Facile synthesis of high purity silica xerogel from rice straw

This research aims to synthesize a silica xerogel from rice straw that is a residue biomass generating from agriculture. Purity and morphological structure of synthesized silica xerogel are also studied. The first step of the synthesis is the preparation of sodium silicate from rice straw ash that is then used as silica source. To prepare a silica source, pretreated rice straw was burnt at 700 °C for 2 h to obtain a rice straw ash. After that resulted rice straw ash is washed and reacted with 1.0 M HCl and 2.0 M NaOH aqueous solution at 80 °C for 1 h, respectively. The reacted solution is then filtrated two times by a no.41 filter paper and ion exchange resin, respectively. The obtained sodium silicate is mixed with 1.0 M HCl under stirring for 6 h to produce the nano-silica. To increase the purity of nano-silica xerogels, as-synthesized silica was washed with deionized water for 3 times. Washed silica is dried in electric oven at 85 °C overnight and calcined at 500 °C for 5 h. Scanning electron microscopy/energy dispersive x-ray spectrometry (SEM/EDS) and % whiteness are employed to evaluate the morphology and purity of particles. Experimental results showed that nano-silica with purity up to 99.0 wt% was completely synthesized. Different morphological structure of silica synthesized under pH of 7, 8 and 9 were obtained.