Mechanism of perchlorate formation on boron-doped diamond film anodes

Orchideh Azizi, David Hubler, Glenn Schrader, James Farrell, Brian P. Chaplin

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Abstract

This research investigated the mechanism of perchlorate (ClO 4-) formation from chlorate (ClO3-) on boron-doped diamond (BDD) film anodes by use of a rotating disk electrode reactor. Rates of ClO4- formation were determined as functions of the electrode potential (2.29-2.70 V/standard hydrogen electrode, SHE) and temperature (10-40 °C). At all applied potentials and a ClO 3- concentration of 1 mM, ClO4- production rates were zeroth-order with respect to ClO4- concentration. Experimental and density functional theory (DFT) results indicate that ClO3- oxidation proceeds via a combination of direct electron transfer and hydroxyl radical oxidation with a measured apparent activation energy of 6.9 ± 1.8 kJ·mol-1 at a potential of 2.60 V/SHE. DFT simulations indicate that the ClO4- formation mechanism involves direct oxidation of ClO3- at the BDD surface to form ClO3, which becomes activationless at potentials > 0.76 V/SHE. Perchloric acid is then formed via the activationless homogeneous reaction between ClO3 and OH in the diffuse layer next to the BDD surface. DFT simulations also indicate that the reduction of ClO 3 can occur at radical sites on the BDD surface to form ClO3- and ClO2, which limits the overall rate of ClO4- formation.

Original languageEnglish (US)
Pages (from-to)10582-10590
Number of pages9
JournalEnvironmental Science and Technology
Volume45
Issue number24
DOIs
StatePublished - Dec 15 2011

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ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry

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