Ultrasound Assisted Electrocatalytic Decomposition Of Chlorophenol In Aqueous Solution

Chlorophenol is one of toxic and bio-refractory pollutants, existed in environment for its using widely in petrochemicals and pesticides. Ultrasound assisted electrocatalytic process has good prospect of application because it is high performance, no selecting for pollutants and friendly to environment. With the aim of providing theoretical buttress and experimental data for the treatment of chlorophenol in aqueous solution, this paper started with the study of parameter analysis and active species formation, then moved on to synergetic effect, decomposition mechanism and kinetic model using ultrasound assisted electrocatalytic process.Experimental parameters, such as current density, original pH value, electrolyte concentration, ultrasonic intensity and ultrasonic frequency, had effect on the decomposition rate of chlorophenol, and the effect was different by the position of chlorine substituent. The results showed that the rate constants of o-chlorophenol, m-chlorophenol and p-chlorophenol were 2.702×10^-4s^-1, 2.996×10^-4s^-1 and 3.014×10^-4s^-1 respectively, under current density of 20 mA/cm², pH of 9.08, electrolyte concentration of 0.10 mol/L, ultrasonic intensity of 38.2 W/cm², ultrasonic frequency of 40 kHz. Synergetic effect had existed, and the enhancement factors of o-chlorophenol, m-chlorophenol and p-chlorophenol expressed by apparent first-order rate constant were 1.324, 1.226 and 1.506. The hydroxyl radical is the main active species in the ultrasound assisted electrocatalytic system. The rate of the hydroxyl radical formation was 1.67×10^-2 under p-hydroxybenzoic acid of 2.0g/L, current density of 20 mA/cm², pH of 6.85, electrolyte concentration of 0.10 mol/L, ultrasonic intensity of 47.8 W/cm², ultrasonic frequency of 40 kHz. The relational expression between hydroxyl radical and input energy was k_·OH=1.77×10^-5 mg/(L·s·W).2-Cl-p-benzoquinone, metacetonic acid, oxalic acid, acetic acid, formic acid, maleic acid were identified as intermediates through chromatograph analysis. It is presumed that o-chlorophenol was attacked by hydroxyl radical to form 2-Cl-p-benzoquinone, the later was oxidized to simple organic acids when the ring was opened. The model, derived by Langmuir adsorption theory in the surface of solid and reaction kinetics equations, could describe exactly the decomposition of o-chlorophenol. Numerical values were in good agreement with experimental data, and model parameters associated with reaction conditions.