A pulse-radiolytic and photochemical study of the oxidation of water by zinc porphyrin π-radical cations
- 1 January 1984
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics
- Vol. 80 (11) , 1451-1464
- https://doi.org/10.1039/f29848001451
Abstract
π-Radical cations of water-soluble zinc porphyrins have been formed by oxidation with Br˙– 2 under pulse-radiolytic conditions. These π-radical cations decay with complex kinetics but the rate of decay was enhanced upon addition of colloidal RuO2·2H2O. For the π-radical cation derived from zinc tetrakis(4-sulphonatophenyl)porphine (ZnTSPP4–) the rate constant for decay was a linear function of the concentration of RuO2·2H2O and the bimolecular rate constant for this interaction was dependent upon pH. At pH 12, interaction was diffusion controlled but the rate decreased with decreasing pH. The form of this pH dependence is consistent with the π-radical cation oxidising water to O2 on the surface of the RuO2·2H2O colloid. Visible-light irradiation of ZnTSPP4– in the presence of persulphate and RuO2·2H2O resulted in formation of O2, and both the rate and total yield of O2 formation were strongly dependent upon pH. Again, the optimum conditions for O2 formation were found at pH 12 where the quantum efficiency was 50%. No O2 was formed with zinc tetrakis (N-methyl-4-pyridyl) porphine, which has a much shorter-lived π-radical cation.Keywords
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