Abstract
In this work, we develop and demonstrate highly stable organic-coated engineered superparamagnetic iron oxide nanoparticles (IONPs), which provide effective osmotic pressure without aggregation, reverse diffusion, or membrane blocking (by nanoparticles) for osmotically driven membrane systems, considering both forward osmosis (FO) and pressure-retarded osmosis (PRO). For this, we synthesized highly water stable, monodisperse 12 nm IONPs with a rational series of water stabilizing surface coatings, including sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and polyethylene glycol (PEG). We then compared the library of surface functionalized IONPs as draw solutes for osmotic pressure-driven membrane processes. As synthesized, surface (organic) coatings are compact, thin, and can have very similar surface charge as the membrane itself, which results in effective osmotic pressure in forward osmosis (FO) mode configuration. To increase the osmotic pressure further, on a per mass basis, we synthesized and demonstrated novel hollow IONPs with identical surface coatings. Finally, water flux was further enhanced for stable particle systems using an oscillating magnetic field, thus physically altering concentration gradients, as a function of particle magnetic properties.
Highlights
Pressure retarded osmosis (PRO) and forward osmosis (FO) have attracted considerable attention with regard to water treatment and energy-based applications, among others[1,2]
Monodisperse 12 nm iron oxide nanoparticles (IONPs) were synthesized by thermal decomposition in the presence of oleic acid (OA)[20,24]
The resulting IONPs and hollow IONPs (HNPs) were highly monodisperse and stable in nonpolar solvent due to the resulting hydrophobic surface[26]
Summary
Pressure retarded osmosis (PRO) and forward osmosis (FO) have attracted considerable attention with regard to water treatment and energy-based applications, among others[1,2]. IONPs aggregation and deposition on the surface of membrane (blocking) remains a critical challenge for effective, long term operation Toward this end, development of extreme stable IONPs is critical for the practical application of IONPs as draw solutes. For synthesizing monodisperse IONPs with high colloidal stability regimes, thermal decomposition methods using nonpolar solvents is an extremely reproducible strategy for highly monodisperse suspensions with precise surface coatings[23]. Taking advantage of these methods, here we prepared and characterized 12 nm IONPs with a series of water stabilizing surface coatings, including sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and polyethylene glycol (PEG), as nano draw solutes. We increased the performance of nano draw solutes by hollowing out the NPs core structure, and applying oscillating magnetic field
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