Elevating the selectivity of layer-by-layer membranes by in situ bioinspired mineralization

• Ultrathin hybrid membranes through LbL assembly and bioinspired mineralization.
• Silica was incorporated into membranes via in situ PEI-induced mineralization.
• The thickness of the hybrid membranes was less than 300 nm.
• The selectivity of LbL membranes was increased by silica nanoparticles.

Layer-by-layer (LbL) assembly is a common method for controlled fabrication of ultrathin membranes, while bioinspired mineralization is a novel method for controlled synthesis of well-dispersed inorganic particles in hybrid membranes. Here, bioinspired mineralization was integrated with LbL assembly to prepare ultrathin polymer-inorganic hybrid membranes by in situ precipitating silica nanoparticles into alternatively assembled polyethyleneimine (PEI) and sodium alginate (Alg). The membrane thickness was manipulated by varying the bilayer numbers. And the synthesized silica nanoparticles were revealed by the surface morphology, Si mapping and chemical properties of the membranes. The surface hydrophilicity, diffusion selectivity and the fractional free volume of the hybrid membranes were all enhanced by the incorporation of silica nanoparticles. As a result, the ultrathin hybrid membrane showed elevated selectivity (2.66-fold higher than that of control membrane) with almost unchanged permeability when used for pervaporation dehydration of 90 wt% ethanol aqueous solution as a model mixture. This study indicates the great potential for overcoming the tradeoff hurdle between permeability and selectivity by the synergy of LbL assembly and bioinspired mineralization to fabricate ultrathin hybrid membranes.

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