Srimala Sreekantan

Fast-rate formation of TiO2 nanotube arrays in an organic bath and their applications in photocatalysis.

In this work, 18.5 microm titanium oxide (TiO(2)) nanotube arrays were formed by the anodization of titanium (Ti) foil in ethylene glycol containing 1 wt% water and 5 wt% fluoride for 60 min at 60 V. The fast growth rate of the nanotube arrays at 308 nm min(-1) was achieved due to the excess fluoride content and the limited amount of water in ethylene glycol used for anodization. Limited water content and excess fluoride in ethylene glycol inhibited the formation of a thick barrier layer by increasing the dissolution rate at the bottom of the nanotubes. This eased the transport of titanium, fluorine and oxygen ions, and allowed the nanotubes to grow deep into the titanium foil. At the same time, the neutral condition offered a protective environment along the tube wall and pore mouth, which minimized lateral and top dissolution. Results from x-ray photoelectron spectra revealed that the TiO(2) nanotubes prepared in ethylene glycol contained Ti, oxygen (O) and carbon (C) after annealing. The photocatalytic activity of the nanotube arrays produced was evaluated by monitoring the degradation of methyl orange. Results indicate that a nanotube with an average diameter of 140 nm and an optimal tube length of 18.5 microm with a thin tube wall (20 nm) is the optimum structure required to achieve high photocatalytic reaction. In addition, the existence of carbon, high degree of anatase crystallinity, smooth wall and absence of fluorine enhanced the photocatalytic activity of the sample.

Morphological and structural studies of titanate and titania nanostructured materials obtained after heat treatments of hydrothermally produced layered titanate

Different types of titanate and titania nanostructured materials have been successfully synthesised and characterized using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and raman spectroscopy. Elemental analysis was determined by energy dispersive X-ray spectroscopy (EDX) analyzer while thermogravimetric-differential scanning calorimetry (TG-DSC) was used to determine thermal stability. In this study, we found that nanotubes were formed during the washing treatment stage with HCl and distilled water. When the pH of the washing solution was 12, sodium titanate nanotubes were obtained, while when the pH of the washing solution was 7, hydrogen titanate nanotubes were obtained. Sodium titanate nanotubes were thermally stable up to 500°C; however, at 700°C, the nanotubes structure transform to solid nanorods. Meanwhile, hydrogen titanate nanotubes decomposed to produce titania nanotubes after heat treatment at 300°C for 2 hours. At 500°C, the tubular structure broke to small segments due to destruction of the nanotube. Further heat treatment at 700°C, led to the destruction and collapse of the nanotubes structure produce titania nanoparticles.

Photoelectrochemical Performance of Smooth TiO2 Nanotube Arrays: Effect of Anodization Temperature and Cleaning Methods

The formation of self-organized titanium dioxide (TiO2) nanotube arrays without bundling or clustering is essential for their high efficiency in photoelectrochemical (PEC) application. The present paper reports on the use of different temperatures to control the specific architecture of nanotube arrays and effective cleaning techniques to ensure the formation of clean TiO2 nanotube surface. The wall thickness of nanotube arrays could be controlled from 12.5 nm to 37.5 nm through different anodization temperature ranging from 10°C to 80°C. Furthermore, ultrasonic cleaning combined with acetone showed the high-ordered TiO2 nanotube arrays without morphological disorder, bundling, and microcrack problems. Based on the results obtained, a higher PEC response of 1 mA/cm2 and a photoconversion efficiency of 1.3% could be achieved using a wall thickness of 12.5 nm and defect-free TiO2 nanotube arrays for low charge transfer resistance.

Effect of applied potential on the formation of self-organized TiO 2 nanotube arrays and its photoelectrochemical response

Self-organized TiO2 nanotube arrays have been fabricated by anodization of Ti foil in an electrochemical bath consisting of 1 M of glycerol with 0.5wt% ofNH4F. The effects of applied potential on the resulting nanotubes were illustrated. Among all of the applied potentials, 30 V resulted in the highest uniformity and aspect ratio TiO2 nanotube arrays with the tubes length approximately 1 µm and pores size of 85 nm. TiO2 nanotube arrays were amorphous in as-anodized condition. The anatase phase was observed after annealing at 400°C in air atmosphere. The effect of crystallization and effective surface area of TiO2 nanotube arrays in connection with the photoelectrochemical response was reported. Photoelectrochemical response under illumination was enhanced by using the annealed TiO2 nanotube arrays which have larger effective surface area to promote more photoinduced electrons.

Effect of pH on TiO2 Nanoparticles via Sol-Gel Method

A series of titania nanoparticles was successfully synthesized via sol gel method using titanium tetraisopropoxide as a precursor. In this paper, data concerning the effect of pH towards the development of TiO2 nanoparticles is reported. The samples were characterised by x-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). XRD results showed the existence of nanocrystalline anatase phases with crystallite size ranging from 7-14 nm. Surface morphological studies obtain from SEM micrograph showed the particles with rodlike shape are rutile while the spherical shapes are anatase in nature. It was also found the pH of the solution affect the agglomeration of the particles. Results of photocatalytic studies exhibits that titania powder prepared at pH 9 has an excellent photocatalytic activity with degradation 74.7% within 60 minutes.

INVESTIGATION OF THE CHARACTERISTICS OF BARIUM STRONTIUM TITANATE (BST) DIELECTRIC RESONATOR CERAMIC LOADED ON ARRAY ANTENNAS

We investigated a dielectric resonator ceramic microstrip patch antenna. The antenna was formed using barium strontium titanate (BST), which had a dielectric constant of 15. A new approach,i.e., the use of a high temperature dielectric probe kit, was used to determine the dielectric constant of BST. A computer simulation technology (CST) microwave studio was used to simulate the BST array antennas, taking into consideration the dielectric constant. We also measured the gain of the antennas loaded with two-, four, and six-element arrays of the BST antenna and found that the gain of a six-element BST array antenna was enhanced by a gain of about 1.6 dB over the four-element BST array antenna at 2.3 GHz. The impedance bandwidths of these BST array antennas for voltage standing wave ratio (VSWR) < 2 were in the application ranges,i.e., 2.30 to 2.50 GHz, established for Worldwide Interoperability for Microwave Access (WiMAX) and Wireless Local Area Network (WLAN). Compared with the conventional array antenna with the same aperture size, the performance of the antenna obviously was improved, and the design is suitable for array applications, including base stations, for example.

The rapid growth of 3 µm long titania nanotubes by anodization of titanium in a neutral electrochemical bath

The length of titania nanotubes formed by anodization of 0.1 mm thick titanium foil was found to be a strong function of the pH of the electrolyte. The longest nanotubes were formed by using an electrolyte consisting of 1 M Na(2)SO(4) plus 5 wt% NH(4)F with pH 7. At this pH, after 30 min of anodization, 3 microm length nanotubular titania arrays with top diameters of approximately 50 nm and bottom diameters of 100 nm were produced. No acid was added to this electrolyte. The formation of titania nanotubes in neutral pH systems was therefore successful due to the excess NH(4)F in the electrolyte which increases the chemical dissolution process at the metal/oxide interface. Since the pH of the electrolyte at the top part of the nanotubes is kept very high, the dissolution of the nanotubes at the surface is minimal. However, the amount is adequate to remove the initial barrier layer, forming a rather well-defined nanoporous structure. All anodized foils were weakly crystalline and the transformation to anatase phase was achieved by heat treatment at temperatures from 200 to 500 degrees C for 1 h in air. Annealing at temperatures above 500 degrees C induce rutile phase formation and annealing at higher temperatures accelerates the diffusion of Ti(4+) leading to excessive growth and the nanotubular structure diminishes.

Well-aligned TiO2 nanotube arrays for energy-related applications under solar irradiation

Abstract Titania nanotube arrays have attracted significant scientific interests due to the interrelation of material functional properties with a controllable nanostructure. Superior properties of well-aligned TiO2 nanotube arrays, such as vectorial pathway of e− transport, suppressed e− recombination, high reaction site and enhanced light scattering render them as the most promising candidate for solar harvesting applications. Photoelectrochemical cells (PECs) and dye-sensitized solar cells (DSSCs) based on TiO2 photoanodes have attracted great interests due to their outstanding potential to convert solar energy into clean and renewable energy. Performance of PECs and DSSCs is greatly determined by the structural morphology of nanotube arrays. In this contribution, the fabrication, properties and energy-related applications of TiO2 nanotube arrays have been reviewed by focusing on synthesis by anodization in fluoride-containing electrolyte. The effect of anodization process parameters, such as applied potential, pH, exposure time, electrolyte type and composition on structural morphologies of TiO2 nanotube arrays has been comprehensively discussed. Several strategies for the electronic structure modification of TiO2 nanotube arrays to efficiently harvest visible-light irradiation, including noble metal loading, metal doping, nonmetal doping, semiconductor composite and sensitization have also been reviewed.

Simulation and Experimental Investigators on Rectangular, Circular and Cylindrical Dielectric Resonator Antenna

In this paper, theoretical and simulation studies on rectangular and annular dielectric resonator antenna (DRA) made of TiO2 was reported. The ceramic was fabricated by solid state reaction at 1200◦C. The structural and dielectric properties were investigated by X-Ray Diffraction (XRD), Field Emission Electron Microscopy (FESEM) and network Analyzer. The XRD results showed the presence of rutile phase and the microstructure comprised of fine grain (0.2–0.5 μm) and large grain 1.0–1.5 μm. The rectangular and annular shape TiO2 DRA with high dielectric constant (e = 84) and low loss tangent (0.080) were fed with 50Ω microstrip transmission line and comparision between the various shape were investigated. The return loss, input impedance and radiation pattern TiO2 DRA was studied. Design simulation results using CST Microwave Studio 2008 also was presented.

OPTIMIZED SPUTTERING POWER TO INCORPORATE WO3 INTO C–TiO2 NANOTUBES FOR HIGHLY VISIBLE PHOTORESPONSE PERFORMANCE

WO3-incorporated C–TiO2 nanotubes were successfully fabricated using radio frequency sputtering technique. The effects of sputtering powers on the nanotube morphology, crystal structure, optical properties and visible photoresponse were investigated. Lattice substitution of WO3 species within the lattice of C–TiO2 nanotubes has an important function in maximizing the photocurrent generation. WO3-incorporated C–TiO2 nanotubes exhibit good visible photoresponse compared with C–TiO2 nanotubes. The interpretation of interband states has an important function in improving photoinduced electron transport.