Photocatalytic CO₂ reduction: Fundamental principles, mechanistic pathways and material-specific kinetic insights

The concentration of carbon dioxide (CO₂) in the atmosphere is increasing rapidly, causing several environmental problems and threatening the sustainability of life on Earth. The photocatalytic CO₂ reduction into renewable fuels and value-added chemicals represents a promising strategy for addressing global warming and the ongoing energy crisis. This review article provides a detailed overview of the basic principles and mechanistic pathways for photocatalytic CO₂ reduction, particularly highlighting the carbene, formaldehyde, and glyoxal pathways. In addition, the role of photocatalyst properties in the CO₂ reduction mechanism is also explained. It also discusses various factors affecting the photocatalytic performance, including photoexcitation strategies such as element doping, defect engineering, and surface plasmon resonance effects, as well as charge separation and transfer through co-catalyst loading and heterojunction formation. Furthermore, the effects of light intensity, CO₂ gas pressure, water activity, and sacrificial agents on photocatalytic CO₂ reduction have been discussed. Special attention is given to recent advances in MXene-, metal-organic framework (MOF)-, and TiO₂-based photocatalysts, whose high interfacial conductivity, structural versatility, and tunable electronic configurations enable efficient CO₂ reduction and value-added product formation. An in-depth interdependence between band structure, surface chemistry, and catalytic activity has been explored. Overall, this review offers mechanistic insights and design guidelines for developing next-generation photocatalysts capable of achieving high efficiency and durability in CO₂ conversion, thereby advancing sustainable carbon utilization and solar-to-fuel technologies.