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.

Automated summary

Due to the small particle size, complex system and high degree of emulsification, traditional separation methods face difficulties in achieving effective oil-water emulsion separation. However, the rapid development of membrane separation technology has shown excellent separation performance. Yet, membrane stability and fouling remain prominent challenges, and the research on demulsification-separation process is insufficient, limiting the practical application of membrane separation technology. In this study, an underwater superoleophobic HKUST-1/PDA@SM membrane was developed using step-by-step deposition and secondary growth method. The membrane demonstrated outstanding anti-fouling performance with a flux recovery ratio of over 95%. It achieved selective separation of surfactant-free and surfactant-stabilized emulsions under gravity-driven conditions. Additionally, the membrane exhibited excellent mechanical stability, chemical stability, thermal stability, and recyclability. The analysis of membrane fouling mechanism revealed membrane pore blockage as the fundamental reason for fouling. Moreover, the migration-transformation of emulsifier in the separation process was proposed, and it was confirmed that most emulsifier entered the filtrate. The demulsification-separation mechanism of the membrane was discussed in detail. Overall, the HKUST-1/PDA@SM membrane with excellent stability and anti-fouling performance holds great potential for practical oil-water emulsion separation.