Photocatalytic Activity of N-Doped TiO2 to Vehicle Exhaust in Road Tunnel

The nitrogen (N)-doped titanium dioxide (TiO2) was synthesized to use as raw materials of coating on the tunnel lining and pavement to purify vehicle exhaust (VE) in a road tunnel. To study photocatalytic activity of N-doped TiO2 to VE, its morphology, surface area, and optical properties were characterized. Then photocatalytic activity tests of TiO2 to VE were conducted under ultraviolet (UV) and visible light irradiation, respectively. Results indicated that the prepared TiO2 showed spherical nanoparticles with the grain size range of 13-16 nm and the agglomeration of TiO2 nanoparticles was decreased with the increase in N-dopant concentration. Synthesized pure and N-doped TiO2 only contain an anatase phase. Also, N-doped TiO2 exhibited higher optical absorptions in UV and visible light region, and the optical absorption edges of N-doped TiO2 present obvious red shift. Additionally, N-doped TiO2 showed higher photocatalytic activity to VE than pure TiO2 under UV and visible light irradiation. The degradation efficiencies of N-doped TiO2 to NOx and HC were higher than those to CO2 and CO in VE under UV light irradiation because of the reversible reaction between CO2 and CO. Furthermore, N-doped TiO2 showed a higher photocatalytic activity to CO2 than that to CO under visible light irradiation, but the reversible reaction was not found. All photocatalytic reactions followed the first-order kinetics in the photocatalytic degradation of VE. It is believed that the N doping is a promising method to improve the photocatalytic activity of TiO2 to VE under visible light irradiation for the air purification in a road tunnel.