Recent advances on cobalt metal organic frameworks (MOFs) for photocatalytic CO2 reduction to renewable energy and fuels: A review on current progress and future directions

Due to ever increasing environmental issues because of combustion of fossil fuels, production of renewable energy and fuels are highly demanding. Phototechnology with the use of solar energy is highly demanding for renewable fuels production. Although, different materials are under exploration, however, they are less efficient to make this technology to practical level of renewable fuels production. Cobalt (Co) based metal organic frameworks are gaining interests as photocatalyst for CO2 reduction due to its simple preparation with high photoactivity and stability. Hence, this review highlights the diverse Co-based MOFs and their applications in converting CO2 into solar fuels. Firstly, fundamentals of MOFs and photocatalytic CO2 reduction are discussed to provide insight over the nomenclature and mechanism of photocatalysis. Different Co-based MOFs are then discussed based on their structural and optical characteristics with their maximum tolerable temperature. Then, an in-depth analysis is carried out on various synthesis method for preparing different types of Co-MOFs. Different parameters such as reaction temperature, time, type of reagent and solvent used are then discussed to provide a clear picture on their effect on the formation and functionalization of MOFs. A comprehensive review is conducted on various approaches to enhance activity of pristine Co-MOFs for CO2 photo-reduction, which includes photosensitization, MOF templating, heterojunction formation and surface sensitization. Finally, a critical evaluation is carried out in view of band engineering, energy harvesting, stability and productivity to further boost the photo-conversion of CO2. The conclusions and future prospective are included for further investigation in solar energy assisted applications.