Photocatalytic debromination of polybrominated diphenyl ethers (PBDEs) on metal doped TiO nanocomposites: Mechanisms and pathways.

Nanoparticles of four noble metal doped titanium dioxide (i.e., Pd/TiO, Ag/TiO, Pt/TiO and Cu/TiO) were synthesized and investigated for their effectiveness to degrade polybrominated diphenyl ethers (PBDEs) under UV light. All the investigated noble metal additives can greatly enhance the performance of TiO to degrade 2,2',4',4'-tetrabromodiphenyl ether (BDE-47). However, the debromination pathways of BDE-47 in Ag/TiO and Cu/TiO systems are just contrary to those in Pd/TiO and Pt/TiO systems, and there was an induction period in the former systems but not in the latter systems. The hydrogenation experiment suggests a direct H-atom transfer mechanism in Pd/TiO and Pt/TiO systems, while in Ag/TiO and Cu/TiO systems, electron transfer is still the dominant mechanism. Electronic method was applied to explain why BDE-47 exhibit different debromination pathways based on different degradation mechanism. In addition, oxygen was proved to be able to capture both electrons and H atoms, and thus can greatly inhibit the degradation of PBDEs in all investigated systems. Finally, the merit and demerit of each metal doped TiO were discussed in detail, including the reactivity, stability and the generation of byproducts. We proposed our study greatly enhance our understanding on the mechanisms of PBDE degradation in various metal doped TiO systems.