Local Environment of Superoxide Radical Formed on the TiO2 Surface Produced From Ti(OiPr)4 Exposed to H2O2

Rimma I. Samoilova, Sergei A. Dikanov

Research output: Contribution to journalArticlepeer-review

Abstract

A selective heterogeneous catalyst with the superoxide anion O2•− stable at room temperature, generated by treating Ti(OR)4 (R = iPr, nBu) with H2O2, was previously reported and used for the oxidation of organic compounds. It was proposed that exceptional stability of the O2•− is resulted from its stabilization near Ti+4 cation on the TiO2 surface with the participation of water molecules and/or OH groups. In this article, we performed high-resolution pulsed EPR study on the O2•− in this catalyst with the aim to obtain quantitative information about its interactions with the surrounding molecules. Our data has shown that the O2•− is involved in weak hyperfine interactions with protons in the nearest environment, which do not exceed a value of 2 MHz. It corresponds to an Os…H distance of ≥ 3 Å that excludes the formation of hydrogen bonds. The analysis of possible structures of O2•− adsorption on TiO2 surface taking into account our results and lack of radical mobility at room temperature previously observed in EPR spectra led us to suggest that the O2•− is stabilized in the form of superoxo bridge coordinated with two titanium atoms.

Original languageEnglish (US)
Pages (from-to)1089-1104
Number of pages16
JournalApplied Magnetic Resonance
Volume53
Issue number7-9
DOIs
StatePublished - Sep 2022

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

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