Study the transport properties of anion and cation exchange membranes toward various ions using chronopotentiometry
The transport properties of various anion and cation exchange membranes were studied in different electrolyte solutions using chronopotentiometry technique to get insight about the influence of the counter ion on the transport properties of the membranes. The investigated samples include heterogeneous ion exchange membranes varying in the functionality of fixed charged groups, physical properties of the polymer and the preparation procedure. Chloride and nitrate were investigated as counter-ion in their sodium salts for anion exchange membranes while sodium, calcium, potassium, and magnesium were selected as counter-ion in their chloride salts to study cation exchange membranes transport properties. First, the current – voltage curve of an ion exchange membrane in a given solution was recorded to obtain the limiting current, then a constant current above the limiting current was used for chronopotentiometry measurement. In all the studied membranes the potential across the membrane remained constant for a time interval called the transition time , when a constant current was applied. Then the potential increased rapidly to reach the steady state potential. The permselectivty and the transport number of a membrane were calculated using the corresponding transition time.
Pencil graphite electrode modified with nitrogen-doped graphene and molecular imprinted polyacrylamide/sol-gel as an ultrasensitive electrochemical sensor for the determination of fexofenadine in biological media
Abstract A sensitive and selective sensor was developed for the determination of fexofenadine (FEX) drug. The sensor was constructed based on the modification of a pencil graphite electrode (PGE) as a low cost, high available and versatile working electrode. The PGE was modified by nitrogen-doped graphene (NDG) and molecularly imprinted polymer (MIP) as receptor to increase the sensitivity and reducing the interference of other chemicals. NDG was electrochemically deposited on the electrode surface which is more homogeneous and facilitated than its conventional chemical synthesis. The molecular imprinted polymer was immobilized on the NDG layer by the sol-gel technique. In the optimum conditions, the imprinting factor was obtained equal to 4.8, indicating the optimal selectivity of the sensor for the determination of FEX. Differential pulse voltammetry (DPV) was used for the determination of FEX, which exhibited a linear calibration graph of Ip versus FEX concentration in the range of 5.0 × 10−10-7.8 × 10-6 M (mol L-1). The detection limit of the sensor was calculated equal to 1.5 × 10−10 M, which displayed a superior detection limit when compared with the other electrochemical sensors reported for the FEX determination. The developed sensor contained advantages of simple design, satisfactory reproducibility, appropriate determination recoveries and high selectivity. These features permitted the successful application of the sensor for the measurement of FEX in pharmaceutical and biological samples.
Metal removal efficiencies of substrates for treating acid mine drainage of the Dalsung mine, South Korea
Abstract A pilot reactor system for testing acid mine drainage treatment was designed, operated at the Dalsung mine, and then evaluated for operating problems. Field analyses of pH and Eh (redox potential) were made. In the laboratory, analyses were made of Cd, Pb, As, Zn, Cu, Fe, Al and Mn. The reactor, containing a mixture of rice stalks, cow manure, and limestone, initially showed decreases of 98% Cu, 100% Zn, 99% Fe, 100% Cd, 97% Al, 61% Mn and 100% Pb when the effluents from the reactor had a pH of 6 and an Eh of about −300 mV. However, as time passed, the Eh rose and the amount of metals removed decreased, except Al. This indicated that maintaining reducing conditions was very important for continued metal removal. During the operating period, there were some problems such as a volume change in the substrate within the reactor and scaling on pipes. These problems appeared to reduce the flow of mine drainage in pipes and the reactor over time.