TiO2-mediated photodegradation of liquid and solid organic compounds

The photocatalytic degradation of several liquid and solid organic compounds, including polymers, with molecular weights covering a wide range from 600 to 500,000 was studied on TiO2 thin films on glass under UV illumination. Nearly exact agreement was found between the weight losses of the solid compounds octadecane and stearic acid and the weights of CO2 produced during photocatalytic degradation. No other gas-phase degradation product was detected for these two compounds other than CO2, which means that potentially harmful products are not expected to pose a problem. For convenient comparison of degradation rates for various compounds and measurement methods, the values were converted to numbers of moles of carbon reacted per square centimeter per hour. Under appropriate conditions (50 degreesC, relative humidity 10% in air), octadecane was completely decomposed (<400 ng cm(-2)). In contrast, stearic acid did not decompose completely, even after more than 80 h of UV illumination. This may be due to the formation of a photocatalytically inert reaction product that blocks the TiO2 surface. The decomposition rates for all of the compounds examined spanned less than two orders of magnitude, suggesting that the photocatalytic reactions involved are rather versatile. (C) 2000 Published by Elsevier Science B.V.