Chemistry of Colloidal Manganese Dioxide. 1. Mechanism of Reduction by an Organic Radical (A Radiation Chemical Study)

Article abstract of DOI:10.1021/j100272a040

Transparent sols of managene(IV) oxide and manganese(III) oxide were prepared by γ-irradiating solutions of potassium pemanganate.The reaction of radiolytically produced 1-hydroxy-1-methylethyl radicals, (CH3)2C^.OH, with the MnO2 colloid was investigated by recording the accompanying changes in optical absorption and conductivity.The yield of reduction is 5.7 MnO2 molecules reduced per 100eV.Electron transfer to the collodial particles leads to the release of OH^- ions, depending on the pH and the degree of reduction.Mn3⁺ centers are formed in the reduction which accelerates the reaction of the radicals.A fast conproportionation reaction between Mn²⁺ and Mn⁴⁺ centers at the surface of the collodial particles is postulated in alkaline sols.A strong accumulation of Mn³⁺ centers thus is achieved.In acidic solutions, the Mn³⁺ centers disproportionate.Mn³⁺ centers also are formed when Mn²⁺ ions are added to a MnO2 sol of pH > 4.Is is also pointed out that the absorption spectra of colloidal and macrocrystalline MnO2 are distinctly different.