Energetics and Stability of Geologically-Confined Water

在地表和近地表地质环境中，限制在奥级到纳米级孔隙中的水在体积和化学上都具有重要意义。水在大块液体和气相之间的分配以及限制在矿物内部和矿物之间的水的分配在决定地球化学和地球生物过程的命运方面发挥着关键作用。尽管在过去的几十年里，相当多的工作集中在承压水的性质上，但能够同时考虑承压水相对于主体水的稳定性的严格热力学模型通常是不存在的，这些模型与广泛使用的地球化学模型是一致的。在一定程度上，这是由于缺乏能够定量描述承压水吸附和解吸之间的滞后现象的物理化学模型。本研究通过结合平衡观测、量热测量和选定的一组包含承压水的系统的热力学建模来满足这些需求。模型沸石和纳米孔系统表现出滞后吸附/解吸行为将被研究，以测试一个新发展的热力学模型，显示出良好的预测滞后行为。此外，还将研究另外两种类型的体系，以填补目前在了解控制承压水稳定性因素方面的空白：a)纯硅沸石，其中的水分子不溶于离子；以及c)含有仅与离子结合的承压水的沸石体系。水在这些系统中展示？端元？结构状态，当组合在一起时，形成了在大多数先前研究的微孔承压水系统中发现的环境(即，那些包含既溶剂化离子又与限制介质相互作用的水分子的系统)。科学成果：这项研究的结果将通过热力学建模来综合，以描述承压水分子的稳定性作为温度、压力和水的化学势的函数。由此产生的热力学数据和模型将大大扩展在符合地球化学热力学标准实践的热力学框架内评估承压水分子的相对稳定性和行为的能力。描述所研究系统中滞后行为的模型将为其他表现这种行为的系统的宏观热力学描述提供启发式的基础。更广泛的影响：拟议的研究将为佛罗里达大学的学生提供更多的教育机会，并将导致数据和热力学模型的广泛获得。研究生和本科生对该项目的参与是其成功不可或缺的一部分。参与这个项目的学生将接受现代实验方法和热力学分析方面的培训和经验。此外，建议的研究方法将用于开发创新的课堂练习，让学生在P.I.S物理地球化学课程中亲身体验热化学方法。研究中产生的数据不仅将作为出版物在国际学术期刊上传播，还将在互联网上免费下载。

Water confined in Å- to nm-scale pores is volumetrically and chemically important in surficial and near surface geological environments. Partitioning of water between bulk liquid and vapor phases and water confined in spaces within and between minerals plays a critical role in determining the fate of geochemical and geobiological processes. Despite considerable effort over the past several decades focused on the properties of confined water, rigorous thermodynamic models permitting simultaneous consideration of confined water stability relative to bulk water that are consistent with widely employed geochemical models are generally not available. In part, this is due to a paucity of physical chemical models permitting quantitative description of the hysteresis that is commonly observed between sorption and desorption of confined water. The present study addresses these needs through a combination of equilibrium observations, calorimetric measurements, and thermodynamic modeling of a selected suite of systems containing confined water. Model zeolite and nanoporous systems exhibiting hysteretic sorption/desorption behavior will be studied in order to test a newly developed thermodynamic model that shows promise in predicting hysteretic behavior. In addition, two other types of systems will be studied to fill in gaps currently present in the understanding of the factors controlling the stability of confined water: a) pure silica zeolites in which water molecules do not solvate ions; and c) zeolite systems containing confined water that is only bonded to ions. Water in these systems exhibits ?endmember? structural states, that when combined form the environments found in most previously studied microporous confined water systems (that is, those containing water molecules that both solvate ions and interact with the confining medium). Scientific outcomes: The results of this study will be synthesized through thermodynamic modeling to describe the stability of confined water molecules as a function of temperature, pressure, and the chemical potential of water. The resulting thermodynamic data and models will significantly expand capabilities for assessing the relative stability and behavior of confined water molecules in a thermodynamic framework that is congruent with standard practices in geochemical thermodynamics. Models describing hysteretic behavior in the systems studied will provide a heuristic basis for macroscopic thermodynamic description of other systems exhibiting this behavior. Broader impacts: The proposed study will provide enhanced educational opportunities for students at the University of Florida and will lead to widespread availability of the data and thermodynamic models. Graduate and undergraduate student involvement in the project is integral for its success. Students participating in this project will receive training and experience in modern experimental methods and thermodynamic analysis. In addition, the methods of the proposed study will be used to develop innovative classroom exercises to give students hands-on experience in thermochemical methods in the P.I.?s physical geochemistry course. Data generated in the study will be disseminated not only as publications in international scholarly journals, but will also be available for free download on the internet.