Infrared and near-infrared spectroscopic study of synthetic hydrotalcites with variable divalent/trivalent cationic ratios

Near-infrared (NIR), X-ray diffraction (XRD) and infrared (IR) spectroscopy have been applied to hydrotalcites of the formula Mg₆ (Fe,Al)₂(OH)₁₆(CO₃)·4H₂O formed by intercalation with the carbonate anion as a function of divalent/trivalent cationic ratio. Such hydrotalcites were found to show variation in the d-spacing attributed to the size of the cation. In the IR (1750–4000 cm⁻¹), the position of all bands except those at approximately 3060 cm⁻¹ shift to higher wavenumbers as the cation ratio increases. Conversely, at wavenumbers below 1000 cm⁻¹, the bands shift to lower wavenumbers as the cation ratio increases. A water bending mode at higher wavenumbers was also observed which indicates that the water is strongly hydrogen bonded. In the NIR spectrum between 8000 and 12,000 cm⁻¹, there is a broad feature which is attributed to electronic bands of the ferrous ion and low intensity sharp bands due to overtones of the OH stretching vibrations. It is also apparent from this region that Fe²⁺ substitutes for Mg²⁺. The intensity of bands at 7750 and 5200 cm⁻¹ increases as the cation ratio increases in the NIR spectrum. Hydrotalcites with a magnesium amount 3 and 4 times greater than that of aluminium and iron combined, in the lower wavenumber region of the NIR spectrum, have very similar spectral profiles. This work has shown that hydrotalcites with different divalent/trivalent ratios can be synthesised and characterised by infrared spectroscopy.     

Intercalation of hydrotalcites with hexacyanoferrate(II) and (III)—a thermoRaman spectroscopic study

Raman spectroscopy using a hot stage indicates that the intercalation of hexacyanoferrate(II) and (III) in the interlayer space of a Mg, Al hydrotalcites leads to layered solids where the intercalated species is both hexacyanoferrate(II) and (III). Raman spectroscopy shows that depending on the oxidation state of the initial hexacyanoferrate partial oxidation and reduction takes place upon intercalation. For the hexacyanoferrate(III) some partial reduction occurs during synthesis. The symmetry of the hexacyanoferrate decreases from O_h existing for the free anions to D_3d in the hexacyanoferrate interlayered hydrotalcite complexes. Hot stage Raman spectroscopy reveals the oxidation of the hexacyanoferrate(II) to hexacyanoferrate(III) in the hydrotalcite interlayer with the removal of the cyanide anions above 250 °C. Thermal treatment causes the loss of CN ions through the observation of a band at 2080 cm⁻¹. The hexacyanoferrate (III) interlayered Mg, Al hydrotalcites decomposes above 150 °C.     

A Raman and infrared spectroscopic study of the phosphate mineral laueite

A laueite mineral sample from Lavra Da Ilha, Minas Gerais, Brazil has been studied by vibrational spectroscopy and scanning electron microscopy with EDX. Chemical formula calculated on the basis of semi-quantitative chemical analysis can be expressed as (Mn²⁺_0.85,Fe²⁺_0.10Mg_0.05)_∑1.00(Fe³⁺_1.90,Al_0.10)_∑2.00(PO₄)₂(OH)₂·8H₂O.The laueite structure is based on an infinite chains of vertex-linked oxygen octahedra, with Fe³⁺ occupying the octahedral centers, the chain oriented parallel to the c-axis and linked by PO₄ groups. Consequentially not all phosphate units are identical. Two intense Raman bands observed at 980 and 1045 cm⁻¹ are assigned to the ν₁ PO₄³⁻ symmetric stretching mode. Intense Raman bands are observed at 525 and 551 cm⁻¹ with a shoulder at 542 cm⁻¹ are assigned to the ν₄ out of plane bending modes of the PO₄³⁻. The observation of multiple bands supports the concept of non-equivalent phosphate units in the structure. Intense Raman bands are observed at 3379 and 3478 cm⁻¹ and are attributed to the OH stretching vibrations of the hydroxyl units. Intense broad infrared bands are observed. Vibrational spectroscopy enables subtle details of the molecular structure of laueite to be determined.     

An infrared and Raman spectroscopic study of polyanilines co-doped with metal ions and H+

Polyanilines doped with (HCl+KCl) and (HCl+CoCl2) were prepared by co-doping method, respectively. For comparison, polyaniline emeraldine salt (ES) by doping with HCl and its emeraldine base (EB) form were also synthesized. The co-doped polyanilines, ES and EB samples were all characterized by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy aiming to understand the transformations in the different doping status. The results show that the doping degree of K+ ions is considerably higher than that of Co2+ ions under the same co-doping conditions possibly due to different pseudoprotonation constants of EB with K+ ions and Co2+ ions. Moreover, morphology difference of polyaniline co-doped with alkaline metal ions or transition meal ions may arise from different coordination geometry of metal ions. Nevertheless, there are similar chemical transformations of quinoid units to benzenoid ones on polyaniline backbones for the ES and both co-doped samples. And the polyaniline backbones co-doped with H+ and metal cations are found to attain weaker charge delocalization than the ES which is doped solely with H+.     

Vibrational spectroscopic study of the nitrate containing hydrotalcite mbobomkulite

Raman spectroscopy has been used to study the nitrate hydrotalcite mbobomkulite NiAl2(OH)16(NO3).4H2O. Mbobomkulite along with hydrombobomkulite and sveite are known as 'cave' minerals as these hydrotalcites are only found in caves. Two types of nitrate anion are observed using Raman spectroscopy namely free or non-hydrogen bonded nitrate and nitrate hydrogen bonded to the interlayer water and to the 'brucite-like' hydroxyl surface. Two bands are observed in the Raman spectrum of Ni-mbobomkulite at 3576 and 3647 cm(-1) with an intensity ratio of 3.36/7.37 and are attributed to the Ni3OH and Al3OH stretching vibrations. The observation of multiple water stretching vibrations implies that there are different types of water present in the hydrotalcite structure. Such types of water would result from different hydrogen bond structures.     

Infrared and Raman spectroscopic study of 1,2-benzenedithiol adsorbed on silver

Adsorption of 1,2-benzenedithiol (1,2-BDT) on a silver surface has been investigated by surface-enhanced Raman (SER) and reflection-absorption infrared (RAI) spectroscopy. The molecule was adsorbed on silver very favorably by forming two Ag---S bonds after deprotonation. From the RAI spectral pattern, the benzene ring of adsorbed 1,2-BDT was presumed to be tilted by ca. 38° from the surface normal. This RAI information was used to test the validity of various proposed SER selection rules. Being frequently quoted in the literature, the presence or absence of the benzene ring CH stretching vibration in the SER spectrum seemed, in fact, to be a very useful indicator in judging the perpendicular or parallel orientation of the benzene ring with respect to the surface. However, the so-called in-plane/out-of-plane dichotomy as well as the more elaborate symmetry-based electromagnetic selection rule was found not to work in the present system.     

Fourier-transform Raman and infrared spectroscopic analysis of dipyrrinones and mesobilirubins

The Fourier-transform Raman (FT-Raman), infrared (FT-IR), and UV-visible absorption spectra of four dipyrrinones and two mesobilirubins have been investigated in the solid state and in CH2Cl2 solutions. A detailed spectral analysis, assignment and discussion of these spectra are presented. The bands at 1735-1738, 1691-1707 and 1359-1377 cm(-1) which were assigned to the stretching vibrations of the C-O-C and C-O-H and symmetric deformation of C-H bonds, respectively, can act as a marker to distinguish the compounds of this class. The striking differences between the spectra of the compounds suggest that mesobilirubin XIIIalpha is tending to adopt as ridge-tile conformation, rather than linear conformation.     

Aurichalcite – An SEM and Raman spectroscopic study

Raman spectroscopy complimented with supplementary infrared spectroscopy has been used to characterise the vibrational spectrum of aurichalcite a zinc/copper hydroxy carbonate (Zn,Cu²⁺)₅(CO₃)₂(OH)₆. XRD patterns of all specimens show high orientation and indicate the presence of some impurities such as rosasite and hydrozincite. However, the diffraction patterns for all samples are well correlated to the standard reference patterns. SEM images show highly crystalline and ordered structures in the form of micron long fibres and plates. EDAX analyses indicate variations in chemical composition of Cu/Zn ratios ranging from 1/1.06 to 1/2.87. The symmetry of the carbonate anion in aurichalcite is C_s and is composition dependent. This symmetry reduction results in multiple bands in both the symmetric stretching and bending regions. The intense band at 1072 cm⁻¹ is assigned to the ν₁(CO₃)²⁻ symmetric stretching mode. Three Raman bands assigned to the ν₃(CO₃)²⁻ antisymmetric stretching modes are observed for aurichalcite at 1506, 1485 and 1337 cm⁻¹. Multiple Raman bands are observed in 800–850 cm⁻¹ and 720–750 cm⁻¹ regions and are attributed to ν₂ and ν₄ bending modes confirming the reduction of the carbonate anion symmetry in the aurichalcite structure. An intense Raman band at 1060 cm⁻¹ is attributed to the δ OH deformation mode.     

Infrared and Raman spectroscopic investigation of crosslinked polystyrenes and radiation‐grafted films

The crosslinking of functionalized polystyrene resins is often of critical importance in determining resin properties and performance in the application of these materials as membranes and supports. In this investigation model systems are developed for quantifying the infrared and Raman spectroscopic properties of copolymers based on poly(styrene‐co‐divinylbenzene). Analytical curves appropriate for the quantification of para‐ and metasubstituted species and pendant double bonds are reported, and corrections to previously reported spectroscopic assignments and analytical methods are made. The usefulness of these two analytical methods in characterizing radiation‐grafted films and commercial copolymers is compared, and typical characterization results are given. The relative concentrations of the species found in the grafted films are quite different from their concentrations in the grafting solution, and empirical relationships between the two are developed. In addition, the graft composition varies as a function of the base polymer film thickness and type and the penetration depth in the grafted film. Radiation‐grafted films are more highly crosslinked in their near surface regions, and thinner films are more extensively crosslinked. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 59–75, 2004     

Hydrated double carbonates – A Raman and infrared spectroscopic study

The Raman spectra of selected double carbonates including pirssonite, gaylussite, shortite and quintinite complemented with infrared spectra have been used to characterise the structure of these carbonate minerals. By using a Libowitzky type function hydrogen bond distances for these minerals of 2.669–2.766 Å are estimated. The variation in the hydrogen bond distances contributed to the stability of the mineral. The Raman spectrum of pirssonite shows a single band at 1080 cm⁻¹ attributed to the (CO₃)²⁻ symmetric stretching mode, in contrast to shortite and quintinite where two bands are observed. Multiple bands are observed for the antisymmetric stretching and bending region for these minerals proving that the carbonate unit is distorted in the structure of pirssonite and gaylussite.     

Raman and infrared spectroscopic study of the anhydrous carbonate minerals shortite and barytocalcite

The Raman spectra of shortite and barytocalcite complimented with infrared spectra have been used to characterise the structure of these carbonate minerals. The Raman spectrum of barytocalcite shows a single band at 1086cm(-1) attributed to the (CO(3))(2-) symmetric stretching mode, in contrast to shortite where two bands are observed. The observation of two bands for shortite confirms the concept of more than one crystallographically distinct carbonate unit in the unit cell. Multiple bands are observed for the antisymmetric stretching and bending region for these minerals proving that the carbonate unit is distorted in the structure of both shortite and barytocalcite.     

Infrared study of aging of edible oils by oxidative spectroscopic index and MCR-ALS chemometric method

One of the most suitable analytical techniques used for edible oil quality control is Fourier transform mid infrared spectroscopy (FT-MIR). FT-MIR spectroscopy was used to continuously characterize the aging of various edible oils thanks to a specific aging cell. There were differences in the spectra of fresh and aged oils from different vegetable sources, which provide the basis of a method to classify them according to the oxidative spectroscopic index value. The use of chemometric treatment such as multivariate curve resolution-alternative least square (MCR-ALS) made it possible to extract the spectra of main formed and degraded species. The concentration profiles gave interesting information about the ability of the various oils to support the oxidative treatment and showed that all oils present the same aging process. Both methods led to concordant results in terms of induction times determined by the oxidative spectroscopic index and the appearance of oxidation products revealed by MCR-ALS.     

Infrared and infrared emission spectroscopy of the zinc carbonate mineral smithsonite

Infrared emission and infrared spectroscopy has been used to study a series of selected natural smithsonites from different origins. An intense broad infrared band at 1440cm(-1) is assigned to the nu(3) CO(3)(2-) antisymmetric stretching vibration. An additional band is resolved at 1335cm(-1). An intense sharp Raman band at 1092cm(-1) is assigned to the CO(3)(2-) symmetric stretching vibration. Infrared emission spectra show a broad antisymmetric band at 1442cm(-1) shifting to lower wavenumbers with thermal treatment. A band observed at 870cm(-1) with a band of lesser intensity at 842cm(-1) shifts to higher wavenumbers upon thermal treatment and is observed at 865cm(-1) at 400 degrees C and is assigned to the CO(3)(2-)nu(2) mode. No nu(2) bending modes are observed in the Raman spectra for smithsonite. The band at 746cm(-1) shifts to 743cm(-1) at 400 degrees C and is attributed to the CO(3)(2-)nu(4) in phase bending modes. Two infrared bands at 744 and around 729cm(-1) are assigned to the nu(4) in phase bending mode. Multiple bands may be attributed to the structural distortion ZnO(6) octahedron. This structural distortion is brought about by the substitution of Zn by some other cation. A number of bands at 2499, 2597, 2858, 2954 and 2991cm(-1) in both the IE and infrared spectra are attributed to combination bands.     

Walsh’s contributions to molecular spectroscopy and its instrumentation

Alan Walsh made major contributions to molecular spectroscopy and its instrumentation, particularly with his invention of the multiple monochromator, which greatly improved the performance of infrared spectrometers.     

Synthesis and vibrational spectroscopic characterisation of nickel containing aurichalcite

Raman spectroscopy complimented with supplementary infrared spectroscopy has been used to characterise a synthetic nickel substituted aurichalcite a zinc/nickel hydroxy carbonate, (Zn²⁺, Cu²⁺, Ni²⁺)₅(CO₃)₂(OH)₆. XRD patterns show high orientation and indicate the presence of some minor impurities. The diffraction patterns for the Ni-aurichalcite are well correlated with the standard reference patterns. EDAX analyses indicate variations in chemical composition of Zn/Ni ratios of ∼20:1. The symmetry of the carbonate anion in aurichalcite is C_s and is composition dependent. This symmetry reduction results in multiple bands in both the symmetric stretching and bending regions. The intense band for the Ni-aurichalcite at 1070 cm⁻¹ is assigned to the ν₁(CO₃)²⁻ symmetric stretching mode. Three Raman bands assigned to the ν₃(CO₃)²⁻ antisymmetric stretching modes are observed for Ni-aurichalcite at 1372, 1480 and 1543 cm⁻¹. Multiple Raman bands are observed in the regions from 800 to 850 cm⁻¹ and 720 to 750 cm⁻¹, and are attributed to ν₂ and ν₄ bending modes confirming the reduction of the carbonate anion symmetry in the aurichalcite structure. This research proves that nickel containing aurichalcites can be synthesised in the laboratory thus mimicing the natural nickel containing aurichalcites.     

The spectroscopic characterization of the sulphate mineral ettringite from Kuruman manganese deposits,South Africa

The mineral ettringite has been studied using a number of techniques, including XRD, SEM with EDX, thermogravimetry and vibrational spectroscopy. The mineral proved to be composed of 53% of ettringite and 47% of thaumasite in a solid solution. Thermogravimetry shows a mass loss of 46.2% up to 1000 °C. Raman spectroscopy identifies multiple sulphate symmetric stretching modes in line with the three sulphate crystallographically different sites. Raman spectroscopy also identifies a band at 1072 cm⁻¹ attributed to a carbonate symmetric stretching mode, confirming the presence of thaumasite. The observation of multiple bands in the ν₄ spectral region between 700 and 550 cm⁻¹ offers evidence for the reduction in symmetry of the sulphate anion from T_d to C_2v or even lower symmetry. The Raman band at 3629 cm⁻¹ is assigned to the OH unit stretching vibration and the broad feature at around 3487 cm⁻¹ to water stretching bands. Vibrational spectroscopy enables an assessment of the molecular structure of natural ettringite to be made.     

Vibrational spectroscopic study of mimetite-pyromorphite solid solutions

A number of compounds of the mimetite Pb₅(AsO₄)₃Cl-pyromorphite Pb₅(PO₄)₃Cl solid solution series were synthesized at room temperature and analyzed with Raman and infrared spectroscopy. The fundamental antisymmetric stretching (ν₃) and bending (ν₄) vibrations of the mimetite-pyromorphite solid solutions occur in the regions 720-1040 cm⁻¹ and 400-580 cm⁻¹. The band originating from the ν₃ and ν₄ modes shifts to higher wavenumbers between mimetite and pyromorphite because the atomic mass of As is higher than P and As-O bonds are longer than P-O bonds. The position, shape and relative intensity of the bands vary primarily as a function of As/(As + P) in the analyzed solid. The strong correlations between the positions of the vibrational modes and the As/(As + P) ratio can be used to determine the composition of the investigated natural and synthetic samples of the minerals from the mimetite-pyromorphite series.     

Infrared, optical absorption, and EPR spectroscopic studies on natural gypsum

The natural gypsum has been investigated by infrared, Raman, X-ray diffraction, optical absorption and electron paramagnetic resonance spectroscopy. The fundamental stretching and bending vibrations observed in the infrared region for SO₄²⁻ and H₂O are compared with the near-infrared overtones and combinations of these vibrations. MIR and Raman spectral features are attributed to sulfate fundamentals and lattice vibrations of H₂O, SO₄²⁻. The charge transfer and ligand field transition bands were observed near 490, 630, and 800–900 nm and were compared to those of iron oxides. The optical absorption spectrum indicates the presence of ferric and ferrous ions in the mineral. The site symmetry of Fe(III) in the sample is tetragonally distorted. EPR results indicate the presence of the ferric ion in a tetragonally distorted state.     

Infrared spectroscopic study of the local structural changes across the metal insulator transition in nickel-doped GdBaCo2O5.5

Phonons in GdBaCo₂O_5.5 have been identified using infrared spectroscopy and their mode assignments have been carried out using ab initio lattice dynamical calculations. Metal insulator transitions in undoped and nickel-doped GdBaCo₂O_5.5 have been probed using infrared absorption spectroscopy. The phonon modes corresponding to the bending mode of the CoO₆ octahedra/pyramids are seen to soften, broaden and develop an asymmetry across the insulator-metal transition pointing to extensive electron phonon interaction effects in these systems. Correlated changes of the phonon line shape parameters associated with the transition indicate a suppression of T_MIT with increased nickel doping of the cobalt sublattice. Temperature dependence of the octahedral stretching mode frequencies in undoped GdBaCo₂O_5.5 points to distinct structural distortions accompanying the high temperature metallic transition.