Udom Tipparach

Preparation and Characterization of Electrospun TiO2 Nanofibers via Electrospinning

In this work, titanium dioxide (TiO2) nanofibers were synthesized by a combination of electrospinning and calcinations process using a solution that contained poly(vinyl pyrolidone)(PVP) and titanium isopropoxide. Titanium isopropoxide/PVP composite fibers were investigated at different titanium isopropoxide concentrations and voltages. The fibers were characterized by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). SEM images showed that the morphology of as-spun TiO2 nanofibers are smooth, uniform and good continuous fiber morphology with fiber diameters of 150–290 nm when calcined of 600°C for 1 h in air. XRD patterns revealed that the crystallinity corresponded to TiO2 in the form of rutile structure. The fiber diameters were slightly decreased with increase of the applied voltages and the titanium tetraisopropoxide concentration.

Synthesis and Structure of Titania Nanotubes For Hydrogen Generation

Titania nanotubes (TiO2 NTs) working electrodes for hydrogen production by photoelectrocatalytic water splitting were synthesized by means of anodization method. The electrolytes were the mixtures of oxalic acid (H2C2O4), ammonium fluoride (NH4F), and sodium sulphate (VI) (Na2SO4) with different pHs. A constant dc power supply at 20 V was used as anodic voltage. The samples were annealed at 450 °C for 2 hrs. Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) were used to characterized TiO2 NTs microstructure. TiO2 NTs with diameter of 100 nm were obtained when pH 3 electrolyte consisting of 0.08 M oxalic acid, 0.5 wt% NH4F, and 1.0 wt% Na2SO4 was used. Without external applied potential, the maximum photocurrent density was 2.8 mA/cm2 under illumination of 100 mW/cm2. Hydrogen was generated at an overall photoconversion efficiency of 3.4 %.

Preparation and Microstructure of Titania (TiO2) Nanotube Arrays by Anodization Method

TiO2 nanotube arrays were successfully synthesized by the anodization method of Ti foils in electrolyte containing the mixtures of ethylene glycol (EG), ammonium fluoride (0.3 wt % NH4F) and deionized water (2 Vol % H2O). A constant dc power supply at 50 V was used anodization process with different anodizing times. The resultant samples were annealed at 450 °C for 2 h. TiO2 nanotube arrays were studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The prepared TiO2 NTs has diameter in 50-200 nm. The minimum of diameter TiO2 nanotube arrays was approximately 50 nm for 1 h of anodization process.

Properties and Photocatalysis of Nanostructured Titania Prepared by Sol-Gel Method for Solar Hydrogen Production

Photoelectrochemical (PEC) devices based on Fe-doped and Pt-loaded nanostructured- TiO2 films acting as working electrodes were fabricated for solar hydrogen production. Anatase nanocrystalline titania (nano-TiO2) thin films were deposited on glass slides and Ti metal sheet substrates by a sol-gel dip-coating method. The sol-gel of nano-TiO2 was prepared in nitrogen atmosphere using a home-made nitrogen dry box and titanium tetraisopropoxide Ti[OCH(CH3)2]4 was used as a precursor. The effects of annealing temperatures on the crystallite size and the phase transformation also were investigated. The diameters of the particles in the rage of 12 nm were obtained in different methods of making the sol-gels and different annealing temperatures. Photoelectrochemical (PEC) devices consist of the Fe-doped and Pt-loaded TiO2 films as working electrodes, Pt as counter electrodes, 1.0 M KOH as electrolyte, and Nafion Perfluorinated membrane as a proton exchange membrane. The maximum photocurrent density occurred of 0.80 mA/cm2 without an external applied bias potential under irradiation of 100 mW/cm2 corresponding with photoconversion efficiency of 0.98 %. Impurity and undesired phases may be the cause of electron-hole recombination that results in lowering photocatalytic activity.

Performance and Stability of Dye-sensitized Solar Cells with Quasi-solid State Electrolytes base on N-methyl-quinoline Iodide

We have fabricated dye-sensitized solar cells (DSSCs) with quasi-solid state electrolytes base on N-methyl-quinoline iodide and studied the performance and stability of the cells at different temperatures. The quasi-solid state electrolytes were prepared from polymer gel electrolyte based on N-methyl-quinoline iodide and iodine. Pure-anatase nanocrystalline TiO2 films with absorption of standard N719 dye were employed as working electrodes. The maximum efficiency of the solar cells was 4.5 % under incident light of 100 mW/cm2. The cells also showed excellent stability for several months under irradiation of sunlight. The ionic conductivity of the electrolytes and the performance of the cells at different temperatures were presented.

The Effect of Preparation Temperature of Electrolytes on Undoped and Ag-Doped TiO2 Nanotube Structures

In this work, we present the effect of preparation temperature of electrolytes for fabricating undoped and silver (Ag) doped titanium dioxide (TiO2) nanotubes by the electrochemical anodic oxidation of pure titanium sheets in electrolytes, mixtures of ethylene glycol (EG), ammonium fluoride (NH4F) and deionized water, that contain with different of silver ions. Heat treatment of electrolytes was carried out at 100 °C during preparation process. The morphology and structure of prepared nanotubes were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The structures of TiO2 nanotubes obtained from heat treatment and non-heat treatment of electrolyte solutions and adding silver ions in electrolyte solution are similar. The nanotubes appear in arrays and the diameters of nanotubes were about 92 nm for non-heat treatment electrolyte solution and undoped TiO2 and about 102 nm for heat treatment electrolyte solution and all Ag-doped TiO2 nanotube arrays. When the concentration of silver nitrate (AgNO3) increases, the TiO2 nanotube arrays cracked and are not well arranged.

Fabrication and Characterization of Titania (TiO2) Nanotube Dye-Sensitized Solar Cells by Anodization Method

Titania (TiO2) nanotubes were synthesized on Ti metal sheets by anodization method. The anodization condition was the variation of the anodization voltage. The nanotubes were characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-vis Spectrometer. The nanotubes can be used to make working electrodes for dye-sensitized solar cells. The pore diameter of TiO2 nanotube increases with the higher anodization voltage. The TiO2 nanotube diameters prepared at applied voltages of 40, 50, 60 and 70 V were approximately 200, 170, 140 and 100 nm, respectively. Furthermore, the dye-sensitized solar cells device based on the N719 dye and electrolytes shows the photovoltaic performance at different voltages of 40, 50, 60 and 70 V were 4.21%, 4.77%, 6.10% and 6.89%, respectively, under irradiation of 60 mW/cm2. The energy conversion efficiency of the dye-sensitized solar cells increased with increasing pore diameter of titania nanotubes.

Synthesis and Characterization Anodized Titania Nanotubes for Enhancing Hydrogen Production

Pure and doped Titania nanotubes (TiO2 NTs) photoanodes were fabricated by means of anodization method. The anodization was carried out in electrolytes prepared by mixing ethylene glycol (EG), ammonium fluoride (0.3 wt % NH4F) and deionized water (2 Vol % H2O) with different concentrations of dopant Fe (NO3)3∙9H2O. A constant dc power supply of 50 V was used as anodic voltage. The samples were annealed at 450 °C for 2 hours. The resultant products were characterized by Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) to determine their microstructures when TiO2 NTs were doped with different amounts of Fe atoms. The diameters of TiO2 NTs were about 60-120 nm. The highest density of TiO2 NTs was obtained when the nanotubes were doped with 0.01 M of Fe. The photocatalytic activity was examined without external applied potential. The maximum photocurrent density was 3.0 mA/cm2 under illumination of 100 mW/cm2.

Designing Apparatus for Highly Precise Measurement of Electrical Conductivity and Seebeck Coefficient from 85 K to 1200 K

We describe the development of apparatus for measuring of electrical conductivity and Seebeck coefficient with high precision from 85 K to 1,200 K. Electrical resistance was measured by means of four-point probe method as a function of temperature. The temperature below 400 K was measured by using type T thermocouple in vacuum system was used and from 400 to 1,200 was measured by using Type S was applied for temperature between 400 and 1200 Kelvin in an inert gas system. With the dimensions of the specimen, the electrical resistivity (ρT) can be obtained in the unit of microohm-centimeter (μΩ-cm) and be written in polynomial, ρT=-0.3191+6.8×10-3T-6.0×10-7 T2+8.0×10-10T3. The electrical conductivity can be obtained by taking inversion of the electrical resistivity. Seebeck coefficient (αT ) can be calculated in microvolt per Kelvin as follows: αT=1.9653-1.49×10-2T+9.0×10-5T2-2.0×10-7T3+2.0×10-10T4-1.0×10-13T5+3.0×10-17T6 , when T is temperature in K. The Seebeck coefficient data was compared with X-ray diffraction (XRD) and X-ray fluorescence (XRF) of the specimen. The result showed that our developrd apparatus yields the same as standard method when copper with purity greater than 99 percent was employed.

Synthesis of Aluminum-Doped TiO2 Nanotubes by Anodization Method

We report the synthesis of Al-doped TiO2 nanotubes (Al-TNT) by DC anodization method at 50 volts. The method is simple, cost effective, environmentally safe and the samples produced are of good quality. The electrolytesolution was composed of ethylene glycol (EG), ammonium fluoride (0.3% wt NH4F), deionized water (2% vol H2O) and varying molar masses of aluminum nitrate - Al (NO3)3. The samples were analyzed XRD before and after annealing at 450 °C for 2 hours. The surface morphology and the elemental analysis of the annealed samples were characterized by SEM and ED-XRF respectively. The results show that phase transformation only occur after annealing. And that the surface organization, uniformity and structure are influenced by the concentration of the dopant element.