Epoxide-Modified Diethylenetriamine for Ambient-Temperature Direct Air Capture

Small amine-based direct air capture materials show promising CO₂ capture performance but suffer stability issues─evaporation losses, oxidative degradation, CO₂-induced urea formation, and moisture-driven leaching─exacerbated by energy-intensive thermal regeneration (80-120 °C). Here, we employed controlled epoxide functionalization of the small amine diethylenetriamine (DETA) to mitigate its stability issues while enabling reversible CO₂ binding and energy-efficient desorption at ambient temperature. Modification with 1,2-epoxybutane across stoichiometric ratios (1:1 to 1:2) produces materials with tailored molecular weights and intermolecular interactions, leading to enhanced thermal stability by suppressing evaporative losses observed in unmodified DETA and markedly improved oxidative resistance. Despite the increased molecular weight compared to DETA, the functionalized DETA molecules exhibit fast CO₂ adsorption rates of 1.03-1.28 mmol/g/h, while achieving rapid CO₂ desorption at ambient temperatures and 66% regeneration within 1 h at 30 °C. The optimized material retains 97.8% capacity after 24 h of oxidative stress testing (60 °C in air), while DETA cannot be properly evaluated due to evaporation during thermal treatment. Real-world validation using ambient atmospheric air demonstrates stable cycling performance over 50 consecutive adsorption-desorption cycles, featuring ambient-temperature regeneration and minimal capacity loss. This facile and effective modification approach using 1,2-epoxybutane to (i) increase the molecular weight of small amines (thus minimizing evaporative loss) and (ii) generate a high fraction of sterically hindered secondary amines for improved oxidative resistance may facilitate the scalable production of small amine-based materials for CO₂ capture applications.