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

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 g_zz values presented in the sample.