High-efficiency photodriven coupling of CO2 and various epoxides via a multi-shelled hollow ZIF/MXene derived composite with low activation energy†

Photo-induced coupling of carbon dioxide (CO₂) and various epoxides is a promising pathway for synthesizing value-added chemicals but the process is hampered by the high activation energy, poor light absorption, and fast recombination of charge carriers. Herein, cobalt nanoparticles encapsulated in N-doped hierarchically porous carbon/TiO₂/MXene (CoNHPC/TM) composites were synthesized by pyrolysis, employing a multilayer ZIF-8@ZIF-67@ZIF-8@ZIF-67 (4L-ZIF)/MXene hybrid as a precursor. During thermolysis, 4L-ZIF was transformed into CoNHPC with a multi-shell hollow structure, while TiO₂ nanoparticles formed in situ on the MXene surface. This unique structure induces multiple reflections of internal light, thus increasing the efficiency of light energy harvesting and photothermal conversion, and improving mass diffusion and the separation efficiency of photogenerated carriers. Consequently, a 96% yield for cyclic carbonate was achieved by optimal CoNHPC/TM-8 under irradiation with full spectrum light at 350 mW cm⁻² for 6 h. Additionally, its high catalytic efficiency was maintained even under simulated flue gas conditions. Further investigations revealed a decrease in the activation energy and a synergistic photocatalytic–photothermal effect in the reaction systems with CoNHPC/TM-8. Our research provides inspiration for the rational design of MOF-based photocatalysts with desirable practical applicability for enhancing CO₂ transformation.