Preprint Article Version 1 This version is not peer-reviewed

Synthesis of Poly-Sodium-Acrylate (PSA) Coated Magnetic Nanoparticles for Use in Forward Osmosis Draw Solutions

Version 1 : Received: 17 July 2019 / Approved: 18 July 2019 / Online: 18 July 2019 (10:02:20 CEST)

A peer-reviewed article of this Preprint also exists.

Ban, I.; Markuš, S.; Gyergyek, S.; Drofenik, M.; Korenak, J.; Helix-Nielsen, C.; Petrinić, I. Synthesis of Poly-Sodium-Acrylate (PSA)-Coated Magnetic Nanoparticles for Use in Forward Osmosis Draw Solutions. Nanomaterials 2019, 9, 1238. Ban, I.; Markuš, S.; Gyergyek, S.; Drofenik, M.; Korenak, J.; Helix-Nielsen, C.; Petrinić, I. Synthesis of Poly-Sodium-Acrylate (PSA)-Coated Magnetic Nanoparticles for Use in Forward Osmosis Draw Solutions. Nanomaterials 2019, 9, 1238.

Journal reference: Nanomaterials 2019, 9, 1238
DOI: 10.3390/nano9091238

Abstract

The synthesis of magnetic nanoparticles (MNPs) coated with hydrophilic poly-sodium-acrylate ligands (PSA) was studied to assess PSA-MNP complexes as draw solution (DS) solutes in forward osmosis (FO). For MNP-based DS, the surface modification and the size of the MNPs are two crucial factors to achieve a high osmolality. Superparamagnetic nanoparticles (NP) with functional groups attached may represent the ideal DS where chemical modifications of the NPs can be used in optimizing the DS osmolality and the magnetic properties allows for efficient recovery (DS re-concentration) using an external magnetic field. In this study MNPs with diameters of 4 nm have been prepared by controlled chemical co-precipitation of magnetite phase from aqueous solutions containing suitable salts of Fe2+ and Fe3+ under inert atmosphere and a pure magnetite phase could be verified by X-ray diffraction. Magnetic colloid suspensions containing PSA coated MNPs with three different molar ratios of PSA : MNP = 1:1, 1:2 and 1:3 were prepared and assessed in terms of osmotic pressure, aggregation propensity and magnetization. FTIR confirmed the presence of PSA on coated MNPs and pristine PSA-MNPs with a molar ratio PSA : MNP = 1:1 exhibited an osmotic pressure of 30 bar. Molar ratios of PSA : MNP = 1:2 and 1:3 lead to formation of less stabile magnetic colloid solutions which led to formation of aggregates with larger average hydrodynamic sizes and modest osmotic pressures (5.5 bar and 0.2 bar respectively). After purification with ultrafiltration, the 1:1 nanoparticles exhibited an osmotic pressure of 9 bar with no aggregation and a sufficient magnetization of 25 emu/g to allow for DS regeneration using an external magnetic field. However, it was observed that the amount of PSA molecules attached to the MNPs decreased during DS recycling steps leaving only strong chelate bonded core-shell PSA as coating on the MNPs. This demonstrates the crucial role of MNP coating robustness in designing an efficient MNP-based DS for FO.

Subject Areas

magnetic nanoparticles, poly-sodium-acrylate, osmotic pressure, forward osmosis, draw solution.

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