Molecular Views of Mineral Carbonation: Reaction of CO ₂ with the Wollastonite (100) Surface

The carbonation of silicate minerals is a key process in the Earth's carbon cycle and offers a promising avenue for long-term CO₂ sequestration. However, the atomistic mechanisms by which CO₂ is activated at silicate surfaces remain poorly understood, largely due to the intrinsic complexity and insulating nature of these materials. To close this gap, wollastonite (CaSiO₃) is used as a model system. Noncontact atomic force microscopy (nc-AFM) with functionalized tips is combined with density functional theory (DFT) to investigate its lowest-energy (100) surface under ultrahigh vacuum (UHV). Upon cleaving the mineral in UHV, water vapor is released from the sample and spontaneously readsorbs into a previously unreported, exceptionally stable configuration. The resulting surface hydration layer promotes spontaneous CO₂ chemisorption and the formation of surface carbonates with negligible kinetic barriers. Our results offer atomic-scale evidence of gas-phase carbonation on a silicate mineral, revealing a water-assisted pathway for CO₂ capture that bypasses aqueous mineral dissolution.