The weak adsorption of CO₂ and the fast recombination of photogenerated charges harshly restrain the photocatalytic CO₂ reduction efficiency. The simultaneous catalyst design with strong CO₂ capture ability and fast charge separation efficiency is challenging. Herein, taking advantage of the metastable characteristic of oxygen vacancy, amorphous defect Bi₂O₂CO₃ (named BO_vC) was built on the surface of defect-rich BiOBr (named BO_vB) through an in situ surface reconstruction progress, in which the CO₃²⁻ in solution reacted with the generated Bi^(3−x)+ around the oxygen vacancies. The in situ formed BO_vC is tightly in contact with the BO_vB and can prevent the further destruction of the oxygen vacancy sites essential for CO₂ adsorption and visible light utilization. Additionally, the superficial BO_vC associated with the internal BO_vB forms a typical heterojunction promoting the interface carriers’ separation. Finally, the in situ formation of BO_vC boosted the BOvB and showed better activity in the photocatalytic reduction of CO₂ into CO (three times compared to that of pristine BiOBr). This work provides a comprehensive solution for governing defects chemistry and heterojunction design, as well as gives an in-depth understanding of the function of vacancies in CO₂ reduction.

Two-dimensional graphitic carbon nitride (2D CN) shows superior photocatalytic performance due to high charge separation efficiency and the rich active sites endowed with a 2D structure. However, the 2D structure also induces the weaknesses of easier agglomeration and wider bandgap which can weaken the H₂ evolution capacity. Aiming to solve these defects, we prepared a brown mesoporous carbon nitride photocatalyst through phosphorus doping (BMCN). The phosphorus doping brings an excellent visible light response, a stable mesoporous structure with rich active sites, and a more negative CB potential. The optimized BMCN-50 shows a high H₂ evolution rate of 2.7 mmol g⁻¹ h⁻¹ which is over 5 times than that of pure 2D CN. The apparent quantum yields (AQYs) of BMCN-50 at 420 nm, 435 nm, 450 nm, and 550 nm are 4.2%, 4.0%, 3.6%, and 0.5%, respectively, which are higher than those of 2D CN (3.2%, 0.9%, 0.2%, and 0%). Besides, BMCN showed stable H₂ evolution performance even after being immersed in 10% TEOA solution for three months. This work presents an easy strategy to prepare a wide spectral response carbon nitride photocatalyst with a stable mesoporous nanostructure for more efficient photocatalytic H₂ evolution reaction.

With the development of the world economy and the rapid advancement of global industrialization, the demand for energy continues to grow. The significant consumption of fossil fuels, such as oil, coal, and natural gas, has led to excessive carbon dioxide emissions, causing global ecological problems. CO₂ hydrogenation technology can convert CO₂ into high-value chemicals and is considered one of the potential ways to solve the problem of CO₂ emissions. Metal/semiconductor catalysts have shown good activity in carbon dioxide hydrogenation reactions and have attracted widespread attention. Therefore, we summarize the recent research on metal/semiconductor catalysts for photocatalytic CO₂ hydrogenation from the design of catalysts to the structure of active sites and mechanistic investigations, and the internal mechanism of the enhanced activity is elaborated to give guidance for the design of highly active catalysts. Finally, based on a good understanding of the above issues, this review looks forward to the development of future CO₂ hydrogenation catalysts.