Switchable superlyophobic PAN@Co-MOF membrane for on-demand emulsion separation and efficient soluble dye degradation

Developing membrane surfaces with double superlyophobicity properties under liquids for different separation applications poses significant challenges in thermodynamics and material science. Switchable superwettability is usually achieved through complex manipulation means and the application of external stimuli such as light, heat, electrical current, and so on. In this study, a reversible superhydrophobic/superoleophobic membrane (PAN@Co-MOF) was fabricated conveniently by in situ growth of Co(Hmim)2 (Co-MOFs) onto the surfaces of electrospun polyacrylonitrile (PAN). The as-prepared PAN@Co-MOF membrane facilitated the selective passage of water or oil in a unidirectional manner, only when water or oil was prewetted, which enabled the efficient separation of oil-in-water (O/W) or water-in-oil (W/O) emulsions on demand. This novel organic and inorganic hybrid material overcame traditional limitations, resulting in a mechanically robust and reusable membrane. Moreover, the PAN@Co-MOF membrane demonstrated the capability to activate peroxymonosulfate (PMS) for efficient dye degradation through interactions of Co-MOF with diverse liquids. Impressively, the O/W emulsion separation flux surpassed 1600 L·m−2·h−1 with chemical oxygen demand (COD) values of the filtrate below 100 mg·L-1, while the W/O emulsion separation flux exceeded 1040 L·m−2·h−1, maintaining the water content of the filtrate under 50 mg·L-1. Furthermore, the degradation efficiency of methylene blue (MB) (50 ppm) achieved a staggering 99.3% within 10 min. This study offers an innovative idea for the development of multifunctional membrane materials with switchable superwettability in the integrated oil–water treatment.