Degradation Of Decabromobiphenyl Ether By Mechanochemical Method

Due to excellent performances of flame retardancy,decabromodiphenyl ether(deca-BDE)has achieved great success as flame-retarding agent in building materials,electronics,and so on.With the ever-growing environmental awareness,high toxicity,persistence,semi-volatility,and easy enrichment of deca-BDE,it becomes more and more important to exploit effective methods to degrade deca-BDE.Many methods have been investigated for the degradation of deca-BDE,such as physical method,biological method,and wet chemical method.However,these methods still endured some controversy.Mechanochemical method is an emerging method because solid pollutants can degrade directly in a closed environment.Hererin,a series of degradation strategies have been designed for the debromination and degradation of deca-BDE by using mechanochemical methods.The main contents are as follows.(1)The mechanochemical process and reaction mechanism were investigated for the degradation and debromination of deca-BDE with TiO₂ as milling agent.It was found that the mechanochemical degradation of deca-BDE was significantly influenced by the reaction atmosphere.When the milling was conducted under air atmosphere,the debromination ratio of deca-BDE was only 15.0%after milling for 120 min.However,when the milling was conducted under nitrogen atmosphere,the debromination ratio was increased to 90.2%.The influences of various operation parameters were investigated on the mechanochemical degradation of deca-BDE,including milling agents,the ratio of deca-BDE to milling agent,rotation speed,the ratio of the ball mass to the mass of deca-BDE and milling agent,and so on.The reaction conditions for the mechanochemical degradation of deca-BDE were optimized as followings:rotation speed,350 rpm;the molar ratio of TiO₂ to deca-BDE,50:1;the mass ratio of the ball mass to the mass of deca-BDE-TiO₂ mixture,100:1.By using XRD,XPS,HPLC and IC,the reaction intermediates were monitored and characterized.Finally,a mechanism was proposed for the mechanochemical degradation of deca-BDE with TiO₂ as milling agent.(2)By using TiO₂ and SiO₂ as the representatives,the influences of co-milling agents were investigated on the mechanochemical degradation and debromination of deca-BDE.In comparison with the use of single TiO₂ as milling agent,the simultaneous use of both TiO₂ and SiO₂ as milling agent promoted much more the degradation and debromination of deca-BDE in the air atmosphere with the removal ratio of 98.3%and the debromination ratio of 95.3%.These results provide a guiding design idea for mechanochemical co-grinding agent systems through adding inorganic oxide as a co-grinding agent to promote lattice distortion in degradation for deca-BDE.(3)Taking into account the finding of“highly brominated are easily reduced and low brominated are easily oxidized”,a co-milling system of Bi₂O₃ and reduced Fe powder was designed to degrade deca-BDE by mechanochemical method.When deca-BDE was degraded by ball milling for 120 min with using either Bi₂O₃ or reduced Fe powders as milling agent,the removal ratio reached 66.3%and 28.6%,respectively,and the debromination ratio was only 17.0%and 16.0%correspondingly.When the atomic ratio of the co-grinder Bi:Fe:Br was 1:1:1,the simultaneous use of both Bi₂O₃ and reduced Fe powders increased the removal ratio of deca-BDE to 96.6%,respectively.During the milling process of the composite abrasive,reduced Fe powder acts as an electron donor,providing electrons to rapidly reduce deca-BDE to low-brominated PBDEs,destroying the symmetrical structure of the original deca-BDE.