The electrocatalytic transformation of HS −, S 2O 32−, S 4O 62− and SO 32− to SO 42− by water-soluble iron porphyrins

Abstract

The electrocatalytic transformation of S 4O 6 2−, S 2O 3 2−, SO 3 2− and HS − to SO 4 2− by water-soluble iron porphyrins was investigated. The electrocatalytic oxidation of S 2O 3 2− to SO 4 2− can be performed by Fe( n-TMPyP) ( n=2,3, and 4). S 4O 6 2− is reduced to S 2O 3 2− by iron(I) species at weak basic aqueous solution, then S 2O 3 2− is oxidized to SO 4 2− through iron(IV) porphyrin species. S 4O 6 2− can be transformed to S 2O 3 2− by a chemical processes first and then the electrocatalytic oxidation of S 2O 3 2− to SO 4 2− is performed through iron(IV) species in a strong basic aqueous solution. HS − can be oxidized to S 2O 3 2− in a solution containing O 2 by chemical process, and then S 2O 3 2− is oxidized by iron porphyrin using electrocatalytic process. At a weak basic solution, S 4O 6 2− as the minor product can be reduced back to S 2O 3 2− by electrocatalytic method and the cyclic process of oxidation and reduction repeated. The electrocatalytic oxidation of S 4O 6 2− to SO 4 2− can be performed directly by Fe( n-TMPyP) ( n=2, 3, 4) in a strong basic aqueous solution. The electrocatalytic oxidation of SO 3 2− 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 SO 3 2− to SO 4 2−. The electrocatalytic oxidation activity is pH dependent in a wide pH range from 2.0 to 13.0, (O)Fe IVP has more catalytic activity than (OH)(O)Fe IVP.