| Summary: | 博士 === 國立臺灣大學 === 化學研究所 === 97 === This thesis focuses on developing facile synthetic approaches to fabricate nanomaterials of different compositions, including tellurium (nanowires), gold-tellurium (nanomatches, nanodumbbells, and nanopeapods), gold (pearl-necklace nanomaterials), and platinum (nanosponges, nanonetworks, and nanodendrites). These nanomaterials were prepared through galvanic replacement reactions between Te nanowires and metal ions (AuCl43– and PtCl62–). Chapter 1 introduces the physical and chemical properties of nanomaterials as well as briefly describes the techniques and background relating to this thesis. The development of synthesizing fluorescent Te nanowires at room temperature is discussed in chapter 2. The nanowires are prepared from the reduction of tellurium dioxide with concentrated hydrazine solution through deposition of Te atoms that are oxidized from telluride ions and dissolved from amorphous Te nanoparticles onto trigonal nanocrystallines. By carefully controlling the growth time from 40 to 120 min, different sizes of trigonal Te nanowires can be prepared; the length changes from 251 to 879 nm while the diameter only grows from 8 to 19 nm. In chapter 3, a simple method for preparing three different surface-enhanced Raman scattering (SERS)-active substrates is described. The as-prepared Te nanowires are used as templates and reducing agents for the deposition of Au nanoparticles. Through the reaction of Te nanowires with AuCl43– ions in the presence of hexadecyltrimethylammonium bromide (CTAB) over reaction times of 10, 20, and 60 min, Au-Te nanodumbbells, Au-Te nanopeapods, and Au pearl-necklace nanomaterials are obtained, respectively. By altering the reaction time, the distance between adjacent Au nanoparticles in each Te nanowire is tunable and allows investigating its effect on the SERS signals. Having shorter distances among Au nanoparticles (greater electromagnetic fields), the Au pearl-necklace nanomaterials provided a reproducible enhancement factor of 5.6 x 109. In chapter 4, an advanced approach for highly selective growth of Au nanoparticles onto Te nanowires is discussed. By carefully selecting the pH values to vary the redox reaction potential between AuCl43– ions and Te nanowires, allowing control of nucleation and growth rates of Au nanoparticles. In the presence of 10 mM CTAB, Au-Te (one end) and Au-Te-Au (both ends) nanowires are obtained at pH 4.0 and 5.0, respectively. Photovoltaic data revealed that the resistance of the Te nanowires-based thin film is controlled by the degree of deposition of Au nanoparticles. It is suspected that Au-Te and/or Au-Te-Au nanowires hold great potential for use in the fabrication of electronic devices. Chapter 5 describes synthesis of various porous Pt nanomaterials in aqueous solution through a similar chemical route. Employing different temperatures and concentrations of sodium dodecyl sulfate (SDS), Pt nanosponges, Pt nanonetworks, and Pt nanodendrites are obtained from the reduction of PtCl62– ions via galvanic replacement reactions with Te nanowires. At ambient temperature, Pt nanosponges and Pt nanodendrites formed selectively in the presence of SDS at concentrations of <10 mM and >50 mM, respectively. At elevated reaction temperatures, Pt nanonetworks and Pt nanodendrites were obtained in the presence of SDS at concentrations of <10 mM and >50 mM, respectively. TEM images revealed that these Pt nanomaterials are all composed of one dimensional Pt nanostructures having widths of 3 nm and lengths of 17 nm. Cyclic voltammetry data indicates that the as-prepared Pt nanonetworks, nanosponges, and nanodendrites possess large electrochemically active surface areas (77.0, 70.4, and 41.4 m2 g–1, respectively). For the electrocatalytic oxidation of methanol, the ratio of the forward oxidation peak current (If) to the backward peak current (Ib) of the Pt nanodendrites, nanosponges, and nanonetworks are all high (If/Ib = 2.88, 2.66, and 2.16, respectively). These three nanomaterials exhibit greater electrocatalytic activities and excellent tolerance toward poisoning species for the oxidation of methanol when comparing with the performance of standard Pt nanomaterials. Because of their low cost of preparation, high purity, good stability, and excellent electrocatalytic activities, it is believed that these as-prepared Pt nanomaterials will be effective catalysts for use in fuel cells.
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