Synthesis of Two-Dimensional Polymers as Ultrathin Membranes for Molecular Sieving

微孔和纳米孔材料作为选择性屏障，在工业过程以及环境技术（如二氧化碳捕获或水处理）中作为高效节能的气体和液体分离膜发挥着重要作用。开发新型膜材料的目标之一是实现高通量和高选择性，同时保持高机械稳定性。由于通过膜的通量与选择层的厚度成反比，具有一到几个原子或分子厚度的坚固的二维（2D）薄片将是超薄高性能膜的绝佳材料。然而，大多数二维薄片在分子尺度上不具有具有明确尺寸的孔，因此开发孔径小于3nm，厚度小于50nm的均孔膜（两端都有均匀孔的薄膜）是一个巨大的挑战。在提议的项目中，一类孔径在0.25 nm到2.6 nm之间的膜将由独立的2D聚合物制成。人们将探索它们的稳定性和柔韧性，以及分子和原子是否可以通过它们进行转移。本项目旨在建立通用可靠的界面合成方法（气-水、表面活性剂-水和液-液界面），制备具有明确孔隙（孔径大小、形状、孔密度和孔外围官能团）的高结晶二维聚合物，并在分子水平上按需合理设计。该项目将生产宏观尺寸的二维聚合物晶体，其厚度从单层到多层。原位（掠射广角x射线散射）和非原位（STM， TEM）技术将阐明前驱体、模型单体、界面反应中间体、模型化合物和二维聚合物晶体的结构。在实验结果的基础上，结合模拟，分析原料与最终产物结构之间的相关性，推导出二维聚合物形成的反应机理。此外，还将讨论单体结构、聚合度、畴大小、晶界、边缘结构、孔结构和厚度对二维聚合物晶体的渗透和选择性的关键影响。将探讨这种有趣的二维聚合物晶体作为分离分子筛的关键功能。作为关键成果，申请人期望可靠的界面合成方法，描述结构-性能关系以及优越的二维聚合物膜分离性能。在拟议的项目中，pi团队联合起来，结合他们在二维材料、聚合物化学、纳米结构制造和膜科学方面的成熟专业知识，探索如何创建独立的均孔二维聚合物，以及它们的结构-性能相关性是什么。

Micro- and nanoporous materials act as selective barriers and play important roles as energy efficient gas and liquid separation membranes in industrial processes as well for environmental technologies, such as CO2 capture or water treatment. One of the goals in developing new membrane materials is to achieve a high flux as well as a high selectivity, while maintaining a high mechanical stability. Since the flux through a membrane is inversely proportional to the thickness of the selective layer, robust two-dimensional (2D) sheets with thicknesses of one to a few atoms or molecules would be excellent materials for ultrathin high-performance membranes. However, most 2D sheets do not have pores with well-defined dimensions at the molecular scale and it is thus a great challenge to develop homoporous membranes (films with homogenous pores open at both ends) with pore diameters below 3 nm and a thickness of less than 50 nm. In the proposed project, a class of such membranes with pore sizes between 0.25 nm and 2.6 nm will be fabricated from freestanding 2D polymers. It will be explored how stable and flexible they are and if molecules and atoms can be translocated through them. The project aims to establish versatile and reliable interfacial synthesis methodologies (gas-water, surfactant-water and liquid-liquid interfaces) towards highly crystalline 2D polymers with well-defined pores (size, shape, pore-density and functional group at the periphery of the pores), which can be rationally designed on demand at the molecular level. The project will produce macroscopic-sized 2D polymer crystals with a thicknesses from single layer to multilayers. Both in-situ (grazing-incidence wide-angle X-ray scattering) and ex-situ (STM, TEM) techniques will elucidate the structure of the precursors, model monomers, reaction intermediates at the interface, model compounds and 2D polymer crystals. Based on the experimental results together with simulation, correlations between structures of raw materials and final products will be analyzed to deduce the reaction mechanism for the formation of 2D polymers. Furthermore, critical effects of monomer structures, polymerization degrees, domain sizes, grain boundaries, edge structures, pore structures and thickness on the permeance and selectivity of the 2D polymer crystals will be addressed. Key functions for the operation of this intriguing class of 2D polymer crystals as molecular sieves for separation will be explored. As the key achievements, the applicants expect reliable interfacial synthesis methodologies, delineation of structure-property relationships and superior separation performance of the 2D polymer membranes. In the proposed project, the groups of the PIs join forces and combine their proven expertise in 2D materials, polymer chemistry, nanostructure fabrication and membrane science to explore how freestanding homoporous 2D polymers can be created and what their structure-property correlations are.