Tailored design of polyamide nanofiltration membrane interlayer via dynamic-polyphenol polymerization for complex inorganic salts separation

In this study, a novel dynamic polyphenol polymerization method for the preparation of nanofiltration membrane intercalations was proposed. In this method, TA, PEI and Al3+ could successively form the first polyphenol-amine crosslink network and the second metal-phenol cross-linked network on the surface of the support layer. The dense crosslinked layer of TA-PEI-Al3+ formed under dynamic conditions maintains high hydrophilicity compared to the crosslinked network formed under a single pH environment. Aluminum ions possess strong electronegativity since they have relatively high valence states and small ionic radius among transition metal ions. Therefore, this is the first time to incorporate Al3+ into phenol-amine crosslinked networks to form the metal-phenol tri-complexes. The tri-complexes of TA and Al3+ are more robust, promoting the coordination with more water molecules and forming more stable hydrophilic intermediate layers. When an interfacial polymerization reaction is performed on the intermediate layer, this hydrophilic intermediate layer can store aqueous-phase PIP and slow down the IP reaction rate through electrostatic interactions. This process helps to form a dense PA separation layer on the support layer surface. The prepared TFC-NF membranes can be used to separate dyes, antibiotics, and compound inorganic salts. The outstanding water permeance of the TFC-NF membrane was determined as 18.7 L/m2·h·bar and the removal rate of mixed pollutants can reach 99 %. The firm intermediate layer enables the optimized modified membrane to maintain stable flux and high rejection rate in 72 h separation test. This modification method provides a useful reference for the preparation of high-performance nanofiltration membranes with plant polyphenols.

在这项研究中，提出了一种用于制备纳滤膜插层的新型动态多酚聚合方法。在该方法中，单宁酸（TA）、聚乙烯亚胺（PEI）和铝离子（Al³⁺）能够依次在支撑层表面形成第一个多酚 - 胺交联网络和第二个金属 - 酚交联网络。在动态条件下形成的TA - PEI - Al³⁺致密交联层与在单一pH环境下形成的交联网络相比，保持了较高的亲水性。铝离子由于在过渡金属离子中具有相对较高的价态和较小的离子半径，因而具有较强的电负性。因此，这是首次将Al³⁺引入酚 - 胺交联网络以形成金属 - 酚三元配合物。TA和Al³⁺的三元配合物更加稳定，促进了与更多水分子的配位，并形成更稳定的亲水中间层。当在中间层上进行界面聚合反应时，这种亲水中间层能够储存水相的哌嗪（PIP），并通过静电相互作用减缓界面聚合（IP）反应速率。这一过程有助于在支撑层表面形成致密的聚酰胺（PA）分离层。所制备的复合纳滤（TFC - NF）膜可用于分离染料、抗生素和复合无机盐。该复合纳滤膜的优异水通量确定为18.7 L/m²·h·bar，对混合污染物的去除率可达99%。坚固的中间层使优化后的改性膜在72小时的分离测试中能够保持稳定的通量和高截留率。这种改性方法为利用植物多酚制备高性能纳滤膜提供了有益的参考。