Synthesis and surface characteristics of nanosilica produced from alkali-extracted rice husk ash

Rice husk is a form of agricultural biomass that provides an abundant silicon source. This study used rice husk as a raw material to prepare nanosilica without adding an extra surfactant. This work investigated a dissolution–precipitation technique as a function of acid treatment, sodium silicate concentration, gelation pH, aging temperature, and aging time to establish optimum conditions for preparing silica nanoparticles. Experimental results showed that silica produced by hydrochloric acid possesses higher surface area than that of sulfuric, oxalic, and citric acids. Surface characteristics of the sample depend mainly upon gelation pH. The highest surface area and pore volume of silica samples were 634 m2/g and 0.811 cm3/g. Pore diameters were controllable from 3 to 9 nm by adjusting the solution pH value. Particles had a uniform size of 5–30 nm. The objective of this study was to develop a method of nanosilica preparation that enhances the economic benefits of re-using rice husk waste.