Bamboo-shaped Nanotubes Research Articles

Nitrogen-doped carbon nanostructures embedded with Fe-Co-Cr alloy based nanoparticles as robust electrocatalysts for Zn-air batteries

Two types of nitrogen-doped carbon nanomaterials embedded with novel transition metal-based medium entropy alloy nanoparticles are synthesized via a simple, scalable, and cost-effective single-step pyrolysis route, by varying the stoichiometric ratio of iron and cobalt. The samples predominantly have bamboo-shaped nanotube morphology with some globular structures. The globules are core-shell type nanoparticles, i.e., containing the metallic-alloy nanoparticles encapsulated by the graphitic shell and embedded within defective amorphous-type carbon matrix. The electrochemical studies using these samples are conducted in basic medium to explore their potential for Zn-air batteries. Electrochemical measurements are carried out in 1 M and 0.1 M KOH, respectively, on a rotating disk electrode setup. The sample with higher cobalt content performs better for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) with regards to lower onset potential, lower Tafel slope and lower activation energy. However, the stability towards OER is better for the sample with higher iron content. The sample with higher cobalt content shows a better overall oxygen electrochemistry compared to the one with higher iron content, is at par with several state-of art electrocatalysts and is utilized for fabrication of a prototype Zn-air battery demonstrating its practical applicability.

A Simple Method for the Synthesis of a Coral-like Boron Nitride Micro-/Nanostructure Catalyzed by Fe

Catalyzed by Fe, novel a coral-like boron nitride (BN) micro-/nanostructure was synthesized from B2O3 by a ball milling and annealing process. Observations of the morphology of the product indicated that the coral-like BN micro-/nanostructure consists of a bamboo-shaped nanotube stem and dense h-BN nanoflakes growing outward on the surface of the nanotube. Experimental results showed that the morphology of the BN nanotube was greatly dependent on the anneal process parameters. With the annealing time increasing from 0.5 h to 4 h, the morphology developed from smooth BN nanotubes, with a diameter size of around 100 nm, to rough, coral-like boron nitride with a large diameter of 3.6 μm. The formation mechanism of this coral-like BN micro-/nanostructure is a two-stage growth process: bamboo-shaped BN nanotubes are first generated through a vapor-liquid-solid (VLS) mechanism and then nanoflakes grow surrounding the surface of the nanotube. Acid pickling and a hydrolysis process were carried out to remove Fe, iron nitrogen and unreacted B2O3 impurities.

Morphology control of CdSe nanocrystallines

CdSe nanocrystallines with different micromorphology were synthesized by inverse microemulsion method. X-ray diffraction and transmission electron microscopy were used to characterize the micromorphology, phase and ingredient compositions of nanocrystallines. The results indicate that nanosphere, necklace-shaped and bamboo-likeCdSe nanocrystals were successfully prepared. The bamboo- like nanotubes have the best crystallization performance. The red shift of the fluorescence peak can be observed clearly, and bamboo-shaped nanotubes have stronger fluorescence emission. Detailed study on the formation of bamboo-like nanotubes was performed. The mechanism is as follows: the difference of the bound water content at the interface and the free water content in the water core leads to the density difference between outer layer and the center. The diffusion of Se2- and Cd2+induces hollow structure of CdSe nanospheres. Due to the small size effect, hollow nanospheres grow into necklace-shaped and bamboo-structure finally

Synthesis and 1-butene hydrogenation activity of platinum decorated bamboo-shaped multiwall carbon nanotubes

Bamboo-shaped carbon nanotubes (BCNT) were prepared from three different amines on supported iron (Fe) and nickel (Ni) catalysts by catalytic chemical vapor deposition. The main factors governing product morphology and defect site density were identified. Post-synthetic oxidative functionalization was used to add carboxyl groups to the nanotubes, and then platinum (Pt) nanoparticles were deposited on the surface by the in situ reduction of a platinum salt. The average Pt nanoparticle diameter was found to be affected by the extent of surface functionalization. The catalytic performance of the synthesized Pt/BCNT samples were examined in the hydrogenation of 1-butene, in order to show that the catalytic activity of the bamboo like carbon nanotube supported Pt catalyst is similar to the conventional Pt catalysts in heterogeneous catalytic hydrogenation. The best overall performance was achieved when the bamboo-shaped nanotube support was synthesized on 5 wt% Fe/Al(OH)3 catalyst from triethylamine and decorated with 5 wt% platinum nanoparticles.

Systematic investigation of the growth mechanisms for conventional, doped and bamboo-shaped nanotubes

Fundamental physico-chemical mechanisms underlying the synthesis of nanotubes wereinvestigated, including conventional, doped, and bamboo-shaped nanotubes. The mechanisms are examined from the viewpoint of the well-known base growth (root growth) and tip growth mechanisms. The analysis of the surface characteristics of nanoparticles is key to the present approach. Surface and interface melting, surface and bulk diffusion through nanoparticle, and the formation of a hill due to over-segregation of the source species to the nanoparticle peripheral surface have also been investigated. The study may have led to an understanding of the basics and the differences between the base growth and the tip growths of nanotubes, and also of the formation of nanotube diaphragms (caps), if any. The proposed mechanisms have been used to attempt to explain various prior observations on the conventional, doped, and bamboo-shaped nanotubes. Experimental results available in the literature have been extensively employed to justify the validity of the mechanisms, and to highlight the possible appeal of these mechanisms.

Biotemplate synthesis of carbon nanostructures using bamboo as both the template and the carbon source

A series of carbon nanostructures were prepared via a biotemplate method by catalytic decomposition of bamboo impregnated with ferric nitrate. The natural nanoporous bamboo was used as both the green carbon source and the template for the in situ growth of carbon nanostructures. Scanning electron microscope, field emission transmission electron microscope and energy dispersive X-ray spectroscope were used to characterize the product. Four distinct structural types of carbon nanostructures have been identified, namely nanofibers, hollow carbon nanospheres, herringbone and bamboo-shaped nanotubes. The effect of reaction temperature (from 600 to 900°C) on the growth behavior of carbon nanostructures was investigated and the corresponding growth mechanism was proposed. At low temperature the production of nanofibers was favored, while higher temperature led to bamboo-shaped nanostructures.

Fabrication of TiO2 nanotubes with extended periodical morphology by alternating-current anodization

Highly uniform TiO2 nanotube arrays with regular periodical sidewall morphology were fabricated by both alternating-voltage (AV) and alternating-current (AC) anodization methods. It was revealed that the AC anodization provided a better control to the sidewall morphology than the AV anodization. Various bamboo-shaped nanotube arrays were prepared by using AC anodization with different current functions. Dye-sensitized solar cells (DSSCs) fabricated using different TiO2 nanotube arrays showed that the AC anodization with square-wave driving current gave the highest photo energy conversion efficiency.

Elastic and electrostatic properties of bamboo-shaped carbon nanotubes

A technology has been developed to synthesize films of bamboo-shaped carbon nanotubes from simple nanotubes by high-frequency oxygen plasma etching for 30 and 60 s. The electronic structure and mechanical properties of bamboo-shaped single-walled carbon nanotubes have been studied theoretically. Compartments in these structures are located at an optimum distance that corresponds to a decrease in the ionization potential and an improvement of the emission properties. It has been revealed that the Young’s and torsion moduli of the bamboo-shaped carbon nanotubes depend on the number of compartments. These tubes have their own dipole moments in contrast to the hollow defect-free tubes. It has been shown that bamboo-shaped nanotubes 1.37 nm in diameter are the most stable nanoclusters.

Growth and microstructures of carbon nanotube films prepared by microwave plasma enhanced chemical vapor deposition process

Well-aligned carbon nanotubes (CNTs) were grown on iron coated silicon substrates by microwave plasma enhanced chemical vapor deposition. Effect of plasma composition on the growth and microstructures of CNTs were investigated by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and optical emission spectroscopy. Morphology and microstructure of nanotubes were found to be strongly dependent on the plasma composition. Aligned bamboo-shaped nanotubes consisting of regular cone shaped compartments were observed for C2H2/NH3/N2 and C2H2/NH3/H2 gas mixtures. Randomly oriented or no nanotubes growth were observed in C2H2/H2 and C2H2/N2 gas mixtures respectively. CNTs grown in nitrogen rich plasma had more frequent short compartments while compartment length increased with decreasing nitrogen concentration in the plasma. Raman spectroscopy of CNTs samples revealed that CNTs prepared in nitrogen rich plasma had higher degree of disorder than those in low nitrogen or nitrogen free plasma. In-situ optical emission spectroscopy investigations showed that CN and H radicals play very important role in both the growth and microstructure of CNTs. Microstructure of CNTs has been correlated as a function of CN radical concentration in the plasma. It is suggested that presence of nitrogen in the plasma enhances the bulk diffusion of carbon through the iron catalyst particles which causes compartment formation. Based on our experimental observations, growth model of nanotubes under different plasma composition has been suggested using base growth mechanism.

Synthesis of Bamboo-shaped TiO2 Nanotubes in Nanochannels of Porous Aluminum Oxide Membrane

Abstract The bamboo-shaped TiO2 nanotubes with diameters of ca. 100 nm have been fabricated in nanochannels of PAO membranes by upright dipping manner. The bamboo-shaped nanotubes consist of many hollow compartments that are separated by TiO2 layers.

Novel BN tassel-like and tree-like nanostructures

Novel BN tassel-like and tree-like nanostructures were synthesized through a CVD method. The tassel-like morphology is made up of a BN bamboo-shaped nanotube and numerous polyhedral particles attached onto it. The tree consists of a BN main stem and many BN nanotube branches growing outward from it. The attachments, either particles or nanotube branches, maintain adhering to the primary stems even after 15 min sonication treatment, indicating the high stability of these nanostructures. The formation of these unusual structures is proposed to arise from a two-stage deposition process: firstly, primary BN stems were formed, followed by subsequent precipitation of amorphous clusters onto the rough outer surfaces. Secondly, polyhedral particles or BN nanotubes nucleated and grew on the outer surface as a result of further deposition from the vapor phase.

Microstructure and growth of bamboo-shaped carbon nanotubes

Bamboo-shaped carbon nanotubes fabricated by the catalytic growth method with Ni/metallic oxide catalyst are systematically studied using transmission electron microscopy. It is found that except for the nodes the bamboo-shaped carbon nanotubes can be regarded as stacking of truncated conical graphene sheets. Depending on the size of a catalyst, the Ni particles can be encapsulated inside the tubes or at the growth front of the tubes with a plug-shape. A linear relationship between size of the nanotube and the catalyst particle is found. The results suggest that the nanometer-sized Ni catalyst particles are in the liquid state during nanotube growth. A simple model for the growth of bamboo-shaped nanotubes is proposed.

Carbon nanotubes filled partially or completely with nickel

We report the catalytic synthesis of carbon nanotubes filled with Ni by chemical vapor deposition over the Raney-Ni catalyst. Straight and two types of bamboo-shaped carbon nanotubes have been discovered under TEM. Further investigation with TEM shows that an obvious tendency exists, i.e. the straight nanotube encapsulating Ni completely; as for the compartments of bamboo-shaped nanotube, either every one filled with a small Ni particle or only the end is capped with a needle-shaped Ni, which suggests different growth mechanism.