2價 및 6價의 添加劑에 따른 PZT 磁器의 誘電的 性質에 關한 硏究

이기옥 漢陽大學校 大學院 1982 국내석사

Natural Mineral Supported Zerovalent Iron Composites for the Remediation of Hexavalent Chromium Contaminated Groundwater

최민희 건국대학교 대학원 2026 국내박사

The contamination of groundwater with hexavalent chromium (Cr(VI)) poses serious environmental and human health risks due to its high toxicity, mobility, and persistence in the subsurface environments. The widespread presence of Cr(VI) in industrially impacted aquifers highlights the urgent need for in situ remediation technologies capable of achieving rapid removal and long-term effectiveness. This dissertation investigates the development, characterization, and performance evaluation of zero-valent iron (ZVI) composites supported on natural and modified zeolites (NZ, PZ) and bentonite (Bt) for effective in situ Cr(VI) remediation. The objective was to enhance the stability, dispersibility, and reactivity of nZVI as an in situ remedial agent, ensuring sustained contaminant removal under realistic subsurface conditions. The effects of alkali treatment on natural zeolites (NZ) were systematically assessed to optimize nZVI incorporation and stabilization. Alkali-modified zeolites (PZ) exhibited increased Fe uptake and uniform nZVI distribution on both external surfaces and internal channels, effectively mitigating nanoparticle aggregation commonly observed in bare nZVI systems. Mechanistic investigations revealed that structural defects, including pore and cage openings, along with Na⁺-mediated ion exchange, were key factors controlling nZVI encapsulation. Three distinct incorporation pathways were identified: (i) surface loading onto NZ, (ii) framework integration within PZ, and (iii) channel encapsulation in PZ. Higher NaOH concentrations favored complete encapsulation, slowing electron transfer and extending nZVI reactive lifespan. These findings indicate that controlled structural modification of zeolites can substantially improve nZVI stability and long-term reactivity. The transport behavior and Cr(VI) removal efficiency of nZVI@zeolite composites were evaluated through batch experiments, column studies, and three-dimensional sandbox simulations replicating realistic aquifer conditions. Among the tested composites, nZVI@PZ(0.1) displayed superior mobility, reduced aggregation, and deeper penetration into porous media. Electrochemical analyses confirmed enhanced corrosion resistance and sustained electron transfer capacity during sustained exposure to Cr(VI). Although nZVI@NZ exhibited higher removal efficiency in batch experiments, nZVI@PZ(0.1) achieved approximately 3.4 times higher in situ removal in flow-through sandbox tests. This difference was attributed to secondary reactions induced by physical interactions with soil particles, which exposed internal Fe(0) and maintained prolonged Cr(VI) reduction, highlighting the importance of considering hydrodynamic and transport effects in nZVI-based remediation design. Bentonite-supported nZVI (bmZVI@Bt) synthesized via mechanochemical ball milling demonstrated enhanced structural and chemical activation compared to pristine and ball-milled ZVI. Characterization revealed uniform nZVI dispersion on bentonite surfaces, increased Fe(0) exposure, and higher Fe²⁺/Fe³⁺ ratios. Batch experiments showed rapid and nearly complete Cr(VI) reduction under both deionized water and groundwater conditions, and continuous-flow column tests confirmed stable long-term removal with a capacity approximately 4.5 times higher than bmZVI alone. Mechanistic analyses indicated that Cr(VI) removal involved adsorption onto reactive Fe sites, reduction to Cr(III), and immobilization via precipitation and coprecipitation. Bentonite served as a stabilizing support, mitigating premature nZVI passivation while enhancing electron transfer and mass transport. This dissertation demonstrates that zeolite- and bentonite-supported nZVI composites are highly promising materials for in situ Cr(VI) remediation. By improving nanoparticle dispersibility, corrosion resistance, and the longevity of reactive Fe sites, these composites offer a sustainable and effective approach for long-term groundwater remediation. The results highlight the critical interplay between material design, structural modification, and subsurface transport behavior, providing a solid scientific basis for scaling up supported nZVI technologies and for developing next-generation in situ remediation strategies that optimize reactivity, durability, and mobility 지하수 내 육가크롬(Cr(VI)) 오염은 높은 독성, 이동성 및 지하 환경에서의 지속성으로 인해 심각한 환경적·보건적 문제를 야기한다. 산업 활동의 영향을 받은 대수층에서 Cr(VI)이 광범위하게 존재함에 따라, 신속한 제거와 장기적인 지속 가능성을 동시에 달성할 수 있는 원위치(in situ) 정화 기술의 개발이 절실히 필요하다. 본 논문에서는 나노영가철(nZVI)을 천연 및 알칼리 전처리 제올라이트(NZ, PZ)와 벤토나이트(Bt)를 지지체로 활용하여 복합체를 개발하고, 이를 활용한 Cr(VI) 원위치 정화 효율과 특성을 종합적으로 평가하였다. 연구의 주요 목표는 실제 지중 환경을 고려한 환경에서 nZVI의 안정성, 분산성 및 반응성을 향상시키고, 장기적인 오염물질 제거를 실현하는 것이었다. 천연 제올라이트에(NZ) 대한 알칼리 처리 효과를 체계적으로 평가하여 nZVI 지지 및 안정화 메커니즘을 최적화하였다. 알칼리 처리된 제올라이트는 철 흡착량을 증가시키고, nZVI가 제올라이트 외부 표면과 내부 채널에 균일하게 분포하도록 하여 일반적인 nZVI 응집 문제를 효과적으로 완화하였다. 분석 결과, 기공 및 케이지 구조의 결함과 Na⁺ 매개 이온교환이 nZVI 캡슐화에 중요한 역할을 하는 것으로 나타났다. 세 가지 주요 Fe 도입 메커니즘은 1) NZ 표면 적재, 2) PZ 구조 내 통합, 3)PZ 채널 캡슐화로 확인되었으며, 높은 NaOH 농도에서는 완전한 캡슐화가 촉진되어 전자 전달 속도가 늦춰지고 nZVI의 반응 수명이 연장되었다. 이러한 결과는 제올라이트 구조의 조절을 통해 nZVI 안정성과 장기적인 반응성을 크게 향상시킬 수 있음을 시사한다. nZVI@제올라이트 복합소재의 이동성과 Cr(VI) 제거 효율은 배치 실험, 컬럼 실험, 3차원 샌드박스 모사 실험을 통해 쳬계적으로 평가하였다. 알칼리 전처리 천연 제올라이트(PZ)에 지지된 nZVI 복합소재(nZVI@PZ(0.1))는 다공성 매질 내에서 뛰어난 이동성을 보였으며, 입자 응집을 억제하면서 오염원이 존재하는 깊은 다공성 매질 내부까지 효과적으로 침투할 수 있었다. 전기화학 분석에서는 Cr(VI) 존재 하에서도 보다 음의 값의 부식 전위(Ecorr)를 유지하여 장기적인 노출에도 전자 전달 능력이 지속됨을 확인하였다. 배치 실험에서는 nZVI@NZ가 더 높은 제거 효율을 보였지만, 연속 흐름 샌드박스 실험에서는 nZVI@PZ(0.1)이 약 3.4배 높은 현장 내 제거 효율을 나타냈다. 이는 모래 입자와의 물리적 상호작용을 통해 내부 Fe(0)가 노출되고 장기적인 Cr(VI) 환원이 지속된 결과로 해석되며, 지하수 내 이동 및 물리적 상호작용이 사질 대수층 내 nZVI 기반 정화 효율에 중요한 영향을 미친다는 것을 보여준다. 또한, 벤토나이트 지지 nZVI(bmZVI@Bt)는 기계화학적 볼밀링을 통해 합성되었으며, 마이크론 크기의 ZVI (mZVI) 및 나노 크기의 볼밀 ZVI (bmZVI) 대비 구조적·화학적 활성화가 향상되었다. 특성 분석 결과, nZVI가 벤토나이트 표면에 균일하게 분산되고 Fe(0) 노출이 증가했으며 Fe²⁺/Fe³⁺ 비율이 높아 반응성이 강화되었다. 배치 실험에서는 탈이온수 및 지하수 조건 모두에서 Cr(VI)의 빠르고 완전한 제거를 나타내고, 연속 유속 컬럼 실험에서도 안정적인 장기 제거 효율이 확인되었다. 제거 용량은 bmZVI 단독 대비 약 4.5배로 나타났으며, Cr(VI) 제거 과정은 반응성 Fe 부위에 의한 흡착, 전자 매개 환원, 그리고 침전 및 공동침전을 통한 고정화 과정을 포함하였다. 벤토나이트는 nZVI의 조기 수동화를 방지하고 전자 전달을 유지하며, 물질 전달을 향상시키는 안정화 지지체로 작용하였다. 본 논문은 제올라이트 및 벤토나이트 지지 nZVI 복합체가 Cr(VI) 오염 지하수와 사질 대수층에서 장기적·지속 가능한 정화 소재로 매우 유망함을 보여준다. 나노입자의 분산성, 부식 저항성, 반응성 Fe 사이트의 장기적 유지를 향상시킴으로써 실제 지중 환경에서도 효과적인 장기 오염물 제거가 가능함을 입증하였다. 연구 결과는 재료 설계, 구조적 조절, 지하수 내 이동성 간 상호작용이 nZVI 성능 최적화에 결정적임을 강조하며, 천연광물 지지체 활용한 nZVI 기술의 현장 적용 확대와 차세대 원위치 정화 전략 개발을 위한 과학적 근거를 제공한다.

Application of electroactive carbon nanotube membrane for wastewater treatment

이정훈 Graduate School, Korea University 2022 국내박사

Humanity is suffering from an increase in non-decomposable pollutants and a decrease in clean water resources as it faces the most rapid development in history. To solve this problem, in environmental engineering, conventional water treatment processes should be improved. General water treatment processes consisted of physical, biological, and chemical treatment processes. These processes constitute the entire sewage treatment plant according to their purpose and target of treatment. The physical processing process, including precipitation and filtration, separates various pollutants from raw water. In particular, the membrane separation process increases the efficiency of the treatment plant field by the production of uniform permeate water and reducing the volume of treatment processes. However, as pollutants are separated, fouling occurs on the surface of the membrane and inside the pores, and a physical and chemical membrane cleaning process is required periodically. This is one of the tasks that must be fundamentally solved because of operating costs. Various bacteria and other microorganisms participate in the biological process. It is a method of decomposing complex organic matter into simple and stable substances. Biological methods include anaerobic methods, aerobic methods, and anaerobic methods. The biological treatment method using microorganisms has the advantage of low operating cost and high organic treatment efficiency. However, there is a problem that microorganisms are sensitive to sudden changes in temperature or influent water composition, making it difficult to maintain constant activity. Chemical treatment methods include the injection of chemicals for removal of suspended substances, turbidity, heavy metals, phosphorus by precipitation, water disinfection, and advanced oxidation process (AOP). This approach is effective in improving treatment water quality, but it causes an increase in consumption operating costs due to continuous chemical injection. These unit processes were researched to improve the process efficiency, and CNT was applied to various processes as one of the promising nanomaterials. CNT has been evaluated as a nanomaterial that can be applied to environmental applications due to its electrical, physicochemical, and mechanical complex properties. CNT has been applied to the membrane separation process by utilizing its high mechanical and chemical strength and fast water molecule transport properties for improvement of water permeability. By using CNTs’ compact and entangled porous structure and high electrical conductivity, CNTs were applied to identify the effect of direct interspecies electron transfer mechanism for biogas production in the anaerobic digester. As a catalytic characteristic of CNT, it was studied in the advanced oxidation process for the reduction of non-degradable organic matters. Further, CNTs have been applied as an electrically conductive material for the membrane fabrication to introduce electroactivity as an additional membrane function, called an electroactive membrane or electrified membrane. This approach could achieve not only the traditional membrane fiction of solute separation, but also electro-based phenomena, including electrochemical oxidation and reduction, electrostatic adsorption and rejection, electrophoresis, and electroporation. Among various conductive materials including carbon, metal or metal oxide, and conductive polymer, CNT is the most extensive material for the electrified membrane, because of its high electrical conductivity and ease of fabrication porous and compact structure. In this way, CNTs are being tried for various environmental applications by utilizing their conductivity. In short, application of electrically conductive membrane has a potential to environmental applications: (i) the degradation of organic compound, (ii) the decontamination of heavy metal ions, and (iii) electro active-based antifouling membranes. Therefore, the potential to address these applications was evaluated in this thesis. First, the recent progress in the synthesis of CNT and fabrication of CNT membrane methods, with particular emphasis on improving water permeability and anti-biofouling properties was reviewed. Then, potential applications of CNT membranes other than water purification (e.g., conductive membranes, electrodes in proton exchange membrane fuel cells, and solar electricity–water generators) have been introduced. Also, future outlooks are provided to overcome the limitations of commercialization and desalination currently faced by CNT membranes. Second, singlet oxygenation and mediated electron transfer as plausible nonradical mechanisms for organic degradation by carbon nanotube-activated peroxymonosulfate were explored by introducing CNT membrane that inhibits ionic substance exchange. The 1O2 scavenging effect was ascribed to a rapid PMS depletion by l-histidine and azide. Also, a comparison of CNT/PMS and photoexcited Rose Bengal (RB) excluded the possibility of singlet oxygenation during heterogeneous persulfate activation. concomitant PMS reduction and trichlorophenol oxidation were achieved when PMS and trichlorophenol were physically separated in two chambers using a conductive vertically aligned CNT membrane. Third, chromium compound could be biologically and sustainably reduced through the vertically aligned carbon nanotube composite without growth inhibition by using electron transfer from an electron shuttle secreted by P. aeruginosa to Cr(VI) even in the microbial inhibitory concentration of Cr(VI). The bioelectrochemical reactor achieved a Cr(VI) removal rate of 99.6 % at 100 mg/L, which is the highest reduction rate using P. aeruginosa. Our developed microbial Cr(VI) reduction system allows microbial Cr(VI) reduction to overcome hurdles of biological treatment on toxic materials and advance our understanding of microbial electron transfer. Next, the electrically conductive CNT membrane was fabricated for anti-biofouling property using electrical repulsion in MF process. The carbon nanotubes on commercial polyvinylidene fluoride microfiltration membrane was fabricated for biofouling control. The fabricated CNT membranes exhibited few anti-bacterial property and transmembrane pressure retardation under applied cathodic voltage. The CNT membrane under cathodic voltage plays critical role by electrical repulsion of bacteria, and a 50.0% of reduction of transmembrane pressure and 58.9 % of reduction of extracellular polymeric substances was achieved on the membrane surface. The irreversible and reversible biofouling resistance were diminished to 32.6 and 3.8 %. This study thus shows a electrical repulsion effect of the CNT membrane can be a useful strategy for controlling biofouling during the MF process without bacterial growth inhibition. Finally, electrified membranes were fabricated using CNT and graphene for self-cleaning through bubble generation on cathodic membrane. The fabricated CNT/graphene membrane had low toxicity to microorganism and exhibited high stability even under overvoltage (i.e., 15 V). The self-cleaning effect was investigated under the applied voltages and application times and evaluated by water flux recovery. The developed self-cleaning membrane achieved more than 4 log viable cell removal, and 95.2% total EPS removal in 10 minutes. Additionally, it improved the irreversible biofouling removal effect by 30.9% in short time than the conventional physical cleaning method. Through filtration and self-cleaning cycle, 100% water flux recovery was achieved and the stability of the CNT/graphene membrane was verified. In this study, it was confirmed that the insufficient recovery of self-cleaning through conventional water electrolysis is due to the residual biofilm caused by EPS and improved the water flux recovery efficiency using high voltage, suggesting that this can be overcome by a combination of various strategies including physical cleaning. 역사상 유래 없는 산업화와 도시화는 새로운 난분해성, 독성 오염물질의 출현을 야기하였고 이에 노출된 환경으로부터 오염물질들을 제거하기 위한 연구들이 수행되어왔다. 수계내 오염물질을 제거하기 위한 기술로써 수처리기술들이 개발되었으며, 기존의 수처리시설은 물리적, 생물학적, 화학적 처리공정으로 구성되어 있다. 하지만 새로운 오염물질의 출현으로 인해 이러한 단위 공정들의 개선이 필요하게 되었다. 탄소나노튜브는 전기적, 물리화학적, 기계적인 특성으로 인해 수처리시설의 단위공정들을 개선하기위해 심도 깊게 연구되어온 나노 물질이다. 물리학적 처리공정의 일환으로 탄소나노튜브의 물 분자 수송 특성을 활용하여 투수성이 향상된 막 분리 공정에 연구되었다. 또한 탄소나노튜브의 다공성 구조와 높은 전기 전도성을 활용해 혐기성 소화조에서 바이오 가스 생산 속도를 개선하기 위한 생물학적 처리 기술 연구에 적용되었다. 뿐만 아니라 난분해성 유기오염물질을 제거하기 위한 고도산화공정에서도 탄소나노튜브의 촉매적 특성을 활용한 연구가 실시되었다. 최근 분리막에 촉매적 특성을 부여하는 전기활성막 연구들이 시도되고 있다. 전기활성막은 기존 분리막에 전도성 재료를 도입하여 전통적인 오염물질의 분리 뿐만 아니라 다양한 전기 기반 현상을 달성할 수 있다. 탄소나노튜브는 타 전도성 재료 대비 높은 전기 전도성과 다공성 구조체 형성의 용이함으로 인해 가장 널리 사용되는 재료이다. 이러한 전기활성막은 (1) 유기 오염물질의 분해, (2) 중금속 이온의 무해화, (3) 전기활성 기반 항오염성 막 분야에 응용 가능성을 가질 것으로 평가받는다. 따라서 본 학위 논문에서는 이러한 응용분야에 대한 적용가능성에 대한 연구를 실시하였다. 첫째, 난분해성 유기오염물질에 대한 분해 메커니즘의 규명하고 둘째, 독성 중금속 이온의 생물학적 처리 공정을 평가하였다. 셋째, 막분리 공정에 적용을 위해 정전기적 반발을 통한 생물막오염 저해 막을 평가하였고 넷째, 생물막오염의 자가세정이 가능한 전기활성막 연구를 실시하였다. 본 학위 논문을 통해 전기활성막의 응용분야에 대한 적용가능성을 평가하였고 현재 개발된 전기활성막의 한계점과 개선방법에 대해 제시하였다.

6가 크롬의 세포독성에 대한 3-HBA, 3,4,5-THBA 및 3,3,4,5,7-PBDA의 해독효과

최병남 원광대학교 2007 국내박사