Surface chemistry-mediated porewater fluctuations boost CO docking in calcium silicate hydrates.

While CO mineralization using carbonatable binders and solid waste has become an overwhelming trend in laboratory and industrial trials, a lack of fundamental understanding of the underlying carbonation mechanisms hinders advancement of carbonation technology for large-scale applications. This study addresses this gap by employing Grand Canonical Monte Carlo simulations to unravel the optimal CO sequestration conditions within the mesopores of calcium silicate hydrates, a ubiquitous component of construction materials. Here we show that CO-surface interactions dominate at low relative humidity (RH), while CO-water interactions prevail at high RH, maximizing CO uptake during capillary condensation, where the metastable porewater boosts CO dissolution. Furthermore, we reveal the influence of surface hydrophilicity on the critical RH for optimal carbonation, indicating that less hydrophilic minerals require higher optimal carbonation RH. These insights into the complex CO-water-surface interactions within minerals' mesopores provide a foundation for developing effective CO mineralization strategies and advancing our understanding of geochemical carbonation processes.