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

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.