Ultrafast molecular separation through all-biomaterial membranes with a hierarchical configuration and mechanism study

Traditional nanofiltration membranes allow high rejection of low molecular weight organic matter, yet suffer from a low flux and a high operation pressure, and they pose an environmental concern because they are made of petroleum-based polymers. Herein, a novel environmentally friendly filter membrane for ultrafast molecular separation has been developed using natural and artificial biomaterials as building units. Cellulose micron fibers, a natural biopolymer, serve as a stable substrate for the growth of hydroxyapatite (HAP) nanowire bunches, which are the main inorganic components of bones and teeth. The vertically aligned HAP nanowire bunches provide abundant nanoscale surfaces and confinement space for the attachment of dopamine and subsequently self-polymerization into polydopamine (PDA) sub-micron particles, which are a melanin-like bioactive polymer. On the one hand, the as-built micro-nano hierarchical configuration enables ultrahigh permeance (>6000 L m(-2) h(-1) bar(-1)) through the filter membrane at a low pressure (62 mbar). On the other hand, molecular dynamics simulations reveal that synergy between multiple molecular interactions of HAP and PDA contributes to the universal separation of different organic pollutants from water (i.e., cationic and anionic dyes and antibiotics) at a high removal rate of > 97 %. Overall, this work ingeniously uses biocompatible biomaterials to build a hierarchical filter membrane, thereby enabling ultrafast and efficient molecular separation.