Optimized deposition of TiO2 thin films produced by a non-aqueous sol–gel method and quantification of their photocatalytic activity

TiO2 thin films have been produced by a dip-coating process using a non-aqueous sol–gel method. This study investigated the influence of the operating variables such as nature of the substrate, sol concentration, withdrawing speed of the dip-coater and number of layers on the physico-chemical properties of the films using XRD, GIXRD, UV–Vis spectroscopy, profilometry, spectroscopic ellipsometry and SEM. Photocatalytic activity of the films was evaluated by following the degradation of methylene blue under artificial UV light at 25 °C. The performances of the catalysts were compared through the reaction rate constants determined using an apparent first-order kinetic model adjusted on the experimental data. This study showed that the photocatalytic activity and the reaction rate constant depend on the film thickness through the synthesis and dipping variable, with an optimum thickness of 80 nm being observed. An optimized transparent film exhibiting a high adhesion, a well crystallized TiO2-anatase phase, a good photocatalytic activity and a reaction rate constant k equal to 0.126 h−1 was obtained using a simple process. The specific photocatalytic activity of this film was higher to the one measured for TiO2 powders in previous works.

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► TiO2 anatase films were produced by a controlled sol–gel method and dip-coating.
► Aim: to relate the photoactivity with synthesis and deposition operating variables.
► Films were transparent, adherent, homogeneous with thickness from 20 nm to 250 nm.
► Best photocatalytic activity under UV light is reached when thickness is ∼80 nm.
► Properties and activity were not influenced by deposition variables beyond 80 nm.