Structuring Pd Nanoparticles on 2H-WS2 Nanosheets Induces Excellent Photocatalytic Activity for Cross-Coupling Reactions under Visible Light.

Effective photocatalysts and their surface engineering are essential for the efficient conversion of solar energy into chemical energy in photocatalyzed organic transformations. Herein, we report an effective approach for structuring Pd nanoparticles (NPs) on exfoliated 2H-WS2 nanosheets (WS2/PdNPs), resulting in hybrids with extraordinary photocatalytic activity in Suzuki reactions under visible light. Pd NPs of different sizes and densities, which can modulate the photocatalytic activity of the as-prepared WS2/PdNPs, were effectively structured on the basal plane of 2H-WS2 nanosheets via a sonic wave-assisted nucleation method without any reductants at room temperature. As the size of Pd NPs on WS2/PdNPs increased, their photocatalytic activity in Suzuki reactions at room temperature increased substantially. In addition, it was found that protic organic solvents play a crucial role in activating WS2/PdNPs catalysts in photocatalyzed Suzuki reactions, although these solvents are generally considered much less effective than polar aprotic ones in the conventional Suzuki reactions promoted by heterogeneous Pd catalysts. A mechanistic investigation suggested that photogenerated holes are transferred to protic organic solvents, whereas photogenerated electrons are transferred to Pd NPs. This transfer makes the Pd NPs electron-rich and accelerates the rate-determining step, i.e., the oxidative addition of aryl halides under visible light. WS2/PdNPs showed the highest turnover frequency (1244 h-1) for photocatalyzed Suzuki reactions among previously reported photocatalysts.