Photocatalytic NOx degradation of concrete surface layers intermixed and spray-coated with nano-TiO2: Influence of experimental factors

TiO2 incorporated Eco-blocks have been successfully developed and widely used worldwide. However, under real-life service, various environmental factors will significantly influence their photocatalytic performance. In this study, the photocatalytic NOx conversion of two sets of concrete surface layers (intermixed and spray-coated with nano-TiO2) was investigated and compared under different NO flow rates, initial NO concentrations, ultraviolet (UV) light intensities, light sources and relative humidity (RH) conditions. In addition, the abrasion resistance of all the samples was examined. The results showed that the TiO2 spray-coated samples (SP) outperformed the 5% TiO2-intermixed samples with respect to NOx removal efficiency under all the investigated conditions. Both the NO flow rate and initial NO concentration had a positive impact on the NOx removal rate but a negative influence on the NOx removal ratio. An increase in photocatalytic NOx removal rate and NOx removal ratio was attained by an increase in UV light intensity. Whereas, the NOx removal efficiency first increased, reached a peak, and then decreased with increasing RH. It was found that the most effective light source for photocatalytic NOx removal was UV-A, but Solar light (SL) irradiation resulted in a comparable NOx removal. Moreover, the SP samples harboured robust resistance to abrading. The findings from this study would provide the basis for effectively evaluating the NOx removal performance of concrete surface layers under atmospheric conditions.