Dual-MOF Janus Nanofiber Membrane for Switchable Oil/Water Separation and Heavy Metal Removal

Nanofiber membrane separation technology is crucial in the field of oily wastewater treatment. However, conventional separation membranes typically focus solely on oil–water separation or the removal of a single pollutant, making it difficult to achieve efficient oil–water separation while simultaneously and effectively removing coexisting heavy metal ions. This limitation constrains their application potential for purifying complex industrial wastewater. To address the key bottlenecks of conventional membranes, namely low flux and poor antifouling performance, this study proposes a PVDF@MOF-303/PVDF@ZIF-67 (PMPZ) Janus composite membrane with dual-functionality for switchable oil/water separation and heavy metal adsorption. The membrane is constructed by forming a lipophilic/hydrophobic nanofibrous base layer of ZIF-67-modified PVDF@ZIF-67 (PZ) via electrospinning and seed-assisted growth, and subsequently creating a fluffy, superhydrophilic/underwater superoleophobic layer of MOF-303-loaded PVDF@MOF-303 (PM) via air-spray spinning and an in situ growth technique. These two distinct layers are then integrated through ultrasonic bonding to form the final bilayer Janus structure. The resulting PMPZ Janus membrane achieves mode switching by flipping its orientation, enabling gravity-driven separation of various oil/water mixtures and emulsions with high flux (oil flux up to 9500 ± 200 L m–2 h–1 , water flux up to 7400 ± 300 L m–2 h–1) and excellent separation efficiency (>99.3 ± 0.1%). More importantly, the PM layer of the composite membrane exhibits outstanding heavy metal adsorption capacity (e.g., for Cu2+ and Ni2+), achieving an adsorption efficiency reached 82.7 ± 0.5% when removing heavy metal ions from simulated oily wastewater. This composite membrane, which integrates efficient separation, switchable operation, and synchronous heavy metal removal, provides a highly promising solution for treating oily wastewater with complex compositions.