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Boron Nitride Nanotubes in Nanomedicine || Boron nitride nanotube films: preparation, properties, and implications for biology?applications
摘要： Boron nitride nanotubes (BNNTs) share the same structure as carbon nanotubes (CNTs), but have boron and nitrogen atoms sitting close to each other. Some properties of BNNTs are similar to their carbon counterparts, such as mechanical strength, thermal conductivity, and wettability. However, there are also many differences between them. BNNTs are insulators with a wide bandgap of about 6 eV, which is not sensitive to their diameter and chirality. Compared to CNTs, BNNTs are more thermally stable in air and, therefore, better candidates as fillers in metal/ceramic composites, field emitters, and thermal management materials at high temperatures. BNNTs show strong light emission at ～227 nm in the deep ultraviolet (DUV) region and are useful in optoelectronic, medical, data storage, and lithography applications. Isotopic 10BNNTs not only exhibit greatly improved thermal conductivity superior to that of CNTs, but also provide radiation shielding. Due to the electric polarization, BNNTs are piezoelectric and suitable for electromechanical devices on the nanoscale.
关键词： biology applications,Boron nitride nanotubes,properties,BNNT films,preparation
更新于2025-09-11 14:15:04
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Exciton Peierls mechanism and universal many-body gaps in carbon nanotubes
摘要： “Metallic” carbon nanotubes exhibit quasiparticle gaps when isolated from a screening environment. The gap-opening mechanism is expected to be of electronic origin, but the precise nature is debated. In this work, we show that hybrid density functional theory predicts a set of excitonic instabilities capable of opening gaps of the size found in experiment. The excitonic instabilities are coupled to vibrational modes and, in particular, the modes associated with the (cid:2) ? E2g and K ? A(cid:2) 1 Kohn anomalies of graphene, inducing Peierls lattice distortions with a strong electron-phonon coupling. In the larger tubes, the longitudinal optical phonon mode becomes a purely electronic dimerization that is fully symmetry conserving in the zigzag and chiral tubes, but breaks the symmetry in the armchair tubes. The resulting gaps are universal (i.e., independent of chirality) and scale as 1/R with tube radius.
关键词： exciton Peierls mechanism,electron-phonon coupling,many-body gaps,carbon nanotubes,hybrid density functional theory
更新于2025-09-11 14:15:04
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Effects of 6H-SiC Substrate Polarity on the Morphology and Microstructure of AlN Films by HVPE with Varied V/III Ratio
摘要： AlN films grown by high temperature hydride vapor phase epitaxy (HVPE) on Si-face and C-face 6H-SiC substrates were investigated. The influences of the substrate polarity with varied V/III ratio on growth mode, structural characteristics and crystalline quality of hetero-epitaxial AlN films have been studied. With the increasing of V/III ratio, AlN grown on Si-face 6H-SiC substrates changed the growth mode from step-flow to 3D island growth, and correspondingly, its surface morphology got rougher. On the contrast, AlN on C-face substrates were consistently in 3D growth mode and maintained a relatively rough surface, with a high density of nanotubes generated, each of which consisting of hexagonal sides defined by {01 0} facets and locating at the bottom of a V-shaped pit on the surface. Based on XRD, Raman and TEM analyses, it was found that the best AlN layer quality was obtained on the Si-face 6H-SiC at V/III ratio of 10.
关键词： Crystalline quality,Morphology,Dislocations,Substrate polarity,Nanotubes,Growth mode
更新于2025-09-11 14:15:04
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Photocatalyst properties depend on the mix
摘要： Photocatalysts use light to power chemical reactions in a whole host of applications from fuel cells to water remediation. There are many ways to improve the performance of titania (TiO2) photocatalysts from using catalyst support materials, which increase photosensitization rates, and help break down organic pollutants, to doping or co-doping with other atoms to expand the absorption range. Since using metal atoms such as dopants is problematic for water treatment if they leach into the environment, non-metallic dopants like nitrogen (N) are considered safer. Researchers from the University of South Africa have used these two strategies in conjunction to produce N-doped TiO2 photocatalysts on a carbon nanotube (CNT) support and systematically compared the effects of using different synthesis routes. Edward N. Nxumalo and his team find that photocatalysts with distinctly different properties and performance are produced depending on whether a hydrothermal or solgel synthetic route is used.
关键词： Carbon nanotubes,Hydrothermal synthesis,Solgel synthesis,Nitrogen doping,Photocatalysts,TiO2
更新于2025-09-11 14:15:04
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Synthesis of nanosized SiC by low-temperature magnesiothermal reduction of nanocomposites of functionalized carbon nanotubes with MCM-48
摘要： Silicon carbide synthesis by a magnesiothermal method was investigated using MCM-48 as the silica source mechanically mixed with carbon nanotubes (CNTs) as the carbon source, and nanocomposites of MCM-48/functionalized CNTs (CNTF). SiC syntheses were carried out with different molar ratios of MCM-48, carbon and magnesium at 700?C in argon. The MCM-48 and carbon nanotube starting materials and the SiC products were characterized by BET, XRD, FESEM, EDX and TEM. The effect of the carbon content and the type of CNTs (either functionalized or unfunctionalized) on the SiC synthesis was studied. The results show that an improved yield of SiC is obtained when the carbon nanotubes are functionalized, producing a better contact with the MCM-48. This improved contact between the reactants ensures a good degree of reaction in a stoichiometric mixture of silicon and carbon, with no improvement in product formation being achieved by the use of additional carbon. These findings suggest that the degree of contact between reactants is an important factor in the magnesiothermal synthesis of SiC. The SiC products from magnesiothermal synthesis of the functionalized nanocomposite precursors were shown by TEM and FESEM to have unusual nanofiber morphologies mimicking the morphology of the CNTF nanotubes.
关键词： MCM-48,Silicon carbide,Magnesiothermal synthesis,Carbon nanotubes,Functionalized carbon nanotubes
更新于2025-09-10 09:29:36
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Impact of TiO2 Nanotubes’ Morphology on the Photocatalytic Degradation of Simazine Pollutant
摘要： There are various approaches to enhancing the catalytic properties of TiO2, including modifying its morphology by altering the surface reactivity and surface area of the catalyst. In this study, the primary aim is to enhance the photocatalytic activity by changing the TiO2 nanotubes’ architecture. The highly ordered infrastructure is favorable for a better charge carrier transfer. It is well known that anodization affects TiO2 nanotubes’ structure by increasing the anodization duration which in turn in?uence the photocatalytic activity. The characterizations were conducted by FE-SEM (?end emission scanning electron microscopy), XRD (X-ray diffraction), RAMAN (Raman spectroscopy), EDX (Energy dispersive X-ray spectroscopy), UV-Vis (Ultraviolet visible spectroscopy) and LCMS/MS/MS (liquid chromatography mass spectroscopy). We found that the morphological structure is affected by the anodization duration according to FE-SEM. The photocatalytic degradation shows a photodegradation rate of k = 0.0104 min?1. It is also found that a mineralization of Simazine by our prepared TiO2 nanotubes leads to the formation of cyanuric acid. We propose three Simazine photodegradation pathways with several intermediates identi?ed.
关键词： Simazine,TiO2 nanotubes,anodization,photodegradation mechanism,photocatalytic,photocatalyst
更新于2025-09-10 09:29:36
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Advantages of the Surface Structuration of KBr Materials for Spectrometry and Sensors
摘要： A potassium bromide (KBr) material, which has been widely used as the key element in Fourier spectrometers and as the output window of the IR-lasers, was studied via applying carbon nanotubes in order to modify the potassium bromide surface. The laser-oriented deposition method was used to place the carbon nanotubes at the matrix material surface in the vertical position at different electric ?elds varying from 100 to 600 V × cm?1. The main idea of the improvement of the spectral properties of the potassium bromide structure is connected with the fact that the refractive index of the carbon nanotubes is substantially less than the refractive index of the studied material, and the small diameter of the carbon nanotubes allows one to embed these nano-objects in the voids of the lattice of the model matrix systems. Moreover, the mechanical characteristics and wetting features of potassium bromide structures have been investigated under the condition mentioned above. Analytical and quantum-chemical simulations have supported the experimental results.
关键词： surface structuration,potassium bromide,mechanical and wetting properties,laser-oriented deposition method,carbon nanotubes,spectra
更新于2025-09-10 09:29:36
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Complex band structure calculations based on the overbridging boundary matching method without using Green's functions
摘要： A complex band structure describes the dispersion relation not only of propagating bulk states but also of evanescent ones, both of which are together referred to as generalized Bloch states and are important for understanding the electronic nature of solid surfaces and interfaces. On the basis of the real-space finite-difference formalism within the framework of the density functional theory, we formulate the Kohn-Sham equation for generalized Bloch wave functions as a generalized eigenvalue problem without using any Green’s function matrix. By exploiting the sparseness of the coefficient matrices and using the Sakurai-Sugiura projection method, we efficiently solve the derived eigenvalue problem for the propagating and slowly decaying/growing evanescent waves, which are essential for describing the physics of surface/interface states. The accuracy of the generalized Bloch states and the computational efficiency of the present method in solving the eigenvalue problem obtained are compared with those by other methods using the Green’s function matrix. In addition, we propose two computational techniques to be combined with the Sakurai-Sugiura projection method and achieve further improvement in the accuracy and efficiency. Complex band structures are calculated with the present method for single- and multiwall carbon nanotubes, and the interwall hybridization and branch points of evanescent electronic states observed in the imaginary parts of the band structures are also discussed.
关键词： Sakurai-Sugiura projection method,density functional theory,generalized Bloch states,carbon nanotubes,complex band structure
更新于2025-09-10 09:29:36
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Effect of CuS nanocrystalline particles on counter electrodes of multi-wall carbon nanotubes for QDSCs
摘要： CuS nanocrystalline particles are deposited into the acid-treated multi-wall carbon nanotubes (MWCNTs) film on the fluorine-doped tin oxide glass substrate through the successive ionic layer adsorption and reaction combined with spin-coating technology to form MWCNTs/CuS composite counter electrode (CE). The CuS adding amount is changed in different cycles to discuss its effect mechanism on the photoelectric properties of MWCNTs/CuS composite CE based quantum dot sensitized solar cells (QDSCs). The TiO2 photoanodes are prepared by the electrospinning technique with CdS and ZnS as co-sensitizer. QDSCs are assembled with photoanodes, the polysulfide electrolyte and abovementioned CEs. The CEs are characterized by X-ray diffraction, transmission electron microscope and energy dispersed X-ray detector, which verifies CuS nanocrystalline particles are attached to MWCNTs successfully. The photoelectric properties are analyzed by Nyquist, Tafel and J–V curves. The results show that the introduction of CuS nanocrystalline particles can promote reduction rate of polysulfide species and the short circuit current density (Jsc) to improve catalytic activity, leading to a higher power conversion efficiency (PCE). The MWCNTs based CE with deposition CuS in eight cycles exhibits the best photoelectric performance within all CE samples and the electrical conductivity of MWCNTs/8CuS CE is superior to that of Pt CE according to Nyquist and Tafel curve analysis. PCE of QDSCs with MWCNTs/8CuS CE is up to 5.186%, which is a little lower than that of Pt CE (5.250%), but it possesses a higher Jsc value (18.028?mA cm?2) than that of Pt CE (16.057?mA cm?2). The low-cost MWCNTs/CuS composite CE with simple preparation is more suitable than Pt CE for commercial application of QDSCs.
关键词： multi-wall carbon nanotubes,quantum dot sensitized solar cells,CuS nanocrystalline particles,photoelectric properties,counter electrode
更新于2025-09-10 09:29:36
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Solid Acids Accelerate the Photocatalytic Hydrogen Peroxide Synthesis over a Hybrid Catalyst of Titania Nanotube with Carbon Dot
摘要： Photocatalytic synthesis of hydrogen peroxide (H2O2) from water and oxygen is an alternative route for clean energy storage and chemical synthesis, but still having problems with insufficient H2O2 productivity and solar-to-chemical energy conversion efficiency. Herein, we reported a hybrid catalyst of proton-form titania nanotube with carbon dot (HTNT-CD) that is highly efficient for the production of H2O2 under visible-light irradiation (λ>420 nm, H2O2 productivity at 3.42 mmol gcat-1·h-1), outperforming the titania catalysts containing noble metals and the carbon nitride catalysts reported previously. Multiple studies demonstrate that the protons on the HTNT-CD are crucial for the production of H2O2 by efficiently accelerating the half reaction of molecular oxygen reduction to form H2O2, and effectively hindering H2O2 decomposition under the irradiation conditions. This HTNT-CD catalyst gives solar-to-H2O2 apparent energy conversion efficiency at 5.2%, which is even 4.9 times of that (1.06%) over the catalyst derived from commercial P25 and CDs. More importantly, the HTNT-CD is stable, giving high H2O2 productivity in the continuous recycle tests.
关键词： photocatalyst,carbon dots,TiO2 nanotubes,H2O2 synthesis
更新于2025-09-10 09:29:36