Defective Graphene Sheets Research Articles

Static and dynamic response of graphene nanocomposite plates with flexoelectric effect

In this work, the electromechanical behaviors of graphene reinforced nanocomposite (GRNC) plates with flexoelectric effect were studied by using Kirchhoff's plate theory, Navier's solution and extended linear piezoelectricity theory in conjunction with the mechanics of materials (MOM) and finite element models. The static and dynamic responses of simply supported flexoelectric GRNC nanoplates under different loadings such as uniformly distributed, varying distributed, inline and point loads were investigated. The developed MOM and FE models envisage that the effective piezoelectric constants of a GRNC account for the actuating capability in its transverse direction due to the applied electric field in the plane. The elastic properties of pristine and defective graphene sheets were also estimated via molecular dynamics (MD) simulations and the obtained results are found in good agreement with the existing experimental and numerical results. Our results reveal that the flexoelectric effect on the static and dynamic responses of GRNC nanoplate is substantial and cannot be neglected. The electromechanical response of GRNC plates can be engineered to attain the desired deflection characteristics and resonant frequencies for a range of nanoelectromechanical systems using different boundary conditions as well as geometrical parameters such as aspect ratio/thickness of nanoplate and volume fraction of graphene.

A numerical method for magneto-hygro-thermal postbuckling analysis of defective quadrilateral graphene sheets using higher order nonlocal strain gradient theory with different movable boundary conditions

Many researchers work on the mechanical analysis of perfect graphene sheets while these structures have some defects actually. In this paper, postbuckling of the defective quadrilateral single layered graphene sheets (SLGS) is presented for the first time. Three types of defects including single vacancy (SV), double vacancy (DV) and Stone–Wales (SW) in conjunction with the influence of vacancy defect reconstruction are considered. Nonlocal higher order strain gradient theory with three parameters for size effects is used. The quadrilateral graphene sheet is subjected to temperature, moisture and in-plane magnetic loads. The elastic foundation is modelled by Pasternak medium. The equations of motion are obtained imposing higher order shear deformation theory and Hamilton’s principle. The transformed weighing (TW) and differential quadrature (DQ) method are applied for postbuckling load–deflection relation of the structure. Due to the hygrothermal load, different movable boundary conditions are used. The influences of various parameters such as defect types, defect degree, defect reconstruction, hygrothermal load, magnetic field, nonlocal parameters, 7 different quadrilateral SLGS, boundary conditions and elastic medium on the postbuckling behaviour of the quadrilateral graphene sheet are shown. The numerical results are validated with other published works in the literature. Results show that with increasing the defect degree, the buckling load decreases.

Defected Graphene as Ammonia Sensor: Theoretical Insight

Defects are often symbolized as deformity in material that deteriorate its performance. However, in nanoscale regime, defects lead to generate a useful and novel material for device applications. In the present report, the vacancy defects, i.e., single vacancy and double vacancy defects (with different symmetry) on graphene sheet have been analyzed to understand the electronic as well as transport properties using density functional theory and NEGF approach. Conductance, current–voltage, and sensitivity analysis of these defected graphene sheets have been examined for its suitability for gas sensing application particularly for ammonia gas. The study observes that a single vacancy defected graphene is a good candidate for ammonia molecule sensing in comparison to double vacancy.

Adsorption of Ethene-1,2-Dione on Materials Based on Graphene

We study the adsorption of ethene-1,2-dione or ethylene-dione (OCCO) on defective graphene sheets with nitrogen. The principal motivation is to determine the feasibility of the OCCO molecule as an ...

Healing mechanism of multi-vacancy defective graphene under carbon irradiation

The irradiation healing process of defective graphene was studied by reactive molecular dynamics simulation of injecting C atoms on a multi-vacancy graphene sheet. We studied the effect of environment temperature and incident energy of injected atoms on healing process of defective graphene. Our simulations show that a relatively high temperature (about 1600 K) is prerequisite for perfect healing of defective graphene. Moreover, an appropriate incident energy for injected atoms (0.16 eV/atom for ∼1800 K) is also necessary for perfect healing, even under a suitable temperature for perfect healing. Defect structures, such as carbon chains and blister-like structures, will occur and hinder the healing process, if the adsorption process (determined basically by incident energy) is faster than the reorganization process (dominated by temperature). In addition, the temperature dependence of reorganization capability of graphene was further studied by molecular dynamics simulation of relaxing an intact graphene sheet with adsorbed atoms. The analysis of the evolution of various micro-structures, emerged during the reorganization simulations, is helpful for deeply understanding the healing mechanism of defective graphene sheet under carbon irradiation.

Atomistic mechanism of the weakened wear resistance of few-layer graphene induced by point defects

Abstract Effect of various point defects on the wear properties of few-layer graphene was investigated by molecular dynamics simulations. Our results show that the presence of Stone-Wales defect, double vacancies and single vacancy reduces the critical normal load for onset of adhesive wear to 85, 15 and 11% of that of the intact graphene, respectively. The analysis of the potential energy surfaces of defective graphene sheets indicates that it is the highest chemical reactivity induced by point defects that determines the onset of adhesive wear. This study provides an atomic-level understanding for the weakening effects of point defects on the wear resistance of few-layer graphene.

Molecular dynamics study of gold nano-clusters aggregation on a model defected graphene

Functionalized graphene sheets have attracted increasing attention due to their novel micro-/nano-electromechanical applications. In this paper, the aggregation of the gold nano-clusters on the defected graphene sheet is studied by using the molecular dynamics simulation method. It is shown that a model defected graphene with randomly distributed vacancies can affect the formation and aggregation of the Au nano-clusters on the graphene sheet. It is found that the Au nano-clusters agglomerate on the pristine parts of the surface rather than on the defected parts. In addition, the results show that increasing the temperature amplifies the above result and varies the Au nano-cluster sizes. Moreover, it is observed that the aggregation of Au clusters changes the surface roughness. The results presented here would help to design more efficient functionalized graphene-based electronic devices.

Effect of Center Crack on Mechanical Properties of Graphene

Graphene is a thin sheet with special properties and complicated mechanical behavior. It’s important to study graphene experimentally and theoretically. Stone–Wales defects, cracks and atom vacancy are popular defects in carbon allotropes especially in graphene. In this paper, effect of center cracks on graphene was discussed. At first, mechanical properties of non-defected graphene sheet was obtained using molecular dynamics simulation. Comparing result with theoretical and experimental studies showing good agreements and proofing the results. Then, 8 different cracks were considered in center of graphene sheets. Stress-strain curves of defected graphene sheets with different tension strain rates were plotted. The results showed that increasing crack length lead to decreasing Young’s modulus of graphene from 870GPa to 670GPa. Also, fracture occurred in less tensile strain. In the following, structural molecular mechanics method was used to simulate cracked graphene sheets. The results showed good agreement between two methods.

Evaluation of Different Oxidizing Agents on Effective Covalent Functionalization of Multiwalled Carbon Nanotubes

Nature of carbon nanotubes (CNTs) varies depending on extend of nanotubes surface oxidation. Chemical oxidation is one of the most widely applied methods in altering the undesired properties of CNTs such as chemical inertness and seamless surface nature. In this research, various oxidizing agents include HNO3, H2SO4, HNO3/H2SO4 and KMnO4 were investigated to assess their effectiveness on covalent functionalization of multiwalled CNTs (MWCNTs). The effects of different oxidizing agent on incorporation of functional groups and development of new defects on nanotubes sidewall are closely associated with their oxidation behavior. FTIR, Boehm titration method, XPS, Raman spectroscopy, and TEM were performed to examine the surface chemistry, extend of oxidation, and surface morphology of MWCNTs. The results revealed that HNO3/H2SO4 mixture is most effective oxidant in incorporating functionality groups on nanotubes surface, as indicated by highest functional groups concentration of 1.625 mmol/gCNTs. The completeness of nanotubes structure was successfully preserved under aggressive treatment, although some defective cylindrical graphene sheets and surface erosion were appeared under the visualization of TEM.

Residual strain in graphene: study of temperature and crack effect

Graphene is a thin sheet with special properties and complicated mechanical behavior. It’s important to study graphene experimentally and theoretically. Stone–Wales defects, cracks and atom vacancy are popular defects in carbon allotropes especially in graphene. In this paper, residual strain in graphene was discussed. At first, stress-strain curve of non-defected graphene sheet was obtained using molecular dynamics simulation and effect of temperature on mechanical properties of graphene was obtained. Then, four different cracks were considered in center of graphene sheets. Stress-strain curves of defected graphene sheets with different tension strain rates were plotted. The results showed that cracks lead to the graphene to fracture sooner. Also, increasing temperature lead to the Young’s modulus of graphene decreases and graphene fractured at lower strain. On the other hand, residual strain of non-defected and cracked graphene increased by increasing temperature from 200 K to 1200 K. It means that graphene had more plasticity behavior by increasing temperature.

Monte Carlo-Based Finite Element Method for the Study of Randomly Distributed Vacancy Defects in Graphene Sheets

This paper proposed an effective stochastic finite element method for the study of randomly distributed vacancy defects in graphene sheets. The honeycomb lattice of graphene is represented by beam finite elements. The simulation results of the pristine graphene are in accordance with literatures. The randomly dispersed vacancies are propagated and performed in graphene by integrating Monte Carlo simulation (MCS) with the beam finite element model (FEM). The results present that the natural frequencies of different vibration modes decrease with the augment of the vacancy defect amount. When the vacancy defect reaches 5%, the regularity and geometrical symmetry of displacement and rotation in vibration behavior are obviously damaged. In addition, with the raise of vacancy defects, the random dispersion position of vacancy defects increases the variance in natural frequencies. The probability density distributions of natural frequencies are close to the Gaussian and Weibull distributions.

Density functional theory study on the adsorption of alkali metal ions with pristine and defected graphene sheet

ABSTRACTThe graphene-based materials along with the adsorption of alkali metal ions are suitable for energy conversion and storage applications. Hence in the present work, we have investigated the structural and electronic properties of pristine and defected graphene sheet upon the adsorption of alkali metal ions (Li+, Na+, and K+) using density functional theory (DFT) calculations. The presence of vacancies or vacancy defects enhances the adsorption of alkali ions than the pristine sheet. From the obtained results, it is found that the adsorption energy of Li+ on the vacancies defected graphene sheet is higher (3.05 eV) than the pristine (2.41 eV) and Stone–Wales (2.50 eV) defected sheets. Moreover, the pore radius of the pristine and defected graphene sheets are less affected by metal ions adsorption. The increase in energy gap upon the adsorption of metal ions is found to be high in the vacancy defected graphene than that of other sheets. The metal ions adsorption in the defective vacancy sheets has high charge transfer from metal ions to the graphene sheet. The bonding characteristic between the metal ions and graphene sheet are analysed using QTAIM analysis. The influence of alkali ions on the electronic properties of the graphene sheet is examined from the Total Density of States (TDOS) and Partial Density of States (PDOS).

Modeling of 2-D hydrogen-edge capped defected & boron-doped defected graphene sheets for the adsorption of CO2, SO2 towards energy harvesting applications

The metal-air batteries are potentially promising energy storage system that attracts due to their high theoretical energy density among other electrochemical energy storage systems. To infiltrate new barriers in the metal-air battery technology, air electrodes and its adsorption mechanisms are pre-eminent to understand the adsorption process at the atomic level. Graphene and its defects are proven as a better air electrode in the metal-air battery technology for the past few decades. Graphene can be tunable, superior compatibility with its defects and dopants, those make graphene as a potentially unique and important material to investigate. In our present study, we investigate 5-8-5, 55-77 (Stone-Waals), 555-777 and 5555-6-7777 defected sheets by functionalizing them with hydrogen around the edges and doping each defect by replacing a carbon atom with boron atom. This density functional study provides the better adsorption mechanism of CO2 and SO2 gas molecules on the defected and boron doped graphene sheets in favour of metal-air battery applications. We found that modeled sheets are favourable for the adsorption of the SO2 gas molecule with the maximum adsorption energy of −0.343 eV, induced by 555-777 defected graphene sheet. After adsorption, it can provide proficient catalyst reactions by expanding the SO bond length to 1.460 Å. Further, we have examined the di-vacancy defects as a hydrogen storage tool and artificial photosynthesis platform. The edges are highly reactive and have shown strong binding energy with hydrogen atom. Similarly, CO2 adsorbed UV absorption graph in sheets exhibit hypsochromic effect other than 5-8-5 and B-555-777 sheets, whereas 5-8-5 and B-555-777 sheets exhibit bathochromic effect and the absorption graphs are fallen in between visible regions, which are good for photosynthesis.

The role of vacancies in electric field mediated graphene oxide reduction

Electric fields are regarded as a promising means of graphene oxide reduction, but previous studies have only focused on pristine graphene. Here, based on first principles density functional theory calculations, we report on electric field mediated reduction of neutral and charged O and hydroxyl groups from both pristine and defective graphene sheets. The critical electric field strengths for different species are determined in facilitating a progressive and selective graphene oxide reduction. Our results demonstrate that the presence of vacancy defects significantly inhibits the effectiveness of electric fields as a means of reduction of O and OH functionals, due to the complexities that arise between the functional group and vacancy edge atoms in the presence of an applied electric field.

Effect of temperature and strain-rate on mechanical properties of defected graphene sheet: A molecular dynamics study

Graphene, a one atom thick sheet of carbon exhibits outstanding mechanical properties, but defects which are unavoidable at the time of synthesis may strongly affect, such as intrinsic properties and fracture toughness of graphene can be altered by topological defects such as vacancy, Stone-Thrower-Wales (STW) defects, dislocations and grain boundaries. In this research article, authors have extensively studied the effect of Stone-Thrower-Wales defect on mechanical properties of a single layer of graphene sheet at different temperature and strain-rates using classical molecular dynamics (MD) based simulations. Also, authors have studied the effect of defect-concentration on the mechanical properties of graphene at different temperature and strain rates. It has been observed that fracture strength and strain is not varying with temperature for STW-1 in zigzag direction and STW-2 in armchair direction respectively. Also, the same scenario was observed for different strain-rate values. Further-more it was observed that at 1K both STW-1 and STW-2 defects shows almost same fracture strength and strain in armchair and zigzag directions for higher strain-rates. On the other hand, at lower strain-rates both STW-1 and STW-2 defects showed different fracture strength and strain at 1K. Also, it was observed that at higher temperatures STW-1 in armchair direction and STW-2 in zigzag direction shows enormous decrease in mechanical properties, it shows STW-1 and STW-2 are not favourable in armchair and zigzag directions respectively. In addition, the effect of defects at different strain-rates and concentration on the fracture strength and failure morphology of graphene sheet has also been studied.

Vibration Analysis of Vacancy Defected Graphene Sheets by Monte Carlo Based Finite Element Method.

The stochastic distributed placement of vacancy defects has evident effects on graphene mechanical property, which is a crucial and challenged issue in the field of nanomaterial. Different from the molecular dynamic theory and continuum mechanics theory, the Monte Carlo based finite element method (MC-FEM) was proposed and performed to simulate vibration behavior of vacancy defected graphene. Based on the Monte Carlo simulation, the difficulties in random distributed location of vacancy defects were well overcome. The beam element was chosen to represent the exact atomic lattice of the graphene. The results of MC-FEM have a satisfied agreement with that in the reported references. The natural frequencies in the certain vibration mode were captured to observe the mechanical property of vacancy defected graphene sheets. The discussion about the parameters corresponding with geometry and material property was accomplished by probability theory and mathematical statistics.

Vibration Behavior of Nanocomposite Plate Reinforced by Pristine and Defective Graphene Sheets; an Analytical Approach

Free vibration characteristics of polymer composite plates reinforced by graphene nanosheets employing the Eringen nonlocal elasticity theory were investigated. Theoretical formulations are derived based on Hamilton’s principle implementing linear orthotropic constitutive equations of lamina while the behavior of nanostructure points affected by all other nonlocal points is also taken into account. For obtaining the mechanical properties, a new modified Halpin–Tsai model is employed. Governing equations are solved by developing an efficient analytical solution. The accuracy of the presented method is examined, by comparing the results with literature in which a good agreement is observed. Effects of different boundary conditions, volume fraction, graphene sheets orientation angle and Eringen nonlocal parameter on frequency of nanocomposite are analyzed. Effects of the presence of vacancy defects in the nanosheet on the behavior of reinforced composites were also studied. The results illustrate that by increasing the nonlocal parameter the natural frequency showed a decreasing trend while by increasing the graphene sheet’s volume fraction, natural frequencies significantly increased. It could be concluded that the orientation angle variations in graphene sheets, did not play an important role on the natural frequency of nanocomposite as well as degradation of properties resulted in from vacancy defects.

Employing an analytical approach to study the thermo-mechanical vibration of a defective size-dependent graphene nanosheet

In this study, an analytical method is developed to study the free vibration of a defected nano graphene sheet coupled with temperature change and embedded on foundation based on Reddy’s third-order shear deformation plate theory. The graphene sheet may be opposed to the structural defect during the production process. Therefore, it is important to analyze the vibration behavior of graphene sheet. Here, some of the defects are modelled as a hole. Reddy’ third-order shear deformation plate theory is employed because it satisfies the zero shear stress condition at the free surfaces and need not use any shear correction coefficient to obtain equations of motion of the defected nanosheet. The interaction of the defected graphene sheet with a viscoelastic medium is simulated as a visco-Pasternak foundation. The influence of the surrounding viscoelastic medium on the natural frequencies is analyzed. To get the equations of dynamic equilibrium and natural boundary conditions of the nanosheet, the Hamilton’s principle is implemented. The presented method is verified by comparing the results with their counterparts reported in the open literature and good agreement is observed. Effects of different boundary conditions such as C-C, S-S, C-F, C-S, inner-radius-outer-radius ratio, Winkler foundation parameter, damping modulus, shear modulus, nonlocal parameter and temperature change on the frequency of the defected graphene sheet are examined. Various natural frequencies in nondimensional form and mode shapes are developed. The results show that, by increasing the inner-radius-outer-radius ratio, the natural frequency has an increasing behavior for all kinds of boundary condition. It is observed that increasing the size of defect has a significant effect on the natural frequency. Moreover, it can be concluded that decreasing the nonlocal parameter as the small-scale effect makes the plate stiffer. Therefore, the natural frequency of the nanoplate increases.

First-principles study of plutonium adsorption on perfect and defective graphene and hexagonal boron nitride

The adsorption of the Pu atom on perfect and defective graphene and hexagonal boron nitride (h-BN) sheet has been systematically investigated by using first-principles calculations. Pu atom is most likely to trap at the hollow site in pure graphene, and the energy barrier is as high as 78.3 meV. For ideal h-BN, the top site of the boron atom is the most stable adsorption site for adatom Pu, and the maximal energy barrier is only 12 meV. Comparing Pu on pure graphene and h-BN sheet, Pu atom is easy to migrate on the surface of ideal h-BN at room temperature, while it is bound to perfect graphene. Besides, Pu atom adsorbed on defective graphene and h-BN sheet, with large adsorption energies in the range of 2.66 ∼ 14.95 eV, is more stable than that on pure graphene and h-BN sheet. We have also found that all the adsorption systems are spin-polarized with the largest magnetic moments of Pu to be 7.67 μB on graphene and 6.71 μB on h-BN with a single vacancy of N atom. These findings suggest that graphene and h-BN two-dimensional materials can be effectively applied in the growth of high-quality plutonium single crystal thin films, as well as in nuclear waste recovery.

FEM study on mechanical properties of nanocomposites reinforced by defective graphene sheets

The main objective of the present study is improvement of the mechanical property estimation of epoxy nanocomposites (NCs) reinforced by defective graphene sheets (GS). For this purpose, the mechanical properties of a defect‐free GS are initially determined using FEM. Then, some well‐known defects are incorporated into the computational model to establish a realistic computational model. In addition, the finite element analyses of a NC reinforced by such defective GSs are conducted using Full Continuum and semi‐continuum FE models. In this regard, the multi‐scale method is used to model the perfect bonds between carbon atoms and the surrounding matrix. Also, the influences of the interphase layer and defective GSs on NC properties are investigated. Finally, the effects of some basic parameters such as the weight fractions and the length of GSs on the mechanical properties are examined. POLYM. COMPOS., 40:E1084–E1093, 2019. © 2018 Society of Plastics Engineers