Application of Polymer-coated Magnetic Nanoparticles for Oil Separation

摘要

Oil spills and storm water runoffs can have serious impact on the environment with potentially major economic impacts. Given the limitation of current oil clean-up technique, the application of nanotechnology for oil remediation has been widely studied showing a promising avenue of research. This dissertation reports a cheap, facile and cost-effective nanotechnology-based oil clean-up technique that has been optimized for effectiveness and feasibility and reduced adverse environmental impacts. The synthesized polyvinylpyrrolidone (PVP)-coated magnetic nanoparticles (NPs) have been characterized using different techniques and the oil removal efficiency investigated under a wide range of environmentally relevant conditions. Based on the characterization data, NPs have a median particle size of 11.2 nm (interquartile range: 6.3--18.3 nm), a dominant phase of magnetite (Fe3O4) and 8.5% of the mass of NPs belong to their PVP coating. Oil removal experiment showed 100% oil removal from ultra-pure water using the optimum condition (NP concentration: 17.6 ppm, magnetic separation: 40 min). Gas chromatography--mass spectrometry results showed 100% removal of lower chain alkanes (C9-C21) and greater than 67% of C22-C25 removal. Using the same NP concentration, essentially 100% oil removal from synthetic freshwaters and sea water in the absence of natural organic macromolecules (NOM) was observed. Also, nearly 100% of C9-C20 alkanes were removed. 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 (p-value< 0.05). Ionic strength facilitated oil sorption presumably by enhancing the magnetic separation of the oil-NP complex or altering PVP hydrophobicity (p-value < 0.05). Alteration of the separation conditions allowed optimal oil removal, with essentially 100% oil removal under most but not all conditions. Using the same type of NPs, the application of high gradient magnetic separation (HGMS) for the rapid removal of oil from oil-water mixtures in a continuous flow system was studied. Using a magnetic field of 0.18 T and 0.56 T, the oil removal percentage was 81.4% +/- 2.9 and 87.3% +/- 4.0, while the NP removal efficiency was 48.8% +/- 3.8 and 84.4% +/- 5.2, respectively. For a low magnetic field (0.18 T) and 1 h mixing, increasing the SS wool content from 0 to 100 mg, the oil and NP removal efficiencies increased from 81.4% +/- 2.0 to 86.7% +/- 0.9 and from 48.8% +/- 2.7 to 68.1% +/- 0.4, respectively. We also tested the HGMS system for a longer time by running the system for 7 h (3.5 h in two consecutive days) and treating nearly 17 L oil-water mixture. Using a magnetic field of 0.56 T and 1 h mixing time, oil and NP removal in presence and absence of SS wool was greater than 80%. This study proposes a promising nanotechnology-based oil remediation technique with a low adverse environmental impact and a significant potential for a large scale oil clean-up.