Narrow Results

Carbon atoms can connect with themselves and with other atoms (both electronegative and electropositive elements) in various ways. Thanks to these abilities, the diversity of carbon compounds is increasing day by day. This growth was even faster after the discovery of carbon nanoallotropes, i.e. carbon nanotubes, fullerenes, and graphene. At present, these carbon nanoallotropes are widely studied, and new hybrid structures have been synthesized based on these nanoallotropes. Hybrid structures formed by the covalent bond of fullerenes to the outside carbon nanotubes are called carbon nanobuds (CNBs). Development of synthesis methods, computational calculations, and the study of CNB properties was much faster than other hybrid structures. However, only fewer articles on CNBs have been published in recent years. CNBs show a synergistic effect and have the unique properties of the carbon nanoallotropes from which they formed. This review discusses CNBs and reports the recent research on CNBs, mostly after 2016.

NiO/Pt nanotubes were obtained by firstly preparing the NiO nanotube with self-sacrificial templating methods and subsequently loading Pt nanoparticles with microwave assistant procedures. The as-prepared NiO/Pt nanotubes sensors displayed better electrocatalytic activities for glucose oxidation. The detection limit and sensitivity for glucose detection are 0.3 $\mu$M and 418.28 $\mu$A⋅ mM${}^{-1}$⋅cm${}^{-2}$ in the range of 1 $\mu$M-4000 $\mu$M. In addition, the practicality of NiO/Pt nanotubes was also confirmed by determining the glucose in serum specimen.

A simple procedure for one-step growing Nb₂O₅ hollow nanospheres and nanotubes was proposed. The final products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The as-obtained hollow spheres present a polycrystal surface while the nanotubes possess single crystal walls. Moreover, the factors that could impact the product morphology and crystal structure were discussed, and the corresponding mechanism was proposed accordingly. The crystal structure and morphology of products can be easily tuned by adjusting the molar ratio of Nb/Ti used, which determines the amount of F^- ions existing in the reaction system. The as-obtained Nb₂O₅ hollow nanospheres and nanotubes may exhibit enhanced applications in a wide range of areas. Additionally, it is rational to expect that this simple method can be extended to systems of other inorganic materials with desired morphologies.

Nanostructured thin-film electrode materials are proposed for supercapacitors due to their outstanding performance over bulk materials. In this work, we fabricated a TiO₂ nanotube film over a titanium foil using a top-down approach for supercapacitor electrodes. We noticed that the fabricated nanotubes are uniform and well aligned, confirmed by FESEM; the TiO₂ nanotube parameters were further simulated using COMSOL Multiphysics. Simulations show an areal capacitance of 1.19393 pF/cm² with oxidation and reduction peak currents of 6.18921×10${}^{-15}$ A and −6.0320×10${}^{-15}$ A, respectively, at 10 mV/s scan rate. The as-prepared nanotubes show a poor areal capacitance of 1.0193 F/cm², which is improved to 12.8764 F/cm² at a scan rate of 10 mV/s, that is approximately 12.63 times with oxidation and reduction peak currents of 0.129 mA/cm² and −0.105 mA/cm², respectively, by performing an electrochemical etching. Further, the surface roughness of both as-prepared and etched samples is studied to comment on their surface area changes. The effect of the etched sample is studied, compared and validated with simulation, which reveals that the etched TiO₂ nanotubes thin-film sample shows considerable similarity with the simulation results.

Here, we report investigations on the relative humidity (RH) sensing property of ZnO nanotubes synthesized via hydrothermal method. Grown nanotubes are formed with a hexagonal shape and possess a wurtzite crystal structure in conjunction with higher oxygen vacancies. ZnO nanotube-based RH sensor shows a small current increase in lower RH (<75% RH) region, due to the frozen motion of H${}^{+}$ ions, where electronic conduction dominates. The sensor conduction increases from 13 to 960 fold upon exposer of 65%–90% RH, respectively. The free motion of H${}^{+}$ ions steers the conduction mechanism to be protonic in higher level physisorbed water layer and is responsible for the observed sharp increase in response. The competitive adsorption and desorption of oxygen species and water molecules play a vital role in defining the conduction to be electronic or protonic during the experiment.

New types of core–shell nanoparticles are reported: Pb@GaS fullerene-like and nanotubular structures, achieved via the continuously high reactor temperatures and ultra-hot strong-gradient annealing environments created by highly concentrated sunlight. Structural and chemical characterizations suggest a formation mechanism where vaporized Pb condenses into nanoparticles that are stabilized as they become covered by molten GaS, the ensuing crystallization of which creates the outer layers. Hollow-core GaS fullerene-like nanoparticles and nanotubes were also observed among the products, demonstrating that a single solar procedure can generate a variety of core–shell and hollow nanostructures. The proposed formation mechanisms can account for their relative abundance and the characterization data.

Carbonaceous nanotubes with a calculated specific heat of 710J K${}^{-1}$ Kg${}^{-1}$, and an outer diameter of 58nm, made by a micro-thermal reaction, using polypyrrole nanotubes precursor is presented here. Three degradation stages from the thermal curves are identified. We observe a decomposition temperature at 371${}^{\circ }$C that relates to the presence of amorphous carbon on samples for the first time in this material. Also, it is identified that gradual decomposition of the fragments provides a different kind of residue percentage in the range 48–32% that is related to stirring speed used in each synthesis. It is worthy to note that electron transmission microscope images of carbonaceous nanotubes present defects as well, wherein we identify chloride and nitrogen as doped agents. Finally, results of nanotubes using Infrared, Raman spectrometry analysis, scanning electron microscopy and electron diffraction are presented here.

Inorganic fullerene-like (IF) nanoparticles of MoS₂ were synthesized using gas-phase reaction starting from MoCl₅ and H₂S. The IF-MoS₂ nanoparticles are spherical and in some cases faceted with diameters in general ranging between 20 and 80 nm. The IF-MoS₂ nanoparticles have large hollow cores, filled in some cases with amorphous material. Various parameters have been investigated to understand the growth and formation of the IF-MoS₂ nanoparticles. The parameters that have been studied include flow rates of the various carrier gases, temperature at which the reaction was carried out, time of the reaction and heating of the precursor material. The best set of conditions wherein maximum yields of the IF-MoS₂ nanoparticles are obtained have been identified. Additionally, annealing the as-obtained samples or heating them in a mixture of H₂ along with H₂S improves the crystallinity and reduces the amorphous material filling in the core. Apart from the fullerene-like nanoparticles under certain experimental conditions nanotubes of MoS₂ have also been obtained nonetheless in small yields.

Titanium oxide nanotube is a promising material for versatile applications. However, its structure and formation mechanism were quite confusedly reported. Therefore, it is essential to fully understand its structure, formation mechanism and stability. In this study, the structure, formation and stability of titanium oxide nanotube were studied in detail. New experimental findings on the morphology of titanium oxide nanotubes were reported, demonstrating close-opened nanotubes, cone-shaped nanotubes, twin and ternary nanotubes etc. A structural model of the titanium oxide nanotubes is proposed on the basis of cylinders of smoothly curved sheets of TiO₆ octahedra, among which H⁺ and H₃O⁺ are intercalated. The formation mechanism of titanium oxide nanotubes was deduced and discussed on the basis of their structural characteristics and chemical bonding behaviors of constituent atoms. The stability of the nanotubes was also studied under different conditions.

Carbon dioxide (CO₂) is an attractive C1 resource because it is cheap and abundant and its more extensive use would be beneficial for the environment. However, its high thermodynamic stability and poor reactivity have seriously limited its utilization as a ready carbon source. The scientific challenges facing CO₂ transformation are accordingly very attractive. This paper summarizes recent advances made in transformation of CO₂ to value-added high-molecular-weight materials such as polymers, star-shaped molecules and nanocarbons.

When one studies the Casimir effect, the periodic (anti-periodic) boundary condition is usually taken to mimic a periodic (anti-periodic) structure for a scalar field living in a flat space with a non-Euclidean topology. However, there could be an arbitrary phase difference between the value of the scalar field on one endpoint of the unit structure and that on the other endpoint, such as the structure of nanotubes. Then, in this paper, a periodic condition on the ends of the system with an additional phase factor, which is called the "quasi-periodic" condition, is imposed to investigate the corresponding Casimir effect. And an attractive or repulsive Casimir force is found, whose properties depend on the phase angle value. Especially, the Casimir effect disappears when the phase angle takes a particular value. High dimensional spacetime case is also investigated.

We report on a number of new effects of self-organization at nanoscale, leading to creation of new functional nanomaterials, including carbon and carbon–metal nanotoroids and nanodiscs and self-assembling of magnetic nanoparticles into helices and chains. We also extensively used a new approach of biopattern nanoengineering to create DNA-based complexes with metal or CdSe/ZnS core-shell nanorods (22 × 4.5 nm) which possess strong linearly polarized photoluminescence due to unidirectional orientation of nanorods along DNA filaments. Optical, electrical, and topological (geometrical) properties of such complexes were investigated. This work is a result of a coherent effort (since 1980s) of a consortium of Russian research groups in Nano-technology (INTC: Interdisciplinary Nanotechnology Consortium) aimed at creating molecular electronic devices based on individual and collective properties of specially designed and fabricated nanoclusters.

Ultralong zinc oxide nanotubes have been synthesized on glass substrate by a simple chemical bath deposition. The nanotubes are hexagonal with the core diameter about ~200 nm. The length of the nanotubes was about 10 μm. No specific alignment of the nanotubes on the glass substrate was observed. The morphology of the nanostructures depends highly on the concentration of zinc acetate solution, duration of mechanical stirring, and temperature during synthesis. Depending upon these experimental conditions nanorods and nanotubes were observed. The material was structurally characterized using grazing incidence X-ray diffraction, showing hexagonal unit cell structure. Transmission electron microscopy results revealed that the walls of the nanotubes are hexagonal. Room temperature photoluminescence spectrum shows a strong violet emission at ~420 nm from the ZnO nanotubes due to transition between zinc interstitial and zinc vacancy level. These results will be very useful in optoelectronic and nanophotonic device applications.

This work presents template synthesis of ordered arrays of nickel, cobalt and nickel hexacyanoferrates (NiHCF) with several distinct morphologies such as dots, rods, and tubes. Anodic alumina oxide (AAO) with preferred pore diameters and thickness was fabricated by electrochemical anodization of aluminum used as template. Ni and Co nanostructures inside AAO template were prepared by electrodeposition using galvanostatic method. NiHCF nanostructures were prepared by electrochemical oxidation of Ni using cyclic voltametry (CV) in the presence of hexacyanoferrate ions. The morphology, chemical, and functional properties of prepared nanostructures were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray microscopy (EDAX), and electrochemical methods. The electrocatalytic properties of NiHCF nanorod arrays electrode and their potential for the detection of hydrogen peroxide and biosensing application were demonstrated.

The effect of ultraviolet, visible and near-infrared irradiation on the yield and morphology of single crystalline C₆₀ fullerene nanowhiskers (FNWs) and nanotubes (FNTs) was investigated in an effort to produce large-scale quantities of FNWs and FNTs. These fullerene nanomaterials were synthesized by the liquid–liquid interfacial precipitation method using pyridine and isopropyl alcohol (IPA) as solvents. The C₆₀–pyridine solution was illuminated using different wavelengths for 24 h at ambient pressure and temperature before addition of IPA. High yields (30–38 mg/L) were obtained upon irradiation using wavelengths in the ultraviolet region in accordance with the increased photoabsorption signal of solid C₆₀ and C₆₀ dissolved in pyridine acquired by a UV-VIS-NIR spectrophotometer. However, elevated yields (21–27 mg/L) were also obtained in the 600–800 nm regions, where C₆₀ absorption is particularly weak. Such an enhanced yield of FNTs and FNWs is probably related to the reported rise in transient absorption of the triplet excited state of C₆₀ in the 740 nm region formed by the decay of the photoexcited singlet C₆₀ through intersystem crossing. The formation of photopolymerized fullerene nanofibers was also observed by Raman spectroscopy, it is attributed to ultraviolet and visible light irradiation. SEM and TEM observations suggest that preparation of FNWs and FNTs by irradiation using different wavelengths of light does not produce apparent morphological transformations on the surface of these fullerene materials.

Ordered arrays of Ni and Co nanowires and nanotubes, with diameters between 30 nm and 60 nm, were prepared by electrodeposition into nanoporous alumina templates. The study of the corresponding magnetization reversal processes was performed by analyzing the angular dependence of coercivity (H_c) and using a simple analytical model. The agreement between experimental and theoretical data shows that magnetization in nanowire arrays reverses by means of nucleation and propagation of a transverse domain wall, independently of the diameter. However, a critical diameter of ~ 50 nm was found in the case of nanotubes, above which a nonmonotonic angular dependent H_c was observed, evidencing a transition between vortex and transverse reversal modes.

Fe-doped In₂O₃ nanotubes were successfully synthesized by electrospinning technique followed by subsequent heat treatment. The as-prepared samples appeared as an apparently open-end one-dimensional (1D) and tubular-like morphology with the diameter of approximately 150 nm and the wall thickness about 20 nm. The diffraction peak of the obtained nanotubes shifts toward bigger angle direction with the increase of the Fe content. Comparing to the In₂O₃ nanotubes, the Fe-doped In₂O₃ nanotubes exhibit better sensing characteristics toward ethanol gases, including higher sensing response, lower operating temperature and higher selectivity. Enhanced sensing properties are attributed to 1D hollow nanostructures and the role of doping Fe element.

A comprehensive ab-initio investigation of the stability, structural, electronic, optical and Raman-active properties has been performed for the small diameter armchair carbon nanotubes. A number of new features not discussed earlier are observed in the present study. The binding energies (BEs) for the ultrathin nanotubes with respect to the graphine sheet are negative and the magnitude of the negative BE decreases with the diameter of the tube approaching zero for the graphine sheet. The separation between the two van Hove singularities (vHs) around the Fermi level increases with the diameter of the tube. The main absorption arises from the transitions between the states at nonzero values of k_z lying in the range 0.38–0.50. There is a large variation in the magnitude of the optical matrix-element with the wave vector. The energy range of the strong optical absorption increases with the diameter of the tube. The presently predicted absorption and the RBM frequencies are in good agreement with the available experimental data. The variation of the radial breathing mode (RBM) frequency with diameter "d" of a tube obeys a relation which is very close to an experimentally determined relation obtained for a number of wide semiconducting nanotubes possessing a wide range of chiral angles.

Nanostructured thin-film electrode materials are proposed for supercapacitors due to their outstanding performance over bulk materials. In this work, we fabricated a TiO₂ nanotube film over a titanium foil using a top-down approach for supercapacitor electrodes. We noticed that the fabricated nanotubes are uniform and well aligned, confirmed by FESEM; the TiO₂ nanotube parameters were further simulated using COMSOL Multiphysics. Simulations show an areal capacitance of 1.19393 pF/cm² with oxidation and reduction peak currents of 6.18921 × 10⁻¹⁵ A and −6.0320 × 10⁻¹⁵ A, respectively, at 10 mV/s scan rate. The as-prepared nanotubes show a poor areal capacitance of 1.0193 F/cm², which is improved to 12.8764 F/cm² at a scan rate of 10 mV/s, that is approximately 12.63 times with oxidation and reduction peak currents of 0.129 mA/cm² and −0.105 mA/cm², respectively, by performing an electrochemical etching. Further, the surface roughness of both as-prepared and etched samples is studied to comment on their surface area changes. The effect of the etched sample is studied, compared and validated with simulation, which reveals that the etched TiO₂ nanotubes thin-film sample shows considerable similarity with the simulation results.

We discuss recent measurements of the interband spectrocopy of carbon nanotubes and studies of cyclotron resonance in graphene, using these to examine the possible dependence of the band structure of graphene on the number of layers present and the role of Coulomb interactions. Cyclotron resonances gives a value for the electron velocity at the Dirac point of 1.093×10⁶ ms^-1, which is ~ 20% larger than would be expected from deductions of the band structure of carbon nanotubes. In addition, a significant asymmetry exists between band structure for electrons and holes, which gives rise to a 5% difference between the velocities at energies of 125 meV away from the Dirac point.