Visible light photocatalytic reduction of U(VI) in water by tea waste biochar/g-C3N4 composites

Tea waste biochar/graphitic carbon nitride (TBC/g-C3N4) composites were prepared by high temperature thermal polymerization with tea waste as raw material and melamine as precursor. The morphology, structure and photoelectric characteristics of the photocatalysts were characterized by SEM, XRD, XPS, UV-Vis DRS, PL and EIS.The performance of TBC/g-C3N4 composites for photocatalytic reduction of U(VI) under visible light irradiation was studied, and the mechanism of photocatalytic reduction of U(VI) by TBC/g-C3N4 composites was discussed.The results show that when the mass fraction of TBC is 5%, the initial pH value is 4 and the amount of catalyst is 1 g/L, the removal rate of U(VI) by TBC/g-C3N4 composites is 99.64% after visible light irradiation for 30 min, which is much higher than that of g-C3N4 (58.8%).The removal rate of U(VI) is above 80% after five cycles, which indicates that TBC/g-C3N4 composites has an excellent photocatalytic stability.The addition of TBC makes the band gap of g-C3N4 reduced from 2.63 eV to 2.14 eV, widens the visible light absorption range, promotes the separation of photogenerated charge, reduces the recombination rate of photogenerated electron-hole pair, and thus enhances the photocatalytic activity of TBC/g-C(3)N(4)composites.This study provides a new idea to design and synthesizethe photocatalysts with efficient, low-cost and environmentally-friendly.