Remediation of polybrominated diphenyl ethers in soil using Ni/Fe bimetallic nanoparticles: Influencing factors, kinetics and mechanism

https://doi.org/10.1016/j.scitotenv.2014.03.039Get rights and content

Highlights

  • Ni/Fe bimetallic nanoparticles could effectively degradate BDE209 in soil.

  • The effects of various factors on remediation of BDE209 in soil using Ni/Fe were considered.

  • The degradation of BDE209 was a process of stepwise debromination from nBr to (n  1)Br.

  • A possible debromination pathway and mechanism about removal of BDE209 in soil were proposed.

Abstract

Polybrominated diphenyl ethers (PBDEs) are commonly used as additive flame retardants in all kinds of electronic products. PBDEs are now ubiquitous in the environment, with soil as a major sink, especially in e-waste recycling sites. This study investigated the degradation of decabromodiphenyl ether (BDE209) in a spiked soil using Ni/Fe bimetallic nanoparticles. The results indicated that Ni/Fe bimetallic nanoparticles are able to degrade BDE209 in soil at ambient temperature and the removal efficiency can reach 72% when an initial pH of 5.6 and at a Ni/Fe dosage of 0.03 g/g. A declining trend in degradation was noticed with decreasing Ni loading and increasing of initial BDE209 concentration. The degradation products of BDE209 were analyzed by GC-MS, which showed that the degradation of BDE209 was a process of stepwise debromination from nBr to (n  1)Br. And a possible debromination pathway was proposed. At last, the degradation process was analyzed as two-step mechanism, mass transfer and reaction. This current study shows the potential ability of Ni/Fe nanoparticles to be used for removal of PBDEs in contaminated soil.

Introduction

Polybrominated diphenyl ethers (PBDEs) have been widely used as brominated flame retardants in various industrial products, especially in electronic and telecommunication equipment (Mrof et al., 2005). It is estimated that 67,000 metric tons/year of PBDEs may have been released into the environment via electronic waste generation alone (Kwan et al., 2013). These compounds are highly recalcitrant to different types of degradation (Kwan et al., 2013). As a result, PBDEs are ubiquitously detected in the environment. Due to their high hydrophobicity and high octanol/water partition coefficients (Kow), PBDEs tend to accumulate in soil, particularly in e-waste disposal and recycling sites. As pointed by Wang et al. (2011), the total concentration of PBDEs (ΣPBDEs) in soil ranged from 4.8 to 533 ng/g dry wt near a typical e-waste recycling site in South China.

PBDEs pose various adverse effects, on human and environmental health, particularly when they accumulate in living organisms, including teratogenicity and carcinogenicity, etc. (Kierkegaard et al., 1999). Therefore, there has been an urgent need for developing effective remediation technologies to eliminate PBDEs in contaminated soils.

The reported methods for remediation of PBDEs contaminated soil include biodegradation (Vonderheride et al., 2006), phytoremediation (Kevin et al., 2006), electrokinetic remediation (Wu et al., 2012) and electric-magnetic methods (Wu et al., 2013a, Wu et al., 2013b). Recently, various nanomaterials, especially those based on nanoscale zero-valent iron (nZVI) have offered a new approach for developing the next generation of environmental remediation technologies. Numerous publications have demonstrated that nanoscale zero-valent iron (nZVI) can be effectively used for soil in-situ remediation of several contaminant groups, such as chlorinated organic compounds, toxic metals and inorganic compounds (Li et al., 2007). However, there is a lack of investigations of its application for PBDEs contaminated soil remediation.

However, previous work has shown that nZVI was able to effectively degrade PBDEs in the aqueous solution (Li et al., 2007, Fang et al., 2011a). For instance, Shih and Tai (2010) reported that nZVI was able to degrade 90% BDE209 in water within 40 min at various initial pHs. The Fang group (Fang et al., 2011b) showed that nZVI prepared from steel pickling liquor degraded 95% of tetrahydrofuran (THF) in water within 24 h at 4 g/L.

While over the years of research, researchers have identified several constraints with nZVI. First, due to the extremely small size and high surface energy, nZVI particles are vulnerable to aggregation via Van der Waals and magnetic attraction forces, hence diminishing their reaction effectiveness (Phenrat et al., 2007). Second, the formation of iron oxide or hydroxide on the surface of nZVI (Li et al., 2006) also decreases the electron transfer and reductive reactivity. Third, the reactivity of nZVI alone was often found insufficient for degrading recalcitrant chemicals such as halogenated chemicals. To prevent the aggregation of nanoparticles, researchers found that loading a second metal catalyst such as Ni or Pd on nZVI can greatly speed up the reaction rate (Fang et al., 2011a, Choi et al., 2008, Choi et al., 2009). Based on literature, bimetallic nanoparticles have been investigated to enhance the reactivity and mobility of nanoparticles. Thus, they have been used to employ for the remediation of Persistent Organic Pollutants (POPs) in soil. For example, Pd/Fe0 bimetallic nanoparticles show significant performance on catalytic dechlorination of polychlorinated biphenyls (PCBs) and gamma-hexachlorocyclohexane (γ-HCH) in soil (He et al., 2009, Singh et al., 2012). Recently, Fang et al. utilized Ni as a catalyst to synthesize Ni/Fe bimetallic nanoparticles, which demonstrated about 53-fold faster debromination rate for BDE209 than plain nZVI (Fang et al., 2011a). And Ni was shown to have better corrosion stability and lower cost while compared to Pd (Theron et al., 2008). However, the degradation of PBDEs in soil using the nano bimetallic Ni/Fe particles needs yet to be explored.

The objectives of this study were to: 1) investigate the degradation effectiveness of BDE209 in soil by Ni/Fe bimetallic nanoparticles, 2) test the influencing factors (pH, dosage of the nanoparticles and BDE209 initial concentration, and Ni loading), and 3) identify the reaction intermediates and products and elucidate the degradation pathways and mechanisms.

Section snippets

Chemicals and materials

Decabromodiphenyl ether (BDE209 > 98%), ferrous sulfate (FeSO4·7H2O,>99%), sodium borohydride (NaBH4 > 98%), nickel chloride (NiCl2·6H2O, > 99%), polyvinylpyrrolidone (PVP, K-30), and ethanol (EtOH, 99.7%) were purchased from Tianjin Damao Company. Acetonitrile and methanol (HPLC grade) were obtained from Tianjin Kermel Chemical Reagents Company. All chemicals were used as received without further purification. We have demonstrated the preparation and characterization of Ni/Fe bimetallic

Effect of Ni/Fe dosage

As shown in Fig. 1, the variations on removal efficiency during the initial phase of reaction showed a marked increase, and then tended to be balanced in the late phase of reaction. Finally, the reaction achieved a balance within 72 h. And BDE209 removal efficiency increased with the increasing Ni/Fe dosage. An increase of removal efficiency ranged from 21.19% to 52.86% (increasing nearly 32%) when the dosage increased from 0.01 g/g to 0.02 g/g. But it enhanced by 12% when the dosage increased

Conclusion

As mentioned above, the use of nZVI and modified-nZVI has been studied intensely for dehalogenation of halogenated organic in aqueous phase. But knowledge about the applicability of nZVI for the remediation of PBDEs contaminated soil is poorly understood. Laboratory experiments presented here involved the preparation of Ni/Fe bimetallic nanoparticles and investigation of remediation of PBDEs in soil using Ni/Fe nanoparticles. Information obtained from these experiments will lead to the

Conflict of interest

We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of the manuscript entitled, “In-situ Remediation of Polybrominated Diphenyl Ethers in Soil Using Ni/Fe Bimetallic Nanoparticles: Influencing Factors, Kinetics and

Acknowledgments

This research was supported by the Guangdong Technology Research Centre for Ecological Management and Remediation of Urban Water Systems (2012gczxA005), Science and Technology Planning Project of Guangdong Province (2012B031000015) and the Scientific Research Foundation of the Graduate School of South China Normal University (2012kyjj239).

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