Jurnal Kimia Sains dan Aplikasi 22 (2) (2019): 52-57 52

Jurnal Kimia Sains dan Aplikasi 22 (2) (2019): 52-57 •outlaw .-auim-w. 'r-C~) Jurnal KimiaH3Sains dan AplikasiISSN:1410-8917

r=llJurnal Kimia-Sains &Aplikasi

e-ISSN: 2597-9914

Jurnal Kimia Sains dan AplikasiJournal of Scientific and Applied Chemistry

Journal homepage: http:/ /ejournal.undip.ac.id /index.php/ksa

Statistical Approach for Water Glass Precursor Preparation fromBamboo Leaf Silica

S Silviana 3 *, Bakti Jos 3, Herry Santosaa, Siswo Sumardiono 3

a Department of Chemical Engineering, Faculty of Engineering, Diponegoro University. Jl. Prof. H. Soedarto, S.H., Kampus TembalangSemarang, Indonesia

*Corresponding author: silviana@che.undip.ac.id

https://doi.0rg/10.iA710/ jksa.22.2.s2-s7

Ar t i c l e In fo Abs t r ac t

Article history:

Received: 7 January 2019Revised: 30 March 2019Accepted: 30 March 2019Online: 31March 2019

The bamboo leaf consists of high silica content. In this study, the bamboo silica wasutilized as water glass. Water glass can also be used as eco-friendly precursors for thepreparation of silica aerogel. The extraction process of silica from bamboo leaf havebeen carried out through acid leaching and combustion process at 750°C based onthermal gravimetry analysis. This paper is aimed to assess the effect of two types ofalkali hydroxide and concentrations producing water glass of bamboo leaf silica. Theresult was analyzed by using a 22-factorial design with six replications. The alkalihydroxide types were sodium hydroxide and potassium hydroxide with aconcentration of 4 M and 6 M, respectively. The study was executed in several steps,i.e. pre-treatment of bamboo leaf , leaching process, combustion, purification ofbamboo leaf silica and synthesis of water glass. The optimum condition of water glassproducts was obtained at silica concentration of 41.08 ppm and density of 1.23 g/L forpotassium hydroxide, while at 40.15 ppm and 1.30 g/ L for sodium hydroxide. ANOVAanalysis resulted in a significant effect for type of hydroxide and concentrationreleasing model for silica concentration response. This study also characterized thesilica structure and composition by instrumentation analysis for silica solid obtainedfrom optimum water glass condition with potassium hydroxide. It can be denoted thephysical behavior of silica solid from water glass by potassium hydroxide did not differfrom previous research of water glass by sodium hydroxide.

Keywords:bamboo leaf silica,potassium hydroxide,silica aerogel, water glass

compound such as tetraethylorthosilicate (TEOS) [3] andtetramethylorthosilicate (TMOS) as a precursor.Unfortunately, TEOS/TMOS are expensive and have a highhazard level causing blindness and unfriendly for theenvironment [4]. The extraction process of silica frombamboo leaf have been carried out through acid leachingand combustion. Then, common chemicals employed inthe conversion of silica to water glass uses sodiumhydroxide [5], while potassium hydroxide has been usedin this paper to compare the result. Bamboo leaftreatment releasing water glass consisted of washing,leaching with hydrochloric acid , calcination, mixing withalkali hydroxide, and filtering. In the end, the solutionwas filtered to remove undissolved purified BLA. All thesesteps referred to previous research [5, 6]. In this paper, itobserves statistical approaching for the effect of alkalihydroxide type and its concentration on the quality ofwater glass produced denoted by concentration anddensity.Afterward, the study further prepared silica from

1. IntroductionBamboo leaf is a promising natural source regard

with the content of bio-silica or silicon dioxide or silica(Si02) equal to 78.71 g/kg of dried bamboo leaf [1]. Thesilica content is influenced by the bamboo type and regionfor bamboo growth. Silica of bamboo leaf has been used asa great deal of natural silica source for preparation ofwater glass due to the high content of silica. It isconsidered that the silica content of bamboo leaf orbamboo leaf ash (BLA) is higher than that of rice husk [2].One of an intermediate product from silica can be madefor water glass as a precursor of silica aerogel. Silicaaerogel in the future can be used as an adsorbent, heatinsulator, supercapacitor or supporting material in thecatalyst [2]. Currently, the application of water glass as aprecursor or sodium orthosilicate ( Na4Si04) from thebamboo leaf is the more environmentally friendly methodto produce silica aerogel than that of a silicon alkoxide

θ

2.3.

λ

Jurnal Kimia Sains dan Aplikasi 22 (2) (2019): 52-57 53

water glass produced from the optimum condition. Thesilica formed was analyzed by instrument analysis such ascrystalline analysis, surface topography, fracturebehavior and elements content analysis.

Characterization

Bamboo leaf ash was obtained from burning infurnace based on decomposition temperature obtained byTGA analysis. UV-Visible analysis has been introduced tomeasure appropriate reaction between BLA with alkalihydroxide with several concentrations. Thetransmittance was measured by a spectrophotometerwith wavelength ( ) of 351 nm for silica compound [7].From the transmittance data, a standard curve of waterglass must be attained with the least square method withthe highest R2. The concentration-response can bedefined by using this least square measured thetransmittance by using Spectrophotometer UV Mini-1240Shimazu. Measuring water glass product density usedpycnometer and compared with the density ofcommercial water glass. Further analysis had beenconfirmed by using XRD to investigate the silica preparedfrom the optimum condition of water glass preparationand SEM-EDX to provide elemental identification andquantitative compositional information from silica.

2. Materials and Methods2.1. Materials

Bamboo leaf was obtained from bamboo petung( Dendrocalamus asper ) delivered from Sragen.Hydrochloric acid (HC1) (Mallinckrodt, 37%), sodiumhydroxide (NaOH) (Merck, 99%) and potassiumhydroxide (KOH) (Merck, 99%) were purchased from thesupplier without any purification treatments.Commercial silica gel was purchased from a chemicalstore in Semarang. The research employed several typesof equipment, such as planetary ball mill to reduce thesize of silica powder, ultrasonic processor FS-250N tohomogenize sodium silicate and spectrophotometry UVMini-1240 Shimadzu to analyze the water glass. A DTG-60 Thermal Gravimetry Analyzer instrument have beenused to analyze decomposition temperature of thebamboo leaf with operation temperature at 30-iooo°C,temperature rate of io°C/min, and flow rate of nitrogen of30 mL/min. The crystalline analysis used Xaltical X-rayDiffraction (XRD) tool, Xpert Pro (Utrecht , Netherland)with 40 kV and 30 mA currents. Results from XRD wererecorded at 2 angles in the io° to 90° range. ScanningElectron Microscope (SEM) Inspect S50 Energy-DisperseX-ray (SEM EDX, FEI) was required to confirm for surfacetopography, fracture, and elements content.2.2. Water Glass Precursor Preparation

In the beginning, the bamboo leaf was washed withhot water many times to remove solid impurities prior tomaking drying. Subsequently, the bamboo leaf wasgrounded into to reduce size. Next, the sized bamboo leafwas soaked with HC11 N for 2 hours purposed to removeimpurities by leaching. Afterward, the leached bambooleaf can be calcined in furnace to remove organiccompound and to release bamboo leaf ash (BLA). Then,purified BLA have been mixed with alkali hydroxide.Shortly after mixing with alkali, the solution was filteredto remain dissolved purified BLA [5]. The experiment wasdesigned by using Design Expert 8.0.6 described in Table1. The experiment design used two factors, i.e. alkali typewith KOH and NaOH, the concentration of 6 M and 4M forKOH and NaOH, respectively. Due to the full factorialdesign with two variables, the experiment design usedupper and lower level in each variable. Optimumconsideration referred to statistical analysis further usedto release silica from water glass. Afterward , water glasswas introduced acid by HC1 lN to reduce impurities bydissolving into an acid solution and obtain the silica solid.Then, the solution was introduced filtration to separatesilica solid. The silica solid was dried under a temperatureof 105°C until constant weight.

Table 1. Experiment design of design factorial 22

3. Results and Discussion3.1. Bamboo leaf characterization

As mention earlier, at the end of BLA preparation wasconducted on calcination or thermal process by usingfurnace at temperature depends on TGA analysis ofbamboo leaf. Figure 1 gives information about thetemperature when the material is introduced thermally.

3 n

^ Water evaporation2.8

~

2.6 -f Organic decomposition5

o.I 2.4 -

2.2

200 400Temperature (°C)

600 800 1000

Figure 1. Thermogravimetric analysis of petung bambooleaf temperature of 30 - iooo°C

Fig.1represents that at the temperature between 30-ioo°C there was a reduction of moisture content [2] atpetung bamboo leaf. In the beginning, bamboo leafconsisted of 8% moisture content. Formerly, the watercontent of bamboo leaf was reduced in order to avoidinhibition of diffusion during the burning process [5]. Atthe temperature above 200°C, the weight of bamboo leafdecreased denoted that decomposition of an organiccompound was started up to a temperature of 6oo°C. Theorganic compound in the bamboo leaf was perfectlydecomposed shown by theconstant weight of the bambooleaf ash at 700°C, so in this research, the burning processof the bamboo leaf was executed at a temperature of750°C produced 20% of the initial weight of bamboo leaf.The bamboo leaf ash, in general, is mostly containingsilica (Si02) with some impurities. Leaching process byacid leaching with HC1 can help to remove the inorganicimpurities which could block in the forming of silica withamorphous structure [3]. In this step of the leaching

Uppervariable ( + )

Lowervariable (-)Experiment factor

Alkali typeAlkali concentration

KOH NaOH6 M 4 M

1

𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛= +0.037 − 0.0021 ∗ 𝑠𝑜𝑙𝑣𝑒𝑛𝑡 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛

1

𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛= +0.0058 + 0.0075 ∗ 𝑠𝑜𝑙𝑣𝑒𝑛𝑡 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛

𝑆𝑞𝑟𝑡(𝑑𝑒𝑛𝑠𝑖𝑡𝑦) = +1.07 + 0.013 ∗ 𝑠𝑜𝑙𝑣𝑒𝑛𝑡 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛

Jurnal Kimia Sains dan Aplikasi 22 (2) (2019): 52-57 54

process, the weight of leached bamboo leaf released about79.03% from the initial.3.2. Concentration Analysis and Density on Water Glass

Products

This study used statistical methods to determine theeffect of significant variables on the quality of water glassproducts referring to the high concentration and properdensity. The alkali hydroxide type (A) and alkalihydroxide concentration (B) denoted as independentvariables, whereas the response was the water glassconcentration analyzed by UV-Vis spectrophotometryand water glass density. The first step, the standard curvewas attained at using this least square of y = o,0364x -0,6488 with R2 of 0.98. This least square can be used tocalculate the concentration of samples (x) by use ofabsorbance (y).A further step, the research conducted theexperiment design with the response of concentrationand density presented in Table 2. The statistical methodapplied in this research employed factorial design 22 withsix (6) replications. Replication is used to maintainconsistency of the response data , thereby reducing theestimated error or error in research conducted with aminimum of 80% accuracy of results [7]. Six replicationswere used in this study resulting in a yield accuracy of83.1%, while four replications that resulted in theinaccuracy of 63.8% and five replication results with anaccuracy of 75%.

Table 2.Factorial design 22 with six replications

This statistic method generated an equation modelusing Analysis of Variance (ANOVA). ANOVA was used toknow not only of each independent variable effect, theinteraction effect between independent variable toresponse, but also an assessment of the chosen model.The significant of the equation model is attributed if thevalue of p > F is less than 0.05 and the F value is greaterthan one [8]. While the appropriate equation model isassessed from the value of R2, adjusted-R2, predicted-R2

and adequate precision where the small difference (< 0.2)of each value of R2 withadjusted-R2 and predicted-R2, andthe value of adequate precision more than four indicatesModel eligible eligibility.Table 3.Analysis of variance (ANOVA) results for water

glass concentration response

Sum of Mean F- Prob > SignificanceSquares square value F

Source

0.0009 3 0.0003 16.68 <0.0001 SignificantAlkali type, A 0.0004 1 0.0001 7-98 0.0105 Significant

Concentration, 0.0002 1 0.0002 9.97 0.0050 Significant

Model

B

0.0006 1 0.0006 32.08 <0.0001 Significant

0.71440.67160.58888.822

AB

R2

Adjusted R2

Predicted R2

Adequateprecision

The results of ANOVA on the water glassconcentration analyzed by UV-Vis spectrophotometry asshown in Table 3 indicated that the chosen model wassignificant (p > F less than 0.05). It was also known thatthe concentration of water glass was significantlyaffected by both variables, alkali hydroxide type, andalkali hydroxide concentration, and the interaction effectbetween alkaline and alkali concentration also givensignificant effect. Based on the interaction between theseindependent variables, the chosen model of ANOVAequation with actual factor are as follows for NaOH andKOH denoted by equation (1) and (2), respectively:

Factor Factor Concentration Density(gr/L) (gr/L)Run A B

6 26.5140.2954.9643.6839.4237.49

KOH 1.281

2 NaOH 4 1.2763 NaOH

4 KOH

5 NaOH6 NaOH

1.294 1.22

6 1.356 1.31

7 NaOH8 KOH

4 29.5241.65

1.22

(1)4 1.249 KOH 4 1.2452.90

33.6635.4922.4126.7032.4232.6543.5827.4435.5856.5424.07

(2)KOH 410 1.25

The R2 value obtained from this model for NaOH wasachieved 0.71 with a small difference with adjusted-R2

and predicted-R2 values, and an adequate precision valueof 8.82 indicating the appropriate model. While for themodel of KOH was achieved R2 value of 0.74 and anadequate precision value of 8.82.

ANOVA results on water glass density response alsoreleased a significant model. The water glass density wassignificantly affected by the concentration of alkalihydroxide (p > F less than 0.05), but the alkali hydroxidetype had no significant effect (0.05 < p > F < 0.10, where p> F of 0.085). The equation model of ANOVA including theinteraction between the independent variables for thedensity of water glass with actual factor can be summedup in equation (3) and (4) which for alkali type of NaOHand KOH, respectively. All this ANOVA analysis can bereported in Table 4.

611 NaOH 1.296KOH12 1.29613 KOH

14 NaOH

15 NaOH16 NaOH

1.311.264

4 1.22

6 1.31617 KOH

18 NaOH1.22

6 1.2919 KOH20 KOH

4 1.256 1.296KOH21 25.79 1.27

22 KOH 4 30.45 1.22

23 NaOH

24 NaOH4 37.55 1.23

1.264 35.23 (3)

𝑆𝑞𝑟𝑡(𝑑𝑒𝑛𝑠𝑖𝑡𝑦) = +1.06 + 0.013 ∗ 𝑠𝑜𝑙𝑣𝑒𝑛𝑡 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛

Jurnal Kimia Sains dan Aplikasi 22 (2) (2019): 52-57 55

(4) too large OHion concentrations in alkali-silica reactionscan induce the formation of an electric double layer. Thisdouble layer can be formed from the interaction betweenelectrolyte solutions containing OH-ions and the surfaceof a solid such as ultrasonic wave transmitter dipped insolution [8]. The existence of this electric double layer canprevent the reaction between bamboo leaf silica which notyet reacted with alkaline ions. However, the alkali type didnot significantly affect the density of the water glass. Itsupposed that the water glass product attained a densityof 1.218-1.352 gr/mL in accordance with the standardwater glass density based on reference [10], i.e. in a rangeof 1.2-1.7 gr/mL. While the alkali concentration affectedthe water glass density since the alkali concentration isrelated to the number of molecules existing in a solutionat a certain volume.

The optimum condition of the water glass product inthis study was determined using numerical statisticalanalysis of software of Design Expert 8.0.6. The waterglass produced under these optimum conditions wereexpected to have large concentrations with densities in arange of the commercial water glass density. The usedalkali type achieved an optimum yield of potassiumhydroxide at 4 M releasing a water glass concentration of41.08 g/L and a density of 1.23 g/mL with a desirabilityvalue of 0.547.

Where A was the coded factor for the alkaline typeand B was the coded factor for the alkali concentration.The R2 value obtained from this model was 0.74 andexisted a small difference with adjusted-R2 andpredicted-R2 values, and an adequate precision value of10.72 indicating the appropriate model.

Table 4. Analysis of variance (ANOVA) results on waterglass density response

Sum of df Mean F- Prob > SignificanceSquares Square value F

Source

0.0039 2 0.0020 29.59 <0.0001 SignificantAlkali type, A 0.0002 1 0.0002 3.27

Model

0.0848 NotSignificant

Concentration, 0.0038 1 0.0038 55-91 <0.0001 SignificantB

Lack of Fit 0.0015 1 0.00002 0.22 0.6401 NotSignificant

R2 0.73810.71320.657910.723

Adjusted R2

Predicted R2

Adequateprecision

Lack of Fit (LOF) is a criterion for assessment ofappropriate model in experimental results. Theinsignificant LOF values (p > F greater than 0.1) indicatesthe appropriate model for the experimental results [8].Table 4 shows the LOF value for the equation model ofdensity response was obtained 0.64 representing anappropriate model for density response. Furthermore,Table 5 concerns to declare average and deviationstandard of an appropriate model, i.e. concentrationmodel and density model with each response data.

Table 5. Error average and error deviation for eachappropriate model

I1 2

Treatments

A:Solvent Type = KOH

4.00 6.00Alkali Concentration-response

DensityResponseType

B:Solvent Concentration = 4.00KOH 12.59% ±10.78%

10.24% ± 6.73%0.81% ±0.43%

1.46% ±0.83%NaOH

Based on ANOVA result, the alkali hydroxide typesignificantly affected the water glass concentration due tothe difference of alkaline ion size which can affect thereactivity of the alkali ion in the reaction of water glassformation [9]. While the concentration of alkalihydroxide given an effect to the water glassconcentration. There was a considerable relationshipbetween the alkali concentration related to the number ofOH-ions that play an important role in the reactionmechanism between silica and alkali solution. The OH-ion will supply the imperfect form of the Si02 tetrahedron,further the OH" ion will be released to form water andreplaced by alkali ion [10] as follows in equation (5) [2],where M is denoted as a symbol for alkali metals.Si02 + 4MOH M4Si04 + 2H20

T22407 56.542

Concentration = 41.0845

1.218 1.352

Density = 1.2347(5)

Desirability = 0.547The combination of interactions between KOH and

low concentration of M~ indicated good results for waterglass concentrations due to the large reactivity of K+ ions.Furthermore, the OH" ions became more easily released infewer concentrations. According to previous research [2],

Figure 2. Ramp report of optimum condition for waterglass product from bamboo leaf silica

θ

θ

θ

Jurnal Kimia Sains dan Aplikasi 22 (2) (2019): 52-57 56Fig. 2 reports the ramp of alkali type and alkali

concentration under optimum conditions as well as theresponse of water glass concentration and density. Thisoptimum condition can be obtained using potassiumhydroxide (KOH) because KOH is more reactive in thereaction of water glass formation resulted by larger K+ ionsize. It signified the distance between the atomic nucleusand outer shell electron is far enough to release the ionOH' [4]. The concentration of 4 M was chosen as theoptimum condition. It was considered this concentrationdid not form an electric double layer which can preventthe bamboo leaf silica reacting with the alkaline solution.3.3. Analysis of X-Ray Diffraction (XRD) on Bamboo

Leaf Silica

Silica ash (Si02) from petung bamboo leaf generatedfrom the combustion process appeared in first color asgrey. Therefore, it was necessary to purify to obtain whitecolor of Si02. Silica released out by optimum condition wasdissolved in acid solution of HC1 to purify the silica. Thepurified silica was then analyzed to acquire its materialstructure by using X-Ray Diffraction analysis asdescribed in Fig. 3.

content based on EDX approximately 20.3 %-wt [5]. Itwas indicated that the silica content produced from waterglass by KOH consisted of more than 40 %-wt.

At*OK 50.18 63.88SiK 49,82 36, 12

ZAFCoirectionManx

ElementOK 57.08 70.01SiK 42.92 29.99Manx Correction ZAF

58.43 71.1641, 57 28.84

Manx Correction ZAF

Figure 4. SEM-EDX analysis of purified Si02 of petungbamboo leaf

4. ConclusionThe isolation of silica oxide from bamboo leaf have

been investigated through acid leaching resulting 79.03%by thermal process at 750°C and weight loss up to 20%.The bamboo leaf silica from the leaching and thermalprocesses released a form with an amorphous structure.The ANOVA of the factorial design 22 with six times ofreplications reported that the alkali concentrationaffected significantly on the concentration-response andthe water glass density. The alkaline type also signifiedthe effect on the water glass concentration, while itimplied a few effects on the water glass density. Theoptimum condition of the water glass product can beobtained by potassium hydroxide (KOH) withconcentration of 4 M producing a water glass with aconcentration of 41.08 g/L and density of 1.23 g/mL.However, the physical properties of silica produced withoptimum water glass by KOH did not contrast withprevious research of water glass by NaOH.

200180 -

160O 140 -

I 120 '

w 100 -

I 80 -

l 60 '

^ 40 -20 -

010 20 30 40 50 60 70 80 90

20 (degree)

Figure 3. X-ray diffractions analysis (XRD) of purifiedSi02 of petung bamboo leaf

Fig. 3 illustrates the XRD analysis on Si02 of bambooleaf observed the XRD patterns of Si02 with the highestpeak of 2 at 22.64° and an intensity of 182 counts, asindicated by black circles in Figure 2. This data in Fig. 3suggest that it was not much different from previousstudies [2, 5]. The high peak of 2 was attained at 23° forSi02. However, less of ZnO and A1203 still appeared inpurified silica, i.e. 2 at 31-74° and at 45.46°, respectively[11]. It can be inferred that the deviation of the peakresulted from heating to a temperature of 750°C duringthe burning of bamboo leaf [7]. Meanwhile, Fig. 3 showsthe silica bamboo leaf having an amorphous structure andmore diffraction peak of the crystalline structure of anoxide compounds.3.4. Scanning Electron Microscopy-Energy Dispersive

X-ray (SEM - EDX) on Bamboo Leaf Silica

The treated silica from bamboo leaf form optimumwater glass has been investigated the elemental structureand quantitative information. Fig. 4 explains thecomposition of silica bamboo leaf consisted of Si elementand O element. This figure also further visualized regardswith the silica size after treated by HC1 leaching andgrounding by High Energy Milling (HEM) for 15 min. Theresult also confirmed that there was still aggregation ofthe silica particle. Previous research of bamboo leafsilica-based to aerogel confirmed the average silica

AcknowledgmentThe authors are grateful to the Advanced Material

Laboratory (AMaL) co-workers of the Department ofChemical Engineering at Diponegoro University forsupport and facilities. The authors sincerely also thankFaculty of Engineering at Diponegoro University withresearch funding of No. 563/UN7.P/HK/2016, June 3,2016.

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N. Filipovi -Vincekovi