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University of Cincinnati UNIVERSITY OF CINCINNATI Date:___________________ I, _________________________________________________________, hereby submit this work as part of the requirements for the degree of: in: It is entitled: This work and its defense approved by: Chair: _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ SYNTHESIS OF ORDERED MESOPOROUS SILICA AND ALUMINA WITH CONTROLLED MACROSCOPIC MORPHOLOGIES A dissertation submitted to the Division of Graduate Studies and Research of the University of Cincinnati in partial fulfillment of the requirements of the degree of DOCTOR OF PHILOSOPHY in the Department of Chemical Engineering of the College of Engineering November, 2004 by Hatem Mohammad Sadi Alsyouri B.Sc. Chemical Engineering, University of Jordan, 1998 Dissertation Advisor and Committee Chair: Dr. Jerry Y. S. Lin ABSTRACT The ability to synthesize nanostructured inorganic materials with controlled microstructural and morphological features will provide materials with unique characteristics in unprecedented ways. This thesis investigates the synthesis of porous silica and alumina materials with controlled microstructures and desirable shapes using novel approaches based on template-assisted synthesis and chemical vapor deposition (CVD) techniques. It primarily focuses on fabricating mesoporous materials with unique microstructures and different morphologies (particles and membranes) and exploring the potential of the particle morphology in a polymer reaction application. The template-assisted growth of mesoporous silica under acidic and quiescent conditions at an oil-water interface can generate mesostructured silica at the interface with fibrous, gyroidal, spherical, and film morphologies. Synthesis conditions can be used to alter the growth environment and control the product morphology. Fiber morphology is obtained at narrow range of experimental conditions due to slow and one- dimensional diffusion of silicon alkoxide through the interface. Variation in these conditions can alter the axial growth of silica and yield non-fibrous shapes. The fibers grow from their base attached to the interface and coalesce to form fibers with larger diameters. Gas transport in the mesoporous silica fibers is governed by combination of Knudsen and surface diffusion mechanisms. Surface diffusion contributes to 40% of the net flow reflecting a highly smooth pore surfaces. Real Knudsen and surface diffusivities are in the order of 10-3 and 10-5 cm2/s respectively. The one-dimensional mesopores are 45 time longer than the macroscopic fiber length and align helically around the fiber axis, confirming the literature observations, with a pitch value of 1.05 micron. For preparation of mesoporous silica materials as membranes, a novel counter diffusion self assembly (CDSA) approach is demonstrated. This approach, adopted from growth of silica fibers, introduces the precursors from the opposite sides of a ceramic supports and yields silica plugs grown within the support pores. Growth of defect-free silica membrane by this approach requires a hydrophobic support to enhance diffusion of the silicon alkoxide. According to gas permeation properties, silica plugs grow with thickness of ~ 0.5 mm and have a mesoporous structure. Such mechanically strong membrane offers high potential in protein separation and polymer reaction applications. Mesoporous membranes with controlled pore microstructure can be also obtained using CVD technique. Cyclic CVD modification of straight 20 nm pore alumina membranes demonstrates that variation of the precursor introduction scheme can affect the microstructure of alumina deposition within the support pores. Leaving residual of precursors in the support pore after introduction of each precursor causes deposition of alumina in a fractal structure suitable for gas separation applications. Purging the pore after each precursor, on the other hand, causes alumina to deposit in an atomic layer fashion to give cylindrical mesopores suitable for membrane reaction applications. The use of ordered mesoporous materials supported with titanocene catalyst as nano-reactors for the extrusion of high quality polyethylene (PE) fibers is demonstrated. The steric effect of the straight 3 nm pores of mesoporous silica template the growth of 60 nm diameter PE fibers with extended-chain crystalline structures. The nascent polymer fibers aggregate into 1−30 µm microfibers which further aggregate into PE fiber bundles. Mechanical properties, measured for the first time, demonstrate that these fibers exhibit improved tensile strength compared to commercial PE fibers. To my parents To my wife And To my son iv “And when your Lord said to the angels, I am going to place in the earth a khalif, they said: What! wilt Thou place in it such as shall make mischief in it and shed blood, and we celebrate Thy praise and extol Thy holiness? He said: Surely I know what you do not know. And He taught Adam all the names, then presented them to the angels; then He said: Tell me the names of those if you are right. They said: Glory be to Thee! we have no knowledge but that which Thou hast taught us; surely Thou art the Knowing, the Wise. He said: O Adam! inform them of their names. Then when he had informed them of their names, He said: Did I not tell you that I know the secrets of heaven and earth, and I know what ye reveal and what ye conceal?” From Holy Qur’an 2:30-32 v ACKNOWLEDGEMENTS First of all I would like to thank our creator the Lord (Allah) for His blessings of brain and senses. Thank you Allah for supporting me with faith, strength, patience, and motivation without which I would not have achieved this. Thanks for blessing me with a righteous wife and decent friends who were good companions through this long journey. O Allah, advance my knowledge and help me utilizing it for your sake. I would like to express my sincere gratitude and respect to my dissertation advisor, Dr. Jerry Y. S. Lin for his support, kindness, patience and commitment to excellence throughout the course of this research. His knowledge, intelligence, efficiency and organization have always been a source of inspiration for me to become a distinguished researcher. Without him, this dissertation would not have finished. I would also like to thank the committee members; Dr. William Krantz, Dr. Gregory Beaucage, and Dr. Chia- Chi Ho for their scientific support and valuable times in reviewing this dissertation. I am grateful to Dr. Shiping Zhu and Dr. Zhibin Ye from McMaster University at Canada for their distinguished efforts in our collaborative polymerization work. I would like also to acknowledge Dr. Vadim Guliants who gave me the opportunity to expand my knowledge and experience in the membrane area by participating in his OCDO membrane project for few months. Thanks are also due to Dr. Sun-Tak Hwang and Dr. Carlos Co for their valuable articles and times for useful discussions. I would like to greet all the former and current members of our group for their kindness, help and friendship during my stay at the University of Cincinnati, especially Dr. M. Pan, Dr. X. Qi, Dr. G. Buelna, Dr. T. Akin, Dr. Z. Yang, Dr. C. Cooper, Dr. W. Yuan, Dr. H. Zou, Dr. J. Ida, C. Langheinrich, S. Cheng, R. Xiong, N. Rane, M. vi Skrobanek , A. Daumichen, Q. Yang, Q. Yin, S. Gladding, A. Chung, Dr. J. Park, V. Gupta, D. Li, D. Singh and Z. Zheng. I owe thanks to Srinivas Subramaniam and Dr. Reghvendra Tewari from the materials characterization center at UC and Dr. Mohamed Hassan from the department of Chemistry at UC for their dedicated help in material characterization of my samples. Outside the academic world, my sincere gratitude and love goes to my parents, brothers, sisters and friends in Jordan for their emotional support and encouragement that made my study more comfortable all these years away from home. I am also indebted to my parents in law who sacrificed lots of their efforts and time to help me complete my dissertation. I wish also to extend my gratitude to all my friends who made my stay in Cincinnati full of happiness and excitement. Finally, I owe a great deal to my wife Malyuba Abu Daabes for her love, patience and understanding. Since we have met in our undergraduate study in Jordan, she has been my real source of encouragement and motivation for excellence in my academic and personal life. I realize how hard was her life as a wife and mother while being a graduate student. Thanks for all your sacrifice and patience. Above of all, thanks for gifting me with the dearest person to my heart, my son, Ibrahim. This little guy whose natural instincts and smile has reduced much of my burden as a father and provided me inspiration as a researcher in performing my work. vii TABLE OF CONTENTS List of Tables xii List of Figures xiv CHAPTER 1. INTRODUCTION 1 1.1. Porous Materials, 1 1.2. Ordered Mesoporous Materials, 3 1.2.1. Overview, 3 1.2.2. Mechanism of formation, 7 1.2.3. Synthesis pathways, 9 1.3. Morphological Control of Mesoporous Materials, 12 1.4. Applications, 14 1.5. Chemical Vapor Deposition, 15 1.6. Research Objectives, 16 1.6.1. Motivation of this research, 16 1.6.2. Synthesis and characterization of ordered mesoporous silica fibers, 20 1.6.3. Ordered mesoporous inorganic membranes with controlled microstructure, 21 1.6.4. Polyethylene extrusion polymerization in ordered mesoporous silica materials, 23 1.7. Structure of Dissertation, 24 1.8. References, 25 CHAPTER 2. QUIESCENT INTERFACIAL SYNTHESIS OF MORPHOLOGICAL NANOSTRUCTURED SILICA 35 2.1. Introduction, 35 2.2. Experimental, 37 viii 2.2.1. Quiescent interfacial growth and characterization of mesoporous silica, 37 2.2.2. Ethylene extrusion polymerization, 40 2.3. Results and Discussion of Interfacial Growth, 42 2.3.1. Results of synthesis, 42 2.3.2. Macroscopic properties of silica fibers, 45 2.3.3. Microscopic properties of silica fibers, 51 2.3.4. Non-fibrous morphologies, 59 2.3.5.
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