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Debra R Rolison

Publications and source records attributed to Debra R Rolison.

7 recordsLinked to original sources
PubMed2005

Using an oxide nanoarchitecture to make or break a proton wire.

We report that long-range proton diffusion (>0.3 mm) is generated in monolithic ultraporous manganese oxide nanoarchitectures upon exposure to gas-phase water. The sol-gel-derived ambigel nanoarchitectures, with bicontinuous networks of covalently bonded nanoscale solid and through-connected mesopores, exhibit conductometric sensitivity to humidity as established by impedance spectroscopy. The spectra contain a Warburg feature from which the concentration and diffusion length of the protonic charge carriers are determined. Water adsorbs conformally onto the architecture's continuous solid network in equilibrium with atmospheric humidity to create a continuous water sheath that acts as a 3-D proton wire. As a result, monolithic manganese oxide ambigels exhibit an equilibrium conductometric response to humidity that is 14 times greater than that of previous reports for electrolytic manganese oxide. A packed bed of 1-10-microm ambigel particulates in physical contact with one another, each with the same nanoscale morphology as the monolithic nanoarchitecture, also support long-range proton diffusion; however, the sensitivity to humidity is four times lower than the monolithic form due to restricted proton transport between adjacent particulates. Films composed of 0.3-12-microm ambigel particulates supported on interdigitated array electrodes with 20-microm electrode spacing express finite-diffusion behavior due to the short distance between the contact electrodes and have a conductometric sensitivity to humidity comparable to electrolytic MnO2 and 17 times lower than the monolithic ambigel. These results suggest that controlling the nature of the porous and solid phases in a nanoarchitecture provides a mechanism to limit interference from condensed water in conductometric gas-phase sensors. In addition, continuous monolithic architectures should improve electrochemical performance in devices where efficient long-range transport of protons or other ions is critical.

Journal Article↗
PubMed2004

Nanocrystalline iron oxide aerogels as mesoporous magnetic architectures.

We have developed crystalline nanoarchitectures of iron oxide that exhibit superparamagnetic behavior while still retaining the desirable bicontinuous pore-solid networks and monolithic nature of an aerogel. Iron oxide aerogels are initially produced in an X-ray-amorphous, high-surface-area form, by adapting recently established sol-gel methods using Fe(III) salts and epoxide-based proton scavengers. Controlled temperature/atmosphere treatments convert the as-prepared iron oxide aerogels into nanocrystalline forms with the inverse spinel structure. As a function of the bathing gas, treatment temperature, and treatment history, these nanocrystalline forms can be reversibly tuned to predominantly exhibit either Fe(3)O(4) (magnetite) or gamma-Fe(2)O(3) (maghemite) phases, as verified by electron microscopy, X-ray and electron diffraction, microprobe Raman spectroscopy, and magnetic analysis. Peak deconvolution of the Raman-active Fe-O bands yields valuable information on the local structure and vacancy content of the various aerogel forms, and facilitates the differentiation of Fe(3)O(4) and gamma-Fe(2)O(3) components, which are difficult to assign using only diffraction methods. These nanocrystalline, magnetic forms retain the inherent characteristics of aerogels, including high surface area (>140 m(2) g(-1)), through-connected porosity concentrated in the mesopore size range (2-50 nm), and nanoscale particle sizes (7-18 nm). On the basis of this synthetic and processing protocol, we produce multifunctional nanostructured materials with effective control of the pore-solid architecture, the nanocrystalline phase, and subsequent magnetic properties.

Journal Article↗
PubMed2004

Silver-colloid-nucleated cytochrome c superstructures encapsulated in silica nanoarchitectures.

We recently discovered that self-organized superstructures of the heme protein cytochrome c (cyt. c) are nucleated in buffer by gold nanoparticles. The protein molecules within the superstructure survive both silica sol-gel encapsulation and drying from supercritical carbon dioxide to form air-filled biocomposite aerogels that exhibit gas-phase binding activity for nitric oxide. In this investigation, we report that viable proteins are present in biocomposite aerogels when the nucleating metal nanoparticle is silver rather than gold. Silver colloids were synthesized via reduction of an aqueous solution of Ag+ using either citrate or borohydride reductants. As determined by transmission electron microscopy and UV-visible absorption spectroscopy, the silver nanoparticles vary in size and shape depending on the synthetic route, which affects the fraction of cyt. c that survives the processing necessary to form a biocomposite aerogel. Silver colloids synthesized via the citrate preparation are polydisperse, with sizes ranging from 1 to 100 nm, and lead to low cyt. c viability in the dried bioaerogels (approximately 15%). Protein superstructures nucleated at approximately 10-nm Ag colloids prepared via the borohydride route, including citrate stabilization of the borohydride-reduced metal, retain significant protein viability within the bioaerogels (approximately 45%).

Chemical Phenomena↗
PubMed2003

Catalytic nanoarchitectures--the importance of nothing and the unimportance of periodicity.

Heterogeneous catalysis has always been an inherently nanoscopic phenomenon with important technological and societal consequences for energy conversion and the production of chemicals. New opportunities for improved performance arise when the multifunctionality inherent in catalytic processes, including molecular transport of reactants and products, is rethought in light of architectures designed and fabricated from the appropriate nanoscale building blocks, including the use of "nothing" (void space) and deliberate disorder as design components. Architectures with all of the appropriate electrochemical and catalytic requirements, including large surface areas readily accessible to molecules, may now be assembled on the benchtop. Designing catalytic nanoarchitectures that depart from the hegemony of periodicity and order offers the promise of even higher activity.

Journal Article↗
PubMed2003

Sonochemically induced decomposition of energetic materials in aqueous media.

This study demonstrates that ultrasound rapidly degrades the energetic compounds RDX (cyclo-1,3,5-trinitramine-2,4,6-trimethylene) and ADN (ammonium dinitramide) in aqueous microheterogeneous media. The conditions for effective degradation of these nitramines, as monitored by UV absorption spectroscopy, were determined by varying sonication time, the heterogeneous phase and its suspension density, and the concentration of NaOH. In the presence of 5 mg/ml of aluminum powder and at pH approximately 12 (10 mM NaOH), 74% of the RDX and 86% of the ammonium dinitramide (ADN) in near-saturated solutions decompose within the first 20 min of sonication (20 kHz; 50 W; < or =5 degrees C). Sonication without Al powder and base yields minimal degradation of either RDX and ADN (approximately 5-10%) or the nitrite/nitrate ions that are expected byproducts during RDX and ADN degradation. Sonication at high pH in the presence of dispersed aluminosilicate zeolite, alumina, or titanium dioxide also yields minimal degradation. Preliminary electrochemical studies and product analyses indicate that in situ ultrasonic generation of metallic aluminum and/or aluminum hydride drives reductive denitration of the nitramines. Sonochemical treatment in the presence of a reductant offers an effective and rapid waste remediation option for energetic waste compounds.

Hazardous Substances↗
PubMed2002

Transmission electron microscopy studies of the nanoscale structure and chemistry of Pt50Ru50 electrocatalysts.

The structural and chemical heterogeneity of 2.5-nm Pt50Ru50 electrocatalysts was studied by transmission electron microscopy using selected area diffraction, lattice imaging, electron-energy loss spectroscopy, and energy-dispersive X-ray spectroscopy. The catalysts with the highest methanol oxidation activities exhibit oxidation-induced phase separation on the nanoscale to from Pt-rich metal embedded in Ru-rich hydrous and anhydrous oxide. Reduction of the oxide-on metal samples produces a true bimetallic face-centered cubic Pt50Ru50 alloy, with 275 times lower oxidation activity.

Alloys↗