Photocatalytic activity of bulk TiO2 anatase and rutile single crystals using infrared absorption spectroscopy.

A systematic study on the photocatalytic activity of well-defined, macroscopic bulk single-crystal TiO(2) anatase and rutile samples has been carried out, which allows us to link photoreactions at surfaces of well-defined oxide semiconductors to an important bulk property with regard to photochemistry, the life time of e-h pairs generated in the bulk of the oxides by photon absorption. The anatase (101) surface shows a substantially higher activity, by an order of magnitude, for CO photo-oxidation to CO(2) than the rutile (110) surface. This surprisingly large difference in activity tracks the bulk e-h pair lifetime difference for the two TiO(2) modifications as determined by contactless transient photoconductance measurements on the corresponding bulk materials.

Relaxation of photogenerated carriers in P3HT:PCBM organic blends.

The after-pulse time-resolved microwave conductivity (TRMC) decays observed in P3HT:PCBM blends display a dependence on time close to t(-beta), independent of excitation intensity, in the 10 ns-1 micros range. This is explained in terms of the relaxation of carriers in a Gaussian density of states (DOS). The model is based on a demarcation level that moves with time by thermal release and retrapping of initially trapped carriers. The model shows that when the disorder is large the after-pulse decay of the type t(-beta) is obtained, while at low disorder and large temperature the carrier distribution becomes independent of time. In the measurements different beta values were observed depending on the solvent used for spin-coating: 0.4-0.6 for chlorobenzene and 0.3-0.4 for toluene. The model was applied to extract the shape of the DOS from the TRMC decays, giving a dispersion parameter of about 120 meV for blends with high P3HT content.

Phenol photodegradation on platinized-TiO2 photocatalysts related to charge-carrier dynamics.

Three commercial TiO2 compounds (Degussa P25, Sachtleben UV100, and Millenium PC50) and their platinized forms have been studied by the time-resolved microwave conductivity (TRMC) method to follow their charge-carrier dynamics and to relate it to the photocatalytic activity for phenol degradation in TiO2 aqueous suspensions. The degradation reaction has been studied in detail, following the time evolution of the concentration of phenol and its intermediates by liquid chromatography. The results show that platinization has a distinct influence on the commercial compounds, decreasing globally the activity of P25 and increasing the activity of PC50 and UV100. An influence of charge-carrier lifetimes on the photoactivity of pure and platinized TiO2 samples has been evidenced.