Tailoring Multiscale Interfaces in Heterojunction Photocatalysis for NOx Removal

Nitrogen oxides (NO_x) severely threaten human health and ecosystems. Photocatalytic technology offers a promising solution for eliminating low-concentration yet highly toxic NO. However, it faces challenges in catalyst stability, control of intermediate and final products, reaction selectivity, and disclosure of interfacial mechanisms. The key to surmounting these hurdles is effective carrier separation, vital for distinct redox reactions in photocatalysts. Additionally, the charge carrier efficiency (formation, transfer, separation, and further dynamics) and catalyst photocorrosion upon light irradiation significantly influence the photocatalytic performance and long-term stability of metal oxide-based systems. Heterojunctions, with their superior charge carrier separation efficiency, can effectively regulate the reaction pathways during NO conversion. Moreover, heterojunction engineering has been proven to mitigate photocorrosion by optimizing interfacial charge transfer and reducing the level of charge accumulation on vulnerable active sites. Despite the proliferation of reviews on photocatalytic heterojunctions, a critical gap exists in works that systematically unify the classification, synthesis, and application of diverse heterojunctions specifically for NO removal, while explicitly linking multiscale interfacial engineering, e.g., atomic-level defects, nanoscale band alignment, molecular adsorption to the precise control of reaction pathways and selectivity. Addressing this gap, this review establishes an innovative, unified framework that integrates heterojunction principles, classifications, and construction methods with their operational performance in NO removal, with an emphasis on their latest advancements. Uniquely, it maps design strategies directly to overcome real-world bottlenecks, such as byproduct suppression, relative humidity resistance, and selectivity enhancement. It interprets the state-of-the-art applications, highlighting how interfacial engineering synergistically enhances carrier efficiency and product control. By emphasizing the significance of improving carrier efficiency and controlling intermediate/final product formation by reactive oxygen species generation, this review provides valuable insights to guide future research toward securing higher NO conversions and reaction selectivity. Additionally, it lays the groundwork for the development of more effective and eco-friendly environmental cleanup technologies.