THE INFLUENCE OF SYNTHESIS PARAMETERS ON THE PRODUCTION OF MULTIWALLED CARBON NANOTUBES BY THE FERROCENE CATALYZED PYROLYSIS OF TOLUENE

A high yield (∼32 wt.%) of multiwalled carbon nanotubes was obtained in an iron catalyzed reaction. This was achieved in the temperature range 800-1000°C under an atmosphere of H₂/Ar by an improved solution injection method in a horizontal reactor using toluene as carbon source and ferrocene as catalyst precursor. The pyrolysis temperature, ferrocene concentration, solution feeding rate and carrier gas flow rate all influenced the yield of carbon nanotubes and the thickness of the aligned carbon nanotube films. The carbon nanotubes was prepared in high purity using optimized pyrolysis conditions.     

己烷低耗喷雾热解法大规模制备多壁碳纳米管

以己烷为碳源,二茂铁为催化剂前躯体,应用喷雾热解法,制备了多壁碳纳米管(MWCNTs).采用酸沥滤和空气氧化对MWCNTs进行纯化.利用SEM、TEM、XRD、EDS、TGA及Raman光谱分析等方法分别对原生和纯化MWCNTs进行表征.为制得优质、高产MWCNTs,对制备工艺参数作了优选,分别研讨了最佳制备参数,包括:二茂铁升华温度、己烷中二茂铁浓度、热解温度和时间,己烷与H2的流量比.MWCNTs具有典型的腊肠状(Sawsage-like)构型,长度大于数十微米,内、外管径分别为15nm～45nm及25nm～70nm,MWCNTs的纯度和产率的质量分数分别高于95%和70%.     

Influence of catalyst particles on multi-walled carbon nanotubes morphology and structure

Multi-walled carbon nanotubes (MWCNTs) have been successfully grown by Chemical Vapor Deposition (CVD) method. Elucidating the key characteristics of catalyst sources that affect carbon nanotubes growth is of great importance for improving and control MWCNTs morphology and structure. In this work we present a systematically study of CVD parameters, such as catalyst source, substrate morphology and temperature and how it affects carbon nanotubes synthesis. The novelty of this work lies on the catalyst composition. Two specific catalyst sources were analyzed: (i) Fe₂Co and (ii) Fe₂Co with ferrocene. Cyclic Voltammetry results confirmed the presence of Fe²⁺ in the Fe₂Co with ferrocene solution. X-Ray Diffraction analysis confirmed the presence of iron particles on the substrate surface after its submission to growth conditions. Raman results suggested an improvement in carbon nanotubes crystalline quality catalyzed by Fe₂Co with ferrocene. For tridimensional substrates such as fibers, the Fe₂Co with ferrocene provided aligned CNTs with lower defects density noticed in Raman spectra and SEM micrographs. Finally, we corroborated the Fe²⁺ encapsulation relation with the growth mechanism and MWCNTs formation.     

裂解温度,裂解时间和原料气流量对CVD法生产碳纳米管的影响

用ＣＶＤ法生产碳纳米管时，裂解温度、裂解时间和原料气流量大小对碳纳米管的产率、形态有很大影响，其中以裂解温度的影响最大。适宜的裂解温度、裂解时间和原料气流量有利于提高碳纳米管的产率和产量。在一定范围内提高裂解温度，可得到缺陷较少的碳纳米管     

Effect of ferrocene concentration on the synthesis of bamboo-shaped carbon-nitrogen nanotube bundles

We have investigated the effect of ferrocene concentration on the synthesis of carbon-nitrogen (C-N) nanotubes. The bamboo-shaped carbon-nitrogen nanotubes were synthesized by spray pyrolysis of Fe(C5H5)2 and CH3CN solution using argon as a carrier gas at the optimum temperature of approximately 900 degrees C. The effect of ferrocene concentration on the length and concentration of nitrogen in nanotubes was studied. Micro-structural features of the nanotubes were monitored employing scanning and transmission electron microscopic techniques. SEM studies reveal that with decreasing ferrocene concentration from 25 mg ml(-1) to 5 mg ml(-1), the length of the nanotubes vary from 80 microm to 430 microm. A feasible growth model has been described and discussed. X-ray photoelectron spectroscopic studies have confirmed the formation of nitrogen-doped carbon nanotubes. These studies reveal that the nitrogen concentration in the nanotubes decreases with the increase of ferrocene concentration. The present synthesis route also provides means of producing carbon nanotubes with different concentrations of nitrogen.     

Formation of carbon nanotubes without iron inclusion and their alignment through ferrocene and ferrocene-ethylene pyrolysis

So far carbon nanotubes grown from the method most common method at present, that is, pyrolysis of ferrocene, invariably contains Fe inclusion. In addition, they are generally grown in random configurations. In the present investigations CNTs without Fe inclusion and in aligned configurations have been prepared by the pyrolysis of ferrocene (C10H10Fe) as well as pyrolysis of ferrocene in the presence of ethylene (C2H4). This has been achieved through optimization of growth parameters, for example, heating rate of ferrocene, pyrolysis temperature, and flow rates of carrier gas argon (Ar) and ethylene (C2H4). The as-synthesized samples have been characterized by transmission and scanning electron microscopic techniques. The optimum results relating to synthesis of carbon nanotubes without Fe inclusion and in aligned configurations have been obtained at 1000 degrees C pyrolysis temperature under flow rates of Ar of approximately 1000 sccm and of C2H4 of approximately 100 sccm. These carbon nanotubes have been found to have an outer diameter between approximately 20 and 60 nm and lengths between approximately 15 and 20 microns.     

Synthesis of bamboo-shaped carbon-nitrogen nanotubes using acetonitrile-ferrocene precursor

We report the formation of bamboo-shaped carbon-nitrogen nanotubes by employing a simple, one-step and economically viable spray pyrolysis technique using new precursor; acetonitrile and ferrocene solution. By varying the concentration of ferrocene with respect to acetonitrile, it has been found that the optimum concentration of ferrocene in acetonitrile is 5 mg/ml. The special feature of the as-synthesized bamboo-shaped carbon-nitrogen nanotubes bundles is that they are produced in a high yield (1.25 gms/run). They also have long linear extents (approximately 430 microm) and are very clean. The average composition of carbon-nitrogen nanotubes comes out to be C26N.     

Simple method for synthesis of carbon nanotubes over Ni-Mo/Al2O3 catalyst via pyrolysis of polyethylene waste using a two-stage process

Synthesis of valuable multi-walled carbon nanotubes (MWCNTs) by thermal pyrolysis of low-density polyethylene (LDPE) waste was investigated via a two-stage process. The first stage was the thermal pyrolysis of LDPE to gaseous hydrocarbons, and the second stage was the catalytic decomposition of the pyrolysis gases over Ni-Mo/Al₂O₃ catalysts. Two catalysts with the compositions of 5.2%Ni-10.96%Mo/Al₂O₃ and 10%Ni-9.5%Mo/Al₂O₃ were tested for carbon nanotubes (CNTs) formation. The catalyst containing 10%Ni showed better activity in terms of CNTs production. Accordingly, the impact of either pyrolysis or decomposition temperatures was investigated using the 10%Ni-9.5%Mo/Al₂O₃ catalyst. TEM, XRD, Raman spectroscopy, TGA, TPR, and BET analysis tools were used to characterize the fresh catalysts as well as the obtained carbon nanomaterials. TEM images proved that MWCNTs with various morphological structures were obtained at all pyrolysis and decomposition temperatures. Moreover, cup-stacked carbon nanotubes (CS-CNTs) were observed at the decomposition temperature of 600°C. MWCNTs with the best quality were produced at decomposition temperature of 750°C. The optimum pyrolysis and decomposition temperatures in terms of CNTs production were at 700 and 650°C, respectively.     

Carbon nanotubes from catalytic pyrolysis of deoiled asphalt

High purity and uniform carbon nanotubes with about 35 nm in diameter were produced by pyrolysis of deoiled asphalt in the presence of ferrocene in an atmosphere of hydrogen and argon at 1000 °C. Characterization of carbon nanotubes was carried out by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), X-ray energy dispersive spectroscopy (EDS), Raman spectroscopy and X-ray diffraction (XRD). The carbon nanotubes were highly graphitized with amorphous carbons covering the outside wall. The influence of temperature on the preparation of carbon nanotubes was also discussed.     

Bulk synthesis of carbon nanocapsules and nanotubes containing magnetic nanoparticles via low energy laser pyrolysis of ferrocene

A one-step synthesis route to carbon nanocapsules and nanotubes containing Fe and Fe₃C nanoparticles is reported. Low power laser assisted pyrolysis of ferrocene yielded carbon nanocapsules (30-100 nm in diameter) and multi-wall carbon nanotubes (30-80 nm in diameter). The developed route is fast and enables one to synthesize the products at a rate of 84 mg/min. The iron content in the product (10-42 wt.%) can be varied by modulating the buffer gas pressure during the synthesis process.     

Preparation of high-yield multi-walled carbon nanotubes by catalytic decomposition of mixture of natural gas and propylene and their electrothermal properties

Abstract

Multi-walled carbon nanotubes (MWNTs) with high-yield were prepared by pyrolysis of mixture of natural gas (NG) and propylene (C₃H₆) over Fe-Ni/Al₂O₃-MgO catalyst. For C₃H₆/NG flow rate ratio ranging from 0 to 0.33, the carbon yield was increased from 903% to 4400%. The synthesized MWNTs after purification were dispersed by ball milling method and mixed with waterborne polyurethane to fabricate the electrothermal film. The mass fraction of CNT filler in the cured electrothermal film was controlled at 50%. The coating after drying was ca. 6?μm and the coating’s volume resistivity was 0.053 Ω·cm. The time-dependent temperature curves indicated that the heating rate of the electrothermal film was very fast under different low voltage and the steady-state temperatures were achieved within 100?s. The steady-state temperature reached 47.9?°C, 76.8?°C, and 102.8?°C, respectively at 10?V, 15?V, and 18?V.     

Synthesis of multiwalled carbon nanotubes from polyethylene waste to enhance the rheological behavior of lubricating grease

Abstract

Carbon nanotubes (CNTs) are attracting great interest in enhancing rheological behavior and thermal performance of lubricating grease. In this study, CNTs were synthesized by catalytic chemical vapor deposition (CCVD) method using low-density polyethylene (LDPE) waste as a cheap carbon source and Co/MgO as an effective catalyst. The effect of temperature on the catalytic pyrolysis of LDPE to produce CNTs has been studied. Catalytic pyrolysis of LDPE waste was conducted in a temperature range of 350–600?°C using the H-ZSM-5 catalyst. The structure and quality of CNTs were fully characterized using HR-TEM, XRD, and Raman spectroscopy. On the other hand, various concentrations of CNTs (0.2, 0.4, 0.6, 0.8, and 1.0?wt%) were mixed with pure lithium grease to determine the optimum percentage that improves the properties of nano-grease. The results showed that a high yield of multiwalled carbon nanotubes (MWCNTs) was obtained with high quality at temperatures ranging from 400 to 550?°C. Also, the addition of CNTs enhanced the rheological behavior of lithium grease, and the optimum percentage of CNTs was 0.8?wt%. Furthermore, the apparent viscosity and shear stress of lithium nano-grease increased by increasing the concentration of CNTs up to 0.8%. At this concentration, the penetration value of lithium nano-grease was greater than pure grease, and the dropping point increased by 12.5%. These results suggested that CNTs prepared from LDPE waste were an excellent additive to enhance the physicochemical properties of lithium grease.     

Synthesis of multi-walled carbon nanotubes via pyrolysis of plastic waste using a two-stage process

The pyrolysis of different plastic waste types such as low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polyethylene terephthalate (PET) and polystyrene (PS) for producing multi-walled carbon nanotubes (MWCNTs) using a two-stage process has been investigated. Firstly, the cracking of plastic wastes was carried out at a temperature of 700°C to produce hydrocarbon gases. In the second stage, the produced hydrocarbon gases were decomposed at 650°C on the surface of the Ni-Mo/Al₂O₃ catalyst to form CNTs. Various analytical tools such as XRD, TPR, TGA, Raman spectroscopy and TEM were used to describe both the fresh catalyst and the obtained CNTs. The results showed that the amount of the hydrocarbon gases was related to the type of plastic waste and hence the CNT yield. Accordingly, LDPE or PP was decomposed to produce the largest gases yield of 72.5 or 70.7 wt%, respectively. As a result, a large CNTs yield of 5.8 and 5 g/g_cat can be achieved by pyrolysis of PP and LDPE waste, respectively. However, a small yield of CNTs with little quality and low purity was obtained by using PS or PET waste as the carbon feedstock.     

New synthesis of Cu2O and Cu nanoparticles on multi-wall carbon nanotubes

Cu₂O and Cu nanoparticles were deposited on the surface of multi-walled carbon nanotubes with a diameter range of 15–90 nm by the impregnate method. Multi-wall carbon nanotubes with a length of 200 μm and a diameter range of 70–110 nm were grown inside of quartz tubing by the spray pyrolysis method using ferrocene/benzene under argon flow. The nanotubes were then treated with nitric acid to clean the surface and generate carboxylic groups. The copper was impregnated on multi-walled carbon nanotubes using a xylene solution of copper(I) phenylacetylide as the precursor. Copper and cuprous oxide nanoparticles were obtained during thermal treatment.     

Synthesis of carbon nanotubes by swirled floating catalyst chemical vapour deposition method

A series of developments have been made in synthesizing Carbon Nanotubes (CNTs) by Catalytic Vapour Deposition (CVD) methods since its discovery as a possible route to the large scale and high quality production of CNTs. In this study, CNTs were synthesized continuously in a swirled floating catalytic chemical vapour deposition reactor using acetylene as carbon source, ferrocene as catalyst, with argon and hydrogen as carrier gases within the temperature range of 900-1050 degrees C. The effects of pyrolysis temperature, acetylene flow rate, hydrogen flow rate, and ratio of flow of acetylene to hydrogen on the rate of production of CNTs were investigated. The CNTs produced were purified with dilute nitric acid and the nature and quality of the CNTs were analysed by TEM, Raman spectrometer, EDX, and TGA. Results obtained revealed that a mixture of single and multi wall carbon nanotubes were produced continuously with a maximum yield rate of 0.31 g/min at 1000 degrees C and a flow ratio of acetylene to hydrogen of one to five.     

Dye sensitized solar cell based on platinum decorated multiwall carbon nanotubes as catalytic layer on the counter electrode

In this study we have employed multiwall carbon nanotubes (MWCNT), decorated with platinum as catalytic layer for the reduction of tri-iodide ions in dye sensitized solar cell (DSSC). MWCNTs have been prepared by a simple one step pyrolysis method using ferrocene as the catalyst and xylene as the carbon source. Platinum decorated MWCNTs have been prepared by chemical reduction method. The as prepared MWCNTs and Pt/MWCNTs have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In combination with a dye adsorbed TiO₂ photoanode and an organic liquid electrolyte, Pt/MWCNT composite showed an enhanced short circuit current density of 16.12 mA/cm² leading to a cell efficiency of 6.50% which is comparable to that of Platinum.     

Carbon nanostructures and graphite-coated metal nanostructures obtained by pyrolysis of ruthenocene and ruthenocene-ferrocene mixtures

Pyrolysis of ruthenocene carried out in an atmosphere of argon or hydrogen is found to give rise to spherical nanoparticles of carbon with diameters in the 10–200 nm range. Pyrolysis of ruthenocene as well as mixtures of ruthenocene and ethylene in hydrogen gives rise to spherical nanoparticles, which contain a high proportion of sp ³ carbon. Under certain conditions, pyrolysis of ruthenocene gives rise to graphite coated ruthenium nanoparticles as well as worm-like carbon structures. Pyrolysis of mixtures of ruthenocene and ferrocene gives rise to nanoparticles or nanorods of FeRu alloys, the composition depending upon the composition of the original mixture. Nanorods of the Ru and FeRu alloys encapsulated in the carbon nanotubes are also formed in the pyrolysis reaction.     

Preparation of carbon nanomaterials through CH4 pyrolysis on (Co + Mo)/MgO catalysts with different metal contents

We have studied the influence of active metal content in (Co + Mo)/MgO catalysts (0.5–5 wt % Co + Mo) on the morphology and properties of catalytic methane pyrolysis products (900°C, CH₄: H₂ volume ratio of 1: 1, pyrolysis time in the range 20–120 min). The results demonstrate that, in addition to the main pyrolysis product, carbon nanotubes, the process may yield graphene shells on MgO particles, graphene shells on relatively large Co particles, and amorphous carbon on carbon nanotubes. The metal content of the catalyst determines the relationship between different carbon species, their net yield, and the specific surface area (S) of the products. Increasing the pyrolysis time increases the S of the materials obtained at low metal concentrations in the catalyst, whereas on the catalyst containing 5 wt % metals S remains unchanged. In contrast, the yield of carbon nanomaterials is more sensitive to the pyrolysis time on the catalyst containing 5 wt % metals.     

Large scale synthesis of bundles of aligned carbon nanotubes using a natural precursor: turpentine oil

Bundles of aligned carbon nanotubes (ACNTs) have been synthesised by spray pyrolysis of turpentine oil (inexpensive precursor) and ferrocene mixture at 800°C. Turpentine oil (C₁₀H₁₆), a plant-based precursor was used as a source of carbon and argon as a carrier gas. The bundles of ACNTs have been grown directly inside the quartz tube. The as-grown ACNTs have been characterised through X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopic techniques. Scanning electron microscope images reveal that the bundles of ACNTs are densely packed and are of ～70–130?µm in length. High-resolution transmission electron microscopy and Raman spectroscopy observations indicate that as-grown multi-walled carbon nanotubes (CNTs) are well graphitised. These CNTs have been found to have outer diameters between ～15 and 40?nm. This technique suggests a low-cost route for the large-scale formation of ACNTs bundles.     

The growth of aligned carbon nanotubes on quartz substrate by spray pyrolysis of hexane

Vertically aligned multiwall carbon nanotubes were grown by spray pyrolysis of hexane as the carbon source in the presence of ferrocene as catalyst precursor on a quartz substrate. In recent work we used optimal experimental parameters for the feeding method, reactor conditions, reaction temperature and time, concentration of catalyst and flow rate of feed and gas. The process parameters were chosen so as to obtain multiwall carbon nanotubes and aligned multiwall carbon nanotubes. The tubes are around 15-80?nm in diameter. The morphology and structure of the samples were characterized by x-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy analyses.