[en] Full text: Magnetic nanocolloids are ultra-stable colloidal dispersions of magnetic nanoparticles in a specific carrier liquid [1]. Recently, cobalt ferrites (CoFe2O4) have been widely studied for their potential application in diverse areas such as biotechnology, biomedicine, for example, for cleaning wastewater through adsorption or as a vector of drugs to treat cancer cells. Thus, this work synthesized a magnetic ferrofluid with nanoparticles based on cobalt ferrite with a maghemite surface layer (γ-Fe₂O₃), by the hydrothermal co-precipitation method [2], in which they were dispersed in an aqueous medium. The nanoparticles then undergo the process of functionalization and separation in size. The magnetic ferrofluid with electric double layer nanoparticles (EDL-MF) was submitted to several characterization techniques. With the data obtained by XDR and MET it was possible to verify the size, structure and shape of the nanoparticles, besides observing that the size separation process was effective. With the AAS we were able to determine the proportion of elements of the core/shell structure and from SAXS the degree of poly dispersion of the nanocolloid. This study aimed at a dispersion in a Deep Eutectic Solvent (DES), considered a green solvent because it is biodegradable, non-toxic, besides having a high thermal stability, among other characteristics that can make viable applications in vivo for being biocompatible [3]. References: [1] Berkovski, B. M. Magnetic fluids and applications handbook; Unesco series of learning materials; New York : Begell House, 1996, 2001. [2] Tourinho, F. A.; Franck, R.; Massart, R. ;Journal of Materials Science 1990, 25, 3249. [3] Zhang, Q.; De Oliveira Vigier, K.; Royer, S.; Jérôme, F. ;Chemical Society Reviews 2012, 41, 7108. (author)