Formation Mechanism Of Carbon Nanotubes Research Articles

Electrochemical Conversion of CO2 into Valuable Carbon Nanotubes: The Insights into Metallic Electrodes Screening

Direct conversion of CO2 to reusable solid carbon products based on the molten salts electrochemistry demonstrates a feasible approach to address the intractable global climate change. In this work, we compare a series of conventional metal electrodes and figure out why Fe cathode and Ni anode are superior to other metallic electrodes for molten carbonates electrolysis by polarization measurements, which could be utilized as a universal methodology for electrode candidates screening. The cyclic voltammetry measurements help to gain a richer understanding on the CO32− reduction and carbon formation process on metal electrodes. Moreover, to elucidate the formation mechanism of carbon nanotubes on Fe cathode, low-current electrolysis was conducted and Ni nanoparticles were observed to disperse on the cathode surface evenly. All of the obtained information provides a reasonable explanation to why carbon deposition occurs and how carbon nanotubes form, which should be of great interest for the following industrial carbon nanotubes production based on the molten salts manner.

A novel preparation and formation mechanism of carbon nanotubes aerogel

A novel preparation and formation mechanism of carbon nanotubes aerogel

Mechanisms and theoretical simulations of the catalytic growth of nanocarbons

Abstract

Preparation of carbon nanotubes on Al foil anode for electrolytic capacitor

Well graphitized carbon nanotubes (CNTs) were directly grown on Al foil for Al electrolytic capacitor by micro-arc discharge in water between catalyst deposited Al foil cathode and Pt anode. Next, aluminum was sputtered onto the Al foil with grown CNTs at fixed sputtering time and power. Finally, aluminum oxide was formed by anodizing in an ammonium adipate solution. A high capacitance was obtained, comparing with blank Al foil without CNTs. High-resolution transmission electron microscopy and Raman spectra were employed to study the structure and formation mechanism of CNTs.

Synthesis of Carbon Nanotube-Nanotubular Titania Composites by Catalyst-Free CVD Process: Insights into the Formation Mechanism and Photocatalytic Properties.

This work presents the synthesis of carbon nanotubes (CNTs) inside titania nanotube (TNTs) templates by a catalyst-free chemical vapor deposition (CVD) approach as composite platforms for photocatalytic applications. The nanotubular structure of TNTs prepared by electrochemical anodization provides a unique platform to grow CNTs with precisely controlled geometric features. The formation mechanism of carbon nanotubes inside nanotubular titania without using metal catalysts is explored and explained. The structural features, crystalline structures, and chemical composition of the resulting CNTs-TNTs composites were systematically characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The deposition time during CVD process was used to determine the formation mechanism of CNTs inside TNTs template. The photocatalytic properties of CNTs-TNTs composites were evaluated via the degradation of rhodamine B, an organic model molecule, in aqueous solution under mercury-xenon Hg (Xe) lamp irradiation monitored by UV-visible spectroscopy. The obtained results reveal that CNTs induces a synergestic effect on the photocatalytic activity of TNTs for rhodamine B degradation, opening new opportunities to develop advanced photocatalysts for environmental and energy applications.

A new understanding of carbon nanotube growth: Different functions of carbon species

Understanding the formation mechanism of carbon nanotubes (CNTs) from carbon source is critical for controlled-production of CNTs. In this study, the functions of carbon species were investigated by a thermogravimetric analyzer coupled with a mass spectroscope in using methane as carbon source of CNT growth in chemical vapor deposition (CVD). It was found that a negative peak of C2H2 species and a positive peak of C2H4 species appeared at the CNT growth moment. Accordingly it is deduced that the C2H2 species react on nucleation and C2H4 species react on CNT growth. This deduction is then verified by the computational chemistry results based on density functional theory (DFT). This finding clarifies the different functions of C2 at growing moment at the first time and makes the controlling of CNT production in such a condition becomes promising.

Carbon nanotubes among diesel exhaust particles: real samples or contaminants?

During three separate studies involving characterization of diesel particulate matter, carbon nanotubes (CNTs) were found among diesel exhaust particles sampled onto transmission electron microscopy (TEM) grids. During these studies, samples were collected from three different diesel engines at normal operating conditions with or without an iron catalyst (introduced as ferrocene) in the fuel. This paper is to report the authors’ observation of CNTs among diesel exhaust particles, with the intent to stimulate awareness and further discussion regarding the formation mechanisms of CNTs during diesel combustion. Implications: Increased attention is being given to CNTs and other nanomaterials and a recent review paper showed that CNTs are capable of inflammation in the lung when inhaled. For this reason and because diesel engines are so common, it is important to acknowledge the existence of CNTs among diesel particles and possible regulation and online measurement method development.

ChemInform Abstract: On the Mechanism of Carbon Nanotube Formation: The Role of the Catalyst

AbstractReview: 55 refs.

On the mechanism of carbon nanotube formation: the role of the catalyst

This work examines the recent developments in non-traditional catalyst-assistedchemical vapour deposition of carbon nanotubes (CNTs) with a view to determiningthe essential role of the catalyst in nanotube growth. A brief overview of thetechniques reliant on the structural reorganization of carbon to form CNTs isprovided. Additionally, CNT synthesis methods based upon ceramic, noble metal, andsemiconducting nanoparticle catalysts are presented. Experimental evidence is providedfor CNT growth using noble metal and semiconducting nanoparticle catalysts.A model for CNT growth consistent with the experimental results is proposed,in which the structural reorganization of carbon to form CNTs is paramount.

A numerical approach to the metal-catalyzed growth process of carbon nanotubes

Thanks to a lot of efforts to understand formation mechanism of carbon nanotubes during metal-catalyzed growth process, there has been a broad consensus that the initial cap structure is nucleated on the surface of the metal nanoparticle, followed by subsequent longitudinal growth. One of the remaining issues is to understand a key factor determining the chirality of the carbon nanotube. Here, recent numerical approaches on this issue, which focus on the orientation relationship between the graphite and metal surface and the structure of catalytic-metal nanoparticle at the high temperature, are introduced after a brief review of relevant literatures.

Structural Units and Their Periodicity in Carbon Nanotubes

It is widely accepted that carbon nanotubes (CNTs) consist of coaxially curved graphene layers. However, some CNTs, synthesized at relatively low temperature, are self-organized into rod- or plate-shaped mesostructural units with periodic structure. These findings give another point of view on the formation mechanism of CNTs.

Synthesis of carbon nanotubes with totally hollow channels and/or with totally copper filled nanowires

Carbon nanotubes (CNTs) with totally hollow channels and/or totally filled copper nanowires have been fabricated by methane decomposition using copper microgrid as a catalyst at 1173 K. The formation mechanism of CNTs with totally hollow channels is carbon precipitation at carbon-metal interface via the preferable surface diffusion mode of carbon. The selectivity of these CNTs can be improved by increasing the purity of copper catalysts and adding hydrogen in the feed gas. To form long and continuous copper nanowires up to 8–10 μm the filling of copper in the CNT channel requires the liquid or quasi-liquid state capillary adsorption of nanosized copper at 1173 K under the thermal driving force. The filling volume ratio of copper to total nano-channel of the CNTs is firstly increased to about 50%. The copper inside the CNTs is of single crystalline form and face centered cubic (fcc) structure. The method is useful for further controlled synthesis of CNTs with totally hollow channels and/or totally copper filled nanowires.

On the mechanism of carbon nanotube formation in electrochemical processes

Quantum-chemical methods are used to analyze the mechanism of carbon nanotube formation in the electrochemical bath, where tiny fragments of graphene planes are in the environment of atoms and ions of alkali metals and halogens. In the optimal configuration, alkali metal atoms move toward the edge of a graphene fragment, whereas halogen atoms remain at the sites of their initial attachment. When the graphene fragments “burdened” by alkali metal and halogen atoms interact with each other, the overall graphene configuration twists in a natural way into a nanotube-like open-end structure.

Microstructure and Formation Mechanism of Carbon Nanotubes Filled with Metallic Silver Nanowires

The filling of multi-walled carbon nanotubes with metallic silver nanowires via wet chemistry method was investigated. The carbon nanotubes were filled with long continuous silver nanowires. The carbon nanotubes were almost opened and cut after being treated with concentrated nitric acid. Silver nitrate solution filled carbon nanotubes by capillarity. Carbon nanotubes were filled with silver nanowires after calcinations by hydrogen. The diameters of silver nanowires were in the range of 20-40 nm, and lengths of 100 nm - 10 μm. We studied the micromorphology of the silver nanowires filled in carbon nanotubes by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Based on the experimental results, a formation mechanism of the Ag nanowire-filled carbon nanotubes was proposed.

On the mechanism of carbon nanotube formation: I. The thermodynamics of formation of carbon molten drops in a metallic catalyst

Carbon molten drops in a metallic catalyst are known to be nucleation centers for carbon nanotubes. The problem of the kinetics of condensation of such drops in wide concentration ranges of carbon and metal vapors is considered. The equilibrium distribution of the drops over the size and mole fraction of the components is obtained. The main result is the calculation of the quasi-steady-state rate of condensation of the molten drops in a supersaturated carbon vapor. This result forms the basis for the calculation of the characteristics of explosive and rapid condensation of the vapor upon its cooling. This calculation is performed in the next part of this work.

On the mechanism of carbon nanotube formation: II. The kinetics of explosive condensation of carbon molten drops in a metallic catalyst

The preliminary stage of the formation of carbon nanotubes by the vapor-liquid-drop mechanism is considered as applied to the condensation of drops from carbon and metal vapors. The problem of the condensation of molten drops is solved for a wide concentration range for both vapors at a condensation temperature. It is shown that, at very high concentrations of the metal vapor (1018–1019 cm−3) and high temperatures (about 0.3 eV), peculiar heterogeneous condensation of the drops can occur at huge supersaturation of the carbon vapor and the saturated metal vapor. This problem of the condensation of the binary vapor is of methodical interest. This condensation is shown to be unrealizable in real experiment at the parameters of the carbon and metal vapors; it virtually merges with the homogeneous condensation of the metal vapor. The maximum concentration of the carbon vapor below which carbon condenses into drops and above which carbon condenses into amorphous soot particles is calculated. The calculation makes it possible to propose a new approach to the controlled growth of carbon nanotubes.

Formation mechanism of carbon nanotubes in the gas-phase synthesis from colloidal solutions of nanoparticles

Abstract Single- and multi-wall carbon nanotubes have been synthesized by the gas-phase catalytic reaction of colloidal solutions of metal nanoparticles using a vertical flow reactor. The reverse micelle solution of the Co–Mo nanoparticles with the mean diameter of 11 nm dissolved in toluene was injected directly into the reactor maintained at 1200 °C. The nanoparticles and the solvent act as the catalyst and carbon source, respectively. When the concentration of the thiophene additive is low (1 wt.%), the formation of SWNT bundles preferentially occurred. The SWNT bundles were present together with the relatively small metal nanoparticles with the diameter of 0.5–5.5 nm. It is likely that the original nanoparticles with the diameter of 11 nm break into smaller ones, 1–2 nm diameters, which is suitable for the SWNT growth. The synactic effect of Co and Mo was also observed.

Low-temperature synthesis of carbon nanotubes using corona discharge plasma at atmospheric pressure

A new method, which combines non-equilibrium plasma reaction with template-controlled growth technology, has been developed for synthesizing aligned carbon nanotubes at atmospheric pressure and low temperature. Multiwall carbon nanotubes with diameters of approximately 40 nm were restrictedly synthesized in the channels of anodic aluminum oxide template from a methane/hydrogen mixture gas by a.c. corona discharge plasma reaction at a temperature below 200 °C. It was observed that amorphous carbon deposited on the tops of the carbon nanotubes. The formation mechanism of carbon nanotubes synthesized by corona discharge plasma method was discussed.

Mechanism of carbon nanotube formation in the arc discharge.

A model for carbon nanotube formation in the arc discharge has been developed. The model is based on the physical properties of the arc discharge plasma where the interplay of the two major components of the bimodal carbon velocity distribution (Maxwellian and directed) dominates the nanotube creation process in a zone near the cathode surface. The processes of seed structures and nanoparticles formation, termination, and restart of nanotube growth, and multishell tube formation are considered self-consistently. The proposed model can explain qualitatively most of the known experimental facts related to the nanotube formation. Comparison to experiments has been provided and some consequences of the model discussed.