Preparation of a PVDF–PDA–DETA@PVP@HNT membrane for high efficiency oil–water emulsion separation

Abstract

Membrane technology is considered to be an effective method for the treatment of oily wastewater. However, membrane fouling caused by oil adsorption seriously hinders its practical application in oil–water separation. In this study, membrane separation technology was combined with surface modification technology. A commercial hydrophobic polyvinylidene fluoride (PVDF) membrane was used as the base membrane material. Polydopamine (PDA) with adhesion was introduced into the PVDF membrane, and DETA was modified on the PVDF membrane by a Schiff base reaction between PDA and diethylenetriamine (DETA). On this basis, polyvinylpyrrolidone (PVP) with high hydrophilicity and halloysite nanotubes (HNTs) with a rough porous structure were introduced, and a PVDF–PDA–DETA@PVP@HNT membrane with superhydrophilicity–underwater superoleophobicity was successfully prepared. Then, the effects of different amounts of HNTs on the surface morphology and chemical composition of the films were studied by scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. When the addition amount of HNTs was 0.05 g, the membrane showed high separation efficiency (more than 99%) and separation flux (2268–2406 L m⁻² h⁻¹) for various oil-in-water emulsions. After 8 cycles, the emulsion separation efficiency was higher than 93%. After soaking in different pH solutions for 12 h, the water contact angle (WCA) was 0° and the underwater oil contact angle (UOCA) was greater than 150°, showing excellent chemical stability. This strategy has the advantages of convenient preparation, economy and high efficiency, and has broad application potential in industrial oily wastewater.