Degradation of phthalate esters in marine sediments by persulfate over Fe–Ce/biochar composites

Owing to public health concerns about phthalate esters (PAEs), the elimination of these compounds from the environment is imperative. Herein, a Fe–Ce/water caltrop shell biochar (WCSB) composite, prepared by coprecipitation method, was applied for the degradation of PAEs in real marine sediments by persulfate, a mostly SO4−-based oxidation process. The effect of composite dosage (0.4–1.7 g/L), pH (2.0–11.0), and seawater to freshwater (weight) ratio (0–100%) on PAEs degradation were examined. The synthesized composites were characterized by SEM, XRD, BET, XPS, zeta potential measurements and cyclic voltammograms (CV). The degradation efficiency and apparent rate constant of PAEs increased with an increase in composite dosage and decreased with increases in initial pH and seawater weight ratio. The kinetics of PAE degradation was described by the Langmuir–Hinshelwood kinetics model. Electrostatic attraction and hydrophobic interactions between PAEs and oxygen-containing functional groups facilitated the degradation of PAEs on Fe–Ce/WCSB. Electrostatic and π–electron donor–acceptor interactions with S2O82− activated by the Fe3+/Fe2+ and Ce4+/Ce3+ redox cycles on the composite surface were assessed as mechanisms for PAE degradation. The high reactivity of the composite is closely related to its redox capability. Hence, SO4−-based oxidation is a promising technology for the remediation of sediments contaminated with PAEs.