Enhanced degradation of monobrominated diphenyl ether by sophorolipid modified nanoscale zerovalent iron: Reactivity, electron selectivity, and mechanism

Abstract

Nanoscale zero-valent iron (nZVI) is regard as a promising reductant for halogenated organic compounds remediation, while it still suffers from low reactivity and poor electron selectivity toward monobrominated diphenyl ether. In this paper, the modified nZVI was successfully prepared via introducing sophorolipid during the synthesis of nZVI by a one-step method (SL-nZVI). The experimental results demonstrated that the degradation efficiency of SL-nZVI for BDE-3 could reach up to 99.96%, which was significantly higher than that of nZVI (59.60%). TEM and BET characterizations indicated that the modified nZVI possessed excellent dispersion properties and higher specific surface area, while the electrochemical tests results revealed that the sophorolipid modification reduced the charge transfer resistance of nZVI and favored the electron transfer. Besides, the introduced sophorolipid enhanced solubilization of hydrophobic organic contaminants via halogen bonding interaction also contributes to the increasement of BDE-3 degradation. More importantly, the experimental results also indicated that the utilization efficiency and electron selectivity of nZVI particles for the BDE-3 were significantly improved after sophorolipid modification (from 56.64% and 2.69% to 74.14% and 7.39%, respectively), and this could be owned to more accessible active sites, as well as the increased hydrophobicity of nZVI, which is not conducive to the adsorption of hydrophobic BDE-3 onto the nZVI surface, but reduces the occurrence of side reaction between nZVI and water. Those results demonstrate that the sophorolipid modification is an efficient strategy for nZVI in the remediation of hydrophobic BDE-3, and also highlight the promising prospects of sophorolipid in increasing the reactivity and electron selectivity of nZVI.