaneothe EDAS/(EDAS/(TiO2(h+/e) occ

50

100

150

200

250

300

350

TOC

(ppm

)

Fig. 8. Photocions at (TiO2)nirradiation. Co

150

200

250

300 TiO2 (P-25)(TiO2-Au)nps

TOC

(ppm

)

Fig. 9. Photocions at (TiO2)nirradiation. Co

are rapidlyinstantaneoCr(III) and tsacricial e

ays ave ins phaneoes thation

ma

ummted nle dEM, eposn (Tie solyst ion atively. The presence of smaller Aunps on the (TiO2)nps surfaceuced holes/electrons at the EDAS/(TiO2Au)nps lm.ed photocatalytic performance is mainly attributed toe of Aunps on the (TiO2)nps surface since the Aunps actron sink for the photogenerated electrons and mini-harge recombination process [19]. The Aunps is a welltron conductor and catalyst, and hence the photogen-rons are rapidly transferred from (TiO2)nps to the Cr(VI)

Aunps [8,19]. The holes formed at the (TiO2)nps oxi-ricial electron donor MB. The deposition of Aunps onso decreases the band-gap energy of (TiO2)nps leadingption of visible light by the (TiO2)nps.hematic representation of the photocatalyzedus reductionoxidation reaction occurring atTiO2Au)nps lm as shown in Fig. S8. When theAu)nps is irradiated with light, the charge separationurs at the (TiO2)nps. The conduction band electrons

TiO2 (P-25)

and pleffectitaneousimultprovidpuric

4. Sum

In ssuppora simpDRS, Twere dpersioprepartocatalreductrespec0 10 20 30 40 50 60

(TiO2-Au)nps EDAS/ (TiO2-Au)nps

c

b

a

Time ( min)

atalytic mineralization of methylene blue in the absence of Cr(VI)ps (P-25) (a), (TiO2Au)nps (b) and EDAS/(TiO2Au)nps (c) lms underncentration of methylene blue = 4 mM.

effectively reduction odye when cnanocompofor environthe photoin

Acknowled

RR acknof Science aCSIR-Seniorto Evonik I(Degussa PSchool of Chments and Scientist, Narea analys0 10 20 30 40 50 60 70

EDAS/(TiO2-Au)nps

c

b

a

Time ( min)

atalytic mineralization of methylene blue in the presence of Cr(VI)ps (P-25) (a), (TiO2Au)nps (b) and EDAS/(TiO2Au)nps (c) lms underncentration of Cr(VI) = 0.4 mM and methylene blue = 4 mM.

transferred to the Aunps at the interface. The Aunpsusly transfer the electrons to reduce the Cr(VI) tohe holes at the valance band of the (TiO2)nps oxidize thelectron donor MB dye. The Aunps act as an electron sink

vital role in the photocatalytic activity by facilitatingterfacial charge transfer process leading to the simul-otocatalytic reduction and oxidation processes. Thisus photocatalytic reduction and oxidation processese dual benets for the environmental remediation and

processes.

ry

ary, the diamine functionalized EDAS silicate solgelanocomposite (TiO2Au)nps material was prepared by

epositionprecipitation method and characterized bySEM, EDAX, BET and XRD analysis. The smaller Aunpsited on the EDAS/TiO2 than on the bare TiO2. The dis-O2Au)nps into EDAS silicate solgel paves the way toid-phase EDAS/(TiO2Au)nps in the lm state. This pho-lm was utilized for the simultaneous photoinducednd oxidation of pollutants like Cr(VI) and MB dye,improves the synergistic action in the photocatalyticf Cr(VI) to Cr(III) and the photocatalytic oxidation of MBompared to the bare (TiO2)nps. The EDAS/(TiO2Au)npssite solid-phase photocatalyst is a potential candidatemental remediation and purication processes throughduced advanced oxidationreduction processes.

gments

owledges the nancial support from the Departmentnd Technology (DST), New Delhi. APK is a recipient of

Research Fellow fellowship. The authors are gratefulndustries, Germany for generously providing the TiO2-25) sample for research purpose. Dr. S. Murugesan,emistry, Madurai Kamaraj University for TOC measure-Mr. S. Suresh for his help. We thank Dr. M.L.P. Reddy,IIST, Thiruvananthapuram for providing the BET surfaceis.

250 A. Pandikumar, R. Ramaraj / Journal of Hazardous Materials 203 204 (2012) 244 250

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.jhazmat.2011.12.019.

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Titanium dioxidegold nanocomposite materials embedded in silicate solgel film catalyst for simultaneous photodegradation...1 Introduction2 Experimental2.1 Chemicals2.2 Synthesis of EDAS/(TiO2Au)nps nanocomposite materials2.3 Characterization of EDAS/(TiO2Au)nps nanocomposite material2.4 Photocatalytic studies and analysis

3 Results and discussion3.1 Spectral characterization of (TiO2Au)nps nanocomposite material3.2 Morphology of EDAS supported (TiO2Au)nps nanocomposite material3.3 BET surface area analysis3.4 XRD pattern of EDAS/(TiO2Au)nps3.5 Photocatalytic activity of (TiO2Au)nps nanomaterials

4 SummaryAcknowledgmentsAppendix A Supplementary dataReferences