纳米复合海水淡化膜中“界面水通道”的构建及性能研究

Desalination was regarded as a major approach to address the water scarcity on the earth in the 21 century.However, polyamide-based reverse osmosis (RO) membranes for desalination faces a major challenge of a limited water permeability as well as rejection ratio, due to the feature of torturous molecular cavity defined by cross-linked and entangled polymer chains in the barrier layer of RO membrane which certainly increases the hydraulic resistance. Based on the strategy of modification of the cellulose nanofiber surface, a molecular level interface will be created between the surface of cellulose nanofiber and the bulky polyamide, as a result, directed “Interfacial Water Channels” will be built in the barrier layer of the RO membrane which is expected to increase the water permeability in the factor of 5-10 while remaining the rejection ratio of 99.5% and up. Meanwhile, by adjusting the nature including channel size and hydrophobic property of the channels, sodium chloride ions and water could be recognized and separated simultaneously, and the mechanism of the transportation of water molecules and solutes in the water channels will be investigated comprehensively. Consequently, the relationships among structure, properties, and efficiency of the proposed desalination membrane should be explored and understood comprehensively, and therefore, to breakdown the bottle-neck of membrane science development on both of theoretical and practical aspects. The major issues of the proposal will be the creation and regulation of interfacial water channels in the barrier layer of the RO membrane, and exploration of the relationships of material structure and properties of the designed polyamide to develop new platform of the membrane science and technology in desalination.

针对传统交联聚酰胺海水淡化膜中，水分子流经曲折无序的过滤层的分子孔道时的传质阻力很大，因而其过滤效率无法提高的问题，通过设计纤维素纳米纤维表面化学结构，将三维网状的“界面水通道”（Interfacial Water Channels）构建到反渗透膜的过滤层中，并通过调控“界面水通道”的尺寸和性质来识别通过“界面水通道”的水分子和离子，揭示水分子在“界面水通道”中的传输和扩散作用机理。从分子设计的角度出发，通过“界面水通道”的构建，缩短了水分子在反渗透膜过滤层中的传输扩散路径，解决当前海水淡化膜科学发展的“瓶颈”问题，重点探索“界面水通道”的形成机制及调控、纳米复合反渗透膜的结构和性质与海水淡化效率的“构效”关系，实现水通量5-10倍提高和脱盐效率99.5%的应用目标。

本项目的研究背景：海水淡化是解决人类21世纪淡水资源缺乏的最行之有效的方法，而基于交联聚酰胺过滤层的反渗透膜则是目前海水淡化的主要研究方向。传统交联聚酰胺海水淡化膜中，水分子流经高分子链间自由体积时所受的传质阻力较大，导致海水淡化膜的过滤效率无法提高。.本课题的主要研究内容及研究成果包括：（1）制备与发展了以静电纺纳米纤维膜为基材、以纤维素纳米纤维和界面聚合反应生成的交联聚酰胺为过滤层的新型高效纳米复合反渗透膜。通过改变纤维素纳米纤维的表面化学结构，在聚酰胺过滤层中构建三维网状的“界面水通道”，从而减小水分子流经过滤层时的传质阻力以提高分离膜的水通量；同时，通过纳米纤维素的表面修饰来调控“界面水通道”的尺寸和性质，实现了对污水、苦咸水和海水的高效分离，最终达到水通量2-4倍提高和保持分离效率99%以上的应用目标。（2）本课题重点研究了“界面水通道”在膜过滤层中的构建方法，并且建立了过滤层的纳米结构、性质与脱盐效率之间的“构效”关系，为未来高效海水淡化膜的设计合成以及其它膜分离过程提供了关键的科学依据。（3）通过对静电纺纳米纤维膜、纤维素表面化学的研究与探索，制备出一系列具有高效吸附和过滤分离功能的纳米纤维复合微滤、超滤、纳滤和反渗透膜，用于海水淡化的预处理过程。同时，构建实际海水淡化过程的完整过滤系统，为海水淡化复合过滤系统的研究和发展奠定了基础。.本课题的主要科学意义在于从基础研究入手，通过改变水分子在聚合物介质中的传输扩散机制，解决当前反渗透膜在海水淡化过程中出现的水通量和截留率无法同时提高的“瓶颈”问题，重点探索“界面水通道”的构建及调控机理，建立膜材料的结构、性质、过滤效率的一体化的“构效”关系；同时，针对海水淡化的实际应用，发展了由高效微滤、超滤、纳滤和反渗透膜组成的复合海水淡化系统，从基础科学、理论研究和实际应用出发，为未来高效海水淡化的发展方向进行了有意义的探索。