A forward osmosis hydrogel draw agent that responds to both heat and CO2

Dual CO2- and thermo-responsive superabsorbent poly(N,N-dimethylallylamine) hydrogel (g-PDMAAm) was synthesized for the first time, via a one pot synthesis. When just using the CO2-response, g-PDMAAm is highly hydrophilic and can absorb large volumes of water but cannot expel all this water upon deprotonation. When using the thermo-response, g-PDMAAm is less hydrophilic and can absorb smaller amounts of water but can release nearly all the water when heated. When the CO2- and thermo-responsive properties are used in unison, g-PDMAAm can reversibly absorb 200 times its weight in carbonated water and expel up to 99.9% of the absorbed water upon application of modest heat (60 degrees C) in both air and water. Raising the temperature decreases both the extent of protonation and the osmotic pressure of the gel, which leads to improved water release. In a forward osmosis apparatus, the PDMAAm gel can extract water from 3.5 wt% NaCl feeds.