Engineering Dual Active Sites of Au Nanoparticles and Nitrogen Vacancies for Enhanced Photocatalytic Toluene Selective Oxidation

The efficient and selective activation of C(sp³)-H bonds in toluene plays a pivotal role in the synthesis of value-added chemicals, yet achieving this transformation under mild conditions remains a challenge. Herein, the Au nanoparticles supported on rich-nitrogen vacancies on C₃N₄ (AuNPs/C₃N₄-N_V) are synthesized via Ar atmosphere calcination and photoinduced deposition. The electronic state and coordination environment of Au species, as well as nitrogen vacancies, are systematically elucidated using X-ray absorption fine structure (XAFS), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and in situ Fourier-transform infrared (in situ FT-IR). Optical and electrochemical analyses further reveal that the synergistic effects of AuNPs and nitrogen vacancies significantly enhanced visible-light absorption and improved the charge carrier separation efficiency. The optimized AuNPs/C₃N₄-N_V photocatalyst demonstrated remarkably raised conversion and selectivity for photocatalytic toluene oxidation to benzaldehyde under an O₂ atmosphere at room temperature. The controlled experiments, TMB oxidation reaction, and in situ spectral analysis and DFT calculations confirmed that during the photocatalytic oxidation of toluene, oxygen preferentially activated at the Au site to form superoxide radicals and then transferred to AuNPs and N vacancy sites to participate in the oxidation of toluene, thereby promoting the selective oxidation of toluene to benzaldehyde. This work shows the great potential of multisite catalysts in C(sp³)-H bond activation under mild conditions driven by renewable solar energy.