Diameter Distribution Of Carbon Nanotubes Research Articles

Aerosol based synthesis of highly conducting carbon nanotube macro assemblies by novel mist assisted precursor purging system

Taking hardware complexity into consideration of traditional continuous precursor purging systems for synthesis of few wall carbon nanotubes (CNTs) is a big challenge. Therefore, a novel precursor purging system for aerosol formation is designed to achieve uniform diameter distribution of CNTs, with the aerosol flow rate controlled either by number of ultrasonic mist makers or flow rate of carrier gas. Large droplets are turned into aerosol via an as-customized mist-producing system without the use of temperature or any chemical reaction. A built-in atomized gas valve is used to introduce the aerosol into a floating catalyst chemical vapour deposition (FCCVD) reactor. After an influential comparison of as-customized purging systems to the mostly used complex and big-budget systems for uniform diameter distribution, the quality of these CNT assemblies, synthesized using two different carrier gases (argon and hydrogen) is examined. Herein, CNT sheets with mostly fewer walls CNTs (diameter 2–10 nm) have been synthesized using this approach, with the controlled size of catalyst nanoparticles, under H2 atmosphere exhibiting low sulphur impurities, as evidenced by Raman, EDS, and XPS spectra, and have a fourteen-fold greater electrical conductivity (5.78 × 104S/m) than those synthesized under Ar atmosphere. Moreover, these sheets are also twisted and wrapped by insulating heat shrink tubes. The maximum current density of these conducting CNT wires having 250 µm diameter is 8.15 × 106A/m2. Further, one of the domestic applications of LED bulb (3–45 W) lightning is also demonstrated which shows the suitability of these conducting wires in numerous hi-profile applications.

The influence of the temperature and Ti and TiN sublayer material on carbon nanotubes growth

The influence of the temperature and Ti and TiN sublayer material on the height, diameter, density, and uniformity of carbon nanotubes (CNTs) growth is studied. It was found that on the TiN sublayer, CNTs form an array with a more uniform diameter distribution of CNTs than on the Ti sublayer (minimum dispersion 5.6 nm versus 8.1 nm). It is shown that for the Ti sublayer, with an increase in the growth temperature, an almost linear increase in the CNT height occurs. It was found that an increase in the CNT height is accompanied by a decrease in their diameter for both sublayers. For a given thickness of Ni, arrays with a density of 3–18 μm−2 were obtained on the Ti sublayer, and on a TiN sublayer in the range of 8–21 μm−2. The greatest uniformity of the surface distribution of CNTs is showed at 660 °C. CNT arrays on the Ti sublayer are characterized by a lower concentration of bundles than on the Ti sublayer.

Controlled growth of crossed ultralong carbon nanotubes by gas flow

Carbon nanotubes (CNTs) work as the promising components of miniature electromechanical systems due to their excellent performances from individual to bundle scales. But it’s challenging to achieve precise patterning at nanoscale resolution with controlled position and orientation. Here, we demonstrate a fluidic strategy to interlace one-dimensional (1D) ultralong CNTs into the crossed pattern in a one-step in-situ process. Semi-circular substrates of different diameters were placed in front of the growth substrate to change the path and momentum of gas flow. Such flow perturbation caused by substrates could be markedly reflected within a micro-channel reactor, which led to formation of crossed ultralong CNTs at definite positions. Furthermore, precise control over the crossing angle as well as the diameter distribution of CNTs was achieved by varying the CNT length and diameter of semi-circular substrates. Our strategy has offered a feasible route for production of crossed ultralong CNTs and will contribute to multidimensional fluidic assembly of flexible nanomaterials.

Oxygen evolution activity limits the nucleation and catalytic growth of carbon nanotubes from carbon dioxide electrolysis via molten carbonates

Controlled catalytic synthesis of technologically valuable carbon nanomaterials by the electrochemical capture and conversion of CO2 is bottlenecked by limited understanding of combined electrochemical and catalytic mechanisms at play during conversion. Here, our findings provide new insight that a key factor for the electrochemical two-electrode catalytic growth of carbon nanotubes (CNTs) on the cathode surface is the oxygen evolution activity (OEA) occurring at the anode. Poor OEA can inhibit catalytic CNT formation altogether, while increased anode OEA is correlated to changes in diameter and crystallinity of CNTs with otherwise identical cathode catalyst layers and synthesis conditions. Specifically, comparing Cu, Ni/Al2O3, and Pt anodes with Fe/stainless steel cathodes we observe over 6x smaller CNT diameter distribution and over 2x lower D/G ratio when using Pt anodes with the highest OEA. This is attributed to the role of transport between the cathode and anode during synthesis; in the case of poor anode OEA, a build-up of oxide species near the cathode surface influences the surface tension at the catalyst-carbonate interface to modify CNT diameter and properties. This mechanistic insight opens the door to routes to controllably produce high quality carbon nanomaterials from the electrochemical capture and conversion of carbon dioxide.

A spark discharge generator for scalable aerosol CVD synthesis of single-walled carbon nanotubes with tailored characteristics

We have designed and built an exhaust-free spark discharge generator for robust aerosol CVD synthesis of single-walled carbon nanotubes. The systematic study has shown the generator to provide a facile and repeatable route to precisely control the size of the catalyst particle and, therefore, carbon nanotube growth. Using a comprehensive set of methods (the analysis of differential mobility of the aerosol particles, optical spectroscopy, scanning and transmission electron microscopy, Raman spectroscopy, and atomic force microscopy) we have revealed the relation between the defectiveness, length, diameter distribution of carbon nanotubes and specific features of a generator such as electrode characteristics (breakdown voltage, composition, and current) as well as the nature of the surrounding media (carrier gas nature, flow rate). The design used has resulted in separation of the nanoparticle formation and carbon nanotube nucleation processes. This provides a mutual independence of the growth parameters and the diameter distribution of the single-walled carbon nanotubes enhancing the scalability of the process. For instance, the breakdown voltage has been shown to have nearly zero effect on diameter and length distribution of carbon nanotubes produced while strictly governing the yield. We focus here on producing specifically short carbon nanotubes (l < 500 nm) of pronounced defectiveness for drug delivery and transistor applications.

Probing the mechanics of aqueous two-phase extraction using large diameter single-walled carbon nanotubes

We have demonstrated that large diameter (1.8 ± 0.4 nm) carbon nanotubes (CNTs) can be separated by means of the aqueous two-phase extraction (ATPE). This rapid and convenient tool has enabled us to isolate fractions of particular CNT diameter distribution. We have shown how a range of parameters can be used to fine tune the characteristics of the isolated material. Interestingly, by varying the pH of the medium, we have suppressed the extraction of low diameter CNTs and only large diameter CNTs were obtained. A number of other factors such as selected surfactant concentration steps, temperature or amount of starting CNT material have been found to have a significant effect on the end result of the CNT differentiation. The findings have provided us with more insight regarding the underlying mechanics of ATPE for processing polydisperse CNT mixtures.

Co-production of hydrogen and carbon nanotubes from the decomposition/reforming of biomass-derived organics over Ni/α-Al2O3 catalyst: Performance of different compounds

Four types of biomass-derived organics (toluene/1-methylnaphthalene/phenol/ethanol) were catalytically decomposed and steam reformed over Ni/α-Al2O3 for co-production of hydrogen and carbon nanotubes (CNTs). In the decomposition reaction, the oxygen functional group in phenol and ethanol promoted the co-production of hydrogen and CNTs, while a small amount of toluene and 1-methylnaphthalene were cracked to hydrogen and amorphous carbon. In the reforming reaction, the yields of hydrogen and CNTs sharply increased. More than 2000mmol/(g-cata∗h) of H2 and 260mg/(g-cata∗h) of CNTs were produced after the reforming of toluene and ethanol. However, 1-methylnaphthalene was difficult to be reformed and small amount of CNTs were formed. The organics with low molecular weight and low degree of unsaturation conduced to the formation of hydrogen and CNTs. The growth of CNTs on Ni/α-Al2O3 mainly follows the tip-growth mechanism. The diameter distribution of CNTs is not only influenced by Ni particle size, but also related to the different organics and steam addition.

Co-production of hydrogen and carbon nanotubes on nickel foam via methane catalytic decomposition

The co-production of COx-free hydrogen and carbon nanotubes (CNTs) was achieved on 3-dimensional (3D) macroporous nickel foam (NF) via methane catalytic decomposition (MCD) over nano-Ni catalysts using chemical vapor deposition (CVD) technique. By a simple coating of a NiO–Al2O3 binary mixture sol followed by a drying–calcination–reduction treatment, NF supported composite catalysts (denoted as NiyAlOx/NF) with Al2O3 transition-layer incorporated with well-dispersed nano-Ni catalysts were successfully prepared. The effects of Ni loading, calcination temperature and reaction temperature on the performance for simultaneous production of COx-free hydrogen and CNTs were investigated in detail. Catalysts before and after MCD were characterized by XRD, TPR, SEM, TEM, TG and Raman spectroscopy technology. Results show that increasing Ni loading, lowering calcination temperature and optimizing MCD reaction temperature resulted in high production efficiency of COx-free H2 and carbon, but broader diameter distribution of CNTs. Through detailed parameter optimization, the catalyst with a Ni/Al molar ratio of 0.1, calcination temperature of 550°C and MCD temperature of 650°C was favorable to simultaneously produce COx-free hydrogen with a growth rate as high as 10.3% and CNTs with uniform size on NF.

Unifying the templating effects of porous anodic alumina on metallic nanoparticles for carbon nanotube synthesis

Carbon nanotubes (CNTs) are a promising material for many applications, due to their extraordinary properties. Some of these properties vary in relation to the diameter of the nanotubes; thus, precise control of CNT diameter can be critical. Porous anodic alumina (PAA) membranes have been successfully used to template electrodeposited catalyst. However, the catalysts used in CNT synthesis are frequently deposited with more precise techniques, such as electron beam deposition. We test the efficacy of PAA as a template for electron beam-deposited catalyst by studying the diameter distribution of CNTs grown catalyst of various thicknesses supported by PAA. These are then compared by ANOVA to the diameter distributions of CNTs grown on metal catalyst supported by a conventional alumina film. These results also allow a unified description of two templating effects, the more common particles-in-pores model, and the recently described particles-between-pores.

Fine-tuning control on CNT diameter distribution, length and density using thermal CVD growth at atmospheric pressure: an in-depth analysis on the role of flow rate and flow duration of acetylene (C2H2) gas

An optimization control has been demonstrated to obtain carbon nanotubes having specific diameter distribution, length, homogeneity, and yield during its growth by thermal chemical vapor deposition technique under atmospheric pressure. Carbon nanotubes (CNTs) were grown on silicon wafer where a predeposition of iron catalyst of 2 nm thickness was made by sputtering. The growth was conducted under two variable parameters, i.e., flow rate and flow duration. Argon and hydrogen mixture was used for pretreatment of catalyst and as etching gas, and acetylene as a carbon precursor. In-depth analysis shows that increase in flow rate from 10 to 50 sccm resulted in increase in the concentration of amorphous carbon, CNTs diameter range and decrease in length, we found best result at 20 sccm flow rate of acetylene gas. On the other hand, as we varied flow duration from 6 to 14 min, with keeping flow rate of acetylene 20 sccm constant, dense homogeneous growth of horizontal CNTs network plus an increase in length and diameter range were observed. An optimization of flow rate and flow duration is presented here to obtain a selective diameter distribution and length as expected by this growth technique. Atomic force microscopy, field emission scanning electron microscopy and Raman spectroscopy were used to investigate the samples’ morphologies in support of the observations made.

Development and characterization of MWNTs/Chitosan biocomposite fiber

The Preparation of conductive biocomposite fiber through Carbon nanotubes (CNTs) incorporation into biopolymer matrixes has stimulated much interest for bio-implant applications. The present study focuses on development and characterization of biocomposite fiber composed of chitosan (CHT) as a biopolymer and multiwall carbon nanotubes (MWNTs) as a conductive filler. In term of processing, the most important challenge is to prepare a highly stable dispersion of MWNTs in biopolymer matrix. The hydrodynamic diameter distribution of CNTs in acetic acid solution acquired by dynamic light scattering (DLS).Results demonstrate the supreme stability of CNTs dispersion which is extremely essential for homogenous distribution of CNT in polymeric matrix. Rheological properties of the spinning solution have also been investigated to adjust the viscosity for fiber processing step. A range of viscosity between 2000–8000 cP, has been recorded in different CNT loading. The scanning electron microscopy (SEM) images of the surface and cross sectional area of the fibers reveal the formation of nano-pores after MWNT addition. The tensile strength show a maximum increase of about 33.65 % compared to bare CHT. Also, the measurement of four probe electrical conductivity for different MWNTs loading shows a maximum conductivity of 0.107 S/cm at percolation threshold of 2.89 wt%.

A comparative study of arc discharge and chemical vapor deposition synthesized carbon nanotubes

A comparative study on carbon nanotubes (CNTs) synthesized by arc discharge and chemical vapor deposition (CVD) techniques have been performed to use CNTs as an application for hydrogen storage. Synthesized CNTs have been characterized by using X-ray diffraction (XRD), Raman spectroscopy, FT-IR spectroscopy and Scanning electron microscopy (SEM) measurements. X-ray diffraction confirms the structure and diameter distribution of CNTs. It is observed from Raman spectroscopy that D-band (1345 cm−1) for CNTs synthesized by arc discharge is broad, while CNTs synthesized by CVD it is almost negligible due to nested layers of carbon. The G band (1707 cm−1) in CVD synthesized CNTs is sharp than the CNTs synthesized by arc discharge. FT-IR spectroscopy confirms the stretching of bonds (CC) due to disordering of CNTs. From scanning electron microscopy (SEM) it is observed that CNTs obtained by arc discharge are agglomerated carbon blobs and almost amorphous type carbon, while CNTs obtained by CVD shows bundles of nanotubes.

Optimizing the synthesis of cobalt-based catalysts for the selective growth of multiwalled carbon nanotubes under industrially relevant conditions

An industrially applicable cobalt-based catalyst was optimized for the production of multiwalled carbon nanotubes (CNTs) from ethene in a hot-wall reactor. A series of highly active Co–Mn–Al–Mg spinel-type oxides with systematically varied Co:Mn ratios was synthesized by precipitation and calcined at different temperatures. The addition of Mn drastically enhanced the catalytic activity of the Co nanoparticles resulting in an extraordinarily high CNT yield of up to 249 g CNT/g cat. All quaternary catalysts possessed an excellent selectivity towards the growth of CNTs. The detailed characterization of the obtained CNTs by electron microscopy, Raman spectroscopy and thermogravimetry demonstrated that a higher Mn content results in a narrower CNT diameter distribution, while the morphology of the CNTs and their oxidation resistance remains rather similar. The temperature-programmed reduction of the calcined precursors as well as in situ X-ray absorption spectroscopy investigations during the growth revealed that the remarkable promoting effect of the Mn is due to the presence of monovalent Mn(II) oxide in the working catalyst, which enhances the catalytic activity of the metallic Co nanoparticles by strong metal-oxide interactions. The observed correlations between the added Mn promotor and the catalytic performance are of high relevance for the production of CNTs on an industrial scale.

Chemical Vapor Deposition of Carbon Nanotubes: A Review on Growth Mechanism and Mass Production

This review article deals with the growth mechanism and mass production of carbon nanotubes (CNTs) by chemical vapor deposition (CVD). Different aspects of CNT synthesis and growth mechanism are reviewed in the light of latest progresses and understandings in the field. Materials aspects such as the roles of hydrocarbon, catalyst and catalyst support are discussed. Many new catalysts and new carbon sources are described. Growth-control aspects such as the effects of temperature, vapor pressure and catalyst concentration on CNT diameter distribution and single- or multi-wall formation are explained. Latest reports of metal-catalyst-free CNT growth are considered. The mass-production aspect is discussed from the perspective of a sustainable CNT technology. Existing problems and challenges of the process are addressed with future directions.

Sorting and transmission electron microscopy analysis of single or double wall carbon nanotubes

AbstractOn the basis of the recent progress on the sorting of carbon nanotubes' structure with respect to their diameter or number of walls, we investigate by transmission electron microscopy the sorting efficiency, with a comparison with optical absorption spectroscopy measurements. We study density gradient ultracentrifugation sorted single walled or double walled carbon nanotubes, showing obviously the ability to separate carbon nanotubes of different diameters or/and number of walls. This microscopic approach affords accurate information about the sorted samples such as the real mean diameter, the relative concentration of double walled carbon nanotubes over single walled carbon nanotubes, standard deviation, and the real diameter distribution of carbon nanotubes, even beyond any possible accurate analysis from optical absorption spectroscopy. Therefore, we demonstrate that the diameter analysis of the sorted samples by TEM can indeed afford some information about the relevant optical properties of carbon nanotubes.

CVD growth of carbon nanotubes using molecular nanoclusters as catalyst

AbstractThe growth of isolated carbon nanotubes (CNTs) using chemical vapour deposition process catalysed by the molecular nanocluster {Mo72Fe30} of the Keplerate structure type in different oxidation states is studied on different substrates. The molecule in its oxidized state (MoVI/FeIII) agglomerates in solution. Thus, nucleation from large catalyst particles cannot provide a narrow CNT diameter distribution. However, a partially reduced and charged form of the same molecule (MoV/MoVI) enables growth from small nucleation sites as evidenced by atomic force microscope imaging, albeit the yield in this case is dramatically reduced.

Catalytic synthesis of carbon nanotubes using Ni- and Co-doped calcium tartrates

Calcium tartrate doped with Ni and/or Co has been used as a catalyst source in the chemical vapor deposition synthesis of carbon nanotubes (CNTs). Thermolysis of doped calcium tartrate in an inert atmosphere was shown to yield Ni, Co or Ni–Co nanoparticles ∼6 nm in diameter dispersed in a calcium oxide matrix. The CNT synthesis was carried out by ethanol vapor decomposition at 800 °C. The structure of the products was characterized by transmission electron microscopy and Raman spectroscopy. It was found that Ni nanoparticles embedded in CaO provide the narrowest diameter distribution of CNTs, while the bimetallic Ni–Co catalyst allows the formation of the thinnest CNTs with the outer diameter of ∼2 nm. This type of CNT is more likely to be responsible for the lowest value of the turn-on field (∼1.8 V/μm) for the emission current detected for the latter sample.

Synthesis of Single- and Double-Wall Carbon Nanotubes by Gas Flow-Modified Catalyst-Supported Chemical Vapor Deposition

The synthesis of single- and double-wall carbon nanotubes by gas flow-modified, catalyst-supported chemical vapor deposition (CCVD) is reported. We have investigated the gas flow condition dependence on the synthesis of carbon nanotubes (CNTs) by placing blocks in the CCVD reactor. Carbon nanotubes having large diameters are preferentially grown under turbulent flow conditions. This indicates that the diameter distribution of CNTs can be controlled by modification of the gas flow condition in the CCVD.

The effect of reaction temperature on the diameter distribution of carbon nanotubes grown from ethylene decomposition over a Co-La-O catalyst

The production of carbon nanotubes (CNTs) by the chemical catalytic vapor deposition (CCVD) process was examined over a Co-La-O catalyst prepared by combustion synthesis method. Some important advantages of preparing nanotubes are obvious with Co-La-O as catalyst, i.e., the product yield is higher (up to 412.6%) and the reaction temperature is lower (<750 °C) compared with other methods. The effects of reaction temperature on the carbon yield, diameter distribution and quality of CNTs were investigated. Transmission electron microscopy (TEM) studies show that an increase in reaction temperature produces CNTs with larger average diameter and broader diameter distribution. This is basically due to the agglomeration of metallic cobalt at higher reaction temperatures to form larger and non-uniform metallic clusters which are responsible for the growth of CNTs. Raman spectra further elucidate that better graphitized CNTs are produced at higher reaction temperatures. After a single-step purification by hydrochloric acid, the purity of CNTs can reach up to 96%.

The effect of substrate morphology on the diameter distribution of carbon nanotubes grown on silica and ceramic substrates

Large-scale well-aligned carbon nanotube film and carbon nanotube bundles have been fabricated on smooth silica and rough polycrystalline ceramic substrates by pyrolysis of ferrocene/melamine mixtures. The images of transmission electron microscopy (TEM) and scanning electron microscope (SEM) show that carbon nanotubes grown on the silica substrate have uniform outer diameters of about ∼ 25 nm and lengths of about 40 μm, while those on the ceramic substrate have outer diameters from 10 to 90 nm and lengths up to 100 μm. Electron energy-loss spectroscopy (EELS) spectra show that nanotubes grown on the two different substrates are pure carbon tubes. The effects of substrate micro-morphologies on the diameters of carbon nanotubes have been discussed.