A Review: Photocatalysts Based on BiOCl and g-C3N4 for Water Purification

Many organic pollutants are discharged into the environment, which results in the frequent detection of organic pollutants in surface water and underground water. Some of the organic pollutants can stay for a long time in the environment due to their recalcitrance. Advanced oxidation processes (AOPs) can effectively treat the recalcitrant organic compounds in water. Photocatalysis as one of the AOPs has attracted a lot of interest. BiOCl and g-C3N4 are nice photocatalysts. However, their catalytic activity should be further improved for industrial utilization. The construction of heterojunction between the two different components is deemed as an efficient strategy for developing a highly efficient photocatalyst. As a typical type-II heterojunction, g-C3N4/BiOCl heterojunctions showed better photocatalytic performance. To date, the g-C3N4/BiOCl composites were mainly studied in the field of water purification. The photoactivity of the pristine catalysts was greatly enhanced by the combination of the two materials. However, three kinds of proposed mechanisms were used to explain the improvement of the g-C3N4/BiOCl heterojunctions. But few researchers tried to explain why there were three different scenarios employed to explain the charge transfer. According to the articles reviewed, no direct evidence could indicate whether the band structures of the heterojunctions based on BiOCl and g-C3N4 were changed. Therefore, many more studies are needed to reveal the truth. Having a clearer understanding of the mechanism is beneficial for researchers to construct more efficient photocatalysts. This article is trying to start a new direction of research to inspire more researchers to prepare highly effective photocatalysts.

Hexagonal WO3·0.33H2O Hierarchical Microstructure with Efficient Photocatalytic Degradation Activity

Structural design and morphological control of semiconductors is considered to be one of the most effective ways to improve their photocatalytic degradation properties. In the present work, a hexagonal WO3·0.33H2O hierarchical microstructure (HWHMS) composed of nanorods was successfully prepared by the hydrothermal method. The morphology of the HWHMS was confirmed by field-emission scanning electron microscopy, and X-ray diffraction, Raman spectroscopy, and thermogravimetric analysis demonstrated that the synthesized product was orthorhombic WO3·0.33H2O. Owing to the unique hierarchical microstructure, the HWHMS showed larger Brunauer–Emmett–Teller (BET) surface and narrower bandgap (1.53 eV) than the isolated WO3·0.33H2O nanorods. Furthermore, the HWHMS showed enhanced photocatalytic activity for degradation of methylene blue under visible-light irradiation compared with the isolated nanorods, which can be ascribed to the narrower bandgap, larger BET specific surface area, and orthorhombic phase structure of the HWHMS. This work provides a potential protocol for construction of tungsten trioxide counterparts and materials similar to tungsten trioxide for application in gas sensors, photocatalysts, electrochromic devices, field-emission devices, and solar-energy devices.

BiOX/BiOY (X, Y = F, Cl, Br, I) superlattices for visible light photocatalysis applications

BiOF/BiOI, BiOCl/BiOBr, BiOCl/BiOI, and BiOBr/BiOI superlattices are suitable for visible light photocatalytic degradation of organic pollutants.