Fouling-resistant robust membranes via electrostatic complexation for water purification

Abstract

Abstract Membrane-based separation provides an energetically efficient and environmentally benign solution to water purification. Biomimetic self-assembled membranes affording full-aqueous-phase membrane fabrication built on underwater bioadhesion create a new paradigm to green and controllable membrane fabrication, but currently are obstructed by fouling and stability hurdles. Inspired by the chemical features of charged cement proteins of sandcastle worm, we propose an electrostatic-driven complexation method to fabricate fouling-resistant robust membranes. Phosphorylated polyanion, quaternized polycation and perfluorinated sulfonic acid polyanion are successively assembled onto the porous substrate to obtain electrostatic-complexed fluorinated membranes (ECFMs), where quaternized cellulose serves as a bridging polyelectrolyte to induce and coordinate electrostatic complexation. Temporal complexation generates 84-nm-thick membranes with precisely controlled physicochemical structure, surface energy and spatial interaction with foulants, harvesting ultrahigh water permeance of 93.3 L m−2 h−1 bar−1 with organic dyes (>450 Da) removal over 90.0%, and high fouling resistance ensuring persistently high production of purified water. Unlike the amino protein of traditional bio-cement whose positive charge strongly relies on pH, the environmentally-independent chargeability of quaternary ammonium and hydrophobic fluorine segment synergistically renders the membranes superior adaptability towards various underwater conditions for dozens or hundreds of days.