Study On The Debromination Performance And Mechanism Of 2,2?,4,4?-tetrabromodiphenyl Ether(BDE-47) By Nano Pd/Fe~0 And Cu/Fe~0

Polybrominated diphenyl ethers(PBDEs)belongs to a class of brominated flame retardants(BFRs),which were widely added into various goods of circuit boards,textiles,furniture,etc.for their excellent heat resistance and low price.PBDEs entered the environment as these goods scraped,then they might be absorbed into human bodies through air,food chain and food net.PBDEs is a kind of persistent organic pollutants(POPs)with the properties of persistence,bioaccumulation,semi-volatile and highly toxic,is thought to be potential endocrine toxicity,hepatotoxicity and neurotoxicity for human beings.Studies on degradation of PBDEs mainly include chemical degradation,photodegradation/photocatalysis degradation and biodegradation.Chemical degradation is thought as an effective and environmentally friendly application method,among which zero-valent iron-based debromination is the best.This research selected the high amount and high toxicity 2,2?,4,4?-tetrabromodiphenyl(BDE-47)as main object.Nano zero-valent iron and nano iron-based bimetals Pd/Fe~0?Cu/Fe~0 had been synthesized by chemical reduction,three different protic solvents ultra-pure water,methanol and ethanol were chose as reaction solution,the debromination pathway and degradation mechanism of BDE-47 under different bimetals had been studied,several research results and discussion are given as followings:(1).High chemical reaction activity iron-based bimetals Cu/Fe~0 and Pd/Fe~0 had been synthesized successfully,scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD)and specific surface area(BET method)showed the synthetic materials were spherical particles with the diameter of about 70 nm and coated with around 1%(w%) additional metal Pd or Cu;(2).The results of gas chromatography-mass spectrometry showed that Pd/Fe~0 and Cu/Fe~0could reduce and degrade BDE-47 in ultra-pure water system.Differences in the types and distributions of debrominated intermediates were found;In the ethanol system,only Pd/Fe~0 showed degradation activity to BDE-47,and the product distribution was similar to that in ultra-pure water,but the by-product Dibenzofuran(DF)was formed;(3).Combined with experimental results and metal properties analysis,there are two different mechanisms of Pd/Fe~0 and Cu/Fe~0 reduction and degradation of BDE-47:Reduction and degradation of BDE-47 by Pd/Fe~0 is mainly based on active H reduction with the preference of removing the para-Br;Cu/Fe~0 is dominated by Fe~0-Cu coupled electrons,and both depolarized Br and ortho-de-Br exist.The former trend is slightly larger than the latter.The rate of active H reduction is higher than that of e~- transfer,accompanied by the formation of by-product DF;(4).Gaussian 09 software was used to calculate the Mulliken Charge of BDE-47 and intermediates replacing Br at different positions.The simulation results were confirmed by the experimental results,which further proved the mechanism of active H reduction and e~-transfer;Combined with product distribution experiment results,the calculation results showed the BDE-47 reduction degradation path diagram by Pd/Fe~0 and Cu/Fe~0,which provided a theoretical basis for the future practical application of engineering.