| Because of its great flame retardant property and simple synthesis process, tetrabromobisphenol A(TBBPA) is one of the most widely used brominated flame retardants. TBBPA has similar structure to thyroid hormones and is considered as a potential endocrine disruptors because of its immunotoxicity and thyroid interference effects, which have caused great threat to human health. Currently, technologies for the treatment of TBBPA in environmental matrices and biomedium mainly include biodegradation, pyrolysis and advanced oxidation process. These methods either had poor degradation rate and long reaction period, or produced PBDFs, PBDDs, and some other brominated volatile byproducts. Therefore, the exploring new technologies of rapid and thorough debromination of TBBPA is necessary.In this study, the degradation of TBBPA by nanoscale zerovalent iron(n ZVI) bimetal particles(n ZVI/Ni and n ZVI/Cu) in methanol/water solutions were investigated. The fresh and aged bimetal particles were characterized by SEM-EDS, BET, XRD, XPS and FTIR to study physico-chemical properties. The effects of noble metal loading, initial p H, n ZVI dosage, initial TBBPA concentration, and reaction temperature on the TBBPA removal and the reaction kinetics were discussed. HPLC and GC-MS were applied to analyze the intermediates and final product in order to investigate and compare the reaction mechanisms.The main conclusions of this study are as follow:(1) The characterization of n ZVI: The freshly prepared n ZVI/Ni and n ZVI/Cu particles were mostly spherical in shape and aggregated in chains. The particle diameters were in the range of 20-80 nm. Their BET surface specific areas were 33.75 m2/g and 32.46 m2/g, respectively. After reacting with TBBPA, the particles evolved from spherical to lamellar structure and surface area decreased markedly. Both of the fresh particles had core-shell structures: the core was α-Fe0 with the strong reductive capacity and the shell contained amorphous iron oxides. Ni was dispersed amorphously at the surface and Cu was distributed as Cu0. After reacting with TBBPA, the thickness of oxide layer increased and mainly composed of Fe3O4.(2) The degradation of TBBPA by n ZVI/Ni: the reaction followed pseudo-first-order reaction kinetics. The observed pseudo-first-order rate(kobs) increased with the increase of Ni loading and n ZVI/Ni dosage, decreased with the increase of initial TBBPA concentration. The nickel utilization rate reached maximum when Ni loading was 0.5 wt%. Weak acidic condition was most favorable for TBBPA degradation. As initial TBBPA concentration was 10 mg/L and n ZVI/Ni dosage was 2.0 g/L, completing degradation of TBBPA was achieved within 120 min and more than 90% of TBBPA could be transformed to bisphenol A(BPA) at p H 5.0 and 6.0. The removal rate was 47% and 100% at p H 9.0 and 3.0, respectively, and dibromobisphenol A(di-BBPA) was found to be the dominant product.(3) The degradation of TBBPA by n ZVI/Cu: the reaction followed pseudo-first-order reaction kinetics. kobs achieved maximum when Cu loading was 0.5 wt% and it depressed with decreasing or increasing Cu loading. The effect of p H on the degradation of TBBPA by n ZVI/Cu was similar to that of n ZVI/Ni, where weak acidic condition was most favorable for the rapid and complete debromination of TBBPA to BPA. kobs increased with increasing n ZVI/Cu dosage and the reaction temperature. At Cu loading 0.5 wt%, the apparent activation energy of the reaction was 69.66, 72.26 and 83.25 k J mol-1 at solution p H 5.0, 7.0 and 9.0, respectively. At solution p H 7.0, apparent activation energy of the reaction with 0.1, 0.3 and 0.5 wt% Cu loading was 120.73, 81.24 and 72.26 k J mol-1, respectively.(4) The removal rat of TBBPA decreased in the order of n ZVI/Cu > n ZVI/Ni > n ZVI. As initial TBBPA concentration was 10 mg/L, n ZVI dosage was 0.5 g/L, kobs of n ZVI/Cu was 3.41(± 0.18) × 10-2 min-1, which were 17 and 68 times than that of n ZVI/Ni and n ZVI, respectively. |
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