The removal of polycyclic aromatic hydrocarbons (PAHs) from marine sediments using persulfate over a nano-sized iron composite of magnetite and carbon black activator

Abstract

The presence of polycyclic aromatic hydrocarbons (PAHs) in sediments is a potential eco-environmental health risk. Fe3O4-carbon black (FCB) nanocomposite was synthesized by a simplified precipitation method and used to activate persulfate (PS) for the degradation of PAHs in contaminated marine sediments. The carbon black was formed by amorphous non-graphite and the Fe3O4 composed of magnetite of cubic crystal structures. FCB exhibited typical ferromagnetic characteristics and high degradation of PAHs in marine sediments via PS oxidation. The pseudo‒first‒order rate constant of PAHs degradation significantly increased with PS dosage but decreased with increase in pH from 3 to 9. Langmuir-Hinshelwood model described the kinetics of PAHs degradation well. The observed rate constant, kobs (1.8 × 10−2 h−1), at Σ[PAH]: [PS] = 1:104 (the optimal condition) was almost 2.7 times that of 1:1 (kobs = 6.6 × 10−3 h−1). At the PS concentration of 2 × 10−4 M (or a Σ[PAH]: [PS] = 1:10), pH 3, and 3 g/L of FCB, the FCB/PS system exhibited 94, 97, 94, 98, and 93% degradation of total PAH (Σ[PAH]), PY, FLU, CH, and PH, respectively, while the highest PAH degradation was 99, 98, 97, and 97%, respectively, for 6‒, 5‒, 4‒ and 3‒ring PAHs. The presence of Fe2+/Fe3+ redox pairs greatly enhanced the catalytic capacity of FCB leading to an increase in PAH degradation. Electron paramagnetic resonance (EPR) spectroscopy revealed SO4–• and HO• radicals as major reactive species for PAHs degradation in FCB/PS system. Results clearly indicated the great potential of FCB for remediation of PAHs contaminated marine sediments.