Visible-Light-Driven CO₂ Reduction Using Imidazole-Based Metal-Organic Frameworks as Heterogeneous Photocatalysts

The development of robust, efficient, and cost-effective heterogeneous photocatalysts for visible light-driven CO₂ reduction continues to be a significant challenge in the quest for sustainable energy solutions. As a result, increasing attention is being directed towards the exploration of high-performance photocatalysts capable of converting CO₂ into valuable chemical feedstocks. In context to this, Imidazolate Frameworks Potsdam (IFPs), a class of metal-organic frameworks (MOFs), can be a promising candidate for CO₂ photoreduction due to their ease of synthesis, use of low-cost, earth-abundant metals, and high chemical and thermal stability. In this study, we report the solvothermal synthesis of Zn(II)- and Co(II)-based IFPs, specifically IFP-1(Zn) and IFP-5(Co), for photocatalytic CO₂ reduction. Moreover, we demonstrate the enhanced photocatalytic activity of redox-innocent Zn-based IFP-1 by partially substituting Zn(II) with redox-active Co(II) in IFP-1(Zn), resulting in the formation of a bimetallic photocatalyst, IFP-1(Zn/Co). The metal-exchanged IFP-1(Zn/Co) exhibited significantly improved CO evolution (637 μmol g^-1 in 1 hour), compared to the pristine IFP-1(Zn) (29 μmol g^-1). Notably, among all the prepared photocatalysts, IFP-5(Co) outperformed both the systems, achieving a CO evolution of 1174 μmol g^-1 within 1 hour, due to the presence of catalytic cobalt sites. In addition, through the combination of photophysical and electrochemical studies, along with DFT calculations, we have proposed a plausible mechanism for the photocatalytic CO₂ reduction.