Carbon Nanotubes In Terms Research Articles

Antimicrobial Properties of Carbon Nanotube: A Succinct Assessment

Carbon nanotubes (CNTs) particularly single-walled carbon nanotubes (SWNT) have been used in pharmacy and medicine for drug delivery systems in therapeutics since the beginning of the twenty-first century. Because carbon nanotubes have demonstrated the ability to transport a wide range of chemicals across membranes and into living cells, they have piqued interest in medicinal applications, such as improved imaging, antimicrobial agents, tissue regeneration, and medication or gene delivery. Despite the abundance of evidence demonstrating the benefits of CNTs in terms of higher efficacy and fewer side effects, numerous recent studies have revealed unanticipated toxicities caused by CNTs. CNTs have recently gained a lot of attention for their antibacterial properties. The antimicrobial properties of carbon nanotubes, as well as their toxicity, are summarized and discussed in this mini review.

Torsional Properties of Bundles with Randomly Packed Carbon Nanotubes.

Carbon nanotube (CNT) bundles/fibers possess promising applications in broad fields, such as artificial muscles and flexible electronics, due to their excellent mechanical properties. The as-prepared CNT bundles contain complex structural features (e.g., different alignments and components), which makes it challenging to predict their mechanical performance. Through in silico studies, this work assessed the torsional performance of CNT bundles with randomly packed CNTs. It is found that CNT bundles with varying constituent CNTs in terms of chirality and diameter exhibit remarkably different torsional properties. Specifically, CNT bundles consisting of CNTs with a relatively large diameter ratio possess lower gravimetric energy density and elastic limit than their counterpart with a small diameter ratio. More importantly, CNT bundles with the same constituent CNTs but different packing morphologies can yield strong variation in their torsional properties, e.g., up to 30%, 16% and 19% difference in terms of gravimetric energy density, elastic limit and elastic constants, respectively. In addition, the separate fracture of the inner and outer walls of double-walled CNTs is found to suppress the gravimetric energy density and elastic limit of their corresponding bundles. These findings partially explain why the experimentally measured mechanical properties of CNT bundles vary from each other, which could benefit the design and fabrication of high-performance CNT bundles.

Interplay Between Competition Pinch Effect and Repulsion Force in Carbon Nanotubes

One of the important phenomena influencing the resistivity behavior of nanotubes based on the change of their radius is a physical effect called “pinch effect”. In this paper, according to the experimental results, the electrical resistivity behavior of carbon nanotubes is modeled as a function of the radius in the radius range of 3–10[Formula: see text]nm. The pinch effect is not observed for weak current, but if the radius of carbon nanotube is very small, this effect will be considerable and affects carbon nanotube resistivity. The deviations observed in [Formula: see text]–[Formula: see text] (resistivity as a function of nanotube radius) diagrams for individual carbon nanotube are justified with different parameters such as pinch effect phenomenon. The results show an acceptable theoretical model for the behavior of electrical resistivity relative to radius reduction. The theory diagram of the electrical resistivity behavior of carbon nanotubes in terms of radius reduction is predicted in very small radii. These results are consistent with the experimental results. It is consistent and generalizable.

Experimental study of thiophene and ferrocene in synthesis of single-walled carbon nanotubes in rich premixed hydrogen/air flames

The effects of varying concentrations of ferrocene and thiophene on the synthesis of carbon nanotubes (CNT) in a floating catalyst, flame-based reaction system were investigated. Pre-vapourised ethanol and a surrounding premixed H2/air flame were used as carbon feedstock and heat source. Samples of the synthesised material were collected and analysed using Raman spectroscopy, scanning electron microscopy, transmission electron microscopy and X-ray diffraction to determine their compostitions and properties. Sulphur to iron mass ratios mS/Fe were varied from 0 up to 10.1, by changing the relative amounts of thiophene and ferrocene. The latter was found to marginally improve the yield of CNTs, but rather led to an enhanced yield of iron oxide nanoparticles. In comparison, the addition of sulphur resulted in an improved production of CNTs in terms of number density and lengths. An optimum window of mass ratios mS/Fe for CNT production was identified as 0.1–2. A numerical model for the diffusion of species coupled with an equilibrium chemical model for the resulting species has been constructed to understand the mechanisms of the synthesis process, which demonstrates the range of elemental proportion conditions and residence times favourable to high yield of CNTs.

Silica nanospheres as a key process element in the Green engineering for the synthesis of carbon nanotubes as a supercapacitors additives

In our study, we got carbon nanotubes by the Green engineering method. In this approach, the key element is silica nanospheres, that act as a catalyst carriers, prepared from the recycled ethanol-ammonia solution and copper wire from used cables. We used copper wires as a source of metal ions that were adsorbed by the silica nanospheres and then serve as a catalyst. Copper particles after synthesis of carbon nanotubes were reused for synthesis of new carbon nanotubes after re-deposition on pristine silica particles. The second material recovered from the waste cable was a polymer sheath, which at high temperature can served as a carbon source in carbon nanotubes growth. Ethanol was main source of carbon used for the chemical vapor deposition process. The synthesized carbon nanotubes were compared to commercial carbon nanotubes in terms of their electrochemical properties when used as a conductive material in supercapacitors electrodes.

Carbon based copper(II) phthalocyanine catalysts for electrochemical CO2 reduction: Effect of carbon support on electrocatalytic activity

Carbon-metal hybrid materials have shown promising performance as electrocatalysts for CO2 reduction. Here, a comparative study of how different carbons supports influence this reaction is presented. The tested carbon supports were graphene oxide, multi-walled carbon nanotubes, carbon black and activated carbon while the metal complex selected was copper(II) phthalocyanine (CuPc). The CuPc supported on carbon nanotubes (CNT) and carbon black were found to give higher faradaic efficiencies (FE) for reduced carbon products, i.e. 66.3% and 81.8%, respectively compared to graphene oxide (0.0%) and activated carbon (12.8%). Amongst various sizes of CNT, long and thin tubes (in the range of 10–30 nm diameter size, 10–30 μm length) demonstrated higher FE (66.3%) relative to shorter and thicker ones (7.4%). Additionally, the novel use of CNT synthesized from post-consumer plastic waste was also explored as a potential carbon support material. It demonstrated comparable performance to commercial CNT in terms of FE (70.4%).

Micromechanical modeling and characterization of elastic behavior of carbon nanotube‐reinforced polymer nanocomposites: A combined numerical approach and experimental verification

AbstractIn this study, a combined analytical and finite element‐based micromechanical modeling is performed to characterize the elastic properties of carbon nanotube (CNT) reinforced polymer nanocomposites and validated with experimental work. First, coordinates of armchair and zigzag type CNTs are generated using MATLAB based on the geometric structure of the CNTs and imported to the computational software ANSYS to model and characterize the elastic properties of the individual single‐walled CNT (SWCNT) and multi‐walled CNT by applying various loading and boundary conditions. The present developed finite element method (FEM) model of CNTs is validated with the available literature in terms of elastic properties. Subsequently, the equivalent elastic properties of CNT reinforced epoxy nanocomposites are determined through representative volume element (RVE) model by finite element simulations and Mori‐Tanaka homogenization techniques by replacing CNTs with equivalent fibers as microinclusions. The equivalent elastic properties of nanocomposite obtained by the FEM and analytical model are compared and validated with the experimental results. Further, the detailed parametric study is performed to investigate the influence of tube chirality, volume fraction, and orientation of CNT in terms of the elastic properties of the nanocomposite. It was observed that the armchair type CNT reinforced nanocomposites are stiffer than the zigzag type SWCNT reinforced nanocomposites in terms of elastic moduli. Further, it was noticed that the tube chirality and the number of walls of CNTs have significantly influenced the elastic behavior of nanocomposites. It can be concluded that the presented combined model provides an efficient methodology and comprehensive understanding to analyze the elastic behavior of CNTs and CNT reinforced nanocomposites. So, the presented combined numerical and experimental study could serve as a guideline in micromechanical modeling and characterization of elastic behavior of CNT‐reinforced polymer nanocomposites.

Enhancement in mechanical properties of polyamide 66-carbon fiber composites containing graphene oxide-carbon nanotube hybrid nanofillers synthesized through in situ interfacial polymerization

Polyamide 66 (PA66)/carbon fiber (CF) composites with acyl chloride-functionalized GO (AGO) and carbon nanotubes (CNTs) as hybrid fillers were prepared through in situ interfacial polymerization. The optimal ratio of AGO to CNTs in terms of hydrogen bonding in the composites was determined to be 2:1 via thermochemical analyses of the as-prepared PA66/AGO-CNT composites. The optimized hybrid filler-reinforced PA66/CF composites showed improvements in the interfacial shear strength, tensile strengh and storage modulus by 160, 136 and 300%, respectively, compared to the control sample, as well as high damping properties due to an enhanced transcrystalline interphase. The superior interfacial bonding between CF and PA66 is attributed to hydrogen bonding, enhanced dispersion, and the mechanical interlocking effect induced by AGO-CNT hybrids, which lead to effective energy absorption and load transfer.

Mechanical, Electrical, and Piezoresistive Sensing Characteristics of Epoxy-Based Composites Incorporating Hybridized Networks of Carbon Nanotubes, Graphene, Carbon Nanofibers, or Graphite Nanoplatelets.

The present study compared the mechanical, electrical, morphological, and piezoresistive characteristics of epoxy-based sensing nanocomposites fabricated with inclusions of hybridized networks of four different carbon nanomaterials (CNMs), such as carbon nanotube (CNT), graphene, carbon nanofiber (CNF), and graphite nanoplatelet (GNP). Enhancements in elastic modulus and electrical conductivity were achieved by CNT–graphene composites and CNT–CNF composites, and these were explained by the morphological observations carried out in the present study and experimental studies found in the literature. The greatest gauge factor was accomplished by the CNT–GNP composite, followed by the CNT–CNF composite among composites where the CNM networks were sufficiently formed with a content ratio of 3%. The two types of the composites outperformed the composites incorporating solely CNT in terms of gauge factor, and this superiority was explained with the excluded volume theory.

Structural, electronic, and optical properties of α-Te tubular nanostructures: A first-principles study

We employed density functional theory to investigate the structural, electronic, and optical properties of α-Te tubular nanostructures. These α-Te tube-like structures, which are similar to carbon nanotubes in terms of their armchair and zigzag structures, are semiconductors with moderate bandgaps. The nanotubes in armchair configurations have an indirect-to-direct bandgap transition as tube diameter is decreased to a specific critical tube size, while those in zigzag configurations are always semiconductors with a direct gap independent of tube diameter. The calculated projected density of states reveals that such an indirect-to-direct bandgap transition found in armchair nanotubes can be attributed to the contributions of the different p-orbitals near the valence band maximum edges. The optical absorption spectra of α-Te nanotubes are found to be anisotropic and vary with the tube diameters. These findings are not only helpful for better understanding the physical characteristics of α-Te nanotubes but also opening up new possibilities for use in device applications.

Advanced Nanoclay-Based Nanocomposite Solid Polymer Electrolyte for Lithium Iron Phosphate Batteries.

High-performance solid polymer electrolytes (SPEs) have long been desired for the next generation of lithium batteries. One of the most promising ways to improve the morphological and electrochemical properties of SPEs is the addition of fillers with specific nanostructures. However, the production of such fillers is generally expensive and requires complicated preparation procedures. Halloysite nanotubes (HNTs), with their tubular structure, resemble carbon nanotubes in terms of geometric features and can be obtained at a relatively low cost. Previously, we reported that the HNT poly(ethylene oxide) composite SPE possesses excellent electrochemical and mechanical properties and outstanding cycling performance for all-solid-state lithium sulfur batteries. However, the HNT/SPE was not effective for lithium iron phosphate (LFP) batteries. The compatibility between the electrodes and the electrolyte sharply decreased, and no decent cycling performance was achieved. Therefore, a modification was studied which involves a minor addition of LFP during the preparation procedure. With this modification, good ionic conductivity (9.23 × 10-5 S cm-1 at 25 °C) is achieved, and compatibility between the electrodes and the electrolyte is enhanced. At the same time, an electrochemical stability window of 5.14 V and lithium-ion transference number of 0.46 are found. All-solid-state LFP batteries possessing excellent cycling performance are further demonstrated.

Effect of Hybrid Carbon Fillers on the Electrical and Morphological Properties of Polystyrene Nanocomposites in Microinjection Molding

The effect of hybrid carbon fillers of multi-walled carbon nanotubes (CNT) and carbon black (CB) on the electrical and morphological properties of polystyrene (PS) nanocomposites were systematically investigated in microinjection molding (μIM). The polymer nanocomposites with three different filler concentrations (i.e., 3, 5 and 10 wt %) at various weight ratios of CNT/CB (100/0, 30/70, 50/50, 70/30, 0/100) were prepared by melt blending, then followed by μIM under a defined set of processing conditions. A rectangular mold insert which has three consecutive zones with decreasing thickness along the flow direction was adopted to study abrupt changes in mold geometry on the properties of resultant microparts. The distribution of carbon fillers within microparts was observed by scanning electron microscopy, which was correlated with electrical conductivity measurements. Results indicated that there is a flow-induced orientation of incorporated carbon fillers and this orientation increased with increasing shearing effect along the flow direction. High structure CB is found to be more effective than CNT in terms of enhancing the electrical conductivity, which was attributed to the good dispersion of CB in PS and their ability to form conductive networks via self-assembly. Morphology observations indicated that there is a shear-induced depletion of CB particles in the shear layer, which is due to the marked difference of shear rates between the shear and core layers of the molded microparts. Moreover, an annealing treatment is beneficial to enhance the electrical conductivity of CNT-containing microparts.

Single- and multi-walled carbon nanotubes for solar cell applications

Emerging nanotechnologies have revealed carbon nanotubes (CNTs) as one of the best materials with immense potential. Considering the outstanding physical, mechanical, electrochemical, thermal, and optoelectronic properties of CNTs, extensive studies have been reported assessing their applications in several disciplines. This paper presents a broad review of the studies in the literature that address the contribution of CNTs in terms of their applications as different parts of solar cells such as photoelectrode, photoconductor, top and back electrode, replacement of indium tin oxide (ITO) as transparent conducting electrode (TCE) in a variety of photovoltaics such as silicon, organic, polymer and dye-sensitized with their subsequent efficiencies.

Crack growth analysis of carbon nanotube reinforced polymer nanocomposite using extended finite element method

In this work, the crack growth analysis of carbon nanotube reinforced polymer nanocomposite has been performed using extended finite element method. The equivalent properties such as elastic modulus, Poisson’s ratio, fracture energy, and fracture toughness of the polymer nanocomposites have been evaluated by varying the percentage of carbon nanotube in terms of weight (both single-walled carbon nanotube and multi-walled carbon nanotube) in the polymer matrix. The elastic modulus of the polymer nanocomposite has been evaluated using modified Halpin–Tsai equation. The fracture energy of the polymer nanocomposite has been computed considering carbon nanotube pull-out and carbon nanotube debonding as the main toughening criterion. In the extended finite element method, the crack faces are modeled by discontinuous Heaviside jump functions, whereas the singularity in the stress field at the crack tip is modeled by crack tip enrichment functions. The value of stress intensity factor is evaluated using the domain form of interaction integral. The level set method has been used to track the crack growth. The numerical examples with an edge and a center crack in the polymer nanocomposite are analyzed and the influence of various parameters such as percentage of carbon nanotube and the aspect ratio on stress intensity factor are observed.

Diversity of Pd-Cu active sites supported on pristine carbon nanotubes in terms of water denitration structure sensitivity

Four Pd-Cu-based (2:1 wt.%) catalysts for water denitration, differing in physico-chemical characteristics and structural quality, were prepared, using carbon nanotubes (CNTs) as supports. The extent of lattice defects in the pristine CNTs turned out to govern resulting varieties of Pd nanoparticle size and the composition of the bimetallic (Pd:Cu) entities in the catalysts, playing an important role in nitrate reduction. Catalyst samples characterized by close proximity of Pd and Cu, as in an alloy, displayed the highest degree of nitrate conversion. At the same time, the size of the Pd particles, alone, or decorated to different extents with Cu atoms, was found to be critical for the second step of denitration reaction, directing the formed nitrite to either N2 or NH3. Water denitration is a structure sensitive reaction related to Pd particle size, and this effect is further emphasized in the decoration of the particle by the incorporation of Cu atoms into Pd particle corners and edges.

Development of Ni- and Fe- based catalysts with different metal particle sizes for the production of carbon nanotubes and hydrogen from thermo-chemical conversion of waste plastics

Co-production of valuable hydrogen and carbon nanotubes (CNTs) has obtained growing interest for the management of waste plastics through thermo-chemical conversion technology. Catalyst development is one of the key factors for this process to improve hydrogen production and the quality of CNTs. In this work, Ni/SiO2 and Fe/SiO2 catalysts with different metal particle sizes were investigated in relation to their performance on the production of hydrogen and CNTs from catalytic gasification of waste polypropylene, using a two-stage fixed-bed reaction system. The influences of the type of metals and the crystal size of metal particles on product yields and the production of CNTs in terms of morphology have been studied using a range of techniques; gas chromatography (GC); X-ray diffraction (XRD); temperature programme oxidation (TPO); scanning electron microscopy (SEM); transmission electron microscopy (TEM) etc. The results show that the Fe-based catalysts, in particular with large particle size (∼80nm), produced the highest yield of hydrogen (∼25.60mmol H2g−1 plastic) and the highest yield of carbons (29wt.%), as well as the largest fraction of graphite carbons (as obtained from TPO analysis of the reacted catalyst). Both Fe- and Ni-based catalysts with larger metal particles produced higher yield of hydrogen compared with the catalysts with smaller metal particles, respectively. Furthermore, the CNTs formed using the Ni/SiO2-S catalyst (with the smallest metal particles around 8nm) produced large amount of amorphous carbons, which are undesirable for the process of CNTs production.

Finite Element Evaluation of Effective Thermal Conductivity of Short Carbon Nano Tubes: A Comparative Study

In the current study, two extreme cases are considered for the dispersion of carbon nanotubes(CNTs) in a polymeric matrix: randomly-oriented and randomly-aligned. The representative volume element (RVE) is used to represent the composite material consisting of epoxy resin matrix and CNT-reinforcement. The finite element method acts as the computational tool to conduct the simulations and investigate the effective parameters, i.e., the influence of the aspect ratio and the orientation, on the thermal conductivity of the matrix. A Fortran subroutine was used for both generation and analysis of the models by means of the MSC Marc finite element package and a Python script was used for the sensitivity analysis. The results indicate that optimum performance of the CNTs in terms of thermal conductivity can be reached by orienting them along the temperature gradient whereas a random distribution improves the conductivity by a smaller magnitude.

A catechin nanoformulation inhibits WM266 melanoma cell proliferation, migration and associated neo-angiogenesis

We validated the anticancer potential of a nanoformulation made by (+)-catechin, gelatin and carbon nanotubes in terms of inhibition of cancer cell proliferation, migration and associated neo-angiogenesis. Gelatin was selected to stabilize the catechin without compromising its anti-oxidant potential and the carbon nanotubes were used to increase its intracellular bioavailability. The anticancer potential of the resulting nanohybrid was validated on an aggressive melanoma cell line, in vitro and in zebrafish xenotransplants. The nanohybrid strongly enhances the cytotoxic effect of (+)-catechin. At a concentration of (+)-catechin 50μg/ml, the nanohybrid inhibited the ability of melanoma cells to proliferate (100% increase of cell doubling time and severe impairment in zebrafish xenotransplants), to migrate (totally inhibition in vitro and 50% reduction of cell motility in zebrafish xenotransplants) and to induce neo-angiogenesis (100% inhibition in zebrafish xenotransplants). Conversely, the free (+)-catechin and carrier (CNT:gel) had no statistically significant effects over the control, at any concentration tested. Our results suggest that the use of the nanohybrid, able to improve the therapeutic efficacy of the catechins, could represent a successful strategy for a future clinical translation.

Contrasts between Mild and Harsh Oxidation of Carbon Nanotubes in terms of their Properties and Electrochemical Performance

AbstractFundamental studies and electrochemical applications of carbon nanotubes (CNTs) have impacted a wide range of disciplines. A key issue for CNT electrochemistry is to understand how the physical, chemical, and electronic properties of different CNT materials affect their electrochemical performance. We investigate the differences arising from CNTs undergoing mild (H2O2) or harsh (HNO3) oxidation processes. Morphological assessment and chemical characterization of CNT materials revealed that HNO3 treatment (CNT–HNO3) was effective in removing a large part of the metallic impurities, whereas H2O2 treatment (CNT–H2O2) was more proficient in eliminating carbonaceous imperfections in the starting CNT material (CNTprist). We investigated the electrocatalytic and electron‐transfer properties of CNTprist and oxidized CNTs on a variety of electrochemical probes, which are sensitive to carbon surfaces as well as its oxygen‐containing groups and/or metallic impurities. Electrochemical results show that, for the studied molecules, CNTprist and CNT–H2O2 exhibit mostly indistinguishable performances, whereas CNT–HNO3 yields an improved performance.

The effects of boron doping on the optical absorption of carbon nanotubes

The frequency behavior of optical conductivity of (9,0) zigzag carbon nanotube doped with Boron atoms, as acceptor impurities, has been addressed. In the context of tight binding model Hamiltonian. In order to study of doping effects, we add a local energy term to original Hamiltonian of the clean system. This term presents the effect of scattering of electrons from impurities through carbon nanotube. Green's function of the disordered system is found using self-consistent Born approximation. Linear response is employed to calculate the optical conductivity of disordered carbon nanotube in terms of electronic Green's function. The effects of both dopant concentration and tube's diameter are investigated in details. The results show the optical conductivity is independent of boron concentrations in high frequency region. At low frequencies values, the increase of boron concentration leads to reduce optical absorption spectra. Moreover, optical conductivity gets the higher amounts at high frequency when the temperature raises.