Spherical Bi2WO6/Bi2S3/MoS2 n-p Heterojunction with Excellent Visible-Light Photocatalytic Reduction Cr(VI) Activity.

Exploiting excellent photocatalytic activity and stable heterostructure composites are of critical importance for environmental sustainability. The spherical Bi2WO6/Bi2S3/MoS2 n-p heterojunction is first prepared via an in situ hydrothermal method using Bi2WO6, Na2MoO4·2H2O, and CH4N2S, in which the intermediate phase Bi2S3 is formed due to chemical coupling interaction of Bi2WO6 and CH4N2S. Scanning electron microscopy indicates that the compactness of the sample can be easily adjusted by changing the contents of S and Mo sources in the solution. The results of ultraviolet-visible (UV-vis) diffuse reflectance spectra, photoluminescence, transient photocurrent response, and electrochemical impedance spectra indicate that the formation of heterojunctions contributes to enhancing visible-light utilization and promoting photogenerated carrier separation and transfer. The composite material is used as a catalyst for the visible light photocatalytic reduction of Cr(VI). Remarkably, the optimal Bi2WO6/Bi2S3/MoS2 n-p heterojunction achieves the greatest Cr(VI) reduction rate of 100% within 75 min (λ > 420 nm, pH = 2); this rate is considerably better than the Cr(VI) reduction rate of pure Bi2WO6. The recycling experiment also reveals that the photocatalytic performance of the n-p heterojunction toward Cr(VI) is still maintained at 80% after three cycles, indicating that the n-p heterojunction has excellent structural stability. The capture experiment proves that the main active species in the system are electrons. The reasonable mechanism of Bi2WO6/Bi2S3/MoS2 photocatalytic reduction Cr(VI) is proposed. Our work provides new research ideas for the design of ternary heterojunction composites and new strategies for the development of photocatalysts for wastewater treatment.