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

金属铬在社会上有许多用途。然而，如果处置不当，它也会进入地下水和地表水。虽然这通常以微量发生，但在较高浓度下，它可能会对健康造成不利影响。它在两个氧化态之间循环，以六价形式有毒。该项目涉及一种理论上合理、但高风险、未经测试、具有重大潜在影响的方法，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、公众健康和监管过程有关的化学过程的理解。这一迫切的项目将开发一种新的现场电化学工具，用于检测饮用水中三价铬铬(III)氧化过程中的铬中间态。由于消毒剂氧化残留的铬(III)，饮用水中可能会无意中形成剧毒的六价铬(VI)，通常以含氧阴离子CrO42-的形式存在。然而，铬(III)的氧化机理在很大程度上尚不清楚。首席研究员实验室的初步研究表明，铬(VI)的产率受元素反应的控制，这些反应涉及形成铬中间物种，然后这些中间物种伴随着分解。本项目旨在开发一种新型的多级旋转环盘电极电化学体系，用于定量研究短寿命四价和五价铬物种，即铬(IV)和铬(V)的形成。目前，有关铬(III)氧化生成铬(VI)的详细机理尚不清楚。虽然人们普遍认为，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是化学惰性的，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，迫切需要了解铬(VI)形成的基本机制，以制定更好的控制策略。这项研究将评估这些中间物种在饮用水中与铬(VI)赋存状态相关的作用。具体地说，在这个项目中，将开发两个新的和先进的电极系统来研究铬中间物种的性质：(1)用于均相铬(III)氧化研究的最先进的贵金属电极(即金和铂)；(2)用于非均相铬(III)氧化研究的内部沉积的铬(III)矿物电极。这项研究的结果将建立一个基于旋转环-盘电极的铬中间体的电化学分析方案，并探索与铬(VI)形成相关的基本机制。这项研究的结果将建立一个基于旋转环-盘电极的铬中间体的电化学分析方案，并探索与水生体系中铬(VI)形成相关的基本机制。该项目涉及一种与传统间歇反应器系统截然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.