Molecular Views of Mineral Carbonation: Reaction of CO2 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.