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Woodward Department of Chemistry UMI Number; 3031278 UMI’ UMI Microform 3031278 Copyright 2002 by Bell & Howell Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. Bell & Howell Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 ABSTRACT This work is aimed at building a zeolite-based hydrogen evolving artificial photosynthetic system. Toward this goal, we have adopted the well-known sacrificial D- S-A model. EDTA-Ru(bpy) 3 -'-bipyridinium-catalyst scheme. The stability of the sensitizer. RuCbpylj-' was evaluated under photolytic conditions by developing a chromatographic method to separate, quantitate and identify the decomposition products. Effect of various photolytic parameters like zeolite encapsulation. pH. photolysis time, quencher concentration, nature and concentration of buffers were studied to find the optimum conditions where the decomposition could be minimized. It was found that the extent of decomposition is dependent on the nature and concentration of the buffer anion and decreases with increasing quenching efficiency in the presence of quenchers. It is well known that the electron acceptor employed in this system, bipyridinium is susceptible to decomposition under hydrogen evolving photolytic conditions, limiting the practical applicability. The catalyst involved in the electron transfer from the relay is widely believed to be responsible for this limiting condition. Our research group has earlier developed a zeolite-based RuGi catalyst for the photooxidation of water to oxygen. This catalyst was evaluated for the photoreduction of water to hydrogen using the above-mentioned system and was found to be effective. Performance of this catalyst was compared with other known catalysts as for as rate of hydrogen evolution, stability and the rate of bipyridinium decomposition. Attempts were made to selectively poison the sites responsible for the bipyridinium reduction, while keeping the sites involved in the hydrogen evolution unperturbed. The sensitizer was also covalently linked to the zeolitic surface that also contains the catalyst as a first step toward a proposed integrated solar water splitting assembly. Intrazeolitic electron transfer was studied with zeolite encapsulated Ru(bpy) 3 -* and bipyridinium ions. Molecular modeling of guest species in constrained zeolitic cages involved in photoelectron transfer allowed to gain insight into their restricted rotational and diffiisional mobility. A systems dynamics modeling approach was employed to simulate the intrazeolitic electron transfer processes and the developed model allowed the extraction of various kinetic parameters. We propose that the zeolite architecture plays a crucial role in aiding long-lived charge separation. Ill Dedicated to my mother Smt. V. Mangaiyarkarasi IV ACKNOWLEDGMENTS I am grateful to my adviser. Prof. Prabir Dutta. for his guidance, support and encouragement, and especially for his patience without which this thesis would not have been possible. His work ethic and dedication are truly inspirational. 1 thank Samar Das and Norma Castagnola for all their help, ideas and suggestions. 1 wish to thank Marcello Vitale and Nancy Ortins-Savage for obtaining time-resolved diffuse reflectance spectra. I also wish to thank all the past and present group members. Mario Castagnola. Michael Coûtant. Amitava Das. John Doolittle. Estelle Each. Marla Frank. Arwa Ginwalla. Astrid Guglielmi. Brian Hogg. Yanghee Kim. Bob Kristovich. Tracy Krueger. Ty Le. Hyunjung Lee. Zhaohui Lei. Vincent Maloney. Kefa Onchoke. Pramatha Payra. Ramachandra Rao. Ramsharan Singh. Nick Szabo and Joe Trimboli for their help, support and for putting up with me during my stay in the Dutta research group. I am grateful to Dr. Gordon Renkes for training me on various analytical instruments and to Tim Henthome for his help with excellent glass blowing. I would like to thank David Amsbary. my roommate for four years, for his friendship and support. I would also like to thank my family for their love, support and patience. VITA March 29. 1972 ............................................ Bom - Pudukottai. India. 1992 ................................................................ B.Sc.. Chemistry. University of Madras. 1995 ................................................................M.Sc., Organic Chemistry Indian Institute of Technology. Bombay. 1995 -present ...................................................Graduate Teaching and Research Assistant. The Ohio State University. PUBLICATIONS A. S. Vaidyalingam, M. A. Coûtant, P. K. Dutta, “Electron-transfer Processes in Zeolites and Related Microheterogeneous Media", in Electron Transfer in Chemistry. V. Balzani (Ed); WILEY-VCH, Weinheim. Germany. 2001. Vol 4. 412. 2. A. Vaidyalingam. P. K. Dutta, “Analysis of the photodecomposition products of Ru(bpy)3 ' ‘ in various buffers and upon zeolite encapsulation"..-Inai. Chem. 2000. 72. 5219. 3. M. Vitale. N. B. Castagnola. N. J. Ortins. J. A. Brooke, A. Vaidyalingam. P. K. Dutta. “Intrazeolitic Photochemical Charge Separation for Ru(bpy)3 -*-Bipyridinium System: Role of the Zeolite Structure". J. Phys. Chem. B 1999. 103, 2408. VI 4. B. D. Hogg, P. K. Dutta, J. F. Long, A. Vaidyalingam, “Carcinogenicity of mineral erionite fibers: measurements and hypothesis of activity”, in Proc. Int. Zeolite Conf, 12th Meeting Date 1998. Treacy, M. M. J (Ed); Materials Research Society, Warrendale, Pa. 1999. Vol 4, 2927. 5. Z. Lei, A. Vaidyalingam, P. K. Dutta, “Photochemistry of azobenzene in microporous aluminophosphate AlPOj-S", J. Phys. Chem. B 1998, 102. 8557. FIELDS OF STUDY Major Field: Chemistry Minor Field: Analytical Chemistry Vll TABLE OF CONTENTS Page Abstract ................................................................................................................................... n Dedication ................................................................................................................................. iv Acknowledgments ......................................................................................................................v V ita.............................................................................................................................................. vi List of Tables........................................................................................................................ xü List of Figures ........................................................................................................................ xiü List of Schemes ...................................................................................................................... xix Chapters: 1. Introduction ....................................................................................................................1 Alternative Energy Sources..........................................................................................3 Fuel Cells and Hydrogen .............................................................................................. 6 Water Splitting ............................................................................................................. 10 Natural Photosynthesis ................................................................................................ II Light-initiated Electron-transfer Reactions ..............................................................13 Kinetics of Electron-transfer Reactions...................................................................