Papers by Author: Jin Wook Ha

Abstract: Fluidized Bed Chemical Vapor Deposition (FB-CVD) method offers advantages over conventional Chemical Vapor Deposition method in coating three dimensional objects. In addition, catalysts prepared by FB-CVD method often show improved physicochemical properties. Thus, FB-CVD seems a useful method for coating TiO2 onto small beads, in view of their photocatalytic application in aqueous environment, for example. In this work, we produced TiO2 coated beads (1~2mm in diameter) of alumina, silica-gel, and glass in ~35nm thickness using FB-CVD method, and examined photocatalytic performance of TiO2 coated beads in the photocatalytic decomposition reaction of methylene blue solution. Based on the combined results of the decomposition reaction kinetics of methylene blue and FE-SEM images of the surface morphology of TiO2 coated beads, we were able to account for the photocatalytic performance with respect to characteristic features detected in the surface morphology.

Abstract: In this study, immobilized nanotubular TiO2 is used to reduce toxic Cr(VI) to non toxic Cr(III) in aqueous solution under UV irradiation. To overcome the limitation of powder TiO2, a novel technique of immobilization based on anodization was applied and investigated under various experimental conditions. Among the samples tested under same anodizing condition, the nanotubular TiO2 annealed at 450 oC and 550 oC showed higher reduction efficiencies of Cr(VI). In addition, the surface characterizations (zeta potential, XRD and SEM) of these samples proved that the Cr(VI) reduction efficiency was higher under acidic conditions and at a lower annealing temperature. Through this study, it was concluded that anodized TiO2 has the potential to be useful technology for environmental remediation as well as hydrogen production in water.

Abstract: In this study, an anodized TiO2 electrode (ATE) on a titanium foil was prepared and used as a photoanode in an enzymatic photoelectrochemical system to split water into oxygen and hydrogen. The effect of applied voltage when anodized, thickness of foil, electrolytes, annealing temperature, and species of cathode was investigated. The optimum conditions were obtained such as 0.25 mm foil thickness, 20V of applied voltage in 0.5 vol% of hydrofluoric acid, and 650 oC of annealing temperature. The samples with higher activities had similar X-ray diffraction (XRD) patterns, clearly indicating that the samples showing the highest evolution rate were composed of both anatase and rutile, while those showing a lower evolution rate were made of either anatase or rutile. Increasing the intensity of the irradiated light caused a remarkable enhancement in the rate of hydrogen production up to 153 μmol/(hr×cm2) under light intensity of 146 mW/cm2.

Abstract: This study investigated the effects of constituents in bio/photocatalytic hydrogen production system using an experimental design tool, a fractional factorial design. The factors considered included species of buffer solution, the amount of hydrogenase (Pyrococcus furiosus, Pfu), electron donor, reaction temperature and electron mediator. The experiments were designed to determine critical conditions that were required to achieve the highest level of H2 production.