Ion and Hydrodynamic Translucency in 1D van der Waals Heterostructured BN-SWCNTs

An unresolved challenge in nanofluidics is tuning ion selectivity and hydrodynamic transport for pores with diameters larger than a nanometer. In contrast to conventional strategies that focus on changing surface functionalization or confinement degree by varying the radial dimension of the pores, we explore a new approach for manipulating ion selectivity and hydrodynamic flow enhancement by externally coating single-wall carbon nanotubes (SWCNTs) with a few layers of hexagonal boron nitride (h-BN). For the van der Waals heterostructured BN-SWCNT, we observed a 50% increase in cation selectivity for K⁺ versus Cl^- compared to pristine SWCNTs of the same diameter, while hydrodynamic slip lengths decreased by more than an order of magnitude. These results suggest that the single-layer-graphene inner surface may be translucent to charge-regulation and hydrodynamic-slip effects arising from h-BN on the outside of the SWCNT. As a consequence, the choice of the matrix material may significantly influence the transport properties of SWCNT membranes. Such 1D heterostructured nanotubes could serve as synthetic platforms with tunable properties for exploring novel nanofluidic phenomena and their potential applications for separations, power generation, and water filtration or desalination.