基于分子结构设计的聚酰胺纳滤膜的孔径分布对分盐选择性影响的机理研究

The nanofiltration membrane had unique advantages and obvious energy-saving effects in water softening, the fractionation and concentration of small organic molecules, the demineralization of organics and the separation of monovalent/divalent ions. Due to the uncontrollable interfacial polymerization technique, it was unable to modify the structure and performance of the nanofiltration membrane directly. Hence existing researches focused on improving the desalination rate and permeability of nanofiltration membranes through mixing, surface modification and interlayer, lacking of the basic study on the relationship between the membrane microstructure (pore size distribution) and membrane properties (desalinaiton selectivity), and lacking of the in-depth study on the mechanism of selective separation for nanofiltration membranes. In this project, aqueous amine monomers with different molecule structures were designed, and then the polyamide nanofiltration membranes with different structures were prepared through the interfacial polymerization. The pore size distribution of the nanofiltration membrane was designed at the molecule level. Combined with the molecular dynamics simulation, the influence of the twisty monomer structures with the increasing steric hindrance on the pore size distribution and the influence of the pore size distribution on the desalinaiton selectivity were studied systematically in order to make up the gap of the basic study between the membrane structures and the membrane performance. Compared with the molecular dynamics simulation data, the experimental data and the nanofiltration separation model calculated data, the existing nanofiltration separation model was verified and the mechanism of the selective separation was deeply studied, which provided a basic study reference for constructing highly selective polyamide nanofiltration membranes.

纳滤膜在水软化、有机小分子分级浓缩、有机物除盐净化和一价/二价离子的分离方面具有独特的优点和明显的节能效果。由于界面聚合的可控性差难以直接调控纳滤膜的结构与性能，现有的研究大多致力于通过掺杂、表面改性和中间层等手段调控膜结构以提高分离性能，缺乏对膜微观结构（孔径分布）与性能（分盐选择性）间相关性的机理研究，以及对纳滤膜选择分离机理的统一认识和深入探讨。本项目首先通过设计不同结构的胺单体，界面聚合制备不同孔径分布的聚酰胺纳滤膜，分子尺度上可控调控纳滤膜的孔径分布。然后，结合分子动力学模拟在微观尺度上研究单体结构对纳滤膜孔径分布的影响，结合纳滤膜分离模型在宏观尺度上研究孔径分布对分盐选择性的影响，旨在弥补膜结构与性能之间基础研究的空白。最后，将纳滤膜分离模型得到的膜参数与分子模拟结果、实验结果对比，验证并修正纳滤膜分离模型，深入研究纳滤膜选择分离机理，为构筑高选择性纳滤膜提供基础研究参考。

聚酰胺（PA）纳滤（NF）膜在水软化、有机物的除盐净化和一价/二价离子的分离方面具有独特的优点和明显的节能效果。在新时代建设下，随着我国对深度水处理工艺的需求越来越高，对NF膜的性能提出了更高的要求，孔径分布范围更加精细、选择性更高并且结构特征可控的NF膜成为新的发展方向，但目前NF膜存在“trade-off”效应和选择性低等问题。首先，本项目设计了一种新型类哌嗪的水相单体1,4,7,10-四氮杂环十二烷（Cyclen），分子尺度上对纳滤膜分离层结构进行调控。结果表明，与PIP基NF膜相比，以Cyclen作为新型水相单体制备的疏松纳滤膜膜交联程度更低，孔径变大，有助于渗透通量的提高和有机微污染物/一价盐选择性分离，克服了渗透通量与选择性的“trade-off”效应。其次，基于文献中广泛应用的中间层技术，采用表面活性剂组装调控界面聚合（SARIP）协同强化Cyclen的相转移过程，在不牺牲渗透通量的前提下，构建了孔径分布集中的高选择性NF膜。所制备的m-SARIP膜具有均匀的亚纳米孔径，孔径减小与孔内电荷分布相结合，实现了对二价离子的高截留和对单价离子的低截留。MgCl2的渗透通量可达18.5 L·m-2·h-1·bar-1，Li+/Mg2+和Na+/Mg2+的选择性分别为21.9和20.3。最后，将前文制备的高选择性m-SARIP膜与商业NF膜NF 270作为对比处理印染废水，探究不同操作条件对复合膜处理效果的影响。利用SEM、AFM和接触角测量仪对污染前后复合膜的表面形貌、粗糙度和亲疏水性进行表征，并对复合膜处理印染废水过程中的污染特性进行分析。在印染废水处理过程中，m-SARIP膜对印染废水的处理效果优于商业膜NF 270，其渗透通量较为稳定，具有良好的抗污染功能和重复使用性能，浓缩倍数可达10倍且不需频繁清洗。本项目基于分子结构设计调控纳滤膜的孔径分布，解决现有纳滤膜“trade-off”效应，结合分子动力学模拟在微观尺度上分析聚酰胺纳滤膜孔径分布的变化，在宏观尺度上建立聚酰胺纳滤膜的孔径分布与分盐选择性的关系，为设计构筑高选择性聚酰胺纳滤膜提供理论依据。