Facile preparation of ZIF-8 membrane with hydrophilic intercrystalline channels for efficient solute recovery from saline wastewater

The efficient recovery of high-value solutes from saline wastewater is highly demanded in dyeing and pharmaceutical industries, yet conventional polyamide nanofiltration membranes face the challenge in combining high solute rejection with rapid salt permeation and water transport. Metal-organic framework (MOF) membranes are attractive for this purpose because of their well-defined porosity; however, the formation of continuous, defect-free MOF separation layer on polymeric supports remains challenging. Herein, a facile precursor-regulated strategy is developed to prepare ZIF-8@PEG composite membranes on hydrolyzed polyacrylonitrile (H-PAN) substrates. The composition of poly(ethylene glycol) (PEG) with zinc hydroxide nanostrands (ZnHNs) can suppress excessive Ostwald ripening and modulate ZIF-8 crystal growth, thereby promoting compact intergrowth and reducing grain-boundary defects. Moreover, PEG retained at crystal interfaces creates hydrophilic transport channels that facilitate the diffusion of water molecules and hydrated ions while restricting the passage of dye molecules. The optimized membrane exhibits high water permeance of 549 L·m −2 ·h −1 ·MPa −1 and high retention rates (>97.5%) to methyl blue and congo red, while maintaining a very low rejection toward inorganic salts (<2.0%). This work provides a simple and scalable route to defect-minimized MOF composite membranes for high-value solute recovery from saline wastewater.