Structural, magnetic, and metal-carboxylate interactions investigations in alginate-encapsulated MFe2O4 (M = Co, Ni, Zn)

Abstract

Magnetic ferrites nanoparticles (MFNs) MFe2O4 (M = Co, Ni, Zn) were synthesized via coprecipitation method and then encapsulated by Alginate polymer through cross-linking in aqueous calcium chloride solution. The obtained products were characterized by XRD, SEM, FTIR spectroscopy, TGA, and VSM. X-ray diffraction results indicate a decrease in diffractions picks intensities after encapsulating the MFNs with Alginate. Furthermore, cation distribution among interstitial sites was determined and it indicates an average inversion degree of 0.017, 0.142, and 0.8 for CoFe2O4, NiFe2O4, and ZnFe2O4 respectively, these values are in good agreement with the Rietveld refinement of X-ray diffraction patterns. The interaction of MFNs surface and the carboxylic group of alginates was investigated in detail for the first time, FTIR spectroscopy and VSM were used for this purpose. Therefore, from the wavenumber separation Δ values, between the frequencies of the characteristic peaks for asymmetric and COO− stretching vibration and symmetric COO− stretching vibration, we found 185.16 for Na-Alginate, 177.45 cm−1 for Alg@CoFe and Alg@Ni, while Alg@Zn have a wavenumber separation of 192.88 cm−1, which is characteristic to bidentate chelating coordination. The study of magnetic properties reveals a decrease of saturation magnetization after the encapsulation of nanoparticles, from 80.86, 47.17, and 4.36 emu/g for CoFe2O4, NiFe2O4 and ZnFe2O4 respectively to reach 18.43, 13.53, and 0.69 for their corresponding beads. This decrease is explained by the interaction between COO− and the surface of the nanoparticles.