Atomic scale study of thermal reduction of nano goethite coexisting with magnetite

Abstract

Evolution of the local structure and magnetic properties of nano particles of goethite having magnetite as a composite due to controlled annealing treatments in vacuum has been studied using Mossbauer spectroscopy. Importance of size, defect associated with structural OH- for the observed structural and magnetic properties of goethite has been emphasized in this study. Present Mossbauer results show that thermal annealing at low temperatures (420-550 K) lead to a partial conversion / reduction of orthorhombic goethite to cubic spinel oxides such as maghemite and off-stochiometric magnetite. This study further establishes that annealing treatments beyond 650 K predominantly results in topotactic conversion of goethite to haematite. Underlying physics of the transitions of goethite to iron oxides and the important role of desorbed hydrogen for the orthorhombic to cubic structural transitions has been elucidated in this study.

Nanoparticulate inorganic UV absorbers: a review

“…While iron(III) oxide-hydroxide can be easily obtained by precipitation, prolonged drying, or relatively mild heat treatment can, however, convert a high percentage of the material into UV-transmitting magnetite. 177 This is a major problem for industrial processes, and while particles smaller than 20 nm can be obtained, they consist mostly of non UV-absorbing magnetite. 178 Among the smallest dispersed nanoparticles reported are those prepared by microemulsion synthesis.…”

Alkali-cation-incorporated and functionalized iron oxide nanoparticles for methyl blue removal/decomposition

“…This implies that the diffusion of alkali cations is higher into the lattice along with the adsorption on the surface of NPs incubated in hydroxide solution. The rearrangement of an fcc stacking sequence to an hcp-type stacking sequence of oxygen layers results in a structural transformation from cubic spinel to α-Fe 2 O 3 [50,51]. The introduction of interstitial defects in between the planes hardens the systems, i.e.…”