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Radiation Physics and Chemistry 76 (2007) 1489–1492

www.elsevier.com/locate/radphyschem

Degradation of chlorophenols in aqueous solution by g-radiation

Jun Hu�, Jianlong Wang

INET, Tsinghua University, Beijing 100084, China

Abstract

Degradation of chlorophenols (CPs) in aqueous solutions by g-radiation was studied. The effect of absorbed dose on degradation,

dechlorination and mineralization of CPs were investigated. The results indicated that the degradation of CPs, Cl� release and

mineralization increased with increase in absorbed dose. When the initial concentration was 100mgL�1 and the dosage was 6 kGy, the

removal efficiencies of CPs were 44.54% for 2-CP, 91.46% for 3-CP, 82.72% for 4-CP and 93.25% for 2,4-DCP, respectively. The

combination of irradiation and H2O2 leads to a synergistic effect, which remarkably increased the degradation efficiency of CPs and TOC

removal. The kinetics of CPs during irradiation are also mentioned.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: g Radiation; Chlorophenols; Degradation; TOC; H2O2; Synergistic effect

1. Introduction

There is growing public concern about the widespreadcontamination of surface and ground water by variousorganic compounds over the past several decades. Inparticular, some chlorophenols (CPs), such as 2-CP and2,4-DCP, are included in the USEPA list of priority toxicpollutants (Jin, 1990). For removing CPs from environ-ment, many conventional processes comprising physical,chemical, biological treatment methods have been studied(Wang and Qian, 1999; Wang, 2002; Marac et al., 2004).Compared with conventional treatment, advanced oxida-tion processes (AOPs) have been suggested as potentialmethods especially for biorefractory or toxic compounds(Benitez et al., 2000). Application of radiation technology,also belonging to AOPs, is a novel and promising researchfield and has received increasing attention in recent years(Getoff, 1986, 1988, 1996b; Zona and Schmid, 1999).Radiation is producing reactive oxidants, such as hydroxylradicals for water treatment.

The paper investigated the g-radiolytic degradation of 2-chlorophenol (2-CP), 3-chlorophenol (3-CP), 4-chlorophe-nol (4-CP), and 2,4-dichlorophenol (2,4-DCP) in aqueous

ee front matter r 2007 Elsevier Ltd. All rights reserved.

dphyschem.2007.02.058

ing author. Tel.: +86 106 279 6427; fax: +86 106 277 1150.

ess: hujun@mail.tsinghua.edu.cn (J. Hu).

solution using a 60Co-g source. The kinetics and synergiceffects in the presence of H2O2 during radiolysis of CPswere also discussed.

2. Materials and methods

2.1. Materials

CPs were purchased from Beijing Chemical Co. Inc.(China). The aqueous solutions of CPs were prepared bydissolving the chemicals in deionized water.

2.2. Analytical equipments and methods

60Co-source was designed and built by the Institute ofNuclear and New Energy Technology, Tsinghua Univer-sity. The dose rate was determined by means of Frickedosimetry using a G-value of G(Fe3+) ¼ 15.6.The analysis of substrate degradation was carried out

using HPLC (Agilent 1100 Series, L-4000 UV–vis detector,Eclipse XDB-C18 column (5 mm, 150� 4.6mm).The inorganic chloride was monitored by DX-100 Ion

Chromatograph from Dionex of USA.Total organic carbon (TOC) was measured by using

elementar high TOC analyser (Model: Elementar Analy-sen-System High, Germany).

ARTICLE IN PRESS

0

20

40

60

80

100

0 6 12 15

Cl- (

%)

4-CP2-CP3-CP2,4-DCP

3 9

Dose (kGy)

Fig. 2. Effect of dose on chloride formation during degradation of

100mgL�1 chlorophenols in aqueous solution by g-radiation.

J. Hu, J. Wang / Radiation Physics and Chemistry 76 (2007) 1489–14921490

3. Results and discussion

3.1. Radiation degradation of CPs

The gross reaction of water radiolysis is presented inEq. (1), where the yields of the primary products areexpressed as Gi-values:

H2O! ½2:7�e�aq þ ½0:6�H � þ½2:8�OHþ ½0:45�H2

þ ½0:72�H2O2 þ ½2:7�H3Oþ

ð1Þ

100mgL�1 solutions of 2-CP, 3-CP, 4-CP and 2,4-DCPwere irradiated in 60Co-g-source at dose rate of10.84Gymin�1. Fig. 1 shows the dose dependence of thedegradation of 2-CP, 3-CP, 4-CP and 2,4-DCP during g-

radiation under air atmosphere.From Fig. 1, it can be concluded that along with the

increase of dose, the removal efficiency of CPs increased.At a dose of 6 kGy, the removal efficiency was 44.54% for2-CP, 91.46% for 3-CP, 82.72% for 4-CP and 93.25% for2,4-DCP when their initial concentration was 100mgL�1,respectively. The presence of CPs 3-CP, 4-CP and 2,4-DCPin irradiated samples was not detected when increasing thedose to 15 kGy. The results revealed that 3-CP was themost degradable. The degradation rate of CPs was in theorder 2,4-DCP43-CP44-CP42-CP. The results indicatedthat the degradation of CPs during irradiation dependedon the position and number of the chlorine substitution inthe bezene ring of CPs.

3.2. Dechlorination effects of CPs

The position of chlorine on the aromatic ring stronglyinfluences the dechlorination and degradation process(Schmid et al., 1997). In addition to the CPs degradation,the amount of inorganic chloride ions was also found toincrease with enhancing dose (Fig. 2). At a dose of 6 kGy,the rate of dechlorination was 52.23% for 2-CP, 64.61%for 3-CP, 56.86% for 4-CP and 71.4% for 2,4-DCP. The

0

20

40

60

80

100

0 9

C/C

0 (%

)

4-CP2-CP3-CP2,4-DCP

3 6

Dose (kGy)

12 15

Fig. 1. Effect of dose on the degradation of 100mgL�1 chlorophenols in

aqueous solutions by g-radiation.

dechlorination rate of CPs was in the order 2,4-DCP43-CP44-CP42-CP.

3.3. Effect of irradiation on the degree of mineralization

In order to get a better insight in the radiolytic products,i.e. whether they are still of organic nature or alreadymineralized, the degree of mineralization of irradiatedaqueous CPs was measured as TOC (Fig. 3).It showed that for 100mgL�1 3-CP, a dose of 15 kGy

resulted in total dechlorination, corresponding to areduction of approximately 12.8% of TOC (Fig. 3). Theresults were similar to the data reported by Zona andSchmid (1999). However, the degree of mineralization ofCPs enhanced when the concentration of 3-CP, 4-CP and2,4-DCP decreased 10 times to 10mgL�1 (Fig. 4). At thedose of 6 kGy, the TOC removal efficiency of 3-CP reached80.8%. Compared with the results of both differentconcentrations of CPs, lower concentration of CPs iseasier to be completely mineralized. The trend of themineralization degree of CPs was in the order 2,4-DCP43-CP44-CP.

3.4. Kinetic and reaction mechanisms of irradiation

degradation of CPs

The radiation degradation of CPs resulted in thereduction of TOC, release of ring-bound chlorine andevolution of dioxide carbon. The concentration change ofphenols at different irradiation time (0, 1.5, 3, 6, 9, 12, 23 h)were measured to monitor the progress of the degradation,and the initial degradation rate from the time-course curvesis depicted in Fig. 5.From Fig. 5, it could be seen that the corresponding lnC

versus time plot is linear. The linear relationship demon-

ARTICLE IN PRESS

0

2

4

6

8

0 4

TO

C (

mg.

L-1

)

4-CP

3-CP

2,4-DCP

2

Dose (kGy)

6

Fig. 4. Effect of dose on the change of TOC in irradiated 10mgL�1

chlorophenols.

0

1

2

3

4

5

0 5 10 15 20 25

lnC

Time (h)

4-CP2-CP3-CP2,4-DCP

Fig. 5. Concentration change of 100mgL�1 CPs as a function of

irradiation time.

0

15

30

45

60

0 3 6 9 12 15

TO

C (

mg.

L-1

)

4-CP

3-CP

2,4-DCP

Dose (kGy)

Fig. 3. Effect of dose on the change of TOC in irradiated 100mgL�1

chlorophenols.

J. Hu, J. Wang / Radiation Physics and Chemistry 76 (2007) 1489–1492 1491

strated that the degradation followed a first-order kineticsequation and the rate constant could be determined fromthe slope of the straight line (k). Table 1 listed the values ofk and b of the resulting linear equations. The rate constantof different CPs was in the following order:

0:442 h�1 ð2; 4�DCPÞ40:2347 h�1 ð3�CPÞ

40:1754 h�1 ð4�CPÞ40:0844 h�1 ð2�CPÞ.

The result indicated that the degradation rate washighest for 2,4-DCP, being 0.442 h�1, which is 4.24, 1.52and 0.88 times higher than those of degradation rates of2-CP, 4-CP and 3-CP, respectively.

3.5. Synergistic effect of irradiation and H2O2

It is well known that H2O2 is an efficient oxidation agent,which is widely applied for wastewater treatment. H2O2

can react with hydrogen atoms (Hd), hydroxyl radicals(dOH), hydrated electrons (eaq

� ) during the radiolysis ofwater (Wu and Bao, 2002).Table 2 shows the results of irradiation alone and

combination of irradiation with H2O2 of 2-CP, 3-CP, 4-CPand 2,4-DCP.Table 2 obviously indicated that the removal rate, TOC

removal and Cl� release were enhanced in the presence of

Table 1

The kinetic equations and rate constants of CPs degradation

(C0 ¼ 100mgL�1)

Different

CPs

Equation Rate constants

(h�1)

R2

2-CP lnC ¼ �0.0844t+4.5321 0.0844 0.9944

3-CP lnC ¼ �0.2347t+4.2839 0.2347 0.9769

4-CP lnC ¼ �0.1754t+4.4726 0.1754 0.9964

2,4-DCP lnC ¼ �0.442t+4.5476 0.442 0.9979

Table 2

The degradation of CPs under different treatment processes

CPs Process Dose

(kGy)

CPs removal

rate (%)

TOC removal

(%)

Cl� release

(%)

2-CP Irradiation 15 86.35 3.42 84.14

Irradiation-

H2O2

15 97.64 5.90 97.90

3-CP Irradiation 15 99.57 12.81 95.26

Irradiation-

H2O2

15 100 29.0 99.60

4-CP Irradiation 15 98.4 9.76 92.10

Irradiation-

H2O2

15 100 23.9 100

2,4-

DCP

Irradiation 15 100 9.01 85.17

Irradiation-

H2O2

15 100 53.65 85.92

Note: [CPs]0 ¼ 100mgL�1, [H2O2] ¼ 35mgL�1, dose rate ¼ 10.84

Gymin�1.

ARTICLE IN PRESSJ. Hu, J. Wang / Radiation Physics and Chemistry 76 (2007) 1489–14921492

H2O2. When irradiation was done without H2O2 with adose of 15 kGy, the TOC removal efficiencies of 2-CP, 3-CP, 4-CP and 2,4-DCP were respectively 3.42%, 12.81%,9.76% and 9.01%. However, TOC removal efficiency wasincreased to 5.9%, 29%, 23.9% and 53.65% in thepresence of 35mgL�1 H2O2, indicating that the miner-alization of CPs was evolved in the reaction with OHradical. The synergic effect of irradiation and hydrogenperoxide, TOC removal efficiency of CPs was in the order2,4-DCP43-CP44-CP42-CP at a dose of 15 kGy.

4. Conclusions

The g-ray-induced degradation of four CPs was studiedin aqueous solutions. The results indicated that CPs can bedecomposed efficiently by g-induced degradation.

(1)

At a dose of 6 kGy, the removal efficiency was 44.54%for 2-CP, 91.46% for 3-CP, 82.72% for 4-CP and93.25% for 2,4-DCP when the initial concentration was100mgL�1.

(2)

The efficiency of degradation and dechlorination was inthe following order: 2,4-DCP43-CP44-CP42-CP.

(3)

In the presence of H2O2, the synergic effect resulted inhigher removal efficiency, dechlorination and TOCremoval, and they were enhanced significantly withincreasing radiation dose.

(4)

The degradation of CPs followed a first-orderkinetics equation, and the rate constant was inthe following order: 0.442 h�1 (2,4-DCP)40.2347 h�1

(3-CP)40.1754 h�1 (4-CP)40.0844 h�1 (2-CP).

Acknowledgements

The work was supported by the National NaturalScience Foundation of China (Grant No. 50325824;50678089) and the Excellent Young Teacher Program ofMOE, P. R. China.

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