Simultaneous removal of perfluorooctanoic acid and thiocyanate by modified activated carbon fiber/persulfate system

In this study, NaOH-modified activated carbon fiber (NaOH-ACF) was used as a catalyst to activate persulfate (PS) for the removal of perfluorooctanoic acid (PFOA) and thiocyanate (SCN⁻) from wastewater. The effects of the crucial parameters in the NaOH-ACF/PS process, including NaOH-ACF dosage, PS concentration and initial pH, were investigated and optimized using response surface methodology. The experimental results indicated showed that under the optimal reaction conditions of NaOH-ACF dosage (0.40 g/L), PS concentration (2.0 mmol/L), pH (3.0), and temperature (25 °C), the removal efficiencies for PFOA and SCN⁻ reached 93.63 % and 95.17 %, respectively, within 60 min of reaction. When PFOA and SCN⁻ coexisted in the reaction system, it was observed that PFOA had minimal effect on the removal of SCN⁻, while SCN⁻ actually enhanced the removal of PFOA. Free radical identification experiments demonstrated that the NaOH-ACF/PS system generated free radicals (O₂[rad]⁻, SO₄[rad]⁻, [rad]OH) and non-free radicals (¹O₂), which cooperatively facilitated the degradation of PFOA and SCN⁻. Furthermore, Liquid Chromatograph-Mass Spectrometer (LC-MS) analysis results have been used to speculate on the possible degradation pathways and intermediates of PFOA. The material characterization results indicated that NaOH-ACF possesses abundant surface functional groups with excellent adsorption and catalytic properties. Thus, the NaOH-ACF-activated PS advanced oxidation process offered a promising approach for the simultaneous removal of Perfluorinated compounds and thiocyanates.