Controllable preparation and properties of composite materials based on ceria nanoparticles and carbon nanotubes

We report a method to prepare composites based on carbon nanotubes (CNTs) and CeO₂ nanoparticles (NPs). The CeO₂ NPs were attached to CNTs by hydrothermal treatment of Ce(OH)₄/CNT mixture in NaOH solution at 180 °C. It was found that larger CeO₂ NPs were formed in the presence of CNTs. Grain size of CeO₂ NPs in the composites can be reduced when NaNO₃ was added in the hydrothermal process. Electrochemical characterizations have shown that the composites possess a specific capacity between those of CNTs and CNTs mechanically mixed with CeO₂. These CeO₂/CNT composites could serve as promising anode materials for Li-ion batteries.     

Diameter control and growth mechanism of single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) have been synthesized using the alcohol chemical vapor deposition technique. On comparing the SWNTs synthesized using different catalyst compositions, an obvious fact has been clarified – the diameter of SWNTs is strongly dependent on the sizes of the catalyst particles and metal species. Iron atoms exhibit a strong interaction with carbon atoms and keep their diameters narrow. Cobalt atoms exhibit a poorer interaction than the iron atoms, but work to decompose ethanol. As a result, narrow SWNTs are generated on the iron-rich catalyst. In this Letter, we propose the most probable growth mechanism of the SWNTs.     

Nitrogen-doped carbon nanotubes: growth, mechanism and structure

Nitrogen-doped bamboo-structured carbon nanotubes have been successfully grown using a series of cobalt/molybdenum catalysts. The morphology and structure of the nanotubes were analysed by transmission electron microscopy and Raman spectroscopy. The level of nitrogen doping, as determined by X-ray photoelectron spectroscopy, was found to range between 0.5 to 2.5 at.%. The growth of bamboo-structured nanotubes in the presence of nitrogen, in preference to single-walled and multi-walled nanotubes, was due to the greater binding energy of nitrogen for cobalt in the catalyst compared to the binding strength of carbon to cobalt, as determined by density functional theory.     

CVD growth of N-doped carbon nanotubes on silicon substrates and its mechanism

In the present study, we report the chemical vapor deposition (CVD) of nitrogen-doped (N-doped) aligned carbon nanotubes on a silicon (Si) substrate using ferrocene (Fe(C5H5)2) as catalyst and acetonitrile (CH3CN) as the carbon source. The effect of experimental conditions such as temperature, gaseous environment, and substrates on the structure and morphology of N-doped carbon nanotubes arrays is reported. From XPS and EELS data, it was found that the nitrogen content of the nanotubes could be determined over a wide range, from 1.9% to 12%, by adding the addition of hydrogen (H2) to the reaction system. It was also shown by SEM that N-doped carbon nanotube arrays could be produced on Si and SiO2 substrates at suitable temperatures, although at different growth rates. Using these concentrations, it was possible to produce three-dimensional (3D) carbon nanotubes architectures on predetermined Si/SiO2 patterns. The mechanism underlying the effect of nitrogen containing carbon sources on nanotube formation was explored using X-ray photoelectron spectroscopy (XPS).     

Controllable interconnection of single-walled carbon nanotubes under ac electric field

We demonstrated the controllable interconnection of single-walled carbon nanotubes (SWNTs) under alternating current (ac) electric field. The interconnected carbon nanotubes were found to be parallel with the electric flux and increased abruptly with deposition time following a self-accelerating process. Theoretical simulation indicates that the alignment and the interconnection of carbon nanotubes were induced by the dielectrophoresis force and the electric field redistribution at the nanotube apexes.     

A growth mechanism for carbon nanotubes using metal oxides as catalysts

Metal oxides have only recently begun to be used as catalysts for the growth of carbon nanotubes. Here, we propose a new model for the growth of carbon nanotubes, based on the intra‐granular charge transfer transition and the lattice strain of the catalyst nanoparticles. This is supported by results obtained from the doped metal oxides like samarium doped zinc oxide (SmZnO) and terbium doped zinc oxide (TbZnO). The intragranular charge transfer transition is believed to be responsible for the dissociation of the hydrocarbon molecules. The lattice strain of the catalyst nanoparticles appears to be responsible for the diffusion of carbon atoms through the catalyst particles.     

Multiwall carbon nanotubes and their applications

The chemical, electrophysical, magnetic, tribological, and physicomechanical properties of multiwall carbon nanotubes (MWCNTs), as well as the characteristics of new nanocomposites and instruments thereof were discussed. These MWCNTs are produced by unique technology and are free from impurities of other carbon modifications. Advantages of multiwall over single-wall carbon nanotubes were demonstrated for applications in electronic devices and preparation of nanocomposites (as filling agents).     

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.     

Controllable delivery of small-molecule compounds to targeted cells utilizing carbon nanotubes

Carbon nanotubes (CNTs) have emerged as a new alternative and efficient tool for transporting molecules with biotechnological and biomedical applications, because of their remarkable physicochemical properties. Encapsulation of functional molecules into the hollow chambers of CNTs can not only stabilize encapsulated molecules but also generate new nanodevices. In this work, we have demonstrated that CNTs can function as controllable carriers to transport small-molecule compounds (SMCs) loaded inside their hollow tunnels onto targeted cells. Using indole as model compound, CNTs can protect indole molecules during transportation. Labeling indole-loaded CNTs (indole@CNTs) with EphB4-binding peptides generates cell-homing indole@CNTs (CIDs). CIDs can selectively target EphB4-expressing cells and release indole onto cell surfaces by near-infrared (NIR) irradiation. Released indole molecules exhibit significant cell-killing effects without causing local overheating. This establishes CNTs as excellent near-infrared controllable delivery vehicles for SMCs as selective cell-killing agents.     

Formation and growth mechanism of dissimilar coiled carbon nanotubes by reduced-pressure catalytic chemical vapor deposition

Dissimilar coiled carbon nanotubes were prepared by catalytic chemical vapor deposition (CCVD) on finely divided Co nanoparticles supported on silica gel under reduced pressure and at lower gas flow rates. The morphology of the regular coiled carbon nanotubes were examined by TEM, while the polygonization characteristics of the helix were examined by SAED. Observations were made on other forms of irregular coils with various shapes by TEM. On the basis of the heptagon-pentagon construction theory, we proposed a helix formation mechanism, which involves a carbon core formation centering on a catalytic particle followed by carbon helices growth controlled by kinetics.     

Anodic zirconia nanotubes: composition and growth mechanism

The compositions of porous anodic films formed on zirconium in glycerol/fluoride electrolytes are examined prior to and following ageing in the electrolyte. The initial films are shown to contain significant amounts of fluorine, with an F:O atomic ratio between 1.0 and 2.5, dependent on the water content of the electrolyte. A three-layered film morphology is indicated, which is related to the migration rates of film species, incorporating a fluoride-rich layer at cell boundaries and bases, and outer layers compositionally differentiated by the presence of carbon species. Preferential loss of fluorine during ageing suggests degradation of the fluoride-rich material.     

Ce改性碳纳米管负载过渡金属磷化物用于电化学水分解

氢能是未来替代化石燃料的理想选择,可以通过电解水的半反应之一析氢反应制得,但其缓慢的反应动力学将会耗费大量的电池电压。因此,通过开发催化剂来降低电解槽的电压是解决这一问题的关键途径。本文经过简便的静电纺丝及碳化工艺得到Ce改性的碳纤维作为载体(Ce-CNFs),接着通过水热法及高温磷化法负载活性组分得到Co_x-Mo_y-P@Ce-CNFs,分别对催化材料的析氢反应(HER)和析氧反应(OER)电催化活性进行了研究。结果表明,在1mol/L KOH电解液中,仅需要160mV和323mV的过电位就能达到10mA/cm²的电流密度。将Co_x-Mo_y-P@Ce-CNFs作为阴极和阳极材料组装为整体水电解槽,在电流密度为10mA/cm²时,电解槽的电池电压为1.65V,在电化学耐久性测试中能够稳定保持8h。     

Controllable fabrication of metal-confined carbon nanotubes from the self-templated conversion of supramolecular gel nanofibers

Nanostructured supramolecular gels with self-assembled fibrillar networks are promising candidates for fabricating advanced functional materials for energy-related applications. Several fundamental challenges, including poor structural stability and monotonous fibrous morphology, greatly hinder their practical applications. To the best of our knowledge, supramolecular gel-derived carbon nanotubes (CNTs) have not been reported in the literature. Herein, we present a unique strategy for controllable fabrication of metal-confined carbon nanotubes (M/CNT) from the self-templated conversion of guanosine-based supramolecular gel (GSMG) nanofibers. Benefitting from the high tunability of GSMGs, it was demonstrated that the introduction of metal source (Ni and Fe) to improve the stability of the material and simply changing the KOH concentrations in the precursor materials, the structure of GSMG nanofibers derived active materials was controllably tuned from metal-constrained solid carbon nanofiber to hollow M/CNT. The optimized NiFe/B, N-CNT showed a superior oxygen evolution reaction catalytic activity with a low overpotential of 355 mV at a current density of 10 mA cm^?2. By taking advantage of the unique structural features of supramolecular gels, this strategy provides a simple and effective synthetic route for functional CNT.     

The mechanism of cavitation-induced scission of single-walled carbon nanotubes

Aqueous suspensions of length selected single-walled carbon nanotubes were studied by atomic force microscopy (AFM) in order to probe the influence of sonication on nanotube scission. The maximum of the tube length distribution, lM, initially exhibits a power law dependence on the sonication time, t - roughly as lM approximately t(-0.5). This and the limiting behavior observed at longer times can be rationalized to first order in terms of a continuum model deriving from polymer physics. In this picture, the strain force associated with cavitation scales with the square of the nanotube length. Scission stops when the strain force falls below the critical value for nanotube disruption.     

Dynamic mechanism of collagen-like peptide encapsulated into carbon nanotubes

Carbon nanotubes (CNTs)-based devices and their applications have received more and more attention, and several biomolecules have been found to be encapsulated into the inner space of the CNTs spontaneously. In this work, the molecular dynamics simulations demonstrate that a collagen-like peptide with a hydrophobic center and hydrophilic surfaces could be inserted into CNTs spontaneously but slowly. Then the dynamic mechanism of the encapsulation process was investigated by a series of steered molecular dynamics simulations. The van der Waals interaction between the peptide and the carbon nanotubes was proved to be a positive factor for this insertion process, whereas the major resistance of this process is attributed to the repelling of the trapped water molecules and the breaking of the hydrogen-bond networks of water molecules around the peptide. Because of the synthetical effect of these interactions, there is an optimal tube size corresponding to effective encapsulation of the protein into the CNTs for a given kind of protein molecule.     

Electrochemical preparation of luminescent graphene quantum dots from multiwalled carbon nanotubes

Green luminescent, graphene quantum dots (GQDs) with a uniform size of 3, 5, and 8.2(±0.3)?nm in diameter were prepared electrochemically from MWCNTs in propylene carbonate by using LiClO(4) at 90?°C, whereas similar particles of 23(±2)?nm were obtained at 30?°C under identical conditions. Both these sets of GQDs displayed a remarkable quantum efficiency of 6.3 and 5.1?%, respectively. This method offers a novel strategy to synthesise size-tunable GQDs as evidenced by multiple characterisation techniques like transmission and scanning electron microscopy, atomic force microscopy, Raman spectroscopy and X-ray diffraction (XRD). Photoluminescence of these GQDs can be tailored by size variation through a systematic change in key process parameters, like diameter of carbon nanotube, electric field, concentration of supporting electrolyte and temperature. GQDs are promising candidates for a variety of applications, such as biomarkers, nanoelectronic devices and chemosensors due to their unique features, like high photostability, biocompatibility, nontoxicity and tunable solubility in water.     

Novel preparation of polyphosphazene-coated carbon nanotubes as a Pt catalyst support

This study reports a noncovalent functionalization of MWCNTs with a fluorinated cross-linked polymer coating of poly[cyclotriphosphazene-co-(4,4'-(hexafluoroisopropylidene)diphenol)] and their application as the support of Pt for electrocatalytic oxidation of methanol.     

A hydrogen storage mechanism in single-walled carbon nanotubes.

We have carried out systematic calculations for hydrogen-adsorption and -storage mechanism in carbon nanotubes at zero temperature. Hydrogen atoms first adsorb on the tube wall in an arch-type and zigzag-type up to a coverage of theta = 1.0 and are stored in the capillary as a form of H(2) molecule at higher coverages. Hydrogen atoms can be stored dominantly through the tube wall by breaking the C--C midbond, while preserving the wall stability of a nanotube after complete hydrogen insertion, rather than by the capillarity effect through the ends of nanotubes. In the hydrogen-extraction processes, H(2) molecule in the capillary of nanotubes first dissociates and adsorbs onto the inner wall and is further extracted to the outer wall by the flip-out mechanism. Our calculations describe suitably an electrochemical storage process of hydrogen, which is applicable for the secondary hydrogen battery.     

Low-temperature growth of carbon nanotubes from the catalytic decomposition of carbon tetrachloride

Multiwall carbon nanotubes (MWNTs) were synthesized via the decomposition of CCl4 in supercritical CO2 at 175 degrees C and 27.6 MPa using an iron-encapsulated dendrimer as a growth catalyst. The average diameter of resultant nanotubes was 20-25 nm, obtained after a 24-h reaction time. Our conditions represent the first application for CX4 precursors, as well as the lowest-reported temperature regime for carbon nanotube growth, allowing the use of other temperature-sensitive catalytic substrates.     

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.