共价有机框架(COFs)的原子层沉积及其纳滤性能的研究

Covalent organic frameworks (COFs) are crystalline porous polymers with intrinsic pores and uniform pore sizes (generally less than 2 nm), which make the COFs promising candidates in nanofiltration and other separation processes. However, conventional manufacturing methods are hard to get thickness controllable, defect free and continuous COFs films, which become the bottleneck to fabricate high-performance COFs based nanofiltration membranes. In this proposal, we put forward a new idea using catalyst-free atomic layer deposition (ALD) to prepare COFs based membranes. During the ALD process, the gaseous precursors are reacted each other with equal amounts, thus forming defect-free crystalline COFs membranes with orderly structure. The thickness of the deposited COFs could be precisely and easily tuned by changing the ALD cycle numbers. Imine and imide bonded COFs, which are highly stable in liquid environment, would be deposited in this research work. Through deliberate selection of ALD precursors and operating parameters, the microstructure and thickness of the COFs membranes could be finely controlled. For this purpose, an innovation of COFs membranes fabrication is set up at the same time. Finally, the COFs will be deposited on the ceramic membranes as separation layers to achieve the fabrication of COFs based composite nanofiltration membranes, which will expect good applications in the water and solvents environment separation processes.

共价有机框架(Covalent Organic Frameworks，COFs)的规整、细小孔道（孔径通常小于2 nm），预示其在纳滤等分离过程的重要应用前景。但通常的液相合成方法，难于获得厚度可控、无缺陷的连续COFs薄膜，成为制备高性能COFs纳滤膜的瓶颈。本项目提出利用原子层沉积(Atomic Layer Deposition，ALD)制备COFs纳滤膜的思路。ALD过程中，前驱体以气相形式发生等当量反应，无需催化剂即可生成结构规整、无缺陷的COFs结晶薄膜；改变ALD循环次数，可精密调控COFs薄膜的厚度。拟沉积高稳定的亚胺及酰亚胺类COFs，通过选择前驱体和ALD参数，对COFs膜的微观结构及厚度进行精密调控，建立COFs合成的ALD方法。在陶瓷膜基底上进行ALD沉积，获得以COFs沉积层为分离层的复合膜，实现高通量、高选择性COFs纳滤膜的制备，并应用于水和溶剂体系的纳滤过程。

本工作研究了原子层沉积（atomic layer deposition，ALD）对分离膜改性过程中膜孔径、孔隙率、厚度、结晶度等因素的影响，以及由微观结构的演变所带来的通量、截留性能、表面电荷等的改变。通过上述研究，深入理解了沉积过程中不同参数对分离膜微观结构与分离性能的影响，从而构建不同ALD参数与最终获得的分离膜性能之间的量化关系。通过筛选具有合适分子构型的共价有机框架（covalent organic frameworks，COFs）材料前驱体以及合适的基底，掌握前驱体分子在不同基底表面的扩散、渗透及发生化学反应的规律，最终确定合适的前驱体和基底材料并完成分离膜的制备。在此基础上，成功将碳纳米管膜、COFs材料及共轭微孔聚合物（conjugated microporous polymers，CMP）等材料运用于包括纳滤、超滤、光降解和电容去离子等一系列水处理过程中。取得的理论成果有利于厘清原子层沉积过程中前驱体与基底材料之间的相互作用，为原子层沉积在分离膜领域的进一步应用提供理论指导。