Study On Photodegradation Of Polybrominated Diphenyl Ethers Based On C-Br Bond Activation

Polybrominated diphenyl ethers（PBDEs）are widely used due to their unique flame retardant ability,resulting in a wide distribution in the environment,which has a serious impact on the environment and human health.Therefore,an effective and environmentally friendly method to degrade PBDEs widely distributed in the environment is urgently needed,preventing them from being harmful to the environment.The bromine atom of PBDEs is the main reason for their high toxicity,high stability,and difficulty in being oxidized.Effective debromination can significantly reduce the toxicity and stability and improve their degradability.In this paper,the degradation of decabromodiphenyl ether（BDE209）by activating C-Br bonds in two different ways was investigated.The specific research results are as follows:1.We reported the effect of the composition and the optical properties of humic acid（HA）on the indirect photolysis of BDE209 by activating C-Br bonds under the visible light.Combined with the main active structure in HA,steady-state absorption spectroscopy and product analysis were used to further reveal the different reaction mechanisms between halogen-bonded complex excitation and HA-sensitized electron injection in the visible light indirect photolysis of PBDEs,and to verify the active part of HA structural components that interact with BDE209.At the same time,by studying the indirect photolysis behavior and debromination ways of BDE209 at different environmental interfaces such as liquid/liquid and solid/liquid interfaces in the presence of HA,it is revealed the constraints between different pathways of electronic stepwise debromination and parallel debromination.The results show that the O-Br halogen bond between HA and PBDEs can effectively activate the C-Br bond and degrade PBDEs in different reaction systems.It provides a theoretical basis for elucidating the photochemical conversion of PBDEs in nature and reducing the environmental impact of PBDEs.2.We investigated the role of oxygen vacancies in the activation of C-Br bonds to degrade BDE209 in the Bi₂MoO₆ system.In this experiment,a series of bismuth molybdate catalysts with different oxygen vacancy concentrations were synthesized by adjusting the amount of tetramethylethylenediamine added.The catalysts were characterized by X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and paramagnetic resonance spectroscopy（ESR）to explore the relationship between the oxygen vacancies on the structure and the reductive debromination of BDE209.It showed that Bi₂MoO₆ can effectively degrade BDE209 under visible light,interface defects are extremely important in the degradation of BDE209,and appropriate oxygen vacancies can promote the activation of C-Br bond of BDE209.In addition,through the tracking analysis of BDE209 degradation products,the debromination process of BDE209 on Bi₂MoO₆ has obvious site selectivity,with the content of meta debromination products is higher than that of ortho and para debromination products.The results show that oxygen vacancies effectively activate the C-Br bond and enhance the ability of Bi₂MoO₆ to degrade PBDEs.It is demonstrated that oxygen hole-assisted debromination is an excellent strategy for photocatalytic treatment of halogenated flame retardant pollutants.