Thermodynamics and Redox Reactivity of Birnessite

在化学系环境化学科学项目的支持下，宾夕法尼亚州立大学的克里斯托弗·戈尔斯基和彼得·希尼及其研究生将研究矿物质和水之间界面处发生的化学反应。这些反应很重要，因为它们在确定环境污染物（如有毒金属和有害有机化合物）在环境和水处理系统中的行为方面起着重要作用。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。水钠锰矿转化水中存在的环境污染物的速率可以取决于水钠锰矿的性质和水化学，但目前没有定量方法来确定原因。为了解决这一差距，该项目将表征水钠锰矿在各种类型水中的元素组成、氧化态、晶体结构、聚集态和表面电荷，并确定不同环境污染物在相同条件下与水钠锰矿反应的速度。为了扩大该项目的社会和科学影响，研究人员还将举办一个研讨会，教授其他科学家和工程师如何使用电化学方法研究矿物质，并在一个针对6-12年级对STEM感兴趣的年轻女性的外联活动中组织一个名为“神秘的锰矿”的演示。该项目将使用介导电化学技术、光谱分析和污染物归宿研究的组合来彻底表征水钠锰矿及其反应性。该项目有三个目标，其复杂性依次增加：（1）确定水钠锰矿中锰的氧化态如何以及为什么影响其热力学性质和pH 5.0时的反应性;（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锰矿的热力学性质和反应性，以及（3）以确定在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沃茨中的污染物氧化速率。如果成功，这项工作将提供环境化学和地球化学社区的一种方法，用于估计水钠锰矿的热力学性质下的一系列溶液化学。这项工作还将为未来表征其他复杂环境相关矿物的热力学性质创建一个框架。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

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.