Fe-doped TiO2 loaded on activated carbon for degrading vehicle exhaust in asphalt pavement

Titanium dioxide (TiO₂) is widely used to purify air pollutants in environmental engineering, but it is only activated by ultraviolet (UV) light. To broaden the spectral response range of TiO₂ to further increase the photocatalytic activity and purification efficiency on vehicle exhaust under visible light, Fe-doped TiO₂ is loaded on the biomass activated carbon (AC) to prepare the composite photocatalyst (Fe-TiO₂/ AC). Then Fe-TiO₂/ AC substituted part of fine aggregates in asphalt mixture of open-graded friction course-16 (OGFC-16) for degrading vehicle exhaust (VE). Results indicates that Fe is doped into crystal lattices of TiO₂ in the predominant form of Fe³⁺ to substitute for Ti⁴⁺, leading to surface defects, lattice distortion and distortion 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. This increases the utilization ratio of visible light irradiation of TiO₂, broadening the spectral response range of TiO₂. Further, HC and NO_x in VE are obviously degraded by OGFC-16 under visible light irradiation because of the synergy between the Fe-doped 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, developing a green and sustainable pavement material.