Debromination of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) by synthetic Pd/Fe0 and Cu/Fe0 in different protic solvents

Polybrominated diphenyl ethers (PBDEs) belong to a class of persistent organic pollutants (POPs), with potential toxicity to the liver, reproductive system, and development of mammals. The highly toxic and concentrated congener, 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47), was chosen to investigate debromination mechanisms by the two synthetic iron-based bimetals (Pd/Fe0 and Cu/Fe0) in two protic solvents (water and ethanol). SEM, XPS, and BET analyses showed that the synthetic bimetals Pd/Fe0 and Cu/Fe0 were spherical with diameters of about 100 nm and loaded with ∼1% (wt%) of Pd and Cu, respectively. GC-MS was used for the analysis of degradation products and the chromatograms showed that both Pd/Fe0 and Cu/Fe0 bimetals had effective reducing properties in water solvent. In ethanol solvent, debromination of BDE-47 by Pd/Fe0 showed a similar high activity, but BDE-47 could be hardly degraded by Cu/Fe0. The dominant debromination products of BDE-47 by Pd/Fe0 and Cu/Fe0 were ortho-substituted and para-substituted BDEs, respectively. Active H-atomic transfer was found to play a key role in the debromination of BDE-47 by Pd/Fe0 in both, water and ethanol, with a preference for para-debromination along with the formation of dibenzo-p-furan (DF) as the by-product, mainly in water. In contrast, electron transfer with a preference for ortho-debromination was found to play a predominant role for Cu/Fe0 system in water. More importance should be provided to active H-atomic transfer for its high efficiency. In-depth study on the mechanism of formation of by-product DF would be significant for its higher toxicity, possibility of accumulation and migration in the environment.