Are Stone−Wales Defect Sites Always More Reactive Than Perfect Sites in the Sidewalls of Single-Wall Carbon Nanotubes?

Stone-Wales Defect in Graphene

2D graphene the most investigated structures from nanocarbon family studied in the last three decades. It is projected as an excellent material useful for quantum computing, artificial intelligence, and next generation advanced technologies. Graphene exists in several forms and its extraordinary thermal, mechanical, and electronic properties, principally depend on the kind of perfection of the hexagonal atomic lattice. Defects are always considered as undesired components but certain defects in graphene could be an asset for electrochemistry and quantum electronics due to the engineered electronclouds and quantum tunnelling. The authors carefully discuss the Stone-Wales imperfections in graphene and its derivatives comprehensively. A specific emphasis is focused on the experimental and theoretical aspects of the Stone-Wales defects in graphene with respect to structure-property relationships. The corroboration of extrinsic defects like external atomic doping, functionalization, edge distortion in the graphene consisting of Stone-Wales imperfections, which are very significant in designing graphene-based electronic devices, are summarized.

Extension of Non-alternant Nanographenes Containing Nitrogen-Doped Stone-Thrower-Wales Defects

Non-alternant topologies have attracted considerable attention due to their unique physiochemical characteristics in recent years. Here, three novel topological nanographenes molecular models of nitrogen-doped Stone-Thrower-Wales (S-T-W) defects were achieved through intramolecular direct arylation. Their chemical structures were unambiguously elucidated by single-crystal analysis. Among them, threefold intramolecular direct arylation compound (C42 H21 N) is the largest nanographene bearing a N-doped non-alternant topology to date, in which the non-benzenoid rings account for 83 % of the total molecular skeleton. The absorption maxima of this compound was located in the near-infrared region with a long tail up to 900 nm, which was much longer than those reported for similarly sized N-doped nanographene with six-membered rings (C40 H15 N). In addition, the electronic energy gaps of these series compounds clearly decreased with the introduction of non-alternant topologies (from 2.27 eV to 1.50 eV). It is noteworthy that C42 H21 N possesses such a low energy gap (Eg opt =1.40 eV; Eg cv =1.50 eV), yet is highly stable under ambient conditions. Our work reported herein demonstrates that the non-alternant topology could significantly influence the electronic configurations of nanocarbons, where the introduction of a non-alternanting topology may be an effective way to narrow the energy gap without extending the molecular π-conjugation.

A dispersion-corrected density functional theory study of the noncovalent interactions between nucleobases and carbon nanotube models containing stone-wales defects

The noncovalent bonding between nucleobases (NBs) and Stone-Wales (SW) defect-containing closed-end single-walled carbon nanotubes (SWNTs) was theoretically studied in the framework of density function theory using a dispersion-corrected functional PBE-G06/DNP. The models employed in this study were armchair nanotube (ANT) (5,5) and zigzag nanotube (ZNT) (10,0), which incorporated SW defects in different orientations. In one of them, the (7,7) junction is tilted with respect to SWNT axis (ANT-t and ZNT-t), whereas in ANT-p and ZNT-p models the (7,7) junction is parallel and perpendicular to the axis, respectively. The binding energies for uracil, thymine, cytosine, 5-methylcytosine, adenine, and guanine interacting with the defect-containing nanotube models were compared to the values previously obtained with the same calculation technique for the case of defect-free SWNTs, both in the gas phase (vacuum) and in aqueous medium. For most models, the interaction strength tends to be higher for purine than for pyrimidine complexes, with a clear exception of the systems including ZNT-p, both in vacuum and in aqueous medium. As it could be expected, the binding strength in the latter case is lower as compared to that in vacuum, roughly by 2-4 kcal/mol, due to the implicit inclusion of a medium (i.e., water) via the conductor-like screening model model. The closest contacts between NBs and SWNT models, frontier orbital distribution, and highest-occupied molecular orbital-lowest-unoccupied molecular orbital gap energies are analyzed as well. © 2019 Wiley Periodicals, Inc.

3D flower-like binary nickel cobalt oxide decorated coiled carbon nanotubes directly grown on nickel nanocones and binder-free hydrothermal carbons for advanced asymmetric supercapacitors

The development of high performance supercapacitors with high energy densities without sacrificing power densities has always been at the leading edge of the emerging field of renewable energy. Herein, the design and fabrication of innovative high performance binder-free electrodes consisting of coiled carbon nanotubes (CNTs) and biomass-derived hydrothermal carbon spheres (HTCSs) as, respectively, positive and negative electrodes is reported. High performance asymmetric supercapacitors (ASCs) were developed using novel 3D core/shell-like binary Ni-Co oxide (NCO) decorated coiled CNTs directly grown on Ni nano-cone arrays (NCAs) and HTCSs directly deposited on NCAs. Novel 3D structures of NCAs were synthesized via a facile and scalable cathodic electrodeposition route and coiled CNTs were directly grown on them by catalytic chemical vapour deposition (CVD) followed by a facile hydrothermal method to integrally decorate the coiled CNTs/NCAs by 3D flower-like NCO. A one-pot hydrothermal method is also used to direct the synthesis of biomass-derived HTCSs on NCAs to fabricate a novel binder-free negative electrode. The ASC based on NCO@coiled CNTs/NCAs//HTCSs/NCAs not only exhibits superior energy density (72.5 W h kg-1) at a reasonable power density of 1.4 kW kg-1, but also represents remarkable cycling durability (retaining almost over 85% of its initial capacitance after 5000 charge-discharge cycles). The fabricated ASC, therefore, seems to be a potent candidate for practical applications in future high performance energy storage systems.

One-step synthesis of fluorescently labelled, single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) can be labelled with functional moieties that endow them with a number of unique characteristics, which can be applicable to biomedical applications such as imaging. Herein we describe a facile, one-step esterification process to functionalize SWNT with fluorescein.

Exploring the Essential Dynamics of B-DNA

The essential dynamics of different normal and chemically modified DNA duplexes pertaining to the B family have been extensively explored from molecular dynamics simulations using powerful data mining techniques. Some of them, which are presented here for the first time, might become standard, powerful tools to characterize the dynamical behavior of complex biomolecular structures such as nucleic acids. Their potential impact is illustrated by examining the extended trajectories sampled for the set of DNA duplexes considered in this study, which allows us to discuss the degree of conservation of the natural flexibility pattern of the different DNAs, which in specific cases contain severe chemical modifications.

Ultrathin Wrinkled N-Doped Carbon Nanotubes for Noble-Metal Loading and Oxygen Reduction Reaction

We describe the fabrication of ultrathin wrinkled N-doped carbon nanotubes by an in situ solid-state method. The positions of Co catalyst were first labeled by good-dispersion and highly loaded Au and Pt, indicating the most of Co are unsealed. The resultant unique nanoarchitecture, which exhibits the features of carbon nanotube and graphene with a combined effect of 1D and 2D carbon-based nanostructures, exhibited a superior ORR activity to carbon nanotubes and graphene. Moreover, the novel catalysts showed a better durability and higher tolerance to methanol crossover and poisoning effects than those of Pt/C.

The effect of nano confinement on the C-h activation and its corresponding structure-activity relationship

The C–H activation of methane, ethane, and t-butane on inner and outer surfaces of nitrogen-doped carbon nanotube (NCNTs) are investigated using density functional theory. It includes NCNTs with different diameters, different N and O concentrations, and different types (armchair and zigzag). A universal structure-reactivity relationship is proposed to characterize the C–H activation occurring both on the inner and outer surfaces of the nano channel. The C–O bond distance, spin density and charge carried by active oxygen are found to be highly related to the C–H activation barriers. Based on these theoretical results, some useful strategies are suggested to guide the rational design of more effective catalysts by nano channel confinement.

Stone-Wales defects can cause a metal-semiconductor transition in carbon nanotubes depending on their orientation

It has been shown that the two different orientations of Stone-Wales (SW) defects, i.e. longitudinal and circumferential SW defects, on carbon nanotubes (CNTs) result in two different electronic structures. Based on density functional theory we have shown that the longitudinal SW defects do not open a bandgap near the Fermi energy, while a relatively small bandgap emerges in tubes with circumferential defects. We argue that the bandgap opening in the presence of circumferential SW defects is a consequence of long-range symmetry breaking which can spread all the way along the tube. Specifically, the distribution of contracted and stretched bond lengths due to the presence of defects, and hopping energies for low-energy electrons, i.e. the 2p(z) electrons, show two different patterns for the two types of defects. Interplay between the geometric features and the electronic properties of the tubes have also been studied for different defect concentrations. Considering π-orbital charge density, it has also been shown that the deviations of bond lengths from their relaxed length result in different doping for two defect orientations around the defects-electron-rich for a circumferential defect and hole-rich for a longitudinal one. We have also shown that, in the tubes having both types of defects, circumferential defects would dominate and impose their electronic properties.

Boron-assisted transformation to rod-like graphitic carbons from multi-walled carbon nanotubes in boron-mixed multi-walled carbon nanotube solids

We produced boron-mixed multi-walled carbon nanotube solids (B-mixed MWCNT solids) by heating and pressing the powder of purified MWCNTs mixed with 1, 5, and 10 wt % boron in the temperature range 1400-1800 °C every 200 °C under a constant pressure of 20 MPa in vacuo, and investigated the influence of boron addition on nanotube structure and the mechanical and electrical properties of the resulting B-mixed MWCNT solids. The structure of the prepared material was characterized by scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy-electron energy loss spectroscopy, Raman scattering spectroscopy, and X-ray diffraction, and their mechanical properties and conductivity were measured using a mechanical and Vickers indentation tester and an electric resistor, respectively. It is notable that part of the nanotubes in the B-mixed MWCNT solids solidified at 1800 °C had dramatically changed into rod-like graphitic carbons (RLGCs). The occupancy distribution of RLGCs increased with increasing boron contents. However, boron was not detected in the energy-loss near-edge structure spectrum of RLGCs. Furthermore, RLGCs were not observed in the boron-unmixed sample treated with the same solidified condition, indicating that adding boron causes a remarkable ability to transform the phase of MWCNT. Transformation from MWCNTs to RLGCs resulted in increased specific bending strength and modulus, Vickers hardness, and electrical conductivity of B-mixed MWCNT solids with increasing boron content and solidified temperature.

Theoretical Studies of Substitutionally Doped Single-Walled Nanotubes

The rich chemistry of single-walled carbon nanotubes (SWCNTs) is enhanced by substitutional doping, a process in which a single atom of the nanotube sidewall is replaced by a heteroatom. These so-called heteroatom-substituted SWCNTs (HSWCNTs) exhibit unique chemical and physical properties not observed in their corresponding undoped congeners. Herein, we present theoretical studies of both main group element and transition metal-doped HSWCNTs. Within density functional theory (DFT), we discuss mechanistic details of their proposed synthesis from vacancy-defected SWCNTs and describe their geometric and electronic properties. Additionally, we propose applications for these nanomaterials in nanosensing, nanoelectronics, and nanocatalysis.

Nanoengineering defect structures on graphene

We present a new way of nanoengineering graphene by using defect domains. These regions have ring structures that depart from the usual honeycomb lattice, though each carbon atom still has three nearest neighbors. A set of stable domain structures is identified by using density functional theory, including blisters, ridges, ribbons, and metacrystals. All such structures are made solely out of carbon; the smallest encompasses just 16 atoms. Blisters, ridges, and metacrystals rise up out of the sheet, while ribbons remain flat. In the vicinity of vacancies, the reaction barriers to formation are sufficiently low that such defects could be synthesized through the thermally activated restructuring of coalesced adatoms.