Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305-4020, USA.
Environ Sci Technol. 2011 Jun 1;45(11):4896-903. doi: 10.1021/es104312h. Epub 2011 May 10.
Nanoscale zerovalent iron particles (nZVI), bimetallic nanoparticles (nZVI/Pd), and nZVI/Pd impregnated activated carbon (nZVI/Pd-AC) composite particles were synthesized and investigated for their effectiveness to remove polybrominated diphenyl ethers (PBDEs) and/or polychlorinated biphenyls (PCBs). Palladization of nZVI promoted the dehalogenation kinetics for mono- to tri-BDEs and 2,3,4-trichlorobiphenyl (PCB 21). Compared to nZVI, the iron-normalized rate constants for nZVI/Pd were about 2-, 3-, and 4-orders of magnitude greater for tri-, di-, and mono-BDEs, respectively, with diphenyl ether as a main reaction product. The reaction kinetics and pathways suggest an H-atom transfer mechanism. The reaction pathways with nZVI/Pd favor preferential removal of para-halogens on PBDEs and PCBs. X-ray fluorescence mapping of nZVI/Pd-AC showed that Pd mainly deposits on the outer part of particles, while Fe was present throughout the activated carbon particles. While BDE 21 was sorbed onto activated carbon composites quickly, debromination was slower compared to reaction with freely dispersed nZVI/Pd. Our XPS and chemical data suggest about 7% of the total iron within the activated carbon was zerovalent, which shows the difficulty with in-situ synthesis of a significant fraction of zerovalent iron in the microporous material. Related factors that likely hinder the reaction with nZVI/Pd-AC are the heterogeneous distribution of nZVI and Pd on activated carbon and/or immobilization of hydrophobic organic contaminants at the adsorption sites thereby inhibiting contact with nZVI.
纳米零价铁颗粒（nZVI）、双金属纳米颗粒（nZVI/Pd）和负载 nZVI/Pd 的活性炭（nZVI/Pd-AC）复合颗粒被合成并研究了其去除多溴二苯醚（PBDEs）和/或多氯联苯（PCBs）的效果。nZVI 的钯化促进了单溴至三溴二苯醚和 2,3,4-三氯联苯（PCB 21）的脱卤动力学。与 nZVI 相比，nZVI/Pd 的铁归一化速率常数对于三溴、二溴和单溴二苯醚分别约为 2、3 和 4 个数量级，主要反应产物为二苯醚。反应动力学和途径表明存在 H 原子转移机制。nZVI/Pd 的反应途径有利于优先去除 PBDEs 和 PCB 上的对位卤原子。nZVI/Pd-AC 的 X 射线荧光映射表明，Pd 主要沉积在颗粒的外部，而 Fe 则存在于整个活性炭颗粒中。虽然 BDE 21 很快被活性炭复合材料吸附，但与自由分散的 nZVI/Pd 反应相比，脱溴反应较慢。我们的 XPS 和化学数据表明，活性炭中约有 7%的总铁为零价铁，这表明在微孔材料中原位合成大量零价铁具有一定的难度。可能阻碍 nZVI/Pd-AC 反应的相关因素包括 nZVI 和 Pd 在活性炭上的不均匀分布和/或疏水性有机污染物在吸附位点的固定化，从而抑制了与 nZVI 的接触。
