Sustainable Biochar Nanosheets Derived from Sweet Sorghum Residues via Superbase Pretreatment

Two-dimensional (2D) sheet-like biochar as promising alternatives to graphene nanosheets has gained significant attention in materials science while being highly restricted by its complicated synthetic steps. In this study, the dimethyl sulfoxide/potassium hydroxide (DMSO/KOH) superbase system was first used to pretreat sweet sorghum residues (SS) and then carbonized to prepare sheet-like biochar. Ascribing to the strong nucleophilicity of DMSO/KOH, a synergistic effect was achieved by partially removing non-cellulosic components in SS and swelling the amorphous region of cellulose, leaving more layered cellulose behind (∼46.5 wt %), which was favorable for the formation of 2D biochar nanosheets with high graphitization degrees (∼93.1%). This strategy was also suitable for other biomass fibers (e.g., straw, wood powders, and nuclear shells) to obtain sheet-like biochar. The resulting sheet-like biochar could be compounded with cellulose nanofibers to achieve the structural design of composites and solve the molding problem of biochar, which was beneficial for dyeing wastewater treatment. Thus, this work provides insight into a simple strategy for developing 2D ultrathin sheet-like biochar from sustainable biomass wastes.