(533e) Thermo-Responsive Hydrogel with Deep Eutectic Mixture Co-Monomer As Drawing Agent for Forward Osmosis

Forward osmosis (FO) is an emerging alternative technology to membrane-based separation process for wastewater treatment and seawater desalination such as reverse osmosis (RO). Unlike RO that requires high pressure in producing clean water, FO employs minimal osmotic pressure difference across the FO membrane. Thus, membrane fouling is less likely to occur in FO which contributes to its energy-efficiency. Recently, membrane development and regenerable draw solutions (DS) are the two areas of interests in various researches for FO technology to progress industrially. The challenge in the DS development is the production of a recyclable DS that will reduce the energy expenditure in post-FO separation of DS and clean water production. Attempts in addressing such challenge include the use of stimuli-responsive DS such as magnetic nanoparticles and hydrogels. However, even if magnetic nanoparticles have high osmotic pressure, the issues on agglomeration and membrane fouling are still a challenge. While in hydrogels, enhancement of the inherent osmotic pressure as well as the release of absorbed water are still under diligent exploration.

Herein, N-Hexyl-N,N-dihydroxyethyl-N-methylammonium chloride–acrylic acid ([DHEA]Cl-AA) deep eutectic mixture (DEM) was used as a co-monomer with N-isopropylacrylamide (NIPAM) to form a thermo-responsive hydrogel. The purpose of which is to enhance the osmotic pressure of the resulting hydrogel without compromising its thermo-responsive property when used as a drawing agent for FO. FT-IR, H¹ NMR and TGA were used to confirm the structure of the synthesized DEM. Meanwhile, FT-IR, DSC and SEM analysis were used to characterize the synthesized hydrogels. Swelling and de-swelling properties of the hydrogels were evaluated by soaking the hydrogel in DI water for 72 h and heating at 45 °C for 30 min, respectively. The water absorbing property of the hydrogels was also investigated as a drawing agent against 2000 ppm NaCl feed solution in FO system. Furthermore, water recovery rate of the swollen hydrogels after FO run was also examined by the de-swelling method mentioned above.

Results reveal an overall improvement in the water absorbing capacity of P(NIPAM-co-DEM) hydrogels relative to the pure PNIPAM hydrogel in terms of swelling ratio and FO water flux. De-swelling data showed an enhanced water release when DEM was co-polymerized into the NIPAM backbone. This study demonstrates the potential of DEM as a co-monomer in producing a thermos-responsive hydrogel with improved FO water flux and water release ability for DS regeneration.

This research was supported by NRF funded by Basic Science Research Program through the Ministry of Education (2021R111A1A01050003 and 2020R1A6A1A03038817).