Obtaining superhydrophopic magnetic nanoparticles applicable in the removal of oils on aqueous surface

Abstract

Iron oxide nanoparticles have high saturation magnetization values and their surfaces are easily modified by the insertion of functional groups such as carboxylic acids, surfactants, and polymers. In this work, iron oxide nanoparticles were functionalized with glycerol molecules modified by an esterification reaction with monocarboxylic acid, for their application in the removal of oils in aqueous surface. The nanoparticles were prepared by the coprecipitation method by alkaline hydrolysis of Fe2+ and Fe3+ ions in aqueous medium. The precursor used in the coating was obtained from functionalization of glycerol with stearic acid. The surfaces of iron oxide were coated by two different procedures: i) adding the precursor to the aqueous suspension of the purified iron oxide particles; and ii) preparation, purification and drying of the iron oxide particles and subsequent mixing with the precursor in isopropanol. The results obtained by the FTIR and NMR techniques showed that modification of glycerol with stearic acid occurs by esterification of the primary hydroxyl forming 2,3-dihydroxypropyl stearate. The characterizations carried out in the nanoparticles suggest the presence of cubic structure of inverse spinel, with lattice parameter and stoichiometry close to that of magnetite, which would be described as partially oxidized magnetite. The results obtained by FTIR, TGA and VSM of nanoparticles coated with 2,3-dihydroxypropyl stearate indicate the presence of organic material coating the magnetic nanoparticles. The particles showed certain sphericity with an average size of 11.17 nm and superhydrophobicity (164°). These samples exhibit chemical affinity for oil and are able to move and remove high and low viscosity oils on the water surface by applying an external magnetic field, obtaining an oil removal capacity of about 68 g of Bardahl oil per gram of nanoparticles. In addition, the nanoparticles are easily removed from the oil by a simple treatment with organic solvent, preserving its hydrophobic and oil removal characteristics.