The photochemistry of titanium dioxide.

The electric properties of irradiated titanium dioxide base pigment have been followed using a simple electrochemical cell containing a layer of pigment on a platinum electrode. Photovoltages and Photocurrents have been observed initially using 0.1 m potassium chloride electrolyte. The effect on these of changing the cell conditions was followed and discussed using the band theory for semiconductors in contact with electrolyte. Addition of easily oxidisable anions to the electrolyte has been shown to decrease the photovoltage and photocurrent but the addition of alcohols and amines lead to an increase of the anodic photocurrent under certain conditions. The adsorption of electron acceptors and donors was found to change the photoelectric properties considerably. It was found to be possible to sensitise pigmentary rutile to visible wavelength using dyes dissolved in the electrolyte. The protecting power of both base (untreated) pigment and coated pigment was followed by several methods when one of these was incorporated into polypropylene, polyethylene, and poly(vinylchloride). The tensile properties, absorption of oxygen (volumetric and transmission infrared measurements) and the mass spectral analysis of photodegraded polymer was studied for pigmented and unpigmented polyolefin films. In nearly all cases films pigmented with the treated rutile were found to degrade more slowly than those containing no pigment while samples containing untreated titanium dioxide were found to be virtually unprotected. Laboratory prepared poly(vinylchloride) samples were analysed by infrared and ultra-violet spectroscopy following irradiation in air. Again pigmented samples were found to protect the polymer to degradation. The dehydrochlorination of P.V.C. under vacuum was followed using mass spectrometry. The wavelength of irradiation was found to be important in this process. Results were discussed in the light of recent literature.