Dehalogenation of Polybrominated Diphenyl Ethers and Polychlorinated Biphenyl by Bimetallic, Impregnated, and Nanoscale Zerovalent Iron

Abstract

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 zero-valent, which shows the difficulty with in-situ synthesis of a significant fraction of zero-valent iron in the micro-porous material. Related factors that likely hinder the reaction with nZVI/Pd-AC are the heterogenous distribution of nZVI and Pd on activated carbon and/or immobilization of hydrophobic organic contaminants at the adsorption sites thereby inhibiting contact with nZVI.

Catalytic dechlorination of Aroclor 1242 by Ni/Fe bimetallic nanoparticles

“…8 also shows bimetallic nZVI systems had a greater reactivity than that of monometallic nZVI. It was proposed that the role of metal additives in enhancing reactivity could be ascribed to the galvanic corrosion [8] and the production of atomic hydrogen [9,10]. As seen in Fig.…”

“…In one instance, the reactivity of nZVI was found to be markedly decreased with the increased reaction time due to surface inactivation, especially in humid conditions [7]. Clearly, bimetallic nanoparticles were superior reductants for PCBs, whereby the metal additives serve to collect H 2 generated from the iron corrosion reaction and decompose it into atomic H, which can be utilized to replace the chlorine in PCBs [8][9][10]. The PCBs adsorbed on Pd or Pd/Fe surfaces are dechlorinated by the active hydrogen species dissolved in Pd lattice.…”

Degradation of γ-HCH spiked soil using stabilized Pd/Fe0 bimetallic nanoparticles: Pathways, kinetics and effect of reaction conditions

“…Coating the surface of nFe 0 with a small amount of second metal (Pd, Pt, Ni) which possesses catalytic activity, significantly enhances the degradation rate of contaminants relative to nFe 0 alone [11][12][13]. Several researchers have successfully applied iron based bimetallic nanoparticles such as Pd/Fe, Pt/Fe, Ni/Fe, Cu/Fe for remediation of pollutants like organic chlorinated hydrocarbons [14,15], polychlorinated biphenyls [16], nitrate [11,17], heavy metals [18], etc.…”

Ex-Situ Remediation Technologies for Environmental Pollutants: A Critical Perspective

“…The more sophisticated microbial dehalogenation types involve the use of microwave-induced and UV-photolytic process (Li et al 2012a ), nanoparticle iron (Zhuang et al 2011 ), and ZVI (Xiu et al 2010 ). In most cases, metals as such or in the form of nanoparticles or biocells are used as electron donors in dehalogenation processes as summarized in Table 6 .…”