Enhanced water flux and dewatering using electric-magnetic-responsive hydrogels as draw agents for forward osmosis

Stimuli-responsive hydrogels are promising draw agents for forward osmosis (FO), minimizing reverse solute diffusion and enabling efficient water release under external stimuli. This research explores electric-magnetic-responsive hydrogels to enhance water flux and dewatering rate in FO process. Hydrogels were synthesized via copolymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) with polyvinyl alcohol (PVA), polyethylene glycol (PEG), and acrylic acid (AA), respectively, at various mass ratios. Among them, AMPS-co-PEG at a mass ratio of 1:1 (AMPS-co-PEG50) demonstrated the highest swelling ratio of 393.6 ± 23.7 g·g⁻¹ and an increased water flux from 2.8 LMH to 3.5 LMH under an applied electric field of 4 V·cm⁻¹. This enhancement in water flux was likely driven by electro-induced ion migration and an increase in osmotic pressure. To further improve performance, magnetite-incorporated AMPS-co-PEG50 hydrogels (MAG-AMPS-co-PEG) were synthesized, achieving 28.7 % higher water flux than AMPS-co-PEG50 when 0.5 wt% magnetite was incorporated due to higher polymer porosity. Additionally, the water flux doubled to 6.9 LMH as the applied cell potential increased from 0 to 12 V because of enhanced ion transport. Even with saline water or reverse osmosis concentrate, a water flux of 2–3 LMH was maintained. Moreover, under 24 V·cm⁻¹ and a 165 mT magnetic field, dewatering reached 72.5 %, outperforming AMPS-co-PEG50 (57.6 %). Eventually, the electric-magnetic-responsive hydrogels maintained stable performance over five 24-h cycles. These findings highlight the potential of electric-magnetic-responsive hydrogels as draw agents to enhance FO performance in desalination.