Thermoresponsive hydrogels for atmospheric water vapor harvesting

Abstract

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.

A Semi-Interpenetrating Network Sorbent of Superior Efficiency for Atmospheric Water Harvesting and Solar-Regenerated Release

“…In the final stage, water molecules diffuse into the porous internal structure via capillary condensation and liquefaction. Consequently, according to Smith’s hypothesis, the sample isotherm may be partitioned into two zones (Figure d) . The first part entails condensing water molecules on the network’s surface (corresponding to the convex part of curve between 0 and 40% RH), which is primarily governed by relative humidity.…”

“…The first part entails condensing water molecules on the network’s surface (corresponding to the convex part of curve between 0 and 40% RH), which is primarily governed by relative humidity. During the second part, water molecules attach to the polymeric sorbent’s interior structure, resulting in a concave curvature (above 50% RH) . Since water vapor could not efficiently diffuse into the interior porous structure with RH of less than 50%, the water vapor sorption increased gradually with RH rise, leading to a water uptake up to 1.8 g w /g BAGY at 23 °C at 50% RH.…”

“…Consequently, according to Smith’s hypothesis, the sample isotherm may be partitioned into two zones ( Figure 2 d). 33 The first part entails condensing water molecules on the network’s surface (corresponding to the convex part of curve between 0 and 40% RH), which is primarily governed by relative humidity. During the second part, water molecules attach to the polymeric sorbent’s interior structure, resulting in a concave curvature (above 50% RH).…”

“…During the second part, water molecules attach to the polymeric sorbent’s interior structure, resulting in a concave curvature (above 50% RH). 33 Since water vapor could not efficiently diffuse into the interior porous structure with RH of less than 50%, the water vapor sorption increased gradually with RH rise, leading to a water uptake up to 1.8 g w /g BAGY at 23 °C at 50% RH. Nonetheless, capillarity can act as a driving force for rapid water transport since the hydrophilic gel matrix is strongly interconnected.…”

Engineered Polymer Architectures for Thermo‐Responsive Desiccants in Dehumidification Applications

“…There has been a recent interest in using thermo‐responsive polymers for removing water from the air. [ 10–24 ] Previous modeling work by Zeng et al. [ 20 ] and Kocher et al.…”