Osorio Cantillo, Celia M.

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    Size controlled synthesis of metallic magnetic nanocrystals for potential data storage and biomedical applications
    (2013) Osorio Cantillo, Celia M.; Perales-Pérez, Oscar J.; College of Arts and Sciences - Sciences; Meléndez, Enrique; Román, Felix; Torres, Jessica; Department of Chemistry; Valentin, Ricky
    Magnetic nanoparticles have attracted extensive interest in recent years due to their potential applications as a consequence of their tunable magnetic properties. Therefore, research efforts are focused on the development and understanding of synthesis routes in order to control their size, structure, composition, and chemical reactivity at the nanoscale. The suitable control of those factors makes these nanomaterials potential candidates for diverse applications, including data storage and nanomedicine. Due to its phase-dependent and size-dependent magnetic properties, metallic cobalt can be considered a promising material for the desired applications. On this basis, the present research addresses the synthesis and characterization of metallic magnetic nanoparticles, and the determination of the relationship between synthesis conditions, metal structure, composition, crystal size and functional properties at the nanoscale. Metalic cobalt was synthesized via a modified polyol route. In this process, the polyol acts as both solvent and reducing agent. The synthesis were carried out using different polyols, e. g. ethyleneglycol (EG), trimethyleneglycol (TMG), triethyleneglycol (TEG), and tetraehtyleneglycol (TREG). The experimental results evidenced that the formation of a specific Co phase was strongly influenced by the synthesis parameters, for instance, the nature of polyol, the presence of OH- ions, and the reaction time. Accordingly, metastable pseudo-cubic epsilon cobalt (ε-Co), the hexagonal close-packed (hcp-Co) phase, and the face-centered cubic (fcc-Co) phases were stabilized. Additionally, the control in the size of the synthesized particles was achieved by the suitable selection of surfactants or stabilizing agents through homogeneous nucleation, or by the proper selection and concentration of seeds of noble metals like Pt, Pd, and Ag, via heterogeneous nucleation. Consequently, highly monodisperse micrometric, submicrometric, and nanometric Co particles exhibiting different structures were produced including: 0.68 ± 0.05μm ε-Co, 2.10 ± 0.4μm hcp-Co in TMG; 5.13 ± 0.6 nm fcc-Co in EG; and 10nm hcp-Co nanocrystals in TREG. Also, 0.20-0.80 μm of fcc-NixCo100-x, particles were synthesized in EG. The strong effect of the crystal structure, size, shape, and composition on the magnetic properties of the synthesized structures was also confirmed. The suitable control of the synthesis conditions allowed the formation of particles with hard magnetic characteristics that exhibited coercivity values between 700 to 1261 Oe, which can be considered suitable for data storage applications. Particles with soft magnetic characteristics were also syntehszied and exhibited saturation magnetization values between 140 emu/g and 155 emu/g. These particles are good potential candidates for biomedical applications. Finally, the capability of controlling the phase stability and growth of pure or alloyed Ni-Co particles and the corresponding tuning of their magnetic properties were also investigated. Attained results open new possibilities for the application of the nanocrystalline Co-based particles in the nanotechnology arena.
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    Dynamic of TNT photo dissociation studied by femtosecond laser-mass spectroscopy
    (2006) Osorio Cantillo, Celia M.; Castro Rosario, Miguel E.; College of Arts and Sciencies - Sciences; Hernández Rivera, Samuel P.; López, Gustavo; Department of Chemistry; Cardona, Nelson
    The 2,4,6-trinitrotoluene, (TNT), is a widely used explosive material whose photo-dissociation both as a solid and in solution using light radiation has been previously studied. TNT can be used as suitable molecule to learn about the elementary process involved in photo induced dissociation. Furthermore, results in TNT photochemistry may provide information on sensing schemes for this explosive, which can be extrapolated to the detection of other nitroexplosives. NOâ‚‚ and NO are typically associated with the photodegradation of TNT. Thus studies that can establish the kinectic energy distribution of nascent NOâ‚‚ and secondary NO have the potential of contributing to selective sensing by adding to a library based on differences in internal energy distribution in photoproducts of nitro explosives. The purpose of this study is to establish the kinetic energy distribution of NOâ‚‚ and NO as a product of photo-fragmentation of neat TNT or and TNT on Ottawa sand using femtosecond laser pulses for molecular dissociation and subsequent mass spectrometry measurements as a function of time. Photolysis experiments on TNT deposits irradiated with 100 femtosecond laser pulses at 400 nm and 266 nm wavelengths were performed. NOâ‚‚ and NO were analyzed as key fragments. The obtained data showed that there are slight differences in the NOâ‚‚ and NO speeds from TNT crystals and TNT deposited on sand and vapor phase of TNT. Those results indicate that the energetic processes that result in fragments ejection are different in all cases. In conclusion, photo-fragmentation using femtosecond lasers followed by mass spectrometry measurement is a sensitive approach for the kinetic energy distribution establishment of NO/NOâ‚‚ fragments; besides, its effectiveness could be enhanced coupling it with another spectroscopic method for trace amounts detection of nitrorganic explosives.