Preparation of Magnetic Nanoparticles via a Chemically Induced Transition: Role of Treating Solution’s Temperature

Abstract

Using FeOOH/Mg(OH)2 as precursor and FeCl2 as the treating solution, we prepared γ-Fe2O3 based nanoparticles. The FeCl2 treating solution catalyzes the chemical reactions, dismutation and oxygenation, leading to the formation of products FeCl3 and Fe2O3, respectively. The treating solution (FeCl2) accelerates dehydration of the FeOOH compound in the precursor and transforms it into the initial seed crystallite γ-Fe2O3. Fe2O3 grows epitaxially on the initial seed crystallite γ-Fe2O3. The epitaxial layer has a magnetically silent surface, which does not have any magnetization contribution toward the breaking of crystal symmetry. FeCl3 would be absorbed to form the FeCl3·6H2O surface layer outside the particles to form γ-Fe2O3/FeCl3·6H2O nanoparticles. When the treating solution’s temperature is below 70 °C, the dehydration reaction of FeOOH is incomplete and the as-prepared samples are a mixture of both FeOOH and γ-Fe2O3/FeCl3·6H2O nanoparticles. As the treating solution’s temperature increases from 70 to 90 °C, the contents of both FeCl3·6H2O and the epitaxial Fe2O3 increased in totality.