Titania Nanotube Films Research Articles

Anodic Oxide Films Grown in Dehydrated Phosphate/Glycerol Electrolytes at High Temperatures.

Traditional anodization was generally conducted in aqueous or water-containing solutions at room temperature or even lower temperatures. The two best known examples of the application of traditional anodization in the fabrication of nanostructured oxides are porous anodic alumina and titania nanotube films. In 1998, Melody et al. first observed that anodic oxide films on some valve metals such as tantalum can continue to grow at low anodization voltages in phosphate/glycerol solutions containing less than 0.1% water at elevated temperatures (>150 °C) in a non-thickness-limited (NTL) manner. Clearly, this type of anodization at high temperatures is conceptually different from traditional anodization. This Perspective provides a relatively thorough review of this topic. Particular attention is given to the main features for the NTL growth of anodic oxide films and the mechanism behind this behavior. The anodization behaviors for the NTL growth and typical microscopic morphologies of the resultant films on various metals are discussed. The main applications of the attained anodic films with different nanostructures and anodization in other dehydrated electrolyte systems such as the molten orthophosphoric acid are also involved. Finally, we highlight some unresolved issues for this type of anodization at high temperatures and the potential future directions of this field.

Inactivation of SARS-CoV-2 and Other Human Coronaviruses Aided by Photocatalytic One-Dimensional Titania Nanotube Films as a Self-Disinfecting Surface.

SARS-CoV-2 and its variants that continue to emerge have necessitated the implementation of effective disinfection strategies. Developing self-disinfecting surfaces can be a potential route for reducing fomite transmissions of infectious viruses. We show the effectiveness of TiO2 nanotubes (T_NTs) on photocatalytic inactivation of human coronavirus, HCoV-OC43, as well as SARS-CoV-2. T_NTs were synthesized by the anodization process, and their impact on photocatalytic inactivation was evaluated by the detection of residual viral genome copies (quantitative real-time quantitative reverse transcription polymerase chain reaction) and infectious viruses (infectivity assays). T_NTs with different structural morphologies, wall thicknesses, diameters, and lengths were prepared by varying the time and applied potential during anodization. The virucidal efficacy was tested under different UV-C exposure times to understand the photocatalytic reaction's kinetics. We showed that the T_NT presence boosts the inactivation process and demonstrated complete inactivation of SARS-CoV-2 as well as HCoV-OC43 within 30 s of UV-C illumination. The remarkable cyclic stability of these T_NTs was revealed through a reusability experiment. The spectroscopic and electrochemical analyses have been reported to correlate and quantify the effects of the physical features of T_NT with photoactivity. We anticipate that the proposed one-dimensional T_NT will be applicable for studying the surface inactivation of other coronaviruses including SARS-CoV-2 variants due to similarities in their genomic structure.

Photocatalytic degradation of azo dyes in aqueous solution by using highly ordered titania nanotube films

Photocatalytic degradation of azo dyes in aqueous solution by using highly ordered titania nanotube films

Developing an efficient approach for preparation of high-performance visible-light assisted ethanol electro-oxidation materials based on Pd, Pt and Pd–Pt nanoparticles supported on iron doped titania nanotube films

Electrochemical anodization and electrodeposition have been used to synthesize highly ordered iron doped titania nanotubes (FeT) loaded with palladium (Pd), platinum (Pt) and Pt–Pd nanoparticles, followed by characterization by FE-SEM and XRD analyses. Higher photoelectrocatalytical activity is shown by the electrodeposited nanotube samples compared with undeposited-FeT sample under identical conditions, according to the photoelectrochemical experiments. The electrochemical behavior of the synthetic electrodes was studied by investigation of ethanol electrocatalytic oxidation in an alkaline medium in the absence or presence of light irradiation. The results of electrochemical studies indicated that Pt–Pd/FeT/Ti was more catalytically active than Pt/FeT/Ti and Pd/FeT/Ti in ethanol electrooxidation in alkaline media both in the dark and under light irradiation. Furthermore, the catalytic activities of nanotube based catalysts were considerably enhanced under light irradiation due to the interaction of electrocatalysis and photocatalysis. The peak current density of ethanol oxidation using sample FeT2 under light irradiation is about 1.45 times the corresponding value in the dark.

The Bioactivity and Photocatalytic Properties of Titania Nanotube Coatings Produced with the Use of the Low-Potential Anodization of Ti6Al4V Alloy Surface.

Titania nanotube (TNT) coatings were produced using low-potential anodic oxidation of Ti6Al4V substrates in the potential range 3–20 V. They were analysed by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The wettability was estimated by measuring the contact angle when applying water droplets. The bioactivity of the TNT coatings was established on the basis of the biointegration assay (L929 murine fibroblasts adhesion and proliferation) and antibacterial tests against Staphylococcus aureus (ATCC 29213). The photocatalytic efficiency of the TNT films was studied by the degradation of methylene blue under UV irradiation. Among the studied coatings, the TiO2 nanotubes obtained with the use of 5 V potential (TNT5) were found to be the most appropriate for medical applications. The TNT5 sample possessed antibiofilm properties without enriching it by additional antimicrobial agent. Furthermore, it was characterized by optimal biocompatibility, performing better than pure Ti6Al4V alloy. Moreover, the same sample was the most photocatalytically active and exhibited the potential for the sterilization of implants with the use of UV light and for other environmental applications.

Effect of hydrogen doping on the loading of titania nanotube films with copper selenide species via alternating current deposition

Fabrication of TiO2 nanotube (TiNT) films nicely decorated with lower band gap semiconducting nanoparticles remains a challenging issue for photocatalytic and solar cell applications active under visible light irradiation. In this study, TiNT films were decorated with copper selenide species via alternating current deposition method. For the first time, to achieve uniform loading of copper selenide species inside the TiNT film, as-grown and calcined TiNT films before depositions were subjected to hydrogen doping in various solutions under DC and AC pretreatments as well as by treating TiNT in H2 atmosphere. Different pretreatments resulted in different architectures of Cu x Se-in-TiNT formed by subsequent AC deposition from the acidic Cu(II)-H2SeO3 solution allowing predictable to encase Cu2Se3, Cu2Se, CuSe, or Cu2−x Se species in nm-scaled size. Field-emission scanning electron microscopy with EDS and X-ray mapping, low-angle X-ray diffraction, and diffuse reflectance spectroscopy were applied to characterize the morphology, composition, uniformity of loading, and optical properties of the fabricated heterostructures. Except light absorption, characteristic for anatase TiO2, the additional absorption edge in the visible region is formed in the TiNT films decorated with copper selenide.

WO3 nanoparticles anchored on titania nanotube films as efficient photoanodes

Tungsten trioxide nanoparticles anchored on titania nanotube arrays (WTiNT) fabricated by a chemical bath deposition technique in combination with a pyrolysis process. The resulting films were characterised by SEM, EDX and XRD. Results showed that the nanomaterials film have the same ordered structure as titania nanotubes. Diffuse reflectance spectra showed an increase in the visible absorption relative to bare titania nanotubes. The tungsten trioxide was successfully anchored on the titania nanotubes, which enhanced the photocatalytic activity of the WTiNT, as indicated by the efficient removal of Rhodamine B and the production of hydrogen. The resultant hybrid nanotubes array showed better photoelectrochemical activity than the bare titania nanotubes (TiNT) under Xe illumination. These WTiNT nanostructured films are promising candidates for practical photochemical reactors that drive useful reactions, such as water reduction (H2 production) and oxidation of pollutants.

Fabrication and Characterization of Dye-sensitized Solar Cells based on Anodic Titanium Oxide Nanotube Arrays Sensitized with Heteroleptic Ruthenium Dyes

Anodic self-organized titania nanotube (TNT) arrays have a great potential as efficient electron-transport materials for dye-sensitized solar cells (DSSC). Herewith we report the photovoltaic and kinetic investigations for a series of heteroleptic ruthenium complexes (RD16-RD18) sensitized on TNT films for DSSC applications. We found that the RD16 device had an enhanced short-circuit current density (<TEX>$J_{SC}/mAcm^{-2}=15.0$</TEX>) and an efficiency of power conversion (<TEX>${\eta}=7.2%$</TEX>) greater than that of a N719 device (<TEX>${\eta}=7.1%$</TEX>) due to the increasing light-harvesting and the broadened spectral features with thiophene-based ligands. However, the device made of RD17 (adding one more hexyl chain) showed smaller <TEX>$J_{SC}(14.1mAcm^{-2})$</TEX> and poorer <TEX>${\eta}(6.8%)$</TEX> compare to those of RD16 due to smaller amount of dye-loading and less efficient electron injection for the RD17 device than for the RD16 device. For the RD18 dye (adding one more thiophene unit and one more hexyl chain), we found that the device showed even lower <TEX>$J_{SC}(13.2mAcm^{-2}) $</TEX> that led to a poorest device performance (<TEX>${\eta}=6.2%$</TEX>) for the RD18 device. These results are against to those obtained from the same dyes sensitized on <TEX>$TiO_2$</TEX> nanoparticle films and they can be rationalized according to the electron transport kinetics measured using the methods of charge extraction and transient photovoltage decays.

Crystallization peculiarities of titania nanotube films under hydrothermal and solvothermal conditions

We report on the peculiarities of crystallization of amorphous TiO2 nanotube (TNT) films produced by Ti anodization in ethylene glycol solution containing some NH4F and H2O. We note that in contrast to the traditional thermal crystallization, carried out usually at 400 °C and higher temperatures, the hydrothermal treatment in water, ethanol, water–ethanol or their vapor environments even at 100 °C results in the formation of crystalline hydrous anatase, O–Ti–OH. The content of chemically attached water molecules depend on the composition of solution applied. Besides, the autoclaving of TNT films in the solutions containing strong reducing agent, such as hydrazine hydrate, leads to the formation of brookite. These findings were confirmed by Raman spectroscopy, thermo gravimetrical, and X-ray diffraction results.

Phase transformation and thermal structure stability of titania nanotube films with different morphologies

Titania nanotube films composed of close-packed and loose-packed titania nanotube arrays were produced by electrochemical anodization of titanium. Phase transformation and thermal structure stability of the titania nanotube films with different morphologies were studied after they were annealed at different temperatures. Results show that the close-packed titania nanotube films started phase transformations from anatase to rutile at a relatively higher temperature, and exhibited higher thermal structure stability than the loose-packed titania nanotube films. The difference in the phase transformation and thermal structure stability of the close-packed and loose-packed titania nanotube films was analyzed from the viewpoints of specific surface area. The results in this paper provided understanding of the morphology effects on phase transformation and thermal structure stability of titania nanotube films.

Dye-sensitized solar cells using branched titania nanotube films

Photovoltaic characteristics of dye-sensitized solar cells fabricated from branched titania nanotube arrays are compared with those obtained from unbranched ones. Branched titania nanotubes result in increased efficiency and short circuit current density without any discernible increases in dark current, than in devices with purely unbranched tubes. Adsorption isotherms show that increased inter-tube porosity exposes the outer surfaces of the branched tubes, providing increased access and area for dye adsorption. Our findings indicate that branched titania nanotubes could be attractive for use in many applications.

Morphology Evolution during Annealing and Electrical Conductivity of Titania Nanotube Films

Titania nanotube films were produced by anodization of titanium foil. The titania nanotube films were annealed at different temperatures. Morphology evolution, phase transformation and electrical conductivity of the titania nanotubes were studied. Results showed that the nanotube walls became rough, porous and even collapsed after annealed at 400, 500 and 600 °C respectively. Titania anatase phase formed after annealed at 400 °C; the amount of anatase phase increased as the annealing temperature increased. The conductivity of the nanotube film annealed at 400 °C was improved greatly compared with the conductivity of the as-anodized nanotube film. However, the conductivity of the nanotube films annealed at higher temperatures decreased. The effect of the morphology on the electronic conductivity of the titania nanotube films was discussed.

Growth of TiO 2-based nanotubes on Ti–6Al–4V alloy

The possibility of tailoring titania nanotube films on Ti–6Al–4V alloy is investigated using electrolytes based on NH 4H 2PO 4 with the addition of different concentrations of NH 4F. Several morphologies from high aspect ratio nanotubes to barrier layers are achieved by the control of the electrolyte composition, regarding its pH and fluoride concentrations. The morphology and composition of the anodic layers were evaluated by scanning and transmission electron microscopy, Rutherford backscattering spectroscopy (RBS) and Wavelength dispersive X-ray fluorescence spectroscopy. The formation efficiency and the fluoride ions content in the nanotubes depend on the F concentration in the electrolyte. The higher concentration of fluoride ions in the electrolyte promotes an increase of the F incorporated in the nanotubes, about 12 at.% but, reduces the nanotube formation efficiency. However, no significant presence of phosphorus was detected into the films by means of the above-mentioned analytical techniques.

Synthesis of Periodically Structured Titania Nanotube Films and Their Potential for Photonic Applications

Periodically structured titania nanotubes are designed and fabricated by current-pulse anodization to create 3D photonic crystal films operating at visible wavelengths, for photon manipulation. In contrast to previous studies, this method combines all the advantages of large-area, low-cost, transparent, flexible, and complete-bandgap materials.

Fabrication of long TiO2 nanotube arrays in a short time using a hybrid anodic method for highly efficient dye-sensitized solar cells

We report a simple hybrid anodic method, with initial potentiostatic anodization followed by galvanostatic anodization, to grow much longer titania nanotube (TNT) arrays in a much shorter anodization period (t). The length of the TNT arrays (L) depends linearly on t and is controlled by the electric current; the growth rates are 5.3, 10.7 and 20.3 μm h−1 for current densities 3.7, 5.6 and 7.5 mA cm−2, respectively. The produced TNT films of L = 15–57 μm sensitized with N719 dye were fabricated into devices for photovoltaic characterization. The NT-DSSC devices show systematically improved cell performance depending on L, reflecting the excellent intrinsic light-scattering property of the NT-DSSC devices to harvest increased sunlight with long TNT arrays. The great effective surface area inside TNT arrays has been shown to significantly increase the dye loading, which might help to enhance the cell performance of the device with co-sensitizing of different dyes for improved efficiency of light harvesting in the future. The best performance of the NT-DSSC device was achieved at L ∼ 30 μm with a spacer of similar thickness, giving JSC = 14.63 mA cm−2, VOC = 0.741 V, FF = 0.70, and η = 7.6%, which is unprecedented for a back-illumination DSSC.

Visible-induced photocatalytic reactivity of polymer–sensitized titania nanotube films

In this study, polythiophene–TiO2 nanotube films (PTh/TNT) were successfully prepared by a two-step electrochemical process of anodization and electropolymerization, in which a highly ordered TiO2 nanotube (TNT) film was anodized at a low-voltage with post calcination first and then the prepared TNT film was deposited with a polythiophene layer by electropolymerization in the BFEE electrolyte. The morphology and structures of PTh/TNT composites were examined by FESEM, EDX, XRD and XPS methods. XPS spectra of PTh/TNT composites indicate the strong interaction between S sites of polymer backbone and TiO2 nanotubes, in which electron transfer from polythiophene to titania takes place. UV–vis DRS analysis shows that these composites have a strong photoresponse in the visible region at 500nm. The prepared PTh/TNT films revealed significant activity for 2,3-dichlorophenols (2,3-DCP) degradation under visible light irradiation and also sunlight irradiation, in which the PTh3/TNT film achieved the best performance. On the other hand, this study also confirmed that the side-chains of polythiophene could influence its photocatalytic activity significantly in an order from high to low as poly3-methylthiophene≈polythiophene>polythiophenecarboxylic acid>poly3-hexylthiophene. The results may provide useful information to further develop some effective polymer-semiconductor catalysts for pollutant degradation under sunlight irradiation for water and wastewater treatment.

Preparation of Titania Nanotube Thin Films by Langmuir–Blodgett Technique

Abstract Preparation of thin titania nanotube films has been attempted using Langmuir–Blodgett (LB) technique. The resulting LB monolayer exhibited closely packed arrangement of the nanotube bundles in a monoparticulate layer on the solid substrate. Also, domain structure due to strong lateral interaction among the bundles lying side-by-side was observed even for the LB films deposited at a low surface pressure. Moreover, multilayer deposition of the monoparticulate films provided precise control of the film thickness.

Low-reflective and super-hydrophilic properties of titanate or titania nanotube thin films via layer-by-layer assembly

Transparent nanotube films of hydrogen titanate were fabricated by a layer-by-layer self assembly. Titania (anatase) nanotube films were also obtained by annealing titanate nanotube films at 673 K in air. Both types of film had an optically low reflectivity and a high transparency compared to polycrystalline anatase thin films. The low reflectivity and the high transparent properties of the nanotube films are due to their nanostructural porosity, i.e. the inner cavities of the nanotubes and the void spaces between nanotubes. Thin films of titanate and titania nanotubes became super-hydrophilic with a water contact angle of zero degrees under UV illumination, but the water contact angle of polycrystalline anatase thin films did not decrease below five degrees. The highly hydrophilic surfaces of the nanotubes are attributed to their nanostructural morphologies.