High-Flux Halloysite Nanotube-Reinforced PVDF Membranes with Zwitterionic Coating for One-Step Separation of Complex...

Industrial oily wastewater containing heavy metal ions threatens ecosystems and human health, and developing high-flux multifunctional membranes for their simultaneous removal is a critical challenge. Herein, a high-flux multifunctional polyvinylidene fluoride composite membrane, HNTs/PVDF@PDA/PSBMA, was fabricated by blending halloysite nanotubes (HNTs) into the PVDF matrix via nonsolvent-induced phase separation (NIPS), followed by surface modification with a polydopamine (PDA)/poly-(sulfobetaine methacrylate) (PSBMA) zwitterionic coating. HNTs introduced one-dimensional water channels via inner/outer surface hydroxyl groups to boost water flux and provide active sites for heavy metal adsorption, while the PDA/PSBMA coating formed a robust hydration layer through electrostatic interactions with water molecules, endowing excellent antifouling and underwater oleophobicity as well as additional heavy metal adsorption capacity. Under optimized conditions (1.0 wt % HNTs, 2.0 mg/mL PSBMA), the HNTs/PVDF@PDA/PSBMA membrane exhibited a drastically enhanced water flux of 528.6 L·m^-2·h^-1·bar^-1 for oil-in-water emulsions, representing a 455.2% increase compared with the pristine PVDF membrane (95.2 L·m^-2·h^-1·bar^-1), and achieved an oil-water separation efficiency of 97.8%. For gravity-driven one-step treatment of oil-in-water emulsions containing 10 ppm heavy metal ions, the membrane maintained an oil-water separation efficiency of 97.5% and achieved a Cu²⁺ removal efficiency of 83.3%, with superior chemical stability, cyclic reusability, and mechanical reinforcement. This work establishes a scalable strategy for high-flux multifunctional membrane fabrication to enable efficient complex oily wastewater treatment.