Charge Effects on the Adsorption of Octanoic Acid and Octanoate at Carbonates

In this work, we investigate the adsorption behavior of protonated and deprotonated acids on carbonate surfaces, employing density functional theory (DFT) simulations and the self-consistent potential correction (SCPC) for the charged deprotonated acid. By comparing the coadsorption models with the SCPC method, we have observed significant differences in the adsorption energies, indicating that coadsorption underestimates the stability of the acid-carbonate interactions, even leading to changes from favorable to unfavorable adsorption on magnesites. Our study highlights the distinct chemical interactions of protonated and deprotonated acids with carbonate surfaces, revealing a more covalent bonding nature for protonated acids and a predominantly ionic character for deprotonated acids. Hence, we highlight the importance of employing charge correction methods, such as the SCPC, for a more accurate representation of the adsorption of charged molecules on mineral surfaces, which could be extended to other systems.