Tuning the reaction pathway of photocatalytic NO oxidation process to control the secondary pollution on monodisperse Au nanoparticles@g-C3N4

Oxidation of low-concentration nitrogen oxides (NOx) to nitrate with solar energy is an efficient way to remove them from atmospheric environment under semi-enclosed or ill-airflow conditions. However, conventional photocatalysts applied in NOx removal face the challenges of low efficiency and generation of toxic byproducts (nitrogen dioxide, NO2) leading to secondary pollution. To tackle these issues, monodisperse gold nanoparticles supported on graphitic carbon nitride (Au@CN) was designed and fabricated by a facile method. The Au@CN exhibited a highly enhanced nitric oxide (NO) oxidation activity and superior NO2 inhibition ability. The microstructures, optical properties and electronic structure of the photocatalysts were analyzed with advanced tools. The in situ diffuse reflectance infrared spectroscopy (DRIFTS) was applied to dynamically monitor and reveal the reaction process at time sequence. Density functional theory (DFT) and electron spin resonance (ESR) were combined to explore the oxidation mechanism at molecular level. It was found that (1) the presence of Au metal site favored the adsorption and activation of the gas molecules; (2) the high separation efficiency of the photogenerated electron-hole pairs enhanced the production of radicals for NO oxidation; (3) the unique electronic structure of Au@CN prefers nitrate formation with a low rate-determining barrier and largely suppress the toxic intermediate NO2, thus effectively controlling the secondary pollution. The present work could provide a novel mechanistic insight into visible-light photocatalytic NO oxidation and selectivity on Au@CN which is beneficial for designing efficient and safe photocatalyst with low environmental risk.