Pure Carbon Nanotubes Research Articles

Protrusion Microstructure-Induced Sensitivity Enhancement for Zinc Oxide–Carbon Nanotube Flexible Pressure Sensors

Carbon nanotubes (CNTs) have broad application prospects in flexible pressure sensors because of their superior mechanical and electrical performance. However, the pressure sensitivity of a pure CNT sensor needs to be enhanced. Herein, a zinc oxide–carbon nanotube (ZnO–CNT) sensor with a protrusion microstructure was prepared to improve the pressure sensitivity of a pure CNT sensor. The results show that the ZnO–CNT sensor achieves a higher pressure sensitivity (8.79 times) than that of the pure CNT sensor. In addition, the ZnO–CNT sensor achieves fast response (125.28 ms), good durability (over 6000 cycles), and a high upper detection limit (up to 422.22 kPa). The enhancement in sensitivity of the ZnO–CNT sensor is explained by the finite element simulation. Benefiting from these characteristics, the ZnO–CNT sensor is expected to be applied in human physiological signs and motion monitoring.

Hydrogen storage in purified multi-walled carbon nanotubes: gas hydrogenation cycles effect on the adsorption kinetics and their performance

Multi-walled carbon nanotubes (MWCNTs) are an alternative for storage with low cost, eco-friendly, and good performance for both process adsorption and desorption. Herein, a purification procedure of MWCNTs was successfully described and studied by using XRD, TEM, Raman spectroscopy and by means of N2 adsorption-desorption isotherms using the BET method. The H2 storage properties at room temperature of the purified carbon nanotubes exposed to gas under pressures between 0.39 and 13.33 kPa was investigated by using the quartz crystal microbalance technique. It was found that the H2 adsorption capacity is strongly dependent on the morphological and structural characteristics of the carbon nanotubes and their specific surface area. The best sample with specific surface area of 729.4 ± 3 m2 g−1 shows a maximum adsorption capacity of 3.46 wt% at 12.79 kPa of H2 exposure pressure. The adsorption kinetics (t95%) from the different purified MWCNTs was also investigated as a function of the H2 exposure pressure as well as the performance of these MWCNTs on the reversibility of the H2 loading/unloading process when underwent to successive cycles of gas exposure.

Mechanism and Mitigation of Irreversible Material Loss within Gel-Based Single-Walled Carbon Nanotube Purification Schemes

Sephacryl-based separation of single-walled carbon nanotubes (SWCNTs) has afforded the enrichment of samples according to both type (metal/semiconducting) and band structure (chirality). However, Sephacryl-based procedures suffer from low process efficiency, in that some of the purified SWCNTs remain irreversibly bound on the gel. This work focuses on the elucidation of mechanistic aspects relating to the irreversible retention of SWCNT by Sephacryl S200 and identification of strategies to reduce material loss. By probing system parameters such as SWCNT or sodium dodecyl sulfate (SDS) concentration during adsorption, loading ratio (number of SWCNTs vs. number of gel binding sites), and the effect of kosmotropic additives on process elution efficiency, this work identifies inhomogeneous features belonging to SWCNTs as the primary factor which promotes their irreversible retention. Process elution efficiency is found to be negatively correlated with increased SDS surfactant concentration and increased SWNT loading, and methods are identified to mitigate material losses in Sephacryl-based SWCNT separation schemes. Application of NaF, a strong kosmotropic agent, to elute SWCNTs from Sephacryl is found to increase process elution efficiency from 54% to 88% compared to SDS surfactant alone. Collectively, this work both improves upon and provides valuable insight into the purification of SWNT with Sephacryl.

Free-standing carbon nanotube film for high efficiency monopole antenna

A flexible radio-frequency (RF) antenna allows wearable smart devices to have various functionalities. To develop a high-performance RF antenna, an outstanding radiation efficiency should be achieved. Metallic films are commonly utilized in RF antenna electrodes owing to their high electrical conductivity, which is related to the radiation efficiency. However, their high density and low mechanical stability under deformed states, such as the folding of metallic films, hinder their use as flexible RF antenna electrodes. In this study, we fabricated a carbon-nanotube (CNT) film via the direct-spinning method for use in a flexible RF antenna electrode. The network structure of the CNT film endows it with a high electrical conductivity and allows it to be freestanding without a polymeric binder. The freestanding CNT film-based RF antenna attained a high radiation efficiency of 85.6%, commercially useable level, and its performance remained stable even under mechanical deformation, such as bending and folding. This high performance is attributed to the network structure of the CNT film composed of pure CNT bundles.

Fundamental frequency analysis of endohedrally functionalized carbon nanotubes with metallic nanowires: a molecular dynamics study.

The endohedral functionalization of carbon nanotubes (CNTs) with nanowires (NWs), i.e., NWs@CNTs, has been the center of attention in a lot of research due to the applications of NWs@CNTs in nanoelectronic devices, heterogeneous catalysis, and electromagnetic wave absorption. To this end, based on the classical molecular dynamics (MD) simulations, the effect of four pentagonal structures of encapsulated metallic nanowires (mNWs), namely the eclipsed pentagon (E), the deformed staggered pentagon (Ds), staggered pentagon (S), and staggered pentagonal structure without the monatomic chain passing through the centers of the parallel pentagons (R) configurations on the vibrational behavior of CNTs, is investigated. Also, the effects of geometrical parameters such as length and radius of CNTs on the natural frequencies of simulated models are explored. The results illustrate that by increasing the length, the natural frequency of pure CNTs and mNWs@CNTs decreases. In a similar length, mNWs@CNTs possess lower natural frequencies compared to the pure CNTs. According to the results, the highest and lowest natural frequencies are calculated by inserting the S structure of sodium NW and Ds structure of aluminum NW inside their proper armchair CNT, i.e., Na-S NW@ (9,9) CNT and Al-Ds NW@ (7,7) CNT, respectively.

Development of zinc oxide-multi-walled carbon nanotube hybrid nanofluid for energy-efficient heat transfer application: A thermal lens study

This paper addresses the need for developing an energy-efficient hybrid nanofluid with zinc oxide–multi-walled carbon nanotube (ZnO-MWCNT) for overcoming the bottleneck of efficient heat transfer in thermal systems. The concentration-dependent thermal diffusivity modifications are analyzed using the highly sensitive mode mismatched thermal lens technique. The hybrid composite is prepared by the solid-state mixing and annealing of a pure multi-walled carbon nanotube (MWCNT) and zinc oxide (ZnO), synthesized by the solution combustion method. The composite formation is studied by structural, morphological, and optical characterization techniques. Among the three nanofluids ZnO, MWCNT, and ZnO-MWCNT, the composite exhibits a drastic enhancement in thermal diffusivity at a lower solid volume fraction of 0.047 mg/ml containing 0.009 mg/ml of MWCNT. All the nanofluids show an optimum concentration beyond which the thermal diffusivity decreases with the nanoparticle concentration. Thus, this study suggests the potential application of ZnO-MWCNT hybrid nanofluids in thermal system design to enhance internal combustion engines' efficiency during cold-start.

Antiviral properties of select carbon nanostructures and their functionalized analogs

The antiviral properties of nanocarbons namely, carbon nanotubes (CNT), graphene oxide (GO), reduced graphene oxide (rGO), hybrid GO-CNT, rGO-CNT and CNTs functionalized with carboxylic (CNT-COOH), phenol (CNT-phenol), silver (CNT-Ag) are presented. Escherichia coli MS2 bacteriophage was the model virus. All the nanocarbons showed antiviral activities and the activity increased with increase in concentration. CNT-phenol showed the highest antiviral activity (97.1%) at 0.3mg/mL followed by CNT-Ag (90%), GO-CNT (85.5%), rGO-CNT (83.5%), CNT-COOH (82.5%), CNT (78%), GO (45.6%) and rGO (39.5%) at the same concentration. At 0.05 mg/ml, compared to pure CNTs, those functionalized with silver and phenol showed 270% and 200% higher removal efficiencies respectively. GO and rGO were less efficient by themselves, but with the CNTs, namely GO-CNT and rGO-CNT, their activities enhanced by factors of 650 and 950% respectively. The antiviral activity of the nanocarbons was quantified based on both the concentration of nanocarbons needed to reach a 50 percent deactivation (LD50) and the rate of deactivation. CNT-Phenol was the most effective antiviral nanocarbon studied here, it’s LD50 was 1400 times lower than the pure CNTs even though it had similar rate of deactivation as the latter, The antiviral efficiency of GO and rGO were relatively lower compared to the other nanocarbons, however they improved by 92% and 89% for GO and rGO when combined with the CNTs in a hybrid form. From the transmission electron microscopy (TEM) analysis, it was observed that the CNTs entangled the viruses which probably led to physical damage to their structure while the functional groups attached to CNTs such as phenol and Ag further enhanced toxicity due to their own properties.

Characterization and comparison of properties of cryogenic conditioned CNT reinforced thermoset (epoxy) and thermoplastic (poly vinyl alcohol) composite yarns

Carbon nanotube (CNT) fiber/yarn reinforced composites are considered as a new generation of advanced materials for applications in aerospace and space industry. In this study, two types of CNT composite yarns were produced by twisting CNT films and infiltrating with thermoset epoxy (EP) and thermoplastic poly vinyl alcohol (PVA) resins. The tensile strength of CNT/PVA and CNT/EP composite yarn was 409.91 MPa and 206.87 MPa, much higher than that of pure CNT yarn (129.94 MPa). After mono-cryogenic condition, the mechanical and electrical properties of CNT/EP and CNT/PVA composite yarns were both enhanced due to the structure reorder of the CNT bundles and improvement of interfacial bonding. However, after 60 times cyclic-cryogenic conditions, CNT/EP composite yarn showed a ∼10% degradation of tensile strength; while CNT/PVA composite yarn exhibited 6% increment. This study provides fundamental data of the CNT reinforced thermoset and thermoplastic composite yarns for their practical applications in cryogenic environment.

Visible near Infrared Spectroscopic Evidence of the Purification and Dispersion of Single-Walled Carbon Nanotubes

The application of dispersible single-walled carbon nanotubes in water is required in many fields, such as mechanics, thermology, electricity, etc. In this paper, single-walled carbon nanotube samples were dispersed in sodium deoxycholate aqueous solution with the assistance of ultrasonic crushing. The effects of centrifugal time, concentration and centrifugal velocity on dispersion were investigated. After centrifugal separation, the dispersible single-walled carbon nanotubes solution in water was obtained. The dispersion behavior of single-walled carbon nanotubes in sodium deoxycholate aqueous solution was further investigated by Uv-visible near infrared spectrum and electrochemical cyclic voltammetry curve. At the same time, characterization results of Uv-visible near infrared spectrum shew that the purity of single-walled carbon nanotubes was improved. The cyclic voltammetry curves of single-walled carbon nanotubes after purification and dispersion were tested by electrochemical method, and the electron transfer behavior of single-walled carbon nanotubes after purification and dispersion was investigated.

Purification of carbon nanotubes produced by the electric arc-discharge method

As-grown carbon nanotubes (CNTs) samples produced by electric arc-discharge method have shown several undesired impurities, such as amorphous carbon, metallic particles and different graphitized carbon materials that prevents their potential use. Therefore, due to the wide variety of impurities present in these samples, the purification process should be carried out in specific steps. For instance, the effective residual catalyst metal nanoparticles removal is a big challenge, since these materials are coated with a graphitic shell which prevents acid treatments from attacking the metals. In this work two different purification protocols based on the combination of gas-phase treatments, followed by the liquid-phase oxidation steps of CNTs with high degree of impurities were investigated. A significant removal of carbon impurities with minimal introduction of defects in the CNTs walls was evaluated, however the presence of active encapsulated metallic particles was still observed. Through TEM, TGA, EDS and XPS analysis, it was possible showed that these metals are encapsulated in different levels of metallic carbides (such as Ni3C), with very difficult removal. Even though the catalytic metals were not completely removed by the protocols used, the combination of the alternating gas phase with the acid treatments ensured CNTs samples with structural integrity and impurities removal of up to 75%.

Flexible Supercapacitors Based on CNT/MnO2-BP Composite Yarn Synthesized by In Situ Reduction

Solid-state flexible supercapacitors are considered significant prospective energy storage devices, and carbon nanotube (CNT) yarn is an ideal electrode material for constructing linear flexible supercapacitors because of its high electrical conductivity and flexibility. However, the relatively low specific capacitance and energy density of a supercapacitor made of pure CNT yarn limits its application. Here, we prepared a CNT/MnO2-BP composite yarn via a facile one-step liquid deposition method by the innovative introduction of few-layer black phosphorous (BP) nanosheets. The redox reaction between the BP and the potassium permanganate forms MnO2 and an electrolyte of phosphorus acids (HxPOy). The two-ply yarn supercapacitor composed of the CNT/MnO2-BP composite yarn shows excellent electrochemical properties with a volumetric capacitance of 441.79 F cm−3 at the scanning rate of 0.01 V s−1 and an energy density of 9.82 mWh cm−3 at a power density of 441.79 mW cm−3. Herein, this work provides a way to improve the electrochemical performance of CNT yarn-based supercapacitors that can act as flexible energy storage devices for wearable electronics.

Removal and surface photocatalytic degradation of methylene blue on carbon nanostructures

Removal and photodegradation of methylene blue on the surface of three distinct carbonaceous materials, pure and nitrogen-doped multi-walled carbon nanotubes, and graphitic nanoribbons, were examined. Carbon nanostructures were characterized by scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, Raman spectroscopy, X-ray photoelectron spectroscopy, and N2 adsorption/desorption isotherms. Removal and photocatalytic activity were evaluated by static adsorption under UV irradiation. Photocatalytic activity on carbon nanostructure exhibited a pseudo-first-order kinetic model. The adsorption capacity and photocatalytic activity of carbon nanostructures were mainly attributed to their defective and reactive surface. Nitrogen-doped multi-walled carbon nanotubes showed the best adsorption capacity and photocatalytic activity, which can be attributed to the highly reactive sites due to nitrogen doping, also by π–π electron donor-acceptor interaction between sp2 lattice of carbon nanostructure surface and negatively charged sites at methylene blue molecules.

Optimization of carbon nanotubes synthesis via pyrolysis over Ni/Al2O3 using response surface methodology

Owing to the rapid expansion of preparing a low-cost and pure carbon nanotubes (CNTs) from large available raw materials as cheap carbon precursors and catalyst depositions via chemical vapor deposition process, Algerian condensate gas over Ni/Al2O3 was used in this study. Response surface methodology was utilized to assess and optimize the preparation parameters. Synthesis of CNTs was studied as a function of three independent parameters: catalyst/condensate-gas weight ratio (5–10 wt %), synthesis time (30-120 min) and temperature (700–1000 °C). Optimum conditions for the CNTS-synthesis were found to be 5%, 112 min and 1000 °C, for catalyst/condensate gas mass ratio, synthesis time and temperature, respectively. Under these conditions, Raman spectrum indicates high values of (IG/ID), which means high-quality CNTs. Examination by SEM and HRTEM revealed that the CNTs grown under optimum conditions had diameters of 10 nm. The carbon yield predicted at the optimum process conditions was 81.76%. Conclusively, the pure and uniformed CNTs can be produced with high yield by the conversion of available-cheap resources via CVD-method. This method is practical, realistic, feasible in industrial scale and thus can reduces the cost manufacture of CNTs, which may help increase the impact of these remarkable materials in many fields.

Carbon Nanotube (CNTs): Structure, Synthesis, Purification, Functionalisation, Pharmacology, Toxicology, Biodegradation and Application as Nanomedicine and Biosensor

It is well acknowledged that carbon nanotubes (CNTs) are a potential new class of nanomaterials for technological advancement. The recent discovery of diverse kinds of carbon nanostructures has sparked interest in the potential applications of these materials in a variety of disciplines. Numerous distinct carbon nanotube (CNT) production methods have been developed, and their characterisation, separation, and manipulation of individual CNTs are now possible. Structure, surface area, surface charge, size distribution, surface chemistry, aggregation state, and purity of the samples all have a significant impact on the reactivity of carbon nanotubes, as does the purity of the samples. Currently, carbon nanotubes (CNTs) are being successfully used in the medicinal, pharmaceutical, and biomedical fields because of their large surface area, which makes them capable of adsorbing or conjugating with a wide range of therapeutic and diagnostic substances (drugs, genes, vaccines, antibodies, biosensors, etc.). They were the first to demonstrate that they are a great vehicle for drug delivery straight into cells without the need for metabolic processing by the body. This paper discusses the different types, structures, and properties of CNTs, as well as CNT synthesis and purification methods, how to functionalize CNTs, and their application in medicinal, pharmaceutical, and biomedical fields, toxicological properties and their assessment, as well as in-vivo pharmacology and biodegradation pathways.

Single-Walled Carbon Nanotube Chiral Selectivity Exhibited by Commercially Available Hydrogels of Varying Composition.

Despite the commercial availability of many different hydrogel formulations, the effective gel-based purification of single-walled carbon nanotubes (SWNT) remains exclusive to the gel Sephacryl S-200. In this study, 12 commercially available gels and two custom-synthesized gels were investigated for their ability to effectively purify SWNT, as determined through quantification of SWNT adsorption, elution, chiral selectivity, and overall process efficiency. The ability of each gel to separate SWNT was found to correlate with physiochemical properties, such as hydrogel pore size, the presence of ionic ligands, and both polysaccharide backbone and cross-linker compositions. While Sephacryl S-200 demonstrated superior separation efficiency and chiral selectivity among the gels studied, Superose 6 was found to adsorb more SWNT than Sephacryl S-200 per cm2 of the gel surface area and exhibited a unique preference for the (7,3) and (7,5) SWNT chiralities, in contrast to the established selectivity of Sephacryl S-200 for the (6,5) chirality. Collectively, this work both identifies gels that exhibit unique SWNT chiral selectivity and provides insights into the rational design of gels tailored for SWNT purification.

Preparation and high-performance lithium storage of intimately coupled MnO2 nanosheets@carbon nanotube-in-nanotube

MnO2 nanosheets@carbon nanotube-in-nanotube is rationally constructed through carbonization of tannic acid-treated zeolitic imidazolate framework-8 string of carbon nanotubes and subsequent chemical reaction of KMnO4 and carbon. The ultrathin MnO2 nanosheets are intimately coupled on the surface of carbon nanotube-in-nanotube. The composite shows large specific surface area (126.6 m2 g−1) and pore volume (0.4 cm3 g−1). Comparative studies of cyclic voltammetry curves and galvanostatic charge-discharge profiles indicate that for MnO2 nanosheets@carbon nanotube-in-nanotube, electrochemical activities and charge-discharge capabilities of MnO2 and carbon are both significantly improved. The cycling measurements reveal that the composite shows much higher reversible capacity and cycling stability than pure MnO2, carbon nanotubes, carbon nanotube-in-nanotube and MnO2 nanosheets@carbon nanotubes. The superior Li storage performance is attributed to synergistic effect of MnO2 nanosheets and carbon nanotube-in-nanotube. The ultrathin nanosheet structure of MnO2 and the unique nanotube-in-nanotube structure of carbon remarkably shorten diffusion paths of Li ions, facilitate transport of electrolyte ions, promote contact between electrode material/electrolyte, improve structural stability of the composite, increase electronic conductivity of MnO2, enhance reaction kinetics.

The Electronic Characteristic and Optical Properties of Doped Single-Walled Carbon Nanotubes from a First-Principles Study

In this contribution, electronic structures and optical properties of pure and doped single-walled carbon nanotubes (SWCNTs) are investigated by the first-principles calculation. It is found that the B- and N-doped systems have the lowest binding energies of [Formula: see text][Formula: see text]eV and [Formula: see text][Formula: see text]eV, respectively, indicating that the configurations are relatively stable. Interestingly, the indirect bandgap is transforming into a direct bandgap in the two systems, which has a good development prospect in the field of light-emitting devices. The charge difference density diagrams show that the electron deletion around all doped atoms is weakened, indicating that the covalence between the doped atom and carbon atom is weakened, which is consistent with the population analysis result. In the absorption spectrum, there is a “blueshift” phenomenon. In the reflection spectrum, the six doping systems show an obvious “redshift” phenomenon. In addition, the polarization ability of all doping systems has become stronger. Also, due to the different changes in the peak values of the imaginary part of the dielectric function, the doping of Al, Ga and P improved the photoresponse of the low-energy region, while the doping of B, N and As weakens it.

Effect of covalent functionalization of multi-walled carbon nanotubes with HDI trimer on mechanical properties of polyaspartate polyurea

To improve the mechanical properties of polyaspartate polyurea (PAEP), functionalized multi-walled carbon nanotubes reinforced polyurea composites (HDIT-MWCNTs/PAEP) were prepared by covalently functionalizing multi-walled carbon nanotubes (MWCNTs) with hexamethylene diisocyanate (HDI) trimer. The dispersibility, wettability and interfacial properties of HDI trimer functionalized MWCNTs (HDIT-MWCNTs) in PAEP were analyzed. The tensile properties of HDIT-MWCNTs/PAEP composites were tested and the reinforcement mechanism revealed. The results showed that compared with the pure multi-walled carbon nanotubes (P-MWCNTs), HDIT-MWCNTs were uniformly dispersed in the matrix and the wettability and interfacial properties were greatly improved. The contact angle of PAEP with HDIT-MWCNTs was 32.92°, a reduction of 46.3% compared with the P-MWCNTs. The interfacial energy and adhesion work between PAEP and HDIT-MWCNTs (25.14 mJ m−2, 95.47 mJ m−2) were 46.7% and 24.2% higher than those of P-MWCNTs. When the content of HDIT-MWCNTs was 0.5 phr, the tensile strength and Young’s modulus of the composites reached a maximum of 17.78 MPa and 170.31 MPa; an increase of 28.4% and 90.8% respectively, compared with pure PAEP. According to the cross-section of HDIT-MWCNTs/PAEP, its strengthening mechanism was mainly manifested by the deflection and bifurcation of cracks and the plastic deformation of PAEP matrix due to HDIT-MWCNTs pulling out from the matrix.

En route to single-step, two-phase purification of carbon nanotubes facilitated by high-throughput spectroscopy

Chirality purification of single-walled carbon nanotubes (SWCNTs) is desirable for applications in many fields, but general utility is currently hampered by low throughput. We discovered a method to obtain single-chirality SWCNT enrichment by the aqueous two-phase extraction (ATPE) method in a single step. To achieve appropriate resolution, a biphasic system of non-ionic tri-block copolymer surfactant is varied with an ionic surfactant. A nearly-monochiral fraction of SWCNTs can then be harvested from the top phase. We also found, via high-throughput, near-infrared excitation-emission photoluminescence spectroscopy, that the parameter space of ATPE can be mapped to probe the mechanics of the separation process. Finally, we found that optimized conditions can be used for sorting of SWCNTs wrapped with ssDNA as well. Elimination of the need for surfactant exchange and simplicity of the separation process make the approach promising for high-yield generation of purified single-chirality SWCNT preparations.

Functionalized Carbon Nanotubes (CNTs) for Water and Wastewater Treatment: Preparation to Application

As the world human population and industrialization keep growing, the water availability issue has forced scientists, engineers, and legislators of water supply industries to better manage water resources. Pollutant removals from wastewaters are crucial to ensure qualities of available water resources (including natural water bodies or reclaimed waters). Diverse techniques have been developed to deal with water quality concerns. Carbon based nanomaterials, especially carbon nanotubes (CNTs) with their high specific surface area and associated adsorption sites, have drawn a special focus in environmental applications, especially water and wastewater treatment. This critical review summarizes recent developments and adsorption behaviors of CNTs used to remove organics or heavy metal ions from contaminated waters via adsorption and inactivation of biological species associated with CNTs. Foci include CNTs synthesis, purification, and surface modifications or functionalization, followed by their characterization methods and the effect of water chemistry on adsorption capacities and removal mechanisms. Functionalized CNTs have been proven to be promising nanomaterials for the decontamination of waters due to their high adsorption capacity. However, most of the functional CNT applications are limited to lab-scale experiments only. Feasibility of their large-scale/industrial applications with cost-effective ways of synthesis and assessments of their toxicity with better simulating adsorption mechanisms still need to be studied.