Chemical Engineering Journal 254 (2014) 538–544

Contents lists available at ScienceDirect

Chemical Engineering Journal

journal homepage: www.elsevier .com/locate /ce j

Enhanced degradation of Tetrabromobisphenol A in water by a UV/base/persulfate system: Kinetics and intermediates

http://dx.doi.org/10.1016/j.cej.2014.05.1431385-8947/� 2014 Elsevier B.V. All rights reserved.

⇑ Corresponding authors. Tel.: +86 21 67792557; fax: +86 21 67792522.E-mail addresses: zhaohuiwang@dhu.edu.cn (Z. Wang), liujianshe@dhu.edu.cn (J.

Liu).

Yaoguang Guo, Jun Zhou, Xiaoyi Lou, Renlan Liu, Dongxue Xiao, Changling Fang, Zhaohui Wang ⇑,Jianshe Liu ⇑State Environmental Protection Engineering Center for Pollution Treatment and Control in Textile Industry, College of Environmental Science and Engineering, DonghuaUniversity, Shanghai 201620, China

h i g h l i g h t s

� Enhanced degradation of TBBPA in water by UV/persulfate system was firstly examined.� Br� has no effect on the degradation of TBBPA in alkaline UV/persulfate system.� Possible pathways of TBBPA degradation by UV/persulfate process were proposed.

a r t i c l e i n f o

Article history:Received 4 February 2014Received in revised form 29 May 2014Accepted 31 May 2014Available online 11 June 2014

Keywords:Brominated flame retardantsPersulfateAlkalineSulfate radicalHydroxyl radical

a b s t r a c t

Tetrabromobisphenol A (TBBPA), one of the most frequently used brominated flame retardants (BFRs), isonly soluble in strongly alkaline solutions where most advanced oxidation processes (AOPs) are ineffi-cient or in organic solvents. It is highly desirable to develop an environmentally friendly cleanup technol-ogy for TBBPA which operates at alkaline pH without the need of organic solvents to enhance itssolubility in water. In this study a favorable UV/base/persulfate (PS) system for rapid degradation ofTBBPA in aqueous solution is reported. Increases of initial pH and PS concentrations have positive effectson the degradation of TBBPA and a high initial TBBPA concentration has a negative influence. The additionof Br� has a negligible effect on the degradation of TBBPA. The low TOC removal and degradation inter-mediates of TBBPA identified by GC–MS suggested that TBBPA was degraded via the cleavage betweenthe isopropyl group and one of the benzene rings rather than complete debromination and degradation.The present study provides a simple and green approach to detoxify TBBPA in water rather than usingtoxic organic solvents.

� 2014 Elsevier B.V. All rights reserved.

1. Introduction

Tetrabromobisphenol A [4,40-isopropylidenebis (2,6-dibromo-phenol), TBBPA], one of the commercially available brominatedflame retardants (BFRs), is widely used in plastics, textiles, papers,electronics and other consumer goods [1–4]. The global consump-tion of TBBPA ranges between 1.2 � 105 and 1.5 � 105 tons peryear, and accounts for nearly 60% of the total BFRs market share[5,6]. Given its extensive use, TBBPA is ubiquitous in various envi-ronmental matrices, such as water (0.2–130 ng/L), sediment (0.5–300 lg/kg dry weights), air (1 pg/m3–1.8 lg/m3), dust (2–230 ng/g)

and organisms (13 ng/kg–0.76 lg/kg) [7–10]. Moreover, many pre-vious reported studies have confirmed that TBBPA can induce bio-toxicity, including immunotoxicity, neurotoxicity, disruption ofendocrine function and cytotoxicity [11–13]. Therefore, it is essen-tial to develop effective methods to eliminate TBBPA from contam-inated environments.

Biological and chemical techniques have both been applied toremove TBBPA contamination. Under anaerobic and aerobic con-ditions TBBPA has a mean half-life of approximately two months,indicating the inefficiency of degradation of TBBPA by biologicalmethods [14]. In contrast, chemical approaches, such as UV pho-tolysis and advanced oxidation processes (AOPs) can achievehigher degradation rates for TBBPA. Degradation by UV photoly-sis is due to the cleavage of the TBBPA molecules rather thanmineralization [15], an incomplete decontamination requiring

Y. Guo et al. / Chemical Engineering Journal 254 (2014) 538–544 539

further processing. By comparison, AOPs should be appropriatetechniques for decontaminating TBBPA, since TBBPA can beachieved cleavage of the TBBPA molecules, debromination, andmineralization via AOPs [16–18]. However, TBBPA has a limitedsolubility in water (ca. 1.25 mg/L at pH ca. 7; octanol–water par-tition coefficient (log Kow) = ca. 5.9) but can be dissolved inaqueous alkaline solutions (pKa P 7.5) or organic solvents (e.g.methanol and acetonitrile) [19]. Some common organic solventshave been employed to increase the solubility of TBBPA in water.For instance, Lin et al. [20] examined the oxidation reaction ofaqueous TBBPA with MnO2 in the mixed solvents of water/meth-anol (50/50, v/v). Guo et al. [21] mixed 50/50 (v/v) of water/ace-tonitrile to prepare reaction solutions for the photocatalyticdegradation of TBBPA. Zhong et al. [22] prepared a mixture ofwater and methanol (60/40, v/v) as a solvent to increase theaqueous solubility of TBBPA in the heterogeneous UV/Fentonreaction. However, organic solvents have a quenching effect onthe degradation reaction, diminishing efficiency and the solventsthemselves become a secondary pollutant requiring treatment.Therefore, it is imperative to explore an environmentally com-patible oxidation system to achieve complete dissolution andrapid degradation of TBBPA without the addition of organicsolvents.

Persulfate (S2O82�, PS) can be activated by bases to generate

sulfate radicals (SO4��) for the chemical oxidation of various

organic contaminants (Eqs. (1) and (2)) [23]. In addition, PScan be activated by transition metal ions [24], heat [25,26], orUV irradiation [26]. The performance of PS-based technologyis expected to be more effective if base/PS is associated withother activation techniques. However, transition metal ionscan hardly activate PS under alkaline conditions due to the for-mation of hydroxide precipitate and metals oxides. Heating theTBBPA-contaminated wastewater during treatment is not eco-nomically feasible. By comparison, UV irradiation to enhancethe activation of PS under alkaline conditions (Eq. (3)) is anon-polluting, economically feasible alternative. The introduc-tion of UV light into the alkaline PS system is assumed toincrease the yields of sulfate radicals and to enhance degrada-tion of organic contaminants.

3�OSAOAOASO�3 þH2Oþ OH� ! 2SO2�

4 þHO�2 þ 2Hþ ð1Þ

3�OSAOAOASO�3 þHO�2 ! SO2�

4 þ SO��4 þ O��2 þHþ ð2Þ

3�OSAOAOASO�3 þ UV! 2SO��4 ð3Þ

Alkaline pH : SO��4 þ OH� ! �OHþ SO2�4

k4 ¼ ð6:5� 1Þ � 107 M�1 s�1 ð4Þ

In general, SO4�� (E0 = (2.5–3.1) V vs. NHE) is more prone to elec-

tron transfer reactions than hydroxyl radicals �OH (E0 = (2.59–2.74)V at acidic pH; E0 = (1.77–1.91) V at alkaline pH) [27,28]. Underalkaline conditions, SO4

�� interconversion to �OH was verified byspin-trapping electron spin resonance spectroscopy (ESR) (Eq.(4)) [29–32]. Therefore, organic pollutants should be efficientlyoxidized by both SO4

�� and �OH. Considering the good solubility ofTBBPA in alkaline solutions, enhanced degradation of TBBPA in aUV/base/PS system is expected.

The aim of this study is to investigate the reaction of TBBPAwith activated PS under UV irradiation and alkaline conditionsby evaluating degradation kinetics as a function of the initialpH of the reaction solution, TBBPA and PS concentrations. Similarto our recent investigation on 2,4,6-trichlorophenol [33],bromide, which is released into solutions via debromination, islikely to react with reactive radicals. The effect of Br� onTBBPA degradation will also be examined. A pathway for the

degradation of aqueous TBBPA in a UV/base/PS system is pro-posed, based on GC–MS data and TOC measurement.

2. Experimental

2.1. Materials

Tetrabromobisphenol A (97%) was supplied by Alfa Aesar. Anhy-drous pyridine (>99.8%) and silylating reagents (chlorotrimethylsi-lane (>99%) and hexamethyldisilazane (>99%)) were purchasedfrom Sigma–Aldrich Co., USA. Methylene dichloride (>99.9%) usedin the extraction process and potassium persulfate (K2S2O8, 99%)were obtained from J & K Technology Co., Ltd., Tert-butyl alcohol(TBA) and isopropyl alcohol (IPA), from Sinopharm ChemicalReagent Co., Ltd., were used as sulfate radical and hydroxyl radicalscavengers (Text S1) [34]. Sodium hydroxide and sulfuric acid wereall from Sinopharm Chemical Reagent Co., Ltd., Methanol (HPLCgrade) was from CNW Technologies GmbH. Barnstead UltraPurewater (>18.2 MX cm) was used for all experiments. All reagentstock solutions were freshly prepared.

2.2. Experimental procedure

All the photochemical experiments for TBBPA degradation wereconducted in a photochemical reactor supplied by Xujiang Electro-mechanical Plant, Nanjing, China. The light source consisted of a100 W medium-pressure Hg lamp (maximal emission: 365.0–366.3 nm) positioned inside a hollow quartz hydrazine in the mid-dle of the reactor. Temperature was maintained at 28 ± 2 �C bycirculating water. Other parameters of the photochemical instru-ment are detailed in our previous study [35]. All experiments wereperformed in 50 mL quartz tubes which were continuously stirredand aerated. The reaction solutions were always freshly preparedwith an initial pH of (12.00 ± 0.05) (adjusted with NaOH andH2SO4) unless specified, and the pH was not controlled duringthe reaction process. A cutoff filter (k > 360 nm) was applied tominimize the direct photolysis of TBBPA that has absorption below350 nm within the UV range (Fig. S1). The samples were with-drawn at various time intervals, and immediately quenched withmethanol for HPLC analysis. Additional samples were extractedfor immediate Total Organic Carbon (TOC) analysis. Most batchexperiments were conducted in duplicate.

After immediately quenching with excess methanol, the con-centrations of TBBPA were measured by a Shimadzu high-perfor-mance liquid chromatography (HPLC) instrument equipped withUV–vis detector set at 310 nm and an Athena C18 column(4.6 mm � 250 mm, 5 lm) maintained at 30 �C, The mobile phasewas methanol/water (85/15 (v/v)) and the flow rate was main-tained at 1.5 mL/min (see HPLC chromatogram of TBBPA inFig. S2). The minimum detection limit (MDL) for HPLC analysiswas 6 nM corresponding to three times the standard deviation ofthe background noise signals. A Shimadzu TOC-VCPH analyzer wasused to measure the TOC.

Gas chromatography–mass spectrometry (GC/MS) analysis wasconducted to identify the intermediates formed during the TBBPAdegradation process. The GC column was operated in a tempera-ture programmed mode with an initial temperature of 40 �C heldfor 4 min. The column temperature was then increased to 80 �Cat a 10 �C/min rate and held at that temperature for 2 min, andthen to 280 �C at a 10 �C/min rate and held at that temperaturefor 10 min. The details of sample pretreatment for GC–MS analysisby the liquid–liquid extraction and silylation method, and the fur-ther information about GC–MS analysis are available in our previ-ous study [36].

540 Y. Guo et al. / Chemical Engineering Journal 254 (2014) 538–544

3. Results and discussion

3.1. Degradation of TBBPA

To evaluate the efficiency of the PS activation system, the deg-radation of TBBPA in alkaline aqueous solutions was investigated.Fig. 1 compares the extent of TBBPA degradation under differentconditions. No substantive degradation of TBBPA was observed ina UV irradiated TBBPA solution. The base/PS and UV/base/PS reac-tions were capable of decomposing TBBPA, but the UV/base/PS sys-tem was the more favorable. In UV/base/PS system more than 80%of TBBPA was degraded within 240 min, possibly due to the asso-ciative oxidation by SO4

�� (Eqs. 1–3) and �OH (Eq. (4)).A differential radical quenching experiment was used to deter-

mine the activity of these two radical(s) in the system (Text S1).The a-hydrogen alcohol, isopropyl alcohol (IPA) scavenges bothsulfate radicals and hydroxyl radicals (k��SO4

= 8.2 � 107 M�1 s�1;k�OH = 1.9 � 109 M�1 s�1), and alcohols without a-hydrogen, tert-Butyl alcohol (TBA) scavenges hydroxyl radicals but not sulfate rad-icals (k�OH = 5.2 � 108 M�1 s�1; (k��SO4

= 8.4� 105 M�1 s�1) [28,37].Therefore, IPA and TBA can be used as quenching agents to differ-entiate SO4

�� and �OH. Generally, in radical identification experi-ments, sulfate and hydroxyl radicals could be differentiated viathe significant inhibition of substrate degradation when the initialalcohols/persulfate/substrate molar ratio was kept at 1000/50/1[38], or alcohols versus oxidant molar ratio was 500/1 [24,39]. Inour present study, the addition of alcohols/persulfate/TBBPA waswith the smaller molar ratio of 1000/200/1, i.e. alcohols versus oxi-dant with molar ratio of 5/1. The inhibition of TBBPA degradationwas less extreme than reported in other studies, however, theeffect was significant and allowed for differentiation of the radi-cals. As shown in Fig. S3, when no quenching agents were added,about 81% of TBBPA was degraded in 240 min. Whereas, the addi-tion of TBA or IPA with the concentration of 0.1 M resulted in 76%and 65% degradation, respectively in 240 min. A significant differ-ence between the three treatments indicates that the enhanceddegradation of TBBPA in the UV/base/PS system could be attributedto the combination of SO4

�� and �OH.To better evaluate the degradation of TBBPA in the UV/base/PS

system, a pseudo-first-order kinetic model (Eq. (5)) and a second-order kinetic model (Eq. (6)) were used to analyze the results of theTBBPA decomposition (Figs. S4 and S5). A second-order kineticmodel (Fig. S5) for the degradation kinetics of TBBPA gave a corre-lation coefficient of R = 0.978, whereas a pseudo-first-order kinetic

Fig. 1. Degradation of TBBPA under various experimental conditions. Experimentalcondition: [TBBPA]0 = 0.1 mM, [PS]0 = 20 mM, pHini = 12.0.

law (Fig. S4) provided a better fit for the data with the rate constantof 0.0074 min�1 (R = 0.995).

�ln ðC=C0Þ ¼ kt ð5Þ

1C� 1

C0¼ 2k0t ð6Þ

where C0 and C are the concentrations of TBBPA at the reaction timet = 0 and t min, respectively; k and k0 are the apparent pseudo-first-order rate constant and second-order rate constant, respectively.

3.2. Effect of pH

The system pH is a critical variable for the decomposition ofTBBPA, because of its significant influences on the solubility ofTBBPA and the generation of sulfate and/or hydroxyl radicals.Experiments of the effect of pH on TBBPA degradation were carriedout at three initial pH values 11.5, 12.0 and 13.0. At pH 11.5–12.0,the degradation of TBBPA was hardly affected by the variation ofpHs. The pKa of �OH is 11.9, and at pH 11.5–12.0 the equilibriumbetween �OH and its conjugate base �O� is rapidly established(Eq. (7)) [28]. �O� is also a reactive oxidative species with the redoxpotential of (1.64–1.78) V, which is almost the same as �OH(E0�OH = (1.77–1.91) V) at alkaline pHs [28]. As such, an increase in

oxidation and degradation of TBBPA by �OH/�O� was not significant.However, when pH was raised to 13, more than 99% of the TBBPAwas oxidized over 180 min (Figs. 2a and S6), possibly because theconcentration of OH� was 10-fold of that at pH 12, favoring the for-mation of SO4

�� and �OH (�O�) via reactions 1, 2 and 4. These resultsare in agreement with the findings of Furman et al. [34], who found,in a study of anisole and nitrobenzene degradation, that PS washighly reactive in more basic systems.

�OHþ OH�¢ �O� þH2O k7�f ¼ 1:2� 1010 M�1 s�1 ; k7�b ¼ 108 s�1

ð7Þ

3.3. Effect of initial TBBPA concentrations

Figs. 2b and S7 illustrate the influence of initial TBBPA concen-trations (0.05–0.2 mM) on its degradation. Increasing the initialconcentration decreases the degradation rate of TBBPA. The rateconstant decreased from 0.0090 to 0.0041 min�1 when the initialconcentration increased from 0.05 to 0.2 mM. However, beyond0.15 mM, the apparent reaction rate constants for TBBPA did notcontinue to decrease significantly. Dependence of the apparentreaction rates on the TBBPA concentrations indicates that themechanism was complex and approximation on pseudo-first-orderkinetics might be not valid at a larger TBBPA concentration. Wespeculate that, as concentration increased, UV radiation wasadsorbed by TBBPA and its intermediate degradation products,inhibiting absorption by PS and the subsequent formation of SO4

��

by photoreaction [40].

3.4. Effect of PS dosage

The effect of initial PS concentration on the degradation ofTBBPA at pH 12.0 is shown in Figs. 2c and S8. An increase in PS con-centration resulted in a greater degradation of TBBPA. The rateconstants for the degradation of TBBPA ascended from 0.0020 to0.0116 min�1 when the initial PS concentrations increased from 2to 30 mM, which was ascribed to more free radical generation dri-ven by higher concentrations of an oxidant source [41]. Theseresults are consistent with previous investigations of tert-butylalcohol, phenol, and nitrobenzene degradation in thermally acti-vated persulfate system [42].

Fig. 2. Effects of pH (a), initial concentrations of TBBPA (b) and PS (c). Experimentalcondition: [TBBPA]0 = 0.1 mM (except for (b)), [PS]0 = 20 mM (except for (c)),pHini = 12.0 (except for (a)).

Fig. 3. Effects of addition of Br� (a) and TOC removal (b). Experimental condition:[TBBPA]0 = 0.1 mM, [PS]0 = 20 mM, pHini = 12.0.

Y. Guo et al. / Chemical Engineering Journal 254 (2014) 538–544 541

3.5. Effect of Br� addition

The identified debrominated intermediates, such as phenol, 4-(2-hydroxyethyl)benzene-1,2-diol, oxalic acid and 3-methylbuta-noic acid, indicated a release of Br� during TBBPA degradation.Br� can potentially scavenge SO4

�� (Eq. (8)) and �OH (Eqs. (9) and(10)) to form Br� (E0

Br�/Br� = 2.00 V) [27,28,43,44], which subsequentlyslows the reaction rate and reacts with available substrates to formtoxic polybrominated intermediates. However, the results unexpect-edly revealed that the added Br� (from 0 to 4.0 mM) hardly inhibitedthe degradation of TBBPA (Fig. 3a). Moreover, no polybrominatedintermediates were identified whether Br� was added or not (data

not shown). The effect of Br� was different from those in our previ-ous studies which showed that chlorinated byproducts could be gen-erated during the sulfate radical-based AOPs in the presence ofchloride ions in acid solutions [33,45]. The pH dependency of bro-mine species might explain the effect of Br� on the treatment ofTBBPA.

At pH > 11, Br� reacts rapidly with Br� to form Br2�� (Eq. (11)),

and again with OH� to form BrOH�� (Eq. (10)). A higher pH shiftsthe equilibrium toward BrOH�� [46–48]. BrOH�� also reacts withBr� to form Br2

�� (Eq. (12)) [47,48]. Br2�� reacts with itself to

form Br3� and Br� (Eq. (13)). On the other hand, Eq. (4) was

the rate-determining step (k4 = (6.5 ± 1) � 107 M�1 s�1) for theformation of �OH and speciation transformation of bromine viaEqs. 9–13. The chemical equilibrium constant K can be calculatedas kf/kb. As such, DG9, �DG10, DG11 and DG12 are all negativevalues calculated from Eq. (14). Therefore, Eqs. 9–12 are allspontaneously shifted to form more BrOH�� and Br2

�� species.At a higher pH, more �OH will be formed (Eq. (4)), and subse-quently favouring the formation of BrOH�� and Br2

�� species,and further promoting the formation Br3

� and Br� (Eq. (13)).Therefore, pH is a critical parameter for the de novo formationof halogenated compounds, owing to the effect of pH on the spe-ciation and reactivity of halide ions.

SO��4 þ Br� ! Br� þ SO2�4 k8 ¼ 3:5� 109 M�1 s�1 ð8Þ

�OHþ Br�¢ BrOH�� k9�f ¼ ð1:06� 0:08Þ � 1010 M�1 s�1;

k9�b ¼ ð3:3� 0:4Þ � 107 s�1 K9 ¼ 321 ð9Þ

542 Y. Guo et al. / Chemical Engineering Journal 254 (2014) 538–544

BrOH��¢ Br� þ OH� k10�f ¼ ð4:2� 0:6Þ � 106 s�1;

k10�b ¼ 1:3� 1010 M�1 s�1 1=K10 ¼ 3095 ð10Þ

Br� þ Br�¢ Br��2 k11�f ¼ ð1:2� 0:1Þ � 1010 M�1 s�1;

k11�b ¼ 1:9� 104 s�1 K11 ¼ 631579 ð11Þ

BrOH�� þ Br�¢ Br��2 þ OH� k12�f ¼ ð1:9� 0:3Þ � 108M�1 s�1;

k12�b ¼ ð2:7� 0:5Þ � 106 s�1 K12 ¼ 70 ð12Þ

Br��2 þ Br��2 ! Br�3 þ Br� k13 ¼ ð1:9� 0:1Þ � 109 M�1 s�1 ð13Þ

DG ¼ �RT ln K ð14Þ

Where DG is Gibbs free energy; R is thermodynamic constant; Tis the temperature; K is the chemical equilibrium constant.

3.6. TOC removal

The mineralization of TBBPA in the UV/base/PS system wasevaluated through analyzing the TOC removal efficiency. Fig. 3bshows that the rate of TBBPA mineralization increased over longerreaction times. However, only about 25% of TBBPA could be miner-alized as the degradation rate (80% within 240 min) well exceededthe rate of mineralization (Fig. 1). The lower mineralization andhigher disappearance of TBBPA in UV/base/PS systems indicatedthat the degradation of TBBPA was possibly due to the cleavageof a TBBPA molecule rather than complete degradation.

Fig. 4. Possible pathways of TBBPA de

3.7. Products identification and mechanism

In addition to the parent TBBPA (1), ten intermediates, assignedas products 2–11, were identified by GC–MS, (Figs. S9–S28). Theinformation of all identified products, including the characteristicfragment ions and molecular structures are summarized inTable S1. The products can be mainly classified into three groups:(I) single-benzene-type compounds, such as 2,6-dibromo-4-(pro-pan-2-ylidene)cyclohexa-2,5-dienone (2), 2,6-dibromophenol (3),2,6-dibromo-4-isopropylphenol (4), 2,6-dibromo-4-(2-hydroxy-propan-2-yl)phenol (5), phenol (6), 2,6-dibromo-4-(hydroxy-methyl)phenol (7), 4-(2-hydroxyethyl)benzene-1,2-diol (8); (II)debrominated bisphenol A, i.e. TriBBPA (11); (III) low molecularweight organic acids, such as oxalic acid (9) and 3-methylbutanoicacid (10), which appear to reflect the variation of pH during thereaction (Fig. S29).

On the basis of the products identified and previous literature[17,20,22,49,50], the potential pathways for the degradation ofTBBPA in a UV/base/PS system are proposed. As shown in Fig. 4,the proposed reaction mechanisms for the degradation of TBBPAinvolves two different pathways (labeled as I and II), correspondingto the two possible sites for the attack on the TBBPA molecule. Forpathway I, initially one TBBPA underwent beta scission (cleavagebetween the isopropyl group and one of the benzene rings) torelease a new radical R1 and cationic intermediate R2 or 2,6-dibromo-4-(propan-2-ylidene)cyclohexa-2,5-dienone (2) [20,22,49,50]. R1 might be transformed into 2,6-dibromophenol (3)[17,49,50], which can yield phenol (6) via debromination [17,22].R2 might be transformed to 2,6-dibromo-4-isopropylphenol (4)and 2,6-dibromo-4-(2-hydroxypropan-2-yl)phenol (5) throughhydrogenation and substitution reactions, respectively [17,20,22,

gradation in a UV/base/PS system.

Y. Guo et al. / Chemical Engineering Journal 254 (2014) 538–544 543

49,50]. This process was followed by hydroxylation and/or debro-mination to form 2,6-dibromo-4-(hydroxymethyl)phenol (7) and4-(2-hydroxyethyl)benzene-1,2-diol (8) [17]. Further oxidationresulted in the generation of oxalic acid (9) and 3-methylbutanoicacid (10) through the cleavage of the aromatic rings and/or debro-mination. Finally, the mineralization of TBBPA to CO2 and H2O wasachieved. For pathway II, the C–Br bond of TBBPA was attacked toform TriBBPA via debromination (11). Subsequently, a possibleoxidative degradation took place through scission, debromination,hydroxylation, or cleavage of the aromatic rings to achieve the finalmineralization. The oxidative debromination of TBBPA had beenfound in the photo-Fenton like reactions, while the debrominationmechanism was not exactly examined [17,22]. To our knowledge,this is the first report of oxidative debromination of TBBPA occur-ring in a UV/base/PS system.

4. Conclusion

Degradation of TBBPA by the UV/base/PS process was investi-gated in this study. The degradation was analyzed using apseudo-first order kinetic model. A positive relationship betweeninitial pH of the reaction solution and PS concentrations, and a neg-ative relationship between initial TBBPA concentrations and thedegradation rate of TBBPA were observed. The addition of Br�

hardly affected the degradation of TBBPA, indicating no highlytoxic polybrominated intermediates formed. The small TOCremoval efficiency and the intermediates identified by GC–MSanalysis indicated that TBBPA could be degraded largely via thecleavage between the isopropyl group and one of the benzene ringsrather than complete debromination and degradation. This studyindicates that the UV/base/PS process can be potentially used forpretreatment of TBBPA-contaminated wastewater.

Acknowledgments

This work was supported by the National Science Foundation ofChina (NSFC) (Nos. 41273108 and 21377023), and the Fundamen-tal Research Funds for Central Universities (2232013A3-08). Y.G.G.also thanks the financial support from Chinese Universities Scien-tific Fund (13D311303). The authors thank Dr. Nicholas Wardand Dr. Michelle Bush at Southern Cross University for their lan-guage improvement.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.cej.2014.05.143.

References

[1] Environmental Health Criteria, No. 172, Tetrabromobisphenol A andDerivatives; International Program on Chemical Safety, World HealthOrganization, Geneva, Switzerland, 1995; see http://www.inchem.org/documents/ehc/ehc/ehc172.htm.

[2] M. Riess, R. van Eldik, Identification of brominated flame retardants inpolymeric materials by reversed-phase liquid chromatography withultraviolet detection, J. Chromatogr. A 827 (1998) 65–71.

[3] M.L. Hardy, Regulatory status of the flame retardant Tetrabromobisphenol A,in: Presented at the Printed Circuits Expo, April 2–6, San Diego, CA, 2000.

[4] T. Debenest, F. Gagné, A. Petit, C. André, M. Kohli, C. Blaise, Ecotoxicity of abrominated flame retardant (Tetrabromobisphenol A) and its derivatives toaquatic organisms, Comp. Biochem. Physiol. C: Pharmacol. Toxicol. 152 (2010)407–412.

[5] M. Alaee, P. Arias, A. Sjödin, A. Bergman, An overview of commercially usedbrominated flame retardant, their applications, their use patterns in differentcountries/regions and possible modes of release, Environ. Int. 29 (2003) 683–689.

[6] A. Covaci, S. Voorspoels, M.A.E. Abdallah, T. Geens, S. Harrad, R.J. Law,Analytical and environmental aspects of the flame retardant

Tetrabromobisphenol-A and its derivatives, J. Chromatogr. A 1216 (2009)346–363.

[7] C.A. de Wit, An overview of brominated flame retardants in the environment,Chemosphere 46 (2002) 583–624.

[8] J.W. Voordeckers, D.E. Fennell, K. Jones, M.M. Haggblom, Anaerobicbiotransformation of TetrabromobisphenolA, tetrachlorobisphenol A, andbisphenol A in estuarine sediments, Environ. Sci. Technol. 36 (2002) 696–701.

[9] M.A.E. Abdallah, S. Harrad, A. Covaci, Hexabromocyclododecanes andTetrabromobisphenol-A in indoor air and dust in Birmingham, UK:implications for human exposure, Environ. Sci. Technol. 42 (2008) 6855–6861.

[10] R. Cariou, J.P. Antignac, P. Marchand, A. Berrebi, D. Zalko, F. Andre, B. Le Bizec,New multiresidue analytical method dedicated to trace level measurement ofbrominated flame retardants in human biological matrices, J. Chromatogr. A1100 (2005) 144–152.

[11] S. Pullen, R. Boecker, G. Tiegs, The flame retardants Tetrabromobisphenol Aand Tetrabromobisphenol A-bisallylether suppress the induction ofinterleukin-2 receptor a chain (CD25) in murine splenocytes, Toxicology 184(2003) 11–12.

[12] H. Viberg, P. Eriksson, Differences in neonatal neurotoxicity ofbrominated flame retardants, PBDE 99 and TBBPA, in mice, Toxicology289 (2011) 59–65.

[13] S. Decherf, I. Seugnet, J.B. Fini, M.S. Clerget-Froidevaux, B.A. Demeneix,Disruption of thyroid hormone-dependent hypothalamic set-points byenvironmental contaminants, Mol. Cell. Endocrinol. 323 (2010) 172–182.

[14] Z. Ronen, A. Abeliovich, Anaerobic–aerobic process for microbial degradationof Tetrabromobisphenol A, Appl. Environ. Microbiol. 66 (2000) 2372–2377.

[15] J. Eriksson, S. Rahm, N. Green, Å. Bergman, E. Jakobsson, Photochemicaltransformations of Tetrabromobisphenol A and related phenols in water,Chemosphere 54 (2004) 117–126.

[16] J. Xu, W. Meng, Y. Zhang, L. Li, C. Guo, Photocatalytic degradation ofTetrabromobisphenol A by mesoporous BiOBr: efficacy, products andpathway, Appl. Catal. B-Environ. 107 (2011) 355–362.

[17] J. An, L. Zhu, N. Wang, Z. Song, Z. Yang, D. Du, H. Tang, Photo-Fenton likedegradation of Tetrabromobisphenol A with grapheme-BiFeO3 composite as acatalyst, Chem. Eng. J. 219 (2013) 225–237.

[18] Y. Ding, L. Zhu, N. Wang, H. Tang, Sulfate radicals induced degradation ofTetrabromobisphenol A with nanoscaled magnetic CuFe2O4 as aheterogeneous catalyst of peroxymonosulfate, Appl. Catal. B-Environ. 129(2013) 153–162.

[19] Summary risk assessment report prepared by the United Kingdom on behalf ofthe European Union in http://www.bsef.com/uploads/library/tbbpahhsum402.pdf (accessed December 2013).

[20] K. Lin, W. Liu, J. Gan, Reaction of Tetrabromobisphenol A (TBBPA) withmanganese dioxide: kinetics, products, and pathways, Environ. Sci. Technol. 43(2009) 4480–4486.

[21] Y. Guo, L. Chen, F. Ma, S. Zhang, Y. Yang, X. Yuan, Y. Guo, Efficient degradationof Tetrabromobisphenol A by heterostructured Ag/Bi5Nb3O15material underthe simulated sunlight irradiation, J. Hazard. Mater. 189 (2011) 614–618.

[22] Y. Zhong, X. Liang, Y. Zhong, J. Zhu, S. Zhu, P. Yuan, H. He, J. Zhang,Heterogeneous UV/Fenton degradation of TBBPA catalyzed bytitanomagnetite: catalyst characterization, performance and degradationproducts, Water Res. 46 (2012) 4633–4644.

[23] O.S. Furman, A.L. Teel, R.J. Watts, Mechanism of base activation of persulfate,Environ. Sci. Technol. 44 (2010) 6423–6428.

[24] G.P. Anipsitakis, D.D. Dionysiou, Radical generation by the interaction oftransition metals with common oxidants, Environ. Sci. Technol. 38 (2004)3705–3712.

[25] R.L. Johnson, P.G. Tratnyek, R.O. Johnson, Persulfate persistence under thermalactivation conditions, Environ. Sci. Technol. 42 (2008) 9350–9356.

[26] M.G. Antoniou, A.A. de la Cruz, D.D. Dionysiou, Degradation of microcystin-LRusing sulfate radicals generated through photolysis, thermolysis and e�

transfer mechanisms, Appl. Catal. B- Environ. 96 (2010) 290–298.[27] P. Neta, R.E. Huie, A.B. Ross, Rate constants for reactions of inorganic radicals in

aqueous solution, J. Phys. Chem. Ref. Data 17 (1988) 1027–1284.[28] G.V. Buxton, C.L. Greenstock, W.P. Helman, A.B. Ross, Critical review of rate

constants for reactions of hydrated electrons, hydrogen-atoms and hydroxylradicals (�OH/�O�) in aqueous solution, J. Phys. Chem. Ref. Data 17 (1988) 513–886.

[29] R.O.C. Norman, P.M. Storey, P.R. West, Electron spin resonance studies. . PartXXV. Reactions of sulphate radical anion with organic compounds, J. Chem.Soc. B-Phys. Org. (1970) 1087–1095.

[30] D.E. Pennington, A. Haim, Stoichiometry and mechanism of the chromium-peroxydisulfate reaction, J. Am. Chem. Soc. 90 (1968) 3700–3704.

[31] E. Hayon, A. Treinin, J. Wilf, Electronic spectra, photochemistry, andautoxidation mechanism of the sulfite–bisulfite–pyrosulfite systems. TheSO2�, SO3

�, SO4�, and SO5

� radicals, J. Am. Chem. Soc. 94 (1972) 47–57.[32] G.R. Peyton, The free-radical chemistry of persulfate-based total organic

carbon analyzers, Mar. Chem. 41 (1993) 91–103.[33] L. Xu, R. Yuan, Y. Guo, D. Xiao, Y. Cao, Z. Wang, J. Liu, Sulfate radical-induced

degradation of 2,4,6-trichlorophenol: a de novo formation of chlorinatedcompounds, Chem. Eng. J. 217 (2013) 169–173.

[34] O.S. Furman, A.L. Teel, M. Ahmad, M.C. Merker, R.J. Watts, Effect of basicity onpersulfate reactivity, J. Environ. Eng. ASCE 137 (2011) 241–247.

[35] Y. Guo, X. Lou, C. Fang, D. Xiao, Z. Wang, J. Liu, Novel photo-sulfite system:toward simultaneous transformations of inorganic and organic pollutants,Environ. Sci. Technol. 47 (2013) 11174–11181.

544 Y. Guo et al. / Chemical Engineering Journal 254 (2014) 538–544

[36] Y. Guo, X. Lou, D. Xiao, L. Xu, Z. Wang, J. Liu, Sequential reduction-oxidation forphotocatalytic degradation of Tetrabromobisphenol A: kinetics andintermediates, J. Hazard. Mater. 241–242 (2012) 301–306.

[37] C.L. Clifton, R.E. Huie, Rate constants for hydrogen abstraction reactions of thesulfate radical, SO4

�.Alcohols, Int. J. Chem. Kinet. 21 (1989) 677–687.[38] C. Liang, Z. Wang, C. Bruell, Influence of pH in persulfate oxidation of TCE at

ambient temperatures, Chemosphere 66 (2007) 106–113.[39] J.G. Muller, P. Zheng, S.E. Rokita, C.J. Burrows, DNA and RNA modification

promoted by [Co(H2O)6]Cl2 and KHSO5: guanine selectivity, temperaturedependence, and mechanism, J. Am. Chem. Soc. 118 (1996) 2320–2325.

[40] V. Saxena, M. Sadoqi, J. Shao, Degradation kinetics of indocyanine green inaqueous solution, J. Pharm. Sci. 92 (2003) 2090–2097.

[41] R.J. Watts, A.L. Teel, Treatment of contaminated soils and groundwater usingin situ chemical oxidation, Pract. Period. Hazard. Toxic Radioact. WasteManage. 10 (2006) 2–9.

[42] C. Liang, H. Su, Identification of sulfate and hydroxyl radicals in thermallyactivated persulfate, Ind. Eng. Chem. Res. 48 (2009) 5558–5562.

[43] T. Hirakawa, Y. Nosaka, Properties of O2�� and �OH formed in TiO2 aqueous

suspensions by photocatalytic reaction and the influence of H2O2 and someions, Langmuir 18 (2002) 3247–3254.

[44] A. Mamou, J. Rabani, D. Behar, Oxidation of aqueous Br� by hydroxyl radicals,studies by pulse radiolysis, J. Phys. Chem. 81 (1977) 1447–1448.

[45] R. Yuan, S.N. Ramjaun, Z. Wang, J. Liu, Effects of chloride ion on degradation ofacid orange 7 by sulfate radical-based advanced oxidation process:Implications for formation of chlorinated aromatic compounds, J. Hazard.Mater. 196 (2011) 173–179.

[46] U.K. Kläning, T. Wolff, Laser flash photolysis of HClO, ClO�, HBrO and BrO� inaqueous solution. Reactions of Cl� and Br-atoms, Ber. Bunsen-Ges. Phys. Chem.89 (1985) 243–245.

[47] J. Fang, C. Shang, Bromate formation from bromide oxidation by the UV/persulfate process, Environ. Sci. Technol. 46 (2012) 8976–8983.

[48] I. Lampre, Jean-L. Marignier, M. Mirdamadi-Esfahani, P. Pernot, P. Archirel, M.Mostafavi, Oxidation of bromide ions by hydroxyl radicals: spectralcharacterization of the intermediate BrOH��, J. Phys. Chem. A 117 (2013)877–887.

[49] Y. Feng, L.M. Colosi, S. Gao, Q. Huang, L. Mao, Transformation and removal ofTetrabromobisphenol A from water in the presence of natural organic mattervia laccase-catalyzed reactions: reaction rates, products, and pathways,Environ. Sci. Technol. 47 (2013) 1001–1008.

[50] S. Pang, J. Jiang, Y. Gao, Y. Zhou, X. Huangfu, Y. Liu, J. Ma, Oxidation of flameretardant Tetrabromobisphenol A by aqueous permanganate: reactionkinetics, brominated products, and pathways, Environ. Sci. Technol. 48(2014) 615–623.