Modulating the H-bond strength by varying the temperature for the high pressure synthesis of nitrogen rich carbon nanothreads

Abstract

Synthesis of carbon nanothreads from pyridine under variable high-pressure and high-temperature conditions discloses the role of H-bonding in the kinetic control of the reaction.

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

“…A similar occurrence is observed in the micrographs obtained by Nobrega et al on the nanothreads recovered by the compression of aniline 26 and could likely be ascribed to the polycrystalline nature of the starting samples, which nevertheless allows the propagation of the thread through differently oriented adjacent crystals. The distance between the threads is very reproducible varying between 3.3 and 3.5Å, a distance remarkably lower, about 30%, than those reported for benzene, 10,16 pyridine 24,25 and aniline, 26 thus evidencing a denser and more compact material.…”

“…Clear evidence of the nanothread formation is the characteristic, generally hexagonal, spotty XRD pattern which attests to the 2D ordered lattice in which the nanothreads are arranged. 16,24,25 In fact, since the threads develop along the applied stress direction, the same direction of the probing X-ray beam, we have from this technique direct evidence of the 2D arrangement of the threads. In Fig.…”

“…Diffraction patterns have been acquired in air with the samples contained in the gasket without the diamonds. The 2D images of the samples produced at ambient temperature exhibit the characteristic pattern of the pseudohexagonal lattice although showing some differences between them, but especially with respect to pyridine 24,25 and benzene, 10,16 where a single diffraction peak was detected. Here the strongest and sharper (FWHM $0.4Å) peak is observed at 5.6Å, as in pyridine and benzene, but another peak is observed at a d value (11.2-11.5Å depending on the sample) slightly larger than the double, and having a FWHM of about 0.9-1.0Å.…”

“…With increasing the temperature above 400 K, the reaction threshold in pyridine has been lowered to 14 GPa improving the quality and yield ($30%) of the synthesized nanothreads and also modifying the packing arrangement. 25 The importance of temperature in the nanothread formation is even more pronounced in the case of aniline 26 and cubane, 30 where temperatures in excess of 500 K are required for inducing the reaction in spite of pressure conditions around or exceeding 30 GPa. In the cubane case, an excess of energy is required to release the internal strain of the molecule, 30 whereas in aniline the reaction threshold experimentally observed, 550 K and 33 GPa, 26 nicely ts with a topochemical mechanism where the reactivity is driven by a complex cooperation between lattice motions 19,31 and Hbonding 32,33 that causes a strongly anisotropic crystal response to compression and favors inter stack bonding while preserving the NH 2 groups.…”

“…With further increasing the temperature and reducing the pressure, the increased amplitude of both thermal oscillation and reaction cavity 35 favors the topochemical path, which leads to the formation of amorphous 2D or 3D carbon nitrides both in the case of aniline 34 as well as pyridine. 25 The presence of heteroatoms or substituents within the threads can be exploited for tuning the electronic properties or to act as potential linkers and active sites for doping. Aromatic or heteroaromatic molecules containing chemically stable or well protected functional groups represent appealing systems for the realization of diamond-like nanothreads where the optical, thermal, electrical and conductivity properties can be suitably adjusted by choosing appropriate substituents.…”