Preparation and Oil-Water Separation Performance of PVDF Membranes Co-modified with Dopamine and Polyvinyl Alcohol
The increasing discharge of oily wastewater from oil extraction and anthropogenic activities necessitates the development of efficient oil-water separation technologies to safeguard ecological and environmental safety and ensure sustainable resource utilization. Membrane separation technology, owing to its high efficiency and operational convenience, has emerged as a viable solution for treating oily wastewater. To enhance the hydrophilic and oleophobic properties of hydrophobic separation membranes, this study employed polyvinylidene fluoride (PVDF) hydrophobic microfiltration membranes with robust mechanical properties as substrates. Through a biomimetic coating approach, dopamine (DA) was first polymerized to form polydopamine (PDA) on the membrane surface, which subsequently reacted with polyvinyl alcohol (PVA) to construct a dense hydrophilic layer, yielding modified membranes with hydrophilic/oleophobic surface characteristics. The morphology and chemical composition of the modified membranes were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Oil-water separation performance was comprehensively evaluated by measuring water contact angle, underwater oil contact angle, emulsion flux, and oil rejection. Under optimal conditions, the modified membrane M3 exhibited a pure water flux of 4893.2 ± 70.2 L/(m²·h), an emulsion flux of 2138.1 ± 29.4 L/(m²·h) for toluene-in-water emulsion, and an oil rejection of 98.5% ± 0.1%. Simulated fouling and regeneration tests using bovine serum albumin (BSA) solution demonstrated a flux recovery rate of 92.0% for M3, indicating excellent antifouling performance. Immersion tests in acid, alkali, and salt solutions confirmed the modified membrane's outstanding chemical stability. The designed PVDF modified membrane offers advantages of simplicity, environmental friendliness, and high efficiency, showing significant application potential in oil-water separation and providing a novel strategy for membrane development.