Quantitative Elucidation of the Role of Natural Organic Matter Fractions and Models on the Redox Reactivity of Iron Oxide Minerals

化学学部的环境化学科学项目资助了明尼苏达大学的Lee Penn教授和Bill Arnold教授进行这个项目。他们研究了在存在和不存在天然有机物（NOM）的情况下氧化铁矿物颗粒上发生的污染物降解反应。NOM可以在大多数天然水域中找到。它是由植物物质分解形成的，由藻类和其他微生物产生。NOM是一种复杂的分子混合物，有些抑制反应，有些促进反应，发生在液矿界面。这意味着NOM影响污染物分子在环境中的持久性。当暴露于矿物表面时，环境中的NOM分子类型会发生变化。留在水中的NOM会随着环境系统中矿物质的暴露而进化，这一过程被称为分馏。关于不同分数的NOM如何影响氧化铁矿物表面的反应性，人们知之甚少。回答这个问题将弥合实验室和实地研究之间的主要差距。研究人员之间的合作结果将加深对环境系统中NOM的性质和演变以及NOM对涉及常见有机污染物的反应的影响的基本理解。这项工作的广泛影响包括对环境系统中矿物表面化学行为的更好理解所带来的潜在社会效益。主要的教育部分通过与明尼苏达州公立学校的科学老师合作，将重点放在高中生身上。学生将接受指导并获得使用定量相机手机比色法模拟水处理的实践经验，该模拟水处理使用稻草柱填充各种材料，包括矿物包覆砂和生物质产生的碳。一个主要的项目重点是NOM的逐步分馏，作为暴露于矿物表面的函数。NOM分馏是通过化学和物理相结合的方法来完成的。反应器中使用的NOM的量与总有机碳量归一化。研究了矿物和不同数量、不同馏分的NOM存在下的污染物降解速率。此外，利用先进的材料表征方法对反应前、反应中、反应后的矿物颗粒进行表征，以确定反应发生在颗粒上的什么位置，以及NOM馏分对反应位置的影响。结果能够阐明最强烈（和最弱）影响反应性的NOM组分的性质，从而影响污染物的持久性。该团队使用了国际腐殖质协会（IHSS）提供的NOM标准和从环境中收集的NOM样本。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Environmental Chemical Sciences Program in the Chemistry Division funds Professors Lee Penn and Bill Arnold of the University of Minnesota for this project. They study pollutant degradation reactions that occur on iron oxide mineral particles in the presence and absence of natural organic matter (NOM). NOM can be found in most natural waters. It is formed from the decomposition of plant material and produced by algae and other microorganisms. NOM is a complex mixture of molecules, with some inhibiting and others facilitating reactions that occur at the liquid-mineral interface. This means that NOM impacts the persistence of pollutant molecules in the environment. The types of NOM molecules in the environment change when exposed to mineral surfaces. The NOM remaining in the water will evolve with exposure to the minerals in environmental systems, a process called fractionation. Little is known about how different fractions of NOM impact the reactivity of iron oxide mineral surfaces. Answering this question will bridge major gaps between laboratory and field studies. Results from the collaboration between the investigators will deepen fundamental understanding of the nature and evolution of NOM in environmental systems and the impact of NOM on reactions involving common organic contaminants. The broader impacts of this work include potential societal benefits caused by improved understanding of the chemical behavior of mineral surfaces in environmental systems. The major educational component focuses on high school students through a collaboration with a science teacher from a Minnesota Public School. Students receive instruction and hands on experience in using quantitative camera phone colorimetry with simulated water treatment using straw columns filled with various materials, including mineral coated sands and carbon produced from biomass.A major project focus is the progressive fractionation of NOM as a function of exposure to mineral surfaces. NOM fractionation is accomplished by a combination of chemical and physical methods. The amount of NOM used in a reactor is normalized to the total organic carbon. The rate of pollutant degradation is studied in the presence of minerals and different amounts and fractions of NOM. In addition, mineral particles are characterized using advanced materials characterization methods before, during, and after reactions to identify where on the particles the reaction occurs and how the NOM fractions affect the reaction location. Results enable elucidation of the nature of NOM fractions that most strongly (and weakly) impact reactivity and thus the persistence of pollutants. The team uses NOM standards obtained from the International Humic Substances Society (IHSS) and NOM samples collected from the environment.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.