pH dependent catalytic redox properties of Mn3O4 nanoparticles.

Manganese-based materials have unique redox properties, attractive to many applications in the energy, environment and biomedical sectors. In particular, Mn 3 O 4 is known to act as both an oxidising and a reducing agent. However, pH-dependence of the redox properties of Mn 3 O 4 nanoparticles is not yet well understood. In this study, Mn 3 O 4 nanoparticles were mechanochemically synthesised and their redox catalytic activities were studied under different pH conditions. Mn 3 O 4 nanoparticles with sizes between 10 and 90 nm were prepared via a mechanically-induced solid-state displacement reaction between MnCl 2 and K 2 CO 3 and subsequent heat treatment. The effect of pH on the oxidative decomposition of a model organic dye revealed that Mn 3 O 4 nanoparticles showed oxidative catalytic activity only when pH was below 5. At a higher pH, Mn 3 O 4 nanoparticles showed strong free-radical scavenging activities, suitable for reducing oxidative stress in many locations of the body and for creating new design of energy-storage materials. • Mn 3 O 4 nanoparticles were synthesised by a green method. • Effect of pH on the catalytic redox properties of Mn 3 O 4 was reported. • Mechanism of the pH dependent redox catalytic property was proposed. [ABSTRACT FROM AUTHOR]