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Synthesis, Characterization, and Application of Transition Metal Oxide Nanoplates : 전이 금속 산화물 판상 나노결정의 합성과 분석 및 응용
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- Authors
- Advisor
- 현택환
- Major
- 공과대학 화학생물공학부
- Issue Date
- 2013-08
- Publisher
- 서울대학교 대학원
- Keywords
- Two-dimensional ; nanoplates ; manganese oxide ; titanate ; sodium manganese oxide ; battery
- Description
- 학위논문 (박사)-- 서울대학교 대학원 : 화학생물공학부, 2013. 8. 현택환.
- Abstract
- 이차원 나노 물질은 이차원 모양만의 독특한 성질들로 인하여 학계에서 관심 받고 있는 물질이다. 그에 따라, 최근 2D 전이금속 산화물 합성에 관한 다양한 연구가 발표되고 있다. 이 학위 논문에서는 상향식 접근방법을 통해 2D 금속 산화물 나노입자를 합성하고 이를 응용하는 한 방법에 대하여 기술하였다.
처음으로, 열분해 방법을 통하여 층상 형 구조를 이루는 매우 얇은 산화망간 나노플레이트를 합성하였다. 2,3-dihydroxynaphthalene을 산화망간 나노 플레이트의 리간드로 사용하여 표면을 효과적으로 제어 할 수 있었을 뿐 아니라, 분자 간 인력을통하여2차원라멜라 구조를 이루는 약1나노정도의두께를지니는산화망간을합성할수있었다. 뿐만 아니라용매와리간드사이의 파이-파이인력을조절하여산화망간 나노플레이트의길이를 8 nm에서70nm까지조절할수있었다. 또한, 표면개질 반응을 통하여 나노플레이트 표면을 친수화 시킬 수 있었으며, 이를 자기공명영상 조영제로응용하여자기공명영상증강 효과를보여주었다.
다음으로앞에서합성된산화망간 나노플레이트를사용하여,소듐산화망간구조를성공적으로합성하였다.소듐산화망간 나노입자의 모양과크기는산화망간 나노플레이트의 크기를변화시켜서 제어가능하였으며, 그의결정구조는 층상 거리가 약 0.56 나노미터 떨어진 turbostratic 구조로 밝혀졌다. 결정성이 좋은 물질을 얻기 위하여 온도를 높여 열처리를진행하였으며, 이를 통해서층상형구조인 P2-Na0.7MnO2.05 마이크로 입자로변화되었다. 이러한소듐산화망간층상구조체는소듐이온배터리의양극물질로적용되었으며, 기존에발표된소듐산화망간물질 전극에비해용량의증가뿐아니라안정된충방전특성을보였다.
마지막으로, 약 0.5 nm 두께의 매우 얇은 타이타네이트 나노시트 구조를 성공적으로 합성하였다. 합성된 나노입자는 알칼리 용액과의 반응을 통하여 손쉽게 층상형구조로 조립할 수 있었으며, 이 과정을 통하여 두께나 모양은 변화 없이 소수성의 표면이 친수성으로 개질 되었다. 이렇게 표면처리된 나노시트를 리튬 이온 배터리 음극물질로 활용되었으며, 얇은 2D구조를 활용하여 안정적이며 빠른 충방전 특성을 보여주었다.
Two-dimensional (2D) nanocrystals have attracted tremendous attention from many researchers in various disciplines, because of their unique properties. Recently, several studies on the colloidal synthesis of 2D transition metal oxide nanostructures have been reported. This dissertation describes the synthesis and utilization of 2D metal oxide nanostructures via the bottom-up approach.
Firstly, lamellar-structured ultrathin manganese oxide nanoplates have been synthesized from the thermal decomposition of manganese(II) acetylacetonate in the presence of 2,3-dihydroxynaphthalene, which promoted 2D growth by acting not only as a strongly binding ligand but also as a structure-directing agent. The pi–pi interactions between the 2,3-dihydroxynaphthalene promoted the synthesis of ultrathin manganese oxide nanoplates with thicknesses of ca. 1 nm. Additionally, the nanoplate widths could be controlled in the range 8–70 nm by controlling the pi–pi interactions using various coordinating solvents. These hydrophobic manganese oxide nanoplates were ligand-exchanged with amine-terminated poly(ethyleneglycol) to generate water-dispersible nanoplates and applied to T1 contrast agents for magnetic resonance imaging (MRI). They exhibited very high longitudinal relaxivity value of up to 5.5 mM−1 s−1 due to the high concentration of manganese ions exposed on the surface.
Secondly, layered sodium manganese oxide nanomaterials were successfully synthesized using ultrathin manganese oxide nanoplates as precursors. The crystal structure of the nanostructured sodium manganese oxides was revealed to be a turbostratic structure. Further, the crystal structure of nanostructured sodium manganese oxide was successfully transformed to P2-Na0.7MnO2.05 by heat treatment. The prepared sodium manganese oxide materials were applied as cathode materials for sodium-ion batteries. The materials were shown to deliver high capacity with stable cycling performance.
Finally, ultrathin titanate nanosheets with a thickness of 0.5 nm were successfully synthesized from the non-hydrolytic sol–gel reaction of tetraoctadecyl orthotitanate via the heat-up method. The synthesized nanosheets were easily assembled into layered structures by reaction with hydroxide ion in basic solutions such as LiOH, NaOH, and KOH. The layer-structured nanosheets were employed as anode materials for lithium ion batteries. The nanosheet materials showed fast rapid charging and discharging rates as well as stable cycling due to mechanical stability of the 2D structure. Ultrathin morphology of 2D titanate electrodes affected not only the diffusion path of Li+ ions but also the reaction mechanism from the insertion reaction of the crystal interior to the surface reaction. Furthermore, electrodes composed of layer-structured nanosheets exhibited superior cycling and rate performances.
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- English
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