The Development of Ionophore-Selective Based Optical Chemical Sensors for the Determination of Heavy Metal Ions in Aqueous Environments A Thesis Presented for the Award of Doctor of Philosophy by Li Li, MSc. (Hons) Department of Chemistry Science National Centre for Sensor Research (NCSR) Dublin City University For Research Carried Out Under the Supervision of Prof. Fiona Regan, School of Chemical Science, DCU September 2010 DECLARATION I hereby certify that the material, which I now submit for the assessment on the progress of study leading to the award of PhD., is entirely my own work and has not been taken from the work of others save to the extent that such work has been cited and acknowledged within the text of my own work. No portion of the work contained in this thesis has been submitted in support of an application for another degree or qualification to this or any other institute or university. Signed: _ Li Li ID number: 56114338 Date: 27th of September 2010 THESIS ABSTRACT “The Development of Ionophore-based Selective Optical Sensors for the Determination of Heavy Metal Ions in the Aqueous Environment” LI LI The development of optical sensors for in-situ, real-time and low-cost monitoring of heavy metal ions is a tremendously and fast growing area of research. This work presents several novel sensing strategies for developing optical chemical sensors that can be used as early warning devices for heavy metal pollution in water. The optical sensors that are comprised of metal chelating reagent, together with an ion carrier immobilised within polymeric thin films, i.e. hybrid sol-gel thin films, PVC membranes, ORMSOLs, and functionalised cellulose membranes. The developed test strips based on 2-(5-bromo-2-2pyridydylazo)-5-diethylaminophenol (Br-PADAP) immobilised on hybrid nafion/sol-gel membranes are capable of selectively monitoring Ni2+ in water samples. A novel sensing strategy, based on electrostatically immobilisation of water soluble indicators on functionalised cationic cellulose membranes, has provided a real “green” procedure for the fabrication of sensing materials. The promising results have been demonstrated by the optical sensor based on Chromoazo S immobilized on cationic cellulose membranes for the determination of Cu2+. A novel series of double armed spirocyclic calix[4]arene compounds has been investigated for their binding abilities with heavy metal ions. Compound 2-144 showed a good selectivity of Pb2+ over other heavy metal ions. This compound has a potential for the use as selective-ionophore for the development of a Pb2+ selective sensing system. 1 Abbreviation & Symbols AAS Atomic absorption spectrometry EDTA 1,2-diaminoethane-N,N,N’N’-tet raacetic acid EU European Union ISE Ion Selective Electrode I Ionic diameter LED Light emitting diode LOD Limit of detection Kf Complex formation constant ! Complex molar absorptivity nm nanometer PAN 1-2-pyridylazo-2-naphtol PVC Poly(vinyl chloride) T90 Time to reach 90 % of the equilibrium signal WHO World Health Organization UV-Vis Ultra-violet and visible wavelength THF Tetrahydrofuran Me Methyl DCM Dichloromethane H+ Proton HCl Hydrochloric acid 2 CAL Calmgite Nitroso-PASP 2-Nitroso-(5-N-propyl-N-sulfopr opiamino)phenol BRPADAP 2-(5-bromo-2-pyridylazo)-5-diet hylaminophenol AVN Acid Alizarin Violet N CAS Chrome Azurol S MES 2-(N-morpholino)ethanesulfonic acid HEPES 4-(2-hydroxyethyl)piperazine-1- ethanesulfonic acid TAPS 3{[tris(hydroxymethyl)methyl]a mino}propanesulfonic CAPS 3-(cyclohexylamino)-1-propane sulfonic acid] 3 Acknowledgements Firstly, I would like to thank my supervisor Prof. Fiona Regan, for her help, inspiration and encouragement. Would like to express my gratitude to; QUESTOR, Queens University, Belfast, UK, for funding of my research. The members of QUESTOR and Dublin City University for their help during my research. Special thanks to the technicians of School of Chemical Science, DCU: Brendan, John, Damien, Ambrose, Veronica, Vinny and Mary. Thanks to Dr. Mary Deasy, Dr. Fintan Kelleher and James Wards in ITT, Dublin, Ireland, Dr Haibo Xie, School of Chemical Science, DCU, for their collaboration work. To my colleagues in DCU, past and present: Yuliya, Emma, Frank, Keith, Aga, James, Tim, Rachael, Lisa, Imogene, Anton, Audrey, Kris Hart, Dr Qiang Zeng, Dr Fei Chen, Dr Fuqiang Nie, Dr Xiliang Luo, Jie Zhu and Dr Yurong Liu and Dr. Haibo Xie. Thank you for your friendship and support throughout my research. Special thanks for Richard Hoban and Dr Huizhong Wu for your patience and helping me during the last 3 years. To my family; Mum and Dad! Thank you for your love, support and belief! 4 Table of Contents Delararation……………………………………………………………………………….i Thesis Abstract…………………………………………………………………...............iii Abbreviation & Symbols…………………………………………………………………iv Acknowledgements………………………………………………………………………vi Chapter1 1.1 Heavy Metals in the Environment............................................................................... 11 1.1.1 The Definition of Heavy Metal Ions ................................................................................ 11 1.1.2 Occurrence of Heavy Metal Pollution............................................................................. 11 1.1.3 Biochemistry & Bio-toxicity of Heavy Metals................................................................ 12 1.1.4 Legislation to Regulate Heavy Metals............................................................................. 13 1.2 Conventional Methods for the Determination of HMs.............................................. 14 1.3 Chemical Sensors for the Determination of Heavy Metals ....................................... 14 1.4 Optical Sensors for Heavy Metal Ions......................................................................... 16 1.4.1 Optical Biosensors ............................................................................................................. 16 1.4.2 Principles of Optical Chemical Sensors .......................................................................... 16 1.4.3 Advantages of Optical Chemical Sensors ....................................................................... 17 1.5 Sensing Schemes of Optical Chemical Sensors.......................................................... 17 1.5.1 Intrinsic Ion Sensing.......................................................................................................... 18 1.5.2 Reagent Mediated Optical sensors .................................................................................. 18 1.5.3 Carrier (Ionophore)-based Metal Ion Sensing............................................................... 19 1.6 Characteristics of an Ideal Optical Chemical Sensor ................................................ 21 1.7 Challenges in Optical Sensors Research for Heavy Metal ........................................ 22 1.8 Metal Recognition Process Based on Macrocyclic Ligands...................................... 23 1.8.1 Principles ............................................................................................................................ 23 1.8.2 Optical Sensors based on Chromo/Fluoro-ionophores................................................. 28 1.9 Development of Immobilization Techniques .............................................................. 29 1.10 Sensing Matrices for Optical Chemical Sensors ...................................................... 30 1.10.1 Polymeric Materials ........................................................................................................ 31 1.10.2 Sol-gel Materials .............................................................................................................. 34 1.11 Mesoporous Materials ................................................................................................ 39 1.12 Aim of the Thesis ........................................................................................................ 42 Reference ............................................................................................................................. 43 Chapter 2 5 2.1. Introduction.................................................................................................................. 52 2.1.1 Spectroscopic Principles ................................................................................................... 52 2.1.2 Beer-Lambert’s Law ......................................................................................................... 53 2.1.3 Indicator-Metal Complexation ........................................................................................ 54 2.1.4 Metal-Ligand Complex Stoichiometry............................................................................ 55 2.1.5 Formation Constants of the Complexes.......................................................................... 57 2.1.6 Indicators Used for the Sensor Application ................................................................... 58 2.1.7Aims and Objectives........................................................................................................... 62 2.2 Experimental................................................................................................................. 63 2.2.1 Materials ............................................................................................................................. 63 2.2.2 Instruments......................................................................................................................... 63 2.2.3