Two dimensional COFs as ultra-thin interlayer to build TFN hollow fiber nanofiltration membrane for desalination and heavy metal wastewater treatment

An ultra-thin interlayer of two-dimensional covalent organic frameworks (COFs) was in-situ formed on polysulfone hollow fiber (HF) substrate surface to manipulate the interfacial polymerization process for the construction of thin film nanocomposite (TFN) HF nanofiltration (NF) membrane with greatly improved separation performance. p-Phenylenediamine and 1,3,5-Triformylphloroglucinol monomers were used for constructing the COFs interlayer, piperazine and trimethyl chloride were used for the fabrication of the HF NF polyamide skin separation layer. A series of optimization of the membrane preparation conditions were carried out to achieve the good separation performance. The results demonstrated that the two-dimensional COFs nanomaterials could effectively control the pore size distribution and hydrophobicity of the HF substrate surface, realize a uniform distribution of piperazine on the interlayer surface, thus effectively manipulate the interfacial polymerization process. Under the optimal conditions, the rejections of Na2SO4, Cr2(SO4)3, CuSO4, ZnSO4 and MnSO4 can achieve 96.6 %, 95.4 %, 94.3 %, 91.7 % and 91.0 %, respectively, and the water permeance reaches 86.6 L m−2 h−1 MPa−1. Meanwhile, the fabricated TFN HF NF membrane shows good long-term stability, fouling resistance, acid and alkali resistance, as well as chlorine resistance, providing its vast potential for application in desalination and heavy metal wastewater treatment.