Materials Design and Development of Photocatalytic NO_x Removal Technology

Nitrogen oxide (NO_x) pollutants have a significant impact on both the environment and human health. Photocatalytic NO_x removal offers a sustainable and eco-friendly approach to combatting these pollutants by harnessing renewable solar energy. Photocatalysis demonstrates remarkable efficiency in removing NO_x at sub-scale levels of parts per billion (ppb). The effectiveness of these catalysts depends on various factors, including solar light utilization efficiency, charge separation performance, reactive species adsorption, and catalytic reaction pathway selectivity. Moreover, achieving high stability and efficient photocatalytic activity necessitates a multifaceted materials design strategy. This strategy encompasses techniques such as ion doping, defects engineering, morphology control, heterojunction construction, and metal decoration on metal- or metal oxide-based photocatalysts. To optimize photocatalytic processes, adjustments to band structures, optimization of surface physiochemical states, and implementation of built-in electric field approaches are imperative. By addressing these challenges, researchers aim to develop efficient and stable photocatalysts, thus contributing to the advancement of environmentally friendly NO_x removal technologies. This review highlights recent advancements in photocatalytic NO_x removal, with a focus on materials design strategies, intrinsic properties, fundamental developmental aspects, and performance validation. This review also presents research gaps, emphasizing the need to understand the comprehensive mechanistic photocatalytic process, favored conditions for generating desired reactive species, the role of water concentration, temperature effects, inhibiting strategies for photocatalyst-deactivating species, and the formation of toxic NO₂.