Kondo Effect in Carbon Nanotube Quantum Dots with Spin-Orbit Coupling

Motivated by recent experimental observation of spin-orbit coupling in carbon nanotube quantum dots [F. Kuemmeth , Nature (London) 452, 448 (2008)], we investigate in detail its influence on the Kondo effect. The spin-orbit coupling intrinsically lifts out the fourfold degeneracy of a single electron in the dot, thereby breaking the SU(4) symmetry and splitting the Kondo resonance even at zero magnetic field. When the field is applied, the Kondo resonance further splits and exhibits fine multipeak structures resulting from the interplay of spin-orbit coupling and the Zeeman effect. A microscopic cotunneling process for each peak can be uniquely identified. Finally, a purely orbital Kondo effect in the two-electron regime is also predicted.

Synthesis of carbon nanotube bundles with mesoporous structure by a self-assembly solvothermal route

A kind of carbon nanotube bundle has been synthesized by a simple one-step solvothermal reaction between Na and hexachlorobenzene (HCB) using NiCl2 as catalyst precursor. Before the reaction, NiCl2 was initially dispersed ultrasonically in cyclohexane then prereduced by Na at 230degreesC to produce small Ni particles in reduced state. The tubes thus-produced have a uniform outer diameter of about 20 nm, an inner diameter of 4 nm, and are highly ordered assembled as bundles which have a 2D hexagonal arrangement as proven by SAXS and TEM experiments.

Preparation and characterization of multiwalled carbon nanotube-supported platinum for cathode catalysts of direct methanol fuel cells

Multiwalled carbon nanotube-supported Pt (Pt/MWNT) nanocomposites were prepared by both the aqueous solution reduction of a Pt salt (HCHO reduction) and the reduction of a Pt ion salt in ethylene glycol solution. For comparison, a Pt/XC-72 nanocomposite was also prepared by the EG method. The Pt/MWNT catalyst prepared by the EG method has a high and homogeneous dispersion of spherical Pt metal particles with a narrow particle-size distribution. TEM images show that the Pt particle size is in the range of 2-5 nm with a peak at 2.6 nm, which is consistent with 2.5 nm obtained from the XRD broadening calculation. Surface chemical modifications of MWNTs and water content in EG solvent are found to be the key factors in depositing Pt particles on MWNTs. In the case of the direct methanol fuel cell (DMFC) test, the Pt/MWNT catalyst prepared by EG reduction is slightly superior to the catalyst prepared by aqueous reduction and displays significantly higher performance than the Pt/XC-72 catalyst. These differences in catalytic performance between the MWNT-supported or the carbon black XC-72-supported catalysts are attributed to a greater dispersion of the supported Pt particles when the EG method is used, in contrast to aqueous HCHO reduction and to possible unique structural and higher electrical properties when contrasting MWNTs to carbon black XC-72 as a support.

Carbon nanotube/gold nanoparticles/polyethylenimine-functionalized ionic liquid thin film composites for glucose biosensing

A novel glucose biosensor based on immobilization of glucose oxidase (GOD) in thin films of polyethylenimine-functionalized ionic liquid (PFIL), containing a mixture of carbon nanotubes (CNT) and gold nanoparticles (AuNPs) and deposited on glassy carbon electrodes, was developed. Direct electrochemistry of glucose oxidase in the film was observed, with linear glucose response up to 12 mM. The PFIL-stabilized gold nanoparticles had a diameter of 2.4 +/- 0.8 nm and exhibited favorable stability (stored even over one month with invisible change in UV-vis spectroscopic measurements).

Self-assembly of single-stranded RNA on carbon nanotube: Polyadenylic acid to form a duplex structure

All messenger-RNA (mRNA) molecules in eukaryotic cells have a polyadenylic acid [poly (rA)] tail at the 3'-end and human poly (rA) polymerase (PAP) has been considered as a tumor-specific target. A ligand that is capable of recognizing and binding to the poly(M) tail of mRNA might interfere with the full processing of mRNA by PAP and can be a potential therapeutic agent. We report here for the first time that single-walled carbon nanotubes (SWNTs) can cause single-stranded poly (M) to self-structure and form a duplex structure, which is studied by UV melting, atomic force microscopy, circular dichroism spectroscopy, and NMR spectrometry.

Electrostatic layer-by-layer a of platinum-loaded multiwall carbon nanotube multilayer: A tunable catalyst film for anodic methanol oxidation

A simple layer-by-layer (LBL) electrostatic adsorption technique was developed for deposition of films composed of alternating layers of positively charged poly(diallyldimethylammonium chloride) (PDDA) and negatively charged multiwall carbon nanotubes bearing platinum nanoparticles (Pt-CNTs). PDDA/Pt-CNT film structure and morphology up to six layers were characterized by scanning electron microscopy and ultraviolet-visible spectroscopy, showing the Pt-CNT layers to be porous and uniformly deposited within the multilayer films.

Direct electron transfer of horseradish peroxidase and its electrocatalysis based on carbon nanotube/thionine/gold composites

Horseradish peroxidase (HRP) was incorporated into multiwalled carbon nanotube/thionine/Au (MTAu) composite film by electrostatic interactions between positively charged HRP and negatively charged MTAu composite. The results of electrochemical impedance spectroscopy (EIS) confirmed adsorption of HRP on the surface of MTAu modified GC electrode.

Preparation of gold nanoparticles/functionalized multiwalled carbon nanotube nanocomposites and its glucose biosensing application

Gold nanoparticles stabilized by amino-terminated ionic liquid (Au-IL) have been in situ noncovalently deposited on poly(sodium 4-styrene-sulfonate) (PSS)-functionalized multiwalled carbon nanotubes (MWCNTs) to form a MWCNTs/PSS/Au-IL nanocomposite. PSS can interact with MWCNTs through hydrophobic interaction. Amino-terminated ionic liquid was applied to reduce aqueous HAuCl4, and the resulting gold nanoparticles were attached to the PSS-functionalized MWCNTs simultaneously. Most gold nanoparticles dispersed well on the functionalized MWCNTs. Transmission electron microscopy, Raman and X-ray photoelectron spectroscopy were used to confirm the composition and structure of the nanocomposites. The resulting MWCNTs/PSS/Au-IL composite exhibits good electrocatalysis toward oxygen and hydrogen peroxide reduction.

Prussian Blue/Multiwalled Carbon Nanotube Hybrids: Synthesis, Assembly and Electrochemical Behavior

Prussian blue/carbon nanotube (PB/CNT) hybrids with excellent dispersibility in aqueous solutions were synthesized by adding CNTs to an acidic solution of Fe3+, [Fe(CN)(6)](3-) and KCl. Fourier transform infrared spectroscopy, UV-vis absorption spectroscopy and scanning electron microscopy were employed to confirm the formation of PB/CNT hybrids. The PB nanoparticles formed on the CNT surfaces exhibit a narrow size distribution and an average size of 40 nm. The present results demonstrate that the selective reduction of Fe3+ to Fe2+ by CNTs is the key step for PB/CNT hybrid formation. The subsequent fabrication of the PB/CNT hybrid films was achieved by layer-by-layer technique. The thus-prepared PB/CNT hybrid films exhibit electrocatalytic activity towards H2O2 reduction.

Gold/platinum hybrid nanoparticles supported on multiwalled carbon nanotube/silica coaxial nanocables: Preparation and application as electrocatalysts for oxygen reduction

A simple approach combining sonication and sol-gel chemistry was employed to synthesize silica coated carbon nanotube (CNTs) coaxial nanocables. It was found that a homogeneous silica layer can be coated on the surface of the CNTs. This method is simple, rapid, and reproducible. Furthermore, gold nanoparticle supported coaxial nanocables were facilely obtained using amino-functionalized silica as the interlinker. Furthermore, to reduce the cost of Pt in fuel cells, designing a Pt shell on the surface of a noble metal such as gold or silver is necessary. High-density gold/platinum hybrid nanoparticles were located on the surface of I-D coaxial nanocables with high surface-to-volume ratios. It was found that this hybrid nanomaterial exhibits a high electrocatalytic activity for enhancing oxygen reduction (low overpotential associated with the oxygen reduction reaction and almost four-electron electroreduction of dioxygen to water).

Carbon Nanotube/Silica Coaxial Nanocable as a Three-Dimensional Support for Loading Diverse Ultra-High-Density Metal Nanostructures: Facile Preparation and Use as Enhanced Materials for Electrochemical Devices and SERS

In this paper, we have reported a very simple strategy (combined sonication with sol-gel techniques) for synthesizing well-defined silica-coated carbon nanotube (CNT) coaxial nanocable without prior CNT functionalization. After functionalization with NH2 group, the CNT/silica coaxial nanocable has been employed as a three-dimensional support for loading ultra-high-density metal or hybrid nanoparticles (NPs) such as gold NPs, Au/Pt hybrid NPs, Pt hollow NPs, and Au/Ag core/shell NPs. Most importantly, it is found that the ultra-high-density Au/Pt NPs supported on coaxial nanocables (UASCN) could be used as enhanced materials for constructing electrochemical devices with high performance. Four model probe molecules (O-2, CH3OH, H2O2, and NH2NH2) have been investigated on UASCN-modified glassy carbon electrode (GCE). It was observed that the present UASCN exhibited high electrocatalytic activity toward diverse molecules and was a promising electrocatalyst for constructing electrochemical devices with high performance. For instance, the detection limit for H2O2 with a signal-to-noise ratio of 3 was found to be 0.3 mu M, which was lower than certain enzyme-based biosensors.

A novel hybrid nanostructure based on SiO2@carbon nanotube coaxial nanocable

We present a simple, generally applicable procedure for obtaining diameter-controlled SiO2@ carbon nanotubes (CNTs) coaxial nanocables. These coaxial nanocables with high solubility in polar solvents, have been used as functional templates for assembling CNTs/Au nanorods heterogeneous nanostructures to form multifunctional assembly system. These hybrid nanostructures may find applications in nanoelectronics, photonics, and nanodevices.