Papers by Author: Dong Seok Rhee

Abstract: The improvement of photocatalytic activity of TiO₂ has been explored. TiO₂ has been doped with some transition metal elements for new photocatalytic materials. They were prepared using nitrates of Fe, Cu and Zn. Their photocatalytic activities were investigated by conducting a semi-batch experiment. The degradation of aqueous humic acid was performed under near-visible irradiation. For examining the photocatalytic characteristics of the new materials, the dissolved organic carbon and the UV254 absorption of humic acid were analyzed. The new metal-doped photocatalysts showed higher photoactivities than the synthesized pure TiO₂. And photodegradation result of humic acid by the new metal-doped material was even better than by the commercial Degussa P-25 TiO₂ at wavelengths of 315 nm - 400 nm.

Abstract: Ozonation of humic acid has been conducted in the presence of hydrogen peroxide as catalyst. Besides the study of total organic carbon removal in the ozonation, ozonation by-products were investigated through the change of injected concentration of H₂O₂, initial pH of aqueous humic acid and injection time of H₂O₂. The variation of hydrogen peroxide and formaldehyde contents in the processes are mainly evaluated. The formaldehyde was formed less in ozonation with hydrogen peroxide system than without it. When initial pH in solution was changed from 3.5 to 10.5, the formaldehyde was formed with the highest concentration at pH 5. In addition, the concentration of H₂O₂ produced by ozonation was found to be increased with decreasing pH of the sample solution in this process.

Abstract: The ozone/hydrogen peroxide system has been introduced for the study of degradation of humic acid in water. The removal ratio of TOC in aquatic humic acid solution has been investigated with some reaction parameter like the change of injected concentration of H₂O₂, initial pH of aqueous humic acid and injection time of H₂O₂. And the formation of formaldehyde concentrations in the treatment system processes has been also evaluated with the variation of its concentration. From the experimental results, it has been concluded that the concentrations of H₂O₂ and the initial pH’s in solution in the ozone/hydrogen peroxide system were very important for enhancing the efficiency of degradation of humic acid in water. The formaldehyde was formed less in ozone/hydrogen peroxide system than in ozone alone system.

Abstract: Ozonation of the ubiquitous and poorly biodegradable humic acid in aquatic system was conducted in the presence of activated carbon with the aim of catalyst. The optimum operating parameters deduced from this study was GAC amount of 16.5 v/v% (GAC column volume per reactor volume) in the humic acid solution of initial pH 9. DOC removal rate in Ozone/GAC process was higher than the sum of Ozone alone and GAC adsorption process. Formaldehyde formation in Ozone/GAC process was less than in Ozone alone and GAC adsorption process. The part of molecular size distribution under 10 k Dalton were increased in the Ozone/GAC process.

Abstract: Titanium dioxides were synthesized from two different titanium salts, which contained chlorine and sulfur respectively. Titanium dioxide prepared from TiCi₄ and had a particle size of ca. 20nm and its phase transition from anatase to rutile stated at 500°C. Titanium dioxide from TiOSO₄ had a particle size of ca. 50nm and retained its anatase and sperit structure until 700°C by calcination. For the photocatalytic evaluation of these titanium dioxides, photocatlytic oxidation of organic model pollutant, humic acid, have been conducted. UV absorbance decrease by titanium dioxides prepared from both from TiCi₄ and TiOSO₄ at room temperature showed very similar results, compared to titanium dioxide prepared from TiCi₄ at higher temperature.

Abstract: Modified polypropylene granules (MDPG) were coated by manganese dioxide and their surface and adsorptive characteristics were studied. Surface characteristics of the adsorbent were investigated by B.E.T. surface area and mercury porosimetry. Coating has significantly increased the surface area of granules from 0.12 m 2 /g B.E.T. N 2 to 15.42 m 2 /g. Gas pycnometry measurements resulted in low density of 0.13 g/cm 3 for uncoated granules, the fact ascribed to 0.65 porosity measured. Coating increased micro pore volume of raw granules by a factor of 58. Adsorption experiments were conducted in column flow-through reactors at pH 6.0 and 10 g/L sorbent dosage for mixture of four metal species, each having 5 mg/L initial concentration. More than 60 % of Pb and Cu was removed within first 20 min, whereas just over 29 and 13 % for Cd and Zn respectively. Furthermore, more than 99, 84, 40, 16 % of Pb, Cu, Cd, and Zn was removed within 1 h. Adsorption efficiencies for 5 ppm of initial metal concentration at pH 5.0 and 10 g/L sorbent/solute ratio resulted in 4.9, 3.9 mg of Pb and Cu sorbed per gram of sorbent. And these ratios for separate metal ions were substantially higher than those for the mixture of the four metal ions. For 5 g/L of sorbent under the same parameters, removal efficiencies of Cd and Zn were respectively 0.98, 0.75 mg/g, correlating well with Freundlich adsorption model. Adsorption kinetics showed relatively fast removal rates within first 5 h of sorption. Desorption resulted in eluting 57, 70, 76, 78 % of the initial feeding concentrations for Pb, Cu, Cd, Zn, respectively.