  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.
