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.
Highlights
Academic Editors: Jürgen Eckert and Faculty of Chemistry and Chemical Engineering, University of Maribor, Smetanova 17, SI-2000 Maribor, Institute of Biomedical Sciences, Faculty of Medicine, University of Maribor, Taborska Ulica 8, SI-2000 Maribor, Slovenia
The Fe3 O4 @citric acid (CA) Magnetic nanoparticles (MNPs) solution was cooled to room temperature
Nonideality of the solutions of ungrafted and grafted CA molecules onto MNPs indicates that the MNP-grafted CA molecule are almost four-fold stronger as osmotic agent as CA alone
Summary
The same transmembrane bulk osmotic pressure resulted in different water fluxes for NaCl and MNPs, respectively. This research demonstrated that the proposed Fe3 O4 @CA can be used as a potential low reverse solute flux DS for FO processes. In ideal FO, a concentrated draw solution (DS) with high osmotic pressure extracts water from a dilute feed solution (FS) while ideally rejecting all FS solutes [13,14]. Nanomaterials 2021, 11, 2965 osmotic pressure of the DS must significantly exceed that of the FS Simple inorganic salts, such as NaCl, remain the most widely used DS agents due to their ability to have high osmotic pressures while maintaining low solution viscosities. The strong affinity of small inorganic ions for water is reflected in their highly exothermic enthalpies of hydration [15]
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