This work aims to investigate the role that defect states play in photoelectric and photocatalytic processes. Ternary Zn x Cd 1Àx S with wurtzite structure is firstly synthesized, and then the defect is characterized by photoluminescence (PL) spectroscopy. It is found that the photoelectrons trapped in surface defect states exhibit different behavior in the processes of photoelectric transfer and photocatalytic hydrogen evolution. During the photocatalytic process, the surface defect states in Zn x Cd 1Àx S act as the electron pool to improve the photocatalytic activity of water-splitting reaction. In comparison, the surface defect states serve as the recombination center that decreases the efficiency of photoelectric transfer. This finding is of great significance for the design of effective photoelectric and photocatalytic material in the field of solar energy conversion.

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The surface/interface synergy effect plays a positive role on the spatial separation and utilization of electrons and holes in photocatalytic process, which suggests a potential strategy for designing high efficiency photocatalysts.

Oxygen vacancies and Ti-related defects (OTDs) are the main lattice defects ofTiO2, which have great influence on its photocatalytic activity. To understand the relationship between the defects and photocatalytic activities, detailed discussions based on the electronic driven force provided by these defects are carried out during the three commonly accepted processes in photocatalytic reactions. It is found that these defects inevitably (i) influence the energy structure of the pristineTiO2as the isolate acceptor/donor level or hybrid with the original orbital, (ii) provide a disordered short-range force that confuses the charge carriers transferring to surface active sites, (iii) act not only as the surface active sites for trapping the charge carriers but also as the main chemisorption sites forO2,H2O, and organic species. These effects of the defects make them one of the key factors that determine the efficiency of heterogeneous photocatalysis. Clarifying the role of the defects will further facilitate the exploration and the construction of high-performance photocatalysts for practical applications.