Modeling the Acid–Base Properties of Montmorillonite Edge Surfaces

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• 作者：Christophe TournassatJames A. Davis ; Christophe Chiaberge ; Sylvain Grangeon ; Ian C. Bourg
• 刊名：Environmental Science & Technology
• 出版年：2016
• 出版时间：December 20, 2016
• 年：2016
• 卷：50
• 期：24
• 页码：13436-13445
• 全文大小：649K
• ISSN：1520-5851

文摘

The surface reactivity of clay minerals remains challenging to characterize because of a duality of adsorption surfaces and mechanisms that does not exist in the case of simple oxide surfaces: edge surfaces of clay minerals have a variable proton surface charge arising from hydroxyl functional groups, whereas basal surfaces have a permanent negative charge arising from isomorphic substitutions. Hence, the relationship between surface charge and surface potential on edge surfaces cannot be described using the Gouy–Chapman relation, because of a spillover of negative electrostatic potential from the basal surface onto the edge surface. While surface complexation models can be modified to account for these features, a predictive fit of experimental data was not possible until recently, because of uncertainty regarding the densities and intrinsic pK_a values of edge functional groups. Here, we reexamine this problem in light of new knowledge on intrinsic pK_a values obtained over the past decade using ab initio molecular dynamics simulations, and we propose a new formalism to describe edge functional groups. Our simulation results yield reasonable predictions of the best available experimental acid–base titration data.