Rivera Betancourt, Omar E.

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    Synthesis and characterization of copper nanoparticles: Architectural morphologies and applications in surface enhanced raman spectroscopy
    (2009) Rivera Betancourt, Omar E.; Hernández Rivera, Samuel P.; College of Arts and Sciences - Sciences; Vega, Carmen A.; Mina Camilde, Nairmen; Department of Chemistry; Crespo, Jose A.
    The preparation of copper colloidal suspensions was conducted by three different methods. These methods used wet chemical synthesis, in which a metal salt solution was mixed with a solution containing the reducing agent. Preparation of the copper seed involved chemical reduction using trisodium citrate. Steadiness varied under conditions such as stirring rate, rate of addition of reducing agent and temperature control. Sizes of nanoparticles prepared ranged from 2 to 20 nm. Morphology and sizes were characterized using High Resolution Transmission Electron Microscopy (HRTEM). Enhanced Raman spectra of o-dinitrobenzene on prepared nanoparticles suspensions of Cu were obtained with visible excitation at 488 and 514.5 nm. It was found that enhanced Raman signal intensities resulted from the interaction of the analytes with the metallic surface resonance plasmon of Cu nanoparticles excited at the laser frequency. The adsorption behavior of the analytes on the Cu nanoparticles was modeled using Density Functional Theory (DFT) of the Gaussian 03 software package. The simplified model used worked reasonably well in describing some enhancement results for the Raman experiments on the noble metal colloidal suspensions. In another chemical procedure copper nanoparticles were synthesized via a one step process. In this procedure the reactant concentration and temperature strongly influenced the shaped of the copper particles. As a result bigger diameters (e.g. 100 nm) were produced. Different shapes and narrow sized distributions were also obtained. At low reagent concentration, the particles were cubic and at high reagent concentration, the particles were spherical. SERS activity was studied for different nitro aromatic compounds at different temperatures and copper colloid concentration. Beta-cyclodextrin (β-CD) in alkaline solution has been observed to produce mono and bimetallic nanoparticles of silver and gold and to provide in-house stability to both of the particles. We report on the use of copper-gold bimetallic nanoparticles to obtain the Raman activity spectra of crystal violet on the surface of these nanoparticles. UV-VIS spectrophotometry was used to characterize the bimetallic nanoparticle architecture and the evolution of the architecture. It was found that the approximate size of the nanoparticle was 20 nm and the morphology of the nanoparticles was club-shaped seeds. Based on experimental data, average FWHM of the absorption band in the visible region for bimetallic structures was around 45 nm which indicates a colloidal suspension of modest monodispersity. Based on these results, synthesized colloids tend to form sort of like double layer cluster architecture, since the composition of the nanoparticles showed a narrow spectrum of sizes and shapes. Raman activity of crystal violet ion using as excitation sources 514.5 and 532 nm lasers was measured. It was found that at an excitation source of 514.5 nm, the signal enhancement of crystal violet (5.0 x 10-6 M) was much greater than at 532 nm. Results suggest that the orientation of crystal violet ion is perpendicular to the surface of the bimetallic structure.