Walls Of Multi-walled Carbon Nanotubes Research Articles

Study of the photocatalytic degradation of toluene over CdS-TiO2 nanoparticles supported on multi-walled carbon nanotubes by back propagation neural network

ABSTRACTTo optimize the photocatalytic conditions for the degradation of volatile organic compounds (VOCs), this study focused on the application of a back propagation (BP) neural network to determine the photocatalytic performance of CdS-TiO2 nanoparticles supported on multi-walled carbon nanotubes (MWCNTs) for toluene degradation. This was accomplished by first characterizing the photocatalyst using transmission electron microscopy (TEM), N2 adsorption-desorption, X-ray diffraction (XRD) and UV-visible absorption spectrum (UV-vis). It was observed that TiO2 and CdS particles were uniformly supported on the inner and outer walls of MWCNTs as a composite catalyst. Second, employing a test that included a training set and a prediction set, the results showed that the designed BP neural network exhibited a fast convergence speed and the system error was 0.0009702. Furthermore, the predictive values of the network were in good agreement with the experimental results, and the correlation coefficient was 0.9880. These results indicated that the network had an excellent training accuracy and generalization ability, which effectively reflected the performance of the system for the catalytic oxidation of toluene on a CdS-TiO2/MWCNTs photocatalyst.

Zinc oxide quantum dots decorated carbon nanotubes for improved opto-electro-mechanical response

Hybrid nanostructures play a major role towards outstanding performance of nano-devices by coupling different functionalities. In this study, we report in-situ decoration of zinc oxide quantum dots (QDs) on the outer walls of multi-walled carbon nanotubes (MWCNT). The coupling of MWCNT and QDs not only provides excellent radiation sensitivity but also a high mechanical actuation induced by electrical polarization. A flexible thin paper-based device demonstrated combined opto-electro-mechanical performance under constant electric field with ∼122% enhancement in the response current for optoelectrical and ∼345% enhancement in actuation for electromechanical properties of the hybrid paper device as compared to the response from the pristine sample.

Effective lubricant additive of nano-Ag/MWCNTs nanocomposite produced by supercritical CO2 synthesis

Abstract Silver nanoparticles dotted on the external walls of multi-walled carbon nanotubes (MWCNTs) were prepared by an aldehyde reduction process in supercritical carbon dioxide (scCO 2 ) fluid. The silver nanoparticles with narrow size distribution of 5–15 nm are uniformly anchored on MWCNT walls. The prepared nanocomposite of nano-Ag/MWCNTs was used as lubricant additive in 10w40 engine oil and its lubricating performances was evaluated by a four-ball tribometer. The friction coefficient and wear scar diameter were reduced by 36.4% and 32.4% respectively, when the engine oil was dispersed with 0.18 wt % nanocomposite. After synthetically analyzing worn surface by means of scanning electron microscopy and X-ray photoelectron spectroscopy, the lubrication mechanism of this nanocomposite as oil additive is discussed and postulated.

Ion irradiation-induced, localized sp 2 to sp 3 hybridized carbon transformation in walls of multiwalled carbon nanotubes

Abstract In this report, ion irradiation-induced localized sp2 to sp3 hybridized carbon transformation in multiwalled carbon nanotubes (MWCNTs) was observed after irradiating MWCNTs with high-energy Au+8 ions (100 MeV). The used MWCNTs were grown using cobaltocene and benzene as catalyst and carbon source, respectively by the thermal CVD technique and consist of both unfilled and Co-filled tubes. Prior to irradiation, the MWCNT sample was characterized using scanning electron microscope and micro-Raman and photoluminescence spectrometers. The effect of ion fluence on MWCNT walls and transformation of sp2 to sp3 sites was analyzed by Raman spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. We found that as the fluence increased, the localized transformation from sp2 to sp3 sites occurred in the walls of MWCNTs, which was evident by the emergence of peak at approximately 1543 cm−1 associated with the G peak in tetrahedral amorphous carbon (ta-C) and the vanishing of 2D band (2700 cm−1). Furthermore, we observed broadening in D and G, with slight shift in their positions and consistent decrease in 2D band intensity, as fluence increased.

Effect of carbon nanotubes irradiation by argon ions on the formation of SnO 2-x /MWCNTs composite

Abstract Methods of transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption near edge structure (XANES) were used to investigate the influence of irradiation by argon ions of multi-walled carbon nanotubes (MWCNTs) on the composites SnO 2-x /MWCNTs formation. It has been shown that irradiation of the MWCNTs leads to the formation of structural defects and oxygen-containing groups in the walls of carbon nanotubes. The presence of the latest in MWCNTs walls leads to chemical interaction of the tin oxide with the surface of MWCNTs through formation of chemical Sn O C bonds at the interfaces “Tin oxide-MWCNTs” at synthesis of the composite by CVD method. It has been established that the crystalline structure of the tin oxide clusters forming on surface of MWCNTs depends essentially on the defectiveness in the structure of the outer walls of carbon nanotubes.

Facile longitudinal unzipped multiwalled carbon nanotubes incorporated overoxidized poly(p-aminophenol) modified electrode for sensitive simultaneous determination of dopamine, uric acid and tryptophan

In the present work, unzipped multiwalled carbon nanotube oxides (UMCNOs) was obtained from longitudinally unzipped multiwalled carbon nanotubes (MWCNTs) by the Hummers method. This hybrid structure could significantly improve the accessible area since both the outer and inner wall of MWCNTs are available. Then a novel strategy based on overoxidized poly(p-aminophenol) (pAPox) and UMCNOs copolymer modified electrode was proposed for the simultaneous determination of dopamine (DA), uric acid (UA), and tryptophan (Trp). Besides, the coexistence of ascorbic acid (AA) has no interference toward the detection of DA, UA and Trp. Also, scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), cyclic voltammetry (CV) and different pulse voltammetry (DPV) were employed to characterize the copolymer. Under the optimal conditions, two linear calibrations for DA and Trp were obtained over ranges of 15.0–95.0μM, 115.0–515.0μM and 5.0–185.0μM, 265.0–1265.0μM respectively with detection limit (S/N=3) of 0.33μM and 0.47μM. Three linear calibrations for UA were obtained over ranges of 7.0–57.0μM, 87.0–582.0μM and 752.0–2402.0μM with detection limit (S/N=3) of 0.40μM. In addition, satisfactory results were obtained using the modified electrode to detect DA, UA and Trp in samples via standard addition method.

Effect of cobalt alloying on the electrochemical performance of manganese oxide nanoparticles nucleated on multiwalled carbon nanotubes

MnO is an electrically insulating material which limits its usefulness in lithium ion batteries. We demonstrate that the electrochemical performance of MnO can be greatly improved by using oxygen-functional groups created on the outer walls of multiwalled carbon nanotubes (MWCNTs) as nucleation sites for metal oxide nanoparticles. Based on the mass of the active material used in the preparation of electrodes, the composite conversion-reaction anode material Mn1−xCoxO/MWCNT with x = 0.2 exhibited the highest reversible specific capacity, 790 and 553 mAhg−1 at current densities of 40 and 1600 mAg−1, respectively. This is 3.1 times higher than that of MnO/MWCNT at a charge rate of 1600 mAg−1. Phase segregation in the Mn1−xCoxO nanoparticles was not observed for x ≤ 0.15. Capacity retention in x = 0, 0.2, and 1 electrodes showed that the corresponding specific capacities were stabilized at 478, 709 and 602 mAhg−1 respectively, after 55 cycles at a current density of 400 mAg−1. As both MnO and CoO exhibit similar theoretical capacities and MnO/MWCNT and CoO/MWCNT anodes both exhibit lower performance than Mn0.8Co0.2O/MWCNT, the improved performance of the Mn1−xCoxO/MWCNT alloy likely arises from beneficial synergistic interactions in the bimetallic system.

Microwave absorption and infrared emissivity of helical polyacetylene@multiwalled carbon nanotubes composites

Hybrids of polyacetylene (PA) with multiwalled carbon nanotubes (MWNTs) were fabricated by wrapping PA derivatives containing stigmasterol and pivalic acid moieties onto MWNTs walls. The PA derivatives with moderate molecular weights (Mn ~ 24409) were proved to adopt a single-handed helical structure stabilized by asymmetric hydrogen bonding force and stereo-hindrance effect. Convincing experimental results show that PA had been wrapped evenly on the surface of MWNTs without damaging their internal structures. Moreover, the helical structure of PA became more compact and ordered after wrapping around MWNTs. The incorporation of stigmasterol moieties could contribute to enhancing the microwave absorbing properties and decreasing infrared emissivities. PA@MWNTs showed a minimum reflection loss value of −20.65 dB at 9.7 GHz and the bandwidth of reflection loss less than −10 dB (90% absorption) was 3.2 GHz. Meanwhile, PA@MWNTs composites had a much lower infrared emissivity value (e = 0.503) than raw MWNTs. The efficient microwave absorption and low infrared emissivity might result from the synergistic effect of the extraordinary helical structure of PA and π-electronic interactions between the organic substituents and inorganic MWNTs walls, which provides a promising method to prepare materials with low infrared emissivities and excellent microwave absorption properties.

Electrochemical Characterization of Phosphorus Encapsulated in Drilled Carbon Nanotubes as Anode Material for Lithium Ion Batteries

Lithium ion batteries (LIBs) are one of attractive candidates for portable electronic devices as well as electric vehicles. For their applications, high energy density is the most important in order to help reduce the cost per unit of energy capacity. In the last decade, various electrode materials have been proposed to replace graphite and lithium cobalt oxides in conventional LIBs to materials with higher energy density. For example, silicon, tin and phosphorus as anode materials have a huge theoretical capacity of about 4200, 1000 and 2600 mAh/g, respectively.[1] However, enormous volumetric change up to 300% in LIBs is known to be a main reason of rapid capacity fading upon Li+ insertion and extraction reaction (i.e.charge and discharge, respectively), which hinder practical applications for LIBs. Up to now, several composite materials have been demonstrated as an electrode for LIBs to circumvent the problem, even though their reversible capacities still showed low value of 200-800 mAh/g in addition to the low capacities after cycling.[2] On the other hand, phosphorus encapsulated in single walled carbon nanotubes (P/SWCNTs) showed a high reversible capacity of 2000 mAh/g at the 1st cycle and a good capacity retention of 50% of the 1st cycle still delivered after 10 cycles.[3] The improved performance is thought to be due to suppressing volumetric expansion of phosphorus. However, it has been reported that there was still the expansion and the capacity fading of 50%, which might be attributed to blocking the Li+ insertion and extraction in and from SWCNTs. Therefore, it is needed to form an effective path of Li+ diffusion to inner carbon nanotubes. In this study, chemically-drilled carbon nanotubes were prepared as starting materials, using an impregnation method[4] and an air-oxidation treatment[4]in order to form the path and insert a large amount of phosphorus. The macro and micro morphologies were evaluated in TEM, SEM, EDX, XRD and Raman spectroscopy before and after electrochemical cycling in an Li based organic electrolyte. Multi walled carbon nanotube (MWCNT) was used in this study because its tensile strength is 10 times higher than that of SWCNTs, in order to reduction of structural expansion during Li+ insertion reaction on phosphorus in the inner tubes. Pristine MWCNT was refluxed in concentrated nitric acid at 110 oC for 24 h to remove amorphous carbon and attach oxygen functional groups on the side walls. The functionalized MWCNT was washed repeatedly with distilled water and then dried over night. To partially cut the side walls of MWCNT, the functionalized MWCNT was impregnated with Co nanoparticles. After the impregnation, the sample was thermally treated at 300 oC under an air environment. Then, the sample was refluxed in concentrated nitric acid at 110 oC for 1 h, followed by washing and drying to obtain drilled-MWCNT with low metal contents. To achieve encapsulation of phosphorus in the drilled-MWCNT (P@DMWCNT), phosphorus powder and DMWCNT powder were placed in a glass tube under vacuum followed by thermal treatment at 500 oC. The excess phosphorus on the outer walls of DMWCNT was removed by re-thermal treatment at 200 oC.[3] After structural analyses of the obtained samples, the electrochemical anode performance for LIBs was observed in a three electrode cell using 1 mol/L LiPF6dissolved in a mixture of ethylene carbonate and dimethyl carbonate with a volume ratio of 1:1. The anodes as working electrodes were prepared using P@DMWCNT and a binder without any carbon additives. Counter and reference electrodes employed were lithium metals. In this presentation, I will discuss the structural analysis of phosphorus encapsulated in drilled-carbon nanotubes upon Li+insertion and extraction processes.

Effect of Interwall Interaction on Phonon Oscillations of Growing Multi-Walled Carbon Nanotube

In this paper, a novel model is presented to explain the growth mechanism of multi-walled carbon nanotube (MWCNT) in chemical vapor deposition. The developed model is based on kinetic theory of gases and interlayer interaction between neighbor walls of MWCNT in addition to phonon vibrations of MWCNT on substrate. All interactions including MWCNT-catalyst and interlayer are investigated by Lennard-Jones potential. Simulations demonstrate that the growth of walls of MWCNT is saturated at a certain time. In addition, effect of temperature and type of catalyst on growth is investigated and it is shown that there is an optimum temperature and an optimum catalyst for growth process. Also it is shown that the optimum temperature is changed using different catalysts. Finally, effect of the partial pressure of decomposed hydrocarbons on the MWCNT growth is presented. It is shown that increasing partial pressure leads to longest MWCNTs and influence of partial pressure on MWCNTs with smaller diameter of outer wall is stronger. All results are in good agreement with reported experimental results, so it can be useful in future experimental and theoretical researches for optimization of MWCNT growth.

Ladder-Inspired SnO-Multiwalled Carbon Nanotubes with Sulfur Impregnation as Robust Cathode Material for High-Rate Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) battery has the theoretical potential to surpass lithium-ion batteries in terms of capacity and energy density for applications in electric vehicles and hybrid electric vehicles. However several drawbacks prevent it from practical application, such as (1) the low electrical conductivity of both sulfur (5 × 10–3 S cm–1), (2) the large volume expansion (about 80%) during lithiation, (3) the intermediate lithium polysulfides (Li2Sx, 3 ≤ x ≤ 8). During the cycling process, the soluble lithium polysulfides may migrate to the anode side by the “shuttle effect”, resulting in significant irreversible capacity loss and corrosion on the lithium metal anode [1]. Many strategies have been developed to enhance the conductivity of sulfur and suppress the dissolution of polysulfides. The carbon host materials used in Li-S cathodes, despite their excellent electrical and mechanical performances, still demonstrate drawbacks such as rapid capacity fading under cycling and reduced entrapment of polysulfide, leading to decreased rate capability [2]. Therefore, a hybrid design is required for a robust cathode material with high conductivity and low volume change during lithiation-delithiation process.Here, we present ladder-inspired multi-walled carbon nanotubes (MWCNT) filled with tin monoxide (SnO) nanoparticles as a new host material. The MWCNT-SnO/S electrode exhibited excellent electrochemical performance such as stable cycling performance and high rate capability. In situ transmission electron microscopy results indicate that the ladder-inspired MWCNT-SnO host efficiently suppresses volume expansion during lithiation and reduces polysulfide dissolution. Furthermore, the ordered SnO nanoparticles facilitate fast electron and ion transfers during the redox reactions, due to act as connecting links between the walls of MWCNT. This development approach can also be applied to other energy storage devices, including lithium-ion batteries and hybrid supercapacitors.

Decorating carbon nanotubes with co-precipitated magnetite nanocrystals

The superior properties of carbon nanotubes (CNTs) are best manifest in bulk materials when the CNTs are organized in tandem and embedded in a continuous matrix. Decorating the CNTs with magnetic nanoparticles (MNPs) facilitates their expedient organization with a magnetic field. One of the most convenient methods for their decoration is to first treat the CNTs with nitric or sulfuric acid, or a mixture of the two, and then co-precipitate MNPs in situ. Here, six variations of this protocol are compared to identify their influence on the decoration of multi-walled CNTs (MWNTs). Acid-treated MWNTs are scrutinized using XPS, and the decorated MWNTs are examined using X-ray diffraction, transmission electron microscopy, Fourier transformer infrared spectroscopy and vibrating sample magnetometry. The results show that (1) treatment with nitric acid provides the highest (~100%) attachment of MNPs to the MWNT walls, (2) sulfuric acid best preserves the MWNTs with only ~8% weight loss, and (3) after acid-treatment, the MWNTs must be washed and filtered prior to co-precipitation to prevent the consumption of up to 70% of the iron through side reactions that yield non-magnetic phases.

Zinc Oxide Encapsulated Carbon Nanotube Thin Films for Energy Storage Applications

Thin films of zinc oxide (ZnO) nanodots decorated onto the multiwalled carbon nanotubes (MWNTs) were prepared by simple and inexpensive two-step chemical method which includes ‘dip and dry’ process followed by successive ionic layer adsorption and reaction (SILAR) method. The as-prepared ZnO/MWNTs (ZCN) composite films were characterized with different physicochemical techniques. The surface morphological analysis shows that the ZnO nanodots with average size less than 15nm get uniformly decorated onto the MWNT walls. Furthermore, the electrochemical analysis carried out for ZCN composites suggests that these are the efficient electrodes for electrochemical charge-storage applications.

Supramolecular Approach to Decorate Multi-Walled Carbon Nanotubes with Negatively Charged Iron(II) Complexes

Poly(4-vinylpyridine) (P4VP) and P4VP/pentacyanoferrate(II) metallopolymer were used to suspend up to 1 mg mL-1 of multi-walled carbon nanotubes (MWCNT) in ethanol/water mixtures, providing noncolavent decoration of MWCNT with electroactive iron complex. The major interaction between polymer side chains and nanotubes is via π-π stacking, rather than charge-transfer interaction reported for many nitrogenated interacting molecules. Preservation of structural integrity of the nanotubes after functionalization was attested by Raman, which was reflected in the semiconducting character of the dried nanocomposites. Proximity of pentacyanoferrate(II) to MWCNT walls was suggested by its solvatochromic shift of metal-to-ligand charge transfer band attributed to [Fe(CN)5]3− bound to P4VP pyridyl moieties. Electronic microscopy revealed smooth films and good adhesion between MWCNT bundles and the matrix. The procedure described herein can be used to combine unique properties of transition metal compounds able to coordinate to pyridyl groups, with the film-forming ability of P4VP and conductivity provided by MWCNT.

Potential and performance of a polydopamine-coated multiwalled carbon nanotube/polysulfone nanocomposite membrane for ultrafiltration application

The addition of multiwalled carbon nanotubes (MWNTs) as inorganic fillers is well known to improve membrane performance for water desalination. Most MWNTs are treated by acid treatment to enhance their hydrophilicity before their applications in membranes. However, acid treatment leads to structural damages of the MWNT wall. An alternative way of improving the hydrophilicity of MWNTs is through coating of polydopamine (Pdop), where MWNT wall damage is avoided. In the present study, polydopamine-coating on MWNT is carried out at pH 8.5 and at room temperature (23–25°C). Different concentrations (0.1–0.5wt%) of Pdop-MWNTs were incorporated into polysulfone (Psf) membranes fabricated by phase inversion. The results showed that the incorporation of Pdop-coated MWNTs has increased the membrane permeability using BSA solution (1000ppm) by 19–50% depending on the amount of Pdop-MWNTs in the membrane, and has maintained good rejection performances (99.88%). Moreover, the antifouling properties of the nanocomposite membranes were also improved. Here, the optimum dose was determined to be 0.1wt% of Pdop-MWNTs. Furthermore, even though the Pdop-MWNT/Psf membranes showed lower permeability than acid-MWNT/Psf membrane, the Pdop-MWNT/Psf membrane obtained higher mechanical strength and would be potentially sustainable for a long term ultrafiltration operation.

Synthesis of TiO2 Nanoparticles and Decorated Multiwalled Carbon Nanotubes With Various Content of Rutile Titania

Synthesis of different phases of titania nanoparticles (TiO2) and decorated multiwalled carbon nanotubes (MWCNTs) with various content of rutile titania have been performed. The samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). The XRD results showed that the amount of precursor strongly influenced by phase transition of TiO2 nanoparticles. TEM images showed that the outer surface of MWCNTs modified with TiO2 nanoparticles. The selected-area electron diffraction (SAED) of TiO2 nanoparticles and MWCNTs-TiO2 revealed the polycrystalline structure of the samples. FTIR analysis confirmed the presence of oxygen containing groups on the surface of oxidized MWCNTs and TiO2 on the surface of decorated MWCNTs. Optical properties of samples measured using UV-Vis spectrophotometer and the achieved results demonstrated that dispersibility of oxidized and decorated MWCNTs is higher than that of pristine MWCNTs. The XPS results showed that TiO2 nanoparticles were covalently attached on the side walls of acid-treated MWCNTs.

Load transfer strengthening in carbon nanotubes reinforced metal matrix composites via in-situ tensile tests

Abstract In-situ observation of tensile tests were performed to investigate the strengthening mechanisms of multi-walled carbon nanotube (MWCNT) reinforced Al matrix composites (AMCs). Carbon nanotubes (CNTs) were effectively incorporated and aligned in AMCs through a conventional powder metallurgy route. During tensile failure, the fracture process of CNTs in fabricated AMCs was clearly observed, suggesting the effective load transfer between the matrix and CNTs, and between inner walls of MWCNTs. Due to the small reinforcing effect of other factors, load transfer strengthening dominantly contributed to the observed high strengthening efficiency in CNT/Al composite, agreeing with the predicted results of the shear-lag model. This study provided evidence supporting the theory behind load transfer strengthening mechanisms of CNTs in metal matrix composites.

Controlling the number of walls in multi walled carbon nanotubes/alumina hybrid compound via ball milling of precipitate catalyst

This paper reports the influence of milling time on the structure and properties of the precipitate catalyst of multi walled carbon nanotubes (MWCNT)/alumina hybrid compound, produced through the chemical vapour deposition (CVD) process. For this purpose, light green precipitate consisted of aluminium, nickel(II) nitrate hexahydrate and sodium hydroxide mixture was placed in a planetary mill equipped with alumina vials using alumina balls at 300rpm rotation speed for various milling time (5–15h) prior to calcinations and CVD process. The compound was characterized using various techniques. Based on high-resolution transmission electron microscopy analysis, increasing the milling time up to 15h decreased the diameter of MWCNT from 32.3 to 13.1nm. It was noticed that the milling time had a significant effect on MWCNT wall thickness, whereby increasing the milling time from 0 to 15h reduced the number of walls from 29 to 12. It was also interesting to note that the carbon content increased from 23.29wt.% to 36.37wt.% with increasing milling time.

Electrocatalytic oxygen evolution at surface-oxidized multiwall carbon nanotubes.

Large-scale storage of renewable energy in the form of hydrogen (H2) fuel via electrolytic water splitting requires the development of water oxidation catalysts that are efficient and abundant. Carbon-based nanomaterials such as carbon nanotubes have attracted significant applications for use as substrates for anchoring metal-based nanoparticles. We show that, upon mild surface oxidation, hydrothermal annealing and electrochemical activation, multiwall carbon nanotubes (MWCNTs) themselves are effective water oxidation catalysts, which can initiate the oxygen evolution reaction (OER) at overpotentials of 0.3 V in alkaline media. Oxygen-containing functional groups such as ketonic C═O generated on the outer wall of MWCNTs are found to play crucial roles in catalyzing OER by altering the electronic structures of the adjacent carbon atoms and facilitates the adsorption of OER intermediates. The well-preserved microscopic structures and highly conductive inner walls of MWCNTs enable efficient transport of the electrons generated during OER.

104 カーポンナノチューブ分散強化アルミニウム複合材料の破壊機構

In-situ observation and evaluation on the fracturing behavior of multi-walled carbon nanotubes (MWCNTs) reinforced powder metallurgy (PM) Al matrix composite materials was carried out by using tensile test equipment installed in scanning electron microscopy (SEM). Peeling and fracturing phenomena of MWCNT embedded hi Al matrix were obviously and directly observed hi this study. The peeling formation and resultant effect on tensile strength of the composites were examined. Through transition electron microscopy (TEM) characterizations, it was clarified that defective structures like inter-wall bridges cross-linked adjacent walls of MWCNTs. This structure was helpful to improve the inter-wall bonding conditions, and resulted in the effective load transfer between the walls and resultant peeling behaviors of MWCNTs. CNT/Al composites indicated a large improvement of strength compared to the monolithic pure Al material.