The electrocatalytic transformation of HS-, S2O32-, S4O62- and SO32- to SO42- by water-soluble iron porphyrins

The electrocatalytic transformation of S4O62-, S2O32-, SO32- and HS- to SO42- by water-soluble iron porphyrins was investigated. The electrocatalytic oxidation of S2O32- to SO42- can be performed by Fe(n-TMPyP) (n = 2,3, and 4). S4O62- is reduced to S2O32- by iron(I) species at weak basic aqueous solution, then S2O32- is oxidized to SO42- through iron(IV) porphyrin species S4O62- can be transformed to S2O32- by a chemical processes first and then the electrocatalytic oxidation of S2O32- to SO42- is performed through iron(IV) species in a strong basic aqueous solution. HS- can be oxidized to S2O32- in a solution containing O-2 by chemical process, and then S2O32- is oxidized by iron porphyrin using electrocatalytic process. At a weak basic solution, S4O62- as the minor product can be reduced back to S2O32- by electrocatalytic method and the cyclic process of oxidation and reduction repeated. The electrocatalytic oxidation of S4O62- to SO42- can be performed directly by Fe(n-TMPyP) (n = 2, 3, 4) in a strong basic aqueous solution. The electrocatalytic oxidation of SO32- by Fe(n-TMPyP) through Fe(IV) was investigated at room temperature in aqueous solution. Fe-III(n-TMPyP) (n = 2,3,4) can be oxidized to iron(IV) species by electrochemical method in the range of basic aqueous solution, then Fe(IV)(n-TMPyP) oxidizes SO32- to SO42-. The electrocatalytic oxidation activity is pH dependent in a wide pH range from 2.0 to 13.0, (O)(FeP)-P-IV has more catalytic activity than (OH)(O)(FeP)-P-IV. (C) 2000 Elsevier Science Ltd. All rights reserved.