Porous tin oxide nanotubes were obtained by vacuum infiltration of tin oxide nanoparticles into porous aluminum oxide membranes, followed by calcination. The porous tin oxide nanotube arrays so prepared were characterized by FE-SEM, TEM, HRTEM, and XRD. The nanotubes are open-ended, highly ordered with uniform cross-sections, diameters and wall thickness. The tin oxide nanotubes were evaluated as a substitute anode material for the lithium ion batteries. The tin oxide nanotube anode could be charged and discharged repeatedly, retaining a specific capacity of 525 mAh/g after 80 cycles. This capacity is significantly higher than the theoretical capacity of commercial graphite anode (372 mAh/g) and the cyclability is outstanding for a tin based electrode. The cyclability and capacities of the tin oxide nanotubes were also higher than their building blocks of solid tin oxide nanoparticles. A few factors accounting for the good cycling performance and high capacity of tin oxide nanotubes are suggested. / Singapore-MIT Alliance (SMA)

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisors: Dionisios G. Vlachos and Raul F. Lobo, Dept. of Chemical Engineering Includes bibliographical references.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Mary E. Galvin-Donoghue, Dept. of Materials Science & Engineering. Includes bibliographical references.

Europium-doped-fluorochlorozirconate glass ceramics, known as ZBLAN, were produced in a glove box which has a controlled environment of argon gas. For imaging applications BaCl2 is used instead of BaF2. Their properties after different thermal processing and different amounts of europium-doping were investigated. After annealing the ZBLAN glass, BaCl2 nanoparticles are precipitated in the glass matrix. These glass ceramic storage phosphors are strong candidates for replacing traditional x-ray screen film system and commercial storage phosphors such as Agfa MD-30. Differential scanning calorimetry (DSC) was used to determine the crystallization temperature of the hexagonal phase of BaCl2, and orthorhombic BaCl2 this in turn determines the subsequent annealing temperature. X-ray diffraction (XRD) and photoluminescence (PL) show that the hexagonal phase of BaCl2 was formed upon annealing at temperatures between 250 °C and 280 °C for 5 minutes. The orthorhombic phase of BaCl2, which has storage properties, was formed at higher annealing temperatures, at approximately 290 °C and above. Secondary ion mass spectroscopy (SIMS) was used to determine adsorbed/diffused oxygen content of the glass. The weight loss of fluorine and chlorine is 3-5 % and was determined using ion chromatography (IC). The concentration of other cations was determined using inductively coupled plasma spectroscopy (ICP). Transmission electron microscopy (TEM) was used to take high resolution pictures and verify the composition of BaCl2 nanoparticles. The relative concentration of Eu2+ to Eu3+ of heated EuCl3 and ZBLAN was studied using Mössbauer spectroscopy. The oxidation of Eu2+ to Eu3+ was also observed during the experiment. This study has reinforced the strong potential for application of glass-ceramic storage phosphors for medical imaging.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references. Also available in electronic version.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 153-161).

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Dendrimer-encapsulated nanoparticles (DENs) were prepared, characterized, and immobilized on solid surfaces. The resulting films were applied as electrocatalysts for the oxygen reduction reaction (ORR). First, the synthesis, physical and chemical properties, and stability of Pd DENs prepared within poly(amidoamine) (PAMAM) dendrimers were studied in aqueous solution. In this part of the study, the following new findings were reported: (1) the maximum Pd ion loading in the dendrimer was correlated to the number of interior amines available for complexation; (2) Pd DENs could be synthesized within amine-terminated Pd DENs by controlling the solution pH; (3) the oxidative stability of Pd DENs was significantly improved by removing solution-phase impurities; (4) exposure to hydrogen gas reversibly converts partially oxidized Pd DENs back to the zerovalent state. Second, Pt and Pd DENs were prepared using amine-terminated PAMAM dendrimers, and then the free amine groups on the periphery were used to immobilize Pt and Pd DENs onto Au surfaces via an intermediate self-assembled monolayer. The resulting DEN films were more robust and had higher coverages of DENs compared to the DEN films prepared via physisorption. Third, Pt DENs were prepared and immobilized on glassy carbon electrodes using an electrochemical coupling method. The resulting films were electrochemically active for the ORR. These electrocatalytic monolayers were also robust, surviving up to 50 consecutive electrochemical scans for ORR and sonication in acid solution with no significant change in activity. Finally, PtPd bimetallic nanoparticles containing an average of 180 atoms (~1.8 nm in diameter) and composed of seven different Pt:Pd ratios were prepared within sixth-generation, hydroxyl-terminated PAMAM dendrimers. Transmission electron microscopy and single-particle energy dispersive spectroscopy confirmed the sizes and compositions of the particles. These DENs were immobilized on glassy carbon electrodes, and their electrocatalytic properties were evaluated as a function of composition using cyclic voltammetry and rotating disk voltammetry. The results showed that the maximum rate for the ORR occurs at a Pt:Pd ratio of 5:1, which corresponds to a relative mass activity enhancement of 2.5 compared to otherwise identical monometallic Pt nanoparticles.

Molecular dynamic simulation is utilized to investigate the adsorption mechanism of water molecules surrounding Au nanoparticle of different sizes. We selected 13, 55, 147 atoms icosahedral gold nanopartilce in our model and their diameter are 7.92Å, 13.2Å, 18.5Å, respectively. We calculated density profile of water molecules and found that there were two adsorption layers out of the surface of gold nanoparticles. We also calculated average number of hydrogen bonds per water . It is higer in the adsorption layer than in bulk water region and we found that the direction of hydrogen bonds are numerously parallel with gold surface in the adsorption layer. We also claculated orientational order parameter for water molecules and explore the difference of the tetrahedral structure of the water molecules between the adsorption layer and bulk water region. Besides, we compared of cases of different gold sizes.

Iron oxyhydroxides are ubiquitous in surface environments, playing a key role in many biogeochemical processes. Their characterization is made challenging by their nanophase nature. Magnetometry serves as a sensitive non-destructive characterization technique that can elucidate intrinsic physical properties, taking advantage of the superparamagnetic behaviour that nanoparticles may exhibit. In this work, synthetic analogues of common iron oxyhydroxide minerals (ferrihydrite, goethite, lepidocrocite, schwertmannite and akaganéite) are characterized using DC and AC magnetometry (cryogenic, room temperature), along with complementary analyses from Mössbauer spectroscopy (cryogenic, room temperature), powder X-ray diffraction and scanning electron microscopy. It was found that all of the iron oxyhydroxide mineral nanoparticles, including lepidocrocite, schwertmannite and akaganéite were superparamagnetic and therefore magnetically ordered at room temperature. Previous estimates of Néel temperatures for these three minerals are relatively low and are understood as misinterpreted magnetic blocking temperatures. This has important implications in environmental geoscience due to this mineral group’s potential as magnetic remanence carriers. Analysis of the data enabled the extraction of the intrinsic physical parameters of the nanoparticles, including magnetic sizes. The study also showed the possible effect on these parameters of crystal-chemical variations, due to elemental structural incorporation, providing a nanoscale mineralogical characterization of these iron oxyhydroxides. The analysis of the intrinsic parameters showed that all of the iron oxyhydroxide mineral nanoparticles considered here have a common magnetic moment formation mechanism associated with a random spatial distribution of iv uncompensated magnetic spins, and with different degrees of structural disorder and compositional stoichiometry variability, which give rise to relatively large intrinsic magnetization values. The elucidation of the magnetic nanostructure also contributes to the study of the surface region of the nanoparticles, which affects the particles’ reactivity in the environment.