Kinetics of Cr(III) ions electroreduction in a deep eutectic solvent (ethaline) was studied by using electrochemical impedance spectroscopy. The influence of water and sodium dodecyl sulfate on the kinetic parameters was established. The developed equivalent circuit included polarization resistance of the electrochemical reaction, constant phase element and finite Warburg impedance. The respective parameters of the accepted equivalent circuit were calculated and discussed. The obtained results indicated that the charge transfer is a rate-determining step of an electrochemical reaction occurring on a heterogeneous electrode surface. An increase in content of water in electrolytes resulted in an increase in polarization resistance, indicating the deceleration of Cr(III) ions electroreduction due to the changes in Cr(III) speciation. In addition, the introduction of extra water caused an increase in the value of a capacitive component of electrochemical impedance because of a rearrangement of the double electrical layer. The polarization resistance of Cr(III) ion discharge was increased in the presence of sodium dodecylsulfate in electrolyte due to adsorption of dodecylsulfate anion on the electrode surface. A Warburg impedance component disappeared in electrolytes containing relatively high water content, which was associated with corresponding reduction of solution viscosity and acceleration of diffusion mass transfer.
The solubility of chlorophenols as affected by surfactant was investigated. Three kinds of surfactant, sodium dodecyl sulfate, Triton X-100, and Brij 35, were utilized. The solubilization of chlorophenols by surfactant follows the order of 2,4,6-trichlorophenol > 2,4-dichlorophenol > 2,6-dichlorophenol > 2-chlorophenol; and the critical micelle concentration is an important index. The adsorption reactions of 2,4-dichlorophenol and 2,4,6- trichlorophenol onto hydrous montmorillonite in the presence of surfactant were examined. The presence of surfactant decreased the adsorption of chlorophenols significantly. The roles of hydrophobicity of chlorophenols in solubilization and adsorption behaviors are discussed.
Effects of water and sodium dodecyl sulfate additives on Cr(III) ions electroreduction in a deep eutectic solvent