Ferrofluids from Magnetic−Chitosan Hybrids

Magnetic nanoparticles coated with chitosan or quaternized chitosan were synthesized by a new route and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature dependent and in-field Mössbauer spectroscopy, FTIR, thermal analysis (TG/DTA), zeta potential, and magnetic measurements. The prepared ferrofluids were stable for a relatively long time. Mössbauer spectra recorded in an external magnetic field of 5 T establish the formation of “nonstoichiometric magnetite” exhibiting the perfect ferrimagnetic ordering with a low degree of spin canting and frustration. Magnetic measurements confirm the desired properties of the magnetic chitosan for biomedical applications including the superparamagnetic character at room temperature and a high saturation magnetization achievable at low applied fields. The successful and full capping of particles is indicated mainly from magnetic and DTA data through the suppressed interparticle interactions and a significant shift in the transformation temperature of the magnetic cores to hematite. The core−shell structure is definitely proved by TEM observations showing the well crystalline cubic particles with the log-normal size distribution between 10 and 40 nm, which are fully coated with narrow shell of the chitosan matrix.