Ti₃C₂T_x Co-Catalyst on CuO: Size Effects on Enhanced Photocatalytic Activity

Co-catalysts play a crucial role in photocatalytic reactions, and titanium carbide (Ti₃C₂T_x) is a promising alternative to expensive noble metal co-catalysts. However, size effects and charge transfer mechanisms of Ti₃C₂T_x co-catalysts on semiconductors for photocatalytic water splitting remain under-researched. Herein, we coupled copper (II) oxide (CuO) semiconductor with either Ti₃C₂T_x nanosheets (T2D) or Ti₃C₂T_x quantum dots (T0D) to create composite photocatalysts: T2D/CuO and T0D/CuO. The effects of size, morphology, and energetics of Ti₃C₂T_x were investigated and hydrogen production rates were tested. The results show that T0D are better co-catalysts for photocatalytic hydrogen production in comparison to T2D. The optimal T0D/CuO sample achieved a hydrogen production rate of 2174 μmol g^-1 h^-1, which is 19 times that of the optimal T2D/CuO samples, and more than 100 times that of pure CuO. The size of T2D in the composites is 200 nm, whereas the size of T0D is only 7 nm. This difference serves to decrease light obstruction and parasitic light absorption. Simultaneously, the surface area increases from 29 cm²/g for T2D/CuO to 43 cm²/g for T0D/CuO, indicating a higher abundance of active sites. This study highlights the impact of the size effects of Ti₃C₂T_x co-catalysts on photocatalytic performance and lays the foundation for the research of other quantum dot sized co-catalysts.