Two bimetal-doped (Fe/Co, Mn) polyoxometalate-based hybrid compounds for visible-light-driven CO2 reduction.

Two polyoxometalate (POM)-based hybrid compounds have been successfully designed and constructed by the hydrothermal method with molecular formulas [K(H2O)2FeII0.33Co0.67(H2O)2(DAPSC)]2{[FeII0.33Co0.67(H2O)(DAPSC)]2[FeII0.33Co0.67(H2O)4]2[Na2FeIII4P4W32O120]}·21.5H2O (1), and [Na(H2O)2FeII0.33Mn0.67(H2O)2(DAPSC)]2{[FeII0.33Mn0.67(H2O)(DAPSC)]2[FeII0.33Mn0.67(H2O)4]2[Na2FeIII4P4W32O120(H2O)2]}·24H2O (2) (DAPSC = 2,6-diacetylpyridine bis-(semicarbazone)), respectively. Structural analysis revealed that 1 and 2 consisted of metal-organic complexes containing DAPSC ligands with dumbbell-type inorganic clusters, iron-cobalt (iron-manganese) and some other ions. By utilizing a combination of strongly reducing {P2W12} units and bimetal-doped centres the CO2 photoreduction catalytic capacity of 1 and 2 was improved. Notably, the photocatalytic performance of 1 was much better than that of 2. In CO2 photoreduction, 1 exhibited CO selectivity as high as 90.8%. Furthermore, for 1, the CO generation rate reached 6885.1 μmol g-1 h-1 at 8 h with 3 mg, and its better photocatalytic performance was presumably due to the introduction of cobalt and iron elements to give 1 a more appropriate energy band structure. Further recycling experiments indicated that 1 was a highly efficient CO2 photoreduction catalyst, which could still possess catalytic activity after several cycles.