(700e) Impact of Metal Ion Contaminants on Amine-Based Solid Sorbents for Direct Air Capture

Amine-functionalized solid sorbents are widely used in direct air capture (DAC) of CO₂ due to their high CO₂ selectivity and ease of regeneration. However, their long-term stability remains a key barrier to deployment, especially under realistic DAC conditions where ambient air introduces unavoidable environmental contaminants. Among these, transition metal ions are of particular concern due to their ability to catalyze oxidative degradation of amines, even at trace levels, ultimately shortening sorbent lifetime and increasing operational costs. Despite these risks, metal contamination remains an underexplored challenge in DAC research.

This study systematically examines the influence of Cu²⁺, Fe²⁺, and Ni²⁺ on the CO₂ adsorption capacity and oxidative degradation of poly(ethyleneimine)-impregnated silica sorbents (30 wt.% PEI/SBA-15). We simulate three metal contamination pathways relevant to industrial and environmental scenarios: (1) metal ions inherently present in commercial aminopolymers, (2) metal ions originating from commercial supports, and (3) environmental deposition from atmospheric sources such as aerosols or rain.

Using thermogravimetric analysis (TGA) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), we demonstrate that metal ions coordinate with amine sites, reducing CO₂ uptake and simultaneously accelerating radical-initiated autoxidation under accelerated aging conditions. The extent of degradation varies with metal identity, concentration, and contamination mode. Ongoing analysis using quasielastic neutron scattering (QENS) and NMR relaxometry is expected to shed further light on the physical effects of metal ions on amine mobility and dynamics. Our findings underscore the importance of accounting for environmental contaminants in DAC sorbent design and long-term deployment strategies.