Purification Of Multi-walled Carbon Nanotubes Research Articles

Arc Discharge Synthesis and Multistep Purification of Multiwall Carbon Nanotubes

This research work describes the cost-effective synthesis and purification of multiwall carbon nanotubes (MWCNTs). Synthesis of CNTs was carried out in distilled water between two electrodes using the electric arc discharge (EAD) method. EAD is a simple and straightforward route in which an electric arc is generated between graphite electrodes through DC power source to produce soot which contains MWCNTs along with impurities. The deposited soot containing MWCNTs was then chipped off and purified. In this case, multistep purification scheme was opted to remove unwanted impurities from produced MWCNTs. Purification route comprised thermal treatment, chemical treatment and a combination of both to yield pure MWCNTs. Thermal treatments were carried out in normal air and under controlled flow of oxygen at different temperatures whereas chemical treatment was performed using acidic solution. Thermo gravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were carried out before and after purification treatments to investigate the outcome of employed treatments. Results showed that the thermal or chemical treatment alone is not sufficient to remove impurities from soot. Moreover, the introduction of an oxide group through chemical treatment reduces the oxidization temperature of graphitic particles. It was found that the chemical treatment followed by thermal annealing under the controlled flow of oxygen is the most appropriate method for successful purification of MWCNTs synthesized via EAD method.

Mild purification of multiwalled carbon nanotubes with increased selectivity for carbon impurity and residual metal removal

Mild purification of multiwalled carbon nanotubes with increased selectivity for carbon impurity and residual metal removal

Polyethyleneglycol-polyhydroxylbutyrate functionalized carbon nanotubes for industrial electroplating wastewater treatment

This study focuses on the production and purification of multi-walled carbon nanotubes (P-CNTs) via a catalytic chemical vapor deposition method and subsequent functionalization with amino polyethylene glycol (NH2-PEG) and its mixture with polyhydroxybutyrate (PHB) through a multi-step purification process to produce NH2-PEG-CNTs and NH2-PEG-PHB-CNTs, respectively. The developed nanoadsorbents were used to treat electroplating wastewater via batch adsorption to sorb potentially toxic metals and emerging pollutants. The nanoadsorbents were characterized before and after treatment with wastewater after thermal regeneration analyzed using HRSEM/EDS/SAED, DLS Nanozetasizer, BET, TGA/DTG, and FTIR. The nanoadsorbents showed a homogeneous distribution of clean and smooth crystalline interwoven tubular/cylindrical shapes and sizes, with broad polydispersed/high aspect ratio, large surface area, mesopores, and functional groups. The batch adsorption study showed simultaneous multi-capturing of toxic metals from industrial electroplating wastewater with a directly proportional relationship between contact time, adsorbent dosage andtemperature, and electrostatic activities via the positive surface charge of the nanoadsorbents (pH > pHzpc). The highest removal of Fe (15.86 %), Ni (79.82 %), Pb (79.82 %), and Cu (84.97 %) were obtained using NH2-PEG-PHB-CNTs. In addition, the ANOVA results show that the adsorption process depends on other parameters such as the concentration of toxic metals in the wastewater, its hydration energy, electronegativity, ionic mobility in the electrostatic activities, pH of the nanoadsorbents, water holding capacity of the polymer-functionalized nanoadsorbents, and synergistic effects of the bi-polymer. Moreover, the nanoadsorbents have a stable morphology after thermal regeneration for reusability purposes, and treated wastewater can be safely reused in the electroplating industry or for other purposes, such as agriculture.

Effect of microwave treatment exposure time on functionalization and purification of multi-walled carbon nanotubes (MWCNTs)

Carbon nanotube (CNT)-reinforced polymer composites are steadily replacing other materials and finding their applications in many structural components. This has been credited to their light weight, ease of processing and extraordinary thermal, mechanical and electrical properties. However, direct addition of CNTs into polymer leads to formation of agglomerates due to strong van der Waals’ force of attraction between individual nanotubes. These agglomerates then act as defects and hinder the properties of polymer/CNT composites. As a result, CNTs are functionalized in acids to minimize their tendency to agglomerate and improve dispersion in polymer matrix. The present study focuses on the microwave treatment of CNTs to achieve better functionalization as compared to the conventional ultra-sonication technique. The time of exposure of multi-walled carbon nanotubes (MWCNT) to the microwave radiation is optimized by investigating the structural integrity of different samples with Raman spectroscopy, infrared spectroscopy (FTIR), microscopy and purification effect by X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). The mechanism of sidewall modification of MWCNTs after functionalization is elucidated schematically as well.

Microwave assisted purification of multi-walled carbon nanotubes by potassium permanganate; effect of acid to oxidant molar ratio and treatment time

Carbon nanotubes (CNTs) benefit from excellent electrical and physical properties and they have attracted considerable interest in different applications like sensors and nanocomposites. Synthesized CNTs usually contain carbonaceous or metallic impurities which limit their beneficial properties. In this study, we experimentally investigate the effects of acid to oxidant molar ratio and treatment time on microwave-assisted purification of MWCNTs.Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images confirm that potassium permanganate (KMnO4) can eliminate impurities such as amorphous carbon and Fe nanoparticles. In addition, an empirical equation for KMnO4 consumption rate is determined based on the results. To sum up, the proposed method can be used as an effective purification route with acceptable removal of impurities.

Microwave purification of multi-wall carbon nanotubes in gas phase

It is a known fact that Multi-Walled Carbon Nanotubes (MWNTs) is one of the best reinforcement in conventional composites. However, impurities (like amorphous carbon blacks, graphite scraps, and catalyst particles) are generated inevitably when MWNTs are prepared. These impurities could affect the excellent properties of MWNTs as a reinforcing phase. In this paper, MWNTs were purified by microwave purification method using their excellent microwave absorbing properties. The simple purification process in the gas phase was expected to remove impurities effectively. Raman spectroscopy (Raman), X-ray Diffraction (XRD), Atomic Fluorescence Spectroscopy (AFS), Specific Surface Area (SSA), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) suggest that impurities are removed efficiently after microwave heating and simple acid pickling. The optimal purification result is obtained when MWNTs are microwave heated at 500°C for 20min, the morphology and structure remain intact. At last, the mechanism of purification is discussed.

Functionalization by Acidic Treatment in the Purification of Multiwalled Carbon Nanotubes (MWCNTs)

Comparative studies of two multi-walled carbon nanotubes (MWCNT) from different manufacturers were reported. The purification and functionalization of commercial multiwall carbon nanotubes were investigated. MWCNTs were treated with boiling concentrated HNO3 under a reflux condenser for 2 hours at 100 °C in order to purify and oxidize the raw material. The oxidized MWCNTs were rinsed with deionized water until stabilization of the filtrate pH. The measurement technique was by thermogravimetric analysis (TGA) for thermal analysis decomposition products. Meanwhile, the chemical shifted in MWCNTs can be determined by using Raman Spectroscopy.

Microstructure changes of polyurethane by inclusion of chemically modified carbon nanotubes at low filler contents

The surface of multi-walled carbon nanotubes (MWCNTs) was modified to introduce acidic groups in either covalent or van der Waals interaction bonding environments to establish cross-linking sites with a host polymer. Nanocomposites based on a polyurethane matrix (PU) containing chemically functionalised multi-walled carbon nanotubes (MWCNTs) have been shown to alter its mechanical performance depending on the nature of the surface functional groups on MWCNTs, which correlates to the type of bonding interaction of the surface group and also the dispersibility of MWCNTs and their influence on the domain structure of polyurethane. The stress at break for nanocomposites containing 0.25wt% of acid-oxidised MWCNTs (MWCNT-ox), bearing covalently attached carboxylic, lactone and phenolic groups, was twice that of the native PU and Young’s Modulus for the nanocomposites increased by four times. Whereas when hemin, which contains carboxylic functionality, was immobilised to the surface of pure MWCNTs, the improvement in Young’s Modulus was only around twice that of pure PU. Differences in the disaggregation of MWCNTs into PU were observed between the samples as well as variation of the native domain structure of PU. The results also infer that the purification of MWCNTs from acid-oxidative lattice fragments (fulvic acids) is vital prior to conducting surface chemistry and polymerisation in order to ensure maximum mechanical performance enhancement in their reinforcement of the host polymer.

Synthesis of N-Butyl Propionate Catalyzed by Multi-Walled Carbon Nanotubes Loaded Cerous Sulfate

Multi-walled carbon nanotubes ( MWCNTs) was used, as a catalyst carrier, to load cerous sulfate for catalyzing the synthesis of n-butyl propionate. The effects of nitric acid concentration, reaction time and reaction temperature on the purification of MWCNTs were investigated. The effects of molar ratio of butyl alcohol to propionic acid, the cerous sulfate load and the reaction time on the conversion of butyl acid were studied by single factor experiment method and orthogonal experiment method, respectively. The results show that the optimal conditions for purifying MWCNTs are: nitric acid concentration of 4 M, reaction time of 8 h and reaction temperature of 103°С and the optimal conditions for synthesizing n-butyl propionate are: molar ratio of butyl alcohol to propionic acid of 1.5:1, use level of loaded cerous sulfate of 0.15 g and reaction time of 70 min. The conversion of butyl acid for the MWCNTs loaded cerous sulfate reaches 96.7% which is higher than that for the unloaded cerous sulfate and the use level of cerous sulfate for the former is much less than that for the latter under same operation conditions.

Rapid purification/oxidation of multi-walled carbon nanotubes under 300 kHz-ultrasound and microwave irradiation

The use of ultrasound (US) and microwaves (MW) in the oxidation and purification of multi-walled carbon nanotubes (MWCNTs) was investigated. These techniques, in particular US at a frequency of 300 kHz, strongly accelerate the process and avoid the heavy structural damage, observed at the 20–35 kHz classic range, even at low power. Due to the residual metal catalyst on the head of MWCNTs, MW heating is strongly absorbed, causing the rupture of the tip and the loss of the metal. All our chemico-physical treatment types were performed by suspending the CNTs in a 3 ∶ 1 H2SO4/HNO3 mixture. The resulting samples were investigated by TEM microscopy, TGA analyses and Raman spectroscopy, while the degree of oxidation was estimated by colourimetric analyses.

Thermal Annealing and Electrochemical Purification of Multi-Walled Carbon Nanotubes Produced by Camphor/Ferrocene Mixtures

Multi-walled carbon nanotubes (MWCNT) were obtained by pyrolysis of camphor/ferrocene mixtures, at different concentrations of ferrocene, on quartz, polished silicon and carbon felt substrates. A detailed study by electron microscopy, Raman spectroscopy, X-ray diffraction and thermogravimetric analysis was carried out to determine the purity degree of MWCNTs. Thermal annealing under vacuum and electrochemical purification were used for iron removal. The thermal annealing brings improvement on crystalline structure of MWCNTs, besides iron elimination from internal structure of the tubes, while the electrochemical treatments remove efficiently the iron from MWCNT surface.

Effects of acid treatment duration and sulfuric acid molarity on purification of multi-walled carbon nanotubes

AbstractMulti-walled carbon nanotubes were synthesized using a Fe-Ni bimetallic catalyst supported by MgO using thermal chemical vapor deposition. Purification processes to remove unwanted carbon structures and other metallic impurities were carried out by boiling in sulfuric acid solution. Various analytical techniques such as TGA/DSC, Raman spectroscopy, SEM, HRTEM and EDAX were employed to investigate the morphology, graphitization and quality of the carbon nanotubes. The obtained results reveal the molarity of sulfuric acid and immersed time of the carbon nanotubes in the acid solution is very effective at purifying multi-walled carbon nanotubes. It was also found that 5 M concentration of boiling sulfuric acid for a 3 h treatment duration led to the highest removal of the impurities with the least destructive effect. Moreover, it was observed that acid treatment results in decreasing of CNTs’ diameter.

Purification of Multiwalled Carbon Nanotubes and Characterization of Their Oxygen-Containing Surface Groups

National Key Basic Research Program of China (973) [2009CB939804]; Fujian Provincial Key Scientific & Technical Project, China [2009HZ0002-1]

Effective Condition for Purification of Multi-walled Carbon Nanotubes by Nitric Acid

The multi-walled carbon nanotubes were synthesized on Fe-Ni bimetallic catalysts supported by MgO using thermal chemical vapor deposition. A comparative study on the effect of nitric acid molarity and time duration of acid treatment on purification of multi-walled nanotubes was done. The studies revealed that for finding a suitable condition for purification of multi-walled carbon nanotubes, it is necessary to determine suitable molarity of acid and immersion time of the carbon nanotubes. It was found that 5 M of boiling nitric acid at 3 h leads to the highest removal of the impurities with the least destructive effect. Various analytical techniques such as: scanning electron microscopy (SEM), high resolution transition electron microscopy (HRTEM), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and Raman spectroscopy techniques were employed to investigate the morphology, graphitization and quality of the carbon nanotubes.

Effective Condition for Purification of Multi-Walled Carbon Nanotubes by Nitric Acid

The multi-walled carbon nanotubes were synthesized on Fe-Ni bimetallic catalysts supported by MgO using thermal chemical vapor deposition. A comparative study on the effect of nitric acid molarity and time duration of acid treatment on purification of multi-walled nanotubes was done. The studies revealed that for finding a suitable condition for purification of multi-walled carbon nanotubes, it is necessary to determine suitable molarity of acid and immersion time of the carbon nanotubes. It was found that 5 M of boiling nitric acid at 3 h leads to the highest removal of the impurities with the least destructive effect. Various analytical techniques such as: scanning electron microscopy (SEM), high resolution transition electron microscopy (HRTEM), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and Raman spectroscopy techniques were employed to investigate the morphology, graphitization and quality of the carbon nanotubes.

Enhanced electrochemical hydrogen storage by catalytic Fe-doped multi-walled carbon nanotubes synthesized by thermal chemical vapor deposition

Hydrogen storage capacities of raw, oxidized, purified and Fe-doped multi-walled carbon nanotubes (MWCNTs) were studied by electrochemical method. Based on transmission electron microscopy and Raman spectroscopic data, thermal oxidation removed defective graphite shells at the outer walls of MWCNTs. The analysis results indicated that the acid treatment dissolved most of the catalysts and opened some tips of the MWCNTs. Thermal gravimetric analysis and differential scanning calorimetry results illustrated that by oxidation and purification of MWCNTs, the weight loss peak shifts toward a higher temperature. N 2 adsorption isotherms of the purified and oxidized MWCNTs showed an increase in N 2 adsorption below P/ P o = 0.05, suggesting that microporous structures exist in the purified and oxidized MWCNTs. The electrochemical results revealed that the Fe-doped MWCNTs produced the highest hydrogen storage capacities compared to the other samples in various sweep rates. According to electrochemical analyses, the peak currents of hydrogen adsorption/desorption increased by increasing the catalyst's active surface.

Purification of Multi-Walled Carbon Nanotubes

The discovery of carbon nanotubes (CNTs) has stimulated intensive research to characterize their structure and to determine their physical properties, both by direct measurement and through predictive methods. Many of the fundamental and remarkable properties of CNTs are now well-known, and their exploitation in a wide range of applications forms a large part of research currently in progress. However, the absence of a reliable, large-volume production capacity, simple and efficient purification methods, the high cost of carbon nanotubes and the fact that there is little selectivity in controlling the properties of the product are factors that have principally inhibited the commercialization of CNT technologies. Ever since CNTs were detected, considerable efforts have been directed at their synthesis, characterization and functionalization. Nevertheless, the CNT sample obtained by different techniques has the disadvantage of containing non-CNT impurities, such as graphitic particles, fullerenes, residual catalyst particles and amorphous carbon, which degrade the intrinsic properties of these materials. If the carbon nanotube is ever to accomplish its promise as an industrial material, large and high-quality aliquots, will be required. A number of purification methods involving elimination processes, such as physical separation, gas-phase and liquid-phase oxidation, in combination with chemical treatments, have been developed for nanotube materials. Though the quantitative determination of purity remains controversial, reported yields are best regarded with an appropriate level of scepticism on the method of assay. This review highlights the past and recent developments in the purification of multi-walled carbon nanotubes.

Decoration of carboxylated multi-wall carbon nanotubes with quantum dots

Purification of multi-wall carbon nanotubes (MWCNTs) from the iron catalyst and amorphous carbon and associated with that process, their oxidation with conc. HNO 3 over 100 °C on sonication to carboxylated MWCNTs (CMWCNTs) is presented. A novel way of decoration of CMWCNTs with ZnO and ZnS quantum dots (QDs) is proposed. It involves the use of corresponding ammonium zincates. CNT–COO–Zn–X where X = OH and SH, respectively, provided nucleation for the QDs growth. That approach does not require any non-covalent mediation from either inorganic or organic carriers.

Purification of Multiwalled Carbon Nanotubes by Annealing and Extraction Based on the Difference in van der Waals Potential

The potential energies of van der Waals interactions between two multiwalled carbon nanotubes (MWNTs) as well as two carbon nanoparticles (CNPs) were calculated and compared on the basis of the continuum Lennard-Jones model. The well depth of the potential is 1 order of magnitude higher for MWNTs than for CNPs, indicating that MWNTs and CNPs can be separated from each other through polymer-induced steric stabilization. On the basis of this prediction, a novel method for the purification of MWNTs was proposed. The method involves a high-temperature annealing (2600 degrees C, 1 h) followed by an extraction treatment with a selected dispersing agent. While the annealing process evaporates the metal particles, the extraction treatment removes CNPs. The quality of the nanotubes obtained after purification was examined by laser Raman, thermogravimetric analysis, and electron microscopy observations.

Multiwalled carbon nanotubes mass-produced by dc arc discharge in He–H2 gas mixture

Uniform cathode deposits (longer than 15 mm), containing multiwalled carbon nanotubes (MWNTs) inside, were produced by dc arc discharge evaporation with a computer-controlled feeder of a pure-carbon electrode without a metal catalyst in a He–H2 gas mixture. The purification of MWNTs was carried out to remove amorphous carbon and carbon nanoparticles. High-resolution transmission electron microscopy observations and Raman scattering studies show that the MWNTs possess a high crystallinity and a mean outermost diameter of ∼ ∼10 nm. It has been confirmed that the current density in the electron field emission from a purified MWNT mat can reach 77.92 mA/cm2, indicating that the purified MWNTs are a promising candidate electron source in a super high-luminance light-source tube or a miniature X-ray source.