Structural and magnetic characterization of Ni nanoparticles synthesized in ionic liquids

Colloidal suspensions of cubic fcc Ni(0) nanoparticles of 5.0-6.0 nm in sizes were obtained in ionic liquids derived of the 1-n-butyl-3-methylimidazolium cation associated with different anions (tetrafluoroborate (BF4), trifluoromethane sulphonate (CF3SO3), and bis-trifluoromethane-sulfonimidate (N(Tf)2)). These ionic liquids act as stabilizing agents of the nanoparticles. X-ray diffraction shows clearly Ni(0) nanoparticles embedded in these ionic liquids avoiding their agglomeration. X-ray absorption spectroscopy evidenced that the Ni(0) nanoparticles are surrounded by a cap layer due to the steric and electrostatic interaction with the ionic liquids. Transmission electron microscopy and Small angle X-ray scattering also show a strong evidence of this interaction. The magnetization curves exhibit typical superparamagnetic behavior with no hysteresis. The thermomagnetic curves show superparamagnetic response with blocking temperatures around 200 K.