Synergistic adsorption-photocatalysis for dyes removal by a novel biochar–based Z-scheme heterojunction BC/2ZIS/WO3: Mechanistic investigation and degradation pathways

• A novel biochar–based Z-scheme heterojunction (BC/ZIS/WO 3 ) was prepared. • BC promoted the light absorption property and charge separation. • BC/ZIS/WO 3 has good adsorption capacity and photocatalytic property. • The π-π, electrostatic and hydrogen bond interactions were the adsorption mechanisms. • The most active sites of MB and RhB were S-19 and N-18 atoms, respectively. As far as we know, biochar-based photocatalysts were rarely used in wastewater treatment, and their application was limited due to the catalyst agglomeration and low electron mobility efficiency. A novel biochar/2Zn 3 In 2 S 6 /WO 3 (BC/2ZIS/WO 3 ) photocatalyst was synthesized by the hydrothermal method, which has synergistic performance of adsorption and photocatalysis. BC, the carrier of the ZIS/WO 3 heterojunction, with a large specific surface area (1161.25 m 2 /g), good electrical conductivity, improved the efficiency of catalyst charge separation, and significantly enhanced the photocatalytic performance. The adsorption isotherm experiment showed that the maximum adsorption capacity of the BC/2ZIS/WO 3 for MB and RhB was 120.04 and 466.55 mg/g, respectively. Under the synergistic effect of adsorption and photocatalysis, the removal rates of MB and RhB reached 80.5% and 99%, respectively, which were significantly higher than that of the single heterojunction. Furthermore, through DFT calculations, trapping experiments, and HPLC-MS, the adsorption, degradation mechanism and pathways were elaborated. In general, this work provided important insights into the role of biochar in improving the photocatalytic degradation of pollutants, and guided the design of environment-friendly photocatalysts in the future.