Sulfur Vacancy-Mediated Electron–Hole Separation at MoS₂/CdS Heterojunctions for Boosting Photocatalytic N₂ Reduction

Defect engineering is considered as an efficient method for improving the photocatalytic activity of semiconductor photocatalysis because defects can not only serve as trapping centers for electrons and holes but also work as active sites for reaction. Herein, we synthesized a series of MoS₂/CdS heterojunctions with abundant sulfur vacancies and used for photocatalytic N₂ reduction. The sulfur vacancies at MoS₂/CdS heterojunctions were confirmed by UV–vis diffuse-reflectance spectroscopy (UV-DRS) and electron paramagnetic resonance. The charge transfer behaviors of the photocatalysts were characterized by X-ray photoelectron spectroscopy, transient photocurrent, steady and transient photoluminescence spectroscopy, and so forth. Under visible light irradiation for 4 h, the production of NH₃ at 3% MoS₂/CdS heterojunctions (249.7 mg L^–1 g^–1) was about 5.4 and 3.9 times higher than that of pure MoS₂ (45.9 mg L^–1 g^–1) and pristine CdS (64.5 mg L^–1 g^–1), respectively. The reaction mechanisms and pathways were further studied by in situ diffuse reflection infrared Fourier transform spectroscopy.