Computational insight into effective decomposition of NO_X gas pollutants using N-vacancies in graphitic carbon nitride

Nitrogen oxide (NOX) gas pollutants pose severe threats to human health, the ozone layer, and the global climate, and thus finding suitable materials and methods to efficiently remove NOX has been of great interest for years. By studying the related photocatalysis and surface reactions, we herein propose to use the graphitic carbon nitride (g-CN) film with N-vacancies (g-CNNV) to decompose NOX. Based on density functional theory (DFT) and time-dependent DFT calculations, we revealed the decomposition mechanism of NO/NO2 gas on g-CNNV. We found that the N-O bond cleavage of NOX is usually accompanied by the N occupying the N-vacancy and oxygen formation, and subsequent light excitation promotes the oxygen desorption from the g-CN surface through photochemical processes of intersystem crossing and conical intersection. We demonstrated that the g-CNNV film under illumination can effectively decompose NOX into harmless oxygen. Therefore, coating the g-CNNV film on the outer walls of buildings or chimneys may be a promising green and economical strategy for NOX removal, given that the sunlight and surface defects can synergistically affect the electronic states of adsorbates and facilitate their favorable transformation by gas-solid interaction. This work offers a deep understanding of the fundamental process of surface photocatalytic reactions.