Chemistry Commons^™

Comments On The Mechanism Of Aging Of Antimony Doped Tin Oxide Based Electrochromic Devices, Joo C. Chan, Nicole A. Hannah, Shankar B. Rananavare, Laura Yeager, Liviu Dinescu, Ashok Saraswat, Pradeep Iyer, James P. Coleman

Chemistry Faculty Publications and Presentations

Electrochromic effects of antimony doped tin oxide (ATO) nanoparticles are investigated to probe device yellowing (degradation). Voltage vs contrast ratio curves exhibit hysteresis, i.e., image-sticking phenomena due to irreversible charge insertion. X-ray, impedance and optical b* studies suggest that the yellowing/charge trapping is nanoparticle size-dependent with 4 nm size particles exhibiting the least yellowing. Yellowing results in increased impedances of electrode–electrolyte interface and electrode corrosion. Plausible sources of discoloration are formation of insulating complex alkali oxide film, carrier inversion (n-to-p type) through electrochemical Li doping, redeposition of the corroded electrode material and perhaps residual concentration of charge-transfer species.

Covalently Networked Monolayer Protected Nanoparticle Films, D. J. Tognarelli, Robert B. Miller, Rebecca R. Pompano, Andrew F. Loftus, Daniel J. Shiebley, Michael C. Leopold

Chemistry Faculty Publications

No abstract provided.

Low-Temperature Activation Conditions For Pamam Dendrimer Templated Pt Nanoparticles, Anil Singh, Bert D. Chandler

Chemistry Faculty Research

Surface immobilized polyamidoamine (PAMAM) dendrimer templated Pt nanoparticles were employed as precursors to heterogeneous catalysts. CO oxidation catalysis and in situ infrared spectroscopy were used to evaluate conditions for dendrimer removal. Infrared spectroscopy showed thatPAMAMdendrimer amide bonds begin decomposing at temperatures as low as 75 °C. Although the amide stretches are completely removed after 3 h of oxidation at 300 °C, 16 h were required to reach maximum catalytic activity. Further treatment under oxidizing or reducing atmospheres did not cause substantial changes in activity. Infrared spectroscopy of the activated materials indicated that organic residues, probably surface carboxylates, are formed during …

Magnetic Properties Of (Γ-Fe₂O₃)₈₀Ag₂₀ Nanocomposites Prepared In Reverse Micelles, Joan A. Wiemann, Jianbiao Dai, Jinke Tang, Gary J. Long, Leonard Spinu

Chemistry Faculty Research & Creative Works

The magnetic properties of nanoparticles of gamma-Fe2O3 prepared by reverse micelles have been studied by dc magnetization, transverse ac susceptibility, and Mössbauer spectroscopy. The nanoparticles of gamma-Fe2O3 in the nanocomposite (gamma-Fe2O3)80Ag20 exhibit superparamagnetic behavior. The blocking temperatures determined by the three methods indicate the superparamagnetic nature of (gamma-Fe2O3)80Ag20 above 70-80 K and show correlation with measuring time. The average particle diameter obtained by transmission electron microscopy of the gamma-Fe2O3 particles is ~10 nm and that of the Ag particles is ~20 nm. The average particle size determined from the magnetic analyses for the gamma-Fe2O3 particles is ~12 nm. Mössbauer spectra …

The Characterization Of Nanosized Nickel-Zinc Ferrites Synthesized Within Reverse Micelles Of Ctab/1-Hexanol/Water Microemulsion, Vuk Uskoković, Miha Drofenik, Irena Ban

Pharmacy Faculty Articles and Research

Stoichiometric nanocrystalline nickel–zinc ferrites were synthesized by a reverse micelle method following a multi-microemulsion approach. Different pH values were chosen for the alkali precipitating reaction during the synthesis of different powders. Synthesized, as-dried and subsequently calcined powders were characterized in terms of their magnetic properties. XRD analyses and specific-surface area measurements were used to determine the average particle sizes of the synthesized samples. DCS and TGA measurements were performed to reveal the phase transitions within the samples at elevated temperatures, whereas TEM was used to view and record the microstructure of the nanosized ferrite samples. A possible mechanism of the …

Synthesis And Characterization Of Dendrimer Templated Supported Bimetallic Pt-Au Nanoparticles, Huifang Lang, S. Maldonado, K. J. Stevenson, Bert D. Chandler

Chemistry Faculty Research

Bimetallic dendrimer-stabilized nanoparticles (DSNs) were used to prepare supported Pt-Au catalysts within the bulk miscibility gap for this binary system. Hydroxy-terminated generation 5 PAMAM dendrimers were used to prepare Cu0 nanoparticles (NPs). The Cu⁰ NPs were subsequently used to reduce K₂PtCl₄ and HAuCl₄, preparing stabilized bimetallic Pt-Au NPs with a 1:1 stoichiometry. The stabilized NPs were adsorbed onto a high surface area silica support and thermally activated to remove the dendrimers. Transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and infrared spectroscopy of adsorbed CO showed that this preparation route resulted in NPs in …

Application Of Microgels For Optical Tagging, J. Michael Carthcart, L. Andrew Lyon, Marcus Weck, Robert D. Bock

Biology, Chemistry, and Environmental Sciences Faculty Books and Book Chapters

In this paper we present results from our research into the use of microgel-based photonic crystals in an optical tagging application. The basis for this research is the phenomena of self-assembly of hydrogel nano- and microparticles (i.e., microgels) into colloidal crystal Bragg reflectors. Previous research has demonstrated the assembly of Bragg structures that are sensitive in the visible spectral region. This current research focuses on the extension of this process into the infrared regime and the use of these infrared-sensitive structures in the creation of an optical tag. In particular, the research effort emphasizes two primary areas: the development of …

Characterization And Magnetic Properties Of Core/Shell Structured Fe/Au Nanoparticles, Sung-Jin Cho, Susan M. Kauzlarich, Justin Olamit, Kai Liu, Fernande Grandjean, Leïla Rebbouh, Gary J. Long

Chemistry Faculty Research & Creative Works

Au-coated Fe nanoparticles have been prepared by using a reverse micelle method through reduction of an aqueous solution. Characterizations have been carried out over time to probe the oxidation of Fe. Immediately after synthesis, the samples exhibit metallic conduction and a negative magnetoresistance, consistent with the presence of α-Fe. The temperature dependence of magnetization displays a maximum at a blocking temperature of around 150 K. After a period of 1 month, the samples exhibit insulating behavior, indicating the oxidation of the Fe core. Mössbauer spectroscopy indicates the presence of an α-Fe component and a broad distribution of local environments.

Self-Assembled Arrays Of Zno Nanoparticles And Their Application As Varistor Materials, Suresh Pillai, Declan Mccormack, John Kelly, Raghavendra Ramesh

Articles

Linear arrays of ZnO nanoparticles have been successfully prepared by a simple sol–gel condensation reaction involving chemical modifiers, followed by drying (80oC) and calcination (500 oC). The calcined material (nanoarray ZnO) is composed of approximately spherical nanoparticles of average diameter 21+/-3 nm, selfassembled to form arrays extending in length to 2–4 mm. The morphology of the ZnO is found to depend sensitively on the amounts of chemical modifiers present. In their absence the ZnO produced (nano-ZnO) is an unstructured agglomerate of nanoparticles. The mechanism for formation of these linear arrays has been investigated by examining the intermediates formed at 80 …

Distance-Dependent Electron Hopping Conductivity And Nanoscale Lithography Of Chemically-Linked Gold Monolayer Protected Cluster Films, Francis P. Zamborini, Laura E. Smart, Michael C. Leopold, Royce W. Murray

Chemistry Faculty Publications

Films of monolayer protected Au clusters (MPCs) with mixed alkanethiolate and ω-carboxylate alkanethiolate monolayers, linked together by carboxylate–Cu2+–carboxylate bridges, exhibit average edge-to-edge cluster spacings that vary with the numbers of methylene segments in the alkanethiolate ligand as determined by a combined atomic force microscopy (AFM)/UV-Vis spectroscopy method. The electronic conductivity (σEL) of dry films is exponentially dependent on the cluster spacing, consistent with electron tunneling through the alkanethiolate chains and non-bonded contacts between those chains on individual, adjacent MPCs. The calculated electronic coupling factor (β) for tunneling between MPCs is 1.2 Å−1, which is similar to …

Growth, Conductivity, And Vapor Response Properties Of Metal Ion-Carboxylate Linked Nanoparticle Films, Michael C. Leopold, Robert L. Donkers, Dimitra Georganopoulou, Megan Fisher, Francis P. Zamborini, Royce W. Murray

Chemistry Faculty Publications

Nanoparticles of metals (Au, Ag, Pd, alloys) in the size range 1–3 nm diameter can be stabilized against aggregation of the metal particles by coating the metal surface with a dense monolayer of ligands (thiolates). The stabilization makes it possible to analytically define the nanoparticle composition (for example, Au140(hexanethiolate)53, I) and to elaborate the chemical functionality of the protecting monolayer (for example, Au140(C6)35(MUA)18, II, where C6 = hexanethiolate and MUA = mercaptoundecanoic acid). Network polymer films (IIfilm) on interdigitated array electrodes can be prepared from II, based on cation coordination (i.e., Cu2+, Zn2+, Ag+, methyl viologen) by the …

Simulations Of Quantized Double Layer Charging Voltammetry Of Poly Disperse And Mono-Disperse Monolayer Protected Clusters, Deon T. Miles, Michael C. Leopold, Jocelyn F. Hicks, Royce W. Murray

Chemistry Faculty Publications

This paper describes simulated differential pulse voltammetry (DPV) of quantized double-layer charging (QDL) in poly-disperse monolayer-protected gold cluster (MPC) solutions. The simulation accounts for the voltage spacing between QDL peaks with a concentric sphere capacitor model, in which core sizes, and the relative proportion of each size, are input using transmission electron microscopy (TEM) data. MPC diffusion coefficients are estimated from hydrodynamic radii, and peaks are broadened to account for DPV pulse height effects. The smallest MPCs are omitted from the simulation because electrochemical HOMO/LUMO gap information is uncertain. The largest ones are shown to produce the underlying DPV current …

Hplc Of Monolayer-Protected Gold Nanoclusters, Victoria L. Jimenez,, Michael C. Leopold, Carolyn Mazzitelli, James W. Jorgenson, Royce W. Murray

Chemistry Faculty Publications

Polydisperse samples of Au nanoparticles protected with monolayers of hexanethiolate ligands (C6 MPCs) and with mixed monolayers of hexanethiolate and mercaptounde- canoic acid (C6/MUA MPCs) have been chromatographically separated using C8 120-Å columns and acetone/toluene mobile phase. The spectral details of eluted peaks and of quantized double-layer charging features in the differential pulse voltammetry of collected fractions were used to show that the elution orders of C6 MPC mixtures and of C6/MUA MPC mixtures were different. For C6 MPCs, the smallest MPCs were eluted first, whereas the smallest C6/MUA MPCs were eluted last. The reversal of order of elution was …

Distributions Of Nobel Metal Pd And Pt In Mesoporous Silica, J. Arbiol, A. Cabot, J. R. Morante, Fanglin Chen, Meilin Liu

Faculty Publications

Mesoporous silicananostructures have been synthesized and loaded with Pd and Pt catalytic noble metals. It is found that Pd forms small nanoclusters (3–5 nm) on the surface of the mesoporous structure whereas Pt impregnation results in the inclusion of Pt nanostructures within the silica hexagonal pores (from nanoclusters to nanowires). It is observed that these materials have high catalyticproperties for CO–CH₄CO–CH₄CO–CH₄ combustion, even in a thick film form. In particular, results indicate that the Pt and Pd dispersed in mesoporous silica are catalytically active as a selective filter for gas sensors.

Electron Hopping Conductivity And Vapor Sensing Properties Of Flexible Network Polymer Films Of Metal Nanoparticles, Francis P. Zamborini, Michael C. Leopold, Jocelyn F. Hicks, Pawel J. Kulesza, Marcin A. Malik, Royce W. Murray

Chemistry Faculty Publications

Films of monolayer protected Au clusters (MPCs) with mixed alkanethiolate and ω-carboxylate alkanethiolate monolayers, linked together in a network polymer by carboxylate-Cu2+-carboxylate bridges, exhibit electronic conductivities (σEL) that vary with both the numbers of methylene segments in the ligands and the bathing medium (N2, liquid or vapor). A chainlength-dependent swelling/contraction of the film's internal structure is shown to account for changes in σEL. The linker chains appear to have sufficient flexibility to collapse and fold with varied degrees of film swelling or dryness. Conductivity is most influenced (exponentially dependent) by the chainlength of the nonlinker (alkanethiolate) ligands, a result consistent …

New Approaches To Processing Nanoparticles And Nanostructures, Mathew M. Maye

Undergraduate Honors Theses

The study of nanoparticles is an emerging field of nanoscience and nanotechnology. A challenging issue is how deliberate tailoring and processing of the nanoscale materials can lead to well defined and functional nanostructures. In this thesis, we explore new strategies of nanoscale design and processing to address the challenge.

A core-shell chemical processing route towards fabrication of functional composite nanomaterials with defined sizes, shapes, compositions and surface properties is demonstrated. New findings of an investigation of thermally-activated core-shell reactivities of nanoparticles in solutions are described. Gold nanoparticles of ~2-nm core size with thiolate monolayer encapsulation were chosen as a model …