Photocatalytic Cascade Reaction Driven by Directed Charge Transfer over VS-Zn0.5Cd0.5S/GO for Controllable Benzyl Oxidation

Photocatalysis is an important technique for synthetic transformations. However, little attention has been paid to light-driven synergistic redox reactions for directed synthesis. Herein, the authors report tunable oxidation of benzyl to phenylcarbinol with the modest yield (47%) in 5 h via singlet oxygen (O-1(2)) and proton-coupled electron transfer (PCET) over the photocatalyst Zn0.5Cd0.5S (ZCS)/graphene oxide (GO) under exceptionally mild conditions. Theoretical calculations indicate that the presence of S vacancies on the surface of ZCS/GO photocatalyst is crucial for the adsorption and activation of O-2, successively generating the superoxide radical (O-center dot(2)-) and O-1(2), attributing to the regulation of local electron density on the surface of ZCS/GO and photogenerated holes (h(+)). Meanwhile, accelerated transfer of photogenerated electrons (e(-)) to GO caused by the pi-pi stacking effect is conducive to the subsequent aldehyde hydrogenation to benzyl alcohol rather than non-selective oxidation of aldehyde to carboxylic acid. Anisotropic charge transport driven by the built-in electric field can further promote the separation of e(-) and h(+) for multistep reactions. Promisingly, one-pot photocatalytic conversion of p-xylene to 4-methylbenzyl alcohol is beneficial for reducing the harmful effects of aromatics on human health. Furthermore, this study provides novel insights into the design of photocatalysts for cascade reactions.

Automated summary

This study reports a light-driven synergistic redox reaction for the selective oxidation of benzyl to phenylcarbinol using Zn0.5Cd0.5S/graphene oxide photocatalyst. The presence of S vacancies on the surface of the photocatalyst plays a crucial role in the adsorption and activation of oxygen, generating superoxide radicals and singlet oxygen. The pi-pi stacking effect between the photocatalyst and graphene oxide accelerates the transfer of photogenerated electrons and promotes the selective hydrogenation of aldehydes.