Controlled synthesis of Eu-SiO2 coated iron oxide nanoparticles

다국어 초록 (Multilingual Abstract)

Colloidal synthesis has been recognized as a useful method for nanoparticle synthesis with controlled size and shape. In a colloidal synthesis, the morphology of nanoparticles is controlled by various parameters such as precursor concentrations, reaction temperature, time, and surfactant ligands. Control of nanoparticle size and shape plays a crucial role in tuning the intrinsic properties in nanoparticle synthesis. After the uniform size and shape of nanoparticles were synthesized, the additional potential of multifunction has arisen in synthesized nanoparticles. In this thesis, it is demonstrated that the selective iron oxide nanoparticle (IONP) synthesis with uniform size and shape depends on the iron precursors and the synthesis of Eu-SiO2 coated IONPs with efficient luminescence and magnetic performance. By depending on the iron precursor, the synthetic conditions of IONPs with uniform morphology were slightly different. In iron oxide synthesis with Fe(acac)3, the shape of IONPs was controlled from an irregular (220, 230oC) to a spherical shape (280, 300oC) depending on the reaction temperature when the IONPs were synthesized with oleylamine (OLAM) and oleic acid (OA). When the reaction temperature was set above 280oC, the size of IONPs was 20 nm with a narrow size distribution. The size of IONPs synthesized with Fe(acac)3 ¬and octadecene (ODE) was dramatically influenced by the concentration of oleic acid (OA) (20 ~ 50 nm). As the concentration of OA was increased, the size of IONPs was decreased by the effect of OA, which can control the nanoparticle growth and prevention of ‘Ostwald ripening’. When the Fe(CO)5 was used as an iron precursor, the oleic acid had a crucial role in the synthesis of IONPs, such as the synthesis with Fe(acac)3 (5 ~ 10 nm). In iron oleate (Fe(OA)3), recognized as a useful iron precursor, controlling the vacuum temperature, which was the synthetic temperature of waxy solid formed iron Fe(OA)3, provided an important condition for IONP synthesis by changing the structure of Fe(OA)3, such as unidentate and bidentate. The size of IONPs synthesized with Fe(OA)3 can be tuned from 5 to 15 nm depending on the pre-treatment condition of vacuum temperature.
After the preparation of size-selective IONPs, europium (Eu)-incorporated IONPs with Eu(TTA)3phen were successfully designed, showing luminescent and magnetic properties. The proposed synthetic method has three steps: (1) IONP synthesis, (2) SiO2 layer coating, and (3) Eu-SiO2 layer coating. First, IONPs with soft magnetic properties were synthesized by the colloidal method. Subsequently, the SiO2 layer was coated on IONPs to prevent the luminescent quenching by introducing the spaces between IONPs and the luminophore. During the 1st coating process, the ethyl acetate content played a crucial role in controlling the interconnection with the neighbouring SiO2 layer on IONPs. Lastly, an Eu(TTA)3phen (ET)-tetraethylorthosilicate (TEOS) complex was introduced through the 2nd coating to endow the SIOPs with the luminescent property. According to the photoluminescence (PL) spectra ranging from 500 to 700 nm, the Eu incorporated SIOPs with Eu(TTA)3phen (ET-SIOPs) exhibited the highest emission intensity compared to the Eu incorporated SIOPs synthesized with other Eu precursors. Furthermore, the ET-SIOPs exhibited long-term luminescence stability for 6 months. In addition, the ET-SIOPs were maintained as paramagnetic properties which were shown in pristine IONPs. The finding of this study will not only provide new insights for the synthesis of luminescent-magnetic NPs with long-term luminescence stability and paramagnetic property but can also offer the design of various multifunctional NPs.

국문 초록 (Abstract)

콜로이드 합성은 크기와 모양이 조절된 나노 입자 합성에 유용한 방법으로 인식되어 왔다. 콜로이드 합성에서 나노 입자의 형태와 크기는 전구체의 종류와 농도, 반응 온도, 시간, 리간드 등의 다양한 변수에 의해 제어된다. 나노 입자 크기 및 모양을 제어하는 것은 나노 입자 합성에서 고유한 특성을 조정하는 데 중요한 역할을 하며, 나노 입자에 다기능성을 부여하는데 있어서도 중요 요소 중 하나이다. 본 연구에서는 크기와 형태가 서로 다른 3개의 전구체를 이용한 산화 철 나노 입자 (IONP) 합성과 합성된 자성 입자에 발광특성을 부여하는 Eu-SiO2 코팅된 IONP의 합성에 관한 연구를 진행하였다. 철 전구체에 따라 균일한 형태와 크기를 갖는 IONP의 합성 조건이 달랐다. Fe(acac)3를 이용하여 합성한 산화철 나노 입자는 oleylamine (OLAM)과 oleic acid (OA)으로 합성한 경우의 반응 온도에 따라 불규칙(220, 230oC)에서 구형(280, 300oC)으로 IONP의 형상을 조절되었다. 반응 온도를 280 oC 이상으로 했을 때, IONP의 크기는 20 nm로 균일하게 합성되었다. Fe(acac)3 및 octadecene (ODE)로 합성된 IONP의 크기는 OA의 농도에 의해 극적으로 영향을 받았다 (20~50 nm). OA의 농도가 높아질수록 나노 입자 성장을 조절할 수 있는 OA의 효과와 'Ostwald ripening' 방지에 의해 IONP의 크기가 감소되는 것을 확인하였다. 철 전구체로 Fe(CO)5를 사용한 경우, OA의 양이 산화 철 나노 입자의 크기를 제어하는데 있어 결정적인 역할을 하였으며, OA의 양이 증가할수록 나노 입자의 크기가 5~10 nm 로 조절되는 것을 확인하였다. Iron oleate (Fe(OA)3)를 이용한 합성에서는 왁스형의 고체를 제조하는 과정에서 진공온도에 따라 Fe(OA)3의 구조를 unidentate형태와 bidentate 형태로 제어할 수 있으며, 이는 나노 입자의 합성에 중요 요소이다. Fe(OA)3로 합성된 IONP의 크기는 진공 온도의 전 처리 조건에 따라 5에서 15 nm로 조절될 수 있었다.
크기 선택형 IONP의 제조 후, Eu(TTA)3phen을 가진 유로퓸(Eu)이 포함된 IONP를 성공적으로 설계하여 발광 및 자기 특성을 보여주었다. 제안된 합성 방법은 (1) IONP 합성, (2) SiO2층 코팅, (3) Eu-SiO2층 코팅의 세 단계를 갖는다. 먼저, 연자성을 갖는 IONP는 콜로이드 방식으로 합성되었다. 이어서, IONP와 발광물질 luminescent quenching을 방지하기 위해 SiO2층을 도입하였다. 첫 번째 코팅 공정에서, 에틸 아세테이트 함량은 인접한 SiO2층과의 상호 연결을 제어하는 데 결정적인 역할을 하였다. 마지막으로 2차 코팅을 통해 Eu(TTA)3phen(ET)-tetraethyl orthosilicate(TEOS) 복합체를 도입하여 발광성을 부여하였다. 500 - 700 nm 범위의 발광 특성 분석을 통해 Eu(TTA)3phen(ET-SIOPs) 가 다른 Eu 전구체와 합성된 Eu-SIOPs에 비해 가장 높은 방출 강도를 보였으며, 6개월 동안 장기 발광 안정성을 보였다. 또한 ET-SIOPs는 IONPs에서 보여지는 상 자기 특성으로 유지되었다. 이 연구의 발견은 장기적인 발광 안정성 및 상 자기 특성을 가진 발광-자기 NP의 합성에 대한 새로운 통찰력을 제공할 뿐만 아니라 다양한 다기능 NP의 설계에 대한 시야를 넓힐 수 있는 연구였다.

목차 (Table of Contents)

• Chapter 1. Introduction 1
• Chapter 2. Controlled synthesis of iron oxide nanoparticles with uniform size and shape 6
• 2.1 Introduction 6
• 2.2 Experimental Section 10
• 2.2.1 Materials 10
• 2.2.2 IONP synthesis by using Fe(acac)3 10
• 2.2.3 IONP synthesis by using Fe(CO)5 11
• 2.2.4 IONP synthesis by using Fe(OA)3 12
• 2.2.5 Characterization 13
• 2.3 Results and discussions 15
• Chapter 3. Design of Eu(TTA)3phen-incorporated SiO2 coated iron oxide nanoparticles for efficient luminescence and magnetic performance 25
• 3.1 Introduction 25
• 3.2 Experimental Section 30
• 3.2.1 Materials 30
• 3.2.2 Synthesis method 31
• 3.2.2.1. Preparation of IONPs 31
• 3.2.2.2. Preparation of SiO2 coated iron oxide nanoparticles (1st coating) 32
• 3.2.2.3. Preparation of Eu(TTA)3phen (ET) powder 33
• 3.2.2.4. Synthesis of ET-, EO, and EN-SIOPs (Eu(TTA)3phen, Eu2O3, and Eu(NO3)36H2O, 2nd coating) 33
• 3.2.2.4. Characterization 34
• 3.2 Results and discussions 36
• Chapter 4. Conclusion 54
• 4.1 Systematization of iron oxide nanoparticle synthesis with various iron precursors and conditions 54
• 4.2 Design of Eu(TTA)3phen-incorporated SiO2 coated iron oxide nanoparticles for efficient luminescence and magnetic performance 56
• References 58
• 국문초록 64
• ACHIEVEMENT 67
• Publications 67
• Presentation 69

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