Evolution of Ti₃C₂ MXene Quantum Dots for Photocatalytic and Photoelectrochemical Applications: A Review

The key transformation of 2D Ti₃C₂ MXene nanosheets into 0D Ti₃C₂ MXene quantum dots (Ti₃C₂ QDs) restructures the landscape of surface-active sites and tunable band gaps, enabling visiblelight-driven photocatalytic activity. Interestingly, the evolution of these fascinating Ti₃C₂ QDs retains ordered structural characteristics like the parent 2D Ti₃C₂ MXene nanosheets with controlled surface chemistry even after the facile hydrothermal process. In particular, evidence of tailoring of Ti₃C₂ QDs smaller than 10 nm reinforces the charge carrier separation and suppresses recombination under the strong association of quantum confinement and edge effects. Thus, the physical effects of Ti₃C₂ QDs effectively control the limitations of semiconductors, such as charge carrier recombination, slow charge carrier separation, and transportation in the resultant photocatalyst, for the implementation of promising toxic matter degradation and clean H₂ production. Special considerations are given to the regulation of charge carrier generation and separation for stable photocatalytic performance, such as appropriate band gap formation, localized surface plasmonic behavior, and Schottky barrier formation at the semiconductor interface. Specifically, pure Ti₃C₂ QDs with a size smaller than 10 nm exhibit a band gap of 2.16 eV, which has been found to be a powerful way to enable semiconductor-like photoresponse behavior. Overall, the above features make Ti₃C₂ QDs the preferred choice for facilitating effective charge carrier dynamics for the optimization of chemical stability in optoelectronic applications. The paper concludes with challenges and future perspectives to guide the 0D Ti₃C₂ QDs practical applicability in light-driven and sustainable environmental applications.