Zhang Mengling, Hu Xiangyang, Peng Lei, Zhou Shilin, Zhou Yong, Xie Shijie, Song Xiaoxiao, Gao Congjie
Center for Membrane Separation and Water Science & Technology, Ocean College, Zhejiang University of Technology, Hangzhou 310014, China.
Bruker Shanghai Office 9F, Building NO.1, Lane 2570 Hechuan Rd, Minhang District, Shanghai 200233, China.
Membranes (Basel). 2022 Apr 11;12(4):417. doi: 10.3390/membranes12040417.
The realistic resistance zone of water and salt molecules to transport across a TFC-RO membrane is the topmost polyamide nanofilm. The existence of hollow voids in the fully aromatic polyamide (PA) film gives its surface ridge-and-valley morphologies, which confuses the comprehensions of the definition of the PA thickness. The hollow voids, however, neither participate in salt-water separation nor hinder water penetrating. In this paper, the influence of intrinsic thickness (single wall thickness) of the PA layer on water permeability was studied by adjusting the concentration of reacting monomers. It confirms that the true permeation resistance of water molecules originates from the intrinsic thickness portion of the membrane. The experimental results show that the water permeability constant decreases from 3.15 ± 0.02 to 2.74 ± 0.10 L·m·h·bar when the intrinsic thickness of the membrane increases by 9 nm. The defects on the film surface generate when the higher concentration of MPD is matched with the relatively low concentration of TMC. In addition, the role of MPD and TMC in the micro-structure of the PA membrane was discussed, which may provide a new way for the preparation of high permeability and high selectivity composite reverse osmosis membranes.
水和盐分子跨TFC-RO膜传输的实际阻力区域是最上层的聚酰胺纳米薄膜。全芳香族聚酰胺（PA）膜中存在中空空隙，使其表面呈现出起伏形态，这使得对PA厚度定义的理解变得复杂。然而，这些中空空隙既不参与盐水分离，也不妨碍水的渗透。本文通过调整反应单体的浓度，研究了PA层的本征厚度（单壁厚度）对水渗透性的影响。结果证实，水分子真正的渗透阻力源于膜的本征厚度部分。实验结果表明，当膜的本征厚度增加9nm时，水渗透常数从3.15±0.02降至2.74±0.10L·m·h·bar。当较高浓度的MPD与相对较低浓度的TMC匹配时，膜表面会产生缺陷。此外，还讨论了MPD和TMC在PA膜微观结构中的作用，这可能为制备高渗透性和高选择性复合反渗透膜提供一条新途径。
