Carbon Nanotubes as Electrically Active Nanoreactors for Multi-Step Inorganic Synthesis: Sequential Transformations of Molecules to Nanoclusters and Nanoclusters to Nanoribbons

Abstract

In organic synthesis, the composition and structure of products are predetermined by the reaction conditions; however, the synthesis of well-defined inorganic nanostructures often presents a significant challenge yielding non-stoichiometric or polymorphic products. In this study, confinement in the nanoscale cavities of single-walled carbon nanotubes (SWNT) provides a new approach for multi-step inorganic synthesis where sequential chemical transformations take place within the same nanotube. In the first step, SWNT donate electrons to the reactant iodine molecules (I2) transforming them to iodide anions (I -). These then react with metal hexacarbonyls (M(CO)6, M = Mo or W) in the next step yielding anionic nanoclusters [M6I14] 2-, the size and composition of which are strictly dictated by the nanotube cavity, as demonstrated by aberration corrected high resolution transmission electron microscopy (AC-HRTEM), scanning transmission electron microscopy (STEM) and energy dispersive X-ray (EDX) spectroscopy. Atoms in the nanoclusters [M6I14] 2-are arranged in a perfect octahedral geometry and can engage in further chemical reactions within the nanotube, either reacting with each other leading to a new polymeric phase of molybdenum iodide [Mo6I12]n, or with hydrogen sulphide gas giving rise to nanoribbons of molybdenum/tungsten disulphide [MS2]n in the third step of the synthesis. Electron microscopy measurements demonstrate that the products of the multi-step inorganic transformations are precisely controlled by the SWNT nanoreactor, with complementary Raman spectroscopy revealing the remarkable property of SWNT to act as a reservoir of electrons during the chemical transformation. The electron transfer from the hostnanotube to the reacting guest-molecules is essential for stabilising the anionic metal iodide 2 nanoclusters and for their further transformation to metal disulphide nanoribbons synthesised in the nanotubes in high yield.Keywords: Carbon Nanotube, Charge Transfer, Nanoparticle, Nanoreactor, Nanoribbon Single-walled carbon nanotubes (SWNT) are among the most effective and universal containers for molecules. Provided that the internal diameter of the host-nanotube is wider than the critical diameter of the guest-molecule, the insertion of molecules into SWNT is spontaneous and, in some cases, such as fullerenes and their derivatives, irreversible due to the ubiquitous van der Waals forces dominating the host guest interactions between the nanotube and molecules [1]. Fullerenes [2,3] or organic molecules [4][5][6][7][8][9][10] encapsulated in SWNT can then be triggered to react inside the nanotube to form unusual oligomers and polymers [11][12][13], graphene nanoribbons [14][15][16], nanotubes [8,17] or extraordinary molecular nanodiamonds [9]. These examples clearly demonstrate the use of SWNT as nanoscale chemical reactors, where the structure of the macromolecular product can be precisely controlled by spatial confinement of the reactions in the nanotube channel.In contrast to organic molecules,...

Host–Guest Hybrid Redox Materials Self‐Assembled from Polyoxometalates and Single‐Walled Carbon Nanotubes

“…Thermogravimetric analysis (TGA) reveals that the average loadings of the POMs in the SWNTs are 11–16 and 11–30 wt% for {W 12 }@SWNT and {W 18 }@SWNT, respectively (Figure S3, Supporting Information), consistent with the HRTEM data (Figure J). The charge distribution within the hybrid materials was elucidated by Raman spectroscopy using an excitation wavelength of 660 nm (1.88 eV), in resonance with the SWNTs . The G‐band of the SWNT shifted positive by 5.5 and 6.5 cm −1 , respectively, upon formation of {W 12 }@SWNT and {W 18 }@SWNT hybrid materials, confirming that electrons were donated from the SWNT to the POM guests (Figure B) .…”

“…Addition of SWNTs to aqueous solutions of {W 12 } and {W 18 } results in reduction of the POMs, as indicated by the dark blue coloration of the solution ( Figure A) at the solid–liquid interface (reminiscent of the formation of “heteropoly blues”) . A similar type of electron transfer from SWNTs to metal‐polyiodide clusters has been demonstrated to stabilize electron‐accepting molecules in SWNTs . Electron density is transferred from the SWNTs to the POMs, resulting in the electrostatically driven encapsulation of the negatively charged POMs within the now positively charged SWNTs.…”

Assembly of Ring‐Shaped Phosphorus within Carbon Nanotube Nanoreactors

“…[11] Carbon nanotubes are effective as nanoreactors to synthesize and contain nanostructures. [18][19][20][21][22][23][24][25][26][27] Carbon nanotubes also serve as narrow and stable one-dimensional cages that protect the enclosed products from degradation under ambient conditions. Herein, we report experimental evidence for the formation of r-P nanostructures,s elf-assembled inside am ultiwalled carbon nanotube (MWCNT).…”

Encapsulation and Polymerization of White Phosphorus Inside Single‐Wall Carbon Nanotubes

“…Recently,P 4 was successfully encapsulated within supramolecular materials, [12] which may be useful for mitigating dangerous phosphorus spills,o rc onversely,f or controlled release of P 4 into chemical reactions or for heat generation. [14] Herein, we fill SWCNTs with white phosphorus and explore the stability of the resulting structures.Along with the experimental approaches,the possible chain structures arising from phase transformations are evaluated using density functional theory (DFT). [14] Herein, we fill SWCNTs with white phosphorus and explore the stability of the resulting structures.Along with the experimental approaches,the possible chain structures arising from phase transformations are evaluated using density functional theory (DFT).…”

“…[12a] Single-wall carbon nanotubes (SWCNTs) offer an appealing potential encapsulation environment, with an inert, light-weight, cylindrical pore well-matched to the diameter of P 4 molecules.S WCNTs have been filled with aw ide range of materials; [13] molecular species can be stabilized sufficiently to allow direct electron microscopy imaging,i ncluding of simple chemical reactions. [14] Herein, we fill SWCNTs with white phosphorus and explore the stability of the resulting structures.Along with the experimental approaches,the possible chain structures arising from phase transformations are evaluated using density functional theory (DFT).…”