Performance of a 3DOM TiO2 Fog Seal Layer in Degrading NOx from Vehicle Exhaust

Nano-TiO2 combined with fogging technology can degrade automobile exhaust near road surfaces. Preparing nano-TiO2 in the form of three-dimensional ordered macroporous titanium dioxide (3DOM TiO2) can reduce the agglomeration of nano-TiO2 and improve the degradation effect. Thus far, in the preparation process of 3DOM TiO2 using the gelatin template method, the influence of the polystyrene (PS) microsphere concentration, particle size, and optimal roasting temperature on the crystal structure of 3DOM TiO2 has not been elucidated, and the influence of construction and external environmental factors on the degradation performance of the 3DOM TiO2 fogging material (termed a fog seal layer) needs further investigation. This study investigated the impact of various materials and environmental factors on the 3DOM TiO2 fog seal layer, proposes essential parameters for its application in construction processes, and enhanced the degradation efficiency of the 3DOM TiO2 material toward exhaust emissions. First, the key preparation parameters of 3DOM TiO2 were analyzed and optimized. Second, the effects of the fogging amount, emulsified asphalt solid content, temperature, and humidity during fogging on the macroscopic degradation performance of the 3DOM TiO2 material were investigated. The results show that in the preparation of 3DOM TiO2, the optimal particle size of the PS microsphere solution, preparation concentration, and roasting temperature are 300 nm, 5%, and 550°C, respectively. An increase in the spray amount and emulsified asphalt solid content can significantly improve the degradation efficiency of photocatalytic materials. However, the degradation efficiency increase is unnoticeable when the application amount is extremely large, and the recommended level is 0.6 kg/m2. Additionally, an increase in the emulsified asphalt solid content will aggravate construction difficulties, and the recommended level is 60%. The degradation efficiency of the 3DOM TiO2 coatings on NOx first increases and then decreases, and the optimal temperature and humidity ranges are 27.1°C–27.3°C and 36.4%–36.8%, respectively. The degradation efficiency of the 3DOM TiO2 coatings after process optimization is 20.2% and 42.9% higher than that of 3DOM TiO2 and nano-TiO2 before process optimization, respectively.