Goethite (α-FeOOH) photocatalytic activity at natural concentrations by the addition of H 2 O 2 at neutral pH and the simultaneous presence of fluoride and bicarbonate.

The effect of the simultaneous presence of fluorine (0.15-1.2 mg L ), bicarbonates (83.6-596 mg L ), and synthesized goethite (0.3 mg L ) at typical concentrations often found in natural groundwater samples was evaluated on the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) at pH 6.9 under simulated sunlight irradiation (300 W m ) and H O concentrations of 10 mg L . 2,4-D removal was strongly enhanced by the presence of fluoride. F could modify the surface of iron (hydr)oxide leading to the formation of surficial Fe-F bonds benefiting the formation of free OH radicals, producing upward band bending, reducing the electron-hole recombination, and enhancing the electron transfer to H O . On the other hand, bicarbonate may react with OH radicals generating CO species which could be able to participate in pollutant oxidation as well while solar light-induced H O photolysis also played an important role in removing 2,4-D. These findings suggest that “natural” tuning of iron (hydr)oxides by fluoride could take place in natural groundwater generating “natural” photocatalysts with a high activity which could participate, by adding H O , in the enhancing of sunlight photoinduced natural abiotic processes to pollutants abatement.