Non-ionic copolymer microgels as high-performance draw materials for forward osmosis desalination

Ionic thermo-responsive microgels have been recently developed as smart draw agents for forward osmosis (FO) desalination. Although ionic microgels are able to demonstrate high water flux, their water recovery performance is compromised due to strong hydration of ionic moieties. In this study, we design and explore various non-ionic thermo-responsive microgels as the FO draw materials. Among these microgels, the copolymer microgels of N-isopropylacrylamide and acrylamide show higher water recovery than ionic microgels, while maintaining high water flux, where the initial water flux and water recovery of the copolymer microgel with 5 wt% acrylamide reach 24.7 LMH and 78.7%. Hansen solubility parameter analysis is launched to theoretically elucidate the mechanism of non-ionic microgels as draw materials in FO operation. The prediction from solubility parameter analysis aligns well with experimental results. This work will guide us in the future development of high performance smart microgels as draw materials in FO desalination.