Synthesis of Ordered Mesoporous Silica and Alumina with Controlled Macroscopic Morphologies

Synthesis of Ordered Mesoporous Silica and Alumina with Controlled Macroscopic Morphologies
Author:
Publisher:
Total Pages:
Release: 2004
Genre:
ISBN:

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.

Mesoporous Silica

Mesoporous Silica
Author: Shunai Che
Publisher: Walter de Gruyter GmbH & Co KG
Total Pages: 216
Release: 2020-12-17
Genre: Technology & Engineering
ISBN: 311055531X

Mesoporous silica has large-scale industrial applications such as catalysis, drug delivery and bio/chemical absorptions. This book is devoted to all aspects and types of this material, focusing synthesis of mesoporous silica with anionic amphiphilic molecules. Characterization, properties, and applications are also discussed, making the book an essential reference for material scientists, chemists, and chemical Engineer.

Update on Silica-based Mesoporous Materials for Biomedical Applications

Update on Silica-based Mesoporous Materials for Biomedical Applications
Author: Luigi Pasqua
Publisher: Smithers Rapra
Total Pages: 182
Release: 2011-11-22
Genre: Medical
ISBN: 1847355099

This book provides an insightful understanding of the mesoporous silica structure and its special properties. The details of synthesis and modification strategies are discussed by reviewing the open literature. The discussion concerning the potential of mesoporous silica in modern biomedical applications will be related to a critical analysis in the field of material science. This book will help the reader rapidly develop the necessary tools to follow the design of the different mesoporous silica-based devices presented in the various studies. The structure of the different devices is examined in detail and the relationship between the structure and the expected activity are discussed. It will also assist in the ability to design new therapeutic devices in a field where the applications seem to be without limits.

Synthesis and Characterization of Ordered Mesoporous Silica with Controlled Macroscopic Morphology for Membrane Applications

Synthesis and Characterization of Ordered Mesoporous Silica with Controlled Macroscopic Morphology for Membrane Applications
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/m2Pas. 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.