Abstract
The great potential of nanoporous membranes for water filtration and chemical separation has been challenged by the trade-off between selectivity and permeability. Here we report on nanoporous polymer membranes with an excellent balance between selectivity and permeability of ions. Our membranes are fabricated by irradiating 2-μm-thick polyethylene terephthalate Lumirror® films with GeV heavy ions followed by ultraviolet exposure. These membranes show a high transport rate of K+ ions of up to 14 mol h−1 m−2 and a selectivity of alkali metal ions over heavy metal ions of >500. Combining transport experiments and molecular dynamics simulations with a polymeric nanopore model, we demonstrate that the high permeability is attributable to the presence of nanopores with a radius of ~0.5 nm and a density of up to 5 × 1010 cm−2, and the selectivity is ascribed to the interaction between the partially dehydrated ions and the negatively charged nanopore wall.
Highlights
The great potential of nanoporous membranes for water filtration and chemical separation has been challenged by the trade-off between selectivity and permeability
We have reported on polymer membranes demonstrating extremely high ionic selectivity, e.g., alkali metal ions over heavy metal ions of 104
The application of the polyethylene terephthalate (PET) Hostaphan® films seems to be limited because their transport rates of K+ ions are only 2.0 × 10−3 mol h−1 m−2
Summary
The great potential of nanoporous membranes for water filtration and chemical separation has been challenged by the trade-off between selectivity and permeability. Instead of using chemical etching of these tracks to form pores (as typically applied in the track-etching technique), sufficient extended ultraviolet (UV) exposure was applied ( this fabrication method is named as the track-UV technique) Despite their excellent selectivity, the application of the PET Hostaphan® films seems to be limited because their transport rates of K+ ions are only 2.0 × 10−3 mol h−1 m−2. Based on molecular dynamics (MD) simulations and transport measurements, this improved performance is ascribed to several factors: the permeability is significantly enhanced mainly due to an increased pore radius to ~0.5 nm; the fine selectivity is maintained due to the electrostatic interaction between the charged pore walls and ions, coupled with the partial dehydration effect This artificial nanopore system marks a major advance to compete with its natural counterpart and shows great potential for industrial applications where ultrafast ionic sieves are required
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