MXenes as noble-metal-alternative co-catalysts in photocatalysis

Photocatalysis has become a focal point in research as a clean and sustainable technology with the potential to solve environmental problems and energy crises. The loading of noble-metal co-catalysts can substantially improve the photocatalytic efficiency of semiconductors. Because the high cost and scarcity of noble metals markedly limit their large-scale applications, finding a noble-metal-alternative co-catalyst is crucial. MXene, a novel 2D transition metal material, has attracted considerable attention as a promising substitute for noble metal co-catalysts owing to its cost-efficiency, unique 2D layered structure, and excellent electrical, optical, and thermodynamic properties. This review focuses on the latest advancements in research on MXenes as co-catalysts in relatively popular photocatalytic applications (hydrogen production, CO2 reduction, nitrogen fixation, and organic pollutant oxidation). The synthesis methods and photocatalytic mechanisms of MXenes as co-catalysts are also summarized according to the type of MXene-based material. Finally, the crucial opportunities and challenges in the prospective development of MXene-based photocatalysts are outlined. We emphasize that modern techniques should be used to demonstrate the effects of MXenes on photocatalysis and that the photocatalytic activity of MXene-based photocatalysts can be further improved using defective engineering and recent phenomena such as the localized surface plasmon resonance effect and single-atom catalysis.