Co-synthesis of single-walled carbon nanotubes and carbon fibers

A new vertical floating catalytic technique is developed and used to prepare both single-walled carbon nanotubes (SWNTs) and carbon fibers (CFs). Scanning electron microscopy (SEM) observation shows a clear separation of these two materials. Thin films of SWNTs can be peeled easily from the CF substrate which just acts as a catalyst support for the SWNT growth. The production process is also semicontinuous, resulting in a yield of ∼1.0 g h⁻¹ of SWNTs film with high purity. Structure and vibrational properties of these materials are investigated by electron microscopy and Raman spectroscopy, respectively.     

Microwave-absorbing properties of Co-filled carbon nanotubes

Co-filled carbon nanotubes composites were synthesized via using a simple and efficient wet chemistry solution method. The samples were characterized by transmission electron microscopy. Microwave-absorbing properties were investigated by measuring complex permittivity and complex permeability of the absorber in a frequency range of 2-18 GHz. The reflection loss (R.L.), matching frequency (f_m) and matching thickness (d_m) were calculated using the theory of the absorbing wall. The electromagnetic properties and microwave-absorbing characteristics effects of the modified carbon nanotubes by the encapsulation of metal Co were investigated. A matching thickness is found corresponding to a matching frequency. The maximum reflection loss is about −39.32 dB and the bandwidth corresponding to the reflection loss below −10 dB is 3.47 GHz. With increasing thickness, the maximum reflection loss shifts to lower frequency.     

Preparation and properties of powder styrene-butadiene rubber composites filled with carbon black and carbon nanotubes

Carbon nanotubes (CNTs) and carbon black (CB) filled powder styrene-butadiene rubber (SBR) composites were prepared by spray drying of the suspension of CNTs and CB in SBR latex. The powders were sphere like and fine with uniform diameters of 10-15 μm. Experimental results showed that the introduction of CNTs into the matrix was beneficial to improve the security of the vulcanization of the rubber composites, and the dynamic and basic mechanical properties of the CNTs/SBR composites were better than those of CB/SBR and neat SBR composites. Observations on the microstructure of the composites indicated that CNTs were well dispersed in the matrix. Morphology of the fracture confirmed that the bonding between CNTs and rubber matrix was strong and load can be transferred to CNTs efficiently during the mechanical property tests. Moreover, the powder SBR composites containing well-dispersed CNTs could be perfect candidate as additives for other polymers.     

CuO microflowers composed of nanosheets: Synthesis, characterization, and formation mechanism

CuO microflowers composed of nanosheets with tunable size have been fabricated through a simple reaction in ammonia solution at 90-180 °C, in which the nanosheets with zigzag edges were 20-40 nm in thickness and 500-800 nm in width. The high ammonia concentration, high ratio of CNH₃ to CCu2+ (R_ac) and elevated temperature were necessary for the formation of microflowers, and the ammonia concentration was critical for the morphology evolution of the particles. The fabrication mechanism of CuO microflowers based on the assembly of Cu(OH)₂ nanobelts was discussed. In addition, the CuO microflowers showed effective catalytic activity on the decomposition of ammonium perchlorate.     

Fabrication and photocatalytic activity of porous TiO2 nanowire microspheres by surfactant-mediated spray drying process

A novel, porous TiO₂ nanowire microsphere with a diameter of 3-8 μm was successfully fabricated via spray drying of TiO₂ nanowire suspension with the assistance of surfactant (F127). The products were characterized by FESEM, XRD and N₂ adsorption-desorption analysis and results revealed that the resulting TiO₂ nanowire microspheres possessed a hierarchically macro/mesoporous structure, as well as a high BET surface area of 38.2 m²/g. Systematic studies showed that the presence of surfactant in the suspension feed for spray drying was critical in the formation of porous microspheres. The structure of the fabricated microspheres depends on the nanowire concentration in the feed. The TiO₂ nanowire microspheres exhibited significant photocatalytic degradation of Methylene blue (MB) as compared to commercial TiO₂ nanoparticles (P25). It was also revealed that the microspheres have excellent stability on photocatalytic activity and mechanical strength, which are both crucial factors when considering reuse of these photocatalysts.     

Influence of the crystallinity of the iron catalysts on the formation of carbon nanotubes

In this work, carbon nanotubes and minor amount of Fe/C core-shell structure nanoparticles were simultaneously synthesized by catalytic pyrolysis of ferrocene. Through high-resolution TEM observation and ED characterization, the results showed that the well-crystallized iron nanoparticles could catalyze the formation of carbon nanotubes, while the amorphous iron nanoparticles could not catalyze the formation of carbon nanotubes but form the Fe/C core-shell nanoparticles.     

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.     

The effect of high-temperature annealing on the structure and electrical properties of well-aligned carbon nanotubes

Systematic work has been performed on the effect of high-temperature annealing on structural defects and impurities of well-aligned carbon nanotubes (ACNTs) in this paper. ACNTs had been prepared by CVD process with ferrocene as catalyst and then the as-grown samples were experienced heat treatment (HT) from 1800 to 3000 °C. X-ray diffraction, Raman spectroscopy and electron dispersive spectroscopy (EDS), etc., have been used to analyze the effect of annealing. Results indicate that some impurities can be removed once annealing temperature exceeds vaporization point of corresponding metal or non-metal. Desorption of O should be attributed to reduced active sites of dangling covalent bonds after heat treatment. Specious discrepancy about interlayer spacing resulted from XRD and Raman tests show that although high-temperature heat treatment can remove in-plane defects of carbon nanotubes greatly, interlayer spacing between graphene shells could not be reduced effectively because of the special concentric cylindrical structure of nanotubes. Electrical resistivity of ACNTs block is about three orders higher than that of copper even after HT at 3000 °C, and the anisotropy of electrical properties increased once experienced heat treatment at increased temperature.     

Synthesis and characterization of spinel Co3O4 octahedra enclosed by the {1 1 1} facets

Spinel Co₃O₄ octahedra synthesized by a facile redox-precipitation method were investigated for the complete oxidation of methane. XRD analysis showed that the spinel structural Co₃O₄ octahedra had a relatively strong (1 1 1) diffraction peak as compared with that of the irregular shaped Co₃O₄ nanoparticles prepared by a conventional precipitation method. The results of methane combustion test demonstrated that the Co₃O₄ octahedra had no catalytic activity at 300-500 °C, while the Co₃O₄ irregular nanoparticles were highly active at the same reaction conditions. HRTEM studies revealed that the Co₃O₄ octahedra were predominantly exposed by the low Miller-index {1 1 1} facets with the lowest surface energy, and the Co₃O₄ irregular nanoparticles were exposed by various crystal facets. The results exhibited that the {1 1 1} facets with the low surface energy of the Co₃O₄ octahedra resulted in the inert catalytic activity in the methane oxidation reaction.     

New synthesis of Cu2O and Cu nanoparticles on multi-wall carbon nanotubes

Cu₂O and Cu nanoparticles were deposited on the surface of multi-walled carbon nanotubes with a diameter range of 15–90 nm by the impregnate method. Multi-wall carbon nanotubes with a length of 200 μm and a diameter range of 70–110 nm were grown inside of quartz tubing by the spray pyrolysis method using ferrocene/benzene under argon flow. The nanotubes were then treated with nitric acid to clean the surface and generate carboxylic groups. The copper was impregnated on multi-walled carbon nanotubes using a xylene solution of copper(I) phenylacetylide as the precursor. Copper and cuprous oxide nanoparticles were obtained during thermal treatment.     

Gel-based separation of single-walled carbon nanotubes for metallic and semiconducting fractions

Common technique for biomaterials recovery in genetics is freeze-squeeze procedure. However, this method found a new application in carbon nanotubes field in a selective separation of metallic and semiconducting nanotubes. None-commercial agarose gel acts as a selective absorbent for semiconducting nanotubes and allows to separate them from metallic type of nanotubes. In this work we point out the great potential of freeze-squeeze technique in the field of separation of nanotubes and prove that the post-separation purification procedure is crucial to perform the quality and quantity estimation of the fractionated samples. Furthermore, the detailed quantitative analysis of the efficiency of this process is shown. Additionally, we emphasize that this technique can be used for high-scale separation of metallic counterparts of single-walled carbon nanotubes due to its simplicity and low cost.     

Studies on nitrogen modified TiO2 photocatalyst prepared in different conditions

Nitrogen modified titania photocatalysts (TiO₂/N) were characterized using high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), dynamic light scattering (DLS), Raman spectroscopy and BET surface area method. The presence of nitrogen in modified photocatalysts has been studied using FT-IR and XPS analyses. The influence of the calcination temperature in the range of 100-350 °C on nanocrystallite as well as particle size of the samples and their photocatalytic activity was investigated. The calcination of TiO₂/N samples caused a growth of the particle size and an increase of their crystallinity. TEM studies present changes of the diameter and shape of TiO₂ particles and nanocrystallites. The XRD and the Raman response of the samples confirmed an increase of the crystallinity of the samples when annealed at higher temperatures.The photocatalytic activity of the modified photocatalysts was determined using the reaction of phenol decomposition. It was shown that phenol decomposition rate was greatly influenced by pH of the solution. The highest phenol degradation using all the modified samples was observed for pH 7.1 which is close to the PZC point established for pristine TiO₂ at pH 6.8.     

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.     

Effect of temperature on the growth of TiO2 thin films synthesized by spray pyrolysis: Structural, compositional and optical properties

Large surface area coatings of oxygen deficient nanocrystalline TiO₂ are of immense use in antifogging mirrors and self cleaning windows. Spray pyrolysis is a simple versatile technique to coat relatively large surface area. A clear understanding of effect of substrate temperature on the coating morphology, structure, composition and optical properties is essential to produce coatings of desired properties. Oxygen deficient nanocrystalline anatase–TiO₂ thin films were synthesized on Si(1 0 0), quartz and glass substrates at 300–550 °C. Well defined platelets like nanograins standing on their edge were obtained at 500 °C. The crystallites were found to be of ∼12 nm thickness and ∼30 nm major diameter. The secondary ion mass spectrometric studies of the films revealed uniform distribution of titanium and oxygen across the thickness of the film up to the film–substrate interface. Presence of lower valent Ti ions and oxygen vacancies were confirmed from XPS studies. The indirect and direct band gap values evaluated from the Tauc plot for films synthesized at 500 °C are 3.3 and 3.62 eV respectively.     

Structure and photocatalytic activity of Ni-doped ZnO nanorods

The one-dimensional (1D) Zn_1−xNi_xO (x = 0, 0.02, 0.05, 0.10) nanorods have been synthesized by a simple hydrothermal method. New bands show at ∼130 cm⁻¹ in the Raman spectra of Ni-doped ZnO nanorods and their relative intensity depends on the doping concentration of nickel. The optical band gap of the ZnO nanorods have been tuned by Ni-doping, which is revealed by absorption spectra. The photocatalytic activity of Zn_1−xNi_xO was studied by comparing the degradation rate of rhodamine B (RB) under UV-light irradiation. It was found that Zn_0.95Ni_0.05O exhibited the highest photocatalytic degradation efficiency among the samples.     

Synthesis and photocatalytic activity of titania microspheres with hierarchical structures

A combined sol-gel and solvothermal process was introduced to fabricate the titania microspheres with hierarchical structures by using lauryl alcohol as the structure-directing agent. Scanning electron microscope, high-resolution transmission electron microscope, Fourier transform infrared spectrograph and powder X-ray powder diffraction indicated that the molar ratio of lauryl alcohol, water and tetra-n-butyl titanate was the key factor for the formation of the mono-dispersed titania with anatase phase and the optimal ratio was 1.2:4:1. The diameter of the end-product was 523 ± 74 nm and it was composed of smaller nanoparticles with about 6.8 nm size in diameter. Photocatalytic activity of the end-product was investigated by employing Rhodamine B and Methylene blue as the model compounds. The target microspheres exhibited the higher photocatalytic efficiency compared with commercial Degussa P25 titania and this result might be due to the hierarchical structures of microspheres according to the analysis of Brunauer-Emmett-Teller specific surface areas.     

Effect of phosphorus incorporation on morphology and optical properties of ZnO nanorods

Phosphorus-doped ZnO nanorods have been prepared on Si substrates by thermal evaporation process without any catalyst. X-ray photoelectron spectroscopy and Raman spectra indicate that phosphorus entering into ZnO nanorods mainly occupies Zn site rather than O one. The introduction of phosphorus leads to the morphological changes of nanorods from hexagonal tip to tapered one, which should be attributed to the relaxation of the lattice strain caused by phosphorus occupying Zn site along the radial direction. Transmission electron microscopy shows that phosphorus-doped ZnO nanorods still are single crystal and grow along [0 0 0 1] direction. The effect of phosphorous dopant on optical properties of ZnO nanorods also is studied by the temperature-dependent photoluminescence spectra, which indicates that the strong ultraviolet emission is connected with the phosphorus acceptor-related emissions.     

Activated carbon catalyzing the formation of carbon nanotubes

Activated carbon (AC), a common carbon material, is employed as catalyst to synthesize carbon nanotubes (CNTs) through chemical vapor deposition (CVD) and detonation-assisted CVD methods. The results show AC can effectively catalyze CNT formation. From the microscopic observations on morphologies and structures of the formed intermediates, it is found that carbon-catalyzed CNT formation follows particle-wire-tube stepwise evolution mechanism, in which carbon nanoparticles first assemble into wire-like nanostructures, then evolve into nanotubes via particle-particle coalescence and structural crystallization.     

Supported zirconium sulfate on carbon nanotubes as water-tolerant solid acid catalyst

A new solid acid of zirconium sulfate (CZ) was successfully supported on carbon nanotube (CNT) for esterification reaction. Preparation conditions of the supported CZ have been investigated, to obtain highest catalytic activity for esterification reaction. XRD, TEM, BET, X-ray photoelectron spectra (XPS) and in situ FTIR analysis has also been carried out to understand the characteristics of the catalyst. In the esterification of acrylic acid with n-octanol, the supported CZ exhibited high catalytic activity and stability. The catalytic activity was nearly unchanged during four times of reuse. XRD and TEM analysis indicated that CZ was finely dispersed on CNT. XPS analysis shows that the CZ species was preserved and the chemical environment of the CZ has changed after loaded on CNT. This finding show that CNT as CZ support is an efficient water-tolerant solid acid.     

Solvothermal synthesis of nanorods of ZnO, N-doped ZnO and CdO

ZnO nanorods with diameters in the 80-800 nm range are readily synthesized by the reaction of zinc acetate, ethanol and ethylenediamine under solvothermal conditions. The best products are obtained at 330 °C with a slow heating rate. Addition of the surfactant Triton^®-X 100 gave nanorods of uniform (300 nm) diameter. By adding a small amount of liquid NH₃ to the reaction mixture, N-doped ZnO nanorods, with distinct spectroscopic features are obtained. CdO nanorods of 80 nm diameter have been prepared under solvothermal conditions using a mixture of cadmium cupferronate, ethylenediamine and ethanol at 330 °C. Similarly, Zn_1−xCd_xO nanorods of a 70 nm diameter are obtained under solvothermal conditions starting with a mixture of zinc acetate, cadmium cupferronate, ethanol and ethylenediamine.