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

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.