Plasmonic Au Nanoparticle of a Au/TiO2–C3N4 Heterojunction Boosts up Photooxidation of Benzyl Alcohol Using LED Light

Plasmonic Au nanoparticles (NPs) employing localized surface plasmon resonance excitation have exhibited superior visible light absorption for many organic transformations. In this work, we prepared a ternary composite catalyst comprising plasmonic Au NPs and a 2D/2D TiO2-C3N4 heterojunction via a photoreduction method of chloroauric acid in the presence of TiO2-C3N4. The introduction of plasmonic nanogold particles embedded onto the TiO2 surface of the TiO2-C3N4 heterojunction can significantly improve the photocatalytic performance during photooxidation of benzyl alcohol to benzaldehyde under mild conditions (1 bar air, white LED irradiation at ambient temperature). The productivity over Au/TiO2-C3N4 (0.25 mmolreacted BA gcat.-1 h-1) is found to be ∼5.6, 8.3, and 8.2-fold of these over the Au/TiO2, TiO2-C3N4, and C3N4-Au-TiO2 heterojunctions, respectively. Trapping experiments and electron spin resonance (ESR) spectroscopy confirm that the superoxide (·O2-) and hydroxyl radicals (·OH) act as the reactive oxygen species during photooxidation. Furthermore, the experimental results combined with density functional theory calculations reveal that the chemisorbed benzyl alcohol population, surface oxygen vacancies, and lifetime of photoexcited electrons and holes are largely improved by plasmonic Au NPs. This study on nanogold composites provides some hints for developing new efficient and practical photocatalysts.