초음파 합성 적용 Cu₂O/TiO₂ 이종접합 소재의 특성 및 활성도 평가에 관한 연구

최정학,이준엽,Choi, Jeong-Hak,Lee, Joon Yeob 한국환경과학회 2020 한국환경과학회지 Vol.29 No.12

In the current study, a Cu2O/TiO2 photoinduced nanocomposite materials prepared by ultrasonification method was evaluated the photocatalytic oxidation efficiency of volatile organic compounds (BTEX) under visible-light irradiation. The results of XRD confirmed the successful preparation of photoinduced nanocomposite materials. However, diffraction peaks belonging to TiO2 were not confirmed for the Cu2O/TiO2. The possible reason for the absence of Cu2O peak is their low content and small particle size. The result of uv-vis spectra exhibited that the fabricated Cu2O/TiO2 can be activated under visible light irradiation. The FE-SEM/EDS and TEM showed the formation of synthesized nanocomposites and componential analysis in the undoped TiO2 and Cu2O/TiO2. The photocatalytic oxidation efficiencies of benzene, toluene, ethylbenzene, and o-xylene with Cu2O/TiO2 were higher than undoped TiO2. According to light sources, the average oxidation efficiencies for BTEX by Cu2OT-0.5 were exhibited in the orer of 8 W day light > violet LEDs > white LEDs. However, the photocatalytic oxidation efficiencies normalized to supplied electric power were calculated to be in the following order of violet LEDs > white LEDs > 8 W day light, indicating that the LEDs could be a much more energy efficient light source for the photo-oxidation of gaseous BTEX using Cu2O/TiO2.

산업폐기물로부터 합성된 제올라이트 물질의 망간 이온 흡착속도 및 등온흡착 특성

최정학,이창한,Choi, Jeong-Hak,Lee, Chang-Han 한국환경과학회 2020 한국환경과학회지 Vol.29 No.8

Zeolite material having XRD peaks of Na-A zeolite in the 2θ range of 7.18 to 34.18 can be synthesized from the waste catalyst using a fusion/hydrothermal method. The adsorption rate of Mn ions by a commercial Na-A zeolite and the synthesized zeolitic material increased as the adsorption temperature increased in the range of 10 ~ 40℃. The adsorption of Mn ion were very rapid in the first 30 min and then reached to the equilibrium state after approximately 60 min. The adsorption kinetics of Mn ions by the commercial Na-A zeolite and the zeolitic material were found to be well fitted to the pseudo-2^nd order kinetic model. Equilibrium data by the commercial Na-A zeolite and the zeolitic material fit the Langmuir, Koble-Corrigan, and Redlich-Peterson isotherm models well rather than Freundlich isotherm model. The removal capacity of the Mn ions by the commercial Na-A zeolite and the zeolitic material obtained from the Langmuir model was 135.2 mg/g and 128.9 mg/g at 30℃, respectively. The adsorption capacity of Mn ions by the synthesized zeolitic material was almost similar to that of commercial Na-A zeolite. The synthesized zeolitic material could be applied as an economically feasible commercial adsorbent.

인 포화 층상이중수산화물의 재생에 관한 기초 연구

최정학 ( Jeong Hak Choi ),정용준 ( Yong Jun Jung ) 한국환경과학회 2014 한국환경과학회지 Vol.23 No.7

LDHs(layered double hydroxides) are of use adsorbent to remove heavy metals, micro-organic pollutants as well as high concentration of phosphorus from wastewater to low concentration of surface water without pH adjustments. This study examined the generation condition of LDHs saturated with phosphorus. Less than 20% regeneration rate was obtained in the absence of alkali and regeneration solution. After the desorption of LDHs with several conditions of acid and alkali solution, more than 60% of regeneration rate could be expected in the case of using MgCl2 as regeneration solution.

영가철 및 개질 영가철을 이용한 triclosan의 환원분해 특성

최정학 ( Jeong-hak Choi ),김영훈 ( Young-hun Kim ) 한국환경과학회 2017 한국환경과학회지 Vol.26 No.7

In this study, the reductive dechlorination of triclosan using zero-valent iron (ZVI, Fe⁰) and modified zero-valent iron (i.e., acid-washed iron (Aw/Fe) and palladium-coated iron (Pd/Fe)) was experimentally investigated, and the reduction characteristics were evaluated by analyzing the reaction kinetics. Triclosan could be reductively decomposed using zero-valent iron. The degradation rates of triclosan were about 50% and 67% when Fe⁰ and Aw/Fe were used as reductants, respectively, after 8 h of reaction. For the Pd/Fe system, the degradation rate was about 57% after 1 h of reaction. Thus, Pd/Fe exhibited remarkable performance in the reductive degradation of triclosan. Several dechlorinated intermediates were predicted by GC-MS spectrum, and 2-phenoxyphenol was detected as the by-product of the decomposition reaction of triclosan, indicating that reductive dechlorination occurred continuously. As the reaction proceeded, the pH of the solution increased steadily; the pH increase for the Pd/Fe system was smaller than that for the Fe⁰ and Aw/Fe system. Further, zero-order, first-order, and second-order kinetic models were used to analyze the reaction kinetics. The first-order kinetic model was found to be the best with good correlation for the Fe⁰ and Aw/Fe system. However, for the Pd/Fe system, the experimental data were evaluated to be well fitted to the second-order kinetic model. The reaction rate constants (k) were in the order of Pd/Fe > Aw/Fe > Fe⁰, with the rate constant of Pd/Fe being much higher than that of the other two reductants.

석탄 비산재로부터 저알칼리 조건에서 합성된 Na-A 제올라이트의 Sr, Cs 및 Na 이온의 흡탈착 특성

최정학 ( Jeong-hak Choi ),이창한 ( Chang-han Lee ) 한국환경과학회 2019 한국환경과학회지 Vol.28 No.6

zeolitic material (Z-Y2) was synthesized from Coal Fly Ash (CFA) using a fusion/hydrothermal method under low-alkali condition (NaOH/CFA = 0.6). The adsorption performance of the prepared zeolite was evaluated by monitoring its removal efficiencies for Sr and Cs ions, which are well-known as significant radionuclides in liquid radioactive waste. The XRD (X-ray diffraction) patterns of the synthesized Z-Y2 indicated that a Na-A type zeolite was formed from raw coal fly ash. The SEM (scanning electron microscope) images also showed that a cubic crystal structure of size 1~3 ㎛was formed on its surface. In the adsorption kinetic analysis, the adsorption of Sr and Cs ions on Z-Y2 fitted the pseudo-second-order kinetic model well, instead of the pseudo-first-order kinetic model. The second-order kinetic rate constant (k₂) was determined to be 0.0614 g/mmol·min for Sr and 1.8172 g/mmol·min for Cs. The adsorption equilibria of Sr and Cs ions on Z-Y2 were fitted successfully by Langmuir model. The maximum adsorption capacity (q_m) of Sr and Cs was calculated as 1.6846 mmol/g and 1.2055 mmol/g, respectively. The maximum desorption capacity (q_dm) of the Na ions estimated via the Langmuir desorption model was 2.4196 mmol/g for Sr and 2.1870 mmol/g for Cs. The molar ratio of the desorption/adsorption capacity (q_dm/q_m) was determined to be 1.44 for Na/Sr and 1.81 for Na/Cs, indicating that the amounts of desorbed Na ions and adsorbed Sr and Cs ions did not yield an equimolar ratio when using Z-Y2.

개질 영가철을 이용한 산성 및 염기성 염료의 탈색 특성

최정학 ( Jeong-hak Choi ),김영훈 ( Young-hun Kim ) 한국환경과학회 2016 한국환경과학회지 Vol.25 No.12

In this study, the reductive decolorization of three acid and basic dyes using modified zero-valent iron (i.e., acid-washed iron (Aw/Fe) and palladium coated iron (Pd/Fe)) at various pH conditions (pH 3~5) was experimentally investigated and the decolorization characteristics were evaluated by analyzing the absorbance spectra and reaction kinetics. In the case of acid dyes such as methyl orange and eriochrome black T, color removal efficiencies increased as initial pH of the dye solution decreased. However, the color removal of methylene blue, a basic dye, was not affected much by the initial pH and more than 70% of color was removed within 10 min. During the decolorization reaction, the absorbance of methyl orange (λ_max = 464 nm) and eriochrome black T (λ_max = 528 nm) decreased in the visible range but increased in the UV range. The absorbance of methylene blue (λ_max = 664 nm) also decreased gradually in the visible range. Pseudo-zero order, pseudo-first order, and pseudo-second order kinetic models were used to analyze the reaction kinetics. The pseudo-second order kinetic model was found to be the best with good correlation. The decolorization reaction rate constants (k₂) of methylene blue were relatively higher than those of methyl orange and eriochrome black T. The reaction rate constants of methyl orange and eriochrome black T increased with a decrease in the initial pH.

Al 함량이 다른 PAC를 이용한 응집 조건 별 인 제거효율 평가

최정학(Jeong-Hak Choi),윤건곤(Geon-Gon Yoon),이창한(Chang-Han Lee) 한국환경과학회 2023 한국환경과학회지 Vol.32 No.10

In this study, lab-scale phosphorus coagulation/precipitation experiments were performed using three types of polyaluminum chloride (PAC) with different Al contents (10%, 12%, and 17%). The PO₄-P removal efficiencies at various operating conditions, such as initial PO₄-P concentration, initial pH, and Al/P molar ratio, were evaluated, and correlations among the operating factors affecting phosphorus coagulation/precipitation with PAC were derived to optimize the process efficiency. When the initial PO₄-P concentration was 0.065 and 0.161 mmol P/L under an initial pH of 8-10, the optimal PAC dose was 0.126-0.378 and 0.189-0.667 mmol Al/L, respectively. Under these conditions, the Al/P molar ratio was 2.16-6.18 and 1.28-4.30, respectively, and the PO₄-P removal efficiency was in the range of 40.2-92.5%. When the Al/P molar ratio was 2 or less under an initial pH condition of 6-8, the PO₄-P removal efficiency was approximately ≤40% owing to insufficient Al<SUP>3+</SUP> ions. However, when the Al/P molar ratio is 3-5, the PO₄-P removal efficiency improved to approximately 80-90%. Thus, the optimal Al/P molar ratio to achieve a PO₄-P removal efficiency of over 90% was determined to be approximately 4 in the PO₄-P coagulation/precipitation process using PAC.

胃·十二指腸潰瘍穿孔 患者의 臨床的 考察

崔正學(Jeong Hak Choi),民丙哲(Peung CHul Min) 대한외과학회 1976 Annals of Surgical Treatment and Research Vol.18 No.12

농약물질 중 살충제 관련 농업 종사자들의 직무-노출 매트릭스 구축을 위한 기초 자료 조사 연구 (Ⅲ) : 과일류

최정학 ( Jeong-hak Choi ),김기연 ( Ki-youn Kim ) 한국산업보건학회 (구 한국산업위생학회) 2016 한국산업보건학회지 Vol.26 No.3

Objectives: This study was performed to estimate domestic usage amount of insecticide for fruit cultivation to suggest job-exposure matrix(JEM) regarding farmers treating agricultural insecticide. Materials and Methods: The domestic usage amount of insecticide for fruit cultivation was investigated according to two research methods. The former method is to use agricultural pesticides published annually from Korea Crop Protection Association(KCPA) and the latter method is to apply cultivation area of fruit provided officially from Statistics Korea(SK). Results: It was found that its domestic usage amount has decreased gradually from the first sale to presence(2012). However, there is a significant difference of annual usage trend of insecticide for fruit cultivation between shipments and estimation. The annual usage trends of insecticide for fruit cultivation based on regional classification were different from those based on total aspect. Conclusions: The region which used insecticide for fruit cultivation the most in Korea was as follows: Gyeonsang-do, followed by Jeolla-do, Chungcheong-do, Jeju-do, Seoul/Gyeonggi-do and Gangwon-do. An averaged ratio of usage amounts of insecticide based on shipments and those based on estimation by cultivation area was 980 ± 186%, which means that usage amounts of insecticide estimated by shipments are ten times higher than those based on cultivation area.

老齡者 急性 虫垂炎의 臨床的 考察

崔正學(Jeong Hak Choi) 대한외과학회 1976 Annals of Surgical Treatment and Research Vol.18 No.10