Hydrophilic Superparamagnetic Nanoparticles: Synthesis, Characterization, and Performance in Forward Osmosis Processes

Abstract

Forward osmosis (FO) is an emerging technology for desalination and water reuse. However, a big challenge is finding suitable draw solutes. In this work, we have synthesized magnetic nanoparticles (MNPs), investigated their potential as draw solutes in FO systems, and explored their recovery and reusability. A series of poly(ethylene glycol)diacid-coated (PEG−(COOH)2-coated) MNPs with different size distributions have been synthesized by means of the thermal decomposition method. The physical properties and chemical compositions of the resultant MNPs are fully characterized. Transmission electron microscopy (TEM) analyses show the characteristics of spherical morphology with narrow size distribution, and a mean size from 4.2 to 17.5 nm depending on the ratio of the two starting materials of PEG−(COOH)2 to ferric triacetylacetonate (Fe(acac)3). Vibrating sample magnetometer analyses confirm the magnetic behavior of the PEG−(COOH)2 MNPs. The PEG−(COOH)2 layer on the MNPs ascertained from Fourier transform infrared (FTIR) analysis and thermogravimetric analysis demonstrates a hydrophilic surface composition. The as-prepared PEG−(COOH)2 MNPs exhibit good dispersibility and generate high osmotic pressures in aqueous solutions. Water fluxes of >10 L m−2 h−1 are achieved across Hydration Technologies Inc. flat sheet membranes when deionized water is used as the feed solution. The MNPs can be easily recovered from draw solutions by applying a magnetic field. The MNPs remain active after nine runs of recycle but with a total water flux decrease of 21% due to slight aggregation. Results have demonstrated that using PEG−(COOH)2 MNPs as draw solutes is feasible in the FO process.

Progress in Forward Osmosis Membrane Separation Process

“…[28,40,69,70] To overcome these problems, synthetic draw solutes have been extensively investigated as draw solutes recently. [46,67,68] Ge and her coworkers [71][72][73] have conducted considerable studies on the design and synthesis of novel draw solutes. Some typically synthetic draw solutes will be specifically discussed as follows.…”

“…MNPs are usually synthesized via a simple one-pot reaction through either thermal decomposition [71] or coprecipitation. [74,75] The synthesis schemes of MNPs via thermal decomposition and coprecipitaion together with some typically structures of MNPs are illustrated in Figures 2 and 3, respectively.…”

“…A series of poly (ethylene glycol) diacid [PEG-(COOH)2] coated MNPs with different sizes have been synthesized by thermal decomposition. [71] The size of PEG-(COOH)2 MNPs ranges from 4.2 to 13.5…”

“…As such, MNPs are able to not only produce high osmotic pressure and hence good water permeability in FO, but also be readily recovered by applying a magnetic field in post-treatment processes. These characteristics make MNPs competitive candidates to be draw solutes for FO.MNPs are usually synthesized via a simple one-pot reaction through either thermal decomposition [71] or coprecipitation. [74,75] The synthesis schemes of MNPs via thermal decomposition and coprecipitaion together with some typically structures of MNPs are illustrated in Figures 2 and 3, respectively.…”

Using UCST Ionic Liquid as a Draw Solute in Forward Osmosis to Treat High-Salinity Water

“…In addition, magnetic nanoparticles lack long-term stability because they tend to agglomerate after several runs of the cycle. [10][11][12] Stimuli-responsive polymer hydrogels can entrap a large volume of water due to the high concentration of hydrophilic groups, and water can be released by a reversible volume change or solution-gel phase transitions in response to heating and pressure [13][14][15] .…”