Multi-walled Nanotubes Research Articles

Droplet combustion and ignition analysis of carbon multiwall nanotube and alumina blended jatropha biodiesel

Biodiesel produced from Jatropha methyl ester was blended with diesel in the 20% volume ratio. Carbon Multiwall Nanotube and Alumina nano additives were added in the proportions of 25 ppm and 50 ppm in Jatropha Biodiesel with the help of a mechanical agitator and magnetic stirrer. In the present study, ignition analysis parameters like ignition delay time and activation energy are evaluated at elevated temperatures in the electric furnace at atmospheric pressure. Also, the stages of combustion are investigated for all the blends. With the addition of energetic nanoparticles, it has been seen that reduced ignition delay period, improved combustion and its catalytic effects are observed. From the droplet ignition analysis in the furnace at the atmospheric pressure, the ignition delay decreased by 6.02% at the temperature of 700 °C and activation energy increased by 0.53% for the JBD20AL50C50 blend in comparison with D-100. Also, three stages for the combustion are observed for the nanoparticles blends of fuels.

Application of CeO2-MWCNTs nanocomposite for heavy metal ion detection in aqueous solutions by electrochemical technique

Heavy metals are most common pollutant found in the water bodies and are very toxic to the ecosystem. This work focuses on the application of cerium oxide and multiwall nanotube (CeO2-MWCNT) nanocomposites for simultaneous detection and quantification of heavy metal ions from aqueous solutions. The CeO2-MWCNTnanocomposite was prepared by hydrothermal method. The morphology, structural characterization and phase evolution studies of nanocomposites were determined by XRD, FE-SEM, XPS and TEM. The experimental results showed that the electrochemical performance of CeO2-MWCNT modified sensor for Hg2+, Pb2+, and Cu2+solutions, is promising and better than glassy carbon electrode. For quantification and calibration, differential pulse voltammetry technique was used for a broad concentration range of 5–5000 µM. The dependence of concentration of Hg2+, Pb2+, and Cu2+ions on the analytical signals can be fitted by quadratic polynomial equation. The modified sensor showed the lower detection limits of 1.98, 1.10 and 3.53 µg/l for Hg2+, Pb2+, and Cu2+,respectively. In addition, the CeO2-MWCNTbased sensor exhibited good sensitivity and high selectivity. The detection limit surpassed the lower limit defined by World Health Organization guidelines for Hg2+, Pb2+, and Cu2+. As a proof-of -concept, the suitability of the sensor was demonstrated in real water samples from tap water and river water. Correspondingly, this work demonstrated a simple and effective sensing platform for heavy metal ion detection.

AA h BN crystal, basic structure of boron nitride nanotubes.

AA h boron nitride (BN) crystal, assigned to an orthorhombic space group (No. 31, Pm21), is reported here. This new AA h BN crystal exhibits a 'linear' morphology for high-resolution transmission electron microscopy (HRTEM) and a (non-hexagonal) 'diagonal' electron-diffraction pattern, which have been experimentally demonstrated in this article. It is also demonstrated that this new crystal is the basic structure of multi-walled BN nanotubes (BNNTs) existing in the form of a helix. The helical AA h BNNTs exist in a metastable phase owing to 〈200〉 texture growth of the orthorhombic crystal, where the energy is ∼15 meV higher than that of stable AB or AA' BN. It is shown that the typical scanning electron microscope 'fluffy cotton-like' morphology of BNNTs is due to secondary growth of diverse BN sheets (including mono-layers) on incoherently scrolled wall strands of BNNTs, providing further evidence for the helical structure with HRTEM evidence for a left-handed helix.

The relation between nanotube diameter, length and surface area and pore volume of multi-walled spiral halloysite nanotubes: A theoretical study

Halloysite (Hal) is a natural clay mineral with nanotube structure. Due to their outstanding specific surface area, loading capacity and selective adsorption ability, Hal have been widely used in the fields of catalysis, adsorption, drug loading and releasing. However, the loading ability of Hal from different halloysite deposits still varies in a large range. The relation between the microstructure properties of Hal and the intrinsic parameters such as length (L), inner/outer diameter (Dinner/Douter) of halloysite nanotubes (HNTs) is still obscure. In this study, we constructed the atomic structures of several multi-walled spiral HNTs with diameters (10–40 nm) in the range of the real size of Hal, and calculated their specific surface area (S) and pore volume (V) to compare with experimental results. By comparing the difference between the calculated values and the theoretical values (based on simple mathematics), the relation between the S/V of HNTs and its Dinner/Douter and L is established using modified equations. The equations were applied to deduce the theoretical values of the specific surface area and pore volumes of HNTs in a wide range of inner/outer diameter (10–200 nm) and length (100–5000 nm). Notably, while the experimental surface area are highly consistent with the theoretical values, the experiment pore volume are mostly lower than the theoretical values, which indicates that the lumen space of HNTs from different deposits are blocked in different degrees by the associated minerals and impurities. It is expected that, in addition to traditional physicochemical purifications, the removal of lumen impurities can help to revive the lumen loading ability of HNTs upto their theoretical limits.

Enhanced performance of CH4 dry reforming over La0.9Sr0.1FeO3/YSZ under chemical looping conditions

Catalytic dry reforming of methane is an attractive route for CO2 valorization that yields syngas (CO + H2) for subsequent synthesis of chemical and fuels. Alternatively, chemical looping approaches based on discontinuous cyclic operation are lately gaining relevance because, among other advantages, these processes are less prone to deactivation, and they are amenable to be used for thermosolar fuel production. With this background, here we investigate the isothermal activity of CO2 and CH4 over La0.9Sr0.1FeO3 perovskite modified with yttria-stabilized zirconia (YSZ), comparing conventional catalytic activity, tested by continuous feeding an equimolar blend of these two gases, with the chemical looping process, where the inlet composition swings between CH4 and CO2 in 20 min intervals. Two preparation methods were used to obtain these composites: direct synthesis by Pechini method of the perovskite in the presence of YSZ support and mechanical mixing by ball-milling of the two pre-synthetized oxides. Catalytic activity feeding a CH4 and CO2 blend showed a moderate but rather stable activity (226 µmols.min−1.g−1 of H2 and 206 µmols.min−1.g−1 of CO) at 850 °C for 24 h, with little difference between catalysts. Chemical looping operation at the same temperature, resulted in enhanced production of syngas, with the sample with perovskite synthetized on the support showing significantly higher peak performance (476 µmols.min−1.g−1 of H2 and 432 µmols.min−1.g−1 of CO). The observed high H2/CO ratio in the methane stage (up to 6.5) indicates the relevant contribution of methane cracking. Characterization of the fresh materials confirmed the formation of the expected phases in both cases, while after CH4 treatment at high temperature the perovskite decomposed mainly into La2O3 and reduced Fe phases. In addition, carbon is also deposited, mainly as multiwall nanotubes. However, the initial perovskite composition is recovered after re-oxidation with CO2, allowing a stable operation of the La0.9Sr0.1FeO3/YSZ system for at least five cycles.

Structure and stability of GaS, GaTe, and Janus-Ga2STe multi-walled nanotubes. Molecular mechanics simulation

For the first time, the structural and stability properties of multi-walled GaS, GaTe, and Janus Ga 2 STe nanotubes have been simulated using molecular-mechanics calculations. The armchair and zigzag nanotubes with different wall numbers and diameters have been considered. The force field used for GaS, GaTe and Ga 2 STe multi-walled nanotubes is based on the interaction potentials recently developed to describe monolayers of the transition and post-transition metal chalcogenides. The Buckingham potentials have been introduced to model the interlayer and interwall interactions. The results of quantum mechanical calculations for a number of bulk crystals, mono and bilayers, as well as small diameter single-wall nanotubes have been employed to check the validity of the proposed force field. With the help of an adapted force field, large eight-walled nanotubes with an outer diameter of 32 nm were simulated, which at present cannot be studied using the first principles of quantum mechanical methods. Molecular mechanics simulations predict the faceted structure of armchair GaS, GaTe, and Ga 2 STe multi-walled nanotubes with a sufficiently large diameter and a cylindrical structure for all zigzag nanotubes. The Janus nanotubes' stability is superior to that of binary nanotubes and may probably achieve a maximum at certain wall numbers and diameters. • Janus Ga 2 STe multi-walled nanotubes are more stable than GaS, GaTe MWNTs • Formation energy dependence on diameter has a minimum for Janus MWNTs • Ga 2 STe armchair nanotubes with more than six walls acquire a faceted structure • Zigzag Janus Ga 2 STe multi-walled nanotubes have a circular cross-section • Zigzag multi-walled nanotubes are more stable than armchair ones

Template-free, facile synthesis of nickel promoted multi-walled MoS2 & nano-bricks containing hierarchical MoS2 nanotubes from the bulk NiMo oxide

A low-temperature and template-free synthesis method was developed to prepare MoS2 nanotubes by sulfidation of bulk NiMo oxide. The ex-situ gas-phase low-pressure sulfidation of NiMo oxide resulted in multi-walled MoS2 nanotubes and NixSy spheres. Meanwhile, the in-situ liquid phase high-pressure sulfidation led to nanotubes formation by self-assembly of MoS2 nano-bricks vertically oriented towards the outer surface as observed by HRTEM analysis. The sulfided catalysts were evaluated for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) in a batch reactor. Catalyst sulfided under ex-situ conditions exhibited good performance (76 % DBT conversion with an initial reaction rate 24 × 10−8 molDBT.(gCat.s)-1). The in-situ sulfided catalyst showed an outstanding activity (99 % DBT conversion with an initial reaction rate 105 × 10−8 molDBT.(gCat.s)-1). Which means that the in-situ sulfidation method dramatically increased the initial reaction rate by four times. A mathematical expression (RKC equation) was derived to correlate the size of the regular hexagonal MoS2 nanoparticles with its activity, for which the experimental results were validated.

A facile approach towards fabrication of multi-walled nanotubes embedded polyurethane high performance nanocomposite with efficient shape recovery

A facile approach towards fabrication of multi-walled nanotubes embedded polyurethane high performance nanocomposite with efficient shape recovery

Higly sensitive active medium of sensor NO2 , based on cholesteric nematic mixture with impurities of carbon nanotubes

The paper presents the results of the study of the parameters of the highly sensitive active medium of the NO2 sensor based on a cholesterol-nematic mixture with an admixture of carbon nanotubes. The dependence of the change in the wavelength of the two transmission minima on the NO2 concentration for cholesterol-nematic mixture with single-walled, double-walled and multi-walled nanotubes at different concentrations of nanotubes and two concentrations of nematically liquid crystal 5CB were obtained. It is established that by changing the ratio between the concentrations of nanotubes and nematic liquid crystals, it is possible to obtain mixtures that have the maximum spectral sensitivity coefficient in a given range of gas concentration.

Probing the Chiral Domains and Excitonic States in Individual WS2 Tubes by Second-Harmonic Generation.

Distinct from carbon nanotubes, transition-metal dichalcogenide (TMD) nanotubes are noncentrosymmetric and polar and can exhibit some intriguing phenomena such as nonreciprocal superconductivity, chiral shift current, bulk photovoltaic effect, and exciton-polaritons. However, basic characterizations of individual TMD nanotubes are still quite limited, and much remains unclear about their structural chirality and electronic properties. Here we report an optical second-harmonic generation (SHG) study on multiwalled WS2 nanotubes on a single-tube level. As it is highly sensitive to the crystallographic symmetry, SHG microscopy unveiled multiple structural domains within a single WS2 nanotube, which are otherwise hidden under conventional white-light optical microscopy. Moreover, the polarization-resolved SHG anisotropy patterns revealed that different domains on the same tube can be of different chirality. In addition, we observed the excitonic states of individual WS2 nanotubes via SHG excitation spectroscopy, which were otherwise difficult to acquire due to the indirect band gap of the material.

Nonlinear Vibration of Multi-Walled Carbon Nanotubes with Initial Curvature Resting on Elastic Foundations in a Nonlinear Thermo-Magnetic Environment

The present work focuses on nonlinear dynamics models of multi-walled carbon nanotubes with initial curvature resting on Winkler-Pasternak elastic foundations in a nonlinear thermomagnetic environment using nonlocal elasticity theory. The derived systems of nonlinear vibration models are solved with the aid of the Galerkin decomposition and the homotopy perturbation method. Effects of temperature, magnetic field, multi-layer, and other thermomechanical parameters on the dynamic responses of the slightly curved multi-walled carbon nanotubes are investigated and discussed. As the temperature increases, the frequency ratio decreases as the linear natural frequency of the system increases. The results reveal that the frequency ratios decrease as the number of nanotube walls, temperature, spring constants, magnetic field strength, and the ratio of the radius of curvature to the length of the slightly curved nanotubes increase. These trends are the same for all the boundary conditions considered. However, clamped-simple and clamped-clamped supported multi-walled nanotube have the highest and lowest frequency ratio, respectively. Also, from the parametric studies to control nonlinear vibration of the carbon nanotubes, it is shown that quadruple-walled carbon nanotubes can be taken as pure linear vibration even at any value of linear Winkler and Pasternak constants. Therefore, this can be used for the restraining of the chaos vibration in the objective structure. These research findings will assist the designers and manufacturers in developing multi-walled carbon nanotubes for various structural, electrical, mechanical, and biological applications, especially in the areas of designing nanoelectronics, nanodevices, nanomechanical systems, nanobiological devices, and nanocomposites, and particularly when they are subjected to thermal loads, magnetic fields and elastic foundations.

High Pressure in Boron Nitride Nanotubes for Kirigami Nanoribbon Elaboration

Cutting and folding 2D systems is one of the explored paths to tune physical and chemical properties in one-atom-thick matter. Contrary to graphene, boron nitride (BN) nanoribbons are difficult to obtain, and folded BN nanoribbon structures have not been reported yet. Here, we show that pressure application in multiwalled boron nitride nanotubes leads to different types of tube internal organizations including BN nanoribbon formation and folds. The new structures are associated with the breaking of a number of the internal tubes, leading to either nonorganized structures in the form of internal tube alveoli or an organized stacking of folded h-BN nanoribbons. Irreversible changes in the morphology of multiwalled BN nanotubes (MWBNNTs) take place from ∼7 GPa, and morphologically modified tubes could be observed up to pressures of at least 49 GPa. The experimental probes utilized included high-resolution transmission microscopy, electron tomography, and Raman spectroscopy. Atomistic modeling shows the formation of pinch structures along the tubes that favor pressure-induced bond-breaking and hybridization changes and confirm the folded structure. Both experiments and modeling show that tube polygonization is a prominent characteristic of MWBNNTs even at ambient pressure. Overall, the pressure evolution of MWBNNTs strongly differs from their carbon analogues. The high mechanical stability of BN tube geometry is of interest for composite-based structural materials. On the other side, the availability of h-BN nanoribbons and folded structures opens new prospects to produce physically modified BN properties.

Carbon nanotubes produced from rubber fruit shell activated carbon

This study used rubber fruit shells (RFS) as raw material for making carbon nanotubes (CNTs). The CNTs were carried out by hydrothermal process at low-temperature after carbonization and chemical activation was done. This experiment succeeded in obtaining a bundle of MWCNT (Multi-Wall Nanotube) from the raw material of RFS. The results of characterization using SEM and TEM showed that the resulting CNTs were not homogeneous in diameter, ranging from 13 to 455 nm, with an average diameter of about 179 nm. XRD was used to identify crystallographic structure; it has two peaks 2[Formula: see text] at around 26.0 and 44.0, index to 002 and 101 reflections hexagonal graphite diffraction of the MWCNTs. This study can provide an alternative inexpensive raw material and a simple method to obtain carbon nanotubes.

Effect of borates on the synthesis of nanoscale hexagonal boron nitride by a solid-state method.

This study delves deeply into the effect of different borates (lithium tetraborate, sodium tetraborate, calcium metaborate, ammonium pentaborate) on the production and fundamental characteristic features of nanoscale hexagonal boron nitride (hBN) structure with the assistant of standard characteristic measurement methods, namely, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM). The hBN samples are synthesized by reaction of powder urea, boron oxide, and different kinds of borates via the modified O'Connor method (performed at a relatively lower main heat treatment temperature of 1,100°C). All the results obtained show that the usage of borates affects positively the formation of nanoscale hBN structure. In more detail, the FTIR experiment results reveal that the presence of two strong c peaks appeared at ~1,380 and ~780 cm-1 in the spectra points out the conventional BN in-plane and out-of-plane vibrations, respectively. The XRD patterns also confirm the production of high-ordered hBN as the existence of the main peaks of the corresponding hexagonal system. As for the SEM examination, it is found that all the hBN materials exhibit totally different crystallinity quality and microstructural characteristics. The hBN compound prepared by the sodium tetraborate content shows the most uniform surface appearance with the smoothest/densest crystal structure, best grain orientations, and finest grain interactions. Hence, the material with strong stretching of interatomic bonds shows the highest material (fracture) strength. Moreover, the TEM images illustrate that all the products are composed of uniform multi-walled nanotubes and nanorods with an average length of ~250 nm.

The Synergistic Effect of a Hybrid Filler Based on Graphene Nanoplates and Multiwalled Nanotubes for Increasing the Thermal Conductivity of an Epoxy Composite

The Synergistic Effect of a Hybrid Filler Based on Graphene Nanoplates and Multiwalled Nanotubes for Increasing the Thermal Conductivity of an Epoxy Composite

Ab Initio Modeling of MultiWall: A General Algorithm First Applied to Carbon Nanotubes.

A general, versatile and automated computational algorithm to design any type of multiwall nanotubes of any chiralities is presented for the first time. It can be applied to rolling up surfaces obtained from cubic, hexagonal, and orthorhombic lattices. Full exploitation of the helical symmetry permits a drastic reduction of the computational cost and therefore opens to the study of realistic systems. As a test case, the structural, electronic, mechanical, and transport properties of multiwall carbon nanotubes (MWCNT) are calculated using a density functional theory approach, and results are compared with those of the corresponding layered (graphene-like) precursors. The interaction between layers has a general minimum for the inter-wall distance of ≈3.4 Å, in good agreement with experimental and computed optimal distances in graphene sheets. The metallic armchair and semiconductor zigzag MWCNT are almost isoenergetic and their stability increases as the number of walls increases. The vibrational fingerprint provides a reliable tool to identify the chirality and the thickness of the nanostructures. Finally, some promising thermoelectric features of the semiconductor MWCNT are reproduced and discussed.

Photoluminescence from Single-Walled MoS2 Nanotubes Coaxially Grown on Boron Nitride Nanotubes.

Single-walled and multiwalled molybdenum disulfide (MoS2) nanotubes have been coaxially synthesized on small-diameter boron nitride nanotubes (BNNTs) that are obtained from removing single-walled carbon nanotubes (SWCNTs) in heteronanotubes of SWCNTs coated by BNNTs. The photoluminescence (PL) from single-walled MoS2 nanotubes supported by core BNNTs is observed in this work, which evidences the direct bandgap structure of single-walled MoS2 nanotubes with a diameter around 6-7 nm. The observation is consistent with our DFT results that the single-walled MoS2 nanotube changes from an indirect-gap to a direct-gap semiconductor when the diameter of a nanotube is more than around 5.2 nm. On the other hand, when there are SWCNTs inside the heteronanotubes of BNNTs and single-walled MoS2 nanotubes, the PL signal from MoS2 nanotubes is considerably quenched. The charge transfer and energy transfer between SWCNTs and single-walled MoS2 nanotubes were examined through characterizations by PL, X-ray photoelectron spectroscopy, and Raman spectroscopy. Moreover, the PL signal from multiwalled MoS2 nanotubes is significantly quenched. Single-walled and multiwalled MoS2 nanotubes exhibit different Raman features in both resonant and nonresonant Raman spectra.

ZnO nucleation into trititanate nanotubes by ALD equipment techniques, a new way to functionalize layered metal oxides

In this contribution, we explore the potential of atomic layer deposition (ALD) techniques for developing new semiconductor metal oxide composites. Specifically, we investigate the functionalization of multi-wall trititanate nanotubes, H2Ti3O7 NTs (sample T1) with zinc oxide employing two different ALD approaches: vapor phase metalation (VPM) using diethylzinc (Zn(C2H5)2, DEZ) as a unique ALD precursor, and multiple pulsed vapor phase infiltration (MPI) using DEZ and water as precursors. We obtained two different types of tubular H2Ti3O7 species containing ZnO in their structures. Multi-wall trititanate nanotubes with ZnO intercalated inside the tube wall sheets were the main products from the VPM infiltration (sample T2). On the other hand, MPI (sample T3) principally leads to single-wall nanotubes with a ZnO hierarchical bi-modal functionalization, thin film coating, and surface decorated with ZnO particles. The products were mainly characterized by electron microscopy, energy dispersive X-ray, powder X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. An initial evaluation of the optical characteristics of the products demonstrated that they behaved as semiconductors. The IR study revealed the role of water, endogenous and/or exogenous, in determining the structure and properties of the products. The results confirm that ALD is a versatile tool, promising for developing tailor-made semiconductor materials.

Improved thermal conductivity of PEG-based fluids using hydrogen bonding and long chain of nanoparticle

An investigation was conducted to examine the extent to which the thermal conductivity of materials in polyethylene glycol (PEG) fluids could be improved using the concept of hydrogen bonding and long chains. Boron nitride (BN), hydroxyl functionalized multiwall nanotube (MWNT-OH), and carbon nanofibers (CNFs) were mixed and exfoliated to form hydrogen bonds between the particles and the PEG fluids. Following this bonding process, clear enhancements in the thermal conductivity were observed. In addition, the long chain boron nitride nanotubes (BNNTs) and carbon nanofibers were shown to significantly enhance the thermal conductivity, due to the resulting increase in the contact and interfacial surface areas. The results of this experimental investigation indicated that PEG400 with a loading of 7.5 wt% MWNT-OH yielded a thermal conductivity increase as high as 89.7% over the base fluid. PEG400 loaded with a combination of 2 wt% CNF and 2 wt% BNNT resulted in a thermal conductivity increase of 73.1%. These results are significantly higher than the best results previously reported in the literature and may in part be attributed to the use of a three roll milling technique to enhance contact. The results presented here will open the way for further exploration of the use of novel phase change materials for thermal energy storage applications.

Comparative trends and molecular analysis on the surfactant-assisted dispersibility of 1D and 2D carbon materials: Multiwalled nanotubes vs graphene nanoplatelets

Most applications of nanocarbons, such as carbon nanotubes and graphene, require that they are well-separated and well-dispersed in a liquid phase. Intensive efforts have been put on exfoliating and dispersing nanocarbons in aqueous solvents, typically using amphiphilic dispersants and sonication/centrifugation procedures, alongside a drive to fundamentally understand and rationally optimize these processes. Herein, we employed a robust method to separate and disperse multiwalled carbon nanotubes (MWNTs), and graphene nanoplatelets (GnPs) either from bulk graphite or from pre-formed GnP powders, using rigorously controlled processing conditions. An ionic (sodium cholate) and a nonionic (Triton X-100) surfactant were used as dispersants. Our aim was to determine high-precision dispersibility curves (concentration of dispersed nanomaterial versus initial surfactant concentration) for the different nanocarbon/dispersant systems, characterize morphologically the dispersed particles and compare the mechanisms of exfoliation of 1D and 2D nanocarbons at molecular level. Typically bell-shaped dispersibility curves with a plateau were obtained, and from the latter several quantitative metrics were extracted that permitted reliable comparisons between nanocarbon/surfactant systems. Scanning electron and atomic force microscopies allowed to characterize the suspended particles in the as-obtained dispersions, namely the MWNT bundle width and GnP dimensions (mean lateral size and layer number). Under fixed conditions (in particular, delivered energy per carbon mass), MWNTs are dispersed in much higher yields, by two orders of magnitude, than GnPs. However, and significantly, a master curve for the dispersibility was obtained, implying that common fundamental features underpin the dispersing process, irrespective of nanocarbon (1D or 2D) or surfactant (ionic or nonionic) types.