Polyamidoamine Demulsifier-Functionalized Polyvinylidene Fluoride Microfiltration Membrane for Antifouling Oil/Water Emulsion Separation

The treatment of oily wastewater has emerged as a critical environmental issue due to the prevalence of oil spills and the discharge of industrial organic pollutants. However, membrane fouling is a major challenge for conventional separation methods, leading to the decreased efficiency and increased maintenance costs. Single hydrophilic modification offers an opportunity to prevent oil fouling but fails to avoid severe permeate flux decline. Herein, we propose a strategy to integrate demulsification and hydrophilicity to a single membrane via incorporation of the polyamidoamine (PAMAM) demulsifier into the hydrophilic tannic acid (TA)-modified membrane through the Schiff base reaction, aiming to alleviate membrane fouling and flux decline during oil/water emulsion separation. The synergy between demulsification and hydrophilicity establishes an oil-repellent barrier surface to prevent oil droplet adhesion on the membrane surface or being squeezed into the membrane pores. When separating oil/water emulsions, the membranes not only showed high separation efficiency with oil content less than 8 ppm in filtrate but demonstrated outstanding antifouling performance with low flux decline ratio (DRt) of 16% even at the high permeate flux of 3679 L m-2 h-1 bar-1, while showing a flux recovery ratio as high as 99.6%, hard to achieve by traditional hydrophilic membranes. In addition, the effect of surface roughness on the demulsification and antifouling separation performance of membranes was also investigated by introducing SiO2 nanoparticles to create a rougher surface. The TA/SiO2-PAMAM membrane with rougher surface exhibited a higher flux DRt of 28%, while showing better demulsification performance with smaller droplet size (∼0.8 nm) in filtrate. This research paves the way for designing membranes for continuous and stable oil/water emulsion separation.