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Innovative Research Unveils New Mechanisms of Carbon Dioxide Behavior in Supercritical Water

A research initiative spearheaded by Associate Professor Ding Pan from the Hong Kong University of Science and Technology (HKUST), in collaboration with Professor Yuan Yao from the Department of Mathematics, has unveiled critical insights into the intricate reaction mechanisms of carbon dioxide (CO2) in supercritical water. These findings hold significant implications for both natural processes and engineering applications related to CO2 mineralization and sequestration, contributing valuable knowledge to the deep carbon cycle within the Earth’s interior. The study has been published in the Proceedings of the National Academy of Sciences (PNAS).

The process of CO₂ dissolving in water followed by hydrolysis reactions is vital for effective carbon capture and mineralization, making it an essential factor in carbon sequestration strategies aimed at addressing global warming. Prof. Pan’s team pioneered the use of first-principles Markov models to illuminate the reaction mechanisms between CO₂ and supercritical water within both bulk and nanoconfined settings. Remarkably, they identified pyrocarbonate (C₂O₅²⁻) as a stable and previously underappreciated reaction intermediate in nanoconfined environments, despite its known instability and tendency to decompose quickly in aqueous solutions. This unexpected emergence of pyrocarbonate is attributed to the unique superionic characteristics of confined water solutions. Moreover, the research indicates that carbonation reactions are characterized by collective proton transfer through transient water chains, showcasing concerted behavior in bulk but a stepwise progression in nanoscale confines. This innovative approach underscores the efficacy of first-principles Markov models in deciphering complex kinetics in aqueous environments.

“Our groundbreaking methodology has enabled us to uncover a novel CO2 dissolution pathway that involves pyrocarbonate ions,” stated Prof. Chu Li, Research Assistant Professor from the Department of Physics. “Our computational framework operates without reliance on prior assumptions, autonomously detecting reaction pathways free from human bias, and revealing previously unknown mechanisms rooted in the fundamentals of physics.”

Prof. Ding Pan further noted, “Our research utilizes unsupervised learning techniques to highlight the significance of large oxocarbons in aqueous reactions, particularly under extreme conditions. It also illustrates that employing nanoconfinement can effectively modulate chemical processes. These revelations are likely to open new avenues for advancing carbon sequestration technologies moving forward.”

The research was made possible through funding from the Hong Kong Research Grants Council, the Croucher Foundation, and the Excellent Young Scientists Fund from the National Natural Science Foundation of China. A portion of the computational analysis was conducted on the Tianhe-2 supercomputer at the National Supercomputer Center located in Guangzhou.

*Note: Prof. Chu Li, who is a Research Assistant Professor, is the primary author of this study and, alongside Prof. Ding Pan, serves as a corresponding author.

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