A detailed study of the effects of pyrolysis temperature and feedstock particle size on the preparation of nanosilica from rice husk

In this paper, an optimized process for preparation of photosensitive nanosilica from rice husk (RH) is described. The rice husk sample was pretreated by soaking in deionized water to remove most of the alkali metals and partial fixed carbon. Most metal oxides, especially alkaline metal oxides and alkaline-earth metal oxides, were removed to a certain extent after the soaking pre-treatment. Soaking pretreatment may remove the hydrogen bonds or extractives between hemi-cellulose and cellulose, which affects the thermal stability of both molecules. To thoroughly analyze the soaking process, thermogravimetric analysis (TGA) was performed to obtain the mass loss behavior of soaked rice husk. The characteristics of the nanosilica prepared from the method described in this paper are superior to those of fumed silica. The silica content of the nanosilica reached a record of 99.92% in pyrolysis method. The optimum preparation conditions were as follows: a rice husk feedstock particle size of between 250 and 420 μm, a pyrolysis temperature of approximately 610 °C, a hydrolysis temperature of 120 °C, a 1:10 (g/ml) ratio of rice husk to acid, a hydrolysis time of 4 h, and a hydrochloric acid (HCl) concentration of 8% (wt.%). A detailed study of the effects of the pyrolysis temperature and feedstock particle size was conducted, filling the gap in systematic research on the nanosilica preparation process using the pyrolysis method. The complete process of pyrolysis for pretreated rice husk is described, including the decomposition of the major constituents, volatilization of gases and the formation of silica. The results of this study provide a deep understanding of nanosilica production by pyrolyzation. The prepared nanosilica is photosensitive and approximately spheroidal with an average particle size of approximately 8-10 nm.