Carbon dioxide reduction catalyzed by a photoactive bimetallic zirconium/cerium metal-organic framework built with a (thieno)thiophene linker.

The development of efficient and stable photocatalysts for CO2 reduction remains a major challenge in solar fuel production. Herein, we report the synthesis and characterization of the novel bimetallic zirconium/cerium metal-organic framework [Zr5.96Ce0.04O4(OH)8(H2O)4(TTp)4] [H2TTp = (thieno)thiophene-2,5-dicarboxylic acid, Zr/Ce_TTp] used for CO2 reduction under UV-visible light irradiation. Crystal structure characterization confirms the formation of a mixed-metal framework of fcu topology with uniform element distribution. The material is porous (BET SSA = 1054 m2 g-1) and shows a good thermodynamic affinity for CO2 [Q st = 23.0 kJ mol-1]. Optical and electrochemical characterization studies reveal enhanced light-harvesting ability and superior charge separation properties compared to the monometallic analogues Zr_TTp and Ce_TTp. Under simulated solar irradiation, Zr/Ce_TTp displays significant photocatalytic activity for CO2 reduction to CO (5.8 µmol g-1 h-1) with no need of auxiliary co-catalysts, while no activity is observed for the individual metal-based materials. The improved performance is attributed to the synergistic interaction between the redox-active Ce centers and the robust Zr nodes, as well as the light-absorbing capability of the H2TTp linker. Periodic DFT calculations support the experimental findings, highlighting the role of open CeIII sites in CO2 activation and the improved spatial separation of the frontier orbitals in the bimetallic framework that reduces e-h+ recombination with respect to its homometallic analogues. These results highlight the potential of heterometallic MOFs featuring π-conjugated heterocyclic linkers as promising platforms for solar-driven CO2 valorization.