Discrimination of B–C–N nanotubes through energy-filtering electron microscopy

Various multi-walled nanotubes in the B–C–N system are thoroughly investigated using a JEOL-3100FEF high-resolution field emission transmission electron microscope operating at 300 kV and equipped with an in-column built Omega filter. Spatially-resolved B, C and N elemental maps of the nanotubes are constructed. It is realized that a wide variety of tubular arrays composed of B, C and N atoms may exist in the system. Sandwich-like BN-rich and C-rich alternating tubular shells, graphitic C layers inside and outside of pure BN shells induced either by surface contamination, or electron beam irradiation, separation of C-rich and BN-rich tubes and/or BN particles within tubular bunches may take place. One should carefully take these effects into account while analyzing nanotube physical properties, e.g., electrical or optical, rather than simply rely on electron energy loss spectra typically collected from B, C and N containing nanostructures as a whole. Striking dependence of an individual nanotube electrical conductivity on tubular shell chemistry is demonstrated using I–V curve recording in an atomic force microscope.     

Thermal conductivity improvement in electrically insulating silicone rubber composites by the construction of hybrid three-dimensional filler networks with boron nitride and carbon nanotubes

In this study, we constructed hybrid three-dimensional (3D) filler networks by simply incorporating a relatively low content of one-dimensional carbon nanotubes (CNTs; 0.0005–0.25 vol %) and a certain content of two-dimensional boron nitride (BN; 30 phr) in a silicone rubber (SIR) matrix. As indicated by transmission electron microscopy observation, flexible CNTs can serve as bridges to connect BN platelets in different layers to form hybrid 3D thermally conductive networks; this results in an increase in thermally conductive pathways, and the isolation between CNTs can prevent the formation of electrically conductive networks. Compared to the SIR–BN composite with the same BN content, the SIR–BN–CNT composites exhibited improved thermal conductivity, slightly increased volume resistivity, and comparable breakdown strength without a largely decreased flexibility. When 0.25 vol % CNTs were incorporated, the SIR–BN–CNT composite exhibited 75 and 25% higher thermal conductivities relative to the neat SIR and SIR–BN composite with 30 phr BN, respectively, and a thermal conductivity that was even comparable to SIR–BN composite with 40 phr BN. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46929.     

Young’s modulus of crystalline C60 nanotubes studied by in situ transmission electron microscopy

Bending tests of crystalline nanotubes composed of fullerene C₆₀ molecules are performed inside a high-resolution transmission electron microscope. We fixed one side of a C₆₀ nanotube with a body-centered tetragonal structure with typical inner and outer diameters, i.e., 180 nm and 510 nm, respectively, and then applied concentrated forces on the other side using piezomanipulation of a silicon nanotip. The bending process was observed in situ by transmission electron microscopy with simultaneous measurements of the forces by an optical deflection method. It was found that the Young’s modulus of the nanotube was estimated to be 62–107 GPa, which was 1.1–3.3 times larger than that of C₆₀ nanowhiskers. The result concerning the increase in the Young’s modulus of the C₆₀ nanotube provided an experimental evidence for the structural model composed of an inner core and a surface shell for C₆₀ nanowhiskers.     

Quantum chemical study of the electronic structure of new nanotubular systems: α-graphyne-like carbon, boron-nitrogen and boron-carbon-nitrogen nanotubes

Single-wall BN and BCN nanotubes in assumed α-graphyne-like wall structures are studied by means of the tight-binding band theory. The electron density of states, total energies and interatomic bond indices (crystal orbital overlap populations) are analyzed as a function of the composition, atomic structure and diameters of zigzag and armchair BN and BCN tubes. The results obtained are compared with the electronic properties of α-graphyne carbon- and graphite-like BN nanotubes.     

Structure–property relationships in thermally-annealed multi-walled carbon nanotubes

The mechanical properties of individual multi-walled carbon nanotubes (MWCNTs) synthesized by a catalytic chemical vapor deposition (CVD) method followed by a series of high temperature annealing steps at 1200, 1800, 2200 and 2600 °C are investigated by a manipulator tool operated inside a scanning electron microscope. To investigate the relationship between the MWCNT structure and mechanical properties, such MWCNTs with a significantly different nanostructure are separately tested in tension, and subsequently observed their nanostructure and fracture morphology by a transmission electron microscope. The results show that the thermal annealing is effective for improving both the strength and modulus of the catalytic CVD-grown MWCNTs. The MWCNTs annealed at 1800, 2200 and 2600 °C display enhancements to their strengths by factors of ∼5.4, ∼5.1 and ∼15.6, and moduli by factors of ∼5.9, ∼13.2 and ∼18.9, respectively, compared to the MWCNTs annealed at 1200 °C. This effect is associated with the degree of waviness of the graphitic planes along the nanotube axis as well as the degree of crystallinity of the MWCNTs: the strength and modulus of the MWCNTs increases with a higher degree of orientation of the 0 0 2 graphitic planes and with a lower degree of defect concentration in the MWCNT structure.     

Synthesis,HRTEM and electron diffraction studies of B/N-doped C and BN nanotubes

Large-scale synthesis of multi-walled BN and single-walled B/N-doped C nanotubes (NT) from C nanotube templates was carried out. The NTs were produced through heating of C templates with B₂O₃ in a flowing N₂ atmosphere at 1503–1773 K. The NTs were analyzed by means of a JEM-3000F high-resolution field emission transmission electron microscope operated at 300 kV and equipped with a parallel detection electron energy loss spectrometer. Particular attention was given to the effects of C template morphology, synthesis temperature and metal oxide promoters on the yield and chemical composition of NTs. Ropes consisting of tens of multi-walled BN NTs were synthesized at 1773 K using MoO₃ and PbO promoters. Ropes of single-walled B/N-doped C NTs were produced at high yields by synthesis at 1553 K. Packing of NTs in the ropes and nanotube helicities were studied by electron diffraction. B/N-doped C and BN NT morphologies, formation mechanism and atomic structures are discussed in this paper.     

Fabrication of Y-junction carbon nanotubes by reduction of carbon dioxide with sodium borohydride

Y-junction carbon nanotubes with a bamboo-shaped structure have been synthesized by reduction of CO₂ with NaBH₄ at 700 °C. The X-ray power diffraction pattern indicates that the products are hexagonal graphite, and transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) images reveal the morphology and structure of carbon nanotubes. The effects of reaction temperature on the growth of the Y-junction carbon nanotubes were also discussed in the paper. Reduction of supercritical CO₂ with sodium borohydride is a promising green chemical method for economically producing Y-junction carbon nanotubes.     

Polypyrrole/carbon nanotube composites: Molecular modeling and experimental investigation as anti-corrosive coating

In this work we present a computational method based on molecular mechanics (MM) and dynamics (MD), to predict mechanical properties of polypyrrole (PPy)/polyaminobenzene sulfonic acid-functionalized single-walled carbon nanotubes (CNT-PABS) and PPy/carboxylic acid-functionalized single-walled carbon nanotubes (CNT-CA) composites. Furthermore, experiments were carried out to assess the anticorrosive features of the PPy film and CNT-PABS and CNT-CA PPy reinforced composite coatings. Computational bulk models of PPy/CNT-PABS and PPy/CNT-CA were implemented at atomistic scale and composite coatings were grown in situ onto carbon steel (OL 48-50) electrodes. PPy, PPy/CNT-PABS and PPy/CNT-CA computational models and films were investigated concerning mechanical properties by using computational tools. The obtained films were assessed experimentally as anticorrosive materials using potentiodynamic measurements, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results clearly confirmed that the CNT-PABS and CNT-CA are properly dispersed in the composite coatings and have beneficial effect on mechanical integrity. Moreover, the anticorrosion protecting ability of the composite coatings is significantly higher than the one characteristic to pure PPy. The Young's moduli generally increased with increasing of CNT content and values ranged from 2.67 GPa in the case of pure PPy to 4.15–4.61 GPa in the case of PPy/CNT-PABS composite system.In agreement with earlier results from the literature for conducting polymer organic coatings, the higher conductivity of material leads to a more efficient anticorrosion protection capability, our results exhibited an enhance of conducting features even for very low mass of CNT-PABS or CNT-CA loaded in composites coatings therefore, an improvement of anticorrosion protecting ability.     

Modification of multi-walled carbon nanotubes with fatty acid and their tribological properties as lubricant additive

Multi-walled carbon nanotubes (MWNTs) were treated with mixture of sulfuric acid and nitric acid. The surface modification of the oxidized MWNTs was achieved by refluxing the MWNTs with stearic acid (SA). The modified MWNTs were examined by the transmission electron microscope, scanning electron microscope, Raman spectroscopy and Infrared spectroscopy. Furthermore, the modified MWNTs were added to base lubricant and the tribological properties of resultant MWNTs lubricant were investigated by using a pin-on-plate wear tester. The results indicated that an esterification was formed in the oxidized MWNTs and SA, and the modification led to an improvement in the dispersion of MWNTs and the tribological properties of MWNTs as lubricant additive.     

Fine study of hierarchical interphase constructed by boron nitride and carbon nanotubes in SiCf/SiC composites

A fine study of the interfacial part in the silicon carbide fiber (SiC_f) reinforced silicon carbide (SiC) composites was conducted by transmission electron microscopy. The boron nitride (BN) and carbon nanotubes (CNTs) were progressively coated on the SiC_f by chemical vapor deposition method to form a hierarchical structure. Three composites with different interfaces, SiC_f–CNTs/SiC, SiC_f@BN/SiC, and SiC_f@BN–CNTs/SiC, were fabricated by polymer infiltration and pyrolysis method. The interfaces and microstructures of the three composites were carefully characterized to investigate the improvement mechanism of strength and toughness. The results showed that BN could protect the surface of SiC_f from corrosion and oxidation so that improved the possibility of debonding and pullout. CNTs could avoid the propagation of cracks in the composites so that improved the damage resistance of the matrix. The synergistic reinforcement brought by BN and CNTs interfaces made the SiC_f@BN–CNTs/SiC composites with a tensile fracture strength as high as 359 MPa, with an improvement of 23% compared to that of SiC_f@BN/SiC.     

机械法合成BN纳米管

Boron nitride nanotubes （BN-NTs） with pure hexagonal BN phase have been synthesized by heating ball-milled boron powders in flowing ammonia gas at a temperature of 1200℃. The as-synthesized products were characterized by X-ray powder diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, and electron energy loss spectroscopy （EELS）. The diameters of nanotubes are in the rage of 40-120nm and the lengths are more than 10μm. EELS result identifies that the ratio of boron and nitrogen is almost 1：1 The growth temperature is a crucial growth parameter in controlling the structure and crystalline of BN-NTs. The nanotubes grown at 1100℃ possesses of a bamboo-like structure, while as the temperature increased to 1200℃, most of the nanotubes exhibited a cylindrical structure. In addition, changing the heating time can control the size of the nanotubes. The gas atmosphere has influence on the yield of BN-NTs during heating process. When heating atmosphere was replaced by nitrogen, the yield of nanotubes was remarkably decreased.     

Effects of AIN Additions and Atmosphere on the Synthesis of Cubic Boron Nitride

Aluminum nitride was found to act as the catalyst for the synthesis of cubic BN by sealing the mixture of hexagonal BN and AIN in a pressure cell under the inert or reducing atmosphere. No conversion of hexagonal BN to cubic BN was observed under pressures below 7×10⁹ Pa (7 GPa, 70 kbar) without AIN addition. All hexagonal BN could be completely converted to cubic BN under 6.5 GPa at 1600°C by the addition of 20 mol% AIN. The cubic BN thus synthesized was a typical tetrahedron (grain size ≅2 μm). The pressure-temperature diagram for the synthesis of cubic BN was determined at >7 GPa and T <1700°C.     

Lithium storage performance of carbon nanotubes prepared from polyaniline for lithium-ion batteries

Carbon nanotubes with large surface area and surface nitrogen and oxygen functional groups are prepared by carbonizing and activating of polyaniline nanotubes, which is synthesized by polymerization of aniline with the self-assembly method in aqueous media. The physicochemical properties of the carbon nanotubes are characterized by scanning electron microscope, transmission electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller, elemental analyses and X-ray photoelectron spectroscopy measurements. The surface area and pore diameter are 618.9 m² g⁻¹ and 3.10 nm. The electrochemical properties of the carbon nanotubes as anode materials in lithium ion batteries are evaluated. At a current density of 100 mA g⁻¹, the activated carbon nanotube shows an enormously first discharge capacity of about 1370 mAh g⁻¹ and a charge capacity of 907 mAh g⁻¹. After 20 cycling tests, the activated carbon nanotube retains a reversible capacity of 728 mAh g⁻¹. These indicate it may be a promising candidate for an anode material for lithium secondary batteries.     

Incorporation of boron and nitrogen in carbon nanomaterials and its influence on their structure and opto-electronical properties

The presence of hexagonal boron nitride in the initial C:BN:Ni:Y₂O₃ mixture in the arc-discharge process leads to the modification of carbon nanostructures and to the creation of B_xC_yN_z entities. BN-incorporation into these carbon nanostructures (single-wall nanotubes and carbon flakes) has been analyzed by high resolution transmission electron microscopy and electron energy loss spectroscopy. The optical absorption spectroscopy measurements have revealed a monotonous increase of the bandgap value of the synthesized nanotubes with the increase of the content of BN phase in the initial mixture of the synthesis compounds. Furthermore, a narrowing of the nanotube diameter distribution in favor of small diameters takes place in the presence of BN during the synthesis process.     

X-ray diffraction of multiwalled carbon nanotube under high pressure: Structural durability on static compression

The structural durability of multiwalled carbon nanotubes under hydrostatic and non-hydrostatic compression was examined by in situ X-ray powder diffraction at room temperature. No interlayer interaction such as sp³ hybridization that could lead to hexagonal diamond in graphite was observed under compression up to 52 GPa, even though the nanotubes were similar in compressibility to graphite. This result could be attributed to the nested structure, which makes the interlayer stacking of carbon atoms take on an irregular arrangement. Despite the history of non-hydrostatic compression, electron microscopic observation revealed that the structure remained nested tubular. This reversibility suggests the nanotubes have strong durability on non-hydrostatic compression under extreme pressures.     

The effect of electrolytic oxidation on the electrochemical properties of multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWNTs) were electrochemically oxidized by a constant-potential electrolysis method and then investigated in detail using scanning electron microscope, transmission electron microscope, FT-IR, electrical impedance spectroscopy, and cyclic voltammetry. The FT-IR spectra showed that the amount of hydroxyl generated on the surface of MWNTs increased with increasing the electrochemical oxidation time of MWNTs. The CV results, being conducted in nitrobenzene solution, showed that the nitrobenzene reduction current increased with the increase in oxidation time of the MWNTs within the first 60 min of electrolysis. An electrical equivalent circuit model for electrical impedance spectroscopy was further established to analyze the surface capacitance and resistance of the MWNTs, and the model results showed that the capacitance of the oxidized MWNTs increased greatly while the charge transfer resistance decreased, suggesting electrochemical oxidized MWNTs modified pyrolytic carbon electrode being an effective electrochemical sensor for nitrobenzene determination.     

Evaluation of antibacterial and catalytic potential of copper-doped chemically exfoliated boron nitride nanosheets

Boron nitride (BN) nanosheets were prepared by chemical exfoliation method and incorporation of Cu as a dopant was achieved using hydrothermal route. Hexagonal phase of BN (h-BN) was detected using x-ray difractometer (XRD). Functional group analysis with fourier transform infrared spectroscope (FTIR) was employed to identify the chemicals used in the process, which was then further confirmed with energy dispersive x-ray spectroscopy (EDS) coupled with FESEM. Optical analysis undertaken with UV–vis. spectroscopy indicated absorption at UV region. Raman spectroscopy was used to acquire molecular fingerprints of BN molecules. Photoluminescence (PL) spectroscopy was carried out to study the exciton behaviour of samples in order to elucidate the electron migration and transfer rate. Field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HRTEM) were employed to examine the morphology and structure of materials. The experimental results indicate that Cu-doped BN nanosheets possess excellent catalytic potential and superior antibacterial activity.     

Perylene derivative sensitized multi-walled carbon nanotube thin film

Perylene-sensitized multi-walled carbon nanotubes (PV-MWNT) have been prepared by a π-stacking between nanotubes and perylene derivatives, N,N′-diphenyl glyoxaline-3,4,9,10-perylene tetracarboxylic acid diacidamide (PV). The resultant nanocomposites have been characterized by transmission electron microscope (TEM), UV-vis absorption, photoluminescence (PL) and photocurrent spectra. Long range ordering can be observed in the form of PV-MWNT via π-stacking by TEM. Red-shift in the optical spectra consisting of the UV-vis absorption and PL spectra with the attraction of PV on the surface of the MWNTs were observed. The evident quenching in PL spectra of PV-MWNT was ascribed to the absorption and transfer of recombination energy by MWNT. Photosensitivity spectra demonstrated an increasing photocurrent in the ultraviolet region and a broadening photosensitivity in the red spectral region for solar cells based on PV-MWNT.     

Formation of self-organized Zircaloy-4 oxide nanotubes in organic viscous electrolyte via anodization

This work reports the formation of self-organized Zircaloy-4 (Zr-4) oxide nanotubes in viscous organic ethylene glycol (EG) electrolyte containing a small amount of fluoride salt and deionized (DI) water via an electrochemical anodization. The structure, morphology, and composition of the Zr-4 oxide nanotubes were studied using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), EDX, and XPS. SEM results showed that the length of the nanotubes is approximately 13 μm, and TEM results showed that the inner diameter of the Zr-4 oxide nanotubes is approximately 20 nm with average wall thickness of approximately 7 nm. XRD and selected area electron diffraction pattern (SAED) results confirmed that the as-anodized Zr-4 oxide nanotubes have cubic crystalline structure. Both cubic and monoclinic phases were found after annealing of Zr-4 oxide nanotubes. The tubular structure morphology of Zr-4 oxide nanotubes did not remain intact after annealing which is attributed to the elimination of F species from the annealed nanotubes.     

紫外光辐照ABS/碳纳米管的研究

丙烯腊—丁二烯—苯乙烯共聚物(ABS)在室温、氮气环境下，通过紫外光辐照，在其分子链上引入了碳纳米管(CNTs)。通过荧光光谱分析，ABS／CNTs在418nm处有强的荧光发射峰；透射电子显微镜观察发现，CNTs在端头处打开及转弯处打断，被ABS包覆，ABS/CNTs的体积电阻率随CNTs的加入量增多而降低；紫外光辐照ABS/CNTs的导电性显著优于熔融共混ABS/CNTs；扫描电子显微镜表明，CNTs在紫外光辐照ABS基体中均匀分布。