UNIVERSITY OF NAIROBI GREEN SYNTHESIS OF SILVER NANOPARTICLES USING EUCALYPTUS CORYMBIA LEAVES EXTRACT; CHARACTERIZATION AND ANTIMICROBIAL APPLICATION

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1 GREEN SYNTHESIS OF SILVER NANOPARTICLES USING EUCALYPTUS CORYMBIA LEAVES EXTRACT; CHARACTERIZATION AND ANTIMICROBIAL APPLICATION JOSHUA SILA MUNYAO I56/68845/2011. A thesis submitted in partial fulfillment of the requirements for the award of the degree of masters of Science (environmental chemistry) of university of Nairobi 2014 i

2 DECLARATION This thesis is the original work of the author except where due references are made. It has not been submitted partially or wholly for the award of degree to this or any other institution of learning. JOSHUA SILA MUNYAO This thesis has been submitted for examination with our approval as the University supervisors. PROF. GEOFREY.N KAMAU DR.DEBORAH A. ABONG O DEPARTMENT OF CHEMISTRY DEPARTMENT OF CHEMISTRY DR. IMMACULATE MICHIRA PROF. F. B. MWAURA DEPARTMENT OF CHEMISTRY SCHOOL OF BIOLOGICAL SCIENCES ii

3 DEDICATION I dedicate this work to entire Munyao s family and Irene Kiio. iii

4 ACKNOWLEDGEMENTS I wish to acknowledge the Almighty God for the grace He has given me, to purpose and complete this work. I would like to thank my supervisors, Prof. G.N Kamau, Prof.F.B Mwaura, Dr. I. Michira and Dr.Abongo for all their inputs during my research work. Special thanks to Prof. Emmanuel I. Iwuoha for the opportunity to carry out my research work at the sensor lab -University of the Western Cape and his support and guidance during my stay in Sensor lab. A lot of thanks to the entire sensor lab group, Dr. Maskini Milua, Dr. Abebaw Tesfaye and postgraduate students for the good working atmosphere and assistance accorded to me. My friend Irene Kiio for support and assistance she accorded me when I was doing part of my project work in the department of Biochemistry. I would also like to acknowledge the Department of biochemistry, university of Nairobi for providing the test micro-organisms. To all my colleagues and staff at the Department of Chemistry, Mr. Katiku, my friend Moses and David for encouragement and guidance in my research work. I wish to thank National Commission for Science, Technology and Innovation for their financial support towards my research work. Last but not the least my family and friends who assisted in any way in my studies. iv

5 ABSTRACT In this study biosynthesis of silver nanoparticles (AgNPs) using Eucalyptus corymbia and their antimicrobial activities have been reported. The report reveals that Eucalyptus corymbia leaf extract contains a variety of bio-molecules responsible for reduction of metal ions and stabilization of nanoparticles. Among these bio-molecules are polyphenols and water soluble heterocyclic compounds. Optimized experimental conditions included using extraction temperature of 90 C; plant extract ph of 5.7 and silver nitrate to plant extract ratio of 4:1. These conditions favoured the formation of higher number of nanoparticles which were stable within the study time. The synthesized nanoparticles were polydispersed with average mean size of nm and were spherical in shape without significant agglomeration, as revealed from the TEM analysis. Synthesized AgNPs exhibits face centered cubic crystals as demonstrated from XRD studies. FT-IR spectra of the plant extract revealed that functional groups OH and C=C are responsible reduction and stabilization of the nanoparticles. Anti- Microbial activity of the synthesized silver nanoparticles were studied against gram negative bacteria Escherichia coli and gram positive bacteria Staphylococcus aureus. In the medium treated with silver nanoparticles, Escherichia coli and Staphylococcus aureus growth was inhibited, as these particles have an excellent biocidal effect and hence effective in inhibiting bacterial growth. These nontoxic nanomaterials, which can be prepared in a simple and costeffective manner, may be suitable for the formulation of new types of bactericidal materials. Key words: Silver nanoparticles, Eucalyptus corymbia, Green synthesis, Escherichia coli. Staphylococcus aureus. v

6 TABLE OF CONTENTS DECLARATION... ii DEDICATION...iii ACKNOWLEDGEMENTS... iv ABSTRACT... v LIST OF FIGURES... ix LIST OF ABBREVIATIONS... xi CHAPTER ONE INTRODUCTION Problem Statement Justification and novelty of the work Overall Objectives Specific objectives... 5 CHAPTER TWO LITERATURE REVIEW Nanotechnology and Green Chemistry Top down versus Bottom up Approach Methods of Synthesis Green Synthesis Mechanism of Formation of Nanoparticles Optical Properties of Nanoparticles Localised Surface Plasmon Resonance Escherichia coli and Staphylococcus aureus Proposed Mechanism of Action against Bacteria Analytical techniques Spectroscopic methods vi