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 3-5 Angstrom, 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 micron thick membranes showed dye rejection efficiencies greater than 98 percent 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 percent. Our highly confined channels exhibit sub-linear ionic conductance related to hydration sizes, steric exclusion, K+ mobility enhancement, and conductance saturation at concentrations less than or equal to 10 mM. This makes highly confined channels interesting for both fundamental science and applications.