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

Abstract

Nitrogen oxide (NO_X) 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 NO_X 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-CN_NV) to decompose NO_X. Based on density functional theory (DFT) and time-dependent DFT calculations, we revealed the decomposition mechanism of NO/NO₂ gas on g-CN_NV. We found that the N–O bond cleavage of NO_X 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-CN_NV film under illumination can effectively decompose NO_X into harmless oxygen. Therefore, coating the g-CN_NV film on the outer walls of buildings or chimneys may be a promising green and economical strategy for NO_X 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.