Bendable poly(vinylidene fluoride)/polydopamine/β-cyclodextrin composite electrospun membranes for highly efficient and bidirectional adsorption of cation and anion dyes from aqueous media

Electrospun fibrous membranes have potential application prospects in various adsorbents. However, challenges remain in the development of flexible adsorbents with multiple adsorption ability and improved efficiency. In this study, we design and fabricate a new class of composite electrospun membranes poly(vinylidene fluoride)/ polydopamine/beta-cyclodextrin (PVDF/PDA/beta-CD) by triggering the self-polymerization of dopamine onto the surface of PVDF electrospun fibers to form PDA coating, and subsequently binding beta-CD molecules on the fibers surface via hydrogen bonding as the result of hydroxyl groups on beta-CD and abundant catechol groups of PDA. The PVDF/PDA/beta-CD fibers exhibit core-shell structure where PVDF as the supporting core component and PDA/ beta-CD layer as the shell with many functional groups to be capable of adsorbing cationic and anionic dye molecules. Accordingly, the composite membranes possess highly efficient adsorption performance toward methylene blue (MB) and phenolphthalein (PHP). Furthermore, the adsorption behaviors for the two dyes fit well with the pseudo second-order kinetic model. And the electrostatic attraction and 7C-7C stacking mostly promote the adsorption of MB whereas the host-guest inclusion complexation and hydrogen bonding are more likely to favor the PHP adsorption. Most importantly, all composite membranes can be bendable, and display excellent mechanical performances, which endow these membranes easy to operate in practical applications, such as filtration, separation and purification purposes. Our developed method provides a new avenue for electrospun membrane to simultaneously achieve robust mechanical properties and multiple contaminants efficient removal.