Structure Of Carbon Allotropes Research Articles

Enhanced non-metal catalyzed CO2 reduction on doped biphenylene

– Using non-metals to replace the rare or precious transition metals as active component in catalyst in electrocatalysts is highly desirable in renewable energy applications. The diverse structures of carbon allotropes make it possible to support emerging non-metallic catalysts. Biphenylene is a recently discovered two-dimensional layered carbon allotrope, which outperforms graphene in terms of catalytic activity. Employing density functional theory calculations, we explore the possibility of non-metal doped biphenylene as promising catalyst for CO2 reduction. In aqueous environment, the active sites on the biphenylene surface are partially occupied by H* under reduction potential. On pure biphenylene, the coverage of H* leads to an large onset potential of U > 1.1 V. On boron-doped biphenylene, part of active sites is covered by H*. The remaining unoccupied sites still have activity for CO2 reduction, and the onset potential is significantly reduced to U = 0.2 V. By contrast, nitrogen-doping does not have obvious effect on reducing the onset potential of CO2 reduction (U = 0.9 V). The reason of influencing catalytic activity is then studied. This work reveals provides guidance for the future application of biphenylene in renewable energy.

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.

A molecular dynamics study on the buckling behavior of x-graphyne based single- and multi-walled nanotubes

There are many two-dimensional (2D) structures of carbon allotropes which have been at the center of theoretical and experimental studies in recent years. α-, α2-, β- and γ-graphyne as the graphene allotropes with mixed sp1 and sp3 bonds are under study in the present work utilizing the molecular dynamics (MD) simulations. These thermodynamically stable forms of 2D carbon structure can also be rolled-up to generate novel nanotubes (NTs). Hence, the armchair (-A) and zigzag (-Z) NTs of the aforementioned one-atom-thick planar structures and their buckling behavior (critical force and strain) are considered. It is observed that γ-A- and γ-Z-graphyne NTs have the highest critical forces through the chosen range of aspect ratios (length/radius), whereas the α-graphyne NTs have the lowest critical forces. Also, α2- and β-graphyne NTs have the highest and lowest critical strains, respectively. Furthermore, the possible multi-walled (MW) NTs are simulated. In agreement with results of the single-walled (SW) NTs, the buckling analysis of MWNTs shows that γ-graphyne and α-graphyne MWNTs have the highest and the lowest mechanical stability under compression, correspondingly. In addition, the results of the critical strain for MWNTs are comparable with those of SWNTs.

Various Allotropes of Diamond Nanoparticles Generated in the Gas Phase during Hot Filament Chemical Vapor Deposition.

Diamond nanoparticles have been synthesized using various methods. Nanodiamonds generated in the gas phase were captured on the membrane of a transmission electron microscope grid during a hot filament chemical vapor deposition (HFCVD) diamond process. In total, ~600 nanoparticles, which were captured for 10 s in six conditions of the capture temperatures of 900 °C, 600 °C and 300 °C and the gas mixtures of 1% CH4-99% H2 and 3% CH4-97% H2, were analyzed for phase identification using high-resolution transmission electron microscopy and fast Fourier transformation. Hexagonal diamond, i-carbon, n-diamond, and cubic diamond were identified. The observation of two or more carbon allotropes captured on the same membrane suggested their coexistence in the gas phase during HFCVD. The crystal structure of carbon allotropes was related to the size of the nanodiamond. The crystal structure of the nanoparticles affected the crystal structure of diamond deposited for 8 h. Confirmation of various carbon allotropes provides new insight into the nanodiamond synthesis in the gas phase and the growth mechanism of HFCVD diamond.

Pauling’s rules guided Monte Carlo search (PAMCARS): A shortcut of predicting inorganic crystal structures

The rapid development of the high-throughput calculations and materials genome approaches in recent years has improved researchers’ ability to design advanced materials. Crystal structure prediction techniques play an important role in high-throughput calculations and materials genome approaches. However, the huge computational cost of the widely used crystal structure prediction techniques based on the global optimization algorithms hinders the researchers from predicting the large or medium-sized crystal structures. In recent years, some metastable materials with excellent electrical, magnetic, optical and catalytic properties have attracted a lot of attention. However, there is currently a lack of a structure prediction technique with high energy resolution near the ground-state structures to meet the growing demands for the prediction of low-energy metastable materials. In this article, a set of easy-operation guidelines for constructing crystal structures is extracted from Pauling’s rules. Based on this set of guidelines, we have designed an algorithm called Pauling’s rules guided Monte Carlo search (PAMCARS), which predict the ground-state and meta-stable inorganic crystal structures of a given composition by combining a classical Monte Carlo search in the configuration space constrained by Pauling’s rules with ab initio structural relaxations. In the actual tests, the crystal structures of carbon allotropes, CaSO4, Ba2TiSi2O8 and BaAlBO3F2 are successfully predicted by this crystal structure prediction algorithm. In addition, a number of unreported high-symmetric metastable crystal structures of carbon, CaSO4 and Ba2TiSi2O8 are also predicted. The successful prediction of graphite layers indicates that PAMCARS is able to predict some layered materials assembled by the Van der Waals forces. Two of the predicted low-energy metastable crystal structures of Ba2TiSi2O8 may explain the property anomaly of Ba2TiSi2O8 around 160 °C. Pauling’s rules guided Monte Carlo search exhibits high efficiency and energy resolution in predicting the ground-state and metastable crystal structures in the tests.

Introduction to the Thematic set: Carbon forms, paths and processes in the Earth

Carbon forms: paths and processes in the Earth is a thematic set of six papers arising from the lectures presented at the Lake Como School, held at Villa del Grumello, Como, Italy (15–20 October 2017), and organized by the Graduate School of Milano Bicocca. This collection of lecture notes focusses on the structure of carbon allotropes, the geodynamics of deep Earth's carbon transport and fixation at mantle conditions, carbon degassing by ascending magmas, and the vast tectonic carbon degassing at the Earth's surface. New science is emerging for carbon, one of the fundamental elements for life, energy, and global climate change on our planet. Carbon is cycled between surface, atmosphere, and oceans. Most of the recyclable carbon is stored deep in the Earth. Ingassing from the atmo-hydrosphere into the mantle occurs by subduction; in the mantle carbon resides in solids such as diamonds and is transported by fluids and melts that migrate upward. Outgassing into the atmosphere is effected by volcanism and tectono-metamorphic soil emissions. The forms and processes of carbon ingassing and outgassing are still poorly constrained. There is as yet no consensus on how and when carbon transforms from solid to fluid …

Ideal and real structures of different forms of carbon, with some remarks on their geological significance

Carbon is found in nature in a huge variety of allotropic forms and recent research in materials science has encouraged the development of technological materials based on nanocarbon. Carbon atoms with sp2 or sp3 hybridization can be thought of as building blocks. Following a bottom-up approach, we show how graphene and diamond molecules are built up and how their properties vary with size, reaching an upper limit with bulk graphite and diamond. Carbon atoms with sp2 hybridization give rise to an impressive number of different materials, such as carbon nanotubes, graphene nanoribbons, porous carbon and fullerene. As in any crystalline phase, the crystal structures of natural carbon allotropes (i.e. graphite and diamond) contain various types of imperfections. These so-called lattice defects are classified by their dimensions into 0D (point), 1D (line), 2D (planar) and 3D (volume) defects. Lattice defects control the physical properties of crystals and are often a fingerprint of the geological environment in which they formed and were modified. Direct observations of lattice defects are commonly accomplished by transmission electron microscopy. We present and discuss the ideal and real structures of carbon allotropes, the energetics of lattice defects and their significance in understanding geological processes and conditions.

Structural and electronic properties of T-graphene and its derivatives

Recent years there has been aroused a growing interest in designing two-dimensional (2D) structures of carbon allotropes, owing to the great success in graphene. The T-graphene is a newly proposed 2D carbon allotrope possessing tetragonal symmetry other than hexagonal symmetry of graphene. Also, the energetic and dynamical stabilities of T-graphene have been revealed. So motivated, we investigate the structural stabilities and electronic properties of T-graphene and especially its derivatives-n(n=1-5) by using the first-principle calculation based on the density function theory. By changing the atomic number (n) of the linear carbon chains connecting the two tetragon rings of T-graphene, a series of sp-sp2 hybrid structures can be formed, which is named T-graphene derivatives-n. The calculation results show that the structural stabilities, chemical bond types and electronic structures of these materials depend greatly on the parity of n. Owing to a strong π-bond formed by eight carbon atoms in T-graphene, it becomes the one with the lowest energy in all these materials studied in this work. An interesting phenomenon is found that the T-graphene derivatives-n with even n are dynamically stable as witnessed by the calculated phonon spectra without imaginary modes, while those with odd n are dynamically unstable. The metallic behaviors are present in the T-graphene derivatives-n with even carbon atoms in the linear carbon chains, showing an alternating single and triple C–C bonds. Besides, we observe that the metallicity of the T-graphene derivatives-n with even n becomes stronger as n increases. On the other hand, the linear carbon chains with odd carbon atoms are comprised of continuous C=C double bonds. These T-graphene derivatives-n with odd n also show metallic behaviors, but turn into magnetic materials (except for n=1), the magnetic moments are about 0.961μB (n=3) and 0.863μB (n=5) respectively, and ferromagnetic ordering is the only possibility for the magnetism, which rarely occurs in carbon material. Our first-principle studies indicate that the introducing carbon chains between the tetragonal carbon rings of T-graphene constitute an efficient method to obtain new two-dimensional carbon allotrope. With different numbers (even or odd) of carbon atoms on the chains, the constructed 2D carbon allotropes could show contrasting dynamical and magnetic properties. These findings provide a theoretical basis for designing two-dimensional carbon materials and carbon-based nanoelectronic devices.

Carbon allotropes with triple bond predicted by first-principle calculation: Triple bond modified diamond andT-carbon

We have designed new structures of carbon allotropes combining a mixture of $sp$ (triple bond) and $s{p}^{3}$ (single bond) hybridization through first-principle calculation. These two structures named yne-carbon (Y-carbon) and tetrayne-carbon (TY-carbon), respectively, not only maintained the cubic structure and space group ($Fd\overline{3}m$) of diamond but were also energetically more stable than recently proposed carbon allotrope, T-carbon. A phonon calculation revealed these structures to be stable, and the nature of the triple bond was illustrated by the unique phonon spectrum with an eigen-frequency of 2200 cm${}^{\ensuremath{-}1}$. The band gap of Y-carbon was found to be larger than that of diamond, whereas the band gap of TY-carbon was smaller than that of T-carbon, which is closely related to the properties of a carbon tetrahedron. The existence of triple bonding of carbon is associated with a dimerization phenomenon due to Peierls instability.

Field emission and electronic structures of carbon allotropes

Field emissions (FEs) of a carbon atom, silicon clusters, graphitic ribbons and diamond surfaces have been investigated within the time-dependent density-functional theory (TD-DFT). The electronic states origin of field emission properties reflecting the atomic geometries and hydrogen (H) termination of edges are elucidated through the analyses of energy band structures, energy distribution of emitted electrons and σ- and π-bonding natures. Findings in this study provide the theoretical basis for understanding the FE mechanism of covalent-bond materials and designing Si- and C-based nanostructured field emitters.