Photocatalytic removal of NO and NO2 using titania nanotubes synthesized by hydrothermal method

In this study, the photocatalysts of titania nanotubes (TNTs) were synthesized at different calcination temperatures using commercial Degussa TiO₂ (P25) as a precursor. The materials were then characterized by BET, SEM, TEM, and XRD analyses. The photocatalytic reactions with NO and NO₂ under UV-A irradiation were both performed. The results showed that the photocatalytic reaction rate of NO was much faster than that of NO₂, and the conversion of NO₂ to nitrate was the rate-limiting step for photocatalytic removal of NOx if the nitrate produced cannot be removed continuously from the photocatalyst surface. For TNTs calcined at different temperatures, a significant enhancement was observed on the total NOx removal efficiency by TNT calcined at 500°C for both NO and NO₂ photocatalytic reaction, which could be attributed to its high anatase crystallinity as well as high surface area. These two factors affect primarily on the NO₂ conversion step in which the high anatase crystallinity could be responsible for the high efficiency at the beginning, while the high surface area could be accounted for retaining this high efficiency from nitric acid poisoning during the test period.