Pillared Graphene Nanostructures Research Articles

Structures, Electronic Properties, and Gas Permeability of 3D Pillared Silicon Carbide Nanostructures.

Silicon carbide (SiC) is recognized as excellent material for high power/temperature applications with a wide-band gap semiconductor. With different structures at the nanosize scale, SiC nanomaterials offer outstanding mechanical, physical, and chemical properties leading to a variety of applications. In this work, new 3D pillared SiC nanostructures have been designed and investigated based on self-consistent charge density functional tight-binding (SCC-DFTB) including Van der Waals dispersion corrections. The structural and electronic properties of 3D pillared SiC nanostructures with effects of diameters and pillar lengths have been studied and compared with 3D pillared graphene nanostructures. The permeability of small gas molecules including H2O, CO2, N2, NO, O2, and NO2 have been demonstrated with different orientations into the 3D pillared SiC nanostructures. The promising candidate of 3D pillared SiC nanostructures for gas molecule separation application at room temperature is highlighted.

Predicting phonon scattering and tunable thermal conductivity of 3D pillared graphene and boron nitride heterostructure

In this work, we have studied the transfer of phonon energy in hybrid structure of pillared graphene and boron nitride film. The obtained results showed that, due to the occurrence of ballistic transfer with the elongation of heterostructure, thermal conductivity was increased. We also found that the amount of interfacial thermal conductivity was changed by changing the direction of thermal flux and the application of thermal flux along the direction of pillared graphene nanostructure was more favorable. We observed that increase of temperature from 100 to 700 K increased the amounts of interfacial thermal conductance (ITC) in C-N and C-B models by 19 and 10%, respectively. Since defects are inevitable during the fabrication and growth of these structures, in this work, we investigated the concentration and arrangement of these defects at joint interface and found that increase of defect concentration decreased thermal flux and ITC and also type of defects had a significant effect on thermal rectification. Also, the detection of these defects in a controlled manner can help making thermal conductivity tunable. We evaluated the effect of tensile from 0 to 10% in heterostructure with and without vacancy defects and found that ITC was decreased by 45% and 30% and temperature jump was increased by 80% and 45% at interface, respectively. In addition, to further analyze the obtained results, phonon vibration power spectra were also examined. Finally, by using Von Mises stress criterion, stress distribution and concentration through sheets and interface in the presence of mechanical strains and various defects were investigated.

Tensile properties of pillared graphene block

Tensile properties of pillared graphene block (PGB) nanostructure are studied in this paper. This nanostructure is composed of four pillared graphene nanostructures connected to each other in a special order which preserves the honeycomb molecular bond order of graphene. Molecular dynamics simulations using AIREBO potential are utilized to investigate the tensile properties and thermodynamic stability of the nanostructure. Four structural parameters are defined for PGB nanostructure. By assigning different values to these geometrical parameters, 28 prototypes are virtually produced. Potential energy profile of each sample is traced to evaluate thermodynamic stability. After relaxation of the nanostructures, virtual uniaxial tensile tests are applied to assess the tensile properties in three dimensions. Young's modulus, fracture strength and fracture strain for each sample are obtained. All samples are thermodynamically stable having high Young's modulus and fracture strength. The strongest sample has fracture strength of 21.5 GPa and Young's modulus of 144 GPa.

Pillared graphene as excellent reinforcement for polymer-based nanocomposites

Three-dimensional (3D) novel architectures consisting of graphene and carbon nanotubes (CNTs) possess a host of attractive properties with applications for numerous fields. In this study, we adopted molecular dynamics (MD) to investigate the capability of a kind of typical 3D carbon nanomaterial (termed as pillared graphene nanostructures (PGNs)) as reinforcement for polymer nanocomposites. The obtained results show that PGNs can significantly enhance the mechanical property of polyethylene (PE) matrix, yielding an increase about 62% in elastic modulus compared with neat PE. Moreover, the PGNs-reinforced PE nanocomposites exhibit excellent property characteristic in all studied three directions, which is quite different compared to the graphene or carbon nanotubes reinforced polymer nanocomposites (which only show improvement in the in-plane direction). Such substantial improvement originates from two aspects: 1) the synergetic effect between the graphene layers and vertically oriented CNTs that enables 3D enhancement; 2) the interlock effect between PE chains and PGNs which is arising from the unique structure of PGNs (graphene layers supported by vertical CNTs). Our results show that PGNs are really extraordinary fillers in reinforcing mechanical property of polymer-based nanocomposites.

Seawater desalination using pillared graphene as a novel nano-membrane in reverse osmosis process: nonequilibrium MD simulation study.

Herein, the applicability and efficiency of two types of pillared graphene nanostructures, namely, (6,6)@G and (7,7)@G, were investigated as membranes in reverse osmosis seawater desalination using extensive nonequilibrium molecular dynamics simulations. The water permeability for (6,6)@G and (7,7)@G membranes was estimated at 4.2 and 6.6 L h-1 cm-2 MPa-1, respectively. According to the results, a complete (100%) and pressure-independent salt rejection was estimated for both membranes. In addition, the mechanism of seawater desalination through the pillared graphene membranes was investigated via the density distribution profile of water molecules inside the pillar channels. Furthermore, a series of steered MD simulations were performed to construct the potential of mean force (PMF) profile of water molecules and salt ions passing through the membranes channels. The passing free energy barriers of Na+ and Cl- ions and water molecules are 0.86, 0.62, and 0.22 eV, respectively, for the (6,6)@G membrane. The corresponding quantities for the (7,7)@G membrane are 0.71, 0.44, and 0.11 eV, respectively.

The effects of intertube bridging through graphene nanoribbons on the mechanical properties of pillared graphene

Abstract In this study, effects of intertube bridging and bridging type on the mechanical properties of pillared graphene are investigated through molecular dynamics (MD) simulations. For this purpose, atomistic models of pillared graphene structures consisting of six carbon nanotubes (CNTs), which are arranged in a regular hexagonal pattern, are built by employing graphene nanoribbons as intertube bridging units. In the first phase, tensile behaviors of two pillared graphene structures (i.e. with and without intertube bridging) are compared to understand the effects of intertube bridging. In the second phase, two different models for the interconnected pillared graphene are prepared by using graphene nanoribbons with different lengths. Numerical tensile tests with the same settings are conducted on the specimens of the proposed nanostructures, and their mechanical properties including tensile strength and toughness are examined. Based on the results, it is shown that intertube bridging between CNT units significantly increases the tensile strength of pillared graphene. Furthermore, it is also demonstrated that, depending on the length of the interconnecting graphene nanoribbons, intertube bridging can either increase or decrease the toughness of pillared graphene nanostructures, thereby providing tunable hybrid mechanical characteristics.

Preparation of a Photoactive 3D Polymer Pillared with Metalloporphyrin

Among the very few efforts for the preparation of stable pillared graphene nanostructures, there is no report of tin porphyrin intercalated between TiO2-graphene (TG) nanosheets. In this study, a nanostructure material of pillared graphene made of tin porphyrin functionalized graphene-TiO2 composite (TG) was successfully synthesized. The prepared compound showed high activity in the photodegradation reaction under irradiation of visible light. Photocatalytic results showed that the composite of graphene-TiO2 containing 3% graphene had the highest photoactivity. The photoactivity of TG (3%) was about 1.5 times higher than that of the pure TiO2. Besides, tin porphyrin-pillared TG composite (TGSP) material exhibited an excellent visible light photocatalytic performance in degradation of methyl orange dye. This compound could destruct 100% of methyl orange dye in 180 min. Such pillared carbon nanostructure exhibited unique photoactivity due to the synergistic effect between the graphene sheets and the SnTCPP pillars. It is found that the highly efficient light-harvesting structure of the SnTCPP pillared TG composite can be attributed to densely embedded porphyrin chromophores with high visible absorptivity within the framework. The investigation of photocatalytic mechanism determined that hydroxyl radical is a main species in photodegradation process of methyl orange over TGSP compound.

Molecular dynamics study of the tensile behavior of pillared graphene nanostructures

The mechanical properties of a three-dimensional (3D) pillared graphene nanostructure subjected to tensile loading are studied by molecular dynamics simulation. The effects of temperature on the Young’s modulus, fracture strain, and strain energy of the nanostructures with carbon nanotubes (CNT) types , , , and are examined. In according with simulation results, the maximum strain energy is obtained under a strain of approximately 0.265 at various temperatures. The Young’s modulus and fracture strain of the nanostructure decrease as the temperature increases. The Young’s modulus of the nanostructure is much lower than that of its composition materials. The Young’s modulus and fracture strain of the nanostructures with armchair-type and CNTs are lower than those with and CNTs.

Ultrafast high energy supercapacitors based on pillared graphene nanostructures

Herein we report the optimized growth of pillared graphene nanostructures (PGNs) on nickel foil substrates. The PGN supercapacitor demonstrates excellent cycling stability, and outstanding electrochemical reversibility under high rate, leading to energy storage devices with superb cycling stability and outstanding power density.

支柱型グラフェンナノ構造のインデンテーションシミュレーション

支柱型グラフェンナノ構造のインデンテーションシミュレーション

GS0312 支柱型グラフェンナノ構造の力学的特性解析

GS0312 支柱型グラフェンナノ構造の力学的特性解析

Junction configuration-induced mechanisms govern elastic and inelastic deformations in hybrid carbon nanomaterials

Although various hybrid 3D carbon-based architectures are reported by covalently connecting low dimensional carbon allotropes, the effect of junction configuration on deformation and mechanical properties of the hybrid carbon architectures remain elusive. Here, we focus on Pillared Graphene Nanostructure (PGN) as a model system with symmetric and asymmetric junctions to explore its diverse elastic and inelastic properties via first-principles and molecular dynamics simulations. By introducing heptagonal and octagonal rings in the junctions, our findings demonstrate that in contrast to the stacked of graphene sheets, which exhibit weak out-of-plane properties, both junction types impart a cooperative two-regime deformation mechanism that provides a number of superior characteristics in PGN, including 3D balance of strength and toughness as well as an outstanding ∼42% out-of-plane ductility preceding the failure. Furthermore, asymmetric junctions impose wrinkles in the PGN sheets, which add extra in-plane flexibility and shear compliance, result in a nearly zero/negative in-plane Poisson's ratio in PGN, and cause the octagonal rings to act as hotspot for initiating of fracture. Our results provide the first atomistic “lens” on fundamental understanding of junction-induced deformation mechanisms in pillared graphene and can potentially provide a new phase space to better control and design mechano-mutable hybrid carbon nanostructures.

Modeling for predicting strength of carbon nanostructures

We have developed a computational scheme to predict stiffness and strength of carbon nanostructures under various loading modes. The prediction method is based on combined molecular mechanics and molecular dynamics simulations to approach a global energy minimum at a given loading level with a preset temperature tolerance of 10−6K. We have applied the present method to various carbon nanostructures including carbon nanotubes (CNTs), graphene, CNT with defects, a CNT-graphene junction and pillared graphene nanostructures. For all cases, we have identified the maximum stress and strain at failure of these carbon nanostructures as well as their critical failure modes, and discussed mechanisms that lead to their catastrophic failure.

Thermal properties of pillared-graphene nanostructures

ABSTRACTThe thermal conductivities of pillared-graphene nanostructures (PGNSs) are obtained using nonequilibrium molecular-dynamics simulation. It is revealed their thermal conductivities are much smaller than the thermal conductivities of carbon nanotubes (CNTs). This fact is explained by examining the density of states (DOS) of the local phonons of PGNSs. It is also found the thermal conductivity of a PGNS linearly decreases with the increase of the inter-pillar distance.

Mechanical properties of pillared-graphene nanostructures using molecular dynamics simulations

The deformation behaviour and mechanical properties of three-dimensional (3D) pillared graphene are investigated using molecular dynamics simulations. The Tersoff–Brenner many-body potential model is employed to evaluate the interactions between 3D pillared-graphene carbon atoms and nanotube carbons. The Lennard-Jones potential model is used to compute the interactions between a conical indenter and 3D pillared-graphene carbon atoms. The effects of the size and geometric structure of 3D pillared-graphene are evaluated in terms of the indentation force and contact stiffness. The simulation results for an armchair nanotube of 3D pillared graphene show that the contact stiffness increases with increasing chiral vector of the 3D-pillared graphene. However, the adhesive force sharply decreases with increasing chiral vector of the 3D-pillared graphene. A zigzag nanotube of 3D-pillared graphene exhibits better mechanical properties compared with those of the armchair nanotube.

ピラードグラフェンナノ構造体の熱的特性解析

ピラードグラフェンナノ構造体の熱的特性解析

20113 せん断荷重下のピラードグラフェンナノ構造体の力学的特性解析(GS-08【セラミックス】)

20113 せん断荷重下のピラードグラフェンナノ構造体の力学的特性解析(GS-08【セラミックス】)

Mechanical Properties of Pillared-Graphene Nanostructures under Shear Loads

ABSTRACTThe shear deformations of pillared-graphene nanostructures are investigated using molecular dynamics simulation. Slight anisotropy regarding the direction of a shear load is detected. Changing the loading area in graphene and the radius of a single-walled carbon nanotube (SWNT) as a pillar, the deformations near the joints of graphene and a SWNT are examined in detail. It is concluded the anisotropy of the shear deformation of the nanostructure is due to the atomic structures at the joints of graphene and a SWNT as a pillar, and the out-of-plane deformations of graphene near the joints dominantly affect the overall shear deformation of the nanostructure.

Supercapacitors Based on Pillared Graphene Nanostructures

We describe the fabrication of highly conductive and large-area three dimensional pillared graphene nanostructure (PGN) films from assembly of vertically aligned CNT pillars on flexible copper foils for applications in electric double layer capacitors (EDLC). The PGN films synthesized via a one-step chemical vapor deposition process on flexible copper foils exhibit high conductivity with sheet resistance as low as 1.6 ohms per square and possessing high mechanical flexibility. Raman spectroscopy indicates the presence of multi walled carbon nanotubes (MWCNT) and their morphology can be controlled by the growth conditions. It was discovered that nitric acid treatment can significantly increase the specific capacitance of the devices. EDLC devices based on PGN electrodes (surface area of 565 m2/g) demonstrate enhanced performance with specific capacitance value as high as 330 F/g extracted from the current density-voltage (CV) measurements and energy density value of 45.8 Wh/kg. The hybrid graphene-CNT nanostructures are attractive for applications including supercapacitors, fuel cells and batteries.

Tuning the Kapitza resistance in pillared-graphene nanostructures

The pillared-graphene architecture is a conceivable way of conjoining graphene nanoribbons and carbon nanotubes (CNTs) in nanoelectronics. Especially promising is its capability to dissipate thermal energy in thermal management applications. However, the thermal boundary resistance (Kapitza resistance) at the graphene nanoribbon-CNT interface is a phonon barricade and a bottleneck for efficacious heat extraction. Parallel to strain studies on thermal conductance, this work is a first report on the effects of mechanical strain on the interfacial phonon dynamics in the pillared-graphene nanostructure (PGN). Molecular dynamics simulations are employed to derive the changes in phononics as axial, torsional, and compound strains of various degrees are applied on the PGN. The pillar lattice structure behaves dissimilarly to the different types of strains. In-plane transverse optical mode softening as induced by torsional strain is more effective than LO softening (triggered by tension) in minimizing the thermal boundary resistance. Essentially, it is shown that there is a strong relationship between strained PGN pillar lattice structure, interfacial phononics, and thermal boundary resistance.