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Aminopolymer‐based adsorbents are commonly investigated for CO2 direct air capture (DAC). In the presence of high temperature and oxygen, which can occur during adsorption‐regeneration cycles, oxidative degradation can significantly reduce adsorbent lifetime. Degradation is typically measured using adsorption performance metrics or chemical characterization. This work demonstrates that the polymer's physical properties, as measured via nuclear magnetic resonance (NMR) relaxometry and differential scanning calorimetry, can be used to quantitatively track degradation. The extent of oxidation of an alumina‐poly(ethylenimine) sample, measured by reductions in amine efficiency (A.E.), is correlated with proton T2 relaxation times. This work hypothesizes that T2 relaxation accurately tracks oxidative degradation in aminopolymers due to the reduction in polymer mobility occurring during the oxidation process. The ability to use NMR relaxometry as a noninvasive technique to probe degradation is demonstrated on a 1‐inch square‐channel monolith adsorbent exposed to actual DAC service conditions. This highlights the potential for relaxometry to evaluate the state of the adsorbent accurately and rapidly compared to typical analytical methods. [ABSTRACT FROM AUTHOR]

Free energy sampling, deep potential molecular dynamics, and characterizations provide insights into the impact of epoxide-functionalization on the hydrogen bonding and mobility of poly(ethylenimine), a promising CO2 sorbent. These findings rationalize the anti-degradation effects of epoxide functionalization and open up new avenues for designing more durable CO2 sorbents. [ABSTRACT FROM AUTHOR]

Correction for 'Improving the direct air capture capacity of grafted amines via thermal treatment' by Melinda L. Jue et al., Chem. Commun., 2024, 60, 7077–7080, https://doi.org/10.1039/D4CC01634C. [ABSTRACT FROM AUTHOR]

Amine-functionalized porous solid materials are effective sorbents for direct air capture (DAC) of CO 2 . However, they are prone to oxidative degradation in service, increasing the materials cost for widespread implementation. While the identification of oxidation products has given insights into degradation pathways, the roles of some species, like CO 2 itself, remain unresolved, with conflicting information in the literature. Here, we investigate the impact of CO 2 on the oxidative degradation of poly(ethylenimine)-alumina (PEI/Al 2 O 3 ) sorbents under conditions encompassing a wide range of CO 2 -air mixture compositions and temperatures relevant to DAC conditions, thereby reconciling the conflicting data in the literature. Degradation profiles characterized by thermogravimetric analysis, in situ ATR-FTIR, and CO 2 capacity measurements reveal nonmonotonic effects of CO 2 concentrations and temperatures on oxidation kinetics. Specifically, 0.04% CO 2 accelerates PEI/Al 2 O 3 oxidation more at low temperatures (<90 °C) compared to 1% and 5% CO 2 , but this trend reverses at high temperatures (>90 °C). First-principles metadynamics, machine learning accelerated molecular dynamics simulations, and 1 H relaxometry experiments show that chemisorbed CO 2 acid-catalyzes critical oxidation reactions, while extensive CO 2 uptake reduces PEI branch mobility, slowing radical propagation. These contrasting kinetic effects of CO 2 explain the complex degradation profiles observed in this work and in prior literature. Collectively, this work highlights the importance of considering atmospheric components in the design of DAC sorbents and processes. Additionally, it identifies the unconstrained branch mobility and local acid environment as two of the major culprits in the oxidation of amine-based sorbents, suggesting potential strategies to mitigate sorbent degradation.