Supporting Information
Degradation of p-Nitrophenol in Soil by Dielectric Barrier
Discharge Plasma
Rui Li1, Yanan Liu1*, Yu Sun1, Wenjuan Zhang1, Ruiwen Mu1, Xiang Li1, Hong Chen1,
Pin Gao1, Gang Xue1, Stephanie Ognier2
1 School of Environmental Science and Engineering, Dong Hua University, Shanghai, China
2 UPMC Univ Paris 06, EA 3492, Laboratoire de Génie des ProcédésetTraitements de Surface,
F-75005, Paris, France
*Corresponding author
E-mail: liuyanan@dhu.edu.cn
Tel: 86-21-67792538
Fax: 86-21-67792522
Supporting Information: 9 pages, 3 tables, 5 figures
S1 Introduction of the plasma reactor
The plasma treatment was operated in a plane-to-plane dielectric barrier discharge reactor.
The stainless steel high voltage electrode and the ground electrode lay on the top and bottom of
the reaction kettle. The reaction kettle (No.1, DBD-100, Corona lab, Nanjing, China) was made of
isoelectronic quartz glass, which ensured the steady formation of micro-electric current filaments
and was beneficial for the generation of plasma species. It was an 8mm high and 150-mm
diameter cylinder, which was covered by a 3mm glass cover. The top glass cover could be
removed so that sand samples could be placed inside to be treated. When analyzing the role of
ozone in this system, another reaction kettle (Kettle No.2) was introduced as a reactor and the
origin kettle (Kettle No.1 would act as an ozone generator). Air was introduced into the system
with an air pump which could moderate the flow rate.
S2 Loading and extracting PNP
A predetermined amount of PNP-contaminated soil were prepared as follows: the 100 g soil
samples were artificially mixed with 40 mL of PNP acetone solution (1000 mg/L). After shaking
for 4 h on a constant temperature shaking table, the contaminated samples were naturally dried for
24 h. The PNP distribution in the sands was uniform at approximately 400 mg/kg. The pH of the
sands was adjusted with NaOH and HCl solutions.
To extract PNP from contaminated soil, 100 mL of deionized water was added into the sand
samples, then shaken for 2 h and centrifuged at 4000 rpm for 10 min before passing through a
0.45-μm filter for measurement. The recovery of PNP was over 80%, satisfying the requirement
for analysis.
S3Ultraviolet spectrophotometry
3.1 The determination of maximum absorption wavelength of UV-vis spectra
The solution of PNP with a concentration of 10mg/L was made, which was scanned by a
UV-vis spectrophotometer at the wavelength of 190 to 900nm. The result was shown in Figure S1.
It was clear that the absorption peak was at 321nm.
Absorbance (a.u.)
0.4
0.3
0.2
0.1
0.0
200
300
400
500
600
700
800
900
Wavelength (nm)
Fig. S1. UV-Vis Absorption Spectra of PNP
3.2 Calibration curve of UV-vis absorption spectra
Standard solutions were made with a concentration of 1, 3, 5, 8, 10 mg/L and then were
detected by the spectrophotometer for the absorbance.Linear-regression analysis was carried out
with the concentration (mg/L) as abscissa and absorbance (a.u.) asordinate. The calibration curve
was shown in Figure S2. It was manifest that the absorbance and the PNP concentration had a
good linear correlation with a R2 of 0.9973.
0.6
y=0.0539x+0.0188
2
R =0.9973
Absorbance (a.u.)
0.5
0.4
0.3
0.2
0.1
0.0
0
2
4
6
8
10
Concentration (mg/L)
Fig. S2. Calibration Curve of PNP for UV-Vis Absorption Spectra
3.3 Method recovery and precision of ultraviolet spectrophotometry
3g of PNP polluted soil were extracted with 100mL of deionized water and then shaken for 2
hours. After being centrifuged at 4000 rpm for 10 min and passed through a 0.45-μm filter, the
soils were then ready for measurement.The concentration was calculated according to the linear
regression equation. The recovery rate and relative standard deviation were shown in Table S1.
Table S1. Method Recovery and Precision of Ultraviolet Spectrophotometry
Detection
Average recycle
Recycle rate
sample
concentration
（mg/L）
PNP
（%）
11.4
95.0
9.5
79.2
10.8
90.0
11.1
92.5
9.6
80.0
11.8
98.3
10.4
86.7
10.9
90.8
9.9
82.5
RSD
rate
（%）
88.1
（%）
7.2
0.858333
10.3
S4 High Performance Liquid Chromatography
4.1 Chromatographic conditions
Chromatographic column: Eclipse XDB-C18 column(150×4.6mm，5μm); mobile phase:
methyl alcohol: water (adjust pH to 2 with phosphoric acid )= 6:4(V:V);flow rate:0.6mL/min;
column temperature: 30℃; wavelength: 242nm;sample volume: 20μL.
After optimization of the conditions, the chromatogram was shown in Figure S3 and the
retention time for these intermediates was illustrated in Table S2.
40
4
2
35
30
Area (mAU)
25
20
15
6
3
10
5
1
5
0
-5
0
2
4
6
8
10
12
Time (min)
Fig. S3. Chromatogram of Intermediates of PNP for HPLC
Table S2. Retention Time of Different Intermediates for HPLC
Number
Byproducts
Retention time (min)
1
maleic acid
2.4
2
hydroquinone
2.8
3
p-benzoquizone
3.8
4
catechol
4.4
5
4-nitrocatechol
6.6
6
PNP
10.5
4.2 Optimization of chromatographic conditions
The mixed standard solutions of five intermediates and PNP with a concentration of 10mg/L
was made for the optimization of chromatographic conditions.
(1) Determination of flow rate
Under the conditions above, the flow rate was changed to 0.2、0.3、0.4、0.5、0.6、0.7、0.8、
0.9、1.0mL/min and the peaks for every intermediate were analyzed. The height and width of
peaks for all intermediates reached maximum so 0.6mL/min was selected as the best flow rate.
(2) Determination of the ratio of mobile phase
With a flow rate of 0.6mL/min, the peaks were observed when the mobile ratio was 70:30、
60:40、55:45、50:50、45:55、15:85、12:88、10:90、9:91、7:93、5:95. The results showed that
60:40 was the best ratio for this situation.
4.3 Calibration curve
Mixed standard solutions were made with a concentration of 1, 3, 5, 8, 10 mg/L for all
intermediates and then were detected by the spectrophotometer for the peak area.Linear-regression
analysis was carried out with the concentration (mg/L) as abscissa and peak area (mAU*min)
asordinate. The calibration curves were shown in Figure S4. It was clear that the peak area and
concentration had a good linear correlation for every intermediate.
5
0.45
0.30
0.15
0.00
0
4
3
2
1
0
2
4
6
8 10
Concentration (mg/L)
3.0
hydroquinone
y=0.0406x+0.0182
2
R =0.9995
Area (mAU*min)
maleic acid
y=0.072x-0.07
2
R =0.9891
0.60
Area (mAU*min)
Area (mAU*min)
0.75
0
2
4
6
8
10
2.5 p-benzoquizone
y=0.2631x+0.0116
2.0
2
R =0.9991
1.5
1.0
0.5
0.0
3.0
1.5
0.0
3
2
1
0
0
2
4
6
8
Concentration (mg/L)
10
4
6
8
10
8
4 -nitroca techo l
y= 0 .34 32 x+ 0.0 28 1
2
R = 0.9 99 5
Area (mAU*min)
4.5
Area (m AU*m in)
Area (mAU*min)
catechol
y=0.6433x+0.0309
2
R =0.9992
2
Concentration (mg/L)
4
6.0
0
Concentration (mg/L)
4
2
0
0
2
4
6
8
10
C o ncen tratio n (m g/L )
PNP
y=0.7091x+0.0219
2
R =0.9995
6
0
2
4
6
8
10
Concentration (m g/L)
Fig. S4. Calibration Curves of Different Intermediates for HPLC
S5 Ion chromatography
To analyze the small molecule produced by the degradation processes, IC was
employed for acetic acid, methanoic acid, nitrate and oxalic acid. The retention times
for these four compounds were illustrated in Table S3.
Table S3. Retention Time of Different Ions for IC
Number
Byproducts
Retention time (min)
1
acetic acid
2.6
2
methanoic acid
2.7
3
nitrate
4.5
4
oxalic acid
7.3
Mixed standard solutions were made with a concentration of 1, 3, 5, 8, 10 mg/L for all
intermediates except nitrate (with standard solutions of 5, 10, 15, 20, 30mg/L) and then were
detected by the spectrophotometer for their peak areas.Linear-regression analysis was carried out
with the concentration (mg/L) as abscissa and peak areas asordinate. The calibration curves
wereshown in Figure S5.
methanoic acid
y=0.0312x+0.0504
2
R =0.9992
0.3
0.2
0.1
0.45
0.30
0.15
0
2
4
6
acetic acid
y=0.0439x+0.1457
2
R =0.9845
0.60
Area (mAU*min)
Area (mAU*min)
0.4
8
10
0
2
4
6
8
10
Concentration (mg/L)
Concentration (mg/L)
0.75
oxalic acid
y=0.0497x+0.1495
2
R =0.9751
0.45
Area (mAU*min)
Area (mAU*min)
0.60
0.30
0.15
0
2
4
6
8
Concentration (m g/L)
10
nitrate
y=0.0227x-0.0158
2
R =0.9992
0.60
0.45
0.30
0.15
0
5
10
15
20
25
30
35
Concentration (mg/L)
Fig. S5. Calibration Curve of Different Ions for IC
S5 GC-MS conditions
The carrier gas was He. The flow rate was 1mL/min. The column temperature started at 30℃
and then increased to 220℃at a rate of 15℃/min. Each time the sample volume was 0.4 μg.