Co-effects of graphene oxide sheets and single wall carbon nanotubes on mechanical properties of cement

The enhancement of mechanical properties of cement composites by a carbon nanomaterial is an important topic. However, the co-effect of two (or more) carbon nanomaterials on the mechanical properties of cement has not been explored. In this paper, it was found that the mixture of graphene oxide (GO) sheets and single-walled carbon nanotubes (SWCNTs) exhibited an excellent co-effect, leading to 72.7% increase in bending strength of cement, which is much larger than the strength enhancements of 51.2% by GO and 26.3% by SWCNTs. Furthermore, it was demonstrated that the bending strength of cement composite materials with GO and SWCNTs is proportional to the sizes of crystal SiO₂ particles.     

Mechanical properties and structures of bulk nanomaterials based on carbon nanopolymorphs

Bulk nanomaterials based on sp² carbon nanopolymorphs are promising candidates for supercapacitors due to their unique properties such as extremely high specific surface area, high conductivity and stability against graphitization. However, the mechanical response of such materials to external loading is not understood well. This Letter studies the effect of hydrostatic pressure on the mechanical properties and structures of these materials via molecular dynamics simulations. Three types of nanopolymorphs‐based nanomaterials that are composed of bended graphene flakes, short carbon nanotubes and fullerenes are considered. It is found that these three materials show a distinct relation between the pressure and volume strain. Moreover, their resistance to graphitization depends on the structure of their constituent components. The phenomena are explained by analysing the radial distribution function and coordination numbers of the atoms. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Influence of the Geometric Shape of Carbon Nanoparticles on the Strength Properties of Nanocomposite Materials Obtained by Filling an Epoxy Matrix

Abstract

The effects of filling an epoxy matrix modified with “Viniflex” with carbon nanotubes, fullerene C₆₀, or graphene on the mechanical properties, surface morphologies and glass transition temperatures of the composite materials obtained after curing were studied. It was shown that the largest decrease in glass transition temperature and an increase in impact strength was achieved by the introduction of 0.1 mass% graphene. Filling with graphene and carbon nanotubes increased the bending strength while filling with C₆₀ fullerenes provided the greatest compressive strength and elasticity modulus. An explanation of the results was based on ideas about the relationship of the geometrical shape of the nanofiller to the load direction and features of the phase composition of the composite materials. It is suggested that the carbon nanomaterials had a template effect on the packing of the epoxy matrix chains.     

Theoretical characterization of layered silica nanostructures from first-principles prediction

Using first-principles calculations, we study the structural, mechanical and electronic properties of the layered silica nanostructures built on base of silica bilayers consisting of four- and six-membered Si–O ring (4 MR and 6 MR) units. These silica nanostructures have high stability and good flexibility comparable to graphene and can serve as a promising precursor for the fabrication of well-ordered silica nanotubes. The porous structure and wide band gap of the silica nanomaterials may find applications in gas separation, slow-release microcapsules, and catalyst supports.     

Electronic properties and quantum transport in Graphene-based nanostructures

Carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) represent a novel class of low-dimensional materials. All these graphene-based nanostructures are expected to display the extraordinary electronic, thermal and mechanical properties of graphene and are thus promising candidates for a wide range of nanoscience and nanotechnology applications. In this paper, the electronic and quantum transport properties of these carbon nanomaterials are reviewed. Although these systems share the similar graphene electronic structure, confinement effects are playing a crucial role. Indeed, the lateral confinement of charge carriers could create an energy gap near the charge neutrality point, depending on the width of the ribbon, the nanotube diameter, the stacking of the carbon layers regarding the different crystallographic orientations involved. After reviewing the transport properties of defect-free systems, doping and topological defects (including edge disorder) are also proposed as tools to taylor the quantum conductance in these materials. Their unusual electronic and transport properties promote these carbon nanomaterials as promising candidates for new building blocks in a future carbon-based nanoelectronics, thus opening alternatives to present silicon-based electronics devices.     

Mechanical properties,lattice thermal conductivity,infrared and Raman spectrum of the fullerite C24

Lightweight carbon materials with excellent thermal and mechanical properties have important applications in aerospace industry. In this study, the stability, mechanical properties, lattice thermal conductivity, electronic structure, infrared and Raman spectrum of sp³ hybridized low-density fullerite C₂₄ were investigated according to density functional theory (DFT) calculations. It was found that the fullerite C₂₄ was both thermodynamic and dynamic stable. Quasi-harmonic approximation and Grüneisen parameter calculations clarified why the fullerite C₂₄ had a positive thermal expansion coefficient at low temperature. The fullerite C₂₄ also exhibited excellent mechanical properties. Interestingly, the Vickers hardness of carbon allotropes was found to almost be linear proportional to the density of a carbon material. HSE06 electronic structure calculations showed that it was a semiconductor with direct bandgap of 2.56 eV. Anharmonic lattice dynamic calculations showed that its thermal conductivity was higher than semiconductor silicon. Besides, Raman and infrared active modes as well as the corresponding spectra were presented.     

Supercapacitive electrochemical performance of graphene-containing carbon aerogel prepared using polyethyleneimine-modified graphene oxide

Graphene-containing carbon aerogel was prepared by a sol–gel polymerization of resorcinol-formaldehyde (RF) method using polyethyleneimine (PEI)-modified chemically exfoliated grapheme oxide, and its electrochemical performance as an electrode for supercapacitor was examined. The effect of PEI in the preparation of RFGO (resorcinol-formaldehyde and graphene oxide) solution on the physicochemical and electrochemical properties of graphene-containing carbon aerogel (CAPG) was investigated. For comparison, graphene-containing carbon aerogel was prepared using PEI-free graphene oxide (CAG). Graphene-free carbon aerogel (CA) was also prepared. CAPG showed the highest BET surface area (792 m²/g) and the largest pore volume (1.64 cm³/g) with well-developed porous structure. Various electrochemical measurements revealed that CAPG showed high specific capacitance (205 F/g), low equivalent series resistance (0.55 Ω), and superior capacitive behavior. The PEI-modified graphene oxide played an important role in enhancing physicochemical properties and supercapacitive electrochemical performance of CAPG.     

单层单晶石墨烯与柔性基底界面性能的实验研究

单晶石墨烯具有更优异的力学及电学性能,有望成为新一代柔性电子器件的核心材料.因此,有必要从实验的角度精细分析化学气相沉积法制得的大尺度单晶石墨烯与柔性基底复合结构的界面力学行为.本文通过显微拉曼光谱实验方法测量了不同长度的单层单晶石墨烯/PET(聚对苯二甲酸乙二醇酯)基底的界面力学性能参数及其在长度方向上界面边缘的尺度效应.实验给出了石墨烯在PET基底加载过程中与基底间黏附、滑移、脱黏三个界面状态的演化过程与应力分布规律.实验发现,单晶石墨烯与柔性基底间由范德瓦耳斯力控制的界面应变传递过程存在明显的边缘效应,并且与石墨烯的长度有关.界面的切应力具有尺度效应,其值随石墨烯长度的增加而减小,而石墨烯界面传递最大应变以及界面脱黏极限则不受试件尺度的影响.     

环氧树脂基碳纳米复合电磁屏蔽材料研究

基于碳纳米材料有序结构优异的结构与功能特点,研究了其在新型电磁防护材料中的应用,结合环氧树脂与碳纳米有序结构在电磁屏蔽效能和力学性能方面表现出的显著优势,论述了环氧树脂基碳纳米管复合电磁屏蔽材料和碳纳米管有序纳米结构研究,通过电磁仿真优化设计构筑三维导电网络结构,得出8~12 GHz电磁波段屏蔽效能≥82.96 dB的理想结构模型,为环氧树脂基碳纳米复合电磁屏蔽材料研究开发提供了指导,有利于该新型电磁屏蔽材料在国防、国民经济各领域的应用。     

The influence of tilt grain boundaries on the mechanical properties of bicrystalline graphene nanoribbons

The mechanical properties of bicrystalline graphene nanoribbons with various tilt grain boundaries (GBs) which typically consist of repeating pentagon–heptagon ring defects are investigated based on the method of molecular structural mechanics. The GB models are constructed via the theory of disclinations in crystals, and the elastic properties and ultimate strength of bicrystalline graphene nanoribbons are calculated under uniaxial tensile loads in perpendicular and parallel directions to grain boundaries. The dependence of mechanical properties is analyzed on the chirality and misorientation angles of graphene nanoribbons, and the experimental phenomena that Young's modulus and ultimate strength of bicrystalline graphene nanoribbons can either increase or decrease with the grain boundary angles are further verified and discussed. In addition, the influence of GB on the size effects of graphene Young's modulus is also analyzed.     

Fracture analysis of monolayer graphene sheets with double vacancy defects via MD simulation

Carbon nanostructures such as carbon nanotubes (CNTs) and graphene sheets have attracted great attention due to their exceptionally high strength and elastic strain. These extraordinary mechanical properties, however, can be affected by the presence of defects in their structures. When a material contains multiple defects, it is expected that the stress concentration of them superposes if the separation distances of the defects are low, which causes a more reduction of the strength. On the other hand, it is believed that if the defects are far enough such that their affected areas are distinct, their behavior is similar to a material with single defect. In this article, molecular dynamics (MD) is used to explore the influence of separation distance of double vacancy defects on the mechanical properties of single-layered graphene sheets (SLGSs). To this end, critical stress and strain of SLGSs containing double vacancy with different distances are determined and the results are compared with those of perfect SLGSs and graphene sheets with single vacancy defect. The results reveal that the ultimate strength of the SLGS with double vacancy tends to the one with a single vacancy when the separation distance becomes further. In this regard, the threshold distance beyond which double defects behave like a single one is examined. Finally, Young’s modulus of perfect, single and double vacancy defected graphene sheets with different separation distances is determined. It is concluded that this property is slightly affected by the separation distance.     

Encapsulation of small fullerenes into nitrogenated holey nanotubes: a density functional theory study

Encapsulation of fullerene into nanotubes based on a C₂N sheet, known as nitrogenated holey graphene, was investigated using density functional theory. The structural and electronic properties of these carbon hybrid materials, consisting of nitrogenated holey nanotubes and a small C₂₀ fullerene, were studied. The formation energies showed that encapsulation of the fullerene into the nitrogenated holey nanotube is an exothermic process. To characterise the electronic properties, the electronic band structure and density of states of armchair and zigzag nitrogenated holey nanotubes were calculated. Filling these nanotubes with the C₂₀ fullerene resulted in a p-type semiconducting character. The energy band gap of the nitrogenated holey nanotubes decreased with fullerene encapsulation. The results are indicative of the possibility of band gap engineering by encapsulation of small fullerenes into nitrogenated holey nanotubes.     

A molecular dynamics study of the mechanical properties of h-BCN monolayer using a modified Tersoff interatomic potential

Using molecular dynamics (MD) simulations, we investigate the mechanical properties of hexagonal BCN monolayer, a newly synthesized two-dimensional material with an atom ratio of B/C/N = 1:1:1. The Tersoff potential is modified to get good agreement between predicted and measured fracture strengths of graphene. With this modified Tersoff potential, we perform extensive MD simulations to study the effect of temperature, strain rate and vacancy defect on the mechanical properties of h-BCN. It is found that h-BCN is a strong material with fracture strength of 81.4–93.5 GPa, albeit ∼35% lower than that of graphene. Similar to graphene, temperature has strong effect on the mechanical properties of h-BCN. As the temperature increases from 10 K to 1300 K, the fracture strength and strain of h-BCN drops by 55% and 62%, respectively. The strain rate is found to have a moderate effect. When the strain rate increases from 0.00002 to 0.0125 ps⁻¹, the fracture strength and strain of h-BCN increases 6.1% and 12%, respectively. As for the atomic defect, a very small concentration (0.028%) of vacancy in h-BCN is able to cause a 28% reduction in fracture strength and a 35.5% reduction in fracture strain. These findings have significance for its future applications in nanodevices.     

氧化石墨烯的多色发光及其在荧光成像中的应用

氧化石墨烯作为石墨烯的一种带隙打开的衍生物,极大地丰富了其光学性质,并拓展了它在传感和成像方面的应用,特别是氧化石墨烯限域的π共轭结构对构建发光碳材料提供了十分便利的条件。目前,有大量的研究工作报道了氧化石墨烯及其衍生物能够产生多种颜色的荧光信号,然而,系统地总结这些研究去揭示氧化石墨烯发光机理的相关工作还比较少。本文总结了关于发光氧化石墨烯纳米材料的合成及其在光学成像方面应用的大量研究工作,为进一步开发新型的发光氧化石墨烯材料提供一些建设性意见。     

Controllable irregular phenomenon induced by Ag atomic segregation on the melting of (AgPd)561 bimetallic clusters

Here focusing on the very new experimental finding on carbon nanomaterials for solid-state electron mediator applications in Z-scheme photocatalysis, we have investigated different graphene-based nanostructures chemisorbed by various types and amounts of species such as oxygen (O), nitrogen (N) and hydroxyl (OH) and their electronic structures using density functional theory. The work functions of different nanostructures have also been investigated by us to evaluate their potential applications in Z-scheme photocatalysis for water splitting. The N-, O?CN-, and N?CN-chemisorbed graphene-based nanostructures (32 carbon atoms supercell, corresponding to lattice parameter of about 1?nm) are found promising to be utilized as electron mediators between reduction level and oxidation level of water splitting. The O- or OH-chemisorbed nanostructures have potential to be used as electron conductors between H₂-evolving photocatalysts and the reduction level (H⁺/H₂). This systematic study is proposed to understand the properties of graphene-based carbon nanostructures in Z-scheme photocatalysis and guide experimentalists to develop better carbon-based nanomaterials for more efficient Z-scheme photocatalysis applications in the future.     

Mechanical properties of thin films of graphene materials: A study on their structural quality and functionalities

Several studies have been done on physiochemical properties of thin films of graphene materials, but less on their mechanical properties. The mechanical properties such as tensile and storage modulus of films of graphene oxide (GO), different reduced graphene oxides (rGO), functionalised reduced graphene oxide (frGO) and a few layers graphene (graphene) were analysed in this study. During syntheses processes, a range of variations occurs due to different reducing agents and functionalising components used; this affects or changes the mechanical properties of the materials. In addition, it has become vital to comprehend the mechanical properties of these films as the potential applications such as sensor and electrodes demand extended life cycles or lifetime. It has been found that the ultimate tensile strength (UTS), tensile modulus, and storage modulus vary across all the samples that highly depend on nature/efficiency of reducing agent used, amount of impurities such as oxygen functional groups and defect density such as discrepancies/holes in the aromatic structure. The highest UTS and modulus have been identified with a few layers graphene and with hydroiodic acid reduced GO among the rGOs. The frGO shows almost similar properties to that of graphene.     

Preparation of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> hollow microsphere/graphene/carbon nanotube flexible film as a binder-free anode material for lithium-ion batteries

A flexible Co₃O₄ hollow microsphere/graphene/carbon nanotube hybrid film is successfully prepared through a facile filtration strategy and a subsequent thermally treated process. The composition, morphology, and structure of the as-prepared film are characterized by X-ray diffraction, X-ray photoelectron spectrometer, scanning electron microscopy, and transmission electron microscopy. Based on the morphology characterizations on the hybrid film, the Co₃O₄ hollow microspheres are uniformly and closely attached on three-dimensional (3D) graphene/carbon nanotubes (GR/CNTs) network, which decreases the agglomeration of Co₃O₄ microspheres effectively. In this hybrid film, the 3D GR/CNT network which enhances conductance as well as prevents aggregation is a benefit to help Co₃O₄ to exert its lithium storage capabilities sufficiently. When used as a binder-free anode material for lithium-ion batteries, the hybrid film delivers excellent electrochemical properties involving reversible capacity (863 mAh g^?1 at a current density of 100 mA g^?1) and rate performance (185 mAh g^?1 at a current density of 1600 mA g^?1).     

The influence of sputtering procedure on nanoindentation and nanoscratch behaviour of W-S-C film

Sulphides of tungsten with its lamellar structure - whereby weak van der Waals forces act between the layers - are commonly believed to be responsible for their excellent self-lubricating properties. The present investigation is undertaken in order to explore the possibility of using this film for MEMS application. In order to achieve this objective, W-S-C films are deposited on 100Cr6 steel using radio frequency magnetron sputtering. Carbon was incorporated in the films via three different ways: (1) using a reactive gas (CH₄), (2) by co-sputtering from separate targets (WS₂ and C targets) and, (3) by co-sputtering from a C target embedded with WS₂ pellets. Microstructural features and mechanical properties of these films are evaluated with the help of scanning electron microscopy and nanoindentation. The topography, structural features and scratch behaviour are analysed using atomic force microscopy, X-ray diffraction and nanoindenter. It is noted that the film deposited by sputtering two targets exhibits the highest hardness due to high oxygen content. The highest elastic modulus pertains to the film deposited from the carbon target containing WS₂ pellets as this film has amorphous structure and the minimum porosity. The friction coefficient under scratching is the highest for reactively sputtered film whereas it is the minimum for the film deposited from the carbon target containing WS₂ pellets as this film has amorphous structure and the minimum roughness.     

Single atom doping in 2D layered MoS2 from a periodic table perspective

Molybdenum Disulfide (MoS₂) is a well-known transition metal dichalcogenide with a hexagonal structure arrangement analogous to graphene. Two dimensional (2D) MoS₂ has attracted wide attention in various applications such as energy storage, catalysis, sensing, energy conversion and optoelectronics due to its unique properties including tunable bandgap, substantial carrier mobility, outstanding mechanical strength and dangling-bond free basal surface. Moreover, MoS₂ has shown an excellent capability to be a host for foreign atoms which tune its physicochemical properties. Herein, currently known structural changes in the MoS₂ crystals introduced by various single atom dopants coming from all over the chemical table of elements are reviewed. Accompanying electrical, optical and magnetic properties of such structures are discussed in detail. Potential applications of the doped MoS₂ are introduced briefly as well. The review concentrates on the recent state-of-the-art results obtained mostly by the high resolution scanning transmission electron microscopy (STEM), such as high angle annular dark field (HAADF) imaging as well as scanning probe microscopy (SPM) such as scanning tunneling microscopy (STM). These techniques have been used to decipher dopant positions and other sub-atomic structural changes introduced to the MoS₂ structure by isolated dopants.     

棱形石墨烯纳米孔道内离子传输性能的分子动力学模拟

纳米通道的尺寸、结构和表面化学对其内部溶液的分布结构和输运性质有着重大影响.本文研究了一种全新的菱形石墨烯纳米通道.这种理想的通道与最近被广泛研究的金属有机框架材料(MOF)的内部结构类似,有着与传统的碳纳米管截然不同的内部结构.本文使用分子动力学模拟的方法研究在不同尺寸的菱形石墨烯纳米通道内的KCl溶液的性质,并将其与同尺寸的单壁碳纳米管进行了比较.研究结果表明在小孔道内(<20?)其内部的溶液结构呈现若干个密度极高的聚集区域,即出现了结晶化的趋势．这一研究结果,将为MOF的结构设计提供思路,从而有望实现类似于生物离子通道的高选择性和高传输能力.