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Adsorption and photocatalysis of colour removal from waste water using flyash and sunlight
Catalysis Communications 2 (2001) 113±117
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Adsorption and photocatalysis of colour removal from waste water using ¯yash and sunlight Debabrata Chatterjee *, Biswajit Ruj, Anima Mahata Chemistry Section, Central Mechanical Engineering Research Institute, Mahatma Gandhi Avenue, Durgapur 713209, India Received 29 January 2001; received in revised form 11 May 2001
Abstract Adsorption of dyes viz. thionine, eosin Y and rhodamine B on ¯yash has been investigated as a function of ¯yash and dye concentrations, contact time and pH. Photodegradation of dyes has been achieved by illuminating the reacting system containing dye and ¯yash with visible light. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Adsorption; Photodegradation; Dyes; Flyash; Visible light
1. Introduction A number of synthetic dyes that are emitted (10±20% of the total consumption) from various textile industries cause a formidable contamination of water as the colour tends to persist even after the conventional treatment given to the waste water. The conventional techniques of waste water treatment are usually based on biological oxygen demand (BOD) and chemical oxygen demand (COD) removal, but are largely ineective in removing colour from euent. Conceptually, combination of more than one process such as adsorption and degradation of colour would probably provide a viable solution to this problem. As a part of our recent research interest [1±3] in investigating visible light assisted catalytic detoxi®cation of organic pollutants we have undertaken
* Corresponding author. Tel.: +91-343-546818; fax: +91-343546745. E-mail address: [email protected] (D. Chatterjee).
the present work in which we explore the possibility of dye removal from textile waste water through adsorption on ¯yash and followed by photocatalytic degradation of dye molecules into non-hazardous product(s). Flyash had been reportedly known to have properties suitable for adsorption studies in aqueous media [4]. We wish to report herein the preliminary results of our studies of adsorption and photodecomposition of some common organic dyes viz. thionine, eosine Y and rhodamine B (Fig. 1) on the surface of the ¯yash. 2. Experimental Flyash was obtained from Durgapur Project Limited, Durgapur, West Bengal. The coarser impurities in ¯yash were separated by a vigorous stirring of ¯yash suspension and allowing the coarser particles to settle. The ¯yash material was then dried at room temperature and used throughout the experiments. Chemical analysis
1566-7367/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 1 5 6 6 - 7 3 6 7 ( 0 1 ) 0 0 0 1 7 - 6
114
D. Chatterjee et al. / Catalysis Communications 2 (2001) 113±117
Fig. 1. Pictorial representation of dyes.
of ¯yash was carried out for its main constituents like silica, alumina and iron oxides by using a Perkin Elmer atomic absorption spectrometer (AAnalyst 300). Percentages (w/w%) of silica, alumina and iron oxides were found to be 58.5, 22.7 and 5.8, respectively. Adsorption of thionine, eosin Y and rhodamine B dyes on ¯yash was estimated spectrophotometrically by using a Cintra 10 GBC UV±visible spectrophotometer. Adsorption studies were carried out in dark by shaking aqueous solution (50 ml; pH 5:6) of dyes of various concentrations containing a required amount of ¯yash in a series of BOD bottles wrapped with carbon paper. The extent of adsorption was estimated by measuring the dierence in absorbances of free dye and the supernatant liquid obtained after centrifugation of the reacting mixture containing ¯yash and dyes. All other chemicals used were of A.R. grade and doubly distilled water was used throughout the experiment. Photolysis of aqueous solution of (50 ml) of dye 10 5 M containing 100 mg of ¯yash was carried out in a ¯at-surfaced glass reactor. A 50 W tungsten lamp (Philips medical spot lamp; inner diameter of the focus tube was 5.1 cm) was used for the irradiation. The distance between the lamp and the glass reactor containing the reaction mixture was ®xed at 8 inch. The pre-aerated reaction mixture was magnetically stirred during irradiation. After 4 h of irradiation the reaction mixture was centrifuged and the supernatant liquid so obtained was then subjected to spectrophotometric analysis.
3. Results and discussion The composition of the ¯yash (see Section 2) with regard to its major constituents reveals that the percentage (w/w%) of silica, alumina and oxides of iron fall in the range that is expected for ¯yash generated in the thermal power stations [5]. Absorption spectra of the aqueous solutions of thionine, eosin Y and rhodamine B revealed characteristic absorption maxima at 600, 518 and 555 nm, respectively. Results of the adsorption of dyes studied by estimating percentage deletion of dyes as a function of the weight of ¯yash, dye concentrations and contact time are summarized in Table 1. The dye uptake by ¯yash enhances with increase in the amount of ¯yash, whereas, for a given amount of ¯yash percentage of unadsorbed dyes increases with the increase in initial concentration of dyes. The percentage removal of dyes increases sharply with time initially, however, attained a limiting value after a certain period of time. Results of adsorption studies reveal that the capacity of ¯yash towards adsorption of dyes under investigations is appreciably good, however, for thionine it is excellent. This is probably due to coordination of thionine through sulphur atom to the Fe content of the ¯yash as Fe(III) has high anity for binding sulphur containing molecules. Prior to the photolysis studies a series of blank reactions were carried out and similar to that reported earlier for all photocatalytic dye degradations, no decomposition of dyes was noticed by irradiating the aqueous solution of dye with visible light in the presence of oxygen for 6 h as evidenced
D. Chatterjee et al. / Catalysis Communications 2 (2001) 113±117
115
Table 1 Results of adsorption of dyes on ¯yasha Dye Thionine
Concentration of dye (M) 10
5
1 10 5 10 1 10 5 10 1 10
Eosin Y
10
10
Contact time (min)
% adsorbed
0.5 1.0 1.5 2.0 2.0
60
2.0
10 20 30 60
52.5 82.7 93.0 98.7 95.3 57.2 47.0 4.9 87.9 95.3 96.4 98.7
1.0 2.0 3.0 4.0 6.0 5.0
60
5.0
10 20 40 60
1.0 2.0 3.0 4.0 6.0 5.0
60
5.0
10 20 40 60
20
4 4 5
5 5
60
4 4 5
5
1 10 5 10 1 10 5 10 1 10
a
5
5
1 10 5 10 1 10 5 10 1 10
Rhodamine B
5
Wt. of ¯yash (g)
5 5
60
4 4 5
18.9 45.3 61.9 79.6 83.2 77.5 29.3 21.0 3.7 54.5 67.7 74.0 77.5 27.0 44.4 62.7 82.4 94.5 86.4 43.2 29.0 8.2 65.6 73.1 79.2 86.4
See Section 2 for reaction conditions.
by no spectral changes observed in the spectra of the 5 h irradiated solution of dyes with visible light in the presence of oxygen without Fe3 ion. Preliminary experiments had also revealed the fact that no change in the spectral pattern was observed after 5 h of stirring the aqueous solution of dyes with Fe(III) ion in dark, however, an appreciable decrease in the absorbance of dye (Fig. 2) was noticed when air equilibrated aqueous dye solutions containing Fe(III) ion were illuminated
with visible light for 5 h. Gradual disappearance of the characteristics bands under prolonged irradiation with visible light essentially implies the occurrence of electron redox transfer process. Spectrum of the photolysed solution kept in dark for 5 h exhibited the characteristic band of Fe(III) ion at 300 nm. This implies that the Fe(II) species formed in the process of photolysis undergoes oxidation in dark by interacting with dissolved oxygen with a concomitant formation of O2 =HO2
116
D. Chatterjee et al. / Catalysis Communications 2 (2001) 113±117
Fig. 2. Spectral changes that occur during photolysis of aerated aqueous solution of thionine 1 10 ion 1 10 4 M at pH 2.5.
radicals which is a very well-known phenomenon in chemistry. Addition of 1,10-phenanthroline (selective reagent for detecting Fe2 ion) to the solution during photolysis developed a red colour which essentially con®rmed the formation of Fe2 ion in the reacting system. The spectrum of the solution exhibited the characteristic absorption maximum at 515 nm. Decomposition of dye species by O2 =HO2 radicals has also been known in the literature [1± 10]. Addition of a strong reductant like L-ascorbic acid to the photolysed solution could not revive the spectra of the dye which implicates irreversible damage of the dye species caused by the O2 =HO2 radical attacks. Above results convincingly demonstrate the role of Fe3 ion in the photocatalytic degradation of dyes. Photolysis of aqueous solution of (50 ml) of dye 10 5 M containing 100 mg of ¯yash for 4 h and subsequent spectral analysis of the photolysed
4
M in the presence of Fe(III)
solution revealed substantial photodegradation of dyes (Table 2) under investigation. Based on the experimental results (Table 2) and considering the ability of Fe(III) species (present in the ¯yash) towards participating in oxidative quenching of dyes at the excited state, as in the cases reported for thionine [6] and other dyes [7] in homogeneous system, the following working mechanism is proposed for the photoassisted degradation of dyes adsorbed on the ¯yash: hm
FA± Ds ! FA± D s
1
FA± D s Fe III ! FA± D s Fe II
2
Fe II O2 ! Fe III O2 O2 H ! HO2
3 4
O2 =HO2 D =D ! Products
(hm visible light; FA Flyash; eosin Y/rhodamine B)
5 D thionine/
Table 2 Removal of dyes through adsorption and photodegradationa Dye Thionine Eosin Y Rhodamine B a b
Concentration of dye (M) 10 10 10
5 5 5
See Section 2 for reaction conditions. After 4 h of irradiation with visible light.
Wt. of ¯yash (g)
Contact time (h)
% adsorbedb dark
light
0.1 0.1 0.1
4.0 4.0 4.0
13.2 5.2 10.0
61.0 21.0 22.0
D. Chatterjee et al. / Catalysis Communications 2 (2001) 113±117
As proposed in Scheme I, surface adsorbed dyes ®rst get excited upon absorption of visible light (Eq. 1). The dye molecules in the excited state behaving as electron donors [8,9] reduce Fe(III) to Fe(II) (Eq. 2). The superoxide radical O2 is subsequently generated in the reacting system through the reaction of reduced Fe(II) sites in ¯yash and oxygen (Eq. 3). The superoxide/hydroperoxide radicals O2 =HO2 in the system initiate degradation of dye species. It is presumed based on the earlier reports [10±12] that the repeated attacks of O2 =HO2 radical on the dye molecule cause the decomposition of dye species (Eq. 5) eventually to carbon dioxide. The rate controlling step in the present case is possibly involved with the adsorption of reactants and oxidation of surface adsorbed organics. 4. Conclusion In conclusion, the results of the present work clearly demonstrate the dye adsorbing capacity of ¯yash obtained from Durgapur Project Limited, Durgapur, West Bengal. Further, the surface adsorbed thionine, eosin Y and rhodamine B dyes undergo photodegradation in the presence of visible light. The results of the present studies imply the rational viability of using ¯yash and visible light for eco-friendly degradation of dyes in textile waste water. Studies pertinent to this matter are in progress.
117
Acknowledgements We gratefully acknowledge the ®nancial support (No.15/6/99-(ST)) obtained from MNES, Govt. of India. We are thankful to Dr. B.K. Sinha, Director of this institute for his encouragement.
References [1] D. Chatterjee, C. Bhattacharya, Indian J. Chem. 32A (1999) 1256. [2] D. Chatterjee, A. Mahata, Catalysis Communications 2 (2001) 1. [3] D. Chatterjee, A. Mahata, Appl. Catal. B Environmental, 2001, in press. [4] A.G. Rowley, F.M. Husband, A.B. Cunningham, Water Res. 18 (1984) 981. [5] P.V. Bush, T.R. Snyder, R.L. Chang, J. APCA 39 (1989) 361. [6] R. Ramraj, R. Tamilarasan, P. Natarajan, J. Chem. Soc. Faraday Trans. 81 (1985) 2763. [7] S.C. Bhattacharya, H. Das, S.P. Moulick, J. Photochem. Photobiol. A 84 (1994) 39. [8] K. Itoh, Y. Chiyokawa, M. Nakao, K. Honda, J. Am. Chem. Soc. 106 (1984) 1620. [9] P.V. Kamat, J. Photochem. 28 (1985) 513. [10] J. Masr, M. Gratzel, J. Am. Chem. Soc. 106 (1984) 6557. [11] K. Venugopal, P.V. Kamat, Environ. Sci. Technol. 29 (1995) 841. [12] J. Zhao, J. Wu, K.Q. Wu, K. Oikawa, H. Hidaka, N. Serpon, Environ. Sci. Technol. 32 (1998) 2394.
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Adsorption and photocatalysis of colour removal from waste water using ¯yash and sunlight Debabrata Chatterjee *, Biswajit Ruj, Anima Mahata Chemistry Section, Central Mechanical Engineering Research Institute, Mahatma Gandhi Avenue, Durgapur 713209, India Received 29 January 2001; received in revised form 11 May 2001
Abstract Adsorption of dyes viz. thionine, eosin Y and rhodamine B on ¯yash has been investigated as a function of ¯yash and dye concentrations, contact time and pH. Photodegradation of dyes has been achieved by illuminating the reacting system containing dye and ¯yash with visible light. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Adsorption; Photodegradation; Dyes; Flyash; Visible light
1. Introduction A number of synthetic dyes that are emitted (10±20% of the total consumption) from various textile industries cause a formidable contamination of water as the colour tends to persist even after the conventional treatment given to the waste water. The conventional techniques of waste water treatment are usually based on biological oxygen demand (BOD) and chemical oxygen demand (COD) removal, but are largely ineective in removing colour from euent. Conceptually, combination of more than one process such as adsorption and degradation of colour would probably provide a viable solution to this problem. As a part of our recent research interest [1±3] in investigating visible light assisted catalytic detoxi®cation of organic pollutants we have undertaken
* Corresponding author. Tel.: +91-343-546818; fax: +91-343546745. E-mail address: [email protected] (D. Chatterjee).
the present work in which we explore the possibility of dye removal from textile waste water through adsorption on ¯yash and followed by photocatalytic degradation of dye molecules into non-hazardous product(s). Flyash had been reportedly known to have properties suitable for adsorption studies in aqueous media [4]. We wish to report herein the preliminary results of our studies of adsorption and photodecomposition of some common organic dyes viz. thionine, eosine Y and rhodamine B (Fig. 1) on the surface of the ¯yash. 2. Experimental Flyash was obtained from Durgapur Project Limited, Durgapur, West Bengal. The coarser impurities in ¯yash were separated by a vigorous stirring of ¯yash suspension and allowing the coarser particles to settle. The ¯yash material was then dried at room temperature and used throughout the experiments. Chemical analysis
1566-7367/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 1 5 6 6 - 7 3 6 7 ( 0 1 ) 0 0 0 1 7 - 6
114
D. Chatterjee et al. / Catalysis Communications 2 (2001) 113±117
Fig. 1. Pictorial representation of dyes.
of ¯yash was carried out for its main constituents like silica, alumina and iron oxides by using a Perkin Elmer atomic absorption spectrometer (AAnalyst 300). Percentages (w/w%) of silica, alumina and iron oxides were found to be 58.5, 22.7 and 5.8, respectively. Adsorption of thionine, eosin Y and rhodamine B dyes on ¯yash was estimated spectrophotometrically by using a Cintra 10 GBC UV±visible spectrophotometer. Adsorption studies were carried out in dark by shaking aqueous solution (50 ml; pH 5:6) of dyes of various concentrations containing a required amount of ¯yash in a series of BOD bottles wrapped with carbon paper. The extent of adsorption was estimated by measuring the dierence in absorbances of free dye and the supernatant liquid obtained after centrifugation of the reacting mixture containing ¯yash and dyes. All other chemicals used were of A.R. grade and doubly distilled water was used throughout the experiment. Photolysis of aqueous solution of (50 ml) of dye 10 5 M containing 100 mg of ¯yash was carried out in a ¯at-surfaced glass reactor. A 50 W tungsten lamp (Philips medical spot lamp; inner diameter of the focus tube was 5.1 cm) was used for the irradiation. The distance between the lamp and the glass reactor containing the reaction mixture was ®xed at 8 inch. The pre-aerated reaction mixture was magnetically stirred during irradiation. After 4 h of irradiation the reaction mixture was centrifuged and the supernatant liquid so obtained was then subjected to spectrophotometric analysis.
3. Results and discussion The composition of the ¯yash (see Section 2) with regard to its major constituents reveals that the percentage (w/w%) of silica, alumina and oxides of iron fall in the range that is expected for ¯yash generated in the thermal power stations [5]. Absorption spectra of the aqueous solutions of thionine, eosin Y and rhodamine B revealed characteristic absorption maxima at 600, 518 and 555 nm, respectively. Results of the adsorption of dyes studied by estimating percentage deletion of dyes as a function of the weight of ¯yash, dye concentrations and contact time are summarized in Table 1. The dye uptake by ¯yash enhances with increase in the amount of ¯yash, whereas, for a given amount of ¯yash percentage of unadsorbed dyes increases with the increase in initial concentration of dyes. The percentage removal of dyes increases sharply with time initially, however, attained a limiting value after a certain period of time. Results of adsorption studies reveal that the capacity of ¯yash towards adsorption of dyes under investigations is appreciably good, however, for thionine it is excellent. This is probably due to coordination of thionine through sulphur atom to the Fe content of the ¯yash as Fe(III) has high anity for binding sulphur containing molecules. Prior to the photolysis studies a series of blank reactions were carried out and similar to that reported earlier for all photocatalytic dye degradations, no decomposition of dyes was noticed by irradiating the aqueous solution of dye with visible light in the presence of oxygen for 6 h as evidenced
D. Chatterjee et al. / Catalysis Communications 2 (2001) 113±117
115
Table 1 Results of adsorption of dyes on ¯yasha Dye Thionine
Concentration of dye (M) 10
5
1 10 5 10 1 10 5 10 1 10
Eosin Y
10
10
Contact time (min)
% adsorbed
0.5 1.0 1.5 2.0 2.0
60
2.0
10 20 30 60
52.5 82.7 93.0 98.7 95.3 57.2 47.0 4.9 87.9 95.3 96.4 98.7
1.0 2.0 3.0 4.0 6.0 5.0
60
5.0
10 20 40 60
1.0 2.0 3.0 4.0 6.0 5.0
60
5.0
10 20 40 60
20
4 4 5
5 5
60
4 4 5
5
1 10 5 10 1 10 5 10 1 10
a
5
5
1 10 5 10 1 10 5 10 1 10
Rhodamine B
5
Wt. of ¯yash (g)
5 5
60
4 4 5
18.9 45.3 61.9 79.6 83.2 77.5 29.3 21.0 3.7 54.5 67.7 74.0 77.5 27.0 44.4 62.7 82.4 94.5 86.4 43.2 29.0 8.2 65.6 73.1 79.2 86.4
See Section 2 for reaction conditions.
by no spectral changes observed in the spectra of the 5 h irradiated solution of dyes with visible light in the presence of oxygen without Fe3 ion. Preliminary experiments had also revealed the fact that no change in the spectral pattern was observed after 5 h of stirring the aqueous solution of dyes with Fe(III) ion in dark, however, an appreciable decrease in the absorbance of dye (Fig. 2) was noticed when air equilibrated aqueous dye solutions containing Fe(III) ion were illuminated
with visible light for 5 h. Gradual disappearance of the characteristics bands under prolonged irradiation with visible light essentially implies the occurrence of electron redox transfer process. Spectrum of the photolysed solution kept in dark for 5 h exhibited the characteristic band of Fe(III) ion at 300 nm. This implies that the Fe(II) species formed in the process of photolysis undergoes oxidation in dark by interacting with dissolved oxygen with a concomitant formation of O2 =HO2
116
D. Chatterjee et al. / Catalysis Communications 2 (2001) 113±117
Fig. 2. Spectral changes that occur during photolysis of aerated aqueous solution of thionine 1 10 ion 1 10 4 M at pH 2.5.
radicals which is a very well-known phenomenon in chemistry. Addition of 1,10-phenanthroline (selective reagent for detecting Fe2 ion) to the solution during photolysis developed a red colour which essentially con®rmed the formation of Fe2 ion in the reacting system. The spectrum of the solution exhibited the characteristic absorption maximum at 515 nm. Decomposition of dye species by O2 =HO2 radicals has also been known in the literature [1± 10]. Addition of a strong reductant like L-ascorbic acid to the photolysed solution could not revive the spectra of the dye which implicates irreversible damage of the dye species caused by the O2 =HO2 radical attacks. Above results convincingly demonstrate the role of Fe3 ion in the photocatalytic degradation of dyes. Photolysis of aqueous solution of (50 ml) of dye 10 5 M containing 100 mg of ¯yash for 4 h and subsequent spectral analysis of the photolysed
4
M in the presence of Fe(III)
solution revealed substantial photodegradation of dyes (Table 2) under investigation. Based on the experimental results (Table 2) and considering the ability of Fe(III) species (present in the ¯yash) towards participating in oxidative quenching of dyes at the excited state, as in the cases reported for thionine [6] and other dyes [7] in homogeneous system, the following working mechanism is proposed for the photoassisted degradation of dyes adsorbed on the ¯yash: hm
FA± Ds ! FA± D s
1
FA± D s Fe III ! FA± D s Fe II
2
Fe II O2 ! Fe III O2 O2 H ! HO2
3 4
O2 =HO2 D =D ! Products
(hm visible light; FA Flyash; eosin Y/rhodamine B)
5 D thionine/
Table 2 Removal of dyes through adsorption and photodegradationa Dye Thionine Eosin Y Rhodamine B a b
Concentration of dye (M) 10 10 10
5 5 5
See Section 2 for reaction conditions. After 4 h of irradiation with visible light.
Wt. of ¯yash (g)
Contact time (h)
% adsorbedb dark
light
0.1 0.1 0.1
4.0 4.0 4.0
13.2 5.2 10.0
61.0 21.0 22.0
D. Chatterjee et al. / Catalysis Communications 2 (2001) 113±117
As proposed in Scheme I, surface adsorbed dyes ®rst get excited upon absorption of visible light (Eq. 1). The dye molecules in the excited state behaving as electron donors [8,9] reduce Fe(III) to Fe(II) (Eq. 2). The superoxide radical O2 is subsequently generated in the reacting system through the reaction of reduced Fe(II) sites in ¯yash and oxygen (Eq. 3). The superoxide/hydroperoxide radicals O2 =HO2 in the system initiate degradation of dye species. It is presumed based on the earlier reports [10±12] that the repeated attacks of O2 =HO2 radical on the dye molecule cause the decomposition of dye species (Eq. 5) eventually to carbon dioxide. The rate controlling step in the present case is possibly involved with the adsorption of reactants and oxidation of surface adsorbed organics. 4. Conclusion In conclusion, the results of the present work clearly demonstrate the dye adsorbing capacity of ¯yash obtained from Durgapur Project Limited, Durgapur, West Bengal. Further, the surface adsorbed thionine, eosin Y and rhodamine B dyes undergo photodegradation in the presence of visible light. The results of the present studies imply the rational viability of using ¯yash and visible light for eco-friendly degradation of dyes in textile waste water. Studies pertinent to this matter are in progress.
117
Acknowledgements We gratefully acknowledge the ®nancial support (No.15/6/99-(ST)) obtained from MNES, Govt. of India. We are thankful to Dr. B.K. Sinha, Director of this institute for his encouragement.
References [1] D. Chatterjee, C. Bhattacharya, Indian J. Chem. 32A (1999) 1256. [2] D. Chatterjee, A. Mahata, Catalysis Communications 2 (2001) 1. [3] D. Chatterjee, A. Mahata, Appl. Catal. B Environmental, 2001, in press. [4] A.G. Rowley, F.M. Husband, A.B. Cunningham, Water Res. 18 (1984) 981. [5] P.V. Bush, T.R. Snyder, R.L. Chang, J. APCA 39 (1989) 361. [6] R. Ramraj, R. Tamilarasan, P. Natarajan, J. Chem. Soc. Faraday Trans. 81 (1985) 2763. [7] S.C. Bhattacharya, H. Das, S.P. Moulick, J. Photochem. Photobiol. A 84 (1994) 39. [8] K. Itoh, Y. Chiyokawa, M. Nakao, K. Honda, J. Am. Chem. Soc. 106 (1984) 1620. [9] P.V. Kamat, J. Photochem. 28 (1985) 513. [10] J. Masr, M. Gratzel, J. Am. Chem. Soc. 106 (1984) 6557. [11] K. Venugopal, P.V. Kamat, Environ. Sci. Technol. 29 (1995) 841. [12] J. Zhao, J. Wu, K.Q. Wu, K. Oikawa, H. Hidaka, N. Serpon, Environ. Sci. Technol. 32 (1998) 2394.