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Highly efficient photochemical hydrogen production system using zinc porphyrin and hydrogenase in CTAB micellar system
ARTICLE IN PRESS
Solar Energy Materials & Solar Cells 79 (2003) 103–111
Highly efficient photochemical hydrogen production system using zinc porphyrin and hydrogenase in CTAB micellar system Yutaka Amaoa,*, Yumiko Tomonoua, Ichiro Okurab b
a Department of Applied Chemistry, Oita University, Dannoharu 700, Oita 870-1192, Japan Department of Bioengineering, Tokyo Institute of Technology, Nagatsuta 4259, Midori-ku, Yokohama 226-8501, Japan
Received 9 September 2002; accepted 13 September 2002
Abstract Photochemical hydrogen production with the system containing triethanolamine, zinc tetraphenylporphyrin tetrasulfonate, methylviologen and hydrogenase in cationic surfactant, cetyltrimethylammonium bromide (CTAB) was investigated. The effective photoreduction of methylviologen and an effective hydrogen production with hydrogenase were accomplished in the presence of CTAB micellar system by optimizing the reaction condition. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Photochemical hydrogen production; Hydrogenase; Zinc porphyrin; Cetyltrimethylammonium bromide
1. Introduction Photochemical hydrogen production systems consisting of an electron donor, a photosensitizer, an electron carrier and a catalyst have been widely studied [1,2]. In the photochemical hydrogen production with four-component system, important step in this system is the charge separation between photoexcited photosensitizer and the reduced electron carrier and suppression of back electron transfer. The effective charge separation and suppression of back electron transfer has been attempted by using micellar systems [3,4], colloidal inorganic suspension [5] or liposomes [6]. *Corresponding author. Fax: +81-975547972. E-mail address: [email protected] (Y. Amao). 0927-0248/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 7 - 0 2 4 8 ( 0 2 ) 0 0 3 7 3 - 2
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Especially, micellar system of surfactant is useful for a homogeneous photochemical hydrogen production. We reported previously the effective charge separation in the system consisting of triethanolamine (TEOA), zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS), methylviologen ðMV2þ Þ and hydrogenase ðH2 aseÞ shown in Scheme 1 was accomplished by addition of anionic surfactant, sodium dodecyl sulfate (SDS) micellar system [7,8]. However, little hydrogen production with hydrogenase in SDS micellar system was observed because of the denaturation of hydrogenase by SDS. On the other hand, the effective photoreduction of MV2þ and an effective hydrogen production with H2 ase were accomplished in the presence of cationic surfactant, cetyltrimethylammonium bromide (CTAB) micellar system [9,10]. In this study, to improve the photochemical hydrogen evolution yield with the system of TEOA, ZnTPPS, MV2þ ; H2 ase and CTAB, the effect of each component concentration on the MV2þ photoreduction and hydrogen evolved rates were investigated under steady-state irradiation.
2. Experimental 2.1. Materials Tetraphenylporphyrin tetrasulfonate (TPPS) was obtained from Dojin Laboratories. CTAB was obtained form Kanto Chemical Co. Ltd. All the other reagents available were of higher grade. 2.2. Synthesis of ZnTPPS ZnTPPS was synthesized by refluxing tetraphenylporphyrin tetrasulfonate ðH2 TPPSÞ with about 10 times molar of zinc acetate in 100 ml of methanol at 401C for 2 h [11]. 2.3. Steady-state irradiation The sample solution containing ZnTPPS, MV2þ ; TEOA, H2 ase and CTAB was deaerated by repeated freeze–pump–thaw cycles. For the photolysis under steadystate irradiation, 200 W tungsten lamp was used at 301C: The light of the wavelength less than 390 nm was removed by Toshiba L-39 cut-off filter. The concentration of
Scheme 1. Photochemical hydrogen production with four-component system consisting of TEOA, ZnTPPS, MV2þ and H2 ase:
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reduced MV2þ was determined by visible spectra at 605 nm: The absorption spectra were measured with using Hitachi U-2000 spectrometer. The molar coefficient of reduced MV2þ at 605 nm is 1:3 104 mol dm3 cm1 [12]. The amount of hydrogen evolved was detected by gas chromatography (detector: TCD, column: active carbon). 2.4. Purification of hydrogenase Hydrogenase was obtained from Desulfovibrio vulgaris (Miyazaki) and purified according to Yagi’s method [13]. The H2 ase has the ability to release 0:7 mmol of hydrogen in the reaction system of 10 ml hydrogenase, 1:2 105 mmol of MV2þ and 7:7 105 mmol of sodium dithionite in 4:0 ml of 50 mmol dm3 Tris–HCl buffer ðpH ¼ 7:4Þ at 301C for 10 min: One unit of H2 ase activity was defined as release of 1:0 mmol of hydrogen per minute.
3. Results and discussion 3.1. Concentration effect of CTAB on the rate of photoreduction of MV 2þ Time dependence of the photoreduction of MV2þ at various concentration of CTAB is shown in Fig. 1. The initial rate was determined by the slopes of the time course at the beginning of the reaction. The effect of CTAB concentration on the initial rate of MV2þ photoreduction is shown in Fig. 2. The MV2þ photoreduction
Fig. 1. Time course of the reduced MV2þ formation under various CTAB concentrations. Reaction condition: 0:25 mol dm3 trethanolamine, 0:22 mmol dm3 MV2þ and 0:15 mmol dm3 ZnTPPS. CTAB concentration: ð’Þ 25 mmol dm3 ; ð~Þ 2:5 mmol dm3 ; ðmÞ 0:25 mmol dm3 ; ðKÞ 25 mmol dm3 ; and ð&Þ 2:5 mmol dm3 :
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Fig. 2. Concentration effect of CTAB on the initial rate of MV2þ photoreduction.
rate increased more than critical micellar concentration of CTAB and then reached a constant value. These results indicated that rate corresponded to critical micellar concentration of CTAB. The reason of the rate increase was explained as follows. In the presence of CTAB micelles, the back electron transfer between ZnTPPS cation radical and the reduced MV2þ was suppressed. The optimum concentration of CTAB in the MV2þ photoreduction was determined to be 25 mmol dm3 : 3.2. Concentration effect of MV 2þ on the rate of photoreduction of MV 2þ Time dependence of the photoreduction of MV2þ in the presence of 25 mmol dm3 CTAB at various concentration of MV2þ is shown in Fig. 3. The effect of MV2þ concentration on the initial rate of MV2þ photoreduction is shown in Fig. 4. The MV2þ photoreduction rate increased the MV2þ concentration until 0:1 mmol dm3 and then the rate decreased through the maximum value. The reason of the rate decrease was explained as follows. The electrostatic complex between ZnTPPS and MV2þ (ZnTPPS–MV2þ ) was formed at ground state under higher concentration of MV2þ : The ZnTPPS–MV2þ complex was not photoreactive complex [13]. Thus, ZnTPPS in this complex did not serve as a photosensitizer, and the photoreduction rate decreased. The optimum concentration of MV2þ in the MV2þ photoreduction was determined to be 0:1 mol dm3 : 3.3. Concentration effect of ZnTPPS on the rate of photoreduction of MV 2þ Time dependence of the photoreduction of MV2þ ð0:1 mmol dm3 Þ in the presence of 25 mmol dm3 CTAB at various concentration of ZnTPPS is shown in Fig. 5. The effect of ZnTPPS concentration on the initial rate of MV2þ photoreduction is shown in Fig. 6. The MV2þ photoreduction rate increased the ZnTPPS concentration until
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Fig. 3. Time course of the reduced MV2þ formation under various MV2þ concentrations. Reaction condition: 0:25 mol dm3 TEOA, 25 mmol dm3 CTAB and 0:15 mmol dm3 ZnTPPS. MV2þ concentration: ð’Þ 0:2 mmol dm3 ; ðKÞ 0:1 mmol dm3 ; ð~Þ 56 mmol dm3 ; ðmÞ 38 mmol dm3 :
Fig. 4. Concentration effect of MV2þ on the initial rate of MV2þ photoreduction.
15 mmol dm3 and then the rate reached constant. The optimum concentration of ZnTPPS in the MV2þ photoreduction was determined to be 15 mmol dm3 :
3.4. Concentration effect of TEOA on the rate of photoreduction of MV 2þ Time dependence of the photoreduction of MV2þ ð0:1 mmol dm3 Þ in the presence of 25 mmol dm3 CTAB and 15 mmol dm3 ZnTPPS at various concentration of TEOA is shown in Fig. 7. The effect of TEOA concentration on the initial rate of MV2þ photoreduction is shown in Fig. 8. The MV2þ photoreduction rate increased the TEOA concentration until 0:5 mol dm3 and then the rate reached constant. The
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Fig. 5. Time course of the reduced MV2þ formation under various ZnTPPS concentrations. Reaction condition: 0:25 mol dm3 trethanolamine, 25 mmol dm3 CTAB and 0:1 mmol dm3 MV2þ : ZnTPPS concentration: ð’Þ 0:13 mmol dm3 ; ð~Þ 5:0 mmol dm3 ; ðmÞ 15 mmol dm3 ; and ð&Þ 50 mmol dm3 :
Fig. 6. Concentration effect of ZnTPPS on the initial rate of MV2þ photoreduction.
optimum concentration of TEOA in the MV2þ photoreduction was determined to be 0:5 mol dm3 : 3.5. Optimum condition of MV 2þ photoreduction in the presence of CTAB The optimum condition of MV2þ photoreduction was summarized in Table 1. When the sample solution containing 15 mmol dm3 ZnTPPS, 0:1 mmol dm3 MV2þ ; 0:5 mol dm3 TEOA and 25 mmol dm3 CTAB in 25 mmol dm3 Tris–HCl ðpH ¼ 7:4Þ buffer solution was irradiated at 301C; accumulation of the reduced MV2þ was observed as shown in Fig. 9. The conversion of MV2þ to reduced MV2þ
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Fig. 7. Time course of the reduced MV2þ formation under various TEOA concentrations. Reaction condition: 15 mmol dm3 ZnTPPS, 25 mmol dm3 CTAB and 0:1 mmol dm3 MV2þ : TEOA concentration: ð’Þ 0:50 mol dm3 ; ð~Þ 0:30 mol dm3 ; ðmÞ 0:25 mol dm3 ; and ð&Þ 25 mmol dm3 :
Fig. 8. Concentration effect of TEOA on the initial rate of MV2þ photoreduction.
Table 1 Optimum condition for photoreduction of MV2þ Component
Optimum concentration
TEOA ZnTPPS MV2þ CTAB
0:50 mol dm3 15 mmol dm3 0:10 mmol dm3 25 mmol dm3
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Fig. 9. Time course of the reduced MV2þ formation. Reaction condition: 15 mmol dm3 ZnTPPS; 25 mmol dm3 CTAB; 0:5 mol dm3 TEOA; and 0:1 mmol dm3 MV2þ :
was ca. 100% after 60 min irradiation. The effective photoreduction system was established by optimizing the reaction condition. 3.6. Optimum condition of photochemical hydrogen evolution with H2 ase As the effective photoreduction system was accomplished, the photochemical hydrogen evolution with H2 ase was attempted above condition. When the sample solution containing 15 mmol dm3 ZnTPPS, 0:1 mmol dm3 MV2þ ; 0:5 mol dm3 TEOA, 25 mmol dm3 CTAB and 0.35 unit H2 ase in 25 mmol dm3 Tris–HCl ðpH ¼ 7:4Þ buffer solution was irradiated at 301C; hydrogen evolution was observed as shown in Fig. 10. In this case, the rate of hydrogen evolved was independent of H2 ase concentration. The rate of hydrogen evolved in the above condition was estimated to be 6:4 107 mol h1 : In the above condition, the rate increased about 50 times as fast as that of conventional condition (0:15 mmol dm3 ZnTPPS, 0:22 mmol dm3 MV2þ ; 0:25 mol dm3 TEOA and 0.35 unit H2 ase in 25 mmol dm3 Tris–HCl ðpH ¼ 7:4Þ buffer solution) in the absence of CTAB. The higher yield of photochemical hydrogen evolution was established.
4. Conclusion In this work, to improve the photochemical hydrogen evolution yield with the system of TEOA, ZnTPPS, MV2þ ; H2 ase and CTAB, the effect of the component concentration on the MV2þ photoreduction rate was investigated under steady-state irradiation. Each component concentration in the MV2þ photoreduction system was investigated. When the sample solution containing 15 mmol dm3 ZnTPPS, 0:1 mmol dm3 MV2þ ; 0:5 mol dm3 TEOA and 25 mmol dm3 CTAB in
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Fig. 10. Time course of the hydrogen evolved. Reaction condition: ð’Þ 15 mmol dm3 ZnTPPS; 25 mmol dm3 CTAB; 0:5 mol dm3 TEOA; 0:1 mmol dm3 MV2þ and 0.35 unit H2 ase: ðmÞ 0:15 mmol dm3 ZnTPPS, 0:25 mol dm3 TEOA, 0:22 mmol dm3 MV2þ and 0.35 unit H2 ase:
25 mmol dm3 Tris–HCl ðpH ¼ 7:4Þ buffer solution was irradiated at 301C; the conversion of MV2þ to reduced MV2þ was ca. 100% after 60 min irradiation. The effective photoreduction system was established by optimizing the reaction condition. The photochemical hydrogen evolution with H2 ase was attempted above the MV2þ photoreduction condition. When the sample solution containing 15 mmol dm3 ZnTPPS, 0:1 mmol dm3 MV2þ ; 0:5 mol dm3 TEOA, 3 25 mmol dm CTAB and 0.35 unit H2 ase in 25 mmol dm3 Tris–HCl ðpH ¼ 7:4Þ buffer solution was irradiated at 301C; the rate of hydrogen evolved in the above condition was estimated to be 6:4 107 mol h1 : The rate increased about 50 times as fast as that of conventional condition in the absence of CTAB. The higher yield of photochemical hydrogen evolution was established by optimizing the reaction condition.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
J.R. Darwent, P. Douglas, A. Harriman, G. Porter, M.-C. Richoux, Coord. Chem. Rev. 44 (1982) 83. C. Laane, I. Willner, J.W. Otvos, M. Calvin, Proc. Nat. Acad. Sci. USA 78 (1981) 5928. P.A. Brugger, P.P Infelta, A.M. Braun, M. Gratzel, J. Am. Chem. Soc. 103 (1981) 320. C.K. Gratzel, M. Gratzel, J. Phys. Chem. 86 (1982) 353. L.A. Kelly, M.A.J. Rodgers, J. Phys. Chem. 98 (1994) 6386. P.J.G. Coutinho, S.M.B. Costa, J. Photochem. Photobiol. A. Chem. 82 (1994) 149. I. Okura, T. Kita, S. Aono, N. Kaji, J. Mol. Catal. 32 (1985) 361. I. Okura, T. Kita, S. Aono, N. Kaji, J. Mol. Catal. 33 (1985) 34. Y. Amao, I. Okura, J. Mol. Catal. 33 (1985) 34. Y. Amao, I. Okura, J. Mol. Catal. 33 (1985) 34. E.B. Fleischer, S.K. Cheung, J. Am. Chem. Soc. 98 (1976) 8381. T. Watanabe, K. Honda, J. Phys. Chem. 86 (1982) 2617. T. Yagi, J. Biochem. 68 (1970) 649.
Solar Energy Materials & Solar Cells 79 (2003) 103–111
Highly efficient photochemical hydrogen production system using zinc porphyrin and hydrogenase in CTAB micellar system Yutaka Amaoa,*, Yumiko Tomonoua, Ichiro Okurab b
a Department of Applied Chemistry, Oita University, Dannoharu 700, Oita 870-1192, Japan Department of Bioengineering, Tokyo Institute of Technology, Nagatsuta 4259, Midori-ku, Yokohama 226-8501, Japan
Received 9 September 2002; accepted 13 September 2002
Abstract Photochemical hydrogen production with the system containing triethanolamine, zinc tetraphenylporphyrin tetrasulfonate, methylviologen and hydrogenase in cationic surfactant, cetyltrimethylammonium bromide (CTAB) was investigated. The effective photoreduction of methylviologen and an effective hydrogen production with hydrogenase were accomplished in the presence of CTAB micellar system by optimizing the reaction condition. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Photochemical hydrogen production; Hydrogenase; Zinc porphyrin; Cetyltrimethylammonium bromide
1. Introduction Photochemical hydrogen production systems consisting of an electron donor, a photosensitizer, an electron carrier and a catalyst have been widely studied [1,2]. In the photochemical hydrogen production with four-component system, important step in this system is the charge separation between photoexcited photosensitizer and the reduced electron carrier and suppression of back electron transfer. The effective charge separation and suppression of back electron transfer has been attempted by using micellar systems [3,4], colloidal inorganic suspension [5] or liposomes [6]. *Corresponding author. Fax: +81-975547972. E-mail address: [email protected] (Y. Amao). 0927-0248/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 7 - 0 2 4 8 ( 0 2 ) 0 0 3 7 3 - 2
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Especially, micellar system of surfactant is useful for a homogeneous photochemical hydrogen production. We reported previously the effective charge separation in the system consisting of triethanolamine (TEOA), zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS), methylviologen ðMV2þ Þ and hydrogenase ðH2 aseÞ shown in Scheme 1 was accomplished by addition of anionic surfactant, sodium dodecyl sulfate (SDS) micellar system [7,8]. However, little hydrogen production with hydrogenase in SDS micellar system was observed because of the denaturation of hydrogenase by SDS. On the other hand, the effective photoreduction of MV2þ and an effective hydrogen production with H2 ase were accomplished in the presence of cationic surfactant, cetyltrimethylammonium bromide (CTAB) micellar system [9,10]. In this study, to improve the photochemical hydrogen evolution yield with the system of TEOA, ZnTPPS, MV2þ ; H2 ase and CTAB, the effect of each component concentration on the MV2þ photoreduction and hydrogen evolved rates were investigated under steady-state irradiation.
2. Experimental 2.1. Materials Tetraphenylporphyrin tetrasulfonate (TPPS) was obtained from Dojin Laboratories. CTAB was obtained form Kanto Chemical Co. Ltd. All the other reagents available were of higher grade. 2.2. Synthesis of ZnTPPS ZnTPPS was synthesized by refluxing tetraphenylporphyrin tetrasulfonate ðH2 TPPSÞ with about 10 times molar of zinc acetate in 100 ml of methanol at 401C for 2 h [11]. 2.3. Steady-state irradiation The sample solution containing ZnTPPS, MV2þ ; TEOA, H2 ase and CTAB was deaerated by repeated freeze–pump–thaw cycles. For the photolysis under steadystate irradiation, 200 W tungsten lamp was used at 301C: The light of the wavelength less than 390 nm was removed by Toshiba L-39 cut-off filter. The concentration of
Scheme 1. Photochemical hydrogen production with four-component system consisting of TEOA, ZnTPPS, MV2þ and H2 ase:
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reduced MV2þ was determined by visible spectra at 605 nm: The absorption spectra were measured with using Hitachi U-2000 spectrometer. The molar coefficient of reduced MV2þ at 605 nm is 1:3 104 mol dm3 cm1 [12]. The amount of hydrogen evolved was detected by gas chromatography (detector: TCD, column: active carbon). 2.4. Purification of hydrogenase Hydrogenase was obtained from Desulfovibrio vulgaris (Miyazaki) and purified according to Yagi’s method [13]. The H2 ase has the ability to release 0:7 mmol of hydrogen in the reaction system of 10 ml hydrogenase, 1:2 105 mmol of MV2þ and 7:7 105 mmol of sodium dithionite in 4:0 ml of 50 mmol dm3 Tris–HCl buffer ðpH ¼ 7:4Þ at 301C for 10 min: One unit of H2 ase activity was defined as release of 1:0 mmol of hydrogen per minute.
3. Results and discussion 3.1. Concentration effect of CTAB on the rate of photoreduction of MV 2þ Time dependence of the photoreduction of MV2þ at various concentration of CTAB is shown in Fig. 1. The initial rate was determined by the slopes of the time course at the beginning of the reaction. The effect of CTAB concentration on the initial rate of MV2þ photoreduction is shown in Fig. 2. The MV2þ photoreduction
Fig. 1. Time course of the reduced MV2þ formation under various CTAB concentrations. Reaction condition: 0:25 mol dm3 trethanolamine, 0:22 mmol dm3 MV2þ and 0:15 mmol dm3 ZnTPPS. CTAB concentration: ð’Þ 25 mmol dm3 ; ð~Þ 2:5 mmol dm3 ; ðmÞ 0:25 mmol dm3 ; ðKÞ 25 mmol dm3 ; and ð&Þ 2:5 mmol dm3 :
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Fig. 2. Concentration effect of CTAB on the initial rate of MV2þ photoreduction.
rate increased more than critical micellar concentration of CTAB and then reached a constant value. These results indicated that rate corresponded to critical micellar concentration of CTAB. The reason of the rate increase was explained as follows. In the presence of CTAB micelles, the back electron transfer between ZnTPPS cation radical and the reduced MV2þ was suppressed. The optimum concentration of CTAB in the MV2þ photoreduction was determined to be 25 mmol dm3 : 3.2. Concentration effect of MV 2þ on the rate of photoreduction of MV 2þ Time dependence of the photoreduction of MV2þ in the presence of 25 mmol dm3 CTAB at various concentration of MV2þ is shown in Fig. 3. The effect of MV2þ concentration on the initial rate of MV2þ photoreduction is shown in Fig. 4. The MV2þ photoreduction rate increased the MV2þ concentration until 0:1 mmol dm3 and then the rate decreased through the maximum value. The reason of the rate decrease was explained as follows. The electrostatic complex between ZnTPPS and MV2þ (ZnTPPS–MV2þ ) was formed at ground state under higher concentration of MV2þ : The ZnTPPS–MV2þ complex was not photoreactive complex [13]. Thus, ZnTPPS in this complex did not serve as a photosensitizer, and the photoreduction rate decreased. The optimum concentration of MV2þ in the MV2þ photoreduction was determined to be 0:1 mol dm3 : 3.3. Concentration effect of ZnTPPS on the rate of photoreduction of MV 2þ Time dependence of the photoreduction of MV2þ ð0:1 mmol dm3 Þ in the presence of 25 mmol dm3 CTAB at various concentration of ZnTPPS is shown in Fig. 5. The effect of ZnTPPS concentration on the initial rate of MV2þ photoreduction is shown in Fig. 6. The MV2þ photoreduction rate increased the ZnTPPS concentration until
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Fig. 3. Time course of the reduced MV2þ formation under various MV2þ concentrations. Reaction condition: 0:25 mol dm3 TEOA, 25 mmol dm3 CTAB and 0:15 mmol dm3 ZnTPPS. MV2þ concentration: ð’Þ 0:2 mmol dm3 ; ðKÞ 0:1 mmol dm3 ; ð~Þ 56 mmol dm3 ; ðmÞ 38 mmol dm3 :
Fig. 4. Concentration effect of MV2þ on the initial rate of MV2þ photoreduction.
15 mmol dm3 and then the rate reached constant. The optimum concentration of ZnTPPS in the MV2þ photoreduction was determined to be 15 mmol dm3 :
3.4. Concentration effect of TEOA on the rate of photoreduction of MV 2þ Time dependence of the photoreduction of MV2þ ð0:1 mmol dm3 Þ in the presence of 25 mmol dm3 CTAB and 15 mmol dm3 ZnTPPS at various concentration of TEOA is shown in Fig. 7. The effect of TEOA concentration on the initial rate of MV2þ photoreduction is shown in Fig. 8. The MV2þ photoreduction rate increased the TEOA concentration until 0:5 mol dm3 and then the rate reached constant. The
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Fig. 5. Time course of the reduced MV2þ formation under various ZnTPPS concentrations. Reaction condition: 0:25 mol dm3 trethanolamine, 25 mmol dm3 CTAB and 0:1 mmol dm3 MV2þ : ZnTPPS concentration: ð’Þ 0:13 mmol dm3 ; ð~Þ 5:0 mmol dm3 ; ðmÞ 15 mmol dm3 ; and ð&Þ 50 mmol dm3 :
Fig. 6. Concentration effect of ZnTPPS on the initial rate of MV2þ photoreduction.
optimum concentration of TEOA in the MV2þ photoreduction was determined to be 0:5 mol dm3 : 3.5. Optimum condition of MV 2þ photoreduction in the presence of CTAB The optimum condition of MV2þ photoreduction was summarized in Table 1. When the sample solution containing 15 mmol dm3 ZnTPPS, 0:1 mmol dm3 MV2þ ; 0:5 mol dm3 TEOA and 25 mmol dm3 CTAB in 25 mmol dm3 Tris–HCl ðpH ¼ 7:4Þ buffer solution was irradiated at 301C; accumulation of the reduced MV2þ was observed as shown in Fig. 9. The conversion of MV2þ to reduced MV2þ
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Fig. 7. Time course of the reduced MV2þ formation under various TEOA concentrations. Reaction condition: 15 mmol dm3 ZnTPPS, 25 mmol dm3 CTAB and 0:1 mmol dm3 MV2þ : TEOA concentration: ð’Þ 0:50 mol dm3 ; ð~Þ 0:30 mol dm3 ; ðmÞ 0:25 mol dm3 ; and ð&Þ 25 mmol dm3 :
Fig. 8. Concentration effect of TEOA on the initial rate of MV2þ photoreduction.
Table 1 Optimum condition for photoreduction of MV2þ Component
Optimum concentration
TEOA ZnTPPS MV2þ CTAB
0:50 mol dm3 15 mmol dm3 0:10 mmol dm3 25 mmol dm3
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Fig. 9. Time course of the reduced MV2þ formation. Reaction condition: 15 mmol dm3 ZnTPPS; 25 mmol dm3 CTAB; 0:5 mol dm3 TEOA; and 0:1 mmol dm3 MV2þ :
was ca. 100% after 60 min irradiation. The effective photoreduction system was established by optimizing the reaction condition. 3.6. Optimum condition of photochemical hydrogen evolution with H2 ase As the effective photoreduction system was accomplished, the photochemical hydrogen evolution with H2 ase was attempted above condition. When the sample solution containing 15 mmol dm3 ZnTPPS, 0:1 mmol dm3 MV2þ ; 0:5 mol dm3 TEOA, 25 mmol dm3 CTAB and 0.35 unit H2 ase in 25 mmol dm3 Tris–HCl ðpH ¼ 7:4Þ buffer solution was irradiated at 301C; hydrogen evolution was observed as shown in Fig. 10. In this case, the rate of hydrogen evolved was independent of H2 ase concentration. The rate of hydrogen evolved in the above condition was estimated to be 6:4 107 mol h1 : In the above condition, the rate increased about 50 times as fast as that of conventional condition (0:15 mmol dm3 ZnTPPS, 0:22 mmol dm3 MV2þ ; 0:25 mol dm3 TEOA and 0.35 unit H2 ase in 25 mmol dm3 Tris–HCl ðpH ¼ 7:4Þ buffer solution) in the absence of CTAB. The higher yield of photochemical hydrogen evolution was established.
4. Conclusion In this work, to improve the photochemical hydrogen evolution yield with the system of TEOA, ZnTPPS, MV2þ ; H2 ase and CTAB, the effect of the component concentration on the MV2þ photoreduction rate was investigated under steady-state irradiation. Each component concentration in the MV2þ photoreduction system was investigated. When the sample solution containing 15 mmol dm3 ZnTPPS, 0:1 mmol dm3 MV2þ ; 0:5 mol dm3 TEOA and 25 mmol dm3 CTAB in
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Fig. 10. Time course of the hydrogen evolved. Reaction condition: ð’Þ 15 mmol dm3 ZnTPPS; 25 mmol dm3 CTAB; 0:5 mol dm3 TEOA; 0:1 mmol dm3 MV2þ and 0.35 unit H2 ase: ðmÞ 0:15 mmol dm3 ZnTPPS, 0:25 mol dm3 TEOA, 0:22 mmol dm3 MV2þ and 0.35 unit H2 ase:
25 mmol dm3 Tris–HCl ðpH ¼ 7:4Þ buffer solution was irradiated at 301C; the conversion of MV2þ to reduced MV2þ was ca. 100% after 60 min irradiation. The effective photoreduction system was established by optimizing the reaction condition. The photochemical hydrogen evolution with H2 ase was attempted above the MV2þ photoreduction condition. When the sample solution containing 15 mmol dm3 ZnTPPS, 0:1 mmol dm3 MV2þ ; 0:5 mol dm3 TEOA, 3 25 mmol dm CTAB and 0.35 unit H2 ase in 25 mmol dm3 Tris–HCl ðpH ¼ 7:4Þ buffer solution was irradiated at 301C; the rate of hydrogen evolved in the above condition was estimated to be 6:4 107 mol h1 : The rate increased about 50 times as fast as that of conventional condition in the absence of CTAB. The higher yield of photochemical hydrogen evolution was established by optimizing the reaction condition.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
J.R. Darwent, P. Douglas, A. Harriman, G. Porter, M.-C. Richoux, Coord. Chem. Rev. 44 (1982) 83. C. Laane, I. Willner, J.W. Otvos, M. Calvin, Proc. Nat. Acad. Sci. USA 78 (1981) 5928. P.A. Brugger, P.P Infelta, A.M. Braun, M. Gratzel, J. Am. Chem. Soc. 103 (1981) 320. C.K. Gratzel, M. Gratzel, J. Phys. Chem. 86 (1982) 353. L.A. Kelly, M.A.J. Rodgers, J. Phys. Chem. 98 (1994) 6386. P.J.G. Coutinho, S.M.B. Costa, J. Photochem. Photobiol. A. Chem. 82 (1994) 149. I. Okura, T. Kita, S. Aono, N. Kaji, J. Mol. Catal. 32 (1985) 361. I. Okura, T. Kita, S. Aono, N. Kaji, J. Mol. Catal. 33 (1985) 34. Y. Amao, I. Okura, J. Mol. Catal. 33 (1985) 34. Y. Amao, I. Okura, J. Mol. Catal. 33 (1985) 34. E.B. Fleischer, S.K. Cheung, J. Am. Chem. Soc. 98 (1976) 8381. T. Watanabe, K. Honda, J. Phys. Chem. 86 (1982) 2617. T. Yagi, J. Biochem. 68 (1970) 649.