Localization of Conduction Band Electrons in Polycrystalline Ti02 Studied by ESR

Abstract

Adsorption of electron acceptors on partially reduced TiO2 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 TiO2 (Ti3+ ions) to adsorbed molecules. The ESR spectra show a decrease of the Ti3+ signal intensity at gr -1.96. Additionally, in the case of O2, SO2 and C6H5NO2 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 O2 and N2O 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

EPR Investigations of G-C3N4/TiO2 Nanocomposites

“…ratio 3:1) measured in the dark at room temperature (RT) and at 100 K. In the EPR spectra of pristine g-C3N4, only a nearly isotropic signal at g = 2.003 (*) was detected (Figure 1), often observed in the EPR spectra of graphitic carbon nitride and attributed to the conduction electrons in the localized π-states of g-C3N4 [30]. An analogous EPR signal found in the TiO2 matrix upon high-temperature treatment was assigned to the medium-polarized conduction electrons or oxygen vacancies [31,32]. Consequently, these electron excess centers may be simultaneously generated during the synthesis of g-C3N4/TiO2 photocatalysts at 550 °C ( Figure 1).…”

Interplay between O2 and SnO2: Oxygen Ionosorption and Spectroscopic Evidence for Adsorbed Oxygen

“…* signals with g av % 1.90 attributed to the 1) the unionised deep donor levels, 2) the singly ionised oxygen vacancy, 3) shallow defects; [87,97] * signals with g av (or g iso ) % 1.98 assigned to Sn 3 + ions; [98,99] * isotropic signal with g % g e (2.0023) gives no explanation for SnO 2 . This signal is usually observed on n-type semiconducting oxides; its interpretation is not clear and very controversial: phrases such as "medium polarised electrons", [100] "conduction electrons localised close to adsorbed surface acceptor-like species" [101] are used;…”

Synthesis, Characterization, and Photocatalytic Activities of Nanoparticulate N, S-Codoped TiO2 Having Different Surface-to-Volume Ratios

“…It is often is assumed that photoexcited electrons in TiO 2 are trapped on Ti IV sites or oxygen vacancies V o , and it is believed that molecular oxygen is adsorbed on the same sites. 2,40,42 By means of LT-ESR, we investigated the presence of V o in undoped TiO 2 and D-TKP 102-A powders (Figure 10). A signal with g ) 2.0030 was found for the powder D-TKP-102-A.…”