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Development of Miniaturized Electrochemical Sensors Based on Ion-Selective Membrane for Environmental Applications

Dehabadi, Monireh | 2023

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55880 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Yaghmaei, Soheila; Legin, Andrey; Kirsanov, Dmitry; Babain, Vasiliy
  7. Abstract:
  8. The first study of the present research aims to the possibility of developing simple, accurate and selective potentiometric sensors for the detection of scandium ions in aqueous solution, which is done for the first time. In this study, a sensor array consisting of 17 miniaturized potentiometric sensors based on polymeric membranes containing various ion-extracting ligands were designed and fabricated. Ligands as the active component of the membranes included phosphine oxides and diamides of various organic acids, which were used in the extraction of rare earth metal ions. The possibility of using these extractants in the polymer matrix of membranes for the development of scandium-sensitive sensors was presented. The influence of the structures of 17 ligands on their sensory properties was discussed. Each of the membranes contains 33 wt. % of PVC as a polymer matrix, 50 mmol/kg of each of the ligands, 10 mmol/kg of ionic additives (CCD or TFPB) and 59-64% wt. % o-NPOE as a plasticizer. The response of the sensors was studied in the concentration range of pC=2-7. Most of the sensors showed Nernstian and super-Nernstian response for scandium ion in the concentration range of pC=3-5 and their detection limit was about 45 µg/L. The interference effect of other ions in the detection of scandium was investigated by calculating selectivity coefficients. Bi-ionic potential method was used to measure selectivity coefficients. Most of the sensors showed the selective response to scandium ion. Other functional parameters of the sensors such as membrane lifetime, reproducibility and stability of electrodes’ responses, as well as their reversibility and response time were investigated. The average lifespan of the sensors was about three months and their response time was less than 30 seconds. The principal component analysis was performed on the sensitivity data of the sensors to check the collinearity between the responses of the sensors. Scores and loadings plots for the first two principal components were examined to study the similarities and differences in the responses of the sensors. The real-life applicability of the sensors was demonstrated in quantification of scandium in industrial solutions – hydrolytic sulfuric acid obtained from pigment titanium dioxide production. The amount of scandium in the sample was obtained by standard addition method and the result was compared with the ICP-AES method. The relative error of potentiometric measurement was less than 13%. The simplicity of construction and low price of the potentiometric sensors as well as the fast, accurate, stable and reproducible responses indicate that these sensors can be promising alternatives to conventional analytical spectroscopic methods for the measurement of scandium in technological process monitoring task. In the second study, the preparation of potentiometric sensors sensitive to rare earth metals was investigated. Four ligands were used, two of which were conventional ionophores in the detection of lanthanides, and two other ligands were chosen from commercial calcium ionophores (ETH 129 and ETH 5234), which have the same chemical structure as two well-known lanthanide ligands. The main goal of this research was to investigate and evaluate the feasibility of using two commercially available ligands in the membrane of potentiometric sensors for the detection of rare earth elements, which was done for the first time. For this purpose, the membranes containing each of the ligands were prepared and the electrochemical behavior of the compounds used in the presence of rare earth metal ions was studied and their efficiency was compared with famous and expensive ligands. Each of the membranes contains 33 wt.% PVC as polymer tissue, 50 mmol/kg of each of the ligands, 10 mmol/kg of ionic additives (CCD or TFPB) and 65-62 wt.% of o-NPOE as a plasticizer. The effect of the type of ligand and ionic additive on the response of the sensors was investigated. The behavior of the sensor containing ETH 5234 as a ligand and CCD as an ionic additive was very similar to that of the sensor containing TODGA. In the next step, the selectivity of the sensors in the presence of calcium ions was evaluated using fixed interference method. The results showed that the sensor containing ETH 5234 in the presence of calcium ion less than 10-5 M is able to detect rare earth metals and at more than this concentration, calcium ion is considered as a disturbing ion. The detection limit of the sensors in the detection of rare earth metal ions was 10-5 – 10-6 M. The results showed that the commercial and available calcium ligand (ETH 5234) is a good substitute for the expensive lanthanide ligands in the detection of rare earth metals, if the calcium ion in the sample is less than a certain amount
  9. Keywords:
  10. Ion Selective Electrode ; Electrochemical Sensor ; Sensors Array ; Rare Earth Element ; Lanthanides Detection ; Potentiometric Sensors ; Scandium Measurement

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