The Chemical Structure of Carbon Nanothreads Analyzed by Advanced Solid-State NMR

Abstract

Carbon nanothreads are a new type of one-dimensional sp-carbon nanomaterial formed by slow compression and decompression of benzene. We report characterization of the chemical structure of C-enriched nanothreads by advanced quantitative, selective, and two-dimensional solid-state nuclear magnetic resonance (NMR) experiments complemented by infrared (IR) spectroscopy. The width of the NMR spectral peaks suggests that the nanothread reaction products are much more organized than amorphous carbon. In addition, there is no evidence from NMR of a second phase such as amorphous mixed sp/sp-carbon. Spectral editing reveals that almost all carbon atoms are bonded to one hydrogen atom, unlike in amorphous carbon but as is expected for enumerated nanothread structures. Characterization of the local bonding structure confirms the presence of pure fully saturated "degree-6" carbon nanothreads previously deduced on the basis of crystal packing considerations from diffraction and transmission electron microscopy. These fully saturated threads comprise between 20% and 45% of the sample. Furthermore, C-C spin exchange experiments indicate that the length of the fully saturated regions of the threads exceeds 2.5 nm. Two-dimensional C-C NMR spectra showing bonding between chemically nonequivalent sites rule out enumerated single-site thread structures such as polytwistane or tube (3,0) but are consistent with multisite degree-6 nanothreads. Approximately a third of the carbon is in "degree-4" nanothreads with isolated double bonds. The presence of doubly unsaturated degree-2 benzene polymers can be ruled out on the basis of C-C NMR with spin exchange rate constants tuned by rotational resonance and H decoupling. A small fraction of the sample consists of aromatic rings within the threads that link sections with mostly saturated bonding. NMR provides the detailed bonding information necessary to refine solid-state organic synthesis techniques to produce pure degree-6 or degree-4 carbon nanothreads.

Local Structure and Bonding of Carbon Nanothreads Probed by High-Resolution Transmission Electron Microscopy

“…The interplanar spacings of the first-order reflections in SAED patterns are 5.7 ± 0.1 Å, which is consistent with the spacings predicted for several candidate degree-6 nanothread structures ( Figures S2-S5), when accounting for thermal expansion and beam-induced dilation of the lattice; these include the structures favored by a detailed solid-state NMR analysis. [26][27] The other reflections in Figure 4a index close to the Figure 1. Nanothread Carbon K-edge Electron Energy−Loss Spectrum.…”

“…An amorphous phase is not evident in the electron diffraction patterns nor in the NMR spectra. 26 In contrast, disregistry in nanothread packing should give a diffuse background that follows the overall lattice symmetry, as is observed for adamantane and C 60 . 42 Extensive diffraction simulations along [0001] were performed each with a single thread type within a supercell large enough to capture some of the effects of disregistry, shown in Figures S6−S8 plus one illustrative case in Figure 4b and Figure 4c.…”

High density mechanical energy storage with carbon nanothread bundle

“…6). Increasing the filament number further leads to a much larger coil radius for the outermost filaments, which results in a more rapid increase in the tensile strain (as seen in bundle- 19). In comparison, the compressive strain exhibits a gradual increase for all nanothread-A bundles.…”

“…In 2015, a class of one-dimensional (1D) carbon nanostructure -the carbon nanothread-was reported 18 . Although experimental efforts are still ongoing to characterize the atomic structures of carbon nanothreads 19,20 , first-principle calculations have systematically enumerated the potential configuration of carbon nanothreads, including the fully saturated (or degree-6) and partially saturated (or degree-4) structures 21,22 . Unlike the sp 2 bonding in CNT, the carbon nanothread is an ultra-thin sp 3bonded carbon structure.…”

Synthesis of double core chromophore-functionalized nanothreads by compressing azobenzene in a diamond anvil cell

“…E-mail: fanetti@lens.uni.it; roberto.bini@uni.it; Fax: +390554572489; Tel: +390554572436 2D lattice (a ¼ 6.5Å) characterized by a correlation length of several tens of nm, but denitely lower, #2.5 nm, along the threads. 17,18 A consequence of the mechanism described above leading to the nanothread formation is that the reaction cannot be quantitative, competing with the topochemical one which leads to the formation of amorphous hydrogenated carbon (a-C:H). 19,20 Aer the discovery of nanothread formation from benzene, computational and experimental studies revealed the possibility of synthesising nanothreads from a large number of aromatics and heteroaromatics.…”