The degradation of phthalate esters in marine sediments by persulfate over iron-cerium oxide catalyst

This study investigated the degradation of phthalate esters (PAEs) in marine sediments by sodium persulfate (Na₂S₂O₈, PS) activated by a series of iron-cerium (Fe-Ce) bimetallic catalysts (FCBCs). The surface structure and chemistry of the FCBCs were characterized by TEM, HRTEM, XRD, FTIR, BET and XPS. Results show successful synthesis of FCBC catalysts. Factors such as PS concentration, Fe to Ce molar ratio, catalyst dosage, and initial pH that might affect PAEs degradation were investigated. Results revealed that PAEs was degraded more effectively over FCBC with a Fe-Ce molar ratio of 1.5:1. Increase in Ce improved the catalytic activity of FCBC due to increase in oxygen storage capacity (OSC). Acidic conditions enhanced PAEs degradation with a maximum degradation of 86% at pH 2 and rate constant (k_obs) of 1.5 × 10^-1 h^-1 when the PS and FCBC concentrations were to 1.0 × 10^-5 M and 1.67 g/L, respectively. Di-(2-ethylhexyl) phthalate (DEHP) was a salient marker of PAE contamination in sediments. Dimethyl phthalate (DMP) and diethyl phthalate (DEP) were easier to degrade than DEHP, diisononyl phthalate (DINP), dioctyl phthalate (DnOP) and diisononyl phthalate (DIDP). The synergistic catalytic effect of Fe³⁺/Fe²⁺ and Ce⁴⁺/Ce³⁺ redox couples, in addition to electron transfer of oxygen vacancies, activated S₂O₈^2- to generate SO₄^- and HO radicals, which played the major role of PAEs degradation. 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trapping EPR studies verified the crucial role of SO₄^- and HO in the oxidative degradation process. FCBC/PS oxidation exhibited high-performance for the remediation of PAEs-contaminated marine sediments.