Morphology Of Nanotubes Research Articles

Preparation, modification and adsorption properties of spinel-type H1.6Mn1.6O4 lithium-ion sieves with spiny nanotube morphology

Preparation, modification and adsorption properties of spinel-type H1.6Mn1.6O4 lithium-ion sieves with spiny nanotube morphology

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.

Preparation of lotus-root-typed TiO2 nanotubes by NH4F/KF based electrolyte and its efficient photocathodic protection for 304 stainless steel

A highly ordered lotus-root-typed TiO2 nanotube array (TNTAs) was prepared by two-step electrochemical anodization in a novel NH4F/KF-based electrolyte. The effects of different morphologies of TiO2 nanotubes on the photoelectrochemical properties of TNTAs were studied. The photoelectrochemical properties of TNTAs were evaluated by measuring the photocurrent density-time curve. The photocathodic protection performance of TNTAs on 304 stainless steel was evaluated by measuring open circuit potential and Tafel curve. The results showed that the TNTAs with lotus-root-type porous structures prepared at 20 V had the optimal photoelectric chemical properties and photocathodic protection properties. Under simulated sunlight, the maximum photocurrent density can reach 306.7 μA·cm−2, and the lowest open circuit potential can reach -0.987 V (vs Ag/AgCl).

Enhanced photocatalytic activity of TiO2 nanostructures produced by anodic oxidation of pre-deformed Cp–Ti

ABSTRACT Arrays of TiO2 nanotubes were prepared on pre-deformed commercially pure titanium (Cp–Ti) foils by anodic oxidation in 1 vol.-% HF-based electrolyte. Prior to the anodic oxidation, the samples were deformed by uniaxial tension and cold rolling at room temperature in three different strain levels. Following the anodic oxidation, the samples were annealed at 450°C to obtain crystalline anatase structure. Effects of the deformation on the produced nano structures were investigated by characterisation studies and photocatalytic activity tests including methylene blue degradation test, photoluminescence, and UV–Vis diffuse reflectance spectra analyses. The results showed that the induced strain has a remarkable effect on the nanotube morphology. It also led to a decrease in the crystallite size in the uniaxial tensioned and cold rolled titanium foils. As a result of the morphological and structural changes, the photocatalytic activity of the samples increased with cold rolling strain, and uniaxial tension strains up to a critical level.

Influences of Synthetic Parameters on Morphology and Growth of High Entropy Oxide Nanotube Arrays

Nanoscale and nanostructured materials have drawn great attention owing to their outstanding and unique properties. Enlightened by the study of “entropy-stabilized oxides”, nanotubes consisting of multi-component mixed metal oxides are developed, which formed on equi-atomic TiZrHfNbTa high-entropy alloy (HEA). However, the growth mechanism and how the oxidation conditions influence the nanotube growth and morphology remains unknown. In the present study, by controlling the anodization parameters (applied voltages and time) and bath compositions (fluoride concentration and water content), scanning electron microscope and transmission electron microscopy are conducted to reveal the morphological evolution. The present work uncovers how the synthetic parameters influence the tube growth and morphology formed on equi-atomic TiZrHfNbTa HEA, therefore gaining insight into the growth mechanism and the feasibility of controlling the morphology of multi-component oxide nanotubes.

The influence of sodium alginate in water-based electrolyte on the morphology of TiO2 nanotube prepared by anodization method

Fabrication of a highly-ordered TiO2 nanotube array (TNA) with an anodization method in a water-based electrolyte using sodium alginate (NaAlg) as a thickening agent was presented for the first time. The titanium foil was anodized with various concentrations of NH4F, NaAlg, and the pH variation for the electrolyte solution. The anodization curve profile (current versus time) in various electrolyte compositions and their correlation to resulting morphologies, depletion layer values, and photocurrent of the fabricated samples were discussed. Based on SEM characterization and Fast Fourier Transformation (FFT) image, it is evidenced that the use of NaAlg can control the oxidation and dissolution rate in the anodization process so that a highly-ordered TNA with better uniformity and circularity can be obtained in 1.5 h anodization time. However, the presence of NaAlg was observed to give a wider variety of tube lengths. The increase in NH4F concentration led to a wider and uncircular nanotube but did not significantly affect wall thickness and tube length. The higher H+ concentration leads to wider tube diameter, thinner tube wall, and shorter tube length. The highest Regularity Ratio of the TNA sample was obtained when 0.3% NH4F and NaAlg at pH 3 was used, while the longest tube length was obtained at pH 4. It was found that the morphology observed follows a certain trend based on the nucleation time and anodization current density. It was also observed that the TNA porosity, wall thickness, tube length, and depletion layer influence photocurrent activity in complex relations. However, it was generally found that the NaAlg addition to the electrolyte resulted in a TNA having better regularity and photocurrent activity compared to the electrolyte without NaAlg.

Morphological, structural and optical properties of dye-doped graphene-supported TiO2 nanotubes for solar water splitting applications

Solar water splitting has attained much attention in recent years for renewable and clean production of hydrogen from water under irradiation by sunlight. Solar water splitting has been progressively at the forefront of chemical research and also provides a promising path for sustainable hydrogen production. TiO2 has a wide range of applications and is considered as one of the most propitious semiconductors due to its photo-stability, low price and chemical stability. TiO2 nanotubes have been prepared by using electrochemical anodization method followed by organic dye deposited onto the TiO2 nanotubes. rGO-supported TiO2 nanotubes and dye-doped graphene-supported TiO2 nanotubes show more efficient behavior for water splitting as compared to pure TiO2 nanotubes. The surface morphology, elemental composition, structure and size of the nanocrystalline TiO2 nanotubes and dye-doped graphene-supported TiO2 nanotubes were examined by using SEM, XRD, EDX and UV/Visible spectroscopy, respectively. Dye-doped graphene-supported TiO2 nanotubes have been utilized for efficient solar water splitting.

Steam reforming of ethanol, acetaldehyde, acetone and acetic acid: Understanding the reaction intermediates and nature of coke

The small aliphatic organics like ethanol, acetaldehyde, acetone and acetic acid are frequently used as feedstocks for hydrogen production via steam reforming. These organics have distinct functionalities, which might result in formation of different reaction intermediates and coke. This was investigated in this study with Ni/KIT-6 as a catalyst under normalized conditions. The results indicated that dehydration to ketene but not cracking was major route for dissociative adsorption of acetic acid on Ni/KIT-6 from 100 °C. Thermally stable CH and CC in alkenes, formed via dehydration of ethanol and aromatization of acetone/intermediates via bimolecular Aldol-condensation, were important precursors of coke in ethanol and acetone reforming. Although acetone strongly adsorbed on Ni/KIT-6, it did not polymerize to heavy oxygen-containing organics that were difficult to be gasified with steam. In comparison, the similar strong adsorption of acetaldehyde led to rapid polymerization even at 100 °C, forming the polymeric coke of highly aliphatic nature. The coking tendency in reforming followed the order: acetone > acetic acid > ethanol > acetaldehyde. Nevertheless, the amorphous form of coke in acetaldehyde reforming led to the rapid deactivation of Ni/KIT-6. The coke in ethanol, acetone and acetic acid reforming were mainly the catalytic type with the highly aromatic nature, high carbon crystal crystallinity, high thermal stability, high resistivity towards oxidation and the carbon nanotube morphology. Nevertheless, the varied reaction intermediates involved in reforming of these varied feedstock also formed the coke of some unique features.

Ultrafast degradation of emerging organic pollutants via activation of peroxymonosulfate over Fe3C/Fe@N-C-x: Singlet oxygen evolution and electron-transfer mechanisms

Fe3C/Fe decorated N-doped magnetic carbon materials (denoted as Fe3C/Fe@N-C-x) were successfully fabricated via facile one-pot calcination of MIL-88B(Fe) with a green precursor of melamine. Benefiting from the co-existence of sp2-hybridized C–π moieties, oxygen-containing groups (CO and O–CO), N-doping species and ferreous nanoparticles (FNPs), the as-obtained Fe3C/Fe@N-C-9 exhibited excellent activation of peroxymonosulfate (PMS) for ultrafast elimination of various emerging organic contaminants with high mineralization capacities. Inspired by the unique nanotube morphology and encapsulation of FNPs, the Fe3C/Fe@N-C-9 possessed trace Fe leaching and can be magnetically separated for an easy recycling. Combining with competitive radical scavenging tests, electron spin resonance (ESR), electrochemical analysis and in-situ Raman spectra, the singlet oxygen (1O2) and electron-transfer can be accounted for the organic pollutant removal. Because of that, the Fe3C/Fe@N-C-9 exhibited good resistance to inorganic anions and natural organic matters (NOMs). It was fascinating that Fe3C/Fe@N-C-9 achieved satisfactory treatment efficiency for real pharmaceutical wastewater.

Pyrolysis of typical plastics and coupled with steam reforming of their derived volatiles for simultaneous production of hydrogen-rich gases and heavy organics

Pyrolysis is a thermochemical route for converting waste plastics into hydrocarbons that might be further upgraded to fine chemicals via the process such as hydrotreatment. In this study, the pyrolysis of five typical plastics (PE, PP, PVC, PS and PET) and steam reforming of their derived volatiles were coupled in one process, named as pyro-reforming. The reaction behaviors, especially the property of their derived cokes, in the pyro-reforming were investigated. The results indicated that the volatiles from the pyrolysis of PE had the highest reactivity with steam to produce H2 of the highest yield, followed by that of PP, PVC, PET and PS. The Cl in PVC promoted nickel sintering, enhanced formation of heavy aromatics through aromatization. Moreover, the existence of Cl interrupted formation of carbon nanotube, forming the highest amount of coke with hemp rope-like fiber form of very coarse surface. This was very different from the carbon nanotube form of coke with smooth surface and uniform outer/inner diameters from the pyro-reforming of PE or PP. The pyro-reforming of PET or PS generated mainly the aromatic intermediates that were chemically more inert in steam reforming, forming polymeric type of coke with no carbon nanotube morphology and very low crystallinity.

The effect of electrophoretic deposition of carbon nanotubes onto carbon fiber on the interlaminar resistance of carbon reinforced aluminum laminates

Functionalized multi-walled carbon nanotubes were deposited on the carbon fabric using ultrasonic-assisted electrophoretic deposition. The effect of carbon nanotubes (CNTs) deposition time and morphology on the mode I interlaminar fracture resistance of carbon reinforced aluminum laminates (CARALL) was investigated. The formation of a proper network of CNTs on the carbon fabric favorably deviated the crack growth into the carbon fabric layer and intensified the fiber bridging during the delamination. The CNT coating on the carbon fiber in conjunction with the alkaline-acid treatment on the Al substrate significantly promoted the interlaminar fracture initiation and propagation energies and stabilized the fracture behavior.

Photoelectrochemical properties and reactivity of supported titanium NTs for bacterial inactivation and organic pollutant removal.

In this work, we report on the effect of anodization time on the morphology, optical, and photocatalytic properties of TiO2 nanotubes (NTs) allowing bacterial inactivation and two organic pollutant degradation under low-intensity solar-simulated light. Scanning electron microscopy (SEM) showed that the length of the TiO2 NTs increased from 2.8 to 25.8μm as anodization time was increased from 15 to 300min at 60V, respectively. The X-ray diffraction (XRD) patterns showed that all samples crystallize in the anatase phase after annealing at 400°C for 3h. Samples anodized for 30 and 60min exhibit low diffuse reflection at 400nm, which was attributed to the disorder-induced exciton scattering at the molecular level. The intensity of the photoluminescence (PL) spectra was found to increase as the length of the NTs increases up to a maximum anodization time of 300min, revealing the contribution of bulk excitonic states. A maximum photoelectric conversion efficiency of 0.55% was obtained at a potential of - 0.5V vs. Ag/AgCl for TiO2 NTs anodized for 60min. The optimized NTs (anodized for 60min) showed a photocatalytic bacterial inactivation of a magnitude of 6 log within 360min and a degradation of indole and methylene blue (MB) under low-intensity solar-simulated light (50 mW/cm2). The stability of the prepared catalyst was tested over several cycles.

Low‐velocity impact response of halloysite nanotube reinforced glass/epoxy multi‐scale composite. Part 1: Dynamic loading performance

AbstractOne of the biggest obstacles to fiber‐reinforced composite laminates is out‐of‐plane dynamic loading. Specifically, low‐velocity impact loading in an out‐of‐plane direction leads to matrix cracking, delamination, and fiber breakage damages due to weak fiber–matrix interactions. This paper aims to examine the dynamic loading behavior of nano reinforced glass/epoxy composite laminates under various impact energies. Moreover, to enhance fiber–matrix interaction, halloysite nanotubes (HNTs) with lower cost among the nanotube morphologies such as carbon and TiO2 were introduced to the epoxy matrix. The impact performance and the damage propagation were also investigated. As a result, the HNT‐reinforced multiscale composite sample had 28% more impact load carrying capacity and absorbed 18% less energy than its unmodified counterpart. Image processing was utilized to determine the damage evaluation by analyzing both front and back surfaces. The improvement of the fiber–matrix interface with HNTs reinforcement resulted 59% and 46% less damage to the front and back damage surfaces, respectively. The acquired results were supported by macro‐size examination and micro‐size analyzing via scanning electron microscopy (SEM). These results pave the way towards designing fiber reinforced composites to be utilized for the transportation of dangerous liquids such as acids or solvents.

Investigation of the effect of catalyst type, concentration, and growth time on carbon nanotube morphology and structure

Investigation of the effect of catalyst type, concentration, and growth time on carbon nanotube morphology and structure

Dimensional Nanoarchitectonics of g-C3N4/Co Nanocomposites for Photo- and Electro-Chemical Applications

Cobalt ions were introduced during thermal polymerization at high temperature to prepare graphic carbon nitride (g-C3N4) and Co composites. The interface engineering induced by Co ions resulted in the variation of morphology as well as photo- and electro-chemical performance of the composite samples. Co-g-C3N4 composite samples revealed superior thin-nanosheet and nanotube morphologies at 680 and 750 °C, respectively. As separation centers, Co–N bonds at the interface promoted the transfer of charges and improved photocatalytic properties. Thus, the Co-g-C3N4 composite nanosheets revealed the best photocatalytic performance, in which the maximum degradation rate constant of rhodamine B reached to 0.126 min–1, which was 9.7 times of that of pure g-C3N4 nanosheets. In contrast, the Co-g-C3N4 composite nanotubes with Co nanoparticles effectively enhanced the hydrogen evolution reaction. In the case of a current density of 10 mA cm–2, the overpotential of the Co-g-C3N4 composite nanotubes was 249 mV and the Tafel slope was 80 mV dec–1. In addition, the Co-g-C3N4 composite nanotubes revealed high charge–discharge capacity as a supercapacitor. This result provided a method for building g-C3N4-based photo- and electro-catalysts for various photo- and electro-chemical applications including photocatalytic degradation of organic pollutants, electrocatalytic hydrogen evolution reaction, and supercapacitors.

Ethyl mercaptan removal from gas streams using regenerable Co/Fe modified hexaniobate nanotubes

In this study, Fe and Co/Fe modified H4Nb6O17 nanotubes as high efficiency materials for C2H5SH removal were synthesized by ion exchange-flocculation-calcination process. The results showed that Co/Fe modified H4Nb6O17 nanotubes can enhance removal effect of C2H5SH. C2H5SH breakthrough adsorption capacity of different materials decline as follows: Co/Fe-HNT-0.3 (36.20 mg·g−1) > Co/Fe-HNT-0.5 (33.70 mg·g−1) = Co/Fe-HNT-0.1 (33.70 mg·g−1) > 10 %Fe-HNT (29.96 mg·g−1) > HNT-450 (11.23 mg·g−1) > HNT (6.24 mg·g−1). After four cycle regenerations, the Co/Fe-HNT-0.3 can still maintain C2H5SH removal efficiency of 96.5 %. The characterization results indicated that the loaded metal of Fe and Co/Fe can improve the structure, morphology, thermal stability, and rich pore structure of the H4Nb6O17 nanotubes. It also indicated that Co/Fe oxides were the mainly active substances on H4Nb6O17 nanotubes. These characteristics enhance the adsorption and activation of C2H5SH by Fe and Co/Fe loaded H4Nb6O17 nanotubes. The introduction of Co additives promotes the reduction of Fe3+ and the formed Fe3O4 serve as the main active species to promote the oxidation of adsorbed C2H5SH. This study presents an efficient material of Co/Fe modified H4Nb6O17 nanotubes for the removal of C2H5SH.

(Digital Presentation) Strategy to Enhance the Power Factor in Carbon Nanotubes

Flexible thermoelectrics, which can convert waste heat into electricity at surfaces with various shapes and moving parts, is one of important techniques for efficient use of our limited energy resources. Carbon nanotubes are one of possible candidates for flexible thermoelectrics, and then we have investigated the relationships between electronic structure, location of Fermi-energy level, morphology, and thermoelectric performance of the carbon nanotubes. Particularly, we have clarified the one-dimensional characteristics in thermoelectric properties of single walled carbon nanotubes (SWCNTs). In the case of metallic SWCNTs, the thermoelectric trade-off is violated when the Fermi-energy level is tuned around van hove-singularity [1]. Thus, simultaneous enhancement of Seebeck coefficient and electrical conductivity is possible in the metallic type. In the case of semiconducting SWCNTs, we theoretically clarified that it is very difficult to identify the 1D characters in the properties of their Seebeck coefficient, power factor, and electrical conductivity. We found it is necessary to clarify the relationships between thermoelectrical conductivity (L12 term) and electrical conductivity (σ) to discuss the dimensionality in thermoelectric properties of semiconducting nanomaterials. We observed clear peak structure in the L12-σ plot in high-purity (6,5) SWCNT thin films, reflecting the 1D traces in semiconducting SWCNTs[2]. Morphology control is also important to enhance power factor of carbon nanotubes. The Seebeck coefficient does not depend on the directions of heat flow and nanotube axis, but the electrical conductivity can be enhanced when the current direction is parallel to the nanotube axis [1, 3]. On the basis of above characteristics, we determined the following strategy to enhance the power factor (PF) of SWCNTs. Fine tuning of Fermi-energy level in the metallic type of nanotube can enhance PFAligned nanotubes with good electrical conductivity can enhance PF. Thus, we started to study the thermoelectric properties of carbon nanotube fibers with extremely good electrical conductivity, which are produced by Prof. Pasquali Group in Rice Univ [4]. As a result, we found the gigantic power factor of the nanotube fiber, which is 14 mWm-1K-2, with proper Fermi-level tuning [5]. Flexible thermoelectrics with such large PF will be useful for active cooling application.

Recent Advancements in Morphologies of TiO2 Nanotube Layers and Their Photocatalytic Performance

Self-organized TiO2 nanotubes arrays, formed by electrochemical anodization of Ti, have attracted tremendous scientific and technological attention, due to their remarkable properties such as the tunability of dimensions, their directionality, high surface area, low density, and ability to absorb significant amount of incident light [1,2].The most widely used electrolyte for the synthesis of TiO2 nanotube layers is based on ethylene glycol containing small amounts of water and fluoride ions. However, nanotubes prepared in these electrolytes present a double-walled structure, with the outer wall consisting of almost pure TiO2 and the inner wall consisting of TiO2 contaminated with carbon and fluoride species [3,4]. In the recent years, the selective etching of the inner nanotube wall on Ti layer enabled synthesis of single-wall nanotubes that showed a superior photo-electrochemical performance compared to their double-walled counterparts [5]. An extensive etching enabled also the synthesis of single tube powders, which could be effectively decorated with Fe3O4 nanoparticles to act as magnetically guidable photocatalyst [6,7].The presentation will focus on the influence of all these nanotube morphologies on the photocatalytic degradation in the liquid phase. In particular, we will discuss, how the annealing temperature of single nanotubes influences their photocatalytic performance [7] and how the wall thickness of the single wall nanotubes can be optimized for the best performance [8]. Experimental details and photocatalytic results will be presented and discussed.

Effects of sputtering power of Ti films on morphology of TiO2 nanotubes synthesized via anodization process

In this paper, we aimed to find the sputtering power most suitable for fabricating anodized TiO2 nanotubes (TNTs) with high dimensions (diameter and length). TNTs were synthesized via anodization of Ti films deposited on a glass substrate at varying sputtering power from 50 W to 200 W. The properties of Ti films such as crystallinity, residual stress, and roughness were investigated, which affected the morphology of TNTs. Sputtering power levels of 150 W and 200 W were suitable for TNTs formation via the anodization process in NH4F concentrations from 1.0 wt% to 2.5 wt% due to the increased density and crystallinity of Ti films. Boosting the sputtering power to 200 W increases the roughness of the surface, resulting in a decrease in tube diameter and length. Increasing the sputtering power to 200 W also causes the residual stress of the film to be converted from compression to tensile stress, which allows for more TNTs structures to be formed on the film. Nanotubes fabricated on 150 W sputtered films have been proven to be superior to those fabricated at 200 W in every NH4F concentration in terms of length and diameter. Thus, they are more suitable for applications.

Morphology and Electrical Characteristics of Single-Walled Carbon Nanotubes Film Prepared by Air Brush Technique

This study is to investigate the morphology and electrical characteristics of single-wall carbon nanotubes (SWCNTs) thin film deposition using air brush technique. A deposition setup consisting of a conventional artist air brush was developed and used to deposit SWCNT thin films and therefore the resulting film’s characteristics need to be investigated to gauge its suitability in producing uniform monolayer. The SWCNTs used were synthesized via Direct Injection Pyrolytic Synthesis (DIPS) method, with diameters ranging from 0.8 to 3 nm. The substrate was deposited using an airbrush with varying nozzle to study its effect to the resulting SWCNTs thin films’ characteristics. Subsequently, scanning electron microscope (SEM) were used to inspect the morphology and surface topography, and followed by preliminary electrical measurements. The result shows that good dispersion promotes uniform distribution of SWCNTs over large area of glass substrate. Moreover, the electrical measurement revealed that at 1 V, best morphology produced highest current at a nozzle distanceof 10 mm (15.3 μA) and the lowest current at a nozzle height of 4 mm (3.24 μA). From the results presented, it is demonstrated that conventional artist airbrush setup can be effectively used to deposit monolayer thin film of SWCNT with high degree of uniformity. This research is necessary for the process of depositing-controlled CNT thin film network, which can influence the material characteristics and performance of the variety of CNT-based device applications.