Kinetics and pathways for the debromination of polybrominated diphenyl ethers by bimetallic and nanoscale zerovalent iron: Effects of particle properties and catalyst

Abstract

Polybrominated diphenyl ethers (PBDEs) are recognized as a new class of widely-distributed and persistent contaminants for which effective treatment and remediation technologies are needed. In this study, two kinds of commercially available nanoscale Fe° slurries (Nanofer N25 and N25S), a freeze-dried laboratory-synthesized Fe° nanoparticle (nZVI), and their palladized forms were used to investigate the effect of particle properties and catalyst on PBDE debromination kinetics and pathways. Nanofers and their palladized forms were found to debrominate PBDEs effectively. The laboratory-synthesized Fe° nanoparticles also debrominated PBDEs, but were slower due to deactivation by the freeze-drying and stabilization processes in the laboratory synthesis. An organic modifier, polyacrylic acid (PAA), bound on N25S slowed PBDE debromination by a factor of three to four compared to N25. The activity of palladized nZVI (nZVI/Pd) was optimized at 0.3 Pd/Fe wt% in our system. N25 could debrominate selected environmentally-abundant PBDEs, including BDE 209, 183, 153, 99, and 47, to end products di-BDEs, mono-BDEs and diphenyl ether (DE) in one week, while nZVI/Pd (0.3 Pd/Fe wt%) mainly resulted in DE as a final product. Step-wise major PBDE debromination pathways by unamended and palladized Fe° are described and compared. Surface precursor complex formation is an important limiting factor for palladized Fe° reduction as demonstrated by PBDE pathways where steric hindrance and rapid sequential debromination of adjacent bromines play an important role.

Removing polybrominated diphenyl ethers in pure water using Fe/Pd bimetallic nanoparticles

“…The removal efficiency of BDE209 in the presence of Pd was more than 3.5 times higher than that without Pd, indicating the engagement of Pd (presumably as a catalyst) in the degradation. This result also agreed with other reports in which rapid dehalogenation occurred in the presence of catalyst Pd [16,17,19]. In addition to potential catalysis by Pd, the large surface area of nanoparticles is also expected to contribute to the removal of PBDEs [28].…”

“…Rapid removal of BDE209 was observed, similar to the results from the acetone/water system [19]. The removal efficiency of BDE209 in the presence of Pd was more than 3.5 times higher than that without Pd, indicating the engagement of Pd (presumably as a catalyst) in the degradation.…”

“…A pseudo-first-order kinetic model was applied to describe degradation of BDE209 [19]. Observed degradation rate constants (k obs ) were calculated according to the following expressions: The residual THF in water was shown in Fig.…”

“…Iron (Fe)-based bimetallic nanoparticles have been tested to degrade PBDEs in the presence of organic solvents [9,[16][17][18]. In such systems, catalytic hydrogenation was proposed as the major pathway for the debromination of PBDEs [19]. Since water could provide protons more quickly than organic co-solvents such as methanol, the degradation efficiency was usually inhibited by organic co-solvents [20][21][22].…”

Reductive transformation of hexabromocyclododecane (HBCD) by FeS

“…Recent studies showed that zero-valent iron (ZVI) could reductively transform TBBPA, decaBDE and HBCD, and that the reduction rates tended to increase with increasing surface area of ZVI (Keum and Li, 2005;Lin et al, 2012;Tso and Shih, 2014;Yu et al, 2012;Zhuang et al, 2012). Bimetallic nanoparticles (such as Ni/Fe, Pd/Fe and Ag/Fe) were also reported to be able to rapidly debrominate either TBBPA or decaBDE (Fang et al, 2011;Huang et al, 2013;Luo et al, 2010).…”