Comparison of Voltammetric Responses of Toluene and Xylenes at Iron(III)-Doped, Bismuth(V)-Doped, and Undoped β-Lead Dioxide Film Electrodes in 0.50 M H[sub 2]SO[sub 4]

Abstract

Voltammetric activities are compared for the designated compounds in 0.50 M H 2 SO 4 at the specified film electrodes configured as rotated disks. The effective number of electrons ͑n eff , equiv mol Ϫ1 ͒ calculated from the Koutecky-Levich plot is 3.1 Ϯ 0.2 for toluene oxidation at the Fe-PbO 2 electrode, compared to 2.0 Ϯ 0.05 and 4.1 Ϯ 0.3 at the Bi-PbO 2 and PbO 2 electrodes, respectively. Gas chromatography-mass spectrometry data confirm that the primary product of toluene oxidation is benzyl alcohol ͑2 equiv mol Ϫ1 ͒ at the Fe-PbO 2 electrode with production of small amounts of benzaldehyde ͑4 equiv mol Ϫ1 ͒ and benzoic acid ͑6 equiv mol Ϫ1 ͒. X-ray photoelectron spectroscopy data indicate the ratio of Fe:Pb is ca. 1:100 ͑atom:atom͒ in the Fe-PbO 2 films. By comparison, a Bi:Pb ratio of 33:100 ͑atom:atom͒ is easily attained in Bi-PbO 2 films. Nevertheless, the apparent heterogeneous rate constant (k app , cm s Ϫ1 ) for toluene oxidation is larger at the Fe-PbO 2 electrode (6.5 Ϯ 0.06 ϫ 10 Ϫ3 ) compared to the Bi-PbO 2 electrode (2.0 Ϯ 0.05 ϫ 10 Ϫ3 ). X-ray absorption near-edge structure data confirm speculation that iron exists in the 3ϩ oxidation state with octahedral coordination by O atoms in Fe-PbO 2 films. The large activity of the Fe-PbO 2 electrode is attributed to the benefit of adsorption of aromatic molecules at Fe͑III͒ sites.

Anodic oxidation of mecoprop herbicide at lead dioxide

“…It has also been reported that the activity and stability of PbO 2 anodes may be significantly improved by the incorporation of dopants such as Fe 3+ , Bi n+ , Co 2+ and mixtures like Fe-F [43][44][45].…”

Status and Prospects of Concentrated Organic Wastewater Degradation

“…A mechanism for the electrochemical oxidation of organics, based on intermediates of oxygen evolution reaction in aqueous media, was formerly proposed by Johnson (Feng & Johnson, 1990;Vitt & Johnson, 1992;Feng et al, 1994;Treimer et al, 2001). The process involves anodic oxygen transfer from H 2 O to organics via hydroxyl radicals formed by water electrolysis.…”

An efficient electron transfer at the Fe0/iron oxide interface for the photoassisted degradation of pollutants with H2O2

“…4, no significant OH formation was observed in aqueous Fe 0 dispersion (curve a), while the quantities of OH increased with the reaction time (curve b) in aqueous Fe-200 suspension under otherwise identical conditions. According to the published works, in the oxidative electrochemical processes, the initial step is the discharge of water molecules to form adsorbed OH at the anode surface whether O 2 exists or not [19][20][21]. Higher oxidation states on the surface of electrodes are present above the thermodynamic potential from H 2 O to OH, which is lower than 1.23 V from H 2 O to oxygen [22].…”