Nanotube Array Films Research Articles

Photo-electro-catalytic performance of highly ordered nitrogen doped TiO2 nanotubes array photoanode

Highly ordered nitrogen doped TiO2 nanotube arrays (N-TNTAs) were synthesized via a one step anodization method at 40 V for 1 hour, in the electrolyte containing ammonium fluoride (NH4F), water and triethylamine solution, followed calcination under N2 atmosphere at 450oC for 3 h. The obtained samples were characterized by means of FE-SEM image showed that the N-TNTs are in a highly ordered array, having inner diameters, wall thickness, tube length of 65 nm, 30 nm and 900 nm, respectively. The X-ray diffraction (XRD) patterns of N-TNTAs and undoped TiO2 nanotubes arrays (TNTAs) are identical consists of anatase phase, which suggests that the doping of N does not affect the crystalline structure. X-ray photoelectron spectroscopy (XPS), revealed that N atom was incorporated into the lattice of a TiO2 nanotube array film. The infrared spectra, showed a new peak at 1240 cm-1 may indicate the incorporation of N into the lattice of TiO2 through substituting O atoms, in the form of ∼N-Ti-O∼. A red shift of the absorption edge toward the visible region of N-TNTAs are observed by diffuse reflectance spectroscopy (DRS), which is corresponding to a band gap of 2.8 eV. The photo-electro-catalytic (PEC) degradation efficiency toward methylene blue solution under visible light illumination of the N-TNTAs electrode was 89%, in which the rate constant of N-TNTAs electrode was 8 times better compared to that the undoped TNTAs photo-electrode.

Cu2O/Ag co-deposited TiO2 nanotube array film prepared by pulse-reversing voltage and photocatalytic properties

In this experiment, Cu2O/Ag co-deposition TiO2 nanotube array (Cu2O-Ag-TNT) film was prepared on pure Ti substrate with the method of combining anodic oxidation and electrodeposition by pulse-reversing voltage power supply in the electrolyte of NH4F, ethylene glycol, CuNO3 · 3H2O and AgNO3. The morphology, phase, chemical composition, photocatalytic property and mechanism of the nanotube array film were studied by means of scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy, UV–vis diffuse reflectance spectra, photoluminescence and photocatalytic degradation under visible light. The results showed that the depositional Cu2O and Ag existed in two forms, being the small-particle dispersion and large-particle sedimentary phase in the nanotube arrays: Cu2O-Ag-TNTs for different doping amounts of Ag could be prepared by adjusting the concentration of AgNO3 and the reverse voltages; with changing of the doping amount of Ag, the band gap and photo-generated electron–hole pair recombination rate also changed, and under the conditions of annealing and the optimized process parameter, the band gap of the nanotube arrays narrowed 0.49 eV and the rate of electron and pair recombination decreased noticeably; the nanotube array film for the concentration of 0.5 cm2 ml−1 degraded the methylene blue of 8 mg L−1, and the degradation rate reached above 98%. The co-deposition Cu2O-Ag-TNT film prepared by the one-step method performed well in the field of photocatalysis under visible light.

Effects of NH4F quantity on N-doping level, photodegradation and photocatalytic H2 production activities of N-doped TiO2 nanotube array films

Series of N-doped TiO2 nanotube array (NTA) films with various N-doping levels and tube lengths were prepared by a facile one-step anodization method, simply changing NH4F quantity in electrolyte. The crystal structures, morphologies and compositions of the samples were analyzed by XRD, SEM, TEM and X-ray photoelectron spectra (XPS). The optical properties were investigated by means of UV–vis absorption spectra and photoluminescence (PL) spectra. Their photocatalytic activities were assessed by photodegradation of rhodamine B (RhB) solution and photocatalytic water splitting to generate hydrogen, respectively. The photocatalytic reaction mechanism was investigated and discussed. The results show that NH4F quantity greatly influences the N-doping level and tube length of the TiO2 NTA, which subsequently affects the optical properties and photocatalytic activities. The photodegradation and photocatalytic H2 production activities of the N-doped TiO2 NTAs can be simply regulated by tuning NH4F quantity in electrolyte during preparation.

Preparation and photocatalytic property of Cu2O-TiO2 composite nanotube arrays film by the anodic oxidation

In the experiment, order anode oxidation TiO2 nanotube arrays (TNTs) film was prepared and achieved Cu electrolytic deposition synchronously in the electrolyte of NH4F, ethylene glycol and CuNO3 by periodic reverse voltage pulsed power. With the concentration of Cu(NO)2·3H2O and reverse voltage changing, the loading condition of Cu compound in the TNTs can also be changed. The photocatalytic performance of TNTs film and Cu2O-TNTs film after annealing at 450℃ were studied by degrading methylene blue (MB) under the condition of ultraviolet light. The morphology, structure, optical property were studied by means of SEM, EDS, XRD, XPS, photoluminescence spectroscopy (PL) and ultraviolet-visible diffuse reflection spectrum (UV-vis DRS). The results show that Cu loaded had no influence to morphology of the nanotubes, and the optical property of TNTs can be further improved after loading Cu by narrowing the band gap of TiO2 about 0.22 and decreasing the recombination rate of photoelectrons and holes. When the addition concentration of Cu2O-TNTs in the MB solution was 0.25cm2/mL, the degradation rate reached 72.63% from 43.45%. When increased concentration to 0.75cm2/mL, the degradation rate of MB reached 96.79%. The photocatalytic performance of Cu2O-TNTs film prepared by using single-step anodic method performed well under ultraviolet light.

Iron oxide nanotube film formed on carbon steel for photoelectrochemical water splitting: effect of annealing temperature

Carbon steels (CSs) were anodized in an ethylene glycol solution containing 3 vol.% H2O and 0.1 m NH4F to coat with nanotube arrays film. The as anodized nanotube arrays film were annealed in argon atmosphere at various temperatures ranging from 250 to 550 °C for 4 h. The morphology and crystal phases of the film developed after annealing processes were examined using field emission scanning electron microscopy, X‐ray diffraction. Morphology transforms from nanobube arrays to nanotube bundles at 250 °C, to nanobube bundles with nanoflakes at 350 and 450 °C, to nanotube bundles with nanobelts at 550 °C. Amorphous transformed completely into maghemite at 350 °C and hematite with minor magnetite at 450 and 550 °C. Diffuse reflectance ultraviolet and visible spectra revealed iron oxide nanotube film annealed at 350 °C, or higher than 350 °C behaved tremendous absorbance ability in visible spectra range. Mott–Schottky analysis and linear scan voltammetry were performed in 1 m NaOH to show that iron oxide nanotube film annealed at 450 °C exhibited best charge carrier transfer ability upon illumination and superior photoelectrochemical properties compared with the films annealed at other temperatures. The film annealed at 450 °C displayed the photocurrent density of 0.13 mA cm−2 at 0.2 VAg/AgCl, but the film annealed at other temperatures with the photocurrent densities of lower than 0.05 mA cm−2 at 0.2 VAg/AgCl. The morphology and phase transform of iron oxide nanotube film at different annealing temperature results in the change of their photoelectrochemical properties. Copyright © 2016 John Wiley & Sons, Ltd.

Fabrication and characterization of novel composite membranes composed of photonic crystals and TiO2 nanotube array films

Novel composite membranes composed of photonic crystals (PCs) and TiO2 nanotube array (TNA) films have been fabricated by combining the room temperature floating self-assembly (RTFSA) method, recently developed by our research group, and the liquid-phase deposition technique. By applying this combined procedure, polystyrene (PS) opal PC/TNA and TiO2 inverse opal PC/TNA composite membranes were prepared. Scanning electron microscopy and ultraviolet/visible spectroscopy analyses showed that the membrane samples possessed very high crystalline quality. Notably, the ordered packing of the PS microspheres from the top to the bottom of the opal PC film was not affected by the surface roughness of the porous TNA substrate. This is attributed to the self-assembly mechanism of the colloidal particles, which produces a three-dimensional ordered structure in the RTFSA method. Herein, the crystallization of the colloidal particles occurred at the surface of the colloidal suspension, and the crystal growth proceeded downward from the surface of the suspension to the substrate.

Remarkably enhanced thermal transport based on a flexible horizontally-aligned carbon nanotube array film.

It has been more than a decade since the thermal conductivity of vertically aligned carbon nanotube (VACNT) arrays was reported possible to exceed that of the best thermal greases or phase change materials by an order of magnitude. Despite tremendous prospects as a thermal interface material (TIM), results were discouraging for practical applications. The primary reason is the large thermal contact resistance between the CNT tips and the heat sink. Here we report a simultaneous sevenfold increase in in-plane thermal conductivity and a fourfold reduction in the thermal contact resistance at the flexible CNT-SiO2 coated heat sink interface by coupling the CNTs with orderly physical overlapping along the horizontal direction through an engineering approach (shear pressing). The removal of empty space rapidly increases the density of transport channels, and the replacement of the fine CNT tips with their cylindrical surface insures intimate contact at CNT-SiO2 interface. Our results suggest horizontally aligned CNT arrays exhibit remarkably enhanced in-plane thermal conductivity and reduced out-of-plane thermal conductivity and thermal contact resistance. This novel structure makes CNT film promising for applications in chip-level heat dissipation. Besides TIM, it also provides for a solution to anisotropic heat spreader which is significant for eliminating hot spots.

Preparation of MoO3/TiO2 Composite Films and Their Application in Photoelectrochemical Anticorrosion

TiO2 nanotube array films were prepared on Ti substrates by a potentiostatic anodization method. Then, MoO3 nanoparticles were deposited on the TiO2 films by a pulse current deposition technique. The properties of the prepared films were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-Vis spectrophotometry, photoluminescence and photoelectrochemical measurements. Besides, the photogenerated cathodic protection performances of the composite films were investigated by recording the potential change of 403 stainless steel coupled to the films under white light illumination. The result showed that the absorption edge of the MoO3/TiO2 composite film was red-shifted compared with the pure TiO2 nanotube film, and the photochemical performance of the composite film was impoved. After 403 stainless steel in a corrosive solution with 0.5 M NaCl was coupled to the MoO3/TiO2 composite film under white light illumination, its potential decreased by 540 mV, showing an improved photogenerated cathodic protection effect on the steel.

Low-temperature synthesis of high-ordered anatase TiO2 nanotube array films coated with exposed {001} nanofacets

High-ordered anatase TiO2 nanotube array films coated with exposed high-reactive {001} nanofacets were fabricated by a modified hydrothermal method using amorphous anodic TiO2 nanotube arrays (ATONAs) as starting materials. It was found that the reaction between gas phase HF and solid ATONAs played a key role in the transformation process from amorphous to anatase TiO2, and the TiO2 tubular structure kept unchanged during the surface modification with an exposed {001} facets up to 76.5%, which could be attributed to the low reaction temperature of 130 °C. Our study provided a novel route for the facile preparation of {001} facets exposed anatase TiO2.

Preparation and UV–Vis photodegradation of gaseous benzene by TiO2 nanotube arrays supporting V2O5 nanoparticles

TiO 2-based catalysts effective in visible radiation for eliminating organic pollutants have attracted intense research activity as a future generation photocatalytic material. However, recombination of electron–hole pairs through trapping/de-trapping as well as the disadvantages of recycling and separation/filtration of powders lead to the limitation of powder TiO 2 materials. TiO 2 nanotube array films supporting vanadium pentoxide nanoparticles (VTNTs) were synthesized by electrophoresis deposition method with the prepared TiO 2 nanotube arrays as the cathode and V 2 O 5 sol as the electrolyte. The results indicate that the formation of Ti – O – V bonds and intimate interaction between host–guest interfaces help to enhance the hybrids’ photodegradation activity of gaseous benzene. Importantly, hybrid film catalysts prepared with 0.05 mol/L V 2 O 5 sol for 10 min electrophoresis deposition perform a 98% conversion rate of benzene and 1028.8 mg/m3 CO 2 production in 80 min under UV–Vis irradiation.

Ag2S/CdS/TiO2 Nanotube Array Films with High Photocurrent Density by Spotting Sample Method.

Ag2S/CdS/TiO2 hybrid nanotube array films (Ag2S/CdS/TNTs) were prepared by selectively depositing a narrow-gap semiconductor—Ag2S (0.9 eV) quantum dots (QDs)—in the local domain of the CdS/TiO2 nanotube array films by spotting sample method (SSM). The improvement of sunlight absorption ability and photocurrent density of titanium dioxide (TiO2) nanotube array films (TNTs) which were obtained by anodic oxidation method was realized because of modifying semiconductor QDs. The CdS/TNTs, Ag2S/TNTs, and Ag2S/CdS/TNTs fabricated by uniformly depositing the QDs into the TNTs via the successive ionic layer adsorption and reaction (SILAR) method were synthesized, respectively. The X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectrum (XPS) results demonstrated that the Ag2S/CdS/TNTs prepared by SSM and other films were successfully prepared. In comparison with the four films of TNTs, CdS/TNTs, Ag2S/TNTs, and Ag2S/CdS/TNTs by SILAR, the Ag2S/CdS/TNTs prepared by SSM showed much better absorption capability and the highest photocurrent density in UV-vis range (320~800 nm). The cycles of local deposition have great influence on their photoelectric properties. The photocurrent density of Ag2S/CdS/TNTs by SSM with optimum deposition cycles of 6 was about 37 times that of TNTs without modification, demonstrating their great prospective applications in solar energy utilization fields.

Interface feature characterization and Schottky interfacial layer confirmation of TiO2 nanotube array film

We report here characterization of the interfacial microstructure and properties of titanium dioxide (TiO2) nanotube array films fabricated by anodization. Field effect scanning electron microscopy (FESEM), X-ray diffraction (XRD), nanoindentation, atomic force microscopy (AFM), selected area electron diffraction (SAED), and high-resolution transmission electron microscopy (HRTEM) were used to characterize the interface of the film. With increasing annealing temperature from 200°C to 800°C, the interfacial fusion between the film and the Ti substrate increased. The phase transformation of the TiO2 nanotube film from amorphous to anatase to rutile took place gradually; as the phase transformation progressed, the force needed to break the film increased. The growth of TiO2 nanotube arrays occurs in four stages: barrier layer formation, penetrating micropore formation, regular nanotube formation, and nanofiber formation. The TiO2 nanotubes grow from the Schottky interface layer rather than from the Ti substrate. The Schottky interface layer's thickness of 35–45nm was identified as half the diameter of the corresponding nanotube, which shows good agreement to the Schottky interface layer growth model. The TiO2 nanotube film was amorphous and the Ti substrate was highly crystallized with many dislocation walls.

Fabrication of CdTe/ZnS core/shell quantum dots sensitized TiO2 nanotube films for photocathodic protection of stainless steel

A highly ordered TiO2 nanotube array film on a titanium substrate was fabricated by an anodic oxidation method. Then CdTe/ZnS core/shell quantum dots were successfully prepared on the film by pulsed potential electrodeposition and chemical bath deposition in succession. The results indicated that the CdTe/ZnS quantum dots sensitized TiO2 composite film displayed a significant increase in photocurrent compared with a pure TiO2 nanotube film, and its photoabsorption was extended to the visible region. Under white light illumination, the composite film as a sustainable photoanode had better photoelectric conversion performance and could provide striking photocathodic protection for 403 stainless steel.

Photoelectrochemical water splitting on chromium-doped titanium dioxide nanotube photoanodes prepared by single-step anodizing

Cr-doped TiO2 nanotubes (Cr–TiO2NTs) with different amounts of chromium were obtained directly by the electrochemical anodic oxidation of titanium foils in a single-step process using potassium chromate as the chromium source. The effects of chromium amount in anodizing solution on the morphologies, structure, photoabsorption and photoelectrochemical water splitting of the TiO2 nanotube array film were investigated. Diffuse reflectance spectra showed an increase in the visible absorption relative to undoped TiO2NTs. The photoelectrochemical performance was examined under visible irradiation in 1M NaOH electrolyte. Photo-electrochemical characterization shows that chromium doping efficiently enhances the photo-catalytic water splitting performance of Cr-doped TiO2 nanotube samples. The sample (Cr–TiO2NTs-1) exhibited better photo-catalytic activity than the undoped TiO2NTs and Cr–TiO2NTs fabricated using other chromium concentrations. This can be attributed to the effective separation of photogenerated electron–hole upon the substitutional introduction of appropriate Cr amount in to the TiO2 nanotube structure.

Highly crystalline Titania nanotube arrays realized by hydrothermal vapor route and used as front-illuminated photoanode in dye sensitized solar cells

Highly crystalline TiO2 nanotube arrays (TNTAs) film is easily realized by treating its amorphous film under the hydrothermal vapor (HV) environment. The freestanding TNTAs film can be lift-off from the Ti foil, which serves as photoanode based on FTO substrate after the transplanting procedure. Compared to the thermal annealing (TA) treated TNTAs photoanode, the HV treated photoanode possesses some excellent properties, such as long optical path, fast charge transporting and easy adsorption of the sensitizer molecules, which can result in high short current density. Notably, the N719 dye sensitized HV treated photoanode prepared under 180 °C shows relatively high photovoltaic response in the visible range due to its hierarchical structure, which gives an impressive performance conversion efficiency of 8.11% without any surface modification. And the present work sheds light on the application of the mild crystalline strategy for performance improvement of the DSSCs based on TiO2 nanotube arrays photoanode.

Pyrite nanotube array films as an efficient photocatalyst for degradation of methylene blue and phenol

The nanotube topography would improve the optical property of the pyrite crystals. The photodegradation of MB and phenol suggested that the pyrite nanotubes array films would be potential to be used in the treatment of pollutants.

Fabrication of a coral/double-wall TiO2 nanotube array film electrode with higher photoelectrocatalytic activity under sunlight

A unique coral/DWNT TiO2 film electrode with a mixed-phase was prepared, and its optical absorption can extend to the visible region.

Nanoscale Optimization and Statistical Modeling of Photoelectrochemical Water Splitting Efficiency of N-Doped TiO2 Nanotubes

Highly ordered nitrogen-doped titanium dioxide (N-doped TiO2) nanotube array films with enhanced photo-electrochemical water splitting efficiency (PCE) for hydrogen generation were fabricated by electrochemical anodization, followed by annealing in a nitrogen atmosphere. Morphology, structure and composition of the N-doped TiO2 nanotube array films were investigated by FE-SEM, XPS, UV–Vis and XRD. The effect of annealing temperature, heating rate and annealing time on the morphology, structure, and photo-electrochemical property of the N-doped TiO2 nanotube array films were investigated. A design of experiments method was applied in order to minimize the number of experiments and obtain a statistical model for this system. From the modelling results, optimum values for the influential factors were obtained in order to achieve the maximum PCE. The optimized experiment resulted in 7.42 % PCE which was within 95 % confidence interval of the predicted value by the model.

Ni(OH)2/NiO/Ni composite nanotube arrays for high-performance supercapacitors

Transition metal oxide nanostructures are one of current investigation focuses for energy storage applications. We herein report a novel template-free electrochemical approach to fabricate Ni(OH)2/NiO/Ni composite nanotube array films on the nickel substrate. The inner diameter of the composite nanotubes can be effectively tuned by tailoring the concentration of Cu2+ in the precursor solutions. The as-constructed composite nanotube array film electrode, which is fabricated by the electrochemical approach using the 0.1 M Cu2+ containing precursor solution, delivers the specific capacitance of 1070 F g−1 at the current density of 15 A g−1 after 10,000 charge–discharge cycles. The specific capacitance of the cycled electrode at 150 A g−1 is as much as 79.3% of that at 15 A g−1, demonstrating its excellent rate capability. The cycled electrode presents a high specific energy density of 31.4 Wh kg−1 at a larger power density of 11.1 kW kg−1. The excellent pseudocapacitive performance of the Ni(OH)2/NiO/Ni composite nanotube array electrodes can be attributed to their unique structure characteristics.

Arrays of ZnxCd1−xSe/TiO2 nanotubes: fabrication by ion-exchange and photovoltaic applications

Free-standing TiO2 nanotube (NT) array films were prepared by anodization approach as support materials for quantum dots sensitized solar cells (QDSSCs). The ZnxCd1−xSe quantum dots (QDs) layers with tunable compositions have been deposited on the TiO2 NT array film via a simple ion-exchange approach. The optical absorptions of the ZnxCd1−xSe/TiO2 NT can be controllably tuned to cover almost the entire visible region by changing the atomic ratio of Zn to Cd. In the fabricated QDSSCs based on these ZnxCd1−xSe/TiO2 NT array photoanodes, the photovoltaic performance gradually improved as the composition changes from Zn-rich to Cd-rich of ZnxCd1−xSe QDs layers on TiO2 NT arrays. In contrast with other ZnxCd1−xSe/TiO2 NT solar cells, the Zn0.13Cd0.87Se/TiO2 NT solar cell yielded a highest power conversion efficiency of 2.15 %, indicating the most effective band alignment is obtained with Cd-rich ZnxCd1−xSe QDs layers. It can be anticipated that tunable energy band of QDs controlled by the ratio of atoms can contribute to higher efficiency QDSSCs.