Bioinspired nanobubble water channel membranes for ultrafast osmosis desalination

Abstract

Biological water channels (BWCs) and artificial water channels (AWCs) exhibit standout water-to-ion selectivity. However, difficult membrane integration threatened their desalination application. Inspired by biological cell membranes, an ultrafast osmosis desalination membrane is fabricated with air nanobubbles adhered on fluorinated carbon nanotubes (ANBs-FCNTs) interlayer sandwiched between polyacrylonitrile (PAN) nanofiber layers. Water transport through nanobubble water channel is accelerated by nanobubble gating for selective transport and nanobubble-lubricated water channels for low friction, which was confirmed by varying combination modes of forward osmosis (FO) and membrane distillation (MD). Superior salt rejection is achieved by efficient nanobubble gating, resulting from the combined action by size screening, fast surface slip, electrostatic shielding and sufficient adsorption of ANBs-FCNTs interlayer. In nanofluidic diode membrane concatenation model, multistep capillary force provides enhanced water flux, whereas multi-staged concatenation layers offer more barrier gating for the ion's diffusion, thus resulting in higher permselectivity. The bioinspired nanobubble membranes can achieve high water flux (479.8 L m−2 h−1), high rejection (>95%) to solutes and low reverse salt flux (0.686 g m−2 h−1) under robust and continuous cross flow operation, which outperformed the state-of-the-art forward osmosis membranes. The electrospinning and deposition technique allows for scalable membrane preparation for desalination, resources and energy production.