Gas-responsive cationic microgels for forward osmosis desalination

Polymers as draw materials for forward osmosis (FO) desalination have attracted increasing attention in recent years, where the water adsorption and dewatering abilities of draw materials are crucial to overall desalination performance. Here, we developed gas-responsive microgels as new draw materials for FO desalination in which water adsorption and dewatering are driven by sweeping CO2 and N-2. Cationic microgels of 2-(diethylamino) ethyl methacrylate (DEAEMA) and 2-(dimethylamino) ethyl methacrylate microgels (DMAEMA) were synthesised. The gas- responsivity of these microgels on water-flux and water recovery was systematically examined in a laboratory FO desalination system. CO2 is able to protonate DEAEMA microgels to enhance water adsorption. The DEAEMA microgels with 1 wt% polyethylene glycol diacrylate crosslinker show the highest water flux of 56 LMH. At the isoelectric points, the adsorbed water can be released by purging N-2 gas at room temperature due to the hydrophobic characteristics of deprotonated DEAEMA microgels. Water recovery by 50% can be achieved for these microgels. Comparing with more hydrophilic DMAEMA microgels, the gas-responsive DEAEMA microgels perform higher swelling ratio, water-flux and recovery capability. Our results reveal that these gas- responsive microgels can be used as promising draw materials for future FO process with high water permeability and low-operation cost.