All-solid-state Z-scheme Co9S8/graphitic carbon nitride photocatalysts for simultaneous reduction of Cr(VI) and oxidation of 2,4-dichlorophenoxyacetic acid under simulated solar irradiation

An all-solid-state Z-scheme heterojunction photocatalyst, Co9S8/graphitic carbon nitride (Co9S8/g-C3N4), was synthesized via a hydrothermal method. The photocatalyst was used in the simultaneous photocatalytic reduction of Cr(VI) and oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D). Co-Nx bonds in Co9S8/g-C3N4 promoted the formation of a well-combined interface between Co9S8 and g-C3N4. The CoeNx bonds served as an electron-transfer medium in Co9S8/g-C3N4, leading to the formation of a Z-scheme photocatalytic system. Photocatalytic reactions were carried out under simulated solar irradiation and involved simultaneous Cr(VI) reduction and 2,4-D oxidation. Co9S8/g-C3N4 showed better photocatalytic activity than pristine g-C3N4 and Co9S8 owing to its effective separation of photo-generated charge-carriers and high redox potential. Compared with the single pollutant system, photocatalytic efficiencies over Co9S8/g-C3N4 were enhanced in the Cr(VI)/2,4D composite pollutant system. This was because the simultaneous reduction and oxidation reactions promoted the separation of charge carriers. This study presents a simple, economic, and efficient method to synthesize an all-solid-state Z-scheme Co9S8/g-C3N4 photocatalytic system. The system has good potential in the solar light photocatalytic removal of complex pollutants.