MECHANISMS FOR AQUEOUS PHOTOLYSIS OF ADSORBED BENZOATE, OXALATE, AND SUCCINATE ON IRON OXYHYDROXIDE (GOETHITE) SURFACES

Photolysis of carboxylate anions adsorbed into highly crystalline goethite (α-FeOOH) with 300-400-nm light produces Fe2+(aq) and .OH from surface and solution redox reactions. The production of Fe2+(aq) and .OH was studied in N2-purged and aerated aqueous suspensions, respectively, of geothite containing equimolar (10-3 M) concentrations of oxalate and benzoate (ob+g), succinate and benzoate (sb+g), benzoate alone (b+g), goethite alone (g). The hydroxyl radical was measured by fluorescence analyis of salicylate formed in a reaction between benzoate and $.$/OH. Fe2+(aq) was determined colorimetrically. A proposed reaction mechanism includes the photoexcitation of Fe(III) surface complexes with OH-, HCO3-, and RCCO- ligands to form Fe2+(aq) and corresponding ligand radicals. Additional .OH is made by the O2 oxidation of Fe2+(aq).