Size Of Multi-walled Carbon Nanotubes Research Articles

Effect of size of multiwalled carbon nanotubes on thermal conductivity and viscosity of ethylene glycol-based nanofluids for solar thermal applications

The paper investigates the influence of the length of multi-walled carbon nanotubes (MWCNTs) dispersed as an additive in solar thermic fluids to enhance thermal conductivity. Here, pure ethylene glycol was chosen as solar thermic fluid due to its low viscosity, high boiling point, excellent chemical stability, and compatibility with the materials used in solar thermal systems. Pristine multi-walled carbon nanotubes are ball milled for 5, 10, and 20 h to reduce the length due to attrition. The effect of ball milling duration on the defect formation and damage to the tubular structure is assessed using Raman spectroscopy. Furthermore, the ball-milled MWCNTs were oxidized to separate amorphous carbon produced during ball milling, increasing their purity. The pristine long nanotubes and ball-milled nanotubes are mixed in pure ethylene glycol in 0.25 wt. %, and the stability of liquids is estimated using Ultraviolet–Visual (UV-Vis) spectroscopy for two months. The stability of the fluids and thermal conductivity have considerably enhanced with the dispersion of shortened MWCNTs. The dispersion of short MWCNTs in ethylene glycol resulted in a 20%–30% increase in thermal conductivity compared to pure ethylene glycol. It was also found that higher ball milling times resulted in ultra-high stability but the properties deteriorated due to the destruction of the MWCNTs' tubular structure, making them useless.

Effect of multiwalled carbon nanotube size on electrical properties of cement mortar composites

Cement mortars (CM) containing different contents and sizes of multiwalled carbon nanotubes (MWCNTs) were prepared using surfactants in combination with ultrasonic dispersion. The effects of the content, diameter and length of MWCNTs on the electrical conductivity of cement mortar and the self-inductive piezoresistive rate under single and cyclic loading were studied using the four-electrode method. The results show that the conductive percolation thresholds of CMs containing MWCNTs with different length–diameter ratios occur at an approximate MWCNT content of 0.1 wt%. The electrical conductivity of cement mortars with MWCNT diameters of 10–20 nm was the largest for a content of 0.1 wt%, and the values were 112% and 128.3% of the conductivity of the MWCNTs/CM with diameters of 20–40 nm and 40–60 nm, respectively. In addition, the fractional change in resistivity of the cement mortar specimens varied most significantly at a content of 0.75 wt% of MWCNTs; the fractional change in resistivity reached 14.27%. Adding small-diameter MWCNTs to cement mortar can maximise the sensitivity of electrical resistance of cement mortar to compressive stress.

Studying the Effect of Shortening Carbon Nanotubes via Ball Milling on Cellulose Acetate Nanocomposite Membranes for Desalination Applications.

Studying the effect of different sizes of multi-walled carbon nanotubes (CNTs) on mixed matrix membranes in nanofiltration applications has not been widely reported in the literature. In this study, two different lengths of functionalized CNTs were used to investigate such effect. First, CNTs were shortened by using high-energy ball milling at 400 RPM, with a ball-to-powder weight ratio (BPR) of 120:1. Characterization of the structure of the CNTs was carried out using TEM, XRD, SEM, BET, and Raman Spectroscopy. Second, 0.001 wt % of unmilled and milled CNTs were incorporated into cellulose acetate nanocomposite membranes, Eli-0 (unmilled), and Eli-400 (milled at 400 RPM) to study their effects on the membranes’ morphology, porosity, hydrophilicity, and performance analysis in terms of permeation and salt retention rates of 5000 ppm Na2SO4. Results showed that shortening CNTs enhanced the membranes’ hydrophilicity and affected macrovoid and micropore formation. Furthermore, shortening CNTs resulted in opening their caps and improved the permeation rates with a slight adverse effect on salt retention.

Wall thikness effects on the infrared spectra of multi-walled carbon nanotubes

In this theoretical work, we investigate the infrared vibrational features of multi-walled carbon nanotubes (MCNTs). We calculate the polarized infrared spectra of multi-walled carbon nanotubes using the spectral moment’s method. This original approach allows us to consider MCNTs with a large number of walls. We discuss the evolution of the low, intermediate and high wavenumber regions of these spectra as a function of the inner diameter and the size of MCNTs. Both the XX and ZZ polarisations are considered. Our results provide benchmark theoretical data for understanding the experimental infrared spectra of MCNTs.

The Effect of Multi-Walled Carbon Nanotubes-Additive in Physicochemical Property of Rice Brand Methyl Ester: Optimization Analysis

Biodiesel as an alternative to diesel fuel produced from vegetable oils or animal fats has attracted more and more attention because it is renewable and environmentally friendly. Compared to conventional diesel fuel, biodiesel has slightly lower performance in engine combustion due to the lower calorific value that leads to lower power generated. This study investigates the effect of multi-walled carbon nanotubes (MWCNTs) as an additive to the rice bran methyl ester (RBME). Artificial neural network (ANN) and response surface methodology (RSM) was used for predicting the calorific value. The interaction effects of parameters such as dosage of MWCNTs, size of MWCNTs and reaction time on the calorific value of RBME were studied. Comparison of RSM and ANN performance was evaluated based on the correlation coefficient (R2), the root mean square error (RMSE), the mean absolute percentage error (MAPE), and the average absolute deviation (AAD) showed that the ANN model had better performance (R2 = 0.9808, RMSE = 0.0164, MAPE = 0.0017, AAD = 0.173) compare to RSM (R2 = 0.9746, RMSE = 0.0170, MAPE = 0.0028, AAD = 0.279). The optimum predicted of RBME calorific value that is generated using the cuckoo search (CS) via lévy flight optimization algorithm is 41.78 (MJ/kg). The optimum value was obtained using 64 ppm of < 7 nm MWCNTs blending for 60 min. The predicted calorific value was validated experimentally as 41.05 MJ/kg. Furthermore, the experimental results have shown that the addition of MWCNTs was significantly increased the calorific value from 36.87 MJ/kg to 41.05 MJ/kg (11.6%). Also, the addition of MWCNTs decreased flashpoint (−18.3%) and acid value (−0.52%). As a conclusion, adding MWCNTs as an additive had improved the physicochemical properties characteristics of RBME. To our best knowledge, no research has yet been performed on the effect of multi-walled carbon nanotubes-additive in physicochemical property of rice brand methyl ester application so far.

Effect of Size of Multiwalled Carbon Nanotubes Dispersed in Gear Oils for Improvement of Tribological Properties

The aim of the paper is to investigate the effect of size of multiwalled carbon nanotubes (MWCNTs) as additives for dispersion in gear oil to improve the tribological properties. Since long pristine MWCNTs tend to form clusters compromising dispersion stability, they are mildly processed in a ball mill to shorten the length and stabilized with a surfactant before dispersing in lubricant. Investigations are made to assess the effect of ball milling on the size and structure of MWCNTs using electron microscopy and Raman spectroscopy. The long and shortened MWCNTs are dispersed in EP 140 gear oil in 0.5% weight. The stability of the dispersed multiwalled carbon nanotubes is evaluated using light scattering techniques. The antiwear, antifriction, and extreme pressure properties of test oils are evaluated on a four-ball wear tester. It is found that ball milling of MWCNTs has a strong effect on the stability and tribological properties of the lubricant. From Raman spectroscopy, it is found that ball milling time of up to 10 hours did not produce any defects on the surface of MWCNTs. The stability of the lubricant and the antiwear, antifriction, and extreme pressure properties have improved significantly with dispersion shortened MWCNTs. Ball milling for longer periods produces defects on the surface of MWCNTs reducing their advantage as oil additives.

Kinetic study of multi-walled carbon nanotube synthesis by thermocatalytic decomposition of methane using floating catalyst chemical vapour deposition

Multiwalled carbon nanotubes (MWCNTs) have been synthesized using methane in a floating catalyst chemical vapour deposition reactor at atmospheric pressure. The catalyst concentration, partial pressure of methane and synthesis temperature have been varied in order to understand their effects on the rate formation of MWCNTs, purity and size of MWCNTs. Reaction mechanism, rate controlling step and overall rate of reaction have been deduced using chemical reaction engineering approach. A systematic study was carried out in order to obtain the kinetic expression based on Langmuir-Hinshelwood type model. The kinetic model was based on the dissociative adsorption pathway of methane and subsequent removal of hydrogen from the adsorbed methyl group with two different active sites. The activation energy for the overall reaction was 46.1 kJ mol−1 in the temperature range of 1073–1273 K. The products have been characterized by transmission electron microscopy, thermogravimetry, BET and Raman spectroscopy. The BET surface area of purified MWCNTs were found to be 157 m2 g−1 with pore volume of 0.176 cc g−1.

Impact and flexural properties of polypropylene composites reinforced with multi-walled carbon nanotubes

The effects of content and size of multi-walled carbon nanotubes (MWCNTs) on the impact and flexural properties of reinforced-polypropylene (PP) composites were investigated at room temperature. The results showed that the flexural modulus and maximum flexural stress increased with increase of the MWCNTs weight fraction, while effects of the diameter and average length-diameter ratio of the fillers on the flexural strength were insignificant. The effects of the size and content of the MWCNTs on the impact fracture toughness were significant, the Izod V-notched impact fracture strength increased roughly with increasing weight fraction and the average diameter of the MWCNTs, while it decreased with increasing length-diameter ratio of the MWCNTs. Finally, the reinforcing and toughening mechanisms of the PP/MWCNTs composites are discussed.

Size-dependent thermal properties of multi-walled carbon nanotubes embedded in phase change materials

This study has focused on the systematical investigation of effect of mass fraction and size of multi-walled carbon nanotubes (MWCNTs) doped in phase change material (PCM) on thermal properties such as thermal conductivity, melting/solidification temperatures and latent heats. Thermal conductivity, melting/solidification temperatures and latent heats of MWCNTs/PCM composites with three different diameters and two different lengths, obtained by doping MWCNTs into PCM at the mass fraction of 1–5%, were evaluated according to the criteria such as particle size and mass fraction. The results demonstrated that not only mass fractions but also size of MWCNTs are effective on the thermal properties of the composites. It was concluded that increase in diameter and length of MWCNTs positively affects enhancement of thermal conductivity; on the other hand, it does not cause a significant change at melting/solidification temperatures. In addition to these, a decline was observed at melting/solidification latent heats of MWCNTs/PCM composites, depending on doped mass fractions of MWCNTs.

Estimation of agglomerate size of multi-walled carbon nanotubes in fluidized beds

The objective of this study was to determine hydrodynamic characteristics of multi-walled carbon nanotubes (MWCNTs) agglomerates and examine their sizes. The bed collapsing process of MWCNTs agglomerates was found to be closer to that of Geldart group C particles than group A particles. Median diameters of MWCNTs agglomerates determined by sedimentation method at initial superficial gas velocity of 0.120 and 0.190m/s were 157 and 221μm, respectively. The size of these MWCNTs agglomerates in fluidization state was measured by image analysis using a high speed camera. Median diameters of these MWCNTs agglomerates in freeboard were increased from 138 to 189μm as superficial gas velocity was increased from 0.088 to 0.190m/s at static bed height of 0.16m. Median diameter and size distribution determined by sedimentation method fitted well with those measured using image analysis. Results were reasonable at superficial gas velocity up to 0.190m/s.

In vitro chromosomal aberrations induced by various shapes of multi-walled carbon nanotubes (MWCNTs).

IARC has classified one type of multi-walled carbon nanotubes (MWCNTs), MWNT-7, as possibly carcinogenic to humans (Group 2B); however, other types of MWCNT were categorized as not classifiable as to their carcinogenicity to humans (Group 3). In vitro chromosomal aberration assays of MWNT-7 showed polyploid formation but not structural abnormalities. This study investigated the influence of the shape and size of MWCNT on in vitro induction of chromosomal aberrations. Microscopic analysis and viable cell counting were used to assay for chromosomal aberrations and cytotoxicity induced in a Chinese hamster lung cell line (CHL/IU) exposed to different MWCNTs. Using scanning electron microscopy, seven MWCNTs were classified into three types: straight fibrous, curved fibrous, and tangled. The straight fibrous MWCNTs were the strongest inducers of polyploidy and the most cytotoxic among the three types of MWCNTs. The curved fibrous MWCNTs induced more polyploidy than the tangled MWCNTs, and the cytotoxicity of both types seemed to be a reflection of their induction of polyploidy. None of the seven MWCNTs induced structural chromosomal aberrations. The non-clastogenicity of the MWCNTs indicates that the MWCNTs may not interact directly with DNA. Since the straight fibrous MWCNTs, which exhibit a structure similar to asbestos, were the strongest inducers of polyploidy, MWCNT shape may be an important factor in induction of polyploidy. We hypothesize that CHL/IU cells endocytosed MWCNTs and formed endosomes with shapes corresponding to those of the endocytosed MWCNTs, and that the long axis diameter of the endosome is important in the capability of MWCNTs to induce polyploidy.

Effects of MWCNTs Size on Melt Flow Properties of Polypropylene Composites During Capillary Extrusion

The influence of multi-walled carbon nanotubes (MWCNTs) size including average diameter and length-diameter ratio on the melt flow behavior of polypropylene composites were investigated by means of a capillary rheometer in a temperature ranging from 190 to 230 °C and under apparent shear rates varying from 100 to 4000 s−1. It was found that the melt shear flow approximately obeyed the power law; the values of the melt shear viscosity increased with an increase of the filler weight fraction, while decreased with increasing the average diameter of the MWCNTs; the dependence of the melt shear viscosity on temperature roughly obeyed the Arrhenius equation; the relationship between the melt shear viscosity and the MWCNTs weight fraction was almost linear; the sensitivity of the melt apparent shear viscosity to the MWCNTs weight fraction was weakened with increasing the MWCNTs average diameter.

Evaluation of the cytotoxic and genotoxic effects of benchmark multi-walled carbon nanotubes in relation to their physicochemical properties

To contribute with scientific evidence to the grouping strategy for the safety assessment of multi-walled carbon nanotubes (MWCNTs), this work describes the investigation of the cytotoxic and genotoxic effects of four benchmark MWCNTs in relation to their physicochemical characteristics, using two types of human respiratory cells.The cytotoxic effects were analysed using the clonogenic assay and replication index determination. A 48h-exposure of cells revealed that NM-401 was the only cytotoxic MWCNT in both cell lines, but after 8-days exposure, the clonogenic assay in A549 cells showed cytotoxic effects for all the tested MWCNTs. Correlation analysis suggested an association between the MWCNTs size in cell culture medium and cytotoxicity.No induction of DNA damage was observed after any MWCNTs in any cell line by the comet assay, while the micronucleus assay revealed that both NM-401 and NM-402 were genotoxic in A549 cells. NM-401 and NM-402 are the two longest MWCNTs analyzed in this work, suggesting that length may be determinant for genotoxicity. No induction of micronuclei was observed in BBEAS-2Beas-2B cell line and the different effect in both cell lines is explained in view of the size-distribution of MWCNTs in the cell culture medium, rather than cell’s specificities.

Thermal properties and thermal stability of PP/MWCNT composites

The effects of the filler size and content on thermal properties and thermal stability of polypropylene (PP) composites filled with four different sizes of multi-walled carbon nanotubes (MWCNTs) were investigated through thermogravimetric analysis. The results showed that the values of the decomposition temperature increased with increasing weight fraction and length–diameter ratio of the filler, while increased with decreasing filler diameter. The values of the residues increased approximately linearly with increasing filler weight fraction. The values of maximum mass loss rate decreased roughly with increasing filler weight fraction, while the influence of the filler diameter and length–diameter ratio on the maximum mass loss rate was insignificant. The thermal stability improvement might be attributed to the barrier function of the MWCNTs. This study provides a basis for further development of MWCNTs reinforced polymer composites with desirable thermal properties for potential application as energy materials.

Effect of textural properties of alumina support on the catalytic performance of Ni/Al2O3 catalysts for hydrogen production via methane decomposition

Catalytic performance of 60 wt.% Ni supported on different morphological structure of alumina was studied for COx-free hydrogen production by methane decomposition. The Al2O3 supports were prepared by reverse microemulsion and precipitation techniques to obtain alumina hollow sphere (HS) and alumina nanoparticles (NP) structures, respectively. These materials were compared with the commercial alumina (bulk) to investigate the effect of the support structure on the catalytic activity and stability of Ni particles. The fresh and used catalysts were characterized by XRD, BET, TGA, H2-TPR, TEM and Raman spectroscopy. The results revealed that the texture properties of Al2O3 support play a crucial role on the catalyst performance. The Ni/Al2O3 nanoparticles (NP) catalyst exhibited the highest catalytic decomposition activity due to its better metal site distribution. The TPR results showed that almost all NiO particles in this catalyst were located extensively on the external surface of Al2O3 nanoparticles. On the other hand, the Ni/Al2O3 hollow sphere (HS) catalyst showed a lower activity due to the formation of large quantities of NiAl2O4 species. TEM and Raman spectroscopy data proved that longer and smaller size of multi-walled carbon nanotubes (MWCNT) with a relatively uniform diameters were obtained on the Ni/Al2O3 nanoparticles, compared to the other catalysts.

Nanofluid PCMs for thermal energy storage: Latent heat reduction mechanisms and a numerical study of effective thermal storage performance

Abstract The latent heat of fusion of paraffin-based nanofluids has been examined to investigate the use of enhanced phase change materials (PCMs) for thermal energy storage (TES) applications. The nanofluid approach has often been exploited to enhance thermal conductivity of PCMs, but the effects of particle addition on other thermal properties affecting TES are relatively ignored. An experimental study of paraffin-based nanofluids containing various particle sizes of multi-walled carbon nanotubes has been conducted to investigate the effect of nanoparticles on latent heat of fusion. Results demonstrated that the magnitude of nanofluid latent heat reduction increases for smaller diameter particles in suspension. Three possible mechanisms – interfacial liquid layering, Brownian motion, and particle clustering – were examined to explain further reduction in latent heat, through the weakening of molecular bond structures. Although additional research is required to explore detailed mechanisms, experimental evidence suggests that interfacial liquid layering and Brownian motion cannot explain the degree of latent heat reduction observed. A finite element model is also presented as a method of quantifying nanofluid PCM energy storage performance. Thermal properties based on modified effective medium theory and an empirical relation for latent heat of fusion were applied as model parameters to determine energy stored and extracted over a given period of time. The model results show that while micro-scale particle inclusions exhibit some performance enhancement, nanoparticles in PCMs provide no significant improvement in TES performance. With smaller particles, the enhancement in thermal conductivity is not significant enough to overcome the reduction in latent heat of fusion, and less energy is stored over the PCM charge period. Therefore, the nanofluid approach may not be justifiable for energy storage applications. However, since the model parameters are dependent on the material properties of the system observed, storage performance may vary for differing nanofluid materials.

Effects of silver nanoparticles and multi-walled carbon nanotubes on certain aquatic species

Aquatic toxicity studies with two different sizes of multi-walled carbon nanotubes (MWCNTs) and silver (Ag) nanoparticles were conducted on Rainbow trout fish Oncorhynchus mykiss, water flea Daphnia magna, and green algae Pseudokirchneriella subcapitata as model organisms. Author (1) along with co-authors (2,3) conducted this research work at IIBAT as a part of PhD. The results of these studies indicated that MWCNTs are low concern whereas, silver nanoparticles are of high concern to the aquatic species tested (Rainbow trout fish, Water flea and Green alga). The present aquatic studies demonstrated the hazard potential of silver nanoparticles to the aquatic species, following acute exposure and calls for surveillance on the impact of the wide release of nanomaterials into the environment.

Frictional and wear properties of cobalt/multiwalled carbon nanotube composite films formed by electrodeposition

Carbon nanotubes (CNTs) have solid lubricity due to their unique structure, and as such, CNT composites are also expected to exhibit superior tribological properties. In this study, Co/CNT composite films were fabricated using a composite electrodeposition technique, and their tribological properties were investigated. Three different sizes of multiwalled carbon nanotubes (MWCNTs) were used as the CNTs in this study. The microstructures of the composite films were examined using scanning electron microscopy. Frictional and wear properties were examined using a ball-on-disk method without any lubricants at room temperature and at high temperatures (100–500°C). The Co/MWCNT composite films had lower coefficients of friction than a cobalt film at room temperature. In contrast, the coefficients of friction of the Co/MWCNT composite film at high temperature became higher than that at room temperature and slightly lower than that of a cobalt film. These results are likely related to the formation of cobalt oxides on the surface and the heat dissipation of the MWCNTs.

Crystalline morphology and properties of multi-walled carbon nanotube filled isotactic polypropylene nanocomposites: Influence of filler size and loading

Isotactic polypropylene (PP) nanocomposites with multi-walled carbon nanotubes (MWCNTs) of various diameters (10–50nm) were fabricated by extrusion and compression-molding techniques and characterized by X-ray diffraction measurements, differential scanning calorimetry, scanning electron microscopy, mechanical test and differential thermal analyses. The pure PP exhibits both the a- and b-axes oriented α-crystal, whereas the MWCNTs induce the b-axis orientation of the α-crystal along with the formation of minor γ-phase crystal in nanocomposites. Crystallinity, long period of lamellae, tensile strength, tensile modulus (TM) and microhardness (H) of PP considerably change by different loading and sizes of MWCNTs. The estimated values H/TM=0.09–0.10 for all samples approach the predicted value of 0.10 for polymers. The increase in crystallinity has been demonstrated by both XRD and DSC studies. Mathematical models have been invoked to explain the changes in mechanical properties. An increase in thermal stability of polymer matrix occurs with increasing MWCNTs size and loading.

Systematic and Quantitative Investigation of the Mechanism of Carbon Nanotubes’ Toxicity toward Algae

Concurrent with the increasing production and application of carbon nanotubes (CNTs) comes an increasing likelihood of CNTs presenting in the aquatic environment, and thereby potentially threatening aquatic organisms via toxic mechanisms that are, at present, poorly understood. This study systematically investigated the toxicity of three multiwalled CNT (MWCNT) samples toward a green alga (Chlorella sp.), focusing on examining and quantifying the contributions of five possible mechanisms to the algal growth inhibition. The results showed that the MWCNTs significantly inhibited the algal growth. The contribution of metal catalyst residues in the MWCNTs to the algal growth inhibition was negligible, as was the contribution from the MWCNTs' adsorption of nutrient elements. The algal toxicity of MWCNTs could mainly be explained by the combined effects of oxidative stress, agglomeration and physical interactions, and shading effects, with the quantitative contributions from these mechanisms depending on the MWCNT size and concentration. At MWCNT concentrations around 96 h IC(50), the oxidative stress accounted for approximately 50% of the algal growth inhibition, whereas the agglomeration and physical interactions, and the shading effects each took approximately 25% of the responsibility.