Semiconductor photochemical treatment is expected to be a green technology for solving the environmental issues induced by organic pollutants. WO₃ are generally considered as an excellent candidate for visible-light photocatalysts [1-3]. However, the activity of pure WO₃ has to be improved due to the rapid recombination of the photogenerated electron-hole pairs. In this work, WO₃ was loaded with hybrid MoS₂-reduced graphene oxide (MoS₂-rGO) to form WO₃/MoS₂-rGO heterojunction composites, in which MoS₂ acts as another efficient light absorbing material and rGO as the charge transfer medium to enhance the photocatalytic efficiency [4-5].

In this work, WO₃ was prepared by hydrothermal synthesis method with WCl₆ as tungsten source and absolute ethanol as solvent, as shown in Fig. 1(a). Clearly, the synthesized WO₃ is a monodispersed microsphere structure with an average size of 2-3um. The hybrid MoS₂-rGO was prepared by adding graphene during the hydrothermal synthesis process of MoS₂ with Na₂MoO₄·2H₂O and thiourea as reacting materials. As shown in Fig. 1(b), the synthesized MoS₂ shows a flower-like structure. Finally, the WO₃/MoS₂-rGO nanocomposites were also prepared by adding the prepared hybrid MoS₂-rGO during the hydrothermal synthesis process of WO₃. As shown in Fig. 1(c) and (d), the close contact is clearly seen between the microsphere-like WO₃ and flower-like hybrid MoS₂-rGO, and the second hydrothermal process had no influence on the structure of WO₃ and hybrid MoS₂-rGO. X-ray diffraction (XRD) patterns and Raman spectra are respectively measured to determine the crystal structure, as shown in Fig.1 (e) and (f).

The photochemical behaviors of WO₃/MoS₂-rGO nanocomposites containing (0, 2%, 5%, 10%, and 20%) of hybrid MoS₂-rGO are characterized through the degradation behaviors of rhodamine (RhB) under visible light irradiation (Fig.2). The experimental results clearly show that the degradation efficiency of WO₃/MoS₂-rGO nanocomposites can be improved by optimizing the mass ratio of WO₃ microspheres to hybrid MoS₂-rGO flowers. The degradation ratios of RhB after 6 h are 78.2%, 79.5%, 82.6%, 95.6%, 91.8%, correspond respectively to the WO₃/MoS₂-rGO nanocomposites containing 0, 2%, 5%, 10%, and 20% of hybrid MoS₂-rGO. The possible reason is that the formed WO₃/MoS₂heterojunction structure and charge transfer medium of rGO is beneficial for separating electron-hole pairs for high efficiency degradation

In summary, the WO₃ microspheres and different WO₃/MoS₂-rGO nanocomposites have been prepared and characterized through adjusting the mass ratio of WO₃ microspheres to hybrid MoS₂-rGO flowers. The results show that the optimized degradation ratio of RhB can be greatly improved from 78.2% up to 95.6% after 6h using WO₃/MoS₂-rGO nanocomposites in comparison with WO₃ microspheres.

References

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[2] S.Y. Yao, X. Zhang, F.Y. Qu, A. Umar, X. Wu, Journal of Alloys and Compounds 689 (2016) 570–574.

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