Oxidation Degradation Of Decabromodiphenyl Ether

Polybromodiphenyl ethers (PBDEs) have been widely used as flame retardant additives in plastics, textiles, electronic circuitry and other products due to their low price and excellent anti-combustion capability. However, as additive retardants, they can be easily leached into the environment through volatilization during their production, use and disposal. Due to their high hydrophobicity and recalcitrant to different types of degradation, PBDEs tend to accumulate in soil, migrate for long distances and accumulate through the food chain. As a result, PBDEs have been found in both aquatic and terrestrial ecosystems and even in human blood serum and breast milk. These heavily used restardants are believed to cause neurodevelopmental toxical and liver tumors. Among these209kinds of congeners used as flame retardants, decabromodiphenyl ether (BDE209) is the most extensively used, and what should be mentioned here is that BDE209can be degradated through photolysis and biodegradation and then generate lower brominated PBDEs with higher toxicity, which are found to be more harmful to the environment and human. Thus, the elimation of BDE209must be concerned.Degradation of BDE209is a significant challenge owing to its extreme persistence and recalcitrance nature. Currently, reductive debromination is the main degradation method. But with the reduction in the number of bromine, it becomes more diffcuclt to further degradation. Therefore, the debrominated efficiency by reductive methods is usually low, leading to the accumulation of less brominated products. Another serious problem is that toxic organic solvents are often extensive used during the degradation process because of the high hydrophobicity of PBDEs, which causes secondary pollution to the environment. The object of this dissertation is committed to study the efficient oxidative degradation of BDE209without using of organic solvents and the mechanism is deeply discussed. The main points of this thesis were summarized as follows: In the first chapter, the required analytical methods were established for identifying and quantitating BDE209, Br-and degradation intermediates. The concentration of produced Br" ions was monitored by ion chromagraphy (IC) and ion selective electrode method (ISE). Quantitative analysis methods of Br2and BrO3-were established using MO fading spectrophotometry and IC. On the HPLC system with a UV detector and C18column (4.6x250mm), we developed a method to quantify the BDE209concentration with the mobile phase set as97%acetonitrile and3%water. By combining Thermo scientific TRACE1300GC Ultra system with the TG-5MS capillary column with and ISQ mass system with the electron ionization mode, we can achieve the qualitation and quantitation of42kinds of PBDEs including1-10brominated congeners.In the second chapter, an efficient photocatalytic oxidative degradation system was developed with TiO2as the photocatalyst. The debromination efficiency of BDE209achieved95.6%after12h reaction with xenon lamp as the lighr source in aqueous environment under UV irradiation. The reaction products were analyzed with FTIR, HPLC-MS and GC-MS. It was found that no low brominated PBDEs were accumulated but only trace brominated acid were found in the degradation solution and can be further degraded, which indicated that BDE209was effective oxidation decomposed. The photocatalytic oxidative debromination of BDE209was further confirmed by the observation that the degradation of BDE209in different solvents was positively correlated with the formation of OH radicals, but not photo-generated electrons. The use of water not only avoided the scavenging of reactive radicals by organic solvent, but also enhanced the adsorption of BDE209on the surface of TiO2, both of which favor the contact of BDE209with photo-generated holes and·OH species and finally achieved its sound treatment.In the third chapter, a mechanochemical treatment method was developed for the oxidative degradation of BDE209with persulfate as the milling reagent. Under the conditions of molar ratio of PS to BDE209,50:1, mass ratio of milling ball to the reaction mixtures,50:1, the number of milling ball d20:d10=1:4,400rpm, BDE209was completely removed and the debrominated efficiency was98.3%within3h milling while no degradation occurred without PS under the same reaction condition. Raman spectroscopy was applied to monitor the change in the reaction solid and found that the C-Br and C-O bonds were gradually reduced and even disappeared with the milling progress. HPLC-MS, GC-MS were used to check the intermediates while no low brominated homologue was detected but trace3-bromohex-3-ene-2,5-diol was found which indicated that BDE209was oxidative degradaed. Radical trapping experiments by ESR futher confirmed that heat produced in the milling process achieve the thermally activatived of PS with the production of strong oxidizing active species SO4·-, which finally realized efficient oxidative degradation of BDE209in situ.In the forth chapter, an efficient mechanochemical treatment system was proposed for the oxidative degradation of BDE209with TiO2as co-milling reagents. Under the conditions of400rpm, mass ratio of milling ball to the reaction mixtures,100:1, the number of milling ball d20:d10=1-4, the debromination efficiency of BDE209increased with the increasing molar ratio of TiO2to BDE209in the range of50:1to750:1, namely, the debrominationg efficiency increased from8.6%to41.4%within1h miliing but dropped to31.4%while it was futher increased to1000:1. Moreover, when small amount of SiO2(molar ratio of SiO2to BDE209,50:1) was added to above system, the debromination efficiency was dramatically increased to81.3%. FTIR, GC-MS, TOC analysis and free radical trapping experiments were used to explore the mechanism of TiO2/SiO2milling system, a small amount of SiO2addition induced rapidly degradation of BDE209and produced low brominated PBDEs intermediates and can be in situ rapid oxidative degraded by·OH, which was generated by TiO2under mechanochemical condition.Using the combination of the two kinds of milling reagent have a synergistic effect on the depth degradation of BDE209.