title: Manganese Oxide Nanoarchitectures as Broad-Spectrum Sorbents for Toxic Gases.
abstract: We demonstrate that sol-gel-derived manganese oxide (MnOx) nanoarchitectures exhibit broad-spectrum filtration activity for three chemically diverse toxic gases: NH3, SO2, and H2S. Manganese oxides are synthesized via the reaction of NaMnO4 and fumaric acid to form monolithic gels of disordered, mixed-valent Na-MnOx; incorporated Na(+) is readily exchanged for H(+) by subsequent acid rinsing to form a more crystalline H-MnOx phase. For both Na-MnOx and H-MnOx forms, controlled pore-fluid removal yields either densified, yet still mesoporous, xerogels or low-density aerogels (prepared by drying from supercritical CO2). The performance of these MnOx nanoarchitectures as filtration media is assessed using dynamic-challenge microbreakthrough protocols. We observe technologically relevant sorption capacities under both dry conditions and wet (80% relative humidity) for each of the three toxic industrial chemicals investigated. The Na-MnOx xerogels and aerogels provide optimal performance with the aerogel exhibiting maximum sorption capacities of 39, 200, and 680 mg g(-1) for NH3, SO2, and H2S, respectively. Postbreakthrough characterization using X-ray photoelectron spectroscopy (XPS) and diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) confirms that NH3 is captured and partially protonated within the MnOx structure, while SO2 undergoes oxidation by the redox-active oxide to form adsorbed sulfate at the MnOx surface. Hydrogen sulfide is also oxidized to form a combination of sulfate and sulfur/polysulfide products, concomitant with a decrease in the average Mn oxidation state from 3.43 to 2.94 and generation of a MnOOH phase.
authors.affiliation: Code 6170, Surface Chemistry Branch, U.S. Naval Research Laboratory , Washington, D.C. 20375, United States.
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Long
authors.affiliation: Nova Research, Inc. , Alexandria, Virginia 22308, United States.
authors.forename: Jean M
authors.initials: JM
authors.lastname: Wallace
authors.affiliation: U.S. Army Research, Development and Engineering Command, Edgewood Chemical Biological Center , Aberdeen Proving Ground, Maryland 21010, United States.
authors.forename: Gregory W
authors.initials: GW
authors.lastname: Peterson
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland , College Park, Maryland 20742, United States.
authors.forename: Kim
authors.initials: K
authors.lastname: Huynh
keywords: air filtration; ammonia; hydrogen sulfide; manganese oxide; sulfur dioxide