Papers by Author: Won Youl Choi

Abstract: Highly ordered TiO₂ nanotube arrays are very attractive to the dental implant due to microstructural advantage for drug loading. We have fabricated the highly ordered TiO₂ nanotube arrays on the surface of the dental implant. The surface of TiO₂ nanotube arrays grown by normal anodic oxidation was not clean and the window of TiO₂ nanotube was closed. These closed nanotubes decrease the surface area to load the drug and also decrease the osseointegration performances. To obtain the clean surface of TiO₂ nanotube arrays, two-step anodic oxidation was used. The microstructures of TiO₂ nanotube arrays from two-step anodic oxidation were compared with those from normal anodic oxidation. The length and diameter of TiO₂ nanotube arrays with anodizing time were measured. TiO₂ nanotube arrays grown by two-step anodic oxidation had the clean surface and the diameter of TiO₂ nanotubes was ~100 nm at anodizing conditions of 60V and 20 min. It was applied to the surface of dental implant to improve the osseointegration. The improved osseointegration was observed by micro CT analysis. TiO₂ nanotube arrays had a promising microstructure to load some drugs such as BMP-2 and anti-inflammatory.

Abstract: TiO₂ nanotube arrays fabricated by anodic oxidation had a large surface area and high refraction index. These microstructural properties are very attractive as interferometric biosensing materials. Label free interferometric biosensor usually used nanoporous Si materials. TiO₂ nanotube arrays had more stability for wide pH range solutions. The interferometric spectrum from nanoporous layer was treated by Fast Fourier Transform and optical thickness was measured. The optical thickness was changed with the materials in nanoporous layer. To fabricate the TiO₂ nanotube arrays, anodizing time, voltage and electrolyte were optimized. The diameter and length of TiO₂ nanotube arrays were ~100 nm and ~4 µm, respectively. To observe the loading and elution of the chlorhexidine in TiO₂ nanotube in real time, the optical thickness was measured with flow cell system. In 10 wt% chlorhexidine, optical thickness change of ~125 nm was observed.

Abstract: Hybrid structure of TiO₂ nanofiber and nanoparticle as a photoelectrode was very attractive in dye-sensitized solar cells (DSCs) because TiO₂ nanoparticle provided a high specific surface area to adsorb the N719 dye and TiO₂ nanofiber was a direct path to transfer photoelectron from dye to electrode. TiO₂ nanofiber film was prepared with titanium-tetraisopropoxide (TTIP) and polyvinylpyrrolidone (PVP) based precursor by electro-spinning process. To fabricate the hybrid structure, TiO₂ nanoparticular paste was screen printed on the TiO₂ nanofiber film. Electrospun TiO₂ nanofiber film and screen printed TiO₂ nanoparticular film were combined in layer by layer method. These films were observed as an anatase phase by X-ray diffraction pattern. Thickness and diameter of TiO₂ nanofibers were ~5μm and ~400nm, respectively. Thickness and particle size of TiO₂ particles were ~5μm and ~20nm, respectively. Compared to conventional DSCs, higher short circuit current densities (Jsc) of 6.47 mA/cm² and higher power conversion efficiency of 3.06 % were measured in DSCs having hybrid structure of TiO₂ nanofiber and nanoparticle. Electrochemical impedance spectroscopy (EIS) was observed to understand an electron transfer and life time.

Abstract: Dental implant with porous surface has been studied by many researchers because it has a good osseointegration. TiO₂ nanotube arrays on the surface of dental implant could provide the porous surface, the space of drug loading, and better biocompatibility than bare surface. To investigate the effects of TiO₂ nanotube arrays for dental implant, commercial dental implant was used and its surface was anodized to fabricate TiO₂ nanotube arrays. Highly ordered TiO₂ nanotube arrays were grown on the surface of dental implant. Ethylene glycol based electrolyte was used in anodic oxidation process. Anodic oxidation voltage and time were 50V and 15 min, respectively. The micro structure was observed by FE-SEM. The diameter and length of TiO₂ nanotube arrays were ~60 nm and 10μm, respectively. BMP-2 was loaded in TiO₂ nanotube arrays. For in-vivo testing, the dental implant with TiO₂ nanotube arrays was applied to rabbit legs for 8 weeks. In dental implant with TiO₂ nanotube arrays, good osseointegration properties were observed. TiO₂ nanotube arrays fabricated by anodic oxidation will be very useful in the field of bone implants and bone tissue engineering.

Abstract: Hybrid structure of TiO₂ nanofiber and nanoparticle as a photoelectrode was very attractive in dye-sensitized solar cells (DSCs) because TiO₂ nanoparticle provided a high specific surface area to adsorb the N719 dye and TiO₂ nanofiber was a direct path to transfer photoelectron from dye to electrode. TiO₂ nanofiber film was prepared with titanium-tetraisopropoxide (TTIP) and polyvinylpyrrolidone (PVP) based precursor by electro-spinning process. To fabricate the hybrid structure, TiO₂ nanoparticular paste was screen printed on the TiO₂ nanofiber film. Electrospun TiO₂ nanofiber film and screen printed TiO₂ nanoparticular film were combined in layer by layer method. These films were observed as an anatase phase by X-ray diffraction pattern. Thickness and diameter of TiO₂ nanofibers were ~5μm and ~400nm, respectively. Thickness and particle size of TiO₂ particles were ~5μm and ~20nm, respectively. Compared to conventional DSCs, higher short circuit current densities (Jsc) of 6.47 mA/cm² and higher power conversion efficiency of 3.06 % were measured in DSCs having hybrid structure of TiO₂ nanofiber and nanoparticle. Electrochemical impedance spectroscopy (EIS) was observed to understand an electron transfer and life time.

Abstract: This study was conducted to investigate the effect of operational parameters in anodized photocatalytic metal membrane reactor (PMMR) for the removal of Isopropyl alcohol in electric wastewater. The effect of UV light type, the strength of UV light, the injection of TiO2 powder and air flowrate was investigated. About 70% of removal of IPA under the condition of UV irradiation (UV-C, 64W) in combination with an anodized TiO₂ metal membrane was achieved within 180 minutes treatment, indicating that the UV/anodized photocatalytic TiO₂ metal membrane process is a promising treatment technology for treating IPA in electric wastewater.

Abstract: An anodized TiO2 membrane has enhanced photocatalytic properties of anatase phase and small crystal size. From the photocatalytic results, the prepared anodized nano-structured TiO2 membrane had an effective organics decomposition capacity and high water permeability. This anodization method enabled the prepared nano-structured TiO2 membrane to have high photocatalytic activity and desired pore structure.