Metal-phenolic network/ZIF-8 nanocomposite membranes fabricated via surface-induced in-situ growth with post-etching: A strategy for highly enhanced nanofiltration desalination

Thin-film composite nanofiltration membranes have demonstrated vital potentials in desalination. However, the trade-off effect between selectivity and permeability still restricts the separation efficiency severely. In this work, we propose a new strategy to develop a nanocomposite nanofiltration membrane by combining porous zeolitic imidazolate frameworks (ZIF-8) nanoparticles with hollow structure into a metal-phenolic networks (MPNs) selective layer for desalination. In detail, ZIF-8 nanoparticles firstly in-situ grow onto the substrate surface induced by a tannic acid (TA) containing modification layer. Subsequently, a selective layer is constructed via the coordination and deposition of TA with Fe 2+ ions, during which the ZIF-8 nanoparticles are synchronously post-etched by TA to generate a hollow structure. The in-situ growth strategy enables well control of the ZIF-8 nanoparticle size while promoting their good dispersion in the MPNs matrix, minimizing non-selective voids caused by nanoparticle agglomeration. Furthermore, the coordinating interaction between TA in MPNs and Zn 2+ in ZIF-8 provides excellent interfacial compatibility between the MPNs matrix and ZIF-8 nanoparticles, leading to a defect-free nanocomposite selective layer and consequently high anion rejection in aqueous solutions (Na 2 SO 4 > 95%). Ascribing to the abundant transmembrane transport channels provided by hollow porous ZIF-8, the permeability of the nanocomposite membrane exhibits 2.15 times higher compared to the MPNs membranes without ZIF-8. In return, the MPNs matrix helps to stabilize the ZIF-8 structure in aqueous environments, enabling the nanocomposite membrane to maintain stable separation performance during a long-term cross-flow filtration process. This work can provide an effective strategy for the development of nanocomposite nanofiltration membranes for high-efficiency desalination.