Engineering nanocomposite metal-phenolic network membranes with hollow MOFs via in-situ etching for High-efficiency organic solvent nanofiltration

Organic solvent nanofiltration (OSN), as an emerging membrane separation technology, holds great potential in pharmaceutical and chemical applications. However, the development of such a promising technology is severely retarded by the trade-off between permeability and selectivity. Herein, we report a novel thin-film nanocomposite (TFN) membrane by incorporating hollow metal-organic frameworks (MOFs) into the metal-phenolic network (MPN) selective layer for highly efficient OSN. This nanocomposite selective layer is fabricated via an aqueous deposition of tannic acid (TA) and FeII ions with MOFs, during which the MOFs are in-situ etched to a hollow structure. Attributed to the extra transfer channels provided by hollow MOFs, the methanol permeance of the TFN membranes increases to 24.7 L·m-2·h-1·bar-1, exhibiting an improvement of 270% compared with the membranes without MOFs (9.1 L·m-2·h-1·bar-1). Meanwhile, the coordination interaction between TA and metal centers in MOFs endows excellent interfacial compatibility between MPN matrix and MOF fillers, guaranteeing a defect-free selective layer and thus high rejection for small organic molecules (>99% for Alcian blue). Furthermore, various MOFs, including ZIF-67, prussian blue (PB), and MIL-53(Al), are also employed to fabricate MPN/MOF nanocomposite membranes, proving the availability and universality of this facial aqueous deposition strategy. Additionally, we also take deep insight into the mechanism of in-situ etching based on the density functional theory (DFT) calculation to pave the way for the fabrication of TFN membranes with other hollow nanofillers. This work provides a sufficient strategy for the design and construction of novel highly efficient OSN nanocomposite membranes with excellent permeability and retention performance.