Browsing by Subject "nanosheets"

Now showing 1 - 3 of 3
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    Fabrication of Zeolite MFI Membranes on Low Cost Polymer Supports
    (2017-07) Zhang, Han
    About 10~15% of total energy consumption in US is attributed to energy intensive chemical separation processes, such as distillation. The alternative membrane-based separation could save up to 90% energy consumption with outstanding separation performance. Zeolite MFI membranes have been demonstrated for xylene and butane isomer separations with high separation factors and permeances. However, high cost and scale-up difficulty prevent the commercialization of MFI membranes in industries. This dissertation attempts to explore the methods for MFI membranes supported on low cost polymer supports. The major challenge is the stability of polymer support during the detemplation treatment of the MFI membrane after secondary growth. Two mild detemplation methods, thermal treatment at 280 °C and UV/ozone treatment, were identified with sub-100 nm MFI membranes supported on quartz supports. These two methods were then applied to MFI membranes supported on mesh-polyethersulfone (PES) supports and MFI membranes supported on mesh-polybenzimidazole supports. However, cracks formed after the treatments due to the damage of polymer layer by UV light and the mismatch of linear thermal expansion co-efficient, respectively. Another approach, which utilizes the open-pore MFI nanosheets, have been demonstrated. The organic structure directing agents (OSDA) occluded inside the micropores of nanosheets were removed by successive piranha solution treatment, while the crystallinity and morphology were still preserved that confirmed by X-ray diffraction(XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and gas adsorption. The simple deposition of such open-pore MFI nanosheets on porous PBI support, without the need of secondary growth and detemplation, exhibited n-/iso-butane ideal selectivity of 5.4 with n-butane permeance of 3.5×10-7 mol/m2-s-Pa. In addition, the nanosheet exfoliation yield was significantly improved by an oligomeric polystyrene resin. Ultrafiltration polymer hollow fibers were also prepared as suitable supports for nanosheet coating.
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    Structure determination of zeolite nanosheets
    (2012) Zhang, Xueyi; Tsapatsis, Michael
    MFI and MWW zeolite nanosheets are building units for state-of-the-art zeolite thin films for gas separation. In this study, the structures of exfoliated MFI and MWW zeolite nanosheets were determined using a combination of experimental and simulation methods. Based on characterization results from atomic force microscopy and transmission electron microscopy, the structures and thicknesses of the exfoliated zeolite nanosheets were proposed. After optimization with Car-Parrinello molecular dynamics, X-ray diffraction patterns and electron diffraction patterns are simulated from these structures. The agreement between experimental and simulated characterization data suggested that the proposed structures should represent the actual structures of the exfoliated zeolite nanosheets. The methods used in this study can be extended to determining structures of other zeolite nanostructures.
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    Synthesis of Zeolite Nanosheets and Applications in Membranes and Adsorption Separation Processes
    (2016-05) Jeon, Mi Young
    In separation processes, desirable products with high purity are acquired at the expense of high energy cost procedures such as distillation. Alternative separation processes, such as zeolite membrane separation and adsorption processes, are promising to reduce the energy cost of production since zeolites can discriminate molecules on the basis of size/shape and functionality. Indeed, the high cost of zeolite membranes can be reduced by fabricating thin membranes with high throughput. High aspect ratio zeolite nanosheets can be used to fabricate zeolite membranes with high throughput on porous supports. To date, however, there is no published evidence that scientists have successfully achieved nanosheet synthesis under the direct hydrothermal treatment route. This dissertation documents a successful direct hydrothermal synthesis of zeolite nanosheets via seeded-growth—a process that leads to zeolite membranes that exhibit high performance on xylene isomer and butane isomer permeation. To the best knowledge, this is the first achievement to prepare zeolite nanosheets without complicated post treatment such as exfoliation and purification process (density gradient centrifugation). Extensive parametric studies are conducted in order to establish the optimal synthesis condition for high quality zeolite nanosheets. Additionally, in an effort to understand the mechanism of nanosheet formation, the sequential evolution of seed crystals into zeolite nanosheets is observed by time-resolved TEM imaging analysis. Keeping in mind that in the future polymers could be used to reduce the costs of membrane manufacture, the de-templation of MFI nanosheets without formation of aggregates is discussed in this dissertation. In addition to membrane applications, this dissertation probes the roles of hydrophobicity in ethanol adsorption when hydrophobic siliceous zeolites, and defective siliceous zeolite nanosheets with house-of-card architecture are provided as adsorbents. Vapor phase ethanol adsorption and aqueous phase ethanol adsorption are compared to investigate how water molecules affect ethanol adsorption onto siliceous zeolites in the aqueous phase.