Effects of carbon nanofiber composites on electrode processes involving liquid|liquid ion transfer

Composite electrodes were prepared from chemical vapor deposition grown carbon nanofibers consisting predominantly of ca. 100 nm diameter fibers. A hydrophobic sol–gel matrix based on a methyl-trimethoxysilane precursor was employed and composites formed with carbon nanofiber or carbon nanofiber—carbon particle mixtures (carbon ceramic electrode). Scanning electron microscopy images and electrochemical measurements show that the composite materials exhibit high surface area with some degree of electrolyte solution penetration into the electrode. These electrodes were modified with redox probe solution in 2-nitrophenyloctylether. A second type of composite electrode was prepared by simple pasting of carbon nanofibers and the same solution (carbon paste electrode). For both types of electrodes it is shown that high surface area carbon nanofibers dominate the electrode process and enhance voltammetric currents for the transfer of anions at liquid|liquid phase boundaries presumably by extending the triple-phase boundary. Both anion insertion and cation expulsion processes were observed driven by the electro-oxidation of decamethylferrocene within the organic phase. A stronger current response is observed for the more hydrophobic anions like ClO₄⁻ or PF₆⁻ when compared to that for the more hydrophilic anions like F⁻ and SO₄²⁻. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005     

Carbon nanofiber vs. carbon microparticles as modifiers of glassy carbon and gold electrodes applied in electrochemical sensing of NADH

Carbon materials (CMs), such as carbon nanotubes (CNTs), carbon nanofibers (CNFs), and carbon microparticles (CMPs) are used as doping materials for electrochemical sensors. The efficiency of these materials (either before or after acidic treatments) while being used as electrocatalysts in electrochemical sensors is discussed for β-nicotinamide adenine dinucleotide (NADH) detection using cyclic voltammetry (CV). The sensitivity of the electrodes (glassy carbon (GC) and gold (Au)) modified with both treated and untreated materials have been deeply studied. The response efficiencies of the GC and Au electrodes modified with CNF and CMP, using dimethylformamide (DMF) as dispersing agent are significantly different due to the peculiar physical and chemical characteristics of each doping material. Several differences between the electrocatalytic activities of CMs modified electrodes upon NADH oxidation have been observed. The CNF film promotes better the electron transfer of NADH minimizing the oxidation potential at +0.352 V. Moreover higher currents for the NADH oxidation peak have been observed for these electrodes. The shown differences in the electrochemical reactivities of CNF and CMP modified electrodes should be with interest for future applications in biosensors.     

泡沫镍及负载型镍催化剂制备纳米碳纤维层的研究

纳米碳纤维可用在催化材料、储氢材料、及纳米电子器件等方面。本文对用泡沫镍及负载型镍催化剂催化分解乙烯或丙烯制备纳米碳纤维进行了研究。利用X射线衍射仪、物理吸附仪、扫描电镜进行了分析表征,并考察了催化剂、碳源、生长温度对纳米碳纤维生长量、形貌、结构的影响。结果表明:在生长温度450℃,乙烯流率30mL/m in的条件下,负载型镍催化剂纳米碳纤维的生长量要高出泡沫镍3~6倍,负载型镍催化剂制备的纳米碳纤维直径为40~60纳米,小于泡沫镍的情况。泡沫镍催化分解乙烯制备纳米碳纤维时,纳米碳纤维的生长量和平均直径随温度的降低而逐渐减小。纳米碳纤维在泡沫镍上的最低生长温度为420℃,在低于480℃生长纳米碳纤维时泡沫镍的骨架结构不会被破坏,由此制备的纳米碳纤维在新型结构催化材料中有很好的的应用前景。     

Rheological and electrical analysis in carbon nanofiber reinforced polypropylene composites

Two different types of carbon nanofibers (CNF) were incorporated in the same polypropylene (PP) matrix by twin‐screw extrusion. The electrical characterization of both CNFs/PP composites as a function of volume fraction show different electrical performance: conducting and nonconducting. The objective of this work is to study the rheological behavior of both composites with the aim of relating it to the electrical behavior. The results indicate that the rheological behaviors are different, suggesting that rheology differentiates the microstructural variations responsible for the electrical performance. Furthermore, the main rheological parameters were correlated to the electrical conductivity. The results show that G′/G″ and G′ are the most sensitive parameters when compared with the onset of electrical percolation. Finally, in spite of the intrinsic measuring differences between electrical and rheological analysis, the two calculated thresholds are very similar: ～0.5 for the rheological and ～0.4 for the electrical. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Preparation and Cytotoxicity of Novel Aliphatic Polycarbonate Synthesized from Dihydroxyacetone

A new cyclic carbonate, 2,2-ethylenedioxypropane-l,3-diol carbonate (EOPDC), was synthesized through a two-step reaction from dihydroxyacetone dimer, and polymerized in bulk initiated by Sn(Oct)2 to give a high molecular weight polycarbonate. The structure of monomer and the polymer were characterized by FT-1R, ^1H NMR, ^13C NMR. The cytotoxicity of the obtained polycarbonate was investigated by MTT assay.     

Magnetic responsive polymer nanofiber composites for easy collecting chemical spills

We describe a simple method to prepare magnetic responsive polydivinylbenzene(PDVB)nanofiber composites by precipitated cationic living polymerization in the present of oleic acid capped Fe3O4 nanoparticles(NPs).The Fe3O4 NPs are encapsulated with the PDVB forming dendrites,from which thin nanofibers are grown in the tip-growth mode.The thin nanofibers are interwoven with the thick nanofibers forming robust composite network.The composites are magnetic responsive and highly efficient to gel almost all chemicals.Separation of the gelled chemicals from water becomes easier with a magnet.The performance is promising for magnetic collection of chemical spills.     

Functionalization of multi-walled carbon nanotubes by epoxide ring-opening polymerization

In this study, covalent functionalization of carbon nanotubes (CNTs) was accomplished by surface-initiated epoxide ring-opening polymerization. FT-IR spectra showed that polyether and epoxide group covalently attached to the sidewalls of CNTs. TGA results indicated that the polyether was successfully grown from the CNT surface, with the final products having a polymer weight percentage of ca. 14-74 wt%. The O/C ratio of CNTs increased significantly from 5.1% to 29.8% after surface functionalization of CNTs. SEM and TEM images of functionalized CNTs exhibited that the tubes were enwrapped by polymer chains with thickness of several nanometers, forming core-shell structures with CNTs at the center.     

Smart synthesis of silver nanoparticles supported in porous polybenzoxazine nanocomposites via a main-chain type benzoxazine resin

Novel silver nanoparticles immobilized on macroporous polybenzoxazine nanocomposites were prepared as catalysts for catalytic reduction reaction.     

聚碳酸酯合成工艺开发的新进展

本文从工艺开发的角度，简要评介了目前聚碳酸酯两大工业生产工艺，即光气化界面缩聚工艺和熔融酯交换缩聚工艺的研究开发新动向。     

Epoxy/amine‐functionalized short‐length vapor‐grown carbon nanofiber composites

Short length vapor‐grown carbon nanofibers (VGCNFs) were functionalized with 4‐aminobenzoic acid in polyphosphoric acid/phosphorous phentoxide medium via “direct” Friedel‐Crafts acylation reaction to afford aminobenzoyl‐functionalized VGCNFs (AF‐VGCNFs). The AF‐VGCNFs as a cocuring agent were mixed with epoxy resin by simple mechanical stirring in methanol which was added to help efficient mixing. After evaporation of methanol, 4,4′‐methylenedianiline as a curing agent was added to the mixture, which was then cured at elevated temperatures. The resultant composites displayed uniform dispersion of AF‐VGCNFs into cured epoxy matrix. During curing process, the amine functionalities on AF‐VGCNF together with 4,4′‐methylenedianiline were expected to be involved in covalent attachment to the epoxy resin. As a result, both tensile modulus and strength of the composites were improved when compared with those of pure epoxy resin. Thus, the AF‐VGCNFs play a role as an outstanding functional additive, which could resolve both dispersion and interfacial adhesion issues at the same time by functionalization of VGCNFs and covalent bonding between the additive and matrix, respectively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7473–7482, 2008     

The direct architecture of carbon fiber‐carbon nanofiber hierarchical reinforcements for superior interfacial properties of CF/epoxy composites

A simple and efficient chemical method was developed to graft directly carbon nanofibers (CNFs) onto carbon fiber (CF) surface to construct a CF‐CNF hierarchical reinforcing structure. The grafted CF reinforcements via covalent ester linkage at low temperature without any usage of dendrimer or catalyst was investigated by FTIR, X‐ray photoelectron spectroscopy, Raman, scanning electron microscopy, atomic force microscopy, dynamic contact angle analysis, and single fiber tensile testing. The results indicated that the CNFs with high density could effectively increase the polarity, wettability, and roughness of the CF surface. Simultaneous enhancements of the interfacial shear strength, flexural strength, and dynamic mechanical properties as well as the tensile strength of CFs were achieved, for an increase of 75.8%, 21.9%, 21.7%, and 0.5%, respectively. We believe the facile and effective method may provide a novel and promising interface design strategy for next‐generation advanced composite structures.     

Coating of multiwalled carbon nanotubes with polymer nanospheres through microemulsion polymerization

We report a simple and noncovalent method for coating multiwalled carbon nanotubes (MWCNTs) with polyaniline (PANI) nanospheres using a microemulsion polymerization method. In this method, aniline polymerization is performed with MWCNTs in the presence of sodium dodecyl sulfate (SDS), which serves as both a surfactant and a dopant. Morphological, structural, thermal, and electrical properties of MWCNT–PANI nanocomposites were analyzed. The TEM results of the nanocomposites prepared with surfactant reveal that 30–50-nm-diameter PANI nanospheres were coated on the surface of the MWCNTs. Composites prepared without surfactant were found to be in core–sheath-type cable structures. The conductivities of the nanocomposites synthesized through microemulsion polymerization were found to be one order of magnitude higher than both the conductivities of pure PANI and the composites prepared via in situ chemical polymerization without an assisting SDS surfactant. The mechanism for the formation of nanostructured composites is presented.     

Polymer/carbon nanotube nanocomposites: Influence of carbon nanotubes on EVA photodegradation

The influence of carbon nanotubes on the photodegradation of EVA/carbon nanotube nanocomposites was studied by irradiation under photooxidative conditions (at λ > 300 nm, at 60 °C and in the presence of oxygen). The influence of the nanotubes on both the photooxidation mechanism of EVA and the rates of oxidation of the matrix was characterized on the basis of infrared analysis. On one hand, it was shown that the carbon nanotubes act as inner filters and antioxidants, which contribute to reduction in the rate of photooxidation of the polymeric matrix. On the other hand, it was shown that light absorption could provoke an increase in the local temperature and then induce the photooxidation of the polymer. The competition between these three effects determines the global rate of photooxidation of the polymeric matrix. Several factors are involved, the concentration of the carbon nanotubes, the morphology of the nanotubes and the functionalization of the nanotube surface.     

Study of the thermal properties of polyester composites loaded with oriented carbon nanofibers using the front-face flash method

In this work, we have prepared polyester resin based composites, loaded with carbon nanofibers decorated with magnetite nanoparticles (m-CNF) in several volumetric concentrations covering from 0 to 3.25% and oriented applying a constant magnetic field before polymerization. A study of the heat transfer along the direction of the alignment of the fibers was performed by measuring the in-depth thermal diffusivity and thermal effusivity using the laser flash method in the front-face configuration. For the maximum volumetric concentration of aligned nanofibers along the thickness of the sample, an improvement of 80% of the thermal conductivity above the thermal conductivity of the polyester resin was observed. In contrast, the increment of the thermal conductivity was only of 20% above the value of the matrix for samples with non-oriented carbon nanofibers. The effects of the m-CNF and their orientation on the effective thermal conductivity of the composites were analyzed using a simple theoretical model, which takes into account the thermal mismatch between the matrix and the fillers, as well as the aspect ratio of the embedded fibers.     

Towards the development of self-healing carbon/epoxy composites with improved potential provided by efficient encapsulation of healing agents in core-shell nanofibers

A self-healing carbon/epoxy composite was fabricated with the incorporation of healing agent loaded core-shell nanofibers between carbon fiber fabric layers. The healing agents, consisting of two components, a low viscosity epoxy resin and its amine-based curing agent, were encapsulated in Styrene acrylonitrile (SAN) nanofibers via a coaxial electrospinning method. Transmission electron microscope (TEM), Fourier Transform Infrared (FTIR), and thermogravimetric analysis (TGA) results confirmed the successful encapsulation of both epoxy and curing agent in SAN nanofiber shells. TGA and the extraction method confirmed a high encapsulation yield (90% for the epoxy resin and 97% for the curing agent). Mechanical studies of the hybrid composite showed that embedding the fabricated core-shell nanofibers did not lead to a reduction in the mechanical properties of host composite, which was corroborated with statistical analysis. Mechanical evaluations and curing behavior studies both showed that incorporation of the aforementioned nanofibers between carbon layers can imbue the conventional carbon/epoxy composite with a self-healing ability, allowing it to repair itself to restore its mechanical properties for up to three cycles at room temperature in absent of any external driving force.     

基于氧化锌/碳纳米纤维材料的氧氟沙星电化学传感器的构建及应用

通过静电纺丝技术合成碳纳米纤维,以循环伏安法在此碳纤维上电聚合乙酸锌制备复合纳米材料作为一种新型的电化学增敏剂,用于修饰玻碳电极,开发了一种基于碳纤维和氧化锌复合材料的新型电化学传感器(ZnO/CNF/GCE)。使用循环伏安法、差分脉冲伏安法等进行电化学催化性能的研究,并优化实验条件。结果表明,与裸电极相比,在pH 5.5磷酸盐缓冲溶液中,ZnO/CNF/GCE修饰电极能使氧氟沙星的峰电流明显提升,线性范围1~200μmol/L,检测限为0.33μmol/L。该ZnO/CNF/GCE修饰电极已用于氧氟沙星滴耳液中氧氟沙星的含量测定。     

Polyethylene thermal oxidative stabilisation in carbon nanotubes based nanocomposites

Multiwall carbon nanotubes (MWNT)/linear low density polyethylene (LLDPE) nanocomposites were studied in order to understand the stabilisation mechanism for their thermal and oxidative degradation. Thermogravimetry coupled with infrared evolved gas analysis and pyrolysis gas chromatography-mass spectrometry demonstrate that MWNT presence slightly delays thermal volatilisation (15-20 °C) without modification of thermal degradation mechanism. Whereas thermal oxidative degradation in air is delayed by about 100 °C independently from MWNT concentration in the range used here (0.5-3.0 wt.%). The stabilisation is due to formation of a thin protective film of MWNT/carbon char composite generated on the surface of the nanocomposites is shown by SEM and ATR FTIR of degradation residues. The film formation mechanism is discussed.     

Carbon nanofiber supported palladium catalyst for liquid-phase reactions: An active and selective catalyst for hydrogenation of cinnamaldehyde into hydrocinnamaldehyde

Carbon nanofibers (CNFs) prepared by decomposition of ethane over a Ni/alumina catalyst, are used as support for palladium clusters. The carbon support displays a mean diameter of 40–50 nm, lengths up to several tens of micrometers, as highlighted by transmission electron microscopy (TEM) observations and a specific surface area of about 50 m²/g. The spheroidal palladium particles have a relatively homogeneous and sharp size distribution, centered at around 4 nm. This novel Pd/carbon nanofiber catalyst displays unusual catalytic properties and is successfully used in the selective hydrogenation of the C=C bond in cinnamaldehyde at a reaction temperature of around 80°C, under continuous hydrogen flowing at atmospheric pressure. The high performances of this novel catalyst in terms of efficiency and selectivity are, respectively, related to the inhibition of the mass-transfer processes over this non-porous material and to peculiar palladium–carbon interactions. It is concluded that the absence of microporosity in the carbon nanofibers favours both the high activity and selectivity which is confirmed by comparison with the commercially available high surface area charcoal supported palladium catalyst.     

Organocatalytic ring-opening polymerization of l-lactide in supercritical carbon dioxide under plasticizing conditions

The synthesis of poly-l-lactide (PLLA) in supercritical carbon dioxide (scCO₂) was accomplished using an organocatalyst. The reaction proceeded smoothly under CO₂ plasticizing polymerization (CPP) conditions at a lower temperature than those conventionally employed. This method allowed the formation of high-molecular-weight, pure PLLA, and therefore has the potential to reduce energy consumption and minimize production costs. Our method is non-toxic and efficient, affording a high-quality product while complying with volatile organic compound regulations. We can produce PLLA that meets the increasing standards (safety and high functionality) of the medical sector, while being applicable to full-scale industrial manufacturing and academic research.     

TGA analysis of polypropylene-carbon nanofibers composites

TGA investigations on the thermal degradation of isotactic polypropylene-vapor grown carbon nanofibers composites in nitrogen are reported. The mass evolution as a function of temperature is a single sigmoid for both polypropylene and polypropylene loaded with carbon nanofibers. The inflection temperature of these sigmoids increases as the concentration of carbon nanofibers is increased. The width of the degradation process narrows as the concentration of carbon nanofibers is increased due to a better homogenization of the local temperature provided by the high thermal conductivity of carbon nanofibers. Thermogravimetric analysis data indicate the formation of polymer-carbon nanofiber interface. Based on TGA data, a two-layer structure is proposed for carbon nanofibers-polypropylene interface. The external layer is soft and has a thickness of about 10² nm that confines most polymer molecules in interaction with nanofibers. The core layer is rigid and has a thickness of the order of few nanometers.