Characterization and magnetic properties of nickel and nickel-iron nanoparticle colloidal suspensions in imidazolium-based ionic liquids prepared by magnetron sputtering

Colloids of Ni and Ni-Fe nanoparticles in two imidazolium-based ionic liquids were prepared by magnetron sputtering of nickel and co-sputtering of nickel and iron, respectively, on the surface of the ionic liquids. The liquids consist of the same cation 1-butyl-3-methylimidazolium [BMIM] and two different anions: hexafluorophosphate [PF6] or bis(trifluoromethylsulfonyl)imide [Tf2N]. The nanoparticle preparation method was based on extremely low vapour pressures of the ionic liquids, which allowed them to be used in vacuum. Magnetic properties of the metal nanocolloids (NCs) and the pure ionic liquids were analysed in detail, including the effect of ageing over a period of more than 30 months. The NCs were studied by TEM microscopy, UV-Vis spectroscopy and SQUID magnetometry. They were stable in time. No sedimentation or agglomeration of nanoparticles was observed after more than 24 months. The ionic liquid ions play more than the role of a surfactant, e.g. magnetic data gave evidence of a strong interaction between the ionic liquids and metal nanoparticles.