Properties Of Multi-walled Carbon Nanotubes Research Articles

Synthesis and Adsorption Properties of Multiwalled Carbon Nanotubes

Synthesis and Adsorption Properties of Multiwalled Carbon Nanotubes

Electrochemical Analysis of Architecturally Enhanced LiFe0.5Mn0.5PO4 Multiwalled Carbon Nanotube Composite

In this work, the effect of carbon on the electrochemical properties of multiwalled carbon nanotube (MWCNT) functionalized lithium iron manganese phosphate was studied. In an attempt to provide insight into the structural and electronic properties of optimized electrode materials, a systematic study based on a combination of structural and spectroscopic techniques was conducted. The phosphor-olivine LiFe0.5Mn0.5PO4 was synthesized via a simple microwave synthesis using LiFePO4 and LiMnPO4 as precursors. Cyclic voltammetry was used to evaluate the electrochemical parameters (electron transfer and ionic diffusivity) of the LiFe0.5Mn0.5PO4 redox couples. The redox potentials show two separate distinct redox peaks that correspond to Mn2+/Mn3+ (4.1 V vs Li/Li+) and Fe2+/Fe3+ (3.5 V vs Li/Li+) due to interaction arrangement of Fe-O-Mn in the olivine lattice. The electrochemical impedance spectroscopy (EIS) results showed LiFe0.5Mn0.5PO4-MWCNTs have high conductivity with reduced charge resistance. This result demonstrates that MWCNTs stimulate faster electron transfer and stability for the LiFe0.5Mn0.5PO4 framework, which demonstrates to be favorable as a host material for Li+ ions.

Effects of nano-SiO2 coated multi-walled carbon nanotubes on mechanical properties of cement-based composites

Interfacial microstructure and interactions largely affect the mechanical properties of multi-walled carbon nanotubes (MWCNTs) reinforced cement-based composites. To improve the interfacial adhesion of MWCNTs-cement composites, a simple and effective method for preparation of SiO2/MWCNTs nano-composites were put forward using polyvinyl pyrrolidone (PVP) as a surfactant without any oxidation treatment on MWCNTs. The morphology, microstructure and chemical composition of SiO2/MWCNTs nano-composites were characterized by electron microscopy, Fourier transform infrared spectroscopy (FTIR), Raman spectrum, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was found that amorphous nano-SiO2 uniformly and densely grown on the surface of MWCNTs, forming a rougher film. The chemical reactivity of the nano-SiO2 film was detected by immersion tests in Ca(OH)2 solution, where EDS and FTIR analysis confirmed the formation of hydrated calcium silicate gel (C-S-H). The effects of SiO2/MWCNTs on mechanical properties of cement mortars were investigated and compared with that of cement-based composites incorporating pristine MWCNTs. When 0.25 wt% and 0.50 wt% SiO2/MWCNTs were added, the flexural strengths of cement mortars were increased by 11.9% and 25.4%, respectively, which were more significant than the enhancement effects on compressive strengths (8.5% and 19.0%). The fracture surfaces of different samples were observed by SEM, and the Ca(OH)2 content was quantitatively determined by TG analysis, indicating that the chemical reaction of nano-SiO2 film with Ca(OH)2 generated from cement hydration process can effectively increase the C-S-H gel content at the interface between MWCNTs and cement matrix, which is the prime reason for the increase of mechanical properties.

Experimental and numerical investigation of T‐joints with multiwalled carbon nanotubes

AbstractCombined experimental and numerical methods were used to study the mechanical properties of multiwalled carbon nanotubes (MWCNTs) enhanced composite T‐joints in this article. Herein, an enhanced interface model was created based on the interface mechanical properties with MWCNTs obtained by a flatwise tension test and a single‐lap shear test. Then, the finite element model of composite T‐joints with MWCNTs was developed with a cohesive zone model to study the damage initiation, evolution, and final failure process of T‐joints. Meanwhile, a quasi‐static tensile test of the T‐joints was carried out to compare with the numerical analysis results. The study results showed that the out‐of‐plane tensile strength and the in‐plane shear strength of MWCNTs enhanced composite increased by up to 26.3%(@3 g/m2) and 23.4%(@2 g/m2), respectively. The properties of the filler, which was the weakest part of the T‐joints, can be enhanced by adding MWCNTs. The overall bearing capacity of the T‐joints was 18.8%(@2 g/m2 MWCNTs) increase under tensile loading. Predictions given by the FEM of composite T‐joints were in good agreement with the experimental results. This article provides a method for analyzing and predicting the complex composite structure enhanced with MWCNTs, which can be used for functional structure design.

Study on the mechanical and electrical properties of twisted CNT yarns fabricated from CNTs with various diameters

The mechanical and electrical properties of multiwalled carbon nanotube (MWCNT) yarns with a wide variety of MWCNT diameters were studied to understand the relationship between the microscopic structures of MWCNTs and the load/charge transport properties of macroscopic MWCNT assemblies. The MWCNT diameters were varied from 14.6 nm to 41.6 nm by varying the amount of catalyst loaded in the synthesis by the chloride-mediated chemical vapor deposition method. We found a drastic change in the tensile behavior of twisted yarns from nonlinear deformation to elastic manner associated with the increases in the tensile strength, Young’s modulus, and electrical conductivity of the twisted MWCNT yarns for smaller-diameter MWCNTs. These improvements are due to the increase in the surface area of MWCNTs in the yarn structure. We also carried out microscopic direct tensile tests on the MWCNTs in a scanning electron microscope to investigate the tensile properties of the individual MWCNTs. The in situ experiments revealed that the obtained high value of the Young’s modulus of the yarn originated from that of the individual MWCNTs.

Preparation and properties of multi-walled carbon nanotube reinforced alumina composites by sol- spray method

Preparation and properties of multi-walled carbon nanotube reinforced alumina composites by sol- spray method

Dielectric properties of MWCNT dispersed conducting polymer nanocomposites films of PVA-CMC-PPy

The structural, dielectric and electrical properties of multiwall carbon nanotube (MWCNT) dispersed polymer nanocomposite films (PPy) of Polyvinyl alcohol (PVA) blended with Sodium Carboxymethyl cellulose (CMC) and doped with Polypyrrole (PPy) is reported here. Free standing and flexible polymer nanocomposite films (PNC) were prepared by solution cast technique. The XRD study shows that amorphousness of the films increases with blending PPy in PVA-CMC matrix and also by increasing concentration of MWCNT nanopowder in PVA-CMC matrix. Molecular interaction between polymer–polymer and polymer- nanoparticle was studied using FTIR in attenuated total reflection (ATR) mode. Frequency dependent dielectric properties of these PNC films were studied in the frequency range of 100 Hz – 2 MHz. Flexible, biocompatible polymer nanocomposite films of PVA-CMC-PPy having MWCNT (5 wt)% showed appreciable rise in the values of dielectric constant and ac conductivity for measured frequency range.

Formation and electrochemical properties of multiwalled carbon nanotubes and polypyrrole composite with (n-Oc4N)Br binder

The electrochemical properties of a three-component composite containing polypyrrole, multiwalled carbon nanotubes and tetra(n-octyl)ammonium bromide as a binder have been investigated. The electrochemical behavior of this system depends on the relative amounts of the components within the composite. In the positive potential range, pseudo-capacitive behavior related to the polypyrrole oxidation is observed. The capacitance is enhanced due to the large surface area of the carbon nanotube substrate. Additionally, a contribution of double layer capacitance of multiwalled carbon nanotubes component leads to the capacitance increase. In consequence, high specific capacitance of approximately 600 F g−1 was obtained for this material. This value is about three times higher in comparison for the polymer deposited at the surface of bare gold electrode. The presence of tetra(n-octyl)ammonium bromide enhances the electrochemical and mechanical stability of the composite. The capacitance behavior of ternary composite is also more stable during cyclic charging/discharging processes in comparison to the polypyrrole film or polypyrrole/multiwalled carbon nanotube composite.

Numerical investigation of the effect of multi-walled carbon nanotube additive on nozzle flow and spray behaviors of diesel fuel

The thermal-physical properties of multi-walled carbon nanotubes (MCNTs) and MCNT blended diesel fuel were analyzed. Internal flow in injector Spray A of Engine Combustion Network and spray in a constant-volume chamber with considering the effect of the turbulence-induced breakup were modeled for pure diesel fuel and MCNT blended diesel fuel. Nozzle flow simulation showed that the addition of MCNTs into diesel fuel increased the flow turbulence at the nozzle hole outlet. Spray simulation statistically coupled with nozzle flow modeling showed that during stable spray development, there were a positive linear relationship between the liquid penetration length and the MCNT content in diesel fuel and a negative linear relationship between the Sauter mean diameter of the droplets and the MCNT content; the addition of MCNTs reduced the liquid cone angle and had an insignificant influence on the vapor penetration length.

Electromagnetic wave absorption properties of MWCNTs-COOH/cement composites with different shapes of chiral, armchair and zigzag

The electromagnetic wave absorption performances and the dielectric properties of multi-walled carbon nanotube (MWCNT) functionalization with carboxyl (-COOH) group/cement composites with different shapes; chiral, zigzag and armchair were investigated. In this study, the influence of the sample thickness and the MWCNT shape on the electromagnetic wave reflection loss, insertion loss and absorption were studied in the frequency range of 8–12 GHz. The addition of 0.1 wt% MWCNT dramatically increases the absorption properties of the cement mortar in the frequency range of 8–10 GHz. With the increase of thickness from 3 mm to 6 mm, the frequency bandwidths of the reflection loss for MWCNT/cement composites increases but the number of peaks decreases. Moreover, the reflection loss peak has increased dramatically with increasing thickness. In composite specimens prepared with a thickness of 3 mm, the chiral sample has higher absorption than the zigzag and armchair samples. The absorption behavior of composites with thickness of 6 mm at 10 GHz to 11.5 GHz is different to each other. The chiral sample shows higher absorption before 9 GHz and after 11 GHz. Experimental results show that the composite specimens at both thicknesses of 3 mm and 6 mm at frequencies below 10–10.5 GHz have higher absorption properties than the control sample. The peaks created on the relative permittivity curves also showed the nonlinear dielectric resonant behavior. Furthermore, the structural analysis and surface morphology of MWCNT/cement composites with different shapes have been explored using SEM technique.

Effect of NaCl concentration on the dispersion, stability and rheological properties of MWNTs by CMC

A detailed study of the dispersion, rheological and adsorption behaviors between multi-walled carbon nanotubes (MWNTs) and sodium carboxymethylcellulose (CMC) at different NaCl concentration were presented. The experimental results suggested that NaCl concentration governed the dispersion and stability of MWNTs. A small amount of NaCl was contributed to the dispersion and stability of MWNTs, while as the NaCl concentration increased, the MWNTs formed aggregates and the MWNTs suspension became unstable. Adsorption amount, Raman spectroscopy, zeta potential, and adsorption conformation were investigated systematically to elucidate the mechanism of this interesting phenomenon. Surprisingly, results from thermogravimetric analysis (TGA) shown that adsorption amount of CMC on MWNTs didn’t change under any circumstances. The value of zeta potential increased slightly at first and then dropped sharply as the increasing of NaCl concentration. The microstructures were measured by TEM. It was found that uniform CMC adsorption layers were formed on the surface of MWNTs at low NaCl concentrations. However, for the high-salt solution, the MWNTs were wrapped by CMC agglomerates, resulting in poor dispersion stability.

Sonication-driven dispersion of multiwalled carbon nanotubes in water with the aid of Na+-montmorillonite

The poor dispersibility of multiwalled carbon nanotubes (MWNTs) in aqueous solvents is a serious obstacle to give full play to the excellent properties of MWNTs. How to effectively disperse MWNTs has become an urgent problem to be solved. Therefore, the addition of tertiary phase became necessary to promote such dispersion. In the present work, the sonication-driven dispersion of multi-wall carbon nanotubes (MWNTs) in aqueous Na+-montmorillonite (MMT) solution has been investigated with the help of UV-vis spectroscopy, particle agglomeration size and Transmission Electron Microscopy (TEM). The impact of ultrasonic power and time as well as MMT/MWNTs ratio on the dispersion of MWNTs was discussed. It was observed that sonication at 240 W for 40 min at MMT/MWNTs weight ratio of 2 resulted in efficient dispersion and formation of stabilized suspensions of individual nanotubes. The ultrasound provided high local shears to overcome the van der Waals interactions between tubes and lead to MWNTs debundling, which facilitate adsorption and immobilization of MMT on the surface of the MWNTs, preventing re-aggregation of MWNTs.

Preparation and characteristics of a magnetic carbon nanotube adsorbent: Its efficient adsorption and recoverable performances

The challenges encountered in solid–liquid separation hinder the wide applications of carbon nanotube adsorbents. To overcome this problem, MnFe2O4/multiwalled carbon nanotubes (MMWCNTs) that combined the satisfactory adsorption properties of multiwalled carbon nanotubes (MWCNTs) with the magnetic separation of nanoparticles (MnFe2O4) was developed. MMWCNTs with a size of 10–50 nm exhibited remarkable magnetic separability (10.8 emu/g) and high adsorption capacity (qm = 494.91 mg/g, 308 K). Batch experiments to study the effect of pH on tetracycline (TC) adsorption showed that when the TC concentration was less than 80 mg L−1, the MMWCNTs could effectively adsorb TC in the pH range of 2–10, with a removal efficiency greater than 80%. The well fitted pseudo-second-order dynamic adsorption model and Langmuir isotherm indicated that the TC adsorption onto MMWCNTs mainly involved chemical and monolayer adsorption. Since the TC adsorption process was endothermic, increasing temperature could favor TC removal. Besides, after six cycles of regeneration with the NaOH solution, the removal efficiency could be maintained at 70% of the original, which indicated that the MMWCNTs had an excellent regeneration performance. At the same time, the results of our research showed that MMCWNT could not only be used as a good adsorbent for TC treatment, but also could be applied to other types of wastewater treatment.

Synthesis of Dihydromyricetin Coated Multi-Walled Carbon Nanotubes (MWCNTs) and Antibacterial Activities.

The weak antimicrobial property of multi-walled carbon nanotubes (MWCNTs) hampers their use as an antimicrobial material. In the report, Dihydromyricetin (DMY) coated multi-walled carbon nanotubes (MWCNTs-DMY) were prepared with poly(ethylene glycol) (PEG1000) as a linker and evaluated for inactivating pathogenic bacteria. UV-visible spectra, FT-IR, transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA) were used to characterize the MWCNTs-DMY. It has been shown that PEG and DMY are covalently attached to MWCNTs with excellent stability. Vibrio parahaemolyticus was employed as the target bacterium. Comparing with the raw and the functionalized MWCNTs (r-MWCNTs and f-MWCNTs), MWCNTs-DMY exhibited stronger antibacterial ability. The MWCNTs-DMY composite showed up to 10-fold higher antimicrobial property than pristine MWCNTs. The deposited DMY was suggested to play an important role in the bactericidal action of MWCNTs-DMY. The results of this study demonstrated that MWCNTs-DMY composite can serve as an effective and economical antimicrobial material.

Microwave Absorbing properties of metal functionalized-CNT-polymer composite for stealth applications

In this study, we report on the electrical properties of multi-wall carbon nanotubes (MWCNT) composites functionalized with metal or metal alloy oxides and embedded in a polyurethane matrix to develop a lightweight material for microwave absorption and shielding. The CNT nanoparticles are functionalized with metallic oxides such as Cobalt oxide, Iron oxide, and Cobalt Iron oxide, at three different concentrations. Metallic oxides are used at 5%, 10%, and 20% concentration of the total CNT percentage weight. The resulting functionalized CNT is mixed with polyurethane polymer at 5% wt of the total composite weight. Three sets of cylindrical samples are developed, and each set contains three different metal oxide concentrations. The dielectric properties of the nine developed samples are obtained by measuring their permittivity spectra using an open-ended coaxial probe technique in the spectral range 5–50 GHz. The absorption efficiency of the composites is then obtained by calculating the reflection loss at normal incidence. The results show that the spectral range of absorption can be tuned by changing the CNT concentration, and the material thickness. Functionalized CNT with different alloyed metal oxides enhanced the absorption efficiency of the polyurethane/CNT composites. Such functionalized composites can be used to replace the common heavyweight materials used for microwave applications.

Comparative study on the electrical, thermal, and mechanical properties of multiwalled carbon nanotubes filled polypropylene and polyamide 6 micromoldings

AbstractIn this work, a series of carbon nanotubes filled polypropylene (PP/CNT) and polyamide 6 (PA6/CNT) composites were prepared by melt blending and subsequently molded by compression molding and microinjection molding (μIM), respectively. Electrical conductivity results indicate that the percolation threshold of corresponding microparts shifted to higher filler concentrations when compared with that of compression molded counterparts, suggesting the prevailing shearing conditions in μIM is unfavorable for the construction of conductive pathways. In addition, Raman spectral analysis shows that there is a preferential alignment of CNTs along the flow direction of microparts. Thermal properties of both melt blended samples and subsequent microparts were evaluated using differential scanning calorimetry and thermogravimetric analysis. The mechanical properties of subsequent microparts are greatly affected by filler concentration, which might be related to the structural change that induced by the state of dispersion of CNTs.

Impedance characterization and microwave permittivity of multi-walled carbon nanotubes/BaTiO3/epoxy composites

Polymer composite materials with mixed fillers are widely investigated due to potentially superior properties they provide compared to a composite with a single filler. In this work, the electrical properties of multi-walled carbon nanotubes (MWCNT)/BaTiO3/epoxy composites are investigated using impedance measurements, modeling with equivalent circuit model, determining of alternating current conductivity in the range 10 Hz–2 MHz, permittivity measurements at frequencies 1–67 GHz, and temperature dependencies (77–290 K) of direct current conductivity. Measurements were processed to define the influence of filler combination (carbon nanotubes and BaTiO3) on dielectric properties of the epoxy composites. Nyquist diagrams indicate that all investigated composites have extensive conductive clusters. Permittivity increases monotonically with carbon nanotubes content with a steeper increase of the real part at lower frequencies. Alternating current conductivity has been determined to increase significantly at frequencies over 1 GHz. Temperature dependencies of direct current conductivity in the range 77–293 K exhibit a maximum near 180–220 K, which is shifted to the higher temperatures with the increase of carbon nanotubes content. The observed enhanced values of complex permittivity and electrical conductivity of three-phase MWCNT/BaTiO3/epoxy composites lead to a comparatively high microwave attenuation constant, which may be tuned by the carbon nanotubes content in the composite. It suggests that these composites might be perspective shielding and absorbing materials used for microwave applications.

Effects of ultrasonication time on stability, dynamic viscosity, and pumping power management of MWCNT-water nanofluid: an experimental study

It is known that ultrasonication has a certain effect on thermophysical properties and heat transfer of nanofluids. The present study is the continuation of the authors’ previous research on the effects of ultrasonication on the thermophysical properties of Multi-Walled Carbon Nanotubes (MWCNTs)-water nanofluid. Investigating the effects of ultrasonication time on samples’ stability, rheological properties, and pumping power of a water-based nanofluid containing MWCNTs nanoparticle is the main objective of the present study. The two-step method has been employed to prepared the samples. Moreover, a probe-type ultrasonic device has been used, and different ultrasonication times have been applied. The samples’ stability is investigated in different periods. The results revealed that prolonging the ultrasonication time to 60 min leads to improving the samples’ stability while prolonging ultrasonication time to higher than 60 min resulted in deteriorating the stability. As for dynamic viscosity, it is observed that increasing ultrasonication time to 60 min leads to decreasing the dynamic viscosity of the samples. As for pumping power, it is observed that the maximum increase in fanning friction factor ratio is less than 3%, which shows that adding MWCNTs to water does not impose a considerable penalty in the required energy for pumping power.

Dispersion and fluorescence properties of multiwalled carbon nanotubes modified with hyperbranched poly(phenylalanine-lysine)

Hyperbranched poly(phenylalanine-lysine) (HBP(P-L)) was synthesized by lysine, phenylalanine and N, N-dimethylbisacrylamide (MBA) via Michael addition reaction and characterized by Fourier transform infrared (FTIR) spectra, 13CNMR and 1HNMR. Furthermore, fluorescence spectroscopy indicates the fluorescence intensity of HBP(P-L) aqueous solutions increases with the concentration of HBP(P-L) increasing; Multiwalled carbon nanotubes (MWCNTs) were modified using HBP(P-L) for the purpose of preparing MWCNTs-HBP(P-L), which was characterized by FTIR, Raman analysis and thermogravimetric analysis (TGA). Visual inspection method, UV–vis absorption spectra and Zeta potential are adopted to evaluate the dispersion properties of MWCNT-HBP(P-L) aqueous solutions, and the results illustrate that HBP(P-L) does improve the dispersibility of MWCNT. Moreover, MWCNT-HBP(P-L) owns the best dispersibility in aqueous solution when the mass ratio is 1:60. Additionally, it presents an excellent linear relationship between the fluorescence intensity of MWCNTs-HBP(P-L) dispersion and the mass ratio of MWCNT-HBP(P-L). MWCNTs-HBP(P-L) exhibits unique dispersion properties as well as excellent fluorescence properties, which make the MWCNT-HBP(P-L) be potentially used in the field of optical materials.

Iron oxide-coated MWCNTs nanohybrid field emitters: a potential cold cathode for next-generation electron sources

In this paper, we have reported that the field emission properties of multiwall carbon nanotubes (MWCNTs) were significantly increased by decorating their surface by iron oxide nanoparticles. MWCNTs were prepared on silicon substrate through low-pressure chemical vapour deposition using acetylene as source gas. The iron oxide nanoparticles were grown on the surface of MWCNTs by thermal evaporation technique. Modified surface morphologies of the prepared films were characterized through field emission scanning electron microscope (FESEM), Raman spectroscopy and X-ray diffraction. A significant change in current density, stability and turn-on voltage has been observed in iron oxide-coated MWCNT films. Decoration of iron oxide nanoparticles reduces turn-on voltage from 4 to 3.4 V/μm, while current density increases from 10.15 to 33.26 mA/cm2. For practical MWCNT-based field emission devices, it is necessary to improve the emission current density and stability. The excellent field emission parameters are obtained and calculated which make them useful for high-performance field emission-based devices. The mechanism of emission of electrons is well described by the Fowler Nordheim theory.