Differing photo-oxidation mechanisms: electron transfer in TiO2 versus iron-doped TiO2

Low-level iron doping has been found to alter the photo-oxidation mechanism of TiO(2) by efficiently activating molecular oxygen. In the absence of iron, TiO(2) either reduces water or stores the electron. Quantitatively, 0.5% Fe-TiO(2) is nearly three times as efficient as undoped TiO(2); 0.1% Fe-TiO(2) is twice as efficient. It is found that the efficiency boost primarily results from a more effective use of the absorbed UV photons. Extension of absorption into the visible region due to iron doping increases the efficiency by a factor of only 1.03 compared with UV-only irradiation. Characterization of these small particles reveals that particle size, crystal structure (anatase in all cases), and exposed faces are all insensitive to iron doping. Iron modifies the electronic states of TiO(2) by introducing an interband state and enhancing population of a newly identified state at +1.48 eV that acts as an efficient electron-hole recombination site. Activation of molecular oxygen effectively competes with electron-hole pair recombination.