Encapsulation of two-dimensional materials inside carbon nanotubes: Towards an enhanced synthesis of single-layered metal halides

Abstract

The unique properties of two-dimensional (2D) nanomaterials make them highly attractive for a wide range of applications. As a consequence, several top-down and bottom up approaches are being explored to isolate or synthesize single-layers of 2D materials in a reliable manner. Here we report on the synthesis of individual layers of several 2D van der Waals solids, namely CeI3, CeCl3, TbCl3 and ZnI2 by templateassisted growth using carbon nanotubes as directing agents, thus proving the versatility of this approach. Once confined, the metal halides can adopt different structures including single-layered metal halide nanotubes, which formation is greatly enhanced by increasing the temperature of synthesis. This opens up a new strategy for the isolation of individual layers of a wide variety of metal halides, a family of 2D materials that has been barely explored.

Selective Laser-Assisted Synthesis of Tubular van der Waals Heterostructures of Single-Layered PbI2 within Carbon Nanotubes Exhibiting Carrier Photogeneration

“…45,46 A higher amount of single-walled nanotubes within CNTs has been recently reported upon increasing the temperature of annealing, from 21.4 % at 475 ºC to 64.9 % at 1000 ºC, for the van der Waals solid ZnI 2 . 18 Nevertheless, not only the production yield is still lower than the one reported here (for PbI 2 using laser) but also much longer tubular structures are obtained by laser irradiation.…”

“…17 The synthetic strategy proved to be versatile but requires the use of high temperatures for prolonged periods of time. Furthermore, even under the best synthetic conditions, a large fraction (at least 35 %) of other nanostructures are formed in the interior of the carbon nanotubes 18 which could strongly influence the properties. Here we present an ultrafast, energy efficient and easily scalable approach that allows the selective synthesis of single-walled lead iodide nanotubes coating the inner walls of carbon nanotubes, thus forming cylindrical van der Waals heterostructures.…”

An overview of the recent advances in inorganic nanotubes

“…7 (a-b)). 68,[70][71][72] This solvent-free high temperature approach was based on the use of the inner cavities of CNTs as hosting templates. Thus, the growth of lead diiodide single wall nanotubes (SWNTs), with diameters ranging from 3.5 to 7.5 nm, as well as nanowires, were reported, see Fig.…”

Structure of inorganic nanocrystals confined within carbon nanotubes

“…A large variety of materials have been shown to also coat the inner cavities of MWCNT forming single-layered inorganic nanotubes (SLINTs), namely PbI 2 [57,58], ZnI 2 [58,59], CeCl 3 [59], CeI 3 [59], TbCl 3 [59], GdCl 3 [29], SmCl 3 [29], BiI 3 [60], GdI 3 [61] and BiCl 3 [62]. The role that the temperature of treatment has on the grown nanostructures was investigated using ZnI 2 and MWCNTs [59]. It was observed that the formation of SLINTs could be favored by increasing the temperature of treatments, reaching a selectivity of ca.…”