Thermoresponsive Acidic Microgels as Functional Draw Agents for Forward Osmosis Desalination.

Thermoresponsive microgels with carboxylic acid functionalization have been recently introduced as an attractive draw agent for forward osmosis (FO) desalination, where the microgels showed promising water flux and water recovery performance. In this study, various comonomers containing different carboxylic acid and sulfonic acid functional groups were copolymerized with N-isopropylacrylamide (NP) to yield a series of functionalized thermoresponsive microgels possessing different acidic groups and hydrophobicities. The purified microgels were examined as the draw agents for FO application, and the results show the response of water flux and water recovery was significantly affected by various acidic comonomers. The thermoresponsive microgel with itaconic acid shows the best overall performance with an initial water flux of 44.8 LMH, water recovery up to 47.2% and apparent water flux of 3.1 LMH. This study shows that the incorporation of hydrophilic dicarboxylic acid functional groups into the microgels leads to the enhancement on water adsorption and overall performance. Our work elucidates in detail on the structure-property relationship of thermoresponsive microgels in their applications as FO draw agents and would be beneficial for future design and development of high performance FO desalination.