Magnetization oscillations in polyaniline-γFe2O3 nanocomposites

• Published in: Journal of magnetism and magnetic materials 2019-10, Vol.487, p.165312, Article 165312
• Main Authors: Monsalve, J.G., Rodrigues, A.R., de Araújo, A.C.V., de Azevedo, W.M., Machado, F.L.A.
• Format: Article
• Language: English
• Subjects: Aniline; Chemical reactions; Iron oxides; Iron sulfates; Magnetic properties; Magnetite; Magnetization; Nanocomposites; Organic chemistry; Oscillations; Oxidation; Polyanilines; Polymerization; Reaction synthesis; Reaction time; Thermogravimetry; Transformations; Ultraviolet radiation; X-ray diffraction
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2019.165312

•Oscillating chemical reaction.•Maghemite reduction.•Model of Lotka-Volterra. PANI-γFe2O3 nanocomposites were synthesized under intense UV radiation, λ = 365 nm, at different temperatures. In this synthesis, the oxide acts as an oxidant of PANI during polymerization. Thermogravimetry measurements confirmed that polymerization was more pronounced for PANI-γFe2O3 than PANI-Fe3O4. This was probably due to the larger number of Fe+3 ions in the former, which are responsible for the aniline oxidation. A large decrease in magnetization over the reaction time was observed in the samples synthesized at 60 °C. This diminution is attributed to the transformation of γ-Fe2O3 into α-Fe2O3, evidenced by both X-Ray diffraction analysis and the corresponding presence of the Morin transition. In samples synthesized at 80 °C, a more accelerated transformation from the γ-Fe2O3 phase to α-Fe2O3 was initially observed, followed by full dissolution of the iron oxide in ferrous sulfate, FeSO4. The magnetic properties of the samples synthesized at 40 °C oscillate as a function of the reaction time. This is because the chemical reaction synthesis presents sustained oscillations, as confirmed by magnetization measurements taken during the process. The maghemite Fe+3 ions were reduced by the polymerization of the aniline, favoring the formation of magnetite. On the other hand, the magnetite Fe+2 ions were oxidized by UV radiation, leading to the opposite transformation. The magnetization of these phases is different, which causes sustained oscillation in their values. The later results were analyzed using the Lotka-Volterra model and the parameters agreed well with the experimental data.