Ultrathin fluorinated self-cleaning membranes via coordination-driven metal-bridging assembly for water purification

Abstract

Amphiphobic fluorine materials hold great promise for fabricating self-cleaning membranes. However, the severely impeded water transport in hydrophobic fluorine-based membranes and the weak interaction with the substrate of the low-surface-energy fluorine materials represent two major obstacles for efficient water purification. Herein, we design an ultrathin fluorine-based membrane via coordination-driven metal-bridging assembly. An Fe³⁺-rich metal–organic layer is constructed on a porous substrate by coordination between polyphosphate ligands and Fe³⁺ ions, accompanied by the assembly of perfluorosulfonate polymer ligands (Nafion®) via the bridging effect of Fe³⁺ ions for the metal-bridging fluorine-based membrane (MBFM). By virtue of the flexible modulation of Fe³⁺ and unique self-assembly of Nafion®, a defect-free 58 nm-thick MBFM featuring an ultrahigh surface fluorine content (47.6 at%) and underwater superoleophobicity (∼160°) is achieved, which displays a superior water permeance of 125.2 L m⁻² h⁻¹ bar⁻¹ (2–10 times higher than that of state-of-the-art membranes with dye rejections above 90%) and versatile resistance towards both spreading and non-spreading foulants (flux decline ratios below 8%). This metal-bridging assembly strategy may shed light on advanced membrane fabrication from rationally designed ligands and functional moieties.