Emerging MXenes in Photocatalysis, Principles, Mechanisms, and Heterostructures: A Review

Two‐dimensional MXenes, a new family of transition metal carbides and nitrides, have emerged as promising materials in photocatalytic heterostructures due to their unique structural and electronic properties. Their layered morphology, high electrical conductivity, tunable surface terminations (–O, –OH, –F), and strong hydrophilicity promote efficient charge separation, wide light absorption, and abundant active sites. These features make MXenes a suitable component in photocatalytic systems for applications in the hydrogen evolution reaction (HER), CO 2 reduction reaction (CO 2 RR), and degradation of organic pollutants. Among various MXenes, Ti 3 C 2 T x has attracted the most attention because its favorable hydrogen adsorption energy and high conductivity enable rapid charge transport, especially when used as a cocatalyst or heterojunction component. Furthermore, MXenes can form Schottky junctions with semiconductors, which enhances charge separation and minimizes electron–hole recombination. Their large surface area and inherent defects also provide reactive sites that facilitate molecular adsorption and activation. However, their long‐term stability remains a challenge, as MXenes are prone to oxidation under ambient conditions. To address these limitations, recent research has focused on surface modification, hybridization with semiconductors, and controlled synthesis techniques. This review summarizes recent developments in MXene‐based photocatalysts and discusses their structure–activity relationships.