Collaborative Research: Interfacial Water Restructuring: An Unrecognized Contribution to Mineral Surface Reactivity

化学系的环境化学科学项目将资助圣路易斯华盛顿大学的Jeffrey G. Catalano教授和爱荷华大学的Sara E. Mason教授，研究矿物表面附近水分子的排列如何影响污染物的吸附。吸附是环境界面上一个关键的化学过程，直接控制污染物的命运和养分的有效性，是沉淀成核和生长、表面催化氧化还原反应以及微生物和配体促进氧化矿物溶解的重要前驱步骤。虽然吸附机理和表面电位对界面反应的影响已经确定，但对界面水的作用知之甚少。从这些研究中收集到的信息有望深入了解涉及重要环境过程的基本反应机制，如污染物的命运、运输和降解、营养物质的生物利用度、二氧化碳的固存和纳米颗粒的动员。该项目将研究生、本科生和高中生实习生纳入研究，并支持新的教育和推广活动。华盛顿大学的一名研究生将接受STEM教学法的培训，然后为一门关于环境和人类健康的课程开发新的主动学习活动。爱荷华大学（University of Iowa）将准备一年一度的博物馆展览，向K-12年级的学生宣传地球化学表面科学的社会重要性。本项目的目的是表征吸附物诱导的矿物表面界面水重构及其对表面结构、表面电荷和流体组成的依赖。初步数据表明，砷酸盐在氧化铝表面的吸附改变了界面水结构。整体结构重构发生在初始水有序性弱的表面上，而在初始水有序性强的表面上观察到小的结构扰动。界面水的这种结构转变预计会影响界面反应的能量学和动力学。本研究结合了砷酸盐吸附过程中铝和铁氧化物表面界面水行为的实验和计算研究。更具体地说，这项工作整合了基于同步加速器的表面晶体学技术、吸附等温线和动力学的实验室测量、密度泛函理论计算和从头算分子动力学模拟，以研究界面水的结构如何响应污染物砷的吸附，以及这种影响如何随矿物表面结构和电荷而变化。这项研究有望揭示一种以前未被认识到的影响界面反应能量学和动力学的机制。

With this award, the Environmental Chemical Sciences Program of the Division of Chemistry is funding Professor Jeffrey G. Catalano of Washington University in St. Louis and Professor Sara E. Mason of the University of Iowa to investigate how the arrangement of water molecules near a mineral surface affects the adsorption of contaminants. Adsorption is a key chemical process at environmental interfaces that directly controls contaminant fate and nutrient availability and is an important precursor step in the nucleation and growth of precipitates, surface-catalyzed redox reactions, and microbial and ligand-promoted dissolution of oxide minerals. While adsorption mechanisms and the effect of surface potential on interfacial reactions are well established, little is known about the role of interfacial water. The information gleaned from these studies is expected to provide insight into fundamental reaction mechanisms involved in important environmental processes such as contaminant fate, transport, and degradation, nutrient bioavailability, carbon dioxide sequestration, and nanoparticle mobilization. This project integrates graduate students, undergraduate students, and high school student interns into the conduct of the research and supports new educational and outreach activities. A graduate student at Washington University will be trained in STEM pedagogies and then develop new active learning activities for a course on the environment and human health. At the University of Iowa, an annual museum exhibit will be prepared to educate K-12 students on the societal importance of geochemical surface science.The objective of this project is to characterize adsorbate-induced interfacial water restructuring on mineral surfaces and its dependence on surface structure, surface charging, and fluid composition. Preliminary data shows that arsenate adsorption on aluminum oxide surfaces alters interfacial water structure. Wholesale restructuring occurred on a surface with weak initial water ordering whereas a small structural perturbation was observed on a surface with strong ordering. Such structural transitions of interfacial water are expected to affect the energetics and kinetics of interfacial reactions. This investigation integrates experimental and computational studies of interfacial water behavior on aluminum and iron oxide surface during arsenate adsorption. More specifically, the work integrates synchrotron-based surface crystallography techniques, laboratory measurements of adsorption isotherms and kinetics, density functional theory calculations, and ab initio molecular dynamics simulations to study how the structure of interfacial water responds to the adsorption of the contaminant arsenic and how such effects vary with mineral surface structure and charging. This study is anticipated to reveal a previously unrecognized mechanism that affects the energetics and kinetics of interfacial reactions.