Design of p–n heterojunction between CoWO4 and Zn-defective Zn0.3Cd0.7S for efficient photocatalytic H2 evolution

To enhance the efficiency of photocatalytic H2 evolution, numerous methods are employed by increasing the utilization of photogenerated charge carriers (PCCs), including catalyst design, defect regulation, and selection of suitable H+ resources. Using self-assembly methods, CoWO4/ZnxCd1−xS with p–n heterojunction was synthesized. Although CoWO4 (CW) cannot produce H2 under visible light irradiation, it can provide photogenerated electrons (e−) to Zn0.3Cd0.7S (ZCS), and largely increase the photocatalytic activity of ZCS. The optimal CW/ZCS composite can reach 15.58 mmol·g−1·h−1, which is 45.8 and 24.3 times higher than the values of the pure CdS and ZCS, respectively. The largely enhanced photocatalytic H2 production is attributed to the Zn vacancies (VZn), p–n heterojunction, and p-chlorobenzyl alcohol (Cl–PhCH2OH) as the source of H2 production. VZn on the ZCS surface as the capture center of photogenerated holes (h+), can regulate the carrier distribution, which results in more photogenerated e− and less generated h+. The combination of p–n heterojunction and VZn can enhance the separation and transfer efficiency of PCCs, and effectively inhibit the recombination of charge carriers. To further improve the utilization rate of PCCs, the photocatalytic H2 evolution is proceeded by Cl–PhCH2OH oxidation in N, N-dimethylformamide solution, with 4-chlorobenzaldehyde (Cl–PhCHO) generated. The separated photogenerated e− and h+ both participated in the redox reaction of H+ reduction and Cl–PhCH2OH oxidation, considering that the amount of H2 and Cl–PhCHO products are close to 1:1. This work not only facilitates the separation and transfer of PCCs, but also provides directions for the design of efficient photocatalysts and H2 evolution in the organic phase.