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@MoS(2)heterostructures under visible light. Without the need for a sacrificial agent, CdS@MoS(2)displayed an excellent hydrogen production rate of 4233 mu mol g(-1)h(-1)with 0.3 mmol benzyl alcohol, which is approximately 53 times higher than that of bare CdS nanorods (80 mu mol 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 mu mol g(-1)h(-1). Scanning electron microscopy and transmission electron microscopy images revealed that p-type MoS(2)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@MoS(2)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@MoS(2)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.