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Investigation of cation ordering in triclinic sodium birnessite via (super 23) Na MAS NMR spectroscopy

Kellie A. Aldi, Jordi Cabana, Paul J. Sideris and Clare P. Grey
Investigation of cation ordering in triclinic sodium birnessite via (super 23) Na MAS NMR spectroscopy
American Mineralogist (May 2012) 97 (5-6): 883-889

Abstract

Birnessite is a widespread, naturally occurring layered manganese oxide that exerts significant influence over the geochemical cycling of environmentally relevant cations due to its high-interlayer adsorption capacity. Triclinic sodium birnessite was used as a synthetic analog to gain a better understanding of the nature of cation adsorption in this important phyllomanganate. Drawing from previous work correlating observed (super 23) Na NMR shifts in manganese oxides with local environment and Mn oxidation state, the (super 23) Na NMR spectra of metastable buserite and two birnessite samples, NaBi-H-I and NaBi-II, were analyzed to determine the nature of the bound interlayer sodium ions in these materials. The small (super 23) Na chemical shift of buserite shows that its interlayer sodium is fully hydrated. X-ray diffraction indicates that NaBi-H-I is a disordered birnessite while NaBi-II is highly crystalline. High-field (14.1 T) fast MAS NMR spectra of NaBi-H-I and NaBi-II supports these observations, resolving multiple sodium environments for NaBi-H-I and only two sodium environments for NaBi-II. The observed hyperfine shifts were less than expected for sodium environments with manganate layers composed of 2/3 Mn (super 4+) and 1/3 Mn (super 3+) ions, and the (super 23) Na line shapes indicated that the Na (super +) ions are in distorted environments. Both these factors suggest that the sodium ions are offset in the interlayers toward a single oxide layer and located near Mn (super 3+) -rich environments within the layer.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 97
Serial Issue: 5-6
Title: Investigation of cation ordering in triclinic sodium birnessite via (super 23) Na MAS NMR spectroscopy
Affiliation: Stony Brook University, Department of Chemistry, Stony Brook, NY, United States
Pages: 883-889
Published: 201205
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 43
Accession Number: 2012-056674
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
Secondary Affiliation: University of Cambridge, GBR, United Kingdom
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201229
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