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 {Mo72Fe30} shell (K shell) on the visible light-assisted catalase-like activity (H2O2 dismutation) of the resulting core-shell clusters PMo12@K, SiMo12@K, and BW12@K was investigated. Superior photodismutation activity of PMo12@K compared to that of K shell and two other core-shell clusters was discovered. The homogeneity of PMo12@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 PMo12@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 × 10-4 s-1 and activation energy of 108.8 kJ mol-1 alongside a turnover frequency of 0.036 s-1 and a total turnover number of up to ∼3800 approved the effective photocatalytic activity and improved the oxidative stability of PMo12@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.

The enhanced visible-light-induced photocatalytic activities of bimetallic Mn-Fe MOFs for the highly efficient reductive removal of Cr(vi).

The photocatalytic efficiencies of bimetallic MOFs, namely STA-12-Mn-Fe, for the reductive removal of Cr(vi) were explored. The best effective variable values were obtained and correlation between the response and influential variables was optimized via experimental design methodology. Complete Cr(vi) removal was achieved under natural sunlight and fluorescent 40 W lamp radiation at pH 2, with an initial Cr(vi) concentration of 20 mg L-1, and 10 mg of photocatalyst within 30 min. A pseudo-first-order rate constant of 0.132 min-1 at T = 298 K was obtained for the Cr(vi) reduction reaction. The title catalysts revealed high performance in the visible region based on photoefficiency measurements, while improved activity was observed compared to the corresponding single-metal MOFs under natural sunlight, highlighting the synergistic effect between the two metal ions. Trapping experiment results proved that direct electron transfer is the main pathway during the photocatalytic Cr(vi) reduction process.

A nanoscopic icosahedral {Mo72Fe30} cluster catalyzes the aerobic synthesis of benzimidazoles.

In this study, the catalytic efficiency of amorphous {Mo72Fe30} nanocapsules as a safe Keplerate polyoxometalate in organic synthesis was exploited. The easy-made solid catalyst exhibited high efficiency using a very low dosage (0.02-0.05 mol%) in the catalyzed condensation of various aromatic 1,2-diamines and aldehydes for the aerobic synthesis of benzimidazoles with very small E-factor values (0.11-0.33). The superior catalytic activity of amorphous nanoclusters compared to that of its crystalline counterpart was demonstrated. The high activity and recyclability of heterogeneous catalysts in a green reaction media under oxygen atmosphere, make this environmentally benign organic process appropriate for our applied goals.