Localization of Conduction Band Electrons in Polycrystalline Ti02 Studied by ESR

Abstract

Adsorption of electron acceptors on partially reduced TiO 2 leads to the localization of mobile conduction band electrons which is indicated by the appearance of an ESR signal with g = 2.003. The localization process is accompanied by an electron transfer from donor centers in reduced TiO 2 (Ti 3+ ions) to adsorbed molecules. The ESR spectra show a decrease of the Ti 3+ signal intensity at gr -1.96. Additionally, in the case of O 2 , SO 2 and C 6 H 5 NO 2 adsorption, the ESR signals of the respective anion radicals are observed. Illumination of samples with an electron acceptor adsorbed enhances the g - 2.003 signal. The activation energy corresponding to the temperature dependence of the localization process has been determined to be ~ 1 kcal/mole in the temperature range - 140 to - 40 °C. In the case of O 2 and N 2 O the signal at g = 2.003 could be annihilated chemically by using propylene which reacted with the adsorbed electron acceptor and thus removed the species which reduced the electron mobility