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与另一种分离。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耐用的高性能膜。共价有机骨架（COFs）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传输途径。这些特性使COF成为构建下一代膜的理想分离材料。先前对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（主要为1 nm）。该研究项目将能够合理设计和可规模化合成具有低于1 nm孔的微孔COF膜，适用于各种气体/蒸汽混合物（如二氧化碳/氮气和二甲苯异构体）的分子分离。从这项研究中获得的基础知识将加速二维（2D）COF膜在化学分离，碳捕获，脱盐，催化和传感等应用中的部署，从而解决从能源供应到全球变暖到淡水稀缺的社会挑战。该项目还需要开展与研究有关的教育和外联工作，包括制作以教育为导向的关于膜分离的在线视频，并创建一个新的关于膜合成的本科生实验室课程模块。 该项目的目标是研究通过更容易扩展的方法合成具有亚1 nm孔的2D COF膜，即，剥离的2D COF纳米片的过滤涂层，并了解合成的微孔2D COF膜中的分子传输。高质量（即，大尺寸和分子薄）剥离的微孔2D COF纳米片将使用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纳米片在商业大孔/中孔载体上的膜辅助过滤涂覆系统地进行，以获得具有亚1 nm孔的无缺陷的纳米（~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叠几何形状和d间距，这反过来决定了所得COF膜的孔拓扑结构和结晶度。最后，将使用尺寸为1 nm的小气体和烃分子（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），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。该团队将创建以教育为导向的TikTok/YouTube关于膜及其应用的内容，以向更广泛的社区介绍膜技术并促进学生招聘。研究成果将被整合到现代分离本科/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，以培训下一代STEM劳动力中的数百名学生。通过科学和工程经验（SCENE）计划设计的项目，如染料排斥，将使当地K-12学生接触到研究环境，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。

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.