Nanotube Diameter Research Articles

Tuning structural and electronic properties of single wall AlN nanotubes

The electronic and structural characteristics of the armchair and zigzag single-walled AlN nanotubes (SWAlNNTs) have been considered by using density functional theory (DFT). The effects of tube diameter on the Al–N bond length, the buckling separation, tube lengths, valence band maximum (VBM), conduction band minimum (CBM), Fermi energy, strain energy, and bandgap have been studied. The strain energy calculation revealed that higher-diameter nanotubes are more stable than those with smaller diameters consequently at the same chirality armchair AlNNTs are more stable than zigzag types. It revealed a correlation between the bandgap and buckling: the smaller the bandgap, the higher the buckling, and the buckling separation increases by decreasing tube diameter. The 2p-orbitals of Al and N atoms have the most contribution to CBM and VBM, respectively. All zigzag and armchair AlNNTs are semiconductors having direct and indirect bandgap, respectively. It is also found that for both zigzag and armchair AlNNTs, with increasing nanotube diameter, the bandgap increased. The conclusions of this study can definitely be useful in future experimental works on optoelectronic devices.

Theoretical investigation of substitutionally doped symmetrical finite phenine nanotubes

Ab initio density functional theory calculations were performed to investigate the substitutional doping of boron and nitrogen in symmetrical phenine nanotubes. It was found that the doped structures are energetically favorable and can be grown experimentally. Furthermore, we investigated how electronic and magnetic properties of these nanotubes change in the presence of electron-rich (nitrogen) and electron-deficient (boron) impurities, and found that doping in these tubes resulted in a non-magnetic structure. The doping changes the electronic structure of the tube by reducing the energy gap and the reduction value is sensitive to the nanotube diameter and impurity type. The gap corresponding to the nitrogen doped tubes is in the range of 2.38 eV-2.64 eV, whereas for boron doped tubes, the value lies in 1.91 eV to 2.11 eV, respectively. Moreover, the nitrogen doped phenine nanotubes tend to be n-type semi-conductor. The doped phenine nanotube molecules with a high stability and tunable electronic properties may offer several interesting applications in nano-electronics.

The structure evolution of halloysite nanotubes during the acid leaching process: A molecular dynamics study

For the acid-leaching process of halloysite nanotubes (HNTs), the structure and energetic evolution is crucial for the basic understanding and further modification of HNTs. The specific surface area, pore volume, and bond distribution of HNTs at different Al leaching percentages were studied by molecular dynamics simulation. With the increase of the Al leaching percentage, the inner diameter of the halloysite nanotubes is gradually enlarged, forming some nanoporous (1–20 nm) interlayer spaces inside the tube wall of HNTs due to the strong bondings between the adjacent layers, and the specific surface area and pore volume of HNTs increased in a complex way at each transition stages. For the transition structures, the interlayer nanopores greatly increase the specific surface area and pore volume of HNTs, which is more obvious after 50% Al leaching. The free water molecules inside lumen structure of HNTs would have an impact on the thermodynamics and the structure evolution of HNTs. Although the transition structures with extremely large loading capacity may not be naturally most stable, they might be stabilized or achieved by some fast transient regulation methods.

Coupling thermal and catalytic cracking of polymer wastes to boost carbon nanotubes production: Effects of HZSM-5 zeolites

The efficient synthesis of carbon nanotubes from polymer wastes has been considered one promising technology for the effective management of current environment crisis. In the two-stage reaction system, HZSM-5 zeolites were introduced into the two-stage reaction system between the upper and lower stages, which was expected to upgrade the pyrolysis gas from polymer wastes and boost the growth of carbon nanotubes on Fe-Al2O3 catalyst. The physicochemical properties of HZSM-5 zeolites, Fe-Al2O3 catalyst and the as-obtained carbon materials were systematically characterized by XRD, N2 physisorption, 27Al MAS NMR, NH3-TPD, H2-TPR, SEM, TEM, TG-DSC and Raman. It was found that the presence of HZSM-5 zeolites increased the length and yield, and narrowed the diameter of carbon nanotubes. In the absence of HZSM-5 zeolites, the yield of carbon nanotubes was 34 mg/g with an average diameter of 19 nm. The introduction of HZSM-5 and meso-HZSM-5 increased the yield of carbon nanotubes to 109 mg/g and 90 mg/g, and recduced the average diameter to 15 nm and 13 nm, respectively. The improvement of HZSM-5 zeolites on the synthesis of carbon nanotubes was observed for divrese polymer wastes inlcluding LDPE, HDPE and PP. It was attributed to the unique acidity and porosity of HZSM-5 zeolites, which enhanced the secondary cracking of the pyrolysis gas and the formation of light hydrocarbons.

Fast Water Transport through Subnanometer Diameter Vertically Aligned Carbon Nanotube Membranes.

Small-diameter carbon nanotubes (CNTs) have outstanding mass-transport properties, especially enhanced water flow. Here, we report on water transport through the first macroscopic membranes with vertically oriented, subnanometer (0.8 nm) CNT pores, made by a scalable, solution-based method with electric-field alignment of bulk-grown single-wall CNTs (SWCNTs). After plasma etching to open pores, vertically aligned CNTs served as the primary pathway for liquid-water transport. The CNT membranes showed fast pressure-driven water transport, with up to 105-fold enhancement compared to no-slip Hagen-Poiseuille flow. Comparing 0.8 and 3 nm CNTs, we found that the hydrodynamic slip lengths increased with decreasing nanotube diameter, reaching 8.5 μm for the smaller-diameter CNTs. The results suggest that pressure-driven water transport in small-diameter CNTs is increasingly dominated by entrance resistance, thus becoming independent of nanotube length. Scalably fabricated membranes incorporating vertically aligned subnanometer CNT pores could have applications in water filtration, desalination, and energy harvesting.

Stereoselective 1,2 migration of a boronate complex inside a nanoreactor: QM/MM study

In this study, we investigate the stereoselective 1,2 migration reaction inside a carbon nanotube (CNT) using a combined quantum mechanics/molecular mechanics (QM/MM) approach. The steric and electronic effects of the CNT are found to significantly influence the stabilization of the guest molecule, highlighting the importance of nanotube diameter. By adjusting the nanotube diameter, it becomes possible to control the stereoselectivity of the migration reaction. Nanoreactors, such as CNTs, have emerged as promising tools for manipulating chemical reactions due to their versatile properties. We explore the impact of the nanotube environment on the migration mechanism and discuss the role of non-covalent interactions, such as van der Waals forces, in promoting stability and selectivity. Our computational results demonstrate that the presence of the CNT affects the reaction kinetics, energy barriers, and overall energetic outcomes. The choice of nanotube diameter is crucial to achieve optimal confinement of the guest molecule while maintaining stabilizing interactions. This study provides valuable insights into the potential of carbon nanotubes as nanoreactors for controlling stereochemistry in organic reactions, offering opportunities for tailored reaction design and synthesis.

Empirical model for optical transitions in inner semiconducting tubes of double wall carbon nanotubes

The inter-wall distance, average diameter, and chirality of the constituent nanotubes play a significant role in determining the electronic structure of double wall carbon nanotubes (DWNTs). In DWNTs, the inner tube possesses a special status, granted by the outer tube, which acts as a shield. Here, we proposed an empirical model for estimating the different optical transitions of inner semiconducting tubes (ISCTs) of DWNTs from the chirality of the constituent single wall carbon nanotubes when the outer tube can be semiconducting or metallic. So far, there have been no well-known theoretical or empirical models to estimate the optical transitions of ISCTs of DWNTs except first principles simulations. The proposed model relates the optical transitions of ISCTs of DWNTs with the chirality of the inner tube and the average diameter of DWNTs. The relation is used to calculate the optical transitions of a number of ISCTs of DWNTs, and the result was found to be in good agreement with the recent experimental reports. The proposed relation can help understand the electronic behavior of DWNTs in terms of their structural parameters and can help in identifying the chirality of unknown DWNTs from its electronic properties.

Fabrication and characterization of field-effect transistors based on MoS2 nanotubes prepared in anodic aluminum oxide templates

Field-effect transistors (FETs) based on MoS2 nanotubes prepared in anodic aluminum oxide (AAO) templates have been fabricated and demonstrated in this work. MoS2 nanotubes were prepared by the thermal decomposition of (NH4)2MoS4 precursors in the AAO template. The diameter of the MoS2 nanotubes was approximately 80 nm, which corresponded to the size of the AAO template. Schottky-type FETs were prepared with Au and Pt electrodes, and the FETs exhibited n-type behavior, with on/off ratios that exceeded 103 at VSD = 0.5 V.

Mechanical Properties of the Pt-CNT Composite under Uniaxial Deformation: Tension and Compression.

Composite materials are gaining increasing attention from researchers worldwide due to their ability to offer tailored properties for various technical challenges. One of these promising fields is metal matrix composites, including carbon-reinforced metals and alloys. These materials allow for the reduction of density while simultaneously enhancing their functional properties. This study is focused on the Pt-CNT composite, its mechanical characteristics, and structural features under uniaxial deformation depending on temperature and mass fractions of carbon nanotube (CNT). The mechanical behavior of platinum reinforced with carbon nanotubes of diameters varying in the interval 6.62-16.55 Å under uniaxial tension and compression deformation has been studied by the molecular dynamics method. Simulations for tensile and compression deformations have been done for all specimens at different temperatures (viz. 300 K, 500 K, 700 K, 900 K, 1100 K, and 1500 K). The calculated mechanical characteristics allow us to conclude that, compared to pure platinum, the Young's modulus increased by about 60%. The results indicate that yield and tensile strength values decreases with increase in temperature for all simulation blocks. This increase was due to the inherent high axial rigidity of CNTs. In this work, these characteristics are calculated for the first time for Pt-CNT. It can be concluded that CNTs can be an effective reinforcing material for composites based on a metal matrix under tensile strain.

DFT study of electronic and structural properties of single‐walled gallium nitride nanotubes

AbstractThe electronic and structural properties of the armchair and zigzag single‐walled GaN nanotubes (GaNNTs) are studied by using density functional theory. The effects of tube diameter on the GaN bond lengths, the axial lattice constant, the Fermi energy, the buckling separation, and the bandgap of the tube are investigated. It is revealed that there is a correlation between the bandgap and the buckling; the smaller the bandgap, the higher the buckling. The results show that by increasing diameter of tubes the buckling separation decreases. The 4p‐orbitals of Ga atoms and 2p‐orbitals of N have the main role to the valence band maximum and the conduction band minimum, respectively. All armchair and zigzag GaNNTs are semiconductors having indirect and direct bandgap, respectively. It is also found that by increasing the diameter of nanotubes the bandgap increases, for both armchair and zigzag GaNNTs. The consequences of this study can undoubtedly be useful in future experimental works on optoelectronic devices.

Ab Initio Study of Optical Properties of Hybrid Films Based on Bilayer Graphene and Single-Walled Carbon Nanotubes

In recent years, the possibility of combining graphene and carbon nanotubes has attracted much attention from researchers attempting to obtain new multifunctional hybrid materials with promising properties. Optoelectronics shows potential as a field of application for such hybrid structures. The variety of existing structural configurations of graphene-nanotube hybrids requires preliminary detailed studies of their optical properties by computer simulation methods. In this paper, we consider island-type graphene-nanotube hybrid films formed by AB-stacked bilayer graphene and single-walled carbon nanotubes (SWCNTs). In this case, bilayer graphene is located above the surface of the nanotube, forming areas with an increased density of carbon atoms, creating so-called “islands.” To meet the conditions of a real experiment, we chose chiral SWCNTs (12,6) with a diameter of 1.2 nm, which are most often synthesized in real experiments. All constructed atomistic models of bilayer graphene-chiral SWCNT films were tested for thermodynamic stability at room temperature and proved their suitability for research. Using Kubo-Greenwood formalism, we calculated the complex optical conductivity tensor and absorbance coefficient in the wavelengths of ultraviolet, visible, and near-infrared radiations. The photocurrent spectra are calculated based on the obtained absorption spectra and solar radiation spectra on the earth’s surface (AM1.5) and outside the earth’s atmosphere (AM0). The results of calculations revealed regularities in the influence of structural parameters (nanotube diameter, graphene width) on the optical and optoelectronic properties of graphene-chiral SWCNT (12,6) with an island structure.

Novel design of power-efficient quaternary logic gates using CNTFET

ABSTRACT This paper presents novel power-efficient designs of quaternary logic gates like Quaternary Minimum (QMIN) and Quaternary Maximum (QMAX), Standard Quaternary Inverter (SQI), Standard Quaternary NAND (SQNAND), Standard Quaternary NOR (SQNOR) and Standard Quaternary XOR (SQXOR) using Carbon Nanotube Field Effect Transistor (CNTFET). The designs are based on Pass Transistor Logic (PTL) and use only three types of Carbon Nanotube (CNT) diameters 0.626 nm, 1.018 nm, and 2.27 nm, which lead to lower fabrication costs and enhanced manufacturability when compared to the state-of-the-art designs. The designs are simulated in HSPICE with a 32 nm CNTFET model provided by Stanford University, and the average power and maximum propagation delay obtained from the simulation results are compared with other existing designs. It shows that the proposed designs require 75% to 90% less power and they achieve 73% to 91% less Power Delay Product (PDP) than the latest designs.

A novel approach for extracting magnetic properties of double-shell nanotubes of Prussian blue and its Cr analog with the use of a mathematical hysteresis decomposition

This work presents the synthesis and investigation of Prussian blue and its chromium analog nanotubes obtained inside porous polycarbonate track etch (PCTE) membranes by electrochemical deposition. The process yielded nanotubes with outer diameters between 50 and 200 nm and thicknesses of approximately 30 nm. It was found that decreasing nanotube diameter had little or no effect on magnetic properties (critical temperature and coercivity). Additionally, the growing process and the basic properties of double-shell nanotubes are described. These double-shell structures show a two-component magnetic behavior. By using the theoretical model, it is possible to decompose the hysteresis loops into the base constituents and derive the relative concentration of each counterpart.

Effect of the kinetic energy on particle ejection process from carbon nanotubes bombarded by kilo-electron-volt C60

Molecular dynamics computer simulations are employed to investigate processes leading to particle ejection from single-wall carbon nanotubes bombarded by keV C60 projectiles. The effect of the primary kinetic energy, the incidence angle, and the nanotube diameter on the ejection process is studied. Armchair nanotubes with diameters of 3.26, 5.4, and 8.2 nm are tested. C60 projectiles bombard these targets with kinetic energy between 3 and 50 keV and the angle of incidence ranging between 0° and 75°. The particle ejection yield is a result of the interplay between the amount of kinetic energy available for breaking interatomic bonds, the size of the bombarded area, and the size and form of projectiles hitting this area. Much of the initial kinetic energy is dissipated in the nanotubes as waves, especially for low-energy impacts. Computer simulations are used to find the optimal conditions leading to the gentle ejection of unfragmented organic molecules adsorbed on nanotube substrates. This knowledge may be helpful in the potential application of nanotube substrates in secondary ion mass spectrometry or secondary neutral mass spectrometry.

Imogolite prepared from cement kiln dust removes arsenite from water

Imogolite belongs to the family of nanotubular metal oxides which are useful for the construction of new materials in nanotechnology. This study aims to develop a simple waste valorization method to obtain imogolite from cement kiln dust (CKD) via solubilization of CKD and subsequent precipitation of imogolite (Imo-CKD) in a hydrothermal process. The newly synthesized Imo-CKD and a conventional imogolite (Imo) showed similar diameter (Ø) and length (L) of nanotubes [Ø≅ 1.9 nm and L ≅ 200 nm] and crystallinity grade but different values of isoelectric point (IEP) [IEPImo−CKD=8.86 and IEPImo=9 .92]. The shift in the IEP value of Imo-CKD to a lower value was attributed to the presence of allophane as a subproduct during Imo-CKD synthesis. Arsenite [As(III)] removal from water by both the imogolites was a rapid (t ≤ 20 min) and spontaneous process. The kinetic As(III) removal data obeyed the pseudo-second order model, while surface diffusion also controlled the As(III) adsorption process. The activation energy (Ea > 40 kJ mol−1) suggested a chemical adsorption of As(III) in both materials. The Imo-CKD (0.377 mmol g−1) removed As(III) from water more efficiently than Imo (0.334 mmol g−1), despite the formation of allophane byproduct in the synthesis process. Results of this study can promote the reuse of inexpensive CKD as a viable alternative to replace costly tetraethyl orthosilicate for imogolite synthesis and use of imogolite for water pollutant removal.

Rheological behaviors and viscosity prediction model of cementitious composites with various carbon nanotubes

This study aims to understand the effects and mechanisms of length, diameter, and functional group of carbon nanotubes (CNTs) on rheological behaviors of cementitious composites. The experimental results show that the addition of CNTs decreases the flow index and increases the critical shear rate of cementitious composites. CNTs with a sub-micrometer length and small diameter endow cementitious composites with high yield stresses and minimum viscosities. Influenced by the high water absorption of hydroxylic groups, the minimum viscosity of cementitious composites with hydroxyl functionalized CNTs is larger than that of composites with pristine carbon nanotubes (p-CNTs). By contrast, the yield stress and minimum viscosity of cementitious composites with carboxyl functionalized CNTs are smaller than that of cementitious composites with p-CNTs at most contents due to the high dispersion induced by carboxyl groups. The effect mechanisms of CNTs on rheological behaviors can be attributed to adsorption effect and entanglement effect, which are closely related to length, diameter and functionalization groups of CNTs. The established minimum viscosity prediction model considering the influence of CNT physicochemical features can provide guidance for regulating the workability and hardened performance of CNTs modified cementitious composites.

Preparation and Ferroelectric Properties of Ba(1-x-y)CaxSryTiO3 Nanotubes

In this paper, Ba(1-x-y)CaxSryTiO3 nanotubes with different doping concentrations were prepared by hydrothermal synthesis, and then their micro morphology, crystal structure, and ferroelectric properties were analyzed by SU8010 scanning electron microscope, D/MAX-2500 X-ray diffraction tester, and TF2000. It is found that the barium titanate nanotubes co doped with Ca and Sr have obvious tubular structure. With the increase of doping concentration, the nanotube diameter becomes smaller, the tube wall becomes thicker, and the ferroelectric properties of the samples increase first and then decrease. When 0.002mol/L Ca(CH3COO)2 and 0.002mol/L Sr(CH3COO)2 are doped, the maximum residual polarization intensity of Ba(1-x-y)CaxSryTiO3 is 0.097µC/cm2. At this time, there is a clear hysteresis loop image, and the ferroelectric performance is the best.

Preparation of Multi-walled Carbon Nanotubes with Ni/SiO2 Composites

Using carbon monoxide as carbon source to manufacture Multi-walled carbon nanotubes on the supported of Ni/SiO2 by chemical vapor deposition. The effects of nickel loading and raw gas to carbon nanotubes were studied. When the content of Ni is 5%, the yield of carbon is very low. As the content of Ni increases from 5% to 35%, the yield gradually increases. When Ni loading exceeds 35%, the yield of carbon decreases. Through the TEM, HRTEM and XRD to characterized carbon nanotubes. The results showed that the morphology of carbon nanotubes became worse with the Ni conten increased In terms of yield and quality,the best synthesis temperature is 600°C. In the absence of hydrogen in the feedgas, the diameter of carbon nanotubes is in the narrow range of 10 to 20 nm. When hydrogen is introduced into the system, the amount of carbon increases, but the form deteriorates.

Simulation of Spin Selectivity of Electrical Conductivity of Chiral Platinum Nanotubes

To study the electronic and spin properties of single-walled platinum nanotubes, two rows of chiral nanotubes have been calculated by the relativistic method of symmetrized linearized augmented cylindrical waves: Pt(5, n2) with 1 ≤ n2 ≤ 4 and Pt(10, n2) with 1 ≤ n2 ≤ 9 and radii from 2.24 to 7.78 Å. In all tubes, the intersection of the top of the valence band and the bottom of the conduction band with the Fermi level is observed, which is characteristic of compounds with a semi-metallic band structure. The spin–orbit coupling manifests itself as a splitting of nonrelativistic dispersion curves, which can exceed 0.5 eV for near-Fermi bands and decreases upon transition to the internal states of the valence band and nanotubes of larger diameter. The spin densities of states for electrons with spin up and down at the Fermi level are noticeably different, which can be used to create pure spin currents through nanotubes using alternating electrical voltage. The (5, 3) and (10, 7) nanotubes are the most suitable for this.

Nanotubes fabricated from a triple helix polysaccharide as a novel carrier delivering doxorubicin for breast cancer therapy

Most current strategies of drug delivery systems face momentous challenges owing to obvious biological barriers. It is urgently necessary to develop artificial nanocarriers with biological and physical properties to reduce the severe system cytotoxicity of chemical drugs. Herein, triggered by the stiffness and amphiphilicity of the triple helix β-glucan (LNT), we developed a novel nanocarrier with the hydrophobic cavity for delivering the anti-cancer drug of doxorubicin. In our findings, based on the law of minimum surface energy, LNT with considerable chain stiffness self-assembled into nanotubes (LNT-NT) with the controlled hydrophobic nanotube diameter at the nanometer level positively depending on the molecular weight through hydrogen bonding and hydrophobic interaction in manners of “shoulder-to-shoulder” and “head-to-head” arrangements. The hydrophobic drug of doxorubicin was then demonstrated to be entrapped into LNT-NT through hydrophobic interaction. Doxorubicin loaded into LNT-NT nanocarriers significantly inhibited tumor growth in vitro and in vivo by promoting tumor cell apoptosis and blocking cell proliferation, showing a higher therapeutic efficacy of 74.5 % and less adverse effects than the free doxorubicin, which was ascribed to the enhanced targetability by LNT-NT. In conclusion, this work proposes an alternative strategy for delivering hydrophobic drugs to reduce cytotoxicity and enhance therapeutic effectiveness by constructing β-glucan-based nanotubes as a promising nanocarrier.