NSF-DFG Confine: Diffusion of Water Confined in Patterned Hydrophilic-Hydrophobic Nanopores

在化学系化学结构，动力学和机制-A（CSDM-A）计划的支持下，芝加哥大学的Laura Gagliardi教授和加州大学伯克利分校的Omar Yaghi教授正在将先进的分子模拟和化学分析工具（如核磁共振）相结合，以探索和表征金属有机框架（MOF）内水分子的运动。水对生命至关重要，了解水分子如何在有限空间中移动是一个根本的兴趣。这项研究的重点是具有交替的吸水（亲水）和斥水（疏水）网格状平铺区域的定义明确的图案的MOFs。 该项目旨在首次揭示水在该图案空间内扩散的分子水平细节以及亲水和疏水区域之间的相互作用。Gagliardi教授，她的学生和德国的合作者（洪堡大学的Joachim Sauer教授）将进行量子力学计算来预测水-MOF相互作用，Yaghi教授和他的学生将用NMR光谱技术表征水-MOF相互作用。该项目的发现可能会导致MOF材料的各种有用应用，包括液体和气体分离和纯化，水收集和CO2捕获。 除了正式的研究培训活动，Gagliardi集团还寻求通过《拓展视野》的芝加哥章节来激励未来几代具有国际意识的科学家。这个合作项目将为参与的学生提供丰富的跨学科和国际经验。Gagliardi教授和她的学生计算化学准确的吸附常数的吸附位点的晶格从头计算自由能的水分子;他们还计算化学准确的扩散速率常数的水分子之间的跳跃吸附网站使用从头计算过渡态理论。为了定义基本扩散步骤，他们定义了吸附单元，并考虑了所有晶体学方向上吸附单元中所有可能的跳跃路径。最后，他们预测吸附等温线和扩散系数作为负载的函数，使用大正则蒙特卡罗（GCMC）和动力学蒙特卡罗（kMC）模拟，分别在晶格的网站。Sauer教授正在提供从头计算的势能面，以提高GCMC和kMC模拟的准确性。Yaghi教授和他的学生将合成MOF材料，并使用脉冲磁场梯度NMR测量研究MOF孔隙中不同水负载下的水自扩散。这应该允许与预测的孔内扩散常数进行直接比较。此外，他们将采用准弹性中子散射（QENS）来获得更多关于不同负载下纳米孔中水流动性的见解。重要的是，QENS将提供有关MOF孔隙中扩散模型和机制的独家信息。该奖项反映了NSF的法定使命，并被认为值得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来支持。

With support from the Chemical Structure, Dynamics and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, Professors Laura Gagliardi of the University of Chicago and Omar Yaghi of the University of California at Berkeley are combining advanced molecular simulation and chemical analysis tools such as nuclear magnetic resonance (NMR) to explore and characterize the motion of water molecules inside metal-organic frameworks (MOFs). Water is essential to life and understanding how water molecules move in confined spaces is of fundamental interest. This research focuses on MOFs with well-defined patterns of alternating water attracting (hydrophilic) and water repelling (hydrophobic) grid-like tiled regions. This project seeks to reveal for the first time the molecular level details of the diffusion of water within this patterned space and the interplay between the hydrophilic and hydrophobic regions. Professor Gagliardi, her student and a collaborator in Germany (Professor Joachim Sauer, Humboldt University) will perform quantum mechanical calculations to predict water-MOF interactions, and Professor Yaghi and his student will characterize the water-MOF interactions with NMR spectroscopic techniques. The discoveries of this project could lead to a variety of useful applications of MOF materials, including liquid and gas separations and purification, water harvesting, and CO2 capture. In addition to formal research training activities, the Gagliardi group also seeks to inspire future generations of internationally aware scientists through the Chicago chapter of Expanding Your Horizons. This collaborative project will provide the students involved with a rich interdisciplinary and international experience. Professor Gagliardi and her student compute chemically accurate adsorption constants for water molecules on a lattice of adsorption sites from ab initio free energies; they also compute chemically accurate diffusion rate constants for jumps of water molecules between adsorption sites using ab initio transition state theory. To define elementary diffusion steps, they define adsorption cells and consider all possible jump pathways between sites in neighbored cells in all crystallographic directions. Finally, they predict adsorption isotherms and diffusivities as a function of loading using Grand Canonical Monte Carlo (GCMC) and kinetic Monte Carlo (kMC) simulation, respectively, on a lattice of sites. Professor Sauer is providing ab initio-calculated potential energy surfaces to augment the accuracy of the GCMC and kMC simulations. Professor Yaghi and his student will synthesize MOF materials and study the water self-diffusion at different water loadings in the MOF pores using pulsed magnetic field gradient NMR measurements. This should allow for a direct comparison with the predicted intrapore diffusion constants. Additionally, they will employ quasi-elastic neutron scattering (QENS) to gain more insight about the water mobility in the nanopores at different loadings. Importantly, QENS would provide exclusive information about the diffusion model and mechanism in the MOF pores.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.