Enhanced thermal activation of peroxymonosulfate by activated carbon for efficient removal of perfluorooctanoic acid

The chemical degradation performance of perfluorooctanoic acid (PFOA), one of the environmentally persistent contaminants, by fresh activated carbon (FAC) and nitrogen-doped activated carbon (NAC) which were used as heterogeneous catalysts in the presence of thermal activating peroxymonosulfate (PMS) were investigated and compared. In this study, the physicochemical properties of FAC and NAC are characterized by scanning electron microscope, Raman spectra, Fourier transform infrared spectra, X-ray photoelectron spectroscopy, and Brunauer Emmett Teller. Furthermore, the dosing amount of catalyst, the concentration of oxidant and the effect of catalytic oxidation are investigated. During the catalytic oxidation process, the concentrations of PFOA and its degradation products are determined by high-performance liquid chromatography combined with tandem mass spectrometry (HPLC-MS/MS). The mineralization efficiency of PFOA employing FAC and NAC coupled with thermal activation of PMS are evaluated via a combination approach of total organic carbon (TOC) and ion chromatography (IC). The results indicate that PFOA can be readily degraded at 60 °C with an optimum concentration of PMS and an appropriate dosage of FAC/NAC. During the degradation process FAC and NAC exhibit superior adsorption and catalytic performance as more acidic oxygen functional groups are obtained from surface modification, which can facilitate the decomposition of PMS and the mineralization of PFOA. Electron paramagnetic resonance detection confirms that both OH and SO4− exist during oxidation. Based on the identified products, a reaction pathway including adsorption, hydroxylation, and catalytic oxidation is proposed. The methods could not only be applied in a wide pH range to effectively remove PFOA, FAC/PMS and NAC/PMS could also be reused, which provide a feasible and cost-effective method for the degradation of PFOA in situ actual ground water remediation.