Synthesis of Core–Shell Inorganic Nanotubes

Abstract New materials and techniques pertaining to the synthesis of inorganic nanotubes have been ever increasing since the initiation of the field in 1992. Recently, WS 2 nanotubes, which are produced now in large amounts, were filled with molten lead iodide salt by a capillary wetting process, resulting in PbI 2 @WS 2 core–shell nanotubes. This work features progress in the synthesis of new core–shell nanotubes, including BiI 3 @WS 2 nanotubes produced in a similar same manner. In addition, two new techniques for obtaining core–shell nanotubes are presented. The first is via electron‐beam irradiation, i.e., in situ synthesis within a transmission electron microscope. This synthesis results in SbI 3 nanotubes, observed either in a hollow core of WS 2 ones (SbI 3 @WS 2 nanotubes), or atop of them (WS 2 @SbI 3 nanotubes). The second technique involves a gaseous phase reaction, where the layered product employs WS 2 nanotubes as nucleation sites. In this case, the MoS 2 layers most often cover the WS 2 nanotube, resulting in WS 2 @MoS 2 core–shell nanotubes. Notably, superstructures of the form MoS 2 @WS 2 @MoS 2 are occasionally obtained. Using a semi‐empirical model, it is shown that the PbI 2 nanotubes become stable within the core of MoS 2 nanotubes only above a critical core diameter of the host (>12 nm); below this diameter the PbI 2 crystallizes as nanowires. These model calculations are in agreement with the current experimental observations, providing further support to the growth mechanism of such core–shell nanotubes.