Highly soluble Ni-salen molecules enable boosted photocatalytic hydrogen evolution of polymeric carbon nitride/CdS heterojunction

The photocatalytic hydrogen (H2) evolution of photocatalyst generally requires the assistance of cocatalysts, which are mainly centered on noble metals, such as Pt and Au. However, noble metals cocatalysts often suffer from the uneven distribution and severe aggregation, as well as scarcity. Herein, we reported nickelsalen (Ni-salen) molecules on the promotion of photocatalytic H2 evolution with polymeric carbon nitride (PCN)/CdS heterojunction, in which the noble metal free Ni-salen molecules are soluble and highly dispersed during photocatalytic H2 evolution under visible light irradiation (lambda >= 420 nm). Under optimized loading concentration of the Ni-salen molecules (0.03 mM), the highest H2 evolution rate is up to 23.3 mmol g-1 h-1, which is more than 4 times higher than that by using PCN/CdS heterojunction alone. In addition, Ni-salen molecules are highly stable and can offer a durable H2 evolution with 28 h. The enhancement on H2 evolution is the result of efficient photogenerated electrons transfer from photoexcited PCN/CdS heterojunction to the coordination unsaturated Ni active centers of Ni-salen molecules. This work demonstrates the great potential of soluble noble metal free Ni-salen molecules on the promotion of photocatalytic H2 evolution.