Reduction in time required for synthesis of high specific surface area silica from pyrolyzed rice husk by precipitation at low pH

Porous silica with a high specific surface area (SSA) was prepared from pyrolyzed rice husk (PRH) by adding H3PO4 to sodium silicate solution (SSS) until the pH values of 5.7, 5.0, 4.1 and 3.2 were achieved. The preparation process involved producing SSS from PRH, forming silica-polyethylene glycol (PEG) composites using SSS, H3PO4 and PEG, and calcinating the composites. The required preparation time was below 10 h, and the SSA of the sample prepared at pH 3.2 reached 1018 m2/g. Decreasing pH significantly increased the amount of PEG incorporated into the silica-PEG composites, and hence more pores were generated in the lower pH sample when the PEG was destroyed by calcination at 500 °C. The process developed in this study could lead to more efficient conversion of rice husk into high value-added porous materials that might be used for the adsorption of gas and heavy metal ions.