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Adsorption and activation of C–H bonds by photocatalysts are crucial for the efficient conversion of C–H bonds to produce high-value chemicals. Nevertheless, the delivery of surface-active oxygen species for C–H bond oxygenation inevitably needs to overcome obstacles due to the separated active centers, which suppresses the catalytic efficiency. Herein, Ni dopants are introduced into a monolayer Bi2WO6 to create cascaded active units consisting of unsaturated W atoms and Bi/O frustrated Lewis pairs. Experimental characterizations and density functional theory calculations reveal that these special sites can establish an efficient and controllable C–H bond oxidation process. The activated oxygen species on unsaturated W are readily transferred to the Bi/O sites for C–H bond oxygenation. The catalyst with a Ni mass fraction of 1.8% exhibits excellent toluene conversion rates and high selectivity towards benzaldehyde. This study presents a fascinating strategy for toluene oxidation through the design of efficient cascaded active units. By introducing Ni dopants into monolayer Bi2WO6, Bi/O frustrated Lewis pairs, unsaturated W atoms, and Ni active units are formed. The authors show that these units facilitate oxygen species transfer and enhance photocatalytic toluene oxidation. [ABSTRACT FROM AUTHOR]

Optimizing the structure of semiconductor materials and introducing functional metal clusters have emerged as an effective strategy to improve the photocatalytic performances of catalysts through the synergistic effect between metals and supports. In this work, Pt nanocluster decorated hierarchical Sb2WO6 microspheres which are assembled from ultra-thin nanosheets with only 3.3 nm thickness (Pt/SWO-NS) jointly achieve an efficient photocatalytic reduction of nitrobenzene to aniline and show 10 times higher activity than Pt decorated bulk Sb2WO6 (Pt/SWO-bulk). More importantly, the respective roles of SWO-NS and Pt nanoclusters are deeply studied. SWO-NS with a unique 2D structure, abundant unsaturated surface sites and good visible light response would be favorable for stabilizing Pt nanoclusters, adsorbing and activating more nitrobenzene molecules and providing abundant photo-generated electrons. Meanwhile, Pt nanoclusters serve as electron enrichment centers to decompose HCOONH4 to produce rich ·CO2− and active H for reducing the activated nitrobenzene molecules. In addition, on combining coordination chemistry, a possible synergistic mechanism for hierarchical Sb2WO6 microspheres and Pt nanoclusters is proposed to elucidate the efficient reduction of nitrobenzene to aniline. We believe that this work would provide an effective strategy to optimize catalytic performance by the design of applicable nanocomposites with synergistic effects. [ABSTRACT FROM AUTHOR]

Creating accessible unsaturated active sites in metal-organic frameworks (MOFs) holds great promise for developing highly efficient catalysts. Herein, ultrathin Ni MOF-74 nanosheets (NMNs) with high-density coordinatively unsaturated Ni II centers are prepared as a photocatalyst. The results of in situ ATR-IR, Raman, UV-vis DRS, and XPS suggest that abundant Ni II centers can act as the active sites for boosting benzylamine (BA) activation via forming -Ni-NH 2 - coordination intermediates. The generation of coordination intermediates assists the transfer of photo-generated holes to BA molecules for producing BA cation free radicals, better impelling the breaking of N-H bonds and the photooxidation of BA molecules. The photo-generated electrons further activate O 2 molecules to O 2 •- radicals for triggering the reaction. The experiments reveal that the coordination activation of BA molecules may be a rate-determining step on NMNs rather than the adsorption and activation of O 2 molecules. Moreover, NMNs possess a better ability for the separation of photo-generated carriers in comparison with bulk Ni MOF-74 (NMBs). As a result, NMNs achieve a kinetic rate constant of 0.538 h -1 for the photocatalytic oxidative coupling of BA under visible light, about 50 times higher than that of NMBs (0.0011 h -1 ). Finally, a probable synergetic catalytic mechanism with coordination activation and photocatalysis is discussed on a molecular level. This study not only highlights the importance of coordination activation for heterogeneous photocatalysis but also affords an inspiration for building ultrathin MOF nanosheets.