O₂/N₂ responsive microgels as functional draw agents for gas-triggering forward osmosis desalination

Abstract

High cost for draw agent recovery during dewatering operation remains challenging for industrial forward osmosis (FO) processes. Hydrogels and microgels have been recently reported as promising draw agents for FO desalination. Aiming to develop an energy-efficient gas-triggering FO desalination process, smart gas-responsive copolymer microgels were developed as draw agents in this study. Functional O2/N2 gas-responsive microgels were synthesised using fluorine monomers of trifluoroethyl methacrylate (FM) or pentafluorostyrene (FS), and water-soluble monomers of diethylaminoethyl methacrylate (DEAEMA), dimethylaminoethyl methacrylate (DMAEMA), hydroxyethyl methacrylate (HEMA) and N-isopropylacrylamide (NIPAM). These microgels become reversibly active to draw water after purging O2 and release the adsorbed water upon N2 purging. Water flux, water recovery and recyclability of microgels were systematically examined in a series of FO operations. Enhanced water flux in FO process can be achieved for the microgels with FM. DEAEMA-FM and DMAEMA-FM microgels provide a high water flux up to 29 LMH for a 2000 ppm NaCl feed at room temperature, while the NIPAM-FM microgels show the best water recovery of 56%. Our results reveal that O2/N2 gas-responsive microgels can be used as emerging smart draw agents for gas-triggering FO desalination.