Titanate Nanotube Films Research Articles

Electrophoretic deposition of titanate nanotubes from commercial titania nanoparticles: Application to dye-sensitized solar cells

The titanate nanotubes were synthesized by hydrothermal process using commercial titania nanoparticles. Subsequently, the titanate nanotubes film was fabricated at room temperature on FTO (F-SnO 2 coated glass) substrates using electrophoretic deposition (EPD) method at 40 V. The titanate nanotubes and the films were characterized with field-emission scanning electron microscope (FESEM), energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD). The average lengths of these nanotubes are few hundreds of nanometers and diameters ∼10–20 nm, with reasonably dense and uniform film. It was found that during EPD, the intercalated sodium (Na) from the titanate nanotubes was removed, as confirmed by XRD and EDX studies. Finally, dye-sensitized solar cells (DSSC) were prepared, after annealing the film from 450 °C to 550 °C, on using the two types of the films fabricated by electrophoretic deposition and doctor-blade method. It was observed that the open circuit voltage ( V oc) in all the cases was ∼0.8 V, with incident radiation intensity adjusted to AM-1.5. The solar cell corresponding to electrodeposited titanate nanotubes annealed at 500 °C showed a photocurrent density ( I sc) of ∼15.67 mA/cm 2 ( η = 6.71%). The solar cell fabricated with doctor-blade method using titanate nanotubes, annealed at 450 °C shows much lower photocurrent density ∼1.31 mA/cm 2 ( η = 0.65%), due to non-conversion of titanate nanotubes to titania, intercalated sodium and poor interfacial adhesion between titanate nanotubes and FTO substrate.

Biosensing Properties of TitanateNanotube Films: Selective Detection of Dopamine in the Presence of Ascorbate and Uric Acid

AbstractA novel strategy based on titanate nanotubes (TNTs) for developing an electrochemical biosensor is proposed. Stable TNT films are fabricated on glassy carbon (GC) electrodes by a casting technique. Cyclic voltammetry, electrochemical impedance spectrometry, and linear‐sweep voltammetry are used to characterize the TNT membrane‐covered GC electrodes (TNT/GCs). The TNT film is shown to demonstrate selectivity by charge exclusion. The TNT film is also shown to be capable of improving the mass transport to the electrode surface and electron transfer between dopamine (DA) and the electrode. Therefore, DA exhibits a quasireversible electrochemical reaction at the TNT/GC electrode. The voltammetric signal of DA is well resolved from those of ascorbate (AA) and uric acid (UA) at the TNT/GC electrode; therefore, DA can be selectively detected in the presence of a large excess of AA and UA at physiological pH. The linear calibration curve for DA is obtained over the concentration range 0.1–30 μM in a physiological solution that contains 0.1 mM AA and 0.3 mM UA.

Direct Electrochemistry of Myoglobin in Titanate Nanotubes Film

Titanate nanotubes (TNT) were proven to be efficient support matrixes for the immobilization of myoglobin (Mb). A comparative study was performed using the corresponding analogue, nanocrystalline anatase TiO2 (TNP). UV-visible absorption and FT-IR spectra show that Mb was not obviously denatured in TNT film in contrast to the significant denaturation of Mb in TNP film. Cyclic voltammetry and square wave voltammetry measurements were carried out using the Mb-TNT or Mb-TNP cast film-covered basal plane pyrolytic graphite electrode. The Mb-TNT film gave a well-defined, nearly reversible redox couple with the apparent formal peak potential (Ep) of -0.239 V (vs Ag/AgCl) in pH 5.5 buffer, whereas a relatively smaller, quais-reversible redox pair with Ep of -0.263 V was observed for the Mb-TNP film. The amounts of electroactive Mb in TNT film and TNP film were 15 and 10%, respectively. Moreover, the Mb-TNT film exerted facile direct electron transfer with the apparent heterogeneous electron-transfer rate constant (kET) of 86+/-7 s-1, almost 4 times the 22+/-5 s-1 value for the Mb-TNP membrane and higher than other Mb-entrapped films reported. Additionally, the Mb-TNT film demonstrates good electrocatalytic reduction of hydrogen peroxide with a detection limit of 0.6 microM, much lower than the 3.0 microM value for the Mb-TNP electrode and other Mb-related film-modified electrodes reported so far. The Mb-TNT film exhibits higher peroxidase-like activity with the apparent Michaelis-Menton constant (KM) of 140 microM, significantly lower than the 1300 microM value for the Mb-TNP film. The functional hydroxyl group and the surface charge as well as tubular morphology of TNT are important factors to stabilize the bound protein.

Nanostructure-Mediated Drug Delivery

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 10 nm 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).