Reaction between Fe³⁺ and aniline in the synthesis of PANI-γFe₂O₃ and PANI-Fe₃O₄ nanocomposites: Mechanistic studies and evaluation of parameters

Abstract

This work presents the results of experiments with PANI-γFe₂O₃ nanocomposites, synthesized in an acidic medium at 40°C under UV irradiation (λ = 365 nm), using maghemite (γFe₂O₃) and magnetite (Fe₃O₄). X-ray diffraction revealed the evolution of the transformations of the iron oxides throughout the synthesis. At the same time, oxidation/reduction reactions of iron interacting with aniline were observed in an electrochemical cell. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed changes in particle morphology during aniline polymerization, including growth and a tendency to agglomeration after 120 minutes of reaction. Energy dispersive spectroscopy (EDS) confirmed variations in the elemental composition, reflecting the partial conversion between maghemite and magnetite and demonstrating the influence of polymerization on the final composition of the material. The results reinforce the proposed model, according to which synthesis occurs in an oscillatory manner: Fe³ ⁺ ions from maghemite are reduced to Fe²⁺ from magnetite (Fe₃O₄), which oxidizes polyaniline in the polymerization process. Subsequently, part of the Fe²⁺ ions is re-oxidized under UV irradiation, reconverting magnetite into maghemite. This study clarifies the redox mechanism responsible for the phase transformations, making it possible to optimize the structural control of these materials for applications in energy storage devices, electrochemical sensors and environmental remediation systems. The results lay a solid foundation for expanding the use of functional nanomaterials in various technological and environmental areas.