Scalable Synthesis of Ultrathin 2D Covalent Organic Framework Membranes with Sub-1 nm Pores for Molecular Separations

生产燃料、化学品和清洁水的工业过程依赖于分离技术来将一种或多种化学物质从另一种物质中分离出来。使用节能膜分离化学品的能力减少了这些工业过程的环境负担。然而，必须为许多相关应用开发坚固、高性能的膜。共价有机骨架(COF)是一种稳定的结晶聚合物，具有高度有序的多孔结构，可以为小分子提供快速和选择性的运输途径。这些特性使COFS成为构建下一代膜的理想分离材料。以前对COF基膜的研究仅限于使用通过难以放大的合成方法获得的大孔COF(主要是1 nm)。这一研究项目将使具有小于1 nm孔径的超薄微孔COF膜的合理设计和可扩展合成成为可能，这些超薄微孔膜适用于二氧化碳/氮气和二甲苯等各种气体/蒸汽混合物的分子分离。从这项研究中获得的基础知识将加快二维(2D)COF膜在化学分离、碳捕获、海水淡化、催化和传感等应用中的部署，从而解决从能源可获得性到全球变暖再到淡水稀缺的各种社会挑战。该项目还包括与研究有关的教育和外联工作，包括开发面向教育的关于膜分离的在线视频，以及创建关于膜合成的新的本科生实验室课程单元。本项目的目的是研究用一种更容易扩展的方法，即剥离的2D COF纳米片的过滤涂层来合成孔径小于1 nm的2D COF膜，并了解所合成的微孔2D COF膜中的分子传输。高质量(即大尺寸和分子薄)的剥离型2D COF纳米片将通过两种互补的方法合成：调制溶剂热生长和合成后离子官能化。将这些完全剥离的2D COF纳米片在商用大孔/介孔载体上进行真空辅助过滤涂层，以获得孔径小于1 nm的无缺陷超薄(~100 nm)微孔2D COF膜。剥离的2D COF纳米片之间的层间相互作用将被精确控制，以调节它们的堆积几何形状和d间距，这反过来又决定了所得到的COF膜的孔拓扑和结晶度。最后，将使用尺寸为1 nm的气体和碳氢化合物小分子(例如二氧化碳/氮气、二氧化碳/甲烷、二甲苯异构体和丙烯/丙烷)进行分子传输和分离测量，以建立这些微孔2D COF膜中的基本孔结构−分子传输−分离性能关系。该团队将创建面向教育的关于膜及其应用的TikTok/YouTube内容，向更广泛的社区介绍膜技术，并促进招生。研究成果将被整合到现代分离本科生/研究生课程中，并将开发一个新的聚合物膜合成实验室模块，以培训数百名下一代STEM劳动力的学生。诸如染料拒绝等项目将通过科学和工程经验(场景)计划来设计，以使当地的K-12学生接触到研究环境，并激发他们对分离科学的兴趣。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。

Industrial processes for producing fuels, chemicals, and clean water rely upon separations technologies to isolate one or more chemical species from another. The ability to separate chemicals using energy-efficient membranes reduces the environmental burden of these industrial processes. However, robust, high-performance membranes must be developed for many relevant applications. Covalent organic frameworks (COFs) are stable, crystalline polymers with highly ordered porous structures that can provide fast and selective transport pathways for small molecules. These characteristics make COFs ideal separation materials from which to construct next-generation membranes. Previous studies on COF-based membranes have been limited to using large-pore COFs (mostly 1 nm) obtained by synthesis methods that are difficult to scale up. This research project will enable the rational design and scalable synthesis of ultrathin microporous COF membranes with sub-1 nm pores that are suitable for the molecular separation of various gas/vapor mixtures such as carbon dioxide/nitrogen and xylene isomers. The fundamental knowledge gained from this research will accelerate the deployment of two-dimensional (2D) COF membranes in applications including chemical separations, carbon capture, desalination, catalysis, and sensing, thus addressing societal challenges ranging from energy availability, to global warming, to freshwater scarcity. The project also entails research-related education and outreach efforts, including the development of education-oriented online videos on membrane separations and the creation of a new undergraduate-level laboratory course module on membrane synthesis. The goal of this project is to study the synthesis of 2D COF membranes with sub-1 nm pores by a more easily scalable method, i.e., filtration coating of exfoliated 2D COF nanosheets, and understand the molecular transport in the synthesized microporous 2D COF membranes. High-quality (i.e., large size and molecularly thin) exfoliated microporous 2D COF nanosheets will be synthesized using two complementary approaches: modulated solvothermal growth and post-synthesis ionic functionalization. Vacuum-assisted filtration coating of these fully exfoliated 2D COF nanosheets on commercial macroporous/mesoporous supports will be systematically conducted to obtain defect-free ultrathin (~100 nm) microporous 2D COF membranes with sub-1 nm pores. The interlayer interactions between the exfoliated 2D COF nanosheets will be precisely controlled to modulate their stacking geometry and d spacing, which in turn dictates the pore topology and crystallinity of the resulting COF membranes. Finally, molecular transport and separation measurements will be conducted using small gas and hydrocarbon molecules 1 nm in size (e.g., carbon dioxide/nitrogen, carbon dioxide/methane, xylene isomers, and propylene/propane) to establish the fundamental pore structure−molecular transport−separation performance relations in these microporous 2D COF membranes. The team will create education-oriented TikTok/YouTube content on membranes and their applications to introduce membrane technologies to the broader community and promote student recruiting. The research results will be integrated into a Modern Separations undergraduate/graduate course, and a new laboratory module on polymer membrane synthesis will be developed to train hundreds of students in the next-generation STEM workforce. Projects such as dye rejection will be designed through the SCience and ENgineering Experience (SCENE) program to expose local K-12 students to a research environment and stimulate their interest in separation science.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.