- Email: [email protected]
IMMOBILIZED PHOTOSENSITIZERS FOR SOLAR PHOTOCHEMICAL APPLICATIONS
Pergamon
PII: S0038 – 092X( 98 )00099 – 1
Solar Energy Vol. 65, No. 1, pp. 71–74, 1999 1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0038-092X / 99 / $ – see front matter
IMMOBILIZED PHOTOSENSITIZERS FOR SOLAR PHOTOCHEMICAL APPLICATIONS D. FAUST*, K.-H. FUNKEN* , †, G. HORNECK**, B. MILOW*, J. ORTNER*, ¨ M. SATTLEGGER*, M. SCHAFER** and C. SCHMITZ** ¨ Luft- und Raumfahrt e.V., Solare Energietechnik, D-51170 Koln, ¨ Germany *Deutsches Zentrum fur ¨ Luft- und Raumfahrtmedizin, D-51170 Koln, ¨ Germany **Institut fur Revised version accepted 17 August 1998
Abstract—New hydrophilic immobilized photosensitizers (heterogeneous phase) were synthesized that overcome some disadvantages of the use of homogeneous phase sensitizers for detoxification and disinfection of water. The chosen sensitizers, based on porphyrin moieties, were bound on poly(methyl methacrylate) (PMMA). The measured production rate of singlet oxygen is significantly higher than that of the well-known rose bengal immobilized on Merrifield polymer. The sensitive polymer can be used for detoxification and disinfection of polluted water. 1998 Elsevier Science Ltd. All rights reserved.
nisms. If living tissue should be damaged by the combined action of a photosensitizer, light and oxygen, the term ‘photodynamic’ effect is also applied to describe the result. The energy transfer starts with the excitation of the sensitizer by irradiation with visible light. Thereby, the sensitizer is shifted from its electronic ground-state ( 1 Sg ) to an excited electronic state ( 1 Dg ). In a second step, intersystem-crossing leads to the reactive molecule in an excited triplet state. The energy transfer process occurs during the collision of triplet state sensitizer with ground state (triplet) oxygen. Among other factors, the efficiency of this water treatment method depends on the production rate of singlet oxygen in the aqueous solutions. The high oxidation strength of generated singlet oxygen is used for the destruction of organic pollutants and the killing of microorganisms. Acher et al. (1997) used methylene blue dissolved homogeneously in water for detoxification experiments under laboratory conditions and in an experimental pilot plant scale. One disadvantage of such systems with homogeneously dissolved sensitizers is the necessity to remove the sensitizer from the water after treatment. In principal, this problem can be solved with heterogeneous phase immobilized sensitizers. The efficiency of immobilized sensitizers is under the influence of many effects. For example, rose bengal, homogeneously dissolved in water, shows a hundredfold higher production rate of singlet oxygen (Braun et al., 1997) compared to the well-known heterogeneous phase rose bengal immobilized on Merrifield polymer (Schaap et al., 1975). One expla-
1. INTRODUCTION
Within the project ‘Comparative Assessment of Technologies for Solar Detoxification and Disinfection of Contaminated Water’, methods were developed and assessed for the purification of contaminated water using solar radiation. One part of the project was to use the reactivity of singlet oxygen generated by irradiation of a sensitizer with visible light in the presence of dissolved oxygen. The degradation of pesticides and the killing rate of microorganisms were investigated. Photochemical generation of singlet oxygen is simple and efficient. Sensitizers (Sen) are well known for use as energy transfer agents, e.g. in the photooxidation chain comprising light, oxygen and a reactant (Fig. 1). Dye sensitizers, such as rose bengal, methylene blue or phthalocyanins, provide convenient means to generate singlet oxygen in excellent quantum yields (Wilkinson et al., 1993; Neckers and Valdes-Aguilera, 1993). For water purification processes, the reactant targets (A) are organic pollutants and microorga-
Fig. 1. Energy transfer from the sensitizer to a target. †Author to whom correspondence should be addressed. Email: [email protected] 71
72
D. Faust et al.
nation for this observation is the hydrophobe character of the photosensitive polymer. The generated singlet oxygen has no possibility of diffusing from the surface into the solution to become active there. In the paper presented here, the use of new especially functional zinc–porphyrin compounds immobilized on poly(methyl methacrylate) (PMMA) is reported to overcome some of the problems. 2. SYNTHESIS AND FIXATION OF ZINC– PORPHYRINS
Porphyrins and, in particular, zinc–tetraphenyl– porphyrins are excellent sensitizers to produce singlet oxygen (Darwent et al., 1982). Some authors report on the preparation of polymers containing the porphyrin moiety (e.g. Lautsch et al., 1955; Kamogawa, 1974; Kamachi et al., 1983; Eichhorn et al., 1995). In general, two approaches seem applicable: (1) monomers containing the sensitizer could be polymerized and (2) uncolored polymers could be modified in a subsequent reaction. The prerequisite of the last synthetic route is the existence of active groups in the polymer and in the sensitizer to build a permanent binding. As a conclusion of the known literature, two new derivatives of zinc(II)–porphyrins were synthesized containing the functional alcoholic group, which can be linked to PMMA. Following the method of Little et al. (1975); Rothemund and Menotti (1948); Srivastava and Tsutsui (1973) zinc(II) - 5 - (4 - hydroxyphenyl) - 10,15,20 - tris(4 sulfonatophenyl)porphyrin (1) and zinc(II)-5-(4hydroxyphenyl) - 10 - 15 - 20 - tris(N - methyl - 4 pyridinium)porphyrin (2) were synthesized (see
Fig. 2). These two derivatives contain hydrophilic functional groups. As the general fixation method, transesterification of PMMA with the new sensitizers in toluene in the presence of p-toluenesulfonic acid was used (Otera, 1993). Related to the number of methyl ester groups in the PMMA polymer, the concentration of the sensitizer fixed on the polymers was 1%. The synthesized new photosensitive PMMA polymers showed a higher hydrophilicity than the regular zinc(II)-5-(4-hydroxyphenyl)10,15,20-triphenylporphyrin immobilized on PMMA, which is not active. Shaped polymer films swelled on contact with water. 3. GENERAL METHOD TO CALCULATE THE PRODUCTION RATE OF SINGLET OXYGEN
To calculate the efficiency as a sensitizer, the production rate of singlet oxygen was measured. In aqueous solution, imidazole (Im) can be used as a singlet oxygen acceptor to give a transannular peroxide. This peroxide oxidizes the yellow N,Ndimethyl-4-nitrosoaniline (RNO) leading to colorless oxidation products (Young et al., 1973; Gandin et al., 1983; Gandin and Lion, 1982; Verlhac and Gaudemer, 1983; Le Guern et al., 1993). Thus, singlet oxygen production can be followed spectrophotometrically by the decay of secondary bleaching of RNO at l 5 440 nm. The bleaching of RNO is directly proportional to the production rate of singlet oxygen. Experiments with sensitizers dissolved homogeneously in aqueous solutions were performed in a newly designed laboratory apparatus (see Fig. 3) using a solar simulator (1 kW) for
Fig. 2. Zinc(II)-5-(4-hydroxyphenyl)-10,15,20-tris(4-sulfonatophenyl)porphyrin (1) and zinc(II)-5-(4- hydroxyphenyl)-10-15-20tris(N-methyl-4-pyridinium)porphyrin (2).
Immobilized photosensitizers for solar photochemical applications
73
Fig. 3. Schematic set-up of the laboratory apparatus.
irradiation. By means of filters, spectral irradiation was adjusted to 350–700 nm. In this apparatus, the production rate of singlet oxygen is measured as a function of various experimental conditions (temperature, pH, concentration of dissolved oxygen, concentration of sensitizer). For suspended heterogeneous phase sensitizers, the production rates of singlet oxygen were measured in Petri dishes. 4. EXPERIMENTAL RESULT OF THE SINGLET OXYGEN PRODUCTION TESTS
In a standard process (T 5 258C, air saturated, irradiated area 20 cm 2 ), the production rates of singlet oxygen were measured using different sensitizer systems. In Table 1, the determined production rates are presented. The experimental conditions were optimized for each sensitizer system, which resulted in specific pH values for each dye system.
5. DISCUSSION OF THE EXPERIMENTAL RESULTS
In aqueous suspension, the measured production rates of singlet oxygen of the porphyrins immobilized on PMMA were higher than that of rose bengal immobilized on Merrifield polymer. The result can be explained by the highly hydrophilic character of the especially functional new photosensitive polymers in comparison with the heterogeneous phase rose bengal. Due to the polymerization process, some of the fixed porphyrin molecules were not directly at the surface of the polymer and, therefore, not in contact with water. Therefore, they could not be used for the production of singlet oxygen and this lead inevitably to apparently less active dyes and lower rates of singlet oxygen production than with homogeneous sensitizers. Further improvements to increase the activity of the suspension of photosensitive polymers are in progress. Consequently, the ratio between the number of fixed
Table 1. Production rates of singlet oxygen using different sensitizer systems Photosensitizer concentration (Sen) (mol l 21 )
Condition
pH
Dc( 1 O 2 ) /Dt (mol l 21 s 21 )
Dc( 1 O 2 ) /Dt (mol l 21 s 21 ) (normalized: concentration (Sen) 5 1 (mol l 21 )
Rose Bengal 1.76 ? 10 26
Homogeneous solution
10
(5.060.5) ? 10 28
2.96 ? 10 22
Immobilized Rose Bengal 4.47 ? 10 25 (incorporated)
Suspension
8.5
(2.3560.5) ? 10 210
5.26 ? 10 26
Methylene blue 2.38 ? 10 24
Homogeneous solution
7
4 ? 10 28
1.67 ? 10 24
Immobilized (1) 8.0 ? 10 25 (incorporated)
Suspension
8.5
(6.060.4) ? 10 29
1.34 ? 10 24
Immobilized (2) 4.77 ? 10 25 (incorporated)
Suspension
4.4
1.8 ? 10 29
3.77 ? 10 25
74
D. Faust et al.
sensitizer molecules and the ester groups of the PMMA will be optimized with the aim of obtaining a higher production rate of singlet oxygen. In contrast to the previously known fixed sensitizers (e.g. rose bengal immobilized on Merrifield polymer), the production rate of singlet oxygen of the new especially functional photosensitive polymers is getting closer to the observed rates of homogeneous dissolved sensitizers.
6. OUTLOOK
With the synthesis of the new sensitive polymers, a solar-driven water treatment process for detoxification and disinfection applications with heterogeneous phase immobilized sensitizers seems feasible in the near future. First, microbiological experiments on a laboratory scale were carried out using the new photosensitive polymers. During the disinfection tests Deinococcus radiodurans was used as a model microorganism and porphyrins containing pyridinium groups were used as heterogeneous phase sensitizers. A killing effect was observed. Furthermore, the use of the heterogeneous phase system will be tested for solar treatment of water on a pilot plant scale. At the University of Malta, a new reactor was constructed for outdoor tests (Braun et al., 1997). The prototype reactor has a volume of up to 150 l and the irradiated sector has a size of 1 m 2 . Contaminated water can be pumped continuously to form a falling film above a polymer sheet coated with the described photosensitive polymers. With this installation, different types of photosensitive polymers will be tested.
Acknowledgements—We would like to thank the European Commission (AVI-CT94-0013) and the BMBF (0329627) for supporting this project.
REFERENCES Acher A. J., Fischer E., Tornheim R. and Manor Y. (1997) Sunlight technologies for photochemical deactivation of organic pollutants in water. In Proc. 8 th Int. Symp. Sol. ¨ M. (Eds), Thermal Conc. Technol., Becker M. and Bohmer ¨ Vol. 3, p. 1403. C. F. Muller Verlag, Heidelberg.
¨ Braun B., Ortner J., Funken K.-H., Schafer M., Schmitz C., Horneck G. and Fsadni M. (1997) Dye-sensitied solar detoxification and disinfection of contaminated water. In Proc. 8 th Int. Symp. Sol. Thermal Conc. Technol., Becker ¨ ¨ M. and Bohmer M. (Eds), Vol. 3, p. 1391. C. F. Muller Verlag, Heidelberg. Darwent J. R., Douglas P., Harriman A., Porter G. and Richoux M. -C. (1982) Metal phthalocycanines and porphyrins as photosensitizers for reduction of water to hydrogen. Coord. Chem. Rev. 44, 83. ¨ Eichhorn H., Sturm M. and Wohrle D. (1995) Polymer-bound porphyrins and their precursors, 11. Synthesis and polymerization of methacryloyloxy and 2,4-hexadienoyloxy derivatives of porphyrins and phthalocyanines. Macromol. Chem. Phys. 196, 115. Gandin E., Lion Y. and van de Vorst A. (1983) Quantum yield of singlet oxygen production by xanthene derivatives. Photochem. Photobiol. 37, 271. Gandin E. and Lion Y. (1982) A simple and convenient method of measuring the number of photons adsorbed by a solution irradiated with polychromatic light. J. Photochem. 20, 77. Kamachi M., Akimoto H. and Nozakura S. (1983) Preparation of polymer containing porphyrin moiety. Radical polymerization of 5-(4-Acrylolylocyphenyl)-10,15,20-Triphenylporphyrin. J. Polym. Sci. Polym. Lett. Ed. 21, 693. Kamogawa M. (1974) Syntheses and reaction of porphyrin and metalloporphyrin polymers. J. Polym. Sci. Polym. Chem. Ed. 12, 2317. Lautsch W., Broser W., Biedermann W. and Gnichel H. (1955) Enzyme models and their relation inclusion compounds. J. Polym. Sci. 17, 479. Le Guern F., Bied-Charreton C. and Faure J. (1993) Singlet oxygen production using porphyrins immobilized on mineral support. Bull. Soc. Chim. Fr. 130, 753. Little R. G., Anton J. A., Loach P. A. and Ibers S. A. (1975) The mixed-aldehyd synthesis of difunctional teraarylporphyrins. J. Heterocycl. Chem. 12, 343. Neckers D. C. and Valdes-Aguilera O. M. (1993) Photochemistry of the xanthene dyes. In Advances in Photochemistry, Volman D. H., Hammond G. S. and Neckers D. C. (Eds), Vol. 8, p. 315. John Wiley and Sons, New York. Otera J. (1993) Transesterfication. Chem. Rev. 93, 1449. Rothemund P. and Menotti A. R. (1948) Porphyrin studies V. The metal complex salts of tetraphenylporphyrin. J. Am. Chem. Soc. 70, 1808. Schaap A. P., Thayer A. L., Blossey E. C. and Neckers D. C. (1975) Polymer-based sensitizers for photooxidations. J. Am. Chem. Soc. 97, 3741. Srivastava T. S. and Tsutsui M. (1973) Preparation and purification of tetrasodium meso tetra(4-sulfonatophenyl)porphyrine. An easy procedure. J. Org. Chem. 38, 2103. Verlhac J. B. and Gaudemer A. (1983) Water soluble porphyrins and metalloporphyrins as photosensitizers in aerated aqueous solutions. I. Detection and determination of quantum yield of formation of singlet oxygen. Nouv. J. Chim. 8, 401. Wilkinson F., Helman W. P. and Ross A. B. (1993) Quantum yields for the photosensitized formation of the lowest electronically excited singlet state of molecular oxygen in solution. J. Phys. Chem. Ref. Data 22, 113. Young R. H., Brewer D. and Keller R. A. (1973) The determination of rate constants of reaction and lifetime of singulet oxygen in solution by a flash photolysis technique. J. Am. Chem. Soc. 95, 375.
PII: S0038 – 092X( 98 )00099 – 1
Solar Energy Vol. 65, No. 1, pp. 71–74, 1999 1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0038-092X / 99 / $ – see front matter
IMMOBILIZED PHOTOSENSITIZERS FOR SOLAR PHOTOCHEMICAL APPLICATIONS D. FAUST*, K.-H. FUNKEN* , †, G. HORNECK**, B. MILOW*, J. ORTNER*, ¨ M. SATTLEGGER*, M. SCHAFER** and C. SCHMITZ** ¨ Luft- und Raumfahrt e.V., Solare Energietechnik, D-51170 Koln, ¨ Germany *Deutsches Zentrum fur ¨ Luft- und Raumfahrtmedizin, D-51170 Koln, ¨ Germany **Institut fur Revised version accepted 17 August 1998
Abstract—New hydrophilic immobilized photosensitizers (heterogeneous phase) were synthesized that overcome some disadvantages of the use of homogeneous phase sensitizers for detoxification and disinfection of water. The chosen sensitizers, based on porphyrin moieties, were bound on poly(methyl methacrylate) (PMMA). The measured production rate of singlet oxygen is significantly higher than that of the well-known rose bengal immobilized on Merrifield polymer. The sensitive polymer can be used for detoxification and disinfection of polluted water. 1998 Elsevier Science Ltd. All rights reserved.
nisms. If living tissue should be damaged by the combined action of a photosensitizer, light and oxygen, the term ‘photodynamic’ effect is also applied to describe the result. The energy transfer starts with the excitation of the sensitizer by irradiation with visible light. Thereby, the sensitizer is shifted from its electronic ground-state ( 1 Sg ) to an excited electronic state ( 1 Dg ). In a second step, intersystem-crossing leads to the reactive molecule in an excited triplet state. The energy transfer process occurs during the collision of triplet state sensitizer with ground state (triplet) oxygen. Among other factors, the efficiency of this water treatment method depends on the production rate of singlet oxygen in the aqueous solutions. The high oxidation strength of generated singlet oxygen is used for the destruction of organic pollutants and the killing of microorganisms. Acher et al. (1997) used methylene blue dissolved homogeneously in water for detoxification experiments under laboratory conditions and in an experimental pilot plant scale. One disadvantage of such systems with homogeneously dissolved sensitizers is the necessity to remove the sensitizer from the water after treatment. In principal, this problem can be solved with heterogeneous phase immobilized sensitizers. The efficiency of immobilized sensitizers is under the influence of many effects. For example, rose bengal, homogeneously dissolved in water, shows a hundredfold higher production rate of singlet oxygen (Braun et al., 1997) compared to the well-known heterogeneous phase rose bengal immobilized on Merrifield polymer (Schaap et al., 1975). One expla-
1. INTRODUCTION
Within the project ‘Comparative Assessment of Technologies for Solar Detoxification and Disinfection of Contaminated Water’, methods were developed and assessed for the purification of contaminated water using solar radiation. One part of the project was to use the reactivity of singlet oxygen generated by irradiation of a sensitizer with visible light in the presence of dissolved oxygen. The degradation of pesticides and the killing rate of microorganisms were investigated. Photochemical generation of singlet oxygen is simple and efficient. Sensitizers (Sen) are well known for use as energy transfer agents, e.g. in the photooxidation chain comprising light, oxygen and a reactant (Fig. 1). Dye sensitizers, such as rose bengal, methylene blue or phthalocyanins, provide convenient means to generate singlet oxygen in excellent quantum yields (Wilkinson et al., 1993; Neckers and Valdes-Aguilera, 1993). For water purification processes, the reactant targets (A) are organic pollutants and microorga-
Fig. 1. Energy transfer from the sensitizer to a target. †Author to whom correspondence should be addressed. Email: [email protected] 71
72
D. Faust et al.
nation for this observation is the hydrophobe character of the photosensitive polymer. The generated singlet oxygen has no possibility of diffusing from the surface into the solution to become active there. In the paper presented here, the use of new especially functional zinc–porphyrin compounds immobilized on poly(methyl methacrylate) (PMMA) is reported to overcome some of the problems. 2. SYNTHESIS AND FIXATION OF ZINC– PORPHYRINS
Porphyrins and, in particular, zinc–tetraphenyl– porphyrins are excellent sensitizers to produce singlet oxygen (Darwent et al., 1982). Some authors report on the preparation of polymers containing the porphyrin moiety (e.g. Lautsch et al., 1955; Kamogawa, 1974; Kamachi et al., 1983; Eichhorn et al., 1995). In general, two approaches seem applicable: (1) monomers containing the sensitizer could be polymerized and (2) uncolored polymers could be modified in a subsequent reaction. The prerequisite of the last synthetic route is the existence of active groups in the polymer and in the sensitizer to build a permanent binding. As a conclusion of the known literature, two new derivatives of zinc(II)–porphyrins were synthesized containing the functional alcoholic group, which can be linked to PMMA. Following the method of Little et al. (1975); Rothemund and Menotti (1948); Srivastava and Tsutsui (1973) zinc(II) - 5 - (4 - hydroxyphenyl) - 10,15,20 - tris(4 sulfonatophenyl)porphyrin (1) and zinc(II)-5-(4hydroxyphenyl) - 10 - 15 - 20 - tris(N - methyl - 4 pyridinium)porphyrin (2) were synthesized (see
Fig. 2). These two derivatives contain hydrophilic functional groups. As the general fixation method, transesterification of PMMA with the new sensitizers in toluene in the presence of p-toluenesulfonic acid was used (Otera, 1993). Related to the number of methyl ester groups in the PMMA polymer, the concentration of the sensitizer fixed on the polymers was 1%. The synthesized new photosensitive PMMA polymers showed a higher hydrophilicity than the regular zinc(II)-5-(4-hydroxyphenyl)10,15,20-triphenylporphyrin immobilized on PMMA, which is not active. Shaped polymer films swelled on contact with water. 3. GENERAL METHOD TO CALCULATE THE PRODUCTION RATE OF SINGLET OXYGEN
To calculate the efficiency as a sensitizer, the production rate of singlet oxygen was measured. In aqueous solution, imidazole (Im) can be used as a singlet oxygen acceptor to give a transannular peroxide. This peroxide oxidizes the yellow N,Ndimethyl-4-nitrosoaniline (RNO) leading to colorless oxidation products (Young et al., 1973; Gandin et al., 1983; Gandin and Lion, 1982; Verlhac and Gaudemer, 1983; Le Guern et al., 1993). Thus, singlet oxygen production can be followed spectrophotometrically by the decay of secondary bleaching of RNO at l 5 440 nm. The bleaching of RNO is directly proportional to the production rate of singlet oxygen. Experiments with sensitizers dissolved homogeneously in aqueous solutions were performed in a newly designed laboratory apparatus (see Fig. 3) using a solar simulator (1 kW) for
Fig. 2. Zinc(II)-5-(4-hydroxyphenyl)-10,15,20-tris(4-sulfonatophenyl)porphyrin (1) and zinc(II)-5-(4- hydroxyphenyl)-10-15-20tris(N-methyl-4-pyridinium)porphyrin (2).
Immobilized photosensitizers for solar photochemical applications
73
Fig. 3. Schematic set-up of the laboratory apparatus.
irradiation. By means of filters, spectral irradiation was adjusted to 350–700 nm. In this apparatus, the production rate of singlet oxygen is measured as a function of various experimental conditions (temperature, pH, concentration of dissolved oxygen, concentration of sensitizer). For suspended heterogeneous phase sensitizers, the production rates of singlet oxygen were measured in Petri dishes. 4. EXPERIMENTAL RESULT OF THE SINGLET OXYGEN PRODUCTION TESTS
In a standard process (T 5 258C, air saturated, irradiated area 20 cm 2 ), the production rates of singlet oxygen were measured using different sensitizer systems. In Table 1, the determined production rates are presented. The experimental conditions were optimized for each sensitizer system, which resulted in specific pH values for each dye system.
5. DISCUSSION OF THE EXPERIMENTAL RESULTS
In aqueous suspension, the measured production rates of singlet oxygen of the porphyrins immobilized on PMMA were higher than that of rose bengal immobilized on Merrifield polymer. The result can be explained by the highly hydrophilic character of the especially functional new photosensitive polymers in comparison with the heterogeneous phase rose bengal. Due to the polymerization process, some of the fixed porphyrin molecules were not directly at the surface of the polymer and, therefore, not in contact with water. Therefore, they could not be used for the production of singlet oxygen and this lead inevitably to apparently less active dyes and lower rates of singlet oxygen production than with homogeneous sensitizers. Further improvements to increase the activity of the suspension of photosensitive polymers are in progress. Consequently, the ratio between the number of fixed
Table 1. Production rates of singlet oxygen using different sensitizer systems Photosensitizer concentration (Sen) (mol l 21 )
Condition
pH
Dc( 1 O 2 ) /Dt (mol l 21 s 21 )
Dc( 1 O 2 ) /Dt (mol l 21 s 21 ) (normalized: concentration (Sen) 5 1 (mol l 21 )
Rose Bengal 1.76 ? 10 26
Homogeneous solution
10
(5.060.5) ? 10 28
2.96 ? 10 22
Immobilized Rose Bengal 4.47 ? 10 25 (incorporated)
Suspension
8.5
(2.3560.5) ? 10 210
5.26 ? 10 26
Methylene blue 2.38 ? 10 24
Homogeneous solution
7
4 ? 10 28
1.67 ? 10 24
Immobilized (1) 8.0 ? 10 25 (incorporated)
Suspension
8.5
(6.060.4) ? 10 29
1.34 ? 10 24
Immobilized (2) 4.77 ? 10 25 (incorporated)
Suspension
4.4
1.8 ? 10 29
3.77 ? 10 25
74
D. Faust et al.
sensitizer molecules and the ester groups of the PMMA will be optimized with the aim of obtaining a higher production rate of singlet oxygen. In contrast to the previously known fixed sensitizers (e.g. rose bengal immobilized on Merrifield polymer), the production rate of singlet oxygen of the new especially functional photosensitive polymers is getting closer to the observed rates of homogeneous dissolved sensitizers.
6. OUTLOOK
With the synthesis of the new sensitive polymers, a solar-driven water treatment process for detoxification and disinfection applications with heterogeneous phase immobilized sensitizers seems feasible in the near future. First, microbiological experiments on a laboratory scale were carried out using the new photosensitive polymers. During the disinfection tests Deinococcus radiodurans was used as a model microorganism and porphyrins containing pyridinium groups were used as heterogeneous phase sensitizers. A killing effect was observed. Furthermore, the use of the heterogeneous phase system will be tested for solar treatment of water on a pilot plant scale. At the University of Malta, a new reactor was constructed for outdoor tests (Braun et al., 1997). The prototype reactor has a volume of up to 150 l and the irradiated sector has a size of 1 m 2 . Contaminated water can be pumped continuously to form a falling film above a polymer sheet coated with the described photosensitive polymers. With this installation, different types of photosensitive polymers will be tested.
Acknowledgements—We would like to thank the European Commission (AVI-CT94-0013) and the BMBF (0329627) for supporting this project.
REFERENCES Acher A. J., Fischer E., Tornheim R. and Manor Y. (1997) Sunlight technologies for photochemical deactivation of organic pollutants in water. In Proc. 8 th Int. Symp. Sol. ¨ M. (Eds), Thermal Conc. Technol., Becker M. and Bohmer ¨ Vol. 3, p. 1403. C. F. Muller Verlag, Heidelberg.
¨ Braun B., Ortner J., Funken K.-H., Schafer M., Schmitz C., Horneck G. and Fsadni M. (1997) Dye-sensitied solar detoxification and disinfection of contaminated water. In Proc. 8 th Int. Symp. Sol. Thermal Conc. Technol., Becker ¨ ¨ M. and Bohmer M. (Eds), Vol. 3, p. 1391. C. F. Muller Verlag, Heidelberg. Darwent J. R., Douglas P., Harriman A., Porter G. and Richoux M. -C. (1982) Metal phthalocycanines and porphyrins as photosensitizers for reduction of water to hydrogen. Coord. Chem. Rev. 44, 83. ¨ Eichhorn H., Sturm M. and Wohrle D. (1995) Polymer-bound porphyrins and their precursors, 11. Synthesis and polymerization of methacryloyloxy and 2,4-hexadienoyloxy derivatives of porphyrins and phthalocyanines. Macromol. Chem. Phys. 196, 115. Gandin E., Lion Y. and van de Vorst A. (1983) Quantum yield of singlet oxygen production by xanthene derivatives. Photochem. Photobiol. 37, 271. Gandin E. and Lion Y. (1982) A simple and convenient method of measuring the number of photons adsorbed by a solution irradiated with polychromatic light. J. Photochem. 20, 77. Kamachi M., Akimoto H. and Nozakura S. (1983) Preparation of polymer containing porphyrin moiety. Radical polymerization of 5-(4-Acrylolylocyphenyl)-10,15,20-Triphenylporphyrin. J. Polym. Sci. Polym. Lett. Ed. 21, 693. Kamogawa M. (1974) Syntheses and reaction of porphyrin and metalloporphyrin polymers. J. Polym. Sci. Polym. Chem. Ed. 12, 2317. Lautsch W., Broser W., Biedermann W. and Gnichel H. (1955) Enzyme models and their relation inclusion compounds. J. Polym. Sci. 17, 479. Le Guern F., Bied-Charreton C. and Faure J. (1993) Singlet oxygen production using porphyrins immobilized on mineral support. Bull. Soc. Chim. Fr. 130, 753. Little R. G., Anton J. A., Loach P. A. and Ibers S. A. (1975) The mixed-aldehyd synthesis of difunctional teraarylporphyrins. J. Heterocycl. Chem. 12, 343. Neckers D. C. and Valdes-Aguilera O. M. (1993) Photochemistry of the xanthene dyes. In Advances in Photochemistry, Volman D. H., Hammond G. S. and Neckers D. C. (Eds), Vol. 8, p. 315. John Wiley and Sons, New York. Otera J. (1993) Transesterfication. Chem. Rev. 93, 1449. Rothemund P. and Menotti A. R. (1948) Porphyrin studies V. The metal complex salts of tetraphenylporphyrin. J. Am. Chem. Soc. 70, 1808. Schaap A. P., Thayer A. L., Blossey E. C. and Neckers D. C. (1975) Polymer-based sensitizers for photooxidations. J. Am. Chem. Soc. 97, 3741. Srivastava T. S. and Tsutsui M. (1973) Preparation and purification of tetrasodium meso tetra(4-sulfonatophenyl)porphyrine. An easy procedure. J. Org. Chem. 38, 2103. Verlhac J. B. and Gaudemer A. (1983) Water soluble porphyrins and metalloporphyrins as photosensitizers in aerated aqueous solutions. I. Detection and determination of quantum yield of formation of singlet oxygen. Nouv. J. Chim. 8, 401. Wilkinson F., Helman W. P. and Ross A. B. (1993) Quantum yields for the photosensitized formation of the lowest electronically excited singlet state of molecular oxygen in solution. J. Phys. Chem. Ref. Data 22, 113. Young R. H., Brewer D. and Keller R. A. (1973) The determination of rate constants of reaction and lifetime of singulet oxygen in solution by a flash photolysis technique. J. Am. Chem. Soc. 95, 375.