Synthesis, Characterization and Applications of Magnetic-Multimetallic Oxide Nanocrystals

Abstract

Nanotechnology has had a great impact in several industries such as medical and electronics, and more recently in the oil and gas industry. In particular, magnetic nanoparticles are receiving great attention in the oil and gas industry because of their capability to enhance down-hole imaging. Ferrites are selected for this kind of applications because of the magnetic properties they exhibit such as high magnetic susceptibilities and high saturation magnetization. These properties could enhance the resolution of currently used geophysical techniques for imaging oil and gas reservoirs or increase the negative contrast in magnetic resonance imaging (MRI). The Colvin group is well known for the synthesis of monodisperse ferrite nanocrystals, in particular Fe3O4. The research presented in this dissertation extends the previous works and shows the synthesis and physical characterization of spinel ferrites (MFe2O4, M= Mn2+, Co2+, Ni2+, and Zn2+) with a narrow diameter distribution. A very stringent control of the composition and size of the nanocrystals is one of the achievements of this work (Chapter 4). By varying these parameters, size and composition, we can tune the magnetic properties. In addition, characterization of their magnetic properties depending on their size, composition and distinctive surface areas is explored and discussed. The effect of other phenomena such as aggregation on the magnetic properties of nanoparticles was also studied (Chapter 5). This effect becomes important when aggregation is controlled causing a significant enhancement on the magnetic properties. For this reason, the synthesis and characterization of controlled magnetic ferrite nanoclusters was investigated. Magnetic susceptibilities observed in ferrite nanoclusters were much higher than any commercial nanomaterial available and synthesized isolated spinel ferrites. Finally in Chapter 6, we explore the use of nanomaterials herein prepared for several applications, including magnetic separation, MRI contrast agents and contrast agents for down-hole imaging for the oil and gas industry. We utilize magnetic separation as a tool to separate magnetic materials based on composition of nanoparticles. For MRI contrast agents, doping of metals for Fe2+ ions, size and aggregation of nanoparticles were found to significantly influence the MRI signal. Lastly, synthesized magnetic nanoparticles were found to have magnetic susceptibilities three times higher in solution and powders than any commercially available nanomaterial. Due to these high magnetic susceptibilities they could have great potential for down-hole imaging in the oil and gas industry.