Metal-organic frameworks for photocatalytic CO₂ reduction: recent advances, design principles, and mechanistic...

The rising atmospheric CO₂ levels demand sustainable technologies for converting CO₂ into fuels and chemicals. Photocatalytic CO₂ reduction mimics natural photosynthesis but faces great challenges from the inertness of CO₂, high CO bond energy, slow kinetics, and competing hydrogen evolution. With ultrahigh surface areas, tunable porosity, and modular architectures, metal-organic frameworks (MOFs) serve as a versatile platform, enabling molecular-level integration of light harvesting and catalysis to overcome these limitations. Rational optimization via linker functionalization, heterometal doping, defect engineering, heterojunctions, and morphology control has improved the efficiency and selectivity in CO₂ photoreduction. This review summarizes recent advances in framework engineering and their photophysical mechanisms. Despite progress, there still remain great challenges, such as limited visible-light absorption, low charge mobility, rapid recombination, poor stability, difficulty achieving C₂₊ products, and insufficient operando understanding. Future efforts should focus on π-conjugated frameworks, conductive linkers, single-atom/dual-site centers to enable C-C coupling, and in situ/operando spectroscopies combined with theoretical analysis. Moreover, developing sacrificial-agent-free systems using water as an electron donor shows great promise for practical solar-fuel production.