Sol–gel preparation of TiO2–ZrO2 thin films supported on glass rings: Influence of phase composition on photocatalytic activity

In order to optimize the characteristics of TiO2–ZrO2 thin films supported on glass for the photocatalytic removal of VOCs, acidic sols of different composition (ZrO2, TiO2 and Ti–Zr mixed oxides) have been prepared using metal alkoxides as starting materials. The photoactive oxides were deposited on “Raschig rings” of borosilicate glass using a dip-coating technique. The phase composition of the thin films was controlled during the sol preparation stage to produce either (1) Ti0.90Zr0.10O2 solid solutions, or (2) ZrO2/TiO2 binary metal oxides (10% and 20% molar content of Zr). The particle size of the different sols was measured by photon correlation spectroscopy, and the xerogels were characterized by XRD, N2 adsorption isotherms, and TG–DTA, so as to monitor the modifications induced by the thermal treatments. Raman spectroscopy was used to determine the crystalline structure of the supported TiO2–ZrO2 oxides, which in all cases corresponded to the anatase phase. The band gap of the thin films was estimated from the UV–vis spectra, and none of them differed significantly from that of unmodified TiO2. The photoactivity of the coated glass “Raschig rings” was measured for the oxidation of acetone and methylcyclohexane vapors using, respectively, total recycle and single pass plug flow photoreactors. The results obtained indicate that, for the same Zr content, the photoactivity of the films containing binary metal oxides is slightly higher than that of the solid solution. In contrast, specific surface area seems to have little influence on the performance of the thin films.