Synthesis and characterization of carbon nanoribbons and single crystal iron filled carbon nanotubes

Carbon nanoribbons and single crystal iron filled multiwall carbon nanotubes (MWCNTs) have been synthesized by simple pyrolysis technique. SEM investigation shows that the material consist mainly carbon nanoribbons and carbon nanotubes (CNTs). X-ray diffraction (XRD), electron energy loss spectroscopy (EELS), electron energy dispersive X-ray (EDX), transmission electron miscroscopy (TEM) and highresolution transmission electron miscroscopy (HRTEM) studies reveal carbon nanotubes are filled with α-Fe. Closer inspection of HRTEM images indicated that the bcc structure α-Fe nanowires are monocrystalline and Fe (1 1 0) plane is indeed perpendicular to the G (0 0 2) plane, whereas orientation of (0 0 2) lattice planes of carbon nanoribbon is perpendicular to the axis of growth. Magnetic properties studied by superconducting quantum interference device (SQUID) at 300 K and 10 K exhibited coercivity of 1037 Oe and 2023 Oe. The large coercitivity is strongly attributed to the small size monocrystalline single phase α-Fe, single domain nature of the encapsulated Fe crystal, magnetocrystalline shape anisotropy and ferromagnetic behaviour of localized states at the edges of the carbon nanoribbons.     

Effect of growth temperature on the CVD grown Fe filled multi-walled carbon nanotubes using a modified photoresist

Fe filled carbon nanotubes were synthesized by atmospheric pressure chemical vapor deposition using a simple mixture of iron(III) acetylacetonate (Fe(acac)₃) with a conventional photoresist and the effect of growth temperature (550-950 °C) on Fe filled nanotubes has been studied. Scanning electron microscopy results show that, as the growth temperature increases from 550 to 950 °C, the average diameter of the nanotubes increases while their number density decreases. High resolution transmission electron microscopy along with energy dispersive X-ray investigation shows that the nanotubes have a multi-walled structure with partial Fe filling for all growth temperatures. The graphitic nature of the nanotubes was observed via X-ray diffraction pattern. Raman analysis demonstrates that the degree of graphitization of the carbon nanotubes depends upon the growth temperature.     

Mechanically activated synthesis of nanocrystalline ternary carbide Fe3Mo3C

In this investigation, Fe₃Mo₃C ternary carbide was synthesized from the elemental powders of 3Mo/3Fe/C by mechanical milling and subsequent heat treatment. Structural and morphological evolutions of powders were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results showed that no phase transformation occurs during milling. A nanostructure Mo (Fe) solid solution obtained after 30 h of milling. With increasing milling time to 70 h no change takes place except grain size reduction to 9 nm and strain enhancement to 0.86%. Milled powders have spheroid shape and very narrow size distribution about 2 μm at the end of milling. Fe₃Mo₃C was synthesized during annealing of 70 h milled sample at 700 °C. Undesired phases of MoOC and Fe₂C form at 1100 °C. No transformation takes place during annealing of 10 h milled sample at 700 °C. Mean grain size and strain get to 69 nm and 0.23% respectively with annealing of 70 h milled sample at 1100 °C.     

Nitrogen beam bombardment induce polarity of carbon nanotubes

The multiwalled carbon nanotubes (MWCNTs) were prepared on SiO₂ substrates using chemical vapor deposition (CVD). N ion beam bombardment to MWCNTs was performed at different beam currents of 5–15 mA in an ion-beam-assisted deposition (IBAD) system. Scanning electron microscope (SEM) and Transmission electron microscope (TEM) proved no significant crack and surface morphological change for MWCNTs after N ion beam bombardment. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometry (FTIR), and Raman studies indicated that higher N ion beam current (15 mA) or N atomic concentration (8.6%) induced formation of polar N-containing functional groups of N–C and N–H bonds on the surfaces of MWCNTs. The content of N–C and N–H bonds increased with N ion beam current.     

Studies on transformation of titanate nanotubes into nanoribbons

High aspect ratio titanate nanostructures were synthesized by simple hydrothermal treatment and the nature of two distinct morphologies, hollow nanotubes and titanate nanoribbons was explored as a function of hydrothermal processing conditions. The samples were characterized by means of SEM, XRD and TEM. The specific surface area of the final products was determined by Brunauer-Emmett-Teller (BET) method. It has been found that hydrothermal temperature and the treatment duration have a strong effect on the morphological control of the resulting products. Transformation of nanotubes into nanoribbons was observed with increase in the treatment temperature from 180 °C to 200 °C which became more dense with further increase in the temperature from 200 °C to 220 °C and treatment duration from 12 h to 24 h.     

Characteristics of multi-walled carbon nanotubes and background aerosols by carbon analysis; particle size and oxidation temperature

Novel carbonaceous nanomaterials such as carbon nanotubes and fullerenes have many beneficial characteristics as industrial materials, but exposure to these nanomaterials also poses health risks. As part of an exposure assessment, we characterized the following carbonaceous nanomaterials, using an aerosol carbon monitor: nine samples of multi-walled carbon nanotubes (MWCNTs), a sample of single-walled carbon nanotubes (SWCNTs), a standard sample of diesel exhaust particles (DEPs), and an ambient particulate matter (APM). The amounts of elemental carbon (EC) determined by the monitor coincided with the mass of MWCNTs calibrated by a microbalance. The carbonaceous nanomaterials were oxidized in three steps of oven temperatures (550, 700 and 920 °C) in this method. The portion of oxidized carbon at each temperature depended on the sample characteristic. We used the monitor to analyze the aerosol samples collected in five stages by a Sioutas cascade impactor (SCI), which collects size-segregated airborne particles having aerodynamic diameters from 6.6 μm to less than 0.25 μm. As MWCNTs aggregate/agglomerate easily, the size was of a good parameter to distinguish the MWCNTs from other materials. Two-dimensional mapping by size and oxidized temperature suggested the origin of the carbonaceous aerosol samples. Based on the results, we reanalyzed our previous data obtained at a factory manufacturing MWCNTs. The characteristics of workplace samples by particle size and carbon analysis were similar to those of MWCNT aerosol particles.     

Low temperature synthesis of multi-walled carbon nanotubes via a sonochemical/hydrothermal method

In this investigation, multi-walled carbon nanotubes (MWCNTs) have been prepared by a facile sonochemical/hydrothermal method. MWCNTs have been hydrothermally fabricated with using dichloromethane, cobalt chloride and metallic lithium as starting materials in 5 mol/lit NaOH aqueous solution. Ultrasonic pre-treatment of the solution mixture had an important step prior to the hydrothermal condition, which could generate a considerable amount of multi-walled carbon nanotubes for the subsequent hydrothermal growth. Finally, high pure MWCNTs with lengths of 2-5 μm and diameters of 60 ± 20 nm could be synthesized at as low temperature as 160 °C. As a matter of fact, the method of sonochemical/hydrothermal guarantees the production of multi-walled carbon nanotubes (MWCNTs) for different applications, especially reinforcement materials.     

Temperature Influence on the Morphology and the Magnetic Properties of Vertically Aligned Fe-filled Carbon Nanotubes

Arrays of vertically aligned Fe-filled multi-wall carbon nanotubes (MWNTs) on oxidized silicon substrates were prepared by pyrolysis of ferrocene in a dual furnace system and characterized by electron microscopy and magnetometry measurement. The effect of the growth temperature on both the filled nanotube morphology and their magnetic behavior was studied. Increasing the growth temperature in the range of 845-1035°C the nanotube alignment becomes worse and the diameter of the encapsulated Fe nanowires increases from 10 to 40 nm. Both the coercivity and the remanence ratio of the arrays of Fe-filled MWNTs decrease with the increase of the growth temperature. Factors causing the observed magnetic behavior are discussed.     

碳纳米管承载纳米Fe_3O_4颗粒的制备(英文)

采用一种简单又经济的方法将Fe3O4纳米颗粒填充到碳纳米管中。透射电镜(TEM)、扫描电镜(SEM)及其能谱附件(EDX)和X射线多晶衍射(XRD)测试结果表明:Fe3O4纳米颗粒成功地填充到碳纳米管中。材料的磁性能测试结果表明:碳纳米管中填充Fe3O4纳米颗粒后,在常温下具有超顺磁性,其饱和磁化强度由0.35emu/g增大到了13.15emu/g。Fe3O4纳米颗粒填充的碳纳米管可望应用于工程和医学领域。     

A study of the electromagnetic properties of Cobalt-multiwalled carbon nanotubes (Co-MWCNTs) composites

Electroless plating was utilized to deposit Cobalt (Co) on the surface of multi-walled carbon nanotubes (MWCNTs), and the technological parameters of electroless plating were optimized. To obtain optimized processing parameters, field-emission scanning electron microscope (FESEM) as well as energy dispersive spectroscopy (EDS) results were presented to show the morphology, components of as-prepared Co-MWCNTs. Based on the optimized processing parameters, Co-MWCNTs were prepared and filled into the epoxy resin to fabricate Co-MWCNTs composites. The electromagnetic properties of pure MWCNTs composites and Co-MWCNTs composites were studied. To sum up, the pure MWCNTs composites with a filler concentration of 2 wt% had an intense absorbing peak at 15.20 GHz, where the highest reflection loss (R) reached −21.41 dB. Compared to the pure MWCNTs composite at the same concentration, the Co-MWCNTs composites showed a higher impedance which implies a better potential absorbing property and makes Co-MWCNTs probable to be utilized in electromagnetic absorbing field.     

Influence of Fe nanoparticles diameters on the structure and electron emission studies of carbon nanotubes and multilayer graphene

In this paper we report the effect of Fe film thickness on the growth, structure and electron emission characteristics of carbon nanotubes (CNTs) and multilayer graphene deposited on Si substrate. It is observed that the number of graphitic shells in carbon nanostructures (CNs) varies with the thickness of the catalyst depending on the average size of nanoparticles. Further, the Fe nanoparticles do not catalyze beyond a particular size of nanoclusters leading to the formation of multilayer graphene structure, instead of carbon nanotubes (CNTs). It is observed that the crystallinity of CNs enhances upon increasing the catalyst thickness. Multilayer graphene structures show improved crystallinity in comparison to CNTs as graphitic to defect mode intensity ratio (I_D/I_G) decreases from 1.2 to 0.8. However, I_2D/I_G value for multilayer graphene is found to be 1.1 confirming the presence of at least 10 layers of graphene in these samples. CNTs with smaller diameter show better electron emission properties with enhancement factor (γ_C = 2.8 × 10³) in comparison to multilayer graphene structure (γ_C = 1.5 × 10³). The better emission characteristics in CNTs are explained due to combination of electrons from edges as well as centers in comparison to the multilayer graphene.     

Influence of crystallinity on CO gas sensing for TiO2 films

In the present research, carbon monoxide (CO) gas sensing response was studied for TiO₂ thick films calcined and sintered between 700 and 900 °C. Crystalline phase, crystallite size, surface area, particle size, and amorphous content were measured for the calcined powder. Crystallinity of the powder was found to affect sensing response significantly towards CO. Anatase phase of TiO₂ thick film was stable up to 900 °C however, as calcination temperature increased from 700 to 900 °C, surface area and amorphous phase content decreased. Films calcined and sintered at 700 °C showed a lower response towards CO than those calcined at 800 °C. Upon increasing the calcination temperature further, particle growth and reduced surface area hindered the sensing response. A calcination temperature of 800 °C was necessary to achieve sufficient order in the crystal structure leading to more efficient adsorption and desorption of oxygen ions on the surface of TiO₂.     

Effect of maleic anhydride modified MWCNTs on the morphology and dynamic mechanical properties of its PMMA composites

This study successfully grafted multiwalled carbon nanotubes (MWCNTs) with maleic anhydride (Mah-g-MWCNTs) via Friedel–Crafts acylation with the aluminum chloride catalyst (AlCl₃), investigated by Raman and TGA analysis. The covalent bonds and carboxylic groups of maleic anhydride provided additional active species, improving adhesion between the MWCNTs and poly(methyl methacrylate) (PMMA). This investigation also studied the morphology and dynamic mechanical properties of pristine MWCNTs (P-MWCNTs) and modified MWCNTs (Mah-g-MWCNTs) reinforced with PMMA. Findings show a homogeneous distribution of MWCNTs throughout the matrix for Mah-g-MWCNTs/PMMA composites, as revealed by transmission electron microscope (TEM). The addition of both MWCNTs influenced the molecular arrangement of the PMMA matrix and also increased the dynamic mechanical properties of MWCNTs/PMMA composites. Glass transition temperature (Tg) and storage moduli (E′) of the Mah-g-MWCNTs/PMMA composites increased significantly comparing with P-MWCNTs/PMMA composites, attributed to improved interfacial adhesion between the reinforcement and the matrix. DMA studies revealed that adding 4.76 wt% Mah-g-MWCNTs into PMMA generates a 184% enhancement in the storage modulus and a 19 °C increase in Tg. However, adding 4.76 wt% P-MWCNTs into PMMA only generates 108% enhancement in the storage modulus and a 14 °C increase in Tg.     

Synthesis, characterization and properties of carbon nanotubes microspheres from pyrolysis of polypropylene and maleated polypropylene

Microspheres assembled from carbon nanotubes (MCNTs), with the diameters ranging from 5.5 to 7.5 μm, were synthesized by means of pyrolysis of polypropylene and maleated polypropylene in an autoclave. The characterization of structure and morphology was carried out by X-ray diffractometer (XRD), field-emission scanning electron microscopy (FESEM), (high resolution) transmission electron microscope [(HR)TEM)], selected-area electron diffraction (SAED) and Raman spectrum. As a typical morphology, the possible growth process of MCNTs was also investigated and discussed. The results of nitrogen adsorption-desorption indicate that the Brunauer-Emett-Teller (BET) surface area (140.6 m²/g) of the MCNTs obtained at 600 °C is about twice as that (74.5 m²/g) of carbon nanotubes obtained at 700 °C. The results of catalytic experiment show that MCNTs based catalyst has higher catalytic activity than the carbon nanotubes based catalyst for the preparation of methanol and dimethoxy-ethane by oxidation of dimethyl ether.     

Magnetic property of FePt nanoparticles encaged in carbon nanotubes

Encapsulation of FePt nanoparticles in carbon nanotubes (CNTs) was attempted using a thermal chemical vapor deposition technique with a Fe/Pt bilayer catalyst. The metal nanoparticles were encapsulated at the tip of multi-walled CNTs. A selected area electron diffraction measurement of the nanoparticles at CNT tips indicated that diffraction spots attributed to an ordered L1₀ phase. Magnetic hysteresis loops indicated existence of magnetic nanoparticles having various coercivities. From numerical fittings assuming that high and low coercivity components contributed to the hysteresis loops, the high coercivity component was estimated to reach 11.3 kOe (902 kA/m).     

Thermal and mechanical properties of phenolic-based composites reinforced by carbon fibres and multiwall carbon nanotubes

The thermal, mechanical and ablation properties of carbon fibre/phenolic composites filled with multiwall carbon nanotubes (MWCNTs) were investigated. Carbon fibre/phenolic/MWCNTs were prepared using different weight percentage of MWCNTs by compression moulding. The samples were characterized by scanning electron microscopy (SEM), flexural tests, thermal gravimetric analysis and oxyacetylene torch tests. The thermal stability and flexural properties of the nanocomposites increased by increasing MWCNTs content (wt% ⩽1), but they decreased when the content of MWCNTs was 2 wt%. The linear and mass ablation rates of the nanocomposites after modified with 1 wt% MWCNTs decreased by about 80% and 52%, respectively. To investigate the material post-test microstructure, a morphological characterization was carried out using SEM. It was shown that the presence of MWCNTs in the composite led to the formation of a strong network char layer without any cracks or opening.     

SiOC ceramic nanotubes of ultrahigh surface area

Silicon oxycarbide ceramic nanotubes have been successfully synthesized by inert atmosphere pyrolysis of polysilicone nanotubes using a sacrificial alumina membrane as a template at different pyrolysis temperatures. Scanning electron microscopy images show that the silicon oxycarbide ceramic nanotubes have well-aligned tubular structures. X-ray diffraction patterns and Raman spectra reveal that the obtained silicon oxycarbide ceramic nanotubes are amorphous below 1200 °C and are mainly composed of SiO₂ crystallites and free carbon when the temperature exceeds 1300 °C. Nitrogen-sorption isotherms indicate that the silicon oxycarbide ceramic nanotubes have high Brunauer–Emmett–Teller (BET) specific surface areas (up to 1387 m²/g), large pore volumes (up to 1.82 cm³/g).     

Temperature optimisation of CNT synthesis by spray pyrolysis of alpha-pinene as the carbon source

Multi-wall carbon nanotubes (MWCNTs) were prepared by spray-pyrolysis of a botanical hydrocarbon, alpha-pinene and ferrocene as the catalyst at 700–1000°C. The MWCNTs were analysed by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray diffraction. The microscopy studies show the formation of carbon nanotubes with diameters between 20 and 30 nm and length greater than 100 µm. Raman spectroscopy revealed that the alpha-pinene-grown carbon nanotubes were graphitised showing both the D and G bands at 1330 and 1590 cm^?1, respectively, and that the corresponding intensity band ratio (I _D/I _G) varied with respect to temperature formation.     

Effect of growth temperature on field emission from an array of carbon nanotubes nested into a silicon nanoporous pillar array

Large scale nest arrays of multi-walled carbon nanotubes (NA-MWCNT) were grown on silicon nanoporous pillar arrays (Si-NPA) by thermal chemical vapour deposition at 700, 800, and 900 °C respectively for 15 min. The corresponding field emission properties were also studied. It was found that growth temperature had a significant effect on the performance of CNTs, the field emission efficiency of NA-MWCNT/Si-NPA synthesized at 900 °C was higher than that of the other two types of samples. By hiring scanning electron microscope observing and high resolution transmission electron microscopy analysis, the reason was attributed to numerous nanoparticles appearance on the surface of the CNT and highly folding graphite sheets formation on both sides of the nanotubes fabricated at 900 °C. Both could enhance emission properties by lowering the effective work function and increasing the field enhancement factor as well as the number of the emission sites.     

Fabrication of epitaxial conductive LaNiO3 films on different substrates by pulsed laser ablation

LaNiO₃ (LNO) thin films were deposited on (1 0 0) MgO, SrTiO₃ (STO) and LaAlO₃ (LAO) crystal substrates by pulsed laser deposition (PLD) under 20 Pa oxygen pressure at different substrate temperatures from 450 to 750 °C. X-ray diffraction (XRD), ex situ reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM) were employed to characterize the crystal structure of LNO films. LNO films deposited on STO and LAO at a temperature range from 450 to 700 °C exhibit high (0 0 l) orientation. XRD ψ scans and RHEED observations indicate that LNO films could be epitaxially grown on these two substrates with cubic-on-cubic arrangement at a wide temperature range. LNO films deposited at 700 °C on MgO (1 0 0) substrate have the (l l 0) orientation, which was identified to be bicrystalline epitaxial growth. La₂NiO₄ phase appears in LNO films deposited at 750 °C on three substrates. The epitaxial LNO films were tested to be good metallic conductive layers by four-probe method.