Synthesis, Characterization, and Application of Transition Metal Oxide Nanoplates

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 인력을통하여2차원라멜라 구조를 이루는 약1나노정도의두께를지니는산화망간을합성할수있었다. 뿐만 아니라용매와리간드사이의 파이-파이인력을조절하여산화망간 나노플레이트의길이를 8 nm에서70nm까지조절할수있었다. 또한, 표면개질 반응을 통하여 나노플레이트 표면을 친수화 시킬 수 있었으며, 이를 자기공명영상 조영제로응용하여자기공명영상증강 효과를보여주었다. 다음으로앞에서합성된산화망간 나노플레이트를사용하여,소듐산화망간구조를성공적으로합성하였다.소듐산화망간 나노입자의 모양과크기는산화망간 나노플레이트의 크기를변화시켜서 제어가능하였으며, 그의결정구조는 층상 거리가 약 0.56 나노미터 떨어진 turbostratic 구조로 밝혀졌다. 결정성이 좋은 물질을 얻기 위하여 온도를 높여 열처리를진행하였으며, 이를 통해서층상형구조인 P2-Na0.7MnO2.05 마이크로 입자로변화되었다. 이러한소듐산화망간층상구조체는소듐이온배터리의양극물질로적용되었으며, 기존에발표된소듐산화망간물질 전극에비해용량의증가뿐아니라안정된충방전특성을보였다. 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.