High-flux loose nanofiltration membrane with anti-dye fouling ability based on TA@ZIF-8 for efficient dye/salt separation

Herein, we report a preparation method based on a modified zeolite imidazolate skeleton loose nanofiltration membrane used to achieve the efficient separation of salt and dye from dye wastewater. In this study, negatively charged hydrophilic TA@ZIF-8 was synthesized using a tannin surface-functionalization-assisted etching process by tannic acid (TA). A novel, highly negatively charged, and loose nanofiltration membrane was then prepared by adding TA@ZIF-8 to a polyethyleneimine (PEI) and tricarboxylic acid (TMA) crosslinking system. The addition of TA@ZIF-8 nanoparticles not only changed the degree of crosslinking of PEI/TMA but also provided a preferential channel for water molecules, thereby improving the flux of the membrane. Then, the success of TA@ZIF-8 NPs and membranes preparation were verified by SEM, XRD, FT-IR, TGA, BET, XPS and other methods. The results showed that the optimal preparation conditions were 0.020 wt% TA@ZIF-8 loading, and the contact angle of the membranes decreased from 79.8° to 53.7°. The water flux of the membrane is 81 L·m−2·h−1·bar−1, which is 1.5 times that of PEI/TMA membrane. In addition, TA@ZIF-8–2 membrane not only has high rejection rate for Methyl blue (98.7 %), Toluidine blue (89.6 %), Cr6+ (91.2 %), but also maintains high transmittance for NaCl and Na2SO4. Besides, the separation performance of the membrane was stable for a long time in a mixed solution of dye and salt and excellent antifouling performance. Therefore, the loose TA@ZIF-8/PEI/TMA nanofiltration membrane has broad application prospects in printing and dyeing wastewater treatments.