Synthesis of bimodal porous silica from rice husk ash via sol–gel process using chitosan as template

In the present work, rice husk ash was used as a low cost raw material and chitosan was used as a template for the bimodal porous silica (BPS) synthesis. The obtained products exhibited type II isotherm of which revealed the existence of macroporous structures. When the pH of mixture was higher than pH 3, the BPS products with wormhole-like mesopore were formed as the result of the loose agglomeration of silica nanoparticles, and macropore structures were occurred from the chitosan template removal. Depending on the pH of mixtures, the BPS products synthesized with the chitosan template had higher specific surface areas (in the range of 366–627 m2/g), total pore volumes (0.65–1.70 cm3/g) and greater thermal stability than those synthesized without the template.