Imine- Nanomaterial Composites as Receptors for Potentiometric and Voltammetric Sensing of Ions

Abstract

This doctoral thesis provides an insight into the development, characterization and application of potentiometric and voltammetric sensor based on Schiff base ionophores (E)-3-((2- aminoethylimino)methyl)-4H-chromen-4-one (IFE), (E)-3-(((2-((2 aminoethyl) amino) ethyl) imino) methyl)-4H-chromen-4-one (ICU) and (E)-3-((2-(2-(2-aminoethylamino) ethylamino) ethylimino)methyl)-4H-chromen-4-one (IFE(III)). These prepared sensors provide better selectivity for the target species (heavy metals of environmental importance). The present thesis work can be divided into two main parts. First approach is the development of ion selective electrodes (ISE) based on modification with multiwalled carbon nanotubes (MWCNTs). It consists of incorporation of multiwalled carbon nanotubes in the polymeric membrane in order to provide improved characteristics of the ISEs. Second approach is the development of voltammetric sensors for the detection of cations using cyclic voltammetry and differential pulse voltammetric techniques. Potentiometric and voltammetric sensor for creating cationic response for Fe(II) based on (E)- 3-((2-aminoethylimino)methyl)-4H-chromen-4-one (IFE) is introduced. The influence of variables including amount of ionophore, plasticizers, anion excluder and multiwalled carbon nanotubes (MWCNTs) on the performance of the potentiometric sensor were investigated. The sensor for Fe(II) improvised the dynamic linear range (1×10-7 to 1×10-1 mol/L) with a slope of 27 mV/decade and a detection limit of 2.5×10-8 mol/L. Selectivity of the ion selective electrode improved after modification with MWCNTs. The reduction and oxidation properties of IFE were studied by voltammetric measurements. Differential pulse voltammetry was applied to the optimized electrode and a linear dynamic range from (9.9×10-7 to 2.9×10-5 mol/L) with a detection limit of 6.13×10-8 mol/L was obtained. The composition and morphology of the modified ion selective electrode were characterized with scanning electron microscopy. The modified electrodes have good selectivity for Fe(II) ions over a number of metal ions. It was successfully applied for direct determination of Fe(II) ions in different real life samples. Theoretical calculations also supported the complexation behavior of Fe(II) with IFE. Electrochemical sensor based on an ionophore (E)-3-(((2-((2 aminoethyl) amino) ethyl) imino) methyl)-4H-chromen-4-one (ICU) has been developed for the detection of Cu (II). The influence of variables including amount of ionophore, plasticizers, anion excluder sodium tetraphenylborate (NaTPB) and multiwalled carbon nanotubes (MWCNT) on performance of the electrode was studied. At optimized conditions, the sensor has a wide linear range of x concentration (1.0x10−7 – 1.0×10−1 mol/L) and a low detection limit of 1.0×10−7 mol/L of Cu (II) ion with a stable response in a working pH range of 4.0–7.0. This electrode was also used as an indicator electrode in potentiometric titration of Cu (II) ion with EDTA. ICU is a promising molecule with a potential of voltammetric sensor for Cu (II) species in DMSO medium in a concentration range 2.5×10-6 M to 4.3×10-4 M and detection limit of 9.32×10-9 M. Scanning electron microscopy combined with energy dispersive X-ray spectra was used to confirm the interaction between Cu (II) ions and ionophore on the surface of the electrode. The proposed ionophore is highly selective for Cu (II) ions from a number of metal ions. It was successfully applied for the determination of Cu (II) ion in different real-life samples from daily use items. Theoretical calculations also support the complexation behaviour of Cu (II) with ICU. A highly sensitive and selective potentiometric and voltammteric assay for the detection of Fe3+ using (E)-3-((2-(2-(2-aminoethylamino) ethylamino) ethylimino)methyl)-4H-chromen-4- one (IFE(III)) ionophore was developed. To demonstrate the ion-to-electron ability of MWCNT, these were incorporated in the ion-selective membrane and response characteristics of Fe3+ electrode was compared with those of the traditional ion selective electrode. The electrode showed an improved Nernstian slope, lower detection limit, response time of less than 5 s and working in a pH range of 3.0 to 8.0. Differential pulse voltammetric studies were performed for IFE(III)-Fe3+ complex in DMSO solvent medium at glassy carbon (GC) electrode. A linear relationship between the cathodic peak current and concentration of Fe3+ was observed in the range of 1.6×10-5 to 4.4×10-5 mol/L with a detection limit of 5.2×10-8 mol/L. The electrode shows remarkable selectivity for Fe3+ ions over alkali, alkaline earth, transition and heavy metal ions. The optimized electrode was successfully applied for the determination of Fe3+ ion in different real-life samples using potentiometric technique. Theoretical calculations were used to support the complexation behavior of Fe3+ with IFE(III). Further, organic nanoparticles of (E)-3-((2-aminoethylimino)methyl)-4H-chromen-4-one (IFE) were synthesized in aqueous dispersion by reprecipitation method with an average particle size of 50-65 nm. It was characterized by the dynamic light scattering (DLS) and transmission electron microscopy (TEM). Based on voltammetric measurements, organic nanoparticles of IFE exhibit good response towards sensing and selective detection of Cu(II) ions in aqueous medium. Under optimum conditions, the sensor shows excellent response for Cu(II) even in the presence of other alkali, alkaline earth, and transition metal ions. Differential pulse voltammetry was applied to the optimized electrode and a linear dynamic range from xi (2.5×10-6 to 1.4×10-5 mol/L) with a detection limit of 8.22×10-8 mol/L was obtained. This system has also been applied as voltammetric sensor for the determination of Cu(II) ion in various real-life samples.