Towards tunable size of silica particles from rice husk

• White rice husk (WRH) produced from rice husk after acid and thermal treatment
• Sodium silicate solutions prepared by dissolving WRH in sodium hydroxide solution
• Four sodium silicate solutions with different concentrations of WRH prepared
• Particle size increased with increasing concentration of white rice husk.
• Increased temperature and water reduced the size and modals of silica particles.

Amorphous spherical silica particles were produced in a variety of sizes ranging from nanometer to micrometer from rice husk by varying the concentration of white rice husk from 0.7 wt.% to 5.6 wt.% in sodium hydroxide to form sodium silicate solutions. The effect of increased reaction temperature (65 °C) and the addition of water on the size of silica particles was also studied. At low concentrations of white rice husk (0.7 wt.% and 1.4 wt.%), uni-modal silica particles in nanometer size range were produced while at higher concentrations (2.8 wt.% and 5.6 wt.%), bi- and tri-modal particles were produced, which were converted to uni- and bi-modal by changing the reaction conditions, i.e. water and temperature, respectively. X-ray fluorescence spectroscopy, inductively coupled plasma optical emission spectroscopy and atomic absorption spectroscopy were employed for the compositional analysis of white rice husk and sodium silicate solution. Scanning electron microscopy was used to study the morphology and particle size of silica while X-ray diffraction confirmed the amorphous state of silica particles. Surface area of silica particles was analyzed by using Brunauer–Emmett–Teller analysis.