Time-resolved and FTIR studies at the TiO{sub 2}-water interface: Novel insight into the mechanism of photocatalysis
- Institut fuer Solarenergieforschung GmbH, Hanover (Germany)
The photocatalytic decomposition of organic pollutants on small semiconducting TiO{sub 2}-particles under illumination with light of sufficient energy to generate electron/hole pairs has been studied extensively in the past. Mechanistic details of the oxidation of organic compounds by the valence band holes are currently under investigation in many laboratories. We have investigated the trapping of electron/hole pairs as well as their transfer to electron acceptors and donors, respectively, by laser flash photolysis using extremely small (diameter < 5 nm) colloidal TiO{sub 2}-particles as photocatalysts. While electrons are trapped in Ti{sup 3+}-sites within the duration of the laser pulse (< 20 ns), hole trapping is considerably slower (k {approx} 10{sup 7} sec{sup -1}). While trapped holes are relatively unreactive, adsorbed electron donors can be oxidized directly thus competing with the recombination of trapped electrons with valence band holes which determines the photocatalytic activity of these TiO{sub 2}-particles. Adsorption which is obviously an important factor influencing the kinetics of the photocatalytic degradation was studied using different FTIR techniques with dichloroacetate (DCA) being the model compound. Between pH 1.2 and 9.3, the position of the asymmetrical and symmetrical vibrational band of DCA are shifted to lower and higher wavenumbers, respectively, when this compound is adsorbed on the TiO{sub 2} surface indicating the formation of a bidental complex where both oxygen atoms of the DCA carboxyl group are bound to adjacent TiO{sub 2} surface sites. At pH 11, on the other hand, the formation of a monodentate surface complex was observed. ATR-FTIR measurements in colloidal TiO{sub 2}-suspensions showed that the informations obtained from the DRIFT measurements of dry samples are in good agreement with the DCA-adsorption in aqueous media.
- OSTI ID:
- 370840
- Report Number(s):
- CONF-960376--
- Country of Publication:
- United States
- Language:
- English
Similar Records
Dry phase titanium dioxide-mediated photocatalysis: Basis for in situ surface destruction of hazardous chemicals
Protonation of phosphate on the surface of goethite as studied by CIR-FTIR and electrophoretic mobility