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 (Pd 1 ) anchored g-C 3 N 4 (48CN/Pd) with UiO-66-NH 2 (UION). Under visible-light irradiation, the 40UION-CN/Pd composite shows 93.91 % of NO removal efficiency with only 2.73 % of NO 2 emissions and negligible catalyst deactivation. The DeNO x 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 SO 2 -rich flue gases. The mechanism exploration based on experimental investigations and density functional theory (DFT) calculations reveals that UION captures the NO 2 selectively produced by 48CN/Pd, simultaneously suppressing NO 2 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 NO 2 emission and catalyst deactivation during photocatalytic NO removal.