Leisel Hickey

Infrared and Raman study of interlayer anions CO32−, NO3−, SO42− and ClO4− in Mg/Al-hydrotalcite

Abstract The difference in the local environment of CO32-, NO3-, SO42-, and ClO4- in Mg/Al-hydrotalcite compared to the free anions was studied by infrared and Raman spectroscopy. In comparison to free CO32- a shift toward lower wavenumbers was observed. A band around 3000-3200 cm-1 has been attributed to the bridging mode H2O-CO32-. The IR spectrum of CO3- hydrotalcite clearly shows the split ν3 band around 1365 and 1400 cm-1 together with weak ν2 and ν4 modes around 870 and 667 cm-1. The ν1 mode is activated and observed as a weak band around 1012 cm-1. The Raman spectrum shows a strong ν1 band at 1053 cm-1 plus weak ν3 and ν4 modes around 1403 and 695 cm-1. The symmetry of the carbonate anions is lowered from D3h to C2s resulting in activation of the IR inactive ν1 mode around 1050-1060 cm-1. In addition, the ν3 shows a splitting of 30-60 cm-1. Although NO0 hydrotalcite has incorporated some CO32- the IR shows a strong ν3 mode at 1360 cm-1 with a weak band at 827 cm-1, and the ν4 band is observed at 667 cm-1, although it is largely obscured by the hydrotalcite lattice modes. The Raman spectrum shows a strong ν1 mode at 1044 cm-1 with a weaker ν4 band at 712 cm-1. The ν3 mode at 1355 cm-1 is obscured by a broad band due to the presence of CO32-. The symmetry of NO3- did not change when incorporated in hydrotalcite. The IR spectrum of SO4-hydrotalcite shows a strong ν3 at 1126, ν4 at 614 and a weak v1 mode at 981 cm-1. The Raman spectrum is characterized by a strong ν1 mode at 982 cm-1 plus medium ν2 and ν4 bands at 453 and 611 cm-1; ν3 cannot be identified as a separate band, although a broad band can be seen around 1134 cm-1. The site symmetry of SO42- is lowered from Td to C2ν. The distortion of ClO4- in the interlayer of hydrotalcite is reflected in the IR spectrum with both ν3 and ν4 bands split around 1096 and 1145 cm-1 and 626 and 635 cm-1, respectively. A weak ν1 band is observed at 935 cm-1. The Raman spectrum shows a strong ν1 mode at 936 cm-1 plus ν2 and ν4 bands at 461 and 626 cm-1, respectively. A ν3 mode cannot be clearly recognized, but a broad band is visible around 1110 cm-1. These data indicative a lowering of symmetry from Td to Cs.

Heating stage Raman and infrared emission spectroscopic study of the dehydroxylation of synthetic Mg-hydrotalcite

The thermal behaviour of synthetic hydrotalcite, Mg5.6Al2.4(OH)16(CO3,NO3)·nH2O, has been studied by Infrared Emission Spectroscopy (IES) and heating stage Raman microscopy. Heating stage Raman microscopy reveals that upon heating and subsequent dehydration the bands at 553, 1052, 3503, 3603 and 3689 cm−1 associated with the (Mg,Al)3–OH translation, deformation and stretching vibrations decrease in intensity due to changes in the stacking order of the hydroxide layers. During this rearrangement around 150–175°C the free interlayer nitrate forms a type of bridging nitrato complex with the metals in the hydroxide layers as evidenced by the disappearance of the normal free nitrate vibrations at 716, 1067 and 1386 cm−1 and the formation of a new band at 1039 cm−1. Further heating to 300°C results in the dehydroxylation and decarbonisation of the hydrotalcite, which is only partially reversed upon cooling in air over a period of more than 12 h. The Mg-hydrotalcite IES spectra show major changes around 350–400°C indicating the end of the dehydroxylation. In this temperature range, “Al”–OH bands at 772, 923 and 1029 cm−1 disappear. New bands are observed around 713, 797 and 1075 cm−1. The first and the last bands plus the 545 cm−1 band indicate the formation of spinel (MgAl2O4). The 713 cm−1 band is also close to the νLO position of MgO at 717 cm−1, which is another product formed after dehydroxylation. However, decarbonisation is not complete at this stage as evidenced by both a continuing weight loss in the TGA up to at least 625°C and a decreasing carbonate signal in the IES up to 800°C.

Characterisation and Al-pillaring of smectites from Miles, Queensland (Australia)

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 Al13 by exchange with an Al(NO3)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/Al13 polymer exchange had occurred. XRD patterns for the raw sample, the Na-exchanged clay and the Al13 exchanged clay resulted in d-spacings of 15.09, 15.73 and 17.42 A, respectively. Calcination at 600°C of the Al13-smectite led to a minor decrease in basal spacing to approximately 16.5 A. The effect of temperature on the Al13-expanded smectite was also apparent when the d-spacing of an air-dried sample (19.44 A) was compared to that of an oven-dried (60 o C) sample (17.42 A). This difference was due to the loss of water molecules from the Al13 outer sphere of hydration.

Infrared absorption and emission study of synthetic mica-montmorillonite in comparison to rectorite, beidellite and paragonite

Barasym SMM-100 (SMM for synthetic mica montmorillonite) from NL industries forms one of the standard clay samples in the Clay Minerals Society Source Clays Project. The nature of this interstratified synthetic material is compared to the natural equivalent of a regularly interstratified MM known as rectorite, whose structure exhibits the regular stratification, a smectite known as beidellite and the sodium-mica paragonite. The comparison is made between Barasym SMM-100 and the natural rectorite Rar-1a, synthetic baidellite and natural paragonite. Infrared spectroscopic evidence suggests that the SMM-100 is an irregularly interstratified phyllosilicate with much more baidellite-like than paragonite-like layers.

Synthesis and spectroscopic characterisation of deuterated hydrotalcite

The synthesis and spectroscopic characterization of deuterated hydrotalcite was discussed using Raman spectroscopy. It was found that the band at 551 cm visible in the normal hydrotalcites spectrum disappeared in the deuterated hydrotalcite spectrum which suggested that this band was associated with a hydroxyl mode. The analysis suggested that the 725 cm band, which was not affected by the deuteration, was associated with two overlapping metal-oxygen modes.

Low temperature synthesis of cobalt clays

Clay minerals are an important group of naturally occurring minerals found in soils and sediments. They have a sheet-like structure and the order of the sheets as well as the sheet composition contributes to the properties of the clay mineral. The tetrahedral sheets contain continuous T-O linkages with tetrahedral geometry, where T is normally Si or Al [1]. The apical oxygen of each tetrahedron forms part of the adjacent octahedral sheet, with six coordinated cations surrounded by oxygens and hydroxyls. If the cation is trivalent (eg. Al

Infrared study of some synthetic saponites: Effect of NH4/Al and H2O/(Si+Al) ratios during the crystallization

Ammonium-saponite samples of (NH)MgSiCuO(OH) compositions were synthesized at 280°C during 74 h at autogenous water pressure. X-ray diffraction of the resulting saponites showed trace amounts of artefact corundum and amorphous material were present. Cation Exchange Capacity (CEC) determination, chemical analyses and 91 magic-angle solid-state nuclear magnetic resonance spectroscopy (MAS-NMR) showed that the interlayer contained only limited amounts of ammonium and mainly Al as the interlayer cation.

A new low temperature synthesis route of fraipontite (Zn,Al)3(Si,Al)2O5(OH)4

A low temperature synthesis method based on the decomposition of urea at 90°C in water has been developed to synthesise fraipontite. This material is characterised by a basal reflection 001 at 7.44 A. The trioctahedral nature of the fraipontite is shown by the presence of a 06l band around 1.54 A, while a minor band around 1.51 A indicates some cation ordering between Zn and Al resulting in Al-rich areas with a more dioctahedral nature. TEM and IR indicate that no separate kaolinite phase is present. An increase in the Al content however, did result in the formation of some SiO2 in the form of quartz. Minor impurities of carbonate salts were observed during the synthesis caused by to the formation of CO32- during the decomposition of urea.