Thermodynamics and Redox Reactivity of Birnessite

在化学系环境化学科学项目的支持下，克里斯托弗·戈尔斯基和彼得·希尼以及他们在宾夕法尼亚州立大学的研究生将研究矿物和水之间发生的化学反应。这些反应很重要，因为它们在确定有毒金属和有害有机化合物等环境污染物在环境和水处理系统中的行为方面发挥着重要作用。该项目的重点是水钠锰矿，这是一种在环境中常见的高活性氧化锰。水钠石转化水中环境污染物的速度取决于水钠石的性质和水的化学成分，但目前还没有确定原因的定量方法。为了解决这一差距，该项目将表征水钠石在不同类型水中的元素组成、氧化态、晶体结构、聚集态和表面电荷，并确定在相同条件下不同的环境污染物与水钠石反应的速度。为了扩大该项目的社会和科学影响，研究人员还将开发一个工作坊，向其他科学家和工程师传授如何使用电化学方法研究矿物，并在6-12年级对STEM(科学、技术、工程和数学)领域感兴趣的年轻女性的外联活动中组织名为“神秘的锰矿”的演示。该项目将结合中介电化学技术、光谱分析和污染物命运研究来彻底表征水钠镁及其反应性。该项目有三个目标，其复杂性依次递增：(1)确定锰在水钠钠盐中的氧化状态如何以及为什么会影响其热力学性质和在pH 5.0下的反应活性；(2)确定溶液中阳离子的类型和浓度以及pH如何以及为什么影响水钠钠矿的热力学性质和反应性；以及(3)确定前两个目标中建立的关系是否可以预测含有多种阳离子和/或天然有机物的复杂水域中的污染物氧化率。如果这项工作取得成功，这项工作将为环境化学和地球化学界提供一种在一系列溶液化学条件下估计水钠锰矿热力学性质的方法。这项工作还将创建一个框架，用于在未来表征其他复杂的环境相关矿物的热力学性质。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Environmental Chemical Sciences Program in the Division of Chemistry, Christopher Gorski and Peter Heaney and their graduate students at Pennsylvania State University will study chemical reactions that occur at the interface between minerals and water. These reactions are important because they play a significant role in determining how environmental contaminants, such as toxic metals and hazardous organic compounds, behave in the environment and in water treatment systems. The project focuses on birnessite, which is a highly reactive manganese oxide commonly found in the environment. The rate at which birnessite transforms environmental contaminants present in water can depend on the properties of the birnessite and the water chemistry, but there is currently no quantitative method for determining why. To address this gap, the project will characterize the elemental composition, oxidation state, crystal structure, aggregation state, and surface charge of birnessite in various types of water and determine how quickly different environmental contaminants react with birnessite under the same conditions. To broaden the societal and scientific impact of the project, the researchers will also develop a workshop to teach other scientists and engineers how to use electrochemical methods to study minerals, and organize a demonstration called “Mysterious Manganese Minerals” at an outreach event for grade 6-12 young women interested in STEM (science, technology, engineering and mathematics) fields.This project will use a combination of mediated electrochemical techniques, spectroscopic analyses, and contaminant fate studies to thoroughly characterize birnessite and its reactivity. The project has three objectives with sequentially increasing complexities: (1) to determine how and why the oxidation state of Mn in sodium birnessite influences its thermodynamic properties and reactivity at pH 5.0; (2) to determine how and why the type and concentration of cations in solution and the pH influence birnessite’s thermodynamic properties and reactivity and (3) to determine if the relationships developed in first two objectives can predict contaminant oxidation rates in complex waters containing multiple cations and/or natural organic matter. If successful, this work will provide the environmental chemistry and geochemistry communities with a method for estimating the thermodynamic properties of birnessite under a range of solution chemistries. The work will also create a framework for characterizing the thermodynamic properties of other complex environmentally relevant minerals in the future.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.