Comprehensive Utilization of Rice Husks

The annual global production of rice husks (RHs) is ca. 170 million tons. The current application of RHs has been very limited, mainly owing to their tough, woody, abrasive nature, low nutrition, great bulk, and high ash content. Therefore, RHs are widely considered as a biowaste. RHs are mainly composed of lignocellulose (ca. 85 wt%) and hydrated silica (ca. 15 wt%). Herein we report a new approach for comprehensive utilization of RHs. A series of value-added products, including sulfonated lignocellulose, i.e., sulfonated cellulose, sulfonated hemicellulose, and sulfonated lignin, as well as silica nanoparticles, have been successfully derived from RH biomass. The RHs were firstly oxidized by sodium periodate and then sulfonated by sodium bisulfite to yield water soluble sulfonated lignocellulose, which has applications as biosurfactant, etc. The remaining residue that contains a high content of silica was thermally treated to synthesize silica nanoparticles with a high purity and surface area. The implication of the present findings is discussed.