Thermal analysis and infrared emission spectroscopic study of halloysite-potassium acetate intercalation compound

The thermal decomposition of halloysite-potassium acetate intercalation compound was investigated by thermogravimetric analysis and infrared emission spectroscopy. The X-ray diffraction patterns indicated that intercalation of potassium acetate into halloysite caused an increase of the basal spacing from 1.00 to 1.41 nm. The thermogravimetry results show that the mass losses of intercalation the compound occur in main three main steps, which correspond to (a) the loss of adsorbed water (b) the loss of coordination water and (c) the loss of potassium acetate and dehydroxylation. The temperature of dehydroxylation and dehydration of halloysite is decreased about 100 °C. The infrared emission spectra clearly show the decomposition and dehydroxylation of the halloysite intercalation compound when the temperature is raised. The dehydration of the intercalation compound is followed by the loss of intensity of the stretching vibration bands at region 3600-3200 cm-1. Dehydroxylation is followed by the decrease in intensity in the bands between 3695 and 3620 cm-1. Dehydration was completed by 300 °C and partial dehydroxylation by 350 °C. The inner hydroxyl group remained until around 500 °C.

Studies of ferrite, borosilicate and intercalation materials

This thesis is concerned with several aspects of the chemistry of iron compounds. The preparation (with particular emphasis on coprecipitation and sol-gel techniques) and processing of ferrites are discussed. Chapter 2 describes the synthesis of Ni-Zn ferrites with various compositions by three methods. These methods include coprecipitation and sol-gel techniques. The Ni-Zn ferrites were characterised by powder X-ray diffactometry (PXRD), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), Mössbauer spectroscopy and resistivity measurements. The results for the corresponding ferrites prepared by each method are compared. Chapter 3 reports the sol-gel preparation of a lead borosilicate glass and its addition to Ni-Zn ferrites prepared by the sol-gel method in Chapter 2. The glass-ferrites formed were analysed by the same techniques employed in Chapter 2. Alterations in the microstructure, magnetic and electronic properties of the ferrites due to glass addition are described. Chapter 4 introduces compounds containing Fe-O-B, Fe-O-Si or B-O-Si linkages. The synthesis and characterisation of compounds containing Fe-O-B units are described. The structure of [Fe(SALEN)]2O.CH2Cl2 (17), used in attempts to prepare compounds with Fe-O-Si bonds, was determined by X-ray crystallography. Chapter 4 also details the synthesis of three new borosilicate compounds containing ferrocenyl groups, i.e. [FcBO)2(OSiBut2)2] (19), [(FcBO)2(OSiPh2)2] (20) and [FcBOSiPh3] (21). The structure of (19) was determined by X-ray Crystallographic analysis. Chapter 5 reviews the intercalation properties of the layered host compound iron oxychloride (FeOCI). Intercalation compounds prepared with the microwave dielectric heating technique are also discussed. The syntheses of intercalation compounds by the microwave method with FeOCI as host and ferrocene, ferrocenylboronic acid and 4-aminopyridine as guest species are described. Characterisation of these compounds by powder X-ray diffractometry (PXRD) and M{ssbauer spectroscopy is reported. The attempted synthesis of an intercalation compound with the borosilicate compound (19) as guest species is discussed. Appendices A-E describe the theory and instrumentation involved in powder X-ray diffractometry (PXRD), scanning electron microscopy (SEM0, vibrating sample magnetometry (VSM), Mössbauer spectroscopy and electrical resistivity measurements, respectively. Appendix F details the attempted syntheses of compounds with Fe-O-B and Fe-O-Si linkages.

Surfactant-assisted intercalation of high molecular weight poly(ethylene oxide) into vanadyl phosphate di-hydrate

A high molecular weight poly(ethylene oxide)/layered vanadyl phosphate di-hydrate intercalation compound was synthesized via the surfactant-assisted approach. Results confirmed that surfactant molecules were replaced with the polymer, while the lamellar structure of the matrix was retained, and that the material presents high specific surface area. In addition, intercalation produced a more thermally stable polymer as evidenced by thermal analysis. (C) 2011 Elsevier Ltd. All rights reserved.

Electrochemical behaviour of spinel LiMn2O4 as positive electrode in rechargeable lithium cells

The spinel, lithium intercalation compound LiMn2O4 is prepared and studied using the techniques of a.c. impedance and cyclic voltammetry. The impedance behaviour of the LiMn2O4 electrode varies as lithium ions are intercalated or de-intercalated. The reversible behaviour of lithium ions in the LiMn2O4 electrode is confirmed by the results of cyclic voltammetry.

NMR study of slow motions of HDA hydrocarbons chains inside lamellar structures

Measurements of H-1 and C-13 Nuclear Magnetic Resonance (NMR) for the nano-composite materials formed by the intercalation of hexadecylamine (HDA) in metal oxides (TiO2, V2O5 and MoO3), are reported. The H-1 NMR spin-lattice relaxation in the rotating frame was described by using the spectral density due to Davidson and Cole, which incorporates a distribution of correlation times characterized by a width parameter epsilon. The fitting of the data was obtained for epsilon = 0.74, indicating that the correlation times are distributed over a narrow range in this system. High-resolution C-13 NMR techniques were used to resolve the NMR lines of middle-chain methylene groups in the spectra and variable contact time cross-polarization {H-1-}C-13 experiments were employed to analyze the reorientation dynamics of the CH3 and CH2 groups in the HDA chains.

Structural and Electronic Properties of Lithiated SnO2. A Periodic DFT Study

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Molecular dynamics of poly(Ethylene Glycol) intercalated in clay, studied using 13C solid-state NMR

In this study, Cross-Polarization Magic-angle Spinning CP/MAS, 2D Exchange, Centerband-Only Detection of Exchange (CODEX), and Separated-Local-Field (SLF) NMR experiments were used to study the molecular dynamics of poly(ethylene glycol) (PEG) inside Hectorite/PEG intercalation compounds in both single- and double-layer configurations. The results revealed that the overall amplitude of the motions of the PEG chain in the single-layer configuration is considerably smaller than that observed for the double-layer intercalation compound. This result indicates that the effect of having the polymer chain interacting with both clay platelets is to produce a substantial decrease in the motional amplitudes of those chains. The presence of these dynamically restricted segments might be explained by the presence of anchoring points between the clay platelets and the PEG oxygen atoms, which was induced by the Na+ cations. By comparing the PEG motional amplitudes of the double-layered nanocomposites composed of polymers with different molecular weights, a decrease in the motional amplitude for the smaller PEG chain was observed, which might also be understood using the presence of anchoring points.

NANOSCALE ELECTROCHEMISTRY BY IN-SITU TRANSMISSION ELECTRON MICROSCOPY

Nanoscale research in energy storage has recently focused on investigating the properties of nanostructures in order to increase energy density, power rate, and capacity. To better understand the intrinsic properties of nanomaterials, a new and advanced in situ system was designed that allows atomic scale observation of materials under external fields. A special holder equipped with a scanning tunneling microscopy (STM) probe inside a transmission electron microscopy (TEM) system was used to perform the in situ studies on mechanical, electrical, and electrochemical properties of nanomaterials. The nanostructures of titanium dioxide (TiO2) nanotubes are characterized by electron imaging, diffraction, and chemical analysis techniques inside TEM. TiO2 nanotube is one of the candidates as anode materials for lithium ion batteries. It is necessary to study their morphological, mechanical, electrical, and electrochemical properties at atomic level. The synthesis of TiO2 nanotubes showed that the aspect ratio of TiO2 could be controlled by processing parameters, such as anodization time and voltage. Ammonium hydroxide (NH4OH) treated TiO2 nanotubes showed unexpected instability. Observation revealed the nanotubes were disintegrated into nanoparticles and the tubular morphology was vanished after annealing. The nitrogen compounds incorporated in surface defects weaken the nanotube and result in the collapse of nanotube into nanoparticles during phase transformation. Next, the electrical and mechanical properties of TiO2 nanotubes were studied by in situ TEM system. Phase transformation of anatase TiO2 nanotubes into rutile nanoparticles was studied by in situ Joule heating. The results showed that single anatase TiO2 nanotubes broke into ultrafine small anatase nanoparticles. On further increasing the bias, the nanoclusters of anatase particles became prone to a solid state reaction and were grown into stable large rutile nanoparticles. The relationship between mechanical and electrical properties of TiO2 nanotubes was also investigated. Initially, both anatase and amorphous TiO2 nanotubes were characterized by using I-V test to demonstrate the semiconductor properties. The observation of mechanical bending on TiO2 nanotubes revealed that the conductivity would increase when bending deformation happened. The defects on the nanotubes created by deformation helped electron transportation to increase the conductivity. Lastly, the electrochemical properties of amorphous TiO2 nanotubes were characterized by in situ TEM system. The direct chemical and imaging evidence of lithium-induced atomic ordering in amorphous TiO2 nanotubes was studied. The results indicated that the lithiation started with the valance reduction of Ti4+ to Ti3+ leading to a LixTiO2 intercalation compound. The continued intercalation of Li ions in TiO2 nanotubes triggered an amorphous to crystalline phase transformation. The crystals were formed as nano islands and identified to be Li2Ti2O4 with cubic structure (a = 8.375 Å). This phase transformation is associated with local inhomogeneities in Li distribution. Based on these observations, a new reaction mechanism is proposed to explain the first cycle lithiation behavior in amorphous TiO2 nanotubes.

Reversible Water Intercalation Accompanied by Coordination and Color Changes in a Layered Metal-Organic Framework

A new two-dimensional 3d-4f mixed-metal mixed dicarboxylate (homocyclic and heterocyclic) of the formula [Gd2(H2O)2Ni(H2O)2(1,2-bdc)2(2,5-pydc)2] 3 8H2O (1; 1,2-H2bdc = 1,2-benzenedicarboxylic acid and 2,5-H2pydc = 2,5- pyridinedicarboxylic acid) has been prepared by employing the hydrothermal method. The structure has infinite onedimensional-Gd-O-Gd- chains formed by the edge-shared GdO9 polyhedral units, resulting exclusively from the connectivity between the Gd3+ ions and the 1,2-bdc units. The chains are connected by the [Ni(H2O)2(2,5-pydc)2]2- metalloligand, forming the two-dimensional layer arrangements. The stacking of the layers creates hydrophilic and hydrophobic spaces in the interlamellar region. A one-dimensional water ladder structure, formed by the extraframework water molecules, occupies the hydrophilic region while the benzene ring of 1,2-bdc occupies the hydrophobic region. To the best of our knowledge, the present compound represents the first example of a 3d-4f mixed-metal carboxylate in which two different aromatic dicarboxylate anions act as the linkers. The stabilization energies of the water clusters have been evaluated using density functional theory calculations. The water molecules in 1 are fully reversible accompanied by a change in color (greenish blue to brown) and coordination around Ni2+ ions (octahedral to distorted tetrahedral).

The intercalation reaction of pyridine with manganese thiophosphate, MnPS3

The intercalation of pyridine in the layered manganese thiophosphate, MnPS3, has been examined in detail by a variety of techniques. The reaction is interesting since none of the anticipated changes in optical and electrical properties associated with intercalation of electron donating molecules is observed. The only notable change in the properties of the host lattice is in the nature of the low-temperature magnetic ordering; while MnPS3 orders antiferromagnetically below 78 K, the intercalated compound shows weak ferromagnetism probably due to a canted spin structure. Vibrational spectra clearly show that the intercalated species are pyridinium ions solvated by neutral pyridine molecules. The corresponding reduced sites of the host lattice, however, were never observed. The molecules in the solvation shell are exchangeable. Although the reaction appears to be topotactic and reversible, from XRD, a more detailed analysis of the products of deintercalation reveal that it is not so. The intercalation proceeds by an ion exchange/intercalation mechanism wherein the intercalated species are pyridinium ions solvated by neutral molecules with charge neutrality being preserved not by electron transfer but by a loss of Mn2+ ions from the lattice. The experimental evidence leading to this conclusion is discussed and it is shown that this model can account satisfactorily for the observed changes (or lack of it) in the optical, electrical, vibrational, and magnetic properties.

Graphite intercalation compounds under pressure

Motivated by recent experimental work, we use first-principles density functional theory methods to conduct an extensive search for low enthalpy structures of C$_6$Ca under pressure. As well as a range of buckled structures, which are energetically competitive over an intermediate range of pressures, we show that the high pressure system ($\gtrsim 18$ GPa) is unstable towards the formation of a novel class of layered structures, with the most stable compound involving carbon sheets containing five- and eight-membered rings. As well as discussing the energetics of the different classes of low enthalpy structures, we comment on the electronic structure of the high pressure compound and its implications for superconductivity.

Preparation and characterization of layered compound zirconium bis(monohydrogenphosphate)intercalated with rare earth complex

Layered compound zirconium bis(monohydrogenphosphate)(alpha-ZrP) intercalated with rare earth complex Eu(DBM)(3)phen was prepared. The pre-intercalation of p-methoxyaniline into alpha-ZrP makes the interlayer separation large enough to exchange PMA with europium complex, thus, the luminescent assembly was prepared. This was confirmed by X-ray diffraction, UV-visible spectra and elemental analysis. The fluorescence spectra and lifetime of the assembly were also presented.

The effect of mechanochemical activation upon the intercalation of a high-defect kaolinite with formamide

The effect of mechanochemical activation upon the intercalation of formamide into a high-defect kaolinite has been studied using a combination of X-ray diffraction, thermal analysis, and DRIFT spectroscopy. X-ray diffraction shows that the intensity of the d(001) spacing decreases with grinding time and that the intercalated high-defect kaolinite expands to 10.2 A. The intensity of the peak of the expanded phase of the formamide-intercalated kaolinite decreases with grinding time. Thermal analysis reveals that the evolution temperature of the adsorbed formamide and loss of the inserting molecule increases with increased grinding time. The temperature of the dehydroxylation of the formamide-intercalated high-defect kaolinite decreases from 495 to 470oC with mechanochemical activation. Changes in the surface structure of the mechanochemically activated formamide-intercalated high-defect kaolinite were followed by DRIFT spectroscopy. Fundamentally the intensity of the high-defect kaolinite hydroxyl stretching bands decreases exponentially with grinding time and simultaneously the intensity of the bands attributed to the OH stretching vibrations of water increased. It is proposed that the mechanochemical activation of the high-defect kaolinite caused the conversion of the hydroxyls to water which coordinates the kaolinite surface. Significant changes in the infrared bands assigned to the hydroxyl deformation and amide stretching and bending modes were observed. The intensity decrease of these bands was exponentially related to the grinding time. The position of the amide C&unknown;O vibrational mode was found to be sensitive to grinding time. The effect of mechanochemical activation of the high-defect kaolinite reduces the capacity of the kaolinite to be intercalated with formamide.