Surface Modification of TiO2 by Hyper-Cross-Linked Polymers for Efficient Visible-Light-Driven Photocatalytic NO Oxidation

Solar-driven photocatalysis offers an environmentally friendly and sustainable approach for the removal of air pollutants such as nitric oxides without chemical addition. However, the low specific surface area and adsorption capacity of common photocatalysts restrict the surface reactions with NO at the ppb-level. In this study, imidazolium-based hyper-cross-linked polymer (IHP) was introduced to modify the surface of TiO2 to construct a porous TiO2/IHP composite photocatalyst. The as-prepared composite with hierarchical porous structure achieves a larger specific surface area as 309 m2/g than that of TiO2 (119 m2/g). Meanwhile, the wide light absorption range of the polymer has brought about the strong visible-light absorption of the TiO2/IHP composite. In consequence, the composite photocatalyst exhibits excellent performance toward NO oxidation at a low concentration of 600 ppb under visible-light irradiation, reaching a removal efficiency of 51.7%, while the generation of the toxic NO2 intermediate was suppressed to less than 1 ppb. The enhanced NO adsorption and the suppressed NO2 generation on the TiO2/IHP surface were confirmed by in situ monitoring technology. This work demonstrates that the construction of a porous structure is an effective approach for efficient NO adsorption and photocatalytic oxidation.