title: Boron-doped diamond electrooxidation of ethyl paraben: The effect of electrolyte on by-products distribution and mechanisms.
abstract: Ethyl paraben (EP), a representative emerging pollutant of the parabens family, was subject to electrochemical oxidation over a boron-doped diamond (BDD) anode. Experiments were carried out in a single-compartment cell at 10-70 mA cm-2current density, 200-600 μg L-1EP concentration, initial solution pH 3-9 and 0.1 M electrolyte concentration. The degradation rate is favored at increased current densities and in the presence of NaCl as the supporting electrolyte, while the pH effect is inconsiderable. For instance, the first order rate constant for the degradation of 200 μg L-1EP at 30 mA cm-2was 0.25, 0.1 and 0.07 min-1with NaCl, Na2SO4and HClO4, respectively. Degradation in secondary treated wastewater was faster than in pure water presumably due to the action of chloride ions present in the effluent. Liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) was employed to determine major transformation by-products (TBPs). The route of EP degradation with Na2SO4involves hydroxylation and demethylation reactions, signifying the role of electrogenerated hydroxyl radicals in the process. Twenty one TBPs were identified with NaCl as the electrolyte, including several chlorinated and non-chlorinated dimers and trimers; these findings suggest that indirect oxidation mediated by chlorine radicals and other chlorine active species also takes place. In this view, the role of the supporting electrolyte is crucial since it can influence both reaction kinetics and pathways.
authors.affiliation: Department of Chemical Engineering, University of Patras, Caratheodory 1, University Campus, GR-26504 Patras, Greece.
authors.forename: Zacharias
authors.initials: Z
authors.lastname: Frontistis
authors.affiliation: Department of Environmental & Natural Resources Management, University of Patras, 2 Seferi St., GR-30100 Agrinio, Greece.
authors.forename: Maria
authors.initials: M
authors.lastname: Antonopoulou
authors.affiliation: Department of Chemical Engineering, University of Patras, Caratheodory 1, University Campus, GR-26504 Patras, Greece.
authors.forename: Melis
authors.initials: M
authors.lastname: Yazirdagi
authors.affiliation: Department of Chemical Engineering, University of Patras, Caratheodory 1, University Campus, GR-26504 Patras, Greece.
authors.forename: Zeynep
authors.initials: Z
authors.lastname: Kilinc
authors.affiliation: Department of Chemistry, University of Ioannina, GR-45110 Ioannina, Greece.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Konstantinou
authors.affiliation: Department of Chemical Engineering, University of Patras, Caratheodory 1, University Campus, GR-26504 Patras, Greece. Electronic address: alex.katsaounis@chemeng.upatras.gr.
authors.forename: Alexandros
authors.initials: A
authors.lastname: Katsaounis
authors.affiliation: Department of Chemical Engineering, University of Patras, Caratheodory 1, University Campus, GR-26504 Patras, Greece.
authors.forename: Dionissios
authors.initials: D
authors.lastname: Mantzavinos
mesh_terms: D001895:Boron / Q000737:chemistry*; D018130:Diamond / Q000737:chemistry*; D004566:Electrodes; D004573:Electrolytes; D010084:Oxidation-Reduction; D062065:Wastewater / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D001895:Boron; D018130:Diamond; D004573:Electrolytes; D062065:Wastewater; D014874:Water Pollutants, Chemical
keywords: BDD; Chloride; Parabens; Pathways; Polymerization; Water matrix