One- and Two-Dimensional Inorganic Crystals inside Inorganic Nanotubes

Various inorganic salts can be encapsulated inside the comparatively narrow (0.8-2 nm) hollow core of single-walled carbon nanotubes (SWNTs) by molten phase capillary wetting. A new synthetic strategy is presented allowing the formation of one dimensional (1D) inorganic crystals or core-shell nanotubular structures by using multiwall WS2 nanotubes as host templates. Molten phase wetting with CsI results in the formation of 1D crystal structures inside WS2 nanocapillaries with a Moire pattern. The relatively large diameter of the WS2 nanotube (with inner and outer diameters of ca. 10 and 20 nm, respectively), allows a conformal folding of the guest PbI2 layers (PbI2@WS2 core-shell nanotubes) on the interior wall of the WS2 nanotube-template, thus leading to relatively defect-free core-shell inorganic nanotubular structures, which have not been previously observed within carbon nanotubes (CNTs). Core-shell WS2@MoS2 nanotubes can be obtained by the gas-phase reaction of MoCl5 with sulfur in the presence of WS2 nanotubes. The mechanism of imbibition/solidification of the molten salt into the hollow cores of MoS2 nanotubes has been studied by molecular dynamics simulations, showing major differences between layered compounds and those with quasi-isotropic structure. Theoretical considerations also show the conditions for the stability of such core-shell 1D nanostructures. These new strategies can open up many possibilities for the synthesis of new nanotubular structures.