Magneto-sensitive hybrid nanocomposites of water-soluble sodium alginate cross-linked with calcium ions and maghemite

A synthetic procedure is described for preparation of magneto-sensitive nanocomposites from maghemite nanoparticles and a natural polysaccharide, sodium alginate cross-linked with calcium ions. With this procedure, a series of nanocomposites was synthesized and characterized by spectrophotometry, transmission electron microscopy, X-ray diffraction, Mossbauer spectroscopy, Fourier transform IR-spectroscopy and magnetometry with the following main conclusions: (a) The nanocomposites retain their solubility in water unless the iron content exceeds 18.1 +/- 0.2 wt%. (b) Only gamma-Fe2O3 nanoparticles are included in the nanocomposite. (c) Size of nanoparticles lies within a 4-20 nm range with a dominant diameter of 7 +/- 1 nm. (d) Maghemite nanoparticles bind to the alginate matrix via formation of electrostatic and coordination contacts between the surface Fe3+ maghemite ions and functional alginate groups. (e) The nanocomposites exhibit properties which are characteristic for soft magnetic materials since they have a low coercive force. (f) Magnetic characteristics of the nanocomposites, saturation magnetization and residual magnetization, are effectively controlled by the maghemite content. (g) An external magnetic field causes the nanocomposites to move in an aqueous dispersion.