Molecular simulation of penetration separation for ethanol/water mixtures using two-dimensional nanoweb graphynes

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.

Nanoindentation Models of Monolayer Graphene and Graphyne under Point Load Pattern Studied by Molecular Dynamics

Molecular dynamics simulations are performed to study the nanoindentation models of monolayer suspended graphene and graphyne. Fullerenes are selected as indenters. Our results show that Young＇s modulus of monolayer-thick graphyne is almost half of that of graphene, which is estimated to be 0.50 TPa. The mechanical properties of graphene and graphyne are different in the presence of strain. A pre-tension has an important effect on the mechanical properties of a membrane. Both the pre-tension and Young＇s modulus plots demonstrate index behavior. The toughness of graphyne is stronger than that of graphene due to Young＇s modulus magnitude. Young＇s moduli of graphene and graphyne are almost independent of the size ratio of indenter to membrane.

Rational design of graphyne-based dual-atom site catalysts for CO oxidation

There are increasing concerns about the environmental impact of rising atmospheric carbon monoxide concentrations,thus it is necessary to develop new catalysts for efficient CO oxidation.Based on first-principles calculations,the potential ofγ-graphyne(GY)as substrate for metals in the 4th and 5th periods under single-atom and dual-atoms concentration modes has been systematically investigated.It was found that single-atom Co,Ir,Rh,and Ru could effectively oxidate CO molecules,especially for single Rh.Furthermore,proper atoms concentration could boost the CO oxidation activity by supplying more reaction centers,such as Rh^(2)/GY.It was determined that two Rh atoms in Rh^(2)/GY act different roles in the catalytic reaction:one structural and another functional.Screening tests suggest that substituting the structural Rh atom in the center of acetylenic ring by Co or Cu atom is a possible way to maintain the reaction performance while reducing the noble metal cost.This systemic investigation will help in understanding the fundamental reaction mechanisms on GY-based substrates.We emphasize that properly exposed frontier orbital of functional metal atom is crucial in adsorption configuration as well as entire catalytic performance.This study constructs a workflow and provides valuable information for rational design of CO oxidation catalysts.

Theory,preparation,properties and catalysis application in 2D graphynes-based materials

Carbon has three hybridization forms of sp^(-),sp^(2-)and sp^(3-),and the combination of diferent forms can obtain diferent kinds of carbon allotropes,such as diamond,carbon nanotubes,fullerene,graphynes(GYs)and graphdiyne(GDY).Among them,the GDY molecule is a single-layer two-dimensional(2D)planar structure material with highlyπ-conjugation formed by sp^(-)and sp^(2-)hybridization.GDY has a carbon atom ring composed of benzene ring and acetylene,which makes GDY have a uniformly distributed pore structure.In addition,GDY planar material have some slight wrinkles,which makes GDY have better self-stability than other 2D planar materials.The excellent properties of GDY make it attract the attention of researchers.Therefore,GDY is widely used in chemical catalysis,electronics,communications,clean energy and composite materials.This paper summarizes the recent progress of GDY research,including structure,preparation,properties and application of GDY in the field of catalysts.

The roles of electrons in the electronic structures and optical properties of graphyne

The electronic structures and optical properties of graphyne consisting of sp-and sp 2-hybridized carbon atoms are studied using first-principles calculations.A tight-binding model of the 2p z orbitals are proposed to describe the electronic bands near the Fermi level.The results show that the natural band gap of graphyne originates from the inhomogeneous bindings between differently-hybridized carbon atoms.The interlayer interactions of bulk graphyne narrow the band gap to 0.16 eV and result in redshift of the optical spectral peaks as compared to single-layered graphyne.

Fracture Toughnesses and Crack Growth Angles of Single-Layer Graphyne Sheets

Recently, Shang et al.(Angew Chem Int Ed 57(3):774-778,2018) have developed a method to synthesize ultrathin (around 1.9 nm) graphyne nanosheets. We reported here the mixed-mode I-II fracture toughnesses and crack growth angles of single-layer graphyne sheets using molecular dynamics (MD) simulations and the finite element (FE) method based on the boundary layer model, respectively. The various carbon-carbon bonds of graphyne sheets in the FE method are equated with the nonlinear Timoshenko beams based on the Tersoff-Brenner potential, where all the parameters of the nonlinear beams are completely determined based on the continuum modeling. All the results from the present FE method are reasonable in comparison with those from our MD simulations using the REBO potential. The present results show that both the critical stress intensity factors (SIFs) and the crack growth angle strongly depend on the chirality and loading angle q @= 90° and #= 0° representing pure mode I and pure mode II, respectively). Meanwhile, the fracture properties of single-layer cyclicgraphene and supergraphene sheets are also studied in order to compare with those of the graphyne sheets. The critical equivalent SIFs are derived as 1.55 < Keq.cy (cyclic)< 1.95 nN A-3/2, 1.64 < Keq.gy (graphyne)< 2.64 nN A_3/<2 and 0.61 < Keq-su (super)< 2.04 nN A-3/2 in the corresponding zigzag and armchair sheets using the MD simulations, while the SIFs are 0.32 < Keq-cy (cyclic)< 0.48 nN A-3/,2, 1.96 < Keq.gy (graphyne)< 2.49 nN A-3^2 and 1.42 < Keq-su (super)< 2.95 nN A_3//2 using the FE method. These findings should be of great help for understanding the fracture properties of carbon allotropes and designing the carbon-based nanodevices.

Movement of Dirac points and band gaps in graphyne under rotating strain

The introduction of lattice anisotropy causes Dirac cones to shift in response to the applied strain, leaving a pseudogap at the original Dirac points. Here, a group-theory analysis is combined with first-principles calculations to reveal the movement characteristics of Dirac points and band gaps in various graphynes under rotating uniaxial and shear strains. Graphene, where linear effects dominate, is different from α-,β-, and γ-graphynes, which generate strong nonlinear responses due to their bendable acetylenic linkages. However, the linear components of the electronic response, which are essential in determining material performance such as intrinsic carrier mobility due to electron-phonon coupling, can be readily separated, and are well described by a unified theory. The movement of the Dirac points in α-graphyne is circular under a rotating strain, and the pseudogap opening is isotropic with a magnitude of only 2% that in graphene. In comparison, the movement in β-graphyne is elliptical and the center is displaced from the origin. For γ-graphyne, three branches of gaps change with the applied strains with a sine/cosine dependence on the strain angle. The developed methodology is useful in determining the electronic response to various strains of Dirac materials and two-dimensional semiconductors,

Study of Transport Properties in Armchair Graphyne Nanoribbons: A Density Functional Approach

In present paper, the non-equilibrium Green function(NEGF) method along with the density functional theory(DFT) are used to investigate the effect of width on transport and electronic properties of armchair graphyne(γ-graphyne) nanoribbons. The results show that all the studied nanoribbons are semiconductor and their band gaps decrease as the widths of nanoribbons increase, which will result in increasing current at a certain voltage. Also our results show the promising application of armchair graphyne nanoribbons in nano-electrical devices.

Polymetallaynes and Molecular Metallaynes Containing Platinum,Mercury and Gold for Optoelectronic and Magnetic Applications

omprehensive Summary,Polymetallaynes are a promising branch of metallopolymers,in which the introduction of metal building blocks to organic conjugated backbones leads to their unique skeletons and versatile properties.Notably,the chemical structures,geometric configurations and functional properties in these organometallic systems can be adjusted flexibly by the appropriate selection of metal centers,auxiliary ligands,or bridging spacers.In recent years,both one-dimensional and two-dimensional polymetallaynes have attracted considerable attention owing to their excellent electronic,optical and magnetic properties.Furthermore,the studies on molecular metallaynes provide substantial insights for the exploration of the structure-property-activity relationships in these organometallic acetylide-containing systems.The recent research progress of polymeric and molecular metallaynes containing platinum,mercury and gold is discussed in this article.A series of functional properties have been realized in these acetylide-containing compounds by the rational structural design and refined synthetic strategies,leading to their emerging applications including energy conversion,nonlinear optics,data storage and memory,as well as chemo/biosensing.