Int. J. Chem. Sci.: 8(4), 2010, 2736-2746
________________________________________
*
Author for correspondence; E-mail: abohasan_hilla@yahoo.com
PHOTOCATALYTIC DECOLORIZATION OF BISMARCK
BROWN R BY SUSPENSION OF TITANIUM DIOXIDE
FALAH H. HUSSEIN*
, MOHAMMED H. OBIES and
ABASS A-ALI DREA
Department of Chemistry, College of Science, Babylon University, HILLA, IRAQ
ABSTRACT
Photocatalytic decolorization of an aqueous bismarck brown R (4-[5-C2, 4-diamino-5-
methylphenyl) diazenyl-2-methylphenyl] diazenyl-6-methylbenzene-1, 3-diamine dihydrochloride solution
in a suspension of titanium dioxide (Degussa P25) was carried with the use of artificial light sources (UVA).
The disappearance of the original colored dye concentrations with irradiation time was monitored
spectrophotometrically by comparison with unexposed controls. It is noticed that the photocatalytic
decolorization process was high at the beginning and then decreased with time following pseudo firstorder
kinetics according to the Langmuir–Hinshelwood model. The effects of various process variables on
decolorization performance of the process such as catalyst concentration, pH and dye concentration have
been investigated.
The results showed that the decolorization efficiency increases by increasing catalyst loading
from 0.5 to 1. 75 g/L, above which the decolorization efficiency decreased with further increase in catalyst
loading. The results also showed that the decolorization efficiency increases with increase in pH, attaining
maximum value at pH 6.61. After pH 7, there was a steep decrease in the percent degradation with
increase in pH value. It was observed that the decolorization efficiency gradually decreased with increase
in initial dye concentration. Results indicated that decolorization efficiency was accelerated by a rise in
temperature.
Key words: Titanium dioxide, Decolorization, Bismarck brown R, Mineralization, Total organic carbon
(TOC).
INTRODUCTION
Heterogeneous photocatalysis is a complex sequence of reactions that contains five
congestive steps. These steps are diffusion of reactants to the surface, adsorption of reactants
onto the surface, reaction on the surface, desorption of products from the surface, and
Int. J. Chem. Sci.: 8(4), 2010 2737
diffusion of products from the surface1
. Heterogeneous photocatalysis as an emerging
technology is an interesting application of advanced oxidation processes (AOP). AOP
processes are characterized by production of the hydroxyl radical (•
OH) (standard redox
potential + 2.8 V) as a primary oxidant, which leads to a complete mineralization of most of
the organic pollutants in the presence of light with certain wavelengths2-5.
Titanium dioxide is one of the semiconductors, which is used widely in the
heterogeneous photocatalysis processes. Titanium dioxide is largely available, inexpensive,
stable, and non-toxic with the large band gap with strong oxidizing power activated under
UV illumination with wavelength less than 388 nm6,7. The band gap of titanium dioxide is ~
3.2 e.V, indicating that their photocatalytic activities are shown only under UV light8-10.
When aqueous titanium dioxide suspension is illuminated with light energy greater
than or equal to its band gap energy (~ 3.2 eV); an electron will be promoted to conduction
band leaving a positive hole in valence band. It is an emerging technology
TiO2 + hv (UV-A) ? TiO2 (eCB?
+ hVB+
) …(1)
•
OH radicals could be produced by two pathways 11:
TiO2 (hvb+
) + H2O ads. ? TiO2 + •
OH ads. + H+
…(2)
TiO2 (hvb+
) + OH?
ads. ? TiO2 + •
OH ads. …(3)
However, the existence of colored materials on the surface of titanium dioxide will
initiate photosensitization processes. In these processes, the adsorbed colored compound(s)
on the surface of the titanium dioxide could absorb a radiation in the visible range12-14. The
degradation of dyes on the surface of titanium dioxide can occurr in three ways 15:
Dye + •
OH ? Degradation products …(4)
Dye + hvb+ ? Oxidation products …(5)
Dye + eCB? ? Reduction products …(6)
Titanium dioxide has wide applications, such as, the photodegradation of various
pollutants16-22, killing bacteria23 and killing tumor cells in cancer treatments24-25.
Chen 26 reported that decolorization of azo dyes was faster than the decrease of total
organic carbon (TOC). The author explained the low concentration of TOC in the solution
may be due to the accumulation of some by products, which resist mineralization.
2738 F. H. Hussein et al.: Photocatalytic Decolorization of….
The aim of the present study is to investigate photocatalytic decolorization of
bismarck brown R using TiO2, as photocatalyst irradiated with artificial light sources (UV-A)
at different conditions.
EXPERIMENTAL
Materials
Bismarck brown R supplied from standard Fluka, for microscopy (Bact., Hist.), TiO2
(Degussa P25) from Degussa AG, D-6000 Frarkfurt1, 1M of hydrochloric acid and sodium
hydroxide were used. The solution of dye was prepared with ultra pure water (resistivity
18.2M? cm at 25Co
of water prepared by water purification system). The materials were used
without any further purification. The structure of bismarck brown R is shown in the Fig. 1.
•2HCl
H N2
H C3
NH2
N
N
CH3
N
N
H N2 NH2
CH3
Fig. 1: The structure of bismarck brown R.
Photoreactor and light source
For UV/TiO2 process, irradiation was performed in a batch reactor (100 mL in
volume; close system) with burgle oxygen and stirring in all the time of reaction. The light
source is mercury lamp Philips (UV-A), (Germany) contains six lamp 15W for each one.
The absorbance was measured with Cary 100Bio UV-visible spectrophotometer Shimadzu
(Varian). Mineralization of dye was assessed by total organic carbon, employing a TOC
5000A Shimadzu analyzer. pH meter (691 pH meter, metrom) was used to adjust the pH of
solution.
Procedure
In all experiments, the required amount of the TiO2 (Degussa P25) was suspended in
100 mL of aqueous solution of bismarck brown R using magnetic stirrer. Procedure is
almost the same as described in our previous work27. The decolorization efficiency and
percentage of TOC are also calculated in the same way as described in our previous work21.
Int. J. Chem. Sci.: 8(4), 2010 2739
RESULTS AND DISCUSSION
Effect of mass catalyst
The effect of TiO2 concentration on photodecolorization efficiency is shown in Figs.
2 and 3. The experiments were performed with different amounts of catalyst from 0.5 g L-1 In C/Co
Time (min)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 20 40 60 80
m=50 mg
m=75 mg
m=100 mg
m=125 mg
m=150 mg
m=175 mg
m=200 mg
m=250 mg
Fig. 2: Photocatalytic activity on different masses of titanium dioxide
80
70
60
50
40
30
20
10
0
0 50 100 150 200 250 300
Mass (mg/100 mL)
P.E.D.
Fig. 3: Effect of mass catalyst
to 2.5 g L-1. The photodecolorization efficiency increased with increase the amount of
catalyst until 1.75 g L-1 and; when the catalyst loading reached 2.0 g L-1, the
2740 F. H. Hussein et al.: Photocatalytic Decolorization of….
photodecolorization efficiency decreased. Fig. 3 shows that a catalyst mass of 1.75 g L-1 was
sufficient to achieve the maximum reaction rate under our experimental conditions. This
behavior can be explained on the basis that on increasing catalyst concentration, the
availability of photocatalysts sites increases21,22-28. However, the additional mass catalyst
reduced the catalytic activity due to increasing of light scattering due to the excess of
catalyst21.
Effect of pH
The effect of pH on photocatalytic decolorization of bismarck R brown was
investigated in range pH 2 to 10, keeping other parameters constant. Fig. 4 shows that as pH
was increased, photocatalytic decolorization efficiency of dye also increases and at pH 6.61,
maximum efficiency was achieved. Above 6.61, the degradation efficiency decreases on
increasing pH. The zero point of charge (ZPC) of Degussa P25 has been reported as 6.2529.
Jolivet30 explained that ZPC refers to the absence of any charge on the surface. In
aqueous solution, when pH is below ZPC, the acidic water donates protons resulting in
positively charged surface (adsorbent surface is attracting anions), whereas, when pH value
is above ZPC, the surface is negatively charged; thus, attracting cations. Hence, at pH higher
than ZPC, the particle surface is negatively charged.
pH
P.D.E
100
90
80
70
60
50
40
30
20
10
0
0 1 2 3 4 5 6 7 8 9 10
Fig. 4: Effect of pH
Fig. 4 shows that photocatalytic decolorization efficiency of bismarck R brown
increased with increasing pH of aqueous solution until the pH exceeds ZPC and then
Int. J. Chem. Sci.: 8(4), 2010 2741
decreased sharply. At low pH (pH < ZPC), catalyst surface of titanium dioxide is positively
charged, and as a result, adsorption of anionic dye increases compared with the adsorption of
hydroxyl ion and then decreases the decolorization efficiency of dye. On the other hand, as
the pH was increased (pH > ZPC), catalyst surface is negatively charged, resulting in
repulsive forces between the substrate and TiO2 surface and hence, adsorption will be less31-
35.
Effect of initial dye concentration
The results in Fig. 5 show the changes in the rate of decolorization of bismarck R
brown on 1.75 g L-1 of titanium dioxide (Degussa P25) at 298.15 K with the initial dye
concentrations (0.2 x 10-4 – 1.0 x 10-4M) at different times. The results indicate that decrease
in dye concentration decreases the time of decolorization. In C/Co
Time (min)
Fig. 5: Effect of initial dye concentration
Fig. 6 shows the photocatalytic decolorization efficiency at different initial dye
concentrations after 60 minutes of irradiation. It was observed that the photocatalytic
decolorization efficiency gradually decreased with increase in initial dye concentration. This
behavior could be explained according to the Lambert-Beer law36. When the dye
concentration was increased, the dye starts acting as an internal filter37 and as a result, the
rate of decolorization of dye decreased. The increasing dye concentration lead to shield the
entering photons in solution and as a result, the rate of decolorization decreased due to
reduction in hydroxyl radical (•
OH) formation.
2742 F. H. Hussein et al.: Photocatalytic Decolorization of…. P.D.E
100
99
98
97
96
95
94
93
92
91
90
0 0.2 0.4 0.6 0.8 1
Conc. x 10 M4
Fig. 6: Photocatalytic decolorization efficiency at different initial dye concentrations
after 60 minutes of irradiation
Effect of light intensity
The results listed in Table 1 indicates that the photocatalytic decolorization
efficiency of bismarck R brown increases with increase in light intensity, attaining
maximum value at 3.52 mW cm-2.
Table 1: Effect of light intensity on photocatalytic decolorization efficiency
Light intensity(I) mW cm-2 P.D.E. (%)
0.55 38.7
1.05 48.3
1.41 54.2
1.93 73.4
2.97 87.6
3.52 92.5
The observed enhancement of photocatalytic decolorization efficiency was due to
the increase in the number of photons exciting dye molecules with the increase in light
intensity38. Dong et al.39 explained this behavior due to the predominance of electron–hole
Int. J. Chem. Sci.: 8(4), 2010 2743
formation at higher light intensity and hence, electron–hole recombination is negligible,
while, at lower light intensity, the formation of free radicals decreased due to the increase in
electron–hole pair recombination.
Mineralization of bismarck brown R
The results shown in Fig.7 indicate that photocatalytic decolorization of bismarck R
brown was faster than the decrease of total organic carbon (TOC). The results indicate that
% TOC reduction was about 73% after 60 minutes of irradiation while the per cent of
decolorization achieved 88% for the same period of irradiation. These findings are in good
agreement with those reported before 26, 39-40. This may be related to the formation of some
by product, which resist the photocatalytic degradation.
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60 70
Time (min)
TOC %
Fig. 7: Mineralization of bismarck brown R
CONCLUSIONS
(i) Control experiments indicated that the existence of UV light, oxygen and
titanium dioxide were essential for the effective destruction of dye.
(ii) The photocatalytic decolorization of bismarck brown R using TiO2 (Degussa P-
25) photocatalyst strongly depends on the amount of catalyst, concentration of
dye, pH, and light intensity.
(iii) Photocatalytic decolorization of bismarck R brown was faster than the decrease
of total organic carbon (TOC).
2744 F. H. Hussein et al.: Photocatalytic Decolorization of….
(iv) The photocatalytic decolorization process can be expressed by both; the pseudo
first order reaction kinetic and the Langmuir-Hinshelwood kinetic model.
ACKNOWLEDGEMENTS
The authors gratefully acknowledge to Prof. Dr. Detlef Bahnemann, Photocatalysis
and Nanotechnology (Head), Institut fuer Technische Chemie, Gottfried Wilhelm Leibniz
Universitaet Hannover (Germany) for providing necessary laboratory facilities.
REFERENCES
1. K. Pirkanniemi and M. Sillanpaa, Chemosphere, 48, 1047 (2002).
2. O. Hennezel, P. Pichat and D. F. Ollis, J. Photochem. Photobiol. A: Chem., 118, 197
(1998).
3. H. Y. Chen, Zahraa O. M. Bouchy, F. Thomas and J. Y. Bottero, J. Photochem.
Photobiol. A: Chem., 85, 179 (1995).
4. A. Mills, C. E. Holland, R. H. Davies and D. Worsley, J. Photochem. Photobiol. A:
Chem., 83, 257 (1994).
5. O. Zahraa, S. Maire, F. Evenou, C. Hachem, M. N. Pons, A. Alinsafi and M. Bouchy,
Int. J. Photoenergy, Article ID 46961, 1 (2006).
6. J. S. Kim, K. Itoh and M. Murabayashi, Chemosphere, 36, 483 (1998).
7. A. A. Fujishima, T. N. Rao and D. A. Tryk, J. Photochem. Photobiol. C Photochem.
Rev., 1 (2000).
8. X. Li, H. Liu, L. Cheng and H. Tong, Environ. Sc. Technol., 37 (17), 3989 (2003).
9. D. Vione, T. Picatonitoo and M. E. Carlotti, J. Cosmet Sci., 54, 513 (2003).
10. S. Antharjanam, R. Philip and D. Suresh, Ann. Chim., 93(9-10), 719 (2003).
11. M. N. Rashed and A. A. El-Amin, Int. J. Phy. Sci., 2(3), 73 (2007).
12. P. Fernandez-Ibanez, J. Planko, S. Maitato and F. de las Nieres, Water Res., 37(13),
3180 (2003).
13. T. Ohno, Water Sci. Technol., 49(4), 159 (2004).
14. A. Alkhateeb, F. Hussein and K. Asker, Asian J. Chem., 17(2), 1155 (2005).
15. N. Guettai and A. H. Amar, Desalination, 185, 427,(2005).
Int. J. Chem. Sci.: 8(4), 2010 2745
16. S. Y. Chae, M. K. Park, S. K. Lee, T. Y. Kim, S. K. Kim and W. I. Lee, Chem. Mater.,
15, 3326 (2003).
17. F. H. Hussein, M. Mashkoor and A. Al-Sharafy, National J. Chem., 9, 94 (2003).
18. Y. Bessekhouad, D. Robert, J. V. Weber and N. Chaoui, J. Photochem. Photobiol. A,
167, 49 (2004).
19. F. B. Li, X. Z. Li and M. F. Hou, Appl. Catal. B, 48, 185 (2004).
20. J. Joo, S. G. Kwon, T. Yu, M. Cho, J. Lee, J. Yoon and T. J. Hyeon, Phys. Chem. B,
109, 15297 (2005).
21. F. H. Hussein and T. A. Abass, Inter. J. Chem. Sci., 8(3), 1353 (2010).
22. F. H. Hussein and T. A. Abass, Inter. J. Chem. Sci., 8(3), 1409 (2010).
23. N. M. Mahmoodi, M. Arami, N. Y. Limaee, and N. S. Tabrizi, Chem. Eng. J., 112,
191 (2005).
24. A. P. Zhang, and Y. P. Sun, World J. Gastroenterol., 10, 3191 (2004).
25. S. Ivankovic, M. Gotic, M. Jurin and S. J. Music, Sol-Gel Sci. Technol., 27, 225
(2003).
26. Chen Chih-Yu, Water Air Soil Pollut., 202, 335 (2009).
27. H. Mohammed Obeis, Falah H. Hussein and Abass A-Ali Dreua, Submitted for
Publication, Inter. J. Chem. Sci. (2010).
28. U. I. Gaya, A. H. Abdullah, Z. Zainal and M. Z. Hussein, Inter. J. Chem., 2(1), 180
(2010).
29. H. K. Singh, M. Muneer and D. Bahnemannb, Photochem. Photobiol. Sci., 2,
151(2003).
30. J. P. Jolivet, Metal Oxide Chemistry, and Synthesis. From Solution to Solid State,
John Wiley & Sons Ltd. (2000).
31. F. Kiriakidou, D. I. Kondarides and X. E. Verykios, Catal. Today, 54, 119 (1999).
32. F. Zhang, J. Zhao, T. Shen, H. Hidaka, E. Pelizzetti and N. Serpone, Appl. Catal., B
15, 147 (1998).
33. M. Noorjahan, M. Pratap Reddy, V. Durga Kumari, B. Lavédrine, P. Boule, M.
Subrahmanyam, J. Photochem. Photobiol. A: Chem., 156, 179 (2003).
34. Priti Bansal, Damanjit Singh and Dhiraj Sud, Asian J. Chem., 21(10), S287 (2009).
2746 F. H. Hussein et al.: Photocatalytic Decolorization of….
35. B. Pare, P. Singh and S. Jonnalgadda, Indian J. Chem., 48A, 1364 (2009).
36. S. Sakthivel, B. Neppolian, M. V. Shankar, B. Arabindoo, M. Palanichamy and V.
Murugesan, Sol. Energy Mater. Sol. Cells, 77, 65 (2003).
37. R. Ameta, J. Vardia, P. B. Punjabi and S. C. Ameta, Indian J. Chem. Tech., 13, 114
(2006).
38. K. Ankur, G. Neelam, S. Vijaya and R. C. Khandelwal, Bull. Catal. Soc. India, 9, 51
(2010).
39. Dianbo Dong, Peijun Li, Xiaojun Li, Qing Zhao, Yinqiu Zhang, Chunyun Jia and
Peng Li, J. Hazardous Mater., 174, 859 (2010).
40. M. Qumar, M. Saquib and M. Muneer, Desalination, 186, 255 (2006).
41. Z. He, S. Song, H. Zhou, H. Ying and J. C. I. Chen, Ultrasonics Sonochem., 14, 298
(2007).
Revised : 25.11.2010 Accepted : 26.11.2010