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Silica Coated Nanocomposites Silica coated nanocomposites By Masih Darbandi A dissertation submitted in requirements for the degree of Doctor der Naturwissenschaften (Dr. rer. Nat.) Faculty of Applied Sciences Albert-Ludwigs-Universität Freiburg im Breisgau 12.12.2007 1 “Silica coated nanocomposites”, a dissertation prepared by Masih Darbandi for the degree, Dr. rer. Nat., has been approved and accepted by the following: Disputation am 12.12. 2007 Dekan: Prof. Nebel Kommissionvorsitzender: Prof. Zacharias 1. Gutachter: Prof. Nann 2. Gutachter: Prof. Rühe Beisitzer: Prof. Urban 2 To my parents Some hadith from Prophet Muhammad: He who travels in the search of knowledge, to him God shows the way of Paradise. The ink of the scholar is more holy than the blood of the martyr. Whoever suppresses his anger, when he has in his power to show it, God will give him a great reward. 3 Contents Abbreviations 9 Preface 10 1 General Introduction 12 1-1-1 Nano & nanotechnology 13 1-1-2 History point in nanotechnology 14 1-1-3 Bottom up & top down 15 1-1-4 A brief review of quantum dots 16 1-1-5 From three- to zero-dimensional systems 18 1-1-6 Quantum dot electronic, absorption and photoluminescence properties 19 1-1-7 Applications of nanocrystals 21 1-2 A brief review on silica encapsulation of nanoparticles 21 1-2-1 Core-shell nanocomposites 22 1-2-2 Advantages of core-shell on bare nanoparticles 23 1-2-3 Advantages of silica shell (colloidal stability, cytotoxicity, etc) 24 1-2-4 Stöber method 26 1-2-5 Modified stöber method (pre-treatment with Silane coupling agents) 28 1-2-6 Microemulsion method 30 1-2-7 Surface derivatization on silica shell 33 References 35 2 Silica encapsulation of CdSe/ZnS nanoparticles by microemulsion (single QD’s in silica spheres) 39 2-1 Introduction 41 2-2 Experimental Section 42 2-2-1 Chemicals 42 2-2-2 Synthesis of CdSe/ZnS core/shell nanocrystals 42 2-2-3 Silica encapsulation of CdSe/ZnS nanocrystals 43 2-2-4 Characterization methods 44 4 2-3 Results and Discussion 44 2-3-1 Characterization of starting CdSe/ZnS nanoparticles 45 2-3-2 Effect of surfactant on CdSe/ZnS/SiO2 nanocomposite 46 2-3-3 Effect of ammonia on CdSe/ZnS/SiO2 nanocomposite 48 2-3-4 Effect of TEOS on CdSe/ZnS/SiO2 nanocomposite 49 2-3-5 Effect of QD’s on CdSe/ZnS/SiO2 nanocomposite 51 2-3-6 Effect of time on CdSe/ZnS/SiO2 nanocomposite 52 2-3-7 Effect of temperature on final nanocomposite 54 2-3-8 Effect of stirring on CdSe/ZnS/SiO2 nanocomposite 55 2-3-9 Room temperature photoluminescence and absorption spectra of CdSe/ZnS/SiO2 nanocomposite 55 2-3-10 Suggestion of mechanism for direct silica encapsulation 56 2-4 Conclusion 59 References 60 3 Generality of silica encapsulation in microemulsion for hydrophobically ligated nanoparticles 62 3- A- Silica encapsulation of hydrophobically ligated PbSe nanocrystals 63 3- A- 1 Introduction 64 3- A- 2 Experimental section 65 3- A- 2- 1 Chemicals 65 3- A- 2- 2 Synthesis of PbSe nanocrystals 65 3- A- 2- 3 Silica encapsulation of PbSe nanocrystals 66 3- A- 2- 4 Characterization methods 67 3- A- 3 Results and Discussion 67 3- A- 3- 1 Characterization of starting PbSe nanoparticles 68 3- A- 3- 2 Characterization of PbSe/SiO2 nanocomposite 69 3- A- 4 Conclusion 73 3- B- Silica coated, water dispersible and photoluminecscent 3+ 3+ Y(V,P)O4:Eu ,Bi nanophosphors 75 3- B- 1 Introduction 76 3- B- 2 Experimental section 77 5 3+ 3+ 3- B- 2- 1 Syntheses of YV(0.7) P(0.3) O4:Eu , Bi nanocrystals 77 3+ 3+ 3- B- 2- 2 Silica encapsulation of YV(0.7) P(0.3) O4:Eu , Bi 78 3- B- 2- 3 Characterization methods 78 3- B- 3 Results and discussion 79 3+ 3+ 3- B- 3- 1 Characterization of the bare YV(0.7) P(0.3) O4:Eu , Bi 79 3+ 3+ 3- B- 3- 2 Characterization of YV(0.7) P(0.3) O4:Eu , Bi /SiO2 80 3- B- 4 Conclusion 85 References 86 4- More investigation on the silica encapsulation, functionalization and Characterization 88 4- 1 Introduction 90 4- 2 Experimental section 91 4- 2- 1 Chemicals 91 4- 2- 2 Preparation of CdSe/ZnS/SiO2 nanoparticles 91 4- 2- 3 Characterization methods 91 4- 3 Result and discussion 92 4- 3- 1 Characterization of CdSe/ZnS/SiO2 nanoparticles synthesized in optimum ondition 92 4- 3- 2 Effect of different catalysts on the synthesis of CdSe/ZnS/SiO2 Nanocomposites 93 4- 3- 3 Effect of electrolyte on synthesis of CdSe/ZnS/SiO2 95 4- 3- 4 Effect of added water on synthesis of CdSe/ZnS/SiO2 97 4- 3- 5 Effect of different surfactant on the synthesis of CdSe/ZnS/SiO2 Nanocomposites 98 4- 3- 6 In- situ functionalization on CdSe/ZnS/SiO2 nanocomposites 100 4- 4 Conclusion 103 References 105 5 Hollow silica nanospheres: synthesis and application 106 5- A Synthesis and characterization of hollow silica nanospheres 107 5- A- 1 Introduction 108 5- A- 2 Experimental Section 109 6 5- A- 2- 1 Chemicals 109 5- A- 2- 2 Preparation of CdSe/ZnS/SiO2 nanocomposite 109 5- A- 2- 3 Characterization 110 5- A- 3 Result and discussion 110 5- A- 3- 1 Characterization of starting CdSe/ZnS/SiO2 110 5- A- 3- 2 Synthesis of hollow silica nanosphere by in-situ way: effect of ammonia 111 5- A- 3- 2 Synthesis of hollow silica nanosphere by in-situ way: effect of time 112 5- A- 3- 3 Synthesis of hollow silica nanosphere by semi in-situ way: etching by base 114 5- A- 3- 4 Synthesis of hollow silica nanosphere by two step way: etching by acid 115 5- A- 3- 5 Different ways to hollow silica nanospheres 116 5- A- 4 Conclusion 117 5- B Hollow silica nanoshperes as nano-mould for synthesising of Au nanoparticles 118 5- B- 1 Introduction 119 5- B- 2 Experimental section 120 5- B- 2- 1 Chemicals 120 5- B- 2- 2 Synthesis of hollow silica nanospheres 120 5- B- 2- 3 Synthesis of Au/silica nanoparticles 120 5- B- 2- 4 Characterization methods 120 5- B- 3 Result and discussion 121 5- B- 4 Conclusion 126 References 127 6 One-pot synthesis of silica coated nanocomposites by Microemulsion 129 6- 1 Introduction 131 6- 2 Experimental section 132 6- 2- 1 Chemicals 132 6- 2- 2 Synthesis process of YF3/SiO2 nanocomposite 132 6- 2- 3 Characterization methods 133 7 6- 3 Result and discussion 133 6- 4 Conclusion 139 References 140 Summary 141 Zusammenfassung 144 VITAE 147 Publication 148 Conference presentation 149 Aknowledgement 150 Declaration 151 8 Abbreviations C Carbon CdSe Cadmium selenide Cu Cupper EDAX Energy Dispersive Analyses of X-ray emission IR Infrared NaCl Natrium Chloride NC Nanocrystal NP Nanoparticle NP-5 Polyethylene glycol nonylphenyl ether O/W Oil in Water microemulsion PB Phosphate Buffer PBS Phospate Buffered Saline PbSe Lead Selenide PL Photoluminescence QD Quantum Dot RT Room Temperature SAED Selected Area Electron Diffraction Si Silicium SiO2 Silica TEM Transmission Electron Microscopy TEOS Tetraethyl orthosilicate Ti Titanium TOP Trioctylphosphine UV Ultraviolet Vis Visible ZnS Zinc Sulphide W/O Water in Oil microemulsion XRD X-ray diffraction YVO4 Yttrium orthovanadate 9 Preface Nanostructured materials are assemblies of nano-sized units which display unique, characteristic properties at a macroscopic scale. The size range of such units lies within the colloidal range, where the individual properties are different to both those of atoms/molecules and to those of the bulk. Therefore, the properties of the nanostructured assemblies can be tuned by varying the colloidal properties of the constituents, mainly particle size, surface properties, interparticle interactions, and interparticle distance. Sometimes nanoparticles can’t be used directly, because of certain limitations such as toxicity, hydrophobicity, interactions with oxygen, etc. These problems can often be solved by intermediate layers or shells. Therefore, derivatization is a pre-requisite for almost any (potential) application of nanoparticles: Either to stabilize functional cores or to functionalize (activate) surfaces. Silica is one of the most flexible and robust surfaces. It’s chemically inert and does not affect redox reactions at the core surface. Moreover, a silica shell is optically transparent in the visible region, so that chemical reactions can be monitored spectroscopically and emitted light is not hindered. Furthermore, the ability to control the thickness of the silica shell implies that the separation between neighbouring particles can be tuned, so that the collective behaviour of the particles within a nanostructure can be tailored. The chemistry of such core/shell particles is well-known and other functional groups could be added to adopt it in desired applications. The preparation of nanoparticles within microemulsions has been shown to be a convenient route towards monodisperse particles of controllable size. This method exploits two useful properties: the capacity to dissolve reactants in the water pool, and the constant exchange of the aqueous phase among micelles. Thus, by mixing microemulsions containing different reactants, it’s possible to perform chemical reactions within the reverse micelles water pools, using it as a nanoreactor. This method has been studied for several years and has been widely used for metal, semiconductor, and oxide nanoparticle synthesis. Regarding above mentioned point, silica encapsulation of nanoparticles by microemulsion method is the main aspect of consideration in this thesis. In the beginning, an overview on nanoparticles and silica encapsulasion are given to create a fundamental background behind the work presented in this thesis.
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