【作者】 罗斯；

【导师】 孙成； 杨绍贵；

【作者基本信息】 南京大学 ， 环境科学， 2011， 博士

【摘要】 溴代阻燃剂作为合成高分子材料的重要助剂之一,主要被用于塑料、纺织品、电子／电器,运输包装、建材以及其他防火材料中。它们可以在生产、使用、废弃品处理等过程中通过各种途径进入环境,对大气、土壤、水体等介质产生污染。本论文以四溴双酚-A (TBBPA)和多溴联苯醚作为研究对象,建立了由纳米Fe-Ag双金属还原和后续类Fenton氧化所组成的两步连续处理的方法,实现了对具有抗氧化性的典型溴代阻燃剂的彻底、有效降解。采取液相化学沉淀法直接置换出金属银包覆在纳米铁颗粒外层,合成具有核壳型结构的纳米Fe-Ag双金属催化还原剂。表征结果显示,所制备的双金属颗粒为核壳型结构,外层金属银为不完全均匀分布态,颗粒粒径分布在20-100 nm之间,分散性较好；纳米粒子连接成链状,少数还呈现出团聚状态。纳米Fe-Ag粉末(Ag含量为1.048 Wt%)的比表面积为72 m2g-1,比纳米Fe0的比表面积大；纳米Fe-Ag双金属的XRD谱图在44.66和64.34°两处出现与Fe(110)和Fe(200)晶面相对应的衍射峰,而38.06°所对应的是Ag(111)晶面的衍射峰。利用所合成的纳米Fe-Ag双金属与超声波(US)协同催化降解目标化合物TBBPA。在常温常压、原始pH的条件下,银化率为1 wt%的Fe-Ag双金属能使初始浓度为2.0 mgL-1的TBBPA水溶液在20 min内完全脱溴,其转化反应遵循准一级动力学。沉积在纳米铁颗粒外层的金属Ag和超声波辅助在还原过程中发挥了重要作用,论文对其可能原因进行了推测分析。考察了纳米Fe-Ag双金属颗粒降解TBBPA的主要影响因素,包括纳米双金属颗粒的用量、TBBPA的初始浓度、溶液初始pH值、银化率以及温度等。比较适合的反应条件为：双金属投加量0.4 g L-1,银化率1 wt%,TBBPA初始浓度2 mg L-1,初始的pH值6.0+0.5,反应温度30℃。开展了纳米Fe-Ag双金属协同微波(MW)催化降解TBBPA、十溴联苯醚(BDE-209)和2,2’,4,4’-四溴联苯醚(BDE-47)的研究。Fe-Ag/MW体系具有很强的还原能力,微波的加入对还原脱溴反应产生了非常显著的促进作用,这主要归因于微波辐射所产生的热效应以及溶液沸腾时对纳米颗粒的分散作用。此外,还原剂金属用量的增大和微波功率的提高能够加速降解反应的进行,分子中溴原子个数对PBDEs的还原降解速率也具有一定影响。通过LC-MS/MS和GC-MS的检测分析,TBBPA的还原脱溴产物主要有：tri-BBPA, di-BBPA, mono-BBPA和BPA; BDE-209被催化还原后主要得到nano-BDEs-di-BDEs的产物,而BDE-47则被降解为DE～tri-BDEs。它们的还原脱溴过程都是以氢原子逐步取代溴原子,从n-bromo-BPA/DE依次转化为(n-1)-bromo-BPA/DE而实现的。由上述结果可以看出,TBBPA和BDE-47还原后的产物仍然具有一定的环境危害,有必要对其进行进一步的降解处理。论文对还原-氧化两步法去除典型溴代阻燃剂的可行性进行了探讨,即利用还原后剩余的双金属颗粒与加入的H202形成类Fenton体系,对目标污染物的完全脱溴产物进行后续的氧化分解。两步处理法实现了TBBPA (5.0 mgL-1)的完全脱溴,并使其脱溴产物双酚A(BPA)的去除效率达到99.2%；同样,BDE-47先被彻底脱溴为联苯醚(DPE),随后DPE得到快速彻底的氧化分解。而单独的类Fenton氧化对TBBPA和BDE-47的处理效果很不理想。类Fenton氧化过程还可以充分利用还原后体系中所剩余的纳米Fe-Ag颗粒。GC-MS和LC-MS/MS的分析结果表明,BPA和DPE的氧化产物包括羟基化产物、二芳基断裂反应产物以及开环产物,据此可以推断·OH自由基进攻是类Fenton氧化的主要作用途径。此外,发光菌的急性毒性实验结果表明：BDE-47的还原脱溴产物表现出更大的急性毒性,而随后的类Fenton氧化反应又使溶液几乎完全除毒。可见,还原-氧化两步处理法取得了理想的环境效果。更多还原

【Abstract】 Brominated flame retardants (BFRs) have been used as important additives in synthetic polymers, such as plastics, textiles, electronics/electrical, transportation packaging, construction materials and other fire prevention materials. Due to leaks, spills, and releases from industrial sourses, they inevitably comtaminate the enviroment. A "two-stage reduction/subsequent oxidation" (T-SRO) process was employed to remove BFRs by the combination of first Fe-Ag debromination and succeeding Fenton-like decomposition.The Fe-Ag bimetallic nanoparticles with core-shell structure were successfully synthesized by the liquid phase reduction method, depositing of Ag onto nanoscale Fe surface. The characterization results revealed that the displacement plating produced a non-uniform overlayer of Ag additive on iron; the as-synthesized bimetallic nanoparticles were spherical with diameters of 20-100 nm aggregated in the form of chains and a surface area of 72 m2 g-1. The three characteristic peaks in XRD spectrum appeared at 44.66 (main peak),64.34 and 38.06°correspond to cubic a-Fe (110,200) and Ag (111) diffraction peaks, respectively.Batch studies demonstrated that the tetrabromobisphenol A (TBBPA,2 mg L-1) solution was completely degraded in 20 min over Fe-Ag nanoparticles under ultrasound (US). It indicated that both the deposition of Ag and US played important roles in the reduction of TBBPA. The effects of Fe-Ag bimetallic nanoparticles loading, initial TBBPA concentration, pH of the solution, Ag loading and temperature on the reduction efficiency of TBBPA were investigated. Reaction conditions were determined selectively as metal addition of 0.4 g L-1, Ag loading of 1 wt.%, initial TBBPA concentration of 2 mg L-1, pH=6.0±0.5, T=30℃.The enhanced debromination of TBBPA, decabromodiphenyl ether (BDE-209) and 2,2’,4,4’-tetrabromodiphenyl ether (BDE-47) with Fe-Ag nanoparticles under microwave (MW) radiation was studied. The rates of debromination revealed that MW irradiation could accelerate the reductive degradation obviously. Attempts were made to compare degradation efficiency under microwave and conventional heating condition, which demonstrated that the thermal effect of MW radiation is the main factor to promote the debromination of TBBPA or PBDEs. The effects of Fe-Ag dosage and MW energy level on the degradation efficiency were also investigated. Moreover, the number of bromines could have an effect on the stability against reduction of PBDEs. Major reduction products of TBBPA and PBDEs were identified by LC-MS/MS and GC-MS, respectively. TBBPA was transformed to tri-BBPA, di-BBPA, mono-BBPA and BPA; di-to nona-brominated congeners were formed during BDE-209 reduction; and DE to tri-BDEs were observed in BDE-47 reduction. The degradation possibly proceeds through stepwise debromination from n-bromo- to (n-1)-bromo-BPA/DE, with bromine being sequentially substituted by hydrogen.It can be seen that the partial or complete debrominated products still pose a threat to the environment and need to be treated further. In this study, the feasibility and effectiveness of the removal of BFRs by T-SRO process were investigated. TBBPA was transformed to bisphenol A (BPA) completely by Fe-Ag/US and then BPA was 99.2% oxidized by the homogeneous Fe-Ag/H2O2/US system. Meanwhile, the T-SRO process resulted in a efficient debromination of BDE-47 and a 99.2% decrease in diphenyl ether (DPE) concentration. However, TBBPA and BDE-47 were difficult to be degraded by Fenton-like processes alone. Fenton-like reactions could make full use of the remaining Fe-Ag nanoparticles after reduction stage. LC-MS/MS and GC/MS were employed to monitor the main intermediates and final products during BPA/DPE oxidation. On the basis of these analysis, reactions with·OH radical were identified as the major pathways in the Fenton-like system.In addition, luminescent bacteria test showed that the acute toxicity of the original solution (before reduction) was evidently lower than that of Fe-Ag/US reduction-treated solution, but no toxicity was detected after the Fenton-like oxidation processes. Evidence for the significance of a T-SRO treatment to decompose BDE-47 was presented.更多还原