Charge translucency and ion transport in 1D SWCNT-BN van der Waals heterostructures*

Atomically thin graphene is known to be optically transparent, as well as partially translucent to van der Waals and electrostatic interactions at interfaces, which suggests that the fluidic properties of graphitic nanochannels may be modulated by the environment around the channel.  Here, we describe aqueous ion-transport studies in membranes fabricated from 2nm-diameter nanotube heterostructures consisting of single-wall carbon nanotubes that are CVD-coated on the outside with boron nitride. In aqueous electrolytes, ion conductance studies reveal that the vertically aligned SWCNT-BN nanotube arrays showed enhanced cation selectivity compared to the original SWCNTs.  The results suggest that the graphene inner surface of the heterostructures is partially transparent to charge regulation at the BN-graphene-water interface, resulting in higher surface charge and thus ion selectivity in an aqueous solution.  The slip length in the SWCNTs may also be affected by the outer BN coating.  These vertically aligned SWCNT-BN membranes enable the fundamental study of the effects of atomic translucency on transport in 1D nanotube heterostructures, as well as the exploration of technological applications like osmotic energy harvesting and separations.