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Novel Synthesis of Metal Oxide Nanoparticles via the Aminolytic Method and the Investigation of Their Magnetic Properties A Thesis Presented to The Academic Faculty by Daniel E. Sabo In Partial Fulfillment
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Novel Synthesis of Metal Oxide Nanoparticles via the Aminolytic Method and the Investigation of Their Magnetic Properties A Thesis Presented to The Academic Faculty by Daniel E. Sabo In Partial Fulfillment of the Requirements for the Doctor of Philosophy in the School of Chemistry and Biochemistry Georgia Institute of Technology December 2012 Novel Synthesis of Metal Oxide Nanoparticles via the Aminolytic Method and the Investigation of Their Magnetic Properties Approved by: Dr. Z. John Zhang, Advisor School of Chemistry and Biochemistry Georgia Institute of Technology Dr. Mostafa El-Sayed School of Chemistry and Biochemistry Georgia Institute of Technology Dr. Jiří Janata School of Chemistry and Biochemistry Georgia Institute of Technology Dr. Dong Qin College of Materials Science and Engineering Georgia Institute of Technology Dr. Angus Wilkinson School of Chemistry and Biochemistry Georgia Institute of Technology Date Approved: November 1, 2012 ACKNOWLEDGEMENTS I would like to convey my gratitude to all those who supported and helped me throughout my graduate program here at Georgia Tech. The first person I would like to thank is Dr. John Zhang, who was always there for me whenever I had a question or concern about a project I was working on. I would go to his office all worried and, within just a few minutes, he had me calm and laughing again. I am not sure I would have made it through the program without his helpful suggestions and great stories. I would also like to thank my committee members; Dr. Mostafa El-Sayed, Dr. Art Janata, Dr. Angus Wilkinson, and Dr. Dong Qin, for their feedback and suggestions which have no doubt improved the quality of this thesis. I would also like to take this opportunity to express my gratitude towards Dr. Ding and Dr. Ye Cai for their help in performing TEM on my zirconia and manganese oxide samples, respectively, and Dr. Wen Zhang for helping me to acquire ICP-MS data for my yttrium iron garnet and yttrium iron perovskite samples. Next, I would like to thank past and present group members for their help and suggestions. The first group member I would like to express my gratitude for is Dr. Man Han, who showed me the ropes around the lab and answered every question I posed to him. I would also like to thank Dr. Lisa Vaughan for our conversations which led to some interesting projects, as well as helping me to keep my cool while teaching undergraduate labs. Also I would like to thank Gabriel Hernandez for his humor and his helpful suggestions while reviewing my thesis. Finally, I would like to thank my family and friends for their support and patience. The first person I am grateful to is my wife, Mary, for her unwavering support and patience throughout my entire graduate program. While Dr. Zhang was able to help iii calm me at work, it was Mary who had my back at home. Second, I would like to thank my parents, who always believed in me from the moment in grade school when I came home and told them I wanted to become a mad scientist. I would also like to express my gratitude for my in-laws, the Bonn family, for eagerly admitting me as an honorary member of the Dr. Bonn Club. Finally, I would like to thank my best friends, Marcelo Molina and Terry Kennedy, who have always been there for me whenever I needed to vent or just relax. Thank you, everyone! I truly appreciate all of your support in helping me become Dr. Daniel Sabo! iv TABLE OF CONTENTS ACKNOWLEDGEMENTS LIST OF TABLES LIST OF FIGURES SUMMARY iii viii ix xii Chapter: 1 1 Introduction 1.1 Background of Magnetism Fundamental Theory of Magnetism Origins of Magnetism Magnetic Classification Magnetic Moment Calculation Hysteresis Domain Theory Multi-Domain Theory Single Domain Theory Superparamagnetism Applications of Magnetic Nanoparticles and Metal Oxide Nanoparticles Catalyst Supports/Catalysts Magnetic Microwave Technologies Sensors Biomedicine Spinel Ferrites, Garnets and Perovskites Spinel Ferrites Magnetic Properties of Spinel Ferrites Garnets Magnetic Properties of Garnets Perovskites Magnetic Properties of Perovskites Synthesis Methods for Metal Oxide Nanoparticles Co-precipitation Utilizing Micelles Thermal Decomposition Hydrothermal Sol-gel Aminolytic Method Instrumentation 37 v 1.5.1 Powder XRD TEM SQUID ICP-OES 46 2 CoFe 2 O 4 and MnFe 2 O 4 Nanoparticles Synthesized via the Aminolytic Method Using Various Carboxylate Precursors Abstract Introduction Experimental Precursor Synthesis of CoFe 2 O 4 and MnFe 2 O 4 Nanoparticles Instrumentation Results/Discussion Conclusion References 73 3 The Effect of Cu Substitution on the Magnetic Properties of Manganese Ferrites Nanoparticles Abstract Introduction Experimental Instrumentation Data/Discussion Conclusion References 88 4 Novel Synthesis of Manganese Oxide Nanoparticles and Size-Dependence of Magnetic Properties Abstract Introduction Experimental Precursor MnO Mn 3 O CoFe 2 O 4 /MnO Core/Shell Synthesis Instrumentation Data/Discussion MnO Mn 3 O CoFe 2 O 4 /MnO Core/Shell Conclusion References 115 vi 5 Phase Selective Synthesis of ZrO 2 Nanoparticles Abstract Introduction Experimental Cubic ZrO 2 synthesis Monoclinic ZrO 2 synthesis CoFe 2 O 4 /ZrO 2 Core/Shell synthesis (c-zro 2 shell) CoFe 2 O 4 /ZrO 2 Core/Shell synthesis (mixed c/m-zro 2 shell) Instrumentation Results/Discussion Cubic ZrO Monoclinic ZrO CoFe 2 O 4 /ZrO 2 Core/Shell Conclusion References Novel Synthesis of YIG and YIP Nanoparticles Produced via the Aminolytic Method and Their Magnetic Characterization Abstract Introduction Experimental YIG YIP Instrumentation Data/Results YIP YIG Conclusion Reference 156 Vita 158 vii LIST OF TABLES Page Table ICP-AES of CoFe 2 O 4 nanoparticles from acetate, valerate, and 64 nonanoate precursors Table Minimum temperature required for proper phase/composition 64 formation Table Compiled magnetic data for CoFe 2 O 4 68 Table ICP-AES of MnFe 2 O 4 nanoparticles from acetate, valerate, and 69 nonanoate precursors Table Table 2.4.5: Compiled magnetic data for MnFe 2 O 4 72 Table ICP-OES Cu x Mn 1-x Fe 2 O 4 81 Table ICP-MS of YIP particles prepared at different temperatures 145 Table ICP-MS of particles produced at temperatures between o C 152 viii LIST OF FIGURES Page Figure Diamagnetic material in an applied magnetic filed 3 Figure Paramagnetic material in an external magnetic field 4 Figure Magnetic Susceptibility as a function of temperature 7 Figure A typical hysteresis loop 9 Figure Magnetic alignment of a multi domain structure 11 Figure Magnetic domain movement 12 Figure Stoner-Wohlfarth magnetization reversal illustration 14 Figure Illustration of a circulator 18 Figure Spinel (AB 2 O 4 ) unit cell 21 Figure Unequal antiparallel alignment of magnetic moments in 23 manganese ferrite Figure Formula structure of garnet 24 Figure Polyhedrons of the different sites within garnet 24 Figure Perovskite structure 26 Figure Schematic of a normal (left) and reverse (right) micelle 30 Figure Illustration of a hydrothermal oxidation process used in some 32 hydrothermal methods Figure Schematic of Sol-Gel reactions to product various phases of 34 product Figure Proposed mechanism for the Aminolytic Method 36 Figure Diagram of Bragg s Diffraction 39 Figure TEM aperture system 41 Figure Josephson Junction 43 - ix - Figure SQUID detection coil system 44 Figure Typical temperature dependent magnetic measurement with T B 46 labeled Figure Detection system used in ICP-OES 47 Figure Unequal antiparallel alignment of magnetic moments in 58 manganese ferrite Figure CoFe 2 O 4 nanoparticles produced using acetate, propionate, 63 valerate, and nonanoate precursors. Figure Temperature dependent magnetization of CoFe 2 O 4 65 nanoparticles Figure Hysteresis curves of CoFe 2 O 4 nanoparticles 66 Figure MnFe 2 O 4 nanoparticles produced using acetate, valerate, and 69 nonanoate precursors Figure Temperature dependent magnetization of MnFe 2 O 4 70 nanoparticles Figure Hysteresis curves of MnFe 2 O 4 nanoparticles 71 Figure Unequal antiparallel alignment of magnetic moments in 77 manganese ferrite Figure XRD of Cu x Mn 1-x Fe 2 O 4 80 Figure Field dependent measurement of Cu x Mn 1-x Fe 2 O 4 82 Figure Magnetic properties of Cu doped MnFe 2 O 4 nanoparticles 84 Figure Blocking Temperature (T B ) dependence on copper doping for 85 ~11 nm Cu x Mn 1-x Fe 2 O 4 nanoparticles Figure XRD of MnO nanoparticles produced via the aminolytic 96 method Figure TEM of ~19 nm MnO nanoparticles 97 Figure Temperature dependent magnetization of MnO nanoparticles 98 Figure Hysteresis curves for MnO nanoparticles at 5 K 100 Figure Size dependent magnetic properties of MnO nanoparticles 102 Figure XRD of different sizes of Mn 3 O 4 nanoparticles produced via 103 the aminolytic method. Figure Hysteresis curves for Mn 3 O 4 nanoparticles at 5 K 104 Figure Size dependent magnetic properties of Mn 3 O 4 nanoparticles x - Figure XRD pattern of the core/shell system 109 Figure Temperature dependent measurement of the CoFe 2 O 4 /MnO 110 core/shell system at 100 G Figure Hysteresis curves CoFe 2 O 4 /MnO core shell system at 5 K 112 Figure XRD pattern comparing the standard peaks for cubic (A) and 124 tetragonal (B) Figure XRD pattern of the cubic samples after annealed in air for hours at different temperatures Figure XRD patterns of cubic samples heated at 400 o C for different 126 lengths of time Figure TEM image of the cubic ZrO 2 nanoparticles 127 Figure XRD pattern of the monoclinic samples after annealed in air for hours at different temperatures Figure XRD patterns of monoclinic samples heated at 600 o C for 129 different lengths of time Figure TEM image of the monoclinic ZrO 2 nanoparticles 130 Figure XRD pattern of the core/shell system. C-ZrO 2 Shell 131 Figure XRD pattern of the core/shell system. Mixed ZrO 2 Shell 133 Figure TEM image of the Core-Shell CoFe 2 O 4 -C-ZrO 2 nanoparticles 134 Figure EDX spectrum of Core-Shell CoFe 2 O 4 -C-ZrO 2 nanoparticles 135 Figure XRD pattern of YIP samples after annealed in air for 20 hours 144 at different temperatures Figure XRD patterns of YIP samples heated at 700 o C for different 146 lengths of time Figure Temperature dependent magnetization of YIP sample 147 Figure Magnetic unit cell of YIP 148 Figure Hysteresis loop of YIP nanoparticles at 5 K 148 Figure XRD pattern of YIG samples after annealed in air for 20 hours 150 at different temperatures Figure XRD patterns of YIG samples heated at 800 o C for different 151 lengths of time Figure Temperature dependent magnetization of YIG sample 151 Figure Hysteresis loop of YIG nanoparticles at 5 K xi - SUMMARY Metal oxide nanoparticles, both magnetic and nonmagnetic, have a multitude of applications in gas sensors, catalysts and catalyst supports, airborne trapping agents, biomedicines and drug delivery systems, fuel cells, laser diodes, and magnetic microwaves. Over the past decade, an inexpensive, simple, recyclable, and environmentally friendly large, scale synthesis method for the synthesis of these metal oxide nanoparticles has been sought. Many of the current techniques in use today, while good on the small, laboratory bench scale, suffer from drawbacks that make them unsuitable for the industrial scale. The aminolytic method, developed by Dr. Man Han while working for Dr. Zhang, fits industrial scale-up requirements. The aminolytic method involves a reaction between metal carboxylate(s) and oleylamine in a noncoordinating solvent. This system was shown to produce a range of spinel ferrites. Dr. Lisa Vaughan showed that this method can be recycled multiple times without degrading the quality of the produced nanoparticles. The purpose of this thesis is to test the versatility of the aminolytic method in the production of a wide range of metal oxides as well as various core/shell systems. Chapter 2 explores the effect of precursor carboxylates chain length on the aminolytic synthesis of cobalt ferrite, and manganese ferrite nanoparticles. In Chapter 3, a series of Cu x Mn 1-x Fe 2 O 4, (x ranges from 0.0 to 0.2), nanoparticles were synthesized via the aminolytic method. This series allows for the investigation of the effects of orbital Jahn-Teller distortion as well as orbital angular momentum on the magnetic properties of this ferrite. The quantum couplings of magnetic ions in spinel ferrites govern their magnetic properties and responses. An understanding - xii - of the couplings between these metal ions allows for tailoring magnetic properties to obtain the desired response needed for various applications. Chapter 4 investigates the synthesis of MnO and Mn 3 O 4 nanoparticles in pure single phase with high monodispersity. To the best of our knowledge, the range of sizes produced for MnO and Mn 3 O 4 is the most extensive, and therefore a magnetic study of these systems shows some intriguing size dependent properties. The final part of this chapter investigates the applicability of the aminolytic method for building a MnO shell on a CoFe 2 O 4 core. Chapter 5 explores the synthesis of another metal oxide, ZrO 2 in both the cubic and monoclinic phases with no impurities. The use of the aminolytic method here removes the need for dangerous/expensive precursors or equipment and eliminates the need for extensive high temperature heat treatments that destroy monodispersity which is required for most techniques. The creation of a core/shell system between CoFe 2 O 4 and ZrO 2 using the aminolytic method was also tested. This core/shell system adds magnetic manipulation which is especially useful for the recovery of zirconia based photocatalyst. Chapter 6 studies the application of the aminolytic method in the synthesis of yttrium iron garnet (YIG) and yttrium iron perovskite (YIP) nanoparticles. Current synthesis techniques used to produce YIG and YIP nanoparticles often requires high temperatures, sensitive to contamination, which could be eliminated through the use of our method. - xiii - CHAPTER 1 INTRODUCTION 1.1 Background of Magnetism Fundamental Theory of Magnetism Origins of Magnetism 1-5 Magnetism arises from two electron motions, the spin of an electron, up or down, and the motion of the electron around the nucleus, known as orbital angular momentum. With this in mind, any atom with at least one electron should show magnetism, however it is observed only in materials containing unpaired electrons. This is due to the Pauli s Exclusion Principle, which states that only two electrons of opposite spins can occupy the same orbital resulting in the cancellation of each of their magnetic moments contribution. Good examples of these types of atoms are the 3-d transition metal ions, such as Mn 2+, Cu 2+, and Fe 3+, which contain unpaired electrons. In these ions, the main contributor of the magnetic moment is the unpaired electron spins. Rare earth metals, such as Gd 3+, Pr 3+, and Nd 3+, show magnetic behavior due to the unpaired electron spin as well as orbital angular momentum, which is larger for these ions than in the 3-d transition metals and therefore cannot be ignored. Metal oxides, alloys, and other compounds that contain these types of ions will exhibit magnetic properties. The magnetic induction (B) of a material when placed in an applied magnetic field (H) can be described by B = H+4πM ( ) - 1 - M represents the magnetic moment of a sample per volume. The susceptibility (κ) of a substance is κ = M/H ( ) The ratio of magnetic induction to an applied magnetic field is a material s permeability (P) and can be described as P = 1+4πχ ( ) where χ mol is a material s molar susceptibility and can be represented with χ mol = κf/d ( ) F is the formula weight of the material and d is its density. A magnetic material can be easily classified using its magnetic susceptibility. Each class has a unique magnetic moment alignment and ordering. These different classes each have characteristic susceptibilities, as well as field and temperature dependencies, which contain important magnetic moment alignment and magnitude information Magnetic Classification 3-18 When classifying a material, there are two possible groups that it can fall into based on its magnetic behavior. The first, which involves no interactions between magnetic moments, are diamagnetism. With diamagnetism, the material contains no - 2 - unpaired electrons and, therefore, no net magnetic moment. When the material is exposed to an external magnetic field, it will magnetize in an opposite direction of the applied field and the number of field lines passing through the material is less than if they were passing through a vacuum of the same size and volume. Figure is a good illustration of this phenomenon. Figure : Diamagnetic material in an applied magnetic filed. These types of materials usually have negative susceptibilities and a permeability value less than one. Any material that contains paired core electrons will exhibit small diamagnetic behavior, though its magnitude is much less when compared to magnetic materials. The second classification group is paramagnetism, which involves materials that contain unpaired electrons; however, the overall magnetic moments still do not interact with one another. When the material is placed in an external magnetic field, the number of force lines passing through it is slightly more than a vacuum of the same shape and size. This can be seen in Figure Figure : Paramagnetic material in an external magnetic field. For materials that contain non-interacting localized electrons, the Langevin model says that, because of thermal agitation, the magnetic moment is randomly oriented. When the material interacts with an external magnetic field, the moments align with the field. With an increase in temperature, the thermal agitation also increases, resulting in an increased difficulty in aligning the magnetic moments. The relationship between a material s susceptibility and temperature is described by Curie s Law C ( ) T χ is a material s susceptibility, C is its Curie constant, and T is temperature. This law is only applicable to systems that contain non-interacting magnetic moments. Paramagnetic material will have a positive susceptibility and a permeability greater than one. Ferromagnetism, antiferromagnetism, and ferrimagnetism all fall into the category of paramagnetic systems that have either a positive or negative exchange interactions between neighboring magnetic moments. In ferromagnetic materials, the magnetic - 4 - moments, due to lattice arrangements, will align parallel to each other and will have a positive exchange interaction. It was proposed by Weiss that within these materials there are domains where the magnetic moments will align with respect to one another. When placed in an external magnetic field, the domain walls will move and result in an induced magnetic moment. Due to this relationship of external field and induced magnetic moment, magnetic susceptibility is much less important than saturation magnetization when comparing ferromagnetic materials. When ferromagnetic materials are heated, their saturation magnetization decreases until a critical temperature, T C (Curie temperature, see Figure b). Above this temperature, the material will behave like a paramagnetic material due to the large thermal fluctuations overriding the exchange interactions of the magnetic moments. At temperatures above T C, the material s susceptibility will vary according to Curie-Weiss Law C T ( ) θ is a temperature constant. Below a material s T C, θ will be positive, while its susceptibility is quite large, and contains a permeability much larger than one. Antiferromagnetism involves materials that contain magnetic moments that are of the same magnitude and have a negative exchange interaction. These materials will exhibit diamagnetic behavior unless heated, where they will show paramagnetic properties because of the statistical alignment of magnetic moments. The critical temperature where antiferromagnetic mate
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