Kinetics of DC discharge-induced degradation of nitrophenol in aqueous solution

Article abstract of DOI:10.1134/S0018143915010026

The kinetics of degradation of nitrophenol and buildup of its products in the liquid cathode (doubly distilled water) of atmospheric-pressure dc discharge in air have been experimentally studied. It has been shown that the main products are formaldehyde a

Full text of DOI:10.1134/S0018143915010026

ISSN 0018ꢀ1439, High Energy Chemistry, 2015, Vol. 49, No. 1, pp. 64–67. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © E.S. Bobkova, A.V. Sungurova, N.A. Kobeleva, 2015, published in Khimiya Vysokikh Energii, 2015, Vol. 49, No. 1, pp. 67–70.
PLASMA CHEMISTRY
Kinetics of DC DischargeꢀInduced Degradation of Nitrophenol
in Aqueous Solution
E. S. Bobkova, A. V. Sungurova, and N. A. Kobeleva
Research Institute of Chemical Thermodynamics and Kinetics, Ivanovo State University of Chemical Technology,
pr. F. Engel’sa 7, Ivanovo, 153000 Russia
eꢀmail: esbobkova@isuct.ru
Received December 25, 2013; in final form, July 21, 2014
Abstract—The kinetics of degradation of nitrophenol and buildup of its products in the liquid cathode (douꢀ
bly distilled water) of atmosphericꢀpressure dc discharge in air have been experimentally studied. It has been
shown that the main products are formaldehyde and carboxylic acids. It has been found that the discharge
treatment is accompanied by the formation of nitric acid in the liquid phase. The kinetic characteristics of the
nitrophenol degradation process and its energy efficiency have been determined.
DOI: 10.1134/S0018143915010026
Water quality impairment in natural sources and of nitrophenols. On the other hand, chemical methꢀ
toughening the standards for drinking water call for ods, such as chlorination and permanganate oxidaꢀ
development of novel, innovative water treatment proꢀ tion, lead to the formation of toxic intermediates
because of incomplete decomposition. Therefore, it is
important to explore whether electric discharges of
various types can be used for cleaning aqueous soluꢀ
tions of nitroaromatic compounds. Hao et al. [12]
cesses. An effective method of removal of various aroꢀ
matic hydrocarbons, synthetic surfactants, and carꢀ
boxylic acids from aqueous solutions is the use of gas
discharge excited either directly in the solution or over
its surface. Investigation of the mechanism of these
processes in plasma–solution systems and determinaꢀ
tion of their reaction routes are of great importance for
both pure science and practical purposes, in particular,
for the development of technology and the design of
devices for use in potable water pretreatment and
wastewater treatment processes. Various types of elecꢀ
tric discharge are use for these purposes.
studied the degradation of pꢀnitrophenol in a pulsed
corona combined with ozonation. This method has
proved effective in the degradation of the test comꢀ
pound (96%); carboxylic (formic and acetic) acids and
nitrate ions were found as products.
The aim of this work was to study the kinetics of
decomposition of nitrophenol and identify the prodꢀ
ucts of its transformation in an electrolyticꢀcathode dc
discharge, which had not been investigated in relation
to the degradation of nitrophenol.
For example, highꢀvoltage pulse discharge is effecꢀ
tive in removal of organic compounds from aqueous
solutions, especially, highly toxic liquids such as soluꢀ
tions containing organic dyes [1, 2], tributyl phosꢀ
phate [3], and 4ꢀchlorophenol [4]. Dielectricꢀbarrier
discharge (DBD) shows good results in the destruction
of synthetic detergents [5], formaldehyde and acetone
[6], and carboxylic acids [7]. The degradation of pheꢀ
nol in atmosphericꢀpressure dc discharge is docuꢀ
mented quite well [8, 9]. However, data on the appliꢀ
cation of highꢀenergy chemistry methods to decomꢀ
position of nitroaromatic compounds are quite scanty.
These toxic compounds are indispensable raw materiꢀ
als and intermediate products in the manufacture of
dyes, pesticides, medicinal drugs, and explosives.
Being toxic to microorganisms, they do not undergo
biodegradation [10]. The biodegradation of nitro
compounds is hampered by a high strength of the bond
EXPERIMENTAL
The experimental setup was described in [13]. An
atmospheric pressure directꢀcurrent discharge in air
was excited by applying dc voltage across the metal
anode and the surface of the solution. The distance
between the anode and the electrolyte surface was
4 mm; the discharge current, 40 mA; and the electroꢀ
lyte volume, 80 mL. A solution of pꢀnitrophenol with
a concentration of 75 mg/L in doubly distilled water
was used. After a certain discharge time, the pH of the
solution and concentrations of nitrophenol, phenol,
carboxylic acids, aldehydes, and nitrate and nitrite
ions were measured. A fresh portion of the solution
was used for each treatment time. The concentration
of the NO2 group with the aromatic ring [11]. Simple of nitrophenol was determined by measuring absorꢀ
physical methods, including adsorption and memꢀ bance of the solution at a wavelength of 350 nm on a
brane filtration are ineffective in reducing the toxicity Hitachi Uꢀ2001 spectrophotometer (Japan). The conꢀ
64

KINETICS OF DC DISCHARGEꢀINDUCED DEGRADATION OF NITROPHENOL
65
с
, mmol/L
pH
6
с
, mmol/L
с
, mmol/L
1.0
0.8
0.6
0.4
0.2
0.7
0.6
0.5
0.4
0.3
0.2
0.1
1
0.4
0.3
0.2
0.1
5
4
3
2
1
2
0
0
10
20
, min
30
40
t
2
35
0
5
10
15
20
25
30
Fig. 2. Dependence of the concentration of (
acids and ( ) aldehydes on the time of atmosphericꢀpresꢀ
1) carboxylic
t
, min
2
sure dc discharge treatment of nitrophenol in aqueous
solution.
Fig. 1. Plots of (
1
) nitrophenol concentration and (
2
) pH
of the solution as a function of time of atmosphericꢀpresꢀ
sure dc discharge treatment of nitrophenol in aqueous
solution.
molecules per 100 eV at a treatment time of
t
→
0, i.e.,
dc
dt
at a rate of
Under the same treatment
= −c0K.
centrations of phenol and aldehydes were found by
measuring the intensity of fluorescence, excited at the
absorption band maximum, with a Fluoratꢀ02 fluoꢀ
rometer (Russia). Phenol was extracted with butyl
acetate and reꢀextracted with an aqueous solution folꢀ
lowed by acidification of the aqueous extract. In the
case of aldehydes, a luminescent compound was the
product of their reaction with 1,3ꢀcyclohexanedione
in the presence of ammonium ions. The concentration
of carboxylic acids was determined from the absorꢀ
bance at 400 nm of the compound produced by the
reaction of an acid with ammonium metavanadate.
The procedure for the determination of nitrate ions
was based on their reaction with sodium salicylate in
the presence of sulfuric acid to form the salt of nitroꢀ
salicylic acid, which absorbs at a wavelength of
400 nm. The method used for determining nitrite ions
was based on their ability to diazotize sulfanilic acid to
form a reddish violet dye of the diazo compound with
1ꢀnaphthylamine. Random error was verified in five
measurement runs using a confidence level of 0.95. On
average, the concentration determination error did
not exceed 15%.
t→0
conditions, this energy yield was 0.003 molecule per
100 eV for phenol [10] or 0.001 molecule per 100 eV
for Sulfonol [14]. The discharge in question has quite
a high energy efficiency with respect to the degradaꢀ
tion of nitrophenol compared to other benzene ringꢀ
containing organic compounds.
Considering the possible nitrophenol degradation
products, it was logical to assume that the detachment
of the nitro group would result in phenol as the main
product, but this was not the case. The absence of pheꢀ
nol in the degradation products of nitrophenol subꢀ
jected to treatment in a positive pulsed discharge was
noted in [12]. We failed to detect hydroxylated phenols
(hydroquinone, catechol); it is likely that they rapidly
decompose into carboxylic acids and aldehydes. This
fact was confirmed by Wang et al. [15], who studied the
pulsed discharge treatment of a soil solution for
removal of nitrophenol. Grymonpre et al. [18] studied
the decomposition of resorcinol, catechol, and 1,4ꢀ
hydroquinone solutions. They found that the degradaꢀ
tion products are carboxylic acids and СО2, with the
degradation rate of dihydroxybenzenes being higher
than that of phenol. In addition, the balance of carbon
in the initial nitrophenol solution and the nitrophenol
RESULTS AND DISCUSSION
Figure 1 illustrates the kinetics of the dischargeꢀ degradation products we have found (carboxylic acids
induced degradation of nitrophenol. It can be seen
that the rate curve is described well by the firstꢀorder
and aldehydes) holds accurate to ~10% (Fig. 2). For
example, at a treatment time of 15 min, the acid conꢀ
tains 1.8 mmol/L of carbon atoms (on acetic acid
basis), the aldehyde contains 0.3 mmol/L (on formalꢀ
dehyde basis), and the residual nitrophenol has
1.2 mmol/L versus the initial carbon content of
3.6 mmol/L. The small deficit of carbon in the prodꢀ
ucts may be due to the formation of carbon dioxide,
law in nitrophenol
with an effective
c = c0 exp(−Kt)
rate constant of 0.073 0.006 s–1 (pair correlation
coefficient 0.98). These data allowed us to calculate
the energy efficiency of decomposition of nitrophenol.
Under the given conditions, the impedance drop is
920 V, which corresponds to the power input to the
discharge of 37 W. Calculation gave a Gꢀvalue of 4.2 which is released to the gas phase.
HIGH ENERGY CHEMISTRY
Vol. 49
No. 1
2015

66
BOBKOVA et al.
ment of the nitrophenol solution. The concentration
с
, mmol/L
с
, mmol/L
0.010
of nitrite ions initially increases after the beginning of
treatment and then decreases, since nitrite rapidly disꢀ
proportionates to give nitrate in an acidic medium.
Assuming that the nitrate ion results from the dissociꢀ
ation of nitric acid, the calculation of the pH in terms
0.012
0.010
0.008
0.006
0.004
0.002
1
0.008
0.006
of NO–3 concentration gives values close to those
0.004
obtained experimentally. Thus, pH is ~2.1 at a treatꢀ
ment time of 15 min. The source of nitrate ions can be
both nitrophenol and nitrogen oxides and nitric acid
produced in the gas phase [8]. However, the amount of
decomposed nitrophenol significantly exceeds the
amount of nitrate ions. Apparently, the nitrophenol
groups during degradation yield nitric oxide, which is
sparingly soluble in water and is released into the gas
phase. A source of nitric acid is the reaction of the
solution with NO2 molecules that are formed by the
discharge in air and readily converted into nitric acid,
2
0.002
0
5
10
15
, min
20
25
30
t
Fig. 3. Dependence of the concentration of (
nitrite ( ) ions on the time of atmosphericꢀpressure dc disꢀ
charge treatment of nitrophenol in aqueous solution.
1) nitrate and
2
e.g. via the reaction 2NO2 + H2O
→
HNO3 + HNO2.
As follows from the data in Fig. 2, which shows the
time dependence of the concentration of carboxylic
acids and aldehydes, these products are intermediate
and undergo degradation. In [16] it was found that the
DBR treatment of aqueous solutions of carboxylic
acids results in aldehydes and carbon oxides and the
treatment of aqueous aldehyde solutions yields only
carbon oxides [17]. This behavior is observed for nitroꢀ
phenol as well.
Although the mechanism of nitrophenol degradaꢀ
tion by the action of electrolyticꢀcathode dc discharge
has not been completely explored, it can be concluded
that the chemical degradation is largely due to the forꢀ
i
mation of active submolecular (i
, O, H+,
,
OH
HO2
solvated electrons, etc.) and molecular (O2, H2O2
)
species [19, 20]. These species have a high oxidation
potential and can effectively decompose organic polꢀ
Figure 3 presents the concentration of (
1) nitrate lutants. A possible nitrophenol degradation scheme is
and ( ) nitrite ions as a function of the time of treatꢀ as follows:
2
а + +
NO–2 NO–3
Nitrophenol
Hydroxy derivatives of phenol
Carboxylic acids
Aldehydes
CO2 + CO
CO2 + CO
CONCLUSIONS
REFERENCES
1. Abdelmalek, F., Gharbia, S., and Benstaali, B., Water
Res., 2004, vol. 38, no. 9, p. 2339.
Directꢀcurrent discharge with electrolytic cathꢀ
ode has a high nitrophenol destruction efficiency
(95%); the degradation of nitrophenol occurs at a
higher rate compared to that for phenol or Sulfonol
in a discharge of this type. The results can be used in
the development of a plasmaꢀchemical water
decontamination technology for removal of nitroꢀ
phenol.
2. Burlica, R., Kirkpatrick, M.J., and Finney, W.C.,
J. Electrost., 2004, vol. 62, no. 9, p. 309.
3. Moussa, D. and Brisset, J.L., J. Hazard Mater., 2003,
vol. 102, no. 2/3, p. 189.
4. Du, C.M., Yan, J.H., and Cheron, B., Plasma Chem.
Plasma Process., 2007, vol. 27, no. 5, p. 635.
5. Bobkova, E.S., Grinevich, V.I., Ivantsova, N.A., and
Rybkin, V.V., Plasma Chem. Plasma Process., 2012,
vol. 32, no. 1, p. 97.
ACKNOWLEDGMENTS
6. Bobkova, E.S., Grinevich, V.I., Ivantsova, N.A., and
Rybkin, V.V., Plasma Chem. Plasma Process., 2012,
vol. 32, no. 4, p. 703.
We are greatly indebted to Professor V.V. Rybkin for
useful discussion of the results.
7. Ognier, S., Iyaꢀsou, D., Fourmond, C., and
Cavadias, S., Plasma Chem. Plasma Process., 2009,
vol. 29, no. 4, p. 261.
This work was supported by the Russian Foundaꢀ
tion for Basic Research, project no. 14ꢀ02ꢀ01113 A.
HIGH ENERGY CHEMISTRY
Vol. 49
No. 1
2015

KINETICS OF DC DISCHARGEꢀINDUCED DEGRADATION OF NITROPHENOL
67
8. Bobkova, E.S., Sungurova, A.V., and Rybkin, V.V., 15. Wang, T.C., Lu, N., and Li, J., J. Hazard Mater., 2011,
High Energy Chem., 2013, vol. 47, no. 4, p. 200.
vol. 195, p. 276.
9. Bobkova, E.S., Krasnov, D.S., Sungurova, A.V., Shishꢀ
16. Bobkova, E.S., Isakina, A.A., Grinevich, V.I., and
Rybkin, V.V., Russ. J. Appl. Chem., 2012, vol. 85, no. 1,
p. 71.
kina, A.I., and Shikova, T.G., High Energy Chem.
2013, vol. 47, no. 2, p. 53.
,
10. Gemma, E., Gianfranco, D., and Gumersindo, F.,
17. Bobkova, E.S., Grinevich, V.I., Isakina, A.A., and
Rybkin, V.V., Izv. Vyssh. Uchebn. Zaved., Khim. Khim.
Tekhnol., 2011, vol. 54, no. 10, p. 85.
J. Biodegrad., 2011, vol. 22, no. 3, p. 539.
11. Bhatti, Z.I., Toda, H., and Furukawa, K., Water Res.
2002, vol. 36, no. 5, p. 1135.
12. Hao, X.L., Zhang, X.W., and Lei, L.C., J. Carbon
,
,
18. Grymonpre, D.R., Sharma, A.K., Finney, W.C., and
Locke, B.R., Chem. Eng. J., 2001, vol. 82, nos. 1–3,
p. 189.
2009, vol. 47, no. 1, p. 153.
13. Bobkova, E.S., Shikova, T.G., Grinevich, V.I., and
Rybkin, V.V., High Energy Chem., 2012, vol. 46, no. 1,
p. 56 (or Bobkova, E.S., Shikova, T.G., and
Rybkin, V.V., High Energy Chem., 2012, vol. 46, no. 2,
p. 141 ?).
14. Shutov, D.A., Konovalov, A.S., Isakina, A.A., and
Bobkova, E.S., High Energy Chem., 2013, vol. 47, no. 4,
p. 203.
19. Shi, J.W., Bian, W.J., and Yin, X.L., J. Hazard Mater.
2009, vol. 171, nos. 1–3, p. 924.
,
20. Bobkova, E.S., Shikova, T.G., Grinevich, V.I., and
Rybkin, V.V., High Energy Chem., 2012, vol. 46, no. 1,
p. 56.
Translated by S. Zatonsky
HIGH ENERGY CHEMISTRY
Vol. 49
No. 1
2015