Fabrication of exfoliated graphite nanoplatelets-reinforced aluminum composites and evaluating their mechanical properties and corrosion behavior

Aluminum composites with different amounts of exfoliated graphite nanoplatelets particles were fabricated by powder metallurgy method. The mixture powders were consolidated at 520 MPa for 5 min and followed by pressureless sintering at 600 °C for 6 h. The mechanical properties of composites were evaluated by compression and hardness tests. The corrosion behavior in 3.5% NaCl solution was investigated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements. The mechanical testing results showed that the maximum strength and Vickers hardness increase as a function of exfoliated graphite nanoplatelets content. Corrosion data indicated that the presence of exfoliated graphite nanoplatelets and the increase of its concentration raise the corrosion rate and reduce the polarization resistance of Al. SEM/EDX investigations revealed that the presence of exfoliated graphite nanoplatelets activates the corrosion of Al due to the occurrence of galvanic corrosion. SEM/EDX investigations confirmed the electrochemical measurements showing that the increase of exfoliated graphite nanoplatelets content increases the corrosion of Al.     

Conducting film from graphite oxide nanoplatelets and poly(acrylic acid) by layer-by-layer self-assembly

A [poly(acrylic acid)/graphite oxide]n [(PAA/GO)(n)] film with a conductivity of 60 S.cm(-1) was grown layer-by-layer (LbL) using Langmuir-Blodgett self-assembly techniques. GO nanoplatelets were prepared from natural graphite by oxidizing, ball milling, exfoliating, and modifying with cationic surfactant cetyltrimethylammonium bromide (CTAB). The X-ray diffraction pattern reveals that PAA and GO stack orderly LbL and repeatedly in the (PAA/GO)(n) films, and about three carbon molecular layers are superposed on each GO sheet. Fourier transform infrared spectra offer evidence for the interaction between the carboxylic groups on PAA and the CTAB on the surface of the GO nanoplatelets. Electrochemistry measurements show that the conductivity of the (PAA/GO)(n) film depends on the carbon-carbon interlayer height of the GO sheet, and the (PAA/GO)(n) film has a typical positive temperature coefficient effect above the PAA melting temperature. The atomic force microscopy images reveal that CTAB molecules stack in a well-ordered head-to-head structure on both surfaces of the GO nanoplatelets and the GO nanoplatelets are embeded between PAA layers.     

Mild-temperature Synthesis of Covellite Copper Sulfide Hexagonal Nanoplatelets via the Hydrothermal Route

Covellite CuS hexagonal nanoplatelets were prepared by a simple hydrothermal process at mild temperature, using sodium dodecyl benzene sulfonate （SDBS） as an assisting reagent. The products were characterized by X-ray powder diffraction （XRD）, transmission electron microscopy （TEM） and UV-vis absorption spectroscopy. An energy-dispersive X-ray spectrometer （EDS） was used to analyze the elementary compositions of the intermediate products. A possible formation mechanism of hexagonal nanoplatelets is discussed, using TEM observations.     

Evaluation and modeling of the mechanical properties of graphite nanoplatelets based rubber nanocomposites for pressure sensing applications

Acrylonitrile butadiene rubber (NBR) compounds filled with different concentrations of graphite nanoplatelets were experimentally investigated. The stress–strain curves of the nanocomposites were studied, which suggest good filler–matrix adhesion. The large reinforcement effect of the filler followed the Guth model for non‐spherical particles. The effect of graphite nanoplatelets on the cyclic fatigue and hysteresis was also examined. The loading and unloading stress–strain relationships for any cycle were described by applying Ogden's model for rubber nanocomposites. With this model for incompressible materials, expressions may be developed to predict the stress–strain relationship for any given cycle. The dissipated energy increased with graphite nanoplatelets concentrations and decrease with number of cycles. The rate of damage accumulation becomes marginal after first ten cycles. The rate of damage increases as the amount of graphite nanoplatelets increase into the rubber matrix. Copyright © 2011 John Wiley & Sons, Ltd.     

单晶MoO3纳米片：静电纺丝法制备及光催化活性

以聚乙烯基吡咯烷酮(PVP)和钼酸铵((NH4)6Mo7O24.4H2O)为原料,利用静电纺丝技术结合溶胶过程制备了PVP/(NH4)6Mo7O24.4H2O前躯体,对前躯体缓慢控温处理制备MoO3纳米材料。通过X-射线光电子能谱(XPS)﹑红外光谱(FTIR)﹑X射线粉末衍射(XRD)和场发射扫描电子显微镜(FE-SEM)等表征手段研究了热处理温度对MoO3晶体生长和结构的影响。以亚甲基蓝(MB)的光降解为模型反应,研究了MoO3微纳米材料的光催化性能。结果表明,热处理温度500℃时生成的MoO3纳米片光催化活性最好,并探讨了其光催化机理。     

Graphene nanoplatelets supported metal nanoparticles for electrochemical oxidation of hydrazine

Graphene nanoplatelets have been applied as the support to electrodeposit monometallic Au and Pd nanoparticles as well as bimetallic Au–Pd nanoparticles. These nanoparticles have been characterized with scanning electron microscope, energy dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, and electrochemical techniques. They are further utilized as the catalysts for electrochemical oxidation of hydrazine. The oxidation peak potential is − 0.35 and 0.53 V (vs. SCE) when monometallic Pd and Au nanoparticle are used as the catalysts. When bimetallic nanoparticles are applied as the catalyst, their composition affects the peak potential and peak current for the oxidation of hydrazine. Higher oxidation current is achieved when bimetallic Au–Pd nanoparticles with an atomic ratio of 3:1 are deposited on graphene nanoplatelets. Metal nanoparticle-loaded graphene nanoplatelets are thus novel platforms for electrocatalytic, electroanalytical, environmental, and related applications.     

Solvothermal Synthesis and Characterization of HgTe Nanoplatelets Using Mercury(Ⅰ) Source

Mercury telluride (HgTe) nanoplatelets were obtained via a facile solvothermal reaction of mercury(Ⅰ) chloride and tellurium powder in ethylenediamine (en). Mercury(Ⅰ) was first applied as the mercury sources to prepare nanocrystal HgTe; moreover, the proposed mechanism for the fabrication of the sample was discussed in detail. The HgTe nanoplatelets were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM),transmission electron microscopy (TEM), high-resolution transmission electron microscopy(HRTEM) and Fourier transform infrared spectroscopy (FT-IR). The absence of IR absorption may render the title nanocrystal useful as an IR transparent material in the region.     

Solvothermal Synthesis and Characterization of HgTe Nanoplatelets Using Mercury（I） Source

Mercury telluride （HgTe） nanoplatelets were obtained via a facile solvothermal reaction of mercury（I） chloride and tellurium powder in ethylenediamine （en）. Mercury（I） was first applied as the mercury sources to prepare nanocrystal HgTe; moreover, the proposed mechanism for the fabrication of the sample was discussed in detail. The HgTe nanoplatelets were characterized by powder X-ray diffraction （PXRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, high-resolution transmission electron microscopy （HRTEM） and Fourier transform infrared spectroscopy （FT-IR）. The absence of IR absorption may render the title nanocrystal useful as an IR transparent material in the region.     

The Role of Oxidative Debris on Graphene Oxide Films

We study the effect of oxidative impurities on the properties of graphene oxide and on the graphene oxide Langmuir–Blodgett films (LB). The starting material was grupo Antolín nanofibers (GANF) and the oxidation process was a modified Hummers method to obtain highly oxidized graphene oxide. The purification procedure reported in this work eliminated oxidative impurities decreasing the thickness of the nanoplatelets. The purified material thus obtained presents an oxidation degree similar to that achieved by chemical reduction of the graphite oxide. The purified and non‐purified graphene oxides were deposited onto silicon by means of a Langmuir–Blodgett (LB) methodology. The morphology of the LB films was analyzed by field emission scanning microscopy (FE‐SEM) and micro‐Raman spectroscopy. Our results show that the LB films built by transferring Langmuir monolayers at the liquid‐expanded state of the purified material are constituted by close‐packed and non‐overlapped nanoplatelets. The isotherms of the Langmuir monolayer precursor of the LB films were interpreted according to the Volmer’s model.     

X-ray spectroscopy study of lithiated graphite obtained by thermal deposition of lithium

X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES), and near edge X-ray absorption fine structure (NEXAFS) spectroscopy are used for in situ studies of the electronic structure of lithiated natural graphite produced by thermal deposition of lithium upon graphite in a vacuum. By XPS and NEXAFS spectroscopy it is found that lithium vapor thermal deposition results in the formation of a lithiated graphite surface layer and a change in its electronic structure. Based on the quantum chemical simulation of the experimental СK_α XES spectrum of lithiated graphite, it is found that lithium atoms are located mostly on the edges of graphite crystallites. Atomic force microscopy reveals that the size of natural graphite flakes varies from 50 nm to 200 nm.     

High-performance supercapacitor based on tantalum iridium oxides supported on tungsten oxide nanoplatelets

Here we report on a novel supercapacitor electrode based on IrO₂–Ta₂O₅ nanoparticles supported on WO₃ nanoplatelets. The nanoplatelets were directly grown on a W plate using a facile hydrothermal method, whereas the IrO₂–Ta₂O₅ nanoparticles were formed via a thermal decomposition technique which can be easily scaled up. The structural, morphological, and electrochemical properties of the WO₃ nanoplatelets and the formed trimetallic oxide nanocomposite have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), cyclic voltammetry (CV), and charging/discharging techniques. The fabricated trimetallic oxide nanocomposite exihibited rectangular cyclic voltamograms even tested at high potential scan rates, a high specific capacitance and high charging/discharging stability, promising utilization in the design of high-performance devices for energy storage.     

Thermal conductivity of exfoliated graphite nanocomposites

Since the late 1990’s, research has been reported where intercalated, expanded, and/or exfoliated graphite nanoflakes could also be used as reinforcements in polymer systems. The key point to utilizing graphite as a platelet nanoreinforcement is in the ability to exfoliate graphite using Graphite Intercalated Compounds (GICs). Natural graphite is still abundant and its cost is quite low compared to the other nano–size carbon materials, the cost of producing graphite nanoplatelets is expected to be ~$5/lb. This is significantly less expensive than single wall nanotubes (SWNT) (>$45000/lb) or vapor grown carbon fiber (VGCF) ($40–50/lb), yet the mechanical, electrical, and thermal properties of crystalline graphite flakes are comparable to those of SWNT and VGCF. The use of exfoliated graphite flakes (xGnP) opens up many new applications where electromagnetic shielding, high thermal conductivity, gas barrier resistance or low flammability are required. A special thermal treatment was developed to exfoliate graphite flakes for the production of nylon and high density polypropylene nanocomposites. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to assess the degree of exfoliation of the graphite platelets and the morphology of the nanocomposites. The thermal conductivity of these composites was investigated by three different methods, namely, by DSC, modified hot wire, and halogen flash lamp methods. The addition of small amounts of exfoliated graphite flakes showed a marked improvement in thermal and electrical conductivity of the composites.     

石墨炉内石墨探针表面上的原子化机理研究(Ⅴ)——锰的原子化机理

在石墨炉原子吸收光谱(GFAAS)法中,反应前后的化合物形态可以借助于X射线衍射(XRD)、俄歇电子能谱(AES)及化学分析光电子能谱(ESCA)等现代分析仪器来鉴定,本文综合利用上述分析方法,对锰化合物在石墨探针表面上于不同温度下的化学形态进行鉴定,结合元素的灰化和原子化曲线,详细地研究和阐述了锰的原子化机理。     

Facile synthesis of mesophase pitch/exfoliated graphite nanoplatelets nanocomposite and its application as anode materials for lithium-ion batteries

Mesophase pitch (MP)/exfoliated graphite nanoplatelets (GNPs) nanocomposite has been prepared by an efficient method with an initiation of graphite intercalation compounds (GIC). X-ray diffraction, optical microscopy, high-resolution transmission electron microscopy and scanning electron microscopy analysis techniques are used to characterize the samples. It is observed that GIC has exfoliated completely into GNPs during the formation of MP/GNPs nanocomposite and the GNPs are distributed uniformly in MP matrix, which represent a conductive path for a movement of electrons throughout the composites. Electrochemical tests demonstrate that the carbonized MP/GNPs nanocomposite displays higher capacity and better cycle performance in comparison with the pure carbonized MP. It is concluded that such a large improvement of electrochemical performance within the nanocomposite may in general be related to the enhanced electronic conductivity, which is achieved by good dispersion of GNPs within MP matrix and formation of a 3D network of GNPs.     

Fabrication and physicochemical characterization of graphene oxide derived from thermally expanded graphite

Graphene oxide was obtained from expanded graphite according to the modified Hummers method. The reaction time was significantly reduced (from 24 to 8 h) by applying the expanded graphite in the oxidation process. The interlayer distance in obtained samples was equal to 0.70–0.74 nm. Structural features of the material were studied by the powder X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, XPS spectroscopy, and NMR spectroscopy.     

Reverse atom transfer radical random copolymerization of styrene and methyl methacrylate in the presence of diatomite nanoplatelets

Diatomite nanoplatelets were used for in situ random copolymerization of styrene and methyl methacrylate by reverse atom transfer radical polymerization to synthesize different well‐defined nanocomposites. Inherent features of the pristine diatomite nanoplatelets were evaluated by Fourier transform infrared spectroscopy, nitrogen adsorption/desorption isotherm, scanning electron microscope, and transmission electron microscope. Gas and size exclusion chromatography was also used to determine conversion and molecular weight determinations, respectively. Considerable increment in conversion (from 81% to 97%) was achieved by adding 3 wt% diatomite nanoplatelets in the copolymer matrix. Moreover, molecular weight of random copolymer chains was increased from 12 890 to 13 960 g·mol⁻¹ by addition of 3 wt% diatomite nanoplatelets; however, polydispersity index (PDI) values increases from 1.36 to 1.59. Proton nuclear magnetic resonance spectroscopy was used to evaluate copolymers composition. Thermal gravimetric analysis results indicate that thermal stability of the nanocomposites is improved by adding diatomite nanoplatelets. Differential scanning calorimetry shows an increase in glass transition temperature from 66°C to 71°C by adding 3 wt% of diatomite nanoplatelets.     

Sensitive and Rapid Flow Injection Amperometric Hydrazine Sensor using an Electrodeposited Gold Nanoparticle Graphite Pencil Electrode

A gold (Au) nanoparticle-modified graphite pencil electrode was prepared by an electrodeposition procedure for the sensitive and rapid flow injection amperometric determination of hydrazine (N₂H₄). The electrodeposited Au nanoparticles on the pretreated graphite pencil electrode surface were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, and electrochemical impedance spectroscopy. Cyclic voltammograms showed that the Au nanoparticle-modified pretreated graphite pencil electrode exhibits excellent electrocatalytic activity toward oxidation of hydrazine because the highly irreversibly and broadly observed oxidation peak at +600?mV at the pretreated graphite pencil electrode shifted to ?167?mV at the Au nanoparticle pretreated graphite pencil electrode; in addition, a significant enhancement in the oxidation peak current was obtained. Thus, the flow-injection (FI) amperometric hydrazine sensor was constructed based on its electrocatalytic oxidation at the Au nanoparticle-modified pretreated graphite pencil electrode. The Au nanoparticle-modified pretreated graphite pencil electrode exhibits a linear calibration curve between the flow injection amperometric current and hydrazine concentration within the concentration range from 0.01 to 100?µM with a detection limit of 0.002?µM. The flow injection amperometric sensor has been successfully used for the determination of N₂H₄ in water samples with good accuracy and precision.     

Cadmium oxide nanoplatelets: synthesis, characterization and their electrochemical sensing property of catechol

Cadmium oxide (CdO) nanoplatelets were synthesized by thermal decomposition of cadmium malonate. The synthesized CdO nanoplatelets were characterized by X-ray diffraction (XRD); from the XRD analysis, it is clear that the phase structure of CdO nanoplatelets was found to be face-centered cubic with the average crystalline size of 40–50 nm. FT-IR analysis shows the presence of surface carboxyl and hydroxyl groups on to the CdO nanoplatelets. From DRS-UV–Vis analysis, both the direct and indirect band gaps of the CdO nanoplatelets were found to be 2.0 and 1.67 eV, respectively. From the FE-SEM analysis, the morphology of the synthesized CdO was found to be nanoplatelets, which were randomly agglomerated. Further, HR-TEM was used to confirm the formation of nanoplatelets. The electrochemical sensing property of CdO nanoplatelets was carried out by cyclic voltammetry (CV) by coating CdO nanoplatelets on Glassy carbon electrode (GCE) and using it as working electrode for sensing of catechol. The enhanced electrochemical behaviour is mainly attributed to the nanometer dimensions and surface hydroxyl groups on the CdO nanoplatelets. Chronoamperometry (CA) was used to determine the sensitivity and repeatability of the modified electrode. The modified electrode shows linear range of catechol concentration between 7.5 × 10^?6 and 1.5 × 10^?4 M with sensitivity of 9.8 nA μM^?1.     

High-yield preparation of uniform cobalt hydroxide and oxide nanoplatelets and their characterization

Cobalt hydroxide nanoplatelets with a uniform hexagonal shape were prepared in high yield ( approximately 95%) by a facile hydrothermal route in the presence of poly(vinylpyrrolidone). This method provides a simple, low-cost, and large-scale route to produce beta-cobalt hydroxide nanoplatelets with an average diameter of 280 nm and a thickness of ca. 26 nm which show a predominant well-crystalline hexagonal brucite-like phase. Their thermal decomposition produced anisotropic nanoplatelets of cobalt oxides (CoO and Co3O4) under designed temperatures. The products were characterized by transmission electronic microscopy, selected-area electron diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetric, and thermogravimetric analysis. The magnetic properties of the products were investigated by a superconducting quantum interference device magnetometer. Co3O4 nanoplatelets exhibit a superparamagnetic behavior, and they might be a promising material to study the magnetic tunneling effect as anisotropic nanostructures.