Anomalous transport in angstrom-sized membranes with exceptional water flow rates and dye/salt rejections

Abstract

Fluidic channels with physical dimensions approaching molecular sizes are crucial for novel desalination, chemical separation, and sensing technologies. However, fabrication of precisely controlled fluidic channels in the angstrom size is extremely challenging. This, along with our limited understanding of nanofluidic transport, hinders practical applications. Here, we fabricated high-quality salt-intercalated vermiculite membranes with channel sizes of ∼3-5 Å, highly dependent on intercalant. Unlike pristine samples, the salt-intercalated membranes are highly stable in water. We tested several such membranes, of which 0.6 μm thick membranes showed dye rejection efficiencies >98% with exceptionally high water permeance of 5400 L m-2 h-1 bar-1 at a differential pressure of 0.9 bar. Interestingly, the same membrane also rejected NaCl ions, with efficiencies of ∼95%. Our highly confined channels exhibit sub-linear ionic conductance related to hydration sizes, steric exclusion, K+ mobility enhancement, and conductance saturation at concentrations ≤10 mM. This makes highly confined channels interesting for both fundamental science and applications.