Preparation Of Multi-walled Carbon Nanotubes Research Articles

Study on the Influences of Ultrasonic Conditions on the Dispersion of Multi-Walled Carbon Nanotubes in Reinforced Epoxy

Absrtract. In this paper, the method of ultrasonic vibration in preparation of multi-walled carbon nanotubes(MWCNTs)/epoxy resin composites was studied. Suspension specimens of MWCNTs/epoxy resin solution prepared by different ultrasonic conditions were compared to find out the influences of operating conditions on dispersion properties. In this study, transmission electron microscopes(TEM) were used to characterize the morphology of the blends and suspension stability was used to evaluate the stability of blends. The results showed that ultrasonic power, ultrasonic time and material quantity have great effect on the dispersion of MWCNTs in epoxy resin solution. Increasing ultrasonic power and time can improve dispersion of MWCNTs, and decreasing material quantity within an appropriate range was helpful to disperse MWCNTs into epoxy resin solution. The results of suspension stability were very similar with TEM results, which demonstrate that suspension stability of MWCNTs/epoxy resin blending could be used as an assistant method to characterize the dispersion of MWCNTs in epoxy resin.

Electrical properties of MWCNT-composite (Se80Te20)100−xAgx (0 ≤ x ≤ 4) chalcogenide glasses

This article describes the preparation of multi-walled carbon nanotube (MWCNT) chalcogenide glass composite by the melt-quenching technique. MWCNT composite (Se80Te20)100−xAgx (0 ≤ x ≤ 4) bulk samples are characterized by the XRD, SEM and EDX. The electrical measurements were carried out in the temperature range of the 308-388 K. Cole–Cole plot has been used to determine the electrical conductivity at room temperature. It has been observed that MWCNT chalcogenide composite have higher value of electrical conductivity than pure glass. The results have been discussed on the basis of increased ionic conductivity (Ag+ ions) in MWCNT doped (Se80Te20)100−xAgx (0 ≤ x ≤ 4) bulk samples.

In-situ preparation of multi-walled carbon nanotube (MWNT)/cellulose nanocomposites and their physical properties

The multi-walled carbon nanotube (MWNT)/cellulose nanocomposites were prepared by using monohydrated Nmethylmorpholine-N-oxide (NMMO) as a solvent for dispersing the acid-treated MWNTs (A-MWNTs) as well as for dissolving the cellulose. The A-MWNTs were well dispersed in both monohydrated NMMO and the nanocomposite films. The nanocomposite films were prepared by a film-casting method onto a glass plate. The tensile strain at break, Young’s modulus, and toughness of nanocomposite films increased by ∼5, ∼2 and ∼12 times, respectively at ϕ (A-MWNT content in the nanocomposite)=0.8 wt%, as compared to those of the pure cellulose film. The thermal degradation temperature of the nanocomposite films also increased from 329 to 339 oC by incorporation of 1 wt% A-MENTs. The electric conductivities of the A-MWNT/cellulose nanocomposites at ϕ =1 and 10 wt% were 2.09×10−5 and 3.68×10−3 S/cm, respectively. The transmittances were 86, 69 and 55 % at 550 nm for 0.4, 0.8 and 1 wt% nanocomposite films, respectively. Thus, these nanocomposites are promising materials in terms of all the properties studied in this paper and can be used for many applications, such as toughened cellulose fibers, transparent electrodes, etc.

Photoluminescent properties of new quantum dot nanoparticles/carbon nanotubes hybrid structures

The preparation of multi-wall carbon nanotubes (CNTs) and sulfide core–shell CdSe@ZnS quantum dot nanoparticles based hybrid materials is reported here. Photoluminescent measurements were carried out on two kinds of QD-CNT heterostructures. Indeed, strong oxidation of CNTs led to shorter nanotubes opened at their ends, allowing the grafting of mercaptotriethoxysilane whereas the generation of diazonium salts in presence of pristine nanotubes led to the functionalization of the whole lateral surface of the nanotubes and was achieved for the first time to anchor sulfide QD nanoparticles to thiol groups borne by carbon nanotubes. In both cases, we observed an important decrease in the photoluminescence peak, highlighting strong interactions between QDs and CNTs even when QDs were anchored to CNTs through a covalent link. Finally, we demonstrated that the morphology of the nanohybrids is governed by the surface chemistry of CNTs, leading to interesting hybrid precursors for photovoltaic applications.

Preparation of multi-walled carbon nanotube incorporated MIL-53-Cu composite metal–organic framework with enhanced methane sorption

Multi-walled carbon nanotubes (MWCNTs) incorporated MIL-53-Cu composite MOF material (MWCNT@MIL-53-Cu) has been synthesized by adding purified multi-walled carbon nanotube (MWCNT) in situ during the synthesis of MIL-53-Cu. Resulting sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmet–Teller (BET), and FT-IR analysis. Methane sorption capacities of MIL-53-Cu were observed to increase from 8.52 to 13.72mmolg−1 at 298K and 35bar. The increment in the methane uptake capacities of composite MOF materials was attributed to the decrease in the pore size and enhancement of micropore volume of MIL-53-Cu by multi-walled carbon nanotube incorporation.

The influence of reagent stoichiometry on the yield and aspect ratio of acid-oxidised injection CVD-grown multi-walled carbon nanotubes

Injection chemical vapour deposition (ICVD) was used for the preparation of multi-walled carbon nanotubes (MWCNTs) with varying lengths and diameters. The concentration of iron injected with the feedstock is related to the resulting average MWCNT dimensions, mass yield, packing density, crystallinity, and iron content. An optimum set of conditions is identified that maintains a constant diameter during growth; higher iron injection concentrations lead to an increasing MWCNT diameter as growth proceeds. Carbon nanotubes are frequently oxidised in mixtures of concentrated nitric and sulphuric acids in order to purify, functionalise, and shorten as-synthesised materials. Here, the carbon:acid stoichiometry is systematically varied, and shown to control the yield and dimensions of the resulting oxidised MWCNTs in a predictable manner, for the various ICVD starting materials. With increasing acid content, the yield of nanotubes decreases, the fraction of oxidised debris increases, and the initial, defect-driven, cutting reaction saturates, whilst thinning reactions continue. The results provide insight into both ICVD synthesis and acid oxidation of MWCNTs, as well as a means to prepare well-dispersed samples with controlled dimensions.

A novel screen-printed electrode array for rapid high-throughput detection

A novel multi-channel electrode array sensing device was fabricated by screen-printing techniques using 96-well plate as the template. To confirm its practical value, we developed a one-step preparation of multi-walled carbon nanotubes (MWCNTs) doped electrode array by an ink containing MWCNTs, which was applied to the simultaneous detection of a variety of biological samples and environmental pollutants. Results demonstrated that the designed sensing device could carry out the multiple measurements of different analytes at the same time, while MWCNTs enhanced the electrocatalytic activity of electrodes toward electroactive molecules. The required amount of each sample was only ∼200 μL. Moreover, the excellent differential pulse voltammetric (DPV) response toward dopamine, hydroquinone and catechol was obtained and the detection limits was determined to be 0.337, 0.289 and 0.369 μM, respectively. Comparing it with the traditional screen-printed electrode (SPE), this sensing device possesses the advantages of high-throughput, fast electron transfer rate for electrodes, short-time analysis and low sample consumption.

Enhanced encapsulation of metoprolol tartrate with carbon nanotubes as adsorbent

A highly water-soluble antihypertensive drug, metoprolol tartrate (MT), was selected as a model drug for preparation of multi-walled carbon nanotubes (MWCNTs)-impregnated ethyl cellulose (EC) microspheres. The present investigation was aimed to increase encapsulation efficiency of MT with excellent adsorbent properties of MWCNTs. The unique surface area, stiffness, strength and resilience of MWCNTs have drawn much anticipation as carrier for highly water-soluble drugs. Carbon nanotubes drug adsorbate (MWCNTs:MT)-loaded EC microspheres were further optimized by the central composite design of the experiment. The effects of independent variables (MWCNTs:MT and EC:adsorbate) were evaluated on responses like entrapment efficiency (EE) and t50 (time required for 50% drug release). The optimized batch was compared with drug alone EC microspheres. The results revealed high degree of improvement in encapsulation efficiency for MWCNTs:MT-loaded EC microspheres. In vitro drug release study exhibited complete release form drug alone microspheres within 15 h, while by the same time only 50–60% drug was released for MWCNTs-impregnated EC microspheres. The optimized batch was further characterized by various instrumental analyses such as scanning electron microscopy, powder X-ray diffraction and differential scanning calorimetry. The results endorse encapsulation of MWCNTs:MT adsorbate inside the matrix of EC microspheres, which might have resulted in enhanced encapsulation and sustained effect of MT. Hence, MWCNTs can be utilized as novel carriers for extended drug release and enhanced encapsulation of highly water-soluble drug, MT.

Fabrication of MWCNT-Reinforced Copper Composite and Thermal Expansion Behavor

A unique method for preparation of multi-walled carbon nanotube (MWCNT)- reinforced copper composite is reported. It involves solution phase systhesis MWCNT-implanted cuprous oxide composite spheres, formation of MWCNT/ copper composite spheres after reduction in H2 atmosphere and preparation of the MWCNT/copper bulk with vacuum hot pressing. Scanning Eelectron Microscope image (SEM) of the fracture surfaces indicate MWCNTs are homogeneously dispersed in the composite and bonded to the matrix. In addition, the thermal expansion of the composites at various MWCNTs (0wt%, 1wt%, 5wt%) were investigated. The coefficient of the thermal expansion (CTE) was decreased with increase of the MWCNT content, which are all much lower than that of pure copper.

Temperature Effects on the Preparation of Multi-Walled Carbon Nanotubes by Floating Catalytic Chemical Vapor Deposition

In this study, we report the synthesis of carbon nanotubes by floating catalytic chemical vapor deposition, which employs ferrocene as the catalyst precursors and ethanol as carbon source. We obtained massive deposits. The deposits were characterized by scanning electron microscopy, transmission electron microscopy, and visual laser Raman spectroscopy. We discussed the effects of synthesis temperature on the synthesis of carbon nanotubes by floating catalytic chemical vapor deposition. Our results indicated that the synthesis temperature could affect not only on the graphitization degree, but also on the aligned growth of carbon nanotubes and the diameter of carbon nanotubes.

A facile preparation of multiwalled carbon nanotubes modified with hydroxyl groups and their high dispersibility in ethanol

The multiwalled carbon nanotubes modified with hydroxyl groups were prepared in deoxygenated tetrahydrofuran using sodium zincate as an electrophilic reagent. NaOH solution and Zn powder were mixed to synthesize sodium zincate. The multiwalled carbon nanotubes were covalently modified with hydroxyl groups by the reaction between sodium zincate and multiwalled carbon nanotubes under sonication at room temperature. The product was characterized with FT-IR spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscope. The results indicate that the multiwalled carbon nanotubes are readily modified with hydroxyl groups, and their diameter and morphology are well retained. Moreover, the multiwalled carbon nanotubes modified with hydroxyl groups can be highly dispersed in ethanol to form a uniform and stable solution.

Structure and Properties of Multiwall Carbon Nanotubes/Polystyrene Composites Prepared via Coagulation Precipitation Technique

Coagulation technique was applied for preparation of multiwall carbon nanotube- (MWNT-)containing polystyrene (PSt) composite materials with different MWNT loading (0.5–10 wt.%). Scanning and transmission electron microscopies were used for investigation of the morphology and structure of produced composites. It was shown that synthesis of MWNT/PSt composites using coagulation technique allows one to obtain high dispersion degree of MWNT in the polymer matrix. According to microscopy data, composite powder consists of the polystyrene matrix forming spherical particles with diameter ca. 100–200 nm, and the surface of MWNT is strongly wetted by the polymer forming thin layer with 5–10 nm thickness. Electrical conductivity of MWNT/PSt composites was investigated using a four-probe technique. Observed electrical percolation threshold of composite materials is near to 10 wt.%, mainly due to the insulating polymer layer deposited on the surface of nanotubes. Electromagnetic response of prepared materials was investigated in broadband region (0.01–4 and 26–36 GHz). It was found that MWNT/PSt composites are almost radiotransparent for low frequency region and possess high absorbance of EM radiation at higher frequencies.

Preparation of multi-walled carbon nanotubes functionalized magnetic particles by sol–gel technology and its application in extraction of estrogens

Magnetic silica particles coated with hydroxy-terminated multi-walled carbon nanotubes (MWCNTs–OH) were prepared by sol–gel technology, characterized and used for the convenient, rapid and efficient extraction of several estrogens (including diethylstilbestrol, estrone and estriol) in water followed by sweeping micellar electrokinetic chromatography analysis with UV detection. The results demonstrated that sol–gel technology was a feasible, simple and effective technique for the preparation of MWCNTs–OH functionalized magnetic silica particles. The factors affecting the extraction efficiency of estrogens (the pre-activation of magnetic particles, adsorption time, desorption time and the amount of elution solvent) were carefully investigated. The extraction efficiencies for diethylstilbestrol, estrone and estriol were 95.9%, 93.9%, and 52.4%, respectively, under the optimum conditions. The method detection limits for the three estrogens were less than 0.2 ng mL −1. The developed method was applied for the analysis of tap water, mineral water, Pearl River water and honey.

Facile One-Pot Preparation of a New Palladium-Supported Nanocatalyst for the Electrochemical Reduction of Oxygen

We report here a simple one-pot method for the preparation of multiwalled carbon nanotube@ silica-supported Pd catalyst. The one-step involves the in-situ surface modification of MWNT with silica (MWNT@silica) and simultaneous loading of Pd NPs using γ-irradiation. FESEM and HRTEM images revealed that silica is present as a layer (thickness in the range of 15―25 nm) on the surface of MWNT. Pd nanoparticles of sizes in the range of 5 to 10 nm were distributed onto MWNT@silica. The electronic properties and the structural aspects of MWNT@silica/Pd were ascertained using UV-visible and FTIR spectroscopy. The electrocatalytic performance of the MWNT@silica/Pd catalyst on oxygen reduction reaction was investigated using cyclic voltammetry. At the MWNT@silica/Pd catalyst electrode, oxygen reduction occurred at a more positive potential (∼0.45 V) which indicated excellent electrocatalytic behavior for the new nanocatalyst.

Metal-free preparation of multi-walled carbon nanotubes based on new-diamond-induced growth mechanism

Multi-walled carbon nanotubes (MWCNTs) were synthesized on uniform new-diamond film by decomposing methane at 900 °C with chemical vapor deposition technique. Based on various spectroscopic characterizations, such as scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, a reasonable growth mechanism of MWCNTs was proposed. The metal-free prepared MWCNTs are easy to be purified and will have broad applications in material sciences.

Preparation of Multiwalled Carbon Nanotube-Supported Nickel Catalysts Using Incipient Wetness Method

In this paper, a systematic study on preparation of multiwalled carbon nanotube (MWCNT)-supported nickel catalyst is pursued. Functional groups are introduced on the surface of MWCNTs using nitric acid, sulfuric acid, and partial oxidation in air. Nickel oxide nanoparticles are formed on the surface of functionalized multiwalled carbon nanotubes by incipient wetness impregnation of nickel nitrate, followed by calcination in air. The effects of acid type and concentration, acid treatment time, partial oxidation, nickel loading, precursor solvent, and calcination temperature on the size of the nickel nanoparticles and homogeneity of the composite material are evaluated. Characteristics of the Ni/MWCNT catalysts were examined using BET, scanning transmission electron microscopy, X-ray diffraction, thermogravimetric analysis in air and nitrogen, temperature-programmed reduction, X-ray photoelectron spectroscopy, acid-base titration, and zeta-potential analyzer. Results of this work are useful for formulating CNT-supported nickel catalysts for a wide range of different applications, such as reforming of hydrocarbons, catalytic hydrothermal gasification of biomass, and energy storage.

Large‐compound vesicle‐encapsulated multiwalled carbon nanotubes: A unique route to nanotube composites

AbstractA simple and unique strategy for preparation of large‐compound vesicle (LCV)‐encapsulated multiwalled carbon nanotubes (MWCNTs) has been developed, and this involves dispersion of MWCNTs in H‐shaped copolymers solution in DMF and encapsulation of MWCNTs with LCVs formed from hydrolysis and polycondensation of Si(OCH3)3 groups in the amphiphilic H‐shaped copolymers, (PTMSPMA)2PEG(PTMSPMA)2. This unique noncovalent approach is nondestructive, and the original structure of MWCNTs remains in the resultant MWCNTs/LCVs nanocomposites. The morphologies of nanocomposites LCVs/MWCNTs are controlled by the chain length ratio (NPTMSPMA/NPEG) of PTMSPMA to PEG. For the H‐shaped copolymers with NPMSPMA/NPEG ≤ 1.7, they self‐assembled to form LCVs with dense cavities in the presence of MWCNTs in a mixture of DMF/H2O. When this ratio was more than 2.0, the large‐compound micelle‐wrapped MWCNTs were produced. This approach is potentially useful for preparation of MWCNTs encapsulated with various morphologies of polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3669–3679, 2009

Preparation of multiwalled carbon nanotubes incorporated silk fibroin nanofibers by electrospinning

Abstract Nanocomposite fibers, including silk fibroin ( Bombyx mori ) and multiwalled carbon nanotube (MWCNT), were successfully prepared using electrospinning. Regenerated silk fibroins and MWCNTs were dissolved in formic acid, with the solution then electrospun into nanofibers. The morphology and microstructure of the electrospun nanofibers were characterized using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The FESEM and TEM images showed the MWCNTs to be well incorporated along the nanofibers. The tensile properties of the nanofibers were also enhanced by the incorporation of a small amount of MWCNTs. The electrospinning of silk/MWCNT composites could potentially supply useful options for the fabrication of biomaterial scaffolds, such as wound dressings.

The preparation of multi-walled carbon nanotubes encapsulated by poly(3-acrylaminopropylsiloxane) with silica nanospheres on the polymer surface

A silica–polymer–carbon nanotube hybrid was prepared in which the nanotubes were encapsulated by poly(3-acrylaminopropylsiloxane) with silica nanospheres on the polymer surface. First, highly reactive poly(acryloyl chloride) (PAC) was grafted onto the nanotubes through the reaction of side acyl chloride groups with hydroxyl groups present on the surface of acid–oxidized nanotubes. Second, reacting 3-aminopropyltriethoxysilane with the grafted PAC through the reaction between amino and acyl chloride groups, siloxane-containing sub-grafts were introduced onto the primary PAC grafts. Third, silica nanospheres were covalently linked to the sub-grafts by condensation to form a nanotube–polymer–silica hybrid. Each intermediate structure was confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy (TEM). TEM observation revealed a nanostructure in which the nanotube was encapsulated with a polymer layer bearing silica nanospheres on its surface.

Structural Defects Play a Major Role in the Acute Lung Toxicity of Multiwall Carbon Nanotubes: Physicochemical Aspects

Carbon nanotubes (CNT) have been reported to elicit toxic responses in vitro and in vivo, ascribed so far to metal contamination, CNT length, degree of oxidation, or extent of hydrophilicity. To examine how structural properties may modulate the toxicity of CNT, one preparation of multiwall CNT has been modified (i) by grinding (introducing structural defects) and subsequently heating either in a vacuum at 600 degrees C (causing reduction of oxygenated carbon functionalities and reduction of metallic oxides) or in an inert atmosphere at 2400 degrees C (causing elimination of metals and annealing of defects) and (ii) by heating at 2400 degrees C in an inert atmosphere and subsequently grinding the thermally treated CNT (introducing defects in a metal-deprived carbon framework). The presence of framework and surface defects, metals, and oxygenated functionalities was monitored by means of a set of techniques, including micro-Raman spectroscopy, adsorption calorimetry, X-ray photoelectron spectroscopy, inductively coupled plasma mass spectrometry, and atomic emission spectroscopy. Contrary to traditional toxicants, such as asbestos, CNT may quench rather than generate oxygenated free radicals. The potential of the modified CNT to scavenge hydroxyl radicals was thus evaluated by means of electron spin resonance spectroscopy (spin trapping). The original ground material exhibited a scavenging activity toward hydroxyl radicals, which was eliminated by heating at 2400 degrees C but restored upon grinding. This scavenging activity, related to the presence of defects, appears to go paired with the genotoxic and inflammatory potential of CNT reported in the companion paper. Thus, defects may be one of the major factors governing the toxic potential of CNT.