Titanate Nanotube Films Research Articles

Functional interfaces of titanate nanotubes with controlled orientation/aggregation

Titanate nanotubes are tubular nano materials for variety of applications. However, because of their large structural aspect ratio, it has been difficult to control aggregation and orientation states for further functionalization. In this review article, summary of our recent achievement on the preparation and functionalization of titanate nanotubes with controlled aggregation or orientations. Titanate nanotube films in which nanotubes oriented to perpendicular to the substrate show adhesive superhydrophobility. On the other hand, hierarchically porous titanate nanotube monoliths are prepared under hydrothermal treatment of condensed titania emulsion which show a large capacity and fast ion exchange capabilities. These achievements clearly indicate that the titanate nanotubes with controlled aggregation/orientation exhibit great potentiality as highly functional materials.

Hierarchically macro–mesoporous TiO2 film via self-assembled strategy for enhanced efficiency of dye sensitized solar cells

The hierarchically porous structure of TiO2 film plays an important role on improved photoelectric conversion efficiency in dye-sensitized solar cells (DSSCs). It is highly required to develop a facile strategy to prepare the hierarchical porous photoelectrode. In this study, a novel hierarchically macro–mesoporous TiO2 film as photoelectrode of DSSCs is fabricated by a self-assembled process of TiO2 nanoparticles via TiF4 hydrolysis. The hydrolysis of TiF4 is accompanied with self-assembled process of TiO2 nanoparticles on the surface of electrophoretic-deposited titanate nanotube film which provides effective active sites for the deposition of TiO2 nanoparticles owing to a large amount of hydroxyl groups, resulting in the formation of hierarchically porous structures. The hierarchically porous TiO2 film is mainly composed of mesopores with a size of 2–50nm and macropores with a wide range of 0.5–5μm, which contribute to an obviously higher conversion performance (6.70%) than nonporous P25-TiO2 film (4.01%). The main reasons for enhanced conversion efficiency of hierarchically porous TiO2 film can be attributed to adsorption of more dye molecules, rapid diffusion and efficient transport of electrolyte, and longer electron lifetime. This work may provide new insights into preparing porous structure of TiO2 films in DSSCs for modification of photoelectric conversion efficiency.

Enhanced protein adsorption and cellular adhesion using transparent titanate nanotube thin films made by a simple and inexpensive room temperature process: Application to optical biochips

A new type of titanate nanotube (TNT) coating is investigated for exploitation in biosensor applications. The TNT layers were prepared from stable but additive-free sols without applying any binding compounds. The simple, fast spin-coating process was carried out at room temperature, and resulted in well-formed films around 10nm thick. The films are highly transparent as expected from their nanostructure and may, therefore, be useful as coatings for surface-sensitive optical biosensors to enhance the specific surface area. In addition, these novel coatings could be applied to medical implant surfaces to control cellular adhesion. Their morphology and structure was characterized by spectroscopic ellipsometry (SE) and atomic force microscopy (AFM), and their chemical state by X-ray photoelectron spectroscopy (XPS). For quantitative surface adhesion studies, the films were prepared on optical waveguides. The coated waveguides were shown to still guide light; thus, their sensing capability remains. Protein adsorption and cell adhesion studies on the titanate nanotube films and on smooth control surfaces revealed that the nanostructured titanate enhanced the adsorption of albumin; furthermore, the coatings considerably enhanced the adhesion of living mammalian cells (human embryonic kidney and preosteoblast).

Switchable and reversible water adhesion on superhydrophobic titanate nanostructures fabricated on soft substrates: photopatternable wettability and thermomodulatable adhesivity

A titanate nanotube (TNT) film is demonstrated to provide a switchable and adhesive hydrophobic surface. The surface adhesivity is reversibly switched from adhesive to repellent by mild heating and spontaneous rehydration. A persistent superhydrophobic/superhydrophilic pattern can be fabricated on the TNT films coated on soft substrates.

In-situ synthesis, local structure, photoelectrochemical property of Fe-intercalated titanate nanotube

The titanate nanotube (TNT) and iron intercalated titanate nanotube (Fe-TNT) were synthesized in-situ single step hydrothermal method at 150 °C for 72 h. The electronic and local coordination structures of iron species intercalated in the interlayer space of ion exchangeable titanate nanotubes were investigated by X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS). The iron intercalated into the nanotube was formed as hydrated iron complex of [FexII(OH)2x−1(OH2)]+ and the iron complex played a harmful role in the photocatalytic hydrogen production from methanol–water mixed solution and the photocatalytic decomposition of acid orange 7 (AO7) under UV light irradiation. A higher photocurrent generation, however, was also observed from the Fe-intercalated titanate nanotube film from 0.1 M NaOH solution under UV light irradiation.

Facile Preparation and Photoinduced Superhydrophilicity of Highly Ordered Sodium-Free Titanate Nanotube Films by Electrophoretic Deposition

Highly ordered sodium-free titanate nanotube films were one-step prepared on F-doped SnO2-coated (FTO) glass via an electrophoretic deposition method by using sodium titanate nanotubes as the precursor. It was found that the self-assembled formation of highly ordered sodium titanate nanotube films was accompanied with the effective removal of sodium ions in the nanotubes during the electrophoretic deposition process, resulting in the final formation of protonated titanate nanotube film. With increasing calcination temperature, the amorphous TiO2phase is formed by a dehydration process of the protonated titanate nanotubes at 300°C and further transforms into anatase TiO2when the calcination temperature is higher than 400°C. Compared with the as-prepared titanate nanotube film, the calcined titanate nanotube film (300–600°C) exhibits attractive photoinduced superhydrophilicity under UV-light irradiation. In particular, 500°C-calcined films show the best photoinduced superhydrophilicity, probably due to synergetic effects of enhanced crystallization, surface roughness, and ordered structures of the films.

Preparation of Protonated Titanate Nanotube Films with an Extremely Large Wetting Contrast

ABSTRACTA facile anodic electrophoretic deposition (EPD) process has been developed to prepare thin uniform films consisting of titanate nanotubes (TNTs) that were synthesized by a hydrothermal approach. Such an EPD process offers easy control in the film thickness and the adhesion to the substrate was found to be strong. The chemical composition and structure of the products have been characterized by HRTEM, FESEM, XRD and TG/DTA. It was found that the functionalization of TNTs plays a key role on the electrolyte stability and the successful formation of a uniform TNT film with good adhesion. The as-prepared TNT films show exceptional superhydrophilic behavior with ultra-fast spreading, while it converts to superhydrophobicity yet with high adhesion after 1H,1H,2H,2H-perfluorooctyl-triethoxysilane modification. This study provides an interesting method to prepare films with extremely high wettability contrast that are useful for producing different kinds of functional materials.

The Preparation of Oriented TiO2 Nanotube Films by Electrophoretic Deposition Method without Hard Template and Enhanced Photocatalytic Activity

Highly oriented titanate nanotube (TNT) film was successfully synthesized by a simple electrophoretic deposition (EPD) method without any hard templates and surfactants. This oriented films adequately utilized the excellent properties of ID nanomaterials such as single crystal semiconductor architectures, large surface area, and superior charge transport, which lead to higher photocatalytic activity. We believe that this versatile method can be extent to fabricate other ordered ID nanomaterials films.

Electrophoretic deposition of titanate nanotube films with extremely large wetting contrast

A facile electrophoretic deposition (EPD) process has been developed to prepare thin films consisting of titanate nanotubes (TNTs) that were synthesized by a hydrothermal approach. Such an EPD process offers easy control in the film thickness and the adhesion to the substrate was found to be strong. The chemical composition and structure of the products have been characterized by XRD, HRTEM, and FESEM. It was found that the functionalization of TNTs plays a key role on the electrolyte stability and the formation of a uniform TNT film with good adhesion. The as-prepared TNT films show exceptional superhydrophilic behavior with ultra-fast spreading, while it converts to superhydrophobicity yet with strong adhesion after 1H,1H,2H,2H-perfluorooctyl-triethoxysilane modification. This study provides an interesting method to prepare films with extremely high wettability contrast that are useful for producing different types of functional materials.

Dye-sensitized solar cells based on ordered titanate nanotube films fabricated by electrophoretic deposition method

Dye-sensitized solar cells (DSSCs) are fabricated based on ordered titanate nanotube (TNT) films obtained by electrophoretic deposition (EPD) method. Calcination temperatures show a great influence on the performance of TNT solar cells. At 300 °C, the cells exhibit very low photo-electric conversion efficiency. At 400 °C, the efficiency obviously increases. At 600 °C, the cells show the highest efficiency, which is higher than the efficiency of the cells made from commercial-grade Degussa P25 TiO 2 nanoparticles (P25).

Effects of calcination temperature on microstructures and photocatalytic activity oftitanate nanotube films prepared by an EPD method

Titanate nanotube films are fabricated on F-dopedSnO2-coated glass substrates via an electrophoretic deposition method using hydrothermallyprepared titanate nanotubes as precursors. The effects of calcination temperature on themicrostructures and photoactivity of as-prepared titanate nanotube films areinvestigated and discussed. The results indicate that the intercalated sodium ions(Na+) in the as-prepared titanate nanotubes are easily removed during the electrophoreticdeposition. The phase transformation of titanate to anatase and diffusion ofNa+ ions from glass substrates into films occur at400 °C. With increasing calcination temperature, the crystallization ofanatase enhances and sodium content in the films increases. At500 °C, the tubular structure still holds and the films show the highest photocatalytic activityprobably due to their good crystallization, large specific surface areas and tubularstructures.

Formation of Sodium Titanate Nanotube Films by Hydrothermal Transcription

A titanium metal plate and a substrate were placed adjacently and treated hydrothermally at 160 °C in NaOH aqueous solution. A sodium titanate nanotube film reflecting the form of the titanium plate and the composition of the substrate was formed on substrates such as Co−Cr alloy and SUS316L.

Electrochemical study of methylene blue/titanate nanotubes nanocomposite and its layer-by-layer assembly multilayer films

Titanate nanotubes (TNT) were proven to be efficient support for the immobilization of methylene blue (MB). UV–vis absorption and Fourier transform infrared spectra showed that the effect of MB absorbed on TNT was better than nanocrystalline anatase TiO2 (TNP). The quantity of MB absorbed onto TNT was found to be greater than that of TNP and the electrode modified with the MB–TNT film was more stable due to the strong interaction between TNT and MB as well. The absorption of MB on TNT was impacted by the pH value of the reaction solution for the change of surface charge. Electrochemical oxidation of dopamine (DA) at different electrodes was studied. The result showed that the MB–TNT composite film exhibited excellent catalytic activities to DA compared to those of pure TNT, which is a result of the great promotion of the electron-transfer rate between DA and the electrode surface by the MB–TNT film. Furthermore, the layer-by-layer self-assembly behavior of the electrochemically functional MB–TNT nanocomposite was also discussed after obtaining the stable colloid suspension of MB–TNT. The excellent electrochemical ability and the easy fabrication of layered nanocomposite make the MB–TNT nanocomposite very promising in electrochemistry study and new nanotube-based devices.

Growth and morphological study of zinc oxide nanoneedles grown on the annealed titanate nanotubes using hydrothermal method

Hydrothermal growth of ZnO on the annealed titanate nanotube films results in the oriented hexagonal-needlelike structures. The size, shape, density, and alignment of ZnO film are significantly affected by annealing temperature and orientation of the beneath titanate layer. It is believed that oxygen and hydrogen vacancies, generated due to dehydration of interlayered OH groups while annealing of the titanate, are responsible for the changes in the morphology of the ZnO. Microscopic observations clearly resolved nanoneedles with the base diameter of ∼150nm and length of ∼5μm with lattice spacing of 0.52nm, indicating single crystalline ZnO and grown along the (0001) direction. A growth model is presented based on the layer-by-layer growth (three-step growth) as a function of growth time (2–6h). Thicknesses of these three steps were found increasing with growth time. The second step (II) of growth exhibits the same feature as that of the first step (I), i.e., bounded with six crystallographic, lower surface energy facets of {011¯0} surfaces and capped with {011¯1} planes, but with higher step thickness and sharper tip. Finally, the obtained ZnO nanoneedles exhibit {011¯1} facets, the third step (III), with sharp tip in the [0001] direction.

Hydrothermal growth of ZnO on annealed electrodeposited titanate film: Influence of zinc nitrate and methenamine

Hydrothermal growth of hexagonal ZnO nanorods on the annealed titanate nanotube films is reported as a function of molar ratio of Zn(NO 3) 2 and methenamine (1:1–1:4). The molar ratio of 1:4 results in a dense and thinner rod in comparison with other molar ratios. Corn-like structures of the rods are believed to be due to the higher amine concentration. Raman peaks at 437 and 331 cm −1 are assigned to E 2 and E 2H–E 2L modes. Near band gap edge and green photoluminescence emission indicates the structural and oxygen vacancy. O 1s peak is found built-up of sub-peaks at 530.62, 531.8 and 532.84 eV corresponding to O 2− on normal wurtzite structure and OH and oxygen vacancies of ZnO, respectively.

Synthesis of TiO2-Based Nanotube on Ti Substrate by Hydrothermal Treatment

TiO2-based titanate nanotube film was directly synthesized by hydrothermal treatment of Ti substrate in NaOH solution. The prepared high aspect ratio nanotubes have diameter of 10 nm and pore size of 5 nm with length of several microns. The nanotubes show the same structure and component characteristics as the nanotubes prepared through hydrothermal treatment of TiO2. Other nanostructured titanate as oriented nanofiber film and translucent film were also prepared by adjusting the hydrothermal conditions. The formation mechanism of nanostructured titanate was discussed.

Effect of annealing temperature on structural and bonded states of titanate nanotube films

A conversion from commercial titania (TiO2) nanoparticles to nanotubes was achieved by a hydrothermal method. The titanate nanotube (titanate) film was then deposited on a Si (001) substrate using an electrophoretic deposition (EPD) technique. The post hydrothermal treatment was then carried out by annealing the films at 300–1000°C for 30min in the static air. A major amount of intercalated sodium (Na) in as-synthesized titanate nanotubes was removed during the electrodeposition process. The collapse of the tubular structure can be seen clearly when annealed above 500°C. X-ray diffraction data indicate a significant increase in the anatase phase peak intensity with annealing temperature. O 1s peak is found to be built up of subpeaks of H2O, −OH, and Ti–O. Annealing results in an increase of the Ti–O peak intensity while other peaks disappear. Clear changes in the O 1s peak positions, symmetry, and shift towards lower energy (0.8eV) are evident with the increasing annealing temperature. The doublet spectral lines of Ti 2p were found separated by an energy of 5.6eV. Photoelectron spectroscopy show that during the annealing treatment, the chemical bonds such as H2O and −OH are removed from the titanate films as well as converting the bonded states of titanate to that of titania.

Super-hydrophilic and transparent thin films of TiO2 nanotube arrays by a hydrothermal reaction

Titanate nanotube arrays were grown on sapphire substrates by sputtering deposition of titanium films and a subsequent hydrothermal treatment in an aqueous NaOH solution. Post annealing in air transformed the crystals from a titanate structure to an anatase structure. Titanate and anatase nanotube arrays were optically transparent and adhered well to the substrates. Both titanate and anatase nanotube films exhibited high-hydrophilic states with water contact angles below 5° even after dark storage for more than three months due to their surface nanostructures. UV illumination caused super-hydrophilic states with 0° water contact angles, i.e. band-gap excitations decreased the initial water contact angles in dark conditions (∼3.5°) to 0°. The hydrophilicizing rate of the anatase nanotubes was faster than that of the titanate nanotubes because the anatase nanotubes had a higher crystallinity and more absorbed photons.

Hydrothermal synthesis of titanate nanotubes followed by electrodeposition process

Titanate nanotubes were synthesized by hydrothermal process using commercial titania nanoparticles. The experiments were carried out as a function of reaction time, temperature, and NaOH concentration. Furthermore, the titanate nanotube film was fabricated on the Si substrate using electrodeposition method with 60 V and at room temperature. The specimens were investigated by using various techniques such as field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman Spectroscopy, and Xray photoelectron spectroscopy (XPS). The formation of sodium titanate nanotubes was affected strongly by the variation in all parameters. The best conditions for the titanate nanotubes were found to be a reaction temperature of 150°C, 10 M NaOH concentration, and reaction time of 48 hr. Under the best conditions, the resulting titanate nanotubes did not contain any remains of starting material, namely P25 nanoparticles, and also the resulting nanotubes had very smooth morphology with a diameter of ∼10 nm and length extending up to several micrometers without presence of any bundlelike structures. The washing of sodium titanate nanotubes with HCl solution leads to conversion into protonic titanate nanotubes via ion exchange reaction. The subsequent sintering of the titanate nanotubes renders dehydration of interlayered OH groups, thereby leading to precipitation of anatase phase. The tubular structure also gets destroyed during phase change, beyond 375°C. The electrodeposited titanate film with 60 V for 10 min at room temperature was dense and uniform. In this work, we suggest that electrochemical deposition method of titanate nanotubes film can be used for its applications.

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.