Two-dimensional Carbon Allotrope Research Articles

Atomistic understanding of the interlayer friction of graphullerene

Graphullerene, an emerging two-dimensional carbon allotrope derived from C60, is endowed with distinctive mechanical and thermal characteristics, positioning it as a potential candidate with superior lubricating properties akin to graphene and C60. This research delves into the interlayer frictional behavior of graphullerene through molecular dynamics simulations, meticulously examining the impact of sliding velocity, normal load, flake orientation, and temperature. The findings reveal a stick-slip mode of friction with an exponential increase in friction force as sliding velocity increases. Additionally, the study captures the formation of puckering at the slider's forefront, which undergoes ballistic motion propelled by the slider's momentum. Notably, at higher velocities, a distinctive "stone skipping" effect is observed, with the graphullerene flake intermittently detaching from the substrate.

Design of a photocatalyst combining graphdiyne (g-CnH2n-2) nanosheets with a PVP-modified co-metal coordination polymer and its hydrogen-evolution performance.

Metal coordination polymers are organometallic frameworks in which a metal and an organic ligand are linked via a dative bond. The material in question exhibits ultra-high porosity, large specific surface area, and abundant active sites, which can be customised in terms of morphology, size, and electronic structure through rational design. Graphdiyne, a novel two-dimensional carbon allotrope, boasts structural stability and enhanced electrical conductivity due to its hybridization of sp2 and sp carbons. A metal-organic framework of Co (MOF-67) was synthesized via hydrothermal synthesis. The introduction of polyvinyl pyrrolidone (PVP) served as a structural regulator and surfactant to obtain a more active metal coordination polymer (Co-MCPS). PVP, in its dual role, significantly amplified the catalytic performance of metal coordinate polymers, as demonstrated in a number of experiments. The incorporation of GDY onto the surfaces of MOF-67 and Co-MCPS induced an electron-rich isolation layer, which could effectively sequester oxidation sites, thereby enhancing the rate of charge carrier separation and hydrogen precipitation evolution efficiency.

Electronic and structural insights into boron nitride counterparts of Net-(Y,W)

Computational materials play a crucial role in comprehending various material classes and their properties, offering valuable insights for predicting novel structures and complementing experimental approaches. Net-(C,Y,W) has emerged as stable two-dimensional carbon allotropes of 4-6-8 carbon rings within this framework. This study uses density functional theory calculations and ab initio molecular dynamics simulations to explore the structural, electronic, optical, and mechanical properties of their boron nitride counterparts, named NetBN-W and NetBN-Y, with NetBN-C already investigated. The electronic analysis reveals an insulating characteristic for NetBN-W and a potential wide band gap semiconducting nature for NetBN-Y, with values of 5.12 eV and 3.71 eV, respectively. Optical properties examination indicates UV activity for these materials, accompanied by optical anisotropy between the x and y directions. Evaluation of mechanical properties also uncovers significant anisotropy in both materials, with Young’s moduli reaching 417.58 GPa for NetBN-W and 433.31 GPa for NetBN-Y when stretched in the y-direction of the basal plane. The nearly zero Young’s modulus for NetBN-Y in the x-direction signifies its substantial instability under tension due to nitrogen bonds parallel to the strain direction. These findings offer valuable insights into the fundamental properties of NetBN-W and NetBN-Y and their potential applications.

Strongly Bound Excitons and Anisotropic Linear Absorption in Monolayer Graphullerene.

Graphullerene is a novel two-dimensional carbon allotrope with unique optoelectronic properties. Despite significant experimental characterization and prior density functional theory calculations, unanswered questions remain as to the nature, energy, and intensity of the electronic and optical excitations. Here, we present first-principles calculations of the quasiparticle band structure, neutral excitations, and absorption spectra of monolayer graphullerene and bulk graphullerite, employing the GW-Bethe-Salpeter equation (GW-BSE) approach. We show that strongly bound excitons dominate the absorption spectrum of monolayer graphullerene with binding energies up to 0.8 eV, while graphullerite exhibits less pronounced excitonic effects. Our calculations also reveal a strong linear polarization anisotropy, reflecting the in-plane structural anisotropy from intermolecular coupling between neighboring C60 units. We further show that the presence of Mg atoms, crucial to the synthesis process, induces structural modifications and polarizability effects, resulting in a ∼1 eV quasiparticle gap renormalization and a reduction in the exciton binding energy to ∼0.6 eV.

On the mechanical, thermoelectric, and excitonic properties of Tetragraphene monolayer

Two-dimensional carbon allotropes have attracted much attention due to their extraordinary optoelectronic and mechanical properties, which can be exploited for energy conversion and storage applications. In this work, we use density functional theory simulations and semi-empirical methods to investigate the mechanical, thermoelectric, and excitonic properties of Tetrahexcarbon (also known as Tetragraphene). This quasi-2D carbon allotrope exhibits a combination of squared and hexagonal rings in a buckled shape. Our findings reveal that tetragraphene is a semiconductor material with a direct electronic bandgap of 2.66eV. Despite the direct nature of the electronic band structure, this material has an indirect exciton ground state of 2.30eV, which results in an exciton binding energy of 0.36eV. At ambient temperature, we obtain that the lattice thermal conductivity (κL) for tetragraphene is approximately 118 W/mK. Young’s modulus and the shear modulus of tetragraphene are almost isotropic, with maximum values of 286.0N/m and 133.7N/m, respectively, while exhibiting a very low anisotropic Poisson ratio value of 0.09.

TD-graphene: Theoretical prediction of a high-performance anode material for sodium-ion batteries with intrinsic metallicity, high capacity, and fast ion mobility

The utilization of pristine graphene as an anode material in sodium-ion batteries (SIBs) is limited by its inherent chemical inertness toward Na-ions. To address this issue, we propose a two-dimensional carbon allotrope (named as TD-graphene) by assembling tricyclo[4.4.1.11,6]dodecane (C12H20) skeleton. The topological non-hexagonal feature of C12H20 increases the degree of local carbon-ring disorder and introduces additional electron-deficient regions on the surface, thus enhancing the adsorption capability of Na. TD-graphene demonstrates exceptional stability across the energetic, thermodynamic, dynamic, and mechanical aspects. As a promising anode for SIBs, it exhibits an intrinsic metallicity, an ultra-high storage capacity (1487.58 mA h g−1), a low diffusion barrier (0.20 eV), a low average open-circuit voltage (0.33 V), and a small lattice expansion (0.6%). The presence of solvents with high dielectric constants improves the adsorption and migration capability of Na. Furthermore, taking into account the limitation of single-layer materials in practical applications, we employ h-BN as a promising substrate for TD-graphene, which can boost the Na adsorption and diffusion performance. These results render TD-graphene as a promising high-performance anode material for SIBs.

Boosting hydrogen storage capacity in modified-graphdiyne structures: A comprehensive density functional study

Graphdiyne (GDY) is a recently discovered two-dimensional carbon allotrope that holds significant promise for applications in hydrogen adsorption and storage technology. This study investigates the impact of nitrogen doping and sodium decoration on the hydrogen adsorption capacity of GDY nanosheets while examining their influence on electronic and structural properties. Various deliberate impurities are introduced to create modified-GDY structures. Nitrogen doping triggers a transition from a semiconductor to a semi-metallic state, driven by differences in electronegativity and adjustments in bond lengths. Cohesive energy (Ecoh) is found to be −7.231 eV for the most stable N-doped GDY. In contrast, sodium decoration enhances conduction by modifying charge distribution. The other most stable structures are Na-decorated GDY with Eads of −3.804 eV and N, Na-decorated GDY with −3.347 eV. Modified-GDY structures exhibit higher hydrogen adsorption energies compared to pristine GDY, with N-doped GDY displaying the highest energy levels (Eads = −0.455 eV). Maximum hydrogen adsorption capacities are assessed for each structure, and a notable improvement is observed in Na-decorated GDY (19 H2), significantly enhancing the storage capacity to 13.8 wt%, which shows a 10.21 wt% increase in H2 adsorption compared to pure GDY (3.59 wt%). These findings underscore the potential of modified-GDY for hydrogen storage applications, highlighting the effectiveness of structural carbon modification in enhancing hydrogen adsorption capacity.

Effect of Strain Rate, Temperature, Vacancy, and Microcracks on Mechanical Properties of 8-16-4 Graphyne.

The 8-16-4 graphyne, a recently identified two-dimensional carbon allotrope, exhibits distinctive mechanical and electrical properties, making it a candidate material for flexible electronic applications. This study endeavors to enhance our comprehension of the fracture behavior and mechanical properties of 8-16-4 graphyne. The mechanical properties of 8-16-4 graphyne were evaluated through molecular dynamics simulations, examining the impact of boundary conditions, temperature, and strain rate, as well as the coupled interactions between temperature, vacancy defects, and microcracks. The findings reveal that 8-16-4 graphyne undergoes fracture via the cleavage of ethylene bonds at a critical strain value of approximately 0.29. Variations in boundary conditions and strain rate influence the fidelity of tensile simulation outcomes. Temperature, vacancy concentration, and the presence of microcracks markedly affect the mechanical properties of 8-16-4 graphyne. In contrast to other carbon allotropes, 8-16-4 graphyne exhibits a diminished sensitivity to vacancy defects in its mechanical performance. However, carbon vacancies at particular sites are more prone to initiating cracks. Furthermore, pre-existing microcracks within the material can potentially alter the fracture mode.

Superpentagraphene C34: A two-dimensional network structure of C20 fullerene

The well-known smallest icosahedral fullerene C20 is comprising five-membered carbon-rings in all sp2 bonding states. Here we identify by ab initio calculations a new quasi two-dimensional (2D) carbon allotrope in sp2-sp3 bonding states, comprising the unusual five-membered C20 fullerene as the basic structural units, with a 34-atom hexagonal cell in P6/mmm(D6h1) symmetry, and term it as spg-C34 superpentagraphene. Total energy calculations show that it is energetically more stable than the previously reported 2D carbon forms such as pentagraphene and ph-graphene. Its structural stability has been verified by phonon mode analysis and ab initio molecular dynamics simulations. Electronic band calculations reveal that this 2D spg-C34 carbon is a semiconductor with a sizable indirect band gap of 3.31 eV. Moreover, we show that such 2D spg-C34 carbon structure has a larger layer modulus (281 N/m), a larger in-plane stiffness (524 N/m), and a smaller Poisson's ratio (0.069) than the values for graphene. These results establish a new exotic quasi-2D carbon phase and offer insights into its outstanding electronic and mechanical properties of two-dimensional carbon structure.

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.

Prediction of highly stable 2D carbon allotropes based on azulenoid kekulene

Despite enormous interest in two-dimensional (2D) carbon allotropes, discovering stable 2D carbon structures with practically useful electronic properties presents a significant challenge. Computational modeling in this work shows that fusing azulene-derived macrocycles – azulenoid kekulenes (AK) – into graphene leads to the most stable 2D carbon allotropes reported to date, excluding graphene. Density functional theory predicts that placing the AK units in appropriate relative positions in the graphene lattice opens the 0.54 eV electronic bandgap and leads to the appearance of the remarkable 0.80 eV secondary gap between conduction bands – a feature that is rare in 2D carbon allotropes but is known to enhance light absorption and emission in 3D semiconductors. Among porous AK structures, one material stands out as a stable narrow-multigap (0.36 and 0.56 eV) semiconductor with light charge carriers (me = 0.17 m0, mh = 0.19 m0), whereas its boron nitride analog is a wide-multigap (1.51 and 0.82 eV) semiconductor with light carriers (me = 0.39 m0, mh = 0.32 m0). The multigap engineering strategy proposed here can be applied to other carbon nanostructures creating novel 2D materials for electronic and optoelectronic applications.

A novel two-dimensional all-carbon Dirac node-line semimetal

Carbon allotropes have vast potential in various applications, including superconductivity, energy storage, catalysis, and photoelectric semiconductor devices. Recently, there has been significant research interest in exploring new carbon materials that exhibit unique electronic structures. Here, we propose a novel two-dimensional (2D) carbon allotrope called TCH-SSH-2D, which possesses a Dirac node-line (DNL) semimetallic state. The structure of TCH-SSH-2D is derived from the TCH-type Archimedean polyhedral carbon cluster units, combined with the SSH lattice model, possessing a space group of tetragonal P4/mmm. Using first-principles calculations, we demonstrate that the system is dynamically, thermodynamically, and mechanically stable. It exhibits an energetically favorable structure with no imaginary frequency in the phonon dispersion curves and elastic constants satisfying the Born-Huang stability criterion. Our findings not only contribute to a deeper understanding of the carbon allotrope family but also provide an opportunity to explore unique Dirac states in two-dimensional pure carbon systems.

Boosting Potassium Adsorption and Diffusion Performance of Carbon Anodes for Potassium-Ion Batteries via Topology and Curvature Engineering: From KT-Graphene to KT-CNTs.

We propose a two-dimensional carbon allotrope (named KT-graphene) by incorporating kagome and tetragonal lattices consisting of trigonal, quadrilateral, octagonal, and dodecagonal rings. The introduction of non-hexagonal rings can give rise to the localized electronic states that improve the chemical reactivity toward potassium, making KT-graphene a high-performance anode material for potassium-ion batteries. It shows a high theoretical capacity (892 mAh g-1), a low diffusion barrier (0.33 eV), and a low average open-circuit voltage (0.51 V). The presence of electrolyte solvents is propitious to boost the K-ion adsorption and diffusion capabilities. Moreover, one-dimensional nanotubes (KT-CNTs), rolled up by the KT-graphene sheet, are metallic regardless of the tube diameter. As the curvature increases, KT-CNTs exhibit significantly increased surface activity, which can promote the electron-donating ability of K. Furthermore, the curvature effect greatly enhances the efficiency of K diffusion on the inner surface compared to that on the outer surface.

Topological electronic states in holey graphyne

We unveil that the holey graphyne (HGY), a two-dimensional carbon allotrope where benzene rings are connected by two −C≡C− bonds fabricated recently in a bottom-up way, exhibits topological electronic states. Using first-principles calculations and Wannier tight-binding modeling, we discover a higher-order topological invariant associated with C 2 symmetry of the material, and show that the resultant corner modes appear in nanoflakes matching to the structure of precursor reported previously, which are ready for direct experimental observations. In addition, we find that a band inversion between emergent g-like and h-like orbitals gives rise to a nontrivial topology characterized by Z2 invariant protected by an energy gap as large as 0.52 eV, manifesting helical edge states mimicking those in the prominent quantum spin Hall effect, which can be accessed experimentally after hydrogenation in HGY. We hope these findings trigger interests towards exploring the topological electronic states in HGY and related future electronics applications.

Two-dimensional carbon allotrope with remarkable electron mobility and tunable band gap under uniaxial strain engineering

Exploring two-dimensional (2D) materials with unique structures and excellent photoelectric properties has always been the foundation content of carbon-based material science and condensed matter physics research. In this work, on the basis of density functional theory, the structural, mechanical, electrical and optical properties of the pure sp2 hybrid 2D carbon allotropes Orth-C14 and Orth-C16 were comprehensively predicted, and the regulatory mechanism of the uniaxial strain on the stability, elastic mechanics and electronic properties were analysed. Orth-C16 and Orth-C14 are semiconductors and metals with extremely narrow bandgaps, respectively. Interestingly, their electronic properties could be tuned to indirect band gap semiconductors, metals or half-metallic states with Dirac cones by applying uniaxial strain. In addition, the extremely low effective mass (0.009 m0) and remarkable room temperature electron mobility (69,708 cm2V-1s-1) of approximately 70 times greater than that of black phosphorene (1100 ∼ 1140 cm2V-1s-1), as well as the strong absorption capacity of visible light, all of these advantages indicate that Orth-C16 has crucial development potential in the field of electronic information and optoelectronics.

Insights into the DHQ-BN: mechanical, electronic, and optical properties

Computational materials research is vital in improving our understanding of various class of materials and their properties, contributing valuable information that helps predict innovative structures and complement empirical investigations. In this context, DHQ-graphene recently emerged as a stable two-dimensional carbon allotrope composed of decagonal, hexagonal, and quadrilateral carbon rings. Here, we employ density functional theory calculations to investigate the mechanical, electronic, and optical features of its boron nitride counterpart (DHQ-BN). Our findings reveal an insulating band gap of 5.11 eV at the HSE06 level and good structural stability supported by phonon calculations and ab initio molecular dynamics simulations. Moreover, DHQ-BN exhibits strong ultraviolet (UV) activity, suggesting its potential as a highly efficient UV light absorber. Its mechanical properties, including Young’s modulus (230 GPa) and Poisson’s ratio (0.7), provide insight into its mechanical resilience and structural stability.

Evaluation of the structural, electronic and magnetic properties of modified 8-16-4 graphyne by 3d transition metals: A DFT-D2 study

A new two-dimensional carbon allotrope called 8-16-4 graphyne (GY) has been recently introduced (in 2021). This allotrope consists of sp. and sp2 hybridized carbon atoms. To investigate the adsorption behavior of single atom of 3d transition metals (TM) on 8-16-4 GY, corrected density functional theory (DFT-D2) was employed. The results reveal that single TM atoms prefer to bind tightly in the center of the 16-carbon ring of GY, and the adsorption energy of TMs decreases from Sc to Zn with a reducible trend from −9.282 to −1.158 eV, respectively. These high adsorption energies show that diffusion of TM atoms and clustering of them are prevented on the surface of the carbon frame. Pristine and 3d TM decorated GY have some Dirac points, zero band gap, and conductivity properties. Also, pristine and all of TM decorated GY except Cr, Mn, and Fe-decorated GY haven't magnetic properties. These findings suggest that 8-16-4 GY is a suitable carbonic substrate to prevent the clustering of TM atoms that is essential for some applications such as effective single-atom catalysts, hydrogen storage, CO2 capture, etcetera.

A short review on graphene derivatives towards photoelectrochemical water splitting

Graphene oxide is vital in photoelectrochemical (PEC) water splitting, serving as an essential photoanode material. Its semiconducting nature allows for the generation of photocurrents, promoting water oxidation at the anode and contributing to hydrogen production efficiency. Additionally, graphene is a two-dimensional carbon allotrope that has quickly emerged as a highly promising material in PEC water splitting, potentially transforming renewable energy and sustainable hydrogen generation. Graphene improves PEC water-splitting efficiency by facilitating efficient charge transport, rapid electron transfer, and effective redox reactions at the electrode-electrolyte interface. It possesses high electrical conductivity, a large specific surface area, and excellent charge carrier mobility. Its unique band structure enables efficient light absorption across a broad spectrum, including visible light, resulting in better light-to-electricity conversion. Furthermore, the inherent catalytic activity of graphene speeds up the oxygen evolution process (OER), increasing water oxidation and aiding hydrogen gas production.

Density functional theory study of the electronic and optical properties of pentagraphyne nanotubes.

Pentagraphyne (PG-yne), a recently predicted two-dimensional (2D) carbon allotrope with appealing properties, has opened up possibilities for a wide range of applications. In this study, we investigate the structural, electronic, optical, and electrical transport properties of a novel one-dimensional (1D) system called pentagraphyne nanotubes (PG-yneNTs), formed by rolling a PG-yne sheet, using density functional theory (DFT) calculations. We design PG-yneNTs with diameters ranging from 6.94 Å to 13.62 Å and employ state-of-the-art theoretical calculations to confirm their energetic, dynamic, and thermodynamic stability. Our electronic band structure calculations reveal that all these nanotubes are wide indirect band gap semiconductors. Remarkably, PG-yneNTs exhibit superior optical properties, including high absorption coefficients and absorption spectra covering the visible regime of the electromagnetic spectrum, making them potential candidates for visible-light-driven photocatalysis and solar cells. Interestingly, both the electronic and optical band gaps increase with the diameter of the nanotubes. Additionally, the observation of negative differential resistance (NDR) phenomena in (4, 0) PG-yneNT suggests their potential applications in NDR devices such as fast switches, frequency multipliers, and memory devices.

Biomass Pyrolysis-Derived Biochar: A Versatile Precursor for Graphene Synthesis.

Graphene, a two-dimensional carbon allotrope with a honeycomb structure, has emerged as a material of immense interest in diverse scientific and technical domains. It is mainly produced from graphite by mechanical, chemical and electrochemical exfoliation. As renewable energy and source utilization increase, including bioenergy from forest and woody residues, processed, among other methods, by pyrolysis treatment, it can be expected that biochar production will increase too. Thus, its useful applications, particularly in obtaining high-added-value products, need to be fully explored. This study aims at presenting a comprehensive analysis derived from experimental data, offering insights into the potential of biomass pyrolysis-derived biochar as a versatile precursor for the controlled synthesis of graphene and its derivatives. This approach comprehended the highest energy output and lowest negative environmental footprint, including the minimization of both toxic gas emissions during processing and heavy metals' presence in the feedstock, toward obtaining biochar suitable to be modified, employing the Hummers and intercalation with persulfate salts methods, aiming at deriving graphene-like materials. Material characterization has revealed that besides morphology and structural features of the original wooden biomass, graphitized structures are present as well, which is proven clearly by Raman and XPS analyses. Electrochemical tests revealed higher conductivity in modified samples, implying their graphene-like nature.