Tannic acid-polyethyleneimine crosslinked loose nanofiltration membrane for dye/salt mixture separation

Fractionation of dyes and salts is a great challenge in high salinity wastewater from the textile industry. In this work, a high performance loose nanofiltration membrane (LNM) was fabricated to fractionate the dyes and salts in the solution via green rapid coating (GRC) process on polyethersulfone (PES) substrate. The organic solvent-free GRC process was achieved within 10 min based on the crosslinking between polyethylenimine (PEI) and tannic acid (TA). The resultant LNM performance was optimized by altering the coating parameters including the TA concentration and the coating time. The microstructure, surface properties and dye/salt separation performance of the LNM were demonstrated by characterizations and filtration experiments, respectively. With the co-existence of dye and salt, the optimized LNM exhibited desirable permeability (40.6 LMH.bar(-1)) and dye rejection (99.8% for 0.1 g/L Congo Red) as well as low salt rejection (6.1% for NaCl and 2.2% for Na2SO4). Furthermore, it was observed that even under 60 g/L of salt content, the satisfying rejection of CR (99.3% in Na2SO4 and 97.6% in NaCl) and high permeation of salts (98.9% for Na2SO4 and 97.9% for NaCl) can still be maintained. Moreover, the LNM showed incredible stability during the filtration process (10 h) towards dye/salt aqueous mixture. The PEI-TA/PES LNM exhibited promising application potential in dye/salt separation.