Chemical vapor deposition of thin graphite films of nanometer thickness

Well-ordered graphite films with a thickness of a few graphene layers have been grown on Ni substrates by chemical vapor deposition (CVD) from a mixture of hydrogen and methane activated by a DC discharge. According to Auger, Raman and scanning tunneling microscopy (STM) data the CVD graphite film thickness is about 1.5 ± 0.5 nm. The graphene layers were perfectly adhered to the substrate surface except for upthrusted ridges of a few tens of nanometers in height. STM has revealed an atomically smooth surface with the atomic arrangement typical of graphite between the ridges. A difference in the thermal expansion coefficients of nickel and graphite is considered as a reason for the ridge formation.     

Synthesis and characterization of mesoporous graphite carbon,and adsorption performance for benzene

In this paper, graphite carbon with a mesoporous structure was synthesized using the template–catalysis procedure with hydrated metal oxide nanoparticle as template and catalyst, phenol and formaldehyde as carbon source. XRD, Raman, BET and TEM analyses were performed to study the effluence of synthetic conditions on the structure of samples. The adsorption performances for benzene vapor were evaluated. The results show that CCo and CFe samples have mesoporous graphitized carbon structures. The molar amount of template to carbon source significantly affects the specific surface area, pore structure and adsorption–desorption performance. The specific surface area of CCo-1, with the best graphite structure, was 287.638 m²/g, the pore size was 19.075 nm, and the adsorption capacity for benzene vapor was 19.615 mmol/g. The synergistic effect between the cobalt element and graphite carbons affects the adsorption capacity of CCo-3, which was 34.643 mmol/g. However, the desorption efficiency was only 89 %, and the adsorption performance of CCo-3 material was degraded greatly after three times run.     

Synthesis and characterization of compound-curved graphite

Crystalline graphite with compound curvature has been produced by precipitation of carbon from metal carbide solutions. Nearly spherical graphitic shells hundreds of microns thick have been synthesized on top of millimeter-sized spherical transition metal cores in high vacuum. Raman spectroscopy, backscatter electron diffraction and X-ray analysis shows the shell to be composed of highly crystalline graphite. Upon cooling, these graphite-like shells routinely undergo a reversible transformation in which the initially smooth surface forms striking geometric facets bounded by ridges of triangular cross section. Evaporation rates and other factors suggest that this transformation represents a phase transition from graphite composed of randomly oriented layers of graphene to fully crystalline graphite having layers in registry.     

Synthesis of two dimensional carbon sheets from adamantane

Graphene-like carbon sheets were synthesized from adamantane in the solution phase at ambient temperature. Adamantane, C₁₀H₁₆, has a tetracyclic ring structure with four cyclohexanes in chair conformation. The two dimensional carbon structures were obtained by introducing ferrocene as the catalyst precursor and adamantane as the carbon source under sonication, proving that cyclohexane structures in adamantane can serve as a building block for graphene formation. The synthesized carbon sheets were characterized and confirmed by X-ray diffraction, high-resolution electron microscopy and atomic force microscopy.     

纳米四氧化三钴的合成表征及各自在电化学性能的研究

以六水合硝酸钴(Ⅱ)、六水合氯化钴(Ⅱ)为原料制备纳米级别的棒状四氧化三钴、管状四氧化三钴及片状四氧化三钴。利用XRD对制备的产物与原料、中间体进行对比研究,利用SEM观察产物形貌,并利用电化学工作站对不同产物的电化学性能进行研究。经研究发现,在以2 mol/L KOH溶液为电解液的条件下,四氧化三钴纳米棒的电化学性能最为优异。     

Fabrication and characterization of ultrafine graphite/carbon foam composites

Journal of Porous Materials - Ultrafine graphite/carbon foam composites were prepared by direct pyrolysis of ultrafine graphite/mesophase pitch mixtures at high pressure, via foaming and...     

Fracture mechanism of flexible graphite sheets

The fracture behavior of flexible graphite sheets (FGSs) was investigated by loading along and perpendicular to the sheet surface. The vertical strength is lower than the tensile strength by two orders of magnitude, at only 0.03 MPa. The fracture processes of a notched specimen of FGS and compressed graphite worms were also studied directly and by in-situ observation by SEM. From observations of the fractured surfaces, structural units for the fracture of FGS are assumed to be interlocked micro-discs composed of orientated graphite layers, which originate from the worm-like particles of the original exfoliated graphite. During the formation of FGS by compression and rolling, micro-discs in the different worms interlock and become structural units. When a static tensile load was applied to FGS, some structural units rotated, cleaved and produced microcracks. When the load was increased, slip between the structural units of FGS started and the structural units slipped away from each other and the FGS was broken. Therefore, The tensile strength of FGS originates from the frictional force between the structural units.     

Synthesis and characterization of stable room temperature bulk ferromagnetic graphite

A novel and inexpensive chemical route leading to obtain macroscopic quantities of room temperature magnetic carbon is reported. This route consists of a controlled etching on the graphite structure, performed by a redox reaction in a closed system between graphite and CuO. X-ray diffraction suggests that this modified graphite could be represented by the coexistence of a matrix of pristine graphite and a foamy-like graphitic structure compressed along the c-axis. This material has a stable and strong ferromagnetic response even at room temperature where it can be attracted by any commercial magnet. At T = 300 K, the saturation magnetic moment, the coercive field and the remnant magnetization are 0.25 emu/g, 350 Oe and 0.04 emu/g, respectively.     

Synthesis and characterization of microporous carbon nitride

This research reports the preparation and characterization of amorphous microporous carbon nitride using HZSM-5 zeolite as template, and ethidene diamine and carbon tetrachloride as chemical precursors. Microporous amorphous carbon nitride is generated by removal of HZSM-5 zeolite in the obtained zeolite/carbon nitride composite using hydrofluoric acid after carbonization the precursor inside the channels of zeolite. The microporous carbon nitride was characterized by nitrogen sorption techniques, scanning electron microscopy, elemental analysis, X-ray diffraction, X-ray photoelectron spectroscopy, IR spectroscopy, Ultraviolet–visible spectroscopy, Raman spectroscopy, and thermo-gravimetric analysis. Amorphous microporous carbon nitride with high surface area and narrow pore size distribution is thermal stable under atmosphere conditions up to 700 K.     

Synthesis and characterization of nitrogen-doped carbon xerogels

Carbon xerogels were prepared from a nitrogen-containing polymer precursor, using melamine and urea as nitrogen sources incorporated into the polymer matrix using the sol-gel process. To investigate the effects of nitrogen on the texture, morphology and surface chemistry, the carbon xerogels were characterized by nitrogen adsorption, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and acid-base titrations. The results showed that nitrogen was incorporated onto the surface as pyridine, pyrrolic/pyridine, quaternary nitrogen, and pyridine-N-oxide. From the deconvolution of the XPS spectra, the pyrrolic/pyridine and quaternary nitrogen functionalities were found to dominate in the samples prepared from urea. All samples showed increased basicity after nitrogen incorporation.     

Synthesis and characterization of double-walled carbon nanotubes from multi-walled carbon nanotubes by hydrogen-arc discharge

Double-walled carbon nanotubes (DWNTs) were synthesized in a large scale by a hydrogen arc discharge method using graphite powders or multi-walled carbon nanotubes/carbon nanofibers (MWNTs/CNFs) as carbon feedstock. The yield of DWNTs reached about 4 g/h. We found that the DWNT product synthesized from MWNTs/CNFs has higher purity than that from graphite powders. The results from high-resolution transmission electron microscopy observations revealed that more than 80% of the carbon nanotubes were DWNTs and the rest were single-walled carbon nanotubes (SWNTs), and their outer and inner diameters ranged from 1.75 to 4.87 nm and 1.06 to 3.93 nm, respectively. It was observed that the ends of the isolated DWNTs were uncapped and it was also found that cobalt as the dominant composition of the catalyst played a vital role in the growth of DWNTs by this method. In addition, the pore structures of the DWNTs obtained were investigated by cryogenic nitrogen adsorption measurements.     

Synthesis and characterization of nanosized-silica gels formed under controlled conditions

Silica gel has been synthesized by the refluxing of rice husk ash with 1 M NaOH and subsequently adjusting the pH using 1 M H₂SO₄. The high purity of the silica gel has been found to be dependent on: (i) reflux time, (ii) water loading by addition of boiling DI water to the silica gel prior to titration with 1 M H₂SO₄ and (iii) rinse time on removal of impurities prior to drying. The surface area, pore size and volume of the silica gel were measured; XRD peaks of Na₂SO₄ impurity were absent after rinsing > 4 times. FTIR spectra showed that all the silica gels made by different schedules had a similar functional composition. The advantages of the present synthesis route are (i) a cost reduction due to the absence of pre-treatment for the rice husks before calcination below 700 °C, and (ii) the formation of a pure high surface area mesoporous amorphous silica gel.     

Structural characterization of carbon nanofibers formed from different carbon-containing gases

Catalytically grown carbon nanofibers, a novel mesoporous carbon material for catalysis, were synthesized by the decomposition of carbon-containing gases (CH₄, C₂H₄ or CO) over supported nickel-iron alloy and unsupported iron. It was shown that the structures of as-synthesized and modified CNFs, including the arrangement of the graphenes in CNF, and the crystallinity and texture of CNF depended on the catalyst composition and the type of carbon-containing gas. Three types of CNFs with different microstructures were obtained: platelet CNF (Fe–CO), fishbone CNF (supported Ni–Fe alloy-CH₄, C₂H₄ or CO) and tubular CNF (supported Ni–CO). All the CNFs were mesoporous carbon materials possessing relatively high surface areas (86.6–204.7 m²/g) and were highly graphitic. Purification with acid-base treatments or high temperature treatment removed the catalyst residue without changing the basic structures of the CNFs. However, annealing significantly decreased their surface areas through the formation of loop-shaped ends on the CNF surfaces. Oxidative modification in the gas and liquid phases changed the structures only slightly, except for oxidation in air at 700 °C. The structures and textures were studied using SEM, TEM, XRD, BET and TGA.     

Preparation and characterization of a graphite electrode containing carbon nanotubes grown in situ by flame synthesis

A crystalline flake graphite electrode (GE) was impregnated with nickel particles using direct current electrochemical deposition. The particles were used for in situ growth of carbon nanotubes (CNTs) by flame synthesis with a liquid ethanol flame. The obtained electrode was characterized by X-ray diffraction, and scanning and transmission electron microscopy. The results showed that the deposited Ni catalyst crystal face was mainly (1 1 1). CNTs with a diameter of about 40 nm were uniformly grown on the GE surface. The electrochemical performance of the CNT–GE was characterized by cyclic voltammetry using a [Fe(CN)6]³⁻/[Fe(CN)6]⁴⁻ solution, and showed a much greater electrochemical response than that obtained using a material in which CNTs were grown by catalytic chemical vapor deposition.     

固相法合成纳米氧化锌

以Zn(NO3)2·6H2O和Na2C2O4为原料,先通过室温固相化学反应合成出前驱体ZnC2O4·2H2O再将前驱体在400℃热分解3h,得到产物纳米氧化锌。借助XRD和TEM等技术对产物进行了表征。结果表明,产物纳米氧化锌为粒度分布均匀的球形六方晶系结构,平均粒径约为14nm。     

电化学沉淀法制备纳米氧化镁粉体及表征

利用阴离子交换膜为隔膜的电解槽，在不添加分散剂的情况下，控制阴极的电流密度在50-500A／m^2范围内，在电解氯化镁溶液过程中，阴极表面形成有利于氢氧化镁均匀沉淀的过饱和环境，得到单分散纳米氢氧化镁沉淀，在不同温度下进行焙烧2h，得到不同粒度的超细氧化镁颗粒，用TEM和XRD分析表明：阴极的电流密度不同，可以得到不同形貌的氧化镁粉体，并对其制备及形成机理进行了初步的探讨。     

微波CVD法制备碳纳米球及结构表征

以甲烷为碳源气体,在不使用催化剂的条件下采用微波化学气相沉积法合成了直径为50nm左右的碳纳米球。采用X射线衍射仪、场发射扫描电镜、高分辨透射电镜和拉曼光谱等手段对碳纳米球的形貌与结构进行观察和分析。实验结果表明,本实验所合成的碳纳米球具有较高的纯度,碳球为实心结构,由围绕着中心排列组成的未闭合的石墨层构成。并结合实验结果对碳纳米球的生长机理进行了探讨。