Molecular-scale mechanisms of CO2 mineralization in nanoscale interfacial water films.

Abstract

The calamitous impacts of unabated carbon emission from fossil-fuel-burning energy infrastructure call for accelerated development of large-scale CO2 capture, utilization and storage technologies that are underpinned by a fundamental understanding of the chemical processes at a molecular level. In the subsurface, rocks rich in divalent metals can react with CO2, permanently sequestering it in the form of stable metal carbonate minerals, with the CO2-H2O composition of the post-injection pore fluid acting as a primary control variable. In this Review, we discuss mechanistic reaction pathways for aqueous-mediated carbonation with carbon mineralization occurring in nanoscale adsorbed water films. In the extreme of pores filled with a CO2-dominant fluid, carbonation reactions are confined to angstrom to nanometre-thick water films coating mineral surfaces, which enable metal cation release, transport, nucleation and crystallization of metal carbonate minerals. Although seemingly counterintuitive, laboratory studies have demonstrated facile carbonation rates in these low-water environments, for which a better mechanistic understanding has come to light in recent years. The overarching objective of this Review is to delineate the unique underlying molecular-scale reaction mechanisms that govern CO2 mineralization in these reactive and dynamic quasi-2D interfaces. We highlight the importance of understanding unique properties in thin water films, such as how water dielectric properties, and consequently ion solvation and hydration behaviour, can change under nanoconfinement. We conclude by identifying important frontiers for future work and opportunities to exploit these fundamental chemical insights for decarbonization technologies in the twenty-first century.