Incorporation of lysine-modified UiO-66 for the construction of thin-film nanocomposite nanofiltration membrane with enhanced water flux and salt selectivity

The utilization of metal-organic frameworks (MOFs) has been proved to be promising in the attainment of high-performance membranes. In this work, lysine-decorated UiO-66 (Lys@UiO-66) is prepared via post-synthetic modification. Then, the controlled positioning of Lys@UiO-66 on a polyethersulfone (PES) substrate membrane is achieved by a pressure-assisted method, followed by interfacial polymerization to fabricate the Lys@UiO-66-based thin-film nanocomposite membrane (TFN-LDU). An even distribution of hydrophilic MOFs atop the substrate induces the formation of regular tent-like and mesh-topology polyamide structures, which enhance the effective membrane surface area and provide additional water transport channels. The optimal membrane with a Lys@UiO-66 loading density of 17.13 mu g cm(-2), TFN-LDU8, achieves a 55% enhancement in water permeability (18.27 L m(-2) h(-1) bar(-1)) without compromising the solute selectivity. Importantly, the TFN-LDU8 membrane exhibits high rejections of divalent cation salts (97.81% for MgCl2 and 92.81% for CaCl2) and improved mono-/divalent cation selectivity due to the pore hindrance and electrostatic exclusion of the Lys@UiO-66. Furthermore, the TFN-LDU8 membrane evinces a stable nanofiltration performance during the long-term nanofiltration experiment and displays a good antifouling ability in the fouling tests. This research provides a promising strategy for the design of nanofiltration membranes with special functions by using modified MOFs.