Visible-light-driven photocatalytic hydrogen production coupled with selective oxidation of benzyl alcohol over CdS@MoS2 heterostructures

Photocatalytic hydrogen production coupled with selective oxidation of organic substrates to produce high-value-added fine chemicals has drawn increasing attention. Herein, we report a noble metal-free photocatalyst for the highly efficient and simultaneous generation of hydrogen and the selective oxidation of benzyl alcohol into benzaldehyde over CdS@MoS2 heterostructures under visible light. Without the need for a sacrificial agent, CdS@MoS2 displayed an excellent hydrogen production rate of 4233 µmol g−1 h−1 with 0.3 mmol benzyl alcohol, which is approximately 53 times higher than that of bare CdS nanorods (80 µmol g−1 h−1). The reaction system was highly selective for the oxidation of benzyl alcohol into benzaldehyde. When the amount of benzyl alcohol increased to 1.0 mmol, the hydrogen production reached 9033 µmol g−1 h−1. Scanning electron microscopy and transmission electron microscopy images revealed that p-type MoS2 sheets with a flower-like structure closely adhered to n-type semiconductor CdS nanorods through the formation of a p-n heterojunction. As a potential Z-scheme photocatalyst, the CdS@MoS2 heterostructure effectively produces and separates electron-hole pairs under visible light. Thus, the electrons are used for reduction to generate hydrogen, and the holes oxidize benzyl alcohol into benzaldehyde. Moreover, a mechanism of photogenerated charge transfer and separation was proposed and verified by photoluminescence, electrochemical impedance spectroscopy, photocurrent and Mott-Schottky measurements. The results reveal that the CdS@MoS2 heterojunctions have rapid and efficient charge separation and transfer, thereby greatly improving benzyl alcohol dehydrogenation. This work provides insight into the rational design of high-performance Z-scheme photocatalysts and the use of holes and electrons to obtain two valuable chemicals simultaneously.