EAGER: Development of a Novel in situ Electrochemical Tool to Understand Redox Pathways of Hexavalent Chromium and Its Intermediate Formation

[1619915]金属铬在社会上有许多用途。然而，如果处理不当，它也会进入地下水和地表水。虽然这种情况通常发生在微量，但浓度较高时可能会对健康造成不利影响。它在两种氧化态之间循环，在六价形式下是有毒的。该项目涉及一种理论上合理，但高风险，未经测试的方法，具有重大潜在影响，以开发一种检测水中铬的新方法。该项目将创造一种新的基于旋转环盘电极的工具，有可能改变环境工程界对与水质、公共卫生和监管过程相关的化学过程的理解。该EAGER项目将开发一种新的原位电化学工具，用于检测饮用水中三价铬Cr（III）氧化过程中的铬中间体。高毒性六价铬Cr（VI）的形成，通常以氧化离子CrO4 2-的形式，可能在饮用水中无意中发生，因为残留的Cr（III）被消毒剂氧化。然而，Cr（III）氧化的机制在很大程度上仍未被探索。在首席研究员（PI）实验室的初步调查表明，Cr（VI）的产率是由元素反应控制的，这些反应涉及Cr中间物质的形成，然后是这些中间物质的相关分解。本项目旨在开发一种具有多级旋转环盘电极的新型电化学系统，以定量研究短寿命四价和五价铬的形成，即Cr（IV）和Cr(V)。目前，通过Cr（III）氧化形成Cr（VI）的详细机制尚不清楚。尽管人们普遍认为，铬（III）的低溶解度阻止了它在饮用水中的释放，而且铬（III）在水处理过程的下游具有化学惰性，但这些假设是不充分的。由于监管机构正在考虑制定更严格的饮用水标准，因此迫切需要了解Cr（VI）形成的基本机制，以制定更好的控制策略。本研究将评估这些中间物种在饮用水中Cr（VI）发生的相关作用。具体来说，在这个项目中，将开发两种新型和先进的电极系统来检查Cr中间物质的性质：(1)最先进的贵金属电极（即金和铂）用于均匀Cr（III）氧化研究；(2)内部内置电极，沉积Cr（III）矿物，用于非均相Cr（III）氧化研究。本研究的结果将为基于旋转环盘电极的铬中间体电化学分析和探索与Cr（VI）形成相关的基本机制建立一个方案。本研究的结果将为基于旋转环盘电极的铬中间体电化学分析和探索水生系统中Cr（VI）形成的基本机制建立一个方案。与传统的间歇式反应器系统相比，该项目涉及一种完全不同的电化学方法来研究金属氧化还原化学，并应用表面电化学和分析化学的新专业知识，在一个新的研究领域进行新发现。

1619915LiuThe metal chromium has many applications in society. However, when disposed of improperly, it can also find its way into ground and surface waters. While this usually happens in trace quantities, at higher concentrations it may cause adverse health effects. It cycles between two oxidation states and is toxic in the hexavalent form. This project involves a theoretically sound, but high-risk, untested approach with significant potential impact, to develop a new method of detection of chromium in water. This project will create a new rotating ring-disk electrodes-based tool with the potential to transform the environmental engineering community's understanding of chemical processes that relate to water quality, public health, and regulatory processes.This EAGER project will develop a novel in situ electrochemical tool for the detection of chromium intermediate species during the oxidation of trivalent chromium Cr(III) species in drinking water. Formation of highly toxic hexavalent chromium Cr(VI, typically in the form of oxyanion CrO4 2-, can inadvertently take place in drinking water due to the oxidation of residual Cr(III) by disinfectants. However, the mechanisms of Cr(III) oxidation remain largely unexplored. Preliminary investigations in the principal investigator's (PI's) laboratory indicates that the yield of Cr(VI) is controlled by elemental reactions involving the formation of Cr intermediate species, followed by the associated decomposition of these intermediate species. This project aims to develop a novel electrochemical system with multi-stage rotating ring-disk electrodes to quantitatively investigate the formation of short-lived tetravalent and pentavalent chromium species, i.e., Cr(IV) and Cr(V). Currently, the detailed mechanisms of Cr(VI) formation via Cr(III) oxidation are poorly understood. Although it is widely presumed that the low solubility of Cr(III) prevents its release in drinking water and that Cr(III) is chemically inert downstream of water treatment processes, these presumptions are inadequate. Since Cr(VI) is under consideration by regulatory agencies for more stringent drinking water standards, it is urgent to understand the fundamental mechanisms of Cr(VI) formation to develop better control strategies. This research will assess the role of these intermediate species relevant to Cr(VI) occurrence in drinking water. Specifically, in this project, two novel and advanced electrode systems will be developed to examine the nature of Cr intermediate species: (1) state-of-the-art noble metal electrodes (i.e., gold and platinum) for homogeneous Cr(III) oxidation investigation; and, (2) in-house built electrode with deposited Cr(III) minerals for heterogeneous Cr(III) oxidation investigation. Outcomes of this research will establish a protocol for rotating ring-disk electrodes-based electrochemical analysis of chromium intermediates and exploration of fundamental mechanisms associated with Cr(VI) formation. Outcomes of this research will establish a protocol for rotating ring-disk electrodes-based electrochemical analysis of chromium intermediates and exploration of fundamental mechanisms associated with Cr(VI) formation in aquatic systems. The project involves a radically different electrochemical approach in contrast to a traditional batch reactor system to study metal redox chemistry, and applies new expertise of surface electrochemistry and analytical chemistry to engage novel discoveries in a new area of research.