Considering the high energy demand in modern society and the widespread acceptance of "carbon neutrality" policies, reducing CO 2 into value-added products through "artificial carbon cycling" seems more reasonable and attractive. [3,4] Among the various methods of CO 2 resource utilization, photocatalysis (PC), electrocatalysis (EC) and photoelectrocatalysis (PEC), which can be operated at room temperature and atmospheric pressure, are considered to be a relatively feasible scheme. [5][6][7][8][9] Photocatalysis based on semiconductor materials can directly absorb solar light and generate charge carriers with redox capability, simultaneously accomplishing energy storage and carbon reduction. [10][11][12][13] Electrocatalysis can be driven by multiple forms of renewable energy (solar energy, water energy, wind energy, biomass energy, wave energy, tidal energy, etc.) to realize the conversion of CO 2 at the suitable negative potential. [14][15][16] Photo electrocatalysis is a special combination of photocatalysis and electrocatalysis, using a semiconductor electrode with light response capability to achieve efficient CO 2 reduction. [17,18] However, CO 2 exhibits chemical inertness due to its linear molecular and high CO bond energy, which is owing to the adoption of sp hybrid orbital when C atoms bond with O atoms. [19][20][21] Therefore, it is challenging to activate CO 2 and convert it into desirable products thermodynamically. [22] In addition, the CO 2 reduction reaction involves multi-step electron transfer, hydrogenation and CC bond coupling, which determines it has a complex and stochastic reaction path. Therefore, developing an ideal catalyst with high activity, stability, and economy for CO 2 reduction is necessary.Since Inoue et al. successfully converted CO 2 into formic acid, formaldehyde, methanol and methane under sunlight irradiation, many semiconductor materials for CO 2 reduction have been developed and evaluated. [23][24][25][26] The n-type semiconductors, including TiO 2 , ZnO 2 and SrTiO 3 , have attracted wide attention due to their low cost, high photostability and environmental harmlessness. [27] However, the excessive band gap limits their light response range, making them unsuitable for the CO 2 conversion systems driven by solar light. [28,29] Cuprous oxide (Cu 2 O), as one of the copper-based semiconductors with abundant reserves on the earth, has a suitable band gap to absorb visible light, which occupies 42-43% of the solar spectrum. More Converting CO 2 into value-added products by photocatalysis, electrocatalysis, and photoelectrocatalysis is a promising method to alleviate the global environmental problems and energy crisis. Among the semiconductor materials applied in CO 2 catalytic reduction, Cu 2 O has the advantages of abundant reserves, low price and environmental friendliness. Moreover, Cu 2 O has unique adsorption and activation properties for CO 2 , which is conducive to the generation of C 2+ products through CC coupling. This review introduces the basic principles of CO...

Photocatalysis driven by solar energy is a feasible strategy to alleviate energy crises and environmental problems. In recent years, significant progress has been made in developing advanced photocatalysts for efficient solar‐to‐chemical energy conversion. Single‐atom catalysts have the advantages of highly dispersed active sites, maximum atomic utilization, unique coordination environment, and electronic structure, which have become a research hotspot in heterogeneous photocatalysis. This paper introduces the potential supports, preparation, and characterization methods of single‐atom photocatalysts in detail. Subsequently, the fascinating effects of single‐atom photocatalysts on three critical steps of photocatalysis (the absorption of incident light to produce electron‐hole pairs, carrier separation and migration, and interface reactions) are analyzed. At the same time, the applications of single‐atom photocatalysts in energy conversion and environmental protection (CO2 reduction, water splitting, N2 fixation, organic macromolecule reforming, air pollutant removal, and water pollutant degradation) are systematically summarized. Finally, the opportunities and challenges of single‐atom catalysts in heterogeneous photocatalysis are discussed. It is hoped that this work can provide insights into the design, synthesis, and application of single‐atom photocatalysts and promote the development of high‐performance photocatalytic systems.

Photocatalytic CO2 reduction to valuable fuels is a promising way to alleviate anthropogenic CO2 emissions and energy crises. Perovskite oxides have attracted widespread attention as photocatalysts for CO2 reduction by virtue of their high catalytic activity, compositional flexibility, bandgap adjustability, and good stability. In this review, the basic theory of photocatalysis and the mechanism of CO2 reduction over perovskite oxide are first introduced. Then, perovskite oxides' structures, properties, and preparations are presented. In detail, the research progress on perovskite oxides for photocatalytic CO2 reduction is discussed from five aspects: as a photocatalyst in its own right, metal cation doping at A and B sites of perovskite oxides, anion doping at O sites of perovskite oxides and oxygen vacancies, loading cocatalyst on perovskite oxides, and constructing heterojunction with other semiconductors. Finally, the development prospects of perovskite oxides for photocatalytic CO2 reduction are put forward. This article should serve as a useful guide for creating perovskite oxide‐based photocatalysts that are more effective and reasonable.

Covalent organic frameworks (COFs) are one type of porous organic materials linked by covalent bonds. COFs materials exhibit many outstanding characteristics such as high porosity, high chemical and thermal stability, large specific surface area, efficient electron transfer efficiency, and the ability for predesigned structures. These exceptional advantages enable COFs materials to exhibit remarkable performance in photocatalysis. Additionally, the activity of COFs materials as photocatalysts can be significantly upgraded by ion doping and the formation of heterojunctions. This paper summarizes the latest research progress on COF‐based materials applied in photocatalytic systems. Initially, typical structures and preparation methods of COFs are analyzed and compared. Moreover, the essential principles of photocatalytic reactions over COFs‐based materials and the latest research developments in photocatalytic hydrogen production, CO2 reduction, pollutants elimination, organic transformation, and overall water splitting are indicated. At last, the outlook and challenges of COF‐based materials in photocatalysis are discussed. This review is intended to permit instructive guidance for the efficient use of photocatalysis based on COFs in the future.