Oberflächen-Koordinationschemie und Redox-Prozesse: Zur Auflösung von Eisen(III)-oxiden unter Lichteinfluss

Abstract

The solubility of iron in surface waters and atmospheric water is partially controlled by photochemical processes. The increase in the solubility of iron in natural aquatic systems occurs most efficiently through reductive dissolution of iron(III)(hydr)oxides. In the presence of light and suitable organic ligands, this process is not restricted to anoxic hypolimnetic water but may also take place in oxic epilimnetic water. As has been shown, processes at the surface and not transport processes control the dissolution kinetics. In light-induced dissolution of iron(III) (hydr)oxides, ligands may act both as electron donors and as surface complex-formers, thereby facilitating the detachment of reduced iron centers from the surface. Part of the photochemically formed iron(II) is readsorbed onto the iron(III) (hydr)oxide surface, probably through ternary surface complexes, and catalyzes the dissolution in a dark reaction. Thus, under certain circumstances, the light-induced dissolution of iron(III) (hydr)oxides is an autocatalytic process, since the dissolution rate depends in part on the concentration of readsorbed- iron(II).