Effect of heat treatment time in oxygen atmosphere on the stabilization of magnetite NPs: synthesis, characterization, and magnetic response

Abstract

Abstract This study describes the synthesis of magnetite (Fe3O4) nanoparticles (NPs) using the sol-gel method with ethylene glycol as a chelating agent. The use of this agent allowed for the complete crystallization of pure magnetite phase at 200°C, without atmosphere control during the thermal treatment for crystallization. Different thermal treatment times (4, 8, 16, 24, and 48 hours) and their effects on the structure, microstructure, and magnetic properties of the nanoparticles were evaluated. The results showed that the magnetite phase remained stable and pure up to 8 hours of thermal treatment in an air atmosphere, with nanoparticles exhibiting a crystallite size of 30 nm and saturation magnetization of 57 emu/g. After 16 hours, the presence of a magnetite/hematite heterostructure was observed, with approximately 22.5% hematite (α-Fe2O3). The presence of hematite increased with the thermal treatment time, reaching 25.4% at 48 hours, and the saturation magnetization decreased with the reduction of magnetite phase in the nanoparticles. Additionally, the NPs dispersion in different liquid media (isopropyl alcohol, distilled water, and ethylene glycol) was verify to evaluated suspension stability and total magnetic collection time, aiming for potential applications as a magnetic fluid.