Amine-Infused Hydrogels with Nonaqueous Solvents: Facile Platforms to Control CO2Capture Performance

Amine-infused hydrogels provide a facile platform for developing solid sorbents with improved CO2 capture performance relative to that of their liquid counterparts. In this study, we develop hydrogel materials that can be easily manufactured at a large scale and have high flow gas permeability characteristics, fast uptake kinetics, and minimal performance degradation after recycling, properties which are particularly important for applications in direct air capture (DAC). To overcome water loss issues associated with hydrogel materials for DAC, we have introduced high-boiling-point/nonaqueous solvent systems, which significantly lowered the solvent loss, leading to dramatically improved recyclability. Among the materials developed, cross-linked poly(N-2-hydroxyethylacrylamide) (PHEAA) infused with diethanolamine (DEA) exhibited 7.82 and 2.90 wt % CO2 uptake with pure CO2 and DAC, respectively. Interestingly, by changing the hydrogel platform between either a cross-linked superabsorbent [i.e., poly(acrylamide/sodium acrylate)], PHEAA, or poly(acrylamide) (PolyAA) and impregnating with different amines/solvents, the uptake kinetics could be controlled and significantly improved. In fact, the PolyAA system impregnated with DEA in ethylene glycol showed 90% of the total capacity (6.37%) in 350 s (vs 4300 s in the case of the PHEAA/DEA system) as well as an enhanced amine efficiency (0.76 vs 0.28 mol CO2 per amine). Thus, this study demonstrates the use of different nonaqueous solvents on readily synthesized hydrogel platforms to improve the DAC uptake efficiency and kinetics. The fast kinetics enable shorter adsorption/desorption cycles, which will be advantageous in improving the CO2 uptake selectivity and reducing the sorption of water in larger-scale implementations of this approach, in both urban and industrial applications.