Ultrasonic-assisted in situ synthesis and characterization of superparamagnetic Fe3O4 nanoparticles

Highlights: → Fe3+ as the only Fe source for preparing Fe3O4 nanoparticles through in situ cover and sonication method. → Surface modification enables the reduction of the grain size of Fe3O4. → Increasing temperature reduces grain size of Fe3O4 until it exceeds 80 deg. C. → Increasing pH values reduces grain size of Fe3O4 until it exceeds 11. → Saturation magnetizations depend on the grain size of Fe3O4 nanoparticles. - Abstract: Superparamagnetic Fe3O4 nanoparticles were synthesized via a modified coprecipitation method, and were characterized with X-ray diffraction (XRD), vibrating sample magnetometer (VSM), Zeta potential and FT-IR, respectively. The influences of different kinds of surfactants (sodium dodecyl benzene sulfonate, polyethyleneglycol, oleic acid and dextran), temperatures and pH values on the grain size and properties were also investigated. In this method, Fe3+ was used as the only Fe source and partially reduced to Fe2+ by the reducing agent with precise content. The following reaction between Fe3+, Fe2+ and hydroxide radical brought pure Fe3O4 nanoparticles. The tiny fresh nanoparticles were coated in situ with surfactant under the action of sonication. Comparing with uncoated sample, the mean grain size and saturation magnetization of coated Fe3O4 nanoparticles decrease from 18.4 nm to 5.9-9.0 nm, and from 63.89 emu g-1 to 52-58 emu g-1 respectively. When oleic was used as the surfactant, the mean grain size of Fe3O4 nanoparticles firstly decreases with the increase of reaction temperature, but when the temperature is exceed to 80 deg. C, the continuous increase of temperature resulted in larger nanoparticles. the grain size decreases gradually with the increasing of pH values, and it remains unchanged when the PH value is up to 11. The saturation magnetization of as-prepared Fe3O4 nanoparticles always decreases with the fall of grain size.