聚酰胺反渗透膜表面的双硫五元环类抗氯分子修饰及抗氯功能的可逆再生调控

Polyamide reverse osmosis membrane has been widely applied in desalination and other water treatments. But polyamide membranes suffer from chlorine-sensitivity, which leads to membrane degradation. Recently, surface grafting method with chlorine-resistant layer has been tried to enhance the chlorine-tolerance of polyamide membrane. However, there exists a chlorinated saturation in those protective layers. This project suggests a long residual action of this modification method by grafting a special molecule, which consists of a five-membered-ring disulfide structure and a multi-amine structure. The disulfide structure is used for a chlorine-resistance with controllable regeneration potential, since this structure can react reversibly with chlorine species. Meanwhile, the multi-amine structure is applied to realize the linkage of the five-membered-ring disulfide group and regulate the characteristics of the whole molecule synergistically, because of its diversity in charge and structure. This project is to establish a strategy of fine control to the chlorine-resistant layer through studying the effect of multi-amine structure on resulting layer. Besides, a reducing method for chlorinated layer would be available by studying the interacting mechanism between disulfide structure and reducing agent. The structure-function relationship between chlorine-resistant layer and resulting membrane performance as well as feedback mechanism of chlorine resistance can be both revealed by this project through the investigation on apparent chlorine-tolerance and in-situ surface charge property. Those results are significant to future chlorine-durable polyamide reverse osmosis membrane for its theoretical and technical support.

聚酰胺反渗透膜已广泛应用于水处理及海水淡化领域，但膜材料本身容易受水体活性氯的氧化降解而失去分离作用。近年来发展的膜表面化学接枝抗氯层法，通过引入牺牲抗氯基团，提高聚酰胺反渗透膜的耐氯性，但抗氯层存在氯化饱和的局限。本项目针对聚酰胺反渗透膜抗氯层的长效性问题，在膜表面接枝双硫五元环结构和多元氨结构。旨在利用双硫五元环具有可逆氧化/还原活性，构建具有可再生修复功能的抗氯层；同时利用多元氨的结构多样性，实现双硫五元环结构与膜表面的化学接枝反应，完成接枝层抗氯功能及亲水性的可控调节。本项目开展多氨结构对抗氯层性质的影响研究，构建抗氯层结构的微调控策略；开展双硫五元环结构与还原剂的相互作用机制研究，建立抗氯层还原再生方法。揭示双硫五元环类抗氯层的宏观表面抗氯性能和微观表面电荷性质演变规律，阐明该抗氯层结构与抗氯性能的构效关系，建立反馈调控机制，为可控再生耐氯膜的研发提供理论支撑和技术支持。

在对海水/苦咸水进行淡化的过程中，聚酰胺复合反渗透膜易被水体中的活性氯攻击破坏，这已成为制约其推广应用的关键因素。氯化会导致分离皮层氧化降解，从而使膜的选择透过性显著下降，进而增大了膜材料的维护成本。受生物内源的α-硫辛酸优越的抗氧活性的启发，本研究将其固载于膜表面用作牺牲基团，以提高膜的抗氯能力。硫辛酸中特异的双硫五元环结构能够与料液中的活性氯优先作用，从而保护内层的聚酰胺结构不被过度氧化。首先将硫辛酸功能单元与聚乙烯亚胺介导单元通过羧酸-胺基耦合进行预组装，再基于胺基-酰氯作用实现一步固载。通过调节修饰液浓度兼顾了功能分子负载量与膜分离性能。与原膜相比，修饰膜对活性氯的耐受能力大幅提升。在酸性条件下经过8000 ppm·h静态氯化处理后，修饰膜的归一化脱盐率仍达到99.3%，且通量损失仅为17%。通过对氯化后膜表面进行表征，辅以理论计算，提出了硫辛酸功能单元的“环氧化-环水解-链氧化”三步串联氧化抗氯机制，每一个牺牲位点最多可以消耗5当量活性氯。硫辛酸牺牲层具有的超高本征氯捕获能力将迟滞氯化饱和点的出现。本研究为聚酰胺复合反渗透膜在含氯条件下的稳定运行提供了一种新颖、简单、有效的表面改性策略，具有一定的理论与现实意义。