Synthesis And Characterization Of Ordered Mesoporous Silica With Controlled Macroscopic Morphology For Membrane Applications
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| Author | : Shriya Seshadri |
| Publisher | : |
| Total Pages | : 214 |
| Release | : 2011 |
| Genre | : Gas separation membranes |
| ISBN | : |
Ordered mesoporous materials have tunable pore sizes between 2 and 50 nm and are characterized by ordered pore structures and high surface areas (~1000 m2/g). This makes them particularly favorable for a number of membrane applications such as protein separation, polymer extrusion, nanowire fabrication and membrane reactors. These membranes can be fabricated as top-layers on macroporous supports or as embedded membranes in a dense matrix. The first part of the work deals with the hydrothermal synthesis and water-vapor/oxygen separation properties of supported MCM-48 and a new Al-MCM-48 type membrane for potential use in air conditioning systems. Knudsen-type permeation is observed in these membranes. The combined effect of capillary condensation and the aluminosilicate matrix resulted in the highest separation factor (142) in Al-MCM-48 membranes, with a water vapor permeance of 610-8mol/m2Pas. The second part focuses on synthesis of embedded mesoporous silica membranes with helically ordered pores by a novel Counter Diffusion Self-Assembly (CDSA) method. This method is an extension of the interfacial synthesis method for fiber synthesis using tetrabutylorthosilicate (TBOS) and cetyltrimethylammonium bromide (CTAB) as the silica source and surfactant respectively. The initial part of this study determined the effect of TBOS height and humidity on fiber formation. From this study, the range of TBOS heights for best microscopic and macroscopic ordering were established. Next, the CDSA method was used to successfully synthesize membranes, which were characterized to have good support plugging and an ordered pore structure. Factors that influence membrane synthesis and plug microstructure were determined. SEM studies revealed the presence of gaps between the plugs and support pores, which occur due to shrinking of the plug on drying. Development of a novel liquid deposition method to seal these defects constituted the last part of this work. Post sealing, excess silica was removed by etching with hydrofluoric acid. Membrane quality was evaluated at each step using SEM and gas permeation measurements. After surfactant removal by liquid extraction, the membranes exhibited an O2 permeance of 1.65x10-6mol/m2. Pa.s and He/O2 selectivity of 3.30. The successful synthesis of this membrane is an exciting new development in the area of ordered mesoporous membrane technology.
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| Total Pages | : |
| Release | : 2004 |
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This thesis investigates the synthesis of ordered mesoporous silica and alumina materials with unique microstructures and different morphologies using novel approaches based on template-assisted synthesis and chemical vapor deposition (CVD) techniques and their potential use in polymer reaction application. Template-assisted growth of mesoporous silica under acidic and quiescent conditions at an oil-water interface can generate mesostructured silica with fibrous and non-fibrous morphologies. Fibers are obtained due to slow and one-dimensional diffusion of precursors through the interface. Variation in conditions can alter the axial growth of silica and yield non-fibrous shapes. Fibers grow from their base attached to the interface and coalesce to form fibers with larger diameters. Gas transport in silica fibers is governed by Knudsen and surface diffusion mechanisms. Surface diffusion contributes to 40% of the flow reflecting highly smooth pores. Real Knudsen and surface diffusivities are in the order of 10E-3 and 10E-5 cm2̂/s respectively. The one-dimensional mesopores are 45 time longer than the fiber length and align helically around the fiber axis with a pitch of 1.05 micron. Mesoporous silica membranes were prepared by a novel counter diffusion self assembly (CDSA) approach. This approach introduces the precursors from the opposite sides of a hydrophobic supports and yields silica plugs grown within its pores. Silica plugs grow with thickness of 0.5 mm and have a mesoporous structure. Such mechanically strong membrane is potential in protein separation and polymer reaction applications. Mesoporous membranes with controlled pore microstructure can be also obtained using cyclic CVD modification of straight 20 nm pore alumina membranes. Leaving residual of precursors in the pore after introduction of each precursor causes deposition of alumina in a fractal structure suitable for gas separation. Purging the pore after each precursor causes deposition in atomic layer with cylindrical mesopores suitable for membrane reaction applications. Titanocene-supported MCM-41 was used as molecular extruder for preparation of 60 nm polyethylene nascent fibers with extended-chain crystalline structures. The nascent fibers aggregate into 1-30 ư m microfibers which further aggregate into fiber bundles. Mechanical properties, measured for the first time, demonstrated an improved tensile strength of the polyethylene product compared to commercial polyethylene fibers.
| Author | : Teeraporn Suteewong |
| Publisher | : |
| Total Pages | : 156 |
| Release | : 2011 |
| Genre | : |
| ISBN | : |
Ordered mesoporous silica materials are characterized by uniform and tunable pore size, high surface area and large pore volume. In particular, nano-sized ordered mesoporous silica particles have drawn interest from several fields, including biorelated areas, because silica is benign, possesses chemical stability and can be integrated with other materials. Structural aspects, such as pore connectivity, geometry and pore size are known to govern materials performance. Extensive efforts have been devoted to synthesize mesoporous silica particles with different structures, functionalities and sizes. In contrast, only a small number of studies so far have concentrated on the formation mechanism of these particles. This is hence the focus of the present dissertation. The first part reports on the synthesis and characterization of ordered mesoporous silica nanoparticles with and without embedded magnetic nanoparticles. The formation mechanism of silica nanocomposites is investigated by capturing particle formation at different time points during the synthesis. A combination of transmission electron microscopy (TEM) and small angle x-ray scattering (SAXS) is used to characterize the structure evolution of resulting materials. Incorporating organic moieties into the silica matrix provides additional functionalities to ordered mesoporous silica nanoparticles. However, it often leads to disordered pore structure or pore blockage. The second part demonstrates the preparation of aminated and ordered mesoporous silica nanoparticles using a cocondensation method. Increasing the amount of aminosilane in the synthesis feed causes a structural transition of organically modified particles from hexagonal to cubic. Pore size of ordered mesoporous silica and aminated ordered mesoporous silica nanoparticles can be tailored by the addition of a swelling agent during the synthesis. The structural transformation from hexagonal to cubic is also observed in the latter case, albeit at different amino silane concentrations. The final part reports on the internalization of nanoparticles into cells. Fluorescent aminated mesoporous silica nanoparticles are first prepared and then coated with poly(ethylene glycol) to improve particle stability and lower protein adsorption. Dye-labeled aminated mesoporous silica nanoparticles are spontaneously internalized by cells.
| Author | : Shewaye Yismaw Wubetu |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2022 |
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| Author | : David Jacques Picciotto |
| Publisher | : |
| Total Pages | : 236 |
| Release | : 2000 |
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The fabrication of advanced electronic devices that operate on quantum effects requires the patterning of semiconductors on the scale of 50 A, which cannot be achieved by any of the currently available patterning technologies. This project pursued a novel approach: the fabrication of a self-assembling template which would allow the deposition of ordered arrays of germanium dots on silicon substrates, on length scales permitting the operation of quantum devices at room temperature. The template is the mesoporous silicate MCM-41, discovered by researchers at Mobil Chemical Corp. This material consists of highly ordered, two-dimensional, hexagonal arrays of very uniform pores in silicon dioxide, with diameters tunable from 20 A to over 100 A. If pore arrays of this material can be grown as thin films on silicon substrates, with the pores oriented normal to the substrate surface, the resulting structure will provide a template for the deposition of germanium dots. Germanium can then be deposited through the pores in the film and onto the silicon substrates by chemical or physical vapor deposition. The template film can then be etched away, leaving a hexagonally ordered array of germanium dots on the silicon substrate. Mesoporous silica films were grown on oxidized silicon substrates by acidic synthesis. The substrates were first patterned by optical lithography to produce vertical features with dimensions of the order of microns. The substrates were then coated with hydrophobic polymer monolayers to alter their surface energy. This monolayer was selectively removed from the horizontal surfaces of some of the substrates, leaving it only on the vertical surfaces of the patterned features. It was thought that the difference in surface energy between horizontal and vertical surfaces would induce the pores to align along the vertical surfaces.
| Author | : David Emmett Cassidy |
| Publisher | : |
| Total Pages | : 212 |
| Release | : 2012 |
| Genre | : Mesoporous materials |
| ISBN | : |
| Author | : Barbara Platschek |
| Publisher | : |
| Total Pages | : 171 |
| Release | : 2007 |
| Genre | : |
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| Author | : Shewaye Yismaw Wubetu |
| Publisher | : |
| Total Pages | : |
| Release | : 2022 |
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| Author | : Yao Sun |
| Publisher | : |
| Total Pages | : 139 |
| Release | : 2014 |
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Mesoporous silica nanoparticles (MSNs) combine the benefits of nanomaterials and mesoporous silica materials. This class of materials is characterized by ordered pore structures, controllable pore size, and large surface area. Significant research efforts have been devoted to achieve the control over particle size, morphology, pore size, and mesostructure. In this dissertation, I will describe the synthetic approaches, characterization, and structural control of three types of silica-based nanoparticles (NPs). Firstly, the water-based synthesis of ultrasmall (sub-10 nm) PEGylated gold-silica core-shell NPs is described. These core-shell NPs are composed of an ultrasmall gold core, a thin silica shell, and a polyethylene glycol (PEG) outer layer. The core-shell NPs show long-term stability for nearly a year in both water and PBS buffer solution. The NP suspensions further exhibit good contrast in a microscale computed tomography (micro-CT) scanner. Secondly a type of stimuli-responsive aminated MSNs with shapeshifting behavior is introduced. The shape change can be achieved when MSNs are exposed to water vapor in solid-state form for 24 hours, or when MSN suspensions in ethanol are evaporated at high humidity, or when MSNs are vacuum-dried from water-rich solvents. Under these circumstances, the cross-sectional shape of animated MSN's can change from hexagonal to six-angle-star, accompanied by the loss of mesostructural long-range hexagonal order, a decrease in surface area and mesopore volume, an increase in micropore volume, and further condensation of the silica matrix. Finally, the synthesis and detailed characterization of a class of quasicrystalline MSNs is discussed. These MSNs exhibit dodecagonal (12-fold) symmetry with particle sizes below 100 nm.
| Author | : An-Hui Lu |
| Publisher | : Royal Society of Chemistry |
| Total Pages | : 279 |
| Release | : 2010 |
| Genre | : Science |
| ISBN | : 0854041885 |
Nanostructured materials with tailored properties are regarded as a fundamental element in the development of future science and technology. Research is still ongoing into the nanosized construction elements required to create functional solids. The recently developed technique, nanocasting, has great advantage over others in terms of the synthesis of special nanostructured materials by the careful choice of suitable elements and nanoengineering steps. This new book summarizes the recent developments in nanocasting, including the principles of nanocasting, syntheses of novel nanostructured materials, characterization methods, detailed synthetic recipes and further possible development in this area. The book focuses on the synthesis of porous solids from the viewpoint of methodology and introduces the science of nanocasting from fundamental principles to their use in synthesis of various materials. It starts by outlining the principles of nanocasting, requirements to the templates and precursors and the tools needed to probe matter at the nanoscale level. It describes how to synthesize nano structured porous solids with defined characteristics and finally discusses the functionalization and application of porous solids. Special attention is given to new developments in this field and future perspectives. A useful appendix covering the detailed synthetic recipes of various templates including porous silica, porous carbon and colloidal spheres is included which will be invaluable to researchers wanting to follow and reproduce nanocast materials. Topics covered in the book include: * inorganic chemistry * organic chemistry * solution chemistry * sol-gel and interface science * acid-base equilibria * electrochemistry * biochemistry * confined synthesis The book gives readers not only an overview of nanocasting technology, but also sufficient information and knowledge for those wanting to prepare various nanostructured materials without needing to search the available literature.
