| Metal pollution refers to the environmental pollution caused by the metal and its compounds. To a great extent, this is attributed to human activities, e.g., mining waste, industrial discharges and coal burning activities. This pollution is reflected in the biological uptake of metal from the environment, the metal can not be biodegradable. On the opposite, the metal a million times enriches in the food chain, and then goes into the living body or ecosystem through the food chain, and enriches in the living body or ecosystem, ultimately resulting in strong toxicity to the organism. Therefore, it is particularly important to promptly and accurately detect the concentration of metallic ions in environmental samples. Currently, spectrophotometry, stripping voltammetry, atomic absorption spectrometry and inductively coupled atomic emission spectrometry have been proposed for the determination of metallic ions. But the above analytical methods are labor, time consuming and require expensive instruments, not easy to detect metallic ions in environmental samples widespreadly and rapidly. So it is necessary to develop a sensitive, convenient and economical method to determine the concentration of metallic ions in the environment. Ion selective electrodes (ISEs) are a kind of emerging electrochemical sensors in modern times. Because of their high sensitivity, wide measuring range, good selectivity, fast response rate, simple instrument and easy operation, ISEs have be widely used in environmental analysis and ion species detection. Since1970, PVC membrane ion selective electrodes have been widely used. However, the dissolution of the membrane ingredients limits the application of membrane electrodes. Since the components can leach from the polymeric film into solution, this leaching results in limited lifetime, resulting in the deterioration of the electrode response (e.g., the detection limits and linear range). ISEs always developed in the direction towards broadening the types of ionophore and optimizing the response performance of the electrode. This work focuses on the use of silica gel composite materials and nanostructured multi-walled carbon nanotubes to design and synthesize a new neutral ligand, it will be as a carrier used in carbon paste electrode, expecting to build high sensitivity, good selectivity and long lifetime metallic ions electrochemical sensors. This paper studies the content of the following: 1. Studies on diazo-thiophenol-functionalized silica gel composite materials modified carbon paste electrode for potentiometric determination of silver ion researchFunctionalized silica gel composite materials are robust inorganic solids with the properties of a rigid three-dimensional structure. They also possess the particular chemical reactivity of organic component. The functionalized silica gel is able to preconcentrate metallic ions on the electrode surface either by complexation or electrostatic attraction, improving the sensitivity of the electrode. This study synthesized diazo-thiophenol-functionalized silica gel composite materials and they were used as the carrier in silver ion carbon paste electrode. According to the hard-soft acid base (HSAB) concept, the presence of S-donor atoms in carrier makes its marked coordination on soft acid-silver ion. Meanwhile, the silica gel composite materials, with group containing S, N and O atoms, is expected to provide a much-needed hydrophobic environment and high complex stability. Compared with the response characteristics of other silver ion selective electrodes, it can be seen that the linear range, pH range and selectivity of the developed electrode have been improved. We utilized the AC impedance to discuss the response mechanism of the electrode. Finally, the electrode was successfully used for the potentiometric titration of the mixture of chloride, bromide ions and the determination of silver ions in radiology films.2. Studies on a novel functionalized MWCNTs incorporated into carbon paste electrode for potentiometric detection of silver ionMWCNTs have been one of the most actively studied materials in carbon paste electrodes due to their unique structure and extraordinary physical properties. In this study, Schiff base (2-(E)-(2-aminoethylimino)methyl)phenol) was synthesized and grafted onto the surface of MWCNTs as a silver modifier in CPEs. The introduction of MWCNTs improves electron transfer between the solution and the electrode and tends to overcome the problem of ionophore leaching, improving electrode performance such as response time (～10s) and lifetime (three months). Importantly, the AC impedance was used to discuss the response mechanism of the electrode. Finally, it was successfully used in the potentiometric titration and the determination of silver ion concentrations in real samples.3. Studies on multi-walled carbon nanotubes derivate based on carbon paste electrode for potentiometric detection of Ag+ion4’-aminobenzo-15-crown-5(B15C5) was grafted onto the MWCNT-COOH through a short2-carbon chain spacer to get a novel multi-walled carbon nanotube derivative, as the silver ionophore. The introduction of MWCNTs in silver carrier has two advantages. On the one hand, MWCNTs have high surface-to-volume ratio, which can combine more B15C5. On the other hand, MWCNTs with electrical conductivity can be used as excellent ion-to-electron transducers in silver carrier. Meanwhile, B15C5-MWCNTs contain strong covalent bonds (amino groups covalently attached to the solid framework via an amino-carbonyl chain) and N, O donor atoms, which are likely to provide a much-needed hydrophobic environment for the complexes formed by silver ions and ionophore. Compared with the response characteristics of the previously reported papers on silver ion selective electrodes, it can be seen that the performance of the developed electrode has been improved, such as linear range widens, detection limit decreases and the pH range increases. The AC impedance was used to investigate the response mechanism of the proposed electrode. Finally, the electrode was successfully used in the determination of silver ions in radiology films and chloride ions in water samples. The results were compared with atomic absorption spectrometry. |
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