High purity silica has been successfully synthesized from rice husk ash (RHA) by alkaline extraction using the reflux process followed by acidification. For this study, rice husk was burned in an electric furnace at 700°C for 5 hours to produce RHA. The RHA was refluxed using sodium hydroxide with concentrations of 1.25×10-3 M (equal to 5% NaOH) and 2.5×10-3 M (equal to 10% NaOH). The acidification process was performed using hydrochloric acid (HCl) 1 M and acetic acid (CH3COOH) 1M to produce silica gel. Then, the silica gel was heated to 120°C for 12 hours to produced silica. The characterization of silica was determined using energy-dispersive X-ray analysis, Fourier-transform infrared spectrometry, the Brunauer-Emmet-Teller method, and X-ray diffraction. The results show HCl acidification produced silica of a higher purity than that produced by CH3COOH acidification. The higher concentration of sodium hydroxide led to higher purity of silica. Based on X-ray diffraction, the silica extracted from RHA was found to be amorphous, and Fourier-transform infrared spectrometry revealed bending and stretching vibrations of Si-O and Si-O-Si. The silica extracted by HCl acidification had a surface area of 236 m 2 /g, a total pore volume of 0.54 cc/g, and an average pore diameter of 9 nm. The silica extracted by CH3COOH acidification had a surface area of 204 m 2 /g, a total pore volume of 0.43 cc/g, and an average pore diameter of 8.4 nm.

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Santa Barbara Amorphous-15 (SBA-15) is an interesting mesoporous silica material with highly ordered nanopores and a large surface area. Due to its unique properties, this material has been widely employed in many areas. This study aimed to predict the number of nanopores per gram of SBA-15 material based on an optimum value of surfactant addition at the desired number of nanopores. For this purpose, SBA-15 was synthesized via a sol-gel process using tetraethyl orthosilicate (TEOS, Si(OC 2 H 5 ) 4 ) as a precursor and pluronic P123 triblock copolymer surfactant (EO 20 PO 70 EO 20 , EO = ethylene oxide, PO = propylene oxide) as a template. There were five different surfactant concentrations, namely 0.35, 2.50, 2.70, 3.00, and 3.30 millimoles, used with a fixed concentration of TEOS. The characterization was performed using small-angle x-ray scattering (SAXS), adsorption-desorption (BET), and transmission electron microscopy (TEM). The results showed that the surfactant concentration did not affect the crystal structure, although an increase in the surfactant concentration linearly correlated with an increase in the surface area. The shape and size of the pore diameter tends to be approximately 3 nm, as characterized using BET adsorption-desorption. The optimum concentration of surfactant for the formation of mesoporous SBA-15 material was 2.70 millimoles. The value obtained in this study was in accordance with the calculated value, indicating that the theoretical calculations can be used to experimentally predict the number of pores.

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The effect of Metakaolinization on the thermal and physicochemical properties of Badau Belitung kaolin is presented. Calcination of Badau Belitung kaolin indicated that kaolin was transformed to metakaolin at temperature above 500°C. The metakaolin was characterized using X-ray Diffraction (XRD), Fourier Transform Infrared (FT-IR) and Brunauer-Emmett-Teller (BET). The XRD diffraction pattern of the metakaolin was highly amorphous as a result of calcination effect on the raw kaolin. The FTIR spectra of the metakaolin produced showed that the material was thermally stable at temperature range of 500–700°C, whereas the specific surface area values of the raw kaolin and the metakaolin formed were increased with increasing calcination temperature from 500°C to 700°C.