Cooperative effect of polyethylene glycol and lignin on SiO2 microsphere production from rice husks

A simple method to the preparation of SiO 2 microspheres from rice husks (RH) was developed. The rice husks were extracted with 2   M NaOH solution to obtain a extract contained silica and lignin, and silica spheres were obtained after addition of distilled water, ethanol, 1   M H 2 SO 4 and PEG (W silica :W PEG   =   2:1) to the extract in a controllable sol–gel process and calcination at 550   °C. The optimum synthesis conditions were, adjustment of the extract to pH 3, a volume ratio of 1:1:2 of ethanol, water, and extract, respectively and a silica to polyethylene glycol weight ratio of 2:1. The SiO 2 microspheres produced under these conditions exhibited a relatively uniform particle size distribution around 500   nm as determined by LPSA, which indicated a cooperative function of added PEG and extracted lignin towards the formation of SiO 2 microspheres.