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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 limes greater than that of previous reports for electrolytic manganese oxide. A packed bed of 1-10-μm 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-μm ambigel particulates supported on interdigitated array electrodes with 20-μm 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. [ABSTRACT FROM AUTHOR]

Abstract: In an adaptation of sol–gel methods recently described for preparing iron oxide (FeO x ) aerogels, we use epichlorohydrin as a proton scavenger to generate mixed metal oxides from ethanol solutions of Mn- and Fe-chloride salts. This reaction forms monolithic gels, which can be processed with supercritical CO2 extraction to form high-surface-area, highly porous Mn–FeO x aerogels. The amorphous as-prepared Mn–FeO x aerogel is transformed into a nanocrystalline form by heating in argon to 300°C. Elemental analysis shows that a Fe:Mn ratio of 2:1 is attained, and the X-ray diffraction pattern for the nanocrystalline aerogel is consistent with that for spinel MnFe2O4, confirming that Mn(II) from the initial sol–gel mixture is incorporated into the crystal structure of the resulting oxide. The nanocrystalline Mn–FeO x aerogel exhibits magnetic properties consistent with a superparamagnetic material, while still retaining the characteristic morphology of an aerogel nanoarchitecture. [Copyright &y& Elsevier]

Abstract: We recently reported the encapsulation of a heme protein superstructure within a sol–gel-derived material processed to form gas-phase-active bioaerogels. The protein superstructure, nucleated in the liquid phase by colloidal gold, protects cytochrome c protein molecules within the superstructure to the extent that they survive the harsh physical and chemical processing conditions necessary to form the aerogel and retain long-lived stability at room temperature. In this investigation, we report the effects of altering the size of the colloidal metal nanoparticle upon the viability of the aerogel-encapsulated proteins, and examine the number of protein molecules that can be assembled into a gold-nanoparticle-nucleated superstructure. The resultant bioaerogels exhibit stable electronic-state spectra at room temperature for 6weeks for the protein molecules encapsulated in the biocomposite nanoarchitecture. [Copyright &y& Elsevier]