How to modify the photocatalytic activity of TiO2 thin films through their roughness by using additives. A relation between kinetics, morphology and synthesis

Abstract

The possibility to improve the photocatalytic activity of TiO2 thin films by using organic additives is investigated. Two non-aqueous sol–gel routes (In Situ and Ex Situ) have been selected to obtain organic/inorganic stable sols and TiO2 thin films have been produced using the dip-coating process optimized in a previous study. The influence of the additive on the physico-chemical properties of the catalysts has been evaluated using XRD, GIXRD, UV–Vis spectroscopy, krypton and nitrogen adsorption–desorption, profilometry and SEM. The photocatalytic activity has been assessed by monitoring the degradation of 4-nitrophenol (4-NP) under UV light and UV–Visible light over time. The performances of the catalysts have been evaluated using the values of the reaction rate coefficient estimated through the adjustment of the first order kinetic model taking in account the variation of the volume inside the reactor due to sampling. The results highlight that the performances of the catalysts were better that the performances of the commercial photocatalytic coating (Saint Gobain Glass Bioclean®) which constitutes a significant step forwards for the production of photocatalytic coating. Moreover, the results highlight that the organic additive induces an alteration of the surface roughness and hence, a modification of the active surface of the films. In the case of the In Situ synthesis an increase of the active surface is associated to a 100% improvement of the photocatalytic activity. On the opposite, for the Ex Situ synthesis, a decrease of the active surface is associated to a 50% decrease of the photocatalytic activity due to the presence of the additive.