Photocatalytic NO abatement by cement blocks covered with Fe–TiO₂ and surface hardening agents: Impacts of Fe–TiO₂ contents of coating solutions

In this study, the photocatalytic activity of commercial TiO₂ particles (R996) in promoting the oxidation of NO under visible light irradiation at 50% relative humidity was enhanced by the temperature-regulated chemical vapor deposition of Fe-oxide (0.4 wt%) and post-annealing (375 °C, 2 h). Fe–TiO₂@SHA/cement block samples were prepared by dispersing the modified TiO₂ particles (Fe–TiO₂) on cement blocks using a surface hardening agent (SHA) as a binder. The Fe–TiO₂@SHA/cement blocks exhibited higher photocatalytic activity in promoting the conversion of NO into NO₃⁻ than the particulate counterparts. The Fe–TiO₂@SHA/cement blocks exhibited dissimilar patterns in terms of the changes in NO removal as a function of the reaction time in the early stage of the reaction (0–150 min) depending on the Fe–TiO₂ contents. The removal of NO increased gradually as the reaction time increased with lower Fe–TiO₂ contents, whereas a gradual decrease in NO removal as a function of the reaction time was observed with higher Fe–TiO₂ contents. The dependence of the response on the Fe–TiO₂ contents was attributed to the dissimilar Fe–TiO₂ structures formed on the cement blocks due to variations in the viscosity of the Fe–TiO₂ coating solutions with different Fe–TiO₂ contents.