Photocatalytic CO₂ reduction using metal-organic frameworks: Recent advances, challenges and machine learning based...

CO₂ conversion to value-added fuels and chemicals under photocatalytic conversion is a sustainable solution towards reducing the increasing carbon emission in the atmosphere as well as aiding in clean energy production. Metal organic frameworks (MOFs), which are comprised of transition-metal nodes and multifunctional organic linkers have been found to be highly promising photocatalysts in CO₂ reduction as they have a high surface area, structural, and CO₂ adsorption capacity. Their photoresponsive property, caused by the transfer of the ligand-to-metal charge, or metal-oxo cluster excitation permits the effective generation and separation of charge carriers, necessary to drive multi-electron reduction reactions of CO₂. This review offers a detailed description of the state-of-the-art MOF-based systems on the photoreduction of CO₂ to major products of CH₄, CH₃OH, HCOOH, and CO. Specific attention is paid to the functionalization of linkers, deposition of metal nanoparticles, heterojunction, and co-catalysts engineering, which have a considerable impact on increasing its activity and selectivity of products. The mechanistic knowledge behind charge transfer, intermediate stabilization, and adsorption phenomena are explained in detail. Besides this, the review demonstrates the prevailing bottlenecks, such as charge recombination, low quantum yields, and poor long-term stability, and how machine learning methods could be used to speed up the prediction and optimization of high-performance MOF photocatalysts. Overall, MOFs still have an enormous potential in solar-based CO₂ valorization, but improvements in stability and reactor integration are required before they can be used in practice.