GOALI: Charge Interactions in Transport of Mixed Solutes in Nanofiltration Membranes

随着人口增长、能源需求和工业化进程的加快，淡水资源日益匮乏，膜系统将在净水中发挥越来越重要的作用。纳滤膜是选择性去除污染物的理想选择，其运行成本比反渗透系统低得多。然而，由于在分子水平上对水污染物与膜之间的电荷相互作用缺乏了解，使得纳滤膜的应用在许多情况下很难理解或预测。科学上的挑战在于预测带电薄膜和多种带电污染物之间的相互作用如何影响薄膜在允许水自由通过的同时去除污染物的能力。一种称为分子动力学模拟的计算方法可以用来在原子水平上模拟膜与污染物的相互作用。这使得更好地预测各种污染物的真实膜性能成为可能，并为计算机辅助设计高级纳滤膜铺平了道路，这些膜经过调整以去除特别麻烦或困难的污染物。本文开发的方法可以推广到其他膜系统，可能导致在广泛的应用中设计和预测膜分子结构和组成的性能的全新范式。非平衡分子动力学模拟将被用于探索纳滤膜的分子尺度的物理和化学。这项研究的目的是了解带电聚合物膜和混合离子溶质之间的电荷相互作用，这些相互作用会影响污染物的截留和水通量。哌嗪和三甲氧基氯单体将被聚合，以创建一种虚拟的聚酰胺纳滤膜，其中的电荷可以通过在膜中的羧酸基之间分配非质子化官能团来调节。膜将在使用压力驱动的非平衡分子动力学的虚拟环境中受到各种单价和多价溶质的挑战。这使得可以探索与膜的多种离子相互作用，例如阳离子如何与带负电的膜相互作用以影响阴离子通道，或者主要盐的存在如何影响痕量离子的通道。此外，这些模拟将提供对带电薄膜中污染物选择性和截留以及水通量的深刻的基本了解，从而导致更严格的方法来预测膜的性能，以及开发更好的“设计型”膜纳米结构和电荷分布的潜力。这里开发的方法可以扩展到反渗透膜和广泛的其他膜应用。分子动力学模拟有可能成为设计和改进净水膜的第一步和决定性步骤。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

As freshwater scarcity increases with growing population, energy demand, and industrialization, membrane systems will play an increasingly important role in water purification. Nanofiltration membranes are ideal for selective contaminant removal and operate at significantly lower energy cost than reverse osmosis systems. However, poor understanding of electric charge interactions between water contaminants and the membrane at the molecular level makes application of nanofiltration membranes difficult to understand or predict in many situations. The scientific challenge lies in predicting how interactions between the charged membrane and multiple charged contaminants affect the membrane's ability to remove the contaminants while allowing water to pass freely. A computational approach called molecular dynamics simulation can be used to model the interactions of the membrane and the contaminants at the atomistic level. This makes possible better prediction of real membrane performance for a wide range of contaminants and paves the way computer-aided design of superior nanofiltration membranes tuned to remove particularly troublesome or difficult contaminants. The approaches developed here can be extended to other membrane systems, perhaps resulting in an entirely new paradigm for designing and predicting the performance of membrane molecular structures and compositions in a wide range of applications.Non-equilibrium molecular dynamics simulations will be used to explore the molecular-scale physics and chemistry of nanofiltration membranes. The objective of the research is to understand the charge interactions between charged polymeric membranes and mixed ionic solutes that affect contaminant rejection and water flux. Piperazine and trimesoyl chloride monomers will be polymerized to create a virtual polyamide nanofiltration membrane in which the charge can be adjusted by assigning non-protonated functionality among the carboxylate groups in the membrane. The membrane will be challenged with a variety of single and multiple mono- and divalent solutes in a virtual environment using pressure-driven non-equilibrium molecular dynamics. This allows the exploration of multiple ion interactions with the membrane, examples of which include how cations interact with the negatively charged membrane to influence anion passage or how the presence of a dominant salt affects the passage of trace ions. Moreover, the simulations will provide a deep fundamental understanding of contaminant selectivity and rejection as well as water flux in charged membranes, leading to more rigorous approaches for prediction of membrane performance and the potential for developing superior "designer" membrane nanostructures and charge distributions. The approaches developed here can be extended to reverse osmosis membranes and a broad range of other membrane applications. Molecular dynamics simulations have the potential to become the first and decisive step in designing and improving membranes for water purification.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.