Typical layered structure bismuth-based photocatalysts for photocatalytic nitrogen oxides oxidation.

Traditional NOx treatment methods require external reducing reagents and harsh reaction conditions, which is not conducive to effectively eliminate NOx at low concentration, especially at ppb levels. Fortunately, low concentration NOx can be removed by photocatalytic oxidation under mild reaction conditions. Bismuth (Bi)-based photocatalysts with the layered structure have obtained considerable concerns of photocatalytic NOx oxidation. This review focused on typical layered Bi-based photocatalysts (Bi2WO6, Bi2O2CO3, BiOY (YCl, Br, and I), BiOIO3, and BiOCOOH) with the structure of [Bi2O2]2+ layer for photocatalytic NOx oxidation. The strategies (morphological control, defect engineering, heterostructure construction, etc.) to improve photocatalytic oxidation activity were summarized. Furthermore, the mechanism involving various free radicals (hydroxyl radical, superoxide radical, etc.) of photocatalytic oxidation of NOx was proposed. In addition, the non-NO2 selectivity was also illuminated. Lastly, the current drawbacks and further research directions for photocatalytic NOx oxidation were elaborated. The development of photocatalysts with high photocatalytic activity, wide light absorption range, and non-NO2 selectivity is the focus of future research. This review aims to provide a pandect and theoretical guidance for the practical application of photocatalytic oxidation of NOx.