Raman spectroscopy of synthetic and natural iowaite

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2005-02, Vol.61 (4), p.613-620
• Main Authors: Frost, Ray L., Adebajo, Moses O., Erickson, Kristy L.
• Format: Article
• Language: English
• Subjects: Air; Aluminum Hydroxide - chemistry; Carbon - chemistry; Chlorides - chemistry; Electrons; Ferrous Compounds - analysis; Ferrous Compounds - chemistry; Hydrotalcite; Infrared spectroscopy; Iowaite; Magnesium - chemistry; Magnesium Hydroxide - chemistry; Molecular Conformation; Oxygen - chemistry; Raman spectroscopy; Spectrophotometry; Spectrophotometry, Infrared - methods; Spectrum Analysis, Raman - methods; Time Factors; X-Ray Diffraction
• ISSN: 1386-1425
• DOI: 10.1016/j.saa.2004.05.015

The chemistry of a magnesium based hydrotalcite known as iowaite Mg 6Fe 2Cl 2(OH) 16·4H 2O has been studied using Raman spectroscopy. Iowaite has chloride as the counter anion in the interlayer. The formula of synthetic iowaite was found to be Mg 5.78Fe 2.09(Cl,(CO 3) 0.5)(OH) 16·4H 2O. Oxidation of natural iowaite results in the formation of Mg 4FeO(Cl,CO 3) (OH) 8·4H 2O. X-ray diffraction (XRD) shows that the iowaite is a layered structure with a d(0 0 1) spacing of 8.0 Å. For synthetic iowaite three Raman bands at 1376, 1194 and 1084 cm −1 are attributed to CO 3 stretching vibrations. These bands are not observed for the natural iowaite but are observed when the natural iowaite is exposed to air. The Raman spectrum of natural iowaite shows three bands at 708, 690 and 620 cm −1 and upon exposure to air, two broad bands are found at 710 and 648 cm −1. The Raman spectrum of synthetic iowaite has a very broad band at 712 cm −1. The Raman spectrum of natural iowaite shows an intense band at 527 cm −1. The air oxidized iowaite shows two bands at 547 and 484 cm −1 attributed to the (CO 3) 2− ν 2 bending mode. Raman spectroscopy has proven most useful for the study of the chemistry of iowaite and chemical changes induced in natural iowaite upon exposure to air.