Chlorine dioxide catalytic oxidation and online FTIR spectroscopic analysis of simulated o-chlorophenol wastewater

Article abstract of DOI:10.1007/s11164-012-0502-4

An activated carbon-MnO₂ catalyst was prepared and used for chlorine dioxide catalytic oxidation of simulated o-chlorophenol wastewater. The COD removal efficiencies of chemical oxidation and catalytic oxidation are 28.6 and 93.5%, respectively

Full text of DOI:10.1007/s11164-012-0502-4

Res Chem Intermed (2012) 38:1781–1790
DOI 10.1007/s11164-012-0502-4
Chlorine dioxide catalytic oxidation and online FTIR
spectroscopic analysis of simulated o-chlorophenol
wastewater
•
•
•
•
Laishun Shi Xiaomei Wang Na Li Chunlei Huai
Jie Liu
Received: 15 September 2011 / Accepted: 1 February 2012 / Published online: 19 February 2012
Ó Springer Science+Business Media B.V. 2012
Abstract An activated carbon-MnO2 catalyst was prepared and used for chlorine
dioxide catalytic oxidation of simulated o-chlorophenol wastewater. The COD
removal efficiencies of chemical oxidation and catalytic oxidation are 28.6 and
93.5%, respectively. The COD removal efficiency of catalytic oxidation is greater
than that of chemical oxidation at the same treatment condition. By using UV–Vis
and online FTIR analysis technique, the intermediates during the degradation pro-
cess were obtained. The benzene ring in o-chlorophenol was degraded into quinone
and carboxylic acid, and finally changed into carbon dioxide and water during the
catalytic oxidation. The degradation reaction mechanism of o-chlorophenol by
chlorine dioxide catalytic oxidation was proposed based upon the experiment
evidence.
Keywords Chlorine dioxide Á Catalytic oxidation Á O-chlorophenol Á
Wastewater treatment Á Online FTIR analysis
Introduction
O-chlorophenol is an important intermediate and raw material in the synthesis of
pesticides, medicines, and dyes. However, o-chlorophenol has the properties of an
unpleasant odor, high skin irritation, and ease of absorption by skin. Therefore, the
treatment of wastewater containing o-chlorophenol is an urgent environmental prob-
lem. Otherwise, it can lead to extreme environmental pollution. Various treatment
techniques have been studied to remove or eliminate phenolic compounds from
wastewaters, including chemical oxidation [1], solvent extraction [2], membrane
L. Shi (&) Á X. Wang Á N. Li Á C. Huai Á J. Liu
School of Chemistry and Chemical Engineering, Shandong University, South Campus,
Jinan 250061, People’s Republic of China
e-mail: lshunsh@sdu.edu.cn
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L. Shi et al.
techniques [3], adsorption [4], photodegradation [5, 6], coagulation flocculation [7],
biological processes [8], and so on. However, such technologies usually involve
complicated procedures and are not economically viable.
The catalytic oxidation process is an interesting technique to decompose toxic and/
or non-biodegradable organic compounds in wastewaters, which is able to oxidize
organic pollutants into carbon dioxide or into products that can be eliminated by
biological treatment. Ozone, oxygen, hydrogen peroxide, or a combination of these are
frequently used as an oxidant. In fact, chlorine dioxide is an effective oxidant.
However, there are few reports on the use of chlorine dioxide in the catalytic
oxidization processes [9–13].
The ClO2 catalytic oxidation is an interesting method for the treatment of high
concentration and non-biodegradable organic wastewater. In this study, activated
carbon-MnO2 catalyst was prepared and used for chlorine dioxide catalytic oxidation
of simulated o-chlorophenol wastewater. The benzene ring in o-chlorophenol was
degraded into quinone and carboxylic acids, and finally changed into carbon dioxide
and water during the catalytic oxidation. Then, the degradation reaction mechanism of
o-chlorophenol by chlorine dioxide catalytic oxidation had been put forward based
upon the experiment evidence.
Experimental
Materials
All the reagents used were of analytical grade. The ClO2 solution was prepared by
mixing a hydrochloric acid solution and a sodium chlorite solution before using.
The concentration of chlorine dioxide solution is 9.38 g/L. Simulated wastewater
containing o-chlorophenol was prepared by dissolving 2.00 mL o-chlorophenol in
water in a 2,000 mL volumetric flask. The chemical oxygen demand (COD) of the
wastewater was 2,085 mg/L.
The activated carbon-MnO2 catalyst was prepared by the dipping-calcination
method. First, the activated carbon was immersed into 8% Mn(NO3)2 aqueous
solution for 24 h, then dried at 120 °C for 4 h and calcined at 300 °C for 4 h. The
formed MnO2 was loaded on the surface of activated carbon.
The wastewater treatment process
Simulated wastewater (100 mL) containing o-chlorophenol was added in a 250-mL
flask. The pH value was adjusted by hydrochloric acid solution. The amounts of the
catalysts and ClO2 solution were added. The treatment was carried out at room
temperature for a certain time under the condition of stirring and keeping from light.
The COD of wastewater before and after treatment was measured by the
international standard of ISO6060-1989.
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1783
UV–Vis spectrophotometric analysis
UV–Vis spectrophotometric measurements were performed in a TU-1800PC UV–
Vis spectrophotometer (Beijing Puxi Tongyong Instrument Company, Beijing,
China). A complete spectrum of the water samples could be obtained in the range of
200–1,000 nm. The simulated wastewater containing o-chlorophenol, the effluent
by chemical oxidation, and the effluent by catalytic oxidation were diluted by 2.1
times before determination.
FTIR analysis
FTIR spectra were obtained using a Bruker Tensor-27 FTIR spectrophotometer.
FTIR spectra were recorded from 400 to 4,000 cm-1 wavenumber range with
averaging 32 scans at a resolution of 4 cm-1. For the effluent by chemical oxidation
and the effluent by catalytic oxidation, it was evaporated in a water bath at 80 °C.
The solid samples were obtained and then determined by FTIR spectrophotometer.
Online FTIR analysis during the wastewater treatment
The online FTIR analysis was performed on a ReactIR 4000 spectrophotometer
(Mettler-Toledo AutoChem, Inc., USA). FTIR spectra were recorded from 400 to
4,000 cm-1 wavenumber range at a resolution of 8 cm-1. An amount of 100 mL of
simulated wastewater containing o-chlorophenol was added into a 250-mL flask.
The pH value was adjusted to 1.2 by hydrochloric acid solution. Then, chlorine
dioxide solution containing 100 mg chlorine dioxide, and 6 g of activated carbon-
MnO2 catalyst were added. The magnetic stirrer was under operation during the
online FTIR measurement.
Results and discussion
The wastewater treatment process
The reaction conditions were as follows: the simulated wastewater containing
o-chlorophenol, 100 mL; pH value, 1.2; the concentration of chlorine dioxide,
1,000 mg/L; the dosage of activated carbon-MnO2 catalyst for catalytic oxidation, 6
g; reaction time, 60 min. The COD removal efficiencies of chemical oxidation and
catalytic oxidation are 28.6% and 93.5%, respectively. The COD removal efficiency
of catalytic oxidation is greater than that of chemical oxidation at the same
treatment condition.
UV–Vis spectrophotometric analysis
In order to study the pollutant changes during the oxidation process, it is necessary
to investigate the UV–Vis spectra before and after chlorine dioxide oxidation
treatment. Figure 1 represents the UV–Vis spectra of water samples before and after
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oxidation. As shown in Fig. 1, the simulated wastewater containing o-chlorophenol
has strong absorption peaks at 227 nm and 261 nm (see curve 1), which belong to
the characteristic absorption peak E2 band and B band of phenol, respectively. The
number of peaks increased after the simulated wastewater was treated by chemical
oxidation (see curve 2). The peak at 333 nm was assigned to the product of
p-quinone. The peaks at 234 and 287 nm were assigned to the benzene ring
structure. The number of peaks decreased for the catalytic oxidation by comparison
with the chemical oxidation. The absorption peak intensity at 287 and 333 nm
weakened obviously (see curve 3). It indicates that the extent of COD removal
efficiency by catalytic oxidation is greater than that of chemical oxidation. This
evidence coincides with the data in ‘‘The wastewater treatment process’’.
FTIR analysis
In order to study the pollutant changes during the oxidation process, the FTIR spectra
before and after chlorine dioxide oxidation treatment were further investigated.
Figure 2 represents the FTIR spectra of o-chlorophenol samples before and after
oxidation.
In the FTIR spectrum of o-chlorophenol (curve 1 in Fig. 2), the absorption near
3,520 cm-1 is assigned to the O–H stretching. The absorptions near 3,076 and
3,040 cm-1 are assigned to the aromatic Ar–H stretching. The absorptions near
1,588, 1,480, and 1,453 cm-1 are assigned to the C=C framework vibration of
benzene ring in aromatic compounds (sharp peak). The absorption near 1,198 cm-1
is assigned to the C–O stretching in phenol. The absorption near 1,056 cm-1 is
assigned to the O–H deformation. The strong absorptions near 883, 832, and
3.5
3.0
2.5
2.0
1.5
1.0
2
3
0.5
1
0.0
-0.5
200
400
600
800
1000
Wavelength (nm)
Fig. 1 UV-Vis spectra of water samples before and after oxidation (curve 1: simulated o-chlorophenol
wastewater; curve 2: chemical oxidation; curve 3: catalytic oxidation)
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Chlorine dioxide catalytic oxidation
1785
Fig. 2 Infrared spectra of o-chlorophenol wastewater before and after oxidation (curve 1: o-
chlorophenol; curve 2: chemical oxidation; curve 3: catalytic oxidation)
678 cm-1 are assigned to the Ar–H out-of-plane bending in phenyl. The absorption
near 747 cm-1 is assigned to the C–Cl stretching.
By comparing the spectra of chemical oxidation and catalytic oxidation with that
of o-chlorophenol, the shapes of the curves changed a lot. This indicated that the
pollutant’s chemical structure changed a lot. In the FTIR spectrum of chemical
oxidation (curve 2 in Fig. 2), the absorption near 3,450 cm-1 is assigned to the O–H
stretching in carboxylic acids. The absorption near 1,634 cm-1 is assigned to the
C=O stretching in p-quinone, which is conjugated with C=C double bond. The
absorption near 1,121 cm-1 is assigned to the C–O stretching. The absorption near
620–564 cm-1 is assigned to the O–H out-of-plane deformation. The absorptions
near 2,968 cm-1 and 2,934 cm-1 are assigned to the C–H stretching of CH2 group,
which is formed from the degradation of benzene ring. The absorption near
1,405 cm-1 is assigned to the aromatic C=C stretches in phenyl, which belongs to
the unoxidized benzene ring. However, the peak intensity of 1,405 cm-1 is greatly
reduced.
In the FTIR spectrum of catalytic oxidation (curve 3 in Fig. 2), the absorption near
3,420 cm-1 is assigned to the O–H stretching in carboxylic acids. The absorption near
1,628 cm-1 is assigned to the C=O stretching in p-quinone, which is conjugated with
C=C double bond. The absorption near 1,152-1,106 cm-1 is assigned to the C–O
stretching. The absorption near 620–564 cm-1 is assigned to the O–H out-of-plane
deformation. The absorptions near 3,076 cm-1 and 3,040 cm-1, which are assigned to
the aromatic Ar–H stretching, and the absorption near 1,405 cm-1, which is assigned
to the aromatic C=C stretches in phenyl, are totally disappeared. This evidence
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indicated that the benzene ring in o-chlorophenol had been totally oxidized by chlorine
dioxide.
The absorption near 747 cm-1, which is assigned to the C–Cl stretching, had totally
disappeared after o-chlorophenol was oxidized by chemical oxidation or catalytic
oxidation. At the same time, the benzene ring was also greatly degraded. There is no
C=O stretching absorption peak in the FTIR spectrum of o-chlorophenol. However,
the new absorption peaks of C=O stretching in p-quinone and carboxylic acids
appeared. That is to say, o-chlorophenol maybe degraded into p-quinone and
carboxylic acids in the chlorine dioxide oxidation process.
Online FTIR analysis
Figure 3 gives the 3D online infrared spectrum of wastewater treatment by the
catalytic oxidation method. In Fig. 3, the strong absorption near 3,346 cm-1 is
assigned to the O–H stretching of water. The strong absorption near 1,656 cm-1 is
assigned to the H–O–H bending of water. Figure 4 represents the peak height
(H) versus reaction time. As shown in Fig. 4, the two peak heights increased greatly
in the beginning of the 5-min reaction time, and then increased slowly with the
reaction time.
Four intermediates were detected automatically during the online FTIR analysis.
Its FTIR spectra were obtained. In the FTIR spectrum of intermediate 1 (Fig. 5), the
absorption near 1,698 cm-1 is assigned to the C=O stretching in carboxylic acids,
which should be product (d) in the degradation reaction mechanism. The absorption
near 1,652 cm-1 is assigned to the C=O stretching in p-quinone or carboxylic acids,
which is conjugated with C=C double bond. It should be product (a), (b), or (c) in
the degradation reaction mechanism. The absorptions near 1,559, 1,544, 1,524, and
1,520 cm-1 are assigned to the C=C stretching in ethylene, which is conjugated
with C=O bond. It should be product (a), (b), or (c) in the degradation reaction
Fig. 3 3D online infrared spectrum of wastewater treatment by catalytic oxidation method
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Chlorine dioxide catalytic oxidation
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1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
A
B
0
10
20
30
40
50
60
70
80
t (min)
Fig. 4 Curve of peak height versus reaction time (curve A: 3,346 cm-1 absorption peak; curve B:
1,656 cm-1 absorption peak)
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900
Wavenumber (cm-1)
Fig. 5 Infrared spectrum of intermediate 1 during the reaction process
mechanism. Therefore, intermediate 1 should be one of the p-quinone, butenedioic
acid, chloro-butenedioic acid, and ethanedioic acid.
In the FTIR spectrum of intermediate 2 (the figure is omitted), the absorption
near 1,644 cm-1 is assigned to the C=O stretching in p-quinone or carboxylic acids,
which is conjugated with C=C double bond. It should be product (a), (b), or (c) in
the degradation reaction mechanism. It indicated that o-chlorophenol was oxidized
by chlorine dioxide to p-quinone, butenedioic acid, chloro-butenedioic acid.
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L. Shi et al.
Therefore, intermediate 2 should be one of the p-quinone, butenedioic acid, and
chloro-butenedioic acid.
In the FTIR spectrum of intermediate 3 (the figure is also omitted), the absorption
near 1,636 cm-1 is assigned to the C=O stretching in p-quinone or carboxylic acids,
which is conjugated with C=C double bond. It should be product (a), (b), or (c) in
the degradation reaction mechanism. Therefore, intermediate 3 should be one of the
p-quinone, butenedioic acid, and chloro-butenedioic acid.
In the FTIR spectrum of intermediate 4 (the figure is also omitted), the absorption
near 1,640 cm-1 is assigned to the C=O stretching in p-quinone or carboxylic acids,
which is conjugated with C=C double bond. It should be product (a), (b), or (c) in
the degradation reaction mechanism. Therefore, intermediate 4 should be one of the
p-quinone, butenedioic acid, and chloro-butenedioic acid.
Figure 6 gives the intermediate 1–4’s relative concentration (c) versus reaction
time. As shown in Fig. 6, the relative concentration of intermediate 1 and 2
decreases slightly with the prolonging of reaction time. The relative concentration
of intermediate 3 increases with the extension of reaction time. The relative
concentration of intermediate 4 decreases with the increase of reaction time.
Therefore, intermediate 4 should be p-quinone.
O-chlorophenol was oxidized by chlorine dioxide into p-quinone and carboxylic
acids during the chemical oxidation or the catalytic oxidation. Finally, it was changed
into carbon dioxide and water. Therefore, the degradation reaction mechanism of
o-chlorophenol by chlorine dioxide oxidation was proposed based upon the
experiment evidence. The mechanism was presented in Fig. 7.
5.0
4.5
4.0
3
3.5
3.0
2.5
2.0
4
1.5
1.0
0.5
0.0
1
2
-0.5
0
10
20
30
40
50
60
70
80
t (min)
Fig. 6 Curve of intermediate 1–4’s relative concentration versus reaction time (curve 1: intermediate 1;
curve 2: intermediate 2; curve 3: intermediate 3; curve 4: intermediate 4)
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Chlorine dioxide catalytic oxidation
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O
OH
Cl
Cl
ClO2
O
(a)
COOH
ClO2
(a)
(a)
CO2
+
+
HCl
COOH
(b)
Cl
COOH
COOH
COOH
ClO
2
+
COOH
(c)
(d)
COOH
COOH
Cl
ClO
2
CO2
+
+
HCl
H2O
COOH
COOH
ClO
2
CO
H O
2
+
2
COOH
ClO
2
CO
H O
2
+
2
COOH
Fig. 7 Degradation reaction mechanism of o-chlorophenol
Conclusions
(1) The chlorine dioxide catalytic oxidation process is an interesting technique for
the treatment of wastewater. The COD removal efficiencies of chemical
oxidation and catalytic oxidation are 28.6 and 93.5%, respectively. The COD
removal efficiency of catalytic oxidation is greater than that of chemical
oxidation at the same treatment condition. It has great practical significance
for the design of actual wastewater treatment process.
(2) By using UV–Vis and an online FTIR analysis technique, the intermediates
during the degradation process were obtained. It was useful to investigate the
degradation reaction mechanism of the pollutants. The result has important
theoretical significance.
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Acknowledgments The authors would like to thank the financial support from the Shandong Provincial
Natural Science Foundation (No. ZR2009BM007), and the Scientific Research Foundation for the
Returned Overseas Chinese Scholars, State Education Ministry, China.
References
1. R.M. Liou, S.H. Chen, M.Y. Hung et al., Chemosphere 59, 117–125 (2005)
2. C.F. Yang, Y. Qian, L.J. Zhang et al., Chem. Eng. J. 117, 179–185 (2006)
3. W. Kujawski, A. Warszawski, W. Ratajczak et al., Desalination 163, 287–296 (2004)
4. M. Ahmaruzzaman, D.K. Sharma, J. Colloid Interface Sci. 287, 14–24 (2005)
5. R.W. Mathews, S.R. McEvoy, J. Photochem. Photobiol. A: Chem. 64, 231–246 (1992)
6. I.B. Will, J.E. Moraes, A.C. Teixeira et al., Sep. Purif. Technol. 34, 51–57 (2004)
7. M. Tomaszewska, S. Mozia, W. Morawski, Desalination 162, 79–87 (2004)
8. G. Tziotzios, M. Teliou, V. Kaltsouni et al., Biochem. Eng. J. 26, 65–71 (2005)
9. X.Y. Jin, J.L. Chen, A.M. Li et al., Ion Exch. Adsorpt. 19, 61–66 (2003)
10. X.Y. Bi, P. Wang, H. Jiang, H.Y. Xu, S.J. Shi, J.L. Huang, J. Environ. Sci. 19, 1510–1515 (2007)
11. L. Shi, N. Li, C. Wang, C. Wang, J. Hazard. Mater. 178, 1137–1140 (2010)
12. X.Y. Bi, P. Wang, H. Jiang, J. Hazard. Mater. 154, 543–549 (2008)
13. X.Y. Bi, P. Wang, C.Y. Jiao, H.L. Cao, J. Hazard. Mater. 168, 895–900 (2009)
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