Enhanced photocatalytic decomposition of NO on portland cement concrete pavement using nano-TiO2 suspension

Abstract

Photocatalyst titanium dioxide (TiO2) has been widely applied on asphalt and concrete pavements to mitigate the air pollution caused by traffic exhaust. In general, most of the TiO2 used in previous studies was pure anatase, which only exhibited excellent photocatalytic activity under ultraviolet (UV) light. Thus, N-doping method was selected to improve the photocatalytic activity, especially under visible light. Additionally, the TiO2 suspension was commonly used on the pavements comparing with other application methods. However, the Nano-TiO2 particles with great surface area-to-volume ratio and surface energy have a strong tendency to agglomerate in the suspension, which has significantly negative effects on the photocatalytic activity. Thus, the objective of this study was to enhance the photocatalytic performance of mortar specimens containing TiO2 by preparing optimum N-doped TiO2 and suspensions using both single-factor and orthogonal experimental design. Methylene blue (MB) decomposition results indicated that the optimum N-doped TiO2 was prepared with 1% N-dosage at 700 °C for 5 h. X-ray diffractometer (XRD) pattern results implied that the phase transformation from anatase to rutile occurred around 700–800 °C and anatase transferred to rutile completely at 900 °C. Absorbance results showed that the optimum suspension was prepared with following conditions: ultrasonic power 100 W, ultrasonic time 120 min, silica sol concentration 0.5%, and sodium hexametaphosphate (SHMP) dosage of 0.3%. Lastly, NO decomposition test was conducted to investigate the effects of TiO2 implementation methods and environmental factors on the photocatalytic performance of mortar specimens. The NO decomposition results showed that the optimum suspension could significantly improve the photocatalytic performance of specimens. Meanwhile, the NO decomposition percentage decreased with the increasing flow rate and NO concentration.