Research Trends in Doping Methods on TiO₂ Nanotube Arrays Prepared by Electrochemical Anodization

유현석,최진섭,Yoo, Hyeonseok,Choi, Jinsub The Korean Society of Industrial and Engineering C 2015 공업화학 Vol.26 No.2

Nanotubular $TiO_2$ prepared by electrochemical anodization has been significantly used for various applications due to high aspect ratio structures showing a high chemical stability. Morphological properties of nanotubular titanium oxide are easily tailored by adjusting types and compositions of electrolyte, pH value, applied voltage, temperature and anodization time. Since their catalytic properties can be enhanced by doping foreign elements into $TiO_2$, metal as well as non-metal elements are doped into $TiO_2$ nanotubes using different methods. For example, single anodization, thermal annealing, precipitation, and electrochemical deposition have been applied to simplify the doping process. In this review, anodization of Ti to produce $TiO_2$ and doping methods will be discussed in detail. 전기화학적 양극산화 기법으로 제조한 타이타늄 나노튜브는 타이타늄 특유의 강한 화학내구성 및 나노튜브의 높은 종횡비로 인하여 넓은 범위에 응용된 소재이다. 전해질의 구성 성분과 종류, pH, 전압, 온도 그리고 양극산화 시간이 타이타늄 나노튜브의 성상을 결정짓는 요소들이며 도핑을 통해 촉매능을 부여할 수 있다. 비금속 및 금속 원소 모두 도핑 가능하며 도핑 방법 역시 다양하다. 도핑 방법에는 합금 양극산화, 열처리법, 함침법, 전기도금법 등 다양한 방법들이 이용되며 점차 간단하고 빠른 도핑 방법을 찾는 방향으로 연구가 진행되고 있다. 본 총설에서는 타이타늄 나노튜브의 생성 원리와 상용된 제법들에 관하여 기술하고 도핑과 그 응용 및 최근의 도핑 연구 동향을 다루도록 하겠다.

Layer-by-layer 기법을 통한 Cu₂(btc)₃-AAO 하이브리드 분리막의 제조

유현석(Hyeonseok Yoo),최진섭(Jinsub Choi) 한국표면공학회 2018 한국표면공학회지 Vol.51 No.1

The Cu₂(btc)₃ metal-organic frameworks (MOF) coated anodic aluminum oxide (AAO) membrane was successfully prepared by layer-by-layer technique using hand spray method. It was confirmed that the Cu₂(btc)₃ layer, which has the pore sized in 2-3 nm, on surface of AAO exhibited the polycrystalline thin film structure by XRD analysis. More than 100 repetitive spray cycles were required to obtain more robust and thick MOFs on AAO and it was possible to uniformly coat both the top and bottom surfaces of the AAO. It should be noted that the MOFs also could be coated on surface of pores resulting in reduce the size of pore from 52 nm to 32 nm.

대기압 플라즈마를 이용한 폐냉매 분해 공정 폐수 처리

고은하 ( Eun Ha Ko ),유현석 ( Hyeonseok Yoo ),정용안 ( Yong-an Jung ),박동화 ( Dong-wha Park ),김동욱 ( Dong-wook Kim ),최진섭 ( Jinsub Choi ) 한국공업화학회 2018 공업화학 Vol.29 No.4

본 연구진은 선행 연구를 통하여 R-22 (CHClF₂) 폐냉매를 질소 열플라즈마 시스템을 이용하여 열분해공정에 관하여 보고한 바 있다. 하지만 해당 공정에서 열분해를 거쳐 발생된 폐수 중 불소이온이 고농도로 존재한다는 문제점이 제기되었다. 본 연구는 폐수 중 불소 이온을 중화하기 위한 추가 후단처리 공정에 관한 연구이다. 선행 연구와 동일한 공정을 통해 R-22의 열분해를 수행하여 발생한 폐수를 대기압 플라즈마를 이용하여 처리하였으며, 이를 물과 중화제인 Ca(OH)₂ 용액으로 후단 처리한 것과 비교하여 폐수 중 F- 이온의 농도 변화를 확인하였다. 물만 사용하여 중화한 경우 폐수 중 불소이온 농도가 가장 높았으며 중화액을 살포하거나 대기압 플라즈마로 추가로 후처리를 수행한 경우 폐수 중 불소이온 농도가 현저하게 감소하는 것이 확인되었다. Our group reported the thermal decomposition of R-22 (CHClF₂) refrigerants by nitrogen thermal plasma in previous studies. However, it was proposed that the wastewater generated from the end part of the process contains high concentration of fluoride ion which is a component of R-22. The additional post-treatment process to neutralize the F- ions in the wastewater was investigated in this study. The wastewater generated through the decomposition of R-22 with the same procedure in the previous work was treated using the neutralizer, Ca(OH)₂, and the atmospheric pressure plasma jet (APPJ) independently as a post-treatment process. Wastewater samples were collected directly after the treatment for ion-chromatography analysis to trace the change of the concentration of F- ion in the wastewater. The fluoride concentration in the wastewater showed the highest value when the single water was used as a neutralizer, and the concentration of fluoride in the wastewater was dramatically reduced when the post-treatments were performed.

몰리브덴 산화물이 도핑된 티타늄 나노튜브전극의 수소 발생 반응 연구

오기석(Kiseok Oh),유현석(Hyeonseok Yoo),이기백(Gibaek Lee),최진섭(Jinsub Choi) 한국표면공학회 2016 한국표면공학회지 Vol.49 No.6

In this study, titanium nanotubes, prepared by anodization method, showing high surface and strong chemical stability in acidic and basic media, have been employed for the application to the electrodes for water splitting in KOH solution. Due to its high polarization resistance of TiO₂ itself, proper catalysts are essentially required to reduce overpotentials for water oxidation and reduction. Most of academic literature showed noble metal catalysts for foreign dopants in TiO₂ electrodes. From commercialization point of view, screening of low-cost catalyst is important. Herein, we propose molybdenum oxide as low-cost catalysts among various catalysts tested in the experiments, which exhibits the highest performance for hydrogen evolution reaction in highly alkaline solution. We showed that molybdenum oxide doped electrode can be operated in extreme acidic and basic conditions as well.

질소 플라즈마 공정을 이용한 염화이불화메탄(CHClF₂) 열분해

고은하 ( Eun Ha Ko ),유현석 ( Hyeonseok Yoo ),정용안 ( Yong-an Jung ),박동화 ( Dong-wha Park ),김동욱 ( Dong-wook Kim ),최진섭 ( Jinsub Choi ) 한국공업화학회 2017 공업화학 Vol.28 No.2

염화이불화메탄(CHClF₂) 냉매를 완전하게 분해하여 회수하기 위한 질소 플라즈마 열분해 공정이 연구되었다. 과열증기를 공급하여 분해가 보다 원활히 이루어질 수 있도록 스팀 발생기가 부착되었다. 60 A, 9.0 kW 이상의 운전 조건에서 94% 이상의 높은 분해율을 보이지만 탄소 성분의 완전 연소를 위해서는 같은 전류 대비 더 높은 power와 specific energy density를 갖춰야 함이 확인되었다. 60 A, 12.6 kW급 이상의 운전 조건에서는 O₂/R-22 ratio가 specific energy density에 비례하여 증가하였을 때 더 높은 분해율을 획득할 수 있었다. 반응물인 산소를 주입하는데 있어서 air를 단독으로 과량 주입하는 것보다는 산소를 air와 혼합하여 주입하는 것이 더 유용함이 밝혀졌다. The nitrogen plasma thermal decomposition and recovery processes for CHClF₂(Chlorodifluoromethane) refringent were investigated. The steam generator was employed to provide superheated steam reactor, supporting the decomposition reaction of refringent. Even though over 94% of R-22 was decomposed on the condition of 60 A and 9.0 kW, a higher power and specific energy density were required to achieve the complete combustion of carbon materials. In the operating condition of 60 A and 12.6 kW, O₂/R-22 ratio in reactants gases are a key factor to obtain much higher decomposition ratio during process. It should be noticed that injecting the mixture of O₂ and air was much more effective than injecting the air consisting equivalent O₂amount.

탈지 정도에 대한 방청유-금속 계면의 영향성 평가

최원영(Wonyoung Choi),김문수(Moonsu Kim),유현석(Hyeonseok Yoo),송연균(Yeongyun Song),정용균(Yong-Gyun Jeong),최진섭(Jinsub Choi) 한국표면공학회 2021 한국표면공학회지 Vol.54 No.6

The use of anti-corrosive oil (AC) is inevitable for production of industrial steels to prevent corrosion. The AC is degreased before application of steels, which crucially effects on final products, such as automobile, electricity etc. However, qualitative/quantitative evaluation of degreasing performance are steal insufficient. In this study, degreasing performance of anti-corrosive oil on steel have been studied through X-ray photon spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Commercial automotive steels (AMS) are coated with 4 different anti-corrosive oils (namely AC1-AC4). In XPS, intensity of C1s peak remained after degreasing indirectly indicates incomplete degreasing. Thus, higher C1s peak intensity means less effective degreasing by degreasing agent. peak intensity of C1s peak shows opposite tendency of peak intensity of O1s. We found that EIS analysis is not applicable to mild steel (such as AMS1) due to corrosion during measurement. However, alloy steel can be fully analyzed by EIS and XPS depth profile.

분광측색계, 색차계의 색 수치 값을 이용한 타이타늄 산화막의 두께 정량화

이다영(Dayoung Lee),한아영(Ayoung Han),하동흔(Dongheun Ha),유현석(Hyeonseok Yoo),김훈식(Hunsik Kim),정나겸(Nagyeom Jung),장관섭(Kwanseop Jang),최진섭(Jinsub Choi) 한국표면공학회 2018 한국표면공학회지 Vol.51 No.3

The anodic TiO₂ layers which are prepared in various anodization conditions exhibit their specific color depending on the thickness of TiO₂. In this study, the relationship between the color of TiO₂ layer, which is grown by PEO (Plasma electrolytic oxidation), and the thickness of the TiO₂ layer is investigated. To evaluate the color change of the TiO₂ layer, the value of color (dE<SUP>*</SUP>ab) is measured and calculated by spectrophotometer and chromameter. As a result, it is found that dE<SUP>*</SUP>ab values and thickness of TiO₂ layers form a linear relationship with meaningful formular. This formula can be helpful to quantify the thickness of the TiO₂ layer by the numerical dE<SUP>*</SUP>ab values. In this process, the spectrophotometer shows more precise results than the chromameter dose. If fluoride ions (F-) are included in the electrolyte, it will affect the dE<SUP>*</SUP>ab values of the TiO₂. layer. This is against the propensity, which is analyzed by XRD (X-ray diffraction) and XPS (X-ray photoelectron spectroscopy). It is important that the formular suggested in this study provides other metals which can be also anodized with the possibility of quantifying the thickness of the TiO₂ layer by the dE<SUP>*</SUP>ab values.

DC 열플라즈마를 이용하여 제조된 산화철 나노입자의 광 전기화학적 물분해 효율 증가연구

이철호 ( Chulho Lee ),이동은 ( Dongeun Lee ),김선규 ( Sunkyu Kim ),유현석 ( Hyeonseok Yoo ),최진섭 ( Jinsub Choi ) 한국공업화학회 2015 공업화학 Vol.26 No.3

In this research, hematite nanoparticles were synthesized by DC thermal plasma process to increase the overall surface area. The effect of binders on hematite electrodes was investigated by changing the type and composition of binders when preparing electrodes. Nitrogen gas was also added to the DC thermal plasma process in order to dope the hematite with N for enhancing photoelectrochemical properties of hematite nanoparticles. The efficiency of water splitting reaction was measured by linear sweep voltammetry (LSV) under solar simulator. In LSV measurements, the onset potential and maximum current density at a fixed voltage were measured. The durability of electrodes was checked by repeating LSV measurements. CMC (carboxymethyl cellulose) binder with 50 : 1 composition exhibits the highest current density of 12 mA/cm2 and CMC binder with 20 : 1 composition, showing the initial current density of 3 mA/cm2, endures 20 times of repetitive LSV measurements. Effects of nitrogen doping on hematite nanoparticles were proven to be insignificant.