Reductive debromination of decabromodiphenyl ether by iron sulfide-coated nanoscale zerovalent iron: mechanistic insights from Fe(II) dissolution and solvent kinetic isotope effects

The mechanism that iron sulfide-coated nanoscale zero valent iron (S-nZVI) has better reduction activity towards organic pollutants than nanoscale zero-valent iron (nZVI) has long been debated. In this work, a systematic study was investigated to compare differences of main influences, BDE-209 degradation pathway, degradation kinetics and reduction mechanism of BDE-209 between nZVI and S-nZVI systems. The observed transformation rate of BDE-209 (k(obs)) by S-nZVI was 58.3 and 7.1 times greater than that by S2- and nZVI, respectively. The valence change of Fe and S on S-nZVI surface before and after BDE-209 degradation process based on XPS characterization confirmed that both Fe-0 and iron sulfide were the reduction entity of the surface-mediated reaction. The presence of tetrahydrofuran (THF) promoted the surface contact of BDE-209 with S-nZVI, thus accelerating the BDE-209 degradation process. Compared with nZVI, the iron sulfide coated on the Fe-0 core surface could not only greatly reduce unnecessary electron loss via Fe-0 corrosion with water, but also accelerate the transmission of electrons from Fe-0 core to organic pollutants according to Fe(II) dissolution and solvent kinetic isotope effects investigations. These findings help to clarify the synergistic degradation mechanism between Fe-0 core and iron sulfide shell layer. (C) 2019 Elsevier Ltd. All rights reserved.