Interfacial polymerization on PES hollow fiber membranes using mixed diamines for nanofiltration removal of salts containing oxyanions and ferric ions

• Hollow fiber NF membranes were fabricated via IP, with mixed diamine monomers.
• NF membrane exhibits PWP of 31.2 L·m-2·h-1 and Na2SO4 rejection of 99.7% at 6 bar.
• NF membrane performance was stable during a 7-day filtration process.

Thin film composite (TFC) hollow fiber nanofiltration (NF) membranes were fabricated via interfacial polymerization, with mixed diamines of piperazine (PIP) and 2,2′-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-triflutoethyl)-4,4′-methylenedianiline (BHTTM) as water phase and trimesoyl chloride (TMC) as organic phase. Fabricated membranes were characterized for ATR-FTIR, SEM, AFM, and water contact angle. Formation conditions of the selective polyamide layer have been optimized for a good NF membrane performance. The pure water flux of NF membrane prepared under optimized conditions was 31.2 L·m− 2·h− 1 and the rejection for Na2SO4 was 99.7% at 6 bar. The rejections of NF membranes for different salts followed the order: Na2SO4 > MgSO4 > NaCl > MgCl2. The molecular weight cut-off of NF membrane was around 300 Da. The performance of NF membranes was stable during a 7-day filtration process for rejecting different species ions including heavy metal ferric ion (FeCl3 and Fe2(SO4)3) and oxyanions (SO42 − and HPO42 −), in addition to different inorganic salts. Also, the NF membranes exhibited chlorine tolerant property. This work demonstrates the potential of PES outer-selective TFC hollow fiber membranes for desalination or water softening process, provides database to fabricate suitable NF membranes for long-term salts removal and raise a simple technique to form a thin chlorine-tolerant polyamide layer.