Enhanced charge carrier separation and transfer in g-C₃N₄ and tungsten oxide/sulfide composite photocatalysts

The performance of photocatalysts is strongly governed by their solar energy harvesting capability and the efficiency of charge carrier separation and transfer. To mitigate the rapid recombination of photogenerated charge carriers and enhance light absorption, ultrathin graphitic carbon nitride (g-C₃N₄) nanosheets have been developed for constructing heterostructures with other semiconductors. Semiconductor materials with narrow band gaps and highly positive valence bands are considered promising candidates. Among them, tungsten-based compounds (e.g., oxides and sulfides) have attracted significant attention due to their ability to absorb light in the near-infrared region and their enhanced oxidation potential. Moreover, defective tungsten compounds with diverse morphologies offer intriguing possibilities for forming g-C₃N₄-based heterostructures. Tungsten oxide (WO_x) and sulfide (WS₂)/g-C₃N₄ heterostructures have been extensively explored for various photocatalytic applications, including water splitting, CO₂ and N₂ reduction, H₂O₂ generation, and chemical-to-fuel conversion. This review highlights recent advances in tungsten oxide (sulfide)/g-C₃N₄ composite photocatalysts, focusing on synthesis control, heterostructure formation, charge carrier dynamics, extended light absorption, and their roles in green energy conversion. It systematically discusses the growth kinetics of WO_x and WS₂ on ultrathin g-C₃N₄ nanosheets, the construction of binary and ternary heterostructures, photocatalytic mechanisms, and the resulting activities. In particular, the influence of tungsten oxides and sulfides on photo-redox capabilities is examined to elucidate their contributions to enhanced photocatalytic performance. Finally, the challenges and future prospects of tungsten oxide (sulfide)/g-C₃N₄ composite catalysts for advanced applications are addressed.