One-step solvothermal approach for preparing soft magnetic hydrophilic PFR coated Fe3O4 nanocrystals

The hydrophilic phenol formaldehyde resin coated Fe3O4 nanocrystals are prepared via a novel one-step solvothermal approach at 160 °C for 6–9 h without inert gas protection. Water–glycol mixture is used as solvent in common air surrounding. FeSO4·7H2O, hexamethylenetetramine and phenol are used as resource materials without any others additives or surfactants. The transmission electronic microscope images show the samples are composed of sphere-like particles with sizes about 10–20 nm. The X-ray diffraction data indicate cube-phase Fe3O4 nanocrystals are obtained at given conditions. Fourier transform infrared spectra further reveal the samples are consisted of Fe3O4 and PFR. Without modified pH and added surfactants, the solubility of the obtained sample is over 1% in water, which is far more than its solubility in toluene. Room-temperature hysteresis loop indicate that the as-obtained nano-crystals possess soft magnetic properties with high saturated mass magnetization (50.6 emu/g) and negligible coercivity.

► We demonstrated a novel solvothermal process for one-step preparing water-soluble PFR coated Fe3O4 nano-crystal.
► The system is performed in water-glycol mixture solvent with an ordinary air surrounding at 140-180°C for 3-6 h.
► The as-obtianed PFR coated Fe3O4 nanocrystals with the size in 10-20 nm reveals remarkable soft magnetic properties including high saturated mass magnetization value (beyond 50.6 emu/g), and negligible coercivity and retentivity value.