2D/2D composites based on graphitic carbon nitride and MXenes for photocatalytic reactions: a critical review

The combination of the two-dimensional (2D) materials g-C₃N₄ and MXenes in photocatalysis offers several advantages. The g-C₃N₄ can serve as a visible light-absorbing material, while MXenes can enhance the charge separation and transfer processes leading to improved photocatalytic efficiency. A critical review of 77 already published articles in the field of photocatalytic reactions using g-C₃N₄ and MXenes, such as hydrogen evolution, the reduction of carbon dioxide, the degradation of organic compounds, the redox reactions of nitrogen, was conducted. For the purpose of greater objectivity, the published results were analysed by non-parametric Mann–Whitney, Kolmogorov–Smirnov, and Mood´s median tests and visualised by box and whisker plots. It was found that MXenes can significantly improve the photocatalytic activity of g-C₃N₄. Adding other co-catalysts to the MXene/g-C₃N₄ composites does not bring a significant improvement in the photocatalytic performance. Promising results were obtained especially in the fields of hydrogen evolution and the reduction of carbon dioxide. Since the MXenes are relatively a new class of materials, there is still a big challenge for finding new photocatalytic applications and for the enhancement of existing photocatalytic systems based on g-C₃N₄, especially in terms of the MXenes and g-C₃N₄ surface and in the heterojunction engineering.