Electrochemical Oxidation of Chlorinated Phenols

Abstract

Electrochemical oxidation has been proposed as a remediation method for chlorinated phenols but is hampered by anode fouling. In this work we explore the mechanism of anode fouling by chlorinated phenols, compare structure vs reactivity for phenols differing in the extent of chlorination, and relate the efficiency of oxidation to the mechanism of oxidation at different electrode types. Linear sweep voltammograms at a Pt anode at several concentrations, sweep rates, and pH were interpreted in terms of deposition of oligomers on the anode surface. Chronopotentiometry at Pt showed that the oxidation potentials of the chlorinated phenol congeners ranged from +0.6 to +1.3 V vs SHE in the pH range 2-12; four electrons are transferred for mono-and trichlorophenols and two for pentachlorophenol. Passivation increased in parallel with the uncompensated resistance of the solution and occurred only at potentials at which water is oxidized, suggesting that the formation of the oligomer film involves attack of hydroxyl radicals on electrochemically oxidized substrate. Seven chlorinated phenols were electrolyzed at PbO 2 , SnO 2 , and IrO 2 anodes. Relative reactivities of congeners were anode-dependent, due to different mechanisms of oxidation: direct electron-transfer oxidation at PbO 2 and hydroxyl radical attack at SnO 2 and IrO 2. At current densities < 0.1 mA cm -2 , current efficiencies > 50% could be achieved with 4-chlorophenol at all three anodes.

Degradation of dye solution by an activated carbon fiber electrode electrolysis system

“…Recent progress in treatment of these kinds of wastewater has led to the development of electrochemical processes [4,5]. Because electrolysis often consumes much energy, especially in dilute wastewater treatment processes, new methods and materials have been proposed [6,7].…”

Anodic Materials with High Energy Efficiency for Electrochemical Oxidation of Toxic Organics in Waste Water

“…This deactivation actually depends on the adsorption properties of the anode surface and the properties of the organic substrates. Aromatic compounds such as phenol (Foti et al, 1997;Gattrell & Kirk, 1993), chlorophenols (Rodgers et al, 1999;Rodrigo et al 2001), naphthol (Panizza & Cerisola, 2003;Panizza & Cerisola, 2004) and pyridine (Iniesta et al, 2001a) were reported to form polymer layer on anode surface easily. In order to accelerate the organics oxidation rate, in practical applications, higher oxidation potential on anode is needed and other side reactions like oxygen evolution occur.…”

Electrooxidation of Phenol on a Ti/RuO2 anode: effect of some electrolysis parameters

“…For the lower NaCl concentration, the low chlorophenols formation rate did not favor the buildup of adsorbed products, which block the anode surface. 6,[30][31][32] Several researchers 5,12,24,25,[33][34][35][36] observed that the decrease of the electrode efficiency due to organic matter adsorption depends on the electrolysis conditions, such as phenol concentration, supporting electrolyte type, electrode material, electrode potential and time. According to Zareie et al, 30 although high NaCl concentrations favor the formation of adsorbed intermediate products on the anode surface, the hypochlorite and chlorine ions act on the destruction of this blocking layer under longer times.…”