Thermoresponsive hydrogels for atmospheric water vapor harvesting

Currently, freshwater scarcity is a global challenge that is threatening four billion people across the world. To satisfy people’s increasing freshwater demand, harvesting atmospheric water from the air could be an alternative way. This work developed copolymer P(NIPAM-co-15%BzDMA) hydrogels to harvest atmospheric water vapor. Two methods were investigated to improve its adsorption performance: decreasing synthesis temperature below the LCST and copolymerizing with the optimum amount of quaternary ammonium salt (QAS). We found these two methods can effectively improve the water vapor uptake. After copolymerizing NIPAM with 15% QAS at 20°C, the water vapor uptake could be increased by almost 20% to 232 mg/g at 20°C and P/P0 of 0.75 compared with pure PNIPAM prepared at 60°C (194 mg/g). The significant increase can be attributed to the more uniform porous structure and the hygroscopicity of QAS. After coating PNIPAM onto the PESPU sponge skeleton, the PESPU-PNIPAM_60 could adsorb 180 mg/g gas water at 20°C and P/P0 of 0.75, and the modified sponges inherit the switchable wettability from PNIPAM. This research provides polymer processing parameters and their character for harvesting water vapor from the air with hydrogels.