Interlayer OH Research Articles

Performance activation mechanism of aluminum-based layered double hydroxides adsorbents for recovering Li+ by pH modulating

Aluminum-based adsorbents, simply prepared by eluting the lithium-aluminum layered double hydroxide precursors with deionized water, is the only industrialized adsorbents for selectively separating Li+ from saline brines. Taking the roles of lattice and surface Li+ active sites on its performances into consideration, influence of ending pH modulating on prominently improving the adsorbing capacity and stability of aluminum-based adsorbents prepared by precipitation method is initially investigated. As experimentally evidenced that, the maximum desorption amount of Li+ at the eluting stage should be controlled to around 20 mg/g Li+ rather than thoroughly removed to effectively avoid the topotactic solid-phase transformation from adsorbent to α-Al(OH)3. As-prepared adsorbents not only has high adsorption capacity up to 8.4 mg/g in 400 ppm LiCl solution, but also owns unique self-healing ability, thus promising the excellent cycling stability. It is firstly proposed that the formation of the layer-structured precursor by precipitation method is well in accordance with the three-step formation mechanism and pH modulating mainly contributes to the anions exchange between solution Cl- and interlayer OH–. This study experimentally proves the importance of pH adjusting for preparing high performance lithium adsorbents by precipitation method, which is very significant and important for effectively extracting lithium resources from the complicated multi-component liquid minerals.

Vibrational spectroscopic study of three Mg–Ni mineral series in white and greenish clay infillings of the New Caledonian Ni-silicate ores

Abstract. This study presents and discusses infrared spectroscopic data of well characterised, naturally occurring trioctahedral layer silicates of the serpentine (Srp), talc (Tlc), and sepiolite (Sep) mineral groups, which are found in reactivated faults and sequences of white and green clay veins (deweylite and garnierite) of the New Caledonian Ni-silicate ores. Bands assigned to the OH stretching vibrations of these 1:1 and 2:1 layer silicates in both the fundamental and first overtone regions of mid- and near-infrared (MIR and NIR) spectra, respectively, are compared to those reported in the literature for synthetic Mg–Ni series of the Srp and Tlc mineral groups. They are also presented according to the sequences of infillings recognised in the white and green veins of the Ni-silicate ores. The study reveals that serpentine-like (SL) minerals of the first sequences of clay infillings are residues of larger crystals of serpentines (lizardite, chrysotile, and antigorite) and that the newly formed talc-like (TL) minerals and Sep are the main Ni-bearing carriers of the Ni-silicate ores. Decreasing crystal size and order in serpentine species have major effects on vibrational bands. They favour the broadening of the OH stretching bands, the degradation of the signals assigned to the interlayer OH, and the enhancement of the signal related to weakly bound water molecules. The replacement of Mg by Ni in octahedral sites of the 2:1 layer silicates (TL, Sep) of the greenish clay infillings can be traced by specific OH stretching bands related to the Mg3OH, Mg2NiOH, MgNi2OH, and Ni3OH configurations in the fundamental (MIR) and first overtone (NIR) regions of the spectra. The dominance of the Mg3OH and Ni3OH configurations with respect to mixed configurations in the Mg–Ni mineral series of the clay infillings (mostly in the dominant TL minerals) suggests that Mg and Ni segregation is related to separate Mg-rich and Ni-rich mineral phases rather than to a cationic clustering within the individual particles. This segregation of Mg and Ni in discrete mineral phases is related to Mg–Ni oscillatory zoning patterns (banded patterns) and is reproduced at the scale of the Ni-silicate ores between the white (deweylite) and greenish (garnierite) veins of the reactivated faults.

Influence of Ni-Al Nanoparticle on the Properties of PMMA/Ni-Al Layered Double Hydroxides based Nanocomposites

ABSTRACT The layered double hydroxide has been synthesised by the co-precipitation method at constant pH 8–9. FTIR analysis and X-ray diffraction technique show a single LDH phase and an anisotropic growth of very small crystallites. The crystal structure of the material is hexagonal, as confirmed from XRD analysis. TEM analysis reveals Ni-Al OLDH aggregates are in fibril form, having lengths 20–70 nm. The SEM study reveals that the loading of the OLDH particle above 3% has increased the rate of agglomerations in nanocomposites. The presence of anions in the interlayer space and OH groups have been found out using IR spectroscopic technique. TGA showed that the thermal stability of PMMA/Ni-Al OLDH nanocomposites have increased as the weight percentage of OLDH is increased; consequently, the value of capacitance also showed enhancement. The mechanical analysis has suggested that the addition of OLDH particles has increased the tensile strength by 15–17% and flexural strength by 20–25%.

Hydration of LiOH and LiCl-Near-Infrared Spectroscopic Analysis.

The hydration behavior of LiOH, LiOH·H2O, and LiCl was observed by near-infrared (NIR) spectroscopy. Anhydrous LiOH showed two absorption bands at 7340 and 7171 cm–1. These NIR bands were assigned to the first overtone of surface hydroxyls and interlayer hydroxyls of LiOH, respectively. LiOH·H2O showed two absorption bands at 7137 and 6970 cm–1. These NIR bands were assigned to the first overtone of interlayer hydroxyls and H2O molecules coordinated with Li+, respectively. The interlayer OH– and the coordinated H2O of LiOH·H2O were not modified even when the LiOH·H2O was exposed to air. In contrast, anhydrous LiOH was slowly hydrated for several hours, to form LiOH·H2O under ambient conditions (RH 60%). Kinetic analysis showed that the hydration of the interlayer OH– of LiOH proceeded as a second-order reaction, indicating the formation of intermediate species—[Li(H2O)x(OH)4]3– (x = 1 or 2). However, the hydration of the LiOH surface did not follow a second-order reaction because the chemisorption of H2O molecules onto the defect sites of the LiOH surface does not need to crossover the energy barrier. Furthermore, we succeeded in observing the hydration of deliquescent LiCl, including the formation of LiCl solution for several minutes by NIR spectroscopy.

Environmental-friendly preparation of Ni–Co layered double hydroxide (LDH) hierarchical nanoarrays for efficient removing uranium (VI)

With the wide application of nuclear energy and the rapid development of mining, a great quantity of uranium (U(VI)) containing wastewater is inevitably generated. In this work, a facile environmental-friendly coprecipitation method was proposed for the green synthesis of binary layered double hydroxides (Ni–Co LDHW-7), which could be used to efficiently adsorb U(VI) from wastewater. Pseudo-second-order kinetic model and Dubinin-Radushkevich model fitted well with the adsorption of U(VI) on Ni–Co LDHW-7, the maximum adsorption capacity of U(VI) on Ni–Co LDHW-7 was 201.09 mg/g calculated by the Langmuir model. Adsorption equilibrium reached after 30 min, which is a spontaneous and endothermic process. Fourier Transform Infrared Spectrometer (FTIR) and X-ray Photoelectron Spectroscopy (XPS) measurements manifested that the favorable U(VI) extraction on Ni–Co LDHW-7 is mainly ascribed to inner-layer surface electrostatic interaction and complexation, which is dominated by abundant oxygen-containing M-OH and interlayer OH− ions. Briefly, this work provides a facial and environmental-friendly Ni–Co LDHW-7 for removing U(VI) in actual uranium-containing wastewater.

Local mode interpretation of the OH overtone spectrum of 1:1 phyllosilicates

Abstract. Although OH overtone bands of 1:1 phyllosilicates are commonly observed in their near-infrared (NIR) spectra, their interpretation in terms of transitions between specific vibrational states is still uncertain. This situation can be traced back to the coupled nature of the fundamental OH-stretching modes involving the interlayer OH groups of 1:1 phyllosilicates. In this case, the overtone spectra cannot be directly related to their fundamental counterparts observed in the mid-infrared (MIR) spectra. In the present study, we use a parameterized quantum-mechanical approach to compute the vibrational frequencies related to the fundamental and overtone bands in serpentine group and kaolinite group minerals. The simple model is based on a description of the vibrational properties of a cluster of OH groups in terms of harmonically coupled anharmonic oscillators. The comparison of the theoretical results with experimental observations makes it possible to interpret most of the salient features of the overtone spectrum of 1:1 phyllosilicates. Unlike the bands observed in the MIR spectra, the overtone bands observed between 7000 and 7300 cm−1 are related to local transitions from the ground state to the second excitation level of OH groups, whereas the weaker bands observed between 7300 and 7400 cm−1 involve a double excitation to the first vibrational level of OH oscillators. The results also support the assignment of specific overtone bands to the occurrence of substituted divalent cations of transition elements in serpentine group minerals.

Layer charge effects on anisotropy of interlayer water and structural OH dynamics in clay minerals probed by high-resolution neutron spectroscopy

The mobility of confined water at clay mineral surfaces underpins many of their functional properties as industrial minerals. Oriented thin films of the sodium (Na+) and calcium (Ca2+) forms of beidellite (Bd) and charge-reduced montmorillonite (Mt), equilibrated at 55% relative humidity using D2O, were studied using high-resolution neutron spectroscopy to determine the overall mobility of the OH groups and interlayer water, as well as the effect of layer charge location and total layer charge on anisotropy of collective motions at clay mineral surfaces. An elastic fixed window approach was applied to follow temperature (T) and scattering vector (Q) dependent changes in the elastic scattering signal at two different film orientations with respect to the instrument configuration. The mean square displacement associated with interlayer D2O was greater when the film (and layer) plane was aligned perpendicular with the instrument's average scattering Q vector. A minor displacement was observed near T = 100 K and assigned to localised isotropic rotational contributions of structural OH. While the anisotropic effect at higher T was minor, Q-dependence was present in all samples and dominated by incoherent scattering from interlayer D2O. The Ca2+-form of reduced charge Mt. had larger correlation lengths in the direction perpendicular to the lattice plane than in the parallel direction. While no obvious direct effect of anisotropy due to total layer charge was observed, higher layer charge resulted in greater overall mobility of both structural OH and interlayer D2O. Despite the challenges of studying smectite thin films by neutron spectroscopy, this study confirmed that hydrated interlayer cations mobilised water above 190 K.

First principles study of structural properties and electric field gradients in kaolinite

This work reports a gauge-including projected augmented waves (GIPAW) method study of the structural and electronic properties of kaolinite (Al2Si2O5(OH)4). Different equilibrium structures were determined, and the corresponding electronic density of states and the electric field gradients (EFG) at each atomic site were calculated. The comparison of those predicted properties with measurements that come from neutron powder diffraction, single crystal synchrotron measurements, and nuclear magnetic resonance spectroscopies allowed a detailed study of the structure. In particular, the first principles calculations considered in this work cover different scales, going from the crystallographic structure to the atomic local environments, and serve as a tool to link both the structural and the hyperfine properties. This methodology predictions successfully solves a kaolinite structure in which the atomic local surroundings are consistent with the EFG measurements, thus providing answers to previous controversies between experimental studies about Al and Si local structures and the orientation of OH groups within the structure. In this sense, the GIPAW calculations support that kaolinite consists of asymmetrically distorted Si tetrahedra and Al octahedra sheets, and the interlayer OH groups are oriented nearly perpendicular to the layer.

Interconvertible structural transformations between two Zn(II) interpenetrating coordination polymers

Two distinct Zn(II) coordination polymers (CPs) have been prepared based on Zn(NO3)2 and 4-(2-ethyl-1H-imidazol-1-yl)benzoic acid (2-Heiba) via different synthetic approaches, solvothermal synthesis and layer diffusion, respectively. Upon solvothermal condition, a 2D undulated CP [Zn2(2-eiba)3(OH)]n (1) can be obtained, which incorporates the polythreading structural motifs and then results in the 3-fold pcu topological network with the aid of interlayer OH⋯N hydrogen bonds. Employment of layer diffusion method affords another 3D CP {[Zn(2-eiba)2](H2O)3}n (2), featuring a dia topological network in 2+2→4-fold interpenetrating pattern. Interestingly, interconvertible structural transformations between 1 and 2 can be achieved by immersing in CH3OH-H2O solution under stirring or solvothermal conditions, respectively. In addition, thermal stability and fluorescence properties of these complexes have also been studied.

Clay-Mineral Transformations and Heavy-Metal Release in Paddy Soils Formed on Serpentinites in Eastern Taiwan

AbstractSerpentinites, which contain high concentrations of Cr and Ni, weather easily into layer silicates and are therefore a possible source of metal contamination in soils. In the present study three soil profiles formed on serpentinites in a paddy field in eastern Taiwan were investigated to understand pedogenic clay-mineral transformations and to determine the relationship between the mineralogical characteristics and labile Cr and Ni in the soil. To this end, physicochemical analyses, micromorphology, X-ray diffraction, and Fourier transform infrared spectroscopy were employed. Serpentine and chlorite were the dominant minerals in the soil parent material, with smaller amounts of pyroxene, amphibole, and talc. Progressive weathering and the release of cations from the parent material resulted in the pedogenic formation of smectite, vermiculite, and interstratified chlorite-vermiculite, demonstrated by their presence in all Ap and AC horizons but their absence from the C horizons. Serpentine, pyroxene, amphibole, and talc are proposed to be transformed to low-charge smectite, while chlorite transformed to vermiculite through an interstratified chlorite-vermiculite phase. The surface soils were enriched in oxalate-extractable Fe relative to the subsoils, which was probably generated by the artificial flooding and draining of the paddy soils. The artificial flooding, which typically releases Fe, may also drive the observed partial hydroxyl interlayering of smectite and incomplete interlayer OH sheets of chlorite. Labile Cr and Ni (extracted with 0.1 N HCl) ranging from 4.7 to 26.8 mg kg−1 and from 56 to 365 mg kg−1, respectively, increased significantly toward the surface soil, consistent with weathering. The heavy metals released may pose a threat to the environment as well as to human health by entering the food chain.

Formation of platinum sites on layered double hydroxide type basic supports: III. Effect of the mechanism of [PtCl6]2− complex binding to aluminum-magnesium layered double hydroxides on the properties of supported platinum in Pt/MgAlO x catalysts

While synthesizing platinum catalysts supported on aluminum-magnesium oxides (Pt/MgAlOx), we established that, in the binding of the Pt(IV) chloro complex to aluminum-magnesium layered double hydroxides (LDHs), the mechanism of the metal complex-support interaction depends on the nature of the interlayer anion of the LDH. The synthesis may yield chemically identical Pt/MgAlOx samples differing in the particle size and electronic structure of supported platinum. The higher dehydrogenating activity of the catalyst obtained by binding the [PtCl6]2− complex in the interlayer space of LDH via exchange with interlayer OH− anions is possibly due to the larger proportion of metallic platinum (Pt0) in this catalyst. In the catalyst prepared from hydrolyzed platinum complex species using LDH with CO32− interlayer anions, platinum is mainly in an oxidized state similar to Pt2+.

Formation of platinum sites on layered double hydroxide type basic supports: II. Effect of the nature of the interlayer anion of the layered aluminum-magnesium hydroxides on platinum binding and Pt/MgAlO x formation

The interaction of aqueous H2PtCl6 solutions with hydrotalcite-type aluminum-magnesium hydroxides differing in the nature of their interlayer anion is reported. In the case of CO32− as the interlayer anion, the introduction of the platinum(IV) chloro complex does exerts no significant effect on the structural properties of the support, on its thermal decomposition dynamics, and on the textural characteristics of the resulting oxide phase. The binding of the platinum complexes to “activated hydrotalcite” with interlayer OH− anions increases the interplanar spacing and enhances the thermal stability of the layered structure. This is accompanied by marked changes in textural characteristics of the material, leading to the formation of a nearly monodisperse mixed oxide phase. In the Pt/MgAlOx samples obtained by reductive treatment, a considerable proportion of platinum is in the form of planar particles, and this corroborates the hypothesis that the metal complex at the sorption stage is mainly localized in the interlayer space of this support. Platinum binds to the support as chloro complexes via rapid anion exchange, and these bound platinum species are characterized by a higher reduction temperature.

Formation of platinum sites on layered double hydroxides type basic supports: I. Effect of the nature of the interlayer anion on the structure characteristics of the layered aluminum-magnesium hydroxide and the formation of an oxide phase

A layered aluminum-magnesium hydroxide of the hydrotalcite type containing interlayer carbonate counterions (HT-CO3) and activated hydrotalcite containing interlayer OH− ions (HT-OH) were studied for the subsequent use as the precursors of supports for platinum catalysts. It was found that the nature of an interlayer anion in the composition of an aluminum-magnesium layered hydroxide is an important factor affecting both the formation of the oxide support and its texture characteristics. The replacement of the interlayer CO32− anion by OH− resulted in changes in the structural parameters of the initial double hydroxide: a decrease in the interlayer distance with the retention of the Mg/Al ratio and an increase in the imperfection of the layered material. X-ray diffraction studies in the temperature range of 30–900°C showed that HT-OH is characterized by the ability to form low-temperature spinel at 375°C. As a result, two types of aluminum-magnesium oxide supports, which were characterized by different pore space organizations at the same Mg: Al ratio, were obtained from the given layered hydroxides.

Fundamental mechanisms for polycarboxylate intercalation into C 3A hydrate phases and the role of sulfate present in cement

The fundamental reactions leading to the intercalation of polycarboxylate (PC) superplasticizers into calcium aluminum hydrates were studied by hydration of pure C 3A in the presence of PC at 75 °C. It was found that the amount of dissolved sulfate present in cement pore solution determines whether organo-mineral phases are formed or not. In the absence of sulfate, PCs easily intercalate during C 3A hydration in alkaline solution. Under these conditions, only excessive steric size of the PC will prevent intercalation. At low sulfate concentrations (SO 4 2−/C 3A molar ratios of 0.1–0.35), PC intercalates with intersalated alkali sulfate, are formed. At high sulfate concentrations (SO 4 2−/C 3A molar ratios of 0.7–2), PC can no longer intercalate. Instead, sulfate, because of its higher negative charge density, fills the interlayer space and monosulfoaluminates with different water contents are formed. Anion exchange experiments confirm that from the initially formed C 4AH 13, PC will exchange the interlayer OH − anion whereas with monosulfoaluminates, no replacement of sulfate by PC was found. Consequently, in alkaline solution, PC intercalates will not exchange their PC against OH − anions whereas sulfate will gradually replace the PC. Generally, intercalation of PC is an unwanted process because it consumes superplasticizer which is effective only when it adsorbs onto the cationic surfaces of AF m and AF t phases. Our experiments demonstrate that intercalation can be avoided by using PCs with long side chains or highly sulfated cements (SO 4 2−/C 3A molar ratio ≥ 0.75) containing alkali or calcium sulfates which dissolve fast. In undersulfated cements, however, PC intercalates can be formed, either directly during the stacking process of the [Ca 2Al(OH) 6] + main layer, with PC acting as the template which determines the interlayer distance, or by anion exchange between initially formed aluminate hydrates (e.g. C 4AH 13 or C 2AH 8) and the PC anion.

Thermal behaviour of chlorite: an in situ single-crystal and powder diffraction study

The high-temperature behaviour of two natural chlorites has been studied by in situ X-ray diffraction: on a single-crystal of clinochlore, triclinic polytype II b -4, space group C 1, with pseudomonoclinic metric and composition (Mg 9.14 Fe 2+ 1.02 Fe 3+ 0.01 Mn 0.01 Ti 0.01 Al 1.76 ) ∑=11.95 (Si 6.32 Al 1.68 ) ∑=8 O 20 (OH) 16 ; by powder diffraction for a chamosite with composition (Mg 3.52 Fe 2+ 4.33 Fe 3+ 1.15 Al 2.85 ) ∑=11.85 (Si 5.45 Al 2.55 ) ∑=8 O 20 (OH) 16 and same symmetry. Unit-cell parameters were measured for both samples up to 550 °C. Diffraction data for structural refinement of clinochlore were collected at 25, 301, 399 and 502 °C. Room temperature 57 Fe Mossbauer spectroscopy measurements were performed on the chamosite sample before and after heating, showing complete Fe oxidation above 500 °C. Mean thermal expansion coefficients of the two samples were: α a = 1.05(3) × 10 −5 , α b = 1.02(3) × 10 −5 , α c = 0.99(5) × 10 −5 and α V = 3.07(7) × 10 −5 /°C for clinochlore and α a = 2.47(25) × 10 −5 , α b = 0.93(5) × 10 −5 , α c = 0.93(12) × 10 −5 and α V = 4.38(25) × 10 −5 /°C for chamosite. These results confirm that the expansion of chlorite depends on the composition, but the dependence is not simply related to the Fe content, as suggested by previous studies. The Si, Al tetrahedral volumes of clinochlore do not significantly change in the T range 25–550 °C. The expansion of M1, M2, M3 and M4 octahedra is 1.5, 1.9, 3.0 and 3.4 % respectively. The interlayer OH–O distances increase of about 1 %, the mean thermal expansion coefficient being 4.5 × 10 −6 /°C, indicating that the hydrogen bonds maintain their moderate strengths also at high temperature. The tetrahedral rotation angle α decreases from 6.38 to 3.34°. A comparison with the modifications induced by pressure on the same sample of clinochlore confirms that the response of the structure to T and P is only approximately opposite. By combining the effects on cell volume, it is possible to formulate the following approximate equation of state: V = V 0 (1 – 1.14 × 10 −2 Δ P + 3.07 × 10 −5 Δ T ), where P is in GPa and T in °Celsius. The equation is valid for a triclinic polytype of chlorite having clinochlore composition.

A newly-identified spectral reflectance signature near the lunar South pole and the South Pole-Aitken Basin

Abstract Signal analysis of Galileo images of the Moon suggests the presence of an absorption band centered near 0.7 μm in the reflectance spectra of areas located adjacent to the equatorward walls of lunar craters at latitudes ranging from −58 to −78°, and areas contained in the South Pole-Aitken Basin. We propose three potential explanations: an Fe2+→Fe3+ charge transfer transition in oxidized iron in clinopyroxenes (high-Ca bearing pyroxenes) or phyllosilicates (Fe- and Mg-bearing sheet silicates containing adsorbed H2O and interlayer OH−), or an effect of titanium in ilmenite (a common lunar opaque material). No identification of the mineralogy is conclusive. The presence and nature of the absorption feature could be confirmed using AMICA images of the lunar far side from the Japanese mission Hayabusa, spectroscopic results from the Japanese mission Selene scheduled for launch in 2007, or the Moon Mineralology Mapper on the Indian mission Chandrayaan-1.

Unique Hydrogen Bonding Correlating with a Reduced Band Gap and Phase Transition in the Hybrid Perovskites (HO(CH2)2NH3)2PbX4 (X = I, Br)

The first hybrid perovskites incorporating alcohol-based bifunctional ammonium cations, (HO(CH(2))(2)NH(3))(2)PbX(4) (X = I, Br), have been prepared and characterized. (HO(CH(2))(2)NH(3))(2)PbI(4) adopts a monoclinic cell, a = 8.935(1) A, b= 9.056(2) A, c = 10.214(3) A, beta = 100.26(1) degrees , V = 813.3(3) A(3), P2(1)/a, and Z = 2, and (HO(CH(2))(2)NH(3))(2)PbBr(4) is orthorhombic, a = 8.4625(6) A, b = 8.647(1) A, c = 19.918(2) A, V = 1457.5(2) A(3), Pbcn, and Z = 4. In the layered structures, a unique hydrogen-bond network connects adjacent perovskite layers, owing to OH....X, NH(3)(+)....X, and intermolecular NH(3)(+)...OH interactions. Its impact on the bonding features of the inorganic framework and on the quite short interlayer distance, in the case of (HO(CH(2))(2)NH(3))(2)PbI(4), is shown. As a result, a significant red shift of the exciton peaks (lambda = 536 nm (X = I), lambda = 417 nm (X = Br)), compared to other PbX(4)(2)(-)-based perovskite hybrids, is observed, revealing a reduced band gap. A reversible structural transition occurs at T = 96 degrees C (X = I) and T = 125 degrees C (X = Br). An orthorhombic cell of the high-temperature phase of (HO(CH(2))(2)NH(3))(2)PbI(4) with a(HT) = 18.567(6) A, b(HT) = 13.833(6) A, c(HT) = 6.437(2) A, and V = 1653 A(3) is proposed from powder X-ray diffraction. A change in the hydrogen bonding occurs, with molecules standing up in the interlayer space and OH parts probably interacting together, leading to a more conventional situation for ammonium groups and a more distorted perovskite layer. This is in accordance with the blue shift of the exciton peak to lambda = 505 nm (X = I) or to lambda = 374 nm (X = Br) during the phase transition.

The effect of pressure upon hydrogen bonding in chlorite: A Raman spectroscopic study of clinochlore to 26.5 GPa

The effect of pressure upon hydrogen bonding in synthetic end-member clinochlore, (Mg5Al)(Si3Al)O10(OH)8, has been studied in situ by high-pressure micro-Raman spectroscopy in a moissanite-anvil cell to 26.5 GPa at 300 K. The ambient spectrum consists of three OH-stretching bands between 3400 and 3650 cm ‐1 , attributed to the hydrogen-bonded interlayer OH, and a narrow band at 3679 cm ‐1 that is assigned to the non-hydrogen-bonded OH groups of the talc-like 2:1 layer. The pressure dependence of the OH modes is linear up to 6 GPa. Near 9 GPa a major discontinuity occurs in the pressure dependence of the interlayer OH-stretching modes. It involves frequency increases >100 cm ‐1 that indicate major changes in hydrogen bonding. The OH mode of the 2:1 layer does not show discontinuous behavior at 9 GPa. A further discontinuity occurs at ~16 GPa. This discontinuity affects both interlayer and 2:1 OH, and is likely to be associated with a change in the overall compression mechanism of clinochlore. The spectroscopic behavior is a completely reversible function of pressure. Predictions based upon recent high-pressure diffraction studies of hydrogen bonding and compression of clinochlore suggest that the 9 GPa transition is associated with attainment of an O 2‐ -O 2‐ -contact distance of 2.7 A.

Characterization and a Fast Method for Synthesis of Sub-Micron Lithiophorite

AbstractLithiophorite is a naturally occurring phyllomanganate which has been identified in soils and ores. Studies on a synthetic version have shed light on the conditions required for the formation of lithiophorite. In this study, we successfully prepared lithiophorite under highly alkaline conditions. In addition, we found that Li+, Al3+ and hydrothermal treatment are all necessary for the formation of lithiophorite. Lithiophorite, birnessite and Li-intercalated gibbsite were examined by infrared (IR) spectroscopy. The Mn oxide sheets of lithiophorite and birnessite were found to have quite similar structural environments. On the other hand, the LiAl2(OH)6 sheets are affected more markedly by the Mn oxide sheets. After intercalation, the symmetry of the six interlayer OH groups of LiAl2(OH)6 is reduced and they are divided into two groups occupying different sites, corresponding to the IR absorption bands at 3480 and 3312 cm−1, respectively.

Novel pressure‐induced phase transformations in hydrous layered materials

High‐pressure Raman and X‐ray diffraction data on single crystals of hydrous layer‐structure minerals, dickite and gibbsite, reveal structural phase transitions occurring between 2.0 and 2.5 GPa. In the case of dickite, this is the first documented occurrence of a pressure‐induced phase transformation in a 1:1 phyllosilicate. Above the transition the structure of individual 1:1 layers remains unchanged, whereas the stacking of individual layers and the interlayer topology change significantly. Similar to dickite, single‐crystal Raman spectra of gibbsite show large perturbations in the v(OH) region and suggest that the interlayer OH groups play a critical role in the phase transformation.