2D/2D CoAl-LDH/BiOBr S-scheme heterojunction photocatalyst for efficient NO oxidation to nitrate under visible light

Photocatalytic NO oxidation to nitrate (NO₃^-) is a promising technology for air pollution control. However, these strategies are hindered by slow kinetics as well as unwanted production of toxic NO₂, which result from the inefficiency in separating charges and poor activation of the reactant molecules. Here, we report on a novel 2D/2D S-scheme heterojunction constructed by coupling CoAl-layered double hydroxide (CoAl-LDH) nanosheets with BiOBr nanoplates. This particular structure enables a S-scheme charge transfer channel that can improve the separation efficiency of photoinduced charge carrier while keeping strong redox ability to generate high-reactive oxygen species (ROS, including hydroxyl radical and superoxide radicals). Furthermore, in situ DRIFTS spectra showed that Co³⁺ sites within the LDH framework are key active centers, significantly enhancing NO adsorption and activation. Consequently, the obtained CoAl-LDH/BiOBr composite exhibited excellent NO removal activity, to reach a conversion rate of 97.3% with negligible NO₂ formation (selectivity <3%) under visible light, and maintained excellent stability for 8 h. This study proposes a synergistic strategy of interfacial charge control coupled with surface catalytic site design, providing new perspectives in design of high-performance catalysts for future applications in environmental protection via photo-catalytic processes.