Advancing metal-organic frameworks and covalent organic frameworks for photocatalytic CO2 reduction.

Increasing atmospheric carbon dioxide concentration necessitates innovative approaches to transform CO2 into valuable compounds utilizing solar energy. The photocatalytic CO2 reduction reaction (PC CRR) offers a sustainable solution, yet wide band gaps, rapid electron-hole recombination, and poor CO2 adsorption capacity limit traditional metal oxide semiconductors for the PC CRR. This review systematically evaluates recent engineering advances in metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) as efficient photocatalysts for the PC CRR. Their intrinsic porosity, structural versatility, and well-defined modular architectures facilitate enhanced light absorption, efficient charge separation, and improved CO2 activation. Their electronic structures are easily regulated by ligand functionalization, metal substitution/introduction, and incorporating photosensitizers. Once they form a favorable heterojunction with other semiconductors, the interfacial electric field facilitates charge separation and transport, increasing the light utilization efficiency. MOFs can also be used as sacrificial templates to fabricate porous photocatalytic materials with enhanced light harvesting and high concentrations of active sites. After thoroughly discussing strategies for photocatalyst engineering, current challenges such as achieving more valuable hydrocarbons as reaction products are addressed, and future research directions are proposed.