Synergistic effect between Fe and Bi2O3 on enhanced mechanochemical treatment of decabromodiphenyl ether

The present work investigated the mechanochemical (MC) treatment of powdery decabromodiphenyl ether (BDE209) with Bi2O3 and/or Fe powders as co-milling reagents. The simultaneous use of Bi2O3 and Fe with a Bi:Fe:Br molar ratio of 1:1:1 led to a BDE209 degradation of 96.6% within 2 h of ball milling at rotation speed of 400 rpm, whereas only 66.0% and 24.0% of BDE209 was removed in the MC-Bi2O3 and MC-Fe system, respectively. It was demonstrated that the MC process activated the lattice oxygen (O2−) of Bi2O3 and promoted its reaction with BDE209, whereas Fe initiated the reduction of BDE209. The MC treatment of BDE209 through a single reductive in the MC-Fe system or oxidative process in the MC-Bi2O3 system was not efficient, due to that BDE209 is rather difficultly oxidized and the debrominated intermediates are resistant to reduction. When combining Bi2O3 with Fe, the reductive debromination of BDE209 over Fe and the subsequent oxidation of debrominated products over Bi2O3 were integrated into a concerted process. The rapid reduction of BDE209 over Fe not only released Br− ions, which acted as the dopant to improve the activity of O2− in Bi2O3, but also generated less brominated intermediates, which were more susceptible to the O2−-participating reaction over Bi2O3. Thus, a strong synergistic effect between Bi2O3 and Fe was observed on the MC degradation of BDE209.