Nanotube Layers Research Articles

Photocatalytic removal of VOCs on TiO2 nanotube layers. Effect of layer thickness and humidity

The current work is focused on the influence of TiO2 nanotube (TNT) layer thickness, texture properties and chemical nature of volatile organic compounds (VOCs) on the efficiency of their photocatalytic oxidative removal. Attention was also given to the evaluation of the degree of mineralisation and the influence of air humidity. The fabricated TNT layers have a thickness from 2to13 μm, TiO2 mass from 0.27 to 1.15 mg cm−2, tube diameter of 108 ± 17 nm and porosity of 74 ± 5 %. Values of areal SBET determined from Kr adsorption are higher than the inner surface area of the TNT layer calculated from morphology parameters, this suggests the rough nature of the inner surface of nanotubes. Acetaldehyde was more easily degraded in comparison to hexane which was explained by a simpler chemical structure. The degree of acetaldehyde mineralisation was almost 100 %, suggesting the formation of no intermediates, analysis confirmed negligible formation of formaldehyde. In contrast, degree of hexane mineralisation was lower, 80 %. An increase in humidity has a negative effect on the photocatalytic performance; this effect is more significant for non-polar hexane compared to water-miscible acetaldehyde. The conversion of hexane and absorptance of the TNT layer at 365 nm increase similarly with increasing thickness. Hexane conversion increases significantly up to a layer thickness of about 4 μm where more than 80 % of incident light is absorbed. The simultaneous degradation of four pollutants (acetaldehyde, acetone, heptane and toluene) results in the highest degradation rate of acetaldehyde and the lowest for heptane, this was attributed to their different solubility in water as well as to their different adsorption.

Rapid Determination of the Optimum Thickness of Doped TiO2 Nanotubes Layer by Local Photoelectrochemistry and Operando Properties Extraction by Data Modeling.

In this work, the optimal thickness of TiO2, M‐doped, N‐doped, and (M:N) codoped TiO2 (with M = Nb or Ta) nanotubes (NTs) for photoelectrochemical (PEC) water splitting is determined, in one step through local photoelectrochemical analysis of electrodes with variable thickness of the photoactive material. A simple anodization method allows the growth, on a single electrode, of aligned doped TiO2 nanotubes whose length gradually changes from 0 to 15 μm. The external quantum efficiency (EQE) as a function of the NTs film thickness is measured using a small beam of UV or visible light to scan the surface and locally trigger the oxygen evolution reaction (OER). The results provide the optimal NT layer thickness for each type of doped TiO2‐NTs and demonstrate that if the (M:N) codoped TiO2‐NTs have the best activity in the visible region, the optimal layer thickness is reduced compared to TiO2 or M:doped TiO2‐NTs. Additionally, by fitting the data with a model that incorporates charge carrier transfer and light absorption mechanisms in the film, it becomes possible to evaluate in operando the interfacial charge transfer, absorption coefficient or majority carrier mean path which are important properties of semiconducting (SC) materials for PEC applications.This article is protected by copyright. All rights reserved.

Vibration energy harvesting in an FG-CNTRC circular microplate with a surface-bonded piezoelectric layer

Piezoelectric energy harvesting using circular microplate has great potential to power microelectromechanical systems (MEMS). This paper studies vibrational energy harvesting by creating a model of a thin-walled circular microplate with a base layer of functional gradient carbon nanotube reinforced composites (FG-CNTRC) and a piezoelectric surface layer. Using the extended modified couple stress theory and the rule of mixture, the size effect and the effective Young's and shear moduli of the carbon nanotube reinforced composite (CNTRC) plate are established. Then, the governing equations are derived through the Lagrange's equations, and the analytical solutions of the relevant physical quantities are obtained. The specific examples are used to investigate the influence of length scale, carbon nanotube distribution, excitation frequency, and the ratio of the upper and lower plate radii on displacement, voltage, and power.

Redox-active NiS@bacterial cellulose nanofiber composite separators with superior rate capability for lithium-ion batteries

Separator is an essential component of lithium-ion batteries (LIBs), which is placed between the electrodes to impede their electrical contact and provide the transport channels for lithium ions. Traditionally, the separator contributes the overall mass of LIBs, thereby reducing the gravimetric capacity of the devices. Herein, a dual-layer redox-active cellulose separator is designed and fabricated to enhance the electrochemical performances of LIBs by introducing NiS. The presented separator is composed of an insulating bacterial cellulose (BC) nanofiber layer and a conductive, and redox-active NiS@BC/carbon nanotubes layer. By using the NiS@BC separator, the discharge capacity of the LiFePO4//Li half battery is enhanced to 117 mAh g-1 at a current of 2C owing to the redox-activity of NiS. Moreover, the functional separator-electrode interface can facilitate the homogenous Li stripping/plating and depress the polarization upon the repeated stripping/plating process. Consequently, the battery containing the redox-active separator exhibits outstanding cycle stability and rate capability. The present study contributes a novel strategy for the developments of functional separators to improve the electrochemical properties of LIBs.

A superhydrophilic and robust fabric, featuring self-assembled layers of chitosan and carbon nanotubes, facilitates high-throughput oil–water separation

Petroleum pollution and industrial emissions of organic pollutants have become significant issues affecting both ecological and human living environments. High-performance oil–water separation membranes, due to their advantages such as low cost, environmental friendliness, and ease of operation, hold vast application prospects. Therefore, the development of efficient oil–water separation membranes is crucial. We propose a clever approach involving the synergistic self-assembly of chitosan (CS) and hydroxylated multi-walled carbon nanotubes (MWCNTs) on cotton fabric to construct a rough structure. Combined with hydrophilic modification using polyvinyl alcohol (PVA), not only does this enhance wettability, but it also addresses challenges related to mechanical strength and dispersibility of cotton fabric. The resulting CMF-PVA fabric performs well under challenging conditions, exhibiting excellent separation efficiency and permeance. Particularly noteworthy is that CMF-PVA achieves separation efficiencies exceeding 99.33 % for various organic substances, with a water flux reaching 35,476.52 L m−2 h−1 and a surfactant-stabilized emulsion permeance of 1199.0 L m−2 h−1·bar−1. Furthermore, CMF-PVA demonstrates outstanding mechanical durability under harsh conditions and excellent acid-base resistance. This method harnesses the inherent properties of CS and MWCNT self-assembly while enhancing the material's applicability on cotton fabric through hydrophilic modification. CMF-PVA fabric is poised to enhance selectivity, efficiency, anti-pollution properties, and accessibility in oil–water separation technology.

Laser-Treated MXene as an Electrochemical Agent to Boost Properties of Semitransparent Photoelectrode Based on Titania Nanotubes.

In this study, Ti3C2Tx underwent laser treatment to reshape it, resulting in the formation of a TiO2/Ti3C2Tx heterojunction. The interaction with laser light induced the formation of spherical TiO2 composed of an anatase-rutile phase on the Ti3C2Tx surface. Such a heterostructure was loaded over a titania nanotube (TNT) layer, and the surface area was enhanced through immersion in a TiCl4 solution followed by thermal treatment. Consequently, the photon-to-electron conversion efficiency exhibits a 10-fold increase as compared to bare TNT. Moreover, for the sample produced with optimized conditions, five times higher photoactivity is observed in comparison to bare TNT. It was shown that under visible light irradiation the most photoactive heterojunction based on the tubular layer reveals a substantial drop in the charge transfer resistance of about 32% with respect to the dark condition. This can be attributed to the narrower band gaps of the modified material and improvement of the separation efficiency of the photogenerated electron-hole pairs. Overall results suggest that this investigation underscores TiO2/Ti3C2Tx as a promising noble-metal-free material that enhances both the electrochemical and photoelectrochemical performances of electrode materials based on TNT that can be further used in light-harvesting applications.

Mediating Zn Ions Migration Behavior via β-Cyclodextrin Modified Carbon Nanotube Film for High-Performance Zn Anodes.

Metallic Zn is considered as a promising anode material because of its abundance, eco-friendliness, and high theoretical capacity. However, the uncontrolled dendrite growth and side reactions restrict its further practical application. Herein, we proposed a β-cyclodextrin-modified multiwalled carbon nanotube (CD-MWCNT) layer for Zn metal anodes. The obtained CD-MWCNT layer with high affinity to Zn can significantly reduce the transfer barrier of Zn2+ at the electrode/electrolyte interface, facilitating the uniform deposition of Zn2+ and suppressing water-caused side reactions. Consequently, the Zn||Zn symmetric cell assembled with CD-MWCNT shows a significantly enhanced cycling durability, maintaining a cycling life exceeding 1000 h even under a high current density of 5 mA cm-2. Furthermore, the full battery equipped with a V2O5 cathode displays an unparalleled long life. This work unveils a promising avenue toward the achievement of high-performance Zn metal anodes.

Deformable Joule heating electrode based on hybrid layers of silver nanowires and carbon nanotubes and its application in a refreshable multi-cell Braille display.

Stretchable electrodes are an essential component in soft actuator systems. In particular, Joule heating electrodes (JHEs) are required for thermal actuation systems. A highly stretchable, patternable, and low-voltage operating JHE based on hybrid layers of silver nanowires (AgNWs) and carbon nanotubes (CNTs) is reported. The conductive layers were applied on a locally pre-strained bistable electroactive polymer (BSEP) membrane to form a wrinkled conductive surface with a low resistance of 300 Ω/sq, and subsequently patterned to a serpentine trace by laser engraving. The resistance of the resulting electrode remains nearly unchanged up to ~80-90% area strain. By applying a voltage of 7 - 9 V to the electrode, the temperature of the BSEP membrane increased to more than 60 °C, well above the polymer's phase transition temperature of 46 °C, thereby lowering its modulus by a factor of 103. An electronic Braille device based on the JHEs on a BSEP membrane was assembled with a diaphragm chamber. The electrode was patterned into 3 × 2 individually addressable pixels according to the standard U.S. Braille cell format. Through Joule heating of the pixels and local expansion of the BSEP membrane using a small pneumatic pressure, the pixels deformed out of the plane by over 0.5 mm to display specific Braille letters. The Braille content can be refreshed for 20,000 cycles at the same operating voltage.

A nanocellulose-based flexible multilayer sensor with high sensitivity to humidity and strain response for detecting human motion and respiration

Biomass-based flexible sensors with excellent mechanical and sensing properties have attracted significant attention. In this study, based on the excellent dispersibility and degradability of nanocellulose crystals, we designed a polyvinyl alcohol/nanocellulose crystals/phytic acid (PCP) composite film with good flexibility and high sensitivity to humidity. A layer of multiwalled carbon nanotubes (MWCNT) and nanocellulose crystals (CNC) was further sandwiched between two PCP layers as a flexible multifunctional sensor (PCPW) to detect human movement and respiration. Phytic acid contains abundant phosphate groups that enhance proton conduction, allowing the PCPW composite film to change its electrical resistance in a sensitive and repeatable manner when the relative humidity was varied between 35 %–93 %. Meanwhile, CNC derived from sisal fibers enhanced the PCPW sensor's conductivity (3.3 S/m) and mechanical properties (elongation at break: 99 %) by improving the dispersion and connectivity of MWCNT. The PCPW sensor displayed a high sensitivity to strain (gauge factor: 49.5) and could monitor both facial expressions (smiling and winking) and the bending of joints. The sensor also generated stable electrical responses during breathing and blowing due to the change in humidity. Therefore, this biodegradable and multifunctional sensor has good application prospects.

Fabrication of reusable bioprotective nanofabric with passive nano-Ag/Joule thermal disinfection properties for real-time wireless fine biomotion and gesture sensing

The frequent outbreaks of new infectious diseases, with increased difficulty in prevention and control, have raised higher requirements for bio-protective smart textiles. However, current wearable sensing materials face challenges with thermal and humidity comfort, bioprotection, reusability, self-disinfection, and wireless real-time sensing ability. Herein, an ultralight and breathable sandwich-structured interlayer nanofiber composite consisting of two outer microporous layers of polyimide nanofibers embedded with AgNPs (Ag@PINFs) and one nanoporous conductive layer (＜100 nm) of carbon nanotubes (CNTs) have been demonstrated by in-situ reduction, electrospinning, and suction filtration to improve the triboelectric output performance and impart passive/active self-disinfection abilities to triboelectric nanogenerators (TENGs). The TENG was designed with a triple bio-protection function. This included a passive physical barrier effect, nano-Ag active disinfection, and active Joule-heat disinfection function, which ensures the reusability of TENG. As-prepared TENG possessed the following advantages: (i) good moisture-penetrability; (ii) good water and blood penetration resistance (≥17.2 kPa; ≥7kpa); (iii) improved triboelectric output performances (∼1.6 W/m2 at Ag content of 500 mg/kg); (iv) ultrahigh UV resistance (UPF＞6480); (v) high particle and wet/dry microbial filtration performance (PFE = 99.95%; wet microbial penetration time＞75 min; penetrated dry microbial: lg(cfu)=0); (vi) active bactericidal abilities with killing rates of ∼100% against E. Coli and S. aureus at Ag content of ≥ 70 mg/kg; (vii) high Joule heat self-disinfection efficiency with killing rates of 100% at applied voltage of ≥ 5 V; (viii) a wireless real-time sensing ability to distinguish fine biomotion such as swallowing, coughing, and normal speech and shouting, as well as recognizing hand gesture by developed two/four-channel wearable wireless monitoring system (∼18 g). The TENG has trinity performances including bio-protection, self-disinfection, and wireless fine biomotion and gesture sensing, which has potential applications in medical field.

Features of electron reflection by layer of carbon nanotubes

The anisotropic properties of a layer of carbon nanotubes upon electron reflection have been studied. Only a small part of the incident electrons is found to reflect from a target with a surface layer of oriented carbon nanotubes. Reflection occurs only from a layer of horizontally oriented nanotubes at an angle of incidence greater than 80° and vertically oriented nanotubes at an angle of incidence less than 10°. The effect is explained by peculiarities of the formation of an electron flux in the surface layers of the target.

Enhancing the cycling stability of commercial silicon nanoparticles by carbon coating and thin layered single-walled carbon nanotube webbing

Silicon-based anode materials are considered as the most attractive alternatives to traditional graphite anodes, thereby advancing the evolution of new-generation lithium-ion battery technology. However, the inadequate electrical conduction of silicon-based materials, along with severe volume expansion during charging and discharging processes, limits their further technological applications. Herein, a dual-layer carbon shell configuration is designed to efficiently alleviate the substantial volumetric expansion of silicon during cycles, while simultaneously improving the efficiency of both electron and lithium ions. The effectiveness of this layered buffering approach is credited to the networked structure of outer single-walled carbon nanotubes (SWCNTs) layer, which is firmly attached to the inner carbon shell's surface. The modified structure not only elevates the level of electrical conduction, but also significantly reduces the internal stress due to silicon's expansion. The developed Si@C@SWCNT electrode materials exhibit high capacity of 1267.3 mA h g−1 after 500 cycles at 1 A g−1, and sustains an elevated rate capacity of 863 mA h g−1 at 8 A g−1. This study highlights the enormous potential of Si@C@SWCNT composites for use in lithium-ion batteries and provides new perspectives for further exploration and utilization of silicon-carbon anodes.

In situ polymerised polyaniline films over multi-walled carbon nanotubes coatings for enhanced photoelectrochemical performance

Polyaniline (PANI), which is a π-conjugated polymer, has stood out as a promising candidate for dihydrogen generation in photoelectrochemical (PEC) cells owing to its suitable optoelectronic properties and excellent stability. Nevertheless, the PEC performance of this material is still far from adequate for technological applications. Herein, we have focused on improving the PEC performance of PANI films by combining this polymer with multi-walled carbon nanotubes (MWCNTs) layers. Specifically, we have assessed the PEC activity of the in situ polymerised PANI films onto FTO substrates coated with different amounts of MWCTNs for the hydrogen evolution reaction (HER). The FTO/MWCNTs/PANI films with the optimum deposited amount of MWCNTs (i.e., 30 μL) featured a 2.4-fold increase of the cathodic photocurrent density response for the HER compared to that of FTO/PANI film. Moreover, the FTO/(30 μL)-MWCNTs/PANI films exhibited good PEC stability, as observed by the relatively low cathodic photocurrent density decay of up to 7% during 3720 s of stability test. Based on joint analyses of physical and PEC characterisation, the improved PEC performance for the FTO/(30 μL)-MWCNTs/PANI films were assigned to the combined contribution of the following factors: (i) enhancement of light absorption; (ii) possible improvement of excitons dissociation; (iii) minimisation of the electron-hole recombination process; and (iv) facilitation of electrons transfer at the PANI|electrolyte interface for the HER. The enhancement of PEC performance achieved in this work for the fully organic photocathode composed of MWCNTs/PANI paves the way to invest in additional modifications seeking to further improve the dissociation of excitons and the interfacial transfer of charge carriers for the light-driven HER.

Synthesis and Study of SrTiO3/TiO2 Hybrid Perovskite Nanotubes by Electrochemical Anodization.

Layers of TiO2 nanotubes formed by the anodization process represent an area of active research in the context of innovative energy conversion and storage systems. Titanium nanotubes (TNTs) have attracted attention because of their unique properties, especially their high surface-to-volume ratio, which makes them a desirable material for various technological applications. The anodization method is widely used to produce TNTs because of its simplicity and relative cheapness; the method enables precise control over the thickness of TiO2 nanotubes. Anodization can also be used to create decorative and colored coatings on titanium nanotubes. In this study, a combined structure including anodic TiO2 nanotubes and SrTiO3 particles was fabricated using chemical synthesis techniques. TiO2 nanotubes were prepared by anodizing them in ethylene glycol containing NH4F and H2O while applying a voltage of 30 volts. An anode nanotube array heat-treated at 450 °C was then placed in an autoclave filled with dilute SrTiO3 solution. Scanning electron microscopy (SEM) analysis showed that the TNTs were characterized by clear and open tube ends, with an average outer diameter of 1.01 μm and an inner diameter of 69 nm, and their length is 133 nm. The results confirm the successful formation of a structure that can be potentially applied in a variety of applications, including hydrogen production by the photocatalytic decomposition of water under sunlight.

Anodic Oxidation of 3D Printed Ti6Al4V Scaffold Surfaces: In Vitro Studies

This study focuses on the surface modification of Ti6Al4V scaffolds produced through additive manufacturing using the Powder-Bed Fusion Electron-Beam Melting (PBF-EB) technique. From our perspective, this technique has the potential to enhance implant osseointegration, involving the growth of a layer of titanium dioxide nanotubes (TiO2) on surfaces through anodic oxidation. Scaffolds with anodized surfaces were characterized, and the formation of a nanoporous and crystalline TiO2 layer was confirmed. The analysis of cell morphology revealed that cells adhered to the anodized surfaces through their filopodia, which led to proliferation during the initial hours. However, it was observed that the adhesion of Saos-2 cells was lower on anodized scaffolds compared to both built and chemically polished scaffolds throughout the cell culture period. The results obtained here suggest that while anodic oxidation is effective in achieving a nanoporous surface, cell adhesion and interaction were affected by the weak adhesion of cell filopodia to the surface. Thus, combining surface treatment techniques to create micro- and nanopores may be an effective alternative for achieving a favorable cellular response when the objective is to enhance the performance of porous titanium scaffolds in the short term.

On Local Stability Loss of Modified Composites with Whiskerized Fibers

This article examines the critical compressive stresses required for a modified fiber composite to remain straight while the fibers within it bend. It was assumed that the modified composite consists of three phases: fiber, whiskerized interfacial layer, and matrix. An example of a composite material made up of carbon fibers, a whiskerized layer of carbon nanotubes with an epoxy matrix, and an epoxy matrix was considered. Its physical parameters affecting the critical compressive stresses were assessed, and methods for determining them were proposed. The effective properties of the inclusion and binder composite material were identified using the Voigt and Reis methods. Similarly, the effective properties of the interfacial whiskerized layer were analyzed by the three-phase method. The influence of fiber wavelength and phase shift, which define the destruction of the composite material, on the critical compressive stress value was explored. The wavelengths at which the composite material is destroyed were found. The effect of the volume content of the modified inclusion on the minimum critical compressive stress value was shown. The results for the modified composites were compared with those for the classical composites with a similar volume content of inclusions.

Low‐Temperature Atomic Layer Deposition Synthesis of Vanadium Sulfide (Ultra)Thin Films for Nanotubular Supercapacitors

Herein, the synthesis of vanadium sulfide (VxSy) by atomic layer deposition (ALD) based on the use of tetrakis(dimethylamino) vanadium (IV) and hydrogen sulfide is presented for the first time. The (ultra)thin films VxSy are synthesized in a wide range of temperatures (100–225 °C) and extensively characterized by different methods. The chemical composition of the VxSy (ultra)thin films reveals different vanadium oxidation states and sulfur‐based species. Extensive X‐ray photoelectron spectroscopy analysis studies the effect of different ALD parameters on the VxSy chemical composition. Encouraged by the rich chemistry properties of vanadium‐based compounds and based on the variable valences of vanadium, the electrochemical properties of ALD VxSy (ultra)thin films as electrode material for supercapacitors are further explored. Thereby, nanotubular composites are fabricated by coating TiO2 nanotube layers (TNTs) with different numbers of VxSy ALD cycles at low temperature (100 °C). Long‐term cycling tests reveal a gradual decline of electrochemical performance due to the progressive VxSy thin films dissolution under the experimental conditions. Nevertheless, VxSy‐coated TNTs exhibit significantly superior capacitance properties as compared to the blank counterparts. The enhanced capacitance properties exhibited are derived from the presence of chemically stable and electrochemically active S‐based species on the TNTs surface.

Ultrathin TiO2 Coatings via Atomic Layer Deposition Strongly Improve Cellular Interactions on Planar and Nanotubular Biomedical Ti Substrates.

This work aims to investigate the chemical and/or structural modification of Ti and Ti-6Al-4V (TiAlV) alloy surfaces to possess even more favorable properties toward cell growth. These modifications were achieved by (i) growing TiO2 nanotube layers on these substrates by anodization, (ii) surface coating by ultrathin TiO2 atomic layer deposition (ALD), or (iii) by the combination of both. In particular, an ultrathin TiO2 coating, achieved by 1 cycle of TiO2 ALD, was intended to shade the impurities of F- and V-based species in tested materials while preserving the original structure and morphology. The cell growth on TiO2-coated and uncoated TiO2 nanotube layers, Ti foils, and TiAlV alloy foils were compared after incubation for up to 72 h. For evaluation of the biocompatibility of tested materials, cell lines of different tissue origin, including predominantly MG-63 osteoblastic cells, were used. For all tested nanomaterials, adding an ultrathin TiO2 coating improved the growth of MG-63 cells and other cell lines compared with the non-TiO2-coated counterparts. Here, the presented approach of ultrathin TiO2 coating could be used potentially for improving implants, especially in terms of shading problematic F- and V-based species in TiO2 nanotube layers.

Analysis of coated samples containing hydroxyapatite/multiwalled carbon nanotubes on 2205 DSS substrate

For biomedical applications, hydroxyapatite and carbon nanotubes are currently being applied over duplex stainless steel (DSS) alone in order to increase corrosion resistance and biocompatibility. A composite of hydroxyapatite and multi-walled carbon nanotubes was used to improve biocompatibility, osseointegration, and corrosion resistance on 2205 DSS using electrophoretic deposition. The study investigates the effects of potential and time on the properties of the deposited layer in order to determine electrophoretic deposition factor values that are appropriate. The coating properties and effective groups of the phase resulting from this process are determined by Fourier transform infrared spectroscopy and X-ray diffraction. The antibacterial properties of E. coli bacterial strains are investigated for the coated layer. The adhesion between the hydroxyapatite and multi-walled carbon nanotube layers on the 2205 duplex stainless steel substrate was qualitatively evaluated using the adhesive tape test. It was found that the optimal suspension, which consists of 65 weight percent hydrogen acetate and 35 weight percent multi-walled carbon nanotubes, had a homogeneous morphology, a thick structure, and no cracks when coated at 50 V for two minutes.

Review of: "About the electrical characteristics and the manufacturing process of a nanocapacitor structure using (metal-insulator-carbon-metal nanotube layers)"

Review of: "About the electrical characteristics and the manufacturing process of a nanocapacitor structure using (metal-insulator-carbon-metal nanotube layers)"