Transformation from single-walled carbon nanotubes to nanohorns by simple heating with Pd at 1600 °C

A route to synthesize single-wall carbon nanohorns (SWCNHs) at a lower than normal temperature is reported. SWCNHs were synthesized at 1600 °C by a transformation from single-walled carbon nanotubes as the result of the catalytic effect of molten Pd. Observations by transmission electron microscope (TEM) on the remaining precursors suggested that SWCNTs were first deformed to highly curled shapes, and then were fragmentized into independent horns. Typical structures of SWCNHs were formed by merging these horn-like fragments.     

Single wall carbon nanohorns coated with anatase titanium oxide

Single wall carbon nanohorns (SWCNHs) were coated with anatase titanium oxide thin films by metal-organic chemical vapour deposition with titanium tetraisopropoxide Ti(OiPr)₄ as the precursor. The pristine SWCNHs and the new hybrid material SWCNHs/TiO₂ were characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction, thermogravimetric thermal analysis and inductively coupled plasma-mass spectrometry, showing that the deposition process does not alter the typical structures of the SWCNHs. Finally, it is shown how the hydrophilic properties of the titanium oxide coating allowed a stable dispersion of SWCNHs/TiO₂ in water, opening new perspectives for water based nanofluids, biological sensing or drug delivery systems.     

Synthesis and Microstructural Investigations of Organometallic Pd(II) Thiol-Gold Nanoparticles Hybrids

In this work the synthesis and characterization of gold nanoparticles functionalized by a novel thiol-organometallic complex containing Pd(II) centers is presented. Pd(II) thiol, trans, trans-[dithiolate-dibis(tributylphosphine)dipalladium(II)-4,4′-diethynylbiphenyl] was synthesized and linked to Au nanoparticles by the chemical reduction of a metal salt precursor. The new hybrid made of organometallic Pd(II) thiol-gold nanoparticles, shows through a single S bridge a direct link between Pd(II) and Au nanoparticles. The size-control of the Au nanoparticles (diameter range 2–10 nm) was achieved by choosing the suitable AuCl₄ ⁻/thiol molar ratio. The size, strain, shape, and crystalline structure of these functionalized nanoparticles were determined by a full-pattern X-ray powder diffraction analysis, high-resolution TEM, and X-ray photoelectron spectroscopy. Photoluminescence spectroscopy measurements of the hybrid system show emission peaks at 418 and 440 nm. The hybrid was exposed to gaseous NO _x with the aim to evaluate the suitability for applications in sensor devices; XPS measurements permitted to ascertain and investigate the hybrid –gas interaction.     

Fabrication of single-wall carbon nanotubes within the channels of a mesoporous material by catalyst-supported chemical vapor deposition

Diameter-controlled single-wall carbon nanotubes (SWCNTs) have been synthesized using Co, Fe/Co and Rh/Pd alloy nanoparticles trapped within the one-dimensional channels of a mesoporous materials (Folded Sheets Mesoporous material: FSM-16) by catalyst-supported chemical vapor deposition (CCVD) using ethanol as carbon source at 973-1173 K. The SWCNTs synthesized are characterized by transmission electron microscopy, Raman spectroscopy and photoluminescence spectroscopy. The yield, diameter distribution and quality of the SWCNTs strongly depend on the reaction temperature during CCVD. The product synthesized at 1173 K contains only SWCNTs, in marked contrast to those synthesized at lower temperatures. As the reaction temperature decreases, the relative abundance of multi-wall carbon nanotubes against SWCNTs significantly increases, whereas the mean diameter of SWCNTs increases as reaction temperature increases. The results show that a careful control of the reaction temperature is crucial to fabricate diameter-controlled SWCNTs from the channels of FSM-16.     

Palygorskite Hybridized Carbon Nanocomposite as PtRuIr Support for the Methanol Oxidation Reaction

A palygorskite/carbon heterogeneous nanocomposite, a unique hybrid of palygorskite and carbon, was prepared and designed as an electrocatalyst support material for PtRuIr nanoparticles and evaluated for methanol electrooxidation. X‐ray diffraction and transmission electron microscopy results showed that PtRuIr nanoparticles were well‐dispersed on the composite support with highly dispersed tiny crystal alloy phase on the surface of PtRuIr amorphous alloy. X‐ray photoelectron spectroscopy results indicated that the formation of Ru and Ir oxides on the surface of the PtRuIr nanoparticles. The electrochemical results show that the palygorskite hybridized carbon used as electrocatalysts support can improve the electrocatalytic activity towards methanol oxidation and CO tolerance.     

Hot-Wire Synthesis of Gold Nanoparticles

Gold nanoparticles were synthesized by a hot-wire generator at atmospheric pressure using a gold-platinum composite wire. At low gas flow velocities the nanoparticles were found to be agglomerates of partially sintered primary particles. By reducing the tube size via the insertion of a nozzle with a throat diameter of 3 mm, the hot-wire generator was found to produce small (<10 nm diameter) crystalline gold particles. Elemental and x-ray photoelectron spectroscopy analysis of the particles showed that they were composed of gold with no platinum impurity. Charging analysis of the “as-produced” nanoparticles showed that fewer than 10% of the particles were charged, but the charge fraction increased as the applied power increased, as did the ratio of negatively-to-positively-charged particles.     

Electrocatalytic properties of Pd clusters on Au nanoparticles in formic acid electro-oxidation

Pd clusters were formed on highly dispersed Au nanoparticles (∼3.5 nm in diameter) using a seed-mediated growth process. The structural information and electrocatalytic activities of these Pd clusters on Au nanoparticles were confirmed by high-resolution-transmission-electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The resulting nanoparticles, which had a uniform size (<5 nm in diameter), were highly dispersed on carbon particles, and Pd clusters (<0.44 nm in size, <2 atomic layers) were formed selectively on Au nanoparticles. XPS results show that the Pd 3d_5/2 peak shifted to lower binding energies and that the amount of surface oxide decreased as the Pd content was decreased on the Au nanoparticles. In formic acid electro-oxidation, these Pd clusters exhibit enhanced electrocatalytic activity relative to that of carbon-supported Pd nanoparticles. These results may be due to the modified electronic and geometric structure of the Pd clusters on the Au nanoparticle substrate.     

Preparation of carbon-encapsulated iron carbide nanoparticles by an explosion method

Fe₇C₃ nanocrystals encapsulated in carbon nanoparticles, with sizes ranging from 10 to 40 nm, were synthesized via the explosion of a hybrid xerogel containing oxidized pitch and iron nitrate. Explosion of the hybrid xerogel was induced by heat treatment. Transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) were employed to determine the structure of the nanoparticles in the explosion product. The results show that the Fe₇C₃ nanocrystals are nested inside amorphous carbon shells that protect them from oxidation by air.     

Experimental and numerical investigation of the position-dependent growth of carbon nanotube–alumina microparticle hybrid structures in a horizontal CVD reactor

The hybrid structures of carbon nanotubes (CNTs) and alumina microparticles were produced in a horizontal chemical vapor deposition (CVD) reactor using ferrocene/xylene/acetylene mixture as the catalyst–carbon source. At a given temperature and hydrogen ratio, the CNT diameter, number density, growth rate and their hybrid structures varied greatly along the axial direction of the reactor. This non-uniform growth is attributed to the position-dependent chemical reaction kinetics inside the reactor, mainly along the gas flow direction. Mass spectrometry was used to identify and quantify the chemical species of the exhaust gas. A numerical simulation of the reacting gas flow in the reactor was conducted in parallel by taking into account the space-dependent pyrolysis kinetics of the catalyst and carbon sources, the reactor temperature gradient and the fluid dynamics. A good agreement existed between the modeling and the experimental results. A double-end-injection method was proposed based on the above results, and the uniform hybrid structures were synthesized in a larger zone inside the CVD reactor. A new kind of CNT structure containing iron crystal particles at their two extremities was obtained under certain conditions, which can be very useful for various CNT junction applications.     

Graphene nanosheets-polypyrrole hybrid material as a highly active catalyst support for formic acid electro-oxidation

A novel electrode material based on graphene oxide (GO)-polypyrrole (PPy) composites was synthesized by in situ chemical oxidation polymerization. Palladium nanoparticles (NPs) with a diameter of 4.0 nm were loaded on the reduced graphene oxide(RGO)-PPy composites by a microwave-assisted polyol process. Microstructure analysis showed that a layer of coated PPy film with monodisperse Pd NPs is present on the RGO surface. The Pd/RGO-PPy catalysts exhibit excellent catalytic activity and stability for formic acid electro-oxidation when the weight feed ratio of GO to pyrrole monomer is 2:1. The superior performance of Pd/RGO-PPy catalysts may arise from utilization of heterogeneous nucleation sites for NPs and the greatly increased electronic conductivity of the supports.     

Sonochemical synthesis of tungsten carbide-palladium nanocomposites and their electrocatalytic activity for hydrogen oxidation reaction

Nanocomposites between β-WC and Pd nanoparticles supported on carbon are synthesized and their electrocatalytic properties for the hydrogen oxidation reaction have been investigated. The Pd nanoparticles are obtained by a chemical reduction reaction of PdCl₂ and the β-WC nanoparticles by a sonochemical decomposition of W(CO)₆ on Pd-loaded carbon followed by heat-treatment. Depending on the relative amounts of W to Pd, the Pd nanoparticles can be reacted with W to form Pd-W alloy nanoparticles. The Pd-W alloy, whose composition is estimated to have W less than 18 at.% based on its lattice parameter, lost most of the catalytic activity of Pd. On the other hand, the nanocomposite between β-WC and pure Pd shows an enhanced activity compared with that of Pd nanoparticles alone. This enhancement can be explained with the H⁺-spill-over to β-WC.     

Controlled assembly of carbon nanotubes encapsulated with amphiphilic block copolymer

An amphiphilic diblock copolymer (PEtOz-PCL) based on hydrophilic poly(2-ethyl-2-oxazoline) (PEtOz) and hydrophobic poly(ε-caprolactone) (PCL) was adsorbed in aqueous phase on the surface of single-wall carbon nanotube to produce PEtOz-PCL-encapsulated SWCNTs (PEtOz-PCL/SWCNT) with the diameter about 30 nm. The Raman spectroscopy analysis indicated that the nanotubes were physically encapsulated by the block copolymer without chemical denaturation of the nanotube. PEtOz-PCL/SWCNTs exhibited pH-responsive reversible complexation with poly(acrylic acid) or poly(methacrylic acid) in aqueous phase due to the pH-dependent hydrogen bonding between the PEtOz outer shell of PEtOz-PCL/SWCNTs with carboxyl groups. In addition, by using PEtOz as a template for the formation of metal nanoparticles, Au and Pd nanoparticles were successfully hybridized with PEtOz-PCL/SWCNTs.     

Gold nanoparticles grown inside carbon nanotubes: synthesis and electrical transport measurements

The hybrid structures composed of gold nanoparticles and carbon nanotubes were prepared using porous alumina membranes as templates. Carbon nanotubes were synthesized inside the pores of these templates by the non-catalytic decomposition of acetylene. The inner cavity of the supported tubes was used as nanoreactors to grow gold particles by impregnation with a gold salt, followed by a calcination-reduction process. The samples were characterized by transmission electron microscopy and X-ray energy dispersion spectroscopy techniques. The resulting hybrid products are mainly encapsulated gold nanoparticles with different shapes and dimensions depending on the concentration of the gold precursor and the impregnation procedure. In order to understand the electronic transport mechanisms in these nanostructures, their conductance was measured as a function of temperature. The samples exhibit a ‘non-metallic’ temperature dependence where the dominant electron transport mechanism is 1D hopping. Depending on the impregnation procedure, the inclusion of gold nanoparticles inside the CNTs can introduce significant changes in the structure of the tubes and the mechanisms for electronic transport. The electrical resistance of these hybrid structures was monitored under different gas atmospheres at ambient pressure. Using this hybrid nanostructures, small amounts of acetylene and hydrogen were detected with an increased sensibility compared with pristine carbon nanotubes. Although the sensitivity of these hybrid nanostructures is rather low compared to alternative sensing elements, their response is remarkably fast under changing gas atmospheres.     

Single-walled carbon nanohorns and their applications

Single-walled carbon nanohorns (SWCNHs) are horn-shaped single-walled tubules with a conical tip. They are generally synthesized by laser ablation of pure graphite without using metal catalyst with high production rate and high yield, and typically form radial aggregates. SWCNHs are essentially metal-free and very pure, which avoids cumbersome purification and makes them user-friendly and environmentally benign. Currently, SWCNHs have been widely studied for various applications, such as gas storage, adsorption, catalyst support, drug delivery system, magnetic resonance analysis, electrochemistry, biosensing application, photovoltaics and photoelectrochemical cells, photodynamic therapy, fuel cells, and so on. This review outlines the research progress on SWCNHs, including their properties, functionalization, applications, and outlook.     

One-pot synthesis of PdAu bimetallic composite nanoparticles and their catalytic activities for hydrogen peroxide generation

We report a facile one-pot aqueous-phase synthesis of PdAu bimetallic nanoparticles with different Pd/Au ratio. The synthesis was conducted by co-reduction of Pd and Au precursor using ascorbic acid as a reducing agent and in the presence of polyallylamine hydrochloride (PAH). By high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectrometry (EDS) analyses, we found that the synthesized nanoparticles had an onion-like core/shell/shell/shell structure with Au-rich core, Pd-rich shell, Au-rich shell, and Pd shell, respectively. We also investigated the catalytic performance of the synthesized PdAu nanoparticles toward hydrogen peroxide generation reaction.     

Preparation of high performance Pd catalysts supported on untreated multi-walled carbon nanotubes for formic acid oxidation

Due to the inherent inertness of carbon nanotubes (CNTs), one of the most significant challenges in the preparation of CNT-supported catalysts is achieving a uniform deposition of nanoparticles on the surface of the nanotubes. In this paper, we report on the preparation and characterization of Pd nanoparticles supported on untreated multi-walled carbon nanotubes (MWCNTs), synthesized in the presence of glutamate. The results of Raman spectroscopy revealed that this synthetic procedure does not have a detrimental effect on the surface structure of MWCNTs. Transmission electron microscopy (TEM) measurements indicated that the dispersion of Pd nanoparticles on untreated-MWCNTs in the presence of glutamate were uniform, and a narrow particle size was observed. X-ray diffraction (XRD) patterns indicated that the Pd/MWCNT catalyst possessed a face-centered cubic crystal structure. Cyclic voltammetry and chronoamperometry tests demonstrated that the obtained Pd/MWCNT catalyst displayed superior electrocatalytic activity and stability in formic acid oxidation, as compared to both a Pd/MWCNT catalyst synthesized without glutamate and a Pd catalyst on acid-oxidized MWCNTs, under otherwise identical experimental conditions. These results indicate that the catalyst developed in this study is a superior candidate for direct formic acid fuel cells (DFAFCs).     

Sonochemical synthesis of Pt-doped Pd nanoparticles with enhanced electrocatalytic activity for formic acid oxidation reaction

Pt-doped Pd nanoparticle catalysts (Pd _n Pt, n is 12, 15 and 19) supported on carbon were synthesized by an ultrasound assisted polyol method. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, and energy dispersive X-ray spectroscopy. The electrochemical activity of the electrocatalysts was investigated in terms of formic acid oxidation reaction (FAOR) at low concentration of formic acid in 0.1 M perchloric acid at room temperature. Formic acid oxidation on the Pd _n Pt/C commences at lower potential than a commercial Pt/C. Pd₁₉Pt/C catalyst showed the highest catalytic activity in FAOR compared to that of other catalysts. The obtained electrochemical results from voltammograms indicate that Pt-doped Pd catalysts can be a promising candidate for the anode material in direct formic acid fuel cells. The synthesis procedure is not only a very facile route but also a mass producible method for preparing carbon supported alloy nanoparticles.     

多壁碳纳米管/硫化铅纳米杂化材料

在经强酸氧化处理的多壁碳纳米管(MWCNT)上修饰以苯环为核心的聚(酰胺-胺)树枝状大分子,然后以树枝状大分子修饰的碳纳米管为模板,在碳纳米管表面原位沉积PbS纳米粒子。用XRD、SEM、TEM和TGA等手段对所得MWCNT/PbS纳米杂化材料进行表征。结果表明,利用这个方法能够使PbS纳米粒子均匀修饰在碳纳米管上,纳米粒子的平均尺寸为6.5 nm。采用开口z扫描技术研究MWCNT/PbS纳米杂化材料在1 064 nm处的非线性光学性质。MWCNT/PbS纳米杂化材料在1 064 nm处的光限幅性能优于未经修饰的碳纳米管。     

Structure and electronic states of single-wall carbon nanohorns prepared under nitrogen atmosphere

Nitrogen-doped single wall carbon nanohorns (N-SWCNHs) were prepared by CO₂ laser ablation of a graphite target under nitrogen atmosphere. X-ray photoelectron spectra showed that the doped nitrogen quantities were about 1.7 and 1.1 at.% under nitrogen and nitrogen/Ar mixed atmospheres, respectively. The nitrogen atoms were implicated as the pyridine-like and threefold coordinated sp² bonding in graphene lattice of SWCNHs, and they were p-type dopants. The number of defect sites of N-SWCNHs was larger than that of SWCNHs prepared under Ar atmospheres, which was revealed by Raman and electron spin resonance measurements.     

Supported Pd Nanoparticles for Carbon–Carbon Coupling Reactions

We intent to present an overview of the available catalysts for the carbon–carbon cross-coupling reactions based on supported palladium (Pd) nanoparticles (NPs). We begin this perspective with a brief introduction about the cross-coupling reactions and the mechanistic implications of using Pd NPs as catalyst, i.e. heterogeneous versus homogeneous catalysis, then we summarize some of the most versatile Pd supported catalysts as a function of its nature. The supported catalysts have been classified in inorganic, organic and hybrid supports. Finally we outline the perspectives for the development of new Pd supported catalysts.