COMPARATIVE STUDY ON THE IMPACT OF SYNTHESIS ROUTE TO THE PHOTOCATALYTIC ACTIVITY OF ZnO-SiO 2 FROM RICE HUSK ASH

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1 PROCEEDING OF 3 RD INTERNATIONAL CONFERENCE ON RESEARCH, IMPLEMENTATION AND EDUCATION OF MATHEMATICS AND SCIENCE YOGYAKARTA, MAY 2016 C 10 COMPARATIVE STUDY ON THE IMPACT OF SYNTHESIS ROUTE TO THE PHOTOCATALYTIC ACTIVITY OF ZnO-SiO 2 FROM RICE HUSK ASH Is Fatimah Chemistry Department, Islamic University of Indonesia isfatimah@uii.ac.id Abstract Zinc Oxide based materials are promising materials as photocatalyst instead of titanium dioxide. One of the ZnO form is ZnO-SiO 2 with several advantageous properties for application. In this research synthesis of ZnO-SiO 2 was reported by using rice husk ash as silica source. Effect of surfactant addition to the physicochemical properties and photocatalytic activity of prepared materials is studied. Physicochemical techniques viz. X-ray diffraction (XRD), scanning electrone microscope(sem) and BET surface analysis were utilized to study the effect of synthetic methodology on the properties of synthesized ZnO-SiO 2. Differences in crystallinity, surface area, particle size by different methods were observed. XRD pattern of ZnO-SiO 2 obtained by sol-gel with cetyl trimethyl ammonium bromide(ctmabr) confirmed larger surface area which also resulted in greater photocatalytic activity in methylene blue degradation. Keywords: ZnO-SiO 2 ; Photocatalyst; Photocatalysis; Rice husk ash I. INTRODUCTION Interest in the functional materials for use in the production and technique for green chemistry has rapidly increased over the years. In the scheme of wastewater treatment and providing clean water for drink and sanitation, such environmental friendly like advance oxidation process and photocatalysis were developed. Furthermore, with an increase in usage and demand for the more efficient systems, development of photocatalyst material due to the potential photoactivity has become a top focus in photocatalysis research[1,2]. To that end, ZnO synthesis, modification and utilization were reported. As reported by previous works, ZnO has a competitive photocatalytic activity (PA) greater in some cases than TiO 2. Therefore in some scheme, the improvement of ZnO photocatalytic activity was attempted by several techniques such as metal dopping and immobilizing in a porous structure materials. The last mentioned technique can be performed by either situ preparation or impregnation into materials like zeolite, clay, MCM-41 etc[3,4]. Refer to some papers reporting the photocatalytic activity of supported ZnO in SiO 2 the technique of in situ preparation for ZnO attached in a porous structure of silica (ZnO-SiO 2 ) is reported in this research paper[5,6]. Related to the improvement sustainability, the utilization of the abundance of agricultural waste generated globally, using rice husk ash as silica sources is conceivable. In addition to adding to the sources of silica for usage in green technology and in alternative way for preparation a functional photocatalyst, this process could lead to an avenue for reducing the amount of environmental waste generated from agriculture activities[3][7]. From several reports in the synthesis of ZnO-SiO 2 from synthetic precursors some routes were reported related to the use of surfactant for gaining high specific surface of the material. Some alkyl ammonium based surfactants has been successfully reported to create an ideal structure of ZnO-SiO 2 [8]. Since the different route of the synthesis will affect to the physicochemical character of the material, this research provide the comparison on the synthesis over cetyl trimethyl ammonium-bromide(ctma-br) molecule as a surfactant template. Study on the structure and surface properties based on x-ray diffraction(xrd), scanning electrone microscope(sem) and photocatalytic activity for methylene blue(mb) photodegradation is reported. A.Materials II. MATERIALS AND METHOD As material precursor, zinc acetate dihydrate [Zn(CH 3 COO) 2 2H 2 O] and isopropanol were supplied from Merck, while CTMABr was purchased from Sigma-Aldrich. Rice husk ash was obtained by ashing rice husk obtained from rural agriculture area in Sardonoharjo district, Sleman, DIY Province at C-69

2 ISBN o C for 3h. For photocatalytic activity, MB photodegradation reaction was chosen. Chemical structure of MB is shown in Figure 1. Figure 1. Structure of MB B. Preparation of ZnO-SiO 2 The procedure for preparation of silica gel is refer to the method of TiO 2 -SiO 2 synthesis from RHA. Three grams of RHA was diluted into 2 M of NaOH and followed by ageing for 24 h. The solution was filtered and the filtrate was titrated with hydrochloric acid of 1 M until the ph of 8.0 was obtained. The clear solution was aged for 48 h to form gel. Into the gel, zinc acetate dehydrate solution was dispersed at the theoretical Zn:Si mole ratio of 1:4 by predicting Si content of 90 wt%. The mixture was then added with NH 4 OH 0.1 M and the stirring was followed until 1 h and homogeneous sol was produced. The solvent was then evaporated by drying in an oven before calcination at 500 o C for 4 h. Similar procedure was engaged for the synthesis using CTMA as template but with the CTMA addition before the dispersion of zinc acetate precursor. From these step obtained ZnO-SiO2 was encoded as ZnO- SiO 2 (ctma). C. Analytical Methods XRD analysis was carried out on a Shimadzu X6000 instrument, scanning electron microscopy (SEM) with elementary dispersive X-ray analysis (EDX) experiments was carried out on an JEOL instrument and surface profile analysis consist of specific surface area, pore volume and pore radius was conducted by NOVA 1200e gas sorption analyzer. XRD was operated at a voltage of 40 kv and a current of 30 ma with Cu Kα radiation. D. Photocatalytic activity MB photodegradation was concudted in a batch reactor under UV lamp of 20watt (Figure 2). An UV lamp was set up at 30cm above the mixture of solution-photocatayst powder. During the treatment, sequential sampling was conducted by put treated solution for certain time and then UV-visible absorbance spectra measurement of the sampling solution were measured over a range of nm with a Hitachi U 2010 instrument. Figure 2: Schematic representation of photocatalytic reactor C-70

3 PROCEEDING OF 3 RD INTERNATIONAL CONFERENCE ON RESEARCH, IMPLEMENTATION AND EDUCATION OF MATHEMATICS AND SCIENCE YOGYAKARTA, MAY 2016 III. RESULTS AND DISCUSSION Figure 3 shows XRD patterns of both prepared ZnO-SiO 2 and ZnO-SiO 2 (ctma) materials. The presence of SiO 2 is reflected by broad peaks at around 20 o and 68 o appeared by both materials while Reflection peaks corresponding to ZnO are (100), (002) and (101) planes are characteristic of the zincite structure(jcpds file no ). By comparing two patterns, it is concluded that ZnO-SiO 2 (ctma) give clear pattern related to the presence of ZnO in more crystalline structure than in ZnO-SiO 2. Even there is no perfect pattern of ZnO in the result, it is concluded that CTMA give contribution to give controlled formation of crystalline structure. The similar results were reported by previous works related with the synthesis of TiO2-SiO2, Zn-SiO2 as well as SiO 2 synthesis[9 12,8]. Figure 3: XRD pattern of prepared materials Effect of CTMA addition is also indicated from surface profile of materials. Figure 4 depicts the N 2 adsorption-desorption profile of both. It is confirmed that ZnO-SiO 2 (ctma) produce higher adsorption capacity compared to another one sample. Calculated surface parameters listed in Table 1 is also in line with the pattern in that specific surface area and the pore volume parameters are in the higher values. Table 1. Calculated surface parameters by gas sorption analysis Sample/Parameters BET Specific Surface Pore Volume (cc/g) Pore radius area (m 2 /g) (Å) ZnO-SiO 2 (ctma) ZnO-SiO C-71

4 Volume (cc/g) ISBN ZnO-SiO 2 (ctma) ZnO-SiO P/Po Figure 4. Adsorption-desorption profile of prepared materials According to the surface parameter data, it is concluded that the sol-gel mechanism involving surfactant action in the synthesis of ZnO-SiO 2 (ctma) produces the higher order structure. Surfactants constitute a separated section of modifying agents. Surfactants are typically applied in sol-gel techniques to minimize the shrinkage, prevent cracking and avoid supercritical drying processes. The surfactants decrease the capillary stress. CTMA influences by its interaction with pore water and Si OH groups on the surface of wet gels. In this process, the chloride groups will be substituted by OH groups[12]. C-72

5 C/Co PROCEEDING OF 3 RD INTERNATIONAL CONFERENCE ON RESEARCH, IMPLEMENTATION AND EDUCATION OF MATHEMATICS AND SCIENCE YOGYAKARTA, MAY 2016 Figure 5: (a) SEM profile of ZnO-SiO 2 (b) SEM profile of ZnO-SiO 2 (ctma) (c) EDX spectra of SEM profile of ZnO-SiO 2 (ctma) Figure 5 exhibits the difference of surface pofile identified by SEM-EDX analysis. As appeared from the profile, the rougher surface is created for ZnO-SiO 2 (ctma) and in addition there are the synthesized ZnO- SiO 2 (ctma) as confirmed by detected carbon ( C) and nitrogen(n). Photocatalytic activity (PA) of both material is reflected by the kinetics of MB photodegradation in Figure 6. The PA was measured in two varied process: photocatalysis means the treatment of photocatalyst addition under UV exposure without oxidant addition and photooxidation which is the same condition with photocatalysis but with oxidant (H 2 O 2 ) addition. From the curve it is concluded that for both material, photooxidation serve the higher MB degradation rate compared with photocatalysis treatment. This condition is related with the photooxidation mechanism involving the radicals formation from H 2 O 2 cleavage under the presence of radical formed from the interaction between UV and photocatalyst: Photocatalysis:ZnO-SiO2 0.6 Photooxidation:ZnO-SiO2 0.4 Photocatalysis: ZnO- 0.2 SiO2(ctma) 0 Photooxidation:ZnO- SiO2(ctma) Time (mins) Figure 6: Kinetic curve of photocatalysis and photooxidation over prepared materials. Electron-hole formation: ZnO-SiO 2 e - CB + h + vb Recombination : e - CB + h + vb heat Radical formation: O 2 (ads) + e - CB O 2 HO formation: h + vb + H 2 O HO + H + h + vb + OH - HO h + vb + H 2 O 2 HO MB + HO degradation products Radicals are actually formed by the interaction of UV light with photocatalyst semiconductor. Since there is the light interaction, the electron in the valence band (VB) of the semiconductor will be excited into conductance band(cb) and creates hole (h + VB). Furthermore the recombination occurred, the radical hydroxide will be released into the solution. Since there is the presence of H 2 O 2 in the solution, the formed radical peroxides will be accelerated so the degradation rate of MB in photooxidation is higher. By comparing two kinds of materials, it is also found that ZnO-SiO 2 (ctma) contributing the increasing rate for both treatments. From the physicochemical parameters it is concluded that the PA is closely related to the characters. C-73

6 ISBN Figure 7: Effect of MB initial concentration on initial rate of MB degradation over prepared materials by (a) photocatalysis (b) photooxidation IV. CONCLUSION In conclusion, the synthesis of ZnO-SiO 2 is affected by synthesis route i.e the addition of CTMABr as surfactant and templatein the sol-gel mechanism. It was observed from the XRD analysis that ZnO-SiO 2 prepared by CTMABr addition gives the higher crystalinity. Similar result is found to surface parameters of specific surface area and pore volume parameters. Improved parameters plays important role in the photocatalysis and photooxidation of methylene blue. REFERENCES [1] Ali AM, Ismail AA, Najmy R, Al-Hajry A. "Preparation and characterization of ZnO-SiO2 thin films as highly efficient photocatalyst. Journal of Photochemistry and Photobiology A: Chemistry", 2014;275: doi: /j.jphotochem [2] Kumara SG, Rao KSRK."Zinc oxide based photocatalysis: tailoring surface-bulk structure and related interfacial charge carrier dynamics for better environmental applications". RSC Adv 2015;5: [3] Halevas E, Nday CM, Kaprara E, Psycharis V, Raptopoulou CP, Jackson GE, et al. "Sol-gel encapsulation of binary Zn(II) compounds in silica nanoparticles. Structure-activity correlations in hybrid materials targeting Zn(II) antibacterial use". Journal of Inorganic Biochemistry 2015;151: doi: /j.jinorgbio [4] Mihai GD, Meynen V, Mertens M, Bilba N, Cool P, Vansant EF. "ZnO nanoparticles supported on mesoporous MCM-41 and SBA-15 : A comparative physicochemical and photocatalytic study" n.d. [5] Soltania RDC, Khoramabadib, Gh. Shams Godini H, Noorimotlagh Z. "The application of ZnO/SiO2 nanocomposite for the photocatalytic degradation of a textile dye in aqueous solutions in comparison with pure ZnO nanoparticles". Desalination and Water Treatment 2015;56: [6] Pantohan EG, Candidato RT, Vequizo RM. "Surface characteristics and structural properties of sol-gel prepared ZnO- SiO2 nanocomposite powders". IOP Conference Series: Materials Science and Engineering 2015;79: doi: / x/79/1/ [7] Valchev I, Lasheva V, Tzolov T, Josifov N. "Silica products from rice hulls". Journal of the University of Technology and Metallurgy 2009: [8] Singh P, Nandanwar R, Haque FZ. "Effect of Surfactants on Synthesis of SiO 2 Nanopowder Using Sol-Gel". 2013;2: [9] Selvi N, Sankar S, Dinakaran K. "Shape Controlled Synthesis, Structural and Morphological Characterization of CeO SiO 2 Core-Shell Hybrid Nanoparticles"n.d.:1 4. [10] Morsy S. "Role of Surfactants in Nanotechnology and Their Applications". Int J Curr Microbiol App Sci 2014;3: [11] Jahromi HS. "Effects of Tritonx100 and Tetraethylorthosilicate on the Morphology and Photocatalyst Properties of TiO2 Thin Film" 2013;260: [12] Sink?? K. "Influence of chemical conditions on the nanoporous structure of silicate aerogels". Materials 2010;3: doi: /ma C-74