• Journal of Korean Society of Water and Wastewater
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• v.34 no.6
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• pp.445-462
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• 2020

Industrial wastewater often contains a number of recalcitrant organic contaminants. These contaminants are hardly degradable by biological wastewater treatment processes, which requires a more powerful treatment method based on chemical oxidation. Advanced oxidation technology (AOT) has been extensively studied for the treatment of nonbiodegradable organics in water and wastewater. Among different AOTs developed up to date, ozonation and the Fenton process are the representative technologies that widely used in the field. Based on the traditional ozonation and the Fenton process, several modified processes have been also developed to accelerate the production of reactive radicals. This article reviews the chemistry of ozonation and the Fenton process as well as the cases of application of these two AOTs to industrial wastewater treatment. In addition, research needs to improve the cost efficiency of ozonation and the Fenton process were discussed.

• Korean Chemical Engineering Research
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• v.59 no.1
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• pp.85-93
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• 2021

For accurate and reliable process design for phenol oxidation in a plug flow reactor with supercritical water, modeling can be very insightful. Here, the velocity and density distribution along the reactor have been predicted by a numerical model and variations of temperature and phenol mass fraction are calculated under various flow conditions. The numerical model shows that as we proceed along the length of the reactor the temperature falls from above 430 ℃ to approximately 380 ℃. This is because the generated heat from the exothermic reaction is less that the amount lost through the walls of the reactor. Also, along the length, the linear velocity falls to less than one-third of the initial value while the density more than doubles. This is due to the fall in temperature which results in higher density which in turn demands a lower velocity to satisfy the continuity equation. Having a higher oxygen concentration at the reactor inlet leads to much faster phenol destruction; this leads to lower capital costs (shorter reactor will be required); however, the operational expenditures will increase for supplying the needed oxygen. The phenol destruction depends heavily on the kinetic parameters and can be as high as 99.9%. Using different kinetic parameters is shown to significantly influence the predicted distributions inside the reactor and final phenol conversion. These results demonstrate the importance of selecting kinetic parameters carefully particularly when these predictions are used for reactor design.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.89-89
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• 2009

높은 소수반송자 수명(life-time)을 가지는 고품위 실리콘 기판은 고효율 실리콘 이종접합 태양전지 제작을 위한 중요 요소 기술 중 하나이다. 본 연구에서는 n-type c-Si 기판을 이용한 고효율 실리콘 이종접합 태양전지제작을 위해 hot water oxidation(HWO) 공정을 이용하여 고품위 실리콘 기판을 제작하였다. 실리콘 기판의 특성 분석은 Qusi-steady state photoconductance (QSSPC)를 이용하여 소수반송자 수명을 측정하였으며, 기판의 면저항 및 wetting angle을 측정하여 공정에 따른 특성변화를 분석하였다. Saw damage etching 된 기판을 웨이퍼 표면으로부터 particle, 금속 불순물, 유기물 등의 오염을 제거하기 위해 $60{\sim}85^{\circ}C$로 가열된 Ammonia수, 과산화수소수($NH_4OH/H_2O_2/H_2O$), 염산 과산화수소수($HCL/H_2O_2/H_2O$) 및 실온 희석불산(DHF) 중에 기판을 각각 10분 정도씩 침적하여, 각각의 약액 처리 후에 매회 10분 정도씩 순수(DI water)에서 rinse하여 RCA 세정을 진행한 후 HWO 공정을 통해 기판 표면에 얇은 산화막 을 형성시켜 패시베이션 해주었다. HF를 이용하여 자연산화막을 제거시 HWO 공정을 거친 기판은 매끄러운 표면과 패시베이션 영향으로 기판의 소수 반송자 수명이 증가하며, 태양전지 제작시 접촉저항을 감소시켜 효율을 증가 시킬수 있다. HWO 공정은 반응조 안의 DI water 온도와 반응 시간에 따라 life-time을 측정하여 진행하였으며, 이후 PE-CVD법으로 증착된 a-Si:H layer 및 투명전도 산화막, 금속전극을 증착하여 실리콘 이종접합 태양전지를 제작하였다.

• Journal of Electrochemical Science and Technology
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• v.12 no.1
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• pp.112-125
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• 2021

The new emerging "High entropy materials" attract the attention of the scientific society because of their simpler structure and spectacular applications in many fields. A novel nanocrystalline high entropy (Be,Mg,Ca,Sr,Zn,Ni)3O4 oxide has been successfully synthesized through mechanochemical treatment followed by sintering and air quenching. The present research work focuses on the possibility of single-phase formation in the aforementioned high entropy oxide despite the great difference in the atomic sizes of reactant alkaline earth and 3d transition metal oxides. Structural properties of (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide were explored by confirmation of its single-phase Fd-3m spinel structure by x-ray diffraction (XRD). Further, nanocrystalline nature and morphology were analyzed by scanning electron microscopy (SEM). Among thermal properties, thermogravimetric analysis (TGA) revealed that the (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide is thermally stable up to a temperature of 1200℃. Whereas phase evolution in (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide before and after sintering was analyzed through differential scanning calorimetry (DSC). Electrochemical studies of (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide consists of a comparison of thermodynamic and kinetic parameters of water and hydrazine hydrate oxidation. Values of activation energy for water oxidation (9.31 kJ mol-1) and hydrazine hydrate oxidation (13.93 kJ mol-1) reveal that (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide is catalytically more active towards water oxidation as compared to that of hydrazine hydrate oxidation. Electrochemical impedance spectroscopy is also performed to get insight into the kinetics of both types of reactions.

• Bulletin of the Korean Chemical Society
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• v.13 no.6
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• pp.680-683
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• 1992

The electrochemistry of benzidine and hydrazobenzene was studied in water-acetonitrile mixed solutions at various pHs and the results are reported. The cyclic voltammetric peak for the oxidation of benzidine shows a pH dependency of -62 mV/pH in the pH range of 0-3.5, no pH dependency between pH values of 3.5 and about 10.5, and of about -50 mV/pH between pH=10.50 and 14.0, indicating that oxidation mechanisms differ depending on the pH of the medium. However, the CV peak for the hydrazobenzene oxidation is shown to be independent of pH of the medium, suggesting that the proton is not involved in the rate limiting step of the electrochemical oxidation of hydrazobenzene to azobenzene. Results of in situ spectroelectrochemical experiments indicate that the oxidation products obtained during the oxidation of benzidine and hydrazobenzene depend on the result of dynamic equilibria taking place at various pHs.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.8
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• pp.579-587
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• 2014

Various kinds of micro organic pollutants have frequently been detected from a water system. Therefore, it is considered to be very important part in the drinking water treatment system. And the research about removal process and processing efficiency have been being conducted briskly. In this study, the removal efficiency was evaluated using advanced water treatment process and nanofiltration process. The removal efficiency of nanofiltration process was very different according to physical and chemical characteristics of materials. The molecular weight of cutoff was the most influential factor in the removal efficiency. And when pKa value was higher than pH of raw water or Log Kow value was below 2, the removal efficiency of material was decreased. In case of oxidation reaction, the bigger the molecular weight of material was and the more hydrophobic a material was, the less oxidation reaction occurred. And the removal efficiency was decreased. Most unoxidized materials were removed by absorption. And the more actively oxidation reaction occurred by $H_2O_2$, the more absorption reaction increased.

• Journal of environmental and Sanitary engineering
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• v.17 no.4
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• pp.29-38
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• 2002

Advanced oxidation of wastewater was studied with a purpose to remove TOC and color by the ozone-assisted Fenton reaction. The optimal conditions were determined by hydrogen peroxide and ozone concentrations. Experimental results indicate that the ozone treatment after Fentons process was found to provide very efficient removal efficiency in the process, avoiding the exclusive ozone treatment. The combined process of ozone in the Fenton oxidation respectively was increased removal efficiences of 10.7％ in comparison with exclusive Fenton oxidation. Also, the treatments of ozone after Fenton's oxidation respectively had increased the removal efficiences of 16.％. As a result, the treatment of ozone after Fentons oxidation had the best removal efficiency of approximately 96％. Removal efficiency of color was significantly increased as mush as 26％ by the advanced Fenton's oxidation in comparison with exclusive Fenton's oxidation. The removal efficiencies in the biological treatment using Bacillus subtilis after Fenton's oxidation and after Fenton's and ozone's oxidation were increased by 14％ and 19％ respectively. Although these combined Bacillus subtilis-assisted Fenton's oxidation was determined to be effective method to treat the dyeing wastewater in an economic point of view, the choice of wastewater treatment can be varied depending on water quality.

• Journal of Korea Water Resources Association
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• v.30 no.3
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• pp.235-245
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• 1997

A pilot scale study for removing odor and trihalomethane formation potential (THMFP) was investigated in the standard water treatment plant equipped with ozone oxidation and granular activated carbon (GAC) adsorption processes. The removal efficiency of dissolved organic carbon (DOC) in the pilot scale standard water treatment process (PSWTP) was about 25%, however, no more removal in the ozone oxidation process. On a GAC after 30 days operation, DOC removal efficiency was about 75%. Odor removal efficiency was about 30% in PSWTP, 60% in ozone oxidation, and almost complete in well as DOC. Mid-1 and 2 that showed breakthrough in odor inducing material as well as DOC. Mid-1 and 2 chlorination was able to reduce trihalomethanes (THM) by 25% compared to prechloringation, while postchlorination alone could reduce them by 30%.

• Korean Journal of Materials Research
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• v.30 no.9
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• pp.441-446
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• 2020

Synthesizing nanostructured thin films of oxide semiconductors is a promising approach to fabricate highly efficient photoelectrodes for hydrogen production via photoelectrochemical (PEC) water splitting. In this work, we investigate the feasibility as an efficient photoanode for PEC water oxidation of zinc oxide (ZnO) nanostructured thin films synthesized via a simple method combined with sputtering Zn metallic films on a fluorine-doped tin oxide (FTO) coated glass substrate and subsequent thermal oxidation of the sputtered Zn metallic films in dry air. Characterization of the structural, optical, and PEC properties of the ZnO nanostructured thin film synthesized at varying Zn sputtering powers reveals that we can obtain an optimum ZnO nanostructured thin film as PEC photoanode at a sputtering power of 40 W. The photocurrent density and optimal photocurrent conversion efficiency for the optimum ZnO nanostructured thin film photoanode are found to be 0.1 mA/㎠ and 0.51 %, respectively, at a potential of 0.72 V vs. RHE. Our results illustrate that the ZnO nanostructured thin film has promising potential as an efficient photoanode for PEC water splitting.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.2
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• pp.168-177
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• 2011

A set of kinetics study on the reduction with $CH_4$, oxidation with steam and oxidation with air was performed for $Fe_2O_3/ZrO_2$. $Fe_2O_3/ZrO_2$ was prepared by aerial oxidation method. The reactivity experiments were performed in a thermogravimetric analyzer (TGA) with different reacting gas concentrations and temperatures. The obtained activation energy of reduction by methane, oxidation by water and oxidation by air are 219 kJ/mol, 238 and 20 respectively.