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

Abstract

In this study, citric acid (CA)-coated magnetite Fe3O4 magnetic nanoparticles (Fe3O4@CA MNPs) for use as draw solution (DS) agents in forward osmosis (FO) were synthesized by co-precipitation and characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), dynamic light scattering (DLS), transmission electron microscopy (TEM) and magnetic measurements. Prepared 3.7% w/w colloidal solutions of Fe3O4@CA MNPs exhibited an osmotic pressure of 18.7 bar after purification without aggregation and a sufficient magnetization of 44 emu/g to allow DS regeneration by an external magnetic field. Fe3O4@CA suspensions were used as DS in FO cross-flow filtration with deionized (DI) water as FS and with the active layer of the FO membrane facing the FS and NaCl as a reference DS. The same transmembrane bulk osmotic pressure resulted in different water fluxes for NaCl and MNPs, respectively. Thus the initial water flux with Fe3O4@CA was 9.2 LMH whereas for 0.45 M NaCl as DS it was 14.1 LMH. The reverse solute flux was 0.08 GMH for Fe3O4@CA and 2.5 GMH for NaCl. These differences are ascribed to a more pronounced internal dilutive concentration polarization with Fe3O4@CA as DS compared to NaCl as DS. This research demonstrated that the proposed Fe3O4@CA can be used as a potential low reverse solute flux DS for FO processes.

Optimization of Magnetic Nanoparticles Draw Solution for High Water Flux in Forward Osmosis

“…The water flux measured in the experiment was 1.98 LMH which is close to the predicted value of 2.06 LMH. The water flux of the synthesized bare iron oxide nanoparticles was low compared to the water flux obtained when using stabilized iron oxide nanoparticles [33][34][35]. Therefore, it is expected to obtain high water flux when stabilizing the optimized bare iron oxide nanoparticles that were synthesized in this study.…”

A Comprehensive Review on Forward Osmosis Water Treatment: Recent Advances and Prospects of Membranes and Draw Solutes

“…A large amount of energy is often consumed in the process of recovering the draw solutes [76]. To circumvent this, magnetic draw solutes, due to their easy separation and low reverse solute flux, have become a hot spot in current research [77].…”

“…Figure 16. Percentages of publications on polymers and nano-additives used for flat-sheet FO membranes and hollow-fiber FO membranes: (a) support layer materials; (b) nano-additives; (c) selective layer materials (modified from[17,76]). …”

Influence of the anionic structure and central atom of a cation on the properties of LCST-type draw solutes for forward osmosis

“…Stimuli-responsive draw solutes are generally closer to this target, thereby facilitating the ease of regeneration compared with non-stimuli-responsive draw solutes. 25 Stimuli-responsive draw solutes can be inferred as compounds with water affinities that can undergo instantaneous changes in response to external stimuli such as magnetic; 26,27 electric eld; 28 changes in temperature, 29 pH, 30 gas, 31 salt, 32 and light. 33 A thermo-responsive property is attractive to draw solute application when separating the draw solution into pure water and draw solute owing to its simplicity and the possibility of utilizing heat sources, such as geothermal, solar thermal energy, and low-grade waste heat from industrial sources.…”

“…Stimuli-responsive draw solutes are generally closer to this target, thereby facilitating the ease of regeneration compared with non-stimuli-responsive draw solutes. 25 Stimuli-responsive draw solutes can be inferred as compounds with water affinities that can undergo instantaneous changes in response to external stimuli such as magnetic; 26,27 electric field; 28 changes in temperature, 29 pH, 30 gas, 31 salt, 32 and light. 33…”