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The Na+ ion diffusion effect on the photocatalytic and photoinduced super-hydrophilicity of TiO2 sol-gel coating

Mohamed Nawfal Ghazzal 1,  Nouari Chaoui ,  Alain Koch ,  Didier Robert 

1. Laboratoire de chimie et méthodologie pour l'environnement (LCME), Rue Victor Demange, Metz 57500, France

Abstract
TiO2 coatings are still widely studied because of numerous potential industrial applications. Recently, it has been reported that the surface of TiO2 becomes highly hydrophilic with a water contact angle close to 0° under ultraviolet (UV) illumination1. This phenomenon constitutes the physical principle at the origin of the development of antifogging mirrors2. Furthermore, TiO2 under its anatase form is particularly known as an excellent photocatalyst. The combination of these peculiar wettability properties and photocatalytic performances of TiO2 coatings allowed the development of self-cleaning glass3,4. In most cases, TiO2 is grown on soda-lime glass containing approximately 14 at.% Na and other alkali elements. To study the effect of ions diffusion from the glass substrate on the photocatalytic and the photoinduced super-hydrophilic (PSH) properties of the TiO2 photocatalyst (see figure), TiO2 thin films were grown on three kinds of glass support (soda-lime glass (SGL), Pyrex and quartz). The TiO2 films were characterized using XRD and scanning electron microscopy (SEM).

The poisoning effect of Na ion diffusion from the SGL to the photocatalytic efficiency of the TiO2 coating was observed on our previous work5. In this study, the influence of the Na ion diffusion on the wettability conversion of TiO2 films was investigated through the evolution of the contact angle on deliberately contaminated TiO2 surface by the film of the stearic acid. We observe that the Na+ diffusion decease the photocatalytic degradation rate of stearic acid and the wettability conversion of the TiO2 surface. The rate of the photoinduced conversion of the TiO2 films depend on the kinetic of the photocatalytic degradation of hydrocarbon adsorbed on the surface.

1. R. Wang et al.,  Nature 388 (1997) 431


2. S. Hata et al.,  JSAE Rev. (2000) 97.


3. A. Fujishima et al., J. Photochem. Photobiol. C: Photochem. Rev. 1 (2000) 1.


4. T. Watanabe et al., Thin Solid Films 351 (1999) 260.

 

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Presentation: Oral at E-MRS Fall Meeting 2008, Symposium D, by Mohamed Nawfal Ghazzal
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-03-28 16:11
Revised:   2009-06-07 00:48