Clays and Clay Minerals, Vol. 58, No. 2, 164–173, 2010.
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Authors
Aouad, Amina
Anastacio, Alexandre S.
Bergaya, Faiza
Stucki, Joseph W.
Issue Date
2010
Type
Article
Language
Keywords
Periodicals , Geology , Akaganeite , Aluminum , Iron , Laponite , Montmorillonite , Mossbauer Spectroscopy , Pillared Clay
Alternative Title
A Mossbauer Spectroscopic Study Of Aluminum- And Iron-pillared Clay Minerals
Abstract
The placement of metal oxide pillars between clay mineral layers modifies their physicalchemical properties, including surface area, acidity, and catalytic activity. Aluminum is the most commonly used pillar cation, but theus eof Fe offers a distinct opportunity to expand therangeof catalytic behavior. The purpose of this study was to prepare Fe-pillared Laponite and montmorillonite and to characterize the resulting Fe phase(s). Laponite or montmorillonite suspension was mixed with different pillaring solutions containing Al oligomer and/or Fe oligomer with Fe:(Al+Fe) percent ratios ranging from 0 to 100%. TheAl oligomer was obtained by hydrolysis of AlCl3·6H2O with NaOH at pH 4.4 and the Fe oligomer was prepared by FeCl3 hydrolysis with Na2CO3 at pH 2.2. Thepillare d clay was obtained by adding the oligomer to the clay suspension, then heating to 300ºC for 3 h. The Fe oligomer and the pillared clay minerals were characterized by variable-temperature Mo¨ssbauer spectroscopy, X-ray powder diffraction, and chemical analysis. The unheated Fe oligomer was akaganeite, an Fe oxyhydroxide phase. Heating the Fe oligomer to 300ºC transformed the akaganeite to hematite, but heating it in the presence of the clay protected it, at least partially, from this transformation, creating instead a phase which resembled a more poorly ordered akaganeite or a mixture of akaganeite and poorly ordered hematite. Mixing of Al and Fe oligomers in the pillaring solution had no effect on the magnetic hyperfine field of the Fe pillars, indicating that Al forms separatepill ars rather than substituting for Fein thepi llar. A small fraction (4%) of the Fe pillar resisted reductive dissolution by citrate-bicarbonate-dithionite.
Description
gsccm58203-aou.pdf : 479KB
Citation
Clays and Clay Minerals, Vol. 58, No. 2, 164–173, 2010.
Publisher
The Clay Minerals Society
License
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