Persulfate activation with rice husk-based magnetic biochar for degrading PAEs in marine sediments

Phthalate esters (PAEs) can interfere with the endocrine systems of humans and wildlife. The main objective of this study was to evaluate the suitability of a composite for remediating marine sediments contaminated with PAEs. The composite was synthesized with magnetite nanoparticles (Fe₃O₄) and rice husk biochar (RHB) by using chemical co-precipitation. Fe₃O₄, RHB, and Fe₃O₄-RHB substantially activated sodium persulfate (Na₂S₂O₈, PS) oxidation to form SO₄^-• and thus degrade PAEs in marine sediments in a slurry system. The morphology and structural composition of the magnetic composites were examined using XRD, FTIR, environmental scanning electron microscopy-energy-dispersive X-ray spectrometry, and superconducting quantum interference device. The Fe₃O₄-RHB composites were confirmed to be prepared successfully. The influences of various parameters, including the PS concentration, composite loading, and initial pH, were investigated. The concentration of high-molecular-weight PAEs (HPAEs) in sediment was much higher than that of low-molecular-weight PAEs (LPAEs); di-(2-ethylhexyl) phthalate (DEHP) was an especially salient marker of PAE contamination in sediments. Furthermore, increasing the PS and Fe₃O₄-RHB doses accelerated PAE oxidation at pH 3.0; 83% degradation of PAEs was achieved when the PS and Fe₃O₄-RHB concentrations were increased to 2.3 × 10^-2 mM and 1.67 g/L, respectively. LPAEs such as dibutyl phthalate (DnBP) are easier to degrade than HPAEs such as DEHP, diisononyl phthalate (DINP), and diisodecyl phthalate (DIDP). In addition, possible activation mechanisms of the interactions between S₂O₈^2- and Fe²⁺/Fe³⁺ on the Fe₃O₄ surface, which involve an efficient electron transfer mediator of the RHB oxygen functional groups promoting the generation of SO₄^-• in the Fe₃O₄-RHB/PS system, were clarified. Thus, the Fe₃O₄-RHB/PS oxidation process is expected to be a viable method for remediating PAE-contaminated marine sediment.