Evaluation of polymer-coated magnetic nanoparticles for oil separation under environmentally relevant conditions: effect of ionic strength and natural organic macromolecules

Abstract

Oil spills in marine and non-marine environments can have dramatic effects on the environment. Previously, we reported near 100% removal of a reference MC252 oil using polyvinylpyrrolidone (PVP)-coated magnetic nanoparticles (NPs) from an oil–water mixture in ultra-pure water and synthetic sea water with a low concentration of Suwannee River fulvic acid (SRFA). In this study, the same type of NPs was used to remove oil from oil–water mixtures (oil concentration used was 0.15 ± 0.05 g L⁻¹) in synthetic freshwaters and sea water in the presence and absence of low (1 ppm) and high (10 ppm) concentrations of SRFA or alginic acid. For the optimum NP concentration (17.6 ppm) and separation time (1 h), the data showed essentially 100% oil removal from synthetic freshwaters and sea water in the absence of natural organic macromolecules (NOM). Nearly 100% of C9–C20 alkanes were removed as measured by gas chromatography–mass spectrometry (GC-MS), although removal of the longer chain alkanes was slightly lower. The presence of NOM led to a statistically significant decrease in oil removal with NOM acting as a competitive phase for either PVP or oil and reducing NP–oil interactions driven by the hydrophobic effect of PVP coating. Ionic strength facilitated oil sorption presumably by enhancing the magnetic separation of the oil–NP complex or altering PVP hydrophobicity. Alteration of the separation conditions allowed optimal oil removal, with essentially 100% oil removal under most but not all conditions. Results show that the use of these NPs is a cheap, facile and reliable technique for removing oil under a wide range of environmentally relevant conditions.