Suppressing NO ₂ Byproduct in Photocatalysis: An Environment-Adaptive Composite Coating via an Engineered Hydrophobic and Thermally Insulating Microenvironment

Conventional photocatalytic coatings for nitric oxide (NO) abatement often suffer from the accumulation of toxic nitrogen dioxide (NO 2 ) as an intermediate byproduct, undermining their environmental friendliness. To address this challenge, a layered composite coating was designed and fabricated by integrating the photocatalytic C 3 N 4 /Bi 2 WO 6 heterojunction onto hollow glass microspheres, followed by fluorination and incorporation into a polymer matrix. This process engineered a robust and hydrophobic surface microenvironment, which remained conducive to the NO/O 2 interfacial reaction even under adverse conditions. Consequently, the composite coating exhibits high selectivity in NO oxidation, achieving substantial removal rates (25.4–69.1%) while minimizing the NO 2 conversion rate (2.6%) in a low-temperature and dry environment, as verified by in situ monitoring. Interface engineering enhances selectivity by optimizing the adsorption and activation of reactants. The synergy between the coating’s excellent durability, inherent antibacterial, and self-cleaning properties underpins its long-term functional stability. In situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations elucidate the enhanced charge separation/transfer, which in turn promotes a reaction pathway conducive to the selective formation of nitrate. Consequently, this work establishes a practical strategy of microenvironment engineering via rational coating design, advancing photocatalytic technology toward sustainable air pollution control.