Semiconductor-based photocatalysis attracts wide attention because of its ability to directly utilize solar energy for production of solar fuels, such as hydrogen and hydrocarbon fuels and for degradation of various pollutants. However, the efficiency of photocatalytic reactions remains low due to the fast electron-hole recombination and low light utilization. Therefore, enormous efforts have been undertaken to solve these problems. Particularly, properly engineered heterojunction photocatalysts are shown to be able to possess higher photocatalytic activity because of spatial separation of photogenerated electron-hole pairs. Here, the basic principles of various heterojunction photocatalysts are systematically discussed. Recent efforts toward the development of heterojunction photocatalysts for various photocatalytic applications are also presented and appraised. Finally, a brief summary and perspectives on the challenges and future directions in the area of heterojunction photocatalysts are also provided.

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Recently, great attention has been paid to fabricating direct Z‐scheme photocatalysts for solar‐energy conversion due to their effectiveness for spatially separating photogenerated electron–hole pairs and optimizing the reduction and oxidation ability of the photocatalytic system. Here, the historical development of the Z‐scheme photocatalytic system is summarized, from its first generation (liquid‐phase Z‐scheme photocatalytic system) to its current third generation (direct Z‐scheme photocatalyst). The advantages of direct Z‐scheme photocatalysts are also discussed against their predecessors, including conventional heterojunction, liquid‐phase Z‐scheme, and all‐solid‐state (ASS) Z‐scheme photocatalytic systems. Furthermore, characterization methods and applications of direct Z‐scheme photocatalysts are also summarized. Finally, conclusions and perspectives on the challenges of this emerging research direction are presented. Insights and up‐to‐date information are provided to give the scientific community the ability to fully explore the potential of direct Z‐scheme photocatalysts in renewable energy production and environmental remediation.

In recent years, heterogeneous photocatalysis has received much research interest because of its powerful potential applications in tackling many important energy and environmental challenges at a global level in an economically sustainable manner. Due to their unique optical, electrical, and physicochemical properties, various 2D graphene nanosheets-supported semiconductor composite photocatalysts have been widely constructed and applied in different photocatalytic fields. In this review, fundamental mechanisms of heterogeneous photocatalysis, including thermodynamic and kinetics requirements, are first systematically summarized. Then, the photocatalysis-related properties of graphene and its derivatives, and design rules and synthesis methods of graphene-based composites are highlighted. Importantly, different design strategies, including doping and sensitization of semiconductors by graphene, improving electrical conductivity of graphene, increasing eloectrocatalytic active sites on graphene, strengthening interface coupling between semiconductors and graphene, fabricating micro/nano architectures, constructing multi-junction nanocomposites, enhancing photostability of semiconductors, and utilizing the synergistic effect of various modification strategies, are thoroughly summarized. The important applications including photocatalytic pollutant degradation, H production, and CO reduction are also addressed. Through reviewing the significant advances on this topic, it may provide new opportunities for designing highly efficient 2D graphene-based photocatalysts for various applications in photocatalysis and other fields, such as solar cells, thermal catalysis, separation, and purification.

Heterogeneous photocatalysis using semiconductors and renewable solar energy has been regarded as one of the most promising processes to alleviate, and even solve, both the world crises of energy supply and environmental pollution. In the past few years, many encouraging achievements have been made in the research area of graphene-based semiconductor photocatalysts. Among them, CdS/graphene nanocomposites have attracted extensive attention as an important kind of photocatalyst in chemical and material science, due to its superior photocatalytic activity and photostability under visible-light irradiation. The aim here is to address the enhancement mechanism of the photocatalytic performance of CdS/graphene composite photocatalysts, and systematically summarize recent progress regarding the design and synthesis of CdS/graphene nanocomposites. These nanocomposites are promising for a great diversity of applications in visible-light photocatalytic fi elds, including artifi cial photosynthetic systems (photocatalytic hydrogen production and CO 2 reduction), environmental remediation, and organic photosynthesis. Special attention is given to the photocatalytic hydrogen production and pollutant photodegradation over CdS/graphene nanocomposite photocatalysts. Furthermore, perspectives on CdS/graphene-based materials are discussed, including the various remaining challenges for large-scale applications, identifying prospective areas for related research in this fi eld.