Amorphous Nanotubes Research Articles

Flexural behavior of carbon/epoxy nanocomposite pipes with interleaved structure

The filament winding process used in this study mainly produces pipe-shaped structures. In this structure, there is an intersection of fiber bundles, which makes the fiber bundles overlapping with other fiber bundles wavy. In that area, the concentration of stress and deformation appears. Therefore, halloysite nanotubes were applied among nanoparticles to supplement this through the study. In the utilization of nanoparticles, the control of agglomeration phenomena and the ease of dispersion are pivotal factors. In consideration of this, general halloysite nanotubes were heat-treated at 1000∘C to produce amorphous halloysite nanotubes to reduce the surface energy of particles, making it easier to control agglomeration phenomena and the ease of dispersion, and it was intended to supplement and improve mechanical properties in local applications through interleaved structure design. In this study, each stacked structure was analyzed through an axial pipe bending test. The fracture pattern for each structure was observed through an optical microscope. As a result, A3 reinforced with A-HNT for all layers had the highest load value (4207N), and the flexural strength was also measured high accordingly. It shows a small degree of fracture compared to other structures. Following that, E2A1, whose innermost layer was reinforced with A-HNT, had the second-highest load value (3864N), and accordingly, the second-highest flexural strength was measured. The observed surface of the pipe was the outermost layer (E), and it was observed that the degree of fracture was more advanced than that of A3.

A Unique Amorphous Porous BiSbOx Nanotube with Abundant Unsaturated Sb‐Stabilized BiO8−x Sites for Efficient CO2 Electroreduction in a Wide Potential Window

AbstractThe CO2 electroreduction reaction using sustainable electricity emerges as a viable strategy to produce high‐value‐added and profitable chemicals. The achievement of superior activity at a lower overpotential and higher selectivity in a wide potential window is vitally important for large‐scale industrial applications. Herein, a carbon‐composite amorphous porous BiSbOx nanotube with abundant unsaturated sites is reported to boost the conversion of CO2 to formate, exhibiting a formate selectivity of >90% in an extremely broad range of potentials from −0.5 to −1.4 V versus reversible hydrogen electrode (RHE) and a maximal energy conversion efficiency of 77.1%. Importantly, pure formic acid solution is directly obtained in a solid‐electrolyte cell for industrial‐scale applications. The porous tubular structure can expose more catalytic active sites, accelerate the mass transfer, and show fast surface charge transfer. Moreover, the unique coordination‐unsaturated Sb‐stabilized BiO8−x site can not only enhance the adsorption and activation of CO2 but also reasonably balance the stabilization and hydrogenation of *OCHO intermediate, thus leading to its obviously higher catalytic performance. As a result, a novel amorphous porous BiSbOx nanotube is successfully designed for efficient CO2 electroreduction, which may shed new light on developing many more amorphous composite metal oxide catalysts for conversion of inert small molecules.

Luminescence in Anion-Deficient Hafnia Nanotubes.

Hafnia-based nanostructures and other high-k dielectrics are promising wide-gap materials for developing new opto- and nanoelectronic devices. They possess a unique combination of physical and chemical properties, such as insensitivity to electrical and optical degradation, radiation damage stability, a high specific surface area, and an increased concentration of the appropriate active electron-hole centers. The present paper aims to investigate the structural, optical, and luminescent properties of anodized non-stoichiometric HfO2 nanotubes. As-grown amorphous hafnia nanotubes and nanotubes annealed at 700 °C with a monoclinic crystal lattice served as samples. It has been shown that the bandgap Eg for direct allowed transitions amounts to 5.65 ± 0.05 eV for amorphous and 5.51 ± 0.05 eV for monoclinic nanotubes. For the first time, we have studied the features of intrinsic cathodoluminescence and photoluminescence in the obtained nanotubular HfO2 structures with an atomic deficiency in the anion sublattice at temperatures of 10 and 300 K. A broad emission band with a maximum of 2.3-2.4 eV has been revealed. We have also conducted an analysis of the kinetic dependencies of the observed photoluminescence for synthesized HfO2 samples in the millisecond range at room temperature. It showed that there are several types of optically active capture and emission centers based on vacancy states in the O3f and O4f positions with different coordination numbers and a varied number of localized charge carriers (V0, V-, and V2-). The uncovered regularities can be used to optimize the functional characteristics of developed-surface luminescent media based on nanotubular and nanoporous modifications of hafnia.

Optimization of interleaved structures with amorphous halloysite nanotubes for superior performance of CFRP pipes in various environmental conditions

The carbon fiber-reinforced polymer (CFRP) pipes are extensively used in various industrial sectors and are routinely exposed to diverse environmental conditions, making it imperative to enhance their performance and durability. To address this need, our study investigates the effects of incorporating amorphous halloysite nanotubes (A-HNTs) in different layers of five distinct layer arrangements on the bending and pipe stiffness properties of interleaved CFRP flat (F) and cylindrical (C) structures under various environmental conditions. Notably, the maximum moisture absorption rate of carbon/epoxy composites (A3), encompassing all layers of epoxy modified with A-HNTs, was 190 % lower than that of carbon/epoxy (E3) composites containing unmodified epoxy resin in all layers. Furthermore, F(A3) exhibited the highest flexural strength at 3141 MPa among all composites tested. A-HNTs significantly improved pipe stiffness, with C(A3) exhibiting remarkable stiffness enhancements of 314 % after moisture absorption and 268 % after drying compared to C(E3). The composite C(E2A1), which included a bottom layer of epoxy modified with A-HNTs, also demonstrated significant stiffness enhancements of 308 % after moisture exposure and 290 % after drying, compared to C(E3). Consequently, we recommend the use of A3 and E2A1 composites for industrial applications.

Au nanoparticles-coated TiO2 SERS active substrate studies-based on plasmonic photonic interference coupling

In this work, gold nanoparticles coated titanium dioxide surface-enhanced Raman scattering (SERS) substrates were fabricated and tested. Amorphous titanium dioxide nanotubes with different geometry were prepared by anodization and subsequent spin-coating of gold nanoparticles is done. SERS signal enhancement for the effective detection of rhodamine 6G molecules is studied using these substrates. SERS enhancement factor of the substrates was dependent on the geometry of nanotubes and plasmonic photonic interference coupling (P-PIC). Analytical SERS enhancement factor of the substrates was estimated with respect to reference materials.

Confining Co-Based Nanocatalysts by Ultrathin Nanotubes for Efficient Transfer Hydrogenation of Biomass Derivatives.

Catalytic transfer hydrogenation (CTH) based on non-noble-metal catalysts has emerged as an environmentally friendly way for the utilization of biomass resources. However, the development of efficient and stable non-noble-metal catalysts is crucially challenging due to their inherent inactivity. Herein, a metal-organic framework (MOF)-transformed CoAl nanotube catalyst (CoAl NT160-H) with unique confinement effect was developed via a "MOF transformation and reduction" strategy, which exhibited excellent catalytic activity for the CTH reaction of levulinic acid (LA) to γ-valerolactone (GVL) with isopropanol (2-PrOH) as the H donor. Comprehensive characterizations and experimental investigations uncovered that the confined effect of the ultrathin amorphous Al2O3 nanotubes could modulate the electronic structure and enhance the Lewis acidity of Co nanoparticles (NPs), thus contributing to the adsorption and activation of LA and 2-PrOH. The synergy between the electropositive Co NPs and Lewis acid-base sites of the CoAl NT160-H catalyst facilitated the transfer of α-H in 2-PrOH to the C atom of carbonyl in LA during the CTH process via a Meerwein-Ponndorf-Verley mechanism. Moreover, the confined Co NPs embedded on am-Al2O3 nanotubes endowed the CoAl NT160-H catalyst with superior stability and the catalytic activity was nearly unchanged for at least ten cycles, far surpassing that of the Co/am-Al2O3 catalyst prepared by the traditional impregnation method.

Stabilizing Copper by a Reconstruction-Resistant Atomic Cu-O-Si Interface for Electrochemical CO2 Reduction.

Copper (Cu), a promising catalyst for electrochemical CO2 reduction (CO2R) to multi-electron reduction products, suffers from an unavoidable and uncontrollable reconstruction process during the reaction, which not only may lead to catalyst deactivation but also brings great challenges to the exploration of the structure-performance relationship. Herein, we present an efficient strategy for stabilizing Cu with silica and synthesize reconstruction-resistant CuSiOx amorphous nanotube catalysts with abundant atomic Cu-O-Si interfacial sites. The strong interfacial interaction between Cu and silica makes the Cu-O-Si interfacial sites ultrastable in the CO2R reaction without any apparent reconstruction, thus exhibiting high CO2-to-CH4 selectivity (72.5%) and stability (FECH4 remains above 60% after 12 h of test). A remarkable CO2-to-CH4 conversion rate of 0.22 μmol cm-2 s-1 was also achieved in a flow cell device. This work provides a very promising route for the design of highly active and stable Cu-based CO2R catalysts.

Effects of Mode of Preparation of Titanium Dioxide Nanotube Arrays on Their Photocatalytic Properties: Application to p-Nitroaniline Degradation

The aim of this study was to investigate the photoactivity of dioxide titanium (TiO2) nanotube films depending on different structure factors including pore size, tube length, tube wall thickness and crystallinity. Aqueous p-nitroaniline was used as a probe to assess the photocatalytic activity of titanium dioxide nanotube layers under UV irradiations. Self-organized titanium dioxide nanotube thin films were prepared by electrochemical anodization of titanium (Ti) foils and Ti thin films sputtered onto silicon (Si). The amorphous as-formed titanium nanotube layers were then annealed at different temperatures ranging from 450 to 900 °C in order to form crystalline phases. The structure and the morphology of the films were characterized by surface analysis techniques and scanning electron microscopy, respectively. The photocatalytic activity of the resulting TiO2 thin films was evaluated by monitoring the UV degradation of p-nitroaniline by UV spectrophotometry and by determining nitrification yields of by ion chromatography. The highest photocatalytic activity was exhibited for titanium nanotubes annealed at 450 °C. The presence of rutile -obtained for an annealing temperature of 900 °C—appeared to reduce the photodegradation yield of p-nitroaniline. Finally, the TiO2 nanotubes obtained from Ti foils revealed the most efficient photocatalytic properties.

Formation mechanism and characteristics of Au-Sn-O and Sn-O nanocompounds with various band gaps through flame chemical vapor deposition process

After forming the double layer of SnO2 and Au, the compound of Sn and O with multiple band gaps was formed in a short time period via flame chemical vapor deposition (FCVD). The Sn component of SnO2 has fluidity and is the only one moving to the discrete Au side and leaving O behind. The capillarity of Sn allows it to form a unique structure with Au-Sn-O nanoparticles and amorphous Sn-O nanotubes of multiple compositions in a single process. For verification, the gradual morphological, crystallographic, compositional, and optical changes in the material were sequentially presented as per the degree of FCVD.

Disordered hyperuniform quasi-one-dimensional materials

Carbon nanotubes are quasi-one-dimensional systems that possess large electronic conductance (for the metallic variants), high mechanical strength, selective emission and detection of light, and can be made chemically functionalized. In this work, we generalize the notion of disorder hyperuniformity, a recently discovered exotic state of matter with hidden long-range order, to quasi-one-dimensional materials. As a proof of concept, we then apply the generalized framework to quantify the density fluctuations in amorphous carbon nanotubes containing randomly distributed Stone-Wales defects. We demonstrate that all of these amorphous nanotubes are hyperuniform; i.e., the infinite-wavelength (normalized) density fluctuations of these systems are completely suppressed, regardless of the diameter, rolling axis, number of rolling sheets, and defect fraction of the nanotubes. We find that these amorphous nanotubes are energetically more stable than nanotubes with periodically distributed Stone-Wales defects. Moreover, certain semiconducting defect-free carbon nanotubes become metallic as sufficiently large amounts of defects are randomly introduced. This structural study of amorphous nanotubes strengthens our fundamental understanding of these systems, and suggests possible exotic physical properties, as endowed by their disordered hyperuniformity. Our findings also shed light on the effect of dimensionality reduction on the hyperuniformity property of materials.

(Digital Presentation) Ti3C2 Tx MXene As an Anode in Li- and Na-Ion Batteries: Where Does Electrochemical Capacity Stem from?

The unique properties of the Ti3C2 Tx MXene continue to attract attention within the energy storage field. Many of the previous reports on the use of this material in Li- and Na-ion batteries mainly concentrate on modifying the surface of the MXene or the cycling protocol in attempts to achieve higher specific capacities. Very few studies have, on the other hand, addressed the nature of the electrochemical reactions taking place during the electrochemical cycling of the material.This study aims at gaining a deeper understanding of the electrochemical behavior of freestanding Ti3C2 Tx electrodes without any binder and conductive additive. The results obtained with these electrodes, which were manufactured by vacuum filtration of MXene suspension in deionized water, are used to identify the electrochemical reactions yielding the observed capacities obtained in Li-metal cells using 1 M LiPF6 in EC:DEC (50:50 vol%) as the electrolyte and in Na-metal cells containing 1 M NaFSI in TEG-DME. Constant current and cyclic voltammetry cycling as well as in-house ex-situ XPS and synchrotron-based ex-situ HAXPES and XAS were used to identify the redox processes taking place upon the charging and discharging of the MXene electrodes.The results, obtained when cycling the freestanding Ti3C2 Tx MXene electrodes in Li-metal cells, indicate that the reversible capacity can be explained by redox reactions involving Ti species present in the Ti3C2 Tx surface layer. The charge storage mechanism is hence faradic. The results of XAS measurements carried out in the transmission mode likewise indicate that the redox reactions are surface confined and do not involve the inner C-Ti-C layer of the Ti3C2 Tx MXene.When cycling material between 0 and 3 V vs. Na+/Na in Na-metal cells, the specific capacity of the Ti3C2 Tx electrodes increases progressively with the cycle number (from 5 mAh/g on the first cycles to 50 mAh/g on the 200th cycle using a cycling rate of 10 mA/g). This effect is suggested to be connected to the deposition of sodium at about 0 V vs. Na+/Na as this count yield an activation of the electrodes. Comparisons of the cycling behavior of freestanding Ti3C2 Tx electrodes with those of monolithic TiO2 (amorphous) nanotube electrodes with nanotubes lengths of about 4 μm suggest that the behavior of the Ti3C2 Tx electrodes cannot be explained by the expected spontaneous formation of TiO2 on the surface of Ti3C2 Tx electrodes. The capacity for the TiO2 nanotube anode was relatively high, i.e., 160 mAh/g, on the first cycle but was seen to decrease to about 90 mAh/g after 100 cycles when cycling at a rate of 10 mA/g. The reasons for the differences seen between the Ti3C2 Tx and TiO2 nanotube electrodes will be discussed based on the general electrochemical behavior of the Ti3C2 Tx electrodes.

Synthesis of a polyphenylacetylene/silica nanotube composite under high-temperature, high-pressure conditions

Phenylacetylene was inserted and polymerized in 5 nm diameter silica nanotubes under high pressure – high temperature conditions of 0.5 GPa and 437 K in an inert gas. The resulting nanocomposite was characterized by infrared and Raman spectroscopy and scanning and transmission electron microscopy. The vibrational spectroscopic data confirmed the formation of π-conjugated polyphenylacetylene and the absence of crystallization of the amorphous nanotubes. Scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, STEM-EDX, measurements confirmed the insertion of the polymer in the channels of the nanotubes and electron diffraction confirmed the amorphous nature of both the polymer and the host SiO2 nanotubes. The obtained nanocomposite is a candidate material for gas sensing applications.

Carbon and Neon Ion Bombardment Induced Smoothing and Surface Relaxation of Titania Nanotubes.

Titania nanotube arrays with their enormous surface area are the subject of much attention in diverse fields of research. In the present work, we show that not only 60 keV and 150 keV ion bombardment of amorphous titania nanotube arrays yields defect creation within the tube walls, but it also changes the surface morphology: the surface relaxes and smoothens in accordance with a curvature-driven surface material’s transport mechanism, which is mediated by radiation-induced viscous flow or radiation-enhanced surface diffusion, while the nanotubes act as additional sinks for the particle surface currents. These effects occur independently of the ion species: both carbon and neon ion bombardments result in comparable surface relaxation responses initiated by an ion energy of 60 keV at a fluence of 1 × 10 ions/cm. Using atomic force microscopy and contact angle measurements, we thoroughly study the relaxation effects on the surface topography and surface free energy, respectively. Moreover, surface relaxation is accompanied by further amorphization in surface-near regions and a reduction in the mass density, as demonstrated by Raman spectroscopy and X-ray reflectivity. Since ion bombardment can be performed on global and local scales, it constitutes a versatile tool to achieve well-defined and tunable topographies and distinct surface characteristics. Hence, different types of nanotube arrays can be modified for various applications.

Synthesis and characterization of self-organized TiO2 nanotubes grown on Ti-15Zr alloy surface to enhance cell response

In recent years, studies have been shown that the presence of TiO2 nanotubes on the titanium alloy surfaces could induce the enhancement of the cell adhesion on the titanium alloys surface. In the present study, the cell response of the surface of the Ti-15Zr alloy after TiO2 nanotubes growth (NTs) via anodic oxidation was evaluated. TiO2 NTs were obtained in organic electrolytes and analyzed after annealing using Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. The attachment and growth of adult human adipose-derived stem cells (ADSCs) were considered for 1 and 7 days for better annealing conditions (450°C). Besides, the influence of the TiO2 NTs growth on the corrosion resistance and Staphylococcus epidermidis bacterial adhesion was evaluated. Results indicated that a self-organized and homogeneous layer of TiO2 nanotubes was formed. XRD analysis and SEM micrographs confirmed that as-anodized, amorphous nanotubes crystallized into anatase phase at 450°C. According to electrochemical analysis, Ti-15Zr alloy exhibited better corrosion resistance compared to commercially pure titanium (cp Ti), but there was no significant difference in passivation capacity between samples evaluated before and after anodization. It was observed that an increase in cellular adhesion and no significant difference in bacterial proliferation occurred despite the presence of TiO2 nanotubes which changed the surface roughness.

Compositional Patterning in Carbon Implanted Titania Nanotubes

AbstractRanging from novel solar cells to smart biosensors, titania nanotube arrays constitute a highly functional material for various applications. A promising route to modify material characteristics while preserving the amorphous nanotube structure is present when applying low‐energy ion implantation. In this study, the interplay of phenomenological effects observed upon implantation of low fluences in the unique 3D structure is reported: sputtering versus readsorption and plastic flow, amorphization versus crystallization and compositional patterning. Patterning within the oxygen and carbon subsystem is revealed using transmission electron microscopy. By applying a Cahn–Hilliard approach within the framework of driven alloys, characteristic length scales are derived and it is demonstrated that compositional patterning is expected on free enthalpy grounds, as predicted by density functional theory based ab initio calculations. Hence, an attractive material with increased conductivity for advanced devices is provided.

Nickel-phosphorus-boron amorphous alloy nanotubes improves the selective hydrogenation of furfural to furfuryl alcohol

Ni–P–B (NPB) amorphous alloy nanotubes were prepared for the selective liquid-phase hydrogenation of furfural to furfuryl alcohol. The content of P in NPB amorphous alloy nanotubes was adjusted by the initial NaH2PO2-containing liquid crystal system of non-ionic/anionic mixed surfactants. The promotion effect of an appropriate amount of P was mainly characterized by its large active surface area, ability for greater absorption of H, strong synergistic interaction, better stability, high conversion and catalytic selectivity. The NPB nanotubes exhibited higher hydrogenation activity when compared with the corresponding NPB nanoparticles, which might be dependent on the specific surface area, uniform active sites and tubular morphology of the catalysts.

Optoelectronic properties of amorphous carbon-based nanotube and nanoscroll

Free-standing monolayer amorphous carbon (MAC) is a pure carbon structure composed of randomly distributed atom rings with different sizes, which was recently synthesized. In this work, we carried out ab initio and tight-binding calculations to investigate the optoelectronic properties of MAC and its derived nanotube and nanoscroll configurations. Our results show MAC, tube, and scrolls exhibit similar electronic behavior. All structures absorb from infrared to ultraviolet, with maximum absorption peaks the visible-ultra violet (~ 3.2 eV). The maximum and minimum reflectivity values are in the range 0.3–0.5 (infrared) and 0.1-0.0 (ultraviolet), making these materials good candidates to ultraviolet filters.

Corrosion and Passivation Behaviors of Tin in Aqueous Solutions of Different pH

Corrosion and passivation of tin at various pH have been investigated using different electrochemical techniques. Tin is a little active metal even if it is less than the hydrogen equilibrium compared to its domain stability set. Tin acts as Sn(II) via the active zone, so it corrodes with evolving H2 gas in an acidic medium. In passive areas, Sn(IV) is oxidized to produce an inclusive variety of passivity outstanding to the permanence of either Sn(OH)4 and/or SnO2 anodic surface of tin(IV), which is stable to lower pH. Tin's active dissolution requires one anodic peak and strengthens with rising acid electrolyte. The cathodic curve shows one cathodic peak consistent with passive tin layer reduction. Adding any polyethylene glycols to a solution of citric acid reduces the existing anodic peak density and changes its peak potential in the negative direction. Those changes depend on the added polyethylene glycol concentration and molecular weight. In an acidic environment comprised chromic, phosphoric, and hydrochloric acids, amorphous SnO nanotubes were manufactured using Sn nanowires (NW) electrodeposited to anodic aluminum oxide frameworks by a local degradation process. The phosphoric acid disintegrates the base initially, while also chromic acid generates an oxide layer of SnO at the NW level. Finally, Sn NWs with 10 μm in length and 30 nm in diameter are completely converted into the polycrystalline SnO form by crystallization of the amorphous nanotubes after heat treatment with rough morphology of the earth.

Ultra-thin dark amorphous TiOx hollow nanotubes for full spectrum solar energy harvesting and conversion‡

Dark titania (TiOx) have been widely used for solar energy harvesting and conversion applications due to its excellent light absorbing performance throughout the ultraviolet to near infrared wavelength band, low cost, and non-toxic nature. However, the synthesis methods of dark TiOx are usually complicated and time-consuming. Here we report a facile and rapid method to fabricate dark amorphous TiOx (am-TiOx) hollow nanotube arrays on nanoporous anodic alumina oxide (AAO) templates using atomic layer deposition. Systematic investigation was performed to demonstrate that Ti3+ and O- species in the am-TiOx ultra-thin films, as well as the spatial distribution of these am-TiOx ultra-thin films on the vertical side walls of AAO templates are two major mechanisms of the black color. Importantly, the film deposition took ~18 min only to produce the optimized ~4‐nm‐thick am-TiOx film. Representative applications were demonstrated using photocatalytic reduction of silver nitrate and photothermal solar vapor generation, revealing the potential of these ultra-thin dark am-TiOx/AAO structures for full spectrum solar energy harvesting and conversion.

Characterization of Optimized TiO2 Nanotubes Morphology for Medical Implants: Biological Activity and Corrosion Resistance.

BackgroundNanostructured surface modifications of Ti-based biomaterials are moving up from a highly-promising to a successfully-implemented approach to developing safe and reliable implants.MethodsThe study’s main objective is to help consolidate the knowledge and identify the more suitable experimental strategies related to TiO2 nanotubes-modified surfaces. In this sense, it proposes the thorough investigation of two optimized nanotubes morphologies in terms of their biological activity (cell cytotoxicity, alkaline phosphatase activity, alizarin red mineralization test, and cellular adhesion) and their electrochemical behavior in simulated body fluid (SBF) electrolyte. Layers of small-short and large-long nanotubes were prepared and investigated in their amorphous and crystallized states and compared to non-anodized samples.ResultsResults show that much more than the surface area development associated with the nanotubes’ growth; it is the heat treatment-induced change from amorphous to crystalline anatase-rutile structures that ensure enhanced biological activity coupled to high corrosion resistance.ConclusionCompared to both non-anodized and amorphous nanotubes layers, the crystallized nano-structures’ outstanding bioactivity was related to the remarkable increase in their hydrophilic behavior, while the enhanced electrochemical stability was ascribed to the thickening of the dense rutile barrier layer at the Ti surface beneath the nanotubes.