Monolayer Ti₃C₂T_x as an Effective Co-catalyst for Enhanced Photocatalytic Hydrogen Production over TiO₂

Titanium dioxide (TiO₂) represents a promising candidate for hydrogen production via photocatalysis. Yet, its large bandgap and fast charge recombination limits its efficiency. To overcome this limitation, we explored in this work two-dimensional titanium carbide MXene, Ti₃C₂T_x (T_x = O, OH, F), as feasible co-catalysts for hydrogen production with TiO₂ as the photocatalyst. We synthesized a series of Ti₃C₂T_x/TiO₂ composite photocatalysts with monolayer Ti₃C₂T_x as the co-catalyst to improve the separation of photoinduced electrons and holes. The physicochemical properties of the Ti₃C₂T_x/TiO₂ composites were investigated by a variety of characterization techniques, and the effect of the monolayer Ti₃C₂T_x on the photocatalytic performance of the Ti₃C₂T_x/TiO₂ composites is elucidated by comparison to the multilayer counterpart. The photocatalytic hydrogen evolution rate of the optimized monolayer Ti₃C₂T_x/TiO₂ composite is over 9 times higher than that of the pure TiO₂ and 2.5 times higher than the multilayer counterpart. The significantly enhanced activity is attributed to the superior electrical conductivity of monolayer Ti₃C₂T_x and charge-carrier separation at the MXene/TiO₂ interface. A mechanism of photocatalytic hydrogen evolution over the Ti₃C₂T_x/TiO₂ system is proposed. Our work reports on the potential of monolayer MXenes as effective co-catalysts for photocatalysis and further broadens the applications of the MXene family of two-dimensional materials.