Hydrophilization of ZIF-8 with tannic acid to enhance forward osmosis membranes performance in lithium concentration

In this study, ZIF-8 was modified with tannic acid (ZIF-TA) using an in-situ method to facilitate its incorporation into the polyamide (PA) active layer of thin-film nanocomposite (TFN) membranes. Unmodified ZIF-8 nanoparticles, owing to their hydrophobic nature, cannot be effectively dispersed in the aqueous phase. However, after hydrophilization with tannic acid, ZIF-8 becomes dispersible in the aqueous monomer solution, enabling its integration into the PA layer structure during the interfacial polymerization process. The ZIF-TA nanoparticles were analyzed using some tests such as water contact angle measurement, atomic force microscopy (AFM), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) to evaluate the impact of the nanoparticles on the membrane’s properties and structure. Results verified that ZIF-TA increases the hydrophilicity of membranes and raises the compatibility of the ZIF-8 and PA layers. Moreover, the performance of the membranes in the fouling test, lithium recovery, and FO process were investigated thoroughly. The results indicate that the optimal concentration of ZIF-TA within the PA layer is 1500 ppm, at which the M-1500 **membrane exhibited a water flux of 21.8 LMH in the FO process, 78.68 % higher than the control TFC membrane, which had a water flux of 12.2 LMH. Additionally, the M-1500 membrane demonstrated superior antifouling properties (only 18.2 % of M-1500 was fouled, and after physical cleaning 5.2 % fouling remained) compared to the control TFC membrane (38.6 % was fouled, and after physical cleaning 16.3 % fouling remained), attributed to its favorable surface characteristics. In lithium concentration applications, the M-1500 membrane achieved a water flux of 19.5 LMH and a specific reverse salt flux of 0.1 g/L when treating a feed solution containing 1200 ppm of lithium.