Performance of Visible-Light-Driven Photocatalytic Pavement in Reduction of Motor Vehicles’ Exhaust Gas

Abstract

Titanium dioxide (TiO2) is a widely used photocatalyst that can oxidize motor vehicle exhaust, for example, carbon monoxide (CO), nitrogen oxides (NOx), hydrocarbons, and sulfur dioxide, under the irradiation of sunlight. It has been reported that nano-scale TiO2particles can be effectively used to modify the concrete-asphalt pavement, and make it as a photocatalytic pavement. However, the pure TiO2additive limits its absorption spectrum to the ultraviolet region, which only occupies a small portion of sunlight irradiance. To increase the utilization of the full spectrum of sunlight, it has been demonstrated that doping TiO2with substances such as Carbon (C), Nitrogen (N), or metal can reduce the band-gap and extend the threshold of the absorption spectrum to the visible light region. Therefore, doped-TiO2has a better photocatalytic performance under sunlight irradiation. This paper conducted computational simulation of the kinetics of photocatalytic pavement to quantify the efficiency of doped-TiO2embedded pavement in reducing exhaust gas from motor vehicles. A three-dimensional model is developed on a section of local road with doped-TiO2embedded pavement. The effects of doped-TiO2concentration, daylight conditions, and traffic flow conditions on the removal of NOxand CO were studied. The results indicate that the pavement with doped-TiO2coating is effective to remove CO and NOxunder different traffic density and daylight intensity conditions. Compared with UV activated TiO2, visible-light-activated doped-TiO2features significantly higher removal efficiency of poisonous exhaustive gas including NOxand CO.