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1.
Quasi‐aligned cylindrical and conical core–shell nanofibers consisting of carbon shells and TiO2 nanowire cores are produced in situ on Ti foils without using a foreign metallic catalyst and template. A cylindrical nanofiber has a TiO2 nanowire core 30–50 nm in diameter and a 5–10 nm‐thick cylindrical carbon shell, while in the conical nanostructure the TiO2 nanowire core has a diameter of 20–40 nm and the thickness of the carbon shell varies from about 200 nm at the bottom to about 5 nm at the tip. Electrochemical analysis reveals well‐defined redox peaks of the [Fe(CN)6]3?/4? redox couple and heterogeneous charge‐transfer rate constants of 0.010 and 0.062 cm s?1 for the cylindrical and conical nanofibers, respectively. The coverage of exposed edge planes on the cylindrical and conical carbon shells is estimated to be 2.5 and 15.5 % respectively. The more abundant exposed edge planes on the conical nanofiber decrease the overpotential and increase the voltammetric resolution during electrochemical detection of uric acid and ascorbic acid. Our results suggest that the density of edge‐plane sites estimated from Raman scattering is not necessarily equal to the density of exposed edge‐plane sites, and only carbon electrodes with a large density of exposed edge planes or free graphene sheet ends exhibit better electrochemical performance.  相似文献   

2.
To assist the development of plasma processes to pattern graphene in a controlled way, interactions between hydrogen plasma species (H, H+, H2 +) and various types of graphene surfaces (monolayer, nanoribbons, multilayer) are investigated using atomic-scale simulations. It is shown that only “hot” H particles (i.e., with a kinetic energy greater than ~0.4 eV at 300 K) can adsorb on the basal plane of surface-clean graphene while adsorption is barrierless on free edges or vacancies. Surface reaction probabilities (reflection, adsorption, penetration) are found to strongly vary with the incident species energy, which allows to determine specific energy ranges (or process windows) for different types of H2 plasma treatment: lateral etching of graphene nanoribbons (GNRs), cleaning of graphene surfaces or vertical etching of multilayer graphene (MLG) stacks. Molecular dynamics simulations of GNRs trimming in downstream H2 plasmas allow to understand the mechanism which governs the anisotropic etching of ribbons and explains the absence of line-edge roughness on their edges. Interactions between low-energy (5–25 eV) H x + (x = 1, 2) ions with MLG are also investigated. Ion-induced damage (hydrogenation of successive graphene sheets, creation of vacancies) and etching of the MLG stack are found to vary with the ion energy, the ion fluence and the ion composition.  相似文献   

3.
Nanocomposites based on PtPd nanoparticles with chemical ordering like disordered solid solution on surface of multilayer graphene have been prepared through thermal shock of mechanically obtained mixture of double complex salt [Pd(NH3)4][PtCl6] and different carbon materials–exfoliated graphite, graphite oxide and graphite fluoride. An effect of original carbon precursors on formation of PtPd bimetallic nanoparticles was studied using X-ray absorption spectroscopy (XAFS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It was shown that the distribution of bimetallic nanoparticles over the multilayer graphene surface as well as the particles size distribution is controlled by the graphene precursors. For all nanocomposites, the surface of the nanoparticles was found to be Pd-enriched. In case when the thermal exfoliated graphite and graphite oxide were used as the graphene precursors a thin graphitized layer covered the nanoparticles surface. Such a graphitized layer was not observed in the nanocomposite, which used the fluorinated graphite as the precursor.  相似文献   

4.
Graphene oxide has widely been employed in various fields, but its structure and composition has still not been fully understood. Here we report that freshly prepared graphene oxide exhibits a large number of π‐conjugated carbon radicals at its π‐network plane, which result from the addition reaction of hydroxyl radicals from H2O2 onto the conjugated double bonds of graphene oxide. The π‐conjugated carbon radicals can directly initiate the long‐lasting visible chemiluminescence of luminol, which is even stronger than that obtained when horseradish peroxidase and H2O2 are used. Previously, graphene oxide was mainly reported to be a quencher of chemiluminescence instead. Remarkably, the reacted radicals can be regenerated, thereby enabling the repetitive initiation of chemiluminescence by re‐treatment of graphene oxide. The results reported here provide a new understanding of the structure, properties, and applications of graphene oxide.  相似文献   

5.
We report a mechanically strong, electrically and thermally conductive, and optically transparent shape‐memory polyurethane composite which was fabricated by introducing a small amount (0.1 wt%) of high‐quality graphene as a filler. Geometrically large (≈4.6 μm2), but highly crystallized few‐layer graphenes, verified by Raman spectroscopy and transmission electron microscopy, were prepared by the sonication of expandable graphite in an organic solvent. Oxygen‐ containing functional groups at the edge plane of graphene were crucial for an effective stress transfer from the graphene to polyurethane. Homogeneously dispersed few‐layered graphene enabled polyurethane to have a high shape recovery force of 1.8 MPa cm−3. Graphene, which is intrinsically stretchable up to 10%, will enable high‐performance composites to be fabricated at relatively low cost and we thus envisage that such composites may replace carbon nanotubes for various applications in the near future.  相似文献   

6.
特殊的单原子层二维sp2碳结构给石墨烯带来众多独特的性能和潜在的应用. 然而, 单层石墨烯容易聚集并会逐渐重新石墨化, 这成为其应用的一个重要障碍. 本文报道了一种新策略来解决这个问题, 即通过在石墨烯表面引入sp2碳纳米结构作为永久的波纹来阻止石墨烯的聚集和石墨化, 并使之在溶液中易于分散和稳定. 和其他功能化方法不同, 该方法没有引入杂原子, 不破坏石墨烯的结构和功能. 制得的石墨烯具有优异的导电性能(~65000 S·m-1), 并具有较好的溶液稳定性.  相似文献   

7.
To better understand the effects of low-level fluorine in graphene-based sensors, first-principles density functional theory (DFT) with van der Waals dispersion interactions has been employed to investigate the structure and impact of fluorine defects on the electrical properties of single-layer graphene films. The results show that both graphite-2 H and graphene have zero band gaps. When fluorine bonds to a carbon atom, the carbon atom is pulled slightly above the graphene plane, creating what is referred to as a CF defect. The lowest-binding energy state is found to correspond to two CF defects on nearest neighbor sites, with one fluorine above the carbon plane and the other below the plane. Overall this has the effect of buckling the graphene. The results further show that the addition of fluorine to graphene leads to the formation of an energy band (BF) near the Fermi level, contributed mainly from the 2p orbitals of fluorine with a small contribution from the p orbitals of the carbon. Among the 11 binding configurations studied, our results show that only in two cases does the BF serve as a conduction band and open a band gap of 0.37 eV and 0.24 eV respectively. The binding energy decreases with decreasing fluorine concentration due to the interaction between neighboring fluorine atoms. The obtained results are useful for sensor development and nanoelectronics.  相似文献   

8.
Vertically aligned few layered graphene (FLGs) nanoflakes were synthesized by microwave plasma deposition for various time durations ranging from 30 to 600 s to yield graphene films of varying morphology, microstructure and areal/edge density. Their intrinsic electrochemical properties were explored using Fe(CN)6 3?/4? and Ru(NH3)6 3+/2+ redox species. All the FLG electrodes demonstrate fast electron transfer kinetics with near ideal ΔEp values of 60–65 mV. Using a relationship between electron transfer rate and edge plane density, an estimation of the edge plane density was carried out which revealed a moderation of edge plane density with increase in growth time. The pristine FLGs also possess excellent electrocatalytic activity towards oxygen reduction reaction (ORR) in alkaline solutions. This ORR activity can be further enhanced by exposing the pristine FLGs to nitrogen electron cyclotron resonance plasma. The metal free N-doped FLGs exhibit much higher electrocatalytic activity towards ORR than pristine FLGs with higher durability and selectivity than Pt-based catalysts. The excellent electrochemical performance of N-doped FLGs is explained in terms of enhanced edge plane exposure, high content of pyridinic nitrogen and an increase in the electronic density of states.  相似文献   

9.
The selective functionalization of graphene edges is driven by the chemical reactivity of its carbon atoms. The chemical reactivity of an edge, as an interruption of the honeycomb lattice of graphene, differs from the relative inertness of the basal plane. In fact, the unsaturation of the pz orbitals and the break of the π conjugation on an edge increase the energy of the electrons at the edge sites, leading to specific chemical reactivity and electronic properties. Given the relevance of the chemistry at the edges in many aspects of graphene, the present Review investigates the processes and mechanisms that drive the chemical functionalization of graphene at the edges. Emphasis is given to the selective chemical functionalization of graphene edges from theoretical and experimental perspectives, with a particular focus on the characterization tools available to investigate the chemistry of graphene at the edge.  相似文献   

10.
The study has focused on polyvinylcarbazole (PVK) composites with graphene. It has been shown that there is a noticeable nonadditive shoulder on the long-wavelength edge of the optical absorption of PVK in these samples, which can be attributed to the formation of a charge-transfer complex between PVK as a donor and graphene as an acceptor. The formation of the complex causes a significant nonlinear optical effect in the PVK/graphene composite. The revealed increase in both the nonlinearity coefficient with increasing laser intensity and the cross section with increasing incident energy density is due to the formation of the graphene radical anion, an additional species contributing to nonlinear absorption, with an increase in the radiation energy density. Nonlinear optical properties of PVK composites with graphene isolated from a solution in tetrachloroethane after 1.5-h centrifugation (sample 1) have been considered. It has been suggested that a significant decrease in optical transmission of laser radiation by the composite T OA = 0.4 at an energy density at focus of 502 J/cm2 is due to the formation of the PVK/graphene charge-transfer complex responsible for the nonadditive shoulder on the long-wavelength optical absorption edge of PVK. During photoexcitation of graphene in the PVK/graphene composites at a laser wavelength of 1064 nm, mobile holes are generated in PVK, indicating the formation of graphene radical anions as a result of charge transfer from PVK to photoexcited graphene. The observed increase in both β with an increase in the laser radiation intensity and the cross section (σexc — σ0) with an increase in the incident energy density may be due to either the contribution of nonlinear transitions (S 0S 2, S 0S 1S 2, T 1T 2) or the formation of the additional species, the graphene-· radical anions, participating in nonlinear absorption by increasing the energy density at the focus (F foc, J/cm2).  相似文献   

11.
The review has been made of recent publications on modification of ZrB2/HfB2–SiC ultra-hightemperature ceramic composite materials (UHTC) by carbon components: amorphous carbon, graphite, graphene, fibers, and nanotubes. Available data have been presented on some aspects of oxidation of such materials at temperatures ≥1500°C and both at the atmospheric pressure and at the reduced oxygen partial pressure; structural features of the formed multilayer oxidized regions have been noted. It has been considered how the type and content of the carbon component and the conditions (first of all, temperature) of UHTC production affect the density, flexural strength, hardness, fracture toughness, and thermal and oxidation resistance of the modified ceramic composites.  相似文献   

12.
A unique hierarchically nanostructured composite of iron oxide/carbon (Fe3O4/C) nanospheres‐doped three‐dimensional (3D) graphene aerogel has been fabricated by a one‐pot hydrothermal strategy. In this novel nanostructured composite aerogel, uniform Fe3O4 nanocrystals (5–10 nm) are individually embedded in carbon nanospheres (ca. 50 nm) forming a pomegranate‐like structure. The carbon matrix suppresses the aggregation of Fe3O4 nanocrystals, avoids direct exposure of the encapsulated Fe3O4 to the electrolyte, and buffers the volume expansion. Meanwhile, the interconnected 3D graphene aerogel further serves to reinforce the structure of the Fe3O4/C nanospheres and enhances the electrical conductivity of the overall electrode. Therefore, the carbon matrix and the interconnected graphene network entrap the Fe3O4 nanocrystals such that their electrochemical function is retained even after fracture. This novel hierarchical aerogel structure delivers a long‐term stability of 634 mA h g?1 over 1000 cycles at a high current density of 6 A g?1 (7 C), and an excellent rate capability of 413 mA h g?1 at 10 A g?1 (11 C), thus exhibiting great potential as an anode composite structure for durable high‐rate lithium‐ion batteries.  相似文献   

13.
The structures of 18-crown-6 (18C6) complexes with K+ and Rb+ in methanolic solutions have been studied by X-ray absorption fine structure (XAFS) at the Br K-edge as well as at the K and Rb K-edges. The XAFS spectrum at the K or Rb K-edge has indicated that either Br or solvent (methanol) molecules are present in the first coordination shell of K+ or Rb+ complexed by 18C6. However, the spectra obtained at the Br-K edge have strongly suggested that the alkali cations do not exist in the vicinity of Br, indicating that no direct ion-pairing occurs between the 18C6 complex and Br. The 18C6-K+ complex maintains D 3d symmetry even in methanol, and two methanol molecules coordinate the cation possibly from above and below the crown plane. In contrast, the corresponding Rb+ complex possibly forms an umbrella-shaped complex, in which Rb+ is situated slightly off the crown plane and three solvent molecules bind With the cation.  相似文献   

14.
Graphene layers are often exposed to gaseous environments in their synthesis and application processes, and interactions of graphene surfaces with molecules particularly H2 and O2 are of great importance in their physico-chemical properties. In this work, etching of graphene overlayers on Pt(111) in H2 and O2 atmospheres were investigated by in-situ low energy electron microscopy. Significant graphene etching was observed in 10-5 Torr H2 above 1023 K, which occurs simultaneously at graphene island edges and interiors with a determined reaction barrier at 5.7 eV. The similar etching phenomena were found in 10-7 Torr O2 above 973 K, while only island edges were reacted between 823 and 923 K. We suggest that etching of graphene edges is facilitated by Pt-aided hydrogenation or oxidation of edge carbon atoms while intercalation-etching is attributed to etching at the interiors at high temperatures. The different findings with etching in O2 and H2 depend on competitive adsorption, desorption, and diffusion processes of O and H atoms on Pt surface, as well as intercalation at the graphene/Pt interface.  相似文献   

15.
《Electroanalysis》2005,17(18):1627-1634
The behavior of chloride, bromide and iodide at edge plane pyrolytic graphite electrodes has been explored in aqueous acid solutions. The voltammetric response in each case has been compared with that of basal plane pyrolytic graphite, glassy carbon and boron‐doped diamond. The electrochemical oxidation of chloride is found to only occur on boron‐doped diamond while the electrochemical reversibility for the oxidation of bromide on edge plane pyrolytic graphite is similar to that seen at glassy carbon whilst being superior to basal plane pyrolytic graphite and boron‐doped diamond. In the case of iodide oxidation, edge plane and basal plane pyrolytic graphite and glassy carbon display similar electrode kinetics but are all superior to boron‐doped diamond. The analytical possibilities were examined using the edge plane pyrolytic graphite electrode for both iodide and bromine where is was found that, based on cyclic voltammetry, detection limits in the order of 10?6 M are possible.  相似文献   

16.
The large internal surface areas and outstanding electrical and mechanical properties of graphene have prompted to blend graphene with NiCo2O4 to fabricate nanostructured NiCo2O4/graphene composites for supercapacitor applications. The use of graphene as blending with NiCo2O4 enhances the specific capacitance and rate capability and improves the cyclic performance when compared to the pristine NiCo2O4 material. Here, we synthesized two different nanostructured morphologies of NiCo2O4 on graphene sheets by solvothermal method. It has been suggested that the morphologies of oxides are greatly influenced by dielectric constant, thermal conductivity, and viscosity of solvents employed during the synthesis. In order to test this concept, we have synthesized nanostructured NiCo2O4 on graphene sheets by facile solvothermal method using N-methyl pyrrolidone and N,N-dimethylformamide solvents with water. We find that mixture of N-methyl pyrrolidone and water solvent favored the formation of nanonet-like NiCo2O4/graphene (NiCoO-net) whereas mixture of N,N-dimethylformamide and water solvent produced microsphere-like NiCo2O4/graphene (NiCoO-sphere). Electrochemical pseudocapacitance behavior of the two NiCo2O4/graphene electrode materials was studied by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy techniques. The supercapacitance measurements on NiCoO-net and NiCoO-sphere electrodes showed specific capacitance values of 1060 and 855 F g?1, respectively, at the current density of 1.5 A g?1. The capacitance retention of NiCoO-net electrode is 93 % while that of NiCoO-sphere electrode is 77 % after long-term 5000 charge-discharge cycles at high current density of 10 A g?1.  相似文献   

17.
在采用溶剂热法制备磷酸锰锂的基础上,以蔗糖和石墨烯为碳源,制备了裂解碳和石墨烯含量不同的磷酸锰锂/碳/石墨烯复合材料,研究了裂解碳和石墨烯对材料性能的影响。采用扫描电镜(SEM)和透射电镜(TEM)对材料的形貌进行了表征。裂解碳包覆可以提高LiMnPO4纳米片表面的电子导电性,对于材料性能的改善起到主要的作用;石墨烯可以提高纳米片之间的电子和离子导电性,改善材料的电化学性能。电化学测试表明,当裂解碳含量为4%、石墨烯含量为2%时,LiMnPO4电极具有较好的电化学性能,在0.5C下的放电比容量为139.1 mAh·g-1,循环100次后,容量保持率为93.6%。与添加单一碳和单一石墨烯的LiMnPO4电极相比,该电极在0.5C下的放电比容量分别提高了35.0%和48.6%。  相似文献   

18.
A new analogue of graphene containing boron, carbon and nitrogen (BCN) has been obtained by the reaction of high‐surface‐area activated charcoal with a mixture of boric acid and urea at 900 °C. X‐ray photoelectron spectroscopy and electron energy‐loss spectroscopy reveal the composition to be close to BCN. The X‐ray diffraction pattern, high‐resolution electron microscopy images and Raman spectrum indicate the presence of graphite‐type layers with low sheet‐to‐sheet registry. Atomic force microscopy reveals the sample to consist of two to three layers of BCN, as in a few‐layer graphene. BCN exhibits more electrical resistivity than graphene, but weaker magnetic features. BCN exhibits a surface area of 2911 m2 g?1, which is the highest value known for a BxCyNz composition. It exhibits high propensity for adsorbing CO2 (≈100 wt %) at 195 K and a hydrogen uptake of 2.6 wt % at 77 K. A first‐principles pseudopotential‐based DFT study shows the stable structure to consist of BN3 and NB3 motifs. The calculations also suggest the strongest CO2 adsorption to occur with a binding energy of 3.7 kJ mol?1 compared with 2.0 kJ mol?1 on graphene.  相似文献   

19.
在采用溶剂热法制备磷酸锰锂的基础上,以蔗糖和石墨烯为碳源,制备了裂解碳和石墨烯含量不同的磷酸锰锂/碳/石墨烯复合材料,研究了裂解碳和石墨烯对材料性能的影响。采用扫描电镜(SEM)和透射电镜(TEM)对材料的形貌进行了表征。裂解碳包覆可以提高LiMnPO_4纳米片表面的电子导电性,对于材料性能的改善起到主要的作用;石墨烯可以提高纳米片之间的电子和离子导电性,改善材料的电化学性能。电化学测试表明,当裂解碳含量为4%、石墨烯含量为2%时,LiMnPO_4电极具有较好的电化学性能,在0.5C下的放电比容量为139.1 m Ah·g-1,循环100次后,容量保持率为93.6%。与添加单一碳和单一石墨烯的LiMnPO_4电极相比,该电极在0.5C下的放电比容量分别提高了35.0%和48.6%。  相似文献   

20.
The electrode materials with hollow structure and/or graphene coating are expected to exhibit outstanding electrochemical performances in energy‐storage systems. 2D graphene‐wrapped hollow C/Fe3O4 microspheres are rationally designed and fabricated by a novel facile and scalable strategy. The core@double‐shell structure SPS@FeOOH@GO (SPS: sulfonated polystyrene, GO: graphene oxide) microspheres are first prepared through a simple one‐pot approach and then transformed into C/Fe3O4@G (G: graphene) after calcination at 500 °C in Ar. During calcination, the Kirkendall effect resulting from the diffusion/reaction of SPS‐derived carbon and FeOOH leads to the formation of hollow structure carbon with Fe3O4 nanoparticles embedded in it. In the rationally constructed architecture of C/Fe3O4@G, the strongly coupled C/Fe3O4 hollow microspheres are further anchored onto 2D graphene networks, achieving a strong synergetic effect between carbon, Fe3O4, and graphene. As an anode material of Li‐ion batteries (LIBs), C/Fe3O4@G manifests a high reversible capacity, excellent rate behavior, and outstanding long‐term cycling performance (1208 mAh g?1 after 200 cycles at 100 mA g?1).  相似文献   

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