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聚合物制造中的前体。对于需要工业气体分离过程的这些应用，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，开发低能量和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包含具有与待分离的小气体分子的尺寸相当的均匀尺寸的孔的材料（分子筛）。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，这将使大规模分离技术的发展成为可能。在网络中，颗粒将通过聚合物界面保持在一起，所述聚合物界面被设计为最小化对颗粒筛分功能的任何不利影响，并且同时保持材料的结构完整性。这种网络的分离性能、气体传输性能和结构性能将在所有相关的长度尺度上进行量化。该项目的结果将为合理设计分子筛形貌奠定基础，这些分子筛可以优化用于所需的气体分离。研究人员还将启动一项新的研究指导计划，目标是教授和培训来自STEM代表性不足群体的学生。现有的机构计划将得到充分利用，并将强调在线工具的使用，以提高计划的有效性。金属有机框架（MOFs）是高孔隙率分子筛，在应用于膜基气体分离时表现出非凡的性能。然而，这些材料不能容易地形成为无缺陷的膜几何形状。因此，利用MOFs的固有传输益处进行膜分离是具有挑战性的。将M0 F晶体与聚合物混合以制备混合基质膜（MMM）是形成基于M0 F的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M0 F的分离性能，因为MMM传输性能受到聚合物相的不利影响，并且在某些情况下受到M0 F-聚合物界面缺陷的不利影响。改善MMM性能的明确途径是增加MOF浓度，甚至达到渗滤阈值，以使扩散主要通过MOF相，即，当MMM中的气体扩散可以主要在互连的MOF晶体上进行时的情况。研究人员将开发跨越MOF-聚合物MMM的MOF相中气体传输的逾渗阈值的基础科学，以使分离性能与纯MOF膜相当。膜制造策略将开发基于一种新的功能化的外表面的MOF晶体结合膜内气体运输的基本理解的发展。先进的核磁共振将被用来调查MMM中的所有相关类型的微观气体输运的变化作为增加的MOF负载和扩散长度尺度的函数。MOF表面功能化也将在增强膜的机械性能方面进行优化。这个项目将导致与复合材料中的逾渗理论相关的基本化学分离知识的发展。如果成功的话，这个概念将使纯的MOF类传输性能在膜中获得，而不需要形成纯的MOF膜。以这种方式，可以实现MMM的新的性能限制，包括不易形成结晶膜的MOF的迁移。作为一个设计平台，该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知识价值和更广泛的影响审查标准进行评估，被认为值得支持。