Fabrication of PFDTES/BiOI/Bi5O7I/WPU photocatalytic self-cleaning coatings for NO green degradation

In this study, a BiOI/Bi₅O₇I photocatalyst is synthesized using a co-precipitation method. The degradation efficiency of NO can reach 70 % under visible light. Subsequently, water-based polyurethane is used as the film-forming matrix, and fluorinated silane is used as low surface energy components, a BiOI/Bi₅O₇I water-based polyurethane photocatalytic superhydrophobic coating (FBIU) is prepared by a layer-by-layer spraying technique. The high catalytic activity of BiOI/Bi₅O₇I comes from the heterojunction effect of the two semiconductors and the improved interface, which enables the degradation rate of NO to reach 76.9 %, accompanied by extremely low NO₂ conversion rate (<1 %). The wettability, chemical stability and mechanical stability of the FBIU coating are studied to investigate its impact on the long-term oxidative degradation performance of NO. And the self-cleaning characteristics and specific micro-nano structure of FBIU improve the wear resistance of the coating, manifested as a contact angle of 157.8° to water after 320 times of sandpaper polishing. Finally, based on the photocatalytic mechanism of BiOI/Bi₅O₇I semiconductor materials, a green long-term purification and degradation mechanism of NO by coatings is proposed. This can provide some insights into the design of air purification coatings for building exterior walls.