New insight into the cosolvent effect on the degradation of tetrabromobisphenol A (TBBPA) over millimeter-scale palladised sponge iron (Pd-s-Fe0) particles

Abstract

The exploration of an effective treatment is necessary to eliminate the emerging environmental pollutant tetrabromobisphenol A (TBBPA). In this study, a direct reduction reaction was adopted to synthesize millimetre-scale palladised sponge iron (Pd0-s-Fe0), the main influencing factors were further explored, the degradation intermediates were identified in detail, and the cosolvent effect on the degradation mechanism was determined. The results show that (1) within a 30 min reaction, Pd(II) ions in aqueous solution were successfully decorated onto the s-Fe0 surface as supported by XPS, SEM, EDS, and ICP-OES analyses, (2) after 120 min of reaction, the normalized removal of TBBPA was ∼92.2% over 0.06 wt%-Pd0-s-Fe0, compared with 98.2% over 0.06 wt%-Pd-nZVI and 44.4% over bare nZVI. Moreover, the extend of debromination of TBBPA surprisingly increased as the ratio of the CH3OH:H2O cosolvent decreased, compared with the debromination rates that were greatly restricted in CH3OH (100%, v/v), CH2Cl2 (100%, v/v) and isopropanol (100%, v/v), respectively. Furthermore, the O-methylation reactions over Pd0-s-Fe0 produced unique intermediates, including 2,6-dibromo-4-(2-(3,5-dibromo-4-methoxyphenyl)propan-2-yl)phenol (MeO-TBBPA) and 5,5′-(propane-2,2-diyl)bis(1,3-dibromo-2-methoxy-benzene) (diMeO-TBBPA) with lower toxicity. This study greatly enriches knowledge regarding the degradation mechanism of TBBPA over millimetre-scale sponge iron.