Slow Equilibration between Spectroscopically Distinct Trap States in Reduced TiO2Nanoparticles.
Understanding the nature of charge carriers in nanoscale titanium dioxide is important for its use in solar energy conversion, photocatalysis, and other applications. UV-irradiation of aqueous, colloidal TiO2nanoparticles in the presence of methanol gives highly reduced suspensions. Two distinct types of electron traps were observed and characterized by EPR and optical spectroscopies. The relative populations of the states depend on temperature, indicating a small energy difference, ΔH° = 3.0 ± 0.6 kcal/mol (130 ± 30 meV). Interconversion between the electron traps occurs slowly over the course of minutes to hours within the temperature range studied here, 0-50 °C. The slow time scale implies that interconversion involves changes in structure or stoichiometry, not just the movement of electrons. This occurrence of slow structural modification with changes in trap state occupancy is likely a general feature of reduced TiO2systems at thermodynamic equilibria or photostationary states and should be considered in the design of TiO2-containing devices.
Department of Chemistry, Yale University , New Haven, Connecticut 06520-8107, United States.
Jennifer L
0000-0002-2611-1011
JL
Peper
Department of Chemistry, Yale University , New Haven, Connecticut 06520-8107, United States.
David J
DJ
Vinyard
Department of Chemistry, Yale University , New Haven, Connecticut 06520-8107, United States.
Gary W
0000-0002-7040-1892
GW
Brudvig
Department of Chemistry, Yale University , New Haven, Connecticut 06520-8107, United States.
James M
JM
Mayer