THE ROLE OF METAL-ION DOPANTS IN QUANTUM-SIZED TIO2 - CORRELATION BETWEEN PHOTOREACTIVITY AND CHARGE-CARRIER RECOMBINATION DYNAMICS

A systematic study of metal ion doping in quantum (Q)-sized (2-4 nm) T iO2 colloids is performed by measuring their photoreactivities and the transient charge carrier recombination dynamics. The presence of meta l ion dopants in the TiO2 crystalline matrix significantly influences photoreactivity, charge carrier recombination rates, and interfacial e lectron-transfer rates. The photoreactivities of 21 metal ion-doped co lloids are quantified in terms of both the conduction band electron re duction of an electron acceptor (CCl4 dechlorination) and the valence band hole oxidation of an electron donor (CHCl3 degradation). Doping w ith Fe3+, MO(5+), RU(3+), OS3+, Re5+, V4+, and Rh3+ at 0.1-0.5 at. % s ignificantly increases the photoreactivity for both oxidation and redu ction while Co(3+)and Al3+ doping decreases the photoreactivity. The t ransient absorption signals upon laser flash photolysis (lambda(ex)= 3 55 nm) at lambda = 600 nm are extended up to 50 ms for Fe3+-, V4+-, Mo 5+-, and Ru3+-doped TiO2 while the undoped Q-sized TiO2 shows a comple te ''blue electron'' signal decay within 200 mu s. Co3+ and Al3+-doped TiO2 are characterized by rapid signal decays with a complete loss of absorption signals within 5 mu s. The quantum yields obtained during CW photolyses are quantitatively correlated with the measured transien t absorption signals of the charge carriers. Photoreactivities are sho wn to increase with the relative concentration of trapped charge carri ers, The photoreactivity of doped TiO2 appears to be a complex functio n of the dopant concentration, the energy level of dopants within the TiO2 lattice, their d electronic configuration, the distribution of do pants, the electron donor concentration, and the light intensity.