Ultrathin WO Nanosheets Converted from Metallic WS Sheets by Spontaneous Formation and Deposition of PdO Nanoclusters for Visible Light-Driven C-C Coupling Reactions.

It is not facile to obtain ultrathin two-dimensional (2D) WO nanosheets through the exfoliation of their bulk counterpart in solution due to strong covalent interaction between interlayers. In addition, they require additional functionalization with cocatalysts to expand their applicability in photocatalytic organic reactions owing to their insufficient conduction band edge position. Here, we report a chemical approach for the simultaneous production and functionalization of ultrathin 2D WO nanosheets through the direct conversion of metallic WS nanosheets, accomplished by the spontaneous formation and deposition of PdO nanoclusters on the nanosheet surface in HO. When chemically exfoliated metallic WS nanosheets were simply mixed with KPdCl in HO under mild conditions (50 °C, 1 h), they were converted to semiconducting WO nanosheets on which PdO nanoclusters of a uniform size (∼3 nm) were spontaneously formed, leading to the production of PdO-functionalized ultrathin WO (PdO@WO) nanohybrids. The conversion yield of WO nanosheets from metallic WS nanosheets increased with increasing coverage of PdO nanoclusters on the nanosheet surface. In addition, the conversion of WO nanosheets induced by PdO nanocluster formation was effective only in HO but not in organic solvents, such as -methylpyrrolidone and acetonitrile. A mechanical study suggests that the chemisorption of hydrated Pd precursors on the chalcogens of metallic WS nanosheets leads to their facile oxidation by water molecules, producing WO nanosheets covered with PdO nanoclusters. The as-prepared PdO@WO nanosheets exhibited excellent photocatalytic activity and recyclability in Suzuki cross-coupling reactions of various aryl halides under visible light irradiation.