“疏松”复合纳滤膜的构筑及其结构与性能调控

The wide application of composite nanofiltration membrane is greatly restricted by the “Trade-off” effect between the rejection rate and permeate flux, and it is still a challenge to enhance both permeability and selectivity performance of nanofiltration membranes at the same time. In this project an ultrathin charged barrier layer will be constructed on nanofibrous substrate to provide high permeability of the composite membrane; The donnan effect, repulsive interaction of like charges when the adsorption of charged barrier layer to polyelectrolyte reaches saturation, is taken advantage of to increase the rejection ratio and decrease the membrane fouling due to the decreased pore size and enhanced “Donnan Effect”. Based on the point, two-tier thin film nanofibrous composite membrane with “loose” structure was constructed for wastewater treatment by taking advantage of membrane fouling in this project. The bother of conventional composite membranes suffering from severe membrane fouling and low permeability can be solved by the two-tier structure coordinated effect. Herein, the material design and the formation mechanism of microstructure during the nanofibrous composite membrane preparation will be studied systematically. The rules and the control methods of the relationship between the microstructure, the sieving pore size and filtration performance of the composite membranes will be explored through the design and adjustment of the microstructure of the composite membranes. The coordinated effect of two-tier structure, the separation and antifouling mechanism to wastewater will also be investigated. It is firmly believed that the study will provide important theoretical basis and technical support for the development of high performance novel polymer separation membranes.

复合纳滤膜的渗透通量和截留率的“Trade-off”效应是制约其广泛应用的瓶颈，目前同时提高复合纳滤膜的渗透通量和截留率仍是一项技术挑战。本项目拟通过纳米纤维支撑的具有“疏松”结构的超薄亲水荷电功能阻隔层提供高渗透性；利用复合膜的荷电表面阻隔层组装聚电解质达到饱和时的孔径缩小以及同种电荷排斥作用（唐南效应），提高复合膜的截留率，减少膜污染。这种双层结构协同作用，能够使复合膜的渗透通量和截留率都保持在较高水平。通过膜材料的设计及功能阻隔层的微孔构筑制备“疏松”复合纳滤膜，系统地研究功能阻隔层微结构形成机制，探索表面功能阻隔层微观结构-筛分尺寸-过滤性能之间相互关系及调控方法，探讨双层结构协同作用和相应的有机污染物去除机制以及抗膜污染机制，为高性能新型高分子分离膜的研究提供理论依据和技术支持。

传统复合滤膜在进行印染废水处理时存在渗透性差和膜污染严重等问题。本项目利用“膜污染”在分子级别对复合膜表面阻隔层的孔径进行精细调控，构筑了一系列具有疏松结构的高渗透性和良好循环使用寿命的染料废水处理用复合纳滤膜，打破“Trade-off效应”瓶颈。制备的PAN-DR80复合滤膜对DR80染料显现出优越的渗透性(0.4 MPa下为128.4 Lm-2h-1) 和高截留率(~99.9%)，并可以实现染料/NaCl混合物的快速分离。以高渗透性静电纺丝纳米纤维替代传统商用超滤膜为基膜，结合“染料污染”，制备出了低压高渗透性CS-DR80/PAN纳米纤维基复合滤膜。壳聚糖与阴离子染料带相互作用形成相对疏松且稳定的CS-DR80阻隔层。同时结合纳米纤维基膜为孔隙率高的开孔结构，双层结构协同作用，使之呈现出高的选择性、渗透性以及抗污性能。CS-DR80/PAN复合膜对DR80染料的渗透通量为~139.1 Lm-2h-1（0.1 MPa），截留率为~99.8%。以柔性壳聚糖电解质调控氧化石墨烯片层，一方面增加了其稳定性，另一方面利用壳聚糖的柔性实现了对GO片层间距的有效调控，制备的具有疏松稳定结构的GO-CS/PAN纳米纤维基复合滤膜对DR80染料的截留率很高（99.3%），0.3 MPa下渗透通量高达351.6 Lm-2h-1。以柔性聚丙烯酸电解质形成半互穿网络结构来调控MXene的片层，制备的具有疏松结构的PAA-MXene/PAN纳米纤维基复合滤膜在0.1 MPa下对DR80染料的渗透通量为~271.26 Lm-2h-1，截留率为~98.9%。系统研究并探讨了各种复合滤膜的成膜机制、过滤性能及分离机制，探索了表面阻隔层微观结构-筛分尺寸-过滤性能之间相互关系及调控方法，探讨双层结构协同作用和相应的有机废水去除及抗污机制，为高性能新型高分子分离膜的研究提供了理论指导和技术支持。