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Infrared (IR) spectroscopy using a smart endurance single bounce diamond attenuated total reflection (ATR) cell has been used to study the changes in the spectra of the surfactant octadecyltrimethylammonium (ODTMA) bromide upon intercalation into a sodium montmorillonite. The wavenumbers of bands attributed to CH-stretching and CH-bending vibrations, in general, decrease as the concentration of the surfactant measured in terms of the cation exchange capacity (CEC) up to 1.0 CEC. After this point, the bands increase approaching a value the same as that of the surfactant. Significant changes occur in the HCH deformation modes of the methyl groups of the surfactant. These changes are attributed to the methyl groups locking into the siloxane (SiO) surface of the montmorillonite. Such a concept is supported by changes in the SiO-stretching bands of the montmorillonite siloxane surface. [Copyright &y& Elsevier]

Infrared spectroscopy has been used to characterise synthesised hydrotalcites of formula MgxZn6−xCr2(OH)16(CO3) · 4H2O and NixCo6−xCr2(OH)16(CO3) · 4H2O. The infrared spectra are conveniently subdivided into spectral features based (a) upon the carbonate anion (b) the hydroxyl units (c) water units. Three carbonate antisymmetric stretching vibrations are observed at around 1358, 1387 and 1482 cm−1. The 1482 cm−1 band is attributed to the CO stretching band of carbonate hydrogen bonded to water. Variation of the intensity ratio of the 1358 and 1387 cm−1 modes is linear and cation dependent. By using the water bending band profile at 1630 cm−1 four types of water are identified (a) water hydrogen bonded to the interlayer carbonate ion (b) water hydrogen bonded to the hydrotalcite hydroxyl surface (c) coordinated water and (d) interlamellar water. It is proposed that the water is highly structured in the hydrotalcite interlayer as it is hydrogen bonded to both the carbonate anion, adjacent water molecules and the hydroxyl surface. [Copyright &y& Elsevier]

FTIR and Infrared emission spectroscopy (IES) has been used to characterise the Uley (Australian) and Garfield nontronites. These clay minerals are characterised by a strong emission band at 3570 cm−1 attributed to the FeFeOH unit. Dehydroxylation is followed by the loss of intensity of this band as a function of temperature. Dehydroxylation is also followed by the loss of intensity of the FeFeOH deformation vibration at 843 cm−1. IES shows that the dehydroxylation occurs as a continuous process in comparison to DTA/TGA studies where the dehydroxylation occurs abruptly at 425 °C. Water in these high iron bearing smectites have been observed through the stretching mode at 3430 cm−1 and the bending mode at 1630 cm−1. Different types of water are identified in the nontronite structure by the analysis of the band profile in the 1590–1680 cm−1 region. Low frequency vibrations show that the Uley green nontronite is similar to the Garfield nontronite. The brown Uley nontronite is closer to the Hohen–Hagen nontronite. The Uley nontronites may, therefore, be used spectroscopically to replace other nontronites as a reference clay mineral. [ABSTRACT FROM AUTHOR]

The existence of life on planets such as Mars depend upon the presence of water. This water may not necessarily be as liquid or crystalline water but may be as interlayer water such as is found in smectitic clays. One group of smectites, relevant to the search for interplanetary life are those which have a high iron content, known as nontronites. Near-IR reflectance spectroscopy has been used to show the presence of water and hydroxyl units in these minerals. Three near-IR spectral regions are identified, (a) the high frequency region between 6400 and 7400 cm−1 attributed to the first overtone of the hydroxyl stretching mode; (b) the 4800–5400 cm−1 region attributed to water combination modes; and (c) the 4000–4800 cm−1 region attributed to the combination of the stretching and deformation modes of the FeFeOH units of nontronite. Two types of hydroxyl groups were identified using near-IR spectroscopy, hydroxyl units coordinated to the iron; and hydroxyl groups from water in the nontronite structure. The first hydroxyls are characterised by several bands, firstly in the 7055–7098 cm−1 region assigned to the first overtone of the AlFeOH stretching unit, secondly in the 6958–6878 cm−1 region attributed to the FeFeOH unit. The overtone of the hydroxyl stretching frequency of water was observed at around 6800 cm−1. These observations show that nontronites can be a source of water that may support life. [ABSTRACT FROM AUTHOR]

Syngenite (K2Ca(SO4)2·H2O), formed during treatment of manure with sulphuric acid, was studied by infrared, near-infrared (NIR) and Raman spectroscopy. Cs site symmetry was determined for the two sulphate groups in syngenite (P21/m), so all bands are both infrared and Raman active. The split ν1 (two Raman+two infrared bands) was observed at 981 and 1000 cm−1. The split ν2 (four Raman+four infrared bands) was observed in the Raman spectrum at 424, 441, 471 and 491 cm−1. In the infrared spectrum, only one band was observed at 439 cm−1. From the split ν3 (six Raman+six infrared) bands three 298 K Raman bands were observed at 1117, 1138 and 1166 cm−1. Cooling to 77 K resulted in four bands at 1119, 1136, 1144 and 1167 cm−1. In the infrared spectrum, five bands were observed at 1110, 1125, 1136, 1148 and 1193 cm−1. From the split ν4 (six infrared+six Raman bands) four bands were observed in the infrared spectrum at 604, 617, 644 and 657 cm−1. The 298 K Raman spectrum showed one band at 641 cm−1, while at 77 K four bands were observed at 607, 621, 634 and 643 cm−1. Crystal water is observed in the infrared spectrum by the OH-liberation mode at 754 cm−1, OH-bending mode at 1631 cm−1, OH-stretching modes at 3248 (symmetric) and 3377 cm−1 (antisymmetric) and a combination band at 3510 cm−1 of the H-bonded OH-mode plus the OH-stretching mode. The near-infrared spectrum gave information about the crystal water resulting in overtone and combination bands of OH-liberation, OH-bending and OH-stretching modes. [Copyright &y& Elsevier]