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Photocatalytic labyrinth flow reactor with immobilized P25 TiO2 bed for removal of phenol from water
Applied Catalysis B: Environmental 46 (2003) 415–419
Letter to the Editor
Photocatalytic labyrinth flow reactor with immobilized P25 TiO2 bed for removal of phenol from water Abstract The photocatalytic oxidation of phenol in water in the labyrinth flow reactor with immobilized catalyst bed was investigated. Degussa P25 was used as a photocatalyst. It was observed that the photocatalytic material considerably losses its activity during repeated test trials for the high initial phenol concentration of 300 mg/dm3 . Diffuse reflectance UV-Vis analysis showed shift in the threshold absorption value and corresponding band gap energy of the photocatalytic material. FTIR analysis revealed the carbon deposits on the catalyst surface. These two factors are considered to be responsible for the activity decrease. © 2003 Elsevier B.V. All rights reserved. Keywords: Photocatalysis; Titanium dioxide; Activity decrease
1. Introduction The industrialization and agriculture development together with the population growth drastically reduced the clean water resources. Most of the various kinds of contaminants get to the waters with industrial wastewater. Developments in the field of chemical water purification have led to an improvement in the oxidative degradation processes applying catalytic and photochemical methods. They are generally called as advanced oxidation processes (AOP) [1–5]. Photocatalysis is one of the AOPs. During the photocatalytic process, organic pollutants present in water are converted to less harmful compounds or most often, by various intermediate products, undergo complete mineralization [6–13]. The photocatalytic processes can be conducted using catalyst suspended in water or immobilized. Advantage of water suspension is that a big surface is accessible for photocatalytic reaction. On the other hand, in this case, there is a necessity of separation of photocatalyst from reaction mixture after the process is completed, which is not easy in the case of small particle photocatalyst. Removal of the catalyst from the re-
action mixture is an additional step in the process and increases its costs. Photocatalyst can be immobilized on the adequate solid support or on the reactor walls, which eliminates arduous step of separation. When the catalyst is immobilized, the surface accessible for the reaction decreases. Moreover, catalyst must be well attached to the support and the support materials are usually not transparent to UV light. Titanium dioxide, the mostly used photocatalyst, was immobilized on various supports and using various methods [14–17]. This paper presents results of the photocatalytic oxidation of phenol in water in the labyrinth flow reactor with immobilized catalyst bed.
2. Experimental Phenol was chosen as a model organic compound in these studies. Fig. 1 shows the scheme of installation setup. The main component of the system is the flow reactor with an internal stirring and immobilized catalyst bed. The reactor is built of plastic in the form of developing dish divided with baffle plates of about 1 cm in height (dish dimensions: 250 mm × 190 mm). The bottom of the reactor is covered with a photo-
0926-3373/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0926-3373(03)00265-0
416
Letter to the Editor / Applied Catalysis B: Environmental 46 (2003) 415–419
1 (a)
2
5
3 4
try method using JascoV-500 spectrometer at a fixed wavelength of 276 nm. Titanium dioxide, Degussa P25, was used as a photocatalyst. It is a white powder having crystallographic structure of anatase and rutile (ca. 25 wt.%) with a surface area of about 52 m2 /g.
3. Results and discussion 3.1. Photocatalytic reactions results
Fig. 1. Scheme of the installation setup for photocatalytic oxidation of phenol in water. 1—Mercury lamp, 2—reactor, 3—stand, 4—waste container, 5—circulating pump. (a) Scheme of the installation; (b) top view of the reactor.
catalyst. The photocatalyst was fixed to the bottom of the reactor using polymer glue. The photocatalyst particles are fixed in such a manner that half of the particle surface is accessible for the UV light. After covering the surface with the glue, the photocatalyst powder was poured and left until the glue set. Next, the reactor was washed with strong stream of water to remove the excess powder. Fig. 2 shows a model of the photocatalyst’s fixation to the reactor. The thickness of phenol’s solution layer over the catalyst is about 1 cm (as the height of the baffle plates). The reaction mixture is fed and drained continuously with the circulating pump (rate of discharge: 4.5 dm3 /h). The reaction solution was illuminated with a mercury lamp, emitting UV-A light. The lamp consists of six bulbs with a total power of 140 W. During the process, samples of the reaction solution were taken for phenol concentration analysis. Phenol concentration was determined by UV-Vis spectromephotocatalyst particles polymer glue reactor bottom
The experiments of photocatalytic oxidation of phenol were conducted for solutions with various phenol concentrations: 10, 30, 60, 100, and 300 mg/dm3 . Table 1 shows loss of phenol concentration during the photocatalytic reaction. Fig. 3 is a graphical presentation of these results. As can be seen from the results, reaction time lengthens with increasing phenol concentrations after reaching the concentration of about 50 mg/dm3 . For example, after 5 h of illumination, for concentration of 10 mg/dm3 , degree of phenol decomposition was 89%; for concentration of 30 mg/dm3 , after equal time, phenol loss was 95%. With further increase of concentration to 60, 100, and 300 mg/dm3 , degree of decomposition of phenol was 75, 75.3, and 76%, respectively. These results indicate that increase of initial phenol concentration in water causes increase of removal degree of phenol from reaction mixture until the maximum value of about 50 mg/dm3 is reached. In order to verify the activity of used catalyst and to check out its lifetime, two more experiments of 100 degree of decomposition [%]
(b)
80 10 mg/dm3
60
30 mg/dm3 60 mg/dm3
40
100 mg/dm3
20
300 mg/dm3
0 0
2
4
6
8
10
12
14
time [h]
Fig. 2. Model of photocatalyst’s fixation to the bottom of the reactor.
Fig. 3. Degree of phenol decomposition for various initial phenol concentrations. Flow rate 4.5 dm3 /h, reaction volume 0.7 dm3 .
Letter to the Editor / Applied Catalysis B: Environmental 46 (2003) 415–419
417
Table 1 Degrees of phenol decomposition during photocatalytic process Time (h)
Decomposition degree (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14
10 mg/dm3
30 mg/dm3
60 mg/dm3
100 mg/dm3
300 mg/dm3
29.47 46.32 61.05 77.89 89.47 – – – – – – – – –
36.05 66.33 80.61 90.82 95.24 96.94 – – – – – – – –
23.95 41.48 57.50 66.10 75.04 81.79 84.65 88.03 90.22 92.58 94.10 95.78 96.63 97.64
31.75 40.65 55.81 68.15 75.33 84.23 86.65 92.01 95.25 96.36 97.80 98.30 – –
9.17 16.50 24.00 70.20 75.95 83.18 – – – – – – – –
Flow rate 4.5 dm3 /h, reaction volume 0.7 dm3 .
3.2. Catalyst characterization An important feature of materials used in photocatalytic processes is the band gap energy. The lower the value of this energy, the broader the range of light that can be absorbed to activate the photocataTable 2 Degrees of phenol decomposition for initial phenol concentration of 300 mg/dm3 Time (h)
1 2 3 4 5 6 7 8
Decomposition degree (%) First trial
Second trial
Third trial
9.17 16.50 24.00 70.20 75.95 83.18 – –
16.94 23.62 27.28 29.62 31.85 33.75 39.66 39.78
9.04 16.72 25.20 28.44 33.20 34.73 35.60 38.78
lyst. Band gap energy of P25 photocatalyst, both fresh and after photocatalytic reaction, was determined using UV-Vis spectrometer (Specord M40, Carl-Zeiss) equipped with an integrating sphere accessory for diffuse reflectance. BaSO4 was used as a reference. Fig. 5 shows derivatives determined from the diffuse reflectance UV-Vis spectra of P25 samples. Shift in the threshold absorption value between fresh and used photocatalyst was observed and corresponding band 100 degree of decomposition [%]
phenol decomposition for concentration of phenol of 300 mg/dm3 were conducted. Results are presented in Table 2 and Fig. 4. In the first test, after 5 h of illumination, decomposition degree of phenol was 76% while in the second test trial decomposition degree was 32% and remained at about the same level during the third trial.
300 mg/dm3 1st trial
80 300 mg/dm3 2nd trial
60
300 mg/dm3 3rd trial
40 20 0 0
2
4
6
8
10
12
14
time [h] Fig. 4. Degree of phenol decomposition in repeated test trials for initial phenol concentration of 300 mg/dm3 . Flow rate 4.5 dm3 /h, reaction volume 0.7 dm3 .
418
Letter to the Editor / Applied Catalysis B: Environmental 46 (2003) 415–419
4. Conclusions
0,005 0 -0,005
b)
-0,01 -0,015 a)
-0,02 -0,025 200
250
300
350
400
450
500
nm
Fig. 5. Diffuse reflectance UV-Vis spectra of photocatalyst samples. (a) Fresh P25; (b) used P25.
gap energy has changed from 3.15 for fresh P25 to 3.24 for used photocatalyst. Photocatalyst samples were also analyzed by FTIR spectroscopy using a Jasco FTIR 430 spectrometer with accessory for diffuse reflectance measurements. Fig. 6 shows the diffuse reflectance FTIR spectra of P25 samples. It can be seen that new absorption bands in the region of 1200–1800 cm−1 appeared on the spectra of photocatalyst used in the reaction of phenol photo-oxidation at concentration of 300 mg/dm3 when the sample color changed to dark brown. These bands are due to carbon deposits on the catalyst surface [18]. The two bands at 1713 and 1690 cm−1 were assigned to C=O stretching vibrations, the band at 1630 cm−1 to aromatic ring vibrations, the band at 1485 cm−1 to C–H asymmetric vibrations, and the band at 1259 cm−1 to C–O vibrations. 30 25 20 % 15 10 5 0 2000
1800
1600
1400
1200
1000
Reaction of photocatalytic oxidation of phenol in water using the flow reactor with immobilized bed of photocatalyst was investigated. Water solutions with various initial phenol concentrations were examined. It was observed that for the initial phenol concentrations up to about 50 mg/dm3 , after 5 h of illumination, phenol decomposition degree increased while after exceeding this value, decomposition degree decreased. It can be explained by the fact that to a certain concentration, the amount of active centers of the photocatalyst is sufficient for correct reaction course and the process is controlled by initial concentration of phenol, and afterwards saturation of active centers occurs. In addition, intermediate products of phenol decomposition compete for active centers onto catalyst surface. Passing (temporary) presence of oxidized forms of phenol, quinones, was confirmed by appearance of new absorption band on UV-Vis spectra of reaction mixture at wavelength about 290 nm. Additionally, activity of the photocatalyst used again with high phenol concentration of 300 mg/dm3 , decreased considerably; so it can be concluded that catalyst surface was covered with products of phenol decomposition. It was even visible to the naked eye— the catalyst surface had dark color. The presence of carbon deposits on the catalyst surface was confirmed by FTIR analysis. This analysis showed new absorption bands in the region of 1800–1200 cm−1 assigned to C=O, C–H, C–C, and aromatic ring vibrations. UV-Vis analysis showed that band gap energy of used photocatalyst was higher than the fresh P25, which can also be responsible for activity decrease. Obtained results show that Degussa P25 titanium dioxide is a effective photocatalyst in the process of oxidation of phenol in the labyrinth flow reactor with immobilized catalyst bed. However the process is effective for low initial phenol concentrations and photocatalyst loses its activity due to carbon deposits on the surface. References
cm
Fig. 6. Diffuse reflectance FTIR spectra of photocatalyst samples. (a) Fresh P25; (b) used P25.
[1] Proceedings of the First International Symposium “Chemical oxidation technologies for the nineties”, Vanderbilt University, Nashville, Tennessee, vol. 1–3, 1991–1993.
Letter to the Editor / Applied Catalysis B: Environmental 46 (2003) 415–419 [2] Handbook: Advanced Photochemical Oxidation Processes, United States Environmental Protection Agency publication EPA/625/R-98/004, 1998. [3] R. Andreozzi, V. Caprio, A. Insola, R. Marotta, Catal. Today 53 (1999) 51. [4] R. Munter, S. Preis, J. Kallas, M. Trapido, Y. Veressinina, Kemia-Kemi 58 (2001) 354. [5] S. Esplugas, J. Gimenez, S. Contreras, E. Pascual, M. Rodriguez, Water Res. 36 (2002) 1034. [6] M. Schiavello, Photocatalysis and environment: trends and applications, NATO ASI Series C, vol. 283, Kluwer Academic Publishers, London, 1987. [7] D.F. Ollis, H. Al-Ekabi, Photocatalytic Purification and Treatment of Water and Air, Elsevier, Amsterdam, 1993. [8] M.R. Hoffman, S.T. Martin, W. Choi, D.W. Bahnemann, Chem. Rev. 95 (1995) 69. [9] A.L. Linsebigler, G. Lu, J.T. Yates Jr., Chem. Rev. 95 (1995) 735. [10] D.M. Blake, Bibliography of Work on the Photocatalytic Removal of Hazardous Compounds from Water and Air, NERL/TP-430-22197, Golden Co., 1997. [11] J.-M. Herrmann, Catal. Today 53 (1999) 115. [12] O.M. Alfano, D. Bahnemann, A.E. Cassano, R. Dillert, R. Goslich, Catal. Today 58 (2000) 199. [13] D.S. Bhatkhande, V.G. Pangarkar, A.A.C.M. Beenackers, J. Chem. Tech. Biotechnol. 77 (2001) 102.
419
[14] R.W. Matthews, Water Res. 25 (1991) 1169. [15] A. Fernandez, G. Lassaletta, V.M. Jimenez, A. Justo, A.R. Gonzalez-Elipe, J.-M. Herrmann, H. Tahiri, Y. Ati-Ichou, Appl. Catal. B: Environ. 7 (1995) 49. [16] J.-M. Herrmann, H. Tahiri, Y. Ati-Ichou, G. Lassaletta, A.R. Gonzalez-Elipe, A. Fernandez, Appl. Catal. B: Environ. 13 (1997) 219. [17] Y.-H. Hsien, C.-F. Chang, Y.-H. Chen, S. Cheng, Appl. Catal. B: Environ. 31 (2001) 241. [18] H. Einaga, S. Futamura, T. Ibusuki, Appl. Catal. B: Environ. 38 (2002) 215.
Joanna Grzechulska Antoni Waldemar Morawski∗ Institute of Chemical and Environment Engineering Technical University of Szczecin, ul. Pułaskiego 10 Szczecin 70-322, Poland ∗ Corresponding author E-mail address: [email protected] (A.W. Morawski) 24 November 2002
Letter to the Editor
Photocatalytic labyrinth flow reactor with immobilized P25 TiO2 bed for removal of phenol from water Abstract The photocatalytic oxidation of phenol in water in the labyrinth flow reactor with immobilized catalyst bed was investigated. Degussa P25 was used as a photocatalyst. It was observed that the photocatalytic material considerably losses its activity during repeated test trials for the high initial phenol concentration of 300 mg/dm3 . Diffuse reflectance UV-Vis analysis showed shift in the threshold absorption value and corresponding band gap energy of the photocatalytic material. FTIR analysis revealed the carbon deposits on the catalyst surface. These two factors are considered to be responsible for the activity decrease. © 2003 Elsevier B.V. All rights reserved. Keywords: Photocatalysis; Titanium dioxide; Activity decrease
1. Introduction The industrialization and agriculture development together with the population growth drastically reduced the clean water resources. Most of the various kinds of contaminants get to the waters with industrial wastewater. Developments in the field of chemical water purification have led to an improvement in the oxidative degradation processes applying catalytic and photochemical methods. They are generally called as advanced oxidation processes (AOP) [1–5]. Photocatalysis is one of the AOPs. During the photocatalytic process, organic pollutants present in water are converted to less harmful compounds or most often, by various intermediate products, undergo complete mineralization [6–13]. The photocatalytic processes can be conducted using catalyst suspended in water or immobilized. Advantage of water suspension is that a big surface is accessible for photocatalytic reaction. On the other hand, in this case, there is a necessity of separation of photocatalyst from reaction mixture after the process is completed, which is not easy in the case of small particle photocatalyst. Removal of the catalyst from the re-
action mixture is an additional step in the process and increases its costs. Photocatalyst can be immobilized on the adequate solid support or on the reactor walls, which eliminates arduous step of separation. When the catalyst is immobilized, the surface accessible for the reaction decreases. Moreover, catalyst must be well attached to the support and the support materials are usually not transparent to UV light. Titanium dioxide, the mostly used photocatalyst, was immobilized on various supports and using various methods [14–17]. This paper presents results of the photocatalytic oxidation of phenol in water in the labyrinth flow reactor with immobilized catalyst bed.
2. Experimental Phenol was chosen as a model organic compound in these studies. Fig. 1 shows the scheme of installation setup. The main component of the system is the flow reactor with an internal stirring and immobilized catalyst bed. The reactor is built of plastic in the form of developing dish divided with baffle plates of about 1 cm in height (dish dimensions: 250 mm × 190 mm). The bottom of the reactor is covered with a photo-
0926-3373/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0926-3373(03)00265-0
416
Letter to the Editor / Applied Catalysis B: Environmental 46 (2003) 415–419
1 (a)
2
5
3 4
try method using JascoV-500 spectrometer at a fixed wavelength of 276 nm. Titanium dioxide, Degussa P25, was used as a photocatalyst. It is a white powder having crystallographic structure of anatase and rutile (ca. 25 wt.%) with a surface area of about 52 m2 /g.
3. Results and discussion 3.1. Photocatalytic reactions results
Fig. 1. Scheme of the installation setup for photocatalytic oxidation of phenol in water. 1—Mercury lamp, 2—reactor, 3—stand, 4—waste container, 5—circulating pump. (a) Scheme of the installation; (b) top view of the reactor.
catalyst. The photocatalyst was fixed to the bottom of the reactor using polymer glue. The photocatalyst particles are fixed in such a manner that half of the particle surface is accessible for the UV light. After covering the surface with the glue, the photocatalyst powder was poured and left until the glue set. Next, the reactor was washed with strong stream of water to remove the excess powder. Fig. 2 shows a model of the photocatalyst’s fixation to the reactor. The thickness of phenol’s solution layer over the catalyst is about 1 cm (as the height of the baffle plates). The reaction mixture is fed and drained continuously with the circulating pump (rate of discharge: 4.5 dm3 /h). The reaction solution was illuminated with a mercury lamp, emitting UV-A light. The lamp consists of six bulbs with a total power of 140 W. During the process, samples of the reaction solution were taken for phenol concentration analysis. Phenol concentration was determined by UV-Vis spectromephotocatalyst particles polymer glue reactor bottom
The experiments of photocatalytic oxidation of phenol were conducted for solutions with various phenol concentrations: 10, 30, 60, 100, and 300 mg/dm3 . Table 1 shows loss of phenol concentration during the photocatalytic reaction. Fig. 3 is a graphical presentation of these results. As can be seen from the results, reaction time lengthens with increasing phenol concentrations after reaching the concentration of about 50 mg/dm3 . For example, after 5 h of illumination, for concentration of 10 mg/dm3 , degree of phenol decomposition was 89%; for concentration of 30 mg/dm3 , after equal time, phenol loss was 95%. With further increase of concentration to 60, 100, and 300 mg/dm3 , degree of decomposition of phenol was 75, 75.3, and 76%, respectively. These results indicate that increase of initial phenol concentration in water causes increase of removal degree of phenol from reaction mixture until the maximum value of about 50 mg/dm3 is reached. In order to verify the activity of used catalyst and to check out its lifetime, two more experiments of 100 degree of decomposition [%]
(b)
80 10 mg/dm3
60
30 mg/dm3 60 mg/dm3
40
100 mg/dm3
20
300 mg/dm3
0 0
2
4
6
8
10
12
14
time [h]
Fig. 2. Model of photocatalyst’s fixation to the bottom of the reactor.
Fig. 3. Degree of phenol decomposition for various initial phenol concentrations. Flow rate 4.5 dm3 /h, reaction volume 0.7 dm3 .
Letter to the Editor / Applied Catalysis B: Environmental 46 (2003) 415–419
417
Table 1 Degrees of phenol decomposition during photocatalytic process Time (h)
Decomposition degree (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14
10 mg/dm3
30 mg/dm3
60 mg/dm3
100 mg/dm3
300 mg/dm3
29.47 46.32 61.05 77.89 89.47 – – – – – – – – –
36.05 66.33 80.61 90.82 95.24 96.94 – – – – – – – –
23.95 41.48 57.50 66.10 75.04 81.79 84.65 88.03 90.22 92.58 94.10 95.78 96.63 97.64
31.75 40.65 55.81 68.15 75.33 84.23 86.65 92.01 95.25 96.36 97.80 98.30 – –
9.17 16.50 24.00 70.20 75.95 83.18 – – – – – – – –
Flow rate 4.5 dm3 /h, reaction volume 0.7 dm3 .
3.2. Catalyst characterization An important feature of materials used in photocatalytic processes is the band gap energy. The lower the value of this energy, the broader the range of light that can be absorbed to activate the photocataTable 2 Degrees of phenol decomposition for initial phenol concentration of 300 mg/dm3 Time (h)
1 2 3 4 5 6 7 8
Decomposition degree (%) First trial
Second trial
Third trial
9.17 16.50 24.00 70.20 75.95 83.18 – –
16.94 23.62 27.28 29.62 31.85 33.75 39.66 39.78
9.04 16.72 25.20 28.44 33.20 34.73 35.60 38.78
lyst. Band gap energy of P25 photocatalyst, both fresh and after photocatalytic reaction, was determined using UV-Vis spectrometer (Specord M40, Carl-Zeiss) equipped with an integrating sphere accessory for diffuse reflectance. BaSO4 was used as a reference. Fig. 5 shows derivatives determined from the diffuse reflectance UV-Vis spectra of P25 samples. Shift in the threshold absorption value between fresh and used photocatalyst was observed and corresponding band 100 degree of decomposition [%]
phenol decomposition for concentration of phenol of 300 mg/dm3 were conducted. Results are presented in Table 2 and Fig. 4. In the first test, after 5 h of illumination, decomposition degree of phenol was 76% while in the second test trial decomposition degree was 32% and remained at about the same level during the third trial.
300 mg/dm3 1st trial
80 300 mg/dm3 2nd trial
60
300 mg/dm3 3rd trial
40 20 0 0
2
4
6
8
10
12
14
time [h] Fig. 4. Degree of phenol decomposition in repeated test trials for initial phenol concentration of 300 mg/dm3 . Flow rate 4.5 dm3 /h, reaction volume 0.7 dm3 .
418
Letter to the Editor / Applied Catalysis B: Environmental 46 (2003) 415–419
4. Conclusions
0,005 0 -0,005
b)
-0,01 -0,015 a)
-0,02 -0,025 200
250
300
350
400
450
500
nm
Fig. 5. Diffuse reflectance UV-Vis spectra of photocatalyst samples. (a) Fresh P25; (b) used P25.
gap energy has changed from 3.15 for fresh P25 to 3.24 for used photocatalyst. Photocatalyst samples were also analyzed by FTIR spectroscopy using a Jasco FTIR 430 spectrometer with accessory for diffuse reflectance measurements. Fig. 6 shows the diffuse reflectance FTIR spectra of P25 samples. It can be seen that new absorption bands in the region of 1200–1800 cm−1 appeared on the spectra of photocatalyst used in the reaction of phenol photo-oxidation at concentration of 300 mg/dm3 when the sample color changed to dark brown. These bands are due to carbon deposits on the catalyst surface [18]. The two bands at 1713 and 1690 cm−1 were assigned to C=O stretching vibrations, the band at 1630 cm−1 to aromatic ring vibrations, the band at 1485 cm−1 to C–H asymmetric vibrations, and the band at 1259 cm−1 to C–O vibrations. 30 25 20 % 15 10 5 0 2000
1800
1600
1400
1200
1000
Reaction of photocatalytic oxidation of phenol in water using the flow reactor with immobilized bed of photocatalyst was investigated. Water solutions with various initial phenol concentrations were examined. It was observed that for the initial phenol concentrations up to about 50 mg/dm3 , after 5 h of illumination, phenol decomposition degree increased while after exceeding this value, decomposition degree decreased. It can be explained by the fact that to a certain concentration, the amount of active centers of the photocatalyst is sufficient for correct reaction course and the process is controlled by initial concentration of phenol, and afterwards saturation of active centers occurs. In addition, intermediate products of phenol decomposition compete for active centers onto catalyst surface. Passing (temporary) presence of oxidized forms of phenol, quinones, was confirmed by appearance of new absorption band on UV-Vis spectra of reaction mixture at wavelength about 290 nm. Additionally, activity of the photocatalyst used again with high phenol concentration of 300 mg/dm3 , decreased considerably; so it can be concluded that catalyst surface was covered with products of phenol decomposition. It was even visible to the naked eye— the catalyst surface had dark color. The presence of carbon deposits on the catalyst surface was confirmed by FTIR analysis. This analysis showed new absorption bands in the region of 1800–1200 cm−1 assigned to C=O, C–H, C–C, and aromatic ring vibrations. UV-Vis analysis showed that band gap energy of used photocatalyst was higher than the fresh P25, which can also be responsible for activity decrease. Obtained results show that Degussa P25 titanium dioxide is a effective photocatalyst in the process of oxidation of phenol in the labyrinth flow reactor with immobilized catalyst bed. However the process is effective for low initial phenol concentrations and photocatalyst loses its activity due to carbon deposits on the surface. References
cm
Fig. 6. Diffuse reflectance FTIR spectra of photocatalyst samples. (a) Fresh P25; (b) used P25.
[1] Proceedings of the First International Symposium “Chemical oxidation technologies for the nineties”, Vanderbilt University, Nashville, Tennessee, vol. 1–3, 1991–1993.
Letter to the Editor / Applied Catalysis B: Environmental 46 (2003) 415–419 [2] Handbook: Advanced Photochemical Oxidation Processes, United States Environmental Protection Agency publication EPA/625/R-98/004, 1998. [3] R. Andreozzi, V. Caprio, A. Insola, R. Marotta, Catal. Today 53 (1999) 51. [4] R. Munter, S. Preis, J. Kallas, M. Trapido, Y. Veressinina, Kemia-Kemi 58 (2001) 354. [5] S. Esplugas, J. Gimenez, S. Contreras, E. Pascual, M. Rodriguez, Water Res. 36 (2002) 1034. [6] M. Schiavello, Photocatalysis and environment: trends and applications, NATO ASI Series C, vol. 283, Kluwer Academic Publishers, London, 1987. [7] D.F. Ollis, H. Al-Ekabi, Photocatalytic Purification and Treatment of Water and Air, Elsevier, Amsterdam, 1993. [8] M.R. Hoffman, S.T. Martin, W. Choi, D.W. Bahnemann, Chem. Rev. 95 (1995) 69. [9] A.L. Linsebigler, G. Lu, J.T. Yates Jr., Chem. Rev. 95 (1995) 735. [10] D.M. Blake, Bibliography of Work on the Photocatalytic Removal of Hazardous Compounds from Water and Air, NERL/TP-430-22197, Golden Co., 1997. [11] J.-M. Herrmann, Catal. Today 53 (1999) 115. [12] O.M. Alfano, D. Bahnemann, A.E. Cassano, R. Dillert, R. Goslich, Catal. Today 58 (2000) 199. [13] D.S. Bhatkhande, V.G. Pangarkar, A.A.C.M. Beenackers, J. Chem. Tech. Biotechnol. 77 (2001) 102.
419
[14] R.W. Matthews, Water Res. 25 (1991) 1169. [15] A. Fernandez, G. Lassaletta, V.M. Jimenez, A. Justo, A.R. Gonzalez-Elipe, J.-M. Herrmann, H. Tahiri, Y. Ati-Ichou, Appl. Catal. B: Environ. 7 (1995) 49. [16] J.-M. Herrmann, H. Tahiri, Y. Ati-Ichou, G. Lassaletta, A.R. Gonzalez-Elipe, A. Fernandez, Appl. Catal. B: Environ. 13 (1997) 219. [17] Y.-H. Hsien, C.-F. Chang, Y.-H. Chen, S. Cheng, Appl. Catal. B: Environ. 31 (2001) 241. [18] H. Einaga, S. Futamura, T. Ibusuki, Appl. Catal. B: Environ. 38 (2002) 215.
Joanna Grzechulska Antoni Waldemar Morawski∗ Institute of Chemical and Environment Engineering Technical University of Szczecin, ul. Pułaskiego 10 Szczecin 70-322, Poland ∗ Corresponding author E-mail address: [email protected] (A.W. Morawski) 24 November 2002