Pyrene degradation in an aqueous system using ferrous citrate complex activated persulfate over a wide pH range

To explore an effective liquid material for the degradation of polycyclic aromatic hydrocarbons (PAHs), sodium citrate (SC) was selected from four kinds of chelating agents for persulfate (PS) activation by transition metals to degrade pyrene in an aqueous system. PS activated by SC chelated ferrous ion (PS/Fe2+/SC) can catalyze pyrene degradation under neutral pH, and when the molar ratio of PS, SC, Fe2+ and pyrene was 2000/2000/2000/1, the maximum degradation percentage reached 94.4% in 720 min through enhancing the PS consumption and oxidative capacity of the system. Furthermore, the pyrene degradation catalyzed by PS/Fe2+/SC was not influenced by pH in the range from 3.0 to 11.0, PS/Fe2+/SC system could effectively catalyze the pyrene degradation over a wide pH range. Additionally, the presence of 0.1 M of SO42- and H2PO4- decreased the pyrene degradation using the PS/Fe2+/SC system, while 0.1 M of Cl- and NO3- had little effect on the pyrene degradation when PS/Fe2+/SC was used under neutral pH. Furthermore, pyrene degradation was attributed to the sulfate and hydroxyl radicals produced from PS/Fe2+/SC system, and these radicals were detected with strong signals of DMPO-SO4 and DMPO-OH through electron paramagnetic resonance (EPR) spectroscopy. Finally, seven pyrene degradation products were identified by gas chromatography-mass spectrometer (GC-MS), and a possible pathway of pyrene degradation was proposed.