Synthetic Mg/Zn/Al-hydrotalcites with atomic ratios of 6 : 0 : 2, 4 : 2 : 2, 2 : 4 : 2 and 0 : 6 : 2 were characterized by FT-Raman and FT-IR spectroscopy. 'Al-OH' IR translation modes are observed at 419, 427, 559, 616 and 771 cm −1 with two corresponding Raman bands at 465-477 and 547-553 cm −1 . 'Mg-OH' IR translation modes are found at 412, 559 and 616 cm −1 with equivalent Raman bands at 464-477 and 547-553 cm −1 . The 'Zn-OH' IR translation mode is found at 445 cm −1 and the Raman modes around 450 and 495 cm −1 . The CO 3 2− group is identified by the n 1 (IR) at 1112 cm −1 and a doublet in the Raman around 1045-1055 and 1060 cm −1 . n 2 (IR) is observed at 874 cm −1 . n 3 (IR) is a doublet at 1359 and 1381 cm −1 . n 4 is observed in both the IR and Raman spectra around 670 and 695-715 cm −1 , respectively. In the OH deformation region, a doublet is observed for 'Al-OH' at 955 and 1033 cm −1 in the IR spectra. The 'Zn-OH' IR deformation mode is observed at 1462 cm −1 . H 2 O is characterized by a bending mode at 1632 cm −1 and an H-bonded interlayer H 2 O mode at 3266 cm −1 with a Raman band between 3244 and 3271 cm −1 . The OH stretching region is characterized by three bands in the Raman spectra around 3355-3360, 3440-3455 and 3535-3580 cm −1 . One band is observed in the IR spectra at 3471 cm −1 .
The difference in the local environment of CO 3 2-, NO 3 -, SO 4 2-, and ClO 4in Mg/Al-hydrotalcite compared to the free anions was studied by infrared and Raman spectroscopy. In comparison to free CO 3 2a shift toward lower wavenumbers was observed. A band around 3000-3200 cm -1 has been attributed to the bridging mode H 2 O-CO 3 2-. The IR spectrum of CO 3hydrotalcite clearly shows the split n 3 band around 1365 and 1400 cm -1 together with weak n 2 and n 4 modes around 870 and 667 cm -1 . The n 1 mode is activated and observed as a weak band around 1012 cm -1 . The Raman spectrum shows a strong n 1 band at 1053 cm -1 plus weak n 3 and n 4 modes around 1403 and 695 cm -1 . The symmetry of the carbonate anions is lowered from D 3h to C 2s resulting in activation of the IR inactive n 1 mode around 1050-1060 cm -1 . In addition, the n 3 shows a splitting of 30-60 cm -1 . Although NO 3hydrotalcite has incorporated some CO 3 2the IR shows a strong n 3 mode at 1360 cm -1 with a weak band at 827 cm -1 , and the n 4 band is observed at 667 cm -1 , although it is largely obscured by the hydrotalcite lattice modes. The Raman spectrum shows a strong n 1 mode at 1044 cm -1 with a weaker n 4 band at 712 cm -1 . The n 3 mode at 1355 cm -1 is obscured by a broad band due to the presence of CO 3 2-. The symmetry of NO 3did not change when incorporated in hydrotalcite. The IR spectrum of SO 4 -hydrotalcite shows a strong n 3 at 1126, n 4 at 614 and a weak n 1 mode at 981 cm -1 . The Raman spectrum is characterized by a strong n 1 mode at 982 cm -1 plus medium n 2 and n 4 bands at 453 and 611 cm -1 ; n 3 cannot be identified as a separate band, although a broad band can be seen around 1134 cm -1 . The site symmetry of SO 4 2is lowered from T d to C 2v . The distortion of ClO 4in the interlayer of hydrotalcite is reflected in the IR spectrum with both n 3 and n 4 bands split around 1096 and 1145 cm -1 and 626 and 635 cm -1 , respectively. A weak n 1 band is observed at 935 cm -1 . The Raman spectrum shows a strong n 1 mode at 936 cm -1 plus n 2 and n 4 bands at 461 and 626 cm -1 , respectively. A n 3 mode cannot be clearly recognized, but a broad band is visible around 1110 cm -1 . These data indicative a lowering of symmetry from T d to C s .
Lecontite, (NH 4 )Na(SO 4 ).2H 2 O, was synthesised at room temperature in high purity compared to earlier work with a minor impurity of mascagnite, (NH 4 ) 2 SO 4 . Rietveld refinement of the XRD results confirmed the crystal structure and unit cell dimensions as published earlier. Raman and Infrared spectroscopy, in conjunction with factor group analysis, resulted in a complex pattern of overlapping sulphate, NH and OH modes. The NH modes υ 1 was observed around 2880 cm -1 , υ 2 around 1700 cmoverlapping with water OH-bending modes, υ 3 around 3300 cm -1 overlapping with water OH-stretching modes around 3023, 3185 and 3422 cm -1 , and υ 4 around 1432, 1447 and 1462 cm -1 . The sulphate group in the crystal structure displays a decrease in symmetry from T d as evidenced by the activation of the ν 1 mode at 982 cm -1 and the ν 2 mode around 452 cm -1 in the Infrared spectrum. The υ 3 mode shows clear splitting in the infrared spectra with a strong band at 1064 cm -1 accompanied by two shoulders at 1107 and 1139 cm -1 . The Raman spectra show three weak bands at 1068, 1109 and 1135 cm -1 with a shoulder at 1155 cm -1 . Similar splitting was observed for the υ 4 mode around 611 and 632 cm -1 in the Infrared and Raman spectra, respectively.
Ten montmorillonite type clay samples from Miles, Queensland, Australia, have been characterised using XRD, ICP-AES and infrared spectroscopy. The Na-exchanged sample DH-30 was used for pillaring with Al 13 by exchange with an Al(NO 3 ) 3 /NaOH solution with an approximate OH/Al molar ratio of 2.2. The XRD pattern for the expanded smectite provided evidence that the Na/Al 13 polymer exchange had occurred. XRD patterns for the raw sample, the Na-exchanged clay and the Al 13 exchanged clay resulted in d-spacings of 15.09, 15.73 and 17.42 Å, respectively. Calcination at 600°C of the Al 13 -smectite led to a minor decrease in basal spacing to approximately 16.5 Å. The effect of temperature on the Al 13 -expanded smectite was also apparent when the d-spacing of an air-dried sample (19.44 Å) was compared to that of an oven-dried (60 o C) sample (17.42 Å). This difference was due to the loss of water molecules from the Al 13 outer sphere of hydration.Keywords: Al 13 , bentonite, infrared spectroscopy, montmorillonite, pillared clay, smectite 2 IntroductionClay minerals such as kaolinites, montmorillonites and saponites are ubiquitous in nature and as such, have been widely investigated. Montmorillonites are hydrous silicates capable of intercalating molecules and ions. Like zeolites, they have ionexchange properties, often with high selectivity, and a wide range of applications including catalysis. In pillared clays very large cations have been intercalated to form "pillars" propping the layers apart. As a result diffusion, sorption and catalytic properties are improved (Kloprogge, 1998). Heating the clays gives stability to the pillared clay by promoting permanent bonding between the pillar and the layers. The resultant materials have small cavities and a large surface area. These properties together with their low cost, make them ideal for use as alternative catalysts to zeolites. They are also commonly employed in the petroleum industry for filtering long-chain hydrocarbons and azeotrope cracking.Barrer and McLeod (1955) did some of the pioneering work on the intercalation of organic compounds into clays. Unfortunately the organic and organometallic pillars that were used decomposed at relatively low temperatures causing the clay interlayers to collapse. Modern pillared clays of this type are used as gelling agents, fillers and thickeners.The oil industry, in subsequent years, instigated a majority of the development of catalysts with research centring on the evolution of materials with relatively large pore-sizes and the ability to deal with larger molecules, as well as good thermal and hydrothermal stability. This led to the development of inorganic polyoxocations as pillaring agents, providing thermally stable clays with a high specific surface area (200 to 500 m 2 g -1 ) which when calcined, produced fixed metal oxide pillars. Brindley and Sempels (1977), Lahav et al. (1978), Vaughan and Lussier (1980) and Vaughan et al. (1979Vaughan et al. ( ,1981a were the first to report on the formation of clay...
Layered double hydroxides containing Ni 2+ and Al 3+ have been synthesized by homogeneous precipitation through urea hydrolysis. The nature of the interlayer species changes according to the treatment of the samples, formation of interlayer (NH 2 )COOspecies being observed immediately after precipitation, which undergo transformation to carbonate after hydrothermal treatment. Simultaneously, liberation of ammonia during decomposition under hydrothermal conditions gives rise to formation of [Ni(NH 3 ) 6 ] 2+ species in solution.
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