CO2 hydration at the air-water interface: A surface-mediated in-and-out mechanism

• 成果类型: Article
• 署名作者: Brookes, Samuel G. H.; Kapil, Venkat; Michaelides, Angelos; Schran, Christoph
• 署名单位: University of Cambridge; University of Cambridge; University of Cambridge; University of London; University College London; University of London; University College London
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-11443
• DOI: 10.1073/pnas.2502684122
• 发表日期: 2025-08-26
• 关键词: generalized gradient approximation; carbon-dioxide; molecular-dynamics; ocean acidification; aqueous carbonate; bicarbonate; dissociation; storage

摘要

An understanding of the CO2 + H2O hydration reaction is crucial for modeling the effects of ocean acidification, for enabling novel carbon storage solutions, and as a model process in the geosciences. While the mechanism of this reaction has been investigated extensively in the condensed phase, its mechanism at the air-water interface remains elusive, leaving uncertain the contribution that surface-adsorbed CO2 makes to the overall acidification reaction. In this study, we employ machine-learned potentials trained to various levels of theory to provide a molecular-level understanding of CO2 hydration at the air-water interface. We show that reaction at the interface follows a surface-mediated in-and-out mechanism: CO2 diffuses into the aqueous surface layer, reacts to form carbonic acid, and is subsequently expelled from solution. We show that this surface layer provides a bulk-like solvation environment, engendering similar modes of reactivity and near-identical free energy profiles for the bulk and interfacial processes. Our study unveils an unconventional reaction mechanism that underscores the dynamic nature of the molecular reaction site at the air-water interface. The similarity between bulk and interfacial profiles shows that CO2 hydration is equally as feasible under these two solvation environments and that acidification rates are likely enhanced by this additional surface contribution.