Ecofriendly hydrophilic modification of microfiltration membranes using pyrogallol/ε-polylysine

Abstract

Microfiltration (MF) membranes need to be hydrophilized to enhance their fouling resistance and applicability. Previous modification strategies are somewhat ineffective and rely on harmful synthetic chemicals. Here, we propose a versatile and ecofriendly strategy to hydrophilize MF membranes via simple coating with the natural compounds, pyrogallol (PG) and ε-polylysine (EPL). The PG/EPL aqueous coating solution produced crosslinked macromolecular PG/EPL complexes via the auto-oxidation of PG and its subsequent reactions with numerous EPL amines. The PG/EPL complexes were densely coated on MF membranes via collective hydrophobic interactions between their abundant PG moieties and membrane surfaces, achieving the excellent hydrodynamic and pH stabilities of the PG/EPL coating. The PG/EPL coating also significantly and uniformly improved the hydrophilicity of the poly(vinylidene fluoride) (PVDF) membrane with no distinct deformation of the membrane pore structure. Hence, the PG/EPL-coated PVDF membrane exhibited remarkably higher organic fouling resistance and water permeance (∼22% enhancement) than its pristine control. Furthermore, the PG/EPL-coated PVDF membrane demonstrated dramatic improvements in oil–water separation (∼27% higher oil rejection) and oil antifouling performance compared with its pristine counterpart. The PG/EPL coating was further extended to hydrophilize other polytetrafluoroethylene and polyethylene MF membranes. The proposed coating strategy provides a versatile and ecofriendly platform for hydrophilizing various membranes.