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

这项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。纳米级（100 nm）的氧化铁颗粒在自然界中普遍存在，从大气中的超细矿物粉尘到水圈中的纳米晶沉淀物，都有其存在。对纳米铁氧化物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，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的强烈影响。因此，在类似于自然的条件下，详细调查的氧化还原化学的Fe oxidoranoparticles是至关重要的了解这些tinyparticles中的Fe在环境中的循环中的作用，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，调查氧化还原过程发生在表面的Fe oxidoranoparticles在水的存在。特别感兴趣的是细菌驱动的相互作用betweenaqueous铁，矿物和细胞表面，以及氧化还原反应发生在（i）铁同位素交换，（ii）运输大气铁矿物粉尘，（iii）污染物减少，和（iv）微生物Feoxidation。这些实验将在批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化学条件（包括微生物、矿物质和水的成分以及流动条件）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，但纳米级Fe氧化物上发生的多相氧化还原反应在很大程度上尚未被探索，这在很大程度上是由于研究Fe在水存在下的多相反应的分析和空间复杂性。所提出的方法克服了这一障碍，通过使用创新的57 Fe穆斯堡尔谱和高精度的水同位素比测量的组合，同时测量同位素特定的氧化态和浓度的铁在铁氧化物-水界面。这种方法，在串联与X射线光电子能谱（XPS）和透射电子显微镜（TEM），将提供新的信息，如何以及在氧化还原反应发生在铁oxanoparticles。铁地球化学，微生物铁呼吸，和大气铁矿物粉尘的专业知识的协同融合与拟议的NIRT一起提供了一个无与伦比的机会，研究氧化还原反应，涉及氧化铁纳米粒子在多个组成部分的铁地球化学循环。观察反应性。四种不同但相关的反应的颗粒尺寸趋势提供了一种强有力的机制来识别纳米尺寸范围内氧化物颗粒所特有的新现象。光谱和同位素技术的创新组合，以及全面的矿物表征方法，将导致对空气，水和土壤中氧化铁纳米颗粒行为的更好理解。我们的发现将直接影响全球碳循环的新理论（通过微生物的铁呼吸和大气中的铁沉积在海洋中），以及挑战我们目前对重要的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（通过铁同位素生物特征）、加速腐蚀和冷凝过程（这可能导致了地球上生命的起源和火星上的生物活动）。该活动具有探索性和跨学科的性质，将为研究生、本科生和高中生提供良好的培训。学生以及参与的科学家将通过三个环境中纳米尺度过程的暑期讲习班获得各种光谱和显微工具的专业知识。在研讨会期间，学生将收集，分析和解释来自他们自己的样本的数据。环境中的氧化铁各大学亦会设立学生论坛。总的目标是让学生接触新的思想，并为学生的跨学科讨论提供一个论坛。throughout the year年.最后，一项新的倡议，地质和艺术，将通过华盛顿大学的地质博物馆推出。麦迪逊教育公众关于铁纳米粒子。这个NIRT解决了NSE研究和教育主题。环境中的纳米尺度过程。

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..