Surface Charge of the Calcite (104) Terrace Measured by Rb+ Adsorption in Aqueous Solutions Using Resonant Anomalous X-ray Reflectivity

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• 作者：Sang Soo Lee ; Frank Heberling ; Neil C. Sturchio ; Peter J. Eng ; Paul Fenter
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：July 21, 2016
• 年：2016
• 卷：120
• 期：28
• 页码：15216-15223
• 全文大小：481K
• 年卷期：0
• ISSN：1932-7455

文摘

Adsorption of Rb⁺ on the (104) plane of single crystal calcite was investigated to estimate the charge of the ionic crystal calcite–water interface. The adsorbed Rb⁺ coverage was quantified as a function of Rb concentration (1–100 mM) in calcite-saturated solutions at pH 8.3 by using in situ resonant anomalous X-ray reflectivity in transmission cell geometry. The Rb⁺ coverages for all solution conditions were small with the maximum ion coverage (Γ_max) of 0.12(4) Rb⁺/nm² estimated by the best-fit Langmuir isotherm model. This result provides an estimate of the upper limit to the effective surface charge density of about −0.02 C/m² considering that any Rb⁺ adsorption to the terrace plane is likely induced by electrostatic attraction. This charge density is significantly lower (by a factor of ≥10) than those estimated from macroscopic measurements, implying that any excess charge likely originates from surface defects.