Photo-adsorption and photo-catalysis on titanium dioxide surfaces. Photo-adsorption of oxygen and the photocatalyzed oxidation of isopropanol

Abstract

A study of the photoadsorption of oxygen by temperature-programmed desorption reveals that, on fully oxidised rutile surfaces, adsorbed hydroxyl groups act as traps for the photo-holes which are produced by irradiating the specimen with ultra-violet light λ 330 nm. The photo-electrons, which are simultaneously produced, are then free to participate in the chemisorption of oxygen. On reduced rutile surfaces it has been established that the photoadsorption of oxygen is enhanced by the additional presence of Ti³⁺ ions which also fulfil the role of traps for photo-holes.

The photo-oxidation of isopropanol has been shown to be quite complex. The initial product is acetone, but the subsequent photo-oxidation of the acetone produces formic acid. Acetaldehyde is also produced, but probably arises from the photo-oxidation of adsorbed propene which is formed by the thermal dehydration of isopropanol. Ultimately the products of prolonged photo-oxidation are carbon dioxide and water.