Quantitative elucidation of the Role of Natural Organic Matter on the Redox Reactivity of Iron Oxide Minerals

在这个由化学系环境化学科学项目资助的项目中，明尼苏达大学的Lee Penn教授和Bill Arnold教授研究了氧化铁矿物颗粒如何参与与有机污染物的化学反应，特别是天然有机物(NOM)如何影响这些反应。NOM存在于地表水和地下水中。它是由植物材料分解形成的，由藻类和其他微生物产生，人们对NOM的存在、浓度和性质如何影响表面反应知之甚少。潘教授和阿诺德教授之间的合作提高了预测常见有机污染物的命运和迁移的能力。这一结果有望从根本上，从机理上理解氧化铁表面如何在有机物存在的情况下调节重要的还原降解反应。本项目侧重于阐明天然有机物如何影响反应表面积的性质，从而阐明涉及有机污染物在矿物-液体界面的还原(和氧化)反应的动力学。在反应前、反应中和反应后，使用先进的材料表征方法对污染物降解率进行量化和固体材料表征。实验在添加和不添加模型NOM分子(例如，儿茶酚和羧酸盐)、从国际腐殖质学会(IHSS)获得的NOM分离物和从环境中收集的NOM样品的情况下进行。这项工作的一个特别新颖的方面是通过低温透射电子显微镜(Cryo-TEM)直接成像反应介质中的颗粒，以评估聚集状态并量化现场可访问的表面积。悬浮矿物颗粒的固态(即矿物学)变化和聚集状态的变化与所观察到的污染物降解动力学定量地联系在一起，这使得能够开发一个完整的氧化铁反应性模型。这项工作的更广泛影响包括通过提高对非生物衰减污染物在天然和工程系统中的作用的理解而产生的潜在社会效益，以及针对初中生和高中生的项目的开发，以教授重要的水和环境化学概念。

In this project funded by the Environmental Chemical Sciences Program of the Chemistry Division, Professors Lee Penn and Bill Arnold of the University of Minnesota study how iron oxide mineral particles participate in chemical reactions with organic contaminants, with particular focus on how natural organic matter (NOM) affects these reactions. NOM is found in surface water and ground water. It is formed from the decomposition of plant material and produced by algae and other microorganisms, and little is known about how the presence, concentration, and nature of NOM impacts reactions at surfaces. The collaboration between Professors Penn and Arnold improves the ability to predict fate and transport of common organic contaminants. Results are expected to lead to a fundamental, mechanistic understanding of how iron oxide surfaces mediate important reductive degradation reactions in the presence of organic matter.This project focuses on elucidating how natural organic matter impacts the nature of reactive surface area and thus the kinetics of reductive (and oxidative) reactions involving organic contaminants at the mineral-liquid interface. Rates of contaminant degradation are quantified and solid materials characterized using advanced materials characterization methods before, during, and after reactions. Experiments are performed with and without the addition of model NOM molecules (e.g., catecholates and carboxylates), NOM isolates obtained from the International Humics Substances Society (IHSS), and NOM samples collected from the environment. A particularly novel aspect of the proposed work is direct imaging of the particles in reaction media by way of cryogenic transmission electron microscopy (cryo-TEM) to evaluate aggregation state and quantify in situ accessible surface area. The solid-state (i.e., mineralogical) changes and changes in the aggregation state of suspended mineral particles are quantitatively linked to the observed contaminant degradation kinetics, which enables the development of an integrated model of iron oxide reactivity. The broader impacts of this work include potential societal benefits via improved understanding of the role of abiotic attenuation of contaminants in natural and engineered systems as well as the development of a program aimed at middle and high school students to teach important concepts of water and environmental chemistry.