Browsing by Subject "Porous materials"

Now showing 1 - 5 of 5
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    Manipulating colloids and surfactants as co-templates for porous nanostructures and nanocomposites.
    (2010-02) Li, Fan
    Templating is a general and efficient strategy for creating nanostructured, particularly nanoporous materials. Two commonly employed classes of templates are colloidal crystals and surfactants. Colloidal crystals typically have an opal-like structure and have been used to produce macroporous (>50 nm pores) solids; surfactants generate various mesoporous structures (2−50 nm pores) as a result of their versatile phase behavior. One aim of this study is to combine colloidal crystals and surfactants to realize simultaneous templating at two length scales. A series of hierarchically structured porous silica samples were synthesized under different synthetic conditions, comprehensive TEM characterization was conducted to reveal the detailed hierarchical porous structures, and simulation was performed to correlate the structures to the surfactant phase behavior within the colloidal crystal confinement. The dual templating approach was further extended to synthesize functional materials with composite porous architectures, in which functional cores were embedded in a hierarchically porous framework for optical ionsensing application. A second aim of this study is to develop a template-based strategy for sculpting nanoparticles of desired shapes and sizes. Owing to the ordered structure and symmetry of the template, a templating-disassembly process was found to produce uniform, nanometer-level, multipodal particles. This method is applicable to a variety of compositions, including oxides, phosphates and carbon, and it could further lead in-situ organization of particles following a self-reassembly process. In addition, through a coupled passivation-disassembly process, site-specific functionalization was achieved to modify only the tips of the multipods with a range of functional groups, and therefore to enable their directional bonding to other colloidal particles. (256 words)
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    Morphology control of porous materials and molecular sieve membrane applications.
    (2010-12) Yoo, Won Cheol
    For advanced applications of porous materials, morphology control of porous materials is desired. Simultaneous dissolution and surfactant-induced re-assembly via micelle formation with dissolved species were performed to introduce mesoporosity in the amorphous silica spheres and zeolite crystals. Textural features of mesoporous silica spheres were controlled from corrugated to smooth. Mesoporous zeolite catalysts were synthesized via surfactant-induced re-assembly with dissolved crystal fragments of zeolite crystals. In addition, the concept of confined synthesis was used for control of morphologies of zeolite crystals. Using 3-D ordered macroporous (3DOM) carbon as a template, growth patterns and shape development of zeolite crystals were studied. Various shaped zeolite crystals, e.g., hollow interior (geode-like structure), corrugated/smooth surface of polycrystalline crystals, needle-shaped crystals and 3DOM imprinted single crystals, were produced by careful choice of reaction parameters during the confined synthesis. Polycrystalline aggregates produced by the confined synthesis were used as seed particles for zeolite membrane fabrication. Novel seeding techniques, rubbing and leveling methods, were applied to deposit the confinement product directly on the surface of porous alumina supports, and zeolite membranes were grown by secondary hydrothermal growth. Moreover, rapid thermal processing and conventional calcination were used to investigate the effect of thermal treatments on the overall membrane quality. To evaluate the membrane quality, permeation measurements to separate p-/o-xylene isomers based on the zeolite's intrinsic capability of size-selective molecular separations were conducted. A high separation factor and high permeance were observed.
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    Nanoporous and nanostructured materials for energy storage and sensor applications
    (2013-03) Vu, Anh D.
    The major objective of this work is to design nanostructured and nanoporous materials targeting the special needs of the energy storage and sensing fields. Nanostructured and nanoporous materials are increasingly finding applications in many fields, including electrical energy storage and explosive sensing. The advancement of energy storage devices is important to the development of three fields that have strong effects on human society: renewable energy, transportation, and portable devices. More sensitive explosive sensors will help to prevent terrorism activities and boost national security. Hierarchically porous LiFePO4 (LFP)/C composites were prepared using a surfactant and colloidal crystals as dual templates. The surfactant serves as the template for mesopores and polymeric colloidal spheres serve as the template for macropores. The confinement of the surfactant-LFP-carbon precursor in the colloidal templates is crucial to suppress the fast crystallization of LFP and helps to maintain the ordered structure. The obtained composites with high surface areas and ordered porous structure showed excellent rate performance when used as cathode materials for LIBs, which will allow them to be used as a power source for EVs and HEVs. The synthesis of LiFePO4 in three dimensionally confined spaces within the colloidal template resulted in the formation of spherical particles. Densely packed LiFePO4 spheres in a carbon matrix were obtained by spin-casting the LFP-carbon precursor on a quartz substrate and then pyrolyzing it. The product showed high capacity and could be charged /discharged with very little capacity fading over many cycles. Three-dimensionally ordered mesoporous carbons were prepared from nano-sized silica sphere colloidal crystal templates. These materials with very high surface areas and ordered porous structure showed high capacitance and excellent rate capability when used as electrodes for supercapacitors. Mesoporous silica thin films of different morphologies, including disordered (wormlike), 2D-hexagonal, 3D-hexagonal, and cubic structure, were prepared. The films were then doped or bridged with fluorescence compounds and used as sensors for nitroaromatic compounds. The sensor performance depended on both the film structure and the mode of fluorophore attachment. The best films showed high quenching rates and were stable during long time storage. The films can potentially be incorporated in portable sensing devices. (351 words)
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    Nanostructured Metal Oxides for Desulfurization and Heterogeneous Catalysis
    (2021-10) Zhao, Wenyang
    Metal oxides have broad applications in industry and manufacturing. In order to maximize the performance of the metal oxides for targeted applications, it is critical that the preparation process is tailored and optimized. This thesis demonstrates the design, synthesis, characterization, and optimization of two types of porous metal oxides for applications for the removal of H2S in natural gas processing and for high temperature heterogenous catalysis.During natural gas production, the use of metal oxides as solid sorbents in the tail gas treatment unit is economically and operationally beneficial compared to the commercialized liquid sorption process. In the first part of this thesis, a type of porous mixed metal oxide (MMO) sorbent with active CuO is prepared through coprecipitation, and is demonstrated to have superior H2S sorption capacity. This sorbent can be recycled in a continuous adsorption–desorption process with stable performance. In addition, a facile pelletization approach was established, and the regeneration conditions of the pellets were optimized. This study demonstrated good reliability and applicability of this sorbent material in simulated testing conditions. The second part of this thesis describes the preparation of MMOs through nanocasting metal–organic frameworks (MOFs). The metal oxo clusters in MOFs are a source of metal species for MMOs, and the casting organometallic precursors provide another component. Nanocasting largely retains the morphological and structural information of the MOF template in the final MMOs, and provides well-defined MOF-derived catalytically active centers with enhanced thermal stability suitable for high temperature catalysis.
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    Synthesis of Porous Materials and Their Applications in Electrochemistry and Additive Manufacturing
    (2020-12) Xiao, Han
    Open cellular porous materials, such as polyurethane foams, ceramic membranes, and silicon aerogels, are useful in many applications, such as gas membranes, seawater desalination, and heat insulation, because they often possess exceptionally high surface area per unit mass (>100 m2/g), high porosity (> 90%), and low mass density (< 100 mg/cm3). The simplest porous structures often consist of only a single solid material, which limits the ability to tune properties. To address this issue, fillers and other additives, such as polymers, metal nanoparticles or carbon-based substances, can be incorporated to synthesize composites with desirable properties. Polymer-carbon composites stand out from the rest, partially because the soft portions (polymers) and hard compounds (carbon) often possess distinctive yet synergistic properties. For example, incorporating a small amount (< 1 wt%) of electrically conductive graphene nanoflakes into polydimethylsiloxane (PDMS) elastomer makes the product both mechanically robust and electrically conductive, which are desirable for applications in contact sensors and flexible electronics. Pore size, morphology, isotropy, and porosity are some of the most important factors to consider when evaluating the inherent performance of porous materials. These parameters are largely determined by the processing conditions, such as temperature, concentration of porogen (a templating substance that can be easily removed during post-processing, such as water or salt, leaving behind the pores), and method of synthesis, in addition to the selection of parent solid materials. Templating is one of the many routes employed to synthesize porous structures, where a sacrificial porogen is used to first form a percolating network and is later replaced by air when removed, typically via sublimation or washing. Compared to other routes such as foaming, sol-gel transition, etching or lithography, templating enables the fabrication of complex pore shapes and geometries over large-scales with tunability in the pore size, morphology, and pore connectivity of the final product; therefore, templating is considered one of the most versatile approaches. This thesis outlines the synthesis of open cellular porous polymers and polymer composites using freezing templated methods. We first designed a carbon-polymer aerogel which is highly porous (99.6% porosity), has low density (~ 5 mg/cm3), and is electrically conductive (5.3 ± 3 × 10-2 S/cm), making it an ideal substitute for the metal current-collectors in lithium-ion batteries. Next, we explored strategies to prepare graphene oxide aerogels with aligned microstructures via bi-directional freezing. Simulations were conducted to predict the structure of the aligned aerogel, which agreed reasonably well with experimental results. Lastly, we explored camphene, a solid cyclic hydrocarbon at room temperature, as the solvent and templating agent for 3D printing porous polymers. Upon subliming camphene, the resulting porous network exhibited improved interlayer strength and reduced anisotropy, and the tensile properties were comparable to those of compression-molded samples. This new strategy to prepare porous polymer materials via direct ink writing could be further applied to other common polymers, such as polyethylene or polypropylene, two commercial-grade materials that are very challenging to print via conventional methods.