Environ. Sci. Technol. 2001, 35, 2988-2994
Transparent Thin-Film TiO2 Photocatalysts with High Activity M. CATHERINE BLOUNT,† DONG HYUN KIM,‡ AND J O H N L . F A L C O N E R * ,† Department of Chemical Engineering, University of Colorado, Boulder, Colorado 80309-0424, and Pepcon, Korea
A transparent, thin-film TiO2 layer prepared by sol-gel deposition is shown to be more active for photocatalytic oxidation (PCO) of acetaldehyde, acetic acid, and toluene than Degussa P25 thin films. The sol-gel TiO2 adsorbs 30-70% less organic, but the PCO activity per adsorbed molecule is 3.5-8.5 times higher on the sol-gel TiO2 than on Degussa P25. In addition, less-reactive intermediates do not appear to form as readily on the sol-gel catalyst as they do on Degussa P25, and thus the sol-gel catalyst deactivates slower during toluene PCO. Rates were measured in transient experiments for a monolayer of adsorbed organic, and transient experiments are shown to be an effective way to measure rates, selectivities, surface coverages, and formation of less-reactive intermediates in the same set of experiments.
Introduction Heterogeneous photocatalytic oxidation (PCO) is a method to remove low concentrations of organic contaminants from gaseous effluents by converting them to environmentally safe products. PCO has been proposed as an effective means of cleaning up waste airstreams contaminated with volatile organic compounds (VOCs) because it has many advantages, including high destruction efficiencies at room temperature and high quantum yields so that low intensity UV lamps can be used. The typical catalyst is TiO2, which is inexpensive, and a large number of VOCs can be completed oxidized to CO2 and H2O. Moreover, TiO2 has high activity for PCO of chlorinated organics, and it is effective for low concentrations of pollutants, even in humid conditions. In addition, PCO is well-suited for modular systems and is effective on a small scale. One of the big advantages of PCO is that quantum efficiencies are high at room temperature for many gas-phase organic and chlorinated organic molecules. These reactions take place on a semiconductor catalyst (usually TiO2) with near-UV light (
