Efficient removal of PFOA with an In2O3/persulfate system under solar light via the combined process of surface radicals and photogenerated holes

Abstract

The environmental persistence, high toxicity and wide spread presence of perfluorooctanoic acid (PFOA) in aquatic environment urgently necessitate the development of advanced technologies to eliminate PFOA. Here, the simultaneous application of a heterogeneous In2O3 photocatalyst and homogeneous persulfate oxidation (In2O3/PS) was demonstrated for PFOA degradation under solar light irradiation. The synergistic effect of direct hole oxidation and in-situ generated radicals, especially surface radicals, was found to contribute significantly to PFOA defluorination. Fourier infrared transform (FTIR) spectroscopy, Raman, electrochemical scanning microscope (SECM) tests and density functional theory (DFT) calculation showed that the pre-adsorption of PFOA and PS onto In2O3 surface were dramatically critical steps, which could efficiently facilitate the direct hole oxidation of PFOA, and boost PS activation to yield high surface−confined radicals, thus prompting PFOA degradation. Response surface methodology (RSM) was applied to regulate the operation parameters for PFOA defluorination. Outstanding PFOA decomposition (98.6%) and near-stoichiometric equivalents of fluorides release were achieved within illumination 10 h. An underlying mechanism for PFOA destruction was proposed via a stepwise losing CF2 unit. The In2O3/PS remediation system under solar light provides an economical, sustainable and environmentally friendly approach for complete mineralization of PFOA, displaying a promising potential for treatment of PFOA-containing water.