Magnetic Fluids Based on γ-Fe2O3 and CoFe2O4 Nanoparticles Dispersed in Ionic Liquids

The disclosure of magnetic ionic liquids (MILs) as stable dispersions of surface modified gamma-Fe2O3 or CoFe2O4 nanoparticles (NPs) in the 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4) ionic liquid is reported. The magnetic NPs were characterized by X-ray powder diffraction, transmission electron microscopy, and Raman spectroscopy. The surface modified NPs have proved to form stable dispersions in BMIBF4 in the absence of water and behave like a magnetic ionic liquid. The MILs have been characterized by Raman spectroscopy, magnetic measurements, and DSC. The stability of the magnetic NPs in BMIBF4 is consistently explained by assuming the formation of a semiorganized protective layer composed of supramolecular aggregates in the form of [(BMI)(2)(BF4)(3)](-). A superparamagnetic behavior and saturation magnetization of ca. 18 emu/g for a sample containing 30% w/w maghemite NPs/BMIBF4 have been inferred from static and dynamic magnetic measurements. DSC results have shown that the MIL composed of 30% w/w CoFe2O4 NPs/BMIBF4 remains a liquid phase down to -84 degrees C.