X-ray Photoelectron Spectroscopic Study of Some Organic and Inorganic Modified Clay Minerals.

Layered clay systems intercalated with inorganic and organic compounds were analyzed to highlight how XPS can provide information on the different environments surrounding a particular atom as well as provide discernments on the size, coordination, and structural and oxidative transformations of the intercalating/pillaring compounds. XPS data on the intercalation of urea and K-acetate in low- and high-defect kaolinite revealed the interaction of the intercalating group NH2 with the siloxane functional groups in the interlayer surface. The intercalation of HDTMA in Mt demonstrated the use of XPS in monitoring the change in conformation assumed by alkylammonium intercalating compounds in Mt with increasing CEC. Studies on the pillaring of Mt by Al13 and Ga13 by XPS allowed determination of the coordination of the pillaring compound within the Mt layer. Lastly, the intercalation of hexacyanoferrate in hydrotalcite demonstrated the capability of XPS in following changes in the oxidation state of the iron compound. These were gleaned from interpretation of the shifts in binding energies and presence of multiplet splitting in the XPS of the component elements of the minerals or the intercalating compounds.

Systematic Raman Spectroscopic Study of the Isomorphy Between the Arsenate Minerals Roselite, Wendwilsonite, Zincroselite, Brandtite, and Rruffite.

In nature, numerous minerals are known with the general formula X2M(TO4)2·2(H2O) and an important group is formed by minerals with T = As. Most of these occur as minor or trace minerals in environments such as hydrothermal alterations of primary sulfides and arsenides. X-ray photoelectron spectroscopy and Raman spectroscopy have been utilized to study the chemistry and crystal structure of the roselite subgroup minerals, Ca2M(AsO4)2·2H2O (with M = Co, Mg, Mn, Zn, and Cu). The AsO4 stretching region exhibited minor differences between the roselite subgroup minerals, which can be explained by the ionic radius of the cation substituting on the M position in the structure. Multiple AsO4 antisymmetric stretching and bending modes were found, pointing to a tetrahedral symmetry reduction. Bands around 450 cm-1 were attributed to ν4 bending modes. Several bands in the 300-350 cm-1 region attributed to ν2 bending modes also provide evidence of symmetry reduction of the AsO4 anion. Two broad bands for roselite were found around 3330 and 3120 cm-1 and were attributed to the OH stretching bands of crystal water. These bands are accompanied by two bands around 1700 and 1610 cm-1 attributed to the corresponding OH-bending modes. In conclusion, both XPS and Raman spectroscopy are valuable nondestructive analytical tools to characterize these secondary arsenate minerals. X-ray photoelectron spectroscopy and Raman microspectroscopy allow the chemistry and molecular structure of the roselite group minerals to be studied in a nondestructive way. The minerals in the roselite subgroup are easily distinguished based on their chemical composition as determined by XPS. As expected for minerals with the same crystal structure, similarities exist in the Raman spectra, sufficient differences exist to be able to identify these minerals.

Urea-Assisted Synthesis and Characterization of Saponite with Different Octahedral (Mg, Zn, Ni, Co) and Tetrahedral Metals (Al, Ga, B), a Review.

Clay minerals surfaces potentially play a role in prebiotic synthesis through adsorption of organic monomers that give rise to highly concentrated systems; facilitate condensation and polymerization reactions, protection of early biomolecules from hydrolysis and photolysis, and surface-templating for specific adsorption and synthesis of organic molecules. This review presents processes of clay formation using saponite as a model clay mineral, since it has been shown to catalyze organic reactions, is easy to synthesize in large and pure form, and has tunable properties. In particular, a method involving urea is presented as a reasonable analog of natural processes. The method involves a two-step process: (1) formation of the precursor aluminosilicate gel and (2) hydrolysis of a divalent metal (Mg, Ni, Co, and Zn) by the slow release of ammonia from urea decomposition. The aluminosilicate gels in the first step forms a 4-fold-coordinated Al3+ similar to what is found in nature such as in volcanic glass. The use of urea, a compound figuring in many prebiotic model reactions, circumvents the formation of undesirable brucite, Mg(OH)2, in the final product, by slowly releasing ammonia thereby controlling the hydrolysis of magnesium. In addition, the substitution of B and Ga for Si and Al in saponite is also described. The saponite products from this urea-assisted synthesis were tested as catalysts for several organic reactions, including Friedel-Crafts alkylation, cracking, and isomerization reactions.

X-ray Photoelectron Spectroscopic and Raman microscopic investigation of the variscite group minerals: Variscite, strengite, scorodite and mansfieldite.

Several structurally related AsO4 and PO4 minerals, were studied with Raman microscopy and X-ray Photoelectron Spectroscopy (XPS). XPS revealed only Fe, As and O for scorodite. The Fe 2p, As 3d, and O 1s indicated one position for Fe2+, while 2 different environments for O and As were observed. The O 1s at 530.3eV and the As 3d 5/2 at 43.7eV belonged to AsO4, while minor bands for O 1s at 531.3eV and As 3d 5/2 at 44.8eV were due to AsO4 groups exposed on the surface possibly forming OH-groups. Mansfieldite showed, besides Al, As and O, a trace of Co. The PO4 equivalent of mansfieldite is variscite. The change in crystal structure replacing As with P resulted in an increase in the binding energy (BE) of the Al 2p by 2.9eV. The substitution of Fe3+ for Al3+ in the structure of strengite resulted in a Fe 2p at 710.8eV. An increase in the Fe 2p BE of 4.8eV was found between mansfieldite and strengite. The scorodite Raman OH-stretching region showed a sharp band at 3513cm-1 and a broad band around 3082cm-1. The spectrum of mansfieldite was like that of scorodite with a sharp band at 3536cm-1 and broader maxima at 3100cm-1 and 2888cm-1. Substituting Al in the arsenate structure instead of Fe resulted in a shift of the metal-OH-stretching mode by 23cm-1 towards higher wavenumbers due to a slightly longer H-bonding in mansfieldite compared to scorodite. The intense band for scorodite at 805cm-1 was ascribed to the symmetric stretching mode of the AsO4. The medium intensity bands at 890, 869, and 830cm-1 were ascribed to the internal modes. A significant shift towards higher wavenumbers was observed for mansfieldite. The strengite Raman spectrum in the 900-1150cm-1 shows a strong band at 981cm-1 accompanied by a series of less intense bands. The 981cm-1 band was assigned to the PO4 symmetric stretching mode, while the weak band at 1116cm-1 was the corresponding antisymmetric stretching mode. The remaining bands at 1009, 1023 and 1035cm-1 were assigned to υ1(A1) internal modes in analogy to the interpretation of the AsO4 bands for scorodite and mansfieldite. The variscite spectrum showed a shift towards higher wavenumbers in comparison to the strengite spectrum with the strongest band observed at 1030cm-1 and was assigned to the symmetric stretching mode of the PO4, while the corresponding antisymmetric stretching mode was observed at 1080cm-1. Due to the band splitting component bands were observed at 1059, 1046, 1013 and 940cm-1. The AsO4 symmetric bending modes for scorodite were observed at 381 and 337cm-1, while corresponding antisymmetric bending modes occurred at 424, 449 and 484cm-1. Comparison with other arsenate and phosphate minerals showed that both XPS and Raman spectroscopy are fast and non-destructive techniques to identify these minerals based on their differences in chemistry and the arsenate/phosphate vibrational modes due to changes in the symmetry and the unique fingerprint region of the lattice modes.

Chemical bonding and electronic structures of microcline, orthoclase and the plagioclase series by X-ray photoelectron spectroscopy.

A detailed analysis was undertaken of the X-ray photoelectron spectra obtained from microcline, orthoclase and several samples of plagioclase with varying Na/Ca ratio. Comparison of the spectra was made based on the chemical bonding and structural differences in the Al- and Si-coordination within each specimen. The spectra for Si 2p and Al 2p vary with the change in symmetry between microcline and orthoclase, while in plagioclase an increase in Al-O-Si linkages results in a small but observable decrease in binding energy. The overall shapes of the O 1s peaks observed in all spectra are similar and show shifts similar to those observed for Si 2p and Al 2p. The lower-VB spectra for microcline and orthoclase are similar intermediate between α-SiO2 and α-Al2O3 in terms of binding energies. In the plagioclase series increasing coupled substitution of Na and Si for Ca and Al results in a change of the overall shape of the spectra, showing a distinct broadening associated with the presence of two separate but overlapping bands similar to the 21 eV band observed for quartz and the 23 eV band observed for corundum. The bonding character for microcline and orthoclase is more covalent than that of α-Al2O3, but less than that of α-SiO2. In contrast, the plagioclase samples show two distinct bonding characters that are comparable with those of α-SiO2 and α-Al2O3.

Comment on "A spectroscopic comparison of selected Chinese kaolinite, coal bearing kaolinite and halloysite--a mid-infrared and near-infrared study" and "Infrared and infrared emission spectroscopic study of typical Chinese kaolinite and halloysite" by Hongfei Cheng et al. (2010).

In two papers Cheng et al. (2010) reported in this journal on the mid-infrared, near-infrared and infrared emission spectroscopy of a halloysite from Hunan Xianrenwan, China. This halloysite contains around 8% of quartz (SiO2) and nearly 9% gibbsite (Al(OH)3). In their interpretation of the spectra these impurities were completely ignored. Careful comparison with a phase pure halloysite from Southern Belgium, synthetic gibbsite, gibbsite from Minas Gerais, and quartz show that these impurities do have a marked influence on the mid-infrared and infrared emission spectra. In the near-infrared, the effect is much less pronounced. Quartz does not show bands in this region and the gibbsite bands will be very weak. Comparison still show that the presence of gibbsite does contribute to the overall spectrum and bands that were ascribed to the halloysite alone do coincide with those of gibbsite.

A X-ray photoelectron spectroscopy study of HDTMAB distribution within organoclays.

X-ray photoelectron spectroscopy (XPS) in combination with X-ray diffraction (XRD) and high-resolution thermogravimetric analysis (HRTG) has been used to investigate the surfactant distribution within the organoclays prepared at different surfactant concentrations. This study demonstrates that the surfactant distribution within the organoclays depends strongly on the surfactant loadings. In the organoclays prepared at relative low surfactant concentrations, the surfactant cations mainly locate in the clay interlayer, whereas the surfactants occupy both the clay interlayer space and the interparticle pores in the organoclays prepared at high surfactant concentrations. This is in accordance with the dramatic pore volume decrease of organoclays compared to those of starting clays. XPS survey scans show that, at low surfactant concentration (<1.0CEC), the ion exchange between Na+ and HDTMA+ is dominant, whereas both cations and ion pairs occur in the organoclays prepared at high concentrations (>1.0CEC). High-resolution XPS spectra show that the modification of clay with surfactants has prominent influences on the binding energies of the atoms in both clays and surfactants, and nitrogen is the most sensitive to the surfactant distribution within the organoclays.

A Raman and infrared spectroscopic study of the uranyl silicates--weeksite, soddyite and haiweeite.

Raman spectroscopy has been used to study the molecular structure of a series of selected uranyl silicate minerals, including weeksite K2[(UO2)2(Si5O13)].H2O, soddyite [(UO2)2SiO4.2H2O] and haiweeite Ca[(UO2)2(Si5O12(OH)2](H2O)3 with UO2(2+)/SiO2 molar ratio 2:1 or 2:5. Raman spectra clearly show well resolved bands in the 750-800 cm-1 region and in the 950-1000 cm-1 region assigned to the nu1 modes of the (UO2)2+ units and to the (SiO4)4- tetrahedra. For example, soddyite is characterized by Raman bands at 828.0, 808.6 and 801.8 cm-1 (UO2)2+ (nu1), 909.6 and 898.0 cm-1 (UO2)2+ (nu3), 268.2, 257.8 and 246.9 cm-1 are assigned to the nu2 (delta) (UO2)2+. Coincidences of the nu1 (UO2)2+ and the nu1 (SiO4)4- is expected. Bands at 1082.2, 1071.2, 1036.3, 995.1 and 966.3 cm-1 are attributed to the nu3 (SiO4)4-. Sets of Raman bands in the 200-300 cm-1 region are assigned to nu2 (delta) (UO2)2+ and UO ligand vibrations. Multiple bands indicate the non-equivalence of the UO bonds and the lifting of the degeneracy of nu2 (delta) (UO2)2+ vibrations. The (SiO4)4- tetrahedral are characterized by bands in the 470-550 cm-1 and in the 390-420 cm-1 region. These bands are attributed to the nu4 and nu2 (SiO4)4- bending modes. The minerals show characteristic OH stretching bands in the 2900-3500 cm-1 and 3600-3700 cm-1.

XPS study of the major minerals in bauxite: gibbsite, bayerite and (pseudo-)boehmite.

Synthetic corundum (Al2O3), gibbsite (Al(OH)3), bayerite (Al(OH)3), boehmite (AlO(OH)) and pseudoboehmite (AlO(OH)) have been studied by high resolution XPS. The chemical compositions based on the XPS survey scans were in good agreement with the expected composition. High resolution Al2p scans showed no significant changes in binding energy, with all values between 73.9 and 74.4 eV. Only bayerite showed two transitions, associated with the presence of amorphous material in the sample. More information about the chemical and crystallographic environment was obtained from the O1s high resolution spectra. Here a clear distinction could be made between oxygen in the crystal structure, hydroxyl groups and adsorbed water. Oxygen in the crystal structure was characterised by a binding energy of about 530.6 eV in all minerals. Hydroxyl groups, present either in the crystal structure or on the surface, exhibited binding energies around 531.9 eV, while water on the surface showed binding energies around 533.0 eV. A distinction could be made between boehmite and pseudoboehmite based on the slightly lower ratio of oxygen to hydroxyl groups and water in pseudoboehmite.

Mid-infrared and infrared emission spectroscopy of Cu-exchanged montmorillonite.

Middle Infrared Spectroscopy (Mid-IR) and Infrared Emission Spectroscopy (IES) were employed to characterise Cu-exchanged montmorillonites, which were derived from two different types of montmorillonite clays, Ca-exchanged montmorillonite (Cheto clay) and Na-exchanged montmorillonite (Miles clay). Copper was exchanged under both acidic and basic conditions at different Cu/clay ratios. All Cu-exchanged montmorillonites experienced a shift in most of non-lattice bands, with hydroxyl bands playing a major role in the characterisation of the clays. Furthermore, a relationship between the ratio of bands at 3630 and 3500 cm(-1) and the Cu concentration of the starting solutions was indicated and used to compare the degree of cation exchange between two preparation methods. Two dehydration stages were observed in the IES experiments. Additional bands were observed in all Cu-exchanged montmorillonites prepared with the 'basic conditions method,' and these bands were assigned to ammonia molecules trapped within the clay structure or absorbed on the surface of the clay.

Modification of kaolinite surfaces through mechanochemical activation with quartz: A diffuse reflectance infrared fourier transform and chemometrics study.

Studies of kaolinite surfaces are of industrial importance. One useful method for studying the changes in kaolinite surface properties is to apply chemometric analyses to the kaolinite surface infrared spectra. A comparison is made between the mechanochemical activation of Kiralyhegy kaolinites with significant amounts of natural quartz and the mechanochemical activation of Zettlitz kaolinite with added quartz. Diffuse reflectance infrared Fourier transform (DRIFT) spectra were analyzed using principal component analysis (PCA) and multi-criteria decision making (MCDM) methods, the preference ranking organization method for enrichment evaluations (PROMETHEE) and geometrical analysis for interactive assistance (GAIA). The clear discrimination of the Kiralyhegy spectral objects on the two PC scores plots (400-800 and 800-2030 cm(-1)) indicated the dominance of quartz. Importantly, no ordering of any spectral objects appeared to be related to grinding time in the PC plots of these spectral regions. Thus, neither the kaolinite nor the quartz are systematically responsive to grinding time according to the spectral criteria investigated. The third spectral region (2600-3800 cm(-1), OH vibrations), showed apparent systematic ordering of the Kiralyhegy and, to a lesser extent, Zettlitz spectral objects with grinding time. This was attributed to the effect of the natural quartz on the delamination of kaolinite and the accompanying phenomena (i.e., formation of kaolinite spheres and water). The mechanochemical activation of kaolinite and quartz, through dry grinding, results in changes to the surface structure. Different grinding times were adopted to study the rate of destruction of the kaolinite and quartz structures. This relationship (i.e., grinding time) was classified using PROMETHEE and GAIA methodology.

Raman spectroscopy of the mineral rhodonite.

The mineral rhodonite an orthosilicate has been characterised by Raman spectroscopy. The Raman spectra of three rhodonites from Broken Hill, Pachapaqui and Franklin were compared and found to be similar. The spectra are characterised by an intense band at around 1000 cm(-1) assigned to the nu(1) symmetric stretching mode and three bands at 989, 974 and 936 cm(-1) assigned to the nu(3) antisymmetric stretching modes of the SiO(4) units. An intense band at around 667 cm(-1) was assigned to the nu(4) bending mode and showed additional bands exhibiting loss of degeneracy of the SiO(4) units. The low wave number region of rhodonite is complex. A strong band at 421.9 cm(-1) is attributed to the nu(2) bending mode. The spectra of the three rhodonite mineral samples are similar but subtle differences are observed. It is proposed that these differences depend upon the cationic substitution of Mn by Ca and/or Fe(2+) and Mg.

Raman spectroscopy of halotrichite from Jaroso, Spain.

Raman spectroscopy complimented with infrared ATR spectroscopy has been used to characterise a halotrichite FeSO(4) x Al(2)(SO(4))(3) x 22 H(2)O from The Jaroso Ravine, Aquilas, Spain. Halotrichites form a continuous solid solution series with pickingerite and chemical analysis shows that the jarosite contains 6% Mg(2+). Halotrichite is characterised by four infrared bands at 3569.5, 3485.7, 3371.4 and 3239.0 cm(-1). Using Libowitsky type relationships, hydrogen bond distances of 3.08, 2.876, 2.780 and 2.718 Angstrom were determined. Two intense Raman bands are observed at 987.7 and 984.4 cm(-1) and are assigned to the nu(1) symmetric stretching vibrations of the sulphate bonded to the Fe(2+) and the water units in the structure. Three sulphate bands are observed at 77K at 1000.0, 991.3 and 985.0 cm(-1) suggesting further differentiation of the sulphate units. Raman spectrum of the nu(2) and nu(4) region of halotrichite at 298 K shows two bands at 445.1 and 466.9 cm(-1), and 624.2 and 605.5 cm(-1), respectively, confirming the reduction of symmetry of the sulphate in halotrichite.

WITHDRAWN: Interlayer structure and morphology of HDTMA(+)/montmorillonite organoclay.

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A spectroscopic study of mechanochemically activated kaolinite with the aid of chemometrics.

The study of kaolinite surfaces is of industrial importance. In this work we report the application of chemometrics to the study of modified kaolinite surfaces. DRIFT spectra of mechanochemically activated kaolinites (Kiralyhegy, Zettlitz, Szeg, and Birdwood) were analyzed using principal component analysis (PCA) and multicriteria decision making (MCDM) methods, PROMETHEE and GAIA. The clear discrimination of the Kiralyhegy spectral objects on the two PC scores plots (400-800 and 800-2030 cm(-1)) indicated the dominance of quartz. Importantly, no ordering of any spectral objects appeared to be related to grinding time in the PC plots of these spectral regions. Thus, neither the kaolinite nor the quartz, are systematically responsive to grinding time according to the spectral criteria investigated. The third spectral region (2600-3800 cm(-1)OH vibrations), showed apparent systematic ordering of the Kiralyhegy and, to a lesser extent, Zettlitz spectral objects with grinding time. This was attributed to the effect of the natural quartz on the delamination of kaolinite and the accompanying phenomena (i.e., formation of kaolinite spheres and water). With the MCDM methods, it was shown that useful information on the basis of chemical composition, physical properties and grinding time can be obtained. For example, the effects of the minor chemical components (e.g., MgO, K(2)O, etc.) indicated that the Birdwood kaolinite is arguably the most pure one analyzed. In another MCDM experiment, some support was obtained for the apparent trend with grinding time noted in the PC plot of the OH spectral region.

Synthetic deuterated erythrite--a vibrational spectroscopic study.

A comparison of deuterated and non-deuterated erythrite has been made using a combination of infrared and Raman spectroscopy. Infrared spectrum shows bands at 3442, 3358, 3194 and 3039 cm(-1). The band at 3442 cm(-1) is attributed to weakly hydrogen bonded water and the band at 3039 cm(-1) to strongly hydrogen bonded water. Deuteration results in the observation of OD bands at 2563, 2407 and 2279 cm(-1). The ratio of these bands change with deuteration. Deuteration shows that the strongly hydrogen bonded water is replaced in preference to the weakly hydrogen bonded water. Three HOH bending modes are observed at 1686, 1633, 1572 and DOD bending modes at 1236, 1203 and 1176 cm(-1). Deuteration causes the loss of intensity of the bands at 841, 710 and 561 cm(-1) and new bands are observed at 692, 648 and 617 cm(-1). These three bands are attributed to the water librational modes. Deuteration results in an additional Raman band at 809 cm(-1) with increasing intensity with extent of deuteration. Deuteration results in the shift of Raman bands to lower wavenumbers.

Raman spectroscopy of selected lead minerals of environmental significance.

The Raman spectra of the minerals cerrusite (PbCO(3)), hydrocerrusite (Pb(2)(OH)(2)CO(3)), phosgenite (Pb(2)CO(3)Cl(2)) and laurionite (Pb(OH)Cl) have been used to qualitatively determine their presence. Laurionite and hydrocerrusite have characteristic hydroxyl stretching bands at 3506 and 3576 cm(-1). Laurionite is also characterised by broad low intensity bands centred at 730 and 595 cm(-1) attributed to hydroxyl deformation vibrations. The minerals cerrusite, hydrocerrusite and phosgenite have characteristic CO (nu(1)) symmetric stretching bands observed at 1061, 1054 and 1053 cm(-1). Phosgenite displays complexity in the CO (nu(3)) antisymmetric stretching region with bands observed at 1384, 1327 and 1304 cm(-1). Cerrusite shows bands at 1477, 1424, 1376 and 1360 cm(-1). The hydrocerrusite Raman spectrum has bands at slightly different positions from cerrusite, with bands at 1479, 1420, 1378 and 1365 cm(-1). The complexity of the nu(3) region is also reflected in the nu(2) and nu(4) regions with the observation of multiple bands. Laurionite is characterised by two intense bands at 328 and 272 cm(-1) attributed to PbO and PbCl stretching bands. Importantly, all four minerals are characterized by their Raman spectra, enabling the mineral identification in leachates and contaminants of environmental significance.

Raman spectroscopy of some complex arsenate minerals-implications for soil remediation.

The application of spectroscopy to the study of contaminants in soils is important. Among the many contaminants is arsenic, which is highly labile and may leach to non-contaminated areas. Minerals of arsenate may form depending upon the availability of specific cations for example calcium and iron. Such minerals include carminite, pharmacosiderite and talmessite. Each of these arsenate minerals can be identified by its characteristic Raman spectrum enabling identification.

The role of water in synthesised hydrotalcites of formula Mg(x)Zn(6 - x)Cr2(OH)16(CO3) x 4H2O and Ni(x)Co(6 - x)Cr2(OH)16(CO3) x 4H2O--an infrared spectroscopic study.

Infrared spectroscopy has been used to characterise synthesised hydrotalcites of formula Mg(x)Zn(6 - x)Cr2(OH)16(CO3) x 4H2O and Ni(x)Co(6 - x)Cr2(OH)16(CO3) x 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.

Molecular assembly in synthesised hydrotalcites of formula Cu(x)Zn(6 - x)Al2(OH)16(CO3) x 4H2O--a vibrational spectroscopic study.

Infrared and Raman spectroscopy have been used to characterise synthetic hydrotalcites of formula Cu(x)Zn(6 - x)Al2(OH)16(CO3) x 4H2O. The spectra have been used to assess the molecular assembly of the cations in the hydrotalcite structure. The spectra may be conveniently subdivided into spectral features based (a) upon the carbonate anion (b) the hydroxyl units (c) water units. The Raman spectra of the hydroxyl-stretching region enable bands to be assigned to the CuOH, ZnOH and AlOH units. It is proposed that in the hydrotalcites with minimal cationic replacement that the cations are arranged in a regular array. For the Cu(x)Zn(6 - x)Al2(OH)16(CO3) x 4H2O hydrotalcites, spectroscopic evidence suggests that 'islands' of cations are formed in the structure. In a similar fashion, the bands assigned to the interlayer water suggest that the water molecules are also in a regular well-structured arrangement. Bands are assigned to the hydroxyl stretching vibrations of water. Three types of water are identified (a) water hydrogen bonded to the interlayer carbonate ion (b) water hydrogen bonded to the hydrotalcite hydroxyl surface and (c) interlamellar water. It is proposed that the water is highly structured in the hydrotalcite as it is hydrogen bonded to both the carbonate anion and the hydroxyl surface.