Degradation of the emerging brominated flame retardant tetrabromobisphenol S using organo-montmorillonite supported nanoscale zero-valent iron

The widespread occurrence of emerging brominated flame retardant tetrabromobisphenol S (TBBPS) has become a major environmental concern. In this study, a nanoscale zero-valent iron (nZVI) impregnated organic montmorillonite composite (nZVI-OMT) was successfully prepared and utilized to degrade TBBPS in aqueous solution. The results show that the nZVI-OMT composite was very stable and reusable as the nZVI was well dispersed on the organic montmorillonite. Organic montmorillonite clay layers provide a strong support, facilitate well dispersion of the nZVI chains, and accelerate the overall TBBPS transformation with a degradation rate constant 5.5 times higher than that of the original nZVI. Four major intermediates, including tribromobisphenol S (tri-BBPS), dibromobisphenol S (di-BBPS), bromobisphenol S (BBPS), and bisphenol S (BPS), were detected by high-resolution mass spectrometry (HRMS), indicating sequential reductive debromination of TBBPS mediated by nZVI-OMT. The effective elimination of acute ecotoxicity predicted by toxicity analysis also suggests that the debromination process is a safe and viable option for the treatment of TBBPS. Our results have shown for the first time that TBBPS can be rapidly degraded by an nZVI-OMT composite, expanding the potential use of clay-supported nZVI composites as an environmentally friendly material for wastewater treatment and groundwater remediation.