Fabrication and thermal analysis of submicron silver tubes prepared from electrospun fiber templates

Submicron silver tubes have been synthesized by a polymer-based template approach. Two different approaches to metallization, electroless deposition and exchange plating, were evaluated within the template approach. Silver films with average thickness approximately 50-100 nm were deposited on polycarbonate fibers approximately 400 nm in diameter by each technique, resulting in tubes with a diameter between 450 and 500 nm after thermal degradation of core fibers. These nanomaterials were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and scanning thermal microscopy. The thermal conductivity of the silver submicron tubes was found to differ depending on the method of preparation, with tubes from electroless plating possessing relative thermal conductivity values that were 1 order of magnitude higher than that from exchange plating, 3000 W/m x K and 660 W/m x K, respectively. Interestingly, these results indicate that silver submicron tubes possess higher thermal conductivity than the bulk metal. This observation is discussed in the context of the continuous conduction path of the tubes and their high surface area-to-volume ratio.     

Preparation of submicron polypyrrole/poly(methyl methacrylate) coaxial fibers and conversion to polypyrrole tubes and carbon tubes

In an effort to prepare electrically conductive nanofiber and nanotube materials, polypyrrole/poly(methyl methacrylate) coaxial fibers have been prepared using polymer fibers produced from an electrospinning process. Poly(methyl methacrylate) (PMMA) fibers with an average diameter of 230 nm were initially fabricated by electrospinning as core materials. The PMMA fibers were subsequently coated as templates with a thin layer of polypyrrole (PPy) by in-situ deposition of the conducting polymer from aqueous solution. Hollow PPy tubes were produced by dissolution of the PMMA core from PPy/PMMA coaxial fibers. High-temperature (1000 degrees C) treatment under inert atmosphere converted PPy/PMMA coaxial fibers into carbon tubes by complete decomposition of PMMA fiber core and carbonization of the PPy wall. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and FT-IR spectroscopy confirmed the formation of the PPy/PMMA coaxial fibers, PPy tubes, and carbon tubes.     

Carbon nanotube bags: catalytic formation, physical properties, two-dimensional alignment and geometric structuring of densely filled carbon tubes

The catalytic CVD synthesis, using propyne as carbon precursor and Fe(NO3)3 as catalyst precursor inside porous alumina, gives carbon nanotube (CNT) bags in a well-arranged two-dimensional order. The tubes have the morphology of bags or fibers, since they are completely filled with smaller helicoidal CNTs. This morphology has so far not been reported for CNTs. Owing to the dense filling of the outer mother CNTs with small helicoidal CNTs, the resulting CNT fibers appear to be stiff and show no sign of inflation, as sometimes observed with hollow CNTs. The fiber morphology was observed by raster electron microscopy (REM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The carbon material is graphitic as deduced from spectroscopic studies (X-ray diffraction, Raman and electron energy-loss spectroscopy (EELS)). From M?ssbauer studies, the presence of two different oxidation states (Fe0 and FeIII) of the catalyst is proven. Geometric structuring of the template by two different methods has been studied. Inkjet catalyst printing shows that the tubes can be arranged in defined areas by a simple and easily applied technique. Laser-structuring creates grooves of nanotube fibers embedded in the alumina host. This allows the formation of defined architectures in the microm range. Results on hydrogen absorption and field emission properties of the CNT fibers are reported.     

Synthesis of carbon nanofibers via hydrothermal conversion of cellulose nanocrystals

Carbon nanofibers of 1–2 nm height and micrometer length were synthesized via a hydrothermal conversion of cellulose nanocrystals at 240 °C. The fibers were characterized by atomic force microscopy, transmission electron microscopy, powder X-ray diffraction and Raman spectroscopy. In the hypothesized mechanism, the self-assembly of cellulose nanocrystals prior to their carbonisation provides a template for the nanofiber formation.     

Continuous Production of Carbon Nanotubes by Using Moving Bed Reactor

Since the discovery in 19911, carbon nanotubes have been the subject of intensive research due to their extraordinary mechanical and electronic properties2-7. However, lack of sufficient amount of materials limited the study of the fundamental properties and development of more practical applications. It is highly desirable to have large quantities of pure nanotubes. To date, few methods have been developed for the production of high-quality tubes which can adapted to industrial production …     

Using collagen fiber as a template to synthesize hierarchical mesoporous alumina fiber

Hierarchical mesoporous alumina fiber was synthesized by using collagen fiber as the template, and characterized by means of scanning electron microscopy, transmission electron microscopy, N2 adsorption techniques, X-ray photoelectron spectroscopy, and X-ray diffraction. The alumina fiber obtained is approximately 1-4 microm in outer diameter and 0.5-1 mm in length. The pore size distribution of the alumina fiber is narrow (2-20 nm), and its pore size is controllable by varying preparation methods. This study indicates that collagen fiber, which has hierarchical supermolecular structure, could be used as an ideal template to prepare well-defined porous metal oxide fibers.     

Tubular carbon nano-/microstructures synthesized from graphite powders by an in situ template process

Through the use of commercial graphite powders as the carbon sources, a variety of interesting tubular carbon nano- and microstructures, such as networked carbon nanotubes, aligned carbon microtubes with hexagonal cross-sections, aligned tapered carbon tubes, and hollow carbon microhorns, have been successfully synthesized. As-grown tubular carbon structures were characterized using scanning electron microscopy, transmission electron microscopy, and X-ray energy-dispersive spectroscopy. An in situ template mechanism was proposed to explain the possible growth process. The vibrational properties of the synthesized tubular carbon structures were also studied by Raman spectroscopy.     

POROUS MEMBRANE TEMPLATED SYNTHESIS OF POLYMER PILLARED LAYER

The anodic porous alumina membranes with a definite pore diameter and aspect ratio were used as templates tosynthesize polymer pillared layer structures. The pillared polymer was produced in the template membrane pores, and thelayer on the template surfaces. Rigid cured epoxy resin, polystyrene and soft hydrogel were chosen to confirm themethodology. The pillars were in the form of either tubes or fibers, which were controlled by the alumina membrane pore surface wettability. The structural features were confirmed by scanning electron microscopy results.     

Facile synthesis and luminescence properties of europium(III)-doped silica nanotubes

Photoluminescent nanomaterials had emerged as an amazing field in a wide range of applications during the past few decades. In this article, fibrous europium tartrates and photoluminescent silica nanotubes were conveniently synthesized by using sol–gel method, in which europium ions entered silica matrix. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, fourier transform infrared spectra, energy-dispersive X-ray spectroscopy and photoluminescence (PL) spectra analysis were used to characterize the growth, structure, morphology and optical property of the products. The results indicated that europium tartrates nanofibers as a template can transform tetraethylorthosilicate into silica nanotubes effectively. Meanwhile, europium(III) was transferred from the fibers to the tubes successfully. A hard template mechanism was proposed to explain the formation process of europium(III)-doped silica nanotubes. Moreover, different morphologies of silica-based nanomaterials were obtained due to varying NH₄OH addition or stirring time. PL spectra from nanofiber and nanotube show a typical emission of europium(III), and 13 % is the quenching concentration of europium(III) in silica matrix for this system. The novel silica nanotubes can be applied potentially in optical and biological areas.     

Fiber - and Tube - Formation by Melt Infiltration of Block Copolymers into Al2O3-Pores

Summary: We report on the formation of polymer nanofibers and nanotubes by melt infiltration of block copolymers (BCPs) containing poly (norbornene) blocks bearing polar and non-polar moieties synthesized via ring opening metathesis polymerization (ROMP) into Al₂O₃ porous templates. The effect of pore size of the Al₂O₃ template and polymer chain length on the formed structure i.e. fibers or hallow tubes is investigated. SEM analysis revealed that a smaller pore size (∼ 180 nm) of the Al₂O₃ template with a BCP of lower molecular weight (< 15 kg/mol) results in complete filling of the pores to yield fibers in contrast to bigger pore size (400 nm) or higher molecular weights (> 25 kg/mol) furnishing hollow tubes.     

Large-area highly-oriented SiC nanowire arrays: synthesis, Raman, and photoluminescence properties

Large-area highly oriented SiC nanowire arrays have been fabricated by chemical vapor reaction using an ordered nanoporous anodic aluminum oxide (AAO) template and a graphite reaction cell. Their microstructures were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy. The results show that the nanowires are single-crystalline beta-SiC's with diameters of about 30-60 nm and lengths of about 8 microm, which are parallel to each other, uniformly distributed, highly oriented, and in agreement with the nanopore diameter of the applied AAO template. The nanowire axes lie along the [111] direction and possess a high density of planar defects. Some unique optical properties are found in the Raman spectroscopy and photoluminescence emission from oriented SiC nanowire arrays, which are different from previous observations of SiC materials. The growth mechanism of oriented SiC nanowire arrays is also analyzed and discussed.     

A simple method to synthesize polyhedral hexagonal boron nitride nanofibers

Hexagonal boron nitride (h-BN) fibers with polyhedral morphology were synthesized with a simple-operational, large-scale and low-cost method. The sample obtained was studied by X-ray photoelectron spectrometer (XPS), electron energy lose spectroscopy (EELS), X-ray powder diffraction (XRD), Fourier transformation infrared spectroscopy (FT-IR), etc., which matched with h-BN. Environment scanning electron microscopy (ESEM) and transmission electron microscope (TEM) indicated that the BN fibers possess polyhedral morphology. The diameter of the BN fibers is mainly in the range of 100–500 nm.     

Bamboo-shaped carbon tubes from coal

Bamboo-shaped carbon tubes (BCTs) were first synthesized in high yields from iron-loaded carbon electrodes prepared from coal by arc discharge. The BCTs were characterized by scanning electron microscopy and transmission electron microscopy (TEM). The TEM characterization reveals that the tubes have bamboo-like structures consisting of hollow compartments separated with conical shaped graphite layers. The diameters of BCTs are in the range of 40–60 nm with their length being about several micrometers. For some BCTs, the hollow compartments are quite uniform with a size of 100 nm. A growth model is suggested to explain the formation of bamboo structure in tubes.     

Characterization of Pt nanoparticles deposited onto carbon nanotubes grown on carbon paper and evaluation of this electrode for the reduction of oxygen

Multiwalled carbon nanotubes (MWCNTs) were grown on the fibers of a commercial porous carbon paper used as carbon-collecting electrodes in fuel cells. The tubes were then covered with Pt nanoparticles in order to test these gas diffusion electrodes (GDEs) for oxygen reduction in H2SO4 solution and in H2/O2 fuel cells. The Pt nanoparticles were characterized by cyclic voltammetry, transmission electron microscopy, and X-ray photoelectron spectroscopy. The majority of the Pt particles are 3 nm in size with a mean size of 4.1 nm. They have an electrochemically active surface area of 60 m2/g Pt for Pt loadings of 0.1-0.45 mg Pt/cm2. Although the electroactive Pt surface area is larger for commercial electrodes of similar loadings, Pt/MWCNT electrodes largely outperform the commercial electrode for the oxygen reduction reaction in GDE experiments using H2SO4 at pH 1. On the other hand, when the same electrodes are used as the cathode in a H2/O2 fuel cell, they perform only slightly better than the commercial electrodes in the potential range going from approximately 0.9 to approximately 0.7 V and have a lower performance at lower voltages.     

Preparation of Polyelectrolyte Nanotubes by a Pressure filter-template Technique Using Microporous Anodic Aluminum Oxide (AAO) as the Template

Polyelectrolyte nanotubes of poly(sodium 4‐styrene‐sulfonate) (PSS) with cationic poly(diallyl dimethyl ammonium chloride) (PDDA) (PSS/PDDA) were fabricated by a pressure‐filter‐template technique using microporous anodic aluminum oxide (AAO) as the template. UV‐Vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and infrared spectroscopy (FT‐IR) were applied to characterize the obtained PSS/PDDA nanotubes. The results have shown that the PSS/PDDA nanotubes exhibit an amorphous structure and have the outer diameter of 200 nm and length of 25 µm respectively, which are in good agreement with the dimensions of the AAO template pores. The wall thickness of the nanotubes may be controlled by the number of the self‐assembled layers. Formation of the nanotubes follows a layer‐by‐layer (LbL) mechanism due to the electrostatic interactions, where the SO^?₃ groups of PSS are first adsorbed on the Lewis acid sites of AAO template pores.     

三步升温法合成阵列碳纳米管

本文使用结构简单的单温炉设备, 以二茂铁/三聚氰胺混合物为原料, 采用独特的三步升温方法于光滑的SiO₂衬底上合成出了大面积的阵列碳纳米管, 并对碳纳米管的形貌和结构进行了研究.     

模板法合成Co纳米线有序阵列的偏光特性

Co nanowire arrays were prepared by anodic alumina oxide template，which formed during DC superposed pulse source anodization process. The structure of porous alumina template and properties of optical polarization of Co nanowire arrays are studied with the help of the scanning electron microscope， X-ray diffraction and infrared spectroscopy. The results showed that Co nanowire arrays have an excellent polarization property in near infrared region in 2700nm. We also found that the properties of optical polarization can also be controlled by adulterating kinds of electrodepositing metal and its alloys， by controlling length of nanowire， and by changing incidence angle.     

Effect of graphitization on the wettability and electrical conductivity of CVD-carbon nanotubes and films

The use of carbon nanomaterials in various applications requires precise control of their surface and bulk properties. In this paper, we present a strategy for modifying the surface chemistry, wettability, and electrical conductivity of carbon tubes and films through annealing in a vacuum. Experiments were conducted with 60-300 nm nanotubes (nanopipes), produced by noncatalytic chemical vapor deposition (CVD) in a porous alumina template, and with thin films deposited by the same technique on a glassy carbon substrate having the same structure and chemistry of the CNTs. The surface of the as-produced CVD-carbon, treated with sodium hydroxide to remove the alumina template, is hydrophilic, and the bulk electrical conductivity is lower by a factor of 20 than that of fully graphitic multiwalled nanotubes (MWNT) or bulk graphite. The bulk electrical conductivity increases to the conductivity of graphite after annealing at 2000 degrees C in a high vacuum. The analysis of CNTs by transmission electron microscopy (TEM) and Raman spectroscopy shows the ordering of carbon accompanied by an exponential increase of the in-plane crystallite size, L(a), with increasing annealing temperature. Environmental scanning electron microscopy (ESEM) was used to study the interaction of CNT with water, and contact angle measurements performed using the sessile drop method on CVD-carbon films demonstrate that the contact angle increases nearly linearly with increasing annealing temperature.     

Carbon nanotube reinforced NiO fibers for rechargeable lithium batteries

Single-wall carbon nanotubes (SWNTs) reinforced NiO fibers with diameter smaller than 50 nm have successfully been prepared by electrospinning method combined with calcination. The SWNTs homogeneously distributed in the NiO fibers were characterized by high resolved transmission electron microscopy, selected area electron diffraction, and Raman spectroscopy. Charge and discharge data showed that 3D network structures of NiO–SWNTs fibers exhibited a relatively higher reversible capacity and lower capacity loss than that of NiO at the charge and discharge current density of 2C, and its discharge capacity was about 337 mAh/g after 20 cycles. Our results demonstrated that the SWNTs reinforced fibers had a better cycling performance at large charge and discharge current densities.     

离子液体中纤维素/纳米层状ZnO复合抗菌纤维的制备及性能

以表面活性剂十二烷基磺酸钠(SDS)为模板,Zn(NO_3)_2·6H_2O和NaOH为锌源和沉淀剂,通过改进的模板法在温和条件下制得纳米层状ZnO.以离子液体1-烯丙基-3-甲基咪唑氯盐([Amim]Cl)为溶剂,木浆纤维素和纳米层状ZnO为原料,采用溶液共混方法,通过干湿法纺丝制备了ZnO质量分数分别为3%,5%,7%及9%的纤维素/ZnO纳米复合纤维.采用X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、场发射扫描电子显微镜(SEM)及热重分析(TG)等方法对纳米层状ZnO及纤维素/ZnO复合纤维进行了表征,并探讨了ZnO的加入对复合体系流变性的影响,同时对复合纤维进行了力学和抗菌性能测试.研究结果表明,所制备氧化锌纯度高,且呈现出重复周期为3.58 nm的层状结构,抗菌性能优异.纳米层状ZnO的加入提高了纤维素纤维的热稳定性和机械强度,同时赋予纤维对金黄色葡萄球菌和大肠杆菌的抑菌性.ZnO片层被纤维素链剥离,并均匀分散于纤维素/ZnO复合物中.ZnO的加入增大了纤维素溶液的黏度,当ZnO含量达到5%以上时,在整个频率范围内,弹性模量大于损耗模量,纳米粒子可稳定悬浮.