Photocatalytic activity of Fe-loaded TiO₂ particles towards NO oxidation: Influence of the intrinsic structures, operating conditions, and synergic effects of the surface hardening agent

The photocatalytic activities of two commercial TiO₂ particles (P25 and R996) and their Fe-modified counterparts (Fe-P25 and Fe-R996) towards NO oxidation were examined under various light and humidity conditions (dry or humid conditions under UV or visible light irradiation). The photocatalytic activity of R996 increased upon the modification under all four experimental conditions but the Fe-R996 particles still exhibited lower activity than the P25-based photocatalytic particles (P25 and Fe-P25) under all of the conditions. However, when the particles were mixed with a surface hardening agent (SHA) and spread onto a cement block, Fe-R996 exhibited much higher photocatalytic activity than Fe-P25 under visible light irradiation and humid conditions in terms of NO₃^– evolution and NO removal. We highlight that not only the intrinsic structure of the photocatalyst powder but also the synergy between the medium embedding the photocatalytic particles and the photocatalyst should be considered in applications for air purification.