Introducing Carbon Nanotubes (CNTs)

This work presents chemical functionalization of multi-walled carbon nano tubes (MWCNTs) through chemical modifications. Antibacterial conjugated MWCNTs were synthesized involving the sequential steps of carboxylation. Formation of the active intermediates using Hydroxy benzo triazole (HOBt) was done in order to achieve conjugated 2-mercapto benzo imidazole (MWCNT-h) as the final compound. The modification of MWCNTs with antibacterial drug was checked by Fourier transform-infrared spectroscopy, Raman spectroscopy and Thermo gravimetric analysis. Size and surface characteristics of chemically modified MWCNTs were monitored by scanning electron microscopy and Atomic Force Microscope (AFM). Minimal Inhibitory Concentration (MIC) and Antimicrobial activity of functionalized and carboxyl MWCNTs was studied on two Gram-negative bacteria as well as one Gram positive bacteria. The MIC results show that functionalized MWCNTs with anti-bacterial drugs have more effective results than bare drug and carboxyl MWCNTs individually against all studied bacteria.

ABSTRACTThe carbon nanotubes (CNTs) and CNTs doping with Fe based composites were rapid fabricated by gaseous detonation decomposition of oxygen, benzene and ferrocene mixed precursors. A series of novel experiments were designed to investigate the condensation and formation of carbon structural nanomaterials. The TEM, EDS, EDX, XRD and Raman characterizations provide fundamental evidence of the high yield and purity of the CNTs, CNTs doping with Fe composites during the gaseous detonation reaction process. The results showed that CNTs, CNTs with Fe based nanocrystals, spherical CCFNPs and their mixed products are with variant morphologies. The obtained CNTs is multi-walled carbon nanotubes and CNTs doping with a body-centered cubic iron or iron carbide cores, which can be obtained respectively through adjusting and controlling the detonation reaction environment and the precursors.

<p>Carbon nanotubes (CNTs) are a group of pure carbon solid materials that possess one-dimensional structures with diameters down to less than one nanometre. They have interesting physical properties such as very high tensile strength, metallic and semiconducting conductivity, and great potential for applications. This work investigates the synthesis, alignment and purification of multi-walled carbon nanotubes, which were characterized by Electron Microscopy, measurement of electrical properties and Raman scattering. Synthesis of multi-walled carbon nanotubes (MWNTs) was carried out by Chemical Vapour Deposition, using three different precursors: Fe(NO3)3, ferrocene and iron phthalocyanine. Vertically aligned "forests" of large numbers of MWNTs were achieved using ferrocene and iron phthalocyanine as precursors. Products from iron phthalocyanine yield more graphitic CNT nanostructures, as determined by Scanning Electron Microscopy, Transmission Electron Microscopy, Thermogravity Analysis, Raman microscopy and Energy Dispersive X-ray spectroscopy. Patterned growth of vertical MWNTs arrays with a resolution of 2 microns was also obtained, using a predeposited substrate. A High Resolution Transmission Electron Microscope was employed to investigate the inner structures of individual MWNTs, giving well-resolved images of concentric nanostructures with inter-lattice spacings of 0.34 nm. Techniques for purification and manipulation of CNTs are required before CNTs' excellent properties can be exploited. In this thesis, dielectrophoresis (DEP) under high-frequency AC voltages using an array of micron-scale electrodes was adopted as the technique to align MWNTs between these, electrodes. This technique is effective for MWNTs since their long cylindrical structure and the high mobility of their charge carriers allow them to be electrically polarised. As a result, MWNTs experience large DEP forces in an AC electric field. In our experiments, inter-digitated electrodes were used to apply the electric field to CNT suspensions in various solvents. Alignment of CNTs along their axis was achieved within the gaps between adjacent electrodes at a frequency larger than 1.1 MHz, The AC admittance changes between the electrodes were monitored and were observed to be a clear reflection of the accumulation process of MWNTs. Also it was identified that distilled water was a better solvent than ethanol and isopropanol for DEP purpose on MWNTs. In addition, a prototype device was built to selectively purify MWNTs from as-grown samples by combining DEP and re-circulating fluid flow. It was found that this device is able to decrease the impurity content of MWNTs, which is collected on the electrode array, from the suspension of as-grown samples.</p>

Perovskite solar cells (PSCs) made with metal halide are affordable and can give better efficiency values than older versions but their low efficiency values is still a concern. Two Perovskite solar cells were fabricated and one had Multi wall Carbon nanotube (MWCNT) in its design. The effect of the Multi-wall Carbon nanotube (MWCNT) on their performance and power conversion were studied. MWCNT and m-TiO2 materials were characterised using UV-vis spectroscopy and their optical energy band gap values were obtained. The TiO2 showed a prominent peak at 319 nm with absorbance 0.5 and its optical energy bandgap of 2.59 eV falls in the visible region showing it is a clean energy source with implications for solar energy conversion. The MWCNT has 2.19 eV and showed multiple peaks. A prominent peak at 329 nm with absorbance 0.6 which was blue shifted and a peak at 517 nm with absorbance 0.3 was red-shifted. The PSC with the MWCNT in the light had a fill factor of 0.53 but 0.47 was obtained for the PSC without the MWCNT. The PSC with MWCNT had power conversion efficiency (PCE) of 40.1 % in the dark, a value which was 2.7 % higher than the PCE of 37.4 % obtained for the same cell in light. Furthermore, the PSC without the MWCNT in the dark had a fill factor of 0.87 while the PSC with MWCNT in the dark had a fill factor was 0.51. The PSC with MWCNT had better power conversion efficiency when in the dark than in light.

The preparation and characterization of the nanocomposite polyelectrolyte membranes, based on Nafion, sulfonated multi‐walled carbon nanotubes (MWCNT‐SO3H) and imidazole modified multi‐walled carbon nanotubes (MWCNT‐Im), for direct methanol fuel cell applications is described. The results showed that the modification of multi‐walled carbon nanotubes (MWCNT) with proton‐conducting groups (sulfonic acid groups or imidazole groups) could enhance the proton conductivity of the nanocomposite membranes in comparison to Nafion 117. Regarding the interactions between the protonated imidazole groups, grafted on the surface of MWCNT, and the negatively charged sulfonic acid groups of Nafion, new electrostatic interactions can be formed in the interface of the Nafion and MWCNT‐Im, which result in both lower methanol permeability and higher proton conductivity. The physical characteristics of these manufactured nanocomposite membranes were investigated by thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, water uptake, methanol permeability, and ion exchange capacity, as well as proton conductivity. The Nafion/MWCNT‐Im membranes showed the higher proton conductivity, lower methanol permeability, and, as a consequence, a higher selectivity parameter in comparison to the neat Nafion or Nafion membrane containing MWCNT‐SO3H or ─OH functionalized multi‐walled carbon nanotubes (MWCNT‐OH) membranes. The obtained results indicated that the Nafion/MWCNT‐Im membranes could be used as efficient polyelectrolyte membranes for direct methanol fuel cell applications.

Nanofillers of type carbon nanotubes (CNTs) were investigated as reinforcing agents in silicone rubber matrix. Two types of CNT, namely, single-wall CNTs (SWCNTs) and multiwall CNTs (MWCNTs), were tested as reinforcing agents in rubber matrix. These CNTs were characterized with different purity, morphology, and sonication treatment (MWCNTs). Rubber nanocomposites were prepared by mixing room temperature vulcanized (RTV) silicone rubber with CNTs. At a filler loading of 3 phr, the modulus increased by 190% for specimens with MWCNTs and 150% for specimens filled with SWCNTs. Sonication was used to de-bundle the MWCNT aggregates into individual particles and to improve filler dispersion in the rubber matrix. The resistance of the MWCNTs was almost 750 times lower than that of the SWCNTs at 3 phr. The sonicated MWCNTs (2.2 kΩ) show lower electrical resistance than the pristine MWCNTs (3 kΩ) at 2 phr. These improvements could be useful for new devices such as flexible electrodes or actuators.

BackgroundIn vitro models are widely used in nanotoxicology. In these assays, a careful documentation of the fraction of nanomaterials that reaches the cells, i.e. the in vitro delivered dose, is a critical element for the interpretation of the data. The in vitro delivered dose can be measured by quantifying the amount of material in contact with the cells, or can be estimated by applying particokinetic models. For carbon nanotubes (CNTs), the determination of the in vitro delivered dose is not evident because their quantification in biological matrices is difficult, and particokinetic models are not adapted to high aspect ratio materials. Here, we applied a rapid and direct approach, based on femtosecond pulsed laser microscopy (FPLM), to assess the in vitro delivered dose of multi-walled CNTs (MWCNTs).Methods and resultsWe incubated mouse lung fibroblasts (MLg) and differentiated human monocytic cells (THP-1) in 96-well plates for 24 h with a set of different MWCNTs. The cytotoxic response to the MWCNTs was evaluated using the WST-1 assay in both cell lines, and the pro-inflammatory response was determined by measuring the release of IL-1β by THP-1 cells. Contrasting cell responses were observed across the MWCNTs. The sedimentation rate of the different MWCNTs was assessed by monitoring turbidity decay with time in cell culture medium. These turbidity measurements revealed some differences among the MWCNT samples which, however, did not parallel the contrasting cell responses. FPLM measurements in cell culture wells revealed that the in vitro delivered MWCNT dose did not parallel sedimentation data, and suggested that cultured cells contributed to set up the delivered dose. The FPLM data allowed, for each MWCNT sample, an adjustment of the measured cytotoxicity and IL-1β responses to the delivered doses. This adjusted in vitro activity led to another toxicity ranking of the MWCNT samples as compared to the unadjusted activities. In macrophages, this adjusted ranking was consistent with existing knowledge on the impact of surface MWCNT functionalization on cytotoxicity, and might better reflect the intrinsic activity of the MWCNT samples.ConclusionThe present study further highlights the need to estimate the in vitro delivered dose in cell culture experiments with nanomaterials. The FPLM measurement of the in vitro delivered dose of MWCNTs can enrich experimental results, and may refine our understanding of their interactions with cells.

Precise assembly of carbon nanotubes (CNTs) in arbitrary 3D space with proper alignment is critically important and desirable for CNT applications but still remains as a long-standing challenge. Using the two-photon polymerization (TPP) technique, it is possible to fabricate 3D micro/nanoscale CNT/polymer architectures with proper CNT alignments in desired directions, which is expected to enable a broad range of applications of CNTs in functional devices. To unleash the full potential of CNTs, it is strategically important to develop TPP-compatible resins with high CNT concentrations for precise assembly of CNTs into 3D micro/nanostructures for functional device applications. We investigated a thiol grafting method in functionalizing multiwalled carbon nanotubes (MWNTs) to develop TPP-compatible MWNT-thiol-acrylate (MTA) composite resins. The composite resins developed had high MWNT concentrations up to 0.2 wt%, over one order of magnitude higher than previously published work. Significantly enhanced electrical and mechanical properties of the 3D micro/nanostructures were achieved. Precisely controlled MWNT assembly and strong anisotropic effects were confirmed. Microelectronic devices made of the MTA composite polymer were demonstrated. The nanofabrication method can achieve controlled assembly of MWNTs in 3D micro/nanostructures, enabling a broad range of CNT applications, including 3D electronics, integrated photonics, and micro/nanoelectromechanical systems (MEMS/NEMS).

Multi-walled carbon nanotubes have been synthesized by Aerosol-Chemical Vapor Deposition method. Carbon nanotubes firstly have been used as filler in affordable and prevalent natural Azerbaijani bentonite clays for fabrication electroconductive ceramic composites. In this paper, multi-walled carbon nanotubes/natural Azerbaijani bentonite ceramic composites were prepared by two-factor mechanical method and followed by calcination at 1050℃ in an inert atmosphere. The ceramic composites were characterized by scanning electron microscope, atomic force microscope, X-ray diffraction and thermogravimetric-differential-thermal analysis. X-ray diffraction analysis confirmed the presence of two principal components – multi-walled carbon nanotube and bentonite in composites. From the thermogravimetric-differential-thermal data, it was revealed that multi-walled carbon nanotube/ bentonite ceramic composites demonstrate thermo-oxidative stability up to 580–640℃. Scanning electron microscope images demonstrated a sufficiently high dispersibility of carbon nanotubes and satisfactory homogeneity in the composites. Experimental results demonstrated that by increasing the mass fraction of multi-walled carbon nanotubes from 1% to 8% in multi-walled carbon nanotube/bentonite ceramic composites, the electrical conductivity enhances substantially. The enhancement of electrical conductivity of the composites explained the mass fraction of multi-walled carbon nanotubes, as well as the uniform dispersion of multi-walled carbon nanotubes in the bentonite clays. Compared with other 8% multi-walled carbon nanotubes/bentonite ceramic composites, the electrical conductivity of heptane-multi-walled carbon nanotube/Gobu bentonite (σ = 397 S·m−1) and heptane-multi-walled carbon nanotubes/Atyali (σ = 305 S·m−1) composites is 2–5 times higher than the conductivity of composites obtained with cyclohexane carbon nanotubes- cyclohexane-multi-walled carbon nanotube/Atyali (σ = 78 S·m−1), cyclohexane-multi-walled carbon nanotube/Gobu (σ = 111,5 S·m−1). These results can be explained with the structure, the number of layers, purity and diameter distribution, as well as the type and amount of defects in internal and external layers of Hep-multi-walled carbon nanotubes which cause better dispersion in bentonite clays. Due to the high conductivity and high temperature stability, these composites can be used as promising material for fabrication heating elements, electrodes, substrates for microelectronic devices, etc.

Carbon nanotubes (CNTs) have been widely investigated as one of the most promising nanomaterials in biomedical applications. Functionalization of CNTs with poly(ethylene glycol) diamine (PEG) is a recognized methodology with good solubility and biocompatibility. In this study, PEG conjugated (PEGylated) multi-walled CNTs (MWCNTs) were prepared and labeled with fluorophore FITC. Using fluorophore-conjugated PEGylated MWCNTs, we monitored their accumulation in transformed cancer cells and in normal cells. The intracellular accumulation of PEGylated MWCNTs was studied under confocal microscope and transmission electron microscope. At the same concentration and exposure time, PEGylated MWCNTs entered all three of the cancer cell lines tested much more efficiently than the three primary human fibroblast lines. This different cell-penetration efficiency was observed both in separate cell culture separate exposure conditions and in co-culture and co-exposure conditions. This study highlights that the cell-penetration efficiency of PEGylated MWCNTs is dependent on cell types, and possibly due to different metabolic rates in different cell types. Furthermore, the intracellular accumulation of PEGylated MWCNTs did not impair membrane integrity, and the treated cells remained normal morphology, indicating good biocompatibility of PEGylated MWCNTs. This study suggests that PEGylated MWCNTs can be developed as potential drug carrier with its intrinsic higher preference to tumor cells than normal cells.

A variety of outstanding experimental results on mechanical properties of carbon nanotube (CNT) are fast appearing. Nevertheless, mechanical properties of CNT have been rarely understood because of measurement difficulties. The response of multi walled carbon nanotube (MWNT) to mechanical strain applied with a nano-manipulator was investigated inside scanning electron microscope (SEM). MWNTs were produced by arc-discharge method and the protruded sample for tensile test was selected among the MWNTs fragment which has rectilinearity and purity above 40%. The average diameter of MWNT was approximately 15nm. In order to measure the resistance of a MWNT during tensile test, an individual MIWNT was attached at the tungsten (W) tip using electron beam induced deposition. We confirmed that the contact resistance between a MWNT and the W tip decrease during the exposure of electron beam. And then the W tip were manipulated and controlled by nano-manipulator and personal computer. We observed that resistance of sample was significantly changed until the MWNT fracture.

Carbon nanotubes (CNTs) are promising nanomaterials for the preparation of nanohybrids and nanocomposites with polymers. In the preparation processes, surface modification and functionalization of CNTs have key roles to enhance the compatibility in organic solvents or water for solution processing routes; furthermore, they improve the interfacial compatibility between CNTs and the polymer matrix to avoid CNT aggregation in CNT/polymer nanocomposites. Hence, we have developed three approaches for directly reacting chemical agents and polymer chains with multi-walled CNTs (MWCNTs). The methods are: (i) sequential atom transfer radical addition to MWCNTs, which conveniently builds up polymer architectures on MWCNT surfaces; (ii) ozone-mediated addition reaction, which effectively chemically bonds non-reactive polymer chains to MWCNTs; and (iii) Diels–Alder reaction-mediated MWCNT functionalization, which achieves thermally reversible functionalization/de-functionalization of MWCNTs. On the basis of the new reaction routes, the scopes of nanohybrids and nanocomposites of MWCNT/polymers and their properties and functions have been significantly enhanced and extended. Some examples are discussed in this review. Three approaches for directly reacting chemical agents and polymer chains with multi-walled CNTs (MWCNTs) are presented, including (i) sequential atom transfer radical addition/polymerization to MWCNTs; (ii) ozone-mediated addition reaction to MWCNTs; and (iii) Diels–Alder reaction-mediated MWCNT functionalization. On the basis of the reaction routes, the scopes and functions of MWCNT-based nanohybrids and nanocomposites have been extended.

Microstructure and mechanical properties of multi-walled carbon nanotubes containing Al2O3–C refractories with addition of polycarbosilane

This chapter discusses about the behavior of Carbon Nanotube (CNT) different structures which can be used as interconnect in Very Large Scale (VLSI) circuits in nanoscale regime. Also interconnect challenges in VLSI circuits which lead to use CNT as interconnect instead of Cu, is reviewed. CNTs are classified into three main types including Single-walled Carbon Nanotube (SWCNT), CNT Bundle, and Multi-walled Carbon Nanotube (MWCNT). Because of extremely high quantum resistance of a SWCNT which is about 6.45 kΩ, rope or bundle of CNTs are used which consist of parallel CNTs in order to overcome the high delay time due to the high intrinsic (quantum) resistance. Also MWCNTs which consist of parallel shells, present much less delay time with respect to SWCNTs, for the application as interconnects. In this chapter, first a short discussion about interconnect challenges in VLSI circuits is presented. Then the repeater insertion technique for the delay reduction in the global interconnects will be studied. After that, the parameters and circuit model of a CNT will be discussed. Then a brief review about the different structures of CNT interconnects including CNT bundle and MWCNT will be presented. At the continuation, the time domain behavior of a CNT bundle interconnect in a driver-CNT bundle-load configuration will be discussed and analyzed. In this analysis, CNT bundle is modeled as a transmission line circuit model. At the end, a brief study of stability analysis in CNT interconnects will be presented.

Carbon nanotubes represent a creative alternative for applications in medicine as therapeutic vectors, imaging and controlled release of active molecules. Although the low density and small size of carbon nanotubes makes respiratory exposures to workers likely during the production or use of commercial products, the potential genotoxicity of multi-walled carbon nanotubes has not been investigated. We have previously shown mitotic spindle aberrations in cultured primary and immortalized human airway epithelial cells exposed to single-walled carbon nanotubes (SWCNT). In order to investigate whether genetic damage was unique to SWCNT, we examined mitotic spindle aberrations following dosing of cells to multi-walled carbon nanotubes (MWCNT) at concentrations anticipated in the workplace. Immortalized and primary respiratory epithelial cells were exposed to 0.024, 0.24, 2.4, and 24μg/cm2 carbon nanotubes. The minimal dose of MWCNT considered for this research was based on the permissible exposure limit for particles with an aerodynamic diameter of less than 5 microns (Occupation Safety and Health Administration). MWCNT induced a dose response of disrupted centrosomes, mitotic spindles and aneuploid chromosome number. The data further showed that monopolar mitotic spindles comprised 95% of the disrupted mitoses. The monopolar phenotype of the disrupted mitotic spindles is in sharp contrast to the multi-polar spindle of SWCNT-induced disruption. Three-dimensional reconstructions showed carbon nanotubes integrated with the microtubules, the DNA and within the centrosome structure. The lower doses did not cause cytotoxicity or apoptosis 24 hours after exposure; however, after 72 hours, significant cytotoxicity was observed in the MWCNT-exposed cells. Disruption of the centrosome is common in many solid tumors including lung cancer. The resulting aneuploidy is a key event in the progression of cancer and is correlated with tumor stage. Our results demonstrate significant disruption of the mitotic spindle by MWCNT at occupationally relevant doses. These results suggest caution should be used in the handling and processing of carbon nanotubes. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5464. doi:1538-7445.AM2012-5464