The present work addresses the effect of nano-silica modification on a carbon-doped titanium dioxide (C-TiO2) suspension for the development of a photocatalytic coating for indoor air improvement. The dosage effect of the applied coating and the effect of the ultraviolet pre-treatment, as an activation technique, on the photocatalytic efficiency were studied. A plug-flow experimental setup was employed for the photo catalytic efficiency assessment under realistic indoor air environment. The results showed that the nano-silica addition and the UV pre-treatment enhanced the photocatalytic efficiency of the developed coatings. The nano-silica modification was more beneficial when the coatings were applied in higher photocatalyst dosages (0.84 mg.cm(-2) or 1.27 mg.cm(-2) of C-TiO2) especially during the UV pre-treatment. The silica-modified samples tested under visible light and reduced flow rate of 1.5 L.min(-1) degraded up to 65% and 78% of NO (up to 43% and 60% of NOx) under initial concentration of 0.5 and 0.1 ppm, respectively. Moreover, the reaction rate and reactive uptake coefficient of the developed coatings were computed. (C) 2016 Elsevier B.V. All rights reserved.