Degradation on BDE209 in the soil by kaolin-supported sulfurized nano-zero-valent iron activated persulfate system: Insights mechanism and DFT calculations

Abstract

The nanoscale zerovalent iron (nZVI) was successfully modified with sulfidation and loaded by kaolin (K@S-nZVI) for enhanced persulfate (PS) activation. K@S-nZVI was characterized by SEM-EDS, TEM, XPS, BET and XRD. The better degradation performance of BDE209 was in the following order: K@S-nZVI/PS> S-nZVI/PS> nZVI/PS> > systems without PS activation. The maximum removal of BDE209 was 88.32% under PS concentration of 0.2 mol/L, soil-water ratio of 1:2.5 and the molar ratio of K@S-nZVI/PS of 2:1. The reactive oxygen species in the K@S-nZVI/PS system were identified by EPR and quenching experiments as SO4-·,·OH,·O2- and the nonracial of 1O2. SO4-· and·O2- dominated the degradation of BDE209 and·OH and 1O2 were involved. According to gas chromatography-mass spectrometer (GC-MS) and density functional theory (DFT) calculations, BDE209 could be degraded to BDE7 by gradual debromination and further degraded into Br- and short-chain acids by ring opening reaction of benzene ring. The coexistence of SO42-, Cl-, CO32-, NO3- and HA reduced the degradation of BDE209. The soil pH did not change significantly during the remediation process. At the beginning of remediation process, soil catalase activities were enhanced while phosphatase and urease activities were weakened but they all recovered finally, exhibiting less damage to microbial cells. The K@S-nZVI/PS system is expected to be practically applied to the remediation of BDE209 contaminated soil.