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.

甲烷等轻质气体在工业应用中起着重要作用，包括它们用作气体和液体燃料以及作为聚合物制造中的前体。这些应用通常需要获得高纯度气体，需要进行工业气体分离过程。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。根据，气体混合的低能和低成本分离的发展对于满足工业需求，解决环境问题并提高生活水平至关重要。将气体分子与混合物分离，需要材料（分子筛），其中含有均匀尺寸的孔，这些孔与要分离的小气体分子的大小相当。但是，通常很难将合适的分子筛子颗粒形成与工业应用或环境补救相关的尺度所需的几何形状。该项目将把形成分子筛子颗粒形成良好连接的网络的基本科学发展，这将使大规模分离技术的发展。在网络中，颗粒将通过聚合物界面组合在一起，旨在最大程度地减少对粒子筛分函数的任何不利影响，同时保留材料的结构完整性。这些网络的分离性能，气体传输特性和结构特性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的分子筛形态奠定基础，该形态可以优化为所需的气体分离。研究人员还将启动一项新的研究心理计划，目的是教学和培训STEM中代表性不足的群体的学生。现有的机构计划将被杠杆化，并将强调使用在线工具以提高程序的有效性。Metal-Organgic框架（MOFS）是高孔隙率分子筛子，当在膜基气体分离中应用时，表现出非常出色的特性。但是，这些材料不能轻易地形成无缺陷的膜几何形状。因此，要利用MOF的固有运输益处用于膜分离是挑战。将MOF晶体与聚合物混合形成混合垫膜（MMMS）是形成基于MOF机制的众所周知的策略。但是，MMM的典型分离性能通常低于相应的MOF，因为MMM传输特性受聚合物相的不利影响，在某些情况下，界面MOF-聚合物缺陷。提高MMM性能的明确途径是增加MOF浓度，甚至达到渗透阈值，以使其主要通过MOF相扩散，即MMMS中的气体扩散可以大多在相互连接的MOF晶体上进行。研究人员将开发基础科学，即在MOF-聚合物MMM的MOF期跨越气体传输的百分比阈值，以使分离性能与纯MOF膜相当。膜制造策略将基于对MOF晶体外表面的新功能化，并结合对膜内气体转运的基本理解的发展。晚期核磁共振将用于研究MMM中所有相关类型的微观气体转运的变化，以增加MOF载荷和扩散长度尺度的函数。 MOF表面功能化还将针对增强机制的机械性能进行优化。该项目将导致与复合材料中与成员理论相关的基本化学分离知识的发展。如果成功，此概念将使纯MOF样的运输特性在机制中访问，而无需形成纯MOF膜。这样，MMM可以实现新的性能限制，包括不容易形成晶体膜的MOF的渗透运输。作为一个设计平台，该方法可用于提高机制化学分离的生产率和效率。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子优点和更广泛的影响评估标准通过评估来支持的。