One-pot synthesis of one-dimensional array Pt nanoparticles on carbon nanotubes via a facile microwave polyol method

High-density attachment and one-dimensional array Pt nanoparticles (NPs) on carbon nanotubes (CNTs) to generate Pt/CNTs heterostructures are obtained via one-pot microwave polyol method. The morphology, composition of as-obtained Pt/CNTs heterostructures is characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD). The Raman spectrum and Fourier transform infrared (FTIR) spectrum show the introduction of defects or functional groups on CNTs surface, which are crucial factors to assist the nucleation and growth of Pt NPs along the skeleton of CNTs.     

High-density attachment of FePt nanoparticles on carbon nanotubes by a facile microwave-assisted polyol method

High-density attachment and one-dimensional (1D) array of FePt nanoparticles (NPs) along carbon nanotubes (CNTs) surface to generate FePt/CNT nanocomposites were successfully obtained via a facile CNT-mediated microwave polyol method. The as-prepared 1D FePt/CNTs is about 10–20 nm in diameter and up to μm scale in length. By adjusting the solvents, the ratio of Fe/Pt and the attached density of FePt NPs on the surface of CNTs could be well controlled. The structures, composition, and magnetic properties of the FePt/CNTs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and magnetic measurements. The possible growth mechanism has also been proposed.     

The interaction between unique hyperbranched polyaniline and carbon nanotubes,and its influence on the dielectric behavior of hyperbranched polyaniline/carbon nanotube/epoxy resin composites

Novel hybridized multi-walled carbon nanotubes (CNTs), consisting of a unique hyperbranched polyaniline (HSiPA) and CNTs, were prepared. The interaction between HSiPA and CNTs was investigated by many techniques, and results show that there are strong π–π and electrostatic interactions between HSiPA and CNTs, so HSiPA can stack firmly onto the surface of CNTs to form a coating. Based on this, a new kind of ternary composites made up of hybridized CNTs and epoxy (EP) resin was prepared, the influence of the ratio of HSiPA to CNTs on the structure and properties of the HSiPA/CNT/EP composites was intensively studied. The percolation threshold of HSiPA/CNT/EP composites is very low (1.26 wt%); besides, with a suitable ratio of HSiPA to CNTs, the HSiPA/CNT/EP composite has much higher dielectric constant and lower dielectric loss than the CNT/EP composite with the same loading of CNTs. When the ratio of HSiPA to CNTs is 0.5:1, the dielectric constant and loss at 100 Hz of the resultant HSiPA/CNT0.5/EP composite are 711 and 1.53, about 7.1 and 4.3 × 10^?3 times the corresponding value of CNT0.5/EP composite, respectively. In addition, compared with traditional CNT/EP composites, the HSiPA/CNT0.5/EP composites have different equivalent circuit models. These attractive results are attributed to unique structure of hybridized CNTs, and thus leading to greatly different structures between the CNT0.5/EP and HSiPA/CNT0.5/EP composites. This investigation reported herein suggests a new approach to prepare new CNTs and related composites with controllable dielectric properties.     

Comparative investigation on decorating carbon nanotubes with different transition metals

The diffusion dynamics and structure evolvement of the transition metal (TM=Ni, Cu, Au, and Pt) atoms decorating carbon nanotubes (CNTs) with differences have been systematically studied by Monte Carlo (MC) simulation. The studies show that TM atoms can be encapsulated inside, aggregated and even wrapped on the surface of the CNT, which depend on the interactions among TM–TM and TM–C during the spontaneous diffusion process. The decorating effect is greatly influenced by the diameters of CNTs, TM atoms tend to be encapsulated inside the tube in the relatively large CNTs, while they are inclined to stack on the surface for the small ones. More interestingly, Au and Pt atoms would wrap around the smaller CNT, whereas Ni and Cu atoms are still clustering outside of the CNTs with the increase of the number of TM atoms. Simulation results indicate that Pt and Au possess a better wetting effect with CNT than Ni and Cu.     

Deposition of silver nanoparticles on carbon nanotube by chemical reduction method: Evaluation of surface,thermal and optical properties

Silver was stabilized on multi-walled carbon nanotubes (MWCNTs) by chemical-reduction technique using N,N-dimethylformamide (DMF) as a reducing agent. The influence of silver on the performance of carbon nanotubes (CNTs) was investigated by employing Fourier-transform infrared spectra (FTIR), Raman spectroscopy (RAS), thermal gravimetric analysis (TGA), zeta potential measurement, scanning electron microscope (SEM), electron dispersive X-ray spectrometer (EDX), transmission electron microscopy (TEM), and reflectance spectroscopy (RS). FTIR as well as RS methods evidenced the synthesis procedure using chemical reduction method was successful. Performing TGA of the samples under oxygen atmosphere demonstrated that the silver nanoparticles (Ag NPs) generated on MWCNTs surface can decrease the thermal stability of the particles by the catalytic oxidation of CNTs. In contrary, the thermal stability of the MWCNTs has improved under nitrogen atmosphere. EDX results showed the presence of Ag, Au and Co on the surface of deposited sample. The synthesised silver multi-walled carbon nanotubes (Ag–MWCNTs) were found to have higher UV reflection activity compared with untreated particles. The Ag–CNTs can be used in producing anti-UV composites.     

Synthesis and characterization of magnetic Fe/CNTs composites with controllable Fe nanoparticle concentration

Fe/CNTs composites, with different concentrations of Fe nanoparticles (NPs) on carbon nanotube (CNT) surfaces, were successfully fabricated via a facile solvothermal method. The lengths of CNTs are up to 10 μm and the mean diameter of the Fe nanoparticles is about 25 nm. The structures, composition and magnetic properties of the Fe/CNTs were characterized by XRD, FTIR, FE-SEM, TEM and PPMS. We found that the concentrations of Fe nanoparticles depositing on the CNTs could be controlled by adjusting the initial mass ratio of ferrocene to CNTs. The Fe/CNTs composites display good ferromagnetic properties at room temperature, with a saturation magnetization of 125 emu/g-Fe and a coercivity of 276 Oe. The Curie temperature of the sample is about 1038 K, slightly lower than that (1043 K) of the bulk iron.     

Ethylene glycol reflux synthesis of carbon nanotube/ceria core-shell nanowires

Carbon nanotube (CNT)/ceria core-shell nanowires were prepared facilely on a large scale under the boiling reflux of ethylene glycol. The composites are characterized by transmission electron microscopy, X-ray diffraction as well as Fourier transformed infrared spectra. It is found that the entire outer surface of CNTs is fully sheathed with a dense layer of uniform nanosized CeO₂, and that the thickness of the coating sheath can be readily manipulated by tuning the molar ratio of ceria to CNTs. Finally, a possible formation mechanism has been suggested as follows: with the high reaction temperature, ethylene glycol is partially converted to oxalic acid, and the surface hydroxyl groups of CeO₂ tiny particles react with oxalic acid to form the polymer-like inorganic-organic compounds. Subsequently, in view of the low-energy point, the polymer-like inorganic-organic compounds are coated on the surface of CNTs, and thus CNTs/ceria core-shell composites are obtained.     

Fabrication of Fe/Fe<Subscript>3</Subscript>C-functionalized carbon nanotubes and their electromagnetic and microwave absorbing properties

Fe/Fe₃C-functionalized carbon nanotubes (CNTs) have been prepared by the floating catalyst chemical vapor-deposition method. It is demonstrated that the Fe and Fe₃C nanostructures are both encapsulated in the CNTs or decorated on the surface of CNTs. The Fe/Fe₃C content in the composites can easily be adjusted by changing the ferrocene concentration in the preparation. The electromagnetic properties of the CNTs have been evaluated in the frequency range of 2–18 GHz, and the nanocomposites exhibit excellent microwave absorbing performance. The CNT composites with higher Fe/Fe₃C content show enhanced microwave reflection losses. The significant influence of the Fe/Fe₃C nanostructures on the microwave absorption is realized by tuning the characteristic impedance of the nanocomposites. With increasing thickness, the maximum reflection loss peak shifts to lower frequency. The microwave absorbing performance of the composites is mainly caused by dielectric loss, resulting from the continuous CNT networks with excellent electrical conductivity.     

Laser-assisted generation of gold nanoparticles and nanostructures in liquid and their plasmonic luminescence

Nanoparticles (NPs) and surface nanostructures (NS) are produced via laser ablation of a bulk gold target in liquid using second harmonics of 10 ps Nd:YAG laser (532 nm) with repetition rate of 50 kHz. The morphology and plasmon photoluminescence (PL) properties of obtained nanoscale objects are described. Transmission electron microscopy and field emission scanning electron microscopy are used for morphology characterization of NPs and NS, respectively. Plasmon PL of both gold NPs and NS is experimentally studied using the third harmonics of the Nd:YAG picosecond laser (355 nm) as a pump. The wavelength of intensity maximum of PL of Au NPs colloidal solution virtually coincides with the position of Au NPs plasmon absorption peak. Real-time excitation of both plasmon PL and Raman scattering of surrounding liquid by picosecond laser pulses in aqueous colloidal solution is also investigated. The efficient cross section of plasmon PL of Au NPs colloid is evaluated using Raman scattering of water as a comparative parameter. The results are in good agreement with values obtained in previous works. Plasmon PL from self-organized NS on the Au surface produced via laser ablation is observed for the first time. Its spectrum is compared to PL spectra of both aqueous colloidal solutions of NPs and of NPs deposited on a Si wafer. The obtained experimental data are discussed with reference to the band structure of bulk Au.     

Seed-mediated growth of gold nanoparticles using self-assembled monolayer of polystyrene microspheres as nanotemplate arrays

Arrays of noble metal nanoparticles show potential applications in (bio-)sensing, optical storage, surface-enhanced spectroscopy, and waveguides. For all such potential devices, controlling the size, morphology, and interparticle spacing of the nanoparticles is very important. Here, we combine seed-mediated growth with nanosphere lithography to study the controllable growth of gold nanoparticles (Au NPs), in which the self-assembly monolayer of polystyrene (PS) on a silicon surface is used to guide the modification of alkanesilanes and the subsequent adsorption of gold seeds; seed-mediated growth is applied to controlling the morphology and size of Au NPs. The size of adsorption region (determining the number of adsorbed gold seeds) is controlled by etching PS microspheres with oxygen plasma or annealing PS microspheres at the glass transition temperature. The size and morphology of the Au NPs are controlled by changing growth conditions. In such a way, we have achieved the dual control of the obtained Au NPs. Preliminary results show that this strategy holds a great promise. This approach can also be extended to a wide range of materials and substrates.     

On the thermal expansion of CNT/Cu composites for electronic packaging applications

Carbon nanotubes (CNTs) exhibit both excellent high thermal conductivity and low coefficient of thermal expansion (CTE), which are an ideal reinforcement in composite materials for high performance electronic packaging applications. In the present study, CNT/Cu composites containing CNTs varying from 0 vol.% to 15 vol.% are prepared, and their CTE behavior is studied in detail. The results indicate that the CTE of 0–10 vol.% CNT/Cu composites is significantly decreased with increasing CNT content. However, as the CNT content increases to 15 vol.%, the decrease in CTE of the composites is pronouncedly reduced. Possible mechanisms are discussed in combination with CTE model predictions.     

Synthesis of carbon nanotubes/alumina composites in supercritical media

Nanosized composites based on multiwall carbon nanotubes (CNTs) and Al₂O₃ have been obtained for the first time in supercritical (SC) media (water, hexane, and their mixture). For comparison, materials of the same net composition have been prepared by hydrothermal synthesis and sol–gel processing. The composites have been characterized by electron microscopy, X-ray diffraction, and thermal analysis. The structure of the materials synthesized in the SC media depends on the fluid composition. The most uniform composite containing alumina particles that are comparable in size to the CNT diameter and are stabilized on the carbon surface can be obtained in the SC mixture of hexane and water. When water and hexane are used separately, the formation of large alumina crystals on the CNT surface and contamination of the composite by the products of hexane pyrolysis and carbonization are, respectively, observed.     

SERS activity of Au nanoparticles coated on an array of carbon nanotube nested into silicon nanoporous pillar

A novel composite structure, Au nanoparticles coated on a nest-shaped array of carbon nanotube nested into a silicon nanoporous pillar array (Au/NACNT/Si-NPA), was fabricated for surface-enhanced Raman scattering (SERS). The morphology of the Au/NACNT/Si-NPA composite structure was characterized with the aid of scanning electron microscopy, X-ray diffraction instrumentation and Transmission electron microscopy. Compared with SERS of rhodamine 6G (R6G) adsorbed on SERS-active Au substrate reported, the SERS signals of R6G adsorbed on these gold nanoparticles were obviously improved. This was attributed to the enlarged specific surface area for adsorption of target molecules brought by the nest-shaped CNTs structure.     

Surfactant-assisted reflux synthesis, characterization and formation mechanism of carbon nanotube/europium hydroxide core-shell nanowires

Carbon nanotube (CNT)/europium hydroxide core-shell nanowires were prepared easily on a large scale under the boiling reflux of water assisted by the surfactant, sodium polystyrenesulfonate (SPS). The core-shell nanowires are characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectrum. A possible formation mechanism has been suggested as follows: The phenyl rings of SPS can react with the carbon ring of CNTs to form the π-π noncovalent bond, which makes the SPS cover the surface of CNTs entirely, and thus the surface of modified CNTs is negatively charged, which repel with each other resulting in the good dispersion. In addition, the negatively charged surface of CNTs adsorbs europium ions (positive). The adsorbed europium ions in situ react with OH⁻ ions to create europium hydroxide nanoparticles, and subsequently, the nanoparticles fuse together to form a dense coating layer on CNTs.     

1-Hexadecylamine as both reducing agent and stabilizer to synthesize Au and Ag nanoparticles and their SERS application

1-Hexadecylamine (HDA)-capped Au and Ag nanoparticles (NPs) have been successfully prepared by a one-pot solution growth method. The HDA is used as both reducing agent and stabilizer in the synthetic process is favorable for investigating the capping mechanism of Au and Ag NPs’ surface. The growth process and characterization of Au and Ag NPs are determined by Ultraviolet–visible (UV–vis) spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). Experimental results demonstrate that the HDA-capped Au and Ag NPs are highly crystalline and have good optical properties. Furthermore, surface-enhanced Raman scattering (SERS) spectra of 2-thionaphthol are obtained on the Au and Ag NPs modified glass surface, respectively, indicating that the as-synthesized noble metal NPs have potentially high sensitive optical detection application.     

Pyridine-thermal synthesis and high catalytic activity of CeO2/CuO/CNT nanocomposites

Carbon nanotubes (CNTs) were controllably coated with the uninterrupted CuO and CeO₂ composite nanoparticles by a facile pyridine-thermal method and the high catalytic performance for CO oxidation was also found. The obtained nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction as well as X-ray photoelectron spectroscopy. It is found that the CuO/CeO₂ composite nanoparticles are distributed uniformly on the surface of CNTs and the shell of CeO₂/CuO/CNT nanocomposites is made of nanoparticles with a diameter of 30-60 nm. The possible formation mechanism is suggest as follows: the surface of CNTs is modified by the pyridine due to the π-π conjugate role so that the alkaline of pyridine attached on the CNT surface is more enhanced as compared to the one in the bulk solvent, and thus, these pyridines accept the proton from the water molecular preferentially, which result in the formation of the OH⁻ ions around the surface of CNTs. Subsequently, the metal ions such as Ce³⁺ and Cu²⁺ in situ react with the OH⁻ ions and the resultant nanoparticles deposit on the surface of CNTs, and finally the CeO₂/CuO/CNT nanocomposites are obtained. The T₅₀ depicting the catalytic activity for CO oxidation over CeO₂/CuO/CNT nanocomposites can reach ∼113 °C, which is much lower than that of CeO₂/CNT or CuO/CNT nanocomposites or CNTs.     

Synthesis and comparative study of optical and electrical properties of Au-doped carbon nanotubes prepared in different reaction media

We introduce the synthesis, characterization and physical properties of gold (Au) doped multiwalled carbon nanotubes (MWCNTs) in different reaction media. In order to dope MWCNTs with Au nanoparticles (NPs), first functionalized carbon nanotubes (f-MWCNTs) were prepared. The reduction of gold (III) chloride trihydrate for synthesizing Au NPs in the presence of f-MWCNTs was performed by using sodium citrate as a reducing agent. The produced nanocomposites were characterized using FTIR, XRD and TEM analyses to explore their chemical structures and morphologies. All of the samples have been characterized by TGA and resultantly, the composite made into ethylene glycol exhibited the most concentration of Au NPs into the composite network. This work probes the optical characteristics, such as UV–vis absorption, and optical band gap. Hall effect analyses declared some pleasing variations in electrical characteristics. Remarkably, the n-type doping of Au NPs in the p-type MWCNTs’ network led to a downshift of the Fermi level. This process increased the doped samples electrical conductivity. The results indicated that modification of MWCNTs with Au NPs has generally an important role in decreasing the band gap and increasing the electrical activity of MWCNTs. Our research outcomes provide a new vision into how different reaction media could affect the characteristics of MWCNT/Au nanocomposites. We discovered that ethylene glycol could be considered as a perfect reaction medium for preparation of high-quality doped CNTs with excellent physical properties. Our effort opens up the door to far more investigations on the role of the reaction medium in products’ characteristics.     

Synthesis of composite gold/tin-oxide nanoparticles by nano-soldering

Composite Au–SnO₂ nanoparticles (NPs) are synthesized by nano-soldering of pure Au and SnO₂ NPs. The multi-step process involves synthesis of pure Au and SnO₂ NPs separately by nanosecond pulse laser ablation of pure gold and pure tin targets in deionized water and post-ablation laser heating of mixed solution of Au colloidal and SnO₂ colloidal to form nanocomposite. Transmission Electron Microscopy (TEM) and High-Resolution Transmission Electron Microscopy (HRTEM) were used to study the effect of laser irradiation time on morphology of the composite Au–SnO₂ NPs. The spherical particles of 4 nm mean size were obtained for 5 min of post-laser heating. Increased mean size and elongated particles were observed on further laser heating. UV–vis spectra of Au–SnO₂ nanocomposites show red shift in the plasmon resonance absorption peak and line shape broadening with respect to pure Au NPs. The negative binding energy shift of Au 4f_7/2 peak observed in X-ray Photoelectron Spectra (XPS) indicates charge transfer in the nano-soldered Au–SnO₂ between gold and tin oxide and formation of soldered nanocomposite.     

Influence of size and surface capping on photoluminescence and cytotoxicity of gold nanoparticles

Hydrophilic and homogeneous sub-10 nm blue light-emitting gold nanoparticles (NPs) functionalized with different capping agents have been prepared by simple chemical routes. Structure, average, size, and surface characteristics of these NPs have been widely studied, and the stability of colloidal NP solutions at different pH values has been evaluated. Au NPs show blue PL emission, particularly in the GSH capped NPs, in which the thiol-metal core transference transitions considerably enhance the fluorescent emission. The influence of capping agent and NP size on cytotoxicity and on the fluorescent emission are analyzed and discussed in order to obtain Au NPs with suitable features for biomedical applications. Cytotoxicity of different types of gold NPs has been determined using NPs at high concentrations in both tumor cell lines and primary cells. All NPs used show high biocompatibility with low cytotoxicity even at high concentration, while Au-GSH NPs decrease viability and proliferation of both a tumor cell line and primary lymphocytes.     

Molecular dynamics study of mechanical properties of carbon nanotube-embedded gold composites

The mechanical properties of nano-single crystal gold and carbon nanotube-embedded gold (CNT/Au) composites under axial tension were investigated using molecular dynamics (MD) simulation method. The interactions between atoms were modeled using the many-body tight-binding (TB) potential and the empirical Tersoff potential coupled with the Lennard-Jones (L-J) potential. We get the yield strain and the yield stress of nano-single crystal gold 0.092, 5.74 GPa, respectively. The computational results show that the increase in Young's modulus of the long CNT-embedded gold composite over pure gold is much large. From the simulation, we also find that the yield stress and the yield strain of short CNT-embedded gold composite are evidently less than that of the nano-single crystal gold.