Artificial Z-scheme photocatalyst can not only reduce the recombination of photogeneraged electron–holepairs, but also retain prominent redox ability. In this study, direct solid-state dual Z-scheme WO 3 /g-C 3 N 4 /Bi 2 O 3 photocatalyst was successfully synthesized by one step co-calcination stratage using tungstic acid, melamine and bismuth (III) nitrate pentahydrate as the precursors. Surface, morphological, and structural properties of the resulting materials were comprehensive characterized by XRD, XPS, SEM, TEM, UV–vis diffuse reflection spectroscopy, BET surface areas, photoluminescence and ESR analysis. The WO 3 /g-C 3 N 4 /Bi 2 O 3 composite exhibited superior photocatalytic activities for tetracycline degradation than that of pure g-C 3 N 4 , WO 3 , Bi 2 O 3 and their binary composites under visible light irradiation. The enhanced photocatalytic performance of WO 3 /g-C 3 N 4 /Bi 2 O 3 composite can be ascribed to improved visible light absorption, increased surface area and enhanced separation efficiency of photo-generated electron-hole pairs. In addition, the photocatalyst exhibits high stability and reusability. On the basis of the results, a novel direct solid-state dual Z-scheme photocatalytic mechanism was also proposed.
Membrane separation technology is a selective physical separation method that is widely used in the fields of wastewater reuse and recycling. However, its separation effect on small molecules in pollutants is not ideal. In this study, the negative pressure filtration method was adopted, combining membrane separation with photocatalytic technology to prepare a sandwich-structured WO 3 /g-C 3 N 4 /CNTs curtain hollow fiber photocatalytic membrane module with. By changing the experimental conditions, membrane anti-pollution property, stability and self-cleaning ability of the membrane module were studied under visible light irradiation. Through characterizations, it was found that when WCN/CNTs = 2:1 and pH = 12, the degradation rate of MB by the membrane module after 4 h of using was still 89.47%, which was 42.60 times higher than that of pure PVDF membrane module, and the water flux recovery rate (FRR) was as high as 98.21%. Stability experiments show that the degradation rate and flux of this membrane module remain stable at various pH levels, and the FRR values are all above 96.80%, while the FRR value of pure PVDF membrane modules is only 72.94%. This study provides a new idea for the preparation of semiconductor-based composite photocatalytic membranes with high self-cleaning ability and photocatalytic activity in the field of wastewater treatment.
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