Valorization of Rice Husk to Value-Added Chemicals and Functional Materials

Agricultural waste, such as rice husk (RH), can be utilized directly or by converting it into various value-added chemicals or functional materials. This minireview has two main objectives: the first is to provide collective information about conversion of RH to value-added products via chemical treatments and the second is to enlist with discussion the various functional materials derived from RH. The chemical treatments help remove recalcitrant structure of lignin and allow carbon-rich organic compounds to separate from RH. The useful products obtained from RH through this method are xylooligosaccharides, bioethanol, levulinic acid, butyric acid, vanillin, benzoic acid, etc. The production of functional materials does not require pretreatment of RH. In this method, RH is combined with metals, non-metals, or their oxides to obtain the functional materials. Due to their porous nature, these RH-based functional materials are used in various applications, such as micro- or nano-adsorbents for the removal of harmful organic and inorganic pollutants; as catalysts because of their active catalytic sites; and as electrode materials because of their high surface area and good carbon quality. In this review, the relevant and latest reports about these applications are discussed with critical analysis.