Self-cleaning characteristics of mesoporous nano-crystalline TiO2-SiO2 thin films

Since titanium dioxide was found to exhibit super-hydrophilicity under ultraviolet light, researches on titanium dioxide self-cleaning films have also been continuing. It has been proved that mesoporous structure of the film can improve its optical transmittance, reduce the light reflection, and improve the utilization of light, thus enhancing its photocatalytic activity. The doping of SiO2 in TiO2 can increase the number of hydroxyl groups on the surface of the film, inhibit the transformation of TiO2 crystals and increase the specific surface area, thus improving its photocatalytic activity and reduce the contact angle of water droplets, and eventually enhancing the self-cleaning effect of the film. In this paper, the effects of different volume fractions of SiO2 on the surface morphology, mechanical stability, wettability and photocatalytic activity of TiO2 films are explored in great detail. It has been found that the film shows a smooth, crack-free surface morphology at a volume fraction of 20% SiO2. After exposure to ultraviolet light, a contact angle of 0.75° can be obtained in a short time, and the film exhibits super-hydrophilicity. Moreover, a low contact angle is maintained for a long time after the lighting is stopped. Methyl orange is adopted to evaluate its photocatalytic performance. Under ultraviolet light, it can be almost completely degraded in a short time, showing great photocatalytic activity. All the mesoporous films prepared exhibit good optical permeability. At the same time, it has been found that the films prepared are of good adhesion and maintain acid and alkaline resistance under natural conditions.