Electrochemical oxidation of polyhydroxybenzenes on boron-doped diamond anodes

The electrochemical oxidation of phenol (Ph), hydroquinone (HQ), and 1,2,4-trihydroxybenzene (THB) using a diamond thin-film anode has been studied. Within the parameter ranges used (temperature 15-60 degreesC, initial concentration 1.1-36 mmol dm(-3), current density 15-60 mA cm(-2)), almost complete mineralization of the organic waste is obtained. Carbon dioxide is the sole final product, and the main intermediates are carboxylic acids C-4 and C-2. Both direct and mediated electrochemical oxidation processes are involved in the electrochemical treatment. Sulfates contained in the waste favor the formation of electrogenerated reagents (persulfates). The instantaneous current efficiency was found to depend only on the controlling mechanism (mass transfer or electrode kinetics). The current efficiency of the process is 1 if it is kinetically controlled and decreases linearly to 0 from the chemical oxygen demand limit value if it is diffusion controlled. Taking into account the information obtained in previous works and the results of the voltammetric and galvanostatic studies of the present work, a simple mechanistic model is proposed to justify the processes involved in the electrochemical oxidation of polyhydroxybenzenes.