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,...
Catalysis of chemical reactions by nanosized clusters of transition metals holds the key to the provision of sustainable energy and materials. However, the atomistic behaviour of nanocatalysts still remains largely unknown due to uncertainties associated with the highly labile metal nanoclusters changing their structure during the reaction. In this study, we reveal and explore reactions of nm-sized clusters of 14 technologically important metals in carbon nano test tubes using time-series imaging by atomically-resolved transmission electron microscopy (TEM), employing the electron beam simultaneously as an imaging tool and stimulus of the reactions. Defect formation in nanotubes and growth of new structures promoted by metal nanoclusters enable the ranking of the different metals both in order of their bonding with carbon and their catalytic activity, showing significant variation across the Periodic Table of Elements. Metal nanoclusters exhibit complex dynamics shedding light on atomistic workings of nanocatalysts, with key features mirroring heterogeneous catalysis.
Carbonyl complexes of transition metals (M x (CO) y , where x ¼ 1, 2, or 3 and y ¼ 6, 10, or 12 for M ¼ W, Re, or Os, respectively) inserted into single walled carbon nanotubes (SWNT, diameter 1.5 nm) transform into metallic nanoparticles (MNPs) under heat treatment or electron beam irradiation. The host-nanotube acts as an efficient template, controlling the growth of MNPs to $1 nm in diameter. The only co-product of nanoparticle formation, carbon monoxide (CO) gas, creates pockets of high pressure between nanoparticles, thus preventing their collision and coalescence into larger structures. As a result, the MNPs stay largely spheroidal in shape and are uniformly distributed throughout the entire length of the SWNT. Despite their extremely small size (on average each MNP contains 30-90 atoms) and no protection of their surface by a capping layer of molecules, the metallic nanoparticles encapsulated in nanotubes are very stable under ambient conditions and even at elevated temperatures. Aberration-corrected high-resolution transmission electron microscopy reveals the crystalline nature of the MNPs, probes their interactions with the nanotube interior and illustrates the complex dynamics of confined MNPs in real-time and direct-space.
For carbon nanotubes filled with fullerenes (''peapods''), it is a key issue to find an analytical method that distinguishes the molecules inside the nanotube from those adsorbed on its surface. High-resolution transmission electron microscopy (HRTEM) detects both encapsulated and adsorbed molecules which are large enough (e.g., fullerenes), but being a localprobe method, it cannot be applied to large amounts of sample. In Raman spectroscopy, the empirical rules for line shifts and splitting are nanotube-type dependent and often ambiguous. We prepared C 60 peapods by nano-extraction using supercritical CO 2 as a solvent, and subsequently removed the adsorbed fullerene molecules by washing the samples. We analyzed the samples by the combination of HRTEM, Raman, and midinfrared attenuated total reflectance (MIR-ATR) spectroscopy. Although the TEM images proved that the nanotubes were filled with fullerenes, we did not observe any shift in the fullerene's A g (2) Raman mode compared to C 60 crystals. ATR spectra, on the other hand, were found to detect only the adsorbed molecules. Therefore, the combination of the two methods provide good basis for determining the success of nanotube filling by spectroscopy alone.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.