1. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456
ISSN:2249-5347
IJSID
International Journal of Science Innovations and Discoveries An International peer
Review Journal for Science
Research Article Available online through www.ijsidonline.info
PHOTO CATALYTIC DEGRADATION OF M-DINITROBENZENE USING SEMICONDUCTOR ZnO AND H 2O2
Rekha Rani Agarwal and Sangita Gupta*
Global College of Technology, Sitapura, Jaipur, India
ABSTRACT
Received: 15-07-2012
Photo catalytic degradation of chemical pollutant in water was investigated for
various parameters such as pH (5-10), irradiation time (0.0-180min.), light intensity
Accepted: 08-10-2012
(40.0-90.0mW/cm2), concentration of substrate (0.10mM-2.50mM), concentration of
catalyst (0.06-0.22grams) and concentration of H2O2(0.05-0.35mL/h) etc. The m-
*Corresponding Author
Dinitrobenzene acts as a substrate, ZnO acts as a photo catalyst and H 2O2 used as an
accelerator. The photo catalytic degradation of 10mM m-Dinitrobenzene is optimum at
pH 8.5, light intensity 70 mW/cm2, with concentration of ZnO is 0.14grams and conc. of
H2O2 is 0.30mL/h respectively.
Keywords : Photo catalytic degradation, Zinc Oxide, m-Dinitrobenzene.
Address: INTRODUCTION
Name:
Sangita Gupta
Place:
Global College of Technology,
Jaipur, India.
E-mail:
sangita.uor@gmail.com INTRODUCTION
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448

2. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456
Photo catalysis is a phenomenon, in which an electron-hole pair is generated on exposing a semiconducting material.
INTRODUCTION
This electron can be used for reducing a substrate, whereas the hole may be utilized for oxidation. Thus the chemical reactions
that occur in the presence of a semiconductor and light are collectively termed as photo catalytic reaction. Semiconductor can
be used as a photo catalyst and degrade organic pollutants in water to less harmful in organic material [1]. m-Dinitrobenzene
is an important compound used as an intermediate or precursor in the manufacture of organic dyes, pesticides ,antiseptic
agents, medicine and the synthesis of pharmaceuticals. Nitro aromatic compounds (NAC) are widely used in chemical
industries (synthesis of dyes, pesticides, explosives, etc.) and have been associated with groundwater contamination [2]. The
large-scale manufacture and use of NAC has led to significant contamination of soils and groundwater. Biological treatment of
aqueous solutions of NAC is a complicated problem. NAC are not well biodegraded [3]. Their biological treatment is limited by
their toxicity at high concentrations to microorganisms and sometimes produces recalcitrant or toxic by-products [4]. Some
chemical oxidation methods have been recommended as a pre-treatment step for the purification of NAC-containing
wastewater. Photocatalytic oxidation with Ti[O.sub.2] [5, 6]; various advanced oxidation processes (AOPs) including ozone, UV
radiation, and hydrogen peroxide [7, 8]; elemental iron ([Fe.sup.0])/ultrasound [9]; etc.. The photo catalytic degradation of
various types of pollutants using solar radiation was studied at pilot scale. This technology has been developed and it is
currently being evaluated for application at pilot plant and semi-industrial scales of testing (Zhang et al., 1994)[10]. The use of
photochemical technologies has been shown to be a promising alternative for the detoxification of industrial effluents [11-13],
especially from the environmental point of view [14]. The possibility of combining heterogeneous catalysis with solar
technology to achieve complete mineralization of toxic organic pollutants has received much attention in recent years [15].
The sun can be used as an economic and ecological source of light, which will save the installation and energy consumption
expenses of an artificial light source [16]. Hussein et al.[17] reported that TiO 2 and ZnO have good photo catalytic properties
nominated both catalyst to be promising substrate for photo-degradation of water pollutant and show the appropriate activity
in the range of solar radiation. Semiconductors (ZnO, TiO 2) and mediated photo catalysis are fast emerging technology for the
treatments of organic contaminants in wastewater[18-22].
Solutions were prepared in absolute alcohol and double distilled water. Reagent such as p- nitro aniline, H2O2 and ZnO
EXPERIMENTAL
were used. Measurements of pH, irradiation time, light intensity and optical density were carried out using digital pH meter
(Systronics Model 335), 200W tungsten lamp (Philips), Solarimeter (Surya Mapi Model CEL201) and spectrophotometer
(Systronics Model 106). The solution of 10mM m-Dinitrobenzene was prepared by dissolving in absolute alcohol and double
distilled water. H2O2 was added in this solution and it was divided into four parts. First part was kept in dark, second part was
exposed to light, third part added with ZnO and it was kept in dark and last fourth part containing above solution and ZnO,
was exposed to light. After keeping these solutions for three hours, the amount of unreacted M m-Dinitrobenzene was
measured in each solution. There was no change in the optical density of first three solutions; however in the fourth solution
the concentration of unreacted M m-Dinitrobenzene decreases with exposure of light, it means optical density changes. From
this observation one can conclude that this reaction requires presence of light as well as ZnO and this reactions follows photo
catalytic route. The solution of 10mM m-Dinitrobenzene with pH = 8.5 was prepared taking, and added the quantity of ZnO =
0.14gram and H2O2 = 0.30mL/h. It was then exposed to 200W tungsten lamp. The optical density of this solution was observed
at regular time intervals. It was observed that the amount of p- nitro aniline decreases with increasing time of exposure as
International Journal of Science Innovations and Discoveries, Volume 2, Issue 5, September-October 2012
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3. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456
shown in Table 1. A plot of 1+log O.D. (optical density) against time was linear as shown in Fig. 1. The rate constant was
calculated with this expression: k = 2.303 × slope .
The above same procedure was repeated at different pH (5.0-10.0) and rate constant was calculated. The effect of pH is
Effect of pH
depicted in Table 1(a) and graphically represented in Fig. 1(a)
The effect of concentration of m-Dinitrobenzene on the rate of its photo catalytic degradation was studied by variation in
Effect of concentration of m-Dinitrobenzene
concentrations of m-Dinitrobenzene, keeping all other factors constant. The results obtained are summarized in Table 1(b)
and Fig. 1(b) .
TABLE-1
0 0.6253
Time (min.) 1+log (O.D.)
15 0.6052
30 0.5934
45 0.5803
60 0.5683
75 0.5564
90 0.5477
105 0.5286
120 0.5204
135 0.5114
150 0.4941
165 0.4805
180 0.4704
TABLE-1(a)
5 1.9
pH K × 105 (sec -1)
5.5 2.13
6 2.38
6.5 2.59
7 2.77
7.5 2.98
8 3.16
8.5 3.26
9 3.1
9.5 2.98
10 2.83
The effect of variation in the amount of photo catalyst on the rate of photo catalytic degradation of m-Dinitrobenzene was
Effect of concentration of photo catalyst
performed. The results give in Table 1(c) and Fig. 1(c)
The effect of addition of amount of H2O2 on the rate of the photo catalytic degradation of m-Dinitrobenzene was also
Effect of concentration of hydrogen peroxide
investigated. The results give in Table 1(d) & Fig.1(d).
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4. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456
The effect of variation of light intensity on the photo catalytic degradation of m-Dinitrobenzene was also investigated and the
Effect of light intensity
observations are summarized in Table 1 (e) and Fig1 (e).
TABLE-1(b)
0.1 1.41
[ m-Dinitrobenzene] ×10-2M k × 105(sec -1)
0.2 1.67
0.3 1.72
0.4 1.83
0.5 1.97
0.6 2.25
0.7 2.71
0.8 3.26
0.9 2.93
1 2.55
1.1 2.44
TABLE-1(c)
0.06 2.16
Amount of photo catalyst(g) k × 105 (sec-1)
0.08 2.27
0.1 2.36
0.12 2.8
0.14 3.26
0.16 3.24
0.18 3.25
0.20 3.22
0.22 3.24
TABLE-1(d)
0.05 2.45
H2O2(mLh-1) k × 105 (sec -1)
0.1 2.6
0.15 2.74
0.2 2.96
0.25 3.11
0.3 3.26
0.35 3.27
Light Intensity (mW cm-2)
TABLE-1(e)
40 1.67
k × 105 (sec -1)
50 2.08
60 2.51
70 3.26
80 3.86
90 4.4
The results of experimental observations have been reported in above Tables 1 (a-e) and Fig. 1(a-e). The effect of various
RESULTS AND DISCUSSION
parameters on the rate of photo catalytic degradation of m-Dinitrobenzene is being presented as follows:
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5. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456
It is evident from the data in the tables that the rate of photo catalytic degradation of m-Dinitrobenzene increases with
Effect of pH
increase in pH up to 8.5 and further increase in pH decreases the rate of reaction. It was observed that the m-Dinitrobenzene
degrade photo catalytically in the presence of H2O2 at pH 8.5. The neutral compound m-Dinitrobenzene degrades in slightly
basic medium. Perret and holleck [23] observed that ArNO 2 show bathochromic effect with increasing pH. The effect of pH is
similar to that observed earlier in the case of trinitrotoluene[24-26] on increasing the pH further a decrease in the rate of
degradation was observed. The bathochromic shift and hypochromic effect will make the solution dark yellow in color and its
λmax is also shifted to the red shift, so that it will not permit the desired light intensity to reach the surface of ZnO.
It was observed that the rate of photocatalytical degradation increases on increasing the concentration of m-Dinitrobenzene
Effect of concentration of p- nitro aniline
reaches an optimum for (m-Dinitrobenzene) =10 mM and further increase in concentration, decreases the rate of reaction. It
may be concluded that the concentration of m-Dinitrobenzene was increased, more molecules were available for excitation
and then the energy transfer but if the concentration of m-Dinitrobenzene was increased above a particular limit, this
compound will start acting like a filter for incident light.
It was observed that the rate of photo catalytically degradation was increased on increasing concentration of photo catalyst
Effect of concentration of photo catalyst
and it was constant with further increase the concentration of photo catalyst. When the amount of semiconductor was
increased, the exposed surface area also increases but after the certain amount (0.14g) of ZnO was increased then there were
no increases in the surface area of the photo catalyst because these saturation points will also increases the thickness of the
layer at the bottom of the vessel.
It was observed that as the rate of addition and consequently amount of H 2O2 was increased; the rate of reaction was increased
Effect of concentration of hydrogen peroxide
and it attained an optimum value at 0.30mLh-1. Virtually no further or negligible increase in the rate of reaction was observed
on increasing the rate of addition further. The increase in reaction rate at higher H 2O2 concentration can consequently be
attributed to an acceleration of the dark reaction by a higher concentration of oxygen formed (27). However, the saturation
like behavior was observed due to the excess of H2O2.
It has been observed that on increasing the light intensity, the rate of reaction was increased. A linear behavior between light
Effect of Light Intensity
intensity and rate of reaction was observed. It can be attributed to the fact that any increase in the light intensity will increase
the number of photons striking per unit area of the semiconductor, which in turn will increase the number of electrons hole
pairs. This increase is clearly reflected in term of increased rate of the reaction. Further increase in the intensity of light may
increase the temperature of the reaction mixture. Thus thermal may occur in place of photo catalytic reaction and therefore
higher intensities of light avoidable.
On the basis of above observations a mechanism has been proposed for the photo catalytic degradation of ArNO 2 in general in
MECHANISM
presence of semiconductor ZnO and H2O2
ArNO2 ⇋ ArNO2*
ArNO2*+H2O2 ArNO2 +H2O2*
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6. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456
2H2O2* 2H2O + O2
SC e-(CB) + h+(VB)
ArNO2*+e ArNO2-.
H2O2+ e- HO. + OH-
ArNO2-. + O2 ArNO2 + O2-.
ArNO2*+ h+ ArNO2 +.
ArNO2+. ArNO2.+ H+
ArNO2. Decomposition products
Aromatic nitro compounds (ArNO2) absorbs incident radiation and it is excited to ArNO 2*, which may transfer its energy to
H2O2 and gives the excited state of H2O2*. It may degrade into water and oxygen; the zinc oxide will also absorb suitable
radiations generating electron hole pair. The electron from the CB may be accepted by exited nitro aromatics to form anion
radicals. However a conductive pathway is reported to in effective for photo degradation of nitro aromatics [28]. This anion
radical will transfer its electron to the O2 generating oxygen radical anion. The (ArNO2) may also transfer its electron to hole
and thus, forming the corresponding cationic radical. It may release a proton and a radical give the decomposition product.
Fig.1
Fig. 1(a)
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7. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456
Fig.1(b)
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8. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456
ZnO could be used powerfully in photo catalytic degradation of textile industrial waste water. The catalyst system is active
CONCLUSION
under the solar radiation which results the photo degradation of nitro aromatic compound in dyes in waste water
Authors wish to thanks the Head, Dept. of Chemistry, Mohan Lal Sukhadiya University, Udaipur and GCT, Sitapura Jaipur for
ACKNOWLEDGEMENT
providing the necessary facilities.
1. Fang Bai Li, Xian Zhang Li and Kok Wai Cheah, Environmental Chemistry, 2005, 2 (2), 130 .
REFERENCES
2. Guittonneau, S., De Laat, J., Duguet, J. P., Bonnel, C. & Dore, M. Oxidation of parachloronitrobenzene in dilute aqueous
solution by [O.sub.3] + UV and [H.sub.2][O.sub.2] + UV: a comparative study. Ozone: Sci. & Engng., 1990, 12, 73-94.
3. Rodgers, J. D. & Bunce, N. J. Electrochemical treatment of 2,4,6-trinitrotoluene and related compounds. Environ. Sci.
Technol., 2001, 35, 406-410.
4. Kuo, C. H., Zappi, M. E. & Chen, S. M. Peroxone oxidation of toluene and 2,4,6-trinitrotoluene. Ozone: Sci. & Engng., 2000,
22, 519-534.
5. Piccinini, P., Minero, C., Vincenti, M. & Pelizzetti, E. Photocatalytic mineralization of nitrogen-containing benzene derivates.
Catal. Today, 1997, 39, 187-195.
6. Makarova, O. V., Rajh, T., Thurnauer, C., Martin, A., Kemme, P. A. & Cropek, D. Surface modification of TiO2 nanoparticles
for photochemical reduction of nitrobenzene. Environ. Sci. Technol., 2000, 34, 4797-4803.
7. Beltran, F. J., Rivas, J., Alvarez, P. M., Alonso, M. A. & Acedo, B. A kinetic model for advanced oxidation processes of aromatic
hydrocarbons in water: application to phenanthrene and nitrobenzene. Ind. Eng. Chem. Res., 1999, 38, 4189-4199.
8. Bin, A. K., Machniewski, P., Sakowicz, R., Ostrowska, J. & Zielinski, J. Degradation of nitro aromatics (MNT, DNT, and TNT)
by AOPs. Ozone: Sci. & Engng., 2001, 23, 343-349.
9. Hung, H. M., Ling, F. H. & Hoffmann, M. R. Kinetics and mechanism of the enhanced reductive degradation of nitrobenzene
by elemental iron in the presence of ultrasound. Environ. Sci. Technol., 2000, 34, 1758-176
10. Zhang, Y., Crittenden, J.C., Hand, D.W. and Perram, D.L., 1994, Fixedbed photocatalysis for solar decontamination of water,
Environ Sci. Technol, 28: 435–442.
11. O. Legrini, E. Oliveros, and A. M. Braun, 1993,“Photochemical Processes for Water Treatment”, Chem. Rev., 93, p. 671.
International Journal of Science Innovations and Discoveries, Volume 2, Issue 5, September-October 2012
455

9. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456
12. U.S. Environmental Protection Agency, “Handbook of Advanced Photochemical Oxidation Processes”, 1998, EPA/625/R-
98/004.
13. S. Parsons (ed.) ,2004, Advanced Oxidation Processes for Water and Wastewater Treatment. London: IWA Publishing.
14. I. Munoz, J. Rieradevall, F. Torrades, J. Peral, and X. Domenech, , “Environmental Assessment of Different Solar Driven
Advanced Oxidation Processes”, Sol. Energy, 79, 369.
15. M. Lindner, D. W. Bahnemann, B. Hirthe, and W. D. Griebler, 1997,J. Sol. Ener. Eng., 119, p. 120.
16. R. Goslich, R. Dillert, and D. Bahnemann,1997, “Solar Water Treatment: Principles and Reactors”, Water Sci. Technol.,35.
17. Ahmed N. Alkhateeb, Falah H. Hussein, Kahtan A. Asker,2005, Asian J. Chemistry,17(2),1155.
18. Li, S., Z. Ma, J. Zang, Y. Wu and Y. Gong;2008, Catalysis Today, 139, 109-112 .
19. Hosseini, S.N., S. M. Borghei, M. Vossoughi and N. Tanghavinia;2007, Applied Catalysis B. Environmental, 74, 53-62.
20. Yashodharan, S. and S. Devipriya; 2005, Solar Energy Matter. Solar Cells, 86, 309-348.
21. Celik, G.Y., B. Aslim and Y. Beyatti; 2008, J. Environ.Biology, 29, 867-870.
22. Madhu, G. M., M. A. Lourdu Antony Raj, K. Vasantha K. Pai; 2009, J Environ. Biology, 30, 259-264.
23. G. Perret and L. Holleck;1956, Ber. Bunsenges Phys. Chem., 60,463.
24. C. C. Andrews; 1980, Weapons Quality Engg. Center, Naval Weapons Support Center, Crane, IN.,84,684.
25. L. A.Kaplan, N. E. Burlinson and M.E. Sitzmann;1975, Explosives Chemistry Branch, Naval Surface Weapon Center, White
Oak, Silver Spring,M.D.75.
26. W. R. Mabey, D.Tse, A. Baraza and T.Mill;1983, Chemosphere,12,3.
27. R. Hass, I.Hchreiber and G.Stork;1990, Unweltchem.Okotox,2,139.
28. H.G.O. Becker (ed.),1991, Einfuhrung; Einfuhrung in die Photochemie, Deutsche, Verlag deg Wissenschaften,Berlin,3rd
edit
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