Carbon Allotropes Research Articles

Synthesis of MWCNTs by chemical vapor deposition of methane using FeMo/MgO catalyst: role of hydrogen and kinetic study

This study aims to investigate the role of hydrogen on CNTs synthesis and kinetics of CNTs formation. The CNTs were synthesized by catalytic chemical vapor deposition of methane over FeMo/MgO catalyst. The experimental results revealed that hydrogen plays an important role in the structural changes of catalyst during the pre-reduction process. The catalyst structure fully transformed into metallic FeMo phases, resulting in an increased yield of 5 folds higher than those of the non-reduced catalyst. However, the slightly larger diameter and lower crystallinity ratio of CNTs was obtained. The hydrogen co-feeding during the synthesis can slightly increase the CNTs yield. After achieving the optimum amount of hydrogen addition, further increase in hydrogen would inhibit the methane decomposition, resulting in lower product yield. The hydrogenation of carbon to methane was proceeded in hydrogen co-feed process. However, the hydrogenation was non-selective to allotropes of carbon. Therefore, the addition of hydrogen would not benefit neither maintaining the catalyst stability nor improving the crystallinity of the CNT products. The kinetic model of CNTs formation, derived from the two types of active site of dissociative adsorption of methane, corresponded well to the experimental results. The rate of CNTs formation greatly increases with the partial pressure of methane but decreases when saturation is exceeded. The activation energy was found to be 13.22 kJ mol−1, showing the rate controlling step to be in the process of mass transfer.

Controlling C–C coupling reactivity through pore shape engineering of B-doped graphyne family

Graphyne is an interesting carbon allotrope characterized by sp-sp2 hybridized carbon bonds, which allow for structure variability. Though there are studies evaluating the electrical and mechanical properties of various structures, studies utilizing its structural variety toward catalyst applications are minor. In electrocatalytic CO2 reduction reactions (CRR), producing valuable C2+ products, such as C2H4 or C2H5OH, under mild conditions is still challenging. The bottleneck has been assigned to the carbon-carbon (C–C) coupling reaction, such as 2*CO → *OCCO. In this reaction, one requires strong binding to the catalyst to enhance neighboring CO concentration, but at the same time, one needs to have low C–C coupling barriers making the OC-CO bond. Following our previous study, which showed B-doped γ-graphyne can be a catalyst for ethanol production, we conducted theoretical investigations on a range of B-doped graphyne families using density functional theory. Out of the 15 different structures studied, four, 4,12,2-, sR-, γ-, and 6,6,12-graphynes, show promising potential for CRR. B-doped 4,12,2-graphyne, with small square and rectangular pores, had a very low C–C coupling barrier of 0.34 eV with strong 2*CO adsorption (−2.5 eV). Furthermore, our research revealed a correlation between the heat of reaction (2*CO → *OCCO) and the average pore area around the acetylenic linker reaction site. Smaller pores give a favorable orientation of two CO molecules, resulting in low reaction barriers.

On-surface synthesis of aromatic cyclo[10]carbon and cyclo[14]carbon.

All-carbon materials based on sp2-hybridized atoms, such as fullerenes1, carbon nanotubes2 and graphene3, have been much explored due to their remarkable physicochemical properties and potential for applications. Another unusual all-carbon allotrope family are the cyclo[n]carbons (Cn) consisting of two-coordinated sp-hybridized atoms. They have been studied in the gas phase since the twentieth century4-6, but their high reactivity has meant that condensed-phase synthesis and real-space characterization have been challenging, leaving their exact molecular structure open to debate7-11. Only in 2019 was an isolated C18 generated on a surface and its polyynic structure revealed by bond-resolved atomic force microscopy12,13, followed by a recent report14 on C16. The C18 work trigged theoretical studies clarifying the structure of cyclo[n]carbons up to C100 (refs. 15-20), although the synthesis and characterization of smaller Cn allotropes remains difficult. Here we modify the earlier on-surface synthesis approach to produce cyclo[10]carbon (C10) and cyclo[14]carbon (C14) via tip-induced dehalogenation and retro-Bergman ring opening of fully chlorinated naphthalene (C10Cl8) and anthracene (C14Cl10) molecules, respectively. We use atomic force microscopy imaging and theoretical calculations to show that, in contrast to C18 and C16, C10 and C14 have a cumulenic and cumulene-like structure, respectively. Our results demonstrate an alternative strategy to generate cyclocarbons on the surface, providing an avenue for characterizing annular carbon allotropes for structure and stability.

Graphdiyne and Nitrogen-Doped Graphdiyne Nanotubes as Highly Efficient Electrocatalysts for Oxygen Reduction Reaction

Electrocatalysts with high efficiency and low cost are always urgently needed for oxygen reduction reaction (ORR). As a new carbon allotrope, graphdiyne (GDY) has received much attention due to its unique chemical structure containing sp- and sp2-hybridized carbons, and intrinsic electrochemical activity ascribed to its inherent conductivity. Herein, we prepared two graphdiyne materials named GDY nanotube and nitrogen-doped GDY (NGDY) nanotube via cross-coupling reactions on the surface of Cu nanowires. As metal-free catalysts, their electrocatalytic activities for ORR were demonstrated. The results showed that the NGDY nanotube presents more excellent electrochemical performance than that of the GDY nanotube, including more positive potential and faster kinetics and charge transfer process. The improvement can be ascribed to the greater number of structural electrocatalytic active sites from nitrogen atoms as well as the hollow nanotube morphology, which is beneficial to the adsorption of oxygen and acceleration of the catalytic reaction. This work helps develop high-quality graphdiyne-based electrocatalysts with well-defined chemical structures and morphologies for various electrochemical reactions.

Topological Descriptors of Crystal Carbon Graphite

Graph theory plays an important role in modeling, designing, and analyzing the structural characteristics of any molecular structure or complex network. The numerical quantities associated with a molecular structure are called topological descriptors. These descriptors are essential for understanding the topology of molecular structures and their physicochemical properties. In this paper, we study the molecular structure of crystal carbon graphite for r-level, which is one of the most well-known allotropes of carbon. Furthermore, some topological descriptors for the molecular structure of crystal carbon graphite have been computed using degree and neighborhood degree sum-based techniques. The obtained results may be used in understanding the structural characteristics and making predictions about certain physiochemical properties of crystal carbon graphite.

Peculiar nonlinear optical absorption and optical limiting behaviors of bismuth-based binary and ternary nanostructures

A single-beam Z-Scan experiment was used to investigate the nonlinear optical absorption and optical limiting properties of pristine Bi2O3, binary rGO/Bi2O3, Bi2O3/WO3 and ternary rGO/Bi2O3/WO3 nanostructures. These nanostructures were synthesized using a facile hydrothermal method. The crystallite size, interplanar spacing, allotropes of carbon and functional groups were characterized using XRD, Raman and FTIR. The morphology of the synthesized compounds was confirmed by SEM and TEM analyses. EDS analysis confirmed the existence of elements such as C, O, Bi and W. A linear optical study illustrates that the pristine Bi2O3 exhibited absorption within the UV range of 200 nm and 400 nm, whereas the binary and ternary nanostructures displayed absorption in the UV–Visible range from 200 nm to 800 nm. The synthesized nanostructures shows exciting nonlinear absorption such as genuine 2PA (pristine Bi2O3), W-type SA to RSA (binary rGO/Bi2O3, Bi2O3/WO3) and sequential 2PA (ternary rGO/Bi2O3/WO3). Bismuth-based nanostructures exhibit the lowest optical limiting (OL) threshold and a greater two-photon absorption coefficient. The extended conjugation for charge transfer and the presence of high defect-induced states in rGO, along with the strong UV–Visible absorption of Bi2O3 and WO3 which leads to a unique nonlinear optical response. This response holds promise for potential applications in energy stabilizers and laser safety devices operating at 532 nm and 9 ns laser domain.

Structure and properties of graphullerene: a semiconducting two-dimensional C60 crystal

Graphullerene is a recently discovered, two-dimensional allotrope of carbon formed from C60 molecules. It has been synthesized in the form (C60Mg4)n and subsequently transformed into (C60)n by removal of the Mg atoms. Ab initio calculations are employed to examine the structure and properties of this material. Structurally, graphullerene is composed of strained C60 molecules. Each of these molecules is connected to six neighbors in a hexagonal network with a total of eight chemical bonds. We find this structure to be meta-stable, owing to the strain produced by the covalent bonding of the molecules. However, the inclusion of Mg atoms transforms the cohesion energy from negative to positive values by forming additional C-Mg bonds, creating an energetically stable material. In the absence of Mg, this allotrope is a pure carbon semiconductor with an indirect band gap. Phonon spectrum calculations confirm the dynamical stability of the material and yield its in- and out-of-plane sound velocities. In addition, symmetry breaking of the C60 molecules results in a distribution of bond lengths and creates vibrational modes that serve as a signature of graphullerene.

Controllable Weyl nodes and Fermi arcs in a light-irradiated carbon allotrope

Controllable Weyl nodes and Fermi arcs in a light-irradiated carbon allotrope

Theoretical characterization of tolanene: A new 2D sp-sp2 hybridized carbon allotrope

The search for new carbon allotrope forms has been the focus of much experimental and theoretical research. Some nonbenzenoid sp2-hybridized carbon allotropes have been proposed and synthesized, revealing properties unlike those observed for graphene. In the present work, first-principles calculations were performed to investigate a new two-dimensional (2D) carbon sheet — named tolanene — which may hypothetically be obtained from diphenylacetylene molecules as building blocks. The nonbenzenoid tolanene sheet has a periodic arrangement of four-, six-, eight-, and twelve-membered rings of sp and sp2 hybridized carbon atoms. Our calculations reveal that tolanene is mechanically and dynamically stable, and can potentially withstand a temperature as high as 1500 K quite easily. The structure presents a strong anisotropy in its mechanical properties, in a similar fashion to biphenylene. Additionally, we verify that the structure presents a metallic behavior, and its low-energy electronic structure is fully determined by pz orbitals, as in most carbon-based 2D materials. The application of tolanene as a potential anode material in Li-ion batteries is also explored. We find that it offers a competitive Li storage capacity and fast Li mobility along with other interesting electronic properties.

Adsorption Affinities of Small Volatile Organic Molecules on Graphene Surfaces for Novel Nanofiller Design: A DFT Study.

The adsorption of organic molecules on graphene surfaces is a crucial process in many different research areas. Nano-sized carbon allotropes, such as graphene and carbon nanotubes, have shown promise as fillers due to their exceptional properties, including their large surface area, thermal and electrical conductivity, and potential for weight reduction. Surface modification methods, such as the "pyrrole methodology", have been explored to tailor the properties of carbon allotropes. In this theoretical work, an ab initio study based on Density Functional Theory is performed to investigate the adsorption process of small volatile organic molecules (such as pyrrole derivatives) on graphene surface. The effects of substituents, and different molecular species are examined to determine the influence of the aromatic ring or the substituent of pyrrole's aromatic ring on the adsorption energy. The number of atoms and presence of π electrons significantly influence the corresponding adsorption energy. Interestingly, pyrroles and cyclopentadienes are 10 kJ mol-1 more stable than the corresponding unsaturated ones. Pyrrole oxidized derivatives display more favorable supramolecular interactions with graphene surface. Intermolecular interactions affect the first step of the adsorption process and are important to better understand possible surface modifications for carbon allotropes and to design novel nanofillers in polymer composites.

Masked alkynes for synthesis of threaded carbon chains

Polyynes are chains of sp1 carbon atoms with alternating single and triple bonds. As they become longer, they evolve towards carbyne, the 1D allotrope of carbon, and they become increasingly unstable. It has been anticipated that long polyynes could be stabilized by supramolecular encapsulation, by threading them through macrocycles to form polyrotaxanes—but, until now, polyyne polyrotaxanes with many threaded macrocycles have been synthetically inaccessible. Here we show that masked alkynes, in which the C≡C triple bond is temporarily coordinated to cobalt, can be used to synthesize polyrotaxanes, up to the C68 [5]rotaxane with 34 contiguous triple bonds and four threaded macrocycles. This is the length regime at which the electronic properties of polyynes converge to those of carbyne. Cyclocarbons constitute a related family of molecular carbon allotropes, and cobalt-masked alkynes also provide a route to [3]catenanes and [5]catenanes built around cobalt complexes of cyclo[40]carbon and cyclo[80]carbon, respectively.

Versatile Surface Chemistry of Carbon-Based Nanoplatforms by Covalent Bonding, Non-Covalent Linking, Crosslinking, and Self-Assembling

This mini-review discussed the best-known chemical and synthetic methodologies used in the last years to modify carbon allotropes, with an interest in nanotechnology. In this perspective, chemistry with optoelectronics applications and recent trends within bio-applications focusing mainly on graphene and its derivatives were considered. So, the mini-review intended to focus on methodologies to add functional groups with varied reactivities, polymer chemistry, and nanoscale control. These methodologies provide insight for further developments. In this manner, traditional methods using strong acid media to convert simple carbon bonds into carboxylic acid and aldehydes organic functional groups were shown and discussed. Hence, chemical modifications in a variety of solvents could be developed. Notably, many organic chemical reactions, such as bimolecular nucleophilic substitution (SN2), click chemistry, and photochemical reactions, showed essential insights in designing the carbon-based material modifications and the bottom-up method. Moreover, incorporating atomic entities within graphene material defects led to interesting spectroscopic and quantum properties. The atomic change added blemishes to this homogeneous structure, which was tuned to modify optical properties. In addition, the review was also oriented towards the discussion on incorporating polymeric films, such as boron- and silicon-based monomers, to form polymeric-modified carbon-based slides. In this way, organoboranes and organosilanes permitted chemical functionalization because their chemical modification was more accessible on nanosurfaces. Moreover, emphasis was placed on exploiting non-covalent bonding with ions and polarized molecules with the highly electronic densities of graphene and its derivatives. In this manner, the manuscript intends to summarize the main types of reactions and synthetic pathways reported until today. Therefore, particular focus was given to chemical composition, 2D and 3D chemical structures, and their properties related to non-covalent interactions. Thus, based on the properties and reactivity of carbon allotropes, the review was intended to open the analysis and discussion, considering the design of new carbon-based materials, hybrid nanocomposites, and metamaterials.

Heterolayered carbon allotrope architectonics via multi-material 3D printing for advanced electrochemical devices

ABSTRACT 3D printing has become a powerful technique in electrochemistry for fabricating electrodes, thanks to readily available conductive nanocomposite filaments, such as those based on carbon fillers (i.e., carbon nanotubes (CNTs) or carbon black (CB)) within an insulating polymeric matrix like polylactic acid (PLA). Inspired by inorganic heterostructures that enhance the functional characteristics of nanomaterials, we fabricated hetero-layered 3D printed devices based on carbon allotropes using a layer-by-layer assembly approach. The heterolayers were customised through the alternate integration of different carbon allotrope filaments via a multi-material 3D printing technique, allowing for a time-effective method to enhance electrochemical performance. As a first demonstration of applicability, CNT/PLA and CB/PLA filaments were utilised to construct ordered hetero-layered carbon-based electrodes. This contrasts with conventional methods where various carbon species are mixed in the same composite-based filament used for building electrochemical devices. Multi-material 3D-printed carbon electrodes exhibit improved electrochemical performance in energy conversion (e.g., hydrogen evolution reaction or HER) and sensing applications (e.g., ascorbic acid detection) compared to single-material electrodes. This work paves the way for manufacturing advanced 3D-printed heterolayered electrodes with enhanced electrochemical activity through multi-material 3D printing technology.

Comprehensive scrutiny of surface mechanical parameters of graphyne-based materials for metal-ions and metal-air batteries applications: A perspective and a hybrid atomistic-continuum model

Graphyne family, as a low-dimensional carbon allotrope, is utilized for metal-ion and –air batteries as the anode and cathode materials due to their unique characteristics. These novel carbon nanomaterials can provide more theoretical storage capacity than graphene, while their specific surface mechanical parameters and vibrational frequencies can influence battery performance. However, there needs to be clear information that can explain the effects of these parameters on battery efficiency. In this respect, the influences of the surface elasticity, residual stress, density, vibrational modes, and frequencies of α, β, and γ-graphyne circular monolayers on anode and cathode materials have been investigated in current research using the hybrid molecular dynamics simulation and modified classical continuum mechanics methods. Concerning metal-ion batteries, the results disclose that the suitability sequence for anode materials can be expressed as γ-graphyne > graphene > β-graphyne > α-graphyne monolayers. In the case of metal-air batteries, the competence sequence for cathode materials is in the order of γ-graphyne > β-graphyne ∼ graphene > α-graphyne monolayers. Therefore, γ-graphyne with suitable storage capacity, low volume expansion, good surface elasticity, low surface residual stress, and appropriate specific surface area is the promising anode and cathode material for metal-ion and -air batteries, respectively.

Sensing studies of acenaphthene and acenaphthylene molecules using penta-graphene sheets – A DFT outlook

The emergence of two-dimensional (2D) material leads to fascinating applications. The stability of one of the new allotropes of carbon, penta-graphene is ascertained based on formation energy. The band gap of penta-graphene is witnessed as 1.621 eV, which is confirmed from the band structure. The penta-graphene is used to adsorb two polycyclic aromatic hydrocarbons, namely acenaphthene and acenaphthylene molecules. The adsorption of acenaphthene and acenaphthylene molecules changes the electronic properties of penta-graphene, which is apparent from electron density difference, density of states, and band structure results. Besides, acenaphthene and acenaphthylene molecules are physisorbed on penta-graphene sheets. The outcome shows that penta-graphene can be deployed as a base substrate for the adsorption of acenaphthene and acenaphthylene molecules.

Progress of Polycyclic Boron-Doped Molecular Carbons

Molecular carbons, namely molecular cutout of carbon materials, are of importance for understanding accurate structures of carbon allotropes and developing functional π-electron materials. Doping the boron atoms into π-conjugated skeletons of molecular carbons enables the construction of boron-doped molecular carbons (BMCs), further leading to new chemistry and attractive material systems, which are distinct from carbon-based and other heteroatom-doped molecular carbons. Herein, the bottom-up organic synthesis methodologies have been employed to synthesize BMCs that feature the boron atoms at the edge or in the center of π-skeletons. They have not only amazing topological structures and good stability but also intriguing photophysical and electronic properties. Moreover, they have sufficient Lewis acidity and can coordinate with Lewis bases to form Lewis acid–base complexes, which exhibit stimuli-responsive functions. Notably, some of these BMCs can be utilized in the fields of organic reactions, optical and electronic devices, as well as supramolecular chemistry and photothermal materials. In this short review, we aim to highlight the design and synthetic strategies of polycyclic BMCs, and their unique physical properties and practical applications.

QSPR analysis of carbon allotropes by employing molecular descriptors and information entropies

The inherent qualities of carbon nanosheets that come from their underlying molecular structure have drawn an enormous amount of interest from researchers. Molecular descriptors are commonly used graph-theoretic metrics to analyze the physicochemical properties of a molecule based on its molecular structure. Our current research validates the use of molecular descriptors in studying three recently developed carbon allotropes: pentagraphene, phagraphene, and phographene. These allotropes have significant thermal, dynamic, and mechanical stabilities that are comparable to graphene. General analytical expressions for both degree and neighborhood degree sum-based indices of these nanosheets are derived through the utilization of graph theoretical methods. Following a filtering process of the significant indices, regression models that accurately predict atomic density, specific heat capacity and total π-electron energy of carbon allotropes are developed. Additionally, Shannon entropy is introduced as an information index, which can be utilized for predictive studies in the future and as a tool for comparing structural complexity by incorporating topological index in its definition.

Instantaneous formation of covalently bonded diamond–graphite–graphene with synergistic properties

Diamond and graphene are the most widely used carbon allotropes and offer great potential for developing mechanical, electronic, energy-storage, and sensor applications. Their combination, especially interfacial covalent bonding, can impart excellent properties. However, achieving interfacial covalent bonding with superior performance using flexible and low-power strategies remains challenging. This study developed a novel instantaneous transformation method from diamond to graphene to prepare a new covalent structure of diamond–nano-graphite–graphene (CDGG). That is, a nanosecond-pulse laser induces sp3-to-sp2 instantaneous transformations from diamond to graphite in air, and the subsequent mechanical cleavage overcomes the weak van der Waals forces to achieve the final transformation of graphite to graphene. First, the key factors influencing laser-induced graphitization and mechanical cleavage were investigated, and a covalent carbon structure with multidirectional graphene was obtained. Furthermore, the mechanisms encompassing the lattice transformation, interface relationships, transformation time, and interface bonding were elucidated. The obtained new structure synergized the excellent properties of diamond, nano-graphite, and graphene, exhibiting superior lubrication, mechanochemical wear resistance, durability, and load-capacity. Compared to polished diamond, the obtained structure exhibited a significant decrease in the stable coefficient of friction by 49–59 % and a reduction of more than one order of magnitude in the relative wear rate under high friction against ferrous metals with a normal load of 1–9 N. Even under a heavy load of 100 N, it still exhibited superior lubrication and mechanochemical wear resistance. Finally, the preparation and patterning of covalent carbon structures were achieved on various diamond surfaces with high efficiency, environmental friendliness, and low power. This study is expected to broaden the scope of developing and applying diamond, diamond films, and graphene devices.

Differentiating Cyclability and Kinetics of Na+ Ions in Surface-Functionalized and Nanostructured Graphite Using Electrochemical Impedance Spectroscopy

The revolution in lithium-ion battery (LIB) technology was partly due to the invention of graphite as a robust negative electrode material. However, equivalent negative electrode materials for complementary sodium ion battery (NIB) technologies are yet to be commercialized due to sluggish reaction kinetics, phase instability, and low energy density originating from the larger size of Na+-ion. Therefore, in search of the next-generation electrode materials for NIBs, we first analyze the failure of graphite during reversible Na+ ion storage. Building upon that, we suggest surface-functionalized and nanostructured forms of analogous carbon allotropes for enhancing Na+ ion storage. During long-term rigorous cycling conditions, Graphene Oxide (GO) and Graphene nanoplatelets (GNP) exhibit higher Na+ ion storage (157 mAh g−1 and 50 mAh g−1 after 60 cycles, respectively) compared to graphite (27 mAh g−1). Optimizing alternative NIBs requires a comprehensive analysis of cycling behavior and kinetic information. Therefore, in this investigation, we further examine ex-situ electrochemical impedance spectroscopy (EIS) at progressive cycles and correlate capacity degradation with impedance arising from the electrolyte, solid electrolyte interphase formation, and charge transfer.

The drug delivery of Ciclopirox anticancer by γ-graphyne and its boron nitride analogue: electronic study via DFT

ABSTRACT A substantial amount of scholarly inquiry has focused on the advancement of innovative methodologies for drug administration. In this research, both graphyne (GY) and BN-analog GY (BNY) nanosheets are presented. The study focuses on the carbon allotrope GY. Density Functional Theory (DFT) calculations were used to assess how GY, BNY, and the anticancer drug ciclopirox (CPX) interact with one another. It was observed that the inherent capability of pristine GY to augment CPX adsorption is intensified by the involvement of nitrogen (N) and boron (B) atoms. Furthermore, examination using Ultraviolet–Visible (UV-Vis) analysis exhibited a shift towards less energetic states, corresponding to longer wavelengths. Moreover, the interaction between CPX and BNY displayed chemical reactivity, rendering it conducive for forming bonds at the adsorption site. Additionally, a thorough investigation via the Atoms-In-Molecules (AIM) analysis furnished a more profound comprehension of the associations between the drug and the nanosheet. Notably robust connections between CPX and BNY were detected. As a consequence, the potential of BNY to function as a viable transporter for CPX in the realm of drug delivery was substantiated.