Fe3+ Promoted the Photocatalytic Defluorination of Perfluorooctanoic Acid (PFOA) over In2O3

In this study, four kinds of In2O3 photocatalysts were prepared by a facile calcination process at different temperatures and used for the removal of perfluorooctanoic acid (PFOA) from contaminated water. Lower calcination temperatures induce higher oxygen vacancy concentrations and larger specific surface areas, thus improving the PFOA degradation performance of In2O3. In2O3 prepared at lower temperatures of 300 °C (In2O3-300) and 400 °C (In2O3-400) demonstrates better catalytic performance, and 10 mg L–1 PFOA could be completely removed within 4 h, with a defluorination ratio of 35% over In2O3-300 and 39% over In2O3-400 in 8 h. Fe3+ only slightly increased the defluorination ratio of PFOA over In2O3-400 to 43%. A defluorination ratio of ∼20% over In2O3-600 was obtained in 8 h, while when Fe3+ was added to the photocatalytic systems, a higher defluorination ratio of ∼60% was obtained in the In2O3-600 system. Combining diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and in situ DRIFTS to track the decomposition of PFOA, we speculated that Fe3+ participated in the coordination between PFOA and In2O3-600, thus promoting the defluorination of PFOA.