Preventing Sodium Poisoning of Photocatalytic TiO₂ Films on Glass by Metal Doping

Titanium dioxide (TiO₂) has received much attention as a photocatalyst, specifically in applications that require a mechanically robust thin film. TiO₂ is particularly useful because it does not absorb visible light, making it well suited for coatings on glass. Photocatalytic activity of TiO₂ films is strongly dependent on the substrate and it has been well established that sodium diffusion from glass has a negative effect on this activity. While the prevention of sodium poisoning is possible through the use of a precoating, this requires an additional coating and/or calcination step. Other remedies, such as acid treatment of the glass surface, are also time consuming. Therefore, it is a more attractive option to negate the effects of sodium diffusion without a separate processing step. In this paper, we examined the effects of silver, cobalt, copper, gallium, molybdenum, and tantalum doping on the prevention of sodium poisoning of sol–gel TiO₂ films by comparing the photocatalytic activities on glass and SiO₂ precoated glass. While sodium poisoning degraded the photocatalytic activity of undoped TiO₂ films by 70%, it was only 10% for Mo- and Ta-doped TiO₂ films. Molybdenum was superior to other dopants in terms of photocatalytic activity, both in the presence of sodium and in a sodium-free environment.