Hydrophilic superparamagnetic nanoparticles: Synthesis, characterization, and performance in forward osmosis processes

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. © 2010 American Chemical Society.