Characterization of defect energy levels due to As, Co, and Ni impurities in pyrite: A step toward understanding charge transfer kinetics at the semiconductor/electrolyte interface

黄铁矿中 As、Co 和 Ni 杂质引起的缺陷能级表征：了解半导体/电解质界面电荷转移动力学的一步

• 批准号: 0617396
• 负责人: Kaye Savage
• 金额: $ 7.91万
• 依托单位: Vanderbilt University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-01-01 至 2010-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0617396&HistoricalAwards=false
• 关键词: Characterization; defect; energy; levels; due

SAVAGE, KayeEAR-0617396Understanding the molecular scale mechanisms of pyrite oxidation is fundamental to a variety of fields including environmental geochemistry, materials science, and mineral processing. In a new electrochemical study using synthetically grown single pyrite crystals doped with As, Co, and Ni, we show that bulk electronic structure, as influenced by these electroactive impurities, influences the rate of oxidation. We observe, in order of highest to lowest oxidation rate: pyrite with As, Co, Ni and negligible impurities. This suggests that electroactive impurities fundamentally affect the rate of pyrite oxidation, raising the questions: How are differences in observed oxidation rates related to charge transfer resistance, carrier concentration and type, and concentration of surface states? What is the effect of different impurities on the concentration and reactivity of surface states? The principle hypotheses to explain the observed behavior are:. Bulk defect states in the band gap arising from impurities become reactive surface states at the electrode-solution interface and act as a conduit for charge transfer. P-type As-doped pyrite oxidizes faster because holes reaching the surface from the valence band accept electrons from Fe2+ and S2 2- surface states, resulting in broken bonds.The research objectives are:. to characterize and measure the energy levels of bulk defect and interface surface states in undoped pyrite and pyrite doped with As, Co, and Ni using EPS;. to characterize the surface atomic environment and valence state of Fe, As, Co, and Ni;. to propose charge transfer mechanisms explaining the observed oxidation ratesWe propose a set of experiments using electrochemical impedance spectroscopy (EIS), electrochemical photocapacitance spectroscopy (EPS) and AC voltammetry aimed at characterizing the kinetic behavior and surface electronic structure of doped and undoped synthetic pyrite. Parallel X-ray absorption spectroscopy experiments, including grazing-incidence XAS, will provide information on the local atomic environment and electronic structure of the impurities in the bulk and at the surface.Intellectual MeritOur collection of well-characterized synthetic doped and undoped pyrite puts us in a unique position to further explore the kinetics and mechanisms of pyrite oxidation. EPS will reveal the energy levels within the bandgap and the nature (donor or acceptor) of active defect states at the pyrite surface. The characterization of surface states in pyrite with different impurities (As-doped: p-type, Co and Nidoped: n-type with shallow and deep donor levels respectively) and its relation to oxidation rates will suggest electron transfer pathways. AC voltammetry will measure charge transfer kinetics, and suggest whether Fermi level pinning is controlling the surface electrochemical behavior. EIS will suggest equivalent circuit models for the charge transfer mechanism and provide additional information about charge transfer kinetics. Relating the energy of the bulk defect and surface states to the acceptor and donor levels of the redox couple in solution will allow us to propose specific charge transfer mechanisms related to the presence of As, Co, and Ni impurities.Broader ImpactsPyrite oxidation in mine tailings and waste rock piles leads to acid drainage posing serious environmental risk. The results of this study will lead to more accurate reaction models and improved ecological risk analysis of mining and proposed mining sites. Understanding pyrite oxidation is critical for the mineral processing industry particularly in the use of flotation methods for ore enrichment. Additionally, materials scientists interested in pyrite for photovoltaic and liquid junction solar applications, and electrochemical storage devices will benefit from this knowledge. This study will continue to foster collaboration between the departments of Earth & Environmental Sciences and Chemistry at Vanderbilt University, and support a new researcher as he completes his doctoral dissertation.

了解黄铁矿氧化的分子尺度机制是包括环境地球化学、材料科学和矿物加工在内的许多领域的基础。在一项新的电化学研究中，我们使用掺杂As、Co和Ni的合成生长的单黄铁矿晶体，发现受这些电活性杂质影响的体电子结构会影响氧化速率。我们观察到，按氧化速率从高到低的顺序：黄铁矿含As、Co、Ni和可忽略的杂质。这表明电活性杂质从根本上影响了黄铁矿的氧化速率，提出了以下问题：观察到的氧化速率差异与电荷转移电阻、载流子浓度和类型以及表面态浓度有何关系？不同杂质对表面态的浓度和反应性有什么影响？解释观察到的行为的主要假设是：。由杂质引起的带隙中的体缺陷态在电极-溶液界面处成为反应性表面态，并充当电荷转移的管道。p型掺as的黄铁矿氧化速度更快，因为从价带到达表面的空穴接受来自Fe2+和S2 -表面态的电子，导致键断裂。研究目标为：。利用EPS表征和测量未掺杂和掺杂As、Co、Ni的黄铁矿的体缺陷和界面表面态的能级；表征Fe、As、Co和Ni的表面原子环境和价态；我们提出了一套电化学阻抗谱（EIS）、电化学光电容谱（EPS）和交流伏安法的实验，旨在表征掺杂和未掺杂的合成黄铁矿的动力学行为和表面电子结构。平行x射线吸收光谱实验，包括掠入射XAS，将提供有关本体和表面杂质的局部原子环境和电子结构的信息。我们收集了表征良好的合成掺杂和未掺杂黄铁矿，这使我们在进一步探索黄铁矿氧化动力学和机制方面处于独特的地位。EPS将揭示带隙内的能级和黄铁矿表面活性缺陷态的性质（供体或受体）。不同杂质（as掺杂：p型，Co和nidop: n型，分别具有浅层和深层供体水平）的黄铁矿表面态的表征及其与氧化速率的关系将提示电子转移途径。交流伏安法将测量电荷转移动力学，并表明费米水平钉钉是否控制表面电化学行为。EIS将提出电荷转移机制的等效电路模型，并提供有关电荷转移动力学的额外信息。将体缺陷和表面状态的能量与溶液中氧化还原对的受体和供体水平联系起来，将使我们能够提出与As， Co和Ni杂质存在相关的特定电荷转移机制。影响范围广泛矿山尾矿和废石堆中铁矿氧化导致酸性排水，造成严重的环境风险。本研究结果将有助于建立更准确的反应模型，并改进采矿和拟议采矿地点的生态风险分析。了解黄铁矿氧化对矿物加工工业，特别是在使用浮选方法进行矿石富集是至关重要的。此外，对黄铁矿用于光伏和液体结太阳能应用以及电化学存储设备感兴趣的材料科学家将受益于这一知识。这项研究将继续促进范德比尔特大学地球与环境科学系和化学系之间的合作，并支持一位新研究员完成他的博士论文。