Unusual Stabilization of Zinc Peroxide by Manganese Oxide: Mechanistic Understanding by Temperature-Dependent EPR Studies

Nanocrystalline zinc peroxide is passivated against further oxidation by the addition of minute, substoichiometric amounts of potassium permanganate, which also endows it with increased thermal stability. The oxidation state of manganese and the passivation mechanism are deciphered by a comparative electron paramagnetic resonance (EPR) study of the manganese-doped zinc peroxide nanoparticles and manganese oxide formed by reduction of permanganate by hydrogen peroxide as well as unmodified ZnO2 nanoparticles. Temperature-dependent in situ EPR studies at elevated temperatures allowed us to trace simultaneously the temperature-dependent changes in abundance of superoxide radicals and the formation of Mn(IV) species and also to identify Mn(III) species at cryotemperatures. We conclude that the passivation is caused by Mn(III) complexes that act as antioxidants removing superoxide radicals, which are abundant in zinc peroxide and even more so in the manganese-doped zinc peroxide.