Experimental validation of molecular simulation of water transport across zeolite membranes of nanoscale-thickness

流体在多孔介质中的传输与从地下提取石油、地下水中的污染物传输、地下水库中二氧化碳的封存以及通过反渗透膜进行海水淡化以生产饮用水有关。多孔介质提供了对质量传输的阻力。化学物质之间的阻力差异允许分离：一种组分可能不受阻碍甚至加速，而另一种组分则受到阻碍。例如，反渗透膜被设计成相当有效地输送水，但输送盐的效率相当低，从而产生纯化的饮用水。为了优化设计，通过多孔介质的流动的工程传输模型通常使用宏观长度尺度和平均阻力来处理系统，但通常忽略分子尺度上的空间变化和特定的流体-表面相互作用。当流体分子被限制在具有相似分子尺寸的孔中时，分子尺度的相互作用变得非常明显。解释分子相互作用的模型包含力场，但还没有充分预测实验观察结果。该项目将通过具有强流体-孔隙相互作用的多孔材料进行分子水平传输的实验验证，并且第一次将实验和理论研究之间的长度尺度对应关系进行探索。在该项目中，通过沸石膜进行海水淡化是探针系统，这是由于在亚纳米（~0.56 nm）孔中限制时增强的强的水-沸石静电相互作用。具有不同铝组成和厚度（从纳米到微米尺度变化）的MFI沸石将通过实验合成和表征，然后转移到支撑表面上以在定制的实验装置中产生用于传输测量的膜。MD模拟将同时进行相同的沸石与不同的力场。 在两种技术中铝含量将变化以改变水-沸石相互作用。实验验证的分子模型将提供水在受限孔隙中的相互作用的基本理解，并有助于在纳米多孔材料中的水的热力学性质和传输行为的预测建模的发展。该项目包括若干外联部分，包括针对代表性不足的少数群体的本科生研究项目、为中学生举办的讲习班以及为锡拉丘兹大学本科生举办的计算方法短期课程。

Transport of a fluid in porous media is relevant to extraction of oil from the subsurface, contaminant transport in groundwater, sequestration of carbon dioxide in underground reservoirs, and desalination of seawater through a reverse osmosis membrane to produce drinking water. The porous media offers a resistance to the transport of mass. Differences in resistance between chemical species allow for separation: one component may be unimpeded or even accelerated, while another is impeded. For example, the reverse osmosis membrane is designed to transport water quite efficiently but transport salt quite inefficiently, leading to the production of purified drinking water. To optimize design, engineering transport models of flow through porous media generally treat the system using macroscopic length scales and average resistances, but generally neglect both spatial variations and specific fluid-surface interactions on the molecular scale. Molecular-scale interactions become quite pronounced when a fluid molecule is confined in a pore that is of similar molecular dimension. Models that account for molecular interactions incorporate forcefields, but have not adequately predicted experimental observations. This project will perform an experimental validation of molecular-level transport through a porous material with strong fluid-pore interactions, and for the first time, there will be a one-to-one length scale correspondence between the experimental and theoretical studies which will probe discrepancies. In this project, desalination of seawater through a zeolite membrane is the probe system, due to strong water-zeolite electrostatic interactions that are enhanced upon confinement in sub-nanometer (~0.56 nm) pores. MFI zeolites with varying aluminum composition and thickness (varying from nano- to micro-scale) will be experimentally synthesized and characterized, then transferred onto a support surface to create membranes for transport measurements in a custom-built experimental apparatus. MD simulations will be simultaneously performed for the same zeolites with varying forcefields. The aluminum content will be varied in both techniques to alter the water-zeolite interaction. The experimentally validated molecular models will provide fundamental understanding of water interaction in confined pores, and assist in the development of predictive modeling of thermodynamic properties and transport behavior of water in nano-porous materials. The project includes several outreach components, including undergraduate research projects that target under-represented minorities, a workshop for middle school female students, and a short course in computational methods for undergraduates at Syracuse University.