Superoxide Radical Formed on the TiO₂ Surface Produced from Ti(OiPr)₄ Exposed to H₂O₂/KOH

Abstract

In this study, the superoxide radical O2•− formed by treating Ti(OR)4 (R = iPr, nBu) with H2O2 in the presence of KOH was detected in the EPR spectra. The g-tensor of this radical differs from the typical values reported for a superoxide on various TiO2 surfaces. On the other hand, similar g-tensor components g||(zz = 2.10 ± 0.01, g⊥ = 2.005 ± 0.003 assigned to the O2•− were previously observed for radicals in aqueous solutions in the presence of K2O, alkaline solutions of DMSO, and water/DMSO mixtures. A common factor in all these systems is the presence of alkali ions. However, there was no structural support for the possible interaction of alkali ions with a superoxide in these systems. The use of multifrequency pulsed EPR techniques in this work revealed the stabilization of the O2•− near the K+ ion and its involvement in a strong hydrogen bond with the surface. These findings are consistent with the features previously reported for superoxides on a Na pre-covered MgO surface. Interactions with a closely located 23Na and a strongly coupled 1H proton were also seen in the HYSCORE spectra but assigned to two different superoxides with various gzz values presented in the sample.

Keywords

• TiO<b>₂</b>
• hydrogen peroxide H₂O₂
• KOH
• superoxide radical
• pulsed EPR
• hyperfine coupling