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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Mesoporous silica SBA-15 has been successfully synthesized and its surface has been modified/functionalized with CPTMS. The making of pure SBA-15 was operated at an optimized concentration of Pluronic 123 surfactant at 60 mM which yields surface area of 831.996 m2/g determined by BET. The modified SBA-15, SBA-15+CPTMS have a lower surface area in comparison with neat SBA-15. In this study, SBA-15+CPTMS have a surface area of about 711.061 m2/g. This very high surface area was utilized to remove the Pb in industrial wastewater using laboratory made water samples. Despite lower surface area and pore diameter of SBA-15+CPTMS in comparison with pure SBA-15, the effectivity of SBA-15+CPTMS in lead adsorption much higher than mesoporous silica SBA-15 especially at a lower concentration of adsorbents. In this paper, we compared the percentage of Pb removal using mesoporous silica SBA-15 and CPTMS-SBA-15 systems. It was found at a low concentration of adsorbent, CPTMS-SBA-15 yields three times percentage of Pb removal than pure SBA-15. However, at high concentration of adsorbent, CPTMS-SBA-15 percentage of Pb removal is just slightly higher than the pure SBA-15 percentage of Pb removal.