Green synthesis of single phase hausmannite Mn3O4 nanoparticles via Aspalathus linearis natural extract

Abstract

Nowadays, green synthesis of nanoparticles using plant precursors has been extensively studied. However, less attention has been given to Mn3O4. This contribution validates the synthesis of single-phase Hausmannite Mn3O4 nanoparticles by a green approach without using any standard acid/base compounds, surfactants, and organic/inorganic dissolving agents. The chemical chelation of the Mn precursor was performed via bioactive compounds of the Aspalathus Linearis’ extract, an African indigenous plant. Annealing at 400 °C for ~ 1 h was required to crystallize the small amorphous nanoparticles with an initial bimodal size distribution peaking at leftlangle {phi_{1} } rightrangle ~ 4.21 nm and leftlangle {phi_{2} } rightrangle ~ 8.51 nm respectively. Such annealing lead to increase in the diameter of the nanoparticles from 17 to 28 nm.The morphological, structural, vibrational, surface, and photoluminescence properties of the single-phase Hausmannite nanoparticles were comprehensively investigated by High Resolution Transmission Electron Microscopy(HRTEM),Energy Dispersive X-ray Spectroscopy (EDS), X-ray Diffraction (XRD), Raman and X-rays Photoelectron Spectroscopy (XPS), spectroscopy as well as room temperature photoluminescence. Structural and morphological investigations revealed the formation of quasi-spherical nanoparticles having a single phase Hausmannite Mn3O4 crystal structure. XPS results also validated the XRD results about the formation of Hausmannite Mn3O4 nanoparticles. Raman investigations allowed a crystal-clear distinction between the Mn3O4 nature of the nanoparticles from the potential γ -Mn2O3 phase as both phases belong to the same space group and both assume tetragonally-distorted cubic lattices of nearly similar dimensions. The optical studies of the single phase Hausmannite crystalline nanoparticles exhibited a broad photoluminescence in the spectral range of 300–700 nm, which is ideal for emission devices.Graphic abstract