Phase Engineering of TiO₂/MXene Heterostructure Nanosheets for Enhanced Photocatalysis

TiO₂-based heterostructures have attracted considerable attention in photocatalytic pollutant degradation owing to their enhanced photoresponse and improved charge separation. The phase structure of TiO₂ strongly affects its band structure and interfacial charge-transfer behavior, making phase structure control critical for optimizing photocatalytic performance. However, due to the small difference in free energy among TiO₂ phase structure and the strong dependence of TiO₂ nucleation and growth on the local reaction environment, it remains challenging to precisely control the phase structure of TiO₂ in the TiO₂-based heterostructure nanomaterials. Herein, we achieved the phase engineering of TiO₂/MXene heterostructure nanomaterials through a solvent-regulation strategy. Specifically, by regulating the acetonitrile/water ratio in the hydrothermal solvent, TiO₂ with distinct phase structures was in situ grown on hydrothermally treated MXene nanosheets, resulting in two representative TiO₂/MXene heterostructure nanosheets: anatase TiO₂/MXene and rutile TiO₂/MXene. Acetonitrile likely acted as a surface-adsorbing agent during TiO₂ formation, stabilizing the anatase phase and promoting the preferential formation of anatase TiO₂. Benefiting from the optimized heterostructure, TiO₂/MXene heterostructure nanosheets promoted the generation of singlet oxygen (¹O₂), leading to enhanced photocatalytic degradation.