Mössbauer studies of core-single-shell and core-double-shell polymer functionalized magnetic nanoparticles

Two different magnetic core–shell nanohybrids, i) single coated magnetic nanoparticles (NPs) with polyacrylonitrile (PAN) and ii) doubly coated with SiO₂ and polyaniline (PANI), were synthesized by a modified chemical co-precipitation method and their structural, vibrational, colloidal, and magnetic properties were systematically studied. XRD and Rietveld refinement have shown the coexistence of 7.4(1) nm γ-Fe₂O₃ NPs, amorphous silica, and the polymeric chains of PANI for the core-double-shell nanohybrid, i.e., γ-Fe₂O₃@SiO₂@PANI NPs. The γ-Fe₂O₃ NPs in this nanohybrid had reduced their sizes when compared to bare γ-Fe₂O₃ NPs or to γ-Fe₂O₃ NPs in the γ-Fe₂O₃@PAN nanohybrid. In addition, it has a controlled surface charge potential, i.e., it has been changed from positive in bare γ-Fe₂O₃/NPs to negative in γ-Fe₂O₃/PAN NPs (or in γ-Fe₂O₃@SiO₂ NPs). Raman and Infrared studies have also confirmed the surface functionalization. ⁵⁷Fe Mössbauer spectra of the 7.4(1) nm γ-Fe₂O₃@SiO₂@PANI NPs revealed superparamagnetic fluctuations above 150 K, suggesting that the coating with PANI has inhibited particle agglomeration and reduced interparticle magnetic interactions. In contrast, ⁵⁷Fe Mössbauer spectra of the γ-Fe₂O₃/PAN NPs displayed static sextets, as commonly found in NPs bigger than 10 nm. Considering the small particle sizes (< 10 nm), the NP controlled surface charge potential and the good magnetic properties, it can be inferred that these nanohybrids are suitable for magnetic remediation processes.