Thermal Oxidation Degradation of 2,2′,4,4′-Tetrabromodiphenyl Ether over Li α TiO x Micro/Nanostructures with Dozens of Oxidative Product Analyses and Reaction Mechanisms

Flowerlike Li α TiO x micro/nanostructures were successfully synthesized to degrade 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) at 250–350 °C. The pseudo-first-order kinetics rate constant of the reaction at 300 °C was in the range of 0.034–0.055 min –1 . The activation energy was as low as 39.9–48.1 kJ/mol. The excellent performance attained over Li α TiO x was attributed to Li dopant having the electron-donating effect, which enhanced the oxygen species mobility. The oxidative reaction was believed to be the dominant degradation pathway following the Mars–van Krevelen mechanism, being accompanied by the weak hydrodebromination occurrence generating the trace mono- to tri-BDEs. More than 70 types of oxidation products containing diphenyl ether backbone, single-benzene rings, and ring-opened products were detected by GC-MS with derivatization, ESI-FT-ICR-MS, and ion chromatography. An increase in the number of ring-cracked oxidative products under prolonged reaction was observed by ESI-FT-ICR-MS analysis according to the van Krevelen diagram. In the oxidative reaction, a series of oxidative products, such as OH-tri-BDEs and OH-tetra-BDEs, first formed via the nucleophilic O 2– attack and subsequently transformed into dibromophenol, tribromophenol, and benzenedicarboxylic and benzoic acids, etc. They could be further attacked by electrophilic O 2 – and O – and completely cracked to small molecules such as formic, acetic, propionic, and butyric acids.