Oxidative Degradation of Methylene Blue Using Mn3O4 Nanoparticles

Abstract

Mn3O4 nanoparticles were synthesized from one-step reduction of KMnO4 with glycerol at 80 °C. The structural and surface morphological characterizations were carried out using FT-IR, XRD, and FESEM analyses. The elemental composition was evidenced from EDX analysis. XRD analysis showed the tetragonal crystal geometry of Mn3O4 nanoparticles with an average crystallite size of ∼20 nm. The surface morphology of the Mn3O4 nanoparticles was found to be spherical from the FESEM image. The Mn3O4 nanoparticles were then tested as a potential oxidant for the decolorization of methylene blue (MB) and found to be capable of N-demethylation of MB forming thionine as the final product, and removing 80% of the dye in approximately 1 h. The decolorization of MB by Mn3O4 occurred through a surface mechanism, i.e., formation of surface precursor complex between MB and surface-bound Mn (II, III), where, electron transfer occurs within the surface complex. The effect of suspension pH (3–4 < pHpzc; 5–10 > pHpzc) on MB decolorization was assessed. Suspension pH exerted double-edged effects on MB decolorization by influencing the formation of surface precursor complex, and reducing potential of the system.