Surface chemistry-mediated porewater fluctuations boost CO₂ docking in calcium silicate hydrates

While CO₂ 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 CO₂ sequestration conditions within the mesopores of calcium silicate hydrates, a ubiquitous component of construction materials. Here we show that CO₂-surface interactions dominate at low relative humidity (RH), while CO₂-water interactions prevail at high RH, maximizing CO₂ uptake during capillary condensation, where the metastable porewater boosts CO₂ 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 CO₂-water-surface interactions within minerals' mesopores provide a foundation for developing effective CO₂ mineralization strategies and advancing our understanding of geochemical carbonation processes.