Semiconductor photocatalysts have attracted increased attention due to their great potential for solving energy and environmental problems. The formation of Z‐scheme photocatalytic systems that mimic natural photosynthesis is a promising strategy to improve photocatalytic activity that is superior to single component photocatalysts. The connection between photosystem I (PS I) and photosystem II (PS II) are crucial for constructing efficient Z‐scheme photocatalytic systems using two photocatalysts (PS I and PS II). The present review concisely summarizes and highlights recent state‐of‐the‐art accomplishments of Z‐scheme photocatalytic systems with diverse connection modes, including i) with shuttle redox mediators, ii) without electron mediators, and iii) with solid‐state electron mediators, which effectively increase visible‐light absorption, promote the separation and transportation of photoinduced charge carriers, and thus enhance the photocatalytic efficiency. The challenges and prospects for future development of Z‐scheme photocatalytic systems are also presented.

Vacancy engineering, that is, self-doping of vacancy in semiconductors, has become a commonly used strategy to tune the photocatalytic performances. However, there still lacks fundamental understanding of the role of the vacancies in semiconductor materials. Herein, the g-C₃N₄ nanosheets with tunable nitrogen vacancies are prepared as the photocatalysts for H₂ evolution and CO₂ reduction to CO. On the basis of both experimental investigation and DFT calculations, nitrogen vacancies in g-C₃N₄ induce the formation of midgap states under the conduction band edge. The position of midgap states becomes deeper with the increasing of nitrogen vacancies. The g-C₃N₄ nanosheets with the optimized density of nitrogen vacancies display about 18 times and 4 times enhancement for H₂ evolution and of CO₂ reduction to CO, respectively, as compared to the bulk g-C₃N₄. This is attributed to the synergistic effects of several factors including (1) nitrogen vacancies cause the excitation of electrons to midgap states below the conduction band edge, which results in extension of the visible light absorption to photons of longer wavelengths (up to 598 nm); (2) the suitable midgap states could trap photogenerated electrons to minimize the recombination loss of photogenerated electron–hole pairs; and (3) nitrogen vacancies lead to uniformly anchored small Pt nanoparticles (1–2 nm) on g-C₃N₄, and facilitate the electron transfer to Pt. However, the overintroduction of nitrogen vacancies generates deeper midgap states as the recombination centers, which results in deterioration of photocatalytic activities. Our work is expected to provide new insights for fabrication of nanomaterials with suitable vacancies for solar fuel generation.