Collaborative Research: Crossing the percolation threshold for selective gas transport using interconnected crystals of metal–organic frameworks in polymer-based hybrid membranes

合作研究：利用聚合物杂化膜中金属有机框架的互连晶体跨越选择性气体传输的渗滤阈值

• 批准号: 2034734
• 负责人: Sergey Vasenkov
• 金额: $ 18.97万
• 依托单位: University of Florida
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-07-15 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2034734&HistoricalAwards=false
• 关键词: Collaborative; Research; Crossing; percolation; threshold

Light gases such as methane, ethane, and ethylene play an important role in industrial applications, including their use as gas and liquid fuels and as precursors in polymer manufacturing. Access to high purity gases is typically required for these applications necessitating an industrial gas separation process. Gas separation technology is also required to reduce the concentration of carbon dioxide and other greenhouse gases in the atmosphere. Accordingly, the development of low-energy and low-cost separations of gas mixtures is critically important to meet industrial demand, address environmental concerns, and improve standards of living. Separating gas molecules from a mixture requires materials (molecular sieves) containing holes with uniform dimensions that are comparable with the sizes of the small gas molecules to be separated. However, suitable molecular sieve particles are usually difficult to form into the geometries necessary for scales relevant to industrial applications or environmental remediation. This project will advance the fundamental science of forming molecular sieve particles into well-connected networks, which will enable the development of large-scale separation technologies. In the networks, the particles will be held together by polymer interfaces designed to minimize any adverse effects on the particle sieving function and, at the same time, preserve the structural integrity of the material. The separation performance, gas transport properties, and structural properties of such networks will be quantified on all relevant length scales. The outcomes of this project will lay the foundation for rationally designed molecular sieve morphologies that can be optimized for the desired gas separation. The investigators will also initiate a new research mentoring program with the objective of teaching and training students from underrepresented groups in STEM. Existing institutional programs will be leveraged, and the use of online tools will be emphasized to enhance the program's effectiveness.Metal-organic frameworks (MOFs) are high porosity molecular sieves exhibiting extraordinary property sets when applied in membrane-based gas separations. However, these materials cannot be easily formed into defect-free membrane geometries. Hence, it is challenging to leverage the intrinsic transport benefits of MOFs for membrane separations. Mixing MOF crystals with polymers to make mixed-matrix membranes (MMMs) is a well-known strategy to form MOF-based membranes. However, the typical separation performance of MMMs is usually lower than that of the corresponding MOFs because MMM transport properties are unfavorably affected by the polymer phase and, in some cases, by interfacial MOF–polymer defects. A clear route to improve MMM performance is to increase MOF concentrations and even reach a percolation threshold to enable diffusion predominantly through the MOF phase, i.e., a situation when gas diffusion in MMMs can proceed mostly over interconnected MOF crystals. The investigators will develop the fundamental science of crossing the percolation threshold for gas transport in the MOF phase of MOF–polymer MMMs to enable separation performance comparable with that of pure MOF membranes. Membrane fabrication strategies will be developed based on a novel functionalization of the external surface of MOF crystals in combination with the development of fundamental understanding of intramembrane gas transport. Advanced nuclear magnetic resonance will be used to investigate changes of all relevant types of microscopic gas transport in MMMs as a function of increasing MOF loading and the diffusion length scale. MOF surface functionalization will also be optimized with respect to enhancing the mechanical properties of the membranes. This project will lead to the development of fundamental chemical separations knowledge related to percolation theory in composites. If successful, this concept will enable pure MOF-like transport properties to be accessed in membranes without the requirement of forming pure MOF films. In this way, new performance limits may be achieved for MMMs, including percolated transport for MOFs that are not easily formed into crystalline films. As a design platform, this approach could be used to improve the productivity and efficiency of chemical separations for membranes.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.

甲烷、乙烷和乙烯等轻质气体在工业应用中发挥着重要作用，包括用作气体和液体燃料以及用作聚合物制造中的前体。这些需要工业气体分离过程的应用通常需要获得高纯度气体。还需要气体分离技术来降低大气中二氧化碳和其他温室气体的浓度。因此，开发低能耗、低成本的气体混合物分离对于满足工业需求、解决环境问题和提高生活水平至关重要。从混合物中分离气体分子需要含有尺寸均匀的孔的材料（分子筛），这些孔的尺寸与待分离的小气体分子的尺寸相当。然而，合适的分子筛颗粒通常难以形成与工业应用或环境修复相关的规模所需的几何形状。该项目将推进将分子筛颗粒形成连接良好的网络的基础科学，从而促进大规模分离技术的发展。在网络中，颗粒将通过聚合物界面结合在一起，该界面旨在最大限度地减少对颗粒筛分功能的任何不利影响，同时保持材料的结构完整性。此类网络的分离性能、气体传输特性和结构特性将在所有相关长度尺度上进行量化。该项目的成果将为合理设计分子筛形态奠定基础，并可针对所需的气体分离进行优化。研究人员还将启动一项新的研究指导计划，旨在教学和培训 STEM 领域代表性不足群体的学生。将利用现有的机构计划，并强调使用在线工具来提高计划的有效性。金属有机框架（MOF）是高孔隙率分子筛，在膜基气体分离中应用时表现出非凡的性能。然而，这些材料不能轻易地形成无缺陷的膜几何形状。因此，利用 MOF 的固有传输优势进行膜分离具有挑战性。将 MOF 晶体与聚合物混合来制造混合基质膜 (MMM) 是形成 MOF 基膜的众所周知的策略。然而，MMM 的典型分离性能通常低于相应的 MOF，因为 MMM 传输性能受到聚合物相的不利影响，在某些情况下还受到 MOF-聚合物界面缺陷的不利影响。提高 MMM 性能的一个明确途径是增加 MOF 浓度，甚至达到渗透阈值，以便主要通过 MOF 相进行扩散，即 MMM 中的气体扩散主要在互连的 MOF 晶体上进行的情况。研究人员将开发跨越 MOF-聚合物 MMM 的 MOF 相中气体传输渗透阈值的基础科学，以使分离性能与纯 MOF 膜相当。膜制造策略的开发将基于 MOF 晶体外表面的新颖功能化，并结合对膜内气体传输的基本理解的发展。先进的核磁共振将用于研究 MMM 中所有相关类型的微观气体传输随着 MOF 负载和扩散长度尺度增加的函数的变化。 MOF 表面功能化也将在增强膜的机械性能方面进行优化。该项目将促进与复合材料渗滤理论相关的基础化学分离知识的发展。如果成功，这一概念将能够在膜中获得类似 MOF 的纯传输特性，而无需形成纯 MOF 薄膜。通过这种方式，MMM 可以实现新的性能极限，包括不易形成晶体薄膜的 MOF 的渗透传输。作为一个设计平台，这种方法可用于提高膜化学分离的生产率和效率。该奖项反映了 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。