Silver particles-modified carbon paste electrodes for differential pulse voltammetric determination of paraquat in ambient water samples

This paper describes the construction of silver particles-impregnated carbon paste electrode (Ag-CPE). The new electrode revealed an interesting determination of paraquat (II). The latter was accumulated on the modified electrode surface by adsorption onto silver particles and was reduced in 0.1 mol L−1 of Na2SO4 electrolyte at −0.70 V and −1.0 V for peaks 1 and 2, respectively. Experimental conditions were optimized by varying the heating temperature of the silver/carbon composite, the Ag/CP ratio, pH of measuring solution and accumulation time. Under the optimized working conditions, calibration graphs were linear for the concentration ranging from 1.0 × 10−7 to 1.0 × 10−3 mol L−1 with detection limits (DL, 3σ) 3.3 and 6.4 × 10−9 mol L−1, respectively, for peaks 1 and 2. The precision of this methodology was evaluated for eight successive measurements of the same samples containing 1.0 × 10−4 mol L−1 of paraquat. The relative standard deviations (D.S.R.) were 1.9% and 2.4% for the peaks 1 and 2, respectively. The Ag/CP composite was characterized by X-ray diffraction (XRD) and BET adsorption analysis

Square wave voltammetric determination of diquat using natural phosphate modified platinum electrode

A platinum electrode modified with natural phosphate (NP) was evaluated as an electrochemical sensor for diquat (DQ) in aqueous medium. The electrode was prepared by the deposition of natural phosphate on the platinum surface. Diquat was preconcentrated on the surface of the modified electrode by adsorbing with natural phosphate and reduced at a negative potential in 0.1 M K2SO4 solution. The influence of accumulation time and pH of the electrolytic solution were investigated. The calibration graph obtained under the optimized conditions was linear with a correlation coefficient of 0.9813 at levels near the detection limits up to at least 5.32 × 10−9 mol L−1 with the relative standard deviation (RSD) lower than 3.37%. Interferences by some metals were investigated. Fe, Zn, Cu, MnO4 and Hg apparently affected the peak currents P1 and P2 of diquat. The natural phosphate modified platinum electrode was applied to the determination of diquat in natural water samples. The results indicate that this electrode is sensitive and effective for the determination of diquat

ISOTHERM, KINETIC AND THERMODYNAMIC STUDIES ON THE ADSORPTION BEHAVIOR OF DISPERSE BLUE 165 DYE ONTO CHITOSAN AND PHOSPHOGYPSUM

Wastewater is environmentally damaged by textile industry due to dyes which are an important class of pollutants. This research explores the possibility of using the biopolymer chitosan and phosphogypsum a by-product of treating phosphate ore as adsorbents for the removal of disperse blue 165 from aqueous solution. Chitosan and Phosphogypsum were characterized by Fourier transform infrared spectroscopy and X-ray diffraction. Optimum adsorption conditions were selected by varying the adsorbent dose, solution pH, initial dye concentration, and contact time. The results show that the removal of disperse blue 165 increases with increasing initial dye concentration and the equilibrium contact time were 60 min and 30 min for chitosan and phosphogypsum respectively. The adsorption isotherms were examined and the Langmuir model gives the best fit. Adsorption capacities were 103.09 mg.g-1 for chitosan and 6.79 mg.g-1 for phosphogypsum. Dynamic adsorption studies show that the adsorption reaction was well represented by the pseudo-first-order kinetic process for both adsorbents. The adsorption behavior was also tested using thermodynamic parameters