Effective regulating interfacial polymerization process of OSN membrane via in-situ constructed nano-porous interlayer of 2D TpHz covalent organic frameworks

In this study, a kind of thin film composite (TFC) membrane with two-dimensional (2D) covalent organic frameworks (COFs) as interlayer, termed as iTFC, which has integrally covalent bonding structure, ultra-thin and ultra-smooth surface, as well as high separation performance was fabricated via interfacial polymerization (IP) and subsequent chemical cross-linking and solvent activation for organic solvent nanofiltration (OSN). The COFs interlayer was in situ constructed using 1,3,5-triformylphloroglucinol (Tp) and hydrazine (Hz) on polyimide (PI) substrate prior to the IP. The optimization of the membrane fabrication process shows that very low concentration for both the COFs aqueous monomer Hz and the IP aqueous monomer m-phenylenediamine (MPD) was conducive to the formation of very smooth (roughness of 2.4 nm), very thin and defect-free cortex, thus improving the organic solvent permeation while remaining the dye rejection. Under optimal conditions, the prepared iTFC OSN membrane has an ethanol permeance of 63.4 L m−2 h−1 MPa−1, a Rhodamine B (RDB) rejection of greater than 99 %, and a molecular weight cut-off (MWCO) of as low as 380 Da. In addition, after filtration of 100 mg L−1 RB/DMF solution for 408 h, the optimized iTFC OSN membrane remained Rose Bengal (RB) rejection above 97 %, which proves its excellent solvent resistance performance.