Developed photocatalytic asphalt mixture of open graded friction course for degrading vehicle exhaust

Abstract

To develop a green and sustainable photocatalytic porous asphalt pavement material for vehicle exhaust (VE) degradation using iron (Fe)-doped titanium oxide (TiO2) nanopowders under visible light irradiation, the influence of Fe doping on various performances of TiO2 were first analyzed. Then the Fe-doped TiO2 was loaded on the biomass activated carbon (AC) to prepare the composite photocatalyst (Fe–TiO2/AC) which was used as fine aggregates in asphalt mixture of open-graded friction course-16 (OGFC-16) for degrading VE. Test results indicate that the Fe are successfully doped into crystal lattices of TiO2 in the predominant form of Fe3+ to substitute for Ti4+, leading to surface defects, lattice distortion and dislocation in the crystal structures of TiO2. The generated non-lattice oxygen due to the Fe doping has a stronger attraction to adsorbed oxygen and hydroxyl, improving the photocatalytic activity of TiO2. Additionally, the reflectance edge of Fe-doped TiO2 shows an obvious red shift to visible light region with the maximum wavelength of 550 nm, and its reflectance is lowered. This increases the utilization ratio of visible light irradiation and improves the photocatalytic efficiency of TiO2 to VE. Further, HC and NOx are obviously degraded by OGFC-16 under visible light irradiation because of the synergy between the Fe–TiO2 degradation and AC adsorption. The photocatalytic efficiency of OGFC-16 to HC and NOx are improved when the Fe–TiO2/AC content is increased. However, there is a reversible reaction between CO2 and CO during their photocatalytic degradations. Thus OGFC-16 asphalt mixture shows lower photocatalytic efficiency to CO and CO2. Finally, the Fe–TiO2/AC replacement percentage of 60% is proposed to replace the fine aggregate in OGFC-16 asphalt mixture, which occupies 3.34% in OGFC-16, improving its pavement properties. This study provides an insight into the photocatalytic performance of OGFC-16 asphalt mixture to VE, developing a green and sustainable pavement material.