Intercalated Water Molecules Research Articles

Weak ferroelectricity of potassium niobate K4Nb6O17 single crystal grown by pulling down technique

Although potassium niobate K4Nb6O17 single crystal is easy to absorb moisture due to the intercalation of water molecules in the crystal, single crystals can be grown in fiber shape using an original pulling down method. K4Nb6O17 single crystals are easy to break down in plate shape by cleavage which is in turn affected by moisture. The dielectric constant and electric polarization measurements show that K4Nb6O17 single crystal is with weak ferroelectricity.

Transforming Anodized WO3 Films into Visible-Light-Active Bi2WO6 Photoelectrodes by Hydrothermal Treatment.

We directly transformed anodized tungsten oxide film (WO3·2H2O) into bismuth tungstate (Bi2WO6) by substituting the intercalated water molecules with [Bi2O2](2+) in a hydrothermal treatment. The resultant Bi2WO6 was readily used as an electrode to produce anodic photocurrent in H2 evolution on the Pt counter electrode observed under visible light irradiation.

Thermo-chemical metastability of multilayer epitaxial graphene oxide: Experiments and density functional theory calculations

ABSTRACTGraphene oxide holds great promise for future applications in nano-technology. The chemistry of this material is not well understood. This understanding is crucial to enable future applications of graphene oxide. In this study, experiments and density functional theory calculations are combined to elucidate the chemical properties of multilayer graphene oxide obtained by oxidizing epitaxial graphene grown on silicon carbide via the Hummers method. This study shows that at room temperature as prepared graphene oxide films exhibit a uniform and homogeneous structure, include a minimal amount of edges and holes, and have an oxidation ratio of about 0.44. The comparison with density-functional calculations shows that graphene oxide includes a minimal amount of intercalated water molecules and well-defined fractions of epoxide and hydroxyl groups.

Synthesis and electrochemical performance of mixed phase α/ β nickel hydroxide

Nickel hydroxide with a unique α/ β mixed phase structure is synthesized by partially substituting Al 3+ for Ni 2+ with chemical coprecipitation method. The physical properties of the synthesized Al-substituted α/ β-nickel hydroxide are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry analysis (TG), scanning electron microscopy (SEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and tap density testing. The results show that the Al-substituted α/ β-nickel hydroxide exhibits an irregular shape and contains many intercalated water molecules. In particular, the tap density of the Al-substituted α/ β-nickel hydroxide reaches 2.02 g cm −3, which is significantly higher than that of α-nickel hydroxide. The electrochemical performances of the prepared samples are characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge tests. The results demonstrate that the Al-substituted α/ β-nickel hydroxide has much higher electrochemical activity, better electrochemical reversibility, lower electrochemical reaction impedance, and higher discharge voltage than the pure β-nickel hydroxide. The specific discharge capacity of the Al-substituted α/ β-nickel hydroxide maintains to be 325.4 mAh g −1 (or 657.3 mA h cm −3) after 100 cycles at a charging/discharging current density of 200 mA g −1 under ambient temperature.

Ab Initio Simulation of Changes in Geometry, Electronic Structure, and Gibbs Free Energy Caused by Dehydration of Hydrotalcites Containing Cl−and CO32−Counteranions

This ab initio study was performed to better understand the correlation between intercalated water molecules and layered double hydroxides (LDH), as well as the changes that occur by the dehydration process of Zn-Al hydrotalcite-like compounds containing Cl⁻ and CO₃²⁻ counterions. We have verified that the strong interaction among intercalated water molecules, cointercalated anions, and OH groups from hydroxyl layers is reflected in the thermal stability of these compounds. The Zn(2/3)Al(1/3)(OH)₂Cl(1/3)·2/3H₂O hydrotalcite loses all the intercalated water molecules around 125 °C, while the Zn(2/3)Al(1/3)(OH)₂(CO₃)(1/6)·4/6H₂O compound dehydrates at about 175 °C. These values are in good agreement with experimental data. The interlayer interactions were discussed on the basis of electron density difference analyses. Our calculation shows that the electron density in the interlayer region decreases during the dehydration process, inducing the migration of the Cl⁻ anion and the displacement of the hydroxyl layer from adjacent layers. Changes in these compound structures occur to recover part of the hydrogen bonds broken due to the removal of water molecules. It was observed that the chloride ion had initially a lower Löwdin charge (Cl(-0.43)), which has increased its absolute value (Cl(-0.58)) after the water molecules removal, while the charges on carbonate ions remain invariant, leading to the conclusion that the Cl⁻ anion can be more influenced by the amount of water molecules in the interlayer space than the CO₃²⁻ anion in hydrotalcite-like compounds.

Raman and IR spectra of K4Nb6O17and K4Nb6O17·3H2O single crystals

AbstractPolarised Raman and IR spectra of K4Nb6O17 and K4Nb6O17· 3H2O single crystals were measured. The obtained spectra are discussed using the factor group approach for the orthorhombic P21nb space group and assignment of bands to the respective motions of atoms is proposed. In particular, we have shown that the bands above 770 cm−1 can be attributed to the stretching modes of short niobium–oxygen bonds, which are present in this material due to the pronounced layered structure, whereas the potassium atoms contribute to the bands observed below 180 cm−1. Our studies have revealed that intercalation of water molecules leads to shifts, broadening and changes in intensity of some bands. These changes have been attributed to slight changes in the bond lengths and angles, interactions of the water molecules with K atoms and structural disorder introduced by the intercalated water molecules. However, the main structural framework was preserved. Copyright © 2010 John Wiley & Sons, Ltd.

Lanthanide-based 0D and 2D molecular assemblies with the pyridazine-3,6-dicarboxylate linker

Two distinct series of lanthanides-based coordination polymers involving the pyridazine-3,6-dicarboxylate (pzdc) ligand have been structurally characterized by means of single-crystal XRD analysis. The structure of the compounds Ln2(H2O)4(pzdc)3·(3/3.5)H2O with Ln = Pr (1), Nd (2), Sm (3), Eu (4) is built up from dinuclear bricks [Ln2O8N5(H2O)4] containing two μ3-oxo bridged nine-fold coordinated lanthanide cations, connected via the pzdc ligand, which acts as tetratendate, tridentate or monodentate linkers. It results in the generation of layers of mixed pzdc-Ln2O8N5(H2O)4 networks, intercalated by free water molecules. The second series with chemical formula Ln2(H2O)6(pzdc)3·3H2O (Ln = Gd (5), Tb (6), Dy (7), Er (8), Lu (9)) is a molecular assembly of discrete dinuclear bricks similar to those of the previous compounds. They only differ by the number of terminal water molecules within the dimer [Ln2O6N5(H2O)6]. Interactions viahydrogen bond occur between terminal water species attached the lanthanide and free intercalated water molecules. Europium- and terbium-based compounds 4 and 6 exhibit fluorescence emission in the visible region at room temperature.

Nature of disorder in synthetic hectorite

The disorder of synthetic Na-hectorite was investigated using structural simulation of X-ray powder patterns.The method used to characterize this clay mineral was based on the comparison between experimental and calculated X-ray diffraction profiles. The study was achieved in two steps: (i) the quantitative interpretation of 00l reflections enabled the determination of the number of intercalated water molecules, their positions and the stacking mode of the clay mineral layers along the normal to the (a, b) plane; and (ii) the study of the hkl reflections with h and/or k≠0 enabled the characterization of the structural evolution in the (a, b) plane of synthetic hectorite. Many models of disorder with random shifts of ±a/3, a/3+b/3, 80% of a/3+b/3 and 20% of a/3 with a total density of defects of 80%, gave the best fit to the observed data at the level of (02, 11), (20, 13), (04, 22), (15, 24, 31) and (06, 33) bands with 5° of tetrahedral cavity distortion (the rotation angle of the tetrahedra).

Structural Model Proposition and Thermodynamic and Vibrational Analysis of Hydrotalcite-Like Compounds by DFT Calculations

We propose a model to calculate the electronic structure of hydrotalcite-like compounds by using periodic boundary conditions and ab initio density functional theory (DFT). The proposed method to build up layered double hydroxides (LDHs) was tested for Zn2/3Al1/3(OH)2Cl1/3·2/3H2O, Zn2/3Al1/3(OH)2(CO3)1/6·4/6H2O, and Mg2/3Al1/3(OH)2(CO3)1/6·4/6H2O with 3R1 polytype. In the model, the occupation of cationic sites in hydroxide layers is ordered and the interlayer anions and water molecules form a film between the layers. Direct comparison with experimental structural parameters shows good agreement. The a parameter is close to that in brucite for all three LDHs. The c parameter is smaller (about 1 A) for the LDHs with CO32− as a consequence of its strong interaction with hydroxide layers. Those interactions were evidenced by the difference of density and vibrational analysis. The intercalated water molecules have small mobility and interact strongly with one another and with interlayer anions and hydroxide l...

Synthesis of porous and nonporous ZnO nanobelt, multipod, and hierarchical nanostructure from Zn-HDS

Zn based hydroxide double salts (Zn-HDS) with an interlayer spacing of 20 Å was produced by dissolving dumbbell-like ZnO crystal. The resulting Zn-HDS with a ribbon-like shape has a suitable morphology to explore the remarkably mild procedure for synthesis of ZnO nanobelts. We found that the intercalated water molecules into the Zn-HDS could play a key role in the ZnO nanobelts porosity. The nonporous ZnO nanobelts were successfully synthesized from the Zn-HDS by soft-solution process at 95 °C through mild dehydration agent as Na 2CO 3. As-synthesized ZnO nanobelts were grown along not only the [0 1 −1 0], but also the [2 −1 −1 0]. On the other hand, the porous ZnO nanobelts were obtained from the Zn-HDS by calcinations at 200 and 400 °C. In addition, flower-like ZnO multipod and hierarchical nanostructures were produced from the Zn-HDS by using of strong dehydration agent (NaOH) through hydrothermal reaction at 150 and 230 °C.

Intercalated Water in Synthetic Fluorhectorite Clay

(7)Li and (1)H nuclear magnetic resonance together with X-ray diffraction measurements in powdered samples and pseudocrystalline films of synthetic fluorhectorite as a function of relative ambient humidity permit to address several aspects of the structure and dynamics of intercalated water molecules. The role of proton exchange as a possibly dominant mechanism of charge transport in the one-water layer regime of hydration is reexamined. The experimental results in Li-fluorhectorite support the result of molecular simulations which predict, for Li-montmorillonite, the existence of an intermediate regime, between one-water layer and two-water layer states.

Reaction–diffusion based co-synthesis of stable α- and β-cobalt hydroxide in bio-organic gels

We report the preparation, dynamics of formation and extensive characterization of a stable two-phase system of crystalline α- and β-Co(OH) 2. The method is based on the reaction and diffusion of hydroxide ions into a biopolymer gel (agar, gelatin) containing Co(II). The spatio-temporal dynamics leading to the formation and coexistence of two polymorphs exhibit a complicated and rich pattern whereby the system proceeds as a propagating Ostwald ripening front that continuously transforms blue/green α-Co(OH) 2 to crystalline β-Co(OH) 2. Depending on the nature of the gel, the system might further exhibit fascinating Liesegang bands. The coexisting polymorphs were characterized using XRD, FTIR, UV–vis, TGA, SEM and TEM, and EPR. The FTIR spectra reveal the intercalation of water molecules and chloride ions between the hydroxyl layers in the case of α-Co(OH) 2. X-ray diffraction and electronic microscopy investigations confirm the aforementioned Ostwald ripening process during the phase transformation whereby almost-amorphous α-Co(OH) 2 dissolves to form crystalline β-Co(OH) 2 5 μm in length. The UV–vis reflectance spectra reveal that the origin of the blue/green color in the α-polymorph is due to the tetrahedrally coordinated Co(II) ions existing within the octahedral Co(II) layers. The reorganization of these tetrahedral Co(II) ions in the α-polymorph to form octahedral Co(II) in the β-polymorph is shown to take place in seconds without induction time. α-Co(OH) 2 was found to be mesoporous while the β-polymorph is microporous with low nitrogen adsorption capacities. Due to dipole–dipole broadening, no EPR spectrum was obtained for the β-polymorphs even at low temperature. In contrast, the obtained EPR spectrum of the α-polymorph was consistent with that of Co(II) in various materials.

Duration dependences of electric and crystal structures of bi layer hydrated NaxCoO2·yH2O

Abstract We succeeded in synthesizing the bi layer hydrated superconducting Na x CoO 2 · y H 2 O powder samples with different T c 's by systematically changing the duration in a high humidity atmosphere after intercalation of water molecules. From the results of 59Co nuclear quadrupole resonance measurements, it was found that resonance frequency ν Q monotonically decreased with increasing the duration after filtration. The electronic states of samples were found being well characterized by the ν Q , and we succeeded in drawing the electronic phase diagram in which there exist two superconducting phases and an in-between magnetic phase. On the other hand, a lattice parameter along c-axis was found to decrease monotonically with increasing the time duration. This result indicates that shrinkage of CoO 2 planes is caused by changes of arrangements and/or contents of ions between CoO 2 planes which evolve during kept in a high humidity atmosphere.

Synthesis and photoluminescence properties of layered oxides intercalated with Eu3+ ions by electrostatic self-assembly method using oxide nanosheets

Layered oxides intercalated with Eu3+ ions were prepared by self-assembly deposition method based on the electrostatic interaction between negative charged oxide nanosheets and Eu3+ ions. The layered oxides were composed of two-dimensional host nanosheet layer with guest Eu3+ ions and gave Eu3+ emission based on an energy transfer from bandgap excitation of the host oxide nanosheets to the Eu3+ ions. The photoluminescence properties of the Eu3+ ions were influenced by the type of nanosheet and the intercalated water molecules. Relatively-strong emission of Eu3+ was observed from Eu3+-intercalated titanate layered oxide. The intensity of Eu3+ emission increased with increasing the amount of intercalated water molecules. This indicates that the energy transfer from TiO2−δ nanosheet to Eu3+ is promoted by the intercalated water molecules. In addition, the intensity of Eu3+ emission was stronger at high pH than at low pH. This emission change is presumably due to two phenomena. One is a fine hydration state change of Eu3+ in the interlayer, and the other is a change in energy transfer from the TiO2−δ nanosheet to Eu3+.

Bromide-ion distribution in the interlayer of the layered double hydroxides of Zn and Al: Observation of positional disorder

AbstractBecause of the anisotropy in bonding, layered hydroxides crystallize with extensive structural disorder due to the incorporation of stacking faults. In contrast, the loss of crystallinity in Br−-ion intercalated layered double hydroxides (LDHs) arises due to the positional disorder of Br− in the interlayer. The structure of the interlayer in other LDHs is poorly understood due to the low X-ray scattering power of the commonly found anions such as Cl− and NO3−\$\end{document} relative to that of the metal hydroxide layers. On heating to 175°C, the Br− ion migrates from positions of lesser site degeneracy to those of greater site degeneracy as dehydration of the interlayer opens up access to positions hitherto occupied by intercalated water molecules. The new (18h) site is situated closer to the proton of the metal hydroxide layer (1.809 Å) compared to the 6c site (2.402 Å). This shows a pre-association of the bromide ion with the proton of the hydroxide layer leading to the release of HBr upon decomposition of the bromide-containing LDHs. The fact that Cl−-containing LDHs also decompose with the evolution of HCl shows that such a redistribution of the atoms in the interlayer is more common than is generally recognized.

Unprecedented Route to Ordered Polyaniline: Direct Synthesis of Highly Crystalline Fibrillar Films with Strong π‐π Stacking Alignment

Films of polyaniline (PANI) featuring about 80% crystallinity and characterised with strong π-π stacking alignment parallel to the film surface have been obtained directly after the original synthesis upon simple drying of the aqueous PANI suspension. A strong anisotropy in the growth of the nano-sized crystals produced during the synthesis results in the formation of micrometer-length fibrils perpendicular to the film surface in the course of water evaporation. The regular intercalation of water molecules between the PANI chains seems to be crucial for their ordering throughout the synthesis and film formation.

Topological Diversification in Metal‐Organic Frameworks: Secondary Ligand and Metal Effects

AbstractA series of interesting coordination polymers have been prepared by the combination of a V‐shaped 4,4′‐oxybis(benzoic acid) (H2oba) and neutral organonitrogen ligands with different metal ions, namely, {[M(oba)(bpe)]·H2O}n [M = Mn (1), Co (2)], [M(oba)(N3)]n [N3 = dipyridin‐2‐ylamine; M = Cd (3), Cu (4)] and {[Zn(oba)(N5)]·2H2O}n (5) [bpe = 1,2‐bis(4‐pyridyl)ethene, N5 = bis(pyridin‐2‐yl)pyridine‐2,6‐diamine]. The framework structures of these neutral polymeric complexes have been determined by single‐crystal X‐ray diffraction studies. Compound 1 has a threefold pcu‐type network structure. Although 2 has the same ligands and coordination modes as 1, it consists of corrugated 2D layers formed of a series of squares, which allows the sheets to interpenetrate in an unusual 2D → 3D parallel fashion. Polymers 3 and 4 exhibit double‐helical chains formed by π–π stacking interactions from the phenyl rings of the N3 ligands. Compound 5 forms a 2D supramolecular architecture directed by hydrogen bonding between the NH groups of the N5 ligand, the uncoordinated carboxylate oxygens, and the intercalated water molecules. This work markedly indicates that the effect of auxiliary ligands is significant in the construction of these network structures, which are also well regulated by the metal centers. Thermogravimetric analysis (TGA) and XRPD results for compound 1 as well as luminescent properties for compounds 3 and 5 are discussed.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Thermo-infrared-spectroscopy analysis of dimethylsulfoxide-kaolinite intercalation complexes

Dimethylsulfoxide (DMSO) kaolinite complexes of low-and high-defect kaolinites were studied by thermo-IR-spectroscopy analysis. Samples were gradually heated up to 170°C, three hours at each temperature. After cooling to room temperature, they were pressed into KBr disks and their spectra were recorded. From the spectra two types of complexes were identified. In the spectrum of type I complex two bands were attributed to asymmetric and symmetric H-O-H stretching vibrations of intercalated water, bridging between DMSO and the clay-O-planes. As a result of H-bonds between intercalated water molecules and the O-planes, Si-O vibrations of the clay framework were perturbed, in the low-defect kaolinite more than in the high-defect. Type II complex was obtained by the thermal escape of the intercalated water. Consequently, the H-O-H bands were absent from the spectrum of type II complex and the Si-O bands were not perturbed. Type I complex was present up to 120°C whereas type II between 130 and 150°C. The presence of intercalated DMSO was proved from the appearance of methyl bands. These bands decreased with temperature due to the thermal evolution of DMSO but disappeared only in spectra of samples heated at 160°C. Intercalated DMSO was H-bonded to the inner-surface hydroxyls and vibrations associated with this group were perturbed. Due to the thermal evolution of DMSO the intensities of the perturbed bands decreased with the temperature. They disappeared at 160°C together with the methyl bands.

Molecular Modeling of the Structure and Dynamics of the Interlayer Species of ZnAlCl Layered Double Hydroxide

Molecular dynamics simulations of the ZnAl layered double hydroxide containing interlayer chloride anions have been performed in the NpT and Np(zz)T statistical ensembles for metal Zn/Al ratios of 2 and 3. We have monitored the interlayer spacing as a function of the number of intercalated water molecules for each statistical ensemble. We have studied how these profiles are affected by the method of calculation of the charges of the hydroxide layer atoms. Diffusion coefficients of the interlayer water molecules have been calculated for different Zn/Al ratios. The calculation of the chemical potential of the interlayer water molecules has been carried out for three amounts of interlayer water molecules. The calculation showed a qualitative agreement with the bulk water chemical potential within a range of interlayer water molecule contents.

Adsorption of Cr(VI) on STAC-modified rectorite

Adsorption of Cr(VI) on stearyl trimethylammonium chloride modified rectorite (STAC-rectorite) was investigated by batch studies, X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) analyses. The Cr(VI) adsorption on STAC-rectorite is well described by the Freundlich isotherm. The adsorption capacity reached as high as 21 g/kg for Cr(VI), or 400 mmol/kg of chromate. The enthalpy change of adsorption (Δ H) is − 9.4 kJ/mol, indicating retention of Cr(VI) on STAC-rectorite is via physical adsorption. Higher Cr(VI) adsorption on STAC-rectorite occurred in acidic solutions (pH 4) and the amount of adsorbed Cr(VI) decreased rapidly with increasing pH as a higher (OH) − concentration will compete against Cr(VI) for adsorption sites, thus, inhibiting formation of Cr(VI)-STAC complex. FTIR analysis shows that the adsorbed STAC forms an admicelle surfactant surface coverage, which is responsible for Cr(VI) adsorption. Band position shifting of Si–O vibration and H–O vibration of water molecules before and after reaction with Cr(VI) indicates that the adsorbed Cr(VI) influences the strength of the Si–O chemical bonds in the siloxane layer and H–O bonds of intercalated water molecules.