Metal-phenolic network as precursor for fabrication of metal-organic framework (MOF) nanofiltration membrane for efficient desalination

Abstract

A continuous and ultra-thin metal-phenolic network top layer on a polyethersulfone substrate surface was used as metal precursor for a metal-organic framework (MOF) membrane synthesis. A plant polyphenol tannic acid (TA) and Zn2+ based network top layer prepared by a layer-by-layer (LBL) self-assembly process was immersed into a 2-methylimidazole aqueous solution, and then a ZIF-8 top layer was facilely formed due to the partial self-conversion of TA-Zn2+ network to ZIF-8. The LBL process provides sufficient controllability of preparing a continuous and ultra-thin ZIF-8 top layer, which are crucial factors for nanofiltration membrane separation performance. The optimized ZIF-8 membrane exhibited a pure water permeance (PWP) of 5.1 L m−2 h−1 bar−1, a 55.2% NaCl rejection and a 93.6% Na2SO4 rejection. This is one of the few MOF membranes that possesses a divalent inorganic salt rejection higher than 90%. The novel zinc source of ZIF-8 synthesis disclosed in this study can provide a new incentive to not only MOF membrane preparation but also engineering MOFs towards a wide energy and environmental applications.