High Purity Multi-walled Carbon Nanotubes Research Articles

Advanced multi-wall carbon nanotube-optimized surfactant-polymer flooding for enhanced oil recovery

In this captivating study, we explored the fascinating potential of carbon nanotube-based nanofluids in improving oil recovery efficiency and transforming interfacial tension. To accomplish this, we acquired high-purity multi-walled carbon nanotubes from Plasma Chem Gmbh, ensuring a purity level exceeding 95 %, which underwent additional functionalization and experimentation to explore their impact. The functionalization of multi-wall carbon nanotubes with ammonium hydroxide and hydrogen peroxide generated diverse surface groups, reduced van der Waals interactions, and increased carbon nanotube dispersibility through enhanced interactions with polymers or solvents. The modified multi-wall carbon nanotubes were characterized using Raman analysis, HRTEM, and zeta potential. Varying concentrations of altered multi-wall carbon nanotube-based fluids were prepared to study their impact on surface tension using a Surface tensiometer. Adsorption studies were conducted to minimize surfactant loss. Contact angle experiments using a Goniometer helped alter the rock surface's wetting characteristics. Finally, the core flooding experiment using two pore volumes of the nanofluid with the optimal concentration of mMWCNT with SDS and 1000 ppm of polymer calculates the oil recovery factor. The study's findings revealed that the modified multi-wall carbon nanotubes significantly reduced surface and interfacial tension by approximately 59 % and 56 %, respectively, at the optimum concentration. Moreover, the nanotubes successfully minimized surfactant loss by about 49.3 %. The contact angle experiments demonstrated that the modified nanotubes transformed the rock surface from oil-wet to water-wet, as evidenced by a substantial reduction of approximately 54 % in the contact angle value. In conclusion, the core flooding experiment, employing a chemical slug composed of SDS at CMC, modified multi-wall carbon nanotubes, and industrial-grade polymer, yielded a remarkable oil recovery factor of approximately 70 % of the original oil in place.

Impact of temperature on the activity of Fe-Ni catalysts for pyrolysis and decomposition processing of plastic waste

Thermal chemical processing of plastic has been seen as an efficient practice for the disposal and resource utilization facing the current plastic waste problem. A pyrolysis followed by catalytic decomposition process was investigated in this work to produce carbon materials from polypropylene plastic over FeNi catalysts. The effects of both catalysis temperature (600, 700 and 800 °C) and catalyst type on the gaseous yields, as well as the physicochemical properties (morphology, porosity, purity and graphitization degree) of the as-obtained carbon materials were systematically explored. Various technologies including high resolution electron microscopies, temperature programmed oxidation, Raman, X-ray diffraction were used for full characterizations of the as-obtained carbons. Results show that the yields of both carbon and hydrogen gas were significantly proportional to the catalysis temperature. In terms of the physiochemical properties of carbon materials, the low catalysis temperature of 600 °C generated the majority amorphous and disordered carbons, due to the insufficient decomposition reactions and low catalyst activity. Catalysis temperature higher than 700 °C was necessary for the successful growth of carbon nanotubes, while further increase in temperature mainly acted on the yield rather than thermal stability and graphitic degree. High purity multi-walled carbon nanotubes with outer diameters of 20–30 nm and length up to few micrometers were generated with FeNi1 at 800 °C. FeNi1 catalyst synthesized by sol–gel method displayed higher activity towards the production of high quality carbon materials than FeNi2 catalyst at any temperature range investigated, due to the porous structure and the uniform dispersion of metal particles.

Multi-walled carbon nanotubes with selected properties for dynamic filtration of pharmaceuticals and personal care products

In this study, multi-walled carbon nanotubes (MWCNT) with selected properties, including pristine MWCNT, hydroxylated MWCNT (H-MWCNT), thin-walled MWCNT with large inner diameter (L-MWCNT), aminated MWCNT, and high-purity MWCNT were investigated for dynamic removal of eight pharmaceuticals and personal care products (PPCP). The removal ratios of different PPCP by the pristine MWCNT followed a decreasing order of triclosan (0.93) > prometryn (0.71) > 4-acetylamino-antipyrine (0.67) > carbendazim (0.65) > caffeine (0.42) > ibuprofen (0.34) > acetaminophen (0.29) at 100 min of filtration. Similar or even higher PPCP removals were obtained for all PPCP as the influent concentration decreased, suggesting potential consistent PPCP removals at environmental PPCP concentrations. The removal ratio of acetaminophen was increased to 0.74 by using H-MWCNT. SRFA (Suwannee River fulvic acid) suppressed PPCP adsorption to MWCNT, to greater extents with increasing SRFA concentrations. The L-MWCNT, despite a large inner diameter of 52 ± 3 nm, did not provide better resistance to the competitive adsorption of SRFA than MWCNT with a small inner diameter of 10 ± 2 nm. Future research will be conducted to minimize the effect of SRFA and facilitate application of MWCNT to the treatment of PPCP-contaminated water.

Al2O3 + FeCo and Al2O3 + FeNi coatings for multiwalled carbon nanotubes growth

In this work the preparation of growth of aligned multiwall carbon nanotubes (MWCNTs) is presented using FeCo and FeNi alumina-based catalysts. The catalysts were prepared using the sol–gel process and some stainless steel substrates were coated using the dip coating technique. These coatings were used for the MWCNT in a Chemical Vapor Deposition (CVD) reactor. X-ray diffraction (XRD) studies of the coating solutions demonstrate the formation of metallic phases rich in iron in both samples. Raman spectroscopy study depicted the characteristic bands of MWCNT and the scanning electron microscopy (SEM) analysis showing the growth of aligned MWCNTs with a length of about 10μm and 20 to 80nm of diameter on both coatings. These results contribute to establishing a new route for the preparation of aligned and high purity MWCNT using catalysts prepared by a very fast and simple way.

High purity multi-walled carbon nanotubes: Preparation, characterization and performance as filler materials in co-polyimide hollow fiber membranes

Functionalized MWCNTS were used as filler materials for the preparation of composite polymeric hollow fiber membranes based on the BTDA-TDI/MDI (P84) co-polyimide. As a first step high purity multi-walled carbon nanotubes (MWCNTs) were synthesized using a novel catalytic CVD (chemical vapor deposition) technique, which enables large-scale production at low cost, while maintaining high purity and exceptional material properties at the same time. Covalent modification of pristine MWCNTs was applied in order to optimize both their nanoscale morphology and their dispersion in organic solvents. The functionalization process introduced certain functional groups, namely phenol groups, on the external surface of the nanotubes. Both pristine and functionalized MWCNTs with phenol groups were characterized using a variety of techniques such as XRD, SEM, TGA and Raman spectroscopy. The functionalized nanotubes were found to result in a uniform dispersion in NMP solvent. The best dispersion was observed in the case of phenol-functionalized MWCNTs. The effect of the concentration of carbon nanotubes on the composite membranes was investigated by carrying out DSC, SEM and gas permeability experiments. The prepared composite membranes were crack free and they presented high permeability values and ideal helium–nitrogen selectivities. In addition, the gas permeance coefficients increased linearly with the MWCNT concentration suggesting an increase of the free volume of the polymer matrix.

Novel Method of Evaluating the Purity of Multiwall Carbon Nanotubes Using Raman Spectroscopy

We propose the quantitative method of evaluating the purity of multiwall carbon nanotubes (MWCNTs) using Raman spectroscopy. High purity MWCNTs were prepared by chemical vapor deposition (CVD) to be used as a reference material with 100% purity. Since the intensity and wavenumber of D′′‐band located at around 1500 cm−1 were found to be independent of the excitation wavelength of a laser, the purity of MWCNTs was measured by comparing the intensity ratio of D′′‐band to G‐band (/IG) of the sample with that of a reference material. The established method was verified by testing the mixture of amorphous carbon particles and reference MWCNTs.

Cerium Oxide Dispersed Multi Walled Carbon Nanotubes as Cathode Material for Flexible Field Emitters

Nanomaterials based electron sources are omnipresent in modern flat panel displays. Multi walled carbon nanotubes (MWNT) are the well studied electron emitter among the carbon materials. Since the surface modification of MWNT with low work function materials would have a positive impact on the field emission property of MWNT, cerium oxide (CeO2) nanoparticles dispersed multi walled carbon nanotubes (CeO2/MWNT) were synthesized by catalytic chemical vapour deposition followed by chemical reduction and its field emission property was investigated. The high-purity MWNT as well as CeO2/MWNT showed crystalline structure conformed by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Further characterisation was done with Raman spectroscopy, UV-Visible absorption spectra and Fourier transform IR spectroscopy (FT-IR). The morphology and structural details of CeO2/MWNT composite was probed by field-emission scanning electron microscopy (FESEM) and energy dispersive X-ray analysis (EDX). The direct evidence of the formation of CeO2/MWNT composites was given by transmission electron microscopy (TEM). The synthesized sample was coated over a flexible carbon paper using spin coating technique. The experiment was performed under a vacuum of 1 x 10(-6) Torr and Fowler-Nordheim equation was used to analyse the data. The turn-on voltage for the cerium oxide dispersed MWNT was found for a current density of 10 microA/cm2. The emission current density from the CeO2 nanoparticles dispersed MWNT reached 0.2 mA/cm2 at a reasonable bias field of 2.58 V/microm. The results were compared with those of pure MWNT and pure CeO2 nanoparticles with literature values.

Synthesis of high purity multi-walled carbon nanotubes over Co–Mo/MgO catalyst by the catalytic chemical vapor deposition of methane

Synthesis of high purity multi-walled carbon nanotubes over Co–Mo/MgO catalyst by the catalytic chemical vapor deposition of methane

Synthesis of high purity multi-walled carbon nanotubes over Co-Mo/MgO catalyst by the catalytic chemical vapor deposition of methane

Nearly uniform diameter multi-walled carbon nanotubes (MWCNTs) were synthesized over a magnesia supported Co-Mo bimetallic catalyst through the catalytic chemical vapor deposition of methane. The bimetallic catalyst with a composition of Co:Mo:MgO=5:20:75 (mass ratio) was prepared by a sol-gel method. Thermagravimetric analysis shows that MWCNTs were synthesized in high yield. The selectivity of the catalyst for MWCNTs over undesired amorphous carbon was 91.17%. Transmission electron microscopy indicates that the MWCNTs grown on the catalyst have an average diameter of 6.2 ± 0.5 nm (mean ± standard deviation). Through simple purification by mild acid treatment, the catalyst residue for the purified samples was reduced to 0.72%.

Catalytic effects of production of carbon nanotubes in a thermogravimetric CVD reactor

Catalytic effects of the production of carbon nanotubes by chemical vapor deposition of ethanol are investigated. More specifically, the rate of deposition, total yield and physical characteristics of the product are examined with respect to physicochemical characteristics of the catalyst. The experiments were carried out at 800 °C in a thermogravimetric chemical vapor deposition (CVD) hot-wall reactor, which enables continuous monitoring of the evolution of carbon mass with time. The carbon precursor was ethanol vapors. Different types of catalytic substrates enriched with iron were employed and the effect of iron concentration and preparation method was studied. It was determined that an optimal iron content of the catalyst results in maximum yield and that yield depends on the preparation method of the catalyst. For a ratio of Al/Fe = 1/4 the yield reached approximately 400% of the initial catalyst weight, after 1 h of exposure to ethanol vapor. The final product was characterized with Scanning Electron Microscopy (SEM) and Raman spectroscopy. The results revealed the existence of high purity multi-wall carbon nanotubes, and the presence of single-wall carbon nanotubes with diameter ranging between 0.76 and 1.14 nm.

The use of camphor-grown carbon nanotube array as an efficient field emitter

Three-dimensional growth of well-aligned high-purity multiwall carbon nanotubes (CNTs) is achieved on silicon, nickel-coated silicon and cobalt-coated silicon substrates by thermal decomposition of a botanical carbon source, camphor, with different catalyst concentrations. Field emission study of as-grown nanotubes in a parallel-plate diode configuration suggests them to be an efficient emitter with a turn-on field of ∼1 V/μm (for 10 μA/cm 2) and a threshold field of ∼4 V/μm (for 10 mA/cm 2). Maximum current density lies in a range of 20–30 mA/cm 2 at 5.6 V/μm with significant reversibility. Prolonged stability test of camphor-grown CNT emitters suggests a life time of ∼5 months under continuous operation. A new feature, metal-assisted electron emission from CNTs, has been addressed. Isolated nanotubes used as a cold cathode in a field emission microscope reveal the pentagonal emission sites and hence the atomic structure of the nanotube tips.

Production of High Purity Multi-Walled Carbon Nanotubes from Catalytic Decomposition of Methane

Acid-based purification process of multi-walled carbon nanotubes (MWNTs) produced via catalytic decomposition of methane with NiO/TiO 2 as a catalyst is described. By combining the oxidation in air and the acid refluxes, the impurities, such as amorphous carbon, carbon nanoparticles, and the NiO/TiO 2 catalyst, are eliminated. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images confirm the removal of the impurities. The percentage of the carbon nanotubes purity was analyzed using thermal gravimetric analysis (TGA). Using this process, 99.9 wt% purity of MWNTs was obtained.

A parametric study of the large scale production of multi-walled carbon nanotubes by fluidized bed catalytic chemical vapor deposition

A parametric study investigating the impact of temperature, run duration, total pressure, and composition of the gaseous phase on the catalytic growth of multi-walled carbon nanotubes (MWCNT) has been performed. MWCNTs have been produced very selectively on the multi-gram scale by catalytic chemical vapor deposition from ethylene in a fluidized bed reactor. The kinetics of MWCNTs growth is fast and, with the catalyst used, no induction period has been observed. The kinetic law is of positive order in ethylene concentration and the process is limited by internal diffusion in the porosity of the catalyst. The formation of MWCNTs in the macroporosity of the catalyst induces an explosion of the catalyst grains. Such a process, thanks to the absence of temperature gradient and to the efficient mixing of the grains allows a uniform and selective treatment of the catalyst powder leading to very high selectivity towards MWCNTs formation. High purity MWCNTs have been obtained after catalyst dissolution. Depending on the temperature of production, the specific surface area of this material ranged between 95 and 455m2/g.

A 20–40 SECOND PROCESS FOR SYNTHESIS OF MULTI-WALLED CARBON NANOTUBES

We report on a 20–40 s process for growing aligned, uniformed, high purity multi-walled carbon nanotubes (MWNTs) using an alcohol lamp burner. With an appropriate catalyst precursor concentration, MWNTs can be grown on a Co-coated 304 stainless steel mesh under incomplete combustion conditions at 680–700°C. The process provides a rapid, easy, economic and safe method for the formation of carbon nanotubes. We suggest that the proposed method be considered as an educational kit for college or high school level experiments.

The effect of feedstock and process conditions on the synthesis of high purity CNTs from aromatic hydrocarbons

High purity multi-walled carbon nanotubes were synthesized from aromatic hydrocarbons (benzene, toluene, xylene and trimethyl benzene) using ferrocene as the source of Fe catalyst. Screening studies of aromatic feeds at 675 °C, residence time of 14 s and Fe/C atom ratio of 1.07%, resulted in feedstock carbon conversion of 20–31%, CNT yield of 19.8–30.5%, and catalyst yield of 5.3–8.3 (g CNT/g catalyst). While the quality of the CNTs as determined by TGA, SEM, TEM and Raman spectroscopy, were high and comparable for different feedstocks; their carbon conversion, CNT yield and catalyst yield differed noticeably. A process optimization study for toluene feed showed that carbon conversion of more than 39%, CNT yield of 38.7% and catalyst yield of 18.3 can be achieved at temperature of 800 °C, Fe/C atom ratio of 0.47%, and residence time of 10–20 s.

In vitro studies of carbon nanotubes biocompatibility

Cellular tests have been applied to study the biocompatibility of high purity multiwalled carbon nanotubes (MWNTs). The viability of fibroblasts, osteoblasts and osteocalcin concentrations in osteoblasts cultures in the presence of nanotubes has been examined, as well as the degree of cells stimulation, based on the amount of released collagen type I, IL-6 and oxygen free radicals. The high level of viability of the examined cells in contact with the nanotubes, the slight increase of collagen formation, the lack of pro-inflammatory IL-6 cytokine as well as the induction of free radicals, confirm a good biocompatibility of nanotubes, which is similar to that of polysulfone currently used in medicine. The collagen synthesis induced on nanotubes by both fibroblasts and osteoblasts may be significant for future medical applications of nanotubes, in particular as substrates for the regeneration of tissues.

Vapor phase deposition of carbon nanotubes using tungsten-organic source and acetylene

We report the vapor phase deposition of carbon nanotubes using a catalytic reaction of tungsten-organic source (C 14H 10O 7W) and acetylene gas. The deposits were high-purity multi-walled carbon nanotubes with a hollow at the tube inside. Transmission electron microscopy study revealed that the inner graphitic layers were highly crystallized but the outer graphitic layers had waving structure. We present the large-scale production of carbon nanotubes using tungsten-based catalyst.

CVD synthesis of high-purity multiwalled carbon nanotubes using CaCO 3 catalyst support for large-scale production

Multiwalled carbon nanotubes (MWCNTs) were synthesized in a catalytic reaction using CaCO 3 as catalyst support. Impregnated with conventional catalysts CaCO 3 enabled the production of MWCNTs in a fixed-bed flow reactor at relatively low reaction temperature. The purification was performed in one step: both metallic particles and catalyst support were dissolved in a diluted acid. Hence, disadvantages, namely multi-step processes and hazardous chemicals, were avoided. A further advantage of CaCO 3 support is efficient and stable growth of MWCNTs. First results obtained in our new rotary-tube oven indicated high quality and pure MWCNTs with a yield of 100 g/day by this method.

High purity multiwalled carbon nanotubes under high pressure and high temperature

We have studied the structural modifications that multi-walled carbon nanotubes (MWNTs) undergo when treated under high pressure and high temperature (HP–HT). Uniaxial pressures of 5.5–6.5 GPa were applied to samples of purified MWNTs between 850 and 950 °C for 30 min. The resulting material was then analysed by X-ray diffractometry, Raman spectroscopy and transmission electron microscopy. Comparison of the data obtained by such analyses before and after treatment does show changes in the Raman spectra, a slight linear decrease of the d 002 spacing, and some structural modifications that could be due to MWNT segmentation and interlinking.

Metal-free production of high-quality multi-wall carbon nanotubes, in which the innermost nanotubes have a diameter of 0.4 nm

The production of high-purity multi-wall carbon nanotubes (MWNTs) without metal catalysts was produced using radio-frequency plasma. The MWNTs had diameters of about 5 nm, with the innermost tubes having a diameter of 0.4 nm, the smallest value possible for a single-wall carbon nanotube. Two types of aggregates were obtained, depending on the conditions of formation: moss-like aggregates (diameter: about 1μm) and long bundles (length: 10μm, diameter: 100 nm). The MWNTs in the moss-like aggregate, referred to as acute MWNTs, had tips with a cone angle of 19.2°.