Phenol degradation by advanced electrochemical oxidation process electro-Fenton using a carbon felt cathode

Oxidation of phenol in aqueous media by electro-Fenton process using carbon felt cathode has been studied. The salts of iron, cobalt, manganese, and copper were used to provide the metal cations as catalyst of Fenton reaction to produce hydroxyl radicals. 10−4 M of soluble iron(II) sulfate salt supplied the optimum catalytic condition, allowing to remove 100% of total organic carbon (TOC) of aqueous phenol solutions. The main reaction intermediates formed during electro-Fenton treatment were identified as hydroquinone, p-benzoquinone, and catechol. Carboxylic acids such as maleic, fumaric, succinic, glyoxylic, oxalic, and formic were predominantly identified as end products, before complete mineralization. The absolute rate constant of phenol degradation by hydroxyl radicals was obtained in acid medium (2.5 < pH < 3.0), being equal to (2.62 ± 0.23) × 109 M−1 s−1. Experiments with electro-Fenton oxidation of each aromatic intermediate allowed to propose a complete mineralization pathway.