美国橡树岭国家实验室Santanu Roy团队报道了，非平衡溶剂效应在促进空气-水氨基酸界面CO₂直接捕获中的作用。相关研究成果发表在2024年12月23日出版的国际知名学术期刊《美国化学会杂志》。

直接空气捕获（DAC）技术受到一定的限制，即对界面在调节二氧化碳从空气到溶液的化学吸附中的动态作用理解不足。虽然非平衡溶剂效应强烈抑制了水性胺基溶剂在本体环境中的反应性，但促进界面处的DAC有可能减少与溶剂的偶联并显著加速DAC。

基于实验证明的概念，即通过与带正电的表面活性剂的离子配对相互作用，将阴离子甘氨酸吸收剂带到界面上，研究人员利用速率理论和增强采样从头计算分子动力学模拟，建立了DAC中涉及的关键基本步骤的基本时间尺度。研究阐明了水影响自由能势垒的机制，以及这些势垒的动态交叉再结晶，从而影响反应速率。

研究发现，水会重新组织以部分脱水[-NH₂]，促进SN₂基CO₂转化为两性离子，然后通过[-NH₂].的过度水合释放质子。低密度界面水有利于脱水而非过度水合，导致质子释放的屏障相对较高（动力学较慢）。屏障跨越抵消了这种影响，使这两个步骤在同一时间尺度（亚微秒）发生，并使界面处的整体DAC过程比在大量水中更快。

这种对环境敏感溶剂对反应动力学的影响的理解，将有助于设计定制的界面，通过控制溶剂化和离子配对来增强二氧化碳捕获动力学。

附：英文原文

Title: The Role of Nonequilibrium Solvent Effects in Enhancing Direct CO2 Capture at the Air–Aqueous Amino Acid Interface

Author: Nitesh Kumar, Vyacheslav S. Bryantsev, Santanu Roy

Issue&Volume: December 23, 2024

Abstract: Direct air capture (DAC) technologies are limited by the poor understanding of the dynamic role of interfaces in modulating the chemisorption of CO2  from air into solutions. While the reactivity of aqueous amine-based solvents in the bulk environment is strongly inhibited by nonequilibrium solvent effects, promoting DAC at interfaces posits a possibility to reduce the coupling with the solvent and significantly accelerate DAC. Building on an experimentally proven concept to bring an anionic glycine absorbent to the interface through ion-pairing interactions with a positively charged surfactant, we establish the fundamental time scales for key elementary steps involved in DAC with rate theory and enhanced-sampling ab initio molecular dynamics simulations. We elucidate the mechanism by which water influences the free energy barriers and dynamical crossing-recrossing of those barriers, affecting the reaction rates. We find that water reorganizes to partially dehydrate [-NH2], facilitating  SN2-based CO2 conversion to a zwitterion, which then releases a proton via overhydration of [-NH2]. The low-density interfacial water favors dehydration over overhydration, leading to a comparatively higher barrier (slower kinetics) for proton release. The barrier-recrossing events neutralize this effect, letting both steps occur at the same time scale (sub-microseconds) and making the overall DAC process faster at the interface than in the bulk water. Such an understanding of environment-sensitive solvent effects on the reaction kinetics will help design tailored interfaces for enhanced CO2 capture kinetics via control of solvation and ion paring.

DOI: 10.1021/jacs.4c14612

Source: https://pubs.acs.org/doi/abs/10.1021/jacs.4c14612