Fabricating CdS/Ag/BiVO4 Z-heterojunction for solvent-free photocatalytic oxidation of amines

Abstract

Imines are vital intermediate chemicals applied in organic synthesis, pharmaceuticals, and materials science. It is desirable but challenging to explore a green photocatalytic system, especially solvent-free photocatalysis, for the synthesis of imines from amines with molecular oxygen as an oxidant under mild reaction conditions. In the present study, a ternary CdS/Ag/BiVO₄ Z-heterojunction photocatalyst was designed and prepared for the photocatalytic oxidative coupling of benzylamine to N-benzylidenebenzylamine. Under solvent-free conditions, a yield of 92% of N-benzylidenebenzylamine with a selectivity of 99% was achieved over CdS/Ag/BiVO₄ in neat benzylamine with dioxygen as an oxidant at room temperature and ambient pressure. In the Z-scheme electronic transmission system, CdS worked as a reductive photocatalyst, while BiVO₄ acted as an oxidative photocatalyst. The oxygen vacancies in the catalyst and Ag nanoparticles in the catalyst with their plasmonic effect boosted light absorption, enhancing charge migration and photogenerated electron–hole separation on the contact interface. A photocatalytic mechanism was proposed based on controlled experiments. The catalyst exhibited good stability for five cycles, and the catalyst can be applied for the oxidative coupling of various amines to imines. This work provides a strategy for the rational design of photocatalytic oxidative coupling of amines to imines.