Zinc Titanate Nanofibers for the Detoxification of Chemical Warfare Simulants

Fabrication of a novel ceramic nanofiber system viz. zinc titanate using the well-known electrospinning technology with polyvinylpyrrolidone as a binder is reported. Use of zinc titanates as reactive sorbents to detoxify chemical warfare agents is hypothesized and proved. The zinc titanate nanofibers are tested against simulants of nerve and mustard agents and show satisfactory destructive activity. The extent of detoxification is measured using GC-MS analysis. The products of reaction of zinc titanate against the simulants are identified and are found to be relatively harmless. The possibility of replacement of conventional-activated carbon by electrospun ceramic nanofibers for face masks and protective clothing is proposed.     

Comparison Between Carbon Nanotube and Carbon Nanofiber Reinforcements in Amorphous Silicon Nitride Coatings

Amorphous silicon nitride coatings were reinforced with carbon nanotubes and dense carbon nanofibers. These reinforcements were all fabricated with graphene layers oriented parallel to the fiber axis, and some of the nanofibers were also heat-treated at high temperature to improve graphitic ordering. The effectiveness of these reinforcements as toughening agents was then compared qualitatively by examining the fiber pull out lengths from fracture surfaces. With the dense nanofibers there was almost no evidence of pull-out, whereas the materials reinforced with multiwalled carbon nanotubes exhibited significant pull-out. Based on these results, the multiwalled carbon nanotubes appear to provide significantly more toughening than the dense nanofibers.     

Sorption of petroleum products by carbon sorbents

A comparative study of the adsorption of petroleum products by micro- and macroporous carbon sorbents was performed. For this purpose, four carbon sorbent samples prepared from various raw materials by various processing techniques were used. The pore structures and adsorption capacities of these sorbents for petroleum products were studied. It was found that the adsorption of petroleum products on porous and nonporous carbon sorbents occurred in different manners. In this case, macroporous sorbents with a weakly developed structure of sorbing micro- and mesopores exhibited a maximum capacity for petroleum products.     

Structural analysis of conical carbon nanofibers

Conical carbon nanofibers are a relatively new type of carbon nanomaterial that has received considerable scientific and commercial interest due to its physical properties. However, its structure and growth mechanism have still not been determined conclusively. In this study the structure of these materials was investigated employing molecular models and structural analyses and compared with reported experimental observations, principally of cone apex angles. The results showed that stacked cone models could not explain the wide variety of apex angles observed for these nanofibers and related structures. Cone-helix models, originally proposed for other carbon conical structures, allow a variety of apex angle structures and were found to be applicable for nanofibers as well. An equation was developed that allows for prediction of cone-helix structures with good graphitic alignment. Such structures were also shown to be more compatible with the physical properties and growth mechanism of nanofibers than stacked cone structures. From these results a cone-helix structure, and a new cone-helical growth mechanism for the nanofibers based on heterogeneous nucleation on conical catalyst particles, are proposed.     

Consolidation of carbon nanofibers with pyrolytic carbon

A strategy of industrial-scale manufacture for a wide range of carbon materials based on carbon nanofibers is proposed. It was shown that porous materials with a high sorption capacity can be obtained with the use of carbon nanofibers by means of conventional manufacturing operations. The results of studying of consolidation of carbon nanofibers with pyrolytic carbon are reported. It was found that the nature of carbon material has a substantial effect on the rate of deposition of pyrolytic carbon. The most appropriate temperature range in which carbon nanofibers should be consolidated for the preparation of materials with a high catalytic activity was determined.     

The effect of graphitic platelet orientation on the properties of carbon nanofiber supported Pd catalysts prepared by ion exchange

Carbon nanofibers with different nanostructures are prepared by catalytic CVD at 873 K using different catalysts and carbon-containing gases. As-grown carbon nanofibers are treated in concentrated nitric acid to introduce oxygen-containing groups, and therefore, to anchor palladium. The TPD-MS method is used to determine the number of acidic oxygen-containing groups and the results show that the number of oxygen-containing groups was strongly dependent on the graphitic platelet orientation. TEM, CO pulse chemisorption, and ICP-AES are used to characterize carbon nanofiber supported palladium catalysts. The results show that palladium particle sizes and palladium loading are dependent on the amounts of oxygen-containing groups on carbon nanofibers. TPR results show that the interaction between the palladium and the oxidized carbon nanofibers can be tailored by the variation of graphitic platelet orientation. A linear correlation between the amount of acidic groups and the palladium loading are observed.     

Isotactic polypropylene–vapor grown carbon nanofibers composites: Electrical properties

Nanocomposites have been obtained by dispersing various amounts of vapor grown carbon nanofibers within isotactic polypropylene. Thermal investigations done by differential scanning calorimetry and dynamic mechanical analysis revealed the effect of the vapor grown carbon nanofibers on the melting, crystallization, α, and β relaxations. Direct current electrical features of these nanocomposites have been investigated and related to the thermal features of these nanocomposites. The effect of the loading with carbon nanofibers on the electrical properties of these nanocomposites is discussed within the percolation theory. The percolation threshold was estimated at about 5.5% wt carbon nanofibers. The temperature dependence of the direct current conductivity is analyzed in detail and it is concluded that the electronic hopping is the dominant transport mechanism. A transition from one‐dimensional hopping towards a three‐dimensional hopping was noticed as the concentration of carbon nanofibers was increased from 10% wt to 20% wt carbon nanofiber. The possibility of a differential negative resistivity is suggested. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45297.     

Preparation, characterization and growth mechanism of platelet carbon nanofibers

The synthesis of platelet carbon nanofibers (PCNFs) on a silicon substrate using chemical vapor deposition method is reported. Scanning electron microscope, high-resolution transmission electron microscopy, and Raman spectroscopy were used to characterize the nanofibers. It is found that these platelet nanofibers are of the order of 10 μm long, and most have a nearly rectangular transverse section with several hundreds nm wide and several tens of nm thick. Structure analysis reveals that the carbon layers of platelet nanofibers are parallel to each other, and have a uniform (0 0 2) orientation that is perpendicular to the fiber axis. Many faults and nanodomain have been found in the nanofibers. It is suggested that the PCNF grow in tip growth mechanism by the precipitation of carbon from the side facet of catalyst flakes.     

Growth of Y-shaped Carbon Nanofibers from Ethanol Flames

Y-shaped carbon nanofibers as a multi-branched carbon nanostructure have potential applications in electronic devices. In this article, we report that several types of Y-shaped carbon nanofibers are obtained from ethanol flames. These Y-shaped carbon nanofibers have different morphologies. According to our experimental results, the growth mechanism of Y-shaped carbon nanofibers has been discussed and a possible growth model of Y-shaped carbon nanofibers has been proposed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Preparation of carbon nanofibers/carbon foam monolithic composite from coal liquefaction residue

Carbon nanofibers/carbon foam composites that are made by growing carbon nanofibers (CNFs) on the surface of a carbon foam (CF) have been prepared from coal liquefaction residues (CLR) by a procedure involving supercritical foaming, oxidization, carbonization, and catalytic chemical vapour deposition (CCVD) treatment. These new carbon/carbon composites were examined using SEM, TEM and XRD. The results show that the as-made CF has a structure with cell sizes of 300-600 μm. X-ray diffraction studies show that iron-containing contaminates are present in the CLR. However, these species may act as a catalyst in the CCVD process as established in the literature. After the CCVD treatment, the cell walls of CF are covered by highly compacted CNFs that have external diameters of about 100 nm and lengths of several tens of micrometers. This work may open a new way for direct and effective utilization of the CLR.     

Bamboo-shaped carbon nanofibers obtained in pyrolytic carbon by thermal gradient chemical vapor deposition

Bamboo-shaped carbon nanofibers were obtained in pyrolytic carbon fabricated by thermal gradient chemical vapor deposition and their micro-and nanostructure were examined by transmission and scanning electron microscopy. The results showed that, bamboo-shaped nanofibers with diameters from a few tens to about 250 nm were distributed homogeneously in the pyrolytic carbon. The nanofibers could be pulled out of the pyrolytic carbon when they were fractured.     

蜡梅花头香的富集及其化学成分研究

用顶空和不同吸附剂吸附法收集蜡梅花的头香,并用GC-MS法对其进行了化学成分研究。对比了不同吸附剂在相同条件下对蜡梅花头香的吸附量与吸附成分。结果表明,不同吸附剂吸附的头香量和化学成分不同。大孔树脂的吸附量是0.22 g,且不具有蜡梅花香味,是自身分解物;阳离子交换树脂、凹凸棒石、活性炭、分子筛吸附量分别是0.52、0.42、0.26、0.29 g,检测出的化学成分种类分别是27、24、12、10种,且与蜡梅花的香味相似;后4种吸附剂所吸附的头香总成分约39种。凹凸棒石和阳离子交换树脂是蜡梅花头香成分的适宜吸附剂。     

Carbon sorbents from waste crumb tires

The applicability of wastes from the chemical utilization of automobile tires as a raw material for the manufacture of carbon sorbents was studied. The thermogravimetric analysis of the thermal degradation of this raw material was performed; the proximate and ultimate analyses were carried out, and a process for the manufacture of crushed and granulated sorbents was developed. The formation of the structural and adsorptive properties of carbon sorbents based on waste crumb tires was studied. It was found that the sorbents were characterized by low and high sorption capacities for substances from aqueous solutions and saturated vapors, respectively. This phenomenon can be explained by the pore structure peculiarities of sorbents from waste crumb tires, which contained supermesopores that turned into capillaries; they are responsible for an entirely different mechanism of absorption: the capillary condensation of vapors.     

New carbon sorbents

The formation of the structural and absorption properties of carbon sorbents based on various carbon-containing materials was studied. Carbon sorbents and catalysts on carbon supports with a wide range of physicochemical properties and structural parameters were prepared and tested in air separation, natural gas-gasoline processing, direct oxidative degradation of hydrogen sulfide, and the recovery of noble metals from solutions and pulps. It was found that the targetoriented synthesis of a pore structure makes it possible to obtain carbon sorbents and catalysts on carbon supports, which are effective in gas decomposition, gas mixture separation, and the recovery of valuable components from liquid media.     

Electrochemical stability of carbon nanofibers in proton exchange membrane fuel cells

This fundamental study deals with the electrochemical stability of several non-conventional carbon based catalyst supports, intended for low temperature proton exchange membrane fuel cell (PEMFC) cathodes. Electrochemical surface oxidation of raw and functionalized carbon nanofibers, and carbon black for comparison, was studied following a potential step treatment at 25.0 °C in acid electrolyte, which mimics the operating conditions of low temperature PEMFCs. Surface oxidation was characterized using cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Cyclic voltammograms clearly showed the presence of the hydroquinone/quinone couple. Furthermore, identification of carbonyl, ether, hydroxyl and carboxyl surface functional groups were made by deconvolution of the XPS spectra. The relative increase in surface oxides on carbon nanofibers during the electrochemical oxidation treatment is significantly smaller than that on carbon black. This suggests that carbon nanofibers are more resistant to the electrochemical corrosion than carbon black under the experimental conditions used in this work. This behaviour could be attributed to the differences found in the microstructure of both kinds of carbons. According to these results, carbon nanofibers possess a high potential as catalyst support to increase the durability of catalysts used in low temperature PEMFC applications.     

Fabrication and Thermal Dissipation Properties of Carbon Nanofibers Derived from Electrospun Poly(Amic Acid) Carboxylate Salt Nanofibers

Polyimides (PIs) possess excellent mechanical properties, thermal stability, and chemical resistance and can be converted to carbon materials by thermal carbonization. The preparation of carbon nanomaterials by carbonizing PI‐based nanomaterials, however, has been less studied. In this work, the fabrication of PI nanofibers is investigated using electrospinning and their transformation to carbon nanofibers. Poly(amic acid) carboxylate salts (PAASs) solutions are first electrospun to form PAAS nanofibers. After the imidization and carbonization processes, PI and carbon nanofibers can then be obtained, respectively. The Raman spectra reveal that the carbon nanofibers are partially graphitized by the carbonization process. The diameters of the PI nanofibers are observed to be smaller than those of the PAAS nanofibers because of the formation of the more densely packed structures after the imidization processes; the diameters of the carbon nanofibers remain similar to those of the PI nanofibers after the carbonization process. The thermal dissipation behaviors of the PI and carbon nanofibers are also examined. The infrared images indicate that the transfer rates of thermal energy for the carbon nanofibers are higher than those for the PI nanofibers, due to the better thermal conductivity of carbon caused by the covalent sp² bonding between carbon atoms.     

Field emission and structure of aligned carbon nanofibers deposited by ECR-CVD plasma method

Aligned carbon nanofibers and hollow carbon nanofibers were grown by MW ECR-CVD method using methane and argon mixture gas at a temperature of 550°C. The carbon nanofibers and the hollow carbon nanofibers were deposited perpendicularly on Si substrates and on Si substrates coated with Ni catalyst, respectively. From TEM analysis the diameter and length of the nanofibers are approximately 60 nm and 15 μm, respectively. Raman spectra of these aligned carbon nanofibers showed new bands of 1340 and 1612 cm⁻¹ of the first-order Raman scattering and 2660, 2940 and 3220 cm⁻¹ of the second-order Raman scattering. The second-order Raman scattering bands were assigned to two overtone and one combination bands on the basis of a similar assignment of micro-crystal graphite by Nemanich and Solin. By the measurement of XPS C1s band energies of 284.6 eV for the carbon nanofiber and 284.7 eV for the hollow carbon nanofiber indicate mainly sp² carbon component in the inclusion of a small amount (<5%) of oxygen in a high binding energy region (∼288 eV). Field emission characteristics of the well-aligned carbon nanofibers and hollow carbon nanofibers were investigated and the current densities were 7.25 and 0.69 mA/cm² at 12.5 V/μm, respectively.     

Fabrication and characterization of carbon nanofibers with a multiple tubular porous structure via electrospinning

Carbon nanofibers with a multiple tubular porous structure were prepared via electrospinning from a polymer blend solution of polyacrylonitrile (PAN) and polylactide (PLA) followed by carbonization. The electrospun composite nanofibers underwent pre-oxidization and carbonization, which selectively eliminated PLA phases and transformed the continuous PAN phase into carbon, thereby porous structure formed in the carbon nanofibers. The morphologies of as-spun, pre-oxidized and carbonized nanofibers were studied by scanning electron microscope (SEM) and transmission electron microscopy (TEM). It was found that carbon nanofibers with an average diameter about 250 nm and a multiple tubular porous structure were obtained. The chemical changes during thermal treatment were studied by Fourier transform infrared spectrometer (FTIR), Raman spectra, differential thermal analysis (DTA) and thermogravimetric analysis (TG). The results showed that PLA phases were effectively removed and the continuous PAN phase was completely carbonized. The obtained carbon nanofibers had more disordered non-graphitized structures than non-porous nanofibers.     

Growth of carbon nanofibers on activated carbon fiber fabrics

Activated carbon fiber fabrics, an excellent adsorbent, were used as catalyst supports to grow carbon nanofibers. Because of the microporous structure of the activated carbon fibers, the catalysts could be distributed uniformly on the carbon surface. Based on this concept, the carbon nanofibers can be grown directly on the activated carbon fiber fabrics. We demonstrate that carbon nanofibers with a diameter between 20 and 50 nm for most of the fibers can be synthesized uniformly and densely on activated carbon fiber fabrics, impregnated by nickel nitrate catalyst precursor, using catalytic chemical vapor deposition. Although the carbon nanofibers are not straight with a crooked morphology, they form a three-dimensional network structure. Structure characterizations by TEM and XRD indicate that the carbon nanofibers have a turbostratic graphite structure and the graphite layers are stacked with a herringbone structure.     

Preparation of carbon nanofibers from electrocracking gas on an iron oxide catalyst

The results of studies on the preparation of carbon nanofibers from electrocracking gas (obtained by the decomposition of a diesel fraction (180–350°C) in electric discharges) on an iron oxide catalyst are presented. The effect of synthesis conditions on the yield and characteristics of the resulting nanofibers was demonstrated.