Dorin Bejan

Competition between electrochemical advanced oxidation and electrochemical hypochlorination of acetaminophen at boron-doped diamond and ruthenium dioxide based anodes

This work was undertaken to distinguish four pathways for the electrochemical oxidation of acetaminophen as a model organic substrate: (i) direct electron transfer from the substrate to the anode, (ii) reaction of the substrate with HO• at boron-doped diamond anodes, (iii) non-radical (two-electron) oxidation of the substrate at Ti/RuO2 anodes, and (iv) electrochemical hypochlorination if Cl– is present. Pathway (i) was isolated as a slow reaction when boron-doped diamond (BDD) was used as the anode in the range of water stability, whereas in the corresponding reaction with Ti/RuO2 only pathway (iii) could be detected. Pathway (ii) predominated for BDD in the potential range of water oxidation, and was the only mechanism leading to mineralization of the substrate. Comparison between chemical hypochlorination and electrochemical oxidation at Ti/RuO2 in the presence of chloride ion indicated that the latter process principally involves mediated hypochlorination. Oxidation at boron-doped diamond anodes in th...

Electrochemical reduction of As(III) and As(V) in acidic and basic solutions

The removal of As(III) and As(V) from acidic and basic solutions by electrochemical reduction was studied using a reticulated vitreous carbon cathode and a IrO2/Ti anode in an electrochemical reactor that could be operated divided or undivided. By using a cascade of 7–9 plug flow reactors, residual concentrations of arsenic less than 20 ppb were achieved upon reduction of 100 ppm As(III) in either acidic or alkaline solutions and for 100 ppm As(V) in acidic solution. The reduction of As(V), generally considered electrochemically inactive in alkaline solutions, was proved possible, but was much less efficient. In all cases, the only product of electrochemical reduction was arsine. A moderate improvement in reduction efficiency was achieved under conditions of electrocatalytic hydrogenation using 5% Pd on alumina as catalyst.

Electrolytic debromination of PBDEs in DE-83TM technical decabromodiphenyl ether

Electrochemical debromination of the commercial decabromodiphenyl ether flame retardant DE-83 in partly aqueous tetrahydrofuran (THF) solution gave lower brominated congeners by sequential loss of bromine atoms. Hydrodebromination was most facile for the most heavily brominated congeners. It involves initial electron transfer and proton transfer from water, rather than hydrogen atom abstraction from THF, as shown by experiments with deuterated water. The product distribution from electrolysis involves preferential loss of bromine meta- and para- to the ether linkage, comparable with the products of metabolism of BDE-209 in various organisms. Significantly, the environmentally relevant congeners BDE-47, BDE-99, and BDE-154 were not major products of debromination of BDE-209 by the electron transfer mechanism.

Erratum to: Acid mine drainage: electrochemical approaches to prevention and remediation of acidity and toxic metals

Acid mine drainage (AMD), caused by biological oxidation of sulfide minerals in the presence of air and water, is a significant environmental problem because of its acidity and the presence of high concentrations of iron and solubilized toxic metal ions. The focus of this review is to consider the prospects for electrochemical technologies for either prevention or remediation of AMD, with physico-chemical technologies mentioned for comparison.

Electrochemical oxidation of sulfide ion in synthetic sour brines using periodic polarity reversal at Ebonex® electrodes

The Magneli phase Ti4O7 (Ebonex®) was used as both anode and cathode in the electrochemical oxidation of sulfide ion in alkaline solution in the absence and presence of chloride and naphthenate ion...

Indirect Oxidation of RDX, HMX, and CL-20 Cyclic Nitramines in Aqueous Solution at Boron-Doped Diamond Electrodes

Environmental Context. Nitramine explosives, including RDX, HMX, and the more newly developed CL-20, are the source of groundwater contamination (‘pinkwater’) especially around military installations. These materials all possess an abundance of nitro (NO2) groups, which, like synthetic organohalogens, render them resistant to biodegradation and thereby allows them to persist in the soil and waters. In this study it was shown that these substances can be indirectly oxidized at a boron-doped diamond electrode to small molecules (carboxylic acids and mineralized nitrogen-containing compounds). Abstract. Electrochemical oxidation at boron-doped diamond (BDD) electrodes was examined as a possible technique for the remediation of water contaminated with nitramine explosives. The advantage of BDD is that it promotes indirect oxidation by electrogenerated active intermediates, such as hydroxyl radicals. For the three explosives RDX, HMX, and CL-20, degradation in both acetonitrile/water mixtures and in water alone was suggested to involve an initial denitration, followed by spontaneous decomposition of the molecules, the net result being the complete transformation of the nitramines to small molecules. Although the rate of degradation increased with current density, the current efficiency was highest at low current densities.