Data from: Molecular-level CO2 adsorption behavior in amine-modified sorbents within a controlled CO2/H2O environment

Sorbents designed for direct air capture (DAC) play a crucial role in the
pursuit of achieving net-zero carbon dioxide emissions. This study
elucidates CO2 adsorption from dilute, humidified CO2 streams onto an
amine-modified benchmark DAC adsorbent via solid-state NMR spectroscopy.
Various NMR techniques, including 1D 1H MAS, 13C MAS, 2D 1H-13C HETCOR
NMR, and 1H R2 and R1ρ relaxometry reveal the impact of CO2 partial
pressure and H2O on CO2 adsorption behavior. We find that CO2
concentration governs the stepwise formation of ammonium carbamate,
carbamic acid, and physisorbed CO2, where relative humidity (RH) at a
desired low (<400ppm) CO2 loading affects total CO2 uptake. The
relaxation studies reveal the cooperative or competitive nature of H2O-CO2
sorption in CO2-dilute humid gas, and in particular polymer swelling upon
humidification. From those results, we demonstrate that the observed
absorption capacity enhancement by humidity is caused by pore opening due
to sorbent swelling, and not by bicarbonate formation. This NMR-discerned
speciation provides insights into sorption behavior at different RHs in
dilute CO2 gas streams, simulating real-world atmospheric conditions, and
governs the design of efficient and adaptable material-process
combinations for solid sorbent DAC.