Synthesis and properties of 1D manganese-doped hematite particles

Abstract

The properties of Mn-doped hematites and their Mn-doped precursors were investigated using the 57Fe Mössbauer spectroscopy, XRD, FT-IR, UV/Vis/NIR and FE SEM. Mn-doped goethite precursors were synthesized in a high alkaline pH medium starting with iron choline citrate. The XRD analysis of all Mn-doped goethites and Mn-doped hematites showed only the presence of a goethite or hematite crystal structure. The RT Mössbauer spectrum of reference goethite showed typical features of precipitated goethite. With increased Mn-doping the spectral lines of the goethite precursor were broadening, the hyperfine magnetic field decreased and the relative intensity of central quadrupole doublets increased. The RT Mössbauer spectra of Mn-doped hematite showed features of the hematite phase and increased relative intensity of a central quadrupole doublet which disappeared in the spectra recorded at liquid N2 temperature. The presence of this superparamagnetic component in the RT Mössbauer spectra is a direct consequence of Mn-doping. In the FT-IR spectra the characteristic IR bands sensitive to Mn-doping were identified. The UV/Vis/NIR spectra showed shifts of optical absorption bands and a strong absorption increase in the visible part of the spectrum. FE SEM images of Mn-doped goethite precursor showed a change in shape from rod to star-like particles. Upon heating at 300 °C for 4 h in air, the obtained Mn-doped hematite particles preserved the original morphologies of Mn-doped goethite precursors. Taking into account the superparamagnetic spectra (RT and liquid N2 temperature), XRD and the corresponding FE SEM images of Mn-doped hematite particles it can be concluded that these particles contained substructure. In this substructure of Mn-doped hematites the fraction of superparamagnetic crystallites (domains) is given by calculated value for the superparamagnetic doublet present.