Types Of Multi-walled Carbon Nanotubes Research Articles

Electrical and piezoresistive sensing capacities of cement paste with multi-walled carbon nanotubes

This study examined the feasibility of using multi-walled carbon nanotubes (MWCNTs) in cement paste for piezoresistive sensors. Two types of MWCNTs with different carbon content (>90% and >99%) were incorporated into cement paste at 1% by weight of binder (1wt%). Plain cement paste and cement composites including 1wt% graphite nanofiber (GNF) and graphene (G) were also considered for comparisons of the electrical conductivity. The test results indicate that the MWCNTs more effectively improved the conductivity of the cement paste than GNF and G. In addition, composites with MWCNTs with lower flowability had less resistivity than those with higher flowability. The size effect in electrical resistivity was observed in the cement pastes with and without the carbon-based nanomaterials, but it was mitigated by incorporating MWCNTs in the cement paste. The stresses and strains under cyclic compression and monotonic tension were well simulated by the measured fraction change in the resistivity of the composites with 1wt% MWCNTs. The gauge factor (GF) for the composites with 1wt% MWCNTs was higher than that of commercially available strain gauges, and it was affected by the loading condition: a higher GF obtained under compression than under tension.

Mechanical properties and reinforcing mechanisms of cementitious composites with different types of multiwalled carbon nanotubes

In this study, reinforcement effect of 12 types of multiwalled carbon nanotubes (MWCNTs) on mechanical properties of cementitious composites was investigated Research results showed that among pristine MWCNTs with different diameters and lengths, the short MWCNTs with large diameter present the best reinforcing effect on strength of composites. Functionalization of MWCNTs is beneficial for enhancing strength of composites. Moreover, hydroxyl-functionalized MWCNTs feature a better reinforcement effect compared to carboxyl-functionalized MWCNTs. The best relative/absolute enhancements of 79%/74 MPa and 64.4%/5.6 MPa in compressive and flexural strength of composites are achieved by incorporating 0.5% of nickel-coated MWCNTs. XRD analyses revealed that the incorporation of MWCNTs decreases the orientation of CH in matrix, which is consistent with SEM observations. TG analyses showed that MWCNTs inhibit hydration of composites due to their absorption effect. However, extensive MWCNT networks improve microstructure of matrix and hinder the crack development under loading through fiber bridging and pull-out.

Effects of noncovalently functionalized multiwalled carbon nanotube with hyperbranched polyesters on mechanical properties of epoxy composites

In order to improve the dispersibility and interface properties of multi-walled carbon nanotubes (MWCNTs) in epoxy resin (EP), aromatic hyperbranched polyesters with terminal carboxyl (HBP) and aromatic hyperbranched polyesters with terminal amino groups (HBPN) were used for noncovalent functionalization of MWCNTs. Epoxy composites reinforced by different types of MWCNT were prepared. The effects of noncovalent functionalization of MWCNTs on the dispersibility, wettability, interface properties and mechanical properties of epoxy composites were investigated. The results show that the dispersibility and wettability of MWCNTs are significantly improved after noncovalent functionalization. A large number of terminal primary amines (NH2) on noncovalently functionalized MWCNT with HBPN (HBPN-MWCNT) form covalent bonds with EP matrix, and thus the interfacial adhesion is enhanced significantly, resulting in high load transfer efficiency and substantial increase in mechanical properties. The interface with covalent bonding formed between the flexible hyperbranched polyester layer on the surface of HBPN-MWCNT and the EP matrix promotes plastic deformation of the surrounding EP matrix. The toughening mechanisms of HBPN-MWCNT are MWCNT pull-out and a large amount of plastic deformation of the surrounding EP matrix.

Multi-walled carbon nanotube-induced genotoxic, inflammatory and pro-fibrotic responses in mice: Investigating the mechanisms of pulmonary carcinogenesis

The International Agency for Research on Cancer has classified one type of multi-walled carbon nanotubes (MWCNTs) as possibly carcinogenic to humans. However, the underlying mechanisms of MWCNT- induced carcinogenicity are not known. In this study, the genotoxic, mutagenic, inflammatory, and fibrotic potential of MWCNTs were investigated. Muta™Mouse adult females were exposed to 36±6 or 109±18μg/mouse of Mitsui-7, or 26±2 or 78±5μg/mouse of NM-401, once a week for four consecutive weeks via intratracheal instillations, alongside vehicle-treated controls. Samples were collected 90days following the first exposure for measurement of DNA strand breaks, lacZ mutant frequency, p53 expression, cell proliferation, lung inflammation, histopathology, and changes in global gene expression. Both MWCNT types persisted in lung tissues 90days post-exposure, and induced lung inflammation and fibrosis to similar extents. However, there was no evidence of DNA damage as measured by the comet assay following Mitsui-7 exposure, or increases in lacZ mutant frequency, for either MWCNTs. Increased p53 expression was observed in the fibrotic foci induced by both MWCNTs. Gene expression analysis revealed perturbations of a number of biological processes associated with cancer including cell death, cell proliferation, free radical scavenging, and others in both groups, with the largest response in NM-401-treated mice. The results suggest that if the two MWCNT types were capable of inducing DNA damage, strong adaptive responses mounted against the damage, resulting in efficient and timely elimination of damaged cells through cell death, may have prevented accumulation of DNA damage and mutations at the post-exposure time point investigated in the study. Thus, MWCNT-induced carcinogenesis may involve ongoing low levels of DNA damage in an environment of persisting fibres, chronic inflammation and tissue irritation, and parallel increases or decreases in the expression of genes involved in several pro-carcinogenic pathways.

Cytotoxicity induced by carbon nanotubes in experimental malignant glioma.

Despite multiple advances in the diagnosis of brain tumors, there is no effective treatment for glioblastoma. Multiwalled carbon nanotubes (MWCNTs), which were previously used as a diagnostic and drug delivery tool, have now been explored as a possible therapy against neoplasms. However, although the toxicity profile of nanotubes is dependent on the physicochemical characteristics of specific particles, there are no studies exploring how the effectivity of the carbon nanotubes (CNTs) is affected by different methods of production. In this study, we characterize the structure and biocompatibility of four different types of MWCNTs in rat astrocytes and in RG2 glioma cells as well as the induction of cell lysis and possible additive effect of the combination of MWCNTs with temozolomide. We used undoped MWCNTs (labeled simply as MWCNTs) and nitrogen-doped MWCNTs (labeled as N-MWCNTs). The average diameter of both pristine MWCNTs and pristine N-MWCNTs was ~22 and ~35 nm, respectively. In vitro and in vivo results suggested that these CNTs can be used as adjuvant therapy along with the standard treatment to increase the survival of rats implanted with malignant glioma.

Systematic evaluation of oligodeoxynucleotide binding and hybridization to modified multi-walled carbon nanotubes

BackgroundIn addition to conventional chemotherapeutics, nucleic acid-based therapeutics like antisense oligodeoxynucleotides (AS-ODN) represent a novel approach for the treatment of bladder cancer (BCa). An efficient delivery of AS-ODN to the urothelium and then into cancer cells might be achieved by the local application of multi-walled carbon nanotubes (MWCNT). In the present study, pristine MWCNT and MWCNT functionalized with hydrophilic moieties were synthesized and then investigated regarding their physicochemical characteristics, dispersibility, biocompatibility, cellular uptake and mucoadhesive properties. Finally, their binding capacity for AS-ODN via hybridization to carrier strand oligodeoxynucleotides (CS-ODN), which were either non-covalently adsorbed or covalently bound to the different MWCNT types, was evaluated.ResultsPristine MWCNT were successfully functionalized with hydrophilic moieties (MWCNT-OH, -COOH, -NH2, -SH), which led to an improved dispersibility and an enhanced dispersion stability. A viability assay revealed that MWCNT-OH, MWCNT-NH2 and MWCNT-SH were most biocompatible. All MWCNT were internalized by BCa cells, whereupon the highest uptake was observed for MWCNT-OH with 40% of the cells showing an engulfment. Furthermore, all types of MWCNT could adhere to the urothelium of explanted mouse bladders, but the amount of the covered urothelial area was with 2–7% rather low. As indicated by fluorescence measurements, it was possible to attach CS-ODN by adsorption and covalent binding to functionalized MWCNT. Adsorption of CS-ODN to pristine MWCNT, MWCNT-COOH and MWCNT-NH2 as well as covalent coupling to MWCNT-NH2 and MWCNT-SH resulted in the best binding capacity and stability. Subsequently, therapeutic AS-ODN could be hybridized to and reversibly released from the CS-ODN coupled via both strategies to the functionalized MWCNT. The release of AS-ODN at experimental conditions (80 °C, buffer) was most effective from CS-ODN adsorbed to MWCNT-OH and MWCNT-NH2 as well as from CS-ODN covalently attached to MWCNT-COOH, MWCNT-NH2 and MWCNT-SH. Furthermore, we could exemplarily demonstrate that AS-ODN could be released following hybridization to CS-ODN adsorbed to MWCNT-OH at physiological settings (37 °C, urine).ConclusionsIn conclusion, functionalized MWCNT might be used as nanotransporters in antisense therapy for the local treatment of BCa.

Removal of bisphenol A by electrochemical carbon-nanotube filter: Influential factors and degradation pathway

Bisphenol A is a chemical with hazardous health effects that is largely used in the manufacture of extensively used products including adhesives, plastics, powder paints, thermal paper and paper coatings, and epoxy resin, and is reported to exist in nature in an accumulative manner. In this study, both pristine and boron-doped multiwalled carbon nanotubes (MWNTs) were employed as filtration and electrochemical filtration materials, resulting in a significant removal of bisphenol A with identical performance for both MWNTs types. It was shown that the presence of salt is not critical for the greatest contaminant removal efficiency, likely due to the vital role of other electroactive species (e.g. reactive oxygen species). Near complete removal of 1 mg L−1 bisphenol A at 2 and 3 V of applied DC potentials was achieved, indicating that the electrochemical filtration process is voltage dependent at both 2 and 3 V. Increasing the residence time by 7.4 fold (from 2.0 to 14.9 s) resulted in a significant removal of bisphenol A and its toxic byproducts, up to 424 min of electrochemical filtration time at 3 V of applied potential. Based on these results, electrochemical filtration using MWNTs is considered a promising technology for the removal of the accumulative bisphenol A and the reduction of its hazardous effects in waters.

STAT1-dependent and -independent pulmonary allergic and fibrogenic responses in mice after exposure to tangled versus rod-like multi-walled carbon nanotubes

BackgroundPulmonary toxicity of multi-walled carbon nanotubes (MWCNTs) is influenced by physicochemical characteristics and genetic susceptibility. We hypothesized that contrasting rigidities of tangled (t) versus rod-like (r) MWCNTs would result in differing immunologic or fibrogenic responses in mice and that these responses would be exaggerated in transgenic mice lacking the signal transducer and activator of transcription-1 (STAT1), a susceptible mouse model of pulmonary fibrosis.MethodsMale wild type (Stat1+/+) and STAT1-deficient (Stat1−/−) mice were exposed to 4 mg/kg tMWCNTs, rMWCNTs, or vehicle alone via oropharyngeal aspiration and evaluated for inflammation at one and 21 days post-exposure via histopathology, differential cell counts, and cytokine levels in bronchoalveolar lavage fluid (BALF). Granuloma formation, mucous cell metaplasia, and airway fibrosis were evaluated by quantitative morphometry. Airway epithelial cell proliferation was assessed by bromodeoxyuridine (BrdU) incorporation. Cytokine protein levels in BALF and serum IgE levels were measured by ELISA. Lung protein Smad2/3 levels and activation were measured by Western blot. Lung mRNAs were measured by PCR.ResultsThere was a 7-fold difference in rigidity between tMWCNTs and rMWCNTs as determined by static bending ratio. Both MWCNT types resulted in acute inflammation (neutrophils in BALF) after one-day post-exposure, yet only rMWCNTs resulted in chronic inflammation at 21 days as indicated by neutrophil influx and larger granulomas. Both MWCNTs induced BrdU uptake in airway epithelial cells, with the greatest proliferative response observed in rMWCNT-exposed mice after one-day. Only rMWCNTs induced mucous cell metaplasia, but this index was not different between genotypes. Stat1−/− mice had higher levels of baseline serum IgE than Stat1+/+ mice. Greater airway fibrosis was observed with rMWCNTs compared to tMWCNTs, and exaggerated airway fibrosis was seen in the Stat1−/− mouse lungs with rMWCNTs but not tMWCNTs. Increased fibrosis correlated with elevated levels of TGF-β1 protein levels in the BALF of Stat1−/− mice exposed to rMWCNTs and increased lung Smad2/3 phosphorylation.ConclusionsRigidity plays a key role in the toxicity of MWCNTs and results in increased inflammatory, immunologic, and fibrogenic effects in the lung. STAT1 is an important protective factor in the fibroproliferative response to rMWCNTs, regulating both induced TGF-β1 production and Smad2/3 phosphorylation status. Therefore, both rigidity and genetic susceptibility should be major considerations for risk assessment of MWCNTs.

Functional characteristics, wettability properties and cytotoxic effect of starch film incorporated with multi-walled and hydroxylated multi-walled carbon nanotubes

Two types of multi-walled carbon nanotubes (CNT and CNT-OH) at different levels (0.1–0.9wt%) were introduced into starch matrix in order to modify its functional properties. The optimum concentration of each nanotube was selected based on the results of water solubility, water permeability and mechanical experiments. The physico-mechanical data showed that CNT up to 0.7wt% led to a notable increase in water resistance, water barrier property and tensile strength, whilst regarding CNT-OH, these improvements found at 0.9wt%. Therefore, effects of optimized level of each nanotube on the starch film were evaluated by XRD, surface hydrophobicity, wettability and surface energy tests. XRD revealed that the position of starch characteristic peak shifted to higher degree after nanotubes introducing. The hydrophobic character of the film was greatly increased with incorporation of nanoparticles, as evidenced by increased contact angle with greatest value regarding CNT-OH. Moreover, CNT-OH notably decreased the surface free energy of the starch film. Finally, the conformity of both nanocomposites with actual food regulations on biodegradable materials was tested by cytotoxicity assay to evaluate the possibility of application in food packaging sector. Both nanocomposite films had potential of cytotoxic effects, since they could increase cytoplasmic lactate dehydrogenase release from L-929 fibroblast cells in contact with their surface.

The role of oxygen-containing groups on the adsorption of bisphenol-A on multi-walled carbon nanotube modified by HNO 3 and KOH

Abstract The adsorption of bisphenol-A (BPA) on multi-walled carbon nanotubes (MWCNTs) was investigated in this study. To distinguish the influences of surface area and oxygen-containing functional groups, the as-purchased MWCNTs ( A -MWCNTs) were treated by HNO 3 ( N -MWCNTs) and KOH ( K -MWCNTs). The adsorption capacity of N -MWCNTs was less than that of A -MWCNTs at neutral pH due to the steric obstruction resulted from the oxygen-containing functional groups on the N -MWCNTs. The adsorption capacities of BPA on all three types of MWCNTs decreased when the pH values increase to 10 or 11, at which the electrostatic repulsions between the dissociated surface groups and BPA arose. Also, it was found that although the N -MWCNTs and the K -MWCNTs had about the same amount of the oxygen-containing surface groups, their ratios of the adsorption amount at solution pH 11 to that at pH 5 ( q 11 /q 5 ) were different. This indicated that not only the amount but also the types of the oxygen-containing groups would affect the interaction between aromatic compounds and MWCNTs. The dissociation of OH groups and water-clustering would have more significant hindering effects than the carboxylic groups for the adsorption of BPA by MWCNTs at high pH.

The efficiency of the multi-walled carbon nanotubes used for antibiotics removal from wastewaters generated by animal farms.

In the recent years, residual antibiotics are considered to be emerging environmental pollutants due to their continuous input and persistence into the aquatic ecosystem even at low concentrations. Therefore, these are necessary to develop efficient methods for the wastewater treatment. The present paper describes the efficiency of several types of multi-walled carbon nanotubes (MWCNTs) for the retention of the selected antibiotics (ampicillin, ceftazidime, cefepime, imipenem, piperacillin, tazobactam, tetracycline, erythromycin, ciprofloxacin, norfloxacin, vancomycin, gentamicin, sulfamethoxazole, and thrimetoprim) from aqueous (synthetic) solutions and wastewater samples. The functionalized MWCNTs were characterized by Fourier transform infrared spectroscopy(FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The obtained antibiotic percentage of retention was evaluated by quantitative assessment using high-performance liquid chromatography coupled with the diode array, fluorescence, and mass spectrometer detector (HPLC-DAD/FD/MS), after the solid-phase extraction (SPE) with Oasis HLB cartridges. The retention percentages of the selected antibiotics from waters ranged between ∼40 and 97%, with the exception of sulfamethoxazole and trimethoprim. The best percentages of retention were obtained for norfloxacin 97.03% and ciprofloxacin 97.10%. The suspensions of the MWCNTs improved the antibiotics removal from wastewaters. Removal of antibiotics from wastewaters using nanotechnology, in order to reduce their negative effects and antibiotic resistance, is a promising tool in the future wastewaters treatment.

Performance and stability of chitosan-MWCNTs-laccase biocathode: Effect of MWCNTs surface charges and ionic strength

A three-dimensional biocathode structure was fabricated by compacting chitosan, multiwall carbon nanotubes (MWCNTs) and laccase from Trametes versicolor in a mechanical press. The effect of functionalizing the MWCNTs with amine groups on the morphology, the electrocatalytic activity and the stability of the biocathode were evaluated for the direct and mediatorless oxygen reduction. The chemical groups bound to the MWCNTs surface influenced the interconnection of the chitosan nanofibers and consequently the surface area (SBET). Biocathodes based on pristine MWCNTs had a larger surface area compared with those made with functionalized MWCNTs. The direct electron transfer (DET) between the enzyme and all studied types of MWCNTs was demonstrated by the open circuit potential (OCP), cyclic voltammetry and chronoamperometry. The most efficient laccase immobilization was obtained for the biocathode with functionalized MWCNTs, whereas a better stability over time was measured when pristine MWCNTs were used. These results can be explained by the better stability of hydrophobic-hydrophobic interactions between laccase and pristine MWCNTs compared with ionic interactions in the case of functionalised MWCNTs which are very sensitive to ionic strength of the buffer solution. In the case of functionalised MWCNTs, laccase was desorbed by increasing salt concentration in the buffer, and it was re-adsorbed again by decreasing salt concentration in the buffer solution.

Fresh and mechanical properties, and strain sensing of nanomodified cement mortars: The effects of MWCNT aspect ratio, density and functionalization

A comprehensive analysis on the effect of aspect ratio, bulk density and functionalization of multi walled carbon nanotubes (MWCNTs) in the development of nanomodified mortars, reinforced with different types of MWCNTs is presented herein. A structural characterization of the pristine and functionalized carbon nanotubes was carried out with scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). A simple one step dispersion method, involving the application of ultrasonic energy and the use of a superplasticizer (SP) was utilized for the preparation of uniformly dispersed MWCNT suspensions. The experimental determination of the fresh and 28d mechanical properties of mortars with w/c = 0.5 and s/c = 3.0, using four different types of well dispersed pristine and functionalized MWCNTs at an amount of 0.1 wt% of cement took place through: (i) flow and time of setting tests; (ii) three point bending experiments on 4 × 4 × 16 cm specimens; and (iii) uniaxial compression on the half prisms of the flexural test specimens (4 × 4 × 8 cm). The piezoresistive behavior of the mortars reinforced with the pristine MWCNTs was experimentally determined using the 4-pole method, and compared with the strain sensing ability of the mortars reinforced with the functionalized MWCNTs. All MWCNT reinforced mortars exhibit a remarkable enhancement in the mechanical properties. However, the 28d flexural strength, young's modulus and energy absorption capability of the mortars reinforced with the mechanically functionalized MWCNTs at an amount of 0.1 wt% increased by 120%, 124%, and 103% respectively. Finally, depending on the procedure of the functionalization, chemical or mechanical, a different effect on the intrinsic properties of MWCNTs was observed. The carboxylic groups attached to the surface of the chemically functionalized MWCNTs indeed provided them with the ability of a uniform and effective dispersion, without the need of a sonication procedure. On the other hand, it was found that functionalized MWCNTs do not always retain the electrical properties of pristine MWCNTs.

An enhancement of mechanical and rheological properties of magnetorheological elastomer with multiwall carbon nanotubes

In this work, a new type of magnetorheological elastomer, which is reinforced by carbon nanotubes, is fabricated and its material properties are experimentally investigated. In order to achieve this goal, as a first step, different types of multiwall carbon nanotubes are incorporated into a series of natural rubber–based magnetorheological elastomers as additives. Several experimental instruments such as X-ray diffractometer, thermogravimetric analysis, and differential scanning calorimetry are utilized. From the test, several salient properties of the proposed magnetorheological elastomer are observed or/and characterized. The results indicate that the interaction between natural rubber–based magnetorheological elastomers and multiwall carbon nanotubes can provide significant improvement in mechanical and rheological properties. More specifically, it is observed that mechanical properties such as tensile strength are enhanced up to 11% by the functionalized multiwall carbon nanotube. It is also found that the field-dependent storage and loss moduli of the proposed magnetorheological elastomer samples are increased compared to magnetorheological elastomer without multiwall carbon nanotube. It is finally identified that magnetorheological efficiency, which indicates force controllability by the magnetic field, of the proposed magnetorheological elastomer samples is consistent with the increased operating frequency. Therefore, it is expected that the results of morphological, thermal, and rheological properties parallel to incorporation of multiwall carbon nanotubes into magnetorheological elastomers are effectively used for proper selection of magnetorheological elastomer applications.

Ice as a Green-Structure-Directing Agent in the Synthesis of Macroporous MWCNTs and Chondroitin Sulphate Composites.

The incorporation of multi-walled carbon nanotubes (MWCNTs) into chondroitin sulphate-based scaffolds and the effect on the structural, mechanical, conductive, and thermal properties of the resulting scaffolds is investigated. Three-dimensional hierarchical materials are prepared upon the application of the ice segregation-induced self-assembly (ISISA) process. The use of ice as structure-directing agents avoids chemicals typically used for this purpose (e.g., surfactants, block copolymers, etc.), hence, emphasising the green features of this soft-templating approach. We determine the critical parameters that control the morphology of the scaffolds formed upon ice-templating (i.e., MWCNTs type, freezing conditions, polymer and MWCNT concentration). MWCNTs are surface functionalized by acidic treatment. MWCNT functionalization is characterized by Raman, Fourier transfer infrared (FTIR) and X-ray Photoelectron (XPS) spectroscopies. Scanning electron microscopy (SEM) analysis and porosity studies reveal that MWCNT content modifies the morphology of the macroporous structure, which decreases by increasing MWCNT concentration. Differences in scaffold morphology should be translated into their conductivity and mechanical properties. As a general trend, the Young’s modulus and the electrical conductivity of the scaffolds increase with the MWCNT content. Preliminary biocompatibility tests with human osteoblast-like cells also reveal the capability of these structures to support cell growth.

Evaluation of multiwalled carbon nanotube cytotoxicity in cultures of human brain microvascular endothelial cells grown on plastic or basement membrane

There is a growing interest in the use of multiwalled carbon nanotubes (MWCNTs) to treat diseases of the brain. Little is known about the effects of MWCNTs on human brain microvascular endothelial cells (HBMECs), which make up the blood vessels in the brain. In our studies, we evaluate the cytotoxicity of MWCNTs and acid oxidized MWNCTs, with or without a phospholipid-polyethylene glycol coating. We determined the cytotoxic effects of MWCNTs on both tissue-mimicking cultures of HBMECs grown on basement membrane and on monolayer cultures of HBMECs grown on plastic. We also evaluated the effects of MWCNT exposure on the capacity of HBMECs to form rings after plating on basement membrane, a commonly used assay to evaluate angiogenesis. We show that tissue-mimicking cultures of HBMECs are less sensitive to all types of MWCNTs than monolayer cultures of HBMECs. Furthermore, we found that MWCNTs have little impact on the capacity of HBMECs to form rings. Our results indicate that relative cytotoxicity of MWCNTs is significantly affected by the type of cell culture model used for testing, and supports further research into the use of tissue-mimicking endothelial cell culture models to help bridge the gap between in vitro and in vivo toxicology.

Unzipping of multi-wall carbon nanotubes with different diameter distributions: Effect on few-layer graphene oxide obtention

Few-layer graphene oxide (FLGO) was obtained by chemical unzipping of multi-wall carbon nanotubes (MWCNT) of different diameter distributions. MWCNT were synthesized by catalytic decomposition of methane using Fe‐Mo/MgO catalysts. The variation in the Fe/Mo ratio (1, 2 and 5) was very influential in MWCNT diameter distribution and type of MWCNT obtained, including textural, chemical, structural and morphological characteristics. MWCNT diameter distribution and surface defects content had a profound impact on the characteristics of the resulting FLGO. Thus, MWCNT obtained with the catalyst with a Fe/Mo: 5 and presenting a narrow diameter distribution centered at 8.6±3.3nm led to FLGO maintaining non-oxidized graphite stacking (according to XRD analysis), lower specific surface area and higher thermostability as compared to FLGO obtained from MWCNT showing wider diameter distributions. The presence of more oxygen-containing functionalities and structural defects in large diameter nanotubes promotes the intercalation of species towards the inner layers of the nanotube, resulting in an enhanced MWCNT oxidation and opening into FLGO, what improves both micro- and mesoporosity.

Interaction of carbon nanotubes coatings with titanium substrate

The aim of this study was to evaluate the impact of multi-walled carbon nanotubes (MWCNTs) after chemical surface functionalization on the interaction with a titanium surface. Two kinds of MWCNTs differing in terms of concentration of functional groups were deposited on the Ti surface using the electrophoretic deposition method (EPD). The study has shown the detailed analysis of the physicochemical properties of this form of carbon nanomaterial and received on their base coatings using various techniques, such as scanning electron microscopy (SEM), confocal microscopy, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The adhesion of the MWCNTs coatings to the Ti surface was determined using the shear test method, according to standard ASTM F-1044-05. These results indicated that one type of MWCNTs characterized by a higher concentration of functional groups has better adhesion to the metal surface than the second type. Analysis of the MWCNT–metal interface using Raman spectroscopy and SEM and STEM indicates the presence of phase built of MWCNT and TiO2. This phase could be a type of nanocomposite that affects the improvement of the adhesion of MWCNT to the Ti surface.

Evaluating Hydrogen Uptake for Two Types of Multi-Wall Carbon Nanotubes from Nitrogen Adsorption/Desorption Data

Two types of multi-wall carbon nanotubes (MWCNT) were studied by low temperature nitrogen adsorption method. Pore size distribution was calculated using non local density functional theory (NLDFT) and Barrett-Joyner-Halenda (BJH) models. The peaks on pore size distribution were attributed to MWCNT with different diameters. Maximum hydrogen uptake by weight was evaluated for both samples and do not exceed 5 % even for the sample with higher specific surface area.

Use of Carbon Nanotubes to Improve Fracture Toughness of Polymer Concrete

Bridge deck overlays often require materials that are durable and easy to apply and that have a long fatigue life. In many applications, polymer concrete (PC) has been chosen not only because it meets such requirements but also because it offers additional features such as high friction. However, the service life of PC overlays is reduced, and cracking occurs because of the continuous increase in traffic loads. This paper investigates the use of multiwalled carbon nanotubes (MWCNTs) to improve the fracture toughness and fatigue service life of PC. Pristine MWCNTs (P-MWCNTs) and MWCNTs functionalized with carboxyl (COOH-MWCNTs) were used at 0.0- (neat), 0.5-, 1.0-, 1.5-, and 2.0-wt.% contents. Three-point bending tests of notched beams were carried out in which the loading rate was controlled by crack mouth opening displacement. Direct tension tests were also used to examine the effect of MWCNTs on the tensile properties of PC. The results showed that MWCNTs improved the fracture toughness of PC by up to 56% and 112% for P-MWCNTs and COOH-MWCNTs, respectively. Samples prepared with P-MWCNTs showed increased ductility; samples with COOH-MWCNTs provided increased tensile strength. Microstructural analysis with a scanning electron microscope and Fourier transform infrared spectroscopy revealed how different types of MWCNTs at different weight contents influenced the behavior of PC.