Microwave synthesis of magnetic Fe3O4 nanoparticles used as a precursor of nanocomposites and ferrofluids

Methods to synthesize magnetic Fe3O4 nanoparticles and to modify the surface of particles are presented in the present investigation. Fe3O4 magnetic nanoparticles were prepared by the co-precipitation of Fe 3+ and Fe 2+. NH3 . H2O was used as the precipitating agent to adjust the pH value, and the aging of Fe304 magnetic nanoparticles was accelerated by microwave (MW) irradiation. The obtained Fe304 magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). The average size of Fe304 crystallites was found to be around 8-9 nm. Thereafter, the surface of Fe304 magnetic nanoparticles was modified by stearic acid. The resultant sample was characterized by FT-IR, scanning electron microscopy (SEM), XRD, lipophilic degree (LD) and sedimentation test. The FT-IR results indicated that a covalent bond was formed by chemical reaction between the hydroxyl groups on the surface of Fe304 nanoparticles and carboxyl groups of stearic acid, which changed the polarity of Fe304 nanoparticles. The dispersion of Fe304 in organic solvent was greatly improved. Effects of reaction time, reaction temperature and concentration of stearic acid on particle surface modification were investigated. In addition, Fe304/polystyrene (PS) nanocomposite was synthesized by adding surface modified Fe304 magnetic nanoparticles into styrene monomer, followed by the radical polymerization. The obtained nanocomposite was tested by thermogravimetry (TG), differential scanning calorimetry (DSC) and XRD. Results revealed that the thermal stability of PS was not significantly changed after adding Fe304 nanoparticles. The Fe304 magnetic fluid was characterized using UV-vis spectrophotometer, Gouy magnetic balance and laser particle-size analyzer. The testing results showed that the magnetic fluid had excellent stability, and had susceptibility of 4.46 x 10-8 and saturated magnetization of 6.56 emu/g. In addition, the mean size d (0.99) of magnetic Fe304 nanoparticles in the fluid was 36.19 nm.