Biochar/iron oxide composite as an efficient peroxymonosulfate catalyst for the degradation of model naphthenic acids compounds.

[Display omitted] • Catalyst activated PMS oxidation process was used for the degradation of model NAs. • PMS catalyst B-FeO x was synthetized and employed for model NAs degradation. • Relative kinetics of model NAs in B-FeO x /PMS oxidation system were studied. • The reaction between SO 4 •− and OH– generated •OH (responsible for model NAs degradation). • The presence of chlorine ions suppressed the degradation rate of model NAs. Naphthenic acids (NAs) are a mixture of aliphatic and alicyclic carboxylic acids which are persistent in the environment. In this study, a sludge-based biochar/iron oxide (B-FeO x) catalyst with 3D flower-like shaped structure was prepared through a facile hydrothermal method. For the first time, the B-FeO x catalyst was employed to activate peroxymonosulfate (PMS) for the removal of two model NA compounds (1-adamantanecarboxylic acid (ACA) and 4-methylheptanoic acid) at pH 8.50. Compared to biochar or FeO x alone, a higher degradation efficiency (96.1%) and faster degradation rate (k = 0.100 min−1) of ACA were obtained by the B-FeO x composite at a catalyst dose of 2.0 g/L and PMS dose of 2.5 mM. The higher degradation efficiency of B-FeO x was attributed to the improved surface area and pore volume as well as the abundant reactive sites induced by the flower-like structure. Furthermore, the hydroxyl radical (•OH) generated in the B-FeO x /PMS system was the dominant radical for both ACA and 4-methylheptanoic acid degradation as demonstrated through radical quenching experiments. The presence of chloride ions in the B-FeO x /PMS system showed a suppression effect on the degradation of ACA and 4-methylheptanoic acid at Cl− concentrations between 5 and 20 mM. No significant difference in the degradation rates of ACA and 4-methylheptanoic acid was observed at different Cl− concentrations. Overall, the results of this study showed that the sludge (waste material)-based B-FeO x composite may have the potential to be utilized as PMS catalyst for the removal of NAs that are especially abundant in oil sands process water. [ABSTRACT FROM AUTHOR]