Theoretical Investigation on Debromination Model of Deca- BromoDiphenyl Ester (BDE209)

The debromination of deca-bromodiphenyl ester (BDE209) is one of the most important processes in its removal from the environment. Despite numerous experimental studies improved the efficiency of poly brominated diphenyl ethers (PBDEs’) debromination, few studies focused on the mechanism. This work provides a preliminary investigation on studying the debromination mechanism of BDE209 with density functional theory (DFT). Experimental results suggest a stepwise process catalyzed by Ni-Fe bimetallic nano particles. So, a potential debromination mechanism of BDE209 via a four-membered ring transition state has been proposed. The B3LYP calculations indicate lower activation energies catalyzed by Ni relative to Fe, which agrees with the experimental result that a much higher debromination efficiency with Ni-Fe bimetallic nano particles than nano zero-valent iron. Also water has small solvent effect on the activation energies of debromination. The efficiency of debromination improves greatly in solvent mixture with higher ratio of water in experiment probably because of more protons provided by more water for the corrosion and debromination. Finally, the meta-bromine atoms are the most susceptible to be debrominated.