Nitric oxide removal by synergistic photooxidation and adsorption using Pd1/g-C3N4-UiO-66-NH2 P-A heterojunction

Simultaneous avoidance of secondary air pollution and catalyst deactivation remains a challenge for existing photocatalytic removal of nitric oxide (NO). Herein, a photocatalysis-adsorption (P-A) heterojunction is synthesized for eco-friendly NO removal by facilely grinding Pd single atoms (Pd1) anchored g-C3N4 (48CN/Pd) with UiO-66-NH2 (UION). Under visible-light irradiation, the 40UION-CN/Pd composite shows 93.91 % of NO removal efficiency with only 2.73 % of NO2 emissions and negligible catalyst deactivation. The DeNOx index increases remarkably from-0.66 for 48CN/Pd to 0.86 for 40UION-CN/Pd. Furthermore, the synthesized P-A heterojunction efficiently removes NO from real flue gases produced by a domestic coal-fired stove and from SO2- rich flue gases. The mechanism exploration based on experimental investigations and density functional theory (DFT) calculations reveals that UION captures the NO2 selectively produced by 48CN/Pd, simultaneously suppressing NO2 emissions and refreshing active sites for NO photooxidation. Moreover, the results of X-ray photoelectron spectroscopy (XPS), charge density difference calculation, energy-resolved distribution of electron traps (ERDT) and in-situ Kelvin probe force microscopy (KPFM) reveal that the built-in electric field and Type-II heterojunction formed between 48CN/Pd and UION promote the separation of photogenerated carriers, enhancing the catalytic activity of the composite. This work provides an innovative strategy to avoid NO2 emission and catalyst deactivation during photocatalytic NO removal.