Photo-oxidatively self-cleaning transparent titanium dioxide films on soda lime glass: The deleterious effect of sodium contamination and its prevention

Abstract

In the context of photocatalytically self-cleaning windows and windshields, clear, abrasion resistant, thin (60 ± 10 nm) photocatalytic films of TiO2 were formed by a sol-gel process on (a) soda lime glass, (b) the proton-exchanged surface of soda lime glass, and (c) fused silica. The hypothesis that diffusion of sodium oxide from the soda lime glass into the titanium dioxide layer during the calcination step causes the lower photoefficiency in films on glass was tested and proven. At high concentration sodium prevented formation of the photoactive anatase phase and, at low concentration, introduced surface and bulk recombination centers. Sodium transport was efficiently blocked by a thin layer at the interface of proton-exchanged (“hydrogen”) glass and nascent TiO2, formed at 400 °C of a poly(titanyl acetylacetonate) TiO2 precursor. The sodium transport blocking layer did not form and the highly photocatalytic film was not obtained when the TiO2-precursor film was applied to glass that was not proton exchanged. Furthermore, only a much less effective sodium transport blocking layer was formed on glass that was proton-exchanged, but was calcined at 400 °C prior to application of the TiO2 precursor layer, showing that the sodium depleted glass surface, by itself, was a less effective barrier against sodium transport than the interfacial product of hydrogen glass and the TiO2 precursor.

Transparent Mesoporous Nanocomposite Films for Self‐Cleaning Applications

“…The substrate was a common float glass, on which was deposited a very thin SiO 2 layer, which acts as a diffusion barrier to prevent the contamination of the film with the sodium ions from the glass during further thermal treatment of the films [12]. This prevents the detrimental effect of sodium ions on the photocatalytic activity of TiO 2 [32]. Just after deposition, the films are dried in air and calcined under air at 450°C for 1.5 h to remove the surfactant.…”

Review of the anatase to rutile phase transformation

“…• Built Environment Self-cleaning coatings [34,38,39,[41][42][43][44][45][46][47][48][49][50]. Non-spotting glass [47,51].…”

Synthesis and application of layered titanates in the photocatalytic degradation of phenol

“…Moreover, the presence of sodium on TiO 2 photocatalysts has been proven to be detrimental for its photocatalytic activity as these ions may act as recombination centres for the photogenerated charges thus reducing the efficiency of the photocatalytic process [33][34][35]. Therefore, a high degree of recombination in the nanotubes before their treatment in acid solutions can be expected, inhibiting the photocatalytic activity of these samples, as it can be clearly observed in Figure 8.…”