Easy synthesis of a nanostructured hybrid array consisting of gold nanoparticles and carbon nanotubes

A nanostructured hybrid consisting of a high-density and uniform assembly of gold nanoparticles (AuNPs) on carbon nanotubes (CNTs) was prepared using easy methods. The pyrolysis of iron(II) phthalocyanine (FePc) on a Si substrate under an atmosphere of hydrogen/argon was used to produce multiwalled carbon nanotubes (MWCNTs) with 12 nm in diameter and 4 μm in length. Then, Au nanocolloid solution, which contained dodecanethiol-capped Au nanoparticles synthesized by solution chemical method, was deposited on the synthesized CNT array and heated at 300 °C for 1 h under Ar. The synthesis temperature of CNT governs the AuNP-CNT hybrid structure and surface nitrogen concentration from decomposition of FePC. CNTs synthesized at 800 °C exhibit the finest particle size and most homogeneous dispersity of assembled AuNPs in comparison to hybrids whose CNTs are synthesized at other temperatures. These features are considered to correlate with the surface nature of the grown CNT; good dispersity of AuNPs on CNT results from interaction between the thiolate molecules capped on the AuNPs and the N atoms doped into the grown CNT. Assembling AuNPs to CNT contributes the electrical conductivity enhancement of the CNT hybrid array.     

Surfactant-free dispersion of silver nanoparticles into MWCNT-aqueous nanofluids prepared by one-step technique and their thermal characteristics

This paper reports a significant enhancement in the thermal conductivity of silver-nanoparticle-based aqueous nanofluids with the addition of negligible amounts of multi-walled carbon nanotubes (MWCNTs). The present work was conducted using purified MWCNTs/water nanofluids prepared by a wet grinding method. Silver nanoparticles were dispersed into the MWCNT/water nanofluids via a one-step method using pulse power evaporation, which was observed to improve the dispersibility and thermal conductivity of the nanofluids. A particle sizing system (PSS) and transmission electron microscopy (TEM) were used to confirm the size of silver nanoparticles in base fluids. The PSS measurement results reveal that the size of the silver nanoparticles was approximately 100 nm, which is in good agreement with the results obtained from TEM and SEM. The maximum absorbance (2.506 abs at a wavelength of 264 nm) and highest thermal conductivity enhancement (14.5% at 40 °C) were achieved by a fluid containing ‘0.05 wt% MWCNTs–3 wt% Ag’ composite.     

Synthesis of carbon nanotubes over gold nanoparticle supported catalysts

The synthesis of carbon nanotubes (CNTs) through the catalytic decomposition of acetylene was carried out over gold nanoparticles supported on SiO₂-Al₂O₃. Monodispersed gold nanoparticles with 1.3-1.8 nm in diameter were prepared by the liquid-phase reduction method with dodecanethiol as protective agent. The carbon products formed after acetylene decomposition consist of multi-walled carbon nanotubes with layered graphene sheets, carbon nanofilaments (CNFs), and carbon nanoparticles encapsulating gold particles. The observed CNTs have outer diameters of 13-25 nm under 850 °C. The influence of several reaction parameters, such as kind of carriers, reaction temperature, gas flow rate, was investigated to search for optimum reaction conditions. The CNTs were observed at a relatively low temperature (550 °C). The silica-alumina carrier showed higher activity for the formation of CNTs than others used in the screening test. With increasing temperature, the CNTs showed cured structures having thick diameters and inside compartments. When Au content on the support was over 5 wt.%, the gold nanoparticles coagulated to form large ones >20 nm in diameter and became encapsulated with graphene layers after decomposition of acetylene.     

Lithographically defined site-selective growth of Fe filled multi-walled carbon nanotubes using a modified photoresist

Partially Fe filled multi-walled carbon nanotubes (MWCNTs) were grown by chemical vapor deposition with propane at 850 °C using a simple mixture of iron (III) acetylacetonate (Fe(acac)₃) powder and conventional photoresist. Scanning electron microscopy revealed that catalytic nanoparticles with an average diameter of 70 nm are formed on the Si substrate which governs the diameter of the MWCNTs. Transmission electron microscopy shows that the nanotubes have a multi-walled structure with partial Fe filling. A site-selective growth of partially Fe filled MWCNTs is achieved by a simple photolithographic route.     

Ultrasonic synthesis of highly dispersed Pt nanoparticles supported on MWCNTs and their electrocatalytic activity towards methanol oxidation

A new method of synthesis of highly dispersed Pt nanoparticles with large catalytic surface area on multi-walled carbon nanotubes (MWCNTs) under high-intensity ultrasonic field was developed. The method, with low processing temperature at 25 °C, took only about 5 min. The surface characterization of MWCNTs was carried out by fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy methods. The electrochemical surface area and pore volume of MWCNTs were also examined. The result showed that functional groups of the MWCNTs which favored the high loading and high dispersion of particles and electrochemical surface area of MWCNTs were reinforced in the case of high-intensity ultrasonic field. The Pt/MWCNT catalysts were characterized by energy dispersion X-ray spectra analysis (EDX), transmission electron microscopy (TEM) and X-ray diffraction (XRD) measurements. The prepared Pt nanoparticles were uniformly dispersed on the MWCNT surface. The mean size of Pt particles was 3.4 ± 0.2 nm. The electrocatalytic properties of Pt/MWCNT composites and kinetic characterization for methanol electro-oxidation were investigated by cyclic voltammetry. The Pt/MWCNT catalysts prepared for 5 min in ultrasonic field present excellent electrochemical activities. The schematic of the reaction was also introduced.     

Selectively attaching Pt-nano-clusters to the open ends and defect sites on carbon nanotubes for electrochemical catalysis

Pt nano-clusters (nano-Pt) have been selectively attached to the open ends and defect sites of mildly oxidized multi-wall carbon nanotubes (MWCNTs) on a glassy carbon electrode (GCE) by a cyclic voltammetry (CV) electrodeposition method. The nano-Pt functionalized MWCNTs were characterized by XPS, XRD, FE-SEM and electrochemical techniques. The catalytic activity of the nano-Pt functionalized MWCNTs were tested by an oxygen reduction reaction (ORR) and a methanol oxidation reaction (MOR). Taking the ORR as an example, we found that the electrocatalytic activity of the nano-Pt functionalized MWCNTs can be well tuned by varying the cycle number and the PtCl₆²⁻ concentration of the deposition conditions. The average size of the nano-Pt was 123 nm, and it was constituted of nano-crystallite of an average size of 10.8 nm. Though the large nano-Pt particles (100-150 nm) were only attached on the open ends and defect sites of the MWCNTs, which were very different from the highly dispersed small Pt nanoparticles (<10 nm) on carbon nanotubes reported by other research groups. In our method, excellent electrocatalytic activity of the nano-Pt functionalized MWCNTs for ORR and MOR can be obtained. The mechanisms for nano-Pt deposition are proposed.     

Solid-phase synthesis of multi-walled carbon nanotubes from butadiynyl-ferrocene-containing compounds

Multi-walled carbon nanotubes (MWCNTs) have been synthesized from novel butadiynyl-ferrocene-containing compounds. The formation of the MWCNTs occurs in the solid phase at ambient pressure in a typical high-temperature furnace. Heat treatment of the various compounds to temperatures up to 1300 °C under atmospheric pressure resulted in the decomposition of the ferrocene units and the formation of Fe nanoparticles in the polymeric-to-carbon nanoparticle-to-carbon nanotube compositions. The Fe atoms, clusters, and/or nanoparticles are the key to the formation of the carbon nanotubes. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy studies show the presence of a large quantity of MWCNTs in the carbonaceous solid residue.     

Electrocatalytic performance of carbon nanotube-supported palladium particles in the oxidation of formic acid and the reduction of oxygen

We describe a simple approach for the synthesis of nanosized Pd particles supported on multiwall carbon nanotubes (MWCNTs) and their electrocatalytic performance in the oxidation of formic acid and the reduction of oxygen. The metal precursors are pre-organized on poly(diallyldimethylammonium) chloride-wrapped MWCNTs by electrostatic interaction and chemically reduced to obtain Pd nanoparticles. The MWCNT-supported nanoparticles are characterized by UV-visible spectroscopy, X-ray diffraction (XRD), scanning and transmission electron microscopy and electrochemical measurements. MWCNTs are uniformly decorated with closely packed array of nanoparticles. The nanoparticles on the MWCNTs have spherical and rod-like shapes with size ranging from 5 to 10 nm. XRD and selected area electron diffraction measurements of the nanoparticles show (1 1 1), (2 0 0) and (2 2 0) reflections of the Pd lattice. The electrocatalytic activity of the nanoparticles towards oxidation of formic acid and reduction of oxygen is examined in acidic solution. The MWCNT-supported particles exhibit excellent electrocatalytic activity. The electrocatalytic reduction of oxygen follows the peroxide pathway. Surface morphology and coverage of particles on the nanotubes control the electrocatalytic activity. The large surface area and high catalytic activity of the MWCNT-supported nanoparticles facilitate the electrocatalytic reactions at a favorable potential.     

Synthesis of Pt nanocatalyst with micelle-encapsulated multi-walled carbon nanotubes as support for proton exchange membrane fuel cells

Micelle-encapsulated multi-walled carbon nanotubes (MWCNTs) with sodium dodecyl sulfate (SDS) were used as catalyst support to deposit platinum nanoparticles. High resolution transmission electron microscopy (HRTEM) images reveal the crystalline nature of Pt nanoparticles with a diameter of ∼4 nm on the surface of MWCNTs. A single proton exchange membrane fuel cell (PEMFC) with total catalyst loading of 0.2 mg Pt cm⁻² (anode 0.1 and cathode 0.1 mg Pt cm⁻², respectively) has been evaluated at 80 °C with H₂ and O₂ gases using Nafion-212 electrolyte. Pt/MWCNTs synthesized by using modified SDS-MWCNTs with high temperature treatment (250 °C) showed a peak power density of 950 mW cm⁻². Accelerated durability evaluation was carried out by conducting 1500 potential cycles between 0.1 and 1.2 V with 50 mV s⁻¹ scan rate, H₂/N₂ at 80 °C. The membrane electrode assembly (MEA) with Pt/MWCNTs showed superior performance stability with a power density degradation of only ∼30% compared to commercial Pt/C (70%) after potential cycles.     

The preparation of multi-walled carbon nanotubes with a Ni-P coating by an electroless deposition process

The multi-walled carbon nanotubes (MWCNTs, mean diameter: 100-200 nm) with nickel-phosphorous (Ni-P) coatings were obtained by an electroless deposition process. To prepare the MWCNTs covered with continual Ni-P layers, a pre-treatment procedure comprised of acid-cleaning, sensitization and activation has been developed. The resulting MWCNTs have a uniform distribution of the Ni-P layers coated on the MWCNTs with the fibrous appearance maintained. X-ray diffraction (XRD) and transmission electron microscopy (TEM) observations revealed that the as-coated MWCNTs were comprised of the amorphous Ni-P layers and inner carbon nanotubes covered with the Ni-P layers. These amorphous Ni-P-coated MWCNTs were used as precursors for preparing MWCNTs with nanocrystalline Ni-P(crystalline Ni and Ni₃P intermetallic compound) layers by the heat-treatment above 400 °C, which were determined by differential scanning calorimeter (DSC) and XRD studies. The results of this work provide an effective electrochemical method for preparing powdery MWCNTs with Ni-P layer as new composite materials from the aqueous solution.     

Tetrahydrofuran-functionalized multi-walled carbon nanotubes as effective support for Pt and PtSn electrocatalysts of fuel cells

A novel and simple method to functionalize multi-walled carbon nanotubes (MWCNTs) is developed using tetrahydrofuran (THF) solvent as the functionalization and anchoring agent. The effectiveness of the method is demonstrated by the synthesis of uniformly distributed Pt and PtSn nanoparticles on THF-functionalized MWCNTs. Transmission electron microscopy and X-ray diffraction results indicate that Pt and PtSn nanoparticles with a narrow particle size distribution and an average particle size of ∼4 nm are synthesized on THF-functionalized MWCNTs. The lattice parameter of PtSn/MWCNTs increases with the Sn content, indicating the successful formation of PtSn binary nanoparticles. The results demonstrate the applicability and effectiveness of the THF-functionalized MWCNTs as effective catalyst supports in the development of highly dispersed and active Pt and Pt-based electrocatalysts for low temperature fuel cells. The successful functionalization of MWCNTs by THF also indicates that there could be a strong σ-π interaction between the MWCNTs and the THF.     

Controllable fabrication of SnO2-coated multiwalled carbon nanotubes by chemical vapor deposition

A simple and efficient approach for coating multiwalled carbon nanotubes (MWCNTs) with size-controllable SnO₂ nanoparticles by chemical vapor deposition has been developed using tin hydride (SnH₄) gas as the source of SnO₂ at 550 °C. The size and coverage of SnO₂ nanoparticles can be adjusted by simply controlling the deposition time and the flow rate of the SnH₄/N₂ mixture gas during the CVD procedure. In addition, by using the MWCNTs as a sacrificial template, a kind of one-dimensional chain-like SnO₂ nanostructure has been synthesized by increasing the deposition temperature to 730 °C. This technique may provide a good way to produce tunable SnO₂-MWCNT composites.     

Sonochemical hybridization of carbon nanotubes with gold nanoparticles for the production of flexible transparent conducing films

We have demonstrated the fabrication of flexible, transparent, conducting multiwalled carbon nanotube (MWCNT)/gold nanoparticle hybrid films with improved optoelectronic properties by combining the ionic liquid-assisted sonochemical method (ILASM) for hybrid synthesis with the vacuum filtration (VF) method for thin film preparation. Au nanoparticles (NPs) with diameters of 10.3 ± 1.5 nm were uniformly distributed onto the sidewalls of MWCNTs through ILASM, and flexible, transparent, conducting films of Au/MWCNT hybrids (HBs) were reproducibly fabricated by the VF method. In particular, the sheet resistance of Au-MWCNT-HB films was more than 2-fold lower than the sheet resistance of pristine MWCNT films due to the well-interconnected three-dimensional nanotube network structure and the synergistic effect of hybridization of MWCNTs with Au-NPs.     

Optimization of deposition parameters of thin films composed of Pt nanoparticles

The optimization of a number of film deposition variables was carried out for thin Pt films formed from a sol (generated by the reduction of hexachloroplatinic acid (CPA) by sodium ethoxide) containing Pt nanoparticles and a partially reduced Pt(II) species (NaPtCl₃(C₂H₄)). Increasing the film drying temperature leads to the thermal decomposition of this species, generating another Pt(II) crystalline species, as well as additional Pt. It also leads to improved inter-particle and particle-substrate contact of the 2 nm Pt nanoparticles, thereby increasing the Pt film charge density up to 200 °C drying temperature. Above this temperature, particle sintering occurs (8 nm diameter when dried to 400 °C), consistent with an observed loss in film charge. Increasing the withdrawal rate of the substrate from the sol leads to a thicker Pt film, while maintaining a constant Pt particle size. By changing the substrate from Au sputter-coated glass to carbon paper (CP), the Pt loading was increased; however, the effective usage of Pt was lower than anticipated, possibly related to the pooling of the liquid sol within the CP structure, resulting in poor nanoparticle dispersion.     

MWCNT coatings obtained by thermal CVD using ethanol decomposition

A low-cost and reliable method to produce MWCNT coatings on large surfaces, with possibility to scale up to larger output, aiming at gas sensor applications is reported. The process was based on ethanol decomposition in the temperature range 700-900 °C. Different qualities of carbon were produced depending on the experimental parameters. For the samples deposited on sapphire and using Ni as catalyst a high diversity of carbon products (amorphous carbon, graphite plates, MWCNTs, onion-like graphene, etc.) were registered, while for the samples deposited on quartz MWCNTs with better crystallinity were observed. Carbon nanofibres (about 50-60 nm diameter) were observed only for the samples with Fe catalyst. Depending on temperature, nanotubes with different thickness of amorphous carbon coating occurred. According to our findings, the deposition of amorphous carbon phase can be minimized depending on the oxygen content in the process.     

Pinecone shape hydroxypropyl-β-cyclodextrin on a film of multi-walled carbon nanotubes coated with gold particles for the simultaneous determination of tyrosine, guanine, adenine and thymine

A conductive composite film containing functionalized multi-walled carbon nanotubes (fMWCNTs), gold nanoparticles (Au) with hydroxypropyl-β-cyclodextrin (HPβCD) as catalysts have been synthesized on glassy carbon, gold and on indium tin oxide electrodes by potentiostatic methods. The presence of fMWCNTs and HPβCD in the composite film enhances the active surface coverage concentration of Au by 397.0%. The presence of nanoparticles of gold catalyst in the film enhances the functional properties and produces an overall increase in the sensitivity of the modified electrodes. These modified electrodes exhibit promising electrocatalytic activity towards the oxidation of tyrosine (TYR), guanine (GU), adenine (AD) and thymine (THY) present in pH 7.4 aqueous solutions. Well separated voltammetric peaks are obtained between TYR and GU (80 mV), GU and AD (290 mV), AD and THY (185 mV) present in the analyte mixture. The sensitivity values of the composite films from cyclic voltammetry (CV) and semi derivative differential pulse voltammetry (DPV) show that, the composite film modified electrodes are efficient and they could be applied in biosensor devices. However, a detailed comparison between the sensitivities obtained using CV and semi derivative DPV shows that, the sensitivity obtained in semi derivative DPV technique is higher than CV. Electrochemical quartz crystal microbalance, scanning electrochemical microscope and scanning electron microscope techniques have been used for the electrochemical characterizations and surface morphology studies.     

Production of single-walled carbon nanotubes with narrow diameter distribution using iron nanoparticles derived from DNA-binding proteins from starved cells

Iron nanoparticles derived from DNA-binding proteins from starved cells (Dps) were used to grow single-walled carbon nanotubes (SWCNTs) with narrow diameter distribution. An atomic force microscopy, Raman spectroscopy, and photoluminescence were used for evaluation of diameter or chirality distribution of the SWCNTs. We found that thin SWCNTs (1.1 nm diameter) were grown from the large Dps-derived nanoparticles (2.4 nm diameter) on and above the substrates. From the size comparison with ferritins and Co-filled apoferritins, we also found that SWCNTs become thinner as the catalyst becomes smaller. The synthesis of smaller catalysts (ca. 1 nm diameter) and their use for growth becomes crucial for the control of SWCNT diameter.     

Solid-phase transformation of glass-like carbon nanoparticles into nanotubes and the related mechanism

Multi-walled carbon nanotubes have been synthesized through the solid-phase transformation of metal-containing glass-like carbon nanoparticles by heating at temperatures of 800-1000 °C. From microscopic observations on the morphologies and structures of the nanotubes and various intermediate objects, it is shown that the transformation occurs by nanoparticles first assembling into wire-like nanostructures, and then transforming into nanotubes via particle-particle coalescence and structural crystallization.     

Carbon nanotubes and onions from carbon monoxide using Ni(acac)2 and Cu(acac)2 as catalyst precursors

New catalyst precursors (copper and nickel acetylacetonates) have been used successfully for the synthesis of carbon nanotubes and onion particles from carbon monoxide. Catalyst nanoparticles and carbon products were produced by metal-organic precursor vapour decomposition and catalytic disproportionation of carbon monoxide in a laminar flow reactor at temperatures between 705 and 1216 °C. Carbon nanotubes (CNTs) were formed in the presence of nickel particles at 923-1216 °C. The CNTs were single-walled, 1-3 nm in diameter and up to 90 nm long. Hollow carbon onion particles (COPs) were produced in the presence of copper particles at 1216 °C. The COPs were from 5 to 30 nm in diameter and consisted of several concentric carbon layers surrounding a hollow core. The results of computational fluid dynamics calculations to determine the temperature and velocity profiles and mixing conditions of the species in the reactor are presented. The mechanisms for the formation of both CNTs and COPs are discussed on the basis of the experimental and computational results.     

Epoxy-based carbon films with high electrical conductivity attached to an alumina substrate

Carbon-based films (0.8-13 μm thick) with good bonding to the substrate and high processability were produced at 650 °C on an alumina substrate, using SU 2.5 bisphenol-A type novolac epoxy (plus triethyleneteramine curing agent) as the carbon precursor. This precursor gave crack-free and scratch resistant carbon films. Interconnected filamentary nickel nanoparticles were more effective for conductivity enhancement than silver nanoparticles or multiwalled carbon nanotubes at 5 vol.% or below, in spite of the high conductivity of silver and the high aspect ratio of nanotubes. The carbon film with 2.5 vol.% nickel showed resistivity 6 × 10⁻³ Ω cm.