(558ci) Hydrophilic Magnetic Ionic Liquid-Based Draw Solutes in Forward Osmosis for Sea Water Desalination

Fresh water demand has become one of the global problems due to the rapid growth of population, climate change, and water pollution. Membrane-based water treatment technologies have an immense potential to solve the water scarcity issue. Amongst the membrane technologies, forward osmosis (FO) has recently attracted attention due to its simplicity and energy efficiency. FO process involves water transport from a saline feed stream (low concentrated solution) to a highly concentrated draw solution across a selective membrane due to osmotic pressure gradient (Δπ). FO encompasses attributes that render it a viable alternative to pressure-driven membrane processes like reverse osmosis (RO) which has higher propensity to fouling. However, the full implementation of FO remains highly constrained by the lack of ideal draw solutes imparting substantial water permeation, low reverse solute leakage, and convenient recyclability for long-term use.

Herein, hydrophilic magnetic ionic liquids (MILs) were synthesized and probed as FO draw solutes. The synthesized MILs were thoroughly characterized by FT-NMR, FTIR, XRD, TEM, DLS, and TGA. Their magnetic properties were confirmed by VSM analysis. Osmotic pressure, ionic strength, and diffusion coefficient of the MILs were measured and correlated with their FO performance as draw solutions (DS). The FO performances of the MILs were assessed in terms of water flux (J_v), reverse solute flux (J_s) and specific solute selectivity (J_s/J_v) against deionized (DI) water and simulated sea water (0.6M NaCl) as feed solution under pressure retarded osmosis (PRO) mode. A step-wise phase separation via mild heating and magnetic separation was applied for the recovery of the MILs as DS and purification of product water. The biocompatability of the MILs was evaluated in vitro both by cell proliferation 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and cytotoxicity by Lactate dehydrogenase (LDH) assay.

The investigated MILs generated considerable J_v with negligible J_s. These was attributed to the combined effects of their high ionicities, moderate molecular weights, acceptable diffusion coefficients, and sufficient osmotic pressure generation. The MILs were successfully tested for seawater desalination and recovered via thermal/magnetic separation. The quality of produced water and in vitro toxicity tests reveal that the MILs can be safely used as DS in FO systems.

This research was supported by the National Research Foundation of Korea (NRF) under the Ministry of Science and ICT (No. 2016R1A2B1009221 and 2017R1A2B2002109) and the Ministry of Education (No. 22A20130012051(BK21Plus)).