Photocatalytic NOx Oxidation and Storage: An Alternative Technology for Airborne NOx Abatement Beyond the Point of Production

Abstract

Airborne nitrogen oxides (NOₓ) are among the most persistent urban pollutants, contributing to ozone formation, acid rain, and respiratory health issues. Beyond emission control at the source, photocatalytic NOₓ oxidation and storage (PHONOS) has emerged as a promising strategy for sustainable environmental remediation. This review systematically discusses the fundamental mechanisms, material developments, and practical aspects of photocatalytic NOₓ abatement. We first summarize the reaction pathways governing NO and NO₂ oxidation on TiO₂ and related semiconductors, emphasizing the roles of photogenerated holes, hydroxyl radicals, and surface-bound intermediates in determining selectivity toward nitrate. Next, we highlight advances in material design, including single-atom catalysts, doped TiO₂, g-C₃N₄ heterostructures, and oxygenate-modified surfaces that enhance visible-light activity and nitrate storage stability. The influence of environmental factors-such as humidity, reactant gas flow rate, and irradiation wavelength are also discussed. Existing scientific literature suggests that as a novel environmental airborne pollution abatement technology, PHONOS has the potential to evolve from a laboratory concept into a viable, sunlight-driven approach for actively improving urban air quality even far away from the point where pollution is generated.