Study on electroactive and electrocatalytic surfaces of single walled carbon nanotube-modified electrodes

An investigation of the electrocatalysis of single-walled carbon nanotubes modified electrodes has been performed in this work. Nanotube-modified electrodes present a surface area much higher than the bare glassy carbon surfaces as determined by capacitance measurements. Several redox probes were selected for checking the reactivity of specific sites at the carbon nanotube surface. The presence of carbon nanotubes on the electrode improves the kinetics for all the reactions studied compared with the bare glassy carbon electrode with variations of the heterogeneous electron transfer rate constant up to 5 orders of magnitude. The most important effects are observed for the benzoquinone/hydroquinone and ferrocene/ferricinium redox couples, which show a remarkable improvement of their electron transfer kinetics on SWCNT-modified electrodes, probably due to strong π–π interaction between the organic molecules and the walls of the carbon nanotubes. For many of the reactions studied, less than 1% of the nanotube-modified electrode surface is transferring charge to species in solution. This result suggests that only nanotube tips are active sites for the electron transfer in such cases. On the contrary, the electroactive surface for the reactions of ferrocene and quinone is higher indicating that the electron transfer is produced also from the nanotube walls.     

Raman characterization of single wall carbon nanotubes prepared by the solar energy route

A Raman scattering characterization is reported that confirms the preparation of single wall carbon nanotubes (SWNT) by the solar energy route. The results are presented for samples synthesized with various catalysts—mixtures of Ni and Co (Y, La)—and compared to those obtained from electric arc discharge or laser ablation. In the light of the calculations of the vibrational spectra of SWNT by Eklund et al. (Carbon, 1995, 33, 959) it is shown that both the diameter and structure of the nanotubes depend strongly on the synthesis conditions. For the first time the presence of nanotubes with “zigzag” or “chiral” helical pitches for some of the samples are shown as well as a large distribution of tube diameters.     

Effects of thermal imidization on mechanical properties of poly(amide‐co‐imide)/multiwalled carbon nanotube composite films

In this study, experimental and numerical studies were performed to investigate the relationship among the functionalization method, weight fraction of MWCNTs, thermal imidization cycle, and mechanical properties of various PAI/MWCNT composite films. Poly(amide‐co‐imide)/multiwalled carbon nanotube composite films were prepared by solution mixing and film casting. The effects of chemical functionalization and weight fraction of multiwalled carbon nanotubes on thermal imidization and mechanical properties were investigated through experimental and numerical studies. The time needed to achieve sufficient thermal imidization was reduced with increasing multiwalled carbon nanotube content when compared with that of a pure poly(amide‐co‐imide) film because multiwalled carbon nanotubes have a higher thermal conductivity than pure poly(amide‐co‐imide) resin. Mechanical properties of pure poly(amide‐co‐imide) and poly(amide‐co‐imide)/multiwalled carbon nanotube composite films were increased with increasing imidization time and were improved significantly in the case of the composite film filled with hydrogen peroxide treated multiwalled carbon nanotubes. Both the tensile strength and strain to failure of the multiwalled carbon nanotube filled poly(amide‐co‐imide) film were increased substantially because multiwalled carbon nanotube dispersion was improved and covalent bonding was formed between multiwalled carbon nanotubes and poly(amide‐co‐imide) molecules. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

碳纳米管—一种新型纳米反应器

具有一维中空管结构的碳纳米管,可以用来填充各种物质。由于碳纳米管的限域作用,填充物在碳纳米管中具有新的结构和性质,其化学反应、相变等行为具有不同于常温常压状态下的特点。该文介绍了碳纳米管管内的化学反应的影响因素,反应类型和准高压效应,并总结出碳纳米管可作为一种新型纳米反应器合成不同材料,最后对这一领域的研究方向和应用进行了展望。     

Synthesis and characterization of multiwall carbon nanotube/waterborne polyurethane nanocomposites

The preparation of thermoplastic nanocomposites of waterborne polyurethane (WBPU) and multiwall carbon nanotubes (MWCNTs) via an in situ polymerization approach is presented. The effects of the presence and content of MWCNTs on the morphology and thermal, mechanical and electrical properties of the nanocomposites were investigated. Carbon nanotubes were modified with amide groups in order to enhance their chemical affinity towards WBPU. Thermogravimetric studies show enhanced thermal stability of the nanocomposites. Scanning and transmission electronic microscopy images prove that functionalized carbon nanotubes can be effectively dispersed in WBPU matrix. Mechanical properties reveal that Young's modulus and tensile strength tend to increase when appropriate amounts of MWCNTs are loaded due to the reinforcing effect of the functionalized carbon nanotubes. Thermal properties show an increase in the glass transition temperature and storage modulus with an increase in MWCNT content. X‐ray diffraction reveals better crystallization of the WBPU in the presence of MWCNTs. The WBPU/MWCNT nanocomposite film containing 1 wt% of MWCNTs exhibits a conductivity nearly five orders of magnitude higher than that of WBPU film. © 2017 Society of Chemical Industry     

Modeling of chemical kinetics of elastomer/hydroxyl‐ and carboxyl‐functionalized multiwalled carbon nanotubes nanocomposites' cross‐linking

Several kinds of (hydrogenated) nitrile elastomer ((H)NBR) compounds were prepared by melt compounding of rubbers with carbon nanotubes. Transmission electron microscopy (TEM) showed that the exfoliation degree of nanotubes was high. Multiwalled carbon nanotubes (MWCNT) were either neat or modified by hydroxyl or carboxyl groups. Morphology was also characterized by scanning electron microscopy (SEM). The cure kinetics of (H)NBR and modified multiwalled carbon nanotubes ((m‐)MWCNT/(H)NBR) nanocomposites was studied. It was found that the apparent curing and over‐cure activation energies (E_A and E_A,1) increased with the increasing amount of (m‐)MWCNT. There was a less obvious change in the apparent orders of curing reactions. The results of n‐th order and autocatalytic kinetic model showed that any studied content of (m‐)MWCNT could increase effective thermal conductivity, but decreased the vulcanization rate of (m‐)MWCNT/(H)NBR nanocomposites. Finally, the effect of (m‐)MWCNT content and functionalization on tensile mechanical properties was presented. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Grafting polyamide 6 onto multi‐walled carbon nanotubes using microwave irradiation

Chemical reactions under microwave irradiation can be very efficient, with a significant shortening of reaction time. Few studies have reported the use of microwaves to functionalize carbon nanotubes. In the work reported, a new method of formulating functionalized multi‐walled carbon nanotubes (MWNTs) was developed by covalent grafting of polyamide 6 (PA6) chains onto the carbon nanotubes assisted by microwave irradiation. PA6 chains were grafted onto acidified MWNTs through condensation reaction between the carboxylic groups of the MWNTs and the terminal amine groups of PA6 using microwave radiation heating. The functionalized carbon nanotubes (MWNT‐g‐PA6) were characterized systematically using infrared and Raman spectroscopy, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). TEM showed that the surface of the MWNTs was covered with a layer of PA6. TGA results indicated that the MWNT‐g‐PA6 contained about 47 wt% of polymer. A novel, convenient and efficient functionalization approach is reported, involving covalently grafting PA6 chains onto MWNTs assisted by microwave irradiation. Copyright © 2010 Society of Chemical Industry     

Luminescent short thiol-functionalized multi-wall carbon nanotubes

Luminescent short thiol-functionalized multi-wall carbon nanotubes (mean length 100-200 nm) were produced by the reaction between 2-aminoethanethiol molecules and oxidized carbon nanotubes with the aid of a coupling agent in ethanol. After the reactions stop the carbon nanotubes suspension was purified and filtered to separate the shorter carbon nanotubes. The short length carbon nanotubes fraction exhibits an intense luminescence visible to the naked eye. The maximum of the luminescence band and its intensity strongly depends on the excitation wavelength. The sample chemistry and morphology were characterized by means of X-ray photoelectron spectroscopy and scanning electron microscopy.     

Study on the performance of syntactic foam reinforced by hybrid functionalized carbon nanotubes

Hollow glass microspheres (HGMs)/epoxy syntactic foam were reinforced by hybrid functionalized carbon nanotubes that were synthesized by simultaneous covalent and noncovalent functionalization of carbon nanotubes. The effect of hybrid functionalized carbon nanotubes on density, mechanical properties, and water absorption of HGMs/epoxy syntactic foam was studied. The study indicated that the dispersion of carbon nanotubes in epoxy resin can be improved by hybrid functionalization. The compression strength of syntactic foam reinforced by hybrid functionalized carbon nanotubes was significantly enhanced. The maximum compressive strength of syntactic foam corresponding to chitosan modified carbon nanotubes approached 60 MPa. Hybrid functionalized carbon nanotubes had little effect on the water absorption ability of syntactic foam, and was less than 1%. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48586.     

Synthesis of branched carbon nanotubes using copper catalysts in a hydrogen-filled DC arc-discharger

Branched multi-walled carbon nanotubes (b-CNTs) were deposited in a collar around the cathode in a DC arc-discharger in the presence of hydrogen and copper catalysts. Irrespective of the gas pressure or oxidation state of the catalysts, common morphologies (compartmentalization/segmentation, branching, partial metal filling) were observed when raw samples from the collar were analyzed by TEM. EDX confirmed the presence of metallic copper in the tips, in the branches and in the partially filled b-CNTs. These features have led to the proposal of a common growth model, in which reactions between metallic copper nanoparticles and gaseous carbon species that were formed in hydrogen, were used to rationalize the various CNT structures synthesised.     

Mechanical properties of carbon fiber reinforced bisphenol A dicyanate ester composites modified with multiwalled carbon nanotubes

A novel electrophoretic deposition (EPD) method was employed for grafting multiwalled carbon nanotubes (MWCNTs) on carbon fibers, which, after impregnation with bisphenol A dicyanate ester (BADCy), synergistically reinforced BADCy matrix composites (CNT‐C/BADCy). The effect of MWCNT presence on the mechanical properties of the composites was investigated. Composite tensile strength increased by 45.2% for an EPD duration of 2 min, while flexural strength exhibited a decreasing trend with EPD duration. Optical microscopy revealed that the existence of MWCNTs enhanced the fiber‐matrix interface while a large number of CNTs were observed to have pulled‐out from the matrix, a finding which explained the observed tensile strength increase in terms of energy dissipation by the specific toughening mechanism. The flexural strength decrease of the composites with CNTs as compared to specimens without nanotubes was found linked to the increased stress concentration in the BADCy matrix due to tube presence which weakens the adhesion between carbon fabrics. In a word, carbon nanotubes will enhance the micro interface and weaken the macro interface of the composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45100.     

Carbon nanotubes for catalytic applications

The unique properties of carbon nanotubes, a new class of nanomaterials, make them usable as catalyst supports for various reactions. A pilot reactor has been constructed for producing nanotubes. The nanotubes obtained in this reactor have displayed high performance in a number of catalytic processes. A continuous laboratory-scale reactor for the synthesis of binary and mixed oxide nanosized catalysts has been tested. Russia has everything necessary for organizing nanotube production.     

In situ electropolymerization of conducting polypyrrole/carbon nanotubes composites on stainless steel: Role of carbon nanotubes types

In situ electropolymerization was used to prepare polypyrrole-oxidized multi-walled carbon nanotubes and polypyrrole-oxidized single-walled carbon nanotubes composites on a stainless steel surface from 0.1 M oxalic acid by using cyclic voltammetry. The electropolymerization process was investigated and discussed, and the results showed that the addition of the oxidized carbon nanotubes greatly enhanced the electropolymerization process, especially in the case of oxidized single walled carbon nanotubes. The results also showed that increasing the pyrrole monomer concentration leads to increasing the amount of polypyrrole electrodeposited, and this is more pronounced in the presence of the carbon nanotubes. The electropolymerization process was mainly under diffusion control as the process was inhibited by increasing the scan rate. In general, the presence of oxidized carbon nanotubes improved the electropolymerization of the polypyrrole and greatly enhanced its thermal and morphological properties.     

碳纳米管功能化的途径、机理和表面特征

由碳纳米管的功能化有共价键和非共价键两种方法。共价键功能化的机理是通过氧化或还原反应在碳纳米管表面生成极性或反应性基团(表面基团化),继而通过化学反应使碳纳米管表面有机化或聚合物化。非共价键功能化的机理是基于碳纳米管表面的?体系和疏水性可与含?电子的芳烯化合物发生?-?相互作用或与含疏水链的表面活性剂发生物理吸附。本文综述碳纳米管功能化的研究进展,完善了Kim等提出的碳纳米管功能化表面的代数表示:表面基团化的为1G,表面有机化的为2G,表面聚合物化的为3G。     

Fast and highly efficient one‐pot synthesis of polyoxadiazole/carbon nanotube nanocomposites in mild acid

Sulfonated poly(4,4′‐diphenylether‐1,3,4‐oxadiazole) (POD) composites have been successfully prepared through solution polycondensation of 4,4′‐diphenylether dicarboxylic acid and hydrazine sulfate. The reactions were performed in the presence of various types of pristine carbon nanotubes, i.e. single‐, double‐ and multi‐walled carbon nanotubes, using mild poly(phosphoric acid) as a condensing agent. The POD composites with high molecular weight (of the order of 10⁵ g mol^?1) were highly soluble in polar aprotic solvents and thermally stable at temperatures as high as 475 °C. The synthesis method used guaranteed an improved interaction between filler and matrix, thus allowing an enhanced load transfer. The overall performance of the composites was enhanced due to a synergistic reinforcement effect. The nanocomposites exhibited an increase of +33% in storage modulus, +56% in tensile strength and +245% in tensile energy to break. Copyright © 2010 Society of Chemical Industry     

Benign enzymatic synthesis of multiwalled carbon nanotube composites uniformly coated with polypyrrole for supercapacitors

BACKGROUND: Recently, various composites of carbon nanomaterials and conducting polymers have been actively investigated as potential electrode materials for supercapacitors which can store and deliver large amounts of electrical energy promptly. Harsh chemical or complex electrodeposition methods have been studied to prepare such composites. In this report, the mild and simple enzymatic catalysis of horseradish peroxidase (EC 1.11.1.7) in aqueous solutions (pH 4.0) was utilized for the first time to prepare composites of multiwalled carbon nanotubes and polypyrrole. RESULTS: Electron micrographs show that in situ enzymatic reaction by horseradish peroxidase enables the uniform coating of multiwalled carbon nanotubes with polypyrrole without containing the polymer aggregates. The specific capacitance of the composites (46.2 F g^?1) measured with a two‐electrode cell containing an electrolyte of 1 mol L^?1 NaNO₃ increased more than four‐fold compared with that obtained with bare multiwalled carbon nanotubes (10.8 F g^?1). CONCLUSIONS: Horseradish peroxidase‐catalyzed in situ synthesis of the composites of multiwalled carbon nanotubes and polypyrrole requires neither the derivatization of multiwalled carbon nanotubes and/or pyrrole monomers nor the post‐doping of the synthesized composites to enhance the capacitance of the composites. © 2012 Society of Chemical Industry     

Differences in cytocompatibility and hemocompatibility between carbon nanotubes and nitrogen-doped carbon nanotubes

The cytocompatibility and hemocompatibility of multiwalled carbon nanotubes and N-doped multiwalled carbon nanotubes grown on carbon papers by chemical vapor deposition were investigated. These materials were characterized using contact-angle measurements, cell- and platelet-adhesion assays, and hemolytic-rate testing, revealing significant effects of nitrogen doping in carbon nanotubes. The results showed that mouse fibroblast cells and mouse adipose-derived stem cells cultured on N-doped multiwalled carbon nanotubes displayed the higher cell-adhesion strength, viability, proliferation, and stretching than those on multiwalled carbon nanotubes without N doping and carbon paper, indicating that N-doped multiwalled carbon nanotubes possessed good cytocompatibility. No toxicity reactions were observed during the culturing period. It also displayed the lowest hemolytic rate.     

Enhancing the performance of polypyrrole composites as electrode materials for supercapacitors by carbon nanotubes additives

In the framework of this study, a facile method to obtain polypyrrole (PPy)/carbon nanotubes composites is presented. Chemical polymerization of PPy directly on the carbon nanotubes allows to obtain a homogenous distribution of the polymer. A low amount of carbon additive, varying from 1.5 to 5.5 wt %, is applied in order to prevent the decrease of capacitance value due to the presence of a low-capacitance component and, at the same time, to protect the electrode material from mechanical changes during cycling electrical measurements. The electrochemical properties, such as capacitance, its retention at different current loads, cycling stability, or self-discharge, are discussed. Improvement of electrochemical performances of the synthesized materials is observed mostly during cyclic stability measurements and at high current regimes. The obtained results confirm that the addition of only 3% of carbon nanotubes provides the best electrochemical performances as electrode materials for supercapacitor application. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48867.     

Characterization of carbon-fullerene-silicone oil composite paste electrodes

The preparation and aqueous electrochemistry of carbon paste electrodes modified by single wall carbon nanotubes and C₆₀ are reported. The matrix of carbon corresponds to an experimental turbostratic carbon black with low surface area. In all cases, the redox reactions studied by Cyclic Voltammetry in 6 M KOH can be assigned to the reduction/oxidation of intrinsic carbon-oxygen complexes and to the hydrogen adsorption/desorption reactions. Modification with less than 10 wt.% carbon nanotubes facilitates hydrogen evolution, while modification with C₆₀ causes the activation of the paste towards oxidation processes. For SWNT-modified paste electrodes, changes in the microstructure of the paste cause the increase in capacitive current, in contrast with the unmodified carbon paste electrode where this increment only occurs after several potential cycles. The fact that the paste electrode required an optimum carbon nanotubes concentration indicates that low-surface area carbon blacks are good candidates for the dispersion of single wall carbon nanotubes, and that a maximum of 200% increase in charge storage capacity can be obtained from carbon black/SWNT silicon oil composites.     

Copolyester nanocomposites based on carbon nanotubes: reinforcement effect of carbon nanotubes on viscoelastic and dielectric properties of nanocomposites

Nanocomposites based on an amorphous copolyester, poly(ethylene glycol‐co‐cyclohexane‐1,4‐dimethanol terephthalate) and carbon nanotubes were fabricated using a simple melt processing technique. The reinforcement effect of carbon nanotubes in the copolyester was investigated experimentally using different approaches based on dynamic mechanical analysis, rheology and dielectric analysis. The nanocomposites show a mechanical reinforcement effect with significant increase in the stiffness especially in the rubbery regime with increasing nanotube content. An increase in T_g and a decrease in damping are seen, which are derived from the presence of a percolating superstructure of the filler. Rheological experiments show an increase in storage modulus up to four orders of magnitude. Viscolelastic characterization shows that the percolation threshold is at 3 wt% of nanotubes. Dielectric relaxation spectroscopy confirms the presence of this percolating structure. We conclude that the responses of both rheological and electrical properties are different, although both are related to the formation of a percolating network superstructure of the filler. Copyright © 2007 Society of Chemical Industry