Au nanoparticles-anchored defective metal–organic frameworks for photocatalytic transformation of amines to imines under visible light

Designing efficient metal organic frameworks (MOF)-based photocatalysts has recently attracted wide attention. In this work, Au nanoparticles(NPs)-decorated defective DUT-67(Zr) (Au@DUT-67(Zr)) with enlarged channels was successfully fabricated and achieved 7.5 times higher conversion than Au NPs-decorated UiO-66(Zr) (Au@UiO-66(Zr)) for photocatalytic selective oxidation of amines to imines driven by visible light. Au NPs are more effectively fixed on DUT-67(Zr) due to its partially hollow structure. Au@DUT-67(Zr) possesses more active sites including unsaturated Zr atoms and oxygen vacancies (VO) than Au@UiO-66(Zr). In situ Fourier transform infrared (FTIR) spectrum reveals that benzylamine is activated on unsaturated Zr sites via HN…Zr species, facilitating deprotonation of -CH2 in benzylamine. VO can not only adsorb and activate oxygen (O2) but also capture plasmonic hot electrons, enhancing the forming of superoxide radical (O2-). Plasmonic hot holes assisted with O2- effectively achieve the selective oxidation of benzylamine. Finally, a possible synergetic mechanism combining the plasmon with the molecular activation is presented to illustrate the photocatalytic pathway at the molecular level.