Constructing sewage waste sludge supported ZnCo₂S₄ with 1D g-CNNR S-scheme ZnCo₂S₄/g-CNNRs/SWS heterojunction with efficient charge separation through metallic elements for stimulating photocatalytic H₂ production

Well-designed sewage-waste-sludge (SWS) derived metallic elements to construct novel S-scheme ZnCo₂S₄/g-CNNRs heterojunctions for photocatalytic hydrogen production have been investigated. The role of SWS as a mediator with the influential effect of metal elements (M = Ni, Cu, Fe, and Mn) for higher charge separation and utilization were explored. The pure SWS was found promising to work as a support and co-catalyst, enabling 25 μmol g⁻¹h⁻¹ of H₂ production due to the presence of metal oxides activated under visible light. Altering g-C₃N₄ structure to 1D g-C₃N₄ nanorods (g-CNNRs) and coupling with SWS stimulated H₂ production to 195 μmol g⁻¹ h⁻¹ due to efficient charge separation and transfer. Constructing S-scheme heterojunction of ZnCo₂S₄/g-CNNR/SWS enabled 393 μmol g⁻¹ h⁻¹ of H₂, which is 9.14 and 15.72 folds higher than using g-CNNRs and SWS, respectively. The significant enhancement in photocatalytic efficiency was due to maximizing redox potential with a larger exposed surface, higher visible light utilization and synergetic effects of SWS elements for efficient charge carrier separation. The ternary composite assisted by SWS was also beneficial to maximize the stability for continuous H₂ production in multiple cycles. Thus, waste sludge with these structured materials can be used in developing low-cost catalysts and would be promising for other energy applications.