Visible light photocatalytic properties of novel molybdenum treated carbon nanotube/titania composites

Two types of molybdenum–carbon nanotubes and molybdenum treated carbon nanotubes/titania composites were prepared using a sol–gel method. These composites were characterized comprehensively by the Brauer–Emett–Teller (BET) surface area, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-vis absorption spectroscopy. It was found that the photocatalytic degradation of a methylene blue solution could be attributed to the combined effects caused by the photo-degradation of titania, the electron assistance of carbon nanotube network, and the enhancement of molybdenum. The proposed redox mechanism of the photodegradation of methylene blue on Mo-CNT/TiO₂ composites is suggested.     

Direct electrochemical determination of ascorbic acid by a cobalt(II) tetra-neopentyloxy phthalocyanine-multi-walled carbon nanotubes glassy carbon electrode

A cobalt(II) tetra-neopentyloxy phthalocyanine-multi-walled carbon nanotubes (CoTNPPc–MWNTs) composite was synthesized and characterized by UV–Vis spectra and transmission electron microscopy. The CoTNPPc–MWNTs glassy carbon electrode (CoTNPPc–MWNTs/GCE) was prepared by drop coating. The electrocatalytic performance of the chemically modified electrode was investigated for oxidation of ascorbic acid (AA). It was found that in phosphate buffer solution at pH = 6.60, the chemically modified electrode exhibited excellent electrocatalytic activity toward the oxidation of AA. The oxidation peak current increased linearly with the concentration of AA in the range of 10 μM–1.6 mM within the detection limit of 5 μM and low response time of 4 s.     

Facile synthesis of poly(<Emphasis Type="Italic">p</Emphasis>-phenylenediamine)/MWCNT nanocomposites and characterization for investigation of structural effects of carbon nanotubes

Poly(p-phenylenediamine) (PpPD)/carboxylic acid-functionalized multiwalled carbon nanotubes (c-MWCNTs) nanocomposites were prepared by chemical oxidative polymerization using potassium persulfate (K₂S₂O₈) as an oxidant. Field-emission scanning electron microscopy (FE–SEM) and field-emission transmission electron microscopy (FE–TEM) showed that a tubular layer of PpPD was coated on the surface of carbon nanotubes with a thickness of 10–20 nm. FT–IR analysis provided an evidence for the formation of nanocomposites. The thermal stability of nanocomposites was improved by addition of c-MWCNTs as confirmed by thermogravimetric analysis (TGA). XRD spectra showed that the crystalline nature of PpPD was not affected much by the addition of c-MWCNTs. As the content of c-MWCNTs was increased, the electrical conductivity of the nanocomposites increased due to the interaction between polymer and nanotubes that enhances electron delocalization.     

Controllable synthesis and magnetic properties of Fe–Co alloy nanoparticles attached on carbon nanotubes

Fe–Co alloy nanoparticles with different size were attached on the carbon nanotubes through adjusting the ratio of the metal to carbon in the mixed solution of nitrate with Fe:Co = 1:1 (molar ratio) via wet chemistry. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectrometry (EDX) indicated that the Fe–Co alloy nanoparticles attached on the surface of carbon nanotubes has body-centered cubic (bcc) structure, with sizes in the range of 13–25 nm and in the shape of spheroids. Magnetization measurements indicated that both the coercivities and the saturation magnetizations altered with size changes of the Fe–Co alloy nanoparticles. The saturation magnetization decreases with decreasing the Fe–Co alloy nanoparticles’ sizes. A decrease in coercivity with increasing Fe–Co size together with a local maximum coercivity at size of ca. 15 nm is visible. A linear relationship between the inverse particle diameter and the coercivity was found for larger particles. These demonstrated that the chemical method here is promising for fabricating Fe–Co alloy nanoparticles coated on carbon nanotubes for magnetic storage applications.     

Fabrication of nanocomposites based on carbon nanotubes containing Pt nanoparticles and TiO<Subscript>2</Subscript>

Using conical multiwalled carbon nanotubes (CNTs), we have prepared Pt/CNT and Pt/TiO₂/CNT nanocomposites with an average platinum particle size of 3–5 nm, Pt/Ti molar ratio on the surface in the range 3.5–4, and C/Pt = 21–22. Titania was deposited onto the CNTs through titanium tetrachloride (TiCl₄) hydrolysis. Platinum particles were produced by reducing chloroplatinic acid (H₂PtCl₆) with sodium borohydride (NaBH₄) in the presence of CNTs. The composition and structure of the composites have been studied using X-ray photoelectron spectroscopy, electron microscopy, X-ray diffraction, and thermogravimetry. The materials have been tested as catalysts for hydrogen oxidation and oxygen reduction. The results demonstrate that the modification of Pt/CNT with titania enhances the catalytic activity of the material.     

Synthesis of ordered ZnS nanotubes by MOCVD-template method

Semiconductor ZnS nanotubes arrays were synthesized in the pores of the porous anodic alumina (PAA) membranes by using metal organic chemical vapor deposition (MOCVD) template methods. The morphology and structure of the ZnS nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and X-ray diffraction (XRD). It is found that the ZnS nanotubes with diameters in range of 140–250 nm and the length up to tens of microns are polycrystalline. Energy-dispersion spectroscopy (EDS) and X-ray photoelectron spectroscopy analysis (XPS) indicate that the stoichiometric ZnS was formed. A green-blue emission band centered at 510 nm was observed in the photoluminescence spectrum of the ZnS nanotubes.     

Dielectric properties of carbon black: SBR composites

A series of styrene–butadiene rubber (SBR) composites have been prepared with different weight ratios of polyacetylene based conducting carbon black (CCB) (0–90 phr). The SBR–CCB systems are characterized for dimensional stability which is enhanced by increasing the CCB loading because of enhancement in polymer-filler interaction. The electrical properties such as dielectric constant (ε_r), dissipation factor (tan δ) and dielectric loss (ε″) of the composites have been studied. The influence of different loading of CCB (0–90 phr), frequency of ac (100 Hz–30 MHz) and temperature (25–75 °C) on the electrical properties was studied. An increase in dielectric constant and tan δ of the SBR composites was observed with increase in CCB content and ac frequency. This is due to enhancement of filler–filler interaction and the increase in continuity of conducting phase. The surface morphology has been studied using scanning electron microscopy (SEM).     

Rapid growth of nanotubes and nanorods of würtzite ZnO through microwave-irradiation of a metalorganic complex of zinc and a surfactant in solution

Large quantities of single-crystalline ZnO nanorods and nanotubes have been prepared by the microwave irradiation of a metalorganic complex of zinc, in the presence of a surfactant. The method is simple, fast, and inexpensive (as it uses a domestic microwave oven), and yields pure nanostructures of the hexagonal würtzite phase of ZnO in min, and requires no conventional templating. The ZnO nanotubes formed have a hollow core with inner diameter varying from 140–160 nm and a wall of thickness, 40–50 nm. The length of nanorods and nanotubes varies in the narrow range of 500–600 nm. These nanostructures have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The ZnO nanorods and nanotubes are found by SAED to be single-crystalline. The growth process of ZnO nanorods and nanotubes has been investigated by varying the surfactant concentration and microwave irradiation time. Based on the various results obtained, a tentative and plausible mechanism for the formation of ZnO nanostructures is proposed.     

Development of pitch-based carbon–copper composites

Carbon–copper composites with varying copper to carbon ratio of 0.66–1.5 (by weight) were developed from coal-tar-pitch-derived green coke (as such or modified with natural graphite) as carbon source and electrolytic grade copper powder at different heat treatment temperatures (HTTs) of 1000–1400 °C. The physical, mechanical, and electrical properties differ depending upon the HTT and also on copper to carbon ratio (Cu/C). The composites prepared at HTT of 1100 °C having Cu/C ratio of 0.66 and 0.9 exhibited a high bending strength of 150 and 140 MPa, bulk density of 2.63 and 2.81 gm/cm³, electrical resistivity of 1.6 and 0.96 m Ω cm and shore hardness of 88 and 84, respectively, in spite of well-known inadequate wettability between copper and carbon. Increasing the temperature from 1100 °C for processing of the composites deteriorated the properties mainly due to the loss of copper through melting above 1100 °C as revealed by X-ray, scanning electron microscopy, thermal analysis and EDAX studies.     

Dielectric properties of epoxy/short carbon fiber composites

The dielectric properties of epoxy/short carbon fiber composites at different concentrations 0, 5, 10 and 15% by weight, different thicknesses 2 and 4 mm, and frequency in the range from 20 Hz to 1 MHz were characterized. Scanning electron microscopy and differential scanning calorimetry were utilized. The alternating current (ac) electrical properties (complex impedance, dielectric constant, dielectric loss, real part of electric modulus, imaginary part of electric modulus, electrical conductivity, and relaxation time) were determined. It was found that the applied frequency, filler concentrations, and composite thickness affected the ac electrical properties of the epoxy/carbon fiber composites. The dielectric behaviors of the interfacial polarization between epoxy matrix and carbon fibers could be described by the Maxwell–Wagner–Sillars relaxation. The analysis of the complex electric modulus in the frequency range from 20 Hz to 1 MHz revealed that the interfacial relaxation followed the Cole–Davidson distribution of relaxation times. The universal power-law of ac conductivity was observed in the epoxy/carbon fiber composites. The calculated power exponent (near unity) is physically acceptable within this applied model.     

Synthesis and variable temperature electrical conductivity studies of highly ordered TiO<Subscript>2</Subscript> nanotubes

Rafts of aligned, high aspect ratio TiO₂ nanotubes were fabricated by an electrochemical anodization method and their axial electrical conductivities were determined over the temperature range 225–400 °C. Length, outer diameter, and wall thickness of the nanotubes were approximately 60–80 μm, 160 nm, and 30 nm, respectively. Transmission electron microscopy studies confirmed that the TiO₂ nanotubes were initially amorphous, and became polycrystalline anatase after heat treatment at temperatures as low as 250 °C in air. The activation energy for conductivity over the temperature range 250–350 °C was found to be 0.87 eV. The conductivity values are comparable to those of nanocrystalline and nanoporous anatase thin films reported in literature.     

Fabrication and properties of CNTs/carbon fabric hybrid multiscale composites processed via resin transfer molding technique

Carbon nanotubes (CNTs) are effective fillers/reinforcements regarding improving the properties of polymer. In the present paper, carboxylic acid functionalized CNTs were used to modify epoxy with intent to develop a nanocomposite matrix for hybrid multiscale composites combining benefits of nanoscale reinforcement with well-established fibrous composites. CNTs were dispersed in epoxy by using high energy sonication. At low contents of CNTs, hybrid multiscale composites specimens were manufactured via resin transfer molding (RTM) process. The processibility of CNTs/epoxy systems was explored with respect to their viscosity. The dispersion quality and re-agglomeration behavior of CNTs in epoxy were characterized using optical microscope. A CNTs loading of 0.025 wt% significantly improved the glass transition temperatures (Tg) of the hybrid multiscale composites. Scanning electron microscopy (SEM) was used to examine the fracture surface of the failed specimens. It is demonstrated that the addition of small amount of CNTs (0.025 wt%) to epoxy for the fabrication of multiscale carbon fabric composites via RTM route effectively improves the matrix-dominated properties of polymer based composites. Hybridization efficiency in carbon fiber reinforced composites using CNTs is found to be highly dependent on the changes in the dispersion state of CNTs in epoxy.     

Carbon nanofibers prepared by a novel co-extrusion and melt-spinning of phenol formaldehyde-based core/sheath polymer blends

A novel route based on the solvent-free core/sheath melt-spinning of polypropylene/(phenol formaldehyde–polyethylene) [PP/(PF–PE)] to prepare the carbon nanofiber (CNF) has been demonstrated in this study. The approach consists of three main steps: co-extrusion of PP (core) and a polymer blend of PF and PE (sheath), followed by melt-spinning, to form the core/sheath fiber, stabilization of core/sheath fiber to form the carbon fiber precursor, and carbonization of carbon fiber precursor to form the final CNF. Both scanning electron microscopy and transmission electron microscopy images reveal long and winding CNF with diameter 100–600 nm and length greater than 80 μm. With a yield of ~45% based on its raw material PF, the CNF exhibits regularly oriented bundles which curl up to become rolls of wavy long fibers with clean and smooth surface. Results from X-ray diffractometry, Raman spectroscopy, and selected area electron diffraction pattern further reveal that the CNF exhibits a mixed-phase carbon material with graphitic particles embedded homogeneously in an amorphous carbon matrix.     

Dispersion assessment and studies on AC percolative conductivity in polymer-derived Si–C–N/CNT ceramic nanocomposites

Nanocomposites comprise polysilazane-derived SiCN ceramic charged with carbon nanotubes (CNTs) have been prepared by dispersion of multi-walled CNTs with a diameter of 80 nm in a cross-linked polysilazane (HTT 1800, Clariant) using a simple roll-mixer method. Subsequently, the composites were warm pressed and pyrolyzed in argon atmosphere. Scanning electron microscopy (SEM) and 3D Raman imaging techniques were used as major tools to assess the dispersion of CNTs throughout the ceramic matrix. Furthermore, studies on the effect of the volume fraction of CNTs in the nanocomposites on their electrical properties have been performed. The specific bulk conductivities of the materials were analyzed by AC impedance spectroscopy, revealing percolation thresholds (ρ_c) at CNT loadings lower than 1 vol%. Maximum conductivity amounted to 7.6 × 10⁻² S/cm was observed at 5 vol% CNT. The conductivity exponent in the SiCN/CNT composites was found equal to 1.71, indicating transport in three dimensions.     

Influence of oligomeric silsesquioxane coating treatment on interfacial properties of CF/PAA composites

Carbon fibres (CF) were modified with different oligomeric silsesquioxane (SSO) coatings to improve the interfacial property of carbon fibres/polyarylacetylene (CF/PAA). The interlaminar shear strength (ILSS) of CF/PAA was tested to determine the effect of the treatment. Atomic force microscopy (AFM) in force modulation mode was adopted to study the cross-section surface of unidirectional CF/PAA composites and the relative stiffness of various phases, including CF, interphase and resin. The probability histogram and line distribution of CF/PAA cross-section surface relative stiffness, obtained from the statistical analysis of relative stiffness image, were used to compare and study the interface characterizations of composites. The results show that the ILSS increases effectively and the effects on interfacial characterizations are distinguished from each other in accordance with the CF surface modified with different SSO coatings owing to the various structures. Cage oligomeric silsesquioxane, including large organic groups (methacryl isobutyl-POSS), has better treatment result. AFM observations lead to the conclusion that an interfacial transition layer with different morphology and stiffness appears in CF/PAA composites after being treated by the SSO coatings of different structures. It can be inferred that the appearance of the transition layer may contribute to the improvement of fibre/matrix adhesion. Translated from Acta Materiae Compositae Sinica, 2006, 23(1): 105–111 [译自: 复合材料学报]     

The effect of substrate morphology on the diameter distribution of carbon nanotubes grown on silica and ceramic substrates

Large-scale well-aligned carbon nanotube film and carbon nanotube bundles have been fabricated on smooth silica and rough polycrystalline ceramic substrates by pyrolysis of ferrocene/melamine mixtures. The images of transmission electron microscopy (TEM) and scanning electron microscope (SEM) show that carbon nanotubes grown on the silica substrate have uniform outer diameters of about ∼ 25 nm and lengths of about 40 μm, while those on the ceramic substrate have outer diameters from 10 to 90 nm and lengths up to 100 μm. Electron energy-loss spectroscopy (EELS) spectra show that nanotubes grown on the two different substrates are pure carbon tubes. The effects of substrate micro-morphologies on the diameters of carbon nanotubes have been discussed.     

Poly(adipic acid-hexamethylene diamine)-functionalized multi-walled carbon nanotube nanocomposites

Poly(adipic acid-hexamethylene diamine) (PA66)-functionalized multi-walled carbon nanotubes (PACNT) were fabricated using amino multi-walled carbon nanotubes (AMWNT), adipic acid-hexamethylene diamine salt as reactants at 260–270 °C. The solubility of AMWNT in formic acid is improved after PA66 functionalization. PA66 was successfully grafted onto the surface of AMWNT to form a core–shell nanostructure. AMWNT are surrounded by PA66 chains with an average thickness of 3 nm. The length of PA66 chains on the surface of AMWNT decreases, with the content of AMWNT increasing. The thermal decomposition temperature of the composite is lower than that of PA66 functionalized carboxylic multi-walled carbon nanotubes. The storage modulus of PACNT containing 5 wt% AMWNT is 2.8-fold that of PA66; and it increases as the content of AMWNT increases.     

Covalent attachment of poly (acrylic acid) onto multiwalled carbon nanotubes functionalized with formaldehyde via electrophilic substitution reaction

The functionalization with formaldehyde via an electrophilic substitution reaction and graft with poly (acrylic acid) (PAA) by “grafting from” technology have been carried out for multiwalled carbon nanotubes (MWNTs) and MWNTs-PAA composites have been formed. The IR and TEM results show presence of covalent band and so-called “core-shell” structures for MWNTs-PAA. The MWNTs-PAA exhibits excellent suspendability in water, which is significant to explore the potential application of carbon nanotube in biological and medical systems.     

Multi-walled carbon nanotubes coated with rare earth fluoride EuF3 and TbF3 nanoparticles

EuF₃ and TbF₃ were successfully coated on the multi-walled carbon nanotubes (MWNTs) via the intermediate of noncovalent hydrophobic interactions of the MWNTs surface with sodium dodecyl sulfate (SDS). They were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The nanoparticle sizes of rare earth fluorides on MWNTs are less than 10 nm. The photophysical properties of the composites were investigated, which indicated the rare earth fluorides/MWNTs composites exhibited the optical transitions within the 4f shell of the rare earth ions.     

Mn<Subscript>3</Subscript>O<Subscript>4</Subscript>/worm-like mesoporous carbon synthesized via a microwave method for supercapacitors

A quick and facile microwave method has been employed to prepare Mn₃O₄/worm-like mesoporous carbon (Mn₃O₄–MC) composites. Structural and morphological characterizations of worm-like mesoporous carbon and Mn₃O₄–MC composites have been carried out using X-ray diffraction, transmission electron microscopy, N₂ adsorption–desorption, and electrochemical measurement. Cyclic voltammograms demonstrate that the Mn₃O₄–MC composites perform improved capacitive behavior at the range of −0.8~0.2 V (vs. Hg/HgO electrode) with reversibility. The Mn₃O₄–MC composite electrode possesses an enhanced specific capacitance of 266 F g⁻¹ at a sweep rate of 1 mV s⁻¹.