Novel Method of Coating Titanium Dioxide on to Asphalt Mixture Based on the Breath Figure Process for Air-Purifying Purpose

Titanium dioxide (TiO2) is a photocatalyst that has the capability of accelerating the oxidation of nitrogen oxides (NOX) and other pollutants under ultraviolet (UV) radiation. A number of studies have been conducted on applying TiO2 onto pavement surface to purify exhaust emissions from vehicles. However, it remains a challenging task to effectively coat TiO2 to asphalt pavements to achieve durable air-purifying performance. This study aims to develop an innovative method, based on the breath figure (BF) process and Pickering emulsion effect, to coat TiO2 particles onto asphalt pavement surfaces. With this method, asphalt binder with micro pores filled with TiO2 particles can be coated to asphalt pavement surfaces. The micro porous structure of the coating material helps to provide larger contact area between TiO2 and UV, thus enhancing NOX degradation efficiency. Microscopic analysis on the coating material prepared using the new method demonstrated that TiO2 particles distributed well on the pore walls of the coating material, indicating that UV can reach TiO2 to activate the photocatalytic process. The nitric oxides (NO) removal efficiencies of the asphalt mixture specimens coated using this new method and the traditional water solution–based method after various numbers of surface abrasions were also measured by a custom-designed environmental test setup. It was found that this new coating method provided not only better NO removal efficiency, but also improved durability to maintain the degradation efficiency after tire abrasion, compared to the traditional method.