Yield Of Multi-walled Carbon Nanotubes Research Articles

In-situ synthesis of carbon nanotubes-graphite hybrid materials

This contribution deals with a commercially scalable catalyst preparation method for the synthesis of a new generation of hybrid materials based on carbon-nanotubes-graphite. Commercial natural graphite in spherical or flake shapes, with varying particle sizes and textural properties, were used as catalyst support. They were impregnated with aqueous solutions containing cobalt nitrate in the presence of a non-ionic surfactant agent and then dried and calcined under controlled experimental conditions. Catalytic activity properties were evaluated in a rotary tube reactor using ethylene as a carbon source at a temperature of 650 °C and a residence time of 5 min. It was observed that the use of a surfactant agent in the impregnation step significantly improved the adsorption and dispersion of the active metal on the hydrophobic catalyst support surface, enabling the formation of a dense coating of carbon nanotubes on the graphite particles after the synthesis. The multi-walled carbon nanotubes (MWCNTs) showed diameters ranging from 10 to 20 nm and lengths between 5 and 10 µm, with most of them growing via the base-mode growth mechanism. The morphology properties of the graphite particles play a key role in influencing the active metal surface deposition, the MWCNT yield, and their aspect ratio properties

Influence of rare earth elements addition in layered double hydroxide catalysts on the yield of growing carbon nanotubes

Efficient preparation of low-cost multi walled carbon nanotubes (MWCNTs) will make them more competitive in the application of lithium ion battery composite additives and conductive paste. For a long time, the catalyst with high activity is the key factor to prepare MWCNT. In this paper, rare earth elements (RE) were introduced into layered double/triple hydroxides (LDH/LTHs) catalyst for the first time to prepare a composite catalyst with high activity, and then MWCNT with high yield was prepared by chemical vapor deposition (CVD). Temperature and the introduction of RE elements will strongly affect the yield of MWCNTs. La, Ce, Dy and Pr can improve the catalytic efficiency of LTHs while Eu, Er and Nd reduce their catalytic efficiency. Specifically, the addition of Dy element can nearly double the productivity of CNTs at 650 °C, reaching to 3093 %. Further analysis shows that the strong magnetic effect of Dy element can surround the iron nanoparticles, effectively inhibiting the fusion of iron particles at high temperatures, and improving the catalytic activity of the catalyst.

Influence of Reaction Temperature on Yields of Multi-Walled CNTs Synthesized with Fe-Co/Al<sub>2</sub>O<sub>3</sub> Bimetallic Nanocatalyst

Aluminum-supported iron and cobalt (Fe-Co/Al2O3) bimetallic nano-sized catalyst has been synthesized by the sol-gel method. The average diameter of the Fe-Co/Al2O­3 catalyst was measured to be around 7 nm from SEM images. EDX measurements revealed that Fe-Co/Al2O­3 consists of 59.98% of Al, 20.00% of Fe, and 20.02% of Co by atomic weight. Multi-walled carbon nanotubes (MWCNT) were prepared with as-synthesized nanocatalyst from a commercial butane gas by the CCVD method at different reaction temperatures. TEM and XRD measurements revealed that Fe-Co/Al2O3 bimetallic nano-sized catalyst is beneficial to fabricating MWCNTs by the CCVD method. The highest yield of MWCNTs was obtained at 690°C.

Thiophene-based Ni-coordination polymer as a catalyst precursor and promoter for multi-walled carbon nanotubes synthesis in CVD

Enormous technological promise of multi-walled carbon nanotubes (MWCNTs) can only be harnessed with the premise of controllable synthesis of MWCNTs, where catalyst precursor and promoter play vital roles. Herein, we have systematically investigated the effects of pre-treatment of catalyst precursor and promoter and growth conditions of MWCNTs. The highest yield of MWCNTs from thiophene-based Ni-coordination polymer is 10 times as that of our previous work. The results indicate that catalyst precursor and promoter can efficiently tune the morphology, yield and quality of MWCNTs.

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

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.

Dependence of MWCNT production via co-pyrolysis of industrial slop oil and ferrocene on growth temperature and heating rate

Multi-walled carbon nanotubes (MWCNTs) could be produced from industrial slop oil via pyrolysis with the presence of ferrocene. Dependence of characteristics of the produced MWCNTs on their growth temperature and heating rate of mixtures of industrial slop oil and ferrocene was experimentally investigated. With low-molecular weighted hydrocarbon, the resultant MWCNTs with nominal diameters of 10–50 nm and yields of 45–65 wt% could be produced within a growth temperature range of 750–950 °C. Meanwhile, high-molecular weighted hydrocarbon could provide substantial yield of MWCNTs only within the growth temperature range of 850–950 °C. It was found that a higher heating rate of 9 °C/min could result in preferable production of MWCNTs with higher purity. Based on comprehensive analyses, a schematic pathway of MWCNT production via co-pyrolysis of mixtures of industrial slop oil and ferrocene was proposed.

Fe-Ni nanoparticle-catalyzed controlled synthesis of multi-walled carbon nanotubes on CaCO3

The synthesis of Multi-Walled Carbon Nanotubes (MWCNTs) by Chemical Vapor Deposition (CVD) is becoming mostideal method for producing large quantity of CNT at different temperature conditions. Nano-porous materials such astransition metal carbonates with bimetallic alloy catalyst were used to fabricate MWCNTs with high yield and lessamorphous carbon. In the present research work, the MWCNTs were successfully fabricated using Fe-Ni bimetallic catalyston CaCO3 support with the 180% optimum yield. The proposed yield was high and less-cost effective catalysts to othermethods. The yield of MWCNTs depends on four parameters such as growth time (30/45 min), growth temperature(700/730 oC), acetylene flow rate (150/190 ml/min) and argon flow rate (800/900 ml/min). The impact of the reactiontemperature and the flow rates were observed to be most significant on the high yield of MWCNTs.

Features of obtaining the catalyst for the synthesis of carbon nanotubes

In this paper, the features of obtaining a Co-Mo/Al2O3 catalyst to synthesize carbon nanotubes (CNTs) by thermal decomposition were studied. It was revealed that the duration of the pre-catalyst thermal decomposition stage in the process of developing a metal oxide system has a significant impact on its activity in the synthesis of carbon nanostructured materials by chemical vapor deposition (CVD). It was proved that an effective catalyst for CNTs synthesis can be obtained by through thermal decomposition of the pre – catalyst, without calcination of the metal oxide system. The use of the Co-Mo/Al2O3 catalyst, synthesized in such a way, in the CVD process makes it possible to reduce the cost of synthesized CNTs. Using scanning electron microscopy, it was shown that the size of the grains, and specific surface area of the formed Co-Mo/Al2O3 catalyst depend on the thermal treatment conditions of the pre-catalyst. Under the conditions for the implementation of the pre-catalyst thermal decomposition stage (temperature, volume, duration, etc.), it is possible to contro not only the characteristics of the resulting catalyst (specific surface area, efficiency), but also the characteristics of the CNTs (diameter, degree of defectiveness). In the course of experiments, the optimal modes of implementation of the method for obtaining the Co-Mo/Al2O3 catalyst allowed forming a system with a specific surface area of ~ 108 m2/g. The use of the resulting catalyst in the synthesis of nanostructured materials provides a high specific yield of multi-walled CNTs with a diameter of 8-20 nm and a degree of defectiveness of 0.97.

Empirical relationship between band gap and synthesis parameters of chemical vapor deposition-synthesized multiwalled carbon nanotubes

In this study, an empirical relationship between the energy band gap of multi-walled carbon nanotubes (MWCNTs) and synthesis parameters in a chemical vapor deposition (CVD) reactor using factorial design of experiment was established. A bimetallic (Fe-Ni) catalyst supported on CaCO3 was synthesized via wet impregnation technique and used for MWCNT growth. The effects of synthesis parameters such as temperature, time, acetylene flow rate, and argon carrier gas flow rate on the MWCNTs energy gap, yield, and aspect ratio were investigated. The as-prepared supported bimetallic catalyst and the MWCNTs were characterized for their morphologies, microstructures, elemental composition, thermal profiles and surface areas by high-resolution scanning electron microscope, high resolution transmission electron microscope, energy dispersive X-ray spectroscopy, thermal gravimetry analysis and Brunauer-Emmett-Teller. A regression model was developed to establish the relationship between band gap energy, MWCNTs yield and aspect ratio. The results revealed that the optimum conditions to obtain high yield and quality MWCNTs of 159.9% were: temperature (700oC), time (55 min), argon flow rate (230.37 mL min–1) and acetylene flow rate (150 mL min–1) respectively. The developed regression models demonstrated that the estimated values for the three response variables; energy gap, yield and aspect ratio, were 0.246 eV, 557.64 and 0.82. The regression models showed that the energy band gap, yield, and aspect ratio of the MWCNTs were largely influenced by the synthesis parameters and can be controlled in a CVD reactor.

Internal field 59Co NMR study of cobalt-iron nanoparticles during the activation of CoFe2/CaO catalyst for carbon nanotube synthesis

CoFe2/CaO catalysts for multi-walled carbon nanotubes (MWCNT) were characterized during the activation period (T = 670 °C; C2H4/Ar = 1:1, 400 sccm) by internal field 59Co nuclear magnetic resonance. During this induction period, although C2H4 is already reacting, the MWCNT yield remains negligible. The NMR spectra of the catalysts revealed the occurrence of several structural and magnetic species. They were not detectable by conventional X-ray diffraction but the heterogeneity of the metal particles was corroborated by high-resolution transmission electronic microscopy coupled with energy dispersive X-ray spectroscopy. Two samples quenched at different activation time contained, beside non-reacted pure metal Co particles, strong and weak ferromagnetic alloys. During activation, the pure Co metal content dropped and an increase of the ordering of the cobalt-iron alloy in the catalyst was evidenced thus revealing a multistage activation mechanism for the reaction. We propose this ordering process during the induction period to be an intermediate step between the strong ferromagnetic Co rich alloy and the weak ferromagnetic Fe rich one and that it favors the onset of MWCNTs growth.

Activation and Decomposition of Methane over Cobalt‐, Copper‐, and Iron‐Based Heterogeneous Catalysts for COx‐Free Hydrogen and Multiwalled Carbon Nanotube Production

AbstractMonometallic 50 wt % Cu/Al2O3 catalyst and bimetallic catalysts containing 25 wt % Co/25 wt % Cu, 25 wt % Co/25 wt % Fe, and 25 wt % Cu/25 wt % Fe, supported on Al2O3, were prepared by impregnation and coimpregnation methods. For bimetallic catalysts, metal oxides were in the form of spinel oxides, which exhibited a strong metal–support interaction. The decomposition of methane over these catalysts led to the formation of pure hydrogen and carbon nanotubes on their surfaces. The activation energy, total carbon yield, and amount of hydrogen formed, by using the prepared catalysts, were in agreement with the metal dispersion and acid–base site ratio on the surface of the catalysts. Cu−Fe/Al2O3 catalyst exhibited a stable hydrogen formation rate of 58 mmol min−1 g−1 at a temperature of 650 °C. All catalysts exhibited deactivation after 500 min, which occurred due to the formation of carbon on the surface of the catalysts. The carbon material deposited predominantly assumed the form of multiwalled carbon nanotubes, as evidenced by high‐resolution TEM and Raman spectroscopy. Thermogravimetric analysis finally confirmed that Cu−Fe/Al2O3 exhibited a higher yield of multiwalled carbon nanotubes.

Synthesize multi-walled carbon nanotubes via catalytic chemical vapour deposition method on Fe-Ni bimetallic catalyst supported on kaolin

In this study, Fe-Ni bimetallic catalyst supported on kaolin is prepared by a wet impregnation method. The effects of mass of kaolin support, pre-calcination time, pre-calcination temperature and stirring speed on catalyst yields are examined. Then, the optimal supported Fe-Ni catalyst is utilised to produce multi-walled carbon nanotubes (MWCNTs) using catalytic chemical vapour deposition (CCVD) method. The catalysts and MWCNTs prepared using the optimal conditions are characterized using high resolution transmission electron microscope (HRTEM), high-resolution scanning electron microscope (HRSEM), electron diffraction spectrometer (EDS), selected area electron diffraction (SAED), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET), and X-ray diffraction (XRD). The XRD/EDS patterns of the prepared catalyst confirm the formation of a purely crystalline ternary oxide (NiFe2O4). The statistical analysis of the variance demonstrates that the combined effects of the reaction temperature and acetylene flow rate predominantly influenced the MWCNT yield. The N2 adsorption (BET) and TGA analyses reveal high surface areas and thermally stable MWCNTs. The HRTEM/HRSEM micrographs confirm the formation of tangled MWCNTs with a particle size of less than 62 nm. The XRD patterns of the MWCNTs reveal the formation of a typical graphitized carbon. This study establishes the production of MWCNTs from a bi-metallic catalyst supported on kaolin.

Ni-Mg Bimetallic Catalysts for Preparation of Multi-Walled Carbon Nanotubes from Polypropylene: Influence of the Ratio of Ni/Mg

This study designs Ni–Mg bimetallic catalysts for preparation of multi-walled carbon nanotubes (MWCNTs) from polypropylene (PP). The study further investigates the influence of Mg content on the catalytic activity of Ni catalyst. It is found that bimetallic Ni–Mg catalysts have higher reduction temperature, smaller Ni particle size and improved stability. Consequently, the addition of Mg not only enhances the yield of MWCNTs, but simultaneously improves the morphology and graphitization of MWCNTs. The activities of the bimetallic Ni–Mg catalysts are dependent on their composition. Among the different Ni–Mg bimetallic catalysts ration, Ni–Mg catalyst shows the highest activity when the ratio of Ni/Mg is 9/1. Moreover, the obtained MWCNTs presents smooth surface with highest graphitization degree. With our bimetallic Ni–Al catalyst, it is promising to achieve mass production of MWCNTs by using waste polymers as feedstock.

Preparation of multi‐walled carbon nanotubes and its application as flame retardant for polypropylene

NiO catalyst supported on Fe-pillared montmorillonite (5–15 wt% Ni) was prepared via a simple conventional impregnation method. The physicochemical properties of the Ni catalyst were characterised by X-ray diffraction, inductively coupled plasma-atomic emission spectrometry and transmission electron microscopy. The Ni catalyst, together with organic montmorillonite (OMMT), was employed to prepare multi-walled carbon nanotubes (MWCNTs) by using polypropylene (PP) as a precursor. An increase in Ni loading of the catalyst led to a significant increase in the yield of MWCNTs at the expense of a slight decline in quality of the obtained MWCNTs. Moreover, OMMT altered the degradation process of PP, which resulted in a much higher fraction of light hydrocarbons in degradation products. As such, a substantial increase in the yield of MWCNTs was attained. In addition, the obtained MWCNTs were used as flame retardant for PP, and significantly enhanced thermal stability and flame retardancy according to thermogravimetry analysis and cone data, respectively. PP/MWCNTs nanocomposite exhibited higher degradation temperature, longer ignition time, much lower heat release rate and smoke production rate. This work offers an efficient Ni catalyst to convert PP into MWCNTs which could be applied as flame retardant for polymers.

Ni–Al bimetallic catalysts for preparation of multiwalled carbon nanotubes from polypropylene: Influence of the ratio of Ni/Al

This study designed a novel Ni–Al bimetallic catalyst for preparation of multiwalled carbon nanotubes (MWCNTs) from polypropylene (PP). The study further investigated the influence of Al content on the catalytic activity of Ni catalyst. A series of bimetallic Ni–Al catalysts were prepared and then characterized by X-ray diffraction, N2-adsorption–desorption isotherms, transmission electron microcopy and temperature programmed reduction analysis. It was found that bimetallic Ni–Al catalysts had higher surface area, higher reduction temperature, smaller Ni particle size and improved stability. Consequently, the addition of Al not only dramatically enhanced the yield of MWCNTs, but simultaneously improved the morphology and graphitization of MWCNTs. The activities of the bimetallic Ni–Al catalysts were dependent on their composition. Among the different Ni–Albimetallic catalysts, Ni–Al catalyst showed the highest activity when the ratio of Ni/Al was 9/1. Moreover, the obtained MWCNTs presented smooth surface with highest graphitization degree. The improvement of catalytic activity and stability obtained for bimetallic Ni–Al catalysts was attributed to an appropriate interaction and synergy between Ni species and amorphous Al2O3. The combined results indicate that the addition of Al to Ni catalyst with an appropriate amount of Al can give rise to a bimetallic catalyst with excellent properties for synthesis of MWCNTs from PP. With our bimetallic Ni–Al catalyst, it is promising to achieve mass production of MWCNTs by using waste polymers as feedstock.

Investigation of the Effect of Reaction Time, Weight Ratio, and Type of Catalyst on the Yield of Multi-Wall Carbon Nanotubes via Chemical Vapor Deposition of Acetylene

The synthesis of multi-wall carbon nanotubes (MWCNTs) was studied using catalytic chemical vapor deposition of acetylene at 500°C for 30 and 60 min. Catalysts were prepared by impregnating Fe, Co, Ni, V, and bimetallic mixture of Fe-Co on MgO with a weight ratio of 1:100, 5:100, and 10:100. The effects of the reaction time, the type, and the weight ratio of the catalysts on the carbon yield of MWCNTs were investigated. Experimental results showed that the 10:100 weight ratio of Fe-Co:MgO had the highest carbon yield (81.97%) and the MWCNT to amorphous carbon ratio (100.6), whereas 10:100 V:MgO had the lowest carbon yield (8.44%). Statistical analyses indicated that increasing weight ratio enhanced the carbon efficiencies of Fe, Co, Fe-Co, and Ni catalyst; moreover, increasing the reaction time had a positive effect on the carbon efficiencies of Fe and V catalysts.

Formation and yield of multi-walled carbon nanotubes synthesized via chemical vapour deposition routes using different metal-based catalysts of FeCoNiAl, CoNiAl and FeNiAl-LDH.

Multi-walled carbon nanotubes (MWCNTs) were prepared via chemical vapor deposition (CVD) using a series of different catalysts, derived from FeCoNiAl, CoNiAl and FeNiAl layered double hydroxides (LDHs). Catalyst-active particles were obtained by calcination of LDHs at 800 °C for 5 h. Nitrogen and hexane were used as the carrier gas and carbon source respectively, for preparation of MWCNTs using CVD methods at 800 °C. MWCNTs were allowed to grow for 30 min on the catalyst spread on an alumina boat in a quartz tube. The materials were subsequently characterized through X-ray diffraction, Fourier transform infrared spectroscopy, surface area analysis, field emission scanning electron microscopy and transmission electron microscopy. It was determined that size and yield of MWCNTs varied depending on the type of LDH catalyst precursor that is used during synthesis. MWCNTs obtained using CoNiAl-LDH as the catalyst precursor showed smaller diameter and higher yield compared to FeCoNiAl and FeNiAl LDHs.

Catalytic Decomposition of Natural Gas to CO/CO2-Free Hydrogen Production and Carbon Nanomaterials Using MgO-Supported Monometallic Iron Family Catalysts

Monometallic Fe, Co, and Ni/MgO catalysts with 50 wt.% metal loadings were prepared and examined for natural gas decomposition to nanocarbonaceous materials, particularly multiwalled carbon nanotubes (MWCNTs) and co-valuable hydrogen. The catalytic testing was carried out in a fixed-bed horizontal reactor at 700°C under atmospheric pressure. The fresh and/or used catalysts were characterized using XRD, TPR, HRTEM, SEM, TG/DTA, Raman spectroscopy, and BET surface measurements. The resulting data showed that the 50%Co/MgO catalyst displayed higher catalytic decomposition activity of natural gas to COx-free hydrogen production (∼88%), higher yield of MWCNTs, and excellent stability up to 10 h time-on-stream. On the other hand, the Ni-containing catalyst showed lower catalytic activity toward hydrogen and CNTs production, principally due to the formation of rock-salt MgxNi(1-x)O solid solution as observed from XRD and TPR data. Accordingly, the concentration of Ni particles required for natural gas feed was extremely low. The d orbital of Ni was presumed to be occupied during the formation of the solid solution, which inhibits the solublization or adsorption of hydrocarbons on Ni particles. The MWCNTs obtained over Ni-based catalyst had narrow and homogeneous diameters (∼11–13 nm). However, the Fe/MgO catalyst exhibited intermediate activity between those of Ni and Co˭MgO catalysts toward hydrogen production (∼44%). This catalyst produced mixtures of carbon nanofibers and nanotubes.

Study of the productivity of MWCNT over Fe and Fe–Co catalysts supported on SiO2, Al2O3 and MgO

In the present study, multi-walled carbon nanotubes (MWCNT) were prepared in good quality and quantity, MWCNT were produced using the catalytic chemical vapor deposition (CCVD) technique and the carbon source was acetylene. Different catalysts were synthesized based on iron and a mixture of iron and cobalt metal supported on SiO2, Al2O3 or MgO. The effect of parameters such as iron concentration, support type, bimetallic catalyst and the method of catalyst preparation has been investigated in the production of MWCNT. The quality of as-made nanotubes was investigated by the high-resolution transmission electron microscopy (HRTEM) and thermogravimetric analysis (TGA). The best yield of MWCNT was 30 times of the amount of the used catalyst. The high yield of MWCNT was gained by 40wt.% Fe on alumina support which was prepared by the sol–gel method. TEM analysis was done for the carbon deposit, which revealed that the walls of the MWCNT were graphitized, with regular inner channel and uniform diameter. It reflected a reasonable degree of purity. The TGA showed that MWCNT was decomposed at 635°C by a small rate indicating a high thermal stability and well crystalline formation of the produced MWCNT.

Cataphoretic assembly of cationic dyes and deposition of carbon nanotube and graphene films

Cathodic electrophoretic deposition (EPD) method has been developed for the fabrication of thin films from aqueous solutions of crystal violet (CV) dyes. The films contained rod-like particles with a long axis oriented perpendicular to the substrate surface. The proposed deposition mechanism involved cataphoresis of cationic CV+ species, base generation in the cathodic reactions, and charge neutralization at the electrode surface. The assembly of rod-like particles was governed by π–π interactions of polyaromatic CV molecules. The deposition kinetics was studied by quartz crystal microbalance. CV dyes allowed efficient dispersion of multiwalled carbon nanotubes (MWCNTs) and graphene in water at relatively low CV concentrations. The feasibility of cathodic EPD of MWCNT and graphene from aqueous suspensions, containing CV, has been demonstrated. The deposition yield was investigated at different CV concentrations and deposition voltages. The relatively high deposition yield of MWCNT and graphene indicated that CV is an efficient dispersing, charging, and film forming agent for EPD. Electron microscopy data showed that at low CV concentrations in MWCNT or graphene suspensions and low deposition voltages, the films contained mainly MWCNT or graphene. The increase in the CV concentration and/or deposition voltage resulted in enhanced co-deposition of CV. The EPD method developed in this investigation paves the way for the fabrication of advanced nanocomposites by cathodic electrodeposition.