Thesis (M.A.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Two theories for the mechanism of cation adsorption of base exchange clays were investigated. The Charged Lattice theory proposes that the negative charge causing the base exchange is due to substitution of divalent for trivalent and trivalent for tetravalent ions in the alumino-silicate structure. The Ion-Pair theory proposes that the base exchange is due to hydroxyl ions chemisorbed in the surface of the colloidal particles. It was the purpose of this work to apply these two theories to a kaolinite clay and determine the results to ascertain the mechanism or adsorption of cations on the clay. Samples or dialyzed clay were prepared and measured amounts of base were added to each. pH and base ion activity mesurements were made of each sample after equilibrium had been reached. These measurements were applied to mathematical equations representing each theory and the results interpreted through graphs. Further tests of the two theories were made by applying them to a base exchange resin known to have an inherent negative charge. This resin was prepared and treated in the same manner as the clay. It was concluded that the Ion-Pair theory was a possible mechanism, and that the Charged Lattice theory was not a possible mechanism for the adsorption of cations on the kaolinite clay. Neither theory gave completely satisfactory results with the resin, although the Charged Lattice mechanism appeared to hold at low pH values.

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Abstract Cationic surfactant cetyltrimethyl ammonium brombide (CTAB) was used as template to synthesize aluminosilicate MCM-41 (plane group P6m, hexagonal array of uniform mesopores derived from crystalline colloidal array (CCA)) molecular sieve and lamellar phases in colloidal solution with negatively charged silicate and aluminate species at pH=10. In the first part, sodium aluminate (up to 0.25 molar ratio) and sodium silicate were the precursor of Al and Si, respectively; in the second part, kaolinite (Al4[Si4O10](OH)8) was used instead. The hydrothermally reacted (100oC in a Teflon sealed container) materials subject to room temperature drying, calcination (540oC) or ethanol rinsing were studied by X-ray diffraction (XRD), optical microscopy under plane polarized light or transmission electron microscopy (TEM) with emphasis on the microstructures and formation mechanism of mesophases, MCM-41, and gibbsite (Al(OH)3) at a relatively low CTAB/water ratio and the effect of Al/Si ratio on micelle interspacing in terms of micelle size and aluminosilicate wall thickness. In the first part, both calcination and ethanol rinsing were shown to remove the template successfully. The resultant MCM-41 particulates were more or less coalesced and the elongated ones tended to be folded. The hexagonal MCM-41 has a tube interspacing 4.5-5.4 nm and tube wall thickness 1.9-3.7 nm, both generally increasing with the increase of sodium aluminate/sodium silicate ratio up to 0.1 molar. ratio. The tube diameter also increased slightly presumably because of competitive electrostatic coordination of the hydrophilic head of CTAB with the negatively charged aluminate (AlO2-) vs. silicate (SiO4-4) species stable at pH=10. The MCM-41 particulates have well-developed {100} faces, the close-packed plane of 2-D hexagonal structure, and rigid amorphous tube walls, suggesting interface-controlled assembly of rod-like CTAB micelles with their polar head already incorporated with aluminosilicate. Tubules-within-a-tubule were corrugated and folded when extended beyond a certain persistence length, typically 1 mm. Spherical particles with disordered mesopores (typically ca. 4 nm in mesh size) due to entanglement of micelles under semi-dilute condition were also formed. In the second part, the CTAB-saturated solution at pH=10 was separated from mud-like kaolinite to form translucent hydrous gel. Upon drying on a glass slide at room temperature, the gel became whitish because of the following crystallization events. First, whitish gibbsite nucleated preferentially at gel/air and gel/glass interface to form spherulites. The spiral and lateral growth of plate-like gibbsite crystal with {100} and {110} growth front was rapid enough to entrap solution droplets. Subsequently, dendritic lamellar (basal spacing ca. 2.6 nm according to XRD and TEM observations) mesophase exhibiting length fast and clino-extinction with extinction angle 42o was formed via 2-D growth near the edge of the drying gel. This lamellar phase was incorporated with aluminate according to TEM-EDX analysis. Finally, explosive nucleation and dendritic growth of isotropic phase concluded the crystallization. This final event involved surface nucleation as best exhibited at the droplets trapped in gibbsite host. Upon calcination to remove the surfactant, the aluminosilicate MCM-41 retained while aluminate-incorporated lamellar mesophase disappeared as indicated by XRD. In an additional experiment to understand the crystallization behavior of CTAB in drying water, we found that the plate-like and then dendritic monoclinic lamellar phase (space group P21/c) with optical extinction angle of 37o was formed as the growth dimensionality decreased toward the edge of the gel. This nucleation and growth process is analogous to the CTAB/water system with negatively charged silicate and aluminate species derived from kaolinite at pH=10.

Thesis (PhD)--University of South Australia, 2003.

Thesis (M.Eng.)--Memorial University of Newfoundland, 2003. / Bibliography: leaves 103-109.

Tese (doutorado)—Universidade de Brasília, Instituto de Química, 2007. / Submitted by Luis Felipe Souza (luis_felas@globo.com) on 2008-12-10T17:05:47Z No. of bitstreams: 1 Tese_2007_EltonCastro.pdf: 4223477 bytes, checksum: 02cdcad1f8f69eda7377b3a116a1dae9 (MD5) / Approved for entry into archive by Georgia Fernandes(georgia@bce.unb.br) on 2009-03-03T19:18:19Z (GMT) No. of bitstreams: 1 Tese_2007_EltonCastro.pdf: 4223477 bytes, checksum: 02cdcad1f8f69eda7377b3a116a1dae9 (MD5) / Made available in DSpace on 2009-03-03T19:18:19Z (GMT). No. of bitstreams: 1 Tese_2007_EltonCastro.pdf: 4223477 bytes, checksum: 02cdcad1f8f69eda7377b3a116a1dae9 (MD5) / Foram realizados cálculos de mecânica molecular, semi-empíricos e abinitio para o estudo de sistemas baseados em caulinita. As posições e freqüências dos hidrogênios foram estudadas na estrutura da caulinita. As posições dos hidrogênios são polêmicas, principalmente os hidrogênios entre as folhas octaédrica e tetraédrica. Também estudou-se a interação deste argilomineral com os hidrocarbonetos monoaromáticos benzeno, tolueno, etilbenzeno, o-xileno e pxileno, bem como com os metais pesados Cd2+, Cu2+, Zn2+, Hg2+ e Ni2+. A caulinita é conhecida pela sua capacidade adsorvente para moléculas orgânicas e metais pesados, sendo importante em técnicas de remediação ambiental. Modelos de aglomerados com 1, 2 e 3 unidades (Al2Si2O9H4) foram usados para estudar o desempenho dos conjuntos de base. A geometria da caulinita foi parcialmente otimizada. Para a otimização da posição do hidrogênio interno empregou-se os métodos RHF/3-21G* e B3LYP/3-21G* com 2 e 3 unidades (Al2Si2O9H4) da caulinita. O método híbrido ONIOM também foi usado com 3 unidades (Al2Si2O9H4) e RHF/3-21G* (ou B3LYP/3-21G*) na camada alta e 12 unidades (Al2Si2O9H4) e o campo de força Dreiding na camada baixa de teoria. Quando comparados com os valores experimentais, os resultados dos cálculos indicamq que o ONIOM2(B3LYP/3-21G*:Dreiding) dá os melhores valores para a distância O-H e ângulos r e l, 0,993Å, 114,8° e 107,6°, respectivamente. Os cálculos de freqüência para os hidrogênios externos e internos com o modelo de 3 unidades (Al2Si2O9H4) mostram que o método RHF/3-21G* se aproxima mais dos resultados experimentais do que os semi-empíricos AM1 e PM3. Estes três métodos apontam para um estiramento da hidroxila interna num número de onda menor do que os das hidroxilas externas. Os espectros teóricos produzidos com o AM1 mostram que há uma redução nas intensidades das bandas de estiramento das hidroxilas externas quando estas interagem com as moléculas BTEX. Também foi encontrado um deslocamento nas bandas de estiramento C-H destas moléculas. As energias de interação, obtidas com os métodos AM1, RHF e B3LYP para os complexos BTEX-Caulinita, sugerem que a adsorção acontece preferencialmente pela superfície hidroxilada da caulinita, ao invés da superfície dos oxigênios. Os métodos de Mülliken e ChelpG indicam que ocorre uma redistribuição nas cargas dos átomos mais próximos das superfícies da caulinita, ficando os hidrogênios mais eletronegativos e os carbonos, mais eletropositivos. Os mapas de potencial eletrostático para os complexos BTEX-Caulinita mostram também uma redistribuição de densidade quando as moléculas interagem com a superfície do argilomineral, corroborando com os resultados de Mülliken e ChelpG. Os orbitais moleculares do benzeno, tolueno e o-xileno adsorvidos pela caulinita sugerem que esta interação acontece através da nuvem p dos compostos aromáticos com as hidroxilas externas da caulinita. Para o estudo dos complexos de metais pesados-caulinita foi usado o ONIOM2(HF/3-21G*:UFF) e ONIOM2(B3LYP/3-21G*:UFF). Para estes modelos da caulinita de 2 camadas, o nível alto de teoria contém um anel da folha octaédrica e um anel da folha tetraédrica mais o cátion. O nível baixo contém 24 unidades (Al2Si2O9H4). A ordem de afinidade encontrada para o resultado B3LYP foi Cu2+>Ni2+>Zn2+>Hg2+>Cd2+, concordando com os resultados experimentais para Cu2+ e Ni2+. O mapa de superfície traçado para a superfície hidroxilada da caulinita sugere que há uma repulsão significativa do metal por esta superfície. _________________________________________________________________________________________ ABSTRACT / Molecular Mechanics, semi-empirical and ab initio calculations were performed in order to study kaolinite based systems. The hydrogen positions and frequencies were studied in the kaolinite structure. Hydrogen positions have been controversial, mainly the hydrogen species between octahedral and tetrahedral sheets. It has also studied the interaction of this clay mineral with the monoaromatic hydrocarbons benzene, toluene, ethylbenzene, o-xylene and pxylene, as well as the interaction with heavy metals Cd2+, Cu2+, Zn2+, Hg2+ and Ni2+. The adsorbent capacity of kaolinite for organic molecules and heavy metals are of main interest on environmental remediation techniques. Cluster models with 1, 2 and 3 units (Al2Si2O9H4) were used to study the basis set performance. The kaolinite geometry was partially optimized. RHF/3-21G* and B3LYP/3-21G* methods with 2 and 3 units (Al2Si2O9H4) of kaolinite were used for optimization of internal hydrogen positions. The hybrid method ONIOM was also used with 3 units (Al2Si2O9H4) and RHF/3-21G* (or B3LYP/3-21G*) on the high layer and with 12 units (Al2Si2O9H4), and Dreiding force field for the low layer theory. Hybrid method results indicate that ONIOM2(B3LYP/3-21G*:Dreiding) gives the best values for OH distance and r and l angles, 0,993Å, 114,8° and 107,6°, respectively, when compared to the experimental values. Frequency calculations, for the external and internal hydrogens with 3 units (Al2Si2O9H4) model, show that RHF/3-21G* approach results are closer to the experimental than AM1 and PM3 semi-empirical methods. These three methods have a internal hydroxyl stretching frequency at wave number smaller than the one of the external hydroxyls. Theoretical spectra produced with AM1 show a reduction in intensities of external hydroxyl stretching bands of kaolinite, when these interact with BTEX molecules. It was also found a displacement on C-H stretching bands of these molecules. Interaction energies obtained with AM1, RHF and B3LYP methods, for BTEX-Kaolinite complexes, suggest that the adsorption occurs preferentially by kaolinite hydroxyl surfaces, instead of kaolinite oxygen surfaces. Mülliken and ChelpG methods indicate that there is charge redistribution on BTEX atoms that are near kaolinite surfaces. These hydrogens become more eletronegatives and the carbons more eletropositives. Eletrostatic potential map for complexes BTEX-Kaolinite show that there is charge redistribution when the molecules interact with clay mineral surfaces, in agreement to the Mülliken and ChelpG results. Benzene, toluene and o-xylene molecular orbitals, when adsorbed on kaolinite, suggest that this interaction is through the p clouds of aromatic compounds with kaolinite external hydroxyls. Complexes heavy metals-kaolinite study was achieved using ONIOM2(HF/3-21G*:UFF) and ONIOM2(B3LYP/3-21G*:UFF) for the kaolinite 2 layers model. The high level of theory has one ring of octaedrical sheet and one ring of tetraedrical sheet plus cation. The low level they contain 24 units(Al2Si2O9H4). The affinity order found for B3LYP result was Cu2+>Ni2+>Zn2+>Hg2+>Cd2+, which is in agreement to the experimental data for Cu2+ and Ni2+. The surface map plotted for kaolinite hydroxyl surface suggests a significant metal repulsion from this surface.