Tetrahedral Keggin Core Tunes the Visible Light-Assisted Catalase-Like Activity of Icosahedral Keplerate Shell.

In this work, the effect of Keggin polyoxometalates encapsulated in Keplerate {MoFe} shell (K shell) on the visible light-assisted catalase-like activity (HO dismutation) of the resulting core-shell clusters PMo@K, SiMo@K, and BW@K was investigated. Superior photodismutation activity of PMo@K compared to that of K shell and two other core-shell clusters was discovered. The homogeneity of PMo@K and its improved oxidative stability, increased redox potential, and reduced band gap caused by a synergistic effect between the Keplerate shell and Keggin core seem reasonable to explain such a superiority. The light-dependent photocatalytic performance of PMo@K evaluated by action spectra revealed a maximum apparent quantum efficiency (AQY) at 400 nm, demonstrating the visible light-driven photocatalytic reaction. A first-order rate constant of 2 × 10 s and activation energy of 108.8 kJ mol alongside a turnover frequency of 0.036 s and a total turnover number of up to ∼3800 approved the effective photocatalytic activity and improved the oxidative stability of PMo@K. A nonradical photocatalytic mechanism through a Fe-OOH intermediate was proposed. Thus, the structure, optical activity, and oxidative stability of a host Keplerate-type nanocluster can be tuned significantly by encapsulation of a guest, like "cluster-in-cluster" structures, which opens the scope for introducing new visible light-sensitive hierarchical nanostructures.