Photocatalytic degradation of perfluorooctanoic acid over Pb-BiFeO3/rGO catalyst: Kinetics and mechanism

Degradation of perfluorooctanoic acid (PFOA) is important because of its global distribution, persistence and toxicity to organisms. In this work, the PbBiFeO3 photocatalyst was prepared by the hydrothermal method. The effect of doping amount of reduced graphene oxide (rGO) on the decomposition of PFOA was investigated under 254 nm UV light. The results indicated that 100 mg L−1 PbBiFeO3 with 0.5 wt% rGO exhibited the highest degradation efficiency for 50 mg L−1 PFOA at pH = 2.0 from aqueous solution. The removal rate of PFOA reached 69.6% after 8 h UV irradiation under the optimal conditions (PFOA concentration of 50 mg L−1, Pb BiFeO3/0.5% rGO concentration of 100 mg L−1, and pH of 2.0). The total organic carbon removal rate and defluorination rate were 28.0% and 37.6%, respectively. During the degradation process, four major intermediates with shorter chain length than PFOA (∼C4C7) were identified. The mechanism responsible for PFOA decomposition was supposed that OH attacked PFOA to form perfluoroalkyl alcohol and then was transferred to perfluoroalkyl fluoride which can easily undergo hydrolysis to form shorter-chain perfluorocarboxylic acids than PFOA. This indicated that the photocatalytic degradation of PFOA was an oxidation process through stepwise losing of CF2 group.