A Cu medium designed Z-scheme ZnO-Cu-CdS heterojunction photocatalyst for stable and excellent H₂ evolution,...

Solar photocatalysis has emerged as a pollution-free and inexhaustible technique that has been extensively researched in the domains of environmental remediation and energy production. Herein, we have integrated ZnO and CdS nanoparticles through Cu as a solid-state electron mediator to design a ZnO-Cu-CdS Z-scheme heterosystem via a sol-gel route and further tested this as a photocatalyst for dye degradation, H₂ evolution, and CO₂ reduction. Within 60 min of visible light exposure, about 97% of methylene blue (MB) is degraded with a degradation rate constant of 0.042 min^-1 for the ZnO_0.45Cu_0.1CdS_0.45 catalyst. The MB degradation with this catalyst is 84, 21, 4.8, and 2 times as high as those of ZnO, CdS, ZnO_0.5CdS_0.5, and Cu_0.1ZnO_0.9 catalysts. The ZnO-Cu-CdS catalyst manifests an H₂ evolution efficiency of 5579 μmol h^-1 g^-1, which is 169, 41, 3.9, and 3.5 times as high as those of ZnO, CdS, ZnO_0.5CdS_0.5, and Cu_0.1ZnO_0.9 catalysts. Using H₂ as a reducing agent, the CO production rate over the ZnO_0.45Cu_0.1CdS_0.45 catalyst reaches 770 μmol h^-1 g^-1, which is 3 and 1.8 times higher than those of ZnO_0.5CdS_0.5 and Cu_0.1ZnO_0.9 catalysts. Besides, the optimal CH₄ production rate over ZnO_0.45Cu_0.1CdS_0.45 reaches 890 μmol h^-1 g^-1. The improved photocatalytic response of the ZnO-Cu-CdS catalyst is assigned to the delayed recombination of photoexcited charge carriers through a Z-scheme charge transport mode, maintaining the photocarriers with strong redox potentials and the dual role of Cu to serve as a conductive bridge to accelerate the charge transfer rate and enhance the light absorption due to its SPR phenomenon. This research offers a promising strategy for developing binary/ternary Z-scheme heterojunction photocatalytic systems for different photocatalytic applications.