Degradation of triphenyl phosphate (TPhP) by CoFe2O4-activated peroxymonosulfate oxidation process: Kinetics, pathways, and mechanisms.

The aryl organophosphate flame retardant triphenyl phosphate (TPhP) has been frequently detected in environment and biota, and the potential risks of TPhP to aquatic organisms have also been demonstrated. The degradation of TPhP by CoFe2O4 activated peroxymonosulfate (PMS) was studied in this work. At initial pH of 7.0, 10 μM TPhP could be removed by 99.5% with 0.25 g/L CoFe2O4 and 0.5 mM PMS after 6 min oxidation, indicating the excellent performance of CoFe2O4 activated PMS process on the treatment of TPhP. The influence of PMS and CoFe2O4 dosage, initial pH, humic acid (HA), and anions (Cl-, NO3-, and HCO3-) on TPhP degradation were investigated systematically. Results showed that the degradation of TPhP was enhanced with increasing PMS concentrations from 0.1 to 1 mM, while it reduced as CoFe2O4 dosage increased. TPhP degradation efficiencies depended on solution pH with neutral pH showing the optimum degradation conditions. Recycling experiment indicated that the CoFe2O4 nanoparticles (NPs) possessed high potential for reusability. The radical identification experiments were performed and SO4•- was confirmed as the dominant radicals in TPhP degradation, and activation mechanism of PMS by CoFe2O4 NPs was hence explained. Humic acids (HA) (2-20 mg/L) as the representative organic natural matter existing in environment inhibited TPhP removal. Anions including Cl-, NO3-, and HCO3- all reduced TPhP degradation. In addition, TPhP degradation products were identified by liquid chromatography-mass spectrometry, and the degradation pathways of TPhP were proposed accordingly.