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

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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.