Photoadsorption and photocatalysis at rutile surfaces: II. Photocatalytic oxidation of isopropanol

The photocatalytic oxidation of isopropanol has been studied in a specially designed rotating reaction vessel affording good contact between the incident uv light and the powdered photocatalyst. It has been shown that when TiO2 (rutile) is illuminated with light of wavelength λ > 300 nm in the presence of isopropanol vapor and oxygen at 300 K, the primary organic oxidation product is acetone. When isopropanol is present as a presorbed layer, the kinetics of the evolution of acetone into the gas phase can be studied as a displacement process. The behavior is discussed in detail with reference to the adsorption isotherms of isopropanol, acetone and water on rutile, and the effect which one component exerts upon the adsorption of the other components. Isopropanol and water are both capable of displacing acetone from the surface. The formation of acetone cannot be sustained in the absence of oxygen, and it is concluded that oxygen photoadsorption is a precursor to the photooxidation. Reaction schemes are discussed.