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

Abstract

The synthesis of magnetic nanoparticles (MNPs) coated with hydrophilic poly-sodium-acrylate (PSA) ligands 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. Fourier Transform Infrared Spectroscopy (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 the formation of less stabile magnetic colloid solutions, which led to the 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.

Solvent-Free Mechanochemical Synthesis and Characterization of Nickel Tellurides with Various Stoichiometries: NiTe, NiTe2 and Ni2Te3

“…Three independent measurements were performed for each of the samples and averaged for particle size calculations, yielding values of 204, 221, and 115 nm for NiTe, NiTe 2 , and Ni 2 Te 3 , as shown in Figure 6 . It must be noted that results obtained by DLS generally tend to give higher values than those obtained by electron microscopy due to the fact that in the former case, particles are surrounded by water molecules [ 48 , 49 , 50 ].…”

Superparamagnetic Fe3O4@CA Nanoparticles and Their Potential as Draw Solution Agents in Forward Osmosis

“…In our previous study [29] a 7% solution of robust PSA-coated MNPs yielded an initial J w of 4.2 LMH and an osmotic pressure of 9 bar and a reverse solute flux J s of 0.05 GMH. Thus, the results presented here where Fe 3 O 4 @CA MNPs a 3.7% solution yielded approximately a two-fold higher initial J w (Figure 8) and osmotic pressure (Figure 9) implies that the Fe 3 O 4 @CA MNPs DS is about four-fold more potent as DS compared to a DS based on PSA-coated MNPs.…”

“…where R is gas constant (8.31447 J/mol K), T is the absolute temperature (K), n is the amount of substance (mol), c is the molarity of a solution (mol/L), and φ is an osmotic coefficient (-). The characterisation methods in detailed is presented in a previous paper [29].…”

“…The significant difference in osmotic pressure between PSA-MNP solutions and free PSA solutions reflect the non-ideality of PSA-MNP solutions similar to what we observe in this study. However, the robustness of PSA-MNP based DSs (i.e., their ability to maintain their osmotic pressure after repeated concentrations) is still an issue [29].…”

“…Over the past years, a variety of compounds have been investigated as draw solutes, including sulfur dioxide [21], various inorganic salts and a variety of sugars [22,23], thermally unstable ammonium salts [24,25] polyelectrolytes [26] and MNP's [27][28][29]. Iron oxide MNPs such as maghemite (γ-Fe 2 O 3 ) and magnetite (Fe 3 O 4 ) MNPs have been widely studied due to well-defined properties such as small uniform particle size in the range of 10 to 100 nm, biocompatibility, heat generation in response to an alternating magnetic field (AMF), easy surface manipulation for targeted release, low toxicity profile, and good colloidal stability [30].…”