Vibrational spectra of barium oxalate hemihydrate

The infrared and Raman spectra of barium oxalate hemihydrate, BaC₂O₄ · 0.5H₂O, were recorded and discussed on the basis of their structural peculiarities and in comparison with the spectra of the previously investigated calcium and strontium oxalates.     

Pressure-induced phase transitions in gypsum

Abstract

We report high-pressure Raman scattering spectroscopy and energy dispersive X-ray diffraction investigations on gypsum, CaSO₄ · 2H₂O, at room temperature in a diamond cell. With increasing pressure, measurements indicate that CaSO₄ · 2H₂O undergoes two stages of crystalline-state phase transitions at 5 and 9 GPa, and then converts to a disordered phase above 11 GPa. The structures of the three high-pressure phases of gypsum have not been determined yet. These phases are tentatively named as “post-gypsum-I” (PG-I), “post-gypsum-II” (PG-II) and “disordered” according to the sequence of their appearance with pressure.

Gypsum shows anisotropic compressibility along three crystallographic axes with b > c > a below 5 GPa. The difference in the behavior of the two OH stretching modes in gypsum is attributed to the different reduction rate in the hydrogen bonding distances by the anisotropic axial compressibility.     

Structure and lithium storage performances of nickel hydroxides synthesized with different nickel salts

Nickel hydroxides with hierarchical micro-nano structures are prepared by a facile homogeneous precipitation method with different nickel salts (Ni(NO₃)₂·6H₂O, NiCl₂·6H₂O, and NiSO₄·6H₂O) as raw materials. The effect of nickel sources on the microstructure and lithium storage performance of the nickel hydroxides is studied. It is found that all the three prepared samples are α-nickel hydroxide. The nickel hydroxides synthesized with Ni(NO₃)₂·6H₂ or NiCl₂·6H₂O show a similar particle size of 20–30 μm and are composed of very thin nano-sheets, while the nickel hydroxide synthesized with Ni(SO₄)₂·6H₂O shows a larger particle size (30–50 μm) and consists of very thin nano-walls. When applied as anode materials for lithium-ion batteries (LIBs), the nickel hydroxide synthesized with NiSO₄·6H₂O exhibits the highest discharge capacity, but its cyclic stability is very poor. The nickel hydroxides synthesized with NiCl₂·6H₂O exhibit higher discharge capacity than the nickel hydroxides synthesized with Ni(NO₃)₂·6H₂O, and both of them show much improved cyclic stability and rate capability as compared to the nickel hydroxide synthesized with Ni(SO₄)₂·6H₂O. Moreover, pseudocapacitive behavior makes a great contribution to the electrochemical energy storage of the three samples. The discrepancies of lithium storage performance of the three samples are analyzed by ex-situ XRD, FT-IR, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) tests.     

A Raman spectroscopic study of the ‘cave’ mineral ardealite Ca2(HPO4)(SO4)·4H2O

The mineral ardealite Ca₂(HPO₄)(SO₄)·4H₂O is a ‘cave’ mineral and is formed through the reaction of calcite with bat guano. The mineral shows disorder and the composition varies depending on the origin of the mineral. Raman spectroscopy complimented with infrared spectroscopy has been used to characterise the mineral ardealite. The Raman spectrum is very different from that of gypsum. Bands are assigned to SO₄²⁻ and HPO₄²⁻ stretching and bending modes. Copyright © 2011 John Wiley & Sons, Ltd.     

Thermal Dehydration and Vibrational Studies of ZnK4(P3O9)2 · 6H2O

The thermal dehydration of ZnK₄(P₃O₉)₂ · 6H₂O was studied in the range 25–500°C by thermogravimetric analysis (TGA and DSC) and X‐ray diffraction. We found, based on the TGA and DSC scans, the dehydration of this salt takes place in three stages with a loss of the six water molecules. The infrared and Raman spectra of ZnK₄(P₃O₉)₂ · 6H₂O have been recorded and interpreted using a factor group analysis. The internal modes are assigned in terms of POP and PO₂ structural units using experimental and theoretical IR and Raman frequencies.     

Infrared and Raman Spectroscopic Characterization of the Silicate Mineral Gilalite Cu5Si6O17 · 7H2O

Gilalite is a copper silicate mineral with a general formula of Cu₅Si₆O₁₇ · 7H₂O. The mineral is often found in association with another copper silicate mineral, apachite, Cu₉Si₁₀O₂₉ · 11H₂O. Raman and infrared spectroscopy have been used to characterize the molecular structure of gilalite. The structure of the mineral shows disorder, which is reflected in the difficulty of obtaining quality Raman spectra. Raman spectroscopy clearly shows the absence of OH units in the gilalite structure. Intense Raman bands are observed at 1066, 1083, and 1160 cm^?1.

The Raman band at 853 cm^?1 is assigned to the –SiO₃ symmetrical stretching vibration and the low-intensity Raman bands at 914, 953, and 964 cm^?1 may be ascribed to the antisymmetric SiO stretching vibrations. An intense Raman band at 673 cm^?1 with a shoulder at 663 cm^?1 is assigned to the ν₄ Si-O-Si bending modes. Raman spectroscopy complemented with infrared spectroscopy enabled a better understanding of the molecular structure of gilalite.     

Thermal stability and photoluminescence property of hexagonal MoO3·0.55H2O microrods

The metastable phase of well-faceted, hexagonal, prism-like molybdenum oxide hydrate (MoO₃·0.55H₂O) was successfully synthesized by evaporating molybdic acid solution prepared through cation membrane electrolysis of Na₂MoO₄·2H₂O aqueous solution. The obtained crystals were characterized by X-ray diffraction (XRD), thermogravimetric (TG), scanning electronic microscopy (SEM) and photoluminescence (PL) spectrophotometry. The as-prepared MoO₃·0.55H₂O rods were of 2–4 μm in width and 5–12 μm in length. The MoO₃·0.55H₂O microrods displayed photoluminescence properties at room temperature and were transformed into stable orthorhombic α-MoO₃ after air annealing at 380 °C. Moreover, the influence of temperature factor on the phase transformation process, morphology and photoluminescence properties of MoO₃·0.55H₂O was investigated in detail.     

A Raman and infrared spectroscopic study of Ca2+ dominant members of the mixite group from the Czech Republic

The minerals of the mixite group—zálesíite CaCu₆[(AsO₄)₂(AsO₃OH)(OH)₆]·3H₂O from abandoned uranium deposit Zálesí, Czech Republic and calciopetersite CaCu₆[(PO₄)₂(PO₃OH)(OH)₆]·3H₂O from a quarry near Domašov na Bystřicí, northern Moravia, Czech Republic—were studied by Raman and infrared spectroscopy. The observed bands were assigned to the stretching and bending vibrations of (AsO₄)³⁻ and (AsO₃OH)²⁻ ions in zálesíite, and (PO₄)³⁻ and (PO₃OH)²⁻ in calciopetersite, and to molecular water, hydroxyl ions, and Cu‐(O,OH) units in both minerals. O H···O hydrogen‐bond lengths in zálesíite and calciopetersite structures were calculated with Libowitzky's empirical relation. Copyright © 2010 John Wiley & Sons, Ltd.     

Electron density characteristics and charge transfer effect of hydrogen bond O–H···Pt(II): atoms in molecules study and natural bond orbital analysis

In this report, we extended the works of Rizzato et al. [Angew. Chem. Int. Ed. 49, 7440 (2010)] on the nature of O–H···Pt hydrogen bond in trans-[PtCl₂(NH₃)(N–glycine)]·H₂O(1·H₂O) complex, by computational study of O–H···Pt interaction in [NBu₄][Pt(C₆F₅)₃(8-hydroxyquinaldine)], with emphasis on charge transfer effect in this interaction of platinum(II) and hydrogen atom. According to the crystallographic geometry reported by José María Casas et al., [NBu₄][Pt(C₆F₅)₃(8-hydroxyquinaldine)] possesses one O–H···Pt hydrogen bridging interaction, similar to the case in trans-[PtCl₂(NH₃)(N–glycine)]·H₂O(1·H₂O) complex. On the basis of topological criteria of electron density, we characterised this O–H···Pt interaction. Charge transferred between platinum(II) and σ^*_O–H orbital in this complex was calculated by using NBO method. The stabilised energy associated to charge transfer was estimated using a direct proportionality, that is 2–3 eV per electron transferred. Charge transfer effects in O–H···Pt hydrogen bonds were studied for these two complexes. Our results indicate that the interaction of O–H···Pt is closed–shell in nature with significant charge transfer, and that charge transfer effect is not negligible in the interaction of O–H···Pt. The second conclusion is different from the result of Rizzato et al.     

The hydrates and deuterates of ferrous sulfate (FeSO4): a Raman spectroscopic study

A comparative analysis has been carried out on the Raman spectra of FeSO₄·nH₂O (n = 1, 4, 7) including the ²D‐analogs. The effects of changing the degrees of hydration have been found from the lattice, SO₄²⁻ internal, and H₂O internal modes. Increasing degrees of hydration shift the intense ν₁(SO₄) peak to lower wavenumbers and reduce the amount of splitting on the ν₃(SO₄) peaks. Some of the water librational bands cause the broadening of the ν₄(SO₄) peaks in FeSO₄·7H₂O and the ν₂(SO₄) peaks in FeSO₄·7D₂O. The ν₂(H₂O) band in FeSO₄·H₂O is red‐shifted in excess of 100 cm⁻¹ relative to the unperturbed H₂O band. Between 240 and 190 K and between 140 and 90 K in the spectra of FeSO₄.4H₂O, two potential phase transitions have been identified from the changes in the lattice and water‐stretching regions. The resolution of the ν₁(H₂O) and ν₃(H₂O) bands in FeSO₄·4H₂O and FeSO₄·H₂O also improved sharply at low temperatures. The capability of distinguishing various forms of FeSO₄ hydrates unambiguously makes the Raman technique a potential analytical tool for the identification of sulfate minerals on planetary surfaces. Copyright © 2006 John Wiley & Sons, Ltd.     

Lanthanum Oxide Effects on the Structure of Calcium Phosphate Glasses

Calcium phosphate glasses, in which part of calcium oxide was replaced by lanthanum oxide, were prepared by using the conventional melt quench method. The structures of xLa₂O₃ · (50-x)CaO · 50P₂O₅ (x = 0, 1, 3, 6, 12 mol%) samples were investigated by X-ray diffraction (XRD), Raman spectrum, Fourier transform infrared spectrum (FTIR), and differential scanning calorimetry (DSC). The results show that lanthanum oxide acts as network modifier in the network space of glass structure. The glass formation occurs at an O/P ratio of about 3.0–3.12. At larger values, the crystalline phases calcium pyrophosphate (Ca₂P₂O₇) and calcium lanthanum phosphate [Ca₉La(PO₄)₇] are detected in the samples. Raman and FTIR spectra indicate that the structure of lanthanum-free sample is chain P–O–P bond metaphosphate–based Q² units. Glass structure will change to Q² and Q¹ units when the lanthanum oxide content is less then 6 mol%. When lanthanum oxide content increases to 9 and 12 mol% more nonbridging oxygen in the glass, resulting in the depolymerization of the phosphate network, the network of glass transforms to Q², Q¹, and Q⁰ units mixture. Based upon DSC results, T_g slightly decreases because of the depolymerization of microstructure. Endothermal peak of DSC curves indicate that crystal phases separate out from vitreous body with the addition of lanthanum oxide content.     

Weathering of gilding decorations investigated by SR: development and distribution of calcium oxalates in the case of Sant Benet de Bages (Barcelona,Spain)

In this paper seventeenth century gilded paintings from the crypt of Sant Benet de Bages, a medieval monastery in the Catalonia region of Spain, near Barcelona, have been studied. Cross sections from two different gilded decorations were studied by means of optical microscopy and electron microscopy and EDS to determine the statigraphy and elemental composition, and by means of FTIR coupled to a microscope to determine the binding media associated to each layer. These preliminary results demonstrated that gilded decorations were made by the application of a gold foil on a mordant substrate on a gypsum base, while the mouldings of the vaults seem to be gilded on a bol with a glaze on top of the gold leaf. It is interesting to notice that the first remained unaltered, while the gilded vault mouldings look almost black, due to the darkening of the organic material. To elucidate the causes involved in the darkening of the sample from the vaults a set of synchrotron μXRD and μFTIR experiments have been carried out on these samples at the ESRF (ID18F and ID21, respectively). High brightness and small spot working conditions revealed the development and distribution of calcium oxalates in the binding media, which seem to be responsible for the darkening. Results point out the fact that weddellite (CaC₂O₄·2H₂O) is the phase formed in those layers where organic material has also been identified or at least it would be supposed to be by bibliographic sources and not necessarily those superficial as it would have been suggested due to the similarities with patinas formation. PACS 78.30-j; 68.37.Hk; 61.10.Nz     

Multi-species laser absorption sensors for in situ monitoring of syngas composition

Tunable diode laser absorption spectroscopy sensors for detection of CO, CO₂, CH₄ and H₂O at elevated pressures in mixtures of synthesis gas (syngas: products of coal and/or biomass gasification) were developed and tested. Wavelength modulation spectroscopy (WMS) with 1f-normalized 2f detection was employed. Fiber-coupled DFB diode lasers operating at 2325, 2017, 2290 and 1352 nm were used for simultaneously measuring CO, CO₂, CH₄ and H₂O, respectively. Criteria for the selection of transitions were developed, and transitions were selected to optimize the signal and minimize interference from other species. For quantitative WMS measurements, the collision-broadening coefficients of the selected transitions were determined for collisions with possible syngas components, namely CO, CO₂, CH₄, H₂O, N₂ and H₂. Sample measurements were performed for each species in gas cells at a temperature of 25 °C up to pressures of 20 atm. To validate the sensor performance, the composition of synthetic syngas was determined by the absorption sensor and compared with the known values. A method of estimating the lower heating value and Wobbe index of the syngas mixture from these measurements was also demonstrated.     

Effective orientation of water in 1,4-dioxane···water: the rotational spectrum of the H2 17O isotopologue

The measurements of the rotational spectrum of 1,4-dioxane-water complex, performed by pulsed jet Fourier transform microwave spectroscopy, have been extended to the 7–18.5 GHz frequency region and to two additional isotopologues, 1,4-dioxane···H₂ ¹⁷O and 1,4-dioxane···HOD. The effective orientation of water in the complex has been obtained from the ¹⁷O quadrupole coupling constants.     

Raman Spectroscopic Study of the Copper Silicate Mineral Apachite Cu9Si10O29 · 11H2O

ABSTRACT

Apachite, Cu₉Si₁₀O₂₉ · 11H₂O, is a mineral named after the American Indian Apache tribe. Raman and infrared spectroscopy have been used to characterize the molecular structure of apachite. The structure of the mineral shows disorder, which is reflected in the difficulty in obtaining quality Raman spectra. Raman spectroscopy clearly shows the presence of OH units in the apachite structure, which attests the formula to be not correct. Both Raman and infrared spectroscopy show the presence of water in the apachite structure. Different water molecules are present with different hydrogen bonding strengths. A suggested formula might be Cu₉Si₁₀O₂₃(OH)₁₂ · 5H₂O.

The Raman band at 967 cm^?1 is assigned to the –SiO₃ symmetrical stretching vibration and the bands at 997 and 1096 cm^?1 are assigned to the ν₃ –SiO₃ antisymmetric stretching vibrations. An intense Raman band at 673 cm^?1 with a shoulder at 663 cm^?1 is assigned to the ν₄ Si-O-Si bending modes. Raman spectroscopy complemented with infrared spectroscopy enabled a better understanding of the molecular structure of apachite.     

Structure of complexes in the H<Subscript>2</Subscript>SO<Subscript>4</Subscript>—2-pyrrolidone system as determined by IR-spectroscopy and quantum-chemical calculations

Specific features of complexation in solutions of a strong dibasic acid in the H₂SO₄–2-pyrrolidone (Pyr) system (in the range of compositions of 0–100% H₂SO₄) are studied using multiple frustrated total internal reflection IR spectroscopy. The conclusions drawn on the structure of the complexes formed in such solutions are confirmed by quantum-chemical calculations of the mPyr · nH₂SO₄ (m, n = 1, 2) heteroassociates and by comparison of their calculated and measured vibrational spectra. It is found that, in the investigated solutions, four types of acid–base complexes, with various degrees of proton transfer in the OHO bridge, are formed: (AHA)^– anions with quasi-symmetric H-bonds, solvated by acid molecules, or entering into the composition of PyrH⁺ · (AHA)^– ion pairs; quasi-ion pairs with incomplete proton transfer to the base molecule of 1: 1 and 2: 2 compositions; and 2Pyr · H₂SO₄ complexes with two O–H···O bridges of molecular type. The main differences in the mechanisms of the acid–base interactions in the H₂SO₄–Pyr system as compared to the CH₃SO₃H–Pyr system result from the participation of two OH-groups of H₂SO₄ molecule in these interactions. Therefore, two types of quasi-ion pairs and complexes of 2Pyr · H₂SO₄ composition are formed.     

The catalytic effects of H2CO3, CH3COOH,HCOOH and H2O on the addition reaction of CH2OO + H2O → CH2(OH)OOH

The addition reaction of CH₂OO + H₂O → CH₂(OH)OOH without and with X (X = H₂CO₃, CH₃COOH and HCOOH) and H₂O was studied at CCSD(T)/6-311+ G(3df,2dp)//B3LYP/6-311+G(2d,2p) level of theory. Our results show that X can catalyse CH₂OO + H₂O → CH₂(OH)OOH reaction both by increasing the number of rings, and by adding the size of the ring in which ring enlargement by COOH moiety of X inserting into CH₂OO···H₂O is favourable one. Water-assisted CH₂OO + H₂O → CH₂(OH)OOH can occur by H₂O moiety of (H₂O)₂ or the whole (H₂O)₂ forming cyclic structure with CH₂OO, where the latter form is more favourable. Because the concentration of H₂CO₃ is unknown, the influence of CH₃COOH, HCOOH and H₂O were calculated within 0–30 km altitude of the Earth's atmosphere. The results calculated within 0–5 km altitude show that H₂O and HCOOH have obvious effect on enhancing the rate with the enhancement factors are, respectively, 62.47%–77.26% and 0.04%–1.76%. Within 5–30 km altitude, HCOOH has obvious effect on enhancing the title rate with the enhancement factor of 2.69%–98.28%. However, compared with the reaction of CH₂OO + HCOOH, the rate of CH₂OO···H₂O + HCOOH is much slower.     

Growth of FePO<Subscript>4</Subscript> nanoparticles on graphene oxide sheets for synthesis of LiFePO<Subscript>4</Subscript>/graphene

FePO₄·xH₂O/graphene oxide (FePO₄·xH₂O/GO) composites were prepared by a facile chemical precipitation method. Using the as-prepared FePO₄·xH₂O/GO and LiOH·H₂O as precursors and followed by carbothermal reduction, LiFePO₄/graphene composites were obtained. Scanning electron microscope (SEM) images indicated that the graphene had very good dispersity and uniformly attached to the LiFePO₄ particles. The conductive framework of graphene improved the electrochemical properties of the composites. The composites deliver high initial discharge capacity of 163.4 mAh g^?1 as well as outstanding rate performance.