First principles modeling of CO2 adsorption on (100), (010), and (001) surfaces of wollastonite for applications in enhanced rock weathering

Abstract

Negative emissions technologies target the removal of carbon dioxide (CO2) from the atmosphere as a way of combating global warming. Enhanced rock weathering (ERW) is a vital negative emissions technology that applied globally could remove gigatonnes of CO2 per year from the atmosphere. In ERW, silicate minerals exposed to the atmosphere trap CO2 via mineral carbonation as thermodynamically stable carbonates. To obtain an atomic scale understanding of the weathering process and to design more reactive silicates for enhanced rock weathering, CO2 adsorption on low index wollastonite (CaSiO3) surfaces was modeled using density functional theory. Atomic scale structure of (100), (010), and (001) surfaces of wollastonite was predicted and the thermodynamics of their interaction with CO2 was modeled. Based on surface energy calculations, (001) and (010) surfaces of wollastonite exhibit similar stabilities, while (100) surface is found to be least stable. Depending on the surface structure and chemistry, different CO2 adsorption geometries are possible. A common trend emerges, wherein CO2 adsorbs molecularly and demonstrates proclivity to bond with surface layer calcium and oxygen binding sites. Mechanisms for electronic charge transfer between the adsorbate and the substrate were studied to shed light on the fundamental aspects of these interactions. The most favorable bent CO2 geometry was bridged between calcium atoms, revealing that the enhancing the likelihood of this geometry and binding site could pave the way to designing reactive silicates for efficient CO2 sequestration via ERW.