Hydrothermal Synthesis of Cd0.5Zn0.5S/ZnO Heterojunctions with Controlled pH and Enhanced Photocatalytic Hydrogen Production Activity

Zinc oxide semiconductor materials are widely used as photocatalysis materials for H2 evolution. However, its wide band gap and low electron–hole separation efficiency limit its application. Herein, we report Cd0.5Zn0.5S/ZnO (CZS/ZnO) heterojunction photocatalysts prepared via a hydrothermal method by controlling the pH of the preparation solution. Moreover, Cd0.5Zn0.5S with the optimal hydrogen production efficiency (CZS10, 28.47 mmol g–1 h–1) has been obtained in the solution with a pH of 10, exhibiting ∼5.9 times H2 production rate in comparison to that of CZS7 (4.83 mmol g–1 h–1). The optimal heterojunction catalyst 20% CZS10/ZnO shows a H2 evolution efficiency of 40.14 mmol g–1 h–1, which is 31.9, 8.3, and 1.4 times higher than that of pure ZnO (1.26 mmol g–1 h–1), CZS7, and CZS10 under full-spectrum irradiation, respectively. The highest apparent quantum efficiency for 20% CZS10/ZnO measured at 420 nm reaches 22.8%. By the study of PEC and ESR, we speculate that this is a Z-scheme photocatalytic system. The photogenerated electrons located in the CB of Cd0.5Zn0.5S preferentially undergo reduction reactions, and the holes present in the VB of ZnO undergo oxidation reactions. This work provides good guidance for the synthesis of the photocatalyst Zn0.5Cd0.5S and opens an avenue for the application of ZnO for photocatalytic H2 evolution.