INTRODUCTION AND OBJECTIVES

Transcription

1 CHAPTER 1 INTRODUCTION AND OBJECTIVES Introduction Molecular imprinting technology has over the past few years developed to become a capable alternative to common analytical methods based on recognition elements 1-3. It concerns the formation of selective sites in a polymer matrix with the memory of a template. In this method macromolecular structures are designed by a polymerization process in which sites are introduced by the template molecule. Following extraction of imprint molecule, specific recognition sites are left in the polymer with spatial arrangements complementary to the functional entities of the polymer network together with the shape image of the imprinted molecule. This gives rise to a specific affinity for the template that was present during the preparation of the molecular imprinted polymer. With the rapid development of molecular imprinting as a research hot spot, it faces a number of challenges, involving biological macromolecule imprinting, heterogeneous binding sites, template leakage, incompatibility with aqueous media, low binding capacity and slow mass transfer, which restricts its application in various aspects. Heavy metal ions are always the focus of attention owing to their difficulty of degradation and ease of bio-enrichment. Pollution due to heavy metals has wide spread attention in recent years 4. Various industrial sources such as leather tanning, electroplating, metal processing, and textile industry and steel fabrication are the main contributor for the contamination of water bodies with heavy metal ions. A number of molecular imprinting materials, capable for higher molecular recognition have been prepared by

2 2 Chapter 1 researchers using metal ions such as Pb(II), Ni(II), Pd(II) and Th(IV) 5-8. Accurate analysis of metal ions, especially at trace levels, is one of the most difficult and complicated analytical tasks, since it requires the rigorous requirements of versatility, specificity, sensitivity and accuracy in the analysis. For the determination of trace metals present in various samples like natural and waste water, biological and alloy samples, direct determination using various industrial methods is not possible owing to matrix effects and low concentration of metal ions in these samples. Thus the need of separation and preconcentration of metal ion arises and ion imprinting is very important Objectives of the present work The work presented in this thesis is aimed at the design of metal ion imprinted polymers based on 4-vinyl pyridine for the specific and selective recognition of metal ions and to exploit the specificity and the selectivity of the successful system for selective concentration of metal ions. To decipher the effect of metal ion imprinting on the specificity and the selectivity of the resulting imprinted polymer, a non-imprinted polymer was also developed and compared. To correlate the role of crosslinking agents on the specificity and selectivity of the imprinted polymers three crosslinkers viz. divinyl benzene (DVB), ethylene glycol dimethacrylate (EGDMA) and 1,4- butanediol dimethacrylate (BDDMA) were employed in this study. Introduction of these crosslinking agents in varying proportion would definitely vary the physicochemical characteristics of the polymers. The metal ion binding conditions also affect the binding of these imprinted polymers towards the template metal ion. The memory of the metal ion desorbed system towards the desorbed metal ion as well as selectivity

3 Introduction and Objectives 3 towards the desorbed metal ion was also investigated. The study can be outlined under the following heads. A. Cu(II) ion imprinted and non-imprinted polymers Synthesis of 25-65% DVB-, EGDMA- and BDDMA-crosslinked Cu(II) ion imprinted and non-imprinted polymers. Physicochemical characterization of the various Cu(II) ion imprinted and non-imprinted polymers. Specificity studies of Cu(II) ion imprinted and non-imprinted polymers. Optimization of the conditions of Cu(II) ion binding. Selectivity studies. Adsorption characteristics of EGDMA-crosslinked Cu(II) ion imprinted and non-imprinted polymers. Kinetic studies of EGDMA-crosslinked Cu(II) ion imprinted and non-imprinted polymers. B. Co(II) ion imprinted and non-imprinted polymers Synthesis of 25-65% DVB-, EGDMA- and BDDMA-crosslinked Co(II) ion imprinted and non-imprinted polymers. Physicochemical characterization of the various Co(II) ion imprinted and non-imprinted polymers. Specificity studies of Co(II) ion imprinted and non-imprinted polymers. Optimization of the conditions of Co(II) ion binding.

4 4 Chapter 1 Selectivity studies. C. Ni(II) ion imprinted and non-imprinted polymers Synthesis of 25-65% DVB-, EGDMA- and BDDMA-crosslinked Ni(II) ion imprinted and non-imprinted polymers. Physicochemical characterization of the various Ni(II) ion imprinted and non imprinted polymers. Specificity studies of Ni(II) ion imprinted and non-imprinted polymers. Optimization of the conditions of Ni(II) ion binding. Selectivity studies Organization of the thesis The thesis consists of five chapters, Chapter I is an introduction to the work stating its objectives and its importance in the field of specific and selective binding of metal ion imprinting. Chapter II gives a background about the previous studies related to molecular imprinting highlights the advantages, applications and recent development of molecular imprinting technology. A retrospective of researches related to metal ion imprinting in various fields have been discussed in this chapter. The experimental part describes in Chapter III give an idea about the synthesis of imprinted and non-imprinted polymers from monomer, template and crosslinkers. Chapter IV deals with the results and discussion of the designed imprinted and non-imprinted polymers including characterization, specificity

5 Introduction and Objectives 5 studies, swelling characteristics, effect of concentration, time of incubation and effect of ph on metal ion binding. The metal ion selectivities of Cu(II), Co(II) and Ni(II) ion imprinted and non-imprinted polymers are also detailed in this chapter. The adsorption studies of Cu(II) ion imprinted polymers are also included in this chapter. The summary of the entire work and results of the investigations are discussed in chapter V. The development of metal ion selective polymers was achieved by molecular imprinting technology using Cu(II), Co(II) and Ni(II) ions as the template metal ions. The study was conducted with optimized DVB, EGDMA and BDDMA crosslinking (25-65%) with functional monomer 4- vinyl pyridine.

6 6 Chapter 1 References 1. Gao, N.; Dong, J.; Liu, M, Analyst, 2012, 137, Chen, L.; Xu, S.; Li, J, Chem. Soc. Rev., 2011, 40, Cui, A.; Singh, A.; Kaplan, D. L, Biomacromolecules, 2002, 3, Ghimire, K. N.; Inoue, K.; Hayashida, T.; Ohto, K, Sep. Sci. Technol., 2007, 42, Yang, Y.; Long, Y.; Cao, Q.; Liu, K.; Liu, F, Anal. Chim. Acta, 2008, 606 (1), Ersoz, A.; Say, R.; Denizli A, Anal. Chim. Acta, 2004, 502, Daniel, S.; Gladis, J. M.; Rao, P, T, Anal. Chim. Acta, 2003, 488, Buyuktiryaki, S.; Say, R.; Ersoz, A.; Birlik, E.; Delinzli, A, Talanta, 2005, 67, 640