Microwave-induced degradation as a novel treatment for destruction of decabromodiphenyl ether sorbed on porous minerals

Decabromodiphenyl ether (deca-BDE or BDE-209) is a major brominated flame retardant released from plastics in thermal processing of e-waste, and there is a significant need for developing effective technologies for its destruction. This study reports a novel treatment for complete debromination and destruction of BDE-209 by adsorbing it onto porous minerals followed by microwave irradiation. Being highly hydrophobic, BDE-209 could be sorbed efficiently by porous mineral sorbents, with the density and type of surface cations of the sorbents apparently playing little role. Microwave irradiation caused rapid degradation of the BDE-209 sorbed on the porous minerals, and the fastest degradation occurred on the microporous minerals, with the density and type of surface cations present in the mineral micropores had significant impact on the degradation rate. Evolution of the degradation intermediates during the course of microwave irradiation indicates that the sorbed BDE-209 underwent pyrolytic decomposition, involving a series of reactions, including cleavage of the ether bond, debromination, hydroxylation, ring cleavage, and oxidation. Microwave-induced degradation could cause full mineralization of the sorbed BDE-209 without producing lower brominated congeners, which is supported by the results of density functional theory (DFT) calculations and infrared spectra. Together, these findings demonstrate that microporous mineral sorption coupled with microwave irradiation could be a rapid and efficient technology for destruction of BDE-209 and other polybrominated diphenyl ethers (PBDEs).