Structure–Property Relationships for Moisture-Swing Direct Air Capture

sorption, NMR cryoporometry, and solid-state NMR and FTIR spectroscopies. Macroporous IERs outperformed gel-type analogues in capacity and kinetics, but only when possessing intermediate-sized, well-connected pores, with the phase lag scaling inversely with the pore size. Ion identity and ammonium functionality acted jointly: Type I and Type II IERs exhibited higher swing capacities with phosphate and carbonate loadings, respectively. Anion choice also governed the kinetics, with phosphate slowing adsorption and carbonate slowing desorption. Acrylic backbones drove greater water uptake than styrenic ones. Solid-state NMR revealed humidity-driven protonation, consistent with the proposed swing mechanism. Together, these findings provide practical design rules for improving direct air capture via moisture-swing sorbents.