Selective Photocatalytic Reduction of CO2 to CH4 over NU-1000 Metal-Organic Frameworks

CO2 adsorption and its subsequent utilization represent a promising avenue for mitigating climate change. The conver-sion of CO2 into valuable and useful products like carbon monoxide, methane, and methanol offers significant economic benefits. However, due to the low reactivity of CO2, the incorporation of CO2 adsorbents alongside catalytic materials has been pivotal in increasing the concentration of CO2 molecules around the catalytic sites. This strategy frequently relies on the precise deposition of the catalyst onto the adsorbent material. In this work, we explore NU-1000, a zirconium-based metal-organic framework originally designed as a CO2 adsorbent, to act as a selective photocatalyst for gas-phase CO2 reduction to CH4. NU-1000 contains UVA light-absorbing chromophore linkers, endowing it with the dual functionality of CO2 adsorbent and photocatalyst, which is crucial for efficient CO2 reutilization. Our research showcases an easily reproducible, and greener synthesis method for NU-1000 using micro-waves. We study the activity of NU-1000, including a functionalised variant, in the gas-phase photoreduction of CO2 to CH4 at room temperature and atmospheric pressure with electrons and protons derived from water. Remarkably, both the native and functionalised MOFs exhibit a rate of 170 and 800 μmol∙g-1∙h-1, respectively, alongside an exceptional selectivity of over 99%. These findings represent some of the highest reported values for gas phase CO2 photoreduction under atmospheric conditions. Our results provide a foundation for exploring materials that can serve as both catalysts and sorbents in the photocatalytic transformation of CO2 to value-added products.