A novel Electro-Fenton-Like system using PW11O39Fe(III)(H2O)4− as an electrocatalyst for wastewater treatment

A novel Electro-Fenton-Like (EFL) system was developed using the Keggin-type iron-substituted heteropolytungstate anion PW11O39Fe(III)(H2O)4− to substitute for Fe3+ in the conventional Electro-Fenton (EF) system for treatment of water polluted with organic compounds. The EFL system overcomes the drawback of low pH in conventional EF approaches and can be directly applied to neutral water treatment without any pH adjustment. Experimental results for dimethylphthalate (DMP) revealed complete degradation in <80 min in pH 6.86 solution containing 0.1 mM DMP at a potential of −0.5 V and O2 flow rate of 60 mL min−1. Total organic carbon removal of ∼56% was achieved at 120 min. Comparison with conventional EF oxidation revealed better efficiency of the present system for DMP degradation, suggesting its potential in treatment of water and wastewater with a relaxed pH requirement. The cumulative H2O2 concentration generated in situ at the electrode was monitored and the observed degradation rate constants kobs were determined for different initial DMP concentrations. The ligand exchange reaction of PW11O39Fe(III)(H2O)4− with H2O2 and the electron transfer resulting in hydroxyl radicals were examined using HPLC and electrochemical impedance spectroscopy. An electrocatalytic model involving inner-sphere electron transfer and a reaction mechanism for PW11O39Fe(III)(H2O)4− electrocatalytic reduction of H2O2 are proposed.