Carbon (v.51, #C)
Dynamics of incipient carbon particle formation in a stabilized ethylene flame by in situ extended-small-angle- and wide-angle X-ray scattering by Frederik Ossler; Linda Vallenhag; Sophie E. Canton; J. Brian A. Mitchell; Jean-Luc Le Garrec; Michael Sztucki; Stefano di Stasio (1-19).
Simultaneous small-angle and wide-angle X-ray scattering (SAXS and WAXS) were used to measure several properties of the nanoparticles and soot being produced and undergoing condensation and phase changes below a stabilizing cooling plate inserted in an ethylene diffusion flame. From the SAXS data several distinct size modes appeared showing interdependent changes in the size, shape/morphology, and concentrations over the time of the experiment. The WAXS data contained information on the internal atomic-level structure of the nanoparticles and soot. They also provided important information on the onset and evolution of the condensation of particles onto the plate and the graphitization process. The concentrations of particles were determined quantitatively from the SAXS data. A very important result was the strong increase for sizes smaller than 100 Å, which increased drastically to very high values with number concentrations orders of magnitude higher than normally reported from flames. The results and methods applied are of interest for future studies of dynamics related to condensation and material synthesis of carbon- and non-carbon based nanoparticles in the gas phase and during deposition on surfaces.
Continuous electrodeposition of polypyrrole on carbon nanotube–carbon fiber hybrids as a protective treatment against nanotube dispersion by J. Saba; Y. Magga; D. He; F. Miomandre; J. Bai (20-26).
This paper describes the electrodeposition of nanometer size polypyrrole layers on carbon fibers coated with multi-wall carbon nanotubes. The obtained carbon nanotubes–carbon fiber hybrids are characterized by electrochemistry, electron microscopy, vibrational spectroscopy and thermogravimetry. The electrical properties are measured for various polymerization times and electrolytes. The conductivity is found decrease with increasing polypyrrole thickness, but all the carbon nanotube–carbon fiber hybrids remain more conductive than pristine carbon fibers having a sizing coating. Finally it is shown that polypyrrole acts as a protecting layer against carbon nanotube dispersion when sonicated in ethanol.
Pore size control of monodispersed starburst carbon spheres by Narihito Tatsuda; Kazuhisa Yano (27-35).
We describe the synthesis of highly monodispersed starburst carbon spheres (MSCS) with pore size of 1.9–3.8 nm by using monodispersed mesoporous silica spheres (MMSS) which is modified with aminopropyl group, as a starting material. The wall thickness of the MMSS could be thickened by solvothermal treatment with increasing the ratio of aminopropyl group. The thickened silica wall of solvothermally treated MMSS (MS) prevented the shrinkage of the mesoporous silica template during carbonization, causing the formation of nanospaces between carbon and the silica. Furthermore, the thicker carbon nanorods obtained from pore-expanded MS would prevent the starburst structure from collapsing. As a result, MSCS with large mesopores could be obtained after removing the silica template by hydrofluoric acid etching.
Electrochemically reduced graphene oxide sheets for use in high performance supercapacitors by Jiang Yang; Sundaram Gunasekaran (36-44).
Graphene oxide (GO) was reduced by a rapid, effective and eco-friendly electrochemical method of repetitive cathodic cyclic potential cycling, without using any reducing reagents. The electrochemically reduced graphene oxide (ERGO) was characterized by UV–vis, EIS and zeta-potential measurements. Most of the oxygen functional groups in ERGO were successfully removed resulting in smaller charge transfer resistance. However, some electrochemically stable residuals still remained, enabling ERGO to facilitate electrolyte penetration and pseudocapacitance. Since ERGO was readily stabilized by cathodic potential cycling, it exhibited an outstanding stability in cycle life, nearly with no capacitive loss from the second cycle on. A specific capacitance of 223.6 F g−1 was achieved at 5 mV s−1, which makes the ERGO a competitive material for electrochemical energy storage.
Phenolic resin-based carbons with ultra-large mesopores prepared in the presence of poly(ethylene oxide)–poly(butylene oxide)–poly(ethylene oxide) triblock copolymer and trimethyl benzene by Nilantha P. Wickramaratne; Mietek Jaroniec (45-51).
The evaporation-induced self assembly (EISA) strategy has been successfully employed to obtain ultra-large mesoporous carbons (UMC) by using Vorasurf 504 poly(ethylene oxide)–poly(butylene oxide)–poly(ethylene oxide), (PEO–PBO–PEO) triblock copolymer as a template. Resorcinol and formaldehyde were used as carbon precursors, whereas trimethyl benzene (TMB) was used as a pore expander. Nitrogen adsorption isotherms revealed that the resulting UMC materials possess ultra-large mesopores (about 27 nm) and relatively narrow pore size distribution. Mesoporous carbons synthesized without TMB show also fairly large mesopores (about 20 nm). These carbons were examined for adsorption of Lysozyme (Lz) from buffered solution at pH 10.8. All Lz adsorption isotherms were reasonably well fitted by Langmuir equation, giving high maximum adsorption capacity (31 μmol/g).
Chemical activation of carbon nano-onions for high-rate supercapacitor electrodes by Yang Gao; Yun Shen Zhou; Min Qian; Xiang Nan He; Jody Redepenning; Paul Goodman; Hao Ming Li; Lan Jiang; Yong Feng Lu (52-58).
Recent studies have demonstrated that carbon nano-onion (CNO) is a promising candidate for high-power supercapacitors due to the nonporous outer shell, which is easily accessible to electrolyte ions. However, the nonporous ion-accessible outer shells also limit the energy density of the CNOs, which requires large specific surface area. Introducing porosity to the outer shells of CNOs can effectively improve the specific surface area by exposing the inner shells to electrolytes. In this study, the electrochemical performance of supercapacitor electrodes based on CNOs is improved through the controlled introduction of porosity on the outer shells of CNOs by chemical activation. The capacitance of the activated CNOs is five times larger than the pristine ones with a measured power density of 153 kW/kg and an energy density of 8.5 Wh/kg in a 2 mol/l potassium nitrate electrolyte. The capacitance retention ratio of activated CNOs decreases slightly as the current density increases from 0.75 to 25 A/g. About 71% of initial capacitance (at 0.75 A/g) is preserved for activated CNOs at current densities up to 25 A/g.
Effects of chirality and impurities on the performance of carbon nanotube-based piezoresistive sensors by Michael A. Cullinan; Martin L. Culpepper (59-63).
This paper presents a method to fabricate high purity, single chirality carbon nanotube (CNT) based sensor systems. Ultracentrifugation is initially used to create an 85% pure (6,5) CNT sample. This 85% pure sample has a gauge factor of −22.7 ± 0.5 which is significantly lower than the predicted gauge factor of 57 for a pure (6,5) CNT. However, this measured gauge factor closely matches the predicted gauge factor for the measured distribution of chiralities in the 85% pure sample. This indicates at a small number of impurities in the sensor can have a large effect on the strain sensitivity of the sensor. In order to increase the gauge factor of the 85% pure (6,5) CNT sample, an electrical breakdown technique is used to remove the low resistance and low gauge factor CNTs from the sensor. Using this technique it is possible to increase the gauge factor of the CNT-based piezoresistive sensor from −22.7 ± 0.5 to 34 ± 1. This result indicates that the majority of the impurities in the sensor can be removed during the fabrication process using the electrical breakdown technique.
Rheological behavior and thermal properties of pitch/poly(vinyl chloride) blends by S.R. Hlatshwayo; W.W. Focke; S. Ramjee; B. Rand; N. Manyala (64-71).
The effect of adding poly(vinyl chloride) (PVC) and coke filler on the rheological behavior and thermal properties of a coal tar pitch was investigated with a view to developing an appropriate viscoelastic binder for the injection molding of graphite components. Dynamic mechanical analysis revealed that the pitch formed compatible blends with PVC featuring a single glass transition temperature (Tg) intermediate to the two parent Tg’s. Adding PVC to the pitch increased melt viscosity substantially and resulted in strong shear thinning behavior at high PVC addition levels. Adding coke powder as filler increased the melt viscosity even further and enhanced shear thinning trends. Pyrolysis conducted in a nitrogen atmosphere revealed interactions between the PVC and pitch degradation pathways: the blends underwent significant thermal decomposition at lower temperatures but showed enhanced carbon yields at high temperatures. Pyrolytic carbon yield at 1000 °C was further improved by a heat treatment (temperature scanned to 400 °C) in air or oxygen. However, carbon yield decreased with addition of PVC. In addition, the degree of ordering attained following a 1 h heat treatment at 2400 °C also decreased with increasing PVC content.
Probing the carbon nanotube-surfactant interaction for the preparation of composites by Weiheng Zhong; Jerome P. Claverie (72-84).
Adsorption isotherms of four different surfactants, sodium dodecyl sulfate (SDS), sodium dodecyl benzyl sulfonate, benzethonium chloride and Triton X-100 were measured on multi-wall carbon nanotubes (MWCNT) in water. With the surfactant SDS, the isotherms were also measured on single-wall carbon nanotubes (SWCNT) as well as on MWCNT under various ionic strength and temperature conditions. The nature of the polar head had only little influence on adsorption which was mainly driven by hydrophobic interactions. However, the outcome of the dispersion experiment was dependent on the purity of the carbon nanotubes. Using these results, it was possible to prepare concentrated colloidaly stable dispersions of MWCNTs in water (c = 32 g/L). Conducting MWCNT/polymer composite films could then readily be prepared by simple formulation of the MWCNTs with a polymeric dispersion.
On the effects of emulsion polymerization of furfuryl alcohol on the formation of carbon spheres and other structures derived by pyrolysis of polyfurfuryl alcohol by Maryam Peer; Ali Qajar; Ramakrishnan Rajagopalan; Henry C. Foley (85-93).
Carbon spheres were synthesized by emulsion polymerization and pyrolysis of polyfurfuryl alcohol. Pluronic F-127 was used as the structure-directing agent to synthesize polymer spheres that after pyrolysis led to carbon spheres with average sizes from 50 nm to few micrometers in diameter depending upon the conditions of polymerization. As-synthesized carbon spheres possess high surface areas of around 480 m2/g with an average mean pore size of 0.5 nm. These spheres can be activated using carbon dioxide to create much higher surface areas (>1500 m2/g). Different compositional regions of the pseudo-ternary phase diagram of surfactant/monomer/solvent were explored in order to determine the effects of changes in the emulsion polymerization variables on the kinds of carbon morphologies that could be derived from polyfurfuryl alcohol after pyrolysis. The diameter of the carbon spheres was found to be sensitive to monomer and surfactant concentrations, acid molarity and solvent composition. In general, the diameter of the spheres grew with increasing furfuryl alcohol concentration and decreasing surfactant concentration, respectively. By varying the acid concentration and solvent composition, a minimum diameter for spheres was found. The formation and size of the spheres are strongly influenced both by micelle growth and the polymerization mechanism.
Influence of the electrochemical reduction process on the performance of graphene-based capacitors by Hongwen Yu; Jianjun He; Ling Sun; Shunitz Tanaka; Bunshi Fugetsu (94-101).
Electrochemically reduced graphene was used as the key element in the preparation of electric double-layer capacitors where the thickness of the electrode was only a few hundred nano-meters. The resultant electrodes showed different specific capacitances after pre-reduction with scanning potential windows of −1.0 to 1.6 V, −1.5 to 0 V and −1.0 to 1.0 V. Also, a specific capacitance of 246 F/g was obtained as the graphene oxide electrode was reduced with an applied potential of −1.0 to 1.0 V for 4000 s. The influence of the residual oxygen functional groups and sp 2 domains in electrochemically reduced graphene were investigated for capacitance performance.
Electromechanical switching in graphene nanoribbons by Nabil Al-Aqtash; Hong Li; Lu Wang; Wai-Ning Mei; R.F. Sabirianov (102-109).
We investigate the effect of twisting on the electronic, magnetic and transport properties of zigzag graphene nanoribbon (ZGNR) using density functional theory (DFT) calculations. We compare electronic and magnetic properties of ZGNR in both planar and 180°-twisted geometries. Furthermore, combining DFT with the nonequilibrium Green’s function method (NEGF), we examine the quantum conductance of twisted ZGNR in its antiferromagnetic and ferromagnetic states. Consequently, the structure of local magnetic moments in the region between electrodes of opposite magnetization behaves as a Bloch/Neel domain wall. Our calculations show that ZGNR in its ground state (antiferromagnetic) is insensitive to twisting, there is no band gap change, and the conductance of the twisted ZGNR is almost unchanged as well. We demonstrate that the electromechanical switching can be realized by twisting a ferromagnetic ZGNR, which is an ideal spin valve in case of oppositely polarized leads (after twisting).
Nucleation and growth kinetics of graphene layers from a molten phase by Shaahin Amini; Reza Abbaschian (110-123).
Nucleation and growth of graphene layers from Ni–C melts were investigated. It is shown that upon cooling of supersaturated liquids, graphite will grow either with flake or sphere morphology depending on the solidification rate and degree of supersaturation. At small solidification rates, graphite crystals are normally bounded by faceted low index basal and prismatic planes which grow by lateral movement of ledges produced by 2D-nucleation or dislocations. At higher growth rates, however, both interfaces become kinetically rough, and growth becomes limited by diffusion of carbon to growing interface. The roughening transition from faceted to non-faceted depends on the driving force and nature of growing plane. Due to high number of C–C dangling bonds in prismatic face, its roughening transition occurs in smaller driving force. As such, at intermediate rates, the prismatic interfaces become rough and grow faster while the basal plane is still faceted, leading to formation of flake graphite. At higher growth rates, both interfaces grow with a relatively similar rate leading to initiation of graphite sphere formation, which later grow by a multi-stage growth mechanism. An analytical model is developed to describe the size and morphology of graphite as a function of solidification parameters.
Carboxymethyl chitosan-functionalized graphene for label-free electrochemical cytosensing by Guohai Yang; Juntao Cao; Lingling Li; Rohit Kumar Rana; Jun-Jie Zhu (124-133).
Here we demonstrate the fabrication of an effective cytosensor using carboxymethyl chitosan-functionalized graphene (CMC-G) prepared through chemical reduction of graphene oxide. The CMC-G hybrid was further characterized with UV–vis spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, transmission electron microscopy and atomic force microscopy. Layer-by-layer assembly of CMC-G with polyethyleneimine and folic acid enabled the fabrication of a label-free electrochemical impedance spectroscopy cytosensor with high stability and biocompatibility. The proposed cytosensor exhibited good electrochemical behavior and cell-capture ability for HL-60 cells, and showed a wide linear range and low detection limit for quantification.
Casimir effect demonstrated by Raman spectroscopy on trilayer graphene intercalated into stiff layered structures of surfactant by Mihaela Baibarac; Ioan Baltog; Lucian Mihut; Iuliana Pasuk; Serge Lefrant (134-142).
Polarized Raman scattering studies on stiff layered structure of surfactant intercalated with trilayer graphene were performed at different intensities and excitation wavelengths. The D and 2D Raman bands reach the highest and lowest intensity when the polarization of laser excitation light is oriented along and perpendicular on the edges. The 2D band discloses two lorentzian components, separated by ∼40 cm−1, which result from the action of interplanar forces, of Casimir nature. The value of ∼40 cm−1 is close to the energy value associated with E2g interplanar layer shear mode evidenced so far only by neutron spectrometry. A new result regards the opposite variation of the intensities of D and 2D bands with the increase of the wavelength of the excitation light. This originates in the different origin of the D and 2D bands; the former is dependent on disorder including also the graphene edges while the latter, results from in a double resonant mechanism combined with a Casimir effect. One demonstrates that the magnitude of Casimir force, which activates interlayer vibration modes, depends on the carrier density on the graphene sheets which can be varied both by the intensity and the wavelength of the excitation laser light.
Ionic conductivity in the Mg intercalated fullerene polymer Mg2C60 by Daniele Pontiroli; Matteo Aramini; Mattia Gaboardi; Marcello Mazzani; Alessandra Gorreri; Mauro Riccò; Irene Margiolaki; Denis Sheptyakov (143-147).
We report the identification of the new intercalated fullerene polymer Mg2C60. Mg intercalation was obtained either by solid state reaction between C60 and Mg, or by thermal decomposition of the metallorganic precursor Mg–Anthracene–(THF)3. High resolution powder synchrotron and neutron diffraction data have clearly shown that Mg2C60 is isostructural to the superionic conductor Li4C60, where fullerenes form a two-dimensional network connected either by four-membered carbon rings, or single C–C bonds. Because of its peculiar structural arrangement Mg2C60 behaves as a good ionic conductor by means of uncorrelated ionic hopping across very small energy barriers (ΔE less than 100 meV), as found from DC and AC conductivity measurements, thus suggesting its possible use in future Mg-ion batteries.
Preparation of graphene/polymer composites by direct exfoliation of graphite in functionalised block copolymer matrix by Zhen Liu; Jingquan Liu; Liang Cui; Rui Wang; Xiong Luo; Colin J. Barrow; Wenrong Yang (148-155).
The preparation of graphene/polymer composites by direct exfoliation of graphene from micro-sized graphite using a pyrene-functionalised amphiphilic block copolymer, poly(pyrenemethyl acrylate)-b-poly[(polyethylene glycol) acrylate] (polyPA-b-polyPEG-A), in either aqueous or organic media is presented. PolyPA-b-polyPEG-A was prepared using reversible addition fragmentation chain transfer (RAFT) polymerization of a pyrene-functionalised monomer to afford a homopolymer (polyPA), followed by copolymerization with PEG-A using polyPA as the macroRAFT agent. The composites were used to prepare sheets that exhibited increased tensile strength comparing to pure graphene and tunable conductivity. The composites were used to generate pure graphene sheets with a large size and increased conductivity comparing to those prepared by oxidation–reduction as shown by transmission electron microscopy and Raman spectroscopy.
Adsorption characteristics of 1,2,4-trichlorobenzene, 2,4,6-trichlorophenol, 2-naphthol and naphthalene on graphene and graphene oxide by Zhiguo Pei; Lingyun Li; Lixiang Sun; Shuzhen Zhang; Xiao-quan Shan; Shuang Yang; Bei Wen (156-163).
Adsorption of 1,2,4-trichlorobenzene (TCB), 2,4,6-trichlorophenol (TCP), 2-naphthol and naphthalene (NAPH) on graphene (G) and graphene oxide (GO) was investigated using a batch equilibration method and micro-Fourier transform infrared spectroscopy. All adsorption isotherms of four aromatics on G and GO were nonlinear, indicating that except for hydrophobic interaction, some specific interactions were involved in adsorption. For G, four aromatics had similar adsorption capacity at pH 5.0 in despite of their different chemical properties. A series of pH-dependent experimental results showed that 2-naphthol had higher adsorption capacity on G at alkaline pH than that at acidic pH. Theoretical calculation ascribed this to higher π-electron density of anionic 2-naphthol than that of neutral 2-naphthol, which facilitated the π–π interaction formation with G. For GO, the adsorption affinity of four aromatics increased in the order: NAPH < TCB < TCP < 2-naphthol. FTIR results revealed that TCB, TCP and 2-naphthol were adsorbed on G mainly via π–π interaction. In contrast, high adsorption of TCP and 2-naphthol on GO was attributed to the formation of H-bonding between hydroxyl groups of TCP and 2-naphthol and O-containing functional groups on GO.
Tailoring the interlayer interaction between doxorubicin-loaded graphene oxide nanosheets by controlling the drug content by Qi Zhang; Weiwei Li; Tao Kong; Ruigong Su; Ning Li; Qin Song; Mingliang Tang; Liwei Liu; Guosheng Cheng (164-172).
We experimentally and theoretically investigated the influence of a model drug, doxorubicin (DOX) on GO interlayer interaction by evaluating the pyrolysis activation energy using thermogravimetric analysis and a mathematical model. It was found that the pyrolysis activation energy of DOX-loaded GO decreased from 145.8 to 119.5 kJ/mol with DOX loading content increasing from 0 to 186.6 w/w%. Theoretical simulation showed that the reduced activation energy could be ascribed to the gradually decreased interlayer interaction with DOX molecule intercalation. This involved distorted π–π stacking originating from the enlarged interlayer distance, and partially blocked interlayer hydrogen bonding. Our study suggested the possibility of tailoring the interlayer interaction and macroscopic properties of GO composites by controlling the density of molecules on the individual sheet, and offered a better understanding of inserted molecules causing interlayer interaction changes.
Improved inter-tube coupling in CNT bundles through carbon ion irradiation by N.P. O’Brien; M.A. McCarthy; W.A. Curtin (173-184).
Carbon ion irradiation of carbon nanotube (CNT) bundles to enhance mechanical performance is investigated using classical molecular dynamics. Strategies to achieve inter-tube cross-linking for improved shear response without a drastic reduction in tensile strength due to induced defects are considered. Deposition energies of 50–300 eV/ion, fluences of 4 × 1013 to 2 × 1014 cm−2, and dosages of 2–60 MGy on 7-tube bundles are studied. Within 100–200 eV/ion, the level of cross-linking is directly proportional to dosage and therefore controllable. Lower energy irradiation produces smaller-sized defects so ∼100 eV/ion is the preferred energy. More than 10 different types of cross-link and a variety of defects are created. The defect level becomes excessive if either the energy or the fluence is set too high. Extension to larger bundles however is significantly more challenging. In 19-tube bundles, ∼500 eV/ion is required to form cross-links with the centre CNT, and at this energy careful control of fluence is required to avoid excessive damage. Thus ion irradiation for improving mechanical properties is best suited to small bundles. However, a scenario whereby small bundles are irradiated prior to twisting into ropes is suggested as a possible future method for producing macro-scale cross-linked CNT fibres.
Structure control and performance improvement of carbon nanofibers containing a dispersion of silicon nanoparticles for energy storage by Ying Li; Bingkun Guo; Liwen Ji; Zhan Lin; Guanjie Xu; Yinzheng Liang; Shu Zhang; Ozan Toprakci; Yi Hu; Mataz Alcoutlabi; Xiangwu Zhang (185-194).
Si/C composite nanofibers were prepared by electrospinning and carbonization using polyacrylonitrile (PAN) as the spinning medium and carbon precursor. The nanofibers were used as lithium-ion battery anodes to combine the advantages of carbon (long cycle life) and silicon (high storage capacity) materials. The effects of Si particle size, Si content, and carbonization temperature on the structure and electrochemical performance of the anodes were investigated. Results show that anodes made from a 15 wt.% Si/PAN precursor with a Si particle size of 30–50 nm and carbonization temperature of 800 °C exhibit the best performance in terms of high capacity and stable cycling behavior. It is demonstrated that with careful structure control, Si/C composite nanofiber anodes are a promising material for next-generation lithium-ion batteries.
One-pot electrochemical synthesis of graphene by the exfoliation of graphite powder in sodium dodecyl sulfate and its decoration with platinum nanoparticles for methanol oxidation by Karim Kakaei (195-201).
We demonstrate a method which directly grows large areas of graphene on carbon paper and glassy carbon (GC) substrates from graphite powder and anionic surfactant, sodium dodecyl sulfate, assisted electrochemical exfoliation. The electrochemically reduced graphene has been carefully characterized by scanning electron microscopy (SEM) and electrochemical techniques. Particularly, SEM images show enhanced growth of graphene structures formed of ‘urchin’ objects. The CV spectra illustrate that a variety of the oxygen-containing functional groups has been thoroughly removed from the graphite plane via electrochemical reduction. Potential peak (Ep) of graphene electrode in [Fe(CN)6]3−/4− solution is as small as 212 mV which is 168 mV smaller than that of graphite electrode. This could be attributed to the high quality graphene accelerating the electron transfer rate in [Fe(CN)6]3−/4− electrochemistry. Finally, platinum was electro reduced onto the GC and graphene modified GC based electrodes for use in methanol oxidation. The catalytic activities of graphene-supported Pt nanoparticles and Pt-GC electrocatalysts for methanol oxidation were 1900 and 915.5 A g−1 Pt, which can reveal the particular properties of the exfoliated graphene supports.
Ultrasensitive strain sensors made from metal-coated carbon nanofiller/epoxy composites by Ning Hu; Takaomi Itoi; Taro Akagi; Takashi Kojima; Junmin Xue; Cheng Yan; Satoshi Atobe; Hisao Fukunaga; Weifeng Yuan; Huiming Ning; Surina; Yaolu Liu; Alamusi (202-212).
A set of resistance-type strain sensors has been fabricated from metal-coated carbon nanofiller (CNF)/epoxy composites. Two nanofillers, i.e., multi-walled carbon nanotubes and vapor growth carbon fibers (VGCFs) with nickel, copper and silver coatings were used. The ultrahigh strain sensitivity was observed in these novel sensors as compared to the sensors made from the CNFs without metal-coating, and conventional strain gauges. In terms of gauge factor, the sensor made of VGCFs with silver coating is estimated to be 155, which is around 80 times higher than that in a metal-foil strain gauge. The possible mechanism responsible for the high sensitivity and its dependence with the networks of the CNFs with and without metal-coating and the geometries of the CNFs were thoroughly investigated.
Chemical control of the characteristics of Mo-doped carbon xerogels by surfactant-mediated synthesis by Francisco J. Maldonado-Hódar; Hana Jirglová; Agustín F. Pérez-Cadenas; Sergio Morales-Torres (213-223).
Carbon xerogels doped with Mo were prepared by a sol–gel modified method for the resorcinol (R) – formaldehyde (F) polymerization (RF-gels). The use of surfactants (S) yields composites (RFS-gels), the S molecules are incorporated to the gel structure generating different metal anchoring sites. The interaction of molybdate ions ( MoO 4 2 - ) with RF and RFS-gels was analysed. The MoO 4 2 - adsorption is favoured by the attractive interactions with the RFS-gel containing a cationic surfactant, and by the presence of oxygenated chemical groups introduced by the non-ionic surfactant. The smallest Mo-loading was obtained in RFS-gels containing anionic surfactant as a consequence of repulsive interactions. The adsorbed Mo-species influence on the curing of the polymeric gels, inducing a larger shrinkage and a lower microporosity of the carbon xerogels. The dispersion and chemical nature of Mo particles depend also on the Mo-gel interactions. Stronger attractive interactions avoid sintering in some extent and favour the reduction of the molybdate with formation of a mixture of α-Mo2C and MoO3, while MoO3 particles were only found in RF-Mo or anionic RFS-Mo carbon xerogels. Only propene was obtained as product of the isopropanol decomposition showing the acid character of these catalysts. The catalytic activity is correlated to the proportion of Mo2C formed in each sample.
Functionalized graphene oxide mediated nucleic acid delivery by Sushil Kumar Tripathi; Ritu Goyal; Kailash Chand Gupta; Pradeep Kumar (224-235).
We report a simple preparation of linear polyethylenimine-grafted graphene oxide (LP-GO) conjugates and their efficacy to transfer nucleic acids into the mammalian cells. Graphene oxide (GO), with epoxy functions on its surface, was reacted with different amounts of linear polyethylenimine (lPEI), a non-toxic polymer, to obtain three different positively charged LP-GO conjugates (LP-GO-1 to LP-GO-3), capable of interacting with negatively charged nucleic acids (gel retardation assay) and transporting them efficiently into the cells. The results show that these conjugates not only exhibited considerably higher transfection efficiency but also possessed even better cell viability than lPEI. LP-GO-2, the best system in terms of transfection efficiency, showed improved buffering capacity compared to lPEI and provided sufficient stability to bound DNA against DNase I. Further, LP-GO-2 was used for the sequential delivery of GFP specific siRNA, which resulted in ∼70% suppression of the target gene expression. Intracellular trafficking using fluorescence microscopy revealed that LP-GO-2 conjugate delivered pDNA in the nucleus within 1 h of exposure. The results indicate the prospect of using these conjugates as efficient carriers of nucleic acids for future gene therapy applications.
Graphene-based transparent strain sensor by Sang-Hoon Bae; Youngbin Lee; Bhupendra K. Sharma; Hak-Joo Lee; Jae-Hyun Kim; Jong-Hyun Ahn (236-242).
Transparent strain sensors based on graphene were fabricated in a form of rosette on a flexible plastic or stretchable rubber substrate by using reactive ion etching and stamping techniques. Their piezoresistive properties were investigated under a tensile strain up to 7.1%. We demonstrated this sensor on a transparent glove and measured magnitudes and directions of the principal strains on the glove induced by the motion of fingers.
Synthesis of nanostructured carbons by the microwave plasma cracking of methane by Mi Tian; Simon Batty; Congxiao Shang (243-248).
One of the attractive methods of producing hydrogen and high value-added carbon is plasma-reforming of hydrocarbons. Here, nanostructured carbon was produced by methane cracking in a relatively low-energy cold plasma reactor designed in-house specifically for such purpose. Carbon samples collected at different positions in the reactor show similar structural morphologies, indicating extensive structural uniformity of the carbon during processing. Surface area and microstructure of the materials were characterized by BET surface area analysis, X-ray diffraction and transmission electron microscopy (TEM). The effects of flow rate, temperature and power were evaluated for the formation of the carbon structures. The results show that the BET surface area and pore volume of the carbon materials vary from 74 to 125 m2/g and from 0.12 to 0.20 cm3/g, respectively. Such variations are closely associated with the magnitude of temperature drop at the sample collection position in the cold-plasma chamber before and after methane loading. The highest BET surface area of 125 m2/g is obtained at a power of 2000 W. TEM shows that the carbon consists of spherical particles of 40.8 ± 8.7 nm in diameter and graphene sheets.
Revealing the atomic structure of the buffer layer between SiC(0 0 0 1) and epitaxial graphene by Sarah Goler; Camilla Coletti; Vincenzo Piazza; Pasqualantonio Pingue; Francesco Colangelo; Vittorio Pellegrini; Konstantin V. Emtsev; Stiven Forti; Ulrich Starke; Fabio Beltram; Stefan Heun (249-254).
On the SiC(0 0 0 1) surface (the silicon face of SiC), epitaxial graphene is obtained by sublimation of Si from the substrate. The graphene film is separated from the bulk by a carbon-rich interface layer (hereafter called the buffer layer) which in part covalently binds to the substrate. Its structural and electronic properties are currently under debate. In the present work we report scanning tunneling microscopy (STM) studies of the buffer layer and of quasi-free-standing monolayer graphene (QFMLG) that is obtained by decoupling the buffer layer from the SiC(0 0 0 1) substrate by means of hydrogen intercalation. Atomic resolution STM images of the buffer layer reveal that, within the periodic structural corrugation of this interfacial layer, the arrangement of atoms is topologically identical to that of graphene. After hydrogen intercalation, we show that the resulting QFMLG is relieved from the periodic corrugation and presents no detectable defect sites.
Fabrication of a graphene oxide–gold nanorod hybrid material by electrostatic self-assembly for surface-enhanced Raman scattering by Chaofan Hu; Jianhua Rong; Jianghu Cui; Yunhua Yang; Lufeng Yang; Yaling Wang; Yingliang Liu (255-264).
An electrostatic self-assembly procedure was used to fabricate graphene oxide (GO) and gold nanorod (AuNR) hybrids (GO–AuNR), in which poly (N-vinyl-2-pyrrolidone) was used as a stabilizing surfactant to prevent the aggregations of GO sheets. AuNRs were loaded onto the surface of GO, which was confirmed by zeta potential measurements, transmission electron microscopy, atomic force microscopy, UV–Vis–NIR and Raman spectroscopy. The GO–AuNR materials show a great increase of Raman signals for adsorbed aromatic dye molecules, which was demonstrated using cationic and anionic aromatic dyes as probe molecules.
The effect of grain size on the lattice thermal conductivity of an individual polyacrylonitrile-based carbon fiber by L. Qiu; X.H. Zheng; J. Zhu; G.P. Su; D.W. Tang (265-273).
The lattice thermal conductivity (λL ) of general purpose grade polyacrylonitrile (PAN)-based carbon fibers with a crystallite size (La ) of several nanometers was examined. Using a modified 3ω method, the λL of the fibers with different heat-treatment temperatures were detected, and it was found that the λL was linearly dependent on −1/La . Based on phonon scattering theory, this observation can be attributed to the combined effect of boundary scattering and point-defect scattering. The constant for point-defect scattering (A) was evaluated and a formula was derived.
The role of nitrogen in a carbon support on the increased activity and stability of a Pt catalyst in electrochemical hydrogen oxidation by Ganghong Bae; Duck Hyun Youn; Suenghoon Han; Jae Sung Lee (274-281).
Nitrogen-containing carbon materials were prepared by acetonitrile pyrolysis on carbon black and used as a support for a Pt catalyst. The Pt particles on N-containing carbon exhibited increased activity and stability in electrochemical hydrogen oxidation relative to Pt on pristine carbon black. The N-doped carbon had a graphitic structure and contained pyridinic and quaternary nitrogen species. The Pt nanoparticles were better-dispersed because of increased hydrophilicity induced by the nitrogen species. The Pt/N-containing carbon showed higher stability in a potential cycling test than Pt/C, because of an increased metal-support interaction. Using XPS and EELS mapping, we demonstrated that the metal-support interaction became stronger and more specific by adding nitrogen into carbon.
Graphene-supported Pd–Ru nanoparticles with superior methanol electrooxidation activity by R. Awasthi; R.N. Singh (282-289).
Pd–Ru bimetallic nanoparticles dispersed on graphene nanosheets (GNS) have been obtained by a microwave-assisted polyol reduction method and investigated for methanol electrooxidation in 1 M KOH + 1 M CH3OH at 25 °C. Structural and electrochemical characterizations of electrocatalysts are carried out by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, CO stripping voltammetry and chronoamperometry. The study shows that introduction of Ru (1–10 wt.%) into 40 wt.%Pd/GNS produces an alloy of Pd and Ru with the face centered cubic crystal structure. The electrocatalytic activity increased with increasing percentage of Ru in the Pd–Ru alloy showing maximum with 5 wt.%Ru. The electrocatalytic activity of the 40 wt.%Pd–5 wt.%Ru/GNS electrode at E = −0.10 V vs. Hg/HgO was ∼2.6 times greater than that of the base (40 wt.%Pd/GNS) electrode. Based on the methanol oxidation current, measured at 1 h during the chronoamperometry tests at E = −0.10 V vs. Hg/HgO, the active 40 wt.%Pd–5 wt.%Ru/GNS electrode exhibited ∼72% and ∼675% higher poisoning tolerance as compared to 40%Pd/GNS and 40%Pd/multiwalled carbon nanotube electrodes, respectively.
Preparation and one-step activation of microporous carbon nanofibers for use as supercapacitor electrodes by Chang Ma; Yan Song; Jingli Shi; Dongqing Zhang; Xiaoling Zhai; Ming Zhong; Quangui Guo; Lang Liu (290-300).
Microporous carbon nanofibers were prepared by electrospinning from resole-type phenolic resin, followed by one-step activation. KOH was utilized to tune the fiber diameter and improve porous texture. By adjusting KOH content in the spinning solution, the fiber diameter could be controlled in the range of 252–666 nm and the microporous volume and specific surface area could be greatly improved. The electrochemical measurements in 6 M KOH aqueous solution showed that the microporous carbon nanofibers possessed high specific capacitance, considerable rate performance, and superior specific surface capacitance to conventional microporous carbons. The maximal specific capacitance of 256 F g−1 and high specific surface capacitance of 0.51 F m−2 were achieved at 0.2 A g−1. Furthermore, the specific capacitance could still remain 170 F g−1 at 20 A g−1 with the retention of 67%. Analysis showed that the high specific surface capacitance of the resultant carbons was mainly attributed to optimized pore size (0.7–1.2 nm) and the excellent rate performance should be principally due to the reduced ion transportation distance derived from the nanometer-scaled fibers.
Cyclic voltammetric and FTIR studies of powdered carbon electrodes in the electrosorption of 4-chlorophenols from aqueous electrolytes by S. Biniak; A. Świątkowski; M. Pakuła; M. Sankowska; K. Kuśmierek; G. Trykowski (301-312).
Several types of carbon materials (activated carbon, carbon black, multiwalled carbon nanotubes) differing in porosity and surface chemistry were used to prepare powdered electrodes. Activated carbon (Norit R3-ex) was demineralized and modified by oxidation with conc. HNO3, heat treatment in NH3 at 900 °C or heat treatment in argon at 1800 °C. Carbon black (Vulcan XC72) was flushed with an organic solvent, while the MWCNTs were functionalized to the hydroxyl and carboxyl forms. Nitrogen adsorption isotherms were used to characterize the pore structure of these materials. Their surface chemistry was assessed using thermogravimetry (TG), elemental analysis, FTIR, EDS and XPS. The ability to adsorb (isotherms) 4-chlorophenol (4-CP) in aqueous solution was determined. Cyclovoltammetric (CV) measurements of powdered carbon electrodes were carried out for blank electrolyte solution (0.1 M Na2SO4) and with different concentrations of 4-CP. Changes in the electric double layer capacity and other electrochemical parameters were estimated from the CV curves. The dependence of the electrochemical behavior of a powdered carbon bed on porosity and surface chemistry is analyzed and discussed. The electrochemical properties were related to chlorophenol adsorption ability and FTIR spectral analysis of the adsorption layer.
Electronic transport of nitrogen-capped monoatomic carbon wires between lithium electrodes by Z.H. Zhang; C. Guo; G. Kwong; X.Q. Deng (313-321).
Nitrogen (N)-capped single-atom carbon wires are chemisorbed onto two identical Li (1 1 1) electrodes to construct nanodevices. First-principles calculations predict that devices with even and odd numbers of carbon wires would show dramatically different and unexpected electronic transport properties. An even number of wires shows a metallic-like ballistic transport at low bias, a nonlinear current–voltage characteristic over the whole bias region, and a very striking negative differential resistance (NDR). An odd number of carbon wires shows the exact opposite behavior. Currents are very small and rise extreme slowly with bias, and no NDR is observed. The zero-bias conductance of an even number of carbon wires is rather high and reaches a value of about 20 times larger than that for an odd number of wires. These intriguing phenomena can be attributed to changes in the molecular states due to charge transfer doping.
Flexible free-standing graphene–TiO2 hybrid paper for use as lithium ion battery anode materials by Tao Hu; Xiang Sun; Hongtao Sun; Mingpeng Yu; Fengyuan Lu; Changsheng Liu; Jie Lian (322-326).
Flexible and binder-free graphene–TiO2 paper was prepared by a simple route. A unique 3-D nano-structure was achieved with nano-sized TiO2 intercalated between graphene layers as pillars, significantly increasing the Li-ion insertion/extraction rate. At a current rate of 2 Ag−1, the specific capacity can reach 122 mAhg−1 after 100 charge/discharge cycles. More remarkably, the flexible graphene/TiO2 hybrid paper shows an excellent stability when the rates decrease from 4 Ag−1 back to 200 mAg−1 with the retained capacity of 175 mAhg−1.
One-step production of monolith-supported long carbon nanotube arrays by Daniel R. Minett; Justin P. O’Byrne; Matthew D. Jones; Valeska P. Ting; Timothy J. Mays; Davide Mattia (327-334).
Aligned carbon nanotube (CNT) arrays over 150 μm long have been grown by catalytic chemical vapour deposition on the walls of bare cordierite monoliths in a single step. The method described avoids the need for the multiple pre-treatment steps currently applied, and is coupled with an increase in the thickness of the carbon layer obtained by an order of magnitude compared to literature. Uniform CNT growth has been obtained over different lengths of monolith. The resulting CNT/cordierite monoliths have a high surface area and low pressure drop, making them a viable support for use in industrial catalysis.
Biomimetic synthesis and characterization of carbon nanofiber/hydroxyapatite composite scaffolds by Meiyu Wu; Qiaoying Wang; Xinqing Liu; Haiqing Liu (335-345).
Three dimensional electrospun carbon nanofiber (CNF)/hydroxyapatite (HAp) composites were biomimetically synthesized in simulated body fluid (SBF). The CNFs with diameter of ∼250 nm were first fabricated from electrospun polyacrylonitrile precursor nanofibers by stabilization at 280 °C for 2 h, followed by carbonization at 1200 °C. The morphology, structure and water contact angle (WCA) of the CNFs and CNF/HAp composites were characterized. The pristine CNFs were hydrophobic with a WCA of 139.6°, resulting in the HAp growth only on the very outer layer fibers of the CNF mat. Treatment in NaOH aq. solutions introduced carboxylic groups onto the CNFs surfaces, and hence making the CNFs hydrophilic. In the SBF, the surface activated CNFs bonded with Ca2+ to form nuclei, which then easily induced the growth of HAp crystals on the CNFs throughout the CNF mat. The fracture strength of the CNF/HAp composite with a CNF content of 41.3% reached 67.3 MPa. Such CNF/HAp composites with strong interfacial bondings and high mechanical strength can be potentially useful in the field of bone tissue engineering.
Estimation of dispersion stability of UV/ozone treated multi-walled carbon nanotubes and their electrical properties by Seil Kim; Young-In Lee; Dong-Hwan Kim; Kun-Jae Lee; Bum-Sung Kim; Manwar Hussain; Yong-Ho Choa (346-354).
Chemical functionalization of multi-walled carbon nanotubes (MWCNTs) was carried out by UV/ozone treatment. MWCNTs were characterized by elemental analysis, transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR) before and after treatment. The dispersion stability was investigated using UV–vis spectroscopy and a dispersion stability analyzer. Results confirmed the presence of oxygen-containing groups on the MWCNT surfaces by UV/ozone treatment resulting in dispersion stability better than for pristine MWCNTs in polar solvents. A simple method described to investigate the solubility behavior of MWCNTs functionalized with UV/ozone treatment in various organic solvents. To illustrate this concept, CNT dispersions were prepared using UV/ozone treatment with controlled times, and their solubility behavior was represented on three-dimensional graphs using Hansen solubility parameters. Based on these solubility data, a MWCNT/PMMA composite was prepared using an appropriate solvent and the sheet resistance was measured using a four-point probe method. As a result, composites made with MWCNTs having undergone UV/ozone treatment showed lower sheet resistance than CNT composites made from pristine or acid-treated MWCNTs.
The controlled formation of hybrid structures of multi-walled carbon nanotubes on SiC plate-like particles and their synergetic effect as a filler in poly(vinylidene fluoride) based composites by Weilong Li; Jinkai Yuan; Youqin Lin; Shenghong Yao; Zhaoyu Ren; Hui Wang; Minqiang Wang; Jinbo Bai (355-364).
Vertically aligned carbon nanotubes (CNTs) grown on plate-like SiC microparticles as nano/micro hybrid structures were produced by floating catalytic chemical vapor deposition. Acetylene and ferrocene were used as carbon source and catalyst precursor, respectively. The effect of experimental conditions on the structure of the CNT-SiC multi-scale hybrids produced was investigated. The results indicated that the organization mode of CNTs on SiC particles could be effectively tuned by changing the hydrogen content in the carrier gases. The effect of the substrate on the hybrid structures was also studied and their formation mechanism was discussed. According to X-ray diffraction and Raman spectra, the asymmetric surface properties of 6H-SiC tended to produce “single-direction” growth of CNTs on SiC particles, while the competition between the nature of the substrate and the experimental conditions can result in a “multi-direction” hybrid structure. The resultant well-organized CNT-SiC hybrid structures can be further used as conductive filler to prepare percolative poly(vinylidene fluoride) composites. The composites containing the “single-direction” hybrid structures exhibited a much lower percolation threshold than those with “multi-direction” hybrid structures. The percolation behavior of the composites can be tuned by controlling the structure of CNT-SiC hybrids.
Improving the thermal conductivity and shape-stabilization of phase change materials using nanographite additives by Jia-Nan Shi; Ming-Der Ger; Yih-Ming Liu; Yang-Cheng Fan; Niann-Tsyr Wen; Chaur-Kie Lin; Nen-Wen Pu (365-372).
Improvements in the thermal conductivity and shape-stability of paraffin phase change materials (PCMs) by adding exfoliated graphite nanoplatelets (xGnP) or graphene were compared. The composite PCMs were fabricated by mixing paraffin with xGnP or graphene in hot toluene, followed by solvent evaporation and vacuum drying. A larger increase in thermal conductivity was observed for paraffin/xGnP, with a 10 wt.% xGnP loading producing a more than 10-fold increase. Graphene shows a lower electrical percolation threshold and offers a much larger increase in the electrical conductivity of paraffin than xGnP. However, its thermal conductivity increase is much lower. Despite the excellent thermal conductivity of single-flake graphene, the large density of nanointerfaces due to the small size of the graphene flakes significantly impedes heat transfer. We also found that graphene is much more effective than xGnP as a shape-stabilizing filler. At 2 wt.% graphene loading, paraffin maintains its shape up to 185.2 °C, well above the operating temperature range of paraffin PCMs, while the paraffin/xGnP counterpart is shape-stable up to 67.0 °C only. Small amounts of graphene and xGnP can be used in combination as a low-cost and effective improver for both the heat diffusion and shape-stabilization of paraffin PCMs.
A theoretical evaluation of the temperature and strain-rate dependent fracture strength of tilt grain boundaries in graphene by Lijun Yi; Zhengnan Yin; Yingyan Zhang; Tienchong Chang (373-380).
Based on molecular dynamic simulations, we investigate the effects of temperature and strain rate on the strength of single layer graphene with tilt grain boundaries under tension. The simulation results show that temperature plays an important role in the strength of graphene with grain boundaries. The strength of graphene with grain boundaries decreases significantly as temperature increases. In particular, we confirm a previous report that graphene with large angle tilt boundaries (which has a high density of defects) may be much stronger than that with low angle boundaries. This finding holds true for temperatures from 10 to 1800 K and strain rates from 0.0001 to 0.01 ps−1.
Transmission electron microscopy study of the microstructure of unidirectional C/C composites fabricated by catalytic chemical vapor infiltration by Yequn Liu; Lianlong He; Xuefeng Lu; Peng Xiao (381-389).
Unidirectional carbon/carbon (C/C) composites were fabricated by catalytic chemical vapor infiltration, using electroless Ni–P as catalyst. Transmission electron microscopy (TEM) investigations indicate that the catalyst particles (100–800 nm) in the pyrocarbon (PyC) matrix are composed of Ni3P and Ni phases, but only the Ni3P phase was observed in the tiny catalyst particles (<50 nm) in carbon fibers. The catalyst particles in the matrix were encapsulated by high-textured PyC shells, in which openings were observed. The thicknesses of the medium-textured PyC in the composites (720–850 nm) are greater than in conventional C/C composites (660–740 nm), but have no significant difference in texture degree. Catalysts were partially extruded out of the PyC shells and migrated into the carbon fibers, leading to the catalytic graphitization of the carbon fibers, and their structural homogeneity was destroyed. Based on the TEM observation, a dissolution/precipitation mechanism was proposed for the catalytic graphitization of carbon fibers, and a dissolution/precipitation/encapsulation/fracture/extrusion mechanism was proposed for the encapsulation of catalyst particles.
Ferromagnetism in nanomesh graphene by Guoqing Ning; Chenggen Xu; Ling Hao; Olga Kazakova; Zhuangjun Fan; Hao Wang; Kunxun Wang; Jinsen Gao; Weizhong Qian; Fei Wei (390-396).
A nanomesh graphene (NMG) was produced by a chemical vapor deposition using porous MgO layers as templates, and its magnetic properties were measured and compared with those of reduced graphene oxide (rGO). Extraordinary ferromagnetism with a saturation magnetization of 0.04 emu/g at room temperature was found in the NMG, four times of that of rGO (0.01 emu/g). The mesh structure with remarkable corrugations indicates the possible existence of a high density of defects in the NMG, which is believed to contribute to the origin of the ferromagnetism. Our results present a direct connection between the mesh structure and the ferromagnetism, which provides valuable clues to explore the essential origination of carbon magnetism.
A simple solid–liquid grinding/templating route for the synthesis of magnetic iron/graphitic mesoporous carbon composites by Yangang Wang; Bo Li; Chengli Zhang; Xiaofeng Song; Hong Tao; Shifei Kang; Xi Li (397-403).
Magnetic iron/graphitic mesoporous carbon composites were prepared by a simple one-step solid–liquid grinding/templating route. X-ray diffraction, nitrogen adsorption–desorption, transmission electron microscopy, vibrating-sample magnetometry and thermogravimetric analysis were used to characterize the samples. It was observed that a high content of magnetic iron nanoparticles could be embedded in the walls of graphitic mesoporous carbon matrix, and the resulting materials have a hierarchical mesostructure with a high specific surface area, large pore volume, and high saturation magnetization, giving the materials wide potential applications as catalyst supports and adsorbents.
A high temperature X-ray diffraction study of the influence of MWCNTs on the thermal expansion of MWCNT/Ni composites by Sebastián Suárez; Esteban Ramos-Moore; Frank Mücklich (404-409).
The inclusion of multiwall carbon nanotubes (MWCNTs) into metallic matrices is expected to improve their electrical and mechanical performance. This work analyses the lattice thermal expansion behavior of MWCNT-reinforced Ni composites in order to understand the influence of CNTs on their thermomechanical properties. The lattice thermal expansion coefficient (CTE) of the composites was estimated from X-ray diffraction measurements as a function of the temperature. The MWCNT-reinforced composites show higher lattice CTE (up to 12%) compared to pure Ni. This behavior is mainly produced by the expansion mismatch between the matrix and the reinforcements. We suggest three main mechanisms that explain the behavior of the CTE of metallic matrices in presence of MWCNT. These mechanisms correlate to the anchoring effect observed in previous macroscopic measurements of thermal expansion carried out on the same system.
Easy synthesis of ordered mesoporous carbon containing nickel nanoparticles by a low temperature hydrothermal method by Ana García; Alejandra Nieto; Mercedes Vila; María Vallet-Regí (410-418).
Ordered mesoporous carbons (OMCs) with embedded metallic nickel (Ni) nanoparticles have been directly synthesized by a simple and low temperature (50 °C) hydrothermal method. The synthesis involved the use of a triblock copolymer Pluronic F127 as the mesostructure directing agent, resorcinol (R) and formaldehyde (F) as carbon precursors, and Ni(NO3)2·6H2O as nickel source. It consisted in the self-assembly of F127, Ni2+ salt and RF polymer in an acidic medium and further carbonization, where the Ni2+ was captured by the network of F127/RF and further reduced into metallic Ni nanoparticles. The resultant Ni/carbon materials were characterised by X-ray diffraction, thermogravimetric analysis, transmission electron microscopy and nitrogen sorption. Ni/carbon materials with a highly ordered mesostructure were obtained using equal moles of resorcinol and formaldehyde molar ratio (R/F = 1/1), whereas an excess amount of formaldehyde (R/F = 1/2) was found to not form an ordered carbon structure. The results showed that nickel particles, with sizes of ∼10–50 nm, were homogeneously dispersed in the carbon matrices, while the pore mesostructure remained intact. The homogeneous Ni/carbon composites synthesized by this easy hydrothermal route have been demonstrated to be effective molecular adsorbents for magnetic separation.
Increased optical nonlinearities of multi-walled carbon nanotubes covalently functionalized with porphyrin by Zhi-Bo Liu; Zhen Guo; Xiao-Liang Zhang; Jian-Yu Zheng; Jian-Guo Tian (419-426).
Multi-walled carbon nanotubes covalently functionalized with tetraphenylporphyrin (MWCNT–TPP) with diameter ranges of <10, 10–30 and 40–60 nm were prepared by the reaction of MWCNTs with in situ generated porphyrin diazonium compounds. The fluorescence quenching data show that the unique direct linkage mode facilitates the effective photoinduced electron transfer between the excited porphyrin moiety and the extended π-system of MWCNT. The MWCNT–TPP hybrids have larger effective nonlinear absorption coefficients than the individual MWCNTs and porphyrin, and a blended sample. Furthermore, large increases in the optical nonlinearities of MWCNT–TPP hybrid materials were obtained as laser pulse width increased from 5.6 to 11.7 ns. By comparing with the nonlinear optical performance of individual MWCNTs and porphyrin, the pulse-width increased optical nonlinearities of these materials could be attributed to the improved efficiency of photoinduced electron transfer between MWCNTs and porphyrin with the increasing of pulse width.
A sandwich structure graphite block with excellent thermal and mechanical properties reinforced by in-situ grown carbon nanotubes by Yun Zhao; Jingli Shi; Huiqi Wang; Zecao Tao; Zhanjun Liu; Quangui Guo; Lang Liu (427-430).
A graphite block derived from natural graphite flakes (NGF) has high thermal conductivity (TC) but poor mechanical properties. An effort to overcome this shortcoming was made by introducing carbon nanotubes (CNTs) onto the NGF surface by chemical vapor deposition (CVD). A block with a CNT–NGF–CNT sandwich structure was then prepared by hot-pressing at 2973 K. The new structure improved bend strength (increasing 52.2%) of the block, while maintaining the TC in the direction perpendicular to hot-pressing.
A high volume and low damage route to hydroxyl functionalization of carbon nanotubes using hard X-ray lithography by Ludovic F. Dumée; Kallista Sears; Benedetta Marmiroli; Heinz Amenitsch; Xiaofei Duan; Robert Lamb; Dario Buso; Chi Huynh; Stephen Hawkins; Sandra Kentish; Mikel Duke; Stephen Gray; Plinio Innocenzi; Anita J. Hill; Paolo Falcaro (430-434).
The efficient functionalization of large quantities of carbon nanotubes entangled in a non-woven fashion into bucky-papers has been demonstrated through exposure to hard X-rays generated by a synchrotron source. The X-ray beam solely functionalized the carbon nanotube outer walls and an optimum X-ray exposure energy between 1048 J cm−2 and 2096 J cm−2 has been found to achieve maximum hydroxyl group density. Sol–gel reaction between a commercial fluoro-silane and the hydroxyl-modified carbon nanotubes was successfully performed resulting in an even distribution of fluoride atoms on the carbon nanotube surface, opening the way for the mass production of functionalized carbon nanotubes.
Synthesis of nitrogen-doped graphene and its catalytic activity for the oxygen reduction reaction in fuel cells by Gui-xiang Ma; Jiang-hong Zhao; Jian-feng Zheng; Zhen-ping Zhu (435).
Graphene was synthesized by the detonation-assisted reduction of graphite oxide (GO) prepared by the modified Hummers method. Nitrogen-doped reduced GO (N-RGO) was obtained through an in situ nitrogen-doping during detonation. The morphology, elemental composition and structure of the N-RGO were characterized by TEM, SEM, IR, XPS, XRD and Raman spectroscopy. The catalytic activity of the N-RGO as a fuel cell electrode for the oxygen reduction reaction (ORR) was investigated by a rotating ring disk electrode technique. Results showed that the GO was exfoliated and reduced to few layer graphene by the detonation. The oxygen-containing species of GO were reduced and the C/O molar ratio was increased to 26.2, which is much higher than for RGO. Nitrogen, as high as 2.11 at.%, was incorporated into the graphene structure. The diffusion-limited current for ORR increased from 0.24 mA for RGO to 0.49 mA for N-RGO, indicating a higher catalytic activity of N-RGO for ORR than that of RGO.
Preparation of oriented graphite/polymer composite sheets with high thermal conductivities by tape casting by Shao-xin Zhou; Yuan Zhu; Hong-da Du; Bao-hua Li; Fei-yu Kang (435).
Oriented graphite/polymer composite sheets were prepared using natural, crystalline flake graphites as raw materials, polyvinyl butyral as binders, polyethylene glycol and dibutyl phthalate as plasticizers by a tape-casting method at room temperature. The dependences of the binder contents and the blade heights on the orientation of the composite sheets were studied, and the effect of the orientation on the thermal conductivity was investigated. X-ray diffraction patterns and scanning electron microscope images showed that as-prepared samples showed different degrees of orientation. The thermal conductivity increased with the degree of orientation. The highest thermal conductivity of 490 W/m K could be achieved by optimizing the binder contents and the blade heights.
Preparation of graphene-supported Pt–Co nanoparticles and their use in oxygen reduction reactions by Yan-wen Ma; Zhong-ru Liu; Bo-lin Wang; Lei Zhu; Jian-ping Yang; Xing-ao Li (435).
Electrocatalysts of graphene-supported Pt–Co alloy nanoparticles (Pt–Co/G) were prepared by a simultaneous reduction of mixtures of graphene oxide and Pt (IV), Co (II) ions with ethylene glycol assisted by a microwave and further H2 treatment at 300 °C. As-prepared Pt–Co/G catalysts were characterized by transmission electron microscopy, energy-dispersive X-ray spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. The Pt–Co binary alloy nanoparticles with a size of 3–8 nm were homogeneously dispersed on the graphene. Compared with the monometallic Pt/G and commercial Pt/C catalysts, the Pt–Co/G catalysts have a high stability and increased electrocatalytic activity that is conducive for the oxygen reduction reaction, suggesting their potential application in fuel cells.
Dispersion of expanded graphite as nanoplatelets in a copolymer matrix and its effect on thermal stability, electrical conductivity and permeability by Gyanaranjan Prusty; Sarat K. Swain (436).
Expanded graphite/polyacrylonitrile-co-poly (methyl methacrylate) (EG/PAN-co-PMMA) composites were prepared by the incorporation of EG at various concentrations (1%, 2%, 3%, and 4%, w/w) into PAN-co-PMMA by an in situ emulsifier-free emulsion polymerization method. As-synthesized composites were characterized by UV/VIS and FT-IR, XRD, SEM, TEM and TGA. The thermal stability of the copolymer was significantly improved by the addition of EG. The oxygen permeabilities of the composites were substantially reduced and the electrical conductivities of the composites were significantly increased by increasing the EG content.
The effect of heat treatment on the electrical conductivity of highly conducting graphene films by Yong-zhen Wang; Yan Wang; Han Fei; Xiao-lan Cai (436).
Graphene oxide films were prepared by the modified Hummers method, which includes sonication, aggregation and self-assembly. The graphene films were obtained by vacuum heat treatment of the graphene oxide films. XRD, SEM, FTIR and Raman spectroscopy were used to investigate the microstructure evolution of the films during preparation. It is found that self-assembly is a simple method to produce graphene oxide films with controllable size and perfect stacks of graphene oxide layers. Heat treatment gives the graphene films high electrical conductivities. The electrical conductivity of the films increases up to 536 S/cm with increasing heat treatment temperature under vacuum.
The performance of dye-sensitized solar cells using different carbon materials as counter electrodes by Jun Feng; Gui-shan Liu; Tie-cheng Ma; Zhi-qiang Hu; Kai-zhuo Wu; Wei-wei Zhang (436).
Counter electrode films for dye-sensitized solar cells (DSSCs) were prepared by screen printing using graphite, activated carbon, carbon black and carbon nanotubes (CNTs) as raw materials. The effects of pore structure, BET surface area and the sheet resistance of the as-prepared counter electrode films on the performance of DSSCs were investigated. Results show that the conductivity of the raw materials is not the crucial factor for the performance of the DSSCs. The performance of the DSSC is not directly improved by increasing the BET surface area of the raw materials. It is also related to the pore size distribution of carbon materials, the particle shape and their alignment. The DSSCs assembled using CNT film counter electrodes with a BET surface area of 31.2 m2 g−1 show the largest photoelectric conversion efficiency of 5.87%.
Effect of the addition of carbon black and carbon nanotubes on the structure and oxidation resistance of pyrolysed phenolic carbons by Feng Liang; Nan Li; Xuan-ke Li; Wen Yan (436).
Carbon black (CB) and carbon nanotubes (CNTs) were used as additives in phenolic resin. The effects of the additives and heat treatment temperature on the oxidation resistance and structure of carbon from the pyrolysed phenolic resin were investigated by differential scanning calorimetric analysis, X-ray diffraction, scanning electron microscopy, and mercury intrusion porosimetry. It was observed that both CNTs and CB improved the graphitization degree and oxidation resistance of the pyrolytic carbons. The graphitization degree of carbons containing CNTs was higher than that of those with CB, but the oxidation resistance of the former was lower due to the higher porosity in the microstructure. An increase in the heat treatment temperature also resulted in an improvement in the graphitization degree and oxidation resistance of the carbons.
Evolution of the skin-core structure of PAN-based carbon fibers with high temperature treatment by Can-jun Su; Ai-jun Gao; Sha Luo; Liang-hua Xu (436-437).
PAN-based carbon fibers were subjected to high temperature heat treatment (HTT) at 1500–2500 °C and the evolution of the skin-core structure of the carbon fibers was investigated by elemental analysis, XRD, TEM and Raman spectroscopy. Results showed that nitrogen content and d 002 decreased, and carbon content and La increased with HTT temperature. La increased sharply with temperature above 1900 °C. The Raman spectra taken at four points in radial directions indicated that the intensity of the G band at the skin was stronger than at the core with no change in peak position at 1700 °C. However, the G peak position decreased from 1588.2 to 1582.2 cm−1, the width of the G band at half maximum intensity decreased from 46.3 to 28.9 and that of D band from 46.9 to 36.7 cm−1 from core to skin after HTT at 2500 °C. The differences of microstructure in the core and skin at different temperatures are related closely to the differences in nitrogen removal efficiency and temperature. At temperatures below 1900 °C, nitrogen near the skin is more easily removed due to a shorter diffusion path and a higher temperature on the skin, leading to a slower increase of La with temperature on the skin than in the core. At temperatures above 1900 °C, nitrogen is removed completely and graphitization on the skin is more rapid than in the core, leading to a large skin-core difference with the skin portion having a high modulus and the core portion a high strength.
Preparation of activated carbons by ZnCl2 activation from herb residues under vacuum by Juan Yang; Ke-qiang Qiu (437).
Activated carbons were prepared by ZnCl2 activation from herb residues under an absolute pressure of 30 kPa and the Doehlert matrix was used to optimize activation temperature and impregnation ratio based on adsorption capacities of methylene blue and iodine by the activated carbons. Results showed that activation temperature and impregnation ratio had little effect on the total yield of the activated carbons. The activation temperature had a greater influence than the impregnation ratio in methylene blue and iodine adsorption. The optimized activated carbon was obtained under an activation temperature of 474 °C and an impregnation ratio of 1.225, and had a methylene blue value and an iodine value of 316 and 994 mg g−1, respectively. The experimental values agree well with those calculated from the Doehlert model. The activated carbon optimized in this study had a higher adsorption capacity compared with commercial ones.
Synthesis of ordered mesoporous carbon with dual templates as structure directing agents by Yu Zhang; Tong-hua Wang; Pan-pan Mi (437).
Ordered mesoporous carbons were prepared by pyrolysis of polymer blends, which were formed by the organic–organic self-assembly of resorcinol–formaldehyde pre-polymers and tri-block copolymers under acidic conditions. The tri-block copolymer mixtures of F127 and P123 were used as structure-directing agents. The samples were characterized by X-ray diffraction, transmission electron microscopy and nitrogen adsorption. Results show that the degree of order of mesoporous carbons exhibits a maximum with increasing holding time from 24 to 72 h. When the molar ratio of the F127 to P123 is 1, the mesoporous carbon obtained has the most ordered hexagonal mesostructure (Pm6m), with a typical BET surface area of 640.3 m2/g, pore size of 3.7 nm and pore volume of 0.59 cm3/g.
Intermittent growth of a diamond film by direct current hot cathode plasma chemical vapor deposition by Hong-wei Jiang; Hai-liang Huang; Xiang-hua Jia; Long-cheng Yin; Yu-qiang Chen; Hong-yan Peng (437).
A diamond film was intermittently prepared by direct-current (DC) hot-cathode plasma chemical vapor deposition (PCVD). The intermittent growth was carried out by alternating deposition under methane flow for 20 min and etching for 10 min without methane flow. For comparison, a diamond film was continuously prepared under the same growth conditions without etching. Scanning electron microscopy, Raman spectroscopy and XRD were used to characterize surface morphology, texture and purity of the two diamond films. Results indicated that the diamond film produced by the intermittent growth had smaller amounts of non-diamond phase and its grains were more uniform than that produced by the continuous growth without etching. Amorphous carbon and graphite formed during deposition on the surface of the diamond film can be reduced by etching.
Effect of hafnium carbide content on the ablative performance of carbon/carbon composites as rocket throats by Shu-ping Li; Ke-zhi Li; Hong-ying Du; Shou-yan Zhang; Xue-tao Shen (437-438).
Hafnium carbide (HfC) modified carbon/carbon (HfC-C/C) composites were prepared by impregnating carbon felts with a saturated HfOCl2 · 8H2O ethanol solution and heat treating at 600 °C to form HfO2/C composites that were then densified with pyrocarbon by chemical vapor infiltration and graphitized at 2100 °C to convert HfO2 into HfC. The HfC-C/C composites as rocket throats were ablated at 7 MPa and around 3200 °C for 3 s by an experimental solid rocket motor. Results showed that the HfC-C/C composites with HfC contents more than 5.7 wt.% had a stable period with a constant ablation rate and the duration of this period increased with HfC content. The overall ablation rate was decreased by 25.2% and 49.6% for the composites having 5.7 and 8.7 wt.% HfC respectively as compared with the composite with 2.5 wt.% HfC.
A brief overview of the Tenth Cross-Strait Symposium on Carbon Materials by Jia Li; Fei-yu Kang (438).
The Tenth Cross-Strait Symposium on Carbon Materials was held in Baotou City, Inner Mongolia, PR China from August 1 to 4, 2012. It was hosted by Tsinghua University and Inner Mongolia University of Science & Technology. More than 60 cross-strait carbon scientists participated in the conference, and 31 presentations were given, including 15 keynote talks and 16 oral presentations. The presentations were classified into the following eight topics: highly efficient conversion and applications of coal, carbon fibers and carbon-based composites, special carbon-graphite materials, nano-structured carbons and their applications, carbon materials for energy storage, preparation and applications of graphene, evaluation and performance of new carbon materials, and other new carbon materials. The 4-day symposium has increased cross-strait academic exchange and has advocated close academic cooperation in the field of carbon materials.
How will carbon material lead to a Low Carbon Society – A review of Carbon 2012 by Xu-guang Liu (438).
A review is given of the Annual World Conference on Carbon, which was held on June 17–22, 2012 in Krakow, Poland and organized by the Polish Carbon Society. In this conference, 5 plenary lectures, 30 keynote lectures, 220 oral presentations and 465 posters were divided into 10 topics, i.e., carbons for energy storage; carbons for health and environmental protection; precursors, processing and technology; carbon nanomaterials; porous carbons; carbon-based composites; graphene; new methods for carbon characterization; computation and modeling; and industrial news. Besides traditional modification on surface area and porosity, doping with hetero atoms such as N, B and P or compositing with metals or metal oxides have been developed into effective means for modifying carbon materials for improved adsorption, catalysis and energy-storage performance. The applications of novel carbon structures like nanotubes are still limited by the controllable and scalable preparation, processability and reactivity. Research on the structure and properties of graphene is moving from curiosity-oriented to application-oriented. Mathematical formulation or modeling of pore structures has been promoted by the progress in characterization methods. The modification of the surface/interface in carbon materials, which plays important roles in determining their physical, chemical or mechanical properties is still a focus of research activity in carbon materials.
Corrigendum to “Applications of a granular model and percolation theory to the electrical resistivity of heat treated endocarp of babassu nut” [CARBON 25 (3) (1987) 417–424] by F.G. Emmerich; J.C. de Sousa; I.L. Torriani; C.A. Luengo (439).