Goethite (α-FeOOH) photocatalytic activity at natural concentrations by the addition of H2O2 at neutral pH and the simultaneous presence of fluoride and bicarbonate

Abstract

The effect of the simultaneous presence of fluoride (0.15–1.2 mg L⁻¹), bicarbonates (83.6–596 mg L⁻¹), and synthesized goethite (0.3 mg L⁻¹) at typical concentrations often found in 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⁻²) and H₂O₂ concentrations of 10 mg L⁻¹. The 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 surface Fe–F bonds benefiting the formation of free ^•OH, producing upward band bending, reducing the electron-hole recombination, and enhancing the electron transfer to H₂O₂. On the other hand, bicarbonate may react with ^•OH generating CO₃^−• species that could participate in pollutant oxidation, while solar light-induced H₂O₂ photolysis also played an important role in removing 2,4-D. These findings suggest that tuning of iron (hydr)oxides by fluoride could take place in real groundwater, generating photocatalysts with a high activity that could participate, by adding H₂O₂, in the enhancement of sunlight photoinduced natural abiotic processes for pollutant abatement.