Production of amorphous silica nanoparticles from rice straw with microbial hydrolysis pretreatment

An enzymatic hydrolysis approach was used in order to develop a less aggressive process for production of amorphous silica from rice straw. In the process, rice straw was firstly hydrolyzed either with a microbial isolate (Trichoderma reesei TISTR 3080) or a microbial community (LDD1), followed by a heat treatment at 500 °C for 8 h. After hydrolysis, the rice straw was decomposed by T. reesei and by LDD1 to 59.6% and 45.2% of the initial weight, of which 12% and 23% ash content was respectively determined by thermogravimetric analysis. X-ray diffraction and transmission electron microscopy analysis confirmed that the major constituent in the ash to be amorphous silica with a particle size ranges between 50 and 80 nm. The silica content in the T. reesei pretreated ash was 82.5%, whereas the content of the LDD1 pretreated ash was 73.6%. Relatively high levels of impurities such as manganese and phosphate, associated with microbial activity were detected in both pretreated ash samples.