Visible-light-induced degradation of polybrominated diphenyl ethers with AgI–TiO2

Abstract

As typical persistent organic pollutants, polybrominated diphenyl ethers (PBDEs) have aroused high environmental concern because of their toxicity and recalcitrant degradation. Here we report the visible-light-induced degradation of PBDEs with AgI–TiO₂ (>420 nm). A series of nano-structured AgI–TiO₂ particles were synthesized by a deposition–precipitation method and characterized by SEM, TEM, XRD, XPS, BET and UV-Vis-DRS. The AgI–TiO₂ hybrids showed high efficiency for degradation of PBDEs and excellent photostability in cyclic run experiments. The absorbance intensity and absorption ability of AgI–TiO₂ hybrids and the properties of the solvents were found to greatly influence the efficiency of degradation of PBDEs. The 0.2-AgI–TiO₂ (the mass ratio of Ag to P25 was about 20%) in CH₃OH solution presented the highest reaction rate with 0.29 ± 0.02 h⁻¹. Most interestingly, mechanistic pathways in the degradation of PBDEs were different under UV and visible light. Unlike the common single-electron transfer in the UV-TiO₂ system, the debromination mechanism in the visible light/AgI–TiO₂ system showed multi-electron transfer. The analysis of products showed that many different lower brominated congeners simultaneously appeared under visible light rather than being stepwise formed under UV. This implies that the special structure of AgI–TiO₂ performs remarkably enhanced electron transfer, multi-electron transfer, and results in high photocatalytic activity. This research may provide a green and efficient method to remove halogenated pollutants by using visible light.