Nanoconfinement Facilitates Reactions of Carbon Dioxide in Supercritical Water

TL;DR

This study uses ab initio molecular dynamics to show that nanoconfinement in supercritical water enhances CO2 reactions, with mineral interfaces influencing acidity and reaction pathways, impacting deep Earth carbon processes.

Contribution

The paper demonstrates that nanoconfinement significantly increases CO2 reactivity in supercritical water, revealing the role of mineral interfaces in reaction mechanisms.

Findings

Nanoconfinement enhances CO2 reactions in supercritical water.

Mineral interfaces increase solution acidity and alter reaction pathways.

Deep Earth CO2 may be more reactive than previously believed.

Abstract

The reactions of CO$_2$ in water under extreme pressure-temperature conditions are of great importance to the carbon storage and transport below Earth's surface, which substantially affect the carbon budget in the atmosphere. We applied ab initio molecular dynamics simulations to study aqueous carbon solutions nanoconfined by graphene and stishovite (SiO$_2$) at 10 GPa and 1000$\sim$1400 K. We found that CO$_2$(aq) reacts more in nanoconfinement than in bulk. The stishovite-water interface makes the solutions more acidic, which shifts the chemical equilibria, and the interface chemistry also affects the reaction mechanisms. Our findings suggest that CO$_2$(aq) in deep Earth may be more active than previously thought, and confining CO$_2$ and water in nanopores may enhance the efficiency of mineral carbonation.