Fish-gill inspired multifunctional nanofibrous membrane for efficient demulsification and pollutant sorption

Importance of multifunctional membranes for efficient purification of contaminated oily wastewater is globally realized due to depleting fresh water sources and environmental pollution. Electrospun superwettable membranes with heterostructures have attracted attention because of their versatile features, high surface area and multifunctionality. Herein, fish gill inspired superhydrophilic nanofibrous membranes of selective wettability were prepared using zeolitic imidazole framework (ZIF-8) decoration. A unique near-gel resin (nGR) emulsion electrospinning was employed to produce core-sheath structured nanofibrous membranes comprised of crosslinked polystyrene (PS) as the core and crosslinked polyvinyl alcohol (PVA) based sheath. An in-situ growth of ZIF-8 over the fibrous membrane's surface ensured retaining membrane's superhydrophilicity and underwater oleophobic behaviour and captured oil droplets to demulsify various oil/water emulsions during separation. ZIF-8 based biomimetic membrane achieved higher emulsion separation efficiency (98.9%) toward surfactant stabilized emulsions as compared to undecorated membrane. The membranes were also developed to attain multifunctionality via variation in ZIF-8 growth process. The membrane was evaluated for emulsion separation under various environmental conditions and its reusability up to 5 separation cycles. The controlled growth of ZIF-8 also facilitated heavy metal ion removal (85% at 100 ppb concentration) along with emulsion separation. The effect of growth loading on sorption capacity was evaluated in different oils and organic solvents. The membrane with high ZIF-8 growth showed excellent sorption capacity (4000%) toward toluene with consistent sorption up to 5 cycles of sorption-desorption. Overall, this study demonstrated a facile strategy to create multifunctional nanofibrous membrane through emulsion electrospinning, which can effectively be used in efficient emulsion separation, heavy metal ion removal and oil sorption.