Removal of Cr(VI) from water by a biochar-coupled g-C3N4 nanosheets composite and performance of a recycled photocatalyst in single and combined pollution systems

A series of biochar-coupled graphitic carbon nitride nanosheets (BPCMSs/g-C3N4 NSs) composites was successfully fabricated through a simple two-step calcination strategy by using waste Camellia oleifera shells (WCOSs) and melamine as raw materials. Hexavalent chromium [Cr(VI)] or total chromium (T-Cr) in water could be completely removed or mostly recovered through adsorption combined with photocatalytic reduction by using the as-prepared BPCMSs/g-C3N4 NSs. The adsorbed Cr(VI) on BPCMSs/g-C3N4 NSs could be reduced by photogenerated electrons into trivalent chromium ions (Cr3+) and stably fixed on BPCMSs/g-C3N4 NSs after strengthening. Interestingly, we found that the photocatalytic activity of the recycled Cr3+/BPCMSs/g-C3N4 NSs was remarkably improved compared with that of the fresh BPCMSs/g-C3N4 NSs for the degradation of aqueous organic pollutants. We tested the photocatalytic performance of the recycled Cr3+/BPCMSs/g-C3N4 NSs in the combined pollution system containing Cr(VI) and 4-fluorophenol (4-FP) and observed that a synergistic photocatalytic effect occurred in the Cr(VI)/4-FP combined pollution system under acidic and neutral conditions.