Pacific Northwest National Laboratory, Richland, Washington, USA.
Langmuir. 2011 Jul 5;27(13):7986-90. doi: 10.1021/la201369g. Epub 2011 Jun 8.
Reaction rates of environmental processes occurring at hydrated mineral surfaces are in part controlled by the electrostatic potential that develops at the interface. This potential depends on the structure of exposed crystal faces as well as the pH and the type of ions and their interactions with these faces. Despite its importance, experimental methods for determining fundamental electrostatic properties of specific crystal faces such as the point of zero charge are few. Here we show that this information may be obtained from simple, cyclic potentiometric titration using a well-characterized single-crystal electrode exposing the face of interest. The method exploits the presence of a hysteresis loop in the titration measurements that allows the extraction of key electrostatic descriptors using the Maxwell construction. The approach is demonstrated for hematite (α-Fe(2)O(3)) (001), and thermodynamic proof is provided for the resulting estimate of its point of zero charge. Insight gained from this method will aid in predicting the fate of migrating contaminants, mineral growth/dissolution processes, and mineral-microbiological interactions and in testing surface complexation theories.
在水合矿物表面发生的环境过程的反应速率部分受界面处产生的静电势控制。该电势取决于暴露的晶体面的结构以及 pH 值以及离子的类型及其与这些面的相互作用。尽管它很重要，但用于确定特定晶面（如零电荷点）的基本静电特性的实验方法却很少。在这里，我们表明可以使用经过良好表征的单晶电极从简单的循环电位滴定中获得该信息，该电极暴露了感兴趣的面。该方法利用了滴定测量中滞后环的存在，该滞后环允许使用麦克斯韦构造提取关键静电描述符。该方法已针对赤铁矿（α-Fe（2）O（3））（001）进行了演示，并为由此得出的零电荷点的估算值提供了热力学证明。该方法提供的见解将有助于预测迁移污染物的命运，矿物生长/溶解过程以及矿物微生物相互作用，并有助于测试表面络合理论。
