NIRT: Nanoparticle Fe as a Reactive Constituent in Air, Water, and Soil

这项拟议工作的目标是了解氧化铁纳米颗粒在空气、水和土壤环境中的反应性。自然界中普遍存在纳米尺寸(100 Nm)的氧化铁颗粒，其赋存范围从大气中的超细矿物粉尘到水圈中的纳米晶沉淀。对纳米氧化铁的反应性的研究主要是为了了解吸附在表面的原子的成键特性。然而，现在人们认识到，铁在环境中的行为受到细菌驱动的氧化还原反应的强烈影响，以及岩石和土壤中矿物表面的局部化学和性质，以及水的存在。因此，在接近自然的条件下详细研究铁氧化物纳米微粒的氧化还原化学，对于了解这些微小微粒在环境中铁的循环中的作用是至关重要的。拟议的研究将使用先进的光谱和分析技术，结合选择性同位素标记，来研究在水存在下发生在铁氧化物纳米微粒表面的氧化还原过程。特别令人感兴趣的是细菌驱动的铁与矿物和细胞表面之间的相互作用，以及在(I)铁同位素交换、(Ii)大气铁矿物粉尘的传输、(Iii)污染物减少和(Iv)微生物铁氧化期间发生的氧化还原反应。这些实验将在间歇式和柱式反应器中使用表征良好的氧化铁纳米颗粒，这些反应器旨在通过改变生物地球化学条件，包括微生物、矿物和水的组成以及流动条件来模拟自然条件。尽管Fe(III)-Fe(II)反应在环境和工业应用中起着关键作用，但发生在纳米Fe氧化物上的多相氧化还原反应在很大程度上还没有被探索过，这在很大程度上是因为在水存在下研究FeO的多相反应的分析和空间复杂性。该方法创新性地结合了~(57)Fe穆斯堡尔谱学和高精度的水同位素比值测量，同时测量了氧化铁-水界面的特定氧化态和铁的浓度，从而克服了这一障碍。这种方法与X射线光电子能谱(XPS)和透射电子显微镜(TEM)相结合，将为氧化还原反应在铁氧化物纳米颗粒上如何以及在哪里发生提供新的信息。铁地球化学专业知识、微生物铁呼吸作用和大气铁矿物粉尘的协同结合，以及拟议的NIRT，提供了一个无与伦比的机会，可以在铁生物地球化学循环的多个组成部分中研究涉及氧化铁纳米颗粒的氧化还原反应。观察反应性。四个不同但相关的反应的颗粒大小趋势提供了一个强大的机制来识别纳米管大小范围内的氧化物颗粒所特有的新现象。除了全面的矿物表征方法外，光谱和同位素技术的创新组合将有助于更好地了解纳米氧化铁在空气、水和土壤中的行为。我们的发现将直接影响新发展的全球碳循环理论(通过微生物Fe呼吸和海洋中Fe的大气沉积)，并挑战我们目前对重要环境和工业过程的理解，包括土壤、沉积物和水质的退化、地球地质/磁性记录的演变(通过Fe同位素生物特征)、加速腐蚀速度和冷凝过程(可能导致地球上生命的起源和火星上的生物活动)。拟议活动的探索性、跨学科性质将为研究生、本科生和高中生提供极好的培训。学生和参与的科学家将在环境暑期研讨会中通过三个实际操作的纳米级过程获得各种光谱和显微工具的专业知识。在研讨会期间，学生将从他们自己的样本中收集、分析和解释数据。《环境中的铁氧化物》双月刊。每所大学还将设立学生论坛。总体目标是让学生接触到新的思想，并为学生的跨学科讨论提供一个论坛。一整年的点子。最后，一项名为.Geology and Art的新倡议将通过位于UW.Madison的地质博物馆发起，以教育公众有关铁纳米颗粒的知识。NIRT阐述了NSE的研究和教育主题。环境中的纳米级过程。

The goal of the proposed work is to understand the reactivity of iron (Fe) oxide nanoparticles inair, water, and soil environments. Fe oxide particles in the nanometer size range ( 100 nm) areubiquitous in nature and their occurrence ranges from ultra-fine mineral dust in the atmosphere tonanocrystalline precipitates in the hydrosphere. Research into the reactivity of nanoparticle Fe oxides hasbeen primarily aimed at understanding the bonding characteristics of atoms adsorbed at the surface. It isnow recognized, however, that the behavior of Fe in the environment is strongly influenced by bacteriallydriven redox reactions, as well as the local chemistry and nature of mineral surfaces in rocks and soils,and by the presence of water. Therefore, detailed investigations of the redox chemistry of Fe oxidenanoparticles under conditions analogous to nature are critical to understanding the role of these tinyparticles in the cycling of Fe in the environment.The proposed research will use advanced spectroscopic and analytical techniques, in conjunctionwith selective isotope labeling, to investigate redox processes occurring at the surface of Fe oxidenanoparticles in the presence of water. Of particular interest is the bacterially driven interaction betweenaqueous Fe, and mineral and cell surfaces, as well as redox reactions occurring during (i) Fe isotopeexchange, (ii) transport of atmospheric Fe mineral dust, (iii) pollutant reduction, and (iv) microbial Feoxidation. The experiments will use well characterized Fe oxide nanoparticles in batch and columnreactors designed to mimic natural conditions by varying biogeochemical conditions, including microbe,mineral, and water composition, as well as flow conditions.Intellectual Merit. Despite the key role of Fe(III)-Fe(II) reactions in environmental and industrialapplications, heterogeneous redox reactions occurring on nanoscale Fe oxides have been largely unexplored.This is due, in large part, to the analytical and spatial complexities of studying heterogeneous reactions of Fein the presence of water. The proposed methodology overcomes this obstacle by using an innovativecombination of 57Fe Mossbauer spectroscopy and high precision aqueous isotope ratio measurements tosimultaneously measure isotope specific oxidation states and concentrations of Fe at the Fe oxide-waterinterface. This approach, in tandem with X-Ray photoelectron spectroscopy (XPS) and transmission electronmicroscopy (TEM), will provide new information on how and where redox reactions occur on Fe oxidenanoparticles. The synergistic blend of expertise in Fe geochemistry, microbial Fe respiration, andatmospheric Fe mineral dust brought together with the proposed NIRT provides an unparalleled opportunityto study redox reactions involving Fe oxide nanoparticles during multiple components of the Febiogeochemical cycle. Observing reactivity . particle size trends for four diverse, but related reactionsprovide a powerful mechanism to identify new phenomena that are unique to oxide particles within thenanometer size range.Broader Impacts. An innovative combination of spectroscopic and isotopic techniques, in additionto comprehensive mineral characterization methods, will result in an improved understanding of the behaviorof Fe oxide nanoparticles in air, water, and soil. Our findings will directly impact newly developing theorieson global carbon cycling (via microbial Fe respiration and atmospheric deposition of Fe in the ocean), as wellas challenge our current understanding of important environmental and industrial processes includingdegradation of soil, sediment, and water quality, the evolution of earth.s geologic/magnetic record (via Feisotope biosignatures), accelerated rates of corrosion, and condensation processes (which may have led to theorigin of life on earth and biological activity on Mars). The exploratory, interdisciplinary nature of theproposed activity will provide excellent training for graduate, undergraduate, and high school students.Students, as well as participating scientists, will gain expertise in a variety of spectroscopic and microscopictools through three hands-on Nanoscale Processes in the Environment Summer Workshops. During theworkshop, students will collect, analyze, and interpret data from their own samples. Bimonthly .Fe Oxides inthe Environment. student forums will also be established at each university. The overall goal is to exposestudents to new ideas and to provide a forum for the interdisciplinary discussion of students. ideas throughoutthe year. Finally, a new initiative, .Geology and Art., will be launched through the Geology Museum atU.W. Madison to educate the public about Fe nanoparticles. This NIRT addresses the NSE research andeducation theme .Nanoscale Processes in the Environment..