Clay minerals such as kaolinite, smectite, chlorite, micas are main components of raw materials of clay and formed in presence of water. A large number of clays used to form the different structure which completely depends on their mining source. They are known as hydrous phyllosilicate having silica, alumina and water with variable amount of inorganic ions like Mg2+, Na+, Ca2+ which are found either in interlayer space or on the planetary surface. Clay minerals are described by presence of two-dimensional sheets, tetrahedral (SiO4) and octahedral (Al2O3). There are different clay minerals which are categorized based on presence of tetrahedral and octahedral layer in their structure like kaolinite (1:1 of tetrahedral and octahedral layers), smectite group of clay minerals (2:1 of tetrahedral and octahedral layers) and chlorite (2:1:1 of tetrahedral, octahedral and octahedral layers). The particle size of clay minerals is <2microns which can be present in form of plastic in presence of water and solidified when dried. The small size and their distinctive crystal structure make clay minerals very special with their unique properties including high cation exchange capacity, swelling behavior, specific surface area, adsorption capacity, etc. which are described in this chapter. Due to all these unique properties, clay minerals are gaining interest in different fields.

Two Schiff bases 2-acetylthiophene thiosemicarbazone (L1) and thiophene-2-aldehyde thiosemicarbazone (L2) were prepared in excellent yield via the condensation of 2-acetyl thiophene/ thiophene-2-aldehyde and thiosemicarbazide. The lead (II) and nickel (II) metal complexes of the Schiff base ligands ([Pb(L1)2]Cl2 and [Ni(L1)2]Cl2 were also prepared. The ligands and complexes were tested against gram-negative [E. Coli (MTCC No: 452)] and gram-positive bacterial strains Bacillus sp [(MTCC No: 297)] by using Kirby-Bauer's method. The compound ([Pb(L1)2]Cl2 was found out to be more active against both bacterial strain (E. coli & Bacillus sp) having zone of inhibition12.45 ± 1.2 and 11.27 ± 1.1 mm respectively.

A new polyvinylchloride membrane sensor for Cd 2+ ions has been prepared using 2-acetylthiophene Semicarbazone (ATS) ligand as an electroactive ionophore and dibutylphthalate (DBP) as a plasticizing agent. The best performance was recorded with a membrane composition of PVC: DBP: Ionophore: NaTPB as 31: 64: 3.2: 1.8 (w/w %). The sensor exhibits a Nernstian response for Cd 2+ ions over a wide concentration range (1.0×10-5 to 1.0×10-1 M) with a slope of 29.4±0.2 mV decade-1. It has a fast response time of ˂10 s and can be used for at least 5 weeks without any divergence in potential. The electrode can be used in the pH range from 3.4 to 7.6. The proposed sensor revealed relatively good selectivity and high sensitivity for Cd 2+ ions in presence of a number of mono, di and trivalent interfering cations within the working range of the electrode. The electrode was successfully applied for the direct determination of Cd 2+ in solution and, as an indicator electrode, in potentiometric titration of cadmium ions using ethylenediamine tetraacetic acid (EDTA) as titrant.

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ISEs possess several advantages, such as high speed, ease of preparation, simple instrumentation, fast response time, wide concentration range, good selectivity and economically affordable. ISE based electrochemical sensors are useful in analysis of food products, drinking water, beverages, fertilizers, soil industrial effluents etc. Generally sensors are based on electroactive materials and provide a rapid and convenient means for quantitative estimation of anions and cations in biological and industrial samples. The aim of present work is to synthesize modified clay with heteropoly acids. These modified clays may have significant electrochemical activity in Ion selective electrodes. These clays can be employed as ionophore to develop chemical sensors for their application as sensors and in potentiometric titrations as indicator electrode.

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The main objective of this work is to provide information on the development of ion selective electrodes (ISEs) based on PVC membrane by incorporating Schiff base ligands and their complexes as ionophores for sensing different metals ion.Ion selective electrodes can be prepared and the electrodes performance may optimized by varying the amounts of PVC, plasticizers and cation/anion excluders. Various characteristic features of chemical sensors with different parameters such as response time, selectivity, lifetime and pH effect on sensor response have been reported. The proposed ISEs have been successfully applied to determine cations and anions and as electrode in potentiometric titrations.