699-29 Synthesis and Characterization of Nano-Mn(IV) Oxide Phases.

Poster Number 228

See more from this Division: Z01 SSSA-ASA-CSSA Special Programs--Invited Abstracts Only
See more from this Session: National Science Foundation Poster Session

Wednesday, 8 October 2008
George R. Brown Convention Center, Exhibit Hall E

Jason Fischel1, Matthew Ginder-Vogel2 and Donald Sparks2, (1)Dept. of Plant and Soil Sciences and the Center for Critical Zone Research, University of Delaware, Newark, DE
(2)Department of Plant and Soil Sciences and the Center for Critical Zone Research, Univ. of Delaware, Newark, DE
Abstract:
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Manganese(IV) oxides represent one of the main redox catalysts in subsurface environments, while also extensively sorbing anions and cations. Their wide-spread distribution in soil, combined with their highly reactive surfaces, allow manganese(IV) [Mn(IV)] oxides , even at low concentration, to oxidize trace metals. For example, they are capable of oxidizing mobile, toxic arsenite [As(III)] to arsenate [As(V)] which is less toxic and mobile. However, in environmental settings many, Mn(IV) oxide minerals form as nanometer-size particles, either through biological or surface catalyzed Mn(II) oxidation. The reactivity and surface chemistry of nano-Mn(IV) oxide phases is poorly understood and may be profoundly different than their more crystalline counterparts. In this paper we characterize nano-Mn(IV) minerals synthesized using both sol-gel and citrate ion reduction methods and compare these to bulk minerals of biogenic and abiotic origin. X-ray diffraction confirmed that the mixed Mn oxidation state mineral hausmanite was formed using both of these syntheses. The Mn oxidation state at the mineral surface is determined using X-ray photoelectron spectroscopy (XPS) and the bulk oxidation state and local structure will be determined using X-ray absorption spectroscopy (XAS). Additionally, mineral morphology has been analyzed using field emission gun scanning electron microscopy (FEG-SEM). A particle size of ~12 nm was determined via XRD, dynamic light scattering (DLS), and high-resolution transmission electron microscopy (HR-TEM).  A comparison of the reactivity of these various particles will be presented in a companion paper.

See more from this Division: Z01 SSSA-ASA-CSSA Special Programs--Invited Abstracts Only
See more from this Session: National Science Foundation Poster Session