Indirect cathodic electrocatalytic degradation of dimethylphthalate with PW₁₁O₃₉Fe(III)(H₂O)^4- and H₂O₂ in neutral aqueous medium

Cyclic voltammetry and degradation of dimethylphthalate (DMP) revealed that the iron-substituted heteropolytungstate anion PW₁₁O₃₉Fe(III)(H₂O)^4- is an excellent indirect cathodic oxidative electrocatalyst in the presence of H₂O₂. PW₁₁O₃₉Fe(III)(H₂O)^4- can electrocatalyze the reduction of H₂O₂ to hydroxyl radicals via an inner-sphere electron transfer mechanism, which cause oxidative decomposition of DMP. Almost complete DMP removal and ca. 30% mineralization were obtained in less than 120 min in a mixed phosphate solution at pH 6.86 containing 0.1 mM DMP. MS analyses of the intermediates and final products suggested that glyoxal, oxalic acid and acetic acid are the main ring-opening products, besides some unstable hydroxylated aromatic intermediates. The effects of added H₂O₂ concentration, applied cathodic potential and DMP initial concentration on the degradation of DMP were also investigated. A concentration of 1.0 mM H₂O₂ and cathodic potential of -0.3 V were optimal conditions for DMP degradation in our experiments. At higher initial DMP concentrations degradation also occurred, but at a slower decay rate compared to lower initial concentrations. The present system thus represents a possible method to use PW₁₁O₃₉Fe(III)(H₂O)^4- as an indirect cathodic oxidative electrocatalyst in water and wastewater treatment