Functionalized carbon nanotubes containing isocyanate groups

Functionalized carbon nanotubes containing isocyanate groups can extend the nanotube chemistry, and may promote their many potential applications such as in polymer composites and coatings. This paper describes a facile method to prepare functionalized carbon nanotubes containing highly reactive isocyanate groups on its surface via the reaction between toluene 2,4-diisocyanate and carboxylated carbon nanotubes. Fourier-transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) confirmed that reactive isocyanate groups were covalently attached to carbon nanotubes. The content of isocyanate groups were determined by chemical titration and thermogravimetric analysis (TGA).     

Surface functionalization of oxidized multi-walled carbon nanotubes: Candida rugosa lipase immobilization

This work examines two approaches for immobilization of lipase from Candida rugosa on oxidized multi-walled carbon nanotubes (o-MWCNTs). One method included the presence of activating agents to promote covalent bonding and the other the adsorption on o-MWCNTs to elucidate if non-specific bonding on the o-MWCNTs surface exists. The influence of the immobilization time and initial enzyme concentration on protein loading and the expressed lypolitic activity of the immobilized preparation were investigated. The results showed that the enzyme adsorbs on o-MWCNTs in a maximal amount of 37 μg mg⁻¹ CNTs, while the attached amount was more than 2-times higher under covalent promoting conditions (80 μg mg⁻¹ CNTs). Furthermore, similar trends were observed for the lypolitic activity, whereby preparations obtained under covalent promoting conditions had almost 3-times higher activity (560 IU g⁻¹ of immobilized enzyme). In addition, immobilization of the enzyme was confirmed by Fourier transformation infrared spectroscopy and thermogravimetric analysis.     

The conversion of polyaniline nanotubes to nitrogen-containing carbon nanotubes and their comparison with multi-walled carbon nanotubes

Polyaniline (PANI) nanotubes were prepared by the oxidation of aniline in solutions of acetic or succinic acid, and subsequently carbonized in a nitrogen atmosphere during thermogravimetric analysis running up to 830 °C. The nanotubular morphology of PANI was preserved after carbonization. The molecular structure of the original PANI and of the carbonized products has been analyzed by FTIR and Raman spectroscopies. Carbonized PANI nanotubes contained about 8 wt.% of nitrogen. The molecular structure, thermal stability, and morphology of carbonized PANI nanotubes were compared with the properties of commercial multi-walled carbon nanotubes.     

Structural characterization and electrochemical lithium insertion properties of carbon nanotubes prepared by the catalytic decomposition of methane

Carbon nanotubes (CNTs) were synthesized by the catalytic decomposition of methane at 773, 873 and 973 K. Structures of these carbon nanotubes were characterized by TEM, HRTEM, XRD and Raman spectra, respectively. The results showed that with the increase of preparation temperature, the d ₀₀₂ value of the CNTs decreased, while the L _a values and the degree of crystallinity of the samples increased. Electrochemical lithium insertion properties of the CNTs used as positive electrodes in CNTs/Li cells were also investigated. The first charge capacities of CNTs/Li cells were 290, 254 and 202 mAh/g for samples produced at 773, 873 and 973 K, respectively. The sample from 773 K showed a larger charge capacity, which is attributed to the accommodation of lithium at microcavities, at edges of graphitic layers and at the surface of single graphitic layers. Its potential hysteresis during Li insertion and deinsertion processes may be related to the interstitial carbon atoms. Electronic Publication     

Production of palladium nanoparticles supported on multiwalled carbon nanotubes by gamma irradiation

Palladium nanoparticles were produced and supported on multiwalled carbon nanotubes (MWCNT) by gamma irradiation. A solution with a specific ratio of 2:1 of water-isopropanol was prepared and mixed with palladium chloride and the surfactant sodium dodecyl sulfate (SDS). The gamma radiolysis of water ultimately produces Pd metallic particles that serve as nucleation seeds. Isopropanol is used as an ion scavenger to balance the reaction, and the coalescence of the metal nanoparticles was controlled by the addition of SDS as a stabilizer. The size and distribution of nanoparticles on the carbon nanotubes (CNT) were studied at different surfactant concentrations and radiation doses. SEM, STEM and XPS were used for morphological, chemical and structural characterization of the nanostructure. Nanoparticles obtained for doses between 10 and 40 kGy, ranged in size 5-30 nm. The smaller nanoparticles were obtained at the higher doses and vice versa. Histograms of particle size distributions at different doses are presented.     

Tip-enhanced near-field optical microscopy of carbon nanotubes

We review recent experimental studies on single-walled carbon nanotubes on substrates using tip-enhanced near-field optical microscopy (TENOM). High-resolution optical and topographic imaging with sub 15 nm spatial resolution is shown to provide novel insights into the spectroscopic properties of these nanoscale materials. In the case of semiconducting nanotubes, the simultaneous observation of Raman scattering and photoluminescence (PL) is possible, enabling a direct correlation between vibrational and electronic properties on the nanoscale. So far, applications of TENOM have focused on the spectroscopy of localized phonon modes, local band energy renormalizations induced by charge carrier doping, the environmental sensitivity of nanotube PL, and inter-nanotube energy transfer. At the end of this review we discuss the remaining limitations and challenges in this field. Figure Tip-enhanced Raman scattering and photoluminescence spectroscopy with sub 15 nm spatial resolution provides novel insights into the electronic and vibronic properties of single-walled carbon nanotubes.     

Layer-by-layer electrostatic self-assembly of anionic and cationic carbon nanotubes

<正>The layer-by-layer(LBL) self assembly of anionic and cationic multi-walled carbon nanotubes(MWNTs) through electrostatic interaction has been carried out to fabricate all-MWNT multilayer films.The alternate uniform assembly of anionic and cationic MWNTs was investigated by UV-vis spectroscopy.Scanning electron microscopy(SEM) images displayed the growth of the MWNT films.     

Detection of influenza A virus based on fluorescence resonance energy transfer from quantum dots to carbon nanotubes

In this paper, a simple and sensitive approach for H5N1 DNA detection was described based on the fluorescence resonance energy transfer (FRET) from quantum dots (QDs) to carbon nanotubes (CNTs) in a QDs-ssDNA/oxCNTs system, in which the QDs (CdTe) modified with ssDNA were used as donors. In the initial stage, with the strong interaction between ssDNA and oxCNTs, QDs fluorescence was effectively quenched. Upon the recognition of the target, the effective competitive bindings of it to QDs-ssDNA occurred, which decreased the interactions between the QDs-ssDNA and oxCNTs, leading to the recovery of the QDs fluorescence. The recovered fluorescence of QDs was linearly proportional to the concentration of the target in the range of 0.01–20 μM with a detection limit of 9.39 nM. Moreover, even a single-base mismatched target with the same concentration of target DNA can only recover a limited low fluorescence of QDs, illustrating the good anti-interference performance of this QDs-ssDNA/oxCNTs system. This FRET platform in the QDs-ssDNA/oxCNTs system was facilitated to the simple, sensitive and quantitative detection of virus nucleic acids and could have a wide range of applications in molecular diagnosis.     

Microwave plasma treated carbon nanotubes and their electrochemical biosensing application

A convenient microwave plasma treatment method with ammonia precursor was proposed to enhance the solubility of carbon nanotubes (CNTs). The SEM, XRD and FTIR spectra clearly demonstrated that the carbon skeleton structure of the resultant ammonia plasma-treated CNTs (ammonia PT-CNTs) was not destroyed and amine groups of different forms were successfully coupled to CNTs in the MWP treatment process. The ammonia PT-CNTs have excellent solubility in water and are insoluble in nonpolar tetrahydrofuran, and the cyclic voltammograms suggest that the enhanced wetting properties clearly favor faster electron transfer kinetics on the ammonia PT-CNT electrodes. By choosing glucose oxidase as a model enzyme, the application of the ammonia PT-CNTs in construction of biosensors was further investigated. Due to the biocompatibility and electron transfer capability of the ammonia PT-CNTs, the resultant GOD biosensor displayed a good sensing performance. The biosensor has a fast response of less than 10 s, and the response current linearly increases with the glucose concentration in the range of 1.2 × 10⁻⁴ to 7.5 × 10⁻³ M with a detection limit of 1.0 × 10⁻⁵ M.     

Coherent electronic transport through the single-walled carbon nanotubes

We present the results for coherent electronic transport through the single walled carbon nanotubes. A large value of conductance is obtained for strong coupling to the electrodes, which is close to the ideal transmission of 4e²/h as in experiment. We also consider the system with ferromagnetic electrodes and analyze in detail conductance for separated channels in the coherent regime.     

Ab initio study of chemical bond interactions between covalently functionalized carbon nanotubes via amide,ester and anhydride linkages

In this paper, we have investigated the chemical bond interactions between covalently functionalized zigzag (5,0) and (8,0) SWCNT–SWCNT via various covalent linkages. Side-to-side junctions connected via amide, ester and anhydride linkages were particularly studied. The geometries and energy of the forming reaction were investigated using first-principles density functional theory. Furthermore, the band structures and the total density of states (DOS) of the junctions have also been analyzed. Our results show that several promising structures could be obtained by using chemical connection strategy and particularly the junctions formed by coupling amino functionalized SWCNT and carboxylic acid functionalized SWCNT was more favorable.     

Structures and electronic states of halogen-terminated graphene nano-flakes

Halogen-functionalized graphenes are utilized as electronic devices and energy materials. In the present paper, the effects of halogen-termination of graphene edge on the structures and electronic states of graphene flakes have been investigated by means of density functional theory (DFT) method. It was found that the ionization potential (Ip) and electron affinity of graphene (EA) are blue-shifted by the halogen termination, while the excitation energy is red-shifted. The drastic change showed a possibility as electronic devices such as field-effect transistors. The change of electronic states caused by the halogen termination of graphene edge was discussed on the basis of the theoretical results.     

Flexible supercapacitors based on carbon nanotubes

This review provides an overview of recent progress towards the development of flexible supercapacitors based on macroscopic carbon nanotubes-based electrodes, including one-dimensional (1D) fibers, 2D films, and 3D foams, with a focus on electrode preparation and configuration design as well as their integration with other multifunctional devices.     

The evaluation of carbon nanotubes as a sorbent for dicamba herbicide

The potential of carbon nanotubes (CNTs) as a novel sorbent for extraction of dicamba, a highly polar acidic herbicide, from aqueous samples was evaluated. The sorption capacity of CNTs increases remarkably with decreasing sample pH. The solution of ACN and ammonia (80:20 v/v) was found to be the most effective as the eluent for desorption from a 0.2 g CNT cartridge. The method was tested for river water samples with the LOD of 2 microg/L (for 100 mL sample) and compared with C18 bonded silica.     

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.     

Preparation and layer-by-layer self-assembly of positively charged multiwall carbon nanotubes

The report described a method of more stably dispersing oxidized carbon nanotubes (CNTs) by forming complex with polycation and the layer-by-layer self-assembly behavior of the complex with polyanion was studied. The properties of the self-assembled multilayer film containing carbon nanotubes were studied. Cyclic voltammetry, UV-vis-NIR spectroscopy, electrochemical impedance spectroscopy and scanning electron microscopy were used for characterization of film assembly. UV-vis-NIR spectroscopy and cyclic voltammetry study indicated the uniform growth of the film. Electrochemical impedance spectroscopy results showed that incorporating of carbon nanotubes in the polyelectrolyte multilayers decreased in the electron-transfer resistance R_ct, indicating more favorable electrochemical reaction interface. The electrocatalytic property of the multilayer modified electrode to NADH was investigated mainly with different numbers of the bilayers and the results showed that along with the increase of the assembled bilayers the overpotential of NADH oxidation decreased. The detection limit could reach 6 μM at a detection potential of 0.4 V.     

Preparation of cobalt hexacyanoferrate nanowires using carbon nanotubes as templates

A simple and convenient method for preparation of cobalt hexacyanoferrate (CoHCF) nanowires by electrodeposition was reported. Multiwall carbon nanotubes (MWNTs) were used as templates to fabricate CoHCF nanowires. MWNTs could affect the size of CoHCF nanoparticles and made them grow on the sidewalls of carbon nanotubes during the process of electrodeposition. Thus CoHCF nanowires could be obtained by this method. Field-emission scanning electron microscopy, UV-vis spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize these nanowires. These results showed the CoHCF nanowires could be easily and successfully obtained and it gave a novel approach to prepare inorganic nanowires.     

Present and future applications of carbon nanotubes to analytical science

This article reviews the impact of carbon nanotubes on analytical science, and the main current and future applications of carbon nanotubes in this field. Given that it is necessary to solubilize carbon nanotubes for many applications, we consider the procedures developed to achieve this. The use of carbon nanotubes in analytical chemistry as a target analyte and as an analytical tool is also discussed. Chromatographic and electrophoretic methods used to separate and characterize carbon nanotubes are presented. The use of carbon nanotubes as an analytical tool in filters and membranes, as sorbent material for solid phase extraction, in electrochemical (bio)sensors, and in separation methods is discussed. It is clear that while nanotubes are being tested for use in many different fields, their truly enormous potential has yet to be realized in analytical chemistry.Dedicated to the memory of Wilhelm Fresenius     

Polymorphism and transcrystallization of syndiotactic polystyrene composites filled with carbon nanotubes

Syndiotactic polystyrene (sPS) composites filled with well-dispersed multi-walled carbon nanotubes (CNTs) were readily prepared through a coagulation method. Fourier-transform infrared spectroscopy and wide-angle X-ray diffraction revealed the effect of CNTs on the polymorphism of sPS. When crystallized from the melted state, the formation of the β-form was always favored after CNT addition regardless of crystallization conditions (isothermal or non-isothermal). In the case where liquid nitrogen was used to quench the melt, the uncrystallized material that was not able to crystallize in the extremely short crystallization time crystallized in the α form upon subsequent cold crystallization. Regardless of the CNT content, the glass transition and equilibrium melting temperature of the sPS matrix were unchanged at ∼96 and 290 °C, respectively. With a gradual increase in CNT loading, the sPS crystallization rate initially increased but then reached a plateau value at high CNT concentrations because of the reduction in chain mobility. Moreover, the Avrami exponent was changed from 2.8 for samples at low CNT contents to 2.0 for samples with a CNT concentration above 0.1 wt.%, at which the rheological threshold was approached and a polymer-CNT hybrid network was formed. The enhanced crystallization kinetics was attributed to the high nucleating ability of CNTs to induce a transcrystalline layer (TCL) at its surface, as revealed by transmission electron microscopy. For composites with low levels of CNT, the growth of sPS spherulites in the bulk between CNTs prevailed. Provided that the CNT-related networks were developed, the two-dimensional growth of cylindrical TCL at the CNT surface became dominant and led to the expected Avrami exponent.