Size Effect of (CuO)n (n=1-6) Clusters on the Modification of Rutile-TiO2 Photocatalysts

The size-dependent properties of metal/metal oxide clusters have received increasing interest due to their significant role in promoting heterogeneous catalysis. Herein, an ab initio method is used to investigate the photocatalytic properties of TiO2-supported (CuO) n nanoclusters (n = 1=6). The molecular configuration and energetic evolution of gas-phase (CuO) n clusters are first investigated using a combined simulated annealing-density functional theory (DFT) method, and the quantum size effect is found in planar cluster structures due to the scarcity of electron levels. Subsequently, by supporting the (CuO) n clusters on rutile-TiO2 (110) facets, the stability, the light-absorption ability, the charge separation efficiency, and the reactivity of excited electrons for different (CuO)(n)-TiO2 heterojunctions are analyzed. It is noted that (CuO)(3) and (CuO) 4 clusters have the best antiaggregation property, and the small clusters usually possess higher charge separation efficiency, whereas large clusters show better light-absorption performance. Photocatalytic hydrogen evolution reaction is favored on middle-sized CuO clusters-modified TiO2, e.g., (CuO)(3)-TiO2, due to its proper band alignment, high photoelectron reactivity, good light-absorption ability, and structural stability.