Abiotic transformation of hexabromocyclododecane by sulfidated nanoscale zerovalent iron: Kinetics, mechanism and influencing factors

Accepted Manuscript Abiotic transformation of hexabromocyclododecane by sulfidated nanoscale zerovalent iron: Kinetics, mechanism and influencing factors Dan Li, Xifen Zhu, Yin Zhong, Weilin Huang, Ping'an Peng PII:

S0043-1354(17)30377-9

DOI:

10.1016/j.watres.2017.05.019

Reference:

WR 12898

To appear in:

Water Research

Received Date: 30 November 2016 Revised Date:

26 April 2017

Accepted Date: 8 May 2017

Please cite this article as: Li, D., Zhu, X., Zhong, Y., Huang, W., Peng, Ping'., Abiotic transformation of hexabromocyclododecane by sulfidated nanoscale zerovalent iron: Kinetics, mechanism and influencing factors, Water Research (2017), doi: 10.1016/j.watres.2017.05.019. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Fe3+

S2-

S22-

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Fe2+

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Abstract ART

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Br Br Br

Br

Br Br

Br

Br Br

Iron oxides FeS/FeS2

e-

Fe0

e-

e-

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HBCD HBCD

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Br

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Br

Br

TBCDe

e-

TBCDe

DBCDi DBCDi

e-

e-

e-

e-

e-

e-

e-

e-

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Abiotic transformation of hexabromocyclododecane by sulfidated nanoscale

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zerovalent iron: kinetics, mechanism and influencing factors

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State Key Laboratory of Organic Geochemistry

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Dan Lia,c, Xifen Zhua,c, Yin Zhonga,*, Weilin Huangb, Ping’an Penga

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Guangzhou Institute of Geochemistry, Chinese Academy of Sciences

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Wushan, Guangzhou 510640, China

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b

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Department of Environmental Sciences, Rutgers

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The State University of New Jersey,

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14 College Farm Road, New Brunswick, NJ 08901 USA

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University of Chinese Academy of Sciences, Beijing 100049, China

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*Corresponding author

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State Key Laboratory of Organic Geochemistry

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Guangzhou Institute of Geochemistry

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Chinese Academy of Sciences

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Wushan, Guangzhou 510640, China

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Tel.: +86-20-85290142

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Fax: +86-20-85290117

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E-mail: [email protected]

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ABSTRACT Recent studies showed that sulfidated nanoscale zerovalent iron (S-nZVI) is a

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better reducing agent than nanoscale zerovalen iron (nZVI) alone for reductive

27

dechlorination of several organic solvents such as trichloroethylene (TCE) due to the

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catalytic role of iron sulfide (FeS). We measured the rates of transformation of

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hexabromocyclododecane (HBCD) by S-nZVI and compared them to those by FeS,

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nZVI, and reduced sulfur species. The results showed that: i) HBCD (20 mg L-1) was

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almost completely transformed by S-nZVI (0.5 g L-1) within 12 h; ii) the reaction with

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β-HBCD was much faster than with α- and γ-HBCD, suggesting the diastereoisomeric

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selectivity for the reaction by S-nZVI; and iii) the reaction with S-nZVI was 1.4-9.3

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times faster than with FeS, S2- and nZVI, respectively. The study further showed that

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the HBCD reaction by S-nZVI was likely endothermic, with the optimal solution pH

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of 5.0, and could be slowed in the presence of Ca2+, Mg2+, NO3 , HCO3 and Cl , and

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by increasing ionic strength, solvent content and initial HBCD concentration, or

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decreasing

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tetrabromocyclododecene and dibromocyclododecadiene were the products. XPS

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spectra indicated that both Fe(II) and S(-II) on the S-nZVI surface were oxidized

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during the reaction, suggesting that FeS might act as both catalyst and reactant. The

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study not only demonstrated the superiority of S-nZVI over other well-known reactive

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reagents, but also provided insight to the mechanisms of the reaction.

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Keywords: HBCD; S-nZVI; Transformation; Mechanism; Influencing factor

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S-nZVI

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1. Introduction Hexabromocyclododecane (HBCD) is a common brominated flame retardants

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(BFRs) primarily employed in extruded or expanded polystyrene, upholstery textiles

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and electric and electronic equipment to decrease the risk of fire (Marvin et al., 2011).

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Technical mixtures of HBCD are comprised predominately of α-, β- and γ-HBCD

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diastereoisomers (Marvin et al., 2011). As an additive flame retardant, HBCD has a

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potential to be released into the environment during the processes of production, use,

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treatment and disposal (Ueno et al., 2010). In the last decade, HBCD has been

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detected at high levels in various environmental matrices (Covaci et al., 2006; La

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Guardia et al., 2013; Morris et al., 2004). For example, Morris et al. (2004) have

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reported that the levels of HBCD in landfill leachates from Dutch were up to 36 mg

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kg-1 dry weight. The concentrations of HBCD in inland and coastal sediments from

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Durban Bay in South Africa were as high as 27 mg kg-1 dry weight (La Guardia et al.,

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2013). HBCD also can be accumulated in organisms and enriched in the human body

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through food chain (Covaci et al., 2006). Toxicity tests indicated that HBCD has

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cytotoxicity, hepatotoxicity, neurotoxicity and developmental toxicity, and can act as

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an endocrine disrupter (Marvin et al., 2011; Ronisz et al., 2004). Indeed, due to its

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persistent, bioaccumulative and toxic properties, HBCD has been identified as one of

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the persistent organic pollutants (POPs), which are priority pollutants targeted by the

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Stockholm Convention (United Nations Environment Programme, 2013). It is

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therefore of great significance to develop effective methods to remove HBCD from

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contaminated environments.

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ACCEPTED MANUSCRIPT Several methods, including photolysis (Yu et al., 2015; Zhou et al., 2014),

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biodegradation (Davis et al., 2006; Peng et al., 2015) and abiotic transformation (Li et

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al., 2016a; Lo et al., 2012; Tso and Shih, 2014), have been proposed as potential

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approaches for eliminating HBCD from contaminated sites. Among them, photolysis

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and biodegradation have been reported to suffer from some inherent limitations.

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Photolysis is easy to be inactivated and the photochemical active substances (i.e.,

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hydroxyl radical) are difficult to be separated and reused, increasing the difficulties of

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the practical application of photolysis (Peng et al., 2015). As to biodegradation, on the

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other hand, it is always time-consuming to isolate and incubate microbes capable of

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degrading HBCD. In fact, only two pure HBCD-degrading bacteria have been isolated

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and reported until now (Yamada et al., 2009; Peng et al., 2015). Therefore, abiotic

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transformation using chemical agents may be a better scheme to deal with HBCD due

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to its high efficiency and low cost (Tso and Shih, 2014).

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Prior studies showed that three types of chemical reductants, including reduced

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sulfur species (HS- and Sn2-), nanoscale zerovalent iron (nZVI) and iron sulfide (FeS),

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are able to mediate reductive transformation of HBCD (Li et al., 2016a; Lo et al.,

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2012; Tso and Shih, 2014). Lo et al. (2012) demonstrated that HS- and Sn2- have high

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reactivities towards HBCD, with rate constants of 8.9 × 10-4 and 2.2 × 10-2 M-1 s-1 at

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40°C, respectively. Tso and Shih (2014) reported that nZVI was also able to

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reductively transform HBCD, with a surface area normalized pseudo-first-order rate

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constant of 4.22 × 10-3 L m-2 min-1 at room temperature. Our recent study found that

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HBCD could be reductively transformed by FeS with a transformation rate of 8.55 ×

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ACCEPTED MANUSCRIPT 10-2 h-1 at about 25°C (Li et al., 2016a). These reported reducing agents may have

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important potential for remediation of HBCD-contaminated environments (Li et al.,

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2016a; Tso and Shih, 2014). Note, however, that the results of these previous studies

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could not be compared directly because different experimental conditions were used

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in different studies. It is thus apparent that efforts should be made to compare the

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efficiencies of the three kinds of abiotic reductants for HBCD under the same

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experimental conditions. Based on this, a critical next step is to screen more efficient

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reductants for abiotic transformation of HBCD.

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Sulfidated nanoscale zerovalent iron (S-nZVI) is a new type of multicomponent reducing

agents,

which

have

unique

physicochemical

properties

due

to

complementary or synergistic effects caused by interactions between nZVI and iron

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sulfides (Kim et al., 2011). These properties of S-nZVI have led a growing number of

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researchers to investigate its ability to remove several ubiquitous pollutants, i.e.,

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trichloroethylene (TCE), pertechnetate (99TcO4-), chromate (Cr), cadmium (Cd), and

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tetrabromobisphenol A (TBBPA) occurred in the environments (Du et al., 2016; Fan

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et al., 2013, 2016; Li et al., 2016b; Su et al., 2015). To date, however, no information

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is available for the reactivity of S-nZVI towards POPs. This represents a significant

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knowledge gap, given the global concerns on the occurrence and remediation of POPs

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in the environment (United Nations Environment Programme, 2013). Therefore,

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exploring the reactivity of S-nZVI towards HBCD will help to narrow such a

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knowledge gap. Note also that the chemical structure of HBCD is far more complex

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than those of the already-tested chemicals that can be transformed by S-nZVI. More

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ACCEPTED MANUSCRIPT specifically, HBCD is distinctive due largely to the fact that it theoretically consists of

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at least ten diastereoisomers (Heeb et al., 2005) and that none of the already-tested

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chemicals are diastereoisomeric pollutants. Indeed, the stereochemistry of HBCD is

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even more complex than that of another halogenated organic pollutant

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1,2,3,4,5,6-hexachlorocyclohexane (HCH, a well-known POP; Heeb et al., 2005).

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Further, there are substantial differences among individual HBCD diastereoisomers in

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stability, polarity, solubility, dipole moment, and so on (Heeb et al., 2005). These

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differing properties likely result in diastereoisomers-specific reductive transformation

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profiles of HBCD by S-nZVI, which deserves special attention.

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Turcio-Ortega et al. (2012) reported that the corrosion of S-nZVI was highly

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dependent on solution conditions. There have been only a few studies examining the

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influences of different solution conditions on the reactivity of S-nZVI towards target

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pollutants until now (Kim et al. 2013, 2014; Su et al., 2015). Despite this, contrasting

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effects of a given parameter of reaction solution were observed. For example, the rate

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of TCE reduction by S-nZVI was found to increase with pH of the reaction solution,

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when pH ranged from 6.3 to 9.0 (Kim et al., 2013). In contrast, pH of the reaction

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solution was reported to have no effect on the rate of Cd removal by S-nZVI in the pH

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range from 6.0 to 9.0 (Su et al., 2015). These findings suggest that the effects of

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solution conditions on the reactivity of S-nZVI may differ greatly between target

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pollutants. Thus, it is necessary to obtain a deep understanding of the reactivity of

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S-nZVI towards HBCD under various solution conditions to assess the potential of

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S-nZVI for remediation of HBCD-contaminated sites.

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by S-nZVI were explored and compared to those by the three kinds of abiotic

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reductants for HBCD (i.e., FeS, S2- and nZVI). Further, the effects of a variety of

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solution conditions (including different pH, ionic strength, inorganic ion, solvent

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content, temperature, S-nZVI dosage and HBCD concentration) on the transformation

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by S-nZVI were examined systematically. The results of this study will help to

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understand the reactivity of S-nZVI towards POPs (represented by HBCD) and pave

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the way for the application of abiotic reductants (especially S-nZVI) in the

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remediation of anoxic aquatic environments contaminated by HBCD.

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2. Materials and methods

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2.1. Chemicals reagents

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The technical HBCD mixtures containing α-HBCD (~20%), β-HBCD (~10%)

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and γ-HBCD (~70%) were obtained from Tokyo Chemical Industry (Tokyo, Japan).

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FeCl2 (ultra dry, 99.99%) and Na2S·9H2O (99.99%) were obtained from Alfa Aesar-A

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Johnson Matthey Company (MA, USA) and Aladdin Reagent Co. Ltd. (Shanghai,

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China), respectively. HCl (97%), NaOH (98%), NaCl (99.5%), NaHCO3 (99.5%),

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NaNO3 (99%), Ca(NO3)2 (96%), Mg(NO3)2·6H2O (98%), NaBH4 (98%) and Na2S2O4

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(99%) were obtained from Kermel (Tianjin, China). HPLC-grade ethanol (Merck,

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Darmstadt, Germany) and hexane (Honeywell Burdick & Jackson, NJ, USA) were

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used as received. The deionized water (18.2 MΩ cm) was autoclaved at 121°C for 20

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min, placed into an anaerobic glovebox (Super 1220/750, Mikrouna Co. Ltd.,

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ACCEPTED MANUSCRIPT Shanghai, China) filled with high purity N2 (99.999%), and then deoxygenated by

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purging with high purity N2 (99.999%) for at least 30 min before used for the

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preparation of reaction solution.

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2.2. Synthesis of nZVI, S-nZVI and FeS

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The three different solids (nZVI, S-nZVI and FeS) used in this study were

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prepared following three different procedures performed in an anaerobic glovebox

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filled with high purity nitrogen (99.999%). Both nZVI and S-nZVI (S/Fe molar ratios

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of 0.2) were synthesized with the methods of Li et al. (2016b) with minor

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modification. Detailed procedures were described in Supporting Information (Text

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S1). FeS was synthesized by reacting FeCl2 with Na2S·9H2O as described in Li et al.

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(2016a). The resulting FeS precipitate was collected and treated in the similar

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manners for nZVI and S-nZVI. The Brunauer-Emmett-Teller (BET) specific surface

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areas of the synthesized nZVI (8.6 m2 g-1), FeS (33.6 m2 g-1) and S-nZVI (19.9 m2 g-1)

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were quantified with the N2 physisorption isotherms measured on an ASAP 2020

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instrument (Micromeritics, Allanta, USA). The surface elemental compositions of

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S-nZVI before or after reaction with HBCD were examined on an ESCALAB-250

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X-ray photoelectron spectrometer (XPS; Thermo VG Scientific, West Sussex, UK)

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following the method described in Li et al. (2016b).

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2.3. Batch experiments

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Unless otherwise specified, all batch experiments were conducted at constant

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temperature in a mixture of water and ethanol (v/v, 50/50) and under O2-free

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conditions (within anaerobic glovebox) using 150 mL glass bottles screw-capped with 8

ACCEPTED MANUSCRIPT PTFE-lined silicone septa as the reactors. The batch reactors were wrapped in dark

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and mixed with a magnetic stirrer at 300 rpm. Ethanol was needed in reaction solution

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due to the low solubility of HBCD (Tso and Shih, 2014; Yu et al., 2015). For

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quantifying the rates of HBCD transformation by S2- (in sodium salt), FeS, nZVI or

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S-nZVI at solution pH 7.0 ± 0.1, the reactors were filled with 100 mL of aqueous

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suspension containing 0.5 g L-1 of solids (including FeS, nZVI or S-nZVI) or 1.6

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mmol L-1 S2- and 20 mg L-1 of HBCD. The dosage of 1.6 mmol L-1 S2- was used

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because it meant that the reaction solution contained 0.16 mmol S (equal to the total

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amount of S coated on surface of S-nZVI used in the ‘S-nZVI’ treatment with a

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dosage of 0.5 g L-1 S-nZVI with a S/Fe molar ratio of 0.2). They were run at 30°C and

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the reaction started as soon as the HBCD was introduced. At pre-designed time

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intervals, an aliquot (1 mL) of reaction suspension was transferred from each batch

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reactor and mixed with 20 µL of 2 M HCl for quenching the reaction and dissolving

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the reacting solid in a 5-mL glass vial with PTFE-lined cap. After the liquid had

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become clear, 3 mL of ethanol was injected into each vial, and the mixture was used

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for quantification of HBCD on an LC-MS with method described below. Total (∑)

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HBCD values were calculated by the summation of the three individual

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diasteroisomers (including α-, β- and γ-HBCD). The experimental controls without

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addition of any nanoparticle were prepared identically, showing no significant loss of

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HBCD (< 5%) during the experimental period.

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Experiments evaluating the effects of initial pH (3.0, 5.0, 7.0 and 9.0; adjusted

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with 0.1 M HCl or NaOH solution), ionic strength (0.01, 0.05 and 0.1 mol L-1; 9

ACCEPTED MANUSCRIPT controlled with NaCl), inorganic cations (Ca2+ and Mg2+; used as their respective 0.01

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mol L-1 nitrate salts) and inorganic anions (NO3-, HCO3- and Cl-; used as their

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respective 0.01 mol L-1 sodium salts) on the transformation efficiency of HBCD by

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S-nZVI were conducted in 150-mL glass bottles under similar experiment conditions

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as described above. The experiment conditions used to study the effects of these three

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influencing factors were kept constant: HBCD concentration, S-nZVI dosage, solvent

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content and temperature were kept at 20 mg L-1, 0.5 g L-1, 50% and 30°C,

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respectively.

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In addition, the effects of solvent content (25%, 50% and 75%, controlled with

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ethanol), temperature (10, 20, 30 and 40°C), initial concentration of S-nZVI (0.1, 0.5,

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1 and 2 g L-1) and HBCD (1, 5, 10 and 20 mg L-1) on the transformation of HBCD by

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S-nZVI were also investigated. The experiment conditions used to study the effects of

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these four influencing factors were kept constant: HBCD concentration, S-nZVI

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dosage, solvent content and temperature were kept at 20 mg L-1, 0.5 g L-1, 50% and

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30°C, respectively. When the effect of a given factor was investigated, the other three

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factors were kept constant. It should be noted that the temperature was set at 20°C

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rather than 30°C to examine the effect of initial concentrations of S-nZVI and HBCD

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on HBCD transformation by S-nZVI. Such temperature (20°C) was used in order to

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obtain more accurate transformation kinetics of HBCD, since preliminary experiments

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showed that the transformation rates of HBCD at the temperature of 30°C were too

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fast to be accurately determined.

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To analyze the transformation patterns of products of HBCD in S-nZVI system, 10

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mg L-1) and ethanol (v/v, 50/50) were taken into 5 mL glass bottles capped with open

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top closures with PTFE-lined silicone septa at sampling intervals, and then were

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acidized with HCl as mentioned above. The resulting solution was extracted three

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times with one mL of hexane for 10 min. The resulting extracts were combined,

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concentrated to one mL, and then used for analysis of HBCD products by GC-MS.

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Moreover, the transformation products of HBCD in the FeS, S2- and nZVI systems

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were also analyzed after reaction of 12 h for comparison of the transformation

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products of HBCD in the S-nZVI system.

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2.4. Instrument analysis

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The concentrations of α-HBCD, β-HBCD, and γ-HBCD and thus ∑HBCD were

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quantified on an Agilent 1200 series LC coupled to an Agilent 6410 electrospray triple

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quadrupole mass spectrometer according to the method described by He et al. (2013).

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The

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chromatography/mass spectrometry (Shimadzu GC/MS-QP 2010 Plus, Kyoto, Japan)

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according to the method reported by Li et al. (2016a). Details of the instrument

238

analysis and the QA/QC procedures in this study were provided in Supporting

239

Information (Text S2 and S3).

HBCD

byproducts

was

performed

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3. Results and discussion

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3.1. Transformation of HBCD in FeS, S2-, nZVI and S-nZVI systems

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The transformation patterns of HBCD in FeS, S2-, nZVI and S-nZVI systems 11

ACCEPTED MANUSCRIPT were shown in Fig. 1. All the transformation kinetics of HBCD with FeS, S2-, nZVI

245

and S-nZVI were well fitted by pseudo-first-order kinetic models (Table S1). As

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shown in Fig. 1A, after reaction of 12 h, 23.0% of HBCD was transformed by FeS,

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and the observed pseudo-first-order transformation rate constant kobs of HBCD with

248

FeS was 0.017 ± 0.002 h-1, which was in good agreement with our recent study (Li et

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al., 2016a). Approximately 74.5% of HBCD was removed by S2- in 12 h reaction,

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being comparable with the results of Lo et al. (2012). The kobs of HBCD in S2- system

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was 0.101 ± 0.006 h-1. In nZVI system, 75.8% of HBCD was transformed after

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reaction of 12 h, with a kobs of 0.117 ± 0.015 h-1, which was consistent with the work

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conducted by Tso and Shih (2014) who have reported that nZVI aggregates had a high

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reactivity towards HBCD and that the transformation kinetic of HBCD was well

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described by a pseudo-first-order rate model. In S-nZVI system, nearly 100% of

256

HBCD was rapidly removed in 12 h, with a kobs of 0.158 ± 0.019 h-1. It was 9.3, 1.6

257

and 1.4 times greater than the transformation rate of HBCD by FeS, S2- and nZVI,

258

respectively, highlighting the superior transformation ability of S-nZVI towards

259

HBCD. Such excellent transformation ability of S-nZVI indicated that S-nZVI could

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be a promising alternative to FeS, S2- and nZVI for remediation of

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HBCD-contaminated anoxic environments.

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The kobs values of three major HBCD diastereoisomers in S-nZVI system

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increased in the following order α-HBCD < γ-HBCD < β-HBCD (Fig. 1B, 1C, 1D

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and Table S1). This pattern suggested the diastereoisomeric selectivity of S-nZVI in

265

reductive transformation of organic pollutants, which has not yet been reported in 12

ACCEPTED MANUSCRIPT prior studies (Kim et al., 2011; Rajajayavel and Ghoshal, 2015; Han and Yan, 2016; Li

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et al., 2016). On the other hand, similar transformation pattern of HBCD

268

diastereoisomers was also observed in FeS, S2- and nZVI systems. Remarkably, it was

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found that the transformation efficiencies of the three major HBCD diastereoisomers

270

in S-nZVI system were much higher than those in FeS, S2- and nZVI systems. As

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shown in Fig. 1B, 1C, 1D and Table S1, the kobs values of α-, β- and γ-HBCD in

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S-nZVI system were 15.3, 7.1 and 12.5 times greater than those in FeS system,

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respectively. The kobs values of α-, β- and γ-HBCD in S-nZVI system were 4.0, 3.7

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and 1.8 times greater than those in S2- system, respectively. And the kobs values of α-,

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β- and γ-HBCD in S-nZVI system were 1.5, 1.0 and 1.1 times greater than those in

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nZVI system, respectively. These results indicated that a higher increase in the kobs of

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α-HBCD as compared to those of β- and γ-HBCD in S-nZVI system, which might be

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an advantage of S-nZVI for remediation of anoxic environments contaminated by

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α-HBCD. Such a finding is of interest, since the abundance and recalcitrance of

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α-HBCD has been well documented in both abiotic and biotic samples (Covaci et al.,

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2006; He et al., 2013).

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3.2. Transformation products and pathway of HBCD in FeS, S2-, nZVI and S-nZVI

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systems

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During the 12-h reaction, two transformation products were found through

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GC-MS

analysis

in

S-nZVI

system,

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tetrabromocyclododecene (TBCDe) and dibromocyclododecadiene (DBCDi) by

287

comparing their mass spectra with those of the corresponding transformation products 13

which

were

identified

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ACCEPTED MANUSCRIPT reported in the literature (Barontini et al., 2001; Davis et al., 2006; Li et al., 2016a).

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Details on identification of HBCD transformation products have been reported by our

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previous study (Li et al., 2016a). The transformation pattern of transformation

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products of HBCD in S-nZVI system was showed in Fig. 2A. The concentration of

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TBCDe first increased to reach its maximum after reaction of 4 h and then gradually

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decreased after reaction of 12 h, which suggested that TBCDe underwent further

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debromination as the reaction proceeded. The concentration of DBCDi steadily

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increased during the reaction of 12 h. On the basis of identified transformation

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products, the possible transformation pathway for the transformation of HBCD with

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S-nZVI was proposed in Fig. 2B. Briefly, HBCD might be debrominated via

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dibromoelimination to form TBCDe, followed by forming DBCDi. Two Br atoms

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were removed from two vicinal carbons, and then a double bond was formed between

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the two adjacent carbon atoms during each step. In contrast, hydrodebromination was

301

proposed as a potential dehalogenation routine for TBBPA by S-nZVI (Li et al.,

302

2016b). In a word, these results indicate that the reductive transformation of HBCD

303

by S-nZVI involves a dehalogenation routine completely different from that of other

304

brominated organic pollutants like TBBPA.

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The two transformation products (i.e., TBCDe and DBCDi) were also found in

306

FeS, S2-, and nZVI systems (Fig. 3), which indicated that the transformation pathways

307

of HBCD in FeS, S2-, and nZVI systems were similar to that in S-nZVI system. In fact,

308

Lo et al. (2012) have also proposed TBCDe and DBCDi as the only two

309

transformation products of HBCD in both HS- and Sn2- systems, although a conclusive 14

ACCEPTED MANUSCRIPT identification for TBCDe and DBCDi has not been achieved by the authors. While

311

Tso and Shih (2014) have found that the debromination efficiency of HBCD by nZVI

312

aggregates was not high and most of HBCD was only transformed to form less

313

brominated BCD byproducts, our recent study has shown that the non-brominated

314

transformation product cyclododecatriene (CDT) of HBCD could be detected in the

315

reaction solutions containing only 2% ethanol after 18 h of the reaction between

316

HBCD and the synthetic FeS (Li et al., 2016a). In this study, CDT was not detected in

317

FeS, S2-, and nZVI systems containing 50% ethanol during 12-h reaction, which

318

might due to 1) the difference of reactivity of reducing agents and experiment

319

conditions, and 2) the insufficiency of reaction time.

320

3.3. Transformation mechanism of HBCD in S-nZVI system

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TcO4-, Cr and Cd) with

(e.g., TCE and TBBPA) and inorganic pollutants (e.g.,

323

S-nZVI were surface-chemical processes (Du et al., 2016; Fan et al., 2013; Kim et al.,

324

2011; Li et al., 2016a; Su et al., 2015). Therefore, it is likely that the transformation of

325

HBCD by S-nZVI is also a surface-chemical reaction. In fact, the XPS analyses of the

326

surfaces of blank, control and HBCD-reacted S-nZVI gave some clues about the

327

mechanisms underlying the surface-chemical transformation of HBCD by S-nZVI

328

(Table 1 and Fig. 4). According to the Fe(2p) spectra (Table 1 and Fig. 4A-C), the

329

relative area of the peak (located at 707.3 eV) corresponding to Fe(II)-S species on

330

the surface of HBCD-reacted S-nZVI was remarkably lower than those on the surface

331

of blank and control S-nZVI. However, increased relative areas of the peaks (located

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333

HBCD-reacted S-nZVI as compared to the other two S-nZVI. These results indicated

334

that the Fe(II)-S species on S-nZVI surface had been involved in the transformation of

335

HBCD and were oxidized into oxides and hydroxyl species of Fe(III) during the

336

transformation. A similar phenomenon was observed by previous studies, which

337

examined the changes of the Fe species on the surface of FeS before and after reaction

338

with contaminants (i.e., Se, As and HBCD) on the basis of XPS analysis (Han et al.,

339

2013; Jeong et al., 2010; Li et al., 2016a). According to the O(1s) spectra (Table 1 and

340

Fig. 4D-F), an increased relative area of the peak (located at 530.0 eV) corresponding

341

to O2- species was found for HBCD-reacted S-nZVI, while an opposite patterns were

342

observed for OH- species and H2O species (located at 531.2 and 532.2 eV,

343

respectively). These results further demonstrated the formation of oxides and

344

hydroxyl species of iron on the surface of S-nZVI after the transformation of HBCD.

345

According to the S(2p) spectra (Table 1 and Fig. 4G-I), the relative area of the peak

346

(located at 161.4 eV) corresponding to S2- species on surface of HBCD-reacted

347

S-nZVI was lower than those on the surface of blank and control S-nZVI, while an

348

increased relative area of the peak (located at 162.3 eV) corresponding to S22- species

349

was observed in HBCD-reacted S-nZVI, indicating that the S2- species on surface of

350

S-nZVI might have been oxidized into S22- species during the reduction process of

351

HBCD. The oxidation of S2- species into S22- species on surface of FeS after reaction

352

with contaminants (i.e., As, HBCD and Se) has also been reported by previous studies

353

on the basis of XPS analysis (Jeong et al., 2010; Li et al., 2016a; Scheinost et al.,

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355

the surface of S-nZVI were oxidized during the transformation of HBCD by S-nZVI,

356

indicating the direct participation of Fe(II) and S(-II) on the surface of S-nZVI in the

357

transformation of HBCD. This finding provides new insights into the surface reaction

358

mechanisms underlying reductive transformation of organic pollutants by S-nZVI. As

359

proposed in prior studies (Kim et al., 2011; Rajajayavel and Ghoshal, 2015; Han and

360

Yan, 2016; Li et al., 2016b), the primary roles of FeS on the surface of S-nZVI in

361

enhancing reductive transformation of organic pollutants (e.g., TCE and TBBPA) are

362

(i) the facilitated conduction of electrons from the iron core (Kim et al., 2011; Li et al.,

363

2016b) and (ii) inhibiting hydrogen recombination (i.e., avoiding formation of H2

364

molecule) as it favors production of ‘atomic hydrogen’, which was believed to be the

365

highly reactive species for pollutant transformation (Han and Yan, 2016). In this study,

366

we found a second important role of FeS as it does participate in the reaction as a

367

reactant.

368

3.4. Effect of temperature on the transformation of HBCD by S-nZVI

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Generally speaking, a process limited by chemical reaction is highly sensitive to

370

change in temperature, and exploring the effect of temperature on such process is thus

371

important for obtaining insights into the reaction mechanism (Liou et al., 2005; Su

372

and Puls, 1999). As shown in Fig. 5 and Table S2, the kobs of HBCD by S-nZVI

373

depended strongly on the reaction temperature. The kobs values were 0.025, 0.074,

374

0.158 and 0.263 h-1 at temperature of 10, 20, 30 and 40°C, respectively, suggesting

375

that the transformation of HBCD by S-nZVI is an endothermic reaction and higher

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reaction temperature is favorable for HBCD transformation. Similar results were

377

reported by Tso and Shih (2014) who examined the effect of temperature on

378

transformation of HBCD by nZVI aggregates. The relationship between kobs and temperature T followed Arrhenius equation,

380

kobs = A exp (-Ea/RT), as evidenced by the linear ln kobs versus 1/T plot (R2 = 0.97, Fig.

381

S1). The activation energy Ea for the transformation of HBCD by S-nZVI was

382

estimated to be 57.83 kJ mol-1 (at the 95% confidence level). The Ea could be

383

considered as a measure of energy that HBCD and S-nZVI must overcome to

384

complete the reduction of HBCD and oxidation of S-nZVI. Although the overall

385

transformation process of HBCD in S-nZVI system may include the following five

386

steps: 1) convection and diffusion of HBCD from the solution to the S-nZVI surface,

387

2) adsorption of HBCD to the S-nZVI surface, 3) transformation of HBCD on the

388

surface, 4) transformation of intermediate products of HBCD to less brominated

389

compounds on the surface, and 5) diffusion of intermediate and final products from

390

the S-nZVI surface to the solution (Su and Puls, 1999), only the rate-limiting step

391

with highest Ea determines the kinetic of the reaction. Typically, diffusion requires

392

less energy (< 20 kJ mol-1) than surface-chemical reaction (Liou et al., 2005; Su and

393

Puls, 1999; Tso and Shih, 2014). Therefore, the high Ea (57.83 kJ mol-1) of this study

394

indicated that surface-chemical reaction rather than diffusion was the predominant

395

process for the transformation of HBCD by S-nZVI (Liou et al., 2005; Su and Puls,

396

1999; Tso and Shih, 2014), which was consistent with our results from XPS analysis

397

(see details in section 3.3). Taken together, the higher temperature has a positive effect

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on the transformation of HBCD by S-nZVI, which can be employed to design a more

399

efficient program for remediation of HBCD-contaminated anoxic environments.

400

3.5. Effect of pH on the transformation of HBCD by S-nZVI The pH of aqueous solution is one of the important environmental parameters,

402

which may significantly affect the stability of pollutants (e.g., hydrolysis) and the

403

surface properties of particles (e.g., corrosion and passivation) (Graham et al., 2004;

404

Song and Carraway, 2005). Previous studies have reported that the solution pH has a

405

remarkable impact on the hydrolysis of halogenated organic pollutants (Liu et al.,

406

2003; Song and Carraway, 2005). For example, HCH is one of the halogenated

407

alicyclic compounds having similar stereochemistry with HBCD, which can be

408

hydrolyzed under neutral and alkaline condition (Liu et al., 2003). In this study,

409

however, no hydrolysis of HBCD was observed as the solution pH ranged from 3.0 to

410

9.0 (data not shown).

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Fig. 6 showed the effect of solution pH (from 3.0 to 9.0) on HBCD

412

transformation by S-nZVI. The lowest transformation rate was found at the initial pH

413

of 3.0, wherein only 60% of HBCD was transformed after 12-h of reaction. This may

414

be due to a scenario that the acid solution caused faster corrosion and disappearance

415

of S-nZVI (Du et al., 2016; Su et al., 2015). Note that the solution pH after 12-h of

416

reaction was increased to 5.4 (Table S3), providing direct evidence for a

417

rapid consumption of H+. Furthermore, the production of a large amount of bubbles

418

(e.g., H2) was observed during the reaction, which might inhibit the adsorption of

419

HBCD on S-nZVI surface (Li et al., 2016c) and thus the transformation of HBCD.

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ACCEPTED MANUSCRIPT The highest kobs was observed at initial pH of 5.0 (Table S3), which declined

421

steadily as pH was increased up to 9.0. The decrease in transformation rate at pH of

422

9.0 might be due to the increase in the adsorption of OH- and formation of iron oxides

423

precipitates on the surface of S-nZVI, which could hinder the transport of the HBCD

424

and block the reactive sites on the surface of S-nZVI (Du et al., 2016; Su et al., 2015).

425

Indeed, it was observed that the solution pH of 9.0 was changed into 8.8 after 12-h of

426

reaction, indicating a consumption of OH- in the reaction solution (Table S3). A linear

427

regression analysis correlating constant kobs with solution pH (from 5.0-9.0) yielded

428

the following equation kobs = -0.013 pH + 0.241 (R2 = 0.97, Fig. S2). It suggested that

429

rate of the HBCD transformation by S-nZVI linearly decreased with pH in a range

430

from 5.0 to 9.0. Note, however, that coefficient factor (i.e., -0.013) for the correlation

431

was low, indicating that the change in transformation rate with varying pH could be

432

not abrupt.

433

3.6. Effect of ionic strength on the transformation of HBCD by S-nZVI

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The ionic strength over a range of 0.01-0.1 mol L-1 (typically occurred in

435

freshwater and seawater) had an adverse effect on the transformation of HBCD by

436

S-nZVI (Fig. S3 and Table S4). The kobs of HBCD was decreased from 0.082 to 0.045

437

h-1 as the ionic strength was increased from 0.01 to 0.1 mol L-1 (added as NaCl).

438

Moreover, there was a negative linear correlation (R2 = 0.96) between the rate

439

constant and the ionic strength (Fig. S4). Tso and Shih (2014) have reported that the

440

transformation rate constant of HBCD by nZVI aggregates decreased linearly as NaCl

441

concentration increased from 0.5 to 5.0 mmol L-1. The adverse effect of ionic strength

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ACCEPTED MANUSCRIPT on the transformation of HBCD by S-nZVI might be attributed to the following two

443

reasons: 1) the corrosion and passivation of iron species on the surface of S-nZVI

444

caused by elevated ionic strength of the solution (Kim et al., 2016; Lv et al., 2013);

445

and 2) the decrease of available reaction sites of S-nZVI surface due to the particle

446

aggregation of S-nZVI caused by elevated ionic strength of the solution (Kim et al.,

447

2013).

448

3.7. Effect of different inorganic ions on the transformation of HBCD by S-nZVI

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As shown in Fig. 7 and Table S5, the presence of either Ca2+ or Mg2+ (two

450

hardness cations, used as their respective NO3- salts) considerably decreased the

451

transformation of HBCD by S-nZVI, although Mg2+ had a less adverse effect than

452

Ca2+. In contrast, Kim et al. (2013) reported that the presence of each of the two

453

hardness cations increased the reduction rate of TCE. This discrepancy could be, at

454

least partly, attributed to the fact that different types of salts were used in the two

455

studies. In this study, the hardness cations were added as their respective NO3- salts,

456

which were different from those Cl- salts used by Kim et al. (2013). In fact, our results

457

showed that NO3- salt has a greater impact than Cl- salt on the transformation of

458

HBCD by S-nZVI (as discussed below). Additionally, it could not be excluded that

459

such discrepancy indicated the difference between HBCD and TCE in the mechanism

460

underlying the transformation by S-nZVI.

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The presence of anion ions (i.e., NO3-, HCO3- and Cl-, used as their respective

462

Na+ salts) also displayed adverse effects on the transformation of HBCD by S-nZVI

463

(Fig. 7 and Table S5). The adverse effect of different anion ions increased in the 21

ACCEPTED MANUSCRIPT following order: Cl- (0.082 h-1) < HCO3- (0.055 h-1) < NO3- (0.015 h-1). Similar results

465

were obtained by Tso and Shih (2014) who investigated the transformation of HBCD

466

by nZVI aggregates. These anions vary in their affinities of surface complexation with

467

iron species (Butler and Hayes, 1998; Liu et al., 2007). It has been hypothesized that

468

the anion with higher affinity for iron species would have greater inhibition in

469

transformation rate of target compounds due to the adsorption of iron-anion

470

complexes to surface reactive sites (Butler and Hayes, 1998; Liu et al., 2007; Tso and

471

Shih, 2014). In accordance with this hypothesis, our results showed that HCO3- that

472

had a higher complexation affinity to iron species than Cl- (Liu et al., 2007) displayed

473

a greater adverse effect than Cl- on the transformation of HBCD. Besides, the greater

474

effect of HCO3- compared to Cl- might be also attributed to the lower solubility of

475

precipitates of iron-carbonate complexes than that of iron-chloride complexes formed

476

on the surface of iron species (Liu et al., 2007). Remarkably, NO3- displayed the

477

greatest adverse effect among the three anion ions examined in this study, although it

478

has the lowest affinity to iron species (Butler and Hayes, 1998; Liu et al., 2007). This

479

result indicated that NO3- could inhibit the HBCD transformation by S-nZVI through

480

other mechanisms beyond the formation of Fe-nitrate complexes that are able to

481

occupy surface reactive sites (Tso and Shih, 2014). Indeed, it has been reported that

482

NO3- was an iron-reducible solute and could compete available reactive sites with

483

pollutants on the surface of iron species (Devlin and Allin, 2005; Lim and Zhu, 2008;

484

Liu et al., 2007).

485

3.8. Effects of S-nZVI dosage and HBCD concentration on the transformation of

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HBCD by S-nZVI The effect of different S-nZVI dosages on the transformation of HBCD was

488

shown in Fig. S5 and Table S6. The kobs of HBCD transformation increased from

489

0.018 to 0.482 h-1 as the dosage of S-nZVI increased from 0.1 to 2.0 g L-1. Further, the

490

relationship between the kobs and S-nZVI dosage showed a good linearity (R2 = 0.98,

491

Fig. S6). These results were reasonable, given that the transformation of HBCD

492

occurred mainly on the surface of S-nZVI (as discussed above) and that increasing the

493

dosage of S-nZVI (at least in the dosage range tested here) tended to increase the total

494

number of surface reactive sites for HBCD. In fact, similar effects of S-nZVI dosage

495

on the transformation of contaminants (i.e., Cr, TBBPA and TCE) were reported by

496

recent studies (Du et al., 2016; Li et al., 2016b; Rajajayavel and Ghoshal, 2015).

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The effect of initial HBCD concentration on the transformation of HBCD was

498

shown in Fig. S7 and Table S7. The kobs of HBCD transformation decreased from

499

0.309 to 0.074 h-1 as initial HBCD concentration increased from 1 to 20 mg L-1. There

500

was a linear relationship between the kobs and the initial HBCD concentration (Fig.

501

S8). There results were in good agreement with those reported recently for the other

502

few pollutants (Du et al., 2016; Li et al., 2016b; Rajajayavel and Ghoshal, 2015) and

503

could be attributed to a scenario that increasing the initial HBCD concentration led to

504

a reduced possibility for individual HBCD molecules to occupy the reactive sites on

505

the surface of S-nZVI.

506

3.9. Effect of solvent on the transformation of HBCD by S-nZVI

507

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As shown in Fig. 8 and Table S8, increasing solvent content in the reaction 23

ACCEPTED MANUSCRIPT solution decreased the HBCD transformation rate. In addition, a negative linear

509

relationship was observed between HBCD transformation rate constant and the

510

solvent content (R2 = 0.99, Fig. S9). Similarly, in a recent study (Li et al., 2016a), it

511

was shown that ethanol in reaction solution had negative effect on the transformation

512

of HBCD by FeS. A possible reason for the negative effect of solvent on

513

transformation of HBCD by S-nZVI was that the presence of solvent suppressed the

514

adsorption of HBCD on the surface of S-nZVI. Additionally, by extrapolating the

515

best-fit line in Fig. S9, the theoretical kobs for the transformation rate of HBCD by

516

S-nZVI in reaction solution without solvent was estimated to be 0.31 h-1, which was

517

nearly 2-times as high as that (0.158 h-1) for 50% ethanol content that was chosen as a

518

reaction solution in other experiments of this study. Nonetheless, information on the

519

effect of solvent on transformation of HBCD by S-nZVI is useful for designing

520

S-nZVI-based systems for treatment of HBCD-containing waste effluents produced

521

during innovative solvent-based extraction procedures that could be employed to

522

recycle plastics and metals from waste electrical and electronic equipment (Zhong et

523

al., 2010, 2012). Note also that effective removal of HBCD in the waste effluents will

524

allow the recovery of reusable solvents, which can help to minimize the expenses for

525

dispose of waste effluents and reduce the risk of secondary pollution.

527

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4. Conclusions

528

S-nZVI is a new type reducing agent with greater reactivity over nZVI towards

529

several halogenated organic pollutants such as TCE and TBBPA. This study 24

ACCEPTED MANUSCRIPT demonstrated that S-nZVI (0.5 g L-1) could transform nearly 100% HBCD (20 mg L-1)

531

within 12 h of reaction, following a pseudo-first-order kinetic model. The

532

transformation rate of HBCD with S-nZVI was 1.4-9.3 times higher than those with

533

FeS, S2-, and nZVI. Among the three HBCD isomers, β-HBCD had slightly faster

534

transformation rate than α- and γ-HBCD, indicating the diastereoisomeric selectivity

535

for reductive transformation by S-nZVI. This study also determined the rate of

536

transformation of HBCD by S-nZVI under different aqueous chemistry conditions.

537

The results showed that the reaction was likely endothermal, with the optimal solution

538

pH of 5.0, and could be suppressed in the presence of different ions (i.e., Ca2+, Mg2+,

539

NO3-, HCO3- and Cl-), and by increasing ionic strength, solvent content and initial

540

HBCD concentration, or decreasing the S-nZVI dosage. Identification of

541

transformation products (TBCDe and DBCDi) suggested that HBCD could be

542

debrominated by S-nZVI via sequential dibromoelimination. The XPS data showed

543

that both Fe(II) and S(-II) on the surface of S-nZVI participated directly in the

544

transformation of HBCD, suggesting that FeS might act as both catalyst and reactant.

545

Overall, these results improved our understanding of kinetics, mechanism and

546

influencing factors of POPs (represented by HBCD) transformation by S-nZVI and

547

demonstrated the superiority of S-nZVI over other well-known reactive reagents such

548

as FeS, S2-, and nZVI (representing the only three kinds of abiotic reductants that are

549

currently known for HBCD transformation). Further work needs to be done to move

550

S-nZVI towards the actual use as an efficient remediation agent.

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Acknowledgments

553

This study was supported financially by the National Natural Science Foundation of

554

China (Nos. 41120134006 and 41473107).

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Supporting Information

557

The Supporting Information gives details on synthesis procedure (Text S1),

558

instrument analysis (Text S2), QA/QC (Text S3), transformation rate constant (kobs) of

559

HBCD and its three major diastereoisomers in different systems (Table S1), kobs of

560

HBCD in S-nZVI system under a variety of solution conditions including different

561

temperature (Table S2), pH (Table S3), ionic strength (Table S4), inorganic ion (Table

562

S5), S-nZVI dosage (Table S6), HBCD concentration (Table S7) and solvent content

563

(Table S8), effects of different temperature (Figure S1), pH (Figure S2), ionic strength

564

(Figure S4), S-nZVI dosage (Figure S6), HBCD concentration (Figure S8) and

565

solvent content (Figure S9) on kobs of HBCD transformation by S-nZVI, effects of

566

ionic strength (Figure S3), S-nZVI dosage (Figure S5) and HBCD concentration

567

(Figure S7) on the transformation of HBCD by S-nZVI.

569

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Available

<

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which

degrades

722

γ-hexabromocyclododecane.

the

persistent

Bioscience,

brominated biotechnology,

flame and

retardant biochemistry

AC C

EP

721

723

from:

TE D

717

73, 1674-1678.

724

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ACCEPTED MANUSCRIPT 729

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735

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737 738 739

744 745 746 747

EP

743

AC C

742

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740 741

(HBCD)

M AN U

of

SC

734

748 749 750 34

by

Fe

(III)

ACCEPTED MANUSCRIPT Figure legends

752

Figure 1. Transformation of HBCD in FeS, S2-, nZVI and S-nZVI systems within 12

753

hours. Initial HBCD concentration, solid dosage, solvent content and

754

temperature were kept at 20 mg L-1, 0.5 g L-1, 50% and 30°C, respectively.

757 758 759 760

12 hours (A) and the proposed transformation pathway (B).

Figure 3. GC-EI/MS chromatograms of HBCD and its transformation products in the

SC

756

Figure 2. Dynamics of the two products of HBCD transformation by S-nZVI within

control, FeS, S2-, nZVI and S-nZVI systems after 12-h of reaction.

M AN U

755

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751

Figure 4. XPS spectra of surfaces of the blank, control and HBCD-reacted S-nZVI. (A-C), Fe(2p) of S-nZVI; (D-F), O(1s) of S-nZVI; and (G-I), S(2p) of S-nZVI. Figure 5. Effect of temperature on the transformation of HBCD by S-nZVI. Initial

762

HBCD concentration, S-nZVI dosage and solvent content were kept at 20 mg L-1,

763

0.5 g L-1 and 50%, respectively.

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Figure 6. Effect of pH on the transformation of HBCD by S-nZVI. Initial HBCD

765

concentration, S-nZVI dosage, solvent content and temperature were kept at 20

766

mg L-1, 0.5 g L-1, 50% and 30°C, respectively.

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Figure 7. Effect of different inorganic ions on the transformation of HBCD by

768

S-nZVI. Initial inorganic ions concentration, HBCD concentration, S-nZVI

769 770

dosage, solvent content and temperature were kept at 0.01 mol L-1, 20 mg L-1, 0.5 g L-1, 50% and 30°C, respectively.

771

Figure 8. Effect of solvent content on the transformation of HBCD by S-nZVI. Initial

772

HBCD concentration, S-nZVI dosage and temperature were kept at 20 mg L-1, 35

ACCEPTED MANUSCRIPT 773

0.5 g L-1 and 30°C, respectively.

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774

36

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Table 1. XPS binding energies (BE) of Fe(2p3/2), O(1s) and S(2p) and the relative abundances of Fe, O and S species on the surfaces

BE (eV)a

Relative abundance(area, %)

Reference

Blank S-nZVIb

Control S-nZVI

HBCD reacted S-nZVI

Fe(2p3/2) 707.3

12.6

12.2

6.5

Fe(III)-O

710.4

55.7

56.1

60.1

Fe(III)-O

713.2

31.7

31.7

33.4

M AN U

Fe(II)-S

530.0

15.8

30.7

-

531.2

59.7

51.5

H2O

532.2

24.6

17.8

S2-

161.4

59.3

58.4

S22-

162.3

40.7

41.6

OH

a

EP

S(2p3/2)c

Mullet et al., 2002; Renock et al., 2009 Rajajayavel and Ghoshal, 2015; Renock et al., 2009 Mullet et al., 2002; Renock et al., 2009

34.2

Mullet et al., 2002; Renock et al., 2009

51.1

Mullet et al., 2002; Renock et al., 2009

14.7

Mullet et al., 2002; Rajajayavel and Ghoshal, 2015

TE D

O(1s) O2-

SC

Species

RI PT

of different S-nZVI samples.

49.1

Mullet et al., 2002; Renock et al., 2009

50.9

Renock et al., 2009

AC C

The binding energies are correct within ± 0.2 eV. Blank, control and HBCD-reacted S-nZVI represented S-nZVI before reaction, S-nZVI after reaction with the water/ethanol solution (v/v, 50/50) for 12 h, and S-nZVI after reaction with HBCD in the water/ethanol solution for 12 h, respectively. c The S(2p) spectra was fitted by the doublets of S(2p3/2) and S(2p1/2) with their binding energies separation being 1.2 eV and their peak area ratio being 2:1. Only the S(2p3/2) peak position was indicated, but the relative abundance for S(2p) included those for S(2p3/2) and S(2p1/2). b

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Fig. 1 1.25

Ct/C0

A

Total-HBCD

1.00

1.00

0.75

0.75

0.50

0.50

Control FeS 2S nZVI S-nZVI

0.25 0.00 0

3

-HBCD

B

0.25 0.00

6

9

0

12

3

6

9

12

Time (hour)

1.25

 -HBCD

C

SC

Time (hour) 1.25 D

1.00

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1.00

-HBCD

0.75

0.75

0.50

0.50

0.25

0.25

0.00

0.00 0

3

6

9

12

EP

TE D

Time (hour)

AC C

Ct/C0

RI PT

1.25

0

3

6

Time (hour)

9

12

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Fig. 2

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Fig. 3

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Fig. 4 15000

A

15000

Fe(2p3/2)

Fe(2p1/2)

12500

Fe(2p3/2)

Fe(2p1/2)

10000 Fe(III)-O

Fe(III)-O

12000 9000

Fe(II)-S

7500

730

720

710

700

730

720

700

B. E. (eV)

OH

8000

O

6000

534

532

530

0 536

528

534

B. E. (eV) 3200

H

G 4000

2800 S2

2-

S

532

S2

2-

2400 3000

530

528

166

164

162

160

1600 168

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B. E. (eV)

TE D

2000 168

0 536

534

S

166

532

530

528

B. E. (eV) 3000

I 2700

2-

S2

2-

2000

2500

2-

O H2O

3000

B. E. (eV)

4500

3500

-

6000

4000

0 536

700

OH

9000

2-

M AN U

12000

710

12000

O H2O

2-

720

F

-

12000 H2O

730

B. E. (eV)

OH

16000

18000

740

15000

E

-

24000

Intensity

710

20000

D

Fe(II)-S

2000

740

B. E. (eV) 30000

Fe(III)-O

4000

2500

740

Fe(III)-O

6000

5000

3000

Fe(2p3/2)

Fe(2p1/2)

8000

Fe(II)-S

6000

Intensity

Fe(III)-O

10000

C

SC

Intensity

Fe(III)-O

12000

B

RI PT

18000

2-

S

2400

2-

2100 1800

164

B. E. (eV)

162

160

1500 168

166

164

B. E. (eV)

162

160

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Fig. 5

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Fig. 6

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Fig. 7

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Fig. 8

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Highlights 1. S-nZVI showed superior reactivity towards HBCD over FeS, S2- and nZVI. 2. HBCD was debrominated sequentially by S-nZVI to form less-brominated products.

RI PT

3. FeS on S-nZVI solid may participate as both reactant and catalyst.

4. The optimal solution pH was 5.0 for HBCD transformation by S-nZVI.

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5. The presence of typical inorganic ions slowed HBCD transformation by S-nZVI.