A peculiar mechanism for the photocatalytic reduction of decabromodiphenyl ether over reduced graphene oxide–TiO2 photocatalyst

• The photocatalytic debromination of BDE209 was efficient on reduced graphene oxide loaded TiO2.
• Much less toxic products were generated during the BDE209 debromination.
• A total different multi-electron reduction path of BDE209 occurred on RGO/TiO2.
• RGO as electron shuttle induced an efficient and distinct reduction path of BDE209.

There remains a significant need for new approaches to photocatalytically destroy refractory halogenated pollutants. Here, efficient photocatalysts (RGO/TiO2) were prepared by UV treatment of graphene oxide (GO) mixed with Degussa P25 TiO2, and used to photocatalytically reduce decabromodiphenyl ether (BDE209). The optimized composite yielded a BDE209 degradation of 72.0% and a debromination of 59.4% in anoxic water with methanol as electron donors after 12 h of UV irradiation, being 2 and 4 times that over naked TiO2, respectively. The BDE209 reduction generated 3Br–9Br PBDEs congeners, which were further debrominated. This led to a debromination of 90% at 24 h of reaction. Unlike the stepwise reduction manner commonly observed in UV–TiO2, the generation, accumulation and distribution of intermediates in the time course implied that the BDE209 reduction skipped some debromination steps. A novel mechanism for the multi-electron induced debromination pathway of BDE209 was proposed. This originated from the abilities of reduced GO in storing and transporting electrons. RGO not only trapped electrons to improve the charge separation on TiO2, but also shuttled the accumulated electrons to initiate multi-electron transfer to BDE209. The markedly enhanced debromination demonstrates the multi-electron transfer over RGO/TiO2 provide a green and efficient method to remove halogenated pollutants.

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