ADSORPTION OF IONIC AND IONOGENIC COMPOUNDS BY CARBONACEOUS SUBSTANCES: pKa SHIFTS AND NOVEL INTERACTIONS AT THE SURFACE

1235459吸附对土壤、沉积物和大气气溶胶中有机污染物的迁移性、生物有效性和反应性起着至关重要的作用，并往往构成修复技术的战略基础。最强的环境吸附剂是有机物质热解或不完全燃烧后残留的碳质物质，称为黑碳。在结构上与黑碳密切相关的是一些人造物质，如生物炭、活性碳和碳纳米管，用于提高土壤肥力或帮助感应或清除水中的污染物，以及稳定受污染的土壤和沉积物。许多新出现的令人关注的污染物是离子的，或者在自然界或处理系统中通常遇到的条件下变成离子的。然而，离子和可电离化合物吸附到黑炭上的分子机制却知之甚少。该项目致力于从药品、个人护理产品、杀虫剂、工业溶剂和干扰内分泌的化合物中选择离子和可电离化合物的吸附。它将探索与聚芳烃表面的新的成键作用，这是环境和人造碳的特征。第一种类型的相互作用适用于弱有机酸，它们被认为形成了非常强的氢键，称为负电荷辅助氢键(CAHB)，具有表面羧基和苯氧基。第二类相互作用适用于带正电荷的芳香胺和杂芳胺。由于这些芳香族阳离子是贫电子的，它们能够在阳离子-pi相互作用的辅助下，与黑碳的富含电子的聚芳烃表面发生pi-pi电子供体-受体相互作用，这种键被称为pi+-pi EDA。为了能够形成CAHB或pi+-pi EDA，假设化合物将与水进行质子交换，释放氢离子到溶液中，导致其表面的pKA相对于其溶液中的pKA发生正移。将进行一些热力学和光谱实验来验证这些假设，确定反应范围，并提供有助于构建吸附结构-性质自由能关系的参数。深入、分子水平地了解污染物分子在环境颗粒表面的吸附是预测污染物在环境中的命运和运动的关键，有助于建立公共卫生法规的知识库，是技术控制的先决条件。该项目将研究新出现的带正电和带负电的污染物与环境黑碳和相关商业产品表面的新的键合作用，这些产品通过预期的用途接触污染物。到目前为止，这种相互作用几乎没有受到环境科学家的关注。对于对这类化合物的命运和风险感兴趣的科学家来说，这将导致具有理论和实践意义的科学进步。将从该项目取得的进展中受益的其他支持者包括监管机构和补救、净水、农业行业及其利益相关者。该项目将与S研究员实验室目前正在进行的其他项目顺利衔接，并将促进与其他机构的合作。该项目将帮助培养研究生、博士后研究人员和访问学者，并将影响高中、大学和研究生教育的进程。结果将在公共和科学论坛上传播。

1235459PignatelloAdsorption plays a critical role in the mobility, biological availability and reactivity of organic pollutants in soil, sediment and atmospheric aerosols, and often forms the strategic basis for remediation technologies. Among the strongest of environmental adsorbents is the carbonaceous substance remaining after pyrolysis or incomplete burning of organic material known as black carbon. Closely related structurally to black carbon are a number of manufactured substances, such as biochar, activated carbon and carbon nanotubes prescribed to improve soil fertility or to assist in the sensing or removal of pollutants in water and stabilization of contaminated soil and sediment. Many contaminants of emerging concern are ionic or become ionic under conditions normally encountered in nature or in treatment systems. The molecular mechanisms by which ionic and ionizable compounds adsorb to black carbon are poorly understood, however. This project addresses adsorption of ionic and ionizable compounds selected among pharmaceuticals, personal care products, pesticides, industrial solvents and endocrine-disrupting compounds. It will explore novel bonding interactions with the polyaromatic surface, which is characteristic of environmental and manufactured carbons. The first type of interaction applies to weak organic acids which are postulated to form exceptionally strong H-bonds, known as negative charge-assisted hydrogen bonds (CAHB), with surface carboxyl and phenoxyl groups. The second type of interaction applies to positively-charged aromatic amines and heteroaromatic amines. Because these aromatic cations are electron-poor they are capable of undergoing pi-pi electron donor-acceptor interactions, assisted by cation-pi interactions, with the electron-rich polyaromatic surface of black carbon, a bond known as pi+-pi EDA. To enable formation of a CAHB or pi+-pi EDA it is postulated that a compound will undergo proton exchange with water, releasing hydroxide ion into solution, and resulting in a positive shift of its pKa on the surface relative to its pKa in solution. A number of thermodynamic and spectroscopic experiments will be carried out to test these hypotheses, determine reaction scope, and provide parameterization useful in constructing structure-property free energy relationships of adsorption. A deep, molecular-level understanding of adsorption of pollutant molecules to the surfaces of environmental particles is a key to predicting the fate and movement of pollutants in the environment, contributes to the knowledge base underlying public health regulations, and is a prerequisite to technological control. This project will investigate novel bonding interactions of positively and negatively charged emerging contaminants with the surfaces of environmental black carbon and related commercial products that contact pollutants through their intended use. Such interactions have so far received little attention by environmental scientists. It will lead to scientific advances of both theoretical and practical importance for scientists interested in the fate and risk of such compounds. Other constituencies that will benefit from advances made in this project include regulatory agencies and the remediation, water purification, and agricultural industries and their stakeholders. The project will link smoothly with other projects now underway in the researcher?s laboratory and will foster collaboration with other institutions. The project will help train graduate students, postdoctoral researchers and visiting scholars, and will influence the course of high school, college and graduate-level educational outreach. The results will be disseminated in both public and scientific forums.