Submicron Tubes Research Articles

Preparation and properties of three‐dimensional boron nitride submicron tube/epoxy resin composites with high thermal conductivity

AbstractHeat dissipation of electronic devices was an urgent problem to be addressed. In this paper, magnesium borate whiskers were used as the template for the preparation of the boron nitride submicron tube (BNST). Then the polymer‐free supported three‐dimensional boron nitride submicron tube skeleton was prepared by sacrificing the material ammonia bicarbonate. Finally, high thermal conductivity boron nitride submicron tube/epoxy resin (BNST/EP) composites were prepared by infiltrating technique. The phase, chemical composition, microstructure, thermal conductivity, and thermal stability of the samples were studied by X‐ray diffraction, scanning electron microscopy, and other characterization methods. The results show that BNST has an average diameter was 2 um and the tube length was 5–20 um. The surface of BNST was loaded with a large number of boron nitride nanosheets. The in‐plane thermal conductivity of the BNST/EP composite was improved by the three‐dimensional BNST skeleton. When the BNST was 39.28 wt%, the in‐plane thermal conductivity reached 1.632 W/(m K). Compared with pure EP, the in‐plane thermal conductivity was increased by 782.2%. BNST played a good physical barrier effect on the matrix, so the thermal stability of the composite was greatly improved. This strategy will open up a new path to prepare heat dissipation materials.

Carbon tube-graphene heterostructure with different N-doping configurations induces an electrochemically active-active interface for efficient oxygen electrocatalysis

• An active-active heterointerface is in-situ constructed by urea-assisted pyrolysis strategy. • The active-active interface with directional electron transfer induces dual active sites. • N-SMCTs@N-rGO exhibits excellent electrocatalytic activities and stability for ORR/OER. • N-SMCTs@N-rGO as air-cathode delivers remarkable performance for zinc-air batteries. To accelerate the sluggish kinetics for oxygen reduction/evolution reaction (ORR/OER) of metal-free carbon catalysts, we here report an electrochemically active-active interface for promoting ORR/OER kinetics, which is constructed by in-situ coupling N-doped sub-micron carbon tubes (N-SMCTs, electron donors) with N-doped reduced graphene oxide (N-rGO, electron acceptors). We find that N-SMCTs@N-rGO yields superior bifunctional ORR/OER activity with high durability ( E 1/2 of 0.87 V for ORR, η 10 of 351 mV for OER). Moreover, the zinc-air battery with this material as an electrode displays high power density of 126 mW cm −2 with excellent cycle stability. Density functional theory (DFT) unveils a dual-site mechanism: the carbon adjacent to graphitic-N in N-SMCTs is the most active site for *OOH intermediate while the carbon neighboring to pyridinic-N in N-rGO is beneficial for the adsorption of *O/*OH intermediates. The unique active-active interface with dual-site mechanism suggests its potential to overcome energy barrier bottleneck in the traditional bifunctional oxygen catalysts.

Controllable synthesis of boron nitride submicron tubes and their excellent mechanical property and thermal conductivity applied in the epoxy resin polymer composites

A simple method was developed for the controllable synthesis of a novel boron nitride submicron tube using magnesium borate whisker as rigid template. XRD, SEM and other characterizations were carried out to study the phase, microstructure, chemical composition of the samples. The results show that the average inner diameter and the tube length of the boron nitride submicron tube are 0.6 μm and 5–30 μm, respectively. And the surface is loaded with abundant boron nitride nanosheets. The temperature and ammonia flow rate had a significant impact on the structure evolution of the submicron tube. The growth mechanism of the boron nitride submicron tube was also definited based on the experiment results. In addition, submicron tube/epoxy resin composites were prepared. The tensile strength of the composite is 281.4% higher than that of the pure epoxy resin at a low load of 1 wt%. When the load is 2 wt%, the thermal conductivity increases by 312%.

Role of defects in modulating the near band edge emissions of sub-micron ZnO crystals

Abstract In this communication, we identify the role of defects in modulating the optical properties of ZnO sub-micron rod and tube structures by measuring and comparing their temperature dependent (18 K–260 K) photoluminescence (PL) behavior. From statistical fitting of the near band edge (NBE) emission region of the spectra, it is observed that the acceptor exciton (A, X) emissions decrease with an increase in temperature for ZnO rod structures, whereas comparatively less variation is recorded for ZnO tubular structures. Employing various mathematical analyses, the emission patterns observed for tubular structures are concluded to arise from their lattice dilation and the electron-phonon interactions. For the rod structures, however, it is concluded that the emission spectra are primarily due to the defects (i.e. oxygen and/or Zn vacancies) present at their polar faces. The defects present at the ZnO basal plane affecting (A, X) emissions will influence the use of ZnO in optoelectronic applications.

Template-Free Electrochemical Deposition of t-Se Nano- and Sub-micro Structures With Controlled Morphology and Dimensions.

Selenium, depending on its crystal structure, can exhibit various properties and, as a result, be used in a wide range of applications. However, its exploitation has been limited due to the lack of understanding of its complex growth mechanism. In this work, template-free electrodeposition has been utilized for the first time to synthesize hexagonal-selenium (t-Se) microstructures of various morphologies at 80°C. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) revealed 5 reduction peaks, which were correlated with possible electrochemical or chemical reaction related to the formation of selenium. Potentiostatic electrodeposition using 100 mM SeO2 showed selenium nanorods formed at−0.389 V then increased in diameter up to −0.490 V, while more negative potentials (-0.594 V) induced formation of sub-micron wires with average diameter of 708 ± 116 nm. Submicron tubes of average diameter 744 ± 130 nm were deposited at −0.696 V. Finally, a mixture of tubes, wires, and particles was observed at more cathodic potential due to a combination of nucleation, growth, dissolution of structures as well as formation of amorphous selenium via comproportionation reaction. Texture coefficient as a function of applied potential described the preferred orientation of the sub-microstructures changed from (100) direction to more randomly oriented as more cathodic potentials were applied. Lower selenium precursor concentration lead to formation of nanowires only with smaller average diameters (124 ± 42 nm using 1 mM, 153 ± 46 nm using 10 mM SeO2 at −0.389 V). Time-dependent electrodeposition using 100 mM selenium precursor at −0.696 V explained selenium was formed first as amorphous, on top of which nucleation continued to form rods and wires, followed by preferential dissolution of the wire core to form tubes.

Polymorphic Single-Layer and Fibrillar Nanostructures of J-Aggregates of a Carbocyanine Dye

Abstract—J-aggregates of a carbocyanine dye (pyridinium salt of 3,3'-di-(γ-sulfopropyl)-4,5,4',5'-di(tieno-3'',2'')-9‑ethyl-tiatrimethine cyanine betaine) (CC) were studied via the high-resolution AFM method at the mesoscale and nanoscale. They were found to exist in two structurally different polymorphic forms of single layers and fibrils. The class of single-layer J-aggregates consists of irregular micron sheets and giant submicron tubes, whose structure is identical to tubular J-aggregates of other cyanine dyes. The fibrillar J-aggregates are composed of 3-nm-high fibrils forming the networks owing to merging and branching, as well as of “elementary” fibrils with a height close to the molecular sizes of dye. Structural models of elementary fibril with molecular “staircase” and “ladder” stacking types were proposed as well.

Preparation of CuAl2O4 submicron tubes from electrospun Al2O3 fibers

In this study, CuAl2O4 submicron tubes were synthesized by using electrospun Al2O3 nanofibers as a template. The electrospun Al2O3 precursor fibers were heat treated to form Al2O3 nanofibers. The Al2O3 nanofibers were used as the template, and the CuO layer was deposited on the Al2O3 nanofibers were dropped with copper nitrate methooxyethanol solution. The CuAl2O4 phase was formed by annealing. The CuAl2O4 was obtained by etching out the residues of the Al2O3 core and CuO shell. The CuAl2O4 submicron tubes with an average diameter of about 200 nm were obtained. The structure of the CuAl2O4 submicron tubes was characterized by X-ray diffraction studies, field-emission scanning electron microscopy, and scanning transmission electron microscopy with energy dispersive spectrometry.

Investigation of the interactions of PVDF shell films with Ni core submicron wires and AAO matrix

Arrays of Ni submicron wires surrounded by poly (vinylidene fluoride) (PVDF) submicron tubes were prepared via solution-processed polymer and Ni electrodeposition into anodic aluminum oxide template. The PVDF solution was filtered in vacuum through the template and the resulting dried structure was used for the electrodeposition of Ni wires. The obtained core-shell submicron wire structure consists of a metallic magnetic nanowire core of about 50 μm in length and about 300 nm diameter surrounded by a polymer tube shell with thickness less than 10 nm. The specific ferroelectric β-phase of the polymer was obtained whereas the magnetic behavior of the Ni-cores was proven to be specific to an array of ferromagnetic Ni cylindrical wires (about 0.62 μB/Ni atom) with magnetization reversal mechanisms dominated by dipolar interactions and domain wall displacements. No significant differences of the magnetization reversal mechanism were observed in case of Ni submicron wires surrounded by PVDF tubes and similar Ni wires without PVDF shell, suggesting that magneto-coupling effects in such systems might be observed only by measuring the perturbation of the electric state of the polymer shell under a magnetic excitation of the Ni cores.

C@MoS2@PPy sandwich-like nanotube arrays as an ultrastable and high-rate flexible anode for Li/Na-ion batteries

Flexible electrode with robust mechanical and electrochemical property is crucial for thin film battery technology, especially in deformable electronics. In present work, a self-supported C@MoS2@PPy sandwich-like nanotube arrays (SNTAs) have been engineered and synthesized on steel substrate through a simple template-based approach and further employed as freestanding anode for Li/Na-ion batteries. For the C@MoS2@PPy SNTAs, ultra-thin MoS2 nanosheets are uniformly covered with conductive polypyrrole (PPy) and synchronically deposited on the carbon submicron tube arrays (CSTAs) which is vertically grown on the substrate. The conductive tubular array-type CSTAs skeleton and outer PPy coating not only endow the SNTAs with superior e-/ion conduction, but also preserve the framework stability when complete volumetric swelling occur in MoS2. As a result, such SNTAs electrode show a robust lithium storage (1050 mA h g−1 at 200 μA cm-2/805 mA g-1 over 600 cycles and a rate property of 630 mA h g-1 at 1000 μA cm-2/4027 mA g-1) and also impressive sodium storage (615 mA h g−1 at 50 μA cm-2/201 mA g-1 over 200 cycles and a rate property of 405 mA h g-1 at 250 μA cm-2/1007 mA g-1). These freestanding SNTAs electrode exhibit its promising future in deformable energy storage technologies.

A kinetic study for NO catalytic reduction on silica sub-micron diameter tubes with platinum nanoparticles

The selective catalytic reduction (SCR) of NOx with C3H6 in the presence of O2 on silica sub-microtubes with platinum nanoparticles was studied in order to establish a possible reaction mechanism at different experimental conditions. This catalyst showed a high NO conversion with very high selectivity to N2 at mild conditions in the presence of excess oxygen when using C3H6 as reducing agent.The influence of both NO and C3H6 concentrations on their conversions was analyzed at different space times. The obtained results suggest that the three reactants (C3H6, NO, and O2) are adsorbed on Pt sites. The kinetic model proposed considers that both dissociative adsorption of NO and activation of the hydrocarbon can take place simultaneously. Nevertheless, the value of the parameters obtained by the resolution of the model equations indicates that the first one presents a major relevance. These results are in concordance with the high selectivity to N2 observed, because the preponderance presence of dissociated NO avoids the formation of N2O by the reaction of molecular NO with N dissociated from NO. Furthermore, both NO reduction and C3H6 oxidation conversions are represented reasonably well by the model presented.

Ni3S2 nanosheet-anchored carbon submicron tube arrays as high-performance binder-free anodes for Na-ion batteries

A binder-free Ni-supported Ni3S2/CST array electrode was prepared by a controllable route and exhibits high capacity and a long cycle life.

Highly-efficient MnO2/carbon array-type catalytic cathode enabling confined Li2O2 growth for long-life Li–O2 batteries

Li–O2 batteries recently have attracted intensive research interest because of the rather high energy density. The electrochemical performance of Li–O2 batteries, however, is largely limited by the insulating and reactive Li2O2, which necessitates a renovation on the design of catalytic cathodes. In this work, we propose a unique MnO2/carbon submicron tube (MnO2/CST) array-type catalytic cathode capable of controlling Li2O2 growth spatially and structurally. The high catalytic activity of ultrathin MnO2 nanosheets enables conformal growth of thin-layered Li2O2 on the MnO2 sheets, which relieves or defers electrode deactivation upon discharge and renders easy catalytic decomposition of Li2O2 upon charge. In situ transmission electron microscopy characterization confirms the presence of Li2O2 on discharged MnO2/CST and reveals the phase transition and morphology changes upon charge. The array-type architecture of the catalytic cathode facilitates barrier-free transportation of oxygen gas and Li ions. The absence of polymer binder and the reduced carbon exposure to Li2O2 (or LiO2) exclude or minimize the parasitic reactions related to binder and carbon. As a result, Li–O2 cells with MnO2/CST catalytic cathode exhibit superior cycling stability and low polarization. At 800mAg–1, the cell can sustain a stable cycling of over 300 cycles at a limited capacity of 1000 mAh g–1.

Au‐Decorated Cracked Carbon Tube Arrays as Binder‐Free Catalytic Cathode Enabling Guided Li2O2 Inner Growth for High‐Performance Li‐O2 Batteries

Owing to their extremely high energy density, Li‐O2 batteries have attained increasing attention in recent studies. However, deposition of the discharge product, insulating Li2O2, is known to seriously limit the electrochemical performance of Li‐O2 batteries. While extensive studies have focused on relieving electrode deactivation by controlling Li2O2 growth, no permanent or effective mechanism is delivered. Here, a unique design comprising a catalytic cathode constructed by cracked carbon submicron tube (CST) arrays decorated with Au nanoparticles on inner walls is proposed. The introduction of Au nanoparticles not only improves electrode conductivity but also provides catalytic sites, guiding conformal growth of thin‐layered Li2O2 inside the cracked CST. Density functional theory calculations support that Au decoration on CST favors the conformal growth of Li2O2 on inner tubular walls. This growth behavior of Li2O2 renders easy decomposition of Li2O2, prevents carbon tube electrode from full, rapid deactivation, and preserves the free space for reactants transport. Li‐O2 cells with Au@CST exhibit good rate capability (1208 mAh g–1 at a high current density of 1000 mA g–1) and long cycle life (112 cycles at a current density of 400 mA g–1 with a limited capacity of 500 mAh g–1).

Synthesis of Porous δ-MnO2 Submicron Tubes as Highly Efficient Electrocatalyst for Rechargeable Li-O2 Batteries.

Lithium-oxygen (Li-O2 ) batteries are receiving intense interest because of their high energy density. A new tubular δ-MnO2 material prepared by a simple hydrothermal synthesis is an efficient electrocatalyst for Li-O2 batteries. The synthesized δ-MnO2 exhibits a unique tubular structure, in which the porous walls are composed of highly dispersed ultrathin δ-MnO2 nanosheets. Such a unique structure and its intrinsic catalytic activity provide the right electrocatalyst characteristics for high-performance Li-O2 batteries. As a consequence, suppressed overpotentials-especially the oxygen evolution reaction overpotential-superior rate capability, and desirable cycle life are achieved with these submicron δ-MnO2 tubes as the electrocatalyst. Remarkably, the discharge product Li2 O2 of the Li-O2 battery exhibits a uniform nanosheet-like morphology, which indicates the critical role of the δ-MnO2 in the electrochemical process, and a mechanism is proposed to analyze the catalysis of δ-MnO2 .

Controlled fabrication of α-GaOOH with a novel needle-like submicron tubular structure and its enhanced photocatalytic performance

Orthorhombic gallium oxide hydroxide (α-GaOOH) with a novel needle-like submicron tubular structure has been firstly fabricated by an organometallic reactant-assisted hydrothermal route. A possible fabrication process indicates that the concentration of OH− ions plays an important role in the formation of submicron tube. Moreover, other four kinds of shape-controllable α-GaOOH particles of nano-, submicron- and micro-size have also been successfully synthesized by changing the pH values of solvent. The photoluminescence (PL) performance demonstrates that there are a plenty of intrinsic defects in α-GaOOH. Furthermore, the photocatalytic activity of α-GaOOH with different morphologies was evaluated by degrading methylene blue (MB) aqueous solution. The efficiency of α-GaOOH with a novel tubular structure improves much more than other catalysts. The enhanced photocatalytic activity can be attributed to the effective inhibition of photo-generated electron–hole pair’s recombination resulted from intrinsic defects.

Jump–slip simulation technique for combustion in submicron tubes and submicron pores

ObjectiveExperimental data on transitional gas flows for large Knudsen number in submicron tubes demonstrates the fast molecular transport that up to 2-3 orders of magnitude exceeds the continuum transport predicted by the theories applied on this length scale. The present research is aimed to develop the jump-slip technique in Knudsen layer simulating the combustion in carbon submicron tubes and pores. The slip velocity boundary conditions as well as the jump boundary conditions for temperature and concentrations of gas components are developed. Materials methodThe approach considered is the generalization of the Cheng’s slip-jump conditions (1963) for blunt body problem in hypersonic flow at low Reynolds number. The velocity slip and the temperature and concentration jump boundary values are applied for simulating the carbon combustion in nanotubes and nanopores. The two-level numerical technique, proposed by Markov (2009) is generalized for carbon combustion in nanopores. ResultsThe numerical simulation using the jump-slip technique is compared with those neglecting the jump-slip effect in Knudsen layer. The results obtained allow us to explain significant acceleration of gas transport on submicron scale during carbon combustion as well as to predict characteristic features of combustion.

The Propulsion of a Miniature Device by Organic Fluid Jetflow through Polymer Submicron Tubes

A miniature device composed of anodic aluminum oxide membrane and aligned polypropylene submicron tubes is fabricated by a simple template method. When organic fluids are dripped on the membrane, the device floating on water could be propelled by organic fluid jetflow through the polymer tubes. The driving force is mainly attributed to the spreading of organic fluids on water surface. Compared to the motions driven by spreading fluids in bulk, the propulsion of this device is more efficient benefiting from the submicron-tube microstructure. This work may provide a feasible approach to enhance the efficiency of chemical driving movements.

Photoelectrochemical performance of a sub-micron structured film with poly(3-methylthiophene) (P3MT)-modified CdTe/ZnO shell-core sub-micron tube arrays

A sub-micron structured film with a poly(3-methylthiophene) (P3MT)-modified CdTe/ZnO shell-core sub-micron tube array has been prepared by a series of electrodeposition processes, and a semiconductor-sensitized solar cell based on this structure was also fabricated. Vertically oriented ZnO sub-micron tubes were obtained on an indium tin oxide (ITO) substrate, and then CdTe nanocrystals and a thin P3MT layer were electrodeposited sequentially onto the walls of the ZnO sub-micron tubes. A suitable thickness of CdTe and P3MT could improve the photovoltaic properties of the solar cell, which was attributed to the enhancement in the light absorption and the decrease in the recombination of photogenerated carriers. In addition, a p-n heterojunction formed between the interface of CdTe and P3MT played an important part in the efficient separation and fast transport of photogenerated carriers in the sub-micron structure. A power conversion efficiency of 1.20% was obtained with this type of solar cell.

Probing hemoglobin confinement inside submicron silica tubes using synchrotron SAXS and electrochemical response

The configuration of hemoglobin in solution and confined inside silica nanotubes has been studied using synchrotron small angle X-ray scattering and electrochemical activity. Confinement inside submicron tubes of silica aid in preventing protein aggregation, which is vividly observed for unconfined protein in solution. The radius of gyration (R g) and size polydispersity (p) of confined hemoglobin was found to be lower than that in solution. This was also recently demonstrated in case of confined hemoglobin inside layered polymer capsules. The confined hemoglobin displayed a higher thermal stability with R g and p showing negligible changes in the temperature range 25-75°C. The differences in configuration between the confined and unconfined protein were reflected in their electrochemical activity. Reversible electrochemical response (from cyclic voltammograms) obtained in case of the confined hemoglobin, in contrary to the observance of only a cathodic response for the unconfined protein, gave direct indication of the differences between the residences of the electroactive heme center in a different orientation compared to that in solution state. The confined Hb showed loss of reversibility only at higher temperatures. The electron transfer coefficient (α) and electron transfer rate constant (k s) were also different, providing additional evidence regarding structural differences between the unconfined and confined states of hemoglobin. Thus, absence of any adverse effects due to confinement of proteins inside the inorganic matrices such as silica nanotubes opens up new prospects for utilizing inorganic matrices as protein "encapsulators", as well as sensors at varying temperatures.

Coaxial InGaN epitaxy around GaN micro-tubes: Tracing the signs

This work focuses on investigations of the luminescence properties of coaxial InGaN layers grown around single GaN micro and sub-micron tubes on top of GaN micro-pyramids. The tube structure was formed after the controlled desorption of ZnO nano-pillar templates during the coaxial GaN epitaxy. A thin layer near the area around the inner diameter of the micro-tube is believed to be heavily doped with Zn impurities leading to an intense and broad photoluminescence (PL) peak centered around 2.85eV that quenches the luminescence from coaxial InGaN quantum wells (QWs). When the thickness of the GaN tube wall before the QW growth was doubled, a clear indication of In incorporation in low temperature PL was observed via an intense peak around 3.1eV. Moreover, as the temperature of the QW growth was changed from 830°C to 780°C, a shift of the peak corresponding to an increase in In incorporation from 3.5% to 7.5% was noticed.