Titanate Nanotube Thin Films Research Articles

Cu–Co‐codoped titanate/TiO2nanocomposite thin films for enhanced visible light absorption

Titanate nanotube thin (TNT) films were synthesised by alkaline hydrothermal method using titanium (Ti) plates as precursors. Copper–cobalt (Cu–Co)-codoped titanate/Ti dioxide (TiO2) nanocomposite thin films were prepared by doping Cu and Co to TNT films through ion exchange method and annealed at 500°C for 120 min. The as-prepared nanocomposite films were characterised by scanning electron microscopy, transmission electron microscopy, X-ray diffractometer, and ultraviolet–visible absorption spectra. The results show that anatase TiO2 particles were grown on the surface of titanate nanomaterial films. The composite materials mainly consisted of anatase TiO2 particles and titanate nanotubes/nanosheets. Cu–Co-codoped titanate/TiO2 nanocomposite thin films exhibited superior visible height adsorption property due to the reduced energy bandgap of composites introduced by additional Cu and Co 3d orbitals.

(Invited) CO2 Photoreduction By Cux０ Nanocluster Loaded SrTiO3 Nanorod Thin Film

Introduction Photocatalytic carbon dioxide reduction, in which CO2 is converted into organic compounds, such as methane, methanol, formic acid, and formaldehyde, has the potential to greatly contribute to reducing global warming and fossil fuel dependence. In artificial photosynthesis systems designed for the reduction of CO2 for solar fuel production, water molecules should ideally serve as the electron donor, similar to photosystems I and II in natural plants. Recently, our group reported that a copper oxide nanocluster cocatalyst drives the multi-electron reduction of both oxygen and CO2, i. e. the production of hydrogen peroxide from oxygen and carbon monoxide (CO) production from CO2.1 Our copper oxide consists of Cu(I) and Cu(II) valence states during the CO2 reduction reaction, and it is designated as CuxO (x=1 or 2). Copper compounds have balanced chemisorption-desorption properties for CO2 and CO, and therefore have high CO2 reduction activity and high selectivity of products, such as CO and formic acid. Herein, we examined the potential of strontium titanate (SrTiO3: STO) to function as a light harvester with loading of CuxO cocatalysts, as the STO has high chemical stability and sufficient negative conduction band for CO2 reduction. In the present research, we used STO nanorod thin films as a UV-light harvester due to its higher crystallinity and increased surface area for the loading of CuxO cocatalyst. The photocatalytic CO2 reduction activity of CuxO cocatalyst loaded STO nanorod (CuxO-STO) thin films was evaluated under UV-light irradiation in the present study. Experimental STO nanorod thin films were synthesized by the annealing of strontium ion-exchanged titanate nanotube thin films. Titanate nanotube thin film was prepared by the hydrothermal treatment of titanium (Ti) foil (2×2×0.1 cm3, Nilaco Co.).2 CuxO nanocluster cocatalyst was loaded onto the STO nanorod thin film using an impregnation method.3 The sample morphologies were observed by SEM and TEM. Chemical compositions of the sample were investigated using an EDX equipped with a TEM apparatus. The valence number of copper nanoclusters was determined by measuring ESR. The prepared CuxO-STO film was immersed into an electrolyte solution in a sealed quartz glass reactor. To purge air in the reactor, CO2 or Ar gasses were bubbled into the reactor through a Teflon tube. Products in the headspace of the reactor were evaluated using a gas chromatograph (FID) equipped with a methanizer unit under UV light irradiation. Results and discussion The TEM image analysis revealed that amorphous nanoclusters of 2-3 nm in size were attached and highly dispersed on the STO nanorods. In the obtained EDX spectrum, a signal corresponding to Cu was clearly observed. ESR spectrum of bare STO nanorod thin film did not showed any obvious peaks corresponding to copper ions or any changes to the spectrum after UV irradiation. In contrast, the CuxO-STO film exhibited a broad ESR peak, which was assigned to Cu2+ species, around 345 mT under dark conditions, and this peak decreased in intensity after UV irradiation. Thus, under UV-light irradiation, photo-excited electrons of STO were injected into the CuxO nanocluster cocatalyst. The time course of photocatalytic CO generation for bare STO and CuxO-STO film under UV irradiation with Ar or CO2 bubbling conditions were measured. The amount of CuxO in the film was optimized to be 0.0005 wt%. The loading of the CuxO-cocatalysts onto STO nanorods clearly improved the photocatalytic CO2 reduction activity compared to bare STO nanorods. We also conducted isotope tracer analysis on the optimized CuxO-STO film. The peaks in the mass chromatography spectra at m/z = 29 and 36 were assigned to 13CO and 18O2, respectively. These results confirmed that the CO generated by the CuxO-STO film originated from CO2, and that O2 molecules were produced through water oxidation. Conclusion We have demonstrated the applicability of modifying SrTiO3 with CuxO nanoclusters as a cocatalyst for CO2 photoreduction. The CuxO-STO film exhibited high activity and selectivity for CO evolution under UV irradiation. The isotope tracer analysis confirmed that water served as an electron donor and that CO molecules were produced by the reduction of CO2 under UV irradiation. As the CuxO-STO material is composed of non-toxic and abundant elements, it has the potential to be an efficient photocatalyst for CO2 reduction.

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).

The visible light absorption property of Cu-doped hydrogen titanate nanotube thin films: An experimental and theoretical study

Hydrogen titanate nanotube thin films were synthesized by alkaline hydrothermal method using titanium plates as starting material and then doped with Cu through ion-exchange method. The experimental results show that Cu ions incorporate into the walls of nanotubes and exist as Cu2+. Cu doping leads to a red shift of the optical absorption edge from the ultraviolet region to the visible light region. First-principles calculation results reveal that Cu doping substantially reduces the band gap of hydrogen titanate nanotubes due to the presence of the impurity energy band of Cu 3d in intrinsic band gap. The valence and conduction band positions of Cu-doped hydrogen titanate nanotubes were determined by valence band spectra. The valence band is shifted to lower potential while the conduction band is shifted to higher potential after Cu doping, explaining the origin of the band gap narrowing and red shift.

Origin of the visible light absorption of Co2+ and NH4+ co‐doped hydrogen titanate nanotube thin films

AbstractHydrogen titanate nanotube (HTNT) thin films were synthesized by hydrothermal method and then Co2+ and NH4+ co‐doped hydrogen titanate nanotube (Co, N‐HTNT) thin films were prepared by ion‐exchange method. The Co, N‐HTNT thin films exhibit strong absorption in the visible light range compared with the HTNT and NH4+ doped hydrogen titanate nanotube (N‐HTNT) thin films. The first‐principles calculations reveal that NH4+ doping has no effect on the visible light absorption of HTNTs. The red shift of Co, N‐HTNTs is only due to the mixture of the Co 3d and O 2p states in the top of the valence band, which results in the band gap narrowing. Relative to HTNTs and N‐HTNTs, both the valence band maximum (VBM) and conduction band minimum (CBM) of Co, N‐HTNTs shift to lower potential based on the valence band XPS spectra. Furthermore, the up‐shift of the VBM is much larger than that of the conduction band, which can result in band gap reduction explaining the origin of the visible light absorption of Co, N‐HTNTs.

Titanate nanotube thin films with enhanced thermal stability and high-transparency prepared from additive-free sols

Titanate nanotubes were synthesized from TiO2 in alkaline medium by a conventional hydrothermal method (150°C, 4.7bar). To obtain hydrogen titanates, the as-prepared sodium titanates were treated with either HCl or H3PO4 aqueous solutions. A simple synthesis procedure was devised for stable titanate nanotube sols without using any additives. These highly stable ethanolic sols can readily be used to prepare transparent titanate nanotube thin films of high quality. The resulting samples were studied by X-ray diffraction, N2-sorption measurements, Raman spectroscopy, transmission and scanning electron microscopy, X-ray photoelectron spectroscopy and spectroscopic ellipsometry. The comparative results of using two kinds of acids shed light on the superior thermal stability of the H3PO4-treated titanate nanotubes (P-TNTs). X-ray photoelectron spectroscopy revealed that P-TNTs contains P in the near-surface region and the thermal stability was enhanced even at a low (∼0.5at%) concentration of P. After calcination at 500°C, the specific surface areas of the HCl- and H3PO4-treated samples were 153 and 244m2g−1, respectively. The effects of H3PO4 treatment on the structure, morphology and porosity of titanate nanotubes are discussed.

Enhanced visible light response of CuO nanoparticle-modified sodium titanate nanotube heterojunction thin films

Sodium titanate nanotube thin films were synthesized on titanium plate by alkaline hydrothermal method. CuO nanoparticle-modified sodium titanate nanotube heterojunction thin films were prepared by a simple ion-exchange method. The p-type CuO nanoparticles with an average diameter of 3nm deposit on the surface of n-type sodium titanate nanotubes, which would form a p–n heterojunction. Ultraviolet–visible absorption spectra revealed that modification of CuO nanoparticles leads to a red shift of the optical absorption edge from 333nm to 422nm compared with pure sodium titanate nanotubes, showing an improvement in visible light response. Based on the energy band structure obtained from the valence band and ultraviolet–visible absorption spectra, we conclude that the red shift observed in the experiment derives from the up-shift of the top of the valence band, which results in the band gap narrowing.

Effects of calcination temperature on the morphology, structure and photocatalytic activity of titanate nanotube thin films

"Titanate nanotube thin films were synthesized on titanium substrate via a simple hydrothermal method. The as-prepared film was composed of Na 2Ti 3O 7, and then transformed into H 2Ti 4O 9·H 2O after acid washing process. However, H 2Ti 4O 9·H 2O was thermally unstable. The effect of calcination temperature on its morphology (nanotube, nanosheet, nanorod or a lotus-root-like appearance), structure and photocatalytic activity was carried out by annealing the films at 300–900 °C in the static air and then analyzing by X-ray diffraction, scanning electron microscope and transmission electron microscope. Based on the results, the possible evolution mechanisms were discussed for no-acid (washed with distilled water) and acid washed (washed with dilute HNO 3) samples, respectively. Finally, the photocatalytic activity of acid washed films calcined at different temperatures was evaluated by photodegradation of methyl orange (MO) under ultraviolet light. The results indicated that the film obtained at 500 °C showed the highest rate for decomposing MO solution, which could be explained by its unique surface morphology and crystal structure.

Apatite-forming ability of titanium compound nanotube thin films formed on a titanium metal plate in a simulated body fluid

We compared the apatite-forming ability of a sodium titanate nanotube thin film, an anatase-type titanium dioxide nanotube thin film, and a silver nanoparticle/silver titanate nanotube nanocomposite thin film, in simulated body fluid. The ability of the silver nanoparticle/silver titanate nanotube nanocomposite thin film is slightly higher than that of the anatase-type titanium dioxide nanotube thin film and significantly higher than that of the sodium titanate nanotube thin film. The high ability of the silver nanoparticle/silver titanate nanotube nanocomposite thin film is a newly observed phenomenon, which is probably due to the crystal structure of silver titanate – specifically, to the surface atomic arrangement, the large amount of Ti–OH formed on the nanotube surface, or both. The anatase-type titanium dioxide nanotube thin film and the silver nanoparticle/silver titanate nanotube nanocomposite thin film may have bright prospects for future use in implant materials such as artificial joints. The silver nanoparticle/silver titanate nanotube nanocomposite thin film is particularly promising for its antibacterial properties.

TiO 2 nanotube, nanowire, and rhomboid-shaped particle thin films fixed on a titanium metal plate

Titanium dioxide thin films having various nanostructures could be formed by various treatments on sodium titanate nanotube thin films approximately 5 μm thick fixed on titanium metal plates. Using an aqueous solution with a lower hydrochloric acid concentration (0.01 mol/L) and a higher reaction temperature (90 °C) than those previously employed, we obtained a hydrogen titanate nanotube thin film fixed onto a titanium metal plate by H + ion-exchange treatment of the sodium titanate nanotube thin film. Calcination of hydrogen titanate nanotube thin films yielded porous thin films consisting of anatase nanotubes, anatase nanowires, and anatase nanoparticles grown directly from the titanium metal plate. H + ion-exchange treatment of sodium titanate nanotube thin films at 140 °C resulted in porous thin films consisting of rhomboid-shaped anatase nanoparticles.

Antibacterial properties of nanostructured silver titanate thin films formed on a titanium plate

Antibacterial activity of various surfaces against methicillin-resistant Staphylococcus aureus (MRSA) was studied. Sodium titanate thin film with a porous network structure and sodium titanate nanotube thin film were formed on titanium surfaces through the reaction of titanium plates with NaOH solutions. Through a silver ion-exchange treatment, Na(+) ions in sodium titanate were exchanged with Ag(+) ions in silver acetate solution, along with the loading of silver nanoparticles on the titanate surfaces. Results of silver ion elution tests of the thin films in fetal bovine serum solution indicate that the release period and the number of silver ions released from the silver titanate thin films can be controlled by altering the crystal structure, nanostructure, and thickness of the titanate phase. The silver ion-exchanged titanate thin films showed high antibacterial activity against MRSA. It was also revealed that although the crystal structure of titanate itself has no large antibacterial effect, higher antibacterial activity mainly arises from the silver ions held in the interlayer spacing of the titanate. The obtained results should aid the development of more convenient and inexpensive antibacterial implants.

Preparation and Microstructure of Titanate Nanotube Thin Films by Spray Layer-by-Layer Assembly Method

Hydrogen titanate nanowires were prepared by hydrothermal method in 10 M NaOH followed by ion-exchanging process. Titanate nanowire thin films were successfully obtained by spray Layer-by-Layer (spray LbL) method within a short time. Due to the good dispersion state of the nanowires in an aqueous suspension and their linear morphology, titanate nanowires effectively adsorbed on the glass substrate. As a reference, TiO2-anatase nanoparticle thin films were also prepared by spray LbL method

The growth of oriented titanate nanotube thin film on titanium metal flake

In this study, oriented titanate nanotubes thin films grow on titanium metal surface via a hydrothermal surface treatment process. A combined SEM and TEM investigation of the reaction products as the functions of reaction temperature, duration and concentration of NaOH solution reveal that several hundreds nanometer long nanotubes are formed by using 10 M NaOH at 110–150 °C for 6–48 h. A general formation mechanism of oriented titanate nanotube thin film was proposed in terms of the detailed observation of the products. The overall formation of titanate nanotubes can be summarized, as a sequence of layered trititanate formation, splitting and scrolling process.

Preparation of titanate nanotube thin film using hydrothermal method

In this study, the technology to grow nanotube thin film from dip-coated TiO 2 using hydrothermal method has been developed. The structure and stability of the film has been studied through the study of preparation parameters. A general formation mechanism of titanate nanotube thin film is proposed in terms of the detailed observation of the products via two dimensional surface scanning electron microscopy studies and transmission electron microscopy images. The overall formation can be summarized with three successive steps: (1) Transform TiO 2 to hydrated polytitanate layer; (2) Layered trititanate formation and growth process; (3) Formation of nanotube thin film via trititanate splitting and multilayer scrolling process of (100) planes around the c axis .

Structure-tunable synthesis of titanate nanotube thin films via a simple hydrothermalprocess

In this study, titanium metal acts as the titanium source to prepare oriented titanatenanotube thin film. The effects of preparation parameters, such as reaction temperature,duration and post-treatment conditions, on the film morphology and stability have beenexamined. A general formation mechanism for oriented titanate nanotube thin film isproposed on the basis of detailed observations of the products using two-dimensionalsurface SEM studies and TEM images. The overall formation of titanate nanotubes canbe summarized as a sequence of four steps: (a) titanium dissolution and alkalititanate hydrogel formation; (b) alkali titanate hydrogel dissolution, increasedTiO32−,TiO2(OH)22− orTinO2n+m2m− concentration andlayered Na2Ti3O7 formation;(c) layered Na2Ti3O7 growth;(d) nanotube formation via Na2Ti3O7 splitting and the multilayer scrolling process. TheNa2Ti3O7 lamellar structures split between the (010) planes into nanosheets.

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.

Photocatalytic Property of Titanate Nanotube Thin Film

Photocatalytic Property of Titanate Nanotube Thin Film