Underwater superoleophobic HKUST-1/PDA@SM membrane with excellent stability and anti-fouling performance for oil-in-water emulsion separation

Owing to having small particle size, complex system and high degree of emulsification, traditional separation methods have shown difficulties to achieve good separation effect of oil-water emulsion system. Despite this truth, the rapid development of membrane separation technology has indicated an excellent separation performance. However, the membrane stability and membrane fouling are still prominent problems, and the research on demulsification-separation process is not in-depth, which restricts the further development of membrane separation technology for practical industrial applications. Therefore, in present work, an underwater superoleophobic HKUST-1/PDA@SM membrane was prepared via the combination of step-by-step deposition and secondary growth method. The as-prepared membrane showed an excellent anti-fouling performance with flux recovery ratio of over 95%. The HKUST-1/PDA@SM membrane could accomplish the selective separation of surfactant-free and surfactant-stabilized emulsions under gravity-driven condition. Further, the as-prepared membrane presented an excellent mechanical stability, chemical stability, thermal stability, and recyclability. More importantly, the analysis of membrane fouling mechanism disclosed that the most fundamental reason for membrane fouling was the blockage of membrane pores. Furthermore, we firstly proposed the assumption of the migration-transformation of emulsifier in the emulsion separation process, and then it was verified that most of emulsifier entered into the filtrate. Finally, the membrane demulsification-separation mechanism was discussed precisely. Overall, HKUST-1/PDA@SM membrane with excellent stability and anti-fouling performance has a broad practical application prospect for oil-water emulsion separation.