Graduate Thesis Or Dissertation
 

Synthesis of Intercalation Compounds and Nanocomposites of Inorganic Layered Hosts

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5712m9221

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  • Novel synthetic strategies are developed to prepare new intercalation compounds and nanocomposites with several layered hosts (NiPS₃, Na-montmorillonite, MoS₂ and MoO₃). In these products, alkali metals are ionic intercalates and linear polymers, dendrimers or amines act as co-intercalates. In addition to new synthetic approaches, new structures are identified and characterized. A template synthesis method to prepare NiPS₃/polymer nanocomposites is reported for the first time. Polymers studied were polyethylene oxide (PEO), polyethylenimine (PEI), polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP). NiPS₃/PEO nanocomposites prepared by this template method contain polymer monolayers (delta d = 0.42 nm) between host layers, in contrast to the polymer bilayers reported in previous reports using a topotactic method. Packing fraction calculations reveals that the interlayer space is denser for template synthesized NiPS₃/PEO than for the topotactically-derived MPS₃/PEO nanocomposites (M = Ni, Fe, Cd, and Mn). NiPS₃/PEI, NiPS₃/PVA and NiPS₃/PVP nanocomposites were prepared for the first time and also have polymer monolayers between host layers (delta d = 0.41, 0.42 and 1.56 nm, respectively). The monomer unit / NiPS₃ formula ratio is ~ 1 for PEO, PEI and PVA nanocomposites and ~ 0.5 for PVP nanocomposites. More dilute conditions, more polar solvents, and longer aging times increase the crystallite size of the obtained products. Reaction progress studies indicate that the P₂S₆⁴⁻ and Ni²⁺ concentrations in the reaction mixture govern nanocomposite nucleation and growth. Intercalated nanocomposites with lower generation (G0.0-2.0) polyamidoamine (PAMAM) dendrimers and Na-montmorillonite (Na-MMT) are synthesized using an exfoliation–adsorption method. This is the first report of the G0.0 and G1.0 PAMAM/Na-MMT nanocomposites and of a structurally-ordered G2.0 PAMAM/Na-MMT nanocomposite. The structures obtained depend on the PAMAM generation and the starting reactant ratio. The spherical PAMAM in aqueous medium transforms to a highly flattened conformation after incorporation between the host layers. G0.0 PAMAM forms only monolayer galleries (delta d = 0.42 nm), while G2.0 PAMAM forms monolayers, bilayers, (delta d = 0.84 nm) and mixed phase structures at lower, higher, and intermediate, organic content, respectively, and exhibits an interesting monolayer to bilayer transition. G1.0 PAMAM shows intermediate behavior, with a monolayer to mixed-phase transition observed at the reactant ratios studied. This is the first report of a monolayer arrangement for PAMAM/clay nanocomposites. The maximum organic contents of G0.0 PAMAM monolayer and G2.0 PAMAM bilayer nanocomposites are ∼7% and ∼14% respectively, and these materials have ~2 times lower packing fractions (0.31-0.32) than for linear polymer intercalate nanocomposites of Na-MMT. Under acidic conditions all these nanocomposites form only monolayer galleries, which is ascribed to the stronger electrostatic attraction between negatively charged MMT layers and protonated PAMAM. Acidic conditions also slow the rate of formation of the nanocomposites and generate more ordered products. The Na⁺ ions in the Na-MMT structure play a significant role in PAMAM/Na-MMT nanocomposite formation. Both Na-MMT and PAMAM structural units are preserved in the nanocomposites obtained. Electride solutions obtained by dissolution of Na(m) in ethylenediamine (en) are used for the first time to generate MoS₂ intercalation compounds with Na and en as intercalate and cointercalate, respectively. Two new phases, labeled α and β, have delta d = 0.35 and 0.57 nm, respectively; the different gallery dimensions are ascribed to parallel vs. perpendicular orientations of en in the galleries. The B phase structure has not been reported previously in any MS₂ intercalation compounds. The intercalation reaction proceeds via the formation of a metastable kinetic product, the β phase, and the subsequent generation of the thermodynamically stable α phase. Lower electride concentrations, lower reaction temperatures and shorter reaction times favor production of the β phase. The products obtained have compositions of Na₀.₂-₀.₃MoS₂·0.3-0.4en with a larger packing fraction than the structurally analogous A-en-GICs (A = alkali metal, GIC = Graphite intercalation compound). The electrochemical reduction of MoS₂ in en/NaPF₆ does not result in these intercalation reactions. The incorporation of dendrimers into MoO₃ is reported for the first time. PAMAM/MoO₃ nanocomposites are synthesized using an exfoliation - adsorption method. G0.0 PAMAM only forms monolayers (delta d = ~ 0.5 nm) between MoO₃ layers and G2.0 PAMAM forms both monolayer and bilayers (delta d = ~ 0.7-0.8 nm). In addition to these two structures, a third unknown phase is observed with a much larger gallery expansion (delta d = ~ 1.4 nm). These nanocomposites have a comparable structures, compositions (12-14% organic component for G0.0 monolayer and 22-25% for G2.0 bilayer) and packing fractions (0.5-0.7 for monolayer and 0.7-0.9 for bilayer) to those in the previously reported linear polymer/MoO₃ nanocomposites. In the above studies, analyses by powder X-ray diffraction (PXRD) are supported by compositional data from thermogravimetric analyses (TGA) and structural optimization (Gaussian). Additionally, the product morphologies, surface properties and constituents are evaluated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared (FTIR) and Raman spectroscopies. UV-visible spectroscopy (UV-vis) is used to monitor reaction progress. Capillary zone electrophoresis (CZE) is used to study compositions and reaction progress.
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