A novel wholly-Tröger's Base-based polyamide nanofiltration membrane constructed for the separation application in strong acidic condition via acid-induced segregation

In this study, a new kind of wholly-Tröger's base-based polyamide (wTB-PA) thin film composite (TFC) nanofiltration (NF) membrane was successfully fabricated for the separation application in strong acidic condition via the acid-induced segregation (AIS) effect. Firstly, the self-synthesized Tröger's base diamine monomer — 2,8-diamino-4,10-dimethyl-6H,12H-5,11-methanodibenzo [1,5]-diazocine (TBDA) was added in the polyethersulfone (PES) casting solution to prepare the TBDA-based PES substrate by synchronously coupling the non-solvent-induced phase transformation (NIPs) and AIS, and then the TBDA molecules on the PES substrate surface further reacted with trimesoyl chloride (TMC) via interfacial polymerization (IP) to obtain the wTB-PA TFC NF membranes. Meanwhile, the acid-induced segregation effect of on the microstructure and separation performance of the wTB-PA TFC NF membrane were systematically investigated. As compared with the conventional poly(piperazine amide) NF membrane (MPIP-TMC), the wTB-PA NF membranes exhibited thinner, smoother but more hydrophobic surface as well as lower isoelectric point, and especially showed much higher tolerance to 20 wt% H2SO4 after soaking 63 days and favorable dye rejection (～99.9 %). Thereinto, the acid segregation agent of citric acid monohydrate (CA) endowed the wTB-PA TFC NF membrane with relatively optimal acid resistance and SO42−/Cl− separation selectivity (about 11.8) than glacial acetic acid (AC), nitric acid (HNO3) and hydrochloric acid (HCl). Moreover, this wTB-PA NF membrane based on CA-induced segregation had higher recovery of the cationic dye of crystal violet (CV) (＞98.0 %) in acidic condition. Therefore, the wTB-PA TFC NF membranes have great potential for the separation application in the strong acidic condition in the future.