Pure Multi-walled Carbon Nanotubes Research Articles

A study of the electromagnetic properties of Cobalt-multiwalled carbon nanotubes (Co-MWCNTs) composites

Abstract Electroless plating was utilized to deposit Cobalt (Co) on the surface of multi-walled carbon nanotubes (MWCNTs), and the technological parameters of electroless plating were optimized. To obtain optimized processing parameters, field-emission scanning electron microscope (FESEM) as well as energy dispersive spectroscopy (EDS) results were presented to show the morphology, components of as-prepared Co-MWCNTs. Based on the optimized processing parameters, Co-MWCNTs were prepared and filled into the epoxy resin to fabricate Co-MWCNTs composites. The electromagnetic properties of pure MWCNTs composites and Co-MWCNTs composites were studied. To sum up, the pure MWCNTs composites with a filler concentration of 2 wt% had an intense absorbing peak at 15.20 GHz, where the highest reflection loss ( R ) reached −21.41 dB. Compared to the pure MWCNTs composite at the same concentration, the Co-MWCNTs composites showed a higher impedance which implies a better potential absorbing property and makes Co-MWCNTs probable to be utilized in electromagnetic absorbing field.

Electromagnetic wave absorbing properties of carbon nanotubes doped rare metal/pure carbon nanotubes double-layer polymer composites

The design of double-layer structure could improve the absorbing properties of electromagnetic (EM) wave absorbing composites. Doping of rare metal (RM) could enhance the EM wave absorbing capability of the multi-walled carbon nanotubes (MWCNTs). In this paper, the polymer matrix composites with the different RM-doped MWCNTs and the pure MWCNTs as the absorber in the first and second layer respectively was fabricated (4 mm in thickness). The EM wave absorbing properties of these composites were studied. The results show all reflection loss curves of these composites have two absorption peaks in the frequency range of 2–18 GHz, and the reflection loss (<−10 dB) of the MWCNTs doped Ni is the widest from the absorption bandwidth (maximum is 5.28 GHz), relatively.

Effects of different carbon precursors on synthesis of multiwall carbon nanotubes: Purification and Functionalization

Cyclohexanol and xylene were used as carbon precursors, for synthesis of multiwall carbon nanotubes (MWCNTs) arrays in a CVD system at temperature of 750 °C, using nitrogen as carrier gas and ferrocene as catalyst. Different characterization methods were employed to compare the MWCNTs structure synthesized by these two precursors. All scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA) and Raman spectroscopy results illustrated that using cyclohexanol could significantly reduce formation of amorphous carbon and catalyst particles in the as-grown CNTs. The less amorphous carbon can be attributed to in situ oxidation in presence of oxygen atom of cyclohexanol. Characterizations showed that MWCNTs with high purity could be obtained using cyclohexanol as carbon precursor. The as-grown MWCNTs were purified by oxidation and acid treatment. Characterization of the purified MWCNTs using HNO 3/H 2SO 4 (1/3 or 1/1), 8 M HCl or 8 M HNO 3 was carried out. The results showed that 8 M HNO 3 could be considered as the best chemical to obtain more pure MWCNTs, less amorphous and metal particles and less damaged MWCNTs. The Raman spectroscopy results demonstrated that HNO 3/H 2SO 4 (1/3) treatment could more disorder the MWCNTs structure and this was attributed to the bigger destroying effect of this acid treatment. Furthermore, the TEM analysis of MWCNTs before and after acid treatment revealed that acid treatment could remove encapsulated catalyst particles. The FTIR analysis illustrated that purification of the MWCNTs with nitric acid could connect the functional groups onto the outer surface of MWCNTs and this resulted in more dispersion of the MWCNTs in water.

Synergetic effect of Co and carbon nanotubes on MgH 2 sorption properties

This paper analyses the synergetic effect of the coupled addition of Co particles (Co, 5 wt%) and pure multi-walled carbon nanotubes (MWCNTs, 5 wt%) on hydrogen sorption kinetics of MgH 2 (M). Experimental results show that MCo co-milled 50 h plus admixed MWCNTs for 5 h exhibits enhanced absorption/desorption performance, which remains stable after 15 hydrogen sorption cycles. About 6.5 wt% of hydrogen was absorbed after 100 s and desorbed in 85 min at 250 °C, being one of the best conditions reported for Mg-based composites. Furthermore, desorption temperature after cycling was reduced by 55 °C due to the introduction of Co, and 136 °C by the combined Co and MWCNT addition as compared to free MgH 2. Activation energy analysis demonstrates that although the MWCNT addition has a slight influence on the energy barrier, the Co particles show a good catalytic effect. Moreover, the coupled effect of Co and MWCNTs reduces the activation energy and it is maintained after cycling. As a consequence of cycling, some nanograins of MgH 2 appear covered with a thin external layer of amorphous carbon while some part of the MWCNTs remains intact in the material. An interpretation of the kinetics effect of Co particles and MWCNT coupled addition is proposed.

Synthesis and Electromagnetic Wave Absorption Properties of Multi-Walled Carbon Nanotubes Decorated by BaTiO3 Nanoparticles

A hybrid composite material, consisting of BaTiO3 and multi-walled carbon nanotubes, was synthesized by an efficient solvent-thermal route. Transmission electron microscopy images clearly indicate that the surfaces of the multi-walled carbon nanotubes were uniformly decorated by well-crystallized BaTiO3 particles, with diameters of 15-30 nm. Electromagnetic wave absorption properties analysis, determined by the electromagnetic parameters measured by a vector network analyzer, shows that the reflection loss in the BaTiO3/multi-walled carbon nanotube composite was higher than that occurring in pure multi-walled carbon nanotubes or BaTiO3 and that was resulted from a better matched characteristic impedance and an enhanced complex permeability in the high frequency, which was improved by the decrease of eddy currents owing to the finite increase in resistivity. The maximum reflection loss of -37.5 dB in the BaTiO3/multi-walled carbon nanotube composite was obtained at a frequency of 10.4 GHz and the absorption range under -10 dB was from 9.6-13.1 GHz range as the absorber thickness was 2 mm.

Preparation of a MWCNT/ZnO nanocomposite and its photocatalytic activity for theremoval of cyanide from water using a laser

Nano-zinc oxide (n-ZnO) was loaded onto multi-walled carbon nanotubes (MWCNTs) via ahydrothermal process. Here pure n-ZnO used for loading was synthesized by thepulsed-laser ablation technique while MWCNTs were used as received. The synthesizedMWCNT/ZnO nanocomposites were characterized using x-ray diffraction, field emissionscanning electron microscopy, high resolution transmission electron microscopy and Fouriertransform infrared spectrometry. A model has been proposed for the structuralnature of the alignment of ZnO on the surface of MWCNTs. The photocatalyticactivity in the removal of highly toxic substances like cyanide (CN) was carried outin a special reactor using pulsed 355 nm UV generated by the third harmonicof an Nd:YAG laser. In order to understand the cyanide removal process, thestudy was carried out at different laser irradiation times, incident laser energies,pH of the solution and dosage of the MWCNT/ZnO nanocomposite. The studydemonstrated that the CN removal process by MWCNT/ZnO composite has higherphotocatalytic activity than pure n-ZnO and MWCNTs alone. The mechanism for thedegradation using MWCNT/ZnO has been schematically explained. It was noticed thatthe oxidation process activity is affected by the pH of the solution, and after20 min of UV laser irradiation, approximately 90% of CN had been degraded.

Effect of modified MWCNT on the properties of PPO/LCP blend

In this work we have coated multiwalled carbon nanotubes (MWCNTs) with SiC by solgel process and these modified MWCNTs are dispersed in PPO/LCP blend. The dispersion of these modified MWCNTs are analyzed by FESEM and found to be improved compared to pure MWCNTs. Thermal and mechanical properties of the modified MWCNTs added nanocomposites are higher than that of the pure MWCNTs added nanocomposites. PPO/LCP forms an incompatible blend while addition of unmodified and modified MWCNTs improves the compatibility between the blend partners.

Techno-economics of carbon nanotubes produced by open air arc discharge method

This paper describes a simplified arc discharge method for synthesis of multi-walled carbon nanotubes (MWNTs). In this method, a continuous and mass production of carbon nanotubes (CNTs) can be achieved with high purity and considerable yield. There is no need for costly setup of the synthesis of MWNTs and the multistep purification, which is needed to obtain high pure MWNTs. The morphology and structure of the CNTs produced were characterized by Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X ray diffraction, Raman spectroscopy and Thermo gravimetric analysis (TGA). The cost analysis for the synthesis of MWNTs through this simplified method was done and compared with the existing commercial methods for CNT production. The production cost of the CNTs synthesized by this simplified method is $3/gm. On comparison, it is considered to be one of the most cost effective and commercially viable production methods for MWNTs. Keywords: Multi-walled Carbon nanotubes, X-ray diffraction, Scanning electron microscope, Transmission electron microscopy, Raman spectroscopy

Roles of nanosized Fe 3O 4 on supercapacitive properties of carbon nanotubes

We synthesized Fe 3O 4 nanoparticle-dispersed multiwalled carbon nanotubes (MWNTs) to evaluate their potential applicability to supercapacitor electrodes. Nanosized Fe 3O 4 was deposited by chemical coprecipitation of Fe 2+ and Fe 3+ in the presence of MWNTs in alkaline solutions. Fe 3O 4 nanoparticles with an average particle size of 14 nm were prepared within several minutes. The structure and morphological characteristics of the Fe 3O 4/MWNT composites were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The electrochemical performance of a Fe 3O 4/MWNT composite electrode and a pure MWNT electrode was tested by cyclic voltammetry (CV) and galvanostatic charge–discharge in a sulfite electrolyte. The results showed that the Fe 3O 4/MWNT electrode had typical pseudo-capacitive behavior in a 1 M Na 2SO 3 solution and a significantly greater specific capacitance than that of the pure MWNT electrode. It could also retain 85.1% of its initial capacitance over 1000 cycles.

Effect of SiC coated MWCNTs on the thermal and mechanical properties of PEI/LCP blend

Multiwalled carbon nanotubes (MWCNTs) were modified by polycarbosilane derived β-SiC particle to improve its dispersion in the polymer matrix. Formation of β-SiC particle onto MWCNTs was conformed by XRD study. Polyetherimide (PEI)/liquid crystalline polymer (LCP) blends with unmodified and modified MWCNTs were prepared by melt blending and the dispersion of the nanofillers in the polymer blend was studied by high resolution transmission electron microscopy, which showed improved dispersion of modified MWCNTs compared to pure MWCNTs. Viscosity of ternary blend with modified MWCNTs was found to be lower than the ternary blend with pure MWCNTs. Incorporation of modified MWCNTs improved the fibrillation of LCP in ternary blend as compared to pure MWCNTs. Thermal analysis revealed the higher thermal stability of the modified MWCNTs added nanocomposites compared to unmodified MWCNTs. Mechanical properties of nanocomposites with SiC coated MWCNTs were found to be higher than that of pure MWCNTs added nanocomposites.

Efficient Vapor Sensors Using Foils of Dispersed Nitrogen-Doped and Pure Carbon Multiwalled Nanotubes

We fabricated vapor sensors using nitrogen-doped (CNx) and pure multi-walled carbon nanotubes (MWNTs), and compared their performance. The sensors were constructed by dispersing the nanotube materials in methanol so as to form millimeter-long foils (nanotube paper), consisting of compact arrays of crisscrossing nanotubes. The devices were characterized by electrical resistance measurements and SEM studies. For CNx-based sensors, we observed that low concentrations of vapors such an acetone, ethanol, and chloroform were efficiently detected within 0.1-0.3 seconds via a physisorption mechanism. This physisorption is explained in terms of a weak interaction of the vapor molecules with the pyridinic sites (N bonded to two carbon atoms) present in the doped tubes. We believe that the methanol used for preparing the foils has a strong effect in saturating substitutional N atoms (N atoms bonded to three carbon atoms) that are also located in the CNx tubes. However, when pure carbon MWNTs were tested as sensors, we witnessed chemisorption of these vapors. First-principles density functional calculations confirmed that the gaseous molecules are able to interact with N-doped carbon nanotubes, via a physisorption mechanism, in which pyridine sites play a crucial role.

Self-Assembly of Carbon Nanotubes via Ethanol Chemical Vapor Deposition for the Synthesis of Gas Chromatography Columns

The synthesis of the gas chromatography stationary phase by molecular self-assembly of carbon nanotubes (CNTs) via a novel ethanol chemical vapor deposition process is presented. A major advantage is that ethanol was found to be an excellent carbon source that generated highly pure multiwalled carbon nanotubes with very little nontubular carbon impurities. The nanotubes were not vertically aligned but lay flat out on the column surface in a randomly distributed configuration. The CNT phase was able to separate a wide range of organic compounds with diverse polarity and volatility, where the number of plates per meter ranged from 900 to 1280. It also showed classical chromatographic behavior and good precision.

Preparation and characterization of MnO2/MWCNTs-modified graphite electrode and its catalysis for oxygen reduction reaction (ORR)

Manganese dioxides were prepared onto multi-walled carbon nanotubes (MWCNTs) by cyclic voltammetry (CV). The obtained manganese oxide-MWCNTs (MnO2/MWCNTs) samples were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), fourier transform infrared spectrometry (FTIR) and thermogravimetry (TG), respectively. The MnO2/MWCNTs-modified graphite electrode was utilized in the electrochemical oxygen reduction reaction (ORR) and the enhanced oxygen reduction peak current strongly suggested that MnO2/MWCNTs has catalysis for ORR when compared to the pure MnO2 or MWCNTs. The catalysis mechanism of MnO2/MWCNTs for ORR was also-discussed.

Influence of purity and surface oxidation on cytotoxicity of multiwalled carbon nanotubes with human neuroblastoma cells

There are conflicting data concerning the safety and biocompatibility of carbon nanotubes (CNTs). In some reports CNTs have been used for gene delivery without significant toxicity, whereas in others various cytotoxic effects were observed, including induction of intracellular reactive oxygen species (ROS), DNA damage, and apoptosis. Although it is clear that CNT production methods, purity, and functionalization treatments impact on biocompatibility, most of the published reports lack detailed characterization of the CNT samples used. We investigated the effect of various physicochemical features of multiwalled carbon nanotubes (MWCNTs) on toxicity and biocompatibility with cultured human neuroblastoma cells by using MTT, WST-1, Hoechst, and oxidative stress assays. In vitro experiments confirm that after 3 days of incubation with three different types of CNTs dispersed in Pluronic F127 solution, 0.01% cell viability is not affected and apoptosis and ROS are not induced in the SH-SY5Y cells. With prolonged cultures and continued propagation in the presence of MWCNTs, the loss of cell viability was minimal for pure MWCNTs (99% purity), but cell proliferation decreased significantly for 97% purity MWCNTs and acid-treated MWCNTs (97% purity, surface oxidation 8%); no intracellular ROS were detected. When the concentration of CNTs increases, purity and surface oxidation seem to affect cell viability (ED 25 is 48, 34.4, and 18.4 μg/mL, respectively, for 99% purity MWCNTs, 97% purity MWCNTs, and acid-treated 97% purity MWCNTs. Our results indicate that concentrations of 5–10 μg/mL MWCNTs seem ideal for studies on the design and development of artificial MWCNT nanovectors for gene and drug therapy against cancer. From the Clinical Editor With prolonged cultures, loss of cell viability was minimal for preparations with 99% purity, but significant adverse effects were detected with 97% purity and with acid-treated preparations. A concentrations of 5–10 μg/mL of MWCNTs seems ideal for gene and drug therapy against cancer.

Effect of MWNTs and SiC-Coated MWNTs on Properties of PEEK/LCP Blend

Multiwall carbon nanotubes (MWNTs) were modified with polycarbosilane-derived silicon carbide (SiC) to improve its dispersion in the polymer matrix. PEEK/LCP/MWNTs nanocomposites were prepared by melt blending. TEM images show the improved dispersion of SiC-coated MWNTs against agglomerated structure of pure MWNTs in the blend. FESEM images shows better fibrillation of LCP in presence of SiC-coated MWNTs. TGA reveals that nanocomposites with SiC-coated MWNTs shows higher thermal stability than MWNTs filled blend system. Based on enhanced dispersion, storage modulus, tensile modulus and tensile strength were increased drastically with the incorporation of SiC-coated MWNTs. Glass transition temperature of the nanocomposites shows significant improvement with the incorporation of MWNTs.

Low temperature synthesis of multi-walled carbon nanotubes via a sonochemical/hydrothermal method

In this investigation, multi-walled carbon nanotubes (MWCNTs) have been prepared by a facile sonochemical/hydrothermal method. MWCNTs have been hydrothermally fabricated with using dichloromethane, cobalt chloride and metallic lithium as starting materials in 5 mol/lit NaOH aqueous solution. Ultrasonic pre-treatment of the solution mixture had an important step prior to the hydrothermal condition, which could generate a considerable amount of multi-walled carbon nanotubes for the subsequent hydrothermal growth. Finally, high pure MWCNTs with lengths of 2–5 μm and diameters of 60 ± 20 nm could be synthesized at as low temperature as 160 °C. As a matter of fact, the method of sonochemical/hydrothermal guarantees the production of multi-walled carbon nanotubes (MWCNTs) for different applications, especially reinforcement materials.

Low-temperature synthesis of Mn3O4 nanoparticles loaded on multi-walled carbon nanotubes and their application inelectrochemical capacitors

A low-temperature, efficient and one-step deposition method, in whichMn(CH3COO)2·4H2O serves as precursorand O2 as oxidant, wasemployed to deposit Mn3O4 nanoparticles on multi-walled carbon nanotubes (MWCNTs) in ethanol solution at 150 and200 °C. Theresulting Mn3O4/MWCNT composites were characterized by means of different techniques including x-ray diffraction, x-rayphotoelectron spectroscopy and transmission electron microscopy. It was indicated that theMn3O4 nanoparticles were attached uniformly on MWCNTs with sizes less than 10 nm, and the loading amountof Mn3O4 could be tuned by changing the initial weight ratio ofMn(CH3COO)2·4H2O/MWCNT. The electrochemicalbehavior of the Mn3O4/MWCNT composites was examined by cyclic voltammetry, and the resultindicated the specific capacitance of the composite electrode was330 F g−1, nearly 18 times higher than that of the pure MWCNT electrode. The good performance of theas-prepared composites as electrode material may be attributed to the synergistic effects of theMn3O4 nanoparticles and the MWCNTs.

Fabrication of porous carbon nanotube network

We used the spin-coating method combined with ultrasonic atomization as a continuous, one-step process to generate a two-dimensional honeycomb network that was constructed from pure multi-walled carbon nanotubes.

Macromol. Rapid Commun. 23/2007

Cover: The cover picture shows SEM pictures displaying the homogeneous wrapping of the outer surface of multi-walled carbon nanotubes (MWCNTs) with poly(N-vinylcarbazole)(PNVC-nanocomposite) in comparison with pure MWCNTs and PNVC extracted from the nanocomposite. This wrapping occurred during polymerization and precipitation from solution. Further details can be found in the article by A. Maity, S. S. Ray,* and S. K. Pillai on page 2224.

Multi-wall carbon nanotubes: Purification, morphology and field emission performance

Highly pure multi-wall carbon nanotubes (MWNTs) were successfully fabricated using an acidic purification process. Treatment with acids, concentrated sulfuric acid (H 2SO 4) and nitric acid (HNO 3) eliminated many of the metal catalysts and impurities from MWNTs. The concentration of H 2SO 4/HNO 3 solution and the purification time were optimized. Experimental data demonstrate that a 1:3 concentrated H 2SO 4:HNO 3 solution after 20 h yields highly pure MWNTs. MWNTs were closed tips that are opened after purification. The intensity ratio of the D band to the G band (ID/IG) is as low as 0.27. The field emission current density is as high as 170 μA/cm 2 at an electric field of 1.9 V/μm.