Environmentally benign synthesis and application of some spinel ferrite nanoparticles.

摘要

In this thesis, the commercial viability of the aminolytic synthesis method is explored through robustness, versatility, and waste reduction studies. Since the development of a versatile, inexpensive, environmentally compatible, and large scale synthesis method for spinel ferrites nanoparticles has been pursued for years, we report the preparation of simplistic metal precursors and the development of a synthetic approach that could be used to prepare a variety of pure and doped spinel ferrites via the aminolytic reaction of metal carboxylates in a mixture of oleylamine and noncoordinating solvent. The magnetic properties of the nanoparticles are studied by a variety of analytical techniques; these properties also show the effect of surface anisotropy for less than 10 nm particles. In turn, the aminolytic reaction is proven to be an inexpensive and versatile synthetic route for manganese ferrites and can be extended to the rest of the spinel ferrite family.;With a consideration towards potential applications, the reaction is tested with a variety of dopants in an effort to correlate atomic arrangements with physical properties. Magnetic nanoparticles are being increasingly incorporated into sensing technology. Magnetostrictive properties of oxide materials are particularly useful in sensing changes in operating systems due to their good response and chemical robustness. The magnetic properties and responses of the spinel ferrites system are greatly influenced by quantum couplings of the magnetic ions. Thus understanding the couplings between these ions allows for manipulation of the desired magnetic properties. Manganese doping in the cobalt ferrite systems allows for the investigation of the effects of orbital momentum quantum coupling by exchanging a metal ion with high orbital momentum contribution, Co2+, with a metal ion with no orbital momentum contribution, Mn2+.;The last test of the versatile and robustness of the aminolytic methods is the synthesis of a series of manganese ferrites dope with chromium. These ferrites show increasing magnetic frustrated responses. This doping allows for the investigation of the effects of orbital momentum quantum coupling by exchanging a metal ion with high orbital momentum contribution, Fe 3+, with a metal ion with no orbital momentum contribution, Cr 3+. Low chromium concentrations strengthen the L-S couplings due to the unquenched angular orbital momentum. High chromium concentration weakens the couplings between the A and B sites which results in the decreasing in the overall magnetic moment by destroying the magnetic arrangement. Chromium coupling on similar sites is very strong and at x=1 result in a disorder state. At higher concentrations, x=2, magnetic spins start canting resulting from the loss of antiparallel alignment that defines the spinel ferrite magnetic system. In our series at the highest doping concentration, there is a dramatic shift in magnetic properties.;Finally, one environmental conscious application, desalination, is explored in this thesis through the use of aminolytic particles, iron oxides. There are many forms of iron oxides and most of these structures are used in arsenic removal techniques. The iron oxide is formed in-situ by adding a non-oxide iron source to water. The exact nature of the arsenic binding and the effect of impurities on binding efficiency are not well known. Synthesizing well characterized iron oxides will afford better understanding of the arsenic surface binding. Better understanding of the binding affinity for arsenic is necessary for the incorporation of iron oxides into the best available technologies (BATs). Several nanometer sized samples of goethite (alpha-FeO(OH)), maghemite (gamma- Fe2O3), magnetite (Fe3O 4), and hematite (alpha-Fe2O3) were synthesized and characterized using XRD, SQUID, PAS-IR, EDS, and TEM.;Our research, along with most of the literature, indicates that the hematite phase has the highest arsenic removal affinity of the iron oxide adsorbent class. In trying to harness this adsorption potential merged with the magnetic control seen in spinel ferrites, we have synthesized core-shell Iron Oxides Cobalt Ferrites. This was done via the aminolytic method using a previously synthesized CoFe2O4 core which was reacted with iron oxide. Both samples, hematite and maghemite core-shell particles, were exposed to various concentration of arsenite and maghemite core-shell particles were found to have the higher removal affinity. This results from the difference in size between the core-shell nanoparticles with the maghemite derivative being 8 nm and the hematite derivative, 20 nm. (Abstract shortened by UMI.).