摘要
氧化鐵奈米粒之合成與其表面改質

藉由高溫的有機溶液法我們可以製備出粒徑六至十二奈米大小的氧化鐵奈米粒。這是利用改變合成的條件參數或是種晶促進長成法(seed-mediated growth)的方法來達成。剛合成出的氧化鐵奈米粒是屬於親油性的粒子，而我們可以經由表面改質的方法進一步的將其改為親水性的粒子。表面改質後的粒子在室溫下，還是具有其改質之前超順磁的性質，但是改質後的阻隔溫度(blocking temperature)卻與改質前的不同。此外我們還成功的合成出CdSe@ZnS此種量子點。所合成出量子點可以和表面改質後而具硫醇基的氧化鐵奈米粒作一個接合(coupling)的動作。由於量子點是具光學特性的材料，並配合上氧化鐵的磁性質，最後所得到的是同時具有光學及磁性的複合材料，而此種材料有機會拿來作生醫上的應用。

Abstract
Synthesis and Surface Modification of Iron Oxide Nanoparticles

Iron oxide nanoparticles were synthesized via hot organic solvent system. The particles’ sizes can be tuned from 6 nm to 12 nm by varying synthetic conditions or seed-mediated growth. The as-synthesized particles are hydrophobic and can be further modified to be hydrophilic ones by surface modifications. The modified particles maintain their superparamagnetic properties under room temperature while the blocking temperature varies after surface modifications. Also we have successfully synthesized CdSe@ZnS quantum dots. The as-synthesized quantum dots are coupled with thiol-functionalized iron oxide nanoparticles. Since QDs are well known with their optical properties and iron oxide nanopartilces are magnetic materials. The resulting nanocomposites are bifunctional with magnetic and optical properties and may have an opportunity for biomedical applications.

Contents

Chapter 1 Introduction…………………………………………………1

1.1 Motivation……………………………………………………………1

Chapter 2 Background………………………………………………….3

2.1 Preparation of Uniform Particles by Wet Chemical Synthesis……….3

2.2 Introduction and Characteristics of Magnetic Nanoparticles………...5
2.2.1 Single Domain…………………………………………………….6
2.2.2 Superparamagnetism……………………………………………...7
2.2.3 Surface Anisotropy………………………………………………..8

2.3 Introduction to Iron Oxide……………………………………….......9
2.3.1 Applications of Iron Oxide………………………………………10
2.3.1.1 Drug Delivery………………………………………………...11
2.3.1.2 Separation…………………………………………………….11
2.3.1.3 Hyperthermia…………………………………………………11
2.3.1.4 Magnetic Resonance Imaging (MRI)………………………...12

2.4 Synthetic Methods of Iron Oxide nanoparticles…………………….13

2.5 Introduction to Quantum Dots………………………………………17
2.5.1 Characteristic: Quantum Size Effect………………………….…18
2.5.2 Advantages of Quantum Dots……………………………………20
2.5.3 Core-Shell structure……………………………………………...20
2.5.4 Synthetic methods……………………………………………….22
2.5.5 Applications of Quantum Dots…………………………………..23
2.6 Surface Modifications……………………………………………….25
2.6.1 Surface Modification by Adding New Materials………………...25
2.6.2 Oil-water Phases Transferring…………………………………...29

Chapter 3 Synthetic Methods and Analysis Technique……………...32

3.1 Experimental Flowchart…………………………………………….32

3.2 Synthetic Methods…………………………………………………..32
3.2.1 The Apparatus of Syntheses……………………………………..33
3.2.2 Reagent List……………………………………………………...33
3.2.3 Details of Experiment Procedures……………………………….34
3.2.3.1 Synthesis of Iron Oxide………………………………………35
3.2.3.2 Surface modification of Iron Oxide…………………………..35
3.2.3.3 Synthesis of CdSe@ZnS..........................................................36
3.2.3.4 Coupling between Iron Oxide and CdSe@ZnS........................37

3.3 Analysis Equipments………………………………………………..37
3.3.1 X-Ray Diffraction (XRD)………………………………………..37
3.3.2 Transmission Electron Microscopy (TEM)……………………...39
3.3.3 Vibrating Sample Magnetometer (VSM)……………………..…40
3.3.4 Superconducting Quantum Interference Device (SQUID)………41
3.3.5 Infrared Spectroscopy (IR)………………………………………42
3.3.6 UV-Visible Absorption Spectroscopy (UV-Vis)…………………43
3.3.7 Photoluminescence Spectroscopy (PL)………………………….44

Chapter 4 Results and Discussion…………………………………….45

4.1 Synthesis, Surface modification, and Magnetic Properties of Iron Oxide Nanoparticles……………………………………….………..45
4.1.1 Controlling Sizes of Iron Oxide Nanoparticles………………….45
4.1.1.1 Controlling the Particles’ Sizes by Changing Different Amounts of Surfactants………………………………………………..45
4.1.1.2 Controlling of Particles’ Sizes by Seed-mediated Growth…...48
4.1.2 Surface Modification of Iron Oxide Nanoparticles……………...49
4.1.3 Characterization of Iron Oxide Nanoparticles…………………...52
4.1.3.1 XRD Analyses………………………………………………..52
4.1.3.2 VSM Measurements………………………………………….54
4.1.3.3 SQUID Measurements………………………………………..55
4.1.3.4 IR Analyses…………………………………………………...57

4.2 Synthesis and Characterization of Quntum Dots (CdSe, CdSe@ZnS)....................................................................................... 58
4.2.1 PL and UV-Vis Analyses………………………………………...59
4.2.2 TEM and EDS Analyses of CdSe and CdSe@ZnS.......................61
4.2.3 PL Spetra of the CdSe and CdSe@ZnS.........................................64

4.3 Results of Coupling between Iron Oxide Nanoparticles and CdSe@ZnS Dots…………………………………………………….64

Chapter 5 Conclusions………………………………………………...69

References…………………………………………………...………….70



List of figures

Figure 2.1 Mechanisms of formation of uniform particles……………………………3
Figure 2.2 Size separating process……………………………………………………5
Figure 2.3 Relations between total energy and sizes of single and multi domain…….7
Figure 2.4 Relations between grain size and coercivity………………………………8
Figure 2.5 Effects of competition between surface anisotropy (Ks) and magneto-crystalline (Ku). Ku/Ks = (a) 1 (b) 10 (c) 40 (d) 60………..……..9
Figure 2.6 Schematic representation of magnetic separation………………………..11
Figure 2.7 MRI images of cancer-targeting iron oxide nanoparticles……………….13
Figure 2.8 TEM images of 2-D hexagonal assembly of γ-Fe2O3 nanoparticles….….14
Figure 2.9 TEM images of (a) 6 nm and (b) 12nm Fe3O4 nanoparticles…………….15
Figure 2.10 TEM images of different shapes of γ- Fe2O3 nanoparticles…………….16
Figure 2.11 TEM images of Fe3O4 nanoparticles with sphere (left) and rod/wire (right) shape…………………………………………………………………...16
Figure 2.12 TEM images of large-scale synthesis of iron oxide nanoparticles. Note that the scale bar is 200nm……………………………………………...17
Figure 2.13 Schematic representation of continuous state to discrete energy states...20
Figure 2.14 CdSe evolution of photoluminescence spectra with ZnSe coating……..21
Figure 2.15 Applications of quantum dots in bioimaging…………………………...24
Figure 2.16 TEM images of Co@CdSe.......................................................................26
Figure 2.17 TEM images of (a) FePt-CdS (b) FePt-ZnS…………………………….26
Figure 2.18 TEM images of combining iron oxide nanoparticles with CdSe@ZnS...28
Figure 2.19 TEM images of (left) FePt@Fe3O4 and (right) Pt@Fe2O3 core shell structures………………………………………………………….…….29
Figure 2.20 Schematic representations of ligand exchage by (right) ionic group and (left) thiol group……………………………………………………..….30
Figure 2.21 TEM images of water-soluble particles by amphiphilic polymer wrapping on the original ones……………………………………………………..31
Figure 3.1 The apparatus of synthesis……………………………………………….33
Figure 3.2 XRD spectrometer……………………………………………………….38
Figure 3.3 The equipment of TEM…………………………………………………..40
Figure 3.4 Scheme of VSM………………………………………………………….41
Figure 3.5 figure of SQUID…………………………….……………………………42
Figure 3.6 The absorption of IR spetra………………………………………….…...43
Figure 4.1 TEM images and histogram of different amounts of surfactants (a) 3 mmole, (b) 0.3 mmole (c) 0.16 mmole, and (d) 0.08 mmole…………….47
Figure 4.2 TEM images of seed-mediated growth of iron oxide nanoparticles (a) once seed-mediated growth with size of 10.0 nm (b) twice seed-mediated growth with size of 12.3nm………………………………………………49
Figure 4.3 TEM images of different siezs of iron oxide nanoparticles after surface modification (a) 7.5 nm (b) 10.3 nm (c) 12.3 nm………………………...51
Figure 4.4 Image of water-soluble and oil-soluble iron oxide nanoparticles. The upper phase is hexane and the bottom phase is water…………………………..52
Figure 4.5 XRD spetra of iron oxide nanoparticles synthesized by
seed-mediated growth with the size of (a) ~8nm (b) ~10nm (c) ~12nm. The particles are dispersed in hexane……………………………….……53
Figure 4.6 XRD spetra of iron oxide nanoparticles after surface modification for the size of (a) ~8nm (b) ~10nm (c) ~12nm. The particles are dispersed in water……………………………………………..……………………….53
Figure 4.7 Hysteresis loops of iron oxide nanoparticles with size of (a) ~8nm (b) ~10nm (c) ~12nm at room temperature. The left hand and right hand side represent before and after surface modifications………………………...55
Figure 4.8 ZFC and FC curves of (a) ~8nm and (b) ~12nm. The left hand and right hand side represent before and after surface modifications…………….57
Figure 4.9 IR analyses of (a) as-prepared and (b) DMSA coated particles………….58
Figure 4.10 Photoluminescence of CdSe dots with spectral range from different sizes.
Excitation is at 366nm ultraviolet light from a hand-held UV lamp……59
Figure 4.11 PL spetra of CdSe obtained from different time intervals……………....60
Figure 4.12 UV-Vis spetra of CdSe obtained from different time intervals………....61
Figure 4.13 (a) HRTEM of CdSe with diameters around 3.3nm and (b) TEM images of CdSe@ZnS with diameters around4.1nm……………………………62
Figure 4.14 EDS spetra of (a) CdSe (b) CdSe@ZnS..................................................63
Figure 4.15 PL spetra of CdSe and CdSe@ZnS..........................................................64
Figure 4.16 TEM images of (a) magnetic nanoparticles coupling with QDs and (b) a local magnified image…………………………………………………..65
Figure 4.17 EDS spetra of figure 4.16(a)…………………………………………....66
Figure 4.18 Images of magnetic nanocomposites attracted by a permanent magnet..67
Figure 4.19 PL spectra of progression from CdSe@ZnS to FeOx+CdSe@ZnS coupling.…………………………………………...…….……………...68

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