Engineering Atomically Precise Nanochannels Using Layered 2D Sheets to Enable Chemical Separation Membranes with Exceptional Permeance and Size-Selectivity

将空气分离成氧气、氮气、二氧化碳、水蒸气和其他微量气体（如氦气）是一项价值数十亿美元的产业。例如：在高性能轮胎中使用纯化氮，并将其注入精品咖啡中；将净化氧用于医疗保健和发射航天飞机；氦气用于气球。任何混合物的分离都需要能量和分离一种成分的策略。大小选择性膜提供了这样一种策略，允许分子以其适应膜通道的能力、扩散率和与表面相互作用的强度决定的速率通过内部通道渗透。减少这种表面相互作用会增加渗透率，从而在降低能耗的情况下提高产量。无摩擦传输的一个候选是由碳原子组成的膜通道，如圆柱形碳纳米管或堆叠的平面石墨烯片。由于微弱的表面相互作用对流动几乎没有阻碍，水通过碳纳米管的渗透性实验表明比经典模型预测的要大1000倍。然而，密集排列的碳纳米管的均匀通道一直难以大量合成。支撑石墨烯片在大规模合成方面表现出更大的前景，但目前石墨是通过高度氧化的分层过程获得的，这会导致大量的氧原子残留，从而使无摩擦传输失效。该项目将采用自底向上的非氧化方法来制造支撑石墨烯膜，该膜具有可控通道，可优化小分子（如氧、氮、氢、氦和水）的尺寸选择性运输。该项目将使用分子间隔剂作为支撑剂，在原始未氧化的平行石墨烯片之间合成可控的纳米通道。坚固的化学将被开发用于精确制造具有亚纳米间隙的纳米通道，其范围从2-8埃到赋予尺寸选择性。候选间隔分子包括对取代苯衍生物，通过[2+2]环加成接枝的官能团，以及非共价吸附的平面和非平面芳香烃。将制备分离的双层通道和多层层状膜。隔离通道将提供基本的表面科学结构和性能测量，而多层膜将实现宏观传输测量，以验证无摩擦、超高渗透传输的理论预测。微观结构表征数据，结合传输测量，将指导设计越来越有效的膜材料。研究生和本科生都将为这个项目进行实验室研究，努力针对代表性不足的群体。这项研究将为针对高中学生的互动课程提供信息，同时向教师分发培训视频。

The separation of air into its components, oxygen, nitrogen, carbon dioxide, water vapor, and other trace gases such as helium, is a billion dollar industry. Examples include: use of purified nitrogen in high performance tires and infusion into specialty coffee; use of purified oxygen for healthcare and the launch space shuttles; use of helium for balloons. Separation of any mixture requires both energy and a strategy to isolate one component. Size selective membranes provide one such strategy, allowing molecules to permeate through internal channels at rates that are dictated by their ability to fit within a membrane channel, their diffusivity, and the strength by which they interact with the surface. Decreasing this surface interaction increases permeation, which translates to an increased production rate at lower energy consumption. One candidate for frictionless transport are membrane channels comprised of carbon atoms, such as cylindrical carbon nanotubes or stacked planar graphene sheets. As weak surface interactions provide little impediment to flow, the permeation of water through carbon nanotubes has been experimentally shown to be 1000 times greater than that predicted from classical models. Yet, homogenous channels of closely packed carbon nanotubes have been difficult to synthesize in large quantities. Propped graphene sheets show more promise for large scale synthesis, but are currently derived from graphite via a highly oxidative delamination process, which imparts significant residual oxygen atoms that invalidate frictionless transport. This project will utilize a bottoms-up nonoxidative approach to create propped graphene membranes with controlled channels optimized for size selective transport of small molecules, such as oxygen, nitrogen, hydrogen, helium, and water.This project will use molecular spacers as proppants to synthesize controlled nanochannels between pristine unoxidized parallel graphene sheets. Robust chemistries will be developed for precisely fabricating nanochannels with sub-nanometer gaps that range from 2-8 Angstroms to impart size selectivity. Candidate spacer molecules include para substituted benzene derivatives, functional groups grafted via [2+2] cycloaddition, and non-covalently adsorbed planar and non-planar aromatic hydrocarbons. Both isolated bilayer channels and multilayered laminate membranes will be fabricated. The isolated channels will afford fundamental surface science measurements of structure and properties whereas the multilayered membranes will enable macroscopic measurements of transport to validate the theoretical prediction of frictionless, ultrahigh permeance transport. Microstructural characterization data, in conjunction with transport measurements, will guide design of increasingly effective membrane materials. Both graduate and undergraduate students will perform laboratory research for this project, with an effort to target underrepresented groups. The research will inform interactive lessons targeted at high school level students, accompanied by dissemination of training videos to teachers.