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

To enhance the efficiency of photocatalytic H 2 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 method, CoWO 4 /Zn x Cd 1−x S with p–n heterojunction was synthesized. Although CoWO 4 (CW) cannot produce H 2 under visible light irradiation, it can provide photogenerated electrons (e − ) to Zn 0.3 Cd 0.7 S (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 H 2 production is attributed to the Zn vacancies (V Zn ), p–n heterojunction, and p-chlorobenzyl alcohol (Cl–PhCH 2 OH) as the H + source of H 2 production. V Zn 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 V Zn 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 H 2 evolution is proceeded by Cl–PhCH 2 OH 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–PhCH 2 OH oxidation, considering that the amount of H 2 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 H 2 evolution in the organic phase.