Time-resolved microwave conductivity. Part 2.—Quantum-sized TiO2and the effect of adsorbates and light intensity on charge-carrier dynamics
Journal of the Chemical Society, Faraday Transactions
Charge-carrier recombination dynamics after a pulsed laser excitation are investigated by time-resolved microwave conductivity (TRMC) for quantum-sized (Q-) TiO, and P25, a bulk-phase TiO, . Adsorbed scavengers such as HNO, , HCI, HCIO, , isopropyl alcohol, trans-decalin, tetranitromethane, and methyl viologen dichloride result in different charge-carrier recombination dynamics for Q-TiO, and P25. The differences include a current doubling with isopropyl alcohol for which electron injection
... ctron injection into Q-TiO, is much slower than into P25 and relaxation of the selection rules of an indirect-bandgap semiconductor due to size quantization. However, the faster interfacial charge transfer predicted for Q-TiO, due to a 0.2 eV gain in redox overpotentials is not observed. The effect of light intensity is also investigated. Above a critical injection level, fast recombination channels are opened, which may be a major factor resulting in the dependence of the steady-state photolysis quantum yields on /-",. The fast recombination channels are opened at lower injection levels for P25 than for Q-TiO" and a model incorporating the heterogeneity of surface-hole traps is presented.