Facile synthesis of Au nanoparticles supported on polyphosphazene functionalized carbon nanotubes for catalytic reduction of 4-nitrophenol

Carbon nanotubes (CNTs) functionalized with cyclotriphosphazene-containing polyphosphazenes (PZS) were found to cause the facile immobilization of Au nanoparticles on the surface. The PZS functional layers not only improved the dispersion of CNTs in aqueous solution but also used as a platform for subsequent immobilization of Au nanoparticles. The functionalized CNTs and the Au@PZS@CNTs nanohybrids were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectrometer, X-ray diffraction, thermogravimetric analysis, Atomic absorption spectrum, and X-ray photoelectron spectroscopy. The results showed that the PZS layers with thickness of about 25 nm were formed uniformly on CNT surfaces by polycondensation between hexachlorocyclotriphosphazene and 4,4′-sulfonyldiphenol, and that high density of homogeneously dispersed spherical Au nanoparticles with average size of 6 nm was immobilized on their outer surface. Meanwhile, the catalytic activity and reusability of the Au@PZS@CNTs nanohybrids were investigated by employing the reduction of 4-nitrophenol into 4-aminophenol by NaBH₄ as a model reaction.     

Template-induced covalent assembly of hybrid particles for the facile fabrication of magnetic Fe3O4–polymer hybrid hollow microspheres

Magnetic Fe₃O₄–poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) hybrid hollow microspheres, in which Fe₃O₄ nanoparticles were firmly incorporated in the cross-linked PZS shell, have been fabricated through the formation of core/shell PS/Fe₃O₄–PZS composites based on template-induced covalent assembly method, followed by core removal in a tetrahydrofuran solution. The morphology, composition, thermal property, and magnetic property of the magnetic hollow microspheres were characterized by scanning electron microscope, transmission electron microscope, Fourier transform infrared spectra, energy dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetric analysis, and vibrating sample magnetometer respectively. Results indicated that the typical hollow microspheres had about 950 nm of inner diameter and about 210 nm of shell thickness, 440 °C of initial decomposition temperature under nitrogen atmosphere, and 13.3 emu g^?1 of magnetization saturation. Furthermore, the shell thickness of magnetic hollow microspheres could be easily controlled by tuning the mass ratio of PS to comonomers. As-fabricated hybrid hollow microspheres exhibit great potential as good catalyst supports.     

Synthesis and electrocatalytic activity of multi-walled carbon nanotubes/Cu–Ag nanocomposites

Cu–Ag bimetallic nanoparticles with atomic ratio of 2.1:1 and diameter in the range of 15–30 nm were decorated on acid-treated multi-walled carbon nanotubes by a chemical reduction method, which was characterized by transmission electron microscope (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). The Cu–Ag/MWNTs nanocomposites were used to construct a modified electrode toward biosensing of H₂O₂ with a high sensitivity. The catalytic ability of MWNTs/Cu–Ag toward H₂O₂ was much better than that of MWNTs/Cu and MWNTs/Ag, which indicated that there is a cooperation effect between Cu and Ag.     

Synthesis and characterization of NiO nanoparticles and their PMMA nanocomposites obtained by in situ bulk polymerization

A nickel oxide (NiO) precursor was prepared using Pechini method. The NiO nanoparticles were prepared by calcination of NiO precursor at temperatures ranging from 300 to 700 °C. The resulting NiO nanoparticles were characterized by X-ray photoelectron spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy. To hamper NiO nanoparticles aggregation, the NiO nanoparticles surface was treated using (3-mercaptopropyl)-trimethoxysilane as a coupling agent. Next, nanocomposites of poly(methyl methacrylate) and modified NiO nanoparticles were successfully prepared by in situ bulk polymerization with 2,2′-azobis(isobutylonitrile) as initiator. The obtained nanocomposites were characterized by XRD and thermogravimetric analysis. L. A. García-Cerda is on sabbatical leave at UT-Dallas, USA.     

Preparation of surface-silvered graphene-CNTs/polyimide hybrid films: Processing,morphology and properties

Silver nanoparticles modified graphene-carbon nanotubes/polyimide (Gr-CNTs/PI) films have been prepared by electrochemical reduction of silver nitrate on potassium hydroxide hydroxylated of Gr-CNTs/PI films surface. The as-prepared nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction analyzer and semiconductor characterization system. The lower content of Gr-CNTs (≤10 wt. %) doping in PI matrix can improve the conductivity of PI films more clearly than pure CNTs. The conductivity can be regulated by controlling Gr-CNTs content in PI matrix. These silver nanoparticles into Gr-CNTs/PI films presented here can act as deposition seeds which can initiate subsequent electroless silver or copper or electrodeposition other metal.     

Influence of metal nanoparticle decorated CNTs on polyurethane based electro active shape memory nanocomposite actuators

Polymer nanocomposites based on thermoplastic polyurethane (PU) elastomer and metal nanoparticle (Ag and Cu) decorated multiwall carbon nanotubes (M-CNTs) were prepared through melt mixing process and investigated for its mechanical, dynamic mechanical and electro active shape memory properties. Structural characterization and morphological characterization of the PU nanocomposites were done using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Morphological characterization revealed better dispersion of M-CNTs in the polyurethane, which is attributed to the improved interaction between the M-CNTs and polyurethane. Loading of the metal nanoparticle coated carbon nanotubes resulted in the significant improvement on the mechanical properties such as tensile strength of the PU composites in comparison to the pristine carbon nanotubes (P-CNTs). Dynamic mechanical analysis showed that the glass transition temperature (Tg) of the polyurethane increases slightly with increasing loading of both pristine and metal nanoparticle functionalized carbon nanotubes. The metal nanoparticles decorated carbon nanotubes also showed significant improvement in the thermal and electrical conductivity of the PU/M-CNTs nanocomposites. Shape memory studies of the PU/M-CNTs nanocomposites exhibit remarkable recoverability of its shape at lower applied dc voltages.     

One-step synthesis of carbon nanotubes–copper composites for fabricating catalyst supports of methanol electrooxidation

One-step synthesis of carbon nanotubes–copper composites was established by catalytic chemical vapor deposition (CCVD) of acetylene over Co–Cu–Al mixed metal oxides derived from layered double hydroxides (LDHs). Power X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Raman spectra, thermogravimetric and differential thermal analysis (TG-DTA) and N₂ adsorption–desorption measurements revealed that multi-walled carbon nanotubes were synthesized during cobalt-catalyzed CCVD, and copper nanoparticles were simultaneously in situ formed in CNTs matrix. Electrodes modified with platinum particles supported on as-fabricated CNTs–Cu composites showed much higher electrocatalytic activity for the oxidation of methanol than that modified with Pt particles supported on the commercial CNTs. The present study greatly enlarges the practical application of hybrid CNTs-based nanocomposites.     

One-step preparation of FeCo nanoparticles in a SBA-16 matrix as catalysts for carbon nanotubes growth

Nanocomposites containing FeCo alloy nanoparticles dispersed in a highly ordered 3D cubic Im3m mesoporous silica (SBA-16) matrix were prepared by a novel, single-step templated-assisted sol-gel technique. Two different approaches were used in the synthesis of nanocomposites; a pure SBA-16 sample was also prepared for comparison. Low-angle X-ray diffraction, transmission electron microscopy and N2 physisorption at 77 K show that after metal loading, calcination at 500 degrees C and reduction in H2 flux at 800 degrees C the nanocomposites retain the cubic mesoporous structure with pore size not very different from the pure matrix. X-ray absorption fine structure (EXAFS) analysis at Fe and Co K-edges demonstrates that the FeCo nanoparticles have the typical bcc structure. The final nanocomposites were tested as catalysts for the production of carbon nanotubes by catalytic chemical vapour deposition and high-resolution TEM shows that good quality multi-walled carbon nanotubes are obtained.     

Decoration of carbon nanotubes with nearly monodisperse MFe2O4 (MFe2O4, M = Fe, Co, Ni) nanoparticles

Magnetic monodisperse ferrite MFe₂O₄ (M = Fe, Co, Ni) nanoparticles have been successfully deposited on carbon nanotubes (CNTs) by in situ high-temperature hydrolysis and inorganic polymerization of metal salts and CNTs in polyol solution. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectrometry (EDS) and vibrating sample magnetometer (VSM) investigations were used to characterize the final products. The influencing factors for formation of CoFe₂O₄ nanoparticles along CNTs have also been discussed briefly. The main advantage of this synthetic strategy is that it is beneficial for the fabrication of magnetic CNTs with a compact layer of nanoparticles and could be extended to prepare series of ferrite/CNTs nanocomposites via the substitution of metal cations.     

Synthesis of noble metal/carbon nanotube composites in supercritical methanol

A simple and efficient route has been employed to deposit noble metal nanoparticles (Pt, Ru, Pt-Ru, Rh, Ru-Sn) onto carbon nanotubes (CNTs) in supercritical methanol solution. In this method, the inorganic metallic salts acted as metal precursors, and methanol as solvent as well as reductant for the precursors. The as-prepared nanocomposites were structurally and morphologically characterized by X-ray diffraction spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy, and X-ray photoelectron spectroscopy analyses. It was demonstrated that the CNTs were decorated by crystalline metal nanoparticles with uniform sizes and a narrow particle size distribution. The size and loading content of the nanoparticles on CNTs could be tuned by manipulating reaction parameters. Furthermore, the formation mechanism of the composites was also discussed.     

Grafting of gold nanoparticles and nanorods on plasma-treated polymers by thiols

Grafting of gold nanoparticles and nanorods on the surface of polymers, modified by plasma discharge, is studied with the aim to create structures with potential applications in electronics or tissue engineering. Surfaces of polyethyleneterephthalate and polytetrafluoroethylene were modified by plasma discharge and subsequently, grafted with 2-mercaptoethanol, 4,4′-biphenyldithiol, and cysteamine. The thiols are expected to be fixed via one of –OH, –SH or –NH₂ groups to reactive places on the polymer surface created by the plasma treatment. “Free” –SH groups are allowed to interact (graft) with gold nanoparticles and nanorods. Gold nano-objects were characterized before grafting by transmission electron microscopy and UV–Vis spectroscopy. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and electrokinetic analysis (zeta potential determination) were used for the characterization of polymer surface at different modification phases. It was proved by FTIR and XPS measurements that the thiols were chemically bonded on the surface of the plasma-treated polymers, and they mediate subsequent grafting of the gold nano-objects. On the surfaces, modified polymers were indicated some objects by AFM, size of which was dramatically larger in comparison with that of original nanoparticles and nanorods. This result and the other results of UV–Vis spectroscopy indicate an aggregation of deposited gold nano-objects.     

Reduced graphene oxide supported palladium–silver bimetallic nanoparticles for ethanol electro-oxidation in alkaline media

Palladium–silver bimetallic nanoparticles loaded on reduced graphene oxide (Pd–Ag/RGO) were prepared by co-reduction of mixed metal salts and graphene oxide (GO) with urea-assisted ethylene glycol (EG). The as-obtained Pd–Ag/RGO nanocomposites were characterized by X-ray diffraction, transmission electronic microscopy, and UV–Vis absorption spectroscopy. The results show that the nanoparticles with an average particle size of 5 nm are dispersed on the surface of RGO highly uniformly, besides the Pd–Ag bimetallic nanoparticles are more helpful to promote the reduction of GO than monometal ones. The electrochemical activities of the as-prepared nanocomposites for ethanol oxidation were investigated by using cyclic voltammetry and chronoamperometry in alkaline solution. Compared to the Pd–Ag/E-tek carbon (Pd–Ag/C) and Pd–Ag/multi-walled carbon nanotubes (Pd–Ag/MWCNTs) which were fabricated by the same method, the Pd–Ag/RGO exhibit much higher electrocatalytic activity, stronger tolerance to CO and better stability during the ethanol electro-oxidation reaction in alkaline media. The electrocatalytic performances of Pd–Ag/RGO with different mass ratios of Pd–Ag toward ethanol oxidation in alkaline media were also studied. The results indicate that the electrocatalytic activity of Pd–Ag/RGO with 1:1 mass ratio of Pd–Ag is the best.     

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.     

Facile synthesis and characterization of novel nanocomposites of titanate nanotubes and rutile nanocrystals

The nanocomposites of one-dimensional (1D) titanate nanotubes and 0D rutile nanocrystals were fabricated by hydrothermal treatment of bulky rutile TiO₂ powders in a 10 M NaOH solution without using any templates and catalysts. The as-prepared samples were characterized with transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, Fourier transform infrared spectroscopy (FTIR), UV–visible spectrophotometry (UV–vis), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that many small rutile nanocrystal particles of about 5 nm could uniformly attach to the outer surface and in the inner of the titanate nanotubes, forming an interesting and novel nanocomposite structure. Adjusting reaction time could control the amount of rutile nanoparticles in the nanocomposites. With increasing reaction time, the specific surface areas, porosity, pore volume, UV absorption and band gap energies of the nanocomposites gradually increased due to the fact that rutile particles were steadily turned into the tubular nanocomposites, finally completely formed titanate nanotubes.     

In situ synthesis of graphene/cobalt nanocomposites and their magnetic properties

Graphene, which possesses unique nanostructure and excellent properties, is considered as a low cost alternative to carbon nanotubes in nanocomposites. In this study, we present a simple in situ approach for the deposition of cobalt (Co) nanoparticles onto surfaces of graphene sheets by hydrazine hydrate reduction. The as-synthesized composites were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM) and thermogravimetry and differential scanning calorimetry. It was shown that the as-formed Co nanoparticles were densely and homogeneously deposited on the surfaces of the graphene sheets and as a result, the restacking of the as-reduced graphene sheets was effectively inhibited. Magnetic studies reveal that the graphene/Co nanocomposite displays ferromagnetic behavior with saturation magnetizations of 53.4 emu g⁻¹, remanent magnetization of 6.0 emu g⁻¹ and coercivity of 226 Oe at room temperature, which make it promising for practical applications in future nanotechnology.     

Synthesis, characterization and fluorescence property of CdS/P(N-iPAAm) nanocomposites

A novel nanocomposite in which CdS nanoparticles were embedded in poly(N-isopropylacrylamide) (P(N-iPAAm)) matrix have been fabricated. The particle size of CdS nanoparticles ranged from 10 nm to 40 nm could be adjusted with the varying of the inorganic contents. The nanocomposites have been characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), thermo-gravimetric analysis (TGA), high resolution transmission electron microscope (HRTEM), UV-vis absorption and fluorescence spectra (FLS) measurements. The cell volume of CdS nanoparticles embedded in polymer matrix was smaller than the standard value and the nanocomposites with 12.0% inorganic content showed a good fluorescence property.     

Improvement of the field emission of carbon nanotubes-metal nanocomposite

Carbon nanotubes (CNT) decorated with Ni and Ag performed by electroless plating, and the effect of Ni and Ag nanoparticles and coating distribution on field emission of CNT are studied. The chemical composition, microstructure of CNT/Ni and CNT/Ag nanocomposites are characterized by an energy dispersion X-ray spectroscope (EDS), a transmission electron microscope and a scanning electron microscope. The field emission properties of CNT/Ni and CNT/Ag cathodes are measured using a diode structure under a pressure of 10^?5 Pa. The experimental results show that fine and well-dispersed metallic nanoparticles and discontinuous coating of Ni and Ag on the CNT surface can be obtained by electroless plating. Moreover, the enhanced field emission properties of CNT decorated with Ni and Ag can be obtained by lowering the work function of emitters and reducing the contact resistance between cathode and substrate. The field enhancement factors as high as 24264 of CNT/Ni and 25565 of CNT/Ag emitters can be improved by the distributed nano-sized Ni and Ag formed on the CNT surface.     

Electrochemical characterization of electrodeposited carbon nanotubes

Carbon nanotubes were electrodeposited in acetonitrile solution at room temperature using Cu, and Fe-Ni nanoparticles as nucleation sites on HF-etched Si(100) wafer substrate. The electrochemical behavior of the deposition was investigated by voltammetry and chronoamperometry techniques. In order to obtain the optimum growth condition, the deposition critical parameters including current density range, potential and time were studied and calculated. Carbon nanotubes with approximate external diameter of 40-100 nm were fabricated under potentiostatic condition and diffusion control at − 20 V in 4-6 h. The film crystallinity was investigated by means of X-ray diffraction and the tubes structure was revealed using scanning electron microscope and transmission electron microscope images. Raman spectroscopy was also employed to characterize the nanostructural features and single wall carbon nanotubes were detected.     

Synthesis and characterization of dual particle (MWCT+B4C) reinforced sintered hybrid aluminum matrix composites

ABSTRACT

Metal matrix nanocomposites (MMNCs) consist of a metal matrix reinforced with nanoparticles, featuring physical and mechanical properties very different from those of the matrix. Especially carbon nanotubes (CNTs) can improve the matrix material in terms of wear resistance, damping properties, and mechanical strength. The present investigation deals with the synthesis and characterization of aluminum matrix reinforced with micro-B₄C particles, and multiwall carbon nanotubes (MWCNTs) which have been prepared by powder metallurgy route. Powder mixture containing fixed weight (%) of B₄C and different wt% of MWCNT as reinforcement constituents that are uniaxial cold pressed and later green compacts are sintered in continues electric furnace. Microstructure and Mechanical properties such as microhardness and density are examined. Microstructure of samples has been investigated using scanning electron microscope (SEM). X-ray diffraction(XRD), energy dispersive x-ray (EDAX), atomic force microscope (AFM), and transmission electron microscope (TEM). TEM microstructure of the nanocomposite shows the homogeneous dispersion of MWCNT in the aluminum matrix. The results indicated that the increase in wt % of MWCNT improves the bonding and mechanical properties.     

Sonochemical preparation of nickel alumina nanotubes templated by anionic surfactant assemblies

Nickel alumina nanotubes templated by dodecylsulfate assemblies have been successfully synthesized for the first time using a sonochemical process. These nanotubes were characterized by scanning electron microscope (SEM), a transmission electron microscope (TEM), X-ray diffraction (XRD). The formation mechanism of these nanotubes is also discussed. They were also calcined to study the change of the nanostructure morphology with the temperature. It was found that the nanotubes transformed from short nanotubes into dendritic structures of aggregations of nanoparticles into monodisperse nanoparticles, and these nanostructures hold high specific surface area.