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For ever-growing demand of clean and renewable energy resources, finding a low-cost, earth abundant, and an efficient electrocatalyst to replace platinum-based catalysts for hydrogen evolution reaction (HER) has drawn the interest of scientific community. In present work, first-row transition metal single atom catalysts supported on graphyne surface have been designed and investigated using density functional theory approach. The results indicate that among all considered systems, the highest thermodynamic stability and best HER catalytic performance is computed for Ni single atom catalyst (SAC) anchored on graphyne support with low Δ G H ∗ value of 0.08 eV. We have calculated density of states, energies of HOMO, LUMO and HOMO-LUMO gap for our designed single atom catalysts as well as hydrogen adsorption. Our results indicate that Ni anchored on graphyne support can be a promising candidate for noble metal free, earth abundant, and low cost electrocatalyst to efficiently catalyze hydrogen evolution reaction process.

The electrochemical synthesis of hydrogen peroxide (H2O2) provides a greener and more efficient method compared with classic catalysts containing toxic metals. Herein, we used first-principles density functional theory (DFT) calculations to investigate 174 different single-atom catalysts with graphyne substrates, and conducted a three-step screening strategy to identify the optimal noble metal-free single atom catalyst. It is found that a single Ni atom loaded on γ-graphyne with carbon vacancies (Ni@V-γ-GY) displayed remarkable thermodynamic stability, excellent selectivity, and high activity with an ultralow overpotential of 0.03 V. Furthermore, based on ab-initio molecular dynamic and DFT calculations under the H2O solvent, it was revealed that the catalytic performance for H2O2 synthesis in aqueous phase was much better than that in gas phase condition, shedding light on the hydrogen bond network being beneficial to accelerate the transfer of protons for H2O2 synthesis.

As a new carbon allotrope, graphyne (GY) has been predicted with singular and abundant electrochemical capabilities. Although it is difficult to prepare GY directly, the preparation of GY derivatives can help us to understand the properties of GY from another perspective. Herein, we developed a facile strategy to prepare GY derivatives such as nitrogen (N) substituted GYs which are comprised by azaaromatic rings and acetylene bonds. Their band gap and lithium storage properties have been tuned by presetting the number of N atoms in the benzene ring. Both properties and applications of the as-prepared GYs have been studied and compared with the calculation results of GY. With the increase of N content in GY, the charge concentration and the conductivity have been improved, while the band gap has been decreased and lithium storage capability has been enhanced, demonstrating the property and performance of GY can be well regulated by precise N introduction. Notably, all these experimental and theoretical results suggested a universal avenue for the preparation of GY based versatile materials with regulated properties by tuning the composition of benzene rings.

Developing efficient catalysis for dinitrogen (N2) fixation is a very important and challenging issue in chemistry. Herein, by means of density functional theory (DFT) computations, we reported that the potential of single-atom Rhenium (Re) supported on the graphyne (Re-GY) for activating N2 and reducing it into ammonia (NH3). It is found that the adsorption energies of N2 on Re-GY for end-on/side-on configuration are −1.05/-0.56 eV, together with the N–N bond length are stretched to 1.14/1.21 A, respectively. The hydrazine intermediate is difficult to release with adsorption energies of −1.71/1.49 eV on Re-GY for different pathways, which ensures it is sequentially hydrogenated and eventually form NH3. All the mechanisms considered are energetically favorable and the most favorable pathway is the mixed mechanism. It is worth noting that there are relatively rare researches on Re-based catalysts for N2 fixation, our findings provide a new option for the design and synthesis of catalysts for N2 reduction reaction.

The high cost and relative scarcity of platinum (Pt) restrict large-scale commercialization of fuel cells, which has spurred researchers to develop low-cost alternatives integrating with high hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) catalytic activity. Herein, we performed density functional theory (DFT) calculations to explore the electrocatalytic activity of graphyne nanotubes (GyNTs). Several GyNTs were found to be potential metal-free electrocatalysts, with both HER and ORR activity superior to Pt. Moreover, we revealed a linear relationship between the Gibbs free energy change of O2 adsorption (ΔGOOH) and binding energy of H adsorption (ΔEH), which could be attributed to the fact that both the C O bond of OOH adsorption and the C H bond of H adsorption are single bonds. Therefore, ΔEH is proposed as a general descriptor for the rational design of bifunctional graphyne materials toward HERs and ORRs. Our findings provide a simple strategy for the rational design of bifunctional materials.

Carbon is an element with extremely versatile bonding properties and theoretical calculations have suggested the possible existence of several hundred structural allotropes. Many, or even most, of these are predicted to be formed under conditions of high pressure and temperature. On the other hand, experimental high pressure studies have identified surprisingly few structural allotropes. In this paper, physical properties and structural transformations observed in high pressure experiments, at and above room temperature, are reviewed for a large number of solid carbon allotropes. The materials discussed include bulk carbon such as graphite, diamond, glass-like and amorphous carbon, two-dimensional graphene, and molecular carbon in the form of one-dimensional carbon nanotubes and zero-dimensional fullerenes. Results from recent studies on twisted graphene, graphdiyne, graphyne, carbon dots and other interesting all-carbon allotropes are also briefly described. Observed similarities and differences between the high pressure behavior and evolution of carbon materials are discussed. In spite of the enormous volume of experimental work carried out on these materials, few new structural allotropes have been identified and most carbon materials studied convert into diamond at sufficiently high temperature and pressure. Further theoretical work thus seems to be needed to elucidate possible transformation processes and transition paths for the many undiscovered allotropes proposed from calculations. In particular, it is recommended that, for every new allotrope predicted by theory, suitable precursors and transformation conditions should also be investigated. Efficient creation of new structural allotropes or functional materials based on pure carbon by high pressure methods should ideally start from designed, preassembled precursor structures or composites for which transition paths can be theoretically predicted.

In this paper, we perform a systematical investigation on searching for defect γ -graphyne nanoribbons ( γ -GYNRs) with optimal thermoelectric performance by utilizing nonequilibrium Green’s function combined with Bayesian optimization. The calculations show that Bayesian optimization could quickly and accurately identify the optimal structure with best thermoelectric efficiency. Even in the worst round of optimization, optimal structure could be obtained by only calculating 719 structure candidates (merely 4.35% of all the 16512 candidates). The room temperature thermoelectric figure of merit of optimal defect γ -GYNR (length 11.846 nm, width 1.453 nm) could approach 2.315, which is 5 times of that of pristine γ -GYNR. The obvious advantage of optimal defect γ -GYNR is mainly attributed to the maximum balance of weakening of thermal power factor (side effect) and suppression of thermal conductance (positive effect). Through analyzing the pair correlation function, we also find that the correlations between perfect (defect) unit and perfect (defect) unit are both extremely low for defect γ -GYNRs with high thermoelectric conversion efficiency. The findings presented in this work indicate the effectiveness and superiority of Bayesian optimization in designing defect γ -GYNRs, and could provide new insights for exploring other low-dimensional materials with excellent thermoelectric properties.

To obtain high hydrogen storage performance, Li and Na co-decorated T4,4,4-graphyne have been studied by the method of first-principles calculations in this paper. Li and Na atoms are bound on hexagonal ring and acetylenic ring included in T4,4,4-graphyne, with the average adsorption energy of 1.73 and 2.38 eV, respectively. Our calculations show that the maximum gravimetric density of H2 uptake is 10.46 wt%, and an appropriate adsorption energy is reached. Moreover, by plotting charge density differences, it is found that the induced electric field between Li/Na and T4,4,4-graphyne can enhance the adsorption for hydrogen molecule. Furthermore, this complex is thermodynamic stable at room temperature, which is certificated by molecule dynamics simulation. Our results demonstrate that Li and Na co-decorated T4,4,4-graphyne is an alternative material for hydrogen storage.

Motivated by novel graphyne-like carbon nanostructure C68-GY, spin-polarized DFT calculations with dispersion-correction were performed to investigate the hydrogen adsorption capacity of Li decorated C68-GY nanosheet. The binding energy between Li and C68-GY was larger than the cohesive energy of bulk metal, indicating Li atoms would prefer to separately attached on C68-GY. The ab initio molecular dynamics simulation has been performed to confirm the stability of Li/C complex. When five Li atoms decorated on C68-GY, 14H2 molecules were captured. The maximum hydrogen storage density was 8.04 wt% with an average hydrogen adsorption energy of −0.227 eV per H2. The positively charged Li atoms aroused electrostatic field and induced the polarization of H2. It was notable to observe strong hybridization between the main peak of H-1s orbitals with Li below Fermi level, which was responsible for the enhancement of hydrogen binding energy, indicating its potential application on hydrogen storage.

The hydrogen storage capacity of yttrium decorated graphyne nanotubes is calculated using spin polarized DFT method. The stabilities, electronic properties and the structures of Y attachment on graphyne tube are investigated. It is revealed that Y can be separately adsorbed on graphyne tube with the binding energy of 6.76 eV and the clustering of metal atoms is hindered. The geometry optimization shows that Y atoms decorated graphyne tube can capture 42H2 molecules through Dewar-Kubas like interaction and the polarization under the electrostatic potential formed by Y and graphyne tubes. The weight percent capacity is 5.71 wt%, with an average hydrogen adsorption energy of −0.153 eV per H2, indicating its potential application on hydrogen storage candidates.

By applying non-equilibrium Green's functions (NEGF) in combination with tight-binding (TB) model, the electronic transport properties of pristine and defected zigzag α-graphyne nanotubes (Z-α-GYNTs) are studied under finite bias. We have considered single vacancy (SV) and double vacancy (DV) and also the effect of tube size. Depending on the position of absent atom(s), different modes arise. Initially the formation energy is calculated for each mode and we observed that in all cases an endothermic process in needed. Moreover by studying the band structure we found that all defects cause gap closing, but not enough to change the semiconducting nature of Z-α-GYNTs entirely. Considering p as a positive integer, I-V characteristics show that for (3p-1, 0) tubes, all defects are found to increase the current but on the contrary presence of them in a (3p, 0) tube results in current reduction. (3p + 1, 0) tubes does not show a defined and specific reaction to the defects. Band structure of electrodes, transmission spectrum, Density of states, molecular energy spectrum and molecular projected self-consistent Hamiltonian (MPSH) are analyzed subsequently to make the electronic transport properties of GYNT devices clearer. Our results can be used in developing nano-scale devices.

Developing highly active and non-precious-metal single-atom catalysts (SAC) for electrochemical water splitting is of great significance to the development of renewable energy technology in future. Herein, 10 first-row transition-metal (TM, from Sc to Zn) single atoms anchored on a graphyne (GY) nanosheet (TM@GY) as electrocatalysts for water splitting are explored through computational screening approach. It is found that the single atoms prefer to tightly bind at the acetylenic-ring center of GY. Meanwhile, these TM@GY catalysts show metallic properties or reduced band gap, favoring electron transfer during the electrochemical processes. Moreover, both Co@GY and Mn@GY catalysts present good catalytic performance for hydrogen evolution reaction (HER) with both the acetylenic C and TM atoms being highly active sites. However, only the Co@GY catalyst shows good oxygen evolution reaction (OER) activity with an overpotential of 0.55 V. Thus, Co@GY could serve as a potential bifunctional electrocatalyst for water splitting. Besides, the d-band center of TM atoms on TM@GY can be turned through controlling TM atoms with different d-electron number and be used to predict the OER performance. This work highlights that GY doped with single non-precious-metals can be considered for designing high-active and low-cost bifunctional electrocatalysts for practical electrochemical reactions.

We design novel graphyne/blue phosphorene van der Waals (vdW) heterostructures (G/BP) under the external electric fields (Efield) and strains. It is demonstrated that the G/BP is a type-I semiconductor with a direct band gap of approximately 0.378 eV. The external Efield and strains not only have important effects on the band structure which undergoes a fascinating direct-indirect and semiconductor-metal transitions, but also influence the band alignment which experiences transition from type-I to type-II. In brief, the features of tunable bandgap and controllable band alignment endow G/BP with potential for application in future optoelectronic devices.

In this work, electronic and structural properties of single Al or N atom doped and Al-N co-doped graphyne (GY) toward hydrogen storage were investigated using DFT-D calculations. Results show that N and Al atoms energetically prefer to lie instead of Csp in the chain and Csp2 in the hexagonal ring, respectively. Al or N doping changes conducting nature of GY from semiconductor to metallic. Pristine GY and more stable structures of Al doped, N doped and Al-N co-doped GY were examined for H2 adsorption. Adsorption energies for the first H2 molecule are about −0.140, −0.224, −0.141 and −0.288 eV/H2, respectively. They can hold 4, 9, 7 and 16 H2 molecules with average adsorption energy of ~−0.089, −0.158, −0.144 and −0.161 eV/H2, respectively. Also, the calculated corresponding hydrogen storage capacities reach up to 5.26, 10.17, 8.75 and 16.67 wt%, respectively. Although, effect of Al atom is more than N atom, when both of them co-doped in GY, its electronic and structural properties, as well as hydrogen storage capacity improve, extremely and they have a synergistic effect onto hydrogen adsorption. These findings show that N-Al co-doped GY can be used for designing new hydrogen storage materials in the future.

Many layered graphene and graphene-like two-dimensional carbon materials have been successively proposed in theory and experiment owing to their exceptional properties and potential applications. By employing the first-principles study, we find that a new graphene-like material, δ -graphyne, whose properties of the zigzag-edged nanoribbon are very similar to those ones of zigzag-edged graphene case. The band structure clearly exhibits a metallic property in non-magnetic state. And we can see a visible spin splitting within the ferromagnetic state, however, spin degeneracy within the antiferromagnetic state. To this end, here we propose a molecular junction based on the zigzag- δ -graphyne nanoribbon symmetrically with additional phenyl rings at both edges. The computational results imply that the device has many good electron transport performances, such as negative differential resistance, spin-filtering and rectification effects, and so on. In particular, the spin-filtering efficiency can be up to 99%, and the maximum of the rectification ratio reaches up to 106%. The mechanisms for these effects are revealed and discussed in terms of the band structure, spin-resolved electron transmission spectrum, the local density of state and the transmission pathway. Therefore, our research results can provide a basis for the experimental preparation of the δ -graphyne-based junction.

Two-dimensional (2D) carbon nitrides are drawing increasing interests due to the structural diversities and unique electronic properties, superiors to the pure 2D carbon materials. Motivated by the recent experimental progresses, we investigated from first-principles a new family of 2D carbon nitrides composed of sp- and sp2-hybridized carbon atoms and with kagome, rhombic and hexagonal lattices. The kagome and rhombic lattices exhibit moderate electronic band gaps (0.98–3.34 eV), high carrier mobility in the order of 3 × 105 cm2V−1s−1, high flexibility with critical strain up to 44%–47%, and type-II band alignment which are desired for applications in electronic devices and solar cells. Our findings are expected to offer theoretical bases for synthesis and applications of these novel 2D carbon nitrides and promote the following experimental exploration.

Carbon nanomaterials are receiving an increasingly large interest in a variety of fields, including also nanomedicine. In this area, much attention is devoted to investigating and modeling the behavior of these nanomaterials when they interact with biological fluids and with biological macromolecules, in particular proteins and oligopeptides. The interaction with these molecules is in fact crucial to understand and predict the efficacy of nanomaterials as drug carriers or therapeutic agents as well as their potential toxicity when they occupy the active site of a protein or severely affect the secondary and tertiary structure, or even the local dynamics, thus inhibiting their biological function. In this review, therefore, we describe the most recent work carried out in the last few years to model the interaction between carbon nanomaterials, either pristine or functionalized, and proteins or oligopeptides using classical atomistic methods, mainly molecular dynamics simulations. The attention is focused on 0-dimensional fullerenes, mainly C60, on 1-dimensional carbon nanotubes, mostly the single-walled armchair and some chiral ones, and on 2-dimensional graphene and graphyne, the latter containing also sp hybridized atoms in addition to the sp2 ones common to the other carbon nanomaterials.

By using of the first-principles calculations based on density functional theory, a novel monolayer planar structure named C64-graphyne is predicted. Tetratomic and hexatomic rings, as well as C C triple bonds exist in this new stable structure with the lattice parameter of 9.291 A. The carbon hexatomic ring in C64-graphyne contains two quite distinct C C bonds, which is known as cyclohexatriene. Its electronic band structures show a semiconductor nature with a narrow direct band gap of 0.35 eV. Interestingly, by substituting a carbon atom with one nitrogen atom either in the hexatomic ring or in the chain of C64-graphyne, two stable planar structures are obtained. Such doping with nitrogen atom induced metallic properties in this monolayer structure. Further investigation shows that the alternating substitution of boron and nitrogen atoms for all carbon atoms in C64-graphyne also induced a new stable structure, the (BN)64 structure. The electronic studies proved its insulator property with the band gap of 4.08 eV.

Graphyne, a single atomic layer structure of the carbon six-member rings connected by one acetilenic linkage, is a promising anode of rechargeable batteries. In this paper, a first-principle study has been carried out on graphyne as a new candidate for the anode material of magnesium-ion batteries, using density functional theory calculations. The main focus is on the magnesium adsorption on graphyne surface. The structural properties such as adsorption height and energy, the most stable adsorption sites, the Band structure and DOS of the pristine graphyne the diverse Mg-decorated graphyne structures, and energy barrier against Mg diffusion are also calculated. As a consequence of the band structure and DOS of graphyne structures, it is found that the pristine graphyne and the Mg-decorated graphyne structures show a semiconducting nature and metallic behavior, respectively. Moreover, the migration behavior of Mg on graphyne for the main diffusion paths is determined by the Nudged Elastic Band (NEB) method., 7 pages, 5 figures

Through Density Functional Theory Simulations we predict that a Ytrrium atom attached on graphyne surface can adsorb up to a maximum of 9 molecular hydrogens (H2), with a uniform binding energy of ∼0.3 eV/H2 and an average desorption temperature of around 400 K (ideal for fuel cell applications), leading to 10 wt% of hydrogen, substantially higher than the requirement by DoE. The higher hydrogen wt% in Y doped graphyne compared to Y doped Single Walled Carbon Nanotubes (SWNT) and graphene is due to the presence of sp hybridized C atoms (in the acetylene linkage) supplying additional in-plane px-py orbitals leading to π (π*) bonding (antibonding) states. Charge transfer from metal to carbon nanostructure results in a redistribution of s, p, d orbitals of the metal leading to a non - spin polarized ground state in Y doped graphyne, due to the presence of the acetylene linkage, whereas Y doped SWNT and graphene remain magnetic like the isolated metal atom. In the non-magnetic graphyne + Y system, the net charge transfer from Y to successive H2 molecules is less than in magnetic Y + graphene and Y + SWNT systems, enabling Y + graphyne to store a larger number of H2 molecules. Furthermore, our ab initio MD simulations show that the system is stable even at room temperature and there is no dissociation of H2 molecules, enabling the system to achieve 100% desorption. So Y doped graphyne is found to be a promising hydrogen storage device with high wt%, 100% recyclability and desirable desorption temperature.

Desalination of sea saline water seems a successful solution to supply clean water. For desalination, novel nanoporous membranes have been proposed as a substitute for the classic reverse osmosis (RO) membranes. The one-atom-thick graphyne membrane has shown great potential in water desalination. By applying functional groups (FGs) into the pores of the monolayer graphyne membranes, the water permeability and the ion rejection were passively increased. The effects of applying various FGs such as Hydrogen, Fluorine, Carboxyl and Amine, effect of the salt concentration, the applied pressure, and the effective diameter of the graphyne pores were determined by molecular dynamics (MD) simulations. Also, the distribution of water density and hydrated ions structure were discussed. The results revealed that graphyne-4 with F FGs may be the best membrane for desalination. Compared with bare graphyne, this membrane increased the water permeability and the ion rejection for the various applied pressures of salt concentrations.

A novel two-dimensional (2D) structurally stable carbon allotrope is proposed using first-principles calculations, which is a promising material for water purification and for electronic devices due to its unique porous structure and electronic properties. Rectangular and hexagonal rings are connected with acetylenic linkages, forming a nanoporous structure with a pore size of 6.41 angstrom, which is known as T-4,T-4,T-4-graphyne. This 2D sheet exhibits a direct bandgap of 0.63 eV at the M point, which originates from the p(z)( )atomic orbitals of carbon atoms as confirmed by a tight-binding model. Importantly, T-4,T-4,T-4-graphyne is found to be energetically more preferable than the experimentally realized beta-graphdiyne, it is dynamically stable and can withstand temperatures up to 1500 K.

We investigate the energy gaps and half-metallicity of the zigzag-edged β-graphyne nanoribbons via a tight-binding approach. In the presence of on-site Coulomb repulsion and proper transverse electric field strengths, the nanoribbons are forced into a half-metallic state by the electric field. A phase transition from half-metal to insulator is realized by changing the electric field or Coulomb potential. Both the electric field and Coulomb repulsion can open direct band gaps, resulting in a metal-insulator phase transition. The band gaps oscillate with the electric field, contrary to linear change with the Coulomb potential.

The effects of tensile deformation on the stability and electronic structure of the O adsorbed graphyne system is studied by using density functional theory based on the first-principles. It is found that in the current research range, the tensile deformation causes the structural stability of the intrinsic graphyne to decrease slightly, but the stability of the O adsorbed graphyne system increases. Compared with the undrawn stretching system, the adsorption energy of the O adsorbed graphyne system which is subjected to stretching increases. The adsorption energy is high in small deformation. Then the adsorption energy becomes smaller as the tensile deformation increases. It is proved that the tensile deformation can exacerbate the adsorption of O atoms. After the intrinsic graphyne is subjected to stretching, the band gap decreases as the tensile deformation increases. The graphyne is changed from a medium band gap semiconductor to a small band gap semiconductor. After the graphyne adsorbs the O atom, the C atom which is closest to the O atom is pulled up, the plane of the graphyne is twisted, the band gap of the graphyne is reduced, and a new impurity level is introduced at the Fermi level. The adsorption of graphyne on O atoms belongs to the category of chemical adsorption, and C atoms have stable bonding. There is a strong electron transfer between them, causing the Fermi level to move. Compared with the density of states of the graphyne, multiple density peaks appear in the density of states. A very pronounced energy gap has also appeared near the energy level of −18 eV. After applying uniaxial tensile deformation, the band gap is reduced from 0.263 eV to 0 eV, exhibiting the Dirac cone, corresponding to the metalloid properties.

Graphdiyne possesses not only high strength but also excellent ductility, making it possible to be used in future high-performance protective structures. In this paper, the mechanical properties of graphdiyne were firstly measured by AFM experiments, and the failure behavior during low velocity perforation was also investigated by molecular dynamics (MD) simulations. Firstly, the elastic modulus was measured to be about 218.5 GPa by AFM experiments, which is about half of its ideal value due to various defects and the layer numbers of the synthesized graphdiyne film. Then, the nanoindentation processes of graphdiyne films were investigated by MD simulations, and the elastic modulus and strength were simulated to be about 489.04 GPa and 33.95 GPa, respectively. The failure behavior of the graphdiyne film was also studied in atomic level. Sequential broken of C C, C C and C C bonds and recombination of the broken bonds were observed to form a unique lathy crack. Furthermore, the effects of loading speed and indenter radius on the mechanical response of graphdiyne were investigated. A revised formula was developed for analyzing the mechanical properties of films in AFM experiments under various loading conditions.

In this paper, the structural and electronic properties of atomic oxygen and hydrogen adsorption on graphdiyne (GDY) and its BN analog (BNdiyne) has been studied by the first-principles calculations. The calculated results show that the most stable adsorption positions of atomic hydrogen (oxygen) for GDY and BNdiyne monolayer are the top site (T2) and the hollow site (H2), respectively. The strong interaction (chemisorption) between atomic hydrogen and the monolayers leads to a decrease of 0.1 eV in the band gap of GDY, while an increase of 0.15 eV in BNdiyne. The shallow impurity energy level introduced by oxygen enhances the conductivity of GDY which could be indicated from the non-zero transmission coefficient at zero bias as well. In addition, a tiny magnetic has occurred in the oxygenated GDY while it has not occurred in the hydrogenated GDY which is different from the graphyne.

By performing molecular dynamics, the thermal transport properties of seven type graphyne (GY) with different structures (nanosheet, nanotube and GY/graphene (GR) heterojunction) are investigated. It can be observed comparing with other six GY, the thermal conductivity (TC) of (14,14,14)-GY shows unexpectedly significant anisotropy, which is consistent with previous study in Phys. Chem. Chem. Phys. 2016, 18, 24210. This anisotropy is mainly due to the lower contribution of high-frequency and short-wavelength phonons weakened by armchair (14,14,14)-GY. Moreover, when GY is rolled up to GY nanotubes (NTs), it is interesting to discover TC of GYNT, especially (14,14,14)-GYNT, shows a diameter-dependent anisotropy. For large-diameter NT, the TC of zigzag model is higher, however, an opposite phenomenon is obtained with small-diameter model. This phenomenon can be explained by the relative alternation of phonon group velocity and phonon lifetime and the appearance of band gap with the change of diameter. At last, we also notice the GY/GR heterojunctions express much lower thermal resistance (TR) comparing with other carbon based heterojunctions, and the in-plane TR of GY/GR heterojunction is two orders of magnitude lower than that of out-of-plane TR. Further, the alternation of TR can be well explained by the coupling degree of different type phonons.

Different sites for K adsorption in γ-graphyne were investigated using density functional theory (DFT) calculations and optical and structural properties of the structures were examined. For the most stable structures, we put one H2 molecule in different directions on the various sites to evaluate the hydrogen adsorption capability of them. Then, one to nine H2 molecules in sequence were added to the best structure. Results show that clustering of the K atoms is hindered on the graphyne surface and the most desirable adsorption site for K atom is the hollow site of 12-membered ring with adsorption energy of 5.86 eV. Also, this site is the best site for H2 adsorption onto K-decorated graphyne with Edas of −0.212 eV. Adding of number of H2 molecule on this site shows that K atom can bind nine H2 molecules at one side of the graphyne with the average adsorption energy of 0.204 eV/H2. Therefore, for one side ca. 8.95 wt % and for both sides of the graphyne with a K atom in each side ca. 13.95 wt % of the hydrogen storage capacity can be achieved. This study shows that K-decorated graphyne can be a promising candidate for the hydrogen storage applications.

Graphyne is expected to be a new-class of highly-efficient sieving membranes due to its controllable uniform pore structure and ultrathin single-atom thickness. Herein, we computationally investigate the permeation performance of liquid ethanol–water mixtures across polyporous two-dimensional γ-graphyne sheets. It was found that, in the mixture, ethanol with larger molecular diameter permeates faster through the graphyne pores than water. The simulations demonstrate that pristine graphynes could act as highly-efficient ethanol-permselective membranes for separation of ethanol–water mixtures, with ethanol permeability remarkably higher than conventional membranes. This separation mechanism is distinctly different from the molecular-size dependent sieving process. The stronger hydrophobic interfacial affinity between graphyne and ethanol makes ethanol molecules preferentially adsorb on graphyne surface and selectively penetrate through graphyne pores. This penetration mechanism provides new understanding of molecular transport through atomically thick two-dimensional nanoporous membranes and this work is expected to be valuable in the potential development of highly-efficient membranes for liquid-phase mixture separation.

We report graphyne nanosheet as a carrier for drugs, namely quercetin and 5-fluorouracil to the target cell for the treatment of hepatocellular carcinoma and colorectal carcinoma, which causes major cancer-related death. In the proposed study, ab initio calculations were performed for the investigation of adsorption energy, bandgap, average bandgap changes, and Bader charge transfer; upon physisorption of the quercetin and 5-fluorouracil on graphyne nanosheets. Furthermore, the chemical hardness, electrophilicity, and chemical potential are also explored upon interaction of quercetin and 5-fluorouracil on graphyne sheets. The significant parameters give the insights on the interaction of the quercetin and 5-fluorouracil drugs onto the graphyne, and the preferential interaction sites of these drugs in graphyne are investigated. The findings of the present research work recommend that the graphyne nanosheet can be effectively utilized as a quercetin and 5-fluorouracil drug delivery vehicle.

Chemical modification of MXenes, as an effective strategy to improve the electronic harmony with other materials, paves huge impetus to their practically industrial application. In this study, by means of Density Functional Theory (DFT) calculations, the adsorption and substitution of single transition metal atoms (M = 3d (Fe, Co, Ni, Cu, Zn), 4d (Ru, Rh, Pd, Ag, Cd), 5d (Os, Ir, Pt, Au, Hg)) on Ti3C2 MXene have been systematically investigated. It is found that the adsorption (adsorption energies Ead = −1.05 ∼ −7.98 eV) of single metal atoms on Ti3C2 are much stronger than those on graphene and graphyne. Interestingly, via a series of electronical structure calculations, we found good linear correlation between Ead and chemically properties (such as the average bond distances dM-Ti, the bader charge and the d-electron centre of metal), shedding light on the harmonic effect of doping metals both electronical and geometrically. In other words, the stronger adsorption, shorter bond distance, more bader charge, less negative d-electron centre. While for the substitution of single metal atom on Ti3C2, a linear relationship is also found except that the volcano curve are formed between the substitution energies and bader charges. Moreover, the charge transfer decrease firstly and then increase in both first and third layer. Generally, single-atom adsorption or substitution is a feasible method to improve the functionalization Ti3C2 MXene.

Novel logarithmic time algorithm is proposed for determining the order of chemical bonds from known valences of the atoms. The algorithm has the order of complexity N · log(N) and is applicable to polycyclic compounds containing a combination of the cycles of any size and the atoms with the valences ≤4 in cycle nodes. The algorithm is applicable to structures containing triple and cumulene bonds in the cycles. It was tested for graphene, C[12,12] nanotubes, graphyne-GY1, graphyne-GY7, graphyne-like nanotube, fullerenes C20, C60, C70, C80, C82 and their aza-analogs, polypentadienes, as well as for porphine. Determining the order of bonds in graphene, graphynes or nanotubes, containing >107 atoms, took less than 2 min on a personal computer. For the compounds containing aromatic cycles with an odd number of atoms, this algorithm becomes probabilistic and successful determination of bond orders is not guaranteed. However, the probability of successful determination of bond order is significant, and Kekule structures, if they existed, were generated for all studied fullerenes and their aza-analogs.

Based on the density functional theory study, we investigated the adsorption behavior of small Agn nanoclusters (n = 1 to 4) on γ-graphyne including the adsorption configurations with the minimum total energy, the charge transfer and charge density. The electronic properties including the band structure and density of states (DOS) were also discussed. The results indicated that Ag2 cluster had the minimum adsorption energy and charge transfer which might result in difficult adsorption process. Except for Ag2, all the introduction of Ag cluster exhibited n-type doping. For different Ag cluster, the interactions of atomic orbitals between Ag and C atom also varied. Our results can have certain guidance meaning for future study of the physical and chemical properties of modified graphyne or other monolayer materials.

The present paper aims to provide in-depth analysis of Raman and IR spectra as well as the assigned vibrational modes of pristine and BN substituted graphynes, considering different dopant sites and concentrations. We have explored the implication of vibrational modes related with the Raman and IR line of pristine graphyne and BN-doped graphynes. The Raman and IR spectra of BN substituted graphyne show quite distinct feature than pristine graphyne and monolayer h-BN sheet. It also shows regular dependence on doping site as well as doping concentrations. Raman spectra help to detect the substitution site of BN while IR spectra help to identify the BN concentration. Hence the combination of IR and Raman spectra would be useful in detecting BN-doped graphyne during synthesis. Thus this study would help the experimentalist in sample characterization in near future.

In this theoretical work, we present the results from Density Functional Theory (DFT) calculations on novel systems formed by graphyne-γ (GY-γ) with defects, and Nitrogen-doped graphyne (GYN) systems. Systems with vacancy defects present a widening on the band gap. We found that the electronic properties of the GYN family may be tuned, from a semiconducting to a metallic character. This may be due to the presence of Nitrogen atoms (N) in acetylenic linkages. The N-doping was shown to generate thermodynamically stable systems with different electronic properties, which can be further confirmed by ab initio Molecular Dynamics simulations. In this work, we also analyzed the chemical stability and reactivity with the following criteria: hardness, chemical potential, and electronic density. The GYN system with defects (GYN-def) presents the lowest-energy of formation and cohesion, indicating that it may correspond to the most energetically stable system. The catalytic character of the series of graphyne systems under study was tested by assessing the capability to adsorb the O2 molecule on the graphyne substrate. It was discovered that the GYN-β and -δ systems represent models able to achieve O2 molecular chemisorption onto the surface, due to the modified electronic structure after N-doping. We found activation barriers below 0.70 eV. This addresses that the process might occur spontaneously at rom temperature. Such graphyne systems represent potential candidates to be implemented as catalysis in devices such as fuel cell cathode materials.

Graphdiyne (GDY) is a new member of carbon allotropes consisting of sp and sp2 hybridized carbon atoms. In this work, the hydrogen adsorption on Calcium (Ca) decorated GDY and the influence of adatom on structural properties of GDY are investigated, using first principles plane wave calculations with Van der Waals corrections. The results show that similar to graphyne (GY) and unlike carbon nanotube (CNT), fullerene and graphene, clustering of Ca on GDY hinders due to the higher binding energy of the adatom to the carbon frame than the Ca cohesive energy. It can be seen that the Ca-decoration promotes hydrogen storage capacity of GDY, extremely (Eads = −0.266 and −0.066 eV for Ca-decorated and pristine GDY, respectively). It is concluded that, the best site for the Ca trapping is 18-membered ring in which, Ca lies in-plane of GDY (Eads = −3.171 eV). Fourteen H2 molecules (with the average adsorption energy of ∼0.2 eV/H2) can be adsorbed on the Ca atom from one side. The hydrogen storage capacity is estimated to be as high as 17.95 wt% for the both sides of GDY. So, the Ca-decorated GDY is offered as a promising candidate for hydrogen storage applications.

It is an ideal route to generate hydrogen peroxide (H2O2) via selective 2e- ORR powered directly by sunlight. In this work, we synthesized a metal-free N doped γ-graphyne catalyst and wired it with n-type semiconductor photoanodes. The introduction of sunlight could lower the onset bias of oxygen reduction reaction (ORR) up to 0.32 V and H2O2 was steadily produced without any sacrificial agents and bias. The 2e- ORR selectivity of N doped γ-graphyne catalyst was bias dependent, and it reached about 74% at 0 bias in 0.1 mol·L-1 KOH. Theoretical calculations showed that in-situ pyridinic-N in N doped γ-graphyne acted as the active site for ORR, accelerating the rate-determining step of proton abstraction. The H2O2 yield reached as high as 7.47 mmol·h-1g-1, outperformed the reported traditional photocatalytic syntheses of H2O2.

Applying Monte Carlo simulation, the critical and compensation behaviors of a graphyne bilayer are explored in this study. The effects of the crystal field and exchange coupling on the magnetic behaviors and the phase diagrams are presented in detail. The results show that the critical temperature increases as the crystal field decreases or the exchange coupling increases. In addition, the double compensation points can also be found in this system. Furthermore, we give the hysteresis loops under different parameters, and the multi-loop hysteresis behaviors are observed.

Among the graphyne family, δ-Graphyne is a new typical representative for instance. In this article, we have studied the spin-splitting phenomena in the band structures and transport properties of zigzag δ-graphyne nanoribbron (ZδGYNR) with edge fluorination. Our results show that the spin-splitting can be observed obviously in the ZδGYNRs with unilateral or bilateral edge fluorinations. Moreover, some distinct physical effects, such as spin-filtering, rectification and negative differential resistance, can be found in the proposed device models. Particularly, the efficiency of spin-filtering can approach to 100% in the antiparallel spin-configuration of the bilateral fluorination model, which would be capable of leading to promising applications in spintronics and nanodevices.

Carbon-based metal free materials (CMFCs) as electrocatalysts have been a hot issue and are receiving growing attention. In this paper, we applied intensive density functional theory (DFT) calculations to study the electrocatalytic activities of γ-graphyne nanoribbons (γGyNRs) toward the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). Our results revealed γGyNRs to be excellent bifunctional CMFCs after functionalization by termination or N-doping at the edge to introduce proper spin densities. The scaling relationship analysis enhanced our earlier understanding that the binding strength of H atom (ΔEH) is a general descriptor for designing bifunctional electrocatalysts for HER and ORR. Further study revealed that the light gradient boosting machine is a promising machine learning algorithm to accurately predict the electrocatalytic activities of γGyNRs. Feature importance analysis suggested that the surrounding environment of the active site plays a more significant role than we previously anticipated. Overall, we suggest promising γGyNRs as HER and ORR bifunctional electrocatalysts for the first time and provide deeper insight into the reaction mechanism, which is beneficial for the rational design of novel CMFCs.

With well-endowed nanopores, graphyne (GY) membranes have attracted considerable interest in alcohol purifications. However, the challenge lies in the rational design of GYs for efficient separation of (C1–C2) alcohol solutions. Herein, GYs are firstly developed for methanol recovery and ethanol dehydration by molecular simulations. Two design strategies including surface charge modification and functional group decoration are proposed in this study. For methanol-water separation, methanol is pre-selected due to the dominated mechanism of preferential adsorption and its flux increases with positive charges within a certain range. An excellent separation performance with 99.1 kg⋅m-2⋅h-1 methanol flux and 15.2 separation factor is achieved by this GY-S membrane with +0.005 e/atom charged surface. This surface charge modification is also effective for methanol-ethanol separation, where the highest performance is harvested by the positively charged GY-M membrane. For water-ethanol separation, water is pre-selected owing to the size sieving effect. To reduce the blocking effect and permeation barrier, the GY-M is functionalized with polar groups so that water flux is promoted regardless of aperture sizes. The hydroxylated GY-M-OH fosters an exceptionally high dehydration performance with 225.8 kg⋅m-2⋅h-1 water flux and 100 wt% water content in permeate. This theoretical study suggests that the GYs membranes might be promising for organic solvent recovery and dehydration.

Similar to pure graphyne, two-dimension carbon nitride graphyne also possesses exceptional properties and potential applications. In this work, by using the density functional theory (DFT) and combining with nonequilibrium Green’s function (NEGF), we study the electronic band structures and transport properties of zigzag rhombic N-graphyne nanoribbons (ZrNGYNRs). Our results show that all of the ZrNGYNRs have similar metallic band structures in no magnetic and ferromagnetic configuration, while the transport properties are directly related to the symmetry of the systems. The electron band structure exhibits a distinct spin splitting in the ferromagnetic state. We propose a device by cutting the ZrNGYNRs in the central scattering region. Negative differential resistance, rectification effects, and spin-filtering effects can be observed in this device. This work highlights the outstanding physics of ZrNGYNRs, and suggest that the ZrNGYNRs is a very promising material in the application of nanoelectronics .

The electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions is an emerging technique to address energy shortages and climate change. Thus, developing efficient but low-cost electrocatalysts is important. In the present paper, we applied γ-graphyne (γGy) doped with B, N, O, P and S as NRR catalysts, and the activities of these catalysts were studied by extensive density functional theory (DFT) calculations. Our results suggest that single N, O, P and S doping are not effective in enhancing γGy NRR activity, and the γGy with B(sp2)-C(sp)-B(sp) configuration has excellent overall NRR activity with a record low limiting potential (−0.12 V), good conductivity, low hydrogen evolution reaction activity and high dynamic stability. We revealed that the sp-C directly connected to active sp-B can be an energy buffer that makes a flat potential energy surface. Overall, our research provides several good NRR catalysts by carefully controlling the doping sites and provides a new strategy for further development of metal-free catalysts for the NRR.

In this work, we propose a new auxetic (negative Poisson's ratio values) structure, based on a $\gamma$-graphyne structure, here named $A\gamma G$ $structure$. Graphynes are 2D carbon allotropes with phenylic rings connected by acetylenic groups. The A$\gamma$G structural/mechanical and electronic properties, as well as its thermal stability, were investigated using classical reactive and quantum molecular dynamics simulations. We found that A$\gamma$G has a large bandgap of 2.48 eV and is thermally stable at a large range of temperatures. It presents a Young's modulus that is an order of magnitude smaller than that of graphene or $\gamma$-graphyne. The classical and quantum results are consistent and validate that the A$\gamma$G is auxetic, both when isolated (vacuum) and when deposited on a copper substrate. We believe that this is the densest auxetic structure belonging to the graphyne-like families., Comment: 3 figures, 1 table

In this work, we investigated the adsorption behaviour of sulfur dioxide on pristine and Au dimer decorated γ-graphyne (γ-GY). From comparing the adsorption energy, electron transfer and band gap, the most energetically adsorption configurations were gained. Then we made a further discussion of charge density difference, electron localization function (ELF), band structure, density of states (DOS) to evaluate the chemical and physical interactions between the SO2 and the γ-GY. The results indicated that the SO2 adsorption on the pristine γ-GY just exhibited van der Waals force with very weak chemical interactions. But SO2 could be adsorbed on Au dimer decorated γ-GY with relatively stronger chemical interactions due to the larger adsorption energy, larger electron transfer, the obvious change of SO2 molecular orbitals and many hybridizations between the Au and the S atom in DOS. Because of the unchanged band gap of Au dimer decorated γ-GY, it is more suitable for Au2-GY to be applied in QCM gas sensor to detect SO2 rather than resistance type gas sensor.

By applying nonequilibrium Green's functions (NEGF) in combination with density functional theory (DFT), the electronic transport properties of α -armchair graphyne nanoribbons ( α -AGyNR) device are investigated, in which the left electrode is doped by Boron (B) atoms and the right electrode is doped by Nitrogen (N) atoms. B and N doping atoms that are substituted in SP and SP 2 sites result in four devices named as A (sp–sp), B (sp 2 –sp 2 ), C (sp 2 –sp) and D (sp–sp 2 ). The current–voltage characteristics of these systems reveal that the proposed devices have a striking nonlinear feature that leads to formation of a p–n junction which results rectifying behavior. The results show that the rectification characteristics are strongly dependent on the site of doping atoms. In A and D devices the rectification ratio (RR) can reach to 10 3 in the bias region from 0.2 V to 0.6 V while in B and C devices the RR can be enlarged to 10 4 in the same bias region. Unlike the most of the previous proposed molecular rectifiers that are vertical hetero structures, the proposed rectifier in this work is in-plane or two dimensional structures. The results provide a new insight and a novel effective pathway for developing applicable high-performance Graphyne-based rectifiers.

First principle study with density functional theory was carried out to investigate the adsorption behavior of nitrogen oxide (NO and NO2) on pristine and B atom embedded γ-graphyne including the adsorption energy, electron transfer, adsorption distance, magnetic moment, band structure, density of states and optical properties. The results indicate that C atom of sp2 hybridization (compared to sp hybridization) is easier to be substituted by B atom with endothermic process. B atom embedded γ-graphyne have notably stronger chemical interactions with NO and NO2 compared to pristine γ-graphyne with larger adsorption energy and greater changes of molecule orbitals. The calculations of optical properties reveal that B atom embedded γ-graphyne has more obvious changes of dielectric function after adsorbed NO or NO2 near 1.5 eV compared to pristine γ-graphyne illustrating that B-graphyne has the prospect to detect nitrogen oxide using not only electrochemical method but also optical method.

In this study, the Young's moduli of armchair and zigzag nanoporous graphyne membranes with various porosities, pore numbers, and pore arrangements were examined under tensile loading by using the atomic-scale finite element method. The results of this study were in agreement with that of a previous study regarding the Young's moduli of pristine graphyne membranes. According to our analysis, the Young's moduli of the armchair and zigzag graphyne membranes significantly decreased with an increase in porosity. Moreover, the porosity effect on the Young's modulus of a membrane with sixteen pores was greater than that of those with one pore. The pore arrangement effect on graphyne with high porosity was evident. This paper facilitates the understanding of the mechanical strength of nanoporous graphyne membranes and the fabrication and application of high performance nanoporous graphyne membranes.

Using non-equilibrium Green's functions (NEGF) in combination with tight-binding (TB) model, the electronic transport properties of pristine and nitrogen (N) doped armchair α-graphyne nanoribbons (A-α-GYNRs) are studied under finite bias. Initially, we have calculated the total energy in order to find the most stable place for N atom. Then we have investigated the effect of width (W) and length (L) of the ribbon and also the position (edge and center of the ribbon) and concentration of doping on the electronic transport properties. Our results reveal that, doping changes the semiconducting behavior of 3n and 3n+1 A-α-GYNRs to semi metallic. Moreover, it is observed that the electronic transport properties are more affected by central doping rather than the edge doping. Interestingly, both edge and central doped ribbons show negative differential resistance (NDR) in all widths. Our results show that doping concentration and the NDR are inversely proportional to each other. We have also found that, as the length of the central region of the device gets longer, the NDR reaches up to 159. Transmission spectrum, bandstructure of the electrodes, Bloch wave functions and density of states (DOS) are analyzed subsequently to more elucidate the electronic transport properties. Our findings could be used to develop the nano-scale NDR devices.

As a new member of the carbon family, γ-graphyne has the advantages of high carriers mobility and semiconductor characteristic. In this work, a simple and high-yield route is proposed to synthesize monocrystalline γ-graphyne by mechanochemistry. Energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy and corresponding selected area electron diffraction were performed to confirm the features of γ-graphyne in terms of composition, morphology and lattice constant. The as-prepared γ-graphyne, which is composed of sp2-hybridized and sp-hybridized carbon, is a monocrystalline with a lattice constant of 0.69 nm. UV–vis diffused reflectance spectroscopy was measured for the resultant sample and its band gap energy is estimated to be 2.58 eV from the absorption edge. The sample exhibited p-type behavior which was confirmed by the negative slope in Mott-Schottky plots and the linear sweep voltammograms under light irradiation. The valence and conduction band positions are around +2.53 and −0.05 V (vs normal hydrogen electrode) respectively, calculating from the flat band potential and its band gap energy. This work provides a novel strategy for the synthesis of γ-graphyne from readily available precursors and presents many experimental parameters of γ-graphyne.