Rapid industrialization leads to increased wastewater discharge encompassing hexavalent chromium (Cr(VI)), which leads to serious environmental problems of toxicity and potential carcinogenicity. Removal of these species is normally carried out by ion‐exchange, precipitation, membrane filtration, sorption, photocatalytic reduction, etc. This review mainly focuses on the photocatalytic and photoelectrocatalytic (PEC) reduction of Cr (VI), because of their advantages over other methods such as reduced risk of secondary pollution by non‐reduced Cr (VI), no sludge formation, no need for a large amount of chemical reagents, clean and easy installation. The main factors influencing the photocatalytic reduction efficiency of Cr (VI) such as catalyst activity, solution pH, Cr adsorption on the catalyst and additives, are briefly discussed. Finally, a special emphasis is provided to the photoelectrocatalytic (PEC) reduction of Cr (VI).

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A facile and efficient WO /g-C N composite photocatalyst was developed by an in situ raw material decomposition method. The photocatalyst 3 3 4 was synthesized by direct heating low-cost ammonium tungstate and melamine together at the same time. The characterization and photocatalytic performance of the WO /g-C N chemical composite samples were compared with those from mechanical mixing. The characterization includes 3 3 4 X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectra (FT-IR), etc. The composite formed by the chemical method exhibited obviously better photocatalytic activity than the mechanical mixing sample under visible light irradiation. The possible mechanism for the enhanced catalytic efficiency may be due to the synergistic effect between the WO and g-C N tighter interface and the improved optical absorption in visible 3 3 4 region.

Single-crystal-like TiO 2 is claimed to be a very promising material among various catalysts. In this study, the (N,F)-co-doped single-crystal-like TiO 2 was prepared by a new molten mixing process in which the mixed nitrates were used both as a morphology modifier and an N-doping agent at the same time. The prepared samples also had well-developed (001) facet due to the addition of HF. The HF can also be an F doping agent to the material. The co-doping of N and F can diminish the band gap of TiO 2 from 3.05 to 2.93 eV, therefore visible light can be used effectively by the material. In addition, NO and fluorine ions existing on the surface of the sample can also help its photocatalyticity. Therefore, the photocatalytic performance of the as-prepared sample was effectively improved.

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