Conclusions

Previously, we have shown a facile synthesis of PVP-coated magnetic NPs which are cheap, environmentally-friendly and reliable as a technique for oil removal under a wide range of environmentally relevant conditions. This study demonstrates that these NPs can be used in a larger scale for the removal of oil from an oil-water mixture (or potentially from oil contaminated soil slurries). Using a high magnetic field (0.56 T) and 1 h mixing time, fluorescence and ICP-OES data showed approximately 85–100% oil and NP removal under most conditions, with the higher magnetic field and the presence of SS wool giving significantly improved separation of both oil and NPs. However, only a fraction of the NPs were used in oil removal (particularly for the aromatic fraction), suggesting that efficiency improvements can be made by more exacting synthesis conditions, which will reduce cost and environmental impact.

Figure 4.1. Schematic diagram of the HGMS system: (A) stirred oil-water-NPs mixture; (B) peristaltic pump; (C) magnet; (D) SS wool (if used); (E) treated solution.

Figure 4.2. Effect of magnetic field strength on the oil and NP removal efficiencies (a) oil and NP removal for the last collected sample, (b) oil removal efficiency and (c) NP removal efficiency (mixing time: 1 h and mass of SS wool: 100 mg).

Figure 4.3. GC–MS results. (a and b) Chromatograms and (c and d) mass spectrometry results for the solution remaining after HGMS (mixing time: 1 h and mass of SS wool: 100 mg).

Figure 4.4. Effect of mixing time on the oil and NP removal efficiencies (a) oil and NP removal for the last collected sample, (b) oil removal efficiency, (c) NP removal efficiency and (d) mass spectrometry results for the solutions remaining after HGMS (magnetic field strength: 0.56 T and mass of SS wool: 100 mg).

Figure 4.5. Effect of SS wool content on oil and NP removal efficiencies (a) oil and NP removal for the last collected sample, (b) oil removal efficiency, (c) NP removal efficiency and (d) mass spectrometry results for the solutions remaining after HGMS (magnetic field: 0.18 T and mixing time: 1 h).

Figure 4.6. Breakthrough experiment in the presence and absence of SS wool. Vertical gridlines show when the new oil-water-NP mixture was pumped (magnetic field: 0.56 T, mixing time: 1 h and for the experiment in the presence of SS wool, 100 mg of SS wool was used). In the absence of SS wool, the average and standard deviation of oil and NP removal efficiencies were 81.2% ± 1.8 and 81.2% ± 1.9 and in the presence of SS wool, the oil and NP removal efficiencies were 89.5% ± 2.9 and 82.0% ± 2.2, respectively.

CHAPTER 5

CONCLUSION

Oil can release into the environment from different sources such as runoff, accidental oil spills and oily wastewater discharges and can have dramatic impacts on the environment. Application of iron oxide NPs for environmental remediation is becoming popular because of their low cost, easy separation from water and low toxicity. In this study, we developed a cheap and facile hydrothermal method to synthesize PVP-coated magnetite NPs to separate a reference MC252 oil from oil-water mixture. The synthesis technique does not use organic solvents and requires lower temperatures compared to other synthesis techniques. Based on the results from AFM and DLS, the median particle size and hydrodynamic size is 11.2 nm (interquartile range: 6.3-18.3 nm) and 127.4±4.2 nm, respectively. According to XRD pattern, the dominant phase of NPs is magnetite (Fe3O4), although the presence of maghemite cannot be discounted. The FT-IR result suggests that NPs are coated by PVP through the PVP carbonyl group as reported in the literature. Moreover, 8.5% of mass of NPs belong to their PVP coating as obtained from the thermogravimetric analysis (TGA).

Following NPs characterization, we studied the oil removal efficiency of NPs under a wide range of environmentally relevant conditions. Results showed 100% oil removal in ultra-pure water using the optimum condition (NP concentration: 17.6 ppm, magnetic separation: 40 min). GC-MS results showed 100% removal of lower chain

alkanes (C9-C21) and greater than 67% of C22-C25 removal. These results are in agreement with H-NMR and UV-Vis data. Using the same NP concentration, essentially 100% oil removal from synthetic freshwaters and sea water in the absence of NOM was observed. Also, nearly 100% of C9-C20 alkanes were removed. To further challenge the NPs and to mimic natural fresh and sea waters, oil removal in soft, hard and sea waters in the presence of 1 and 10 ppm SRFA and AA was performed. 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 higher NP concentrations and longer magnetic separation times, nearly 100% removal was observed in most of the conditions.

Using the same type of NPs, the application of HGMS technique for the rapid removal of oil from oil-water mixtures in a continuous flow system was studied. In the absence of SS wool, 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. Inserting the SS wool in the column can energize SS wool and creates larger magnetic field gradients around the fine ferromagnetic wires, thereby improving

the removal efficiency. 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%.

Moreover, in our other study28 (appendix A), a novel continuous flow-through synthesis technique, which converted the co-precipitation synthesis conditions, was developed to produce large quantities of PVP-coated magnetic NPs for oil remediation. Results showed that NPs produced by this technique largely maintained the structural properties, although both core and hydrodynamic size of the NPs were slightly larger than those from the batch method, potentially affecting specific surface area and their ability to remove oil from aqueous solutions under challenging conditions. Nevertheless, oil removal from synthetic seawater in the presence and absence of NOM indicated excellent oil removal capacity (essentially 100% removal) which is comparable to the efficiency of the NPs synthesized from batch method.

In this dissertation, we developed a facile and cost-effective synthesis technique to produce PVP-coated magnetic NPs, tested their oil removal efficiency under a wide range of environmentally relevant conditions, scaled-up the synthesis technique and proposed a deployment technique for oil separation. PVP-coated magnetic NPs were shown to be a reliable technique for oil separation from water under different realistic conditions. Possible deployment scenarios include a) using a magnetic separation technique to remove PVP-coated magnetic NPs from the environment, or b) releasing PVP-coated magnetic NPs in the contaminated environment to facilitate oil biodegradation. In the first technique NPs can be reused which decreases operational

cost, although collection itself increases the cost and complexity. This method could be used in a protective manner at sensitive sites (such as aquaculture farms, sites of particular natural beauty or scientific interest, etc.). The second technique is simpler in term of deployment and might allow control of exposure of oil and NPs, however large- scale release may present risks. This technique is applicable for incidents where

REFERENCES

1. National Research Council Committee on Oil in the Sea: Inputs, Fates and Effects , Oil in the Sea III: Inputs, Fates, and Effects. 2003.

2. National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, Deep Water: the Gulf Oil Disaster and the Future of Offshore Drilling. Washington, D.C. 2014.

3. Deng, D.; Prendergast, D. P.; MacFarlane, J.; Bagatin, R.; Stellacci, F.;

Gschwend, P. M., Hydrophobic Meshes for Oil Spill Recovery Devices. ACS Applied Materials & Interfaces 2013, 5, (3), 774-781.

4. Vajdi Hokmabad, B.; Faraji, S.; Ghaznavi Dizajyekan, T.; Sadri, B.;

Esmaeilzadeh, E., Electric field-assisted manipulation of liquid jet and emanated droplets. International Journal of Multiphase Flow 2014, 65, 127-137.

5. Faraji, S.; Sadri, B.; Vajdi Hokmabad, B.; Jadidoleslam, N.; Esmaeilzadeh, E., Experimental study on the role of electrical conductivity in pulsating modes of

electrospraying. Experimental Thermal and Fluid Science 2017, 81, 327-335. 6. Karn, B.; Kuiken, T.; Otto, M., Nanotechnology and in Situ Remediation: A Review of the Benefits and Potential Risks. Environmental Health Perspectives 2009, 117, (12), 1823-1831.

7. Yan, W.; Lien, H.-L.; Koel, B. E.; Zhang, W.-x., Iron nanoparticles for

environmental clean-up: recent developments and future outlook. Environmental Science: Processes & Impacts 2013, 15, (1), 63-77.

8. Chen, X., Molecular Imaging Probes for Cancer Research. World Scientific: 2012.

9. Xue, Z.; Cao, Y.; Liu, N.; Feng, L.; Jiang, L., Special wettable materials for oil/water separation. Journal of Materials Chemistry A 2014, 2, (8), 2445-2460. 10. Su, C., Environmental implications and applications of engineered nanoscale magnetite and its hybrid nanocomposites: A review of recent literature. Journal of Hazardous Materials 2016.

11. Mirshahghassemi, S.; Lead, J. R., Oil Recovery from Water under

Environmentally Relevant Conditions Using Magnetic Nanoparticles. Environmental Science & Technology 2015, 49, (19), 11729-11736.

12. Zhu, Q.; Tao, F.; Pan, Q. M., Fast and Selective Removal of Oils from Water Surface via Highly Hydrophobic Core-Shell Fe2O3@C Nanoparticles under Magnetic Field. Acs Applied Materials & Interfaces 2010, 2, (11), 3141-3146.

13. Gui, X. C.; Zeng, Z. P.; Lin, Z. Q.; Gan, Q. M.; Xiang, R.; Zhu, Y.; Cao, A. Y.; Tang, Z. K., Magnetic and Highly Recyclable Macroporous Carbon Nanotubes for Spilled Oil Sorption and Separation. Acs Applied Materials & Interfaces 2013, 5, (12), 5845-5850.

14. Chu, Y.; Pan, Q. M., Three-Dimensionally Macroporous Fe/C Nanocomposites As Highly Selective Oil-Absorption Materials. Acs Applied Materials & Interfaces 2012, 4, (5), 2420-2425.

15. Banerjee, A.; Gokhale, R.; Bhatnagar, S.; Jog, J.; Bhardwaj, M.; Lefez, B.; Hannoyer, B.; Ogale, S., MOF derived porous carbon-Fe3O4 nanocomposite as a high performance, recyclable environmental superadsorbent. Journal of Materials Chemistry 2012, 22, (37), 19694-19699.

16. Wang, X.; Shi, Y.; Graff, R. W.; Lee, D.; Gao, H., Developing recyclable pH- responsive magnetic nanoparticles for oil–water separation. Polymer 2015, 72, 361-367. 17. Madhusudhana Reddy, P.; Chang, C.-J.; Chen, J.-K.; Wu, M.-T.; Wang, C.-F., Robust polymer grafted Fe3O4 nanospheres for benign removal of oil from water. Applied Surface Science 2016, 368, 27-35.

18. Wang, B.; Liang, W.; Guo, Z.; Liu, W., Biomimetic super-lyophobic and super- lyophilic materials applied for oil/water separation: a new strategy beyond nature. Chemical Society Reviews 2015, 44, (1), 336-361.

19. Calcagnile, P.; Fragouli, D.; Bayer, I. S.; Anyfantis, G. C.; Martiradonna, L.; Cozzoli, P. D.; Cingolani, R.; Athanassiou, A., Magnetically Driven Floating Foams for the Removal of Oil Contaminants from Water. ACS. Nano. 2012, 6, (6), 5413-5419. 20. Zhang, J.; Shao, Y.; Hsieh, C.-T.; Chen, Y.-F.; Su, T.-C.; Hsu, J.-P.; Juang, R.-S., Synthesis of magnetic iron oxide nanoparticles onto fluorinated carbon fabrics for

contaminant removal and oil-water separation. Separation and Purification Technology 2017, 174, (Supplement C), 312-319.

21. Patil, S. S.; Shedbalkar, U. U.; Truskewycz, A.; Chopade, B. A.; Ball, A. S., Nanoparticles for environmental clean-up: A review of potential risks and emerging solutions. Environmental Technology & Innovation 2016, 5, 10-21.

22. Sánchez, A.; Recillas, S.; Font, X.; Casals, E.; González, E.; Puntes, V., Ecotoxicity of, and remediation with, engineered inorganic nanoparticles in the environment. TrAC Trends in Analytical Chemistry 2011, 30, (3), 507-516. 23. Petschacher, C.; Eitzlmayr, A.; Besenhard, M.; Wagner, J.; Barthelmes, J.; Bernkop-Schnürch, A.; Khinast, J. G.; Zimmer, A., Thinking continuously: a microreactor for the production and scale-up of biodegradable, self-assembled nanoparticles. Polymer Chemistry 2013, 4, (7), 2342-2352.

24. Wu, W.; He, Q.; Jiang, C., Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies. Nanoscale Research Letters 2008, 3, (11), 397-415. 25. Palchoudhury, S.; Lead, J. R., A Facile and Cost-Effective Method for Separation of Oil-Water Mixtures Using Polymer-Coated Iron Oxide Nanoparticles. Environ. Sci. Technol. 2014, 48, (24), 14558-14563.

26. Reddy, L. H.; Arias, J. L.; Nicolas, J.; Couvreur, P., Magnetic Nanoparticles: Design and Characterization, Toxicity and Biocompatibility, Pharmaceutical and Biomedical Applications. Chemical Reviews 2012, 112, (11), 5818-5878.

27. Hasany, S.; Ahmed, I.; Rajan, J.; Rehman, A., Systematic review of the preparation techniques of iron oxide magnetic nanoparticles. Nanoscience and Nanotechnology 2012, 2, (6), 148-158.

28. Kadel, K.; Mirshahghassemi, S.; Lead, J. R., Facile Flow-Through Synthesis Method for Production of Large Quantities of Polyvinylpyrrolidone-Coated Magnetic Iron Oxide Nanoparticles for Oil Remediation. Environmental Engineering Science 2017.

29. Lam, U. T.; Mammucari, R.; Suzuki, K.; Foster, N. R., Processing of Iron Oxide Nanoparticles by Supercritical Fluids. Industrial & Engineering Chemistry Research 2008, 47, (3), 599-614.

30. Xu, J.; Yang, H.; Fu, W.; Du, K.; Sui, Y.; Chen, J.; Zeng, Y.; Li, M.; Zou, G., Preparation and magnetic properties of magnetite nanoparticles by sol–gel method. Journal of Magnetism and Magnetic Materials 2007, 309, (2), 307-311.

31. Xu, C.; Teja, A. S., Continuous hydrothermal synthesis of iron oxide and PVA- protected iron oxide nanoparticles. The Journal of Supercritical Fluids 2008, 44, (1), 85- 91.

32. Woo, K.; Lee, H. J.; Ahn, J. P.; Park, Y. S., Sol–Gel Mediated Synthesis of Fe2O3 Nanorods. Advanced Materials 2003, 15, (20), 1761-1764.

33. Vijayakumar, R.; Koltypin, Y.; Felner, I.; Gedanken, A., Sonochemical synthesis and characterization of pure nanometer-sized Fe3O4 particles. Materials Science and Engineering: A 2000, 286, (1), 101-105.

34. Pinkas, J.; Reichlova, V.; Zboril, R.; Moravec, Z.; Bezdicka, P.; Matejkova, J., Sonochemical synthesis of amorphous nanoscopic iron(III) oxide from Fe(acac)3. Ultrasonics Sonochemistry 2008, 15, (3), 257-264.

35. Bee, A.; Massart, R.; Neveu, S., Synthesis of very fine maghemite particles. Journal of Magnetism and Magnetic Materials 1995, 149, (1), 6-9.

36. Sun, S.; Zeng, H., Size-Controlled Synthesis of Magnetite Nanoparticles. Journal of the American Chemical Society 2002, 124, (28), 8204-8205.

37. Xu, C.; Lee, J.; Teja, A. S., Continuous hydrothermal synthesis of lithium iron phosphate particles in subcritical and supercritical water. The Journal of Supercritical Fluids 2008, 44, (1), 92-97.

38. Wang, J.; Sun, J.; Sun, Q.; Chen, Q., One-step hydrothermal process to prepare highly crystalline Fe3O4 nanoparticles with improved magnetic properties. Materials Research Bulletin 2003, 38, (7), 1113-1118.

39. Zheng, Y.-h.; Cheng, Y.; Bao, F.; Wang, Y.-s., Synthesis and magnetic properties of Fe3O4 nanoparticles. Materials Research Bulletin 2006, 41, (3), 525-529.

40. Hu, X.; Yu, J. C.; Gong, J., Fast Production of Self-Assembled Hierarchical α- Fe2O3 Nanoarchitectures. The Journal of Physical Chemistry C 2007, 111, (30), 11180- 11185.

41. Giri, S.; Samanta, S.; Maji, S.; Ganguli, S.; Bhaumik, A., Magnetic properties of α-Fe2O3 nanoparticle synthesized by a new hydrothermal method. Journal of Magnetism and Magnetic Materials 2005, 285, (1–2), 296-302.

42. Şengül, H.; Theis, T. L.; Ghosh, S., Toward sustainable nanoproducts. Journal of Industrial Ecology 2008, 12, (3), 329-359.

43. Mirshahghassemi, S.; Ebner, A. D.; Cai, B.; Lead, J. R., Application of high gradient magnetic separation for oil remediation using polymer-coated magnetic nanoparticles. Separation and Purification Technology 2017, 179, 328-334. 44. Arita, T.; Hitaka, H.; Minami, K.; Naka, T.; Adschiri, T., Synthesis of iron nanoparticle: Challenge to determine the limit of hydrogen reduction in supercritical water. The Journal of Supercritical Fluids 2011, 57, (2), 183-189.

45. Ito, D.; Yokoyama, S.; Zaikova, T.; Masuko, K.; Hutchison, J. E., Synthesis of Ligand-Stabilized Metal Oxide Nanocrystals and Epitaxial Core/Shell Nanocrystals via a Lower-Temperature Esterification Process. ACS Nano 2014, 8, (1), 64-75.

46. Kim, H. C.; Fthenakis, V., Life cycle energy and climate change implications of nanotechnologies. Journal of Industrial Ecology 2013, 17, (4), 528-541.

47. Yu, L.; Hao, G.; Liang, Q.; Jiang, W., Fabrication of Magnetic Porous Silica Submicroparticles for Oil Removal from Water. Industrial & Engineering Chemistry Research 2015, 54, (38), 9440-9449.

48. Ge, B.; Zhang, Z.; Zhu, X.; Ren, G.; Men, X.; Zhou, X., A magnetically superhydrophobic bulk material for oil removal. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2013, 429, (0), 129-133.

49. Wu, H.-C.; Chang, R.-C.; Hsiao, H.-C., Research of minimum ignition energy for nano Titanium powder and nano Iron powder. Journal of Loss Prevention in the Process Industries 2009, 22, (1), 21-24.

50. Peijnenburg, W.; Baalousha, M.; Chen, J. W.; Chaudry, Q.; Von der kammer, F.; Kuhlbusch, T. A. J.; Lead, J.; Nickel, C.; Quik, J. T. K.; Renker, M.; Wang, Z.;

Koelmans, A. A., A Review of the Properties and Processes Determining the Fate of Engineered Nanomaterials in the Aquatic Environment. Critical Reviews in

Environmental Science and Technology 2015, 45, (19), 2084-2134.

51. Fabrega, J.; Luoma, S. N.; Tyler, C. R.; Galloway, T. S.; Lead, J. R., Silver nanoparticles: behaviour and effects in the aquatic environment. Environ. Int. 2011, 37, (2), 517-31.

52. Mirshahghassemi, S.; Cai, B.; Lead, J. R., Evaluation of polymer-coated magnetic nanoparticles for oil separation under environmentally relevant conditions: effect of ionic strength and natural organic macromolecules. Environmental Science: Nano 2016, 3, (4), 780-787.

53. Tejamaya, M.; Römer, I.; Merrifield, R. C.; Lead, J. R., Stability of Citrate, PVP, and PEG Coated Silver Nanoparticles in Ecotoxicology Media. Environ. Sci. Technol. 2012, 46, (13), 7011-7017.

54. Lowry, G. V.; Gregory, K. B.; Apte, S. C.; Lead, J. R., Transformations of Nanomaterials in the Environment. Environ. Sci. Technol. 2012, 46, (13), 6893-6899. 55. Grillo, R.; Rosa, A. H.; Fraceto, L. F., Engineered nanoparticles and organic matter: a review of the state-of-the-art. Chemosphere 2015, 119, 608-619.

56. Römer, I.; Gavin, A. J.; White, T. A.; Merrifield, R. C.; Chipman, J. K.; Viant, M. R.; Lead, J. R., The critical importance of defined media conditions in Daphnia magna nanotoxicity studies. Toxicology letters 2013, 223, (1), 103-108.

57. Levard, C.; Hotze, E. M.; Lowry, G. V.; Brown Jr, G. E., Environmental transformations of silver nanoparticles: impact on stability and toxicity. Environ. Sci. Technol 2012, 46, (13), 6900-6914.

58. Wang, Q.; Ebbs, S. D.; Chen, Y.; Ma, X., Trans-generational impact of cerium oxide nanoparticles on tomato plants. Metallomics 2013, 5, (6), 753-759.

59. Baalousha, M.; Manciulea, A.; Cumberland, S.; Kendall, K.; Lead, J. R., Aggregation and surface properties of iron oxide nanoparticles: Influence of ph and natural organic matter. Environmental Toxicology and Chemistry 2008, 27, (9), 1875- 1882.

60. Kirschling, T. L.; Golas, P. L.; Unrine, J. M.; Matyjaszewski, K.; Gregory, K. B.; Lowry, G. V.; Tilton, R., D, Microbial bioavailability of covalently bound polymer coatings on model engineered nanomaterials. Environmental science & technology 2011, 45, (12), 5253-5259.

61. Alabresm, A.; Mirshahghassemi, S.; Chandler, G. T.; Decho, A. W.; Lead, J., Use of PVP-coated magnetite nanoparticles to ameliorate oil toxicity to an estuarine

meiobenthic copepod and stimulate the growth of oil-degrading bacteria. Environmental Science: Nano 2017, 4, (9), 1859-1865.

62. Singh, N.; Jenkins, G. J. S.; Asadi, R.; Doak, S. H., Potential toxicity of superparamagnetic iron oxide nanoparticles (SPION). Nano Reviews 2010, 1, 10.3402/nano.v1i0.5358.

63. Soenen, S. J. H.; De Cuyper, M., Assessing iron oxide nanoparticle toxicity in vitro: current status and future prospects. 2010, 5, (8), 1261(15).

64. Wahajuddin; Arora, S., Superparamagnetic iron oxide nanoparticles: magnetic nanoplatforms as drug carriers. Int J Nanomedicine 2012, 7, 3445-71.

65. Reddy, C. M.; Arey, J. S.; Seewald, J. S.; Sylva, S. P.; Lemkau, K. L.; Nelson, R. K.; Carmichael, C. A.; McIntyre, C. P.; Fenwick, J.; Ventura, G. T.; Van Mooy, B. A. S.; Camilli, R., Composition and fate of gas and oil released to the water column during the Deepwater Horizon oil spill. Proceedings of the National Academy of Sciences of the United States of America 2012, 109, (50), 20229-20234.

66. Wang, Y.; Deng, L.; Caballero-Guzman, A.; Nowack, B., Are engineered nano iron oxide particles safe? an environmental risk assessment by probabilistic exposure, effects and risk modeling. Nanotoxicology 2016, 10, (10), 1545-1554.

67. Gao, Y.; Zhou, Y. S.; Xiong, W.; Wang, M.; Fan, L.; Rabiee-Golgir, H.; Jiang, L.; Hou, W.; Huang, X.; Jiang, L.; Silvain, J.-F.; Lu, Y. F., Highly Efficient and Recyclable