Role of Epoxide Functionalization of Amines for Development of Direct Air Capture Sorbents with High Cyclic Working Capacity at Low Desorption Temperatures

ABSTRACT Broad implementation of the direct air capture (DAC) technology requires sorbents that can achieve high cyclic CO 2 working capacities (WC cyclic ) at low desorption temperatures. This study shows that appropriate degrees of butylene oxide (BO) functionalization on amines with different molecular weights (polyethyleneimine (PEI1200 and PEI300) and tris(2‐aminoethyl)amine (TREN)) can achieve excellent WC cyclic at low desorption temperatures (40–70°C). Through systematic screening, 0.30BO‐PEI300‐SY and 0.54BO‐TREN‐SY are identified as the optimal sorbents with the highest WC cyclic at desorption temperatures of 45 and 40°C, respectively. Both sorbents exhibit excellent stability under oxygen‐rich and humid conditions, maintaining outstanding WC cyclic compared to other benchmark DAC materials. Molecular dynamics simulations reveal that CO 2 adsorption on 1° amine sites plays a dominant role in determining the overall CO 2 capture capacity of pristine amines, and the reduction in CO 2 uptake after BO treatment is primarily attributable to the loss of accessible 1° amine sites. Both experimental and simulation results highlight that the fraction of 1° amines is a key factor governing WC cyclic and desorption behavior after BO modification.