Shaped Carbon Nanomaterials Research Articles

Microwave irradiation for the production of graphene-nanodiamond composite carbon spheres

Structured spherically shaped carbon nanomaterials exhibit great application potential in various fields. In this work, sub-micron composite carbon spheres (CCSs) were successfully fabricated directly from graphite (Gra) and a small percentage of nanodiamonds (NDs) mixture under microwave irradiation. This was achieved using a scalable micro-mixing of xylene solution of NDs with a colloidal suspension of Gra in dimethylformamide (DMF), with no surfactants, catalysts, or other auxiliary chemicals. The diameters, shape, and yield of the produced CCSs were found to depend on the microwave operating parameters, including reaction time, power, and relative concentration of NDs to that of Gra. The structure of CCSs was established/optimized using the microwave-assisted chemical route at a fixed power of 1000 W for 30 min. These CCSs were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). This new composite structure might be useful for various applications including energy harvesting, storage, batteries, supercapacitors, etc.

Physicochemical properties of nitrogen-doped carbon nanotubes from metallocenes and ferrocenyl imidazolium compounds

Shaped carbon nanomaterials (SCNMs) were synthesized via the chemical vapour deposition (CVD) technique by using typical metallocenes (ferrocene, nickelocene, cobaltocene, and ruthenocene), and more interestingly, by use of novel ferrocenyl imidazolium derivatives, containing -Cl (FcImCl), -NO2 (FcImNO2) and -CH3 (FcImCH3) substituents as catalysts. Acetonitrile was applied both as a carbon and nitrogen source at temperatures 800–900 °C. The SCNMs, namely, carbon nanotubes (CNTs), carbon spheres (CS), carbon fibres (CF) and amorphous carbons (ACs) were obtained in varying ratios depending on the catalyst and carbon sources. The ferrocenyl imidazolium catalysts produced nitrogen-doped CNTs (N-CNTs) with bamboo-like structures. The yields of various reactions were temperature-dependent, with the highest amount of N-CNTs obtained at 850 °C. In all samples, the composition was mainly of CS and N-CNTs except for nickelocene at 800 °C that gave CFs as a “minor” product. Ferrocene and nickelocene in acetonitrile produced well-aligned N-CNTs while cobaltocene and ruthenocene gave ‘spaghetti-like’ structures. In the case of ferrocenyl imidazolium catalyst, a coiled N-CNTs morphology was produced from FcImCl catalyst. Also, higher percentage of N-CNTs with traces of CS were obtained from the FcImCl and FcImCH3 catalysts in acetonitrile at 850 °C, while higher percentage of CS and AC were obtained for FcImNO2 catalyst. In all the catalysts, the use of acetonitrile promoted nitrogen-doping (samples with more disordered and with smaller outer-diameters). Thus, this study demonstrates that the synthesis of N-CNTs from nitrogen-containing ferrocenyl imidazolium compounds as catalyst sources, provided higher percentage of N-CNTs which can be suitable for various application.

Comparative toxicity of three differently shaped carbon nanomaterials on Daphnia magna: does a shape effect exist?

The acute toxicity of three differently shaped carbon nanomaterials (CNMs) was studied on Daphnia magna, comparing the induced effects and looking for the toxic mechanisms. We used carbon nano-powder (CNP), with almost spherical primary particle morphology, multi-walled carbon nanotubes (CNTs), tubes of multi-graphitic sheets, and cubic-shaped carbon nanoparticles (CNCs), for which no ecotoxicological data are available so far. Daphnids were exposed to six suspensions (1, 2, 5, 10, 20 and 50 mg L−1) of each CNM, and then microscopically analyzed. Ultrastructural analyses evidenced cellular uptake of nanoparticle in CNP and CNT exposed groups, but not in samples exposed to CNCs. Despite this difference, very similar effects were observed in tissues exposed to the three used CNMs: empty spaces between cells, cell detachment from the basal lamina, many lamellar bodies and autophagy vacuoles. These pathological figures were qualitatively similar among the three groups, but they differed in frequency and severity. CNCs caused the most severe effects, such as partial or complete dissolution of the brush border and thinning of the digestive epithelium. Being the cubic shape not allowed to be internalized into cells, but more effective than others in determining physical damages, we can conclude that shape is an important factor for driving nanoparticle uptake by cells and for determining the acute toxicological endpoints. Shape also plays a key role in determining the kind and the severity of pathologies, which are linked to the physical interactions of CNMs with the exposed tissues.

A facile approach towards increasing the nitrogen-content in nitrogen-doped carbon nanotubes via halogenated catalysts

Nitrogen-doped carbon nanotubes (N-CNTs) have been synthesized at 850°C via a CVD deposition technique by use of three ferrocenyl derivative catalysts, i.e. para-CN, -CF3 and -Cl substituted-phenyl rings. The synthesized catalysts have been characterized by NMR, IR, HR-MS and XRD. The XRD analysis of the para-CF3 catalyst indicates that steric factors influence the X-ray structure of 1,1′-ferrocenylphenyldiacrylonitriles. Acetonitrile or pyridine was used as carbon and nitrogen sources to yield mixtures of N-CNTs and carbon spheres (CS). The N-CNTs obtained from the para-CF3 catalysts, in pyridine, have the highest nitrogen-doping level, show a helical morphology and are less thermally stable compared with those synthesized by use of the para-CN and -Cl as catalyst. This suggests that fluorine heteroatoms enhance nitrogen-doping in N-CNTs and formation of helical-N-CNTs (H-N-CNTs). The para-CF3 and para-Cl catalysts in acetonitrile yielded iron-filled N-CNTs, indicating that halogens promote encapsulation of iron into the cavity of N-CNT. The use of acetonitrile, as carbon and nitrogen source, with the para-CN and -Cl as catalysts also yielded a mixture of N-CNTs and carbon nanofibres (CNFs), with less abundance of CNFs in the products obtained using para-Cl catalysts. However, para-CF3 catalyst in acetonitrile gave N-CNTs as the only shaped carbon nanomaterials.

Application of heteroatom-containing iron(II) piano-stool complexes for the synthesis of shaped carbon nanomaterials

Based on iron(II) piano-stool complexes, five compounds were synthesized by varying the organo-heteroatom ligands in their structure. Two different heteroatoms were considered, namely, nitrogen and sulfur, as constituents of the ligands on the complexes. Compounds 1 and 2 contained the nitrogen heteroatom in their ligands whilst 3 to 5 contained sulfur. These compounds were used as catalysts in the synthesis of shaped carbon nanomaterials (SCNMs) by means of the floating catalyst chemical vapour deposition method (CVD). The nitrogen-containing catalysts produced nitrogen-doped carbon nanotubes (N-CNTs) with bamboo morphology. On the other hand, the sulfur-containing catalysts produced mainly carbon spheres (CS) and some amorphous carbon (AC) as the bulk of the resulting SCNM products. In the case of compounds 1 and 2, higher nitrogen content and reaction temperatures were shown to promote nitrogen-doping which led to more disordered N-CNTs and an increase in the outer diameter of the N-CNTs. In the case of compounds 3 to 5, higher reaction temperatures led to more graphitic CS and an increase in the average diameter of the CS. The various results and analyses show that the synthetic variations of not only reaction conditions, but also the type of substituent on the organometallic catalyst ligand and its structure, can lead to a level of control towards the resulting carbon nanostructures.

Nitrogen‐Doped Carbon Nanotubes Synthesised by Pyrolysis of (4‐{[(pyridine‐4‐yl)methylidene]amino}phenyl)ferrocene

Nitrogen‐doped carbon nanotubes (N‐CNTs) were synthesized by pyrolysis of (4‐{[(pyridine‐4‐yl)methylidene]amino}phenyl)ferrocene in a solution of either acetonitrile or toluene as carbon source. This was achieved by testing three different growth temperatures (800, 850, and 900°C), and the 850°C was found to be the most favourable condition for N‐CNT growth. At the lower temperature of 800°C, amorphous carbon was mainly formed while at the higher temperature of 900°C, the yield of carbon spheres (CSs) increased. Apart from the variation in temperature, the formation of other shaped carbon nanomaterials (SCNMs) was found to be carbon source dependent. Acetonitrile was found to produce mainly N‐CNTs with “bamboo” morphology while toluene formed a mixture of pristine CNTs and N‐CNTs in the ratio of 1 : 1. N‐CNTs, and other SCNMs synthesized were characterized by means of TEM, SEM, Raman spectroscopy, TGA, and elemental analysis.

Heteroatom‐containing ferrocene derivatives as catalysts for MWCNTs and other shaped carbon nanomaterials

The effects of heteroatom‐containing ferrocene catalysts on the materials produced from chemical vapour deposition (CVD) floating catalyst synthesis were investigated. Specifically, the influence of nitrogen‐ and oxygen‐containing ferrocenoyl imidazolide and (N‐phenylcarbamoyl)ferrocene, and sulfur‐ and oxygen‐containing S,S‐bis(ferrocenylmethyl)dithiocarbonate on the structural morphology and distribution of the products as well as properties such as the thermal stability and crystallinity were studied. In addition, the influence of reaction parameters such as catalyst concentration and temperature were also investigated. The nitrogen‐containing catalysts produced N‐doped multi‐walled carbon nanotubes (N‐MWCNTs), whereas the sulfur‐containing catalyst produced primarily nano‐ and microspheres. A concentration of 2.5 wt% ferrocenoyl imidazolide was shown to be optimal for the synthesis of MWCNTs at 850 °C, with very low metal iron residue, highest thermal stability and highest yield (95%). In general, bamboo compartment length for N‐doped MWCNTs increased with temperature. Crystallinity trends were shown to be independent of catalyst and catalyst concentration in all cases and only dependent on temperature. The average diameter for MWCNTs was shown to be dependent on temperature, choice of catalyst and catalyst concentration in all cases. Copyright © 2012 John Wiley & Sons, Ltd.

The effect of substituted alkynes on nickel catalyst morphology and carbon fiber growth

The growth of shaped carbon nanomaterials from a range of substituted alkynes over a NiO catalyst was investigated. It was found that the structure of the substituted alkyne affected both catalyst morphology and carbon fiber growth. For linear alkynes (1-pentyne to 1-octyne) the fiber morphology and yield varied with the type of alkyne used. It was also found that hetero-atoms (Cl, Br, OH and NH 2) greatly impacted carbon fiber growth and structure. An analysis of the catalyst particles associated with the carbon fibers grown from various alkynes showed that different alkynes gave differently shaped Ni catalyst particles. It was found that pre-treatment of the catalyst with an alkyne such as trimethylsilyl acetylene or ethynyl aniline (that did not give fiber growth), followed by treatment with acetylene initiated fiber growth morphologies (Y-junction, helical or straight fibers) different from that observed after direct treatment with acetylene. Further, sequential fiber growth from two alkynes that were both capable of producing fibers (e.g. methyl prop-2-ynoate followed by prop-2-yn-1-amine) resulted in ‘co-block’ fiber growth. These results highlight the dynamic relationships that exists between carbon source, catalyst morphology and carbon nanomaterial growth.

A review of shaped carbon nanomaterials

Materials made of carbon that can be synthesised and characterised at the nano level have become a mainstay in the nanotechnology arena. These carbon materials can have a remarkable range of morphologies. They can have structures that are either hollow or filled and can take many shapes, as evidenced by the well-documented families of fullerenes and carbon nanotubes. However, these are but two of the shapes that carbon can form at the nano level. In this review we outline the types of shaped carbons that can be produced by simple synthetic procedures, focusing on spheres, tubes or fibres, and helices. Their mechanisms of formation and uses are also described.

A review of shaped carbon nanomaterials

A review of shaped carbon nanomaterials

Nitrogen Doped Carbon Nanotubes from Organometallic Compounds: A Review

Nitrogen doped carbon nanotubes (N-CNTs) have become a topic of increased importance in the study of carbonaceous materials. This arises from the physical and chemical properties that are created when N is embedded in a CNT. These properties include modified chemical reactivity and modified conductivity and mechanical properties. A range of methodologies have been devised to synthesize N-CNTs. One of the procedures uses a floating catalyst in which an organometallic complex is decomposed in the gas phase in the presence of a nitrogen containing reactant to give N-CNTs. Most studies have been limited to ferrocene, ring substituted ferrocene and Fe(CO)5. This review covers the synthesis (and properties) of N-CNTs and other shaped carbon nanomaterials (SCNMs) produced using organometallic complexes. It summarizes the effects that physical parameters such as temperature, pressure, gas flow rates, type and concentration of N source etc. have on the N-CNT type, size and yields as well as the nitrogen content incorporated into the tubes that are produced from organometallic complexes. Proposed growth models for N-CNT synthesis are also reported.

Influence of methylimidazole isomers on ferrocene-catalysed nitrogen doped carbon nanotube synthesis

Nitrogen doped multi-walled carbon nanotubes (N-CNTs) were synthesized by the solid state pyrolysis of ferrocenylmethylimidazole or a mixture of ferrocene (FcH)/ i-methylimidazole ( i = 1, 2 and 4) at 800 °C at different ratios in sealed quartz tubes. Transmission electron microscopy (TEM) images confirmed that the carbon nanotubes (CNTs) obtained were doped with nitrogen to give nitrogen doped multi-walled CNTs (N-CNTs). N-CNTs showed bamboo-like structures for the CNTs produced from both ferrocenylmethylimidazole and the mixtures of FcH/ i-methylimidazole at varying ratios. The study revealed that the different imidazoles produced different types/size distributions of shaped carbon nanomaterials (SCNMs) including N-CNTs with different diameters. An investigation of the bamboo structures revealed that the three methylimidazole isomers led to tubes with different individual bamboo compartment distances and different morphologies including different N contents. This confirms that the synthesis of N-CNTs is determined by fragments (ratios, types) produced by decomposition of reactants at high temperature.

The effect of arylferrocene ring substituents on the synthesis of multi-walled carbon nanotubes

Abstract The synthesis of shaped carbon nanomaterials (SCNMs) such as carbon nanotubes (CNTs), amorphous carbon, carbon fibres (CFs) and carbon spheres (CSs) was achieved using para -substituted arylferrocenes, FcPhX (X = H, OH, Br, COCH 3 ) or a mixture of ferrocene (FcH) and substituted benzenes (PhX; X = H, OH, Br, COCH 3 ). The reactions were carried out by an injection chemical vapour deposition (CVD) method using toluene solutions (carrier gas: 5% H 2 in Ar at a flow rate of 100 ml/min) in the temperature range of 800–1000 °C. In most instances multi-walled CNTs (MWCNTs) were produced. Variations in the concentrations of precursor catalysts, the injection rate and temperature affected the type, distribution and dimensions of the SCNMs produced. The overall finding is that the presence of Br and O in these studies significantly reduces CNT growth. A comparative study on the effect of FcPhX versus FcH/PhX mixtures was investigated. The SCNMs were characterized by transmission electron microscopy (TEM), Raman spectroscopy and thermal gravimetric analysis (TGA).