Charging of the Ice/Solution Interface by Deprotonation of Dangling Bonds, Ion Adsorption, and Ion Uptake in an Ice Crystal As Revealed by Zeta Potential Determination

• Published in: Journal of physical chemistry. C Vol. 123; no. 10; pp. 6062 - 6069
• Main Authors: Inagawa, Arinori, Harada, Makoto, Okada, Tetsuo
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.03.2019
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.8b12435

We reveal the charging mechanism and behavior of ions at the ice/solution interface through measurements of the zeta potential of ice. The zeta potential of ice, which is calculated from the migration of a probe in an ice channel under various conditions, is interpreted using the Stern double layer model. The zeta potential of ice is generated by the deprotonation of dangling OH bonds, the adsorption of ions on the ice surface, and ion uptake in the ice crystal lattice. The deprotonation of the dangling OH bonds on the surface of ice is enhanced compared to that in bulk liquid water; the pK a of the former is estimated to be ∼3. Interestingly, only 1.41% of the total dangling OH bonds on the ice surface are deprotonated, even at pH > 6, suggesting that the deprotonation of a dangling bond suppresses further dissociation of the nearby OH sites. This is caused by the facilitated reorientation of the water molecules in ice in the presence of L-defects. The ion adsorption constants indicate that the interaction of ions other than H+ with the ice surface is mainly driven by coordination of the dangling bonds to the ions. Therefore, smaller ions are adsorbed more readily on the ice surface than their larger counterparts. Additionally, uptake of F– in the ice crystal lattice is suggested. Elucidation of the ice/water interface properties will allow us not only to understand the unique properties found in nano- or micro-sized liquid phases confined in ice but also to develop novel separations and reactions using frozen aqueous media as platforms.