AgNPs-thiols modified PVDF electrospun nanofiber membrane with a highly rough and pH-responsive surface for controllable oil/water separation

Abstract

To develop a novel membrane with controllable wettability in response to external stimuli for intelligent oil/water separation is always in urgent demand. In this study, a pH-responsive nanofibrous membrane was prepared through the step-by-step modification of polyvinylidene fluoride (PVDF) electrospun nanofiber membrane, including mussel-inspired self-polymerization of polydopamine (PDA), immobilization of silver nanoparticles (AgNPs) and self-assembly of thiols. A rough membrane surface could be formed by the loading of AgNPs, and the subsequent introduction of HS(CH2)11CH3/HS(CH2)10COOH via metal-thiol coordination could endow the membrane with pH-responsive wettability. The surface of the membrane was able to quickly and reversely switch between superhydrophobicity and superhydrophilicity through simply applying pH stimulus at pH 7 and 13, respectively. The membrane can be applied for separating multiphase oil/water mixtures, achieving separation efficiency of over 99.2% for light oil/water mixture and 96.5% for heavy oil/water mixture with a stable flux of around 2500 L/m2·h for water and 11,000 L/m2·h for oil over the 10-cycle separation process. Meanwhile, the membrane exhibited separation efficiency of higher than 99% for all the tested oil-in-water emulsions, and the water flux of the membrane could be effectively recovered by water rinsing. Moreover, the membrane demonstrated a good structural stability against rigorous mechanical abrasion. The pH-responsive membrane could be potentially applied for smart and energy-saving separation and recycle of oil or water from oily wastewater.