An electron spin resonance study of the superoxide radical anion in polycrystalline magnesium oxide and titanium dioxide powders

Abstract

Treatment of a titanium dioxide polycrystalline powder with hydrogen peroxide produces a paramagnetic species with g₁= 2.022, g₂= 2.010, g₃= 2.003. This radical, observed at atmospheric pressure, is proposed to be subsurface O^˙–₂i.e. the superoxide radical anion. The same species, although with different g values; g₁= 2.074, g₂= 2.007, g₃= 2.002, is found for magnesium oxide (MgO) treated with H₂O₂. Two further sites for O^˙–₂ are also indicated by the spectra. Two of these O^˙–₂ species, similar to those found for the MgO product, are detected in an untreated mixture of 25% MgO₂–75% MgO. The concentration of the O^˙–₂ species in this mixture is increased by γ-irradiation.