Photoinduced Hydrogen Production from Cellulose Derivative with

using the visible light photosensitization of Mg chlorophyll-a (Mg Chl-a) from Spilurina, has been developed. When the sample solution containing cell...
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Energy & Fuels 2003, 17, 1641-1644

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Photoinduced Hydrogen Production from Cellulose Derivative with Chlorophyll-a and Platinum Nanoparticles System Noriko Himeshima and Yutaka Amao* Department of Applied Chemistry, Oita University, Dannoharu 700, Oita 870-1192, Japan Received May 17, 2003. Revised Manuscript Received September 15, 2003

A photoinduced hydrogen production system, coupling cellulose hydrolysis by cellulase and glucose dehydrogenase (GDH) and hydrogen production with platinum nanoparticles as a catalyst using the visible light photosensitization of Mg chlorophyll-a (Mg Chl-a) from Spilurina, has been developed. When the sample solution containing cellulose derivative (methylcellulose), cellulase, nicotinamide adenine dinucleotide (NAD+), Mg Chl-a, methyl viologen (MV2+, an electron carrier reagent), and platinum nanoparticles was irradiated, continuous hydrogen production was observed with irradiation time. The amount of hydrogen production was about 12 µmol after 4 h irradiation.

Introduction Hydrogen production from renewable bio-resources of timber waste, including cellulose and lignin, is important in the environmental and the development of energy source research fields.1-5 Cellulose and other polysaccharides can be hydrolyzed to monosaccharides, such as glucose. Monosaccharides can be converted to hydrogen gas. Hydrogen production from glucose using a combination of the glucose dehydrogenase (GDH) and hydrogenase has been reported.6-8 However, the enzymatic photoinduced hydrogen production from polysaccharides, such as cellulose, has not been developed. Photoinduced hydrogen production systems consisting of an electron donor, photosensitizer, electron carrier, and a catalyst have been reported.9,10 In these systems, Mg chlorophyll-a (Mg Chl-a), which acts as the effective * Corresponding author. Phone: +81-97-554-7972. Fax: +81-97554-7972. E-mail: [email protected]. (1) Helena, L. C.; Overend, R. P. Biomass and renewable fuels. Fuel Process. Technol. 2001, 71, 187-195. (2) Barbosa, M. J.; Rocha, J. M.; Tramper, J.; Wijffels, R. H. Acetate as a carbon source for hydrogen production by photosynthetic bacteria. J. Biotechnol. 2001, 85, 25-33. (3) Garcia, L.; French, R.; Czernik, S.; Chornet, E. Catalytic steam reforming of bio-oils for the production of hydrogen: effects of catalyst composition. Appl. Catal. A: General 2000, 201, 225-239. (4) Wang, D. Production of hydrogen from biomass by catalytic steam reforming of fast pyrolysis oils. Fuel Energy Abstracts 1998, 39, 188. (5) Minowa, T.; Inoue, S. Hydrogen production from biomass by catalytic gasification in hot compressed water. Renewable Energy 1999, 16, 1114-1117. (6) Woodward, J.; Orr, M.; Cordray, K.; Greenbaum, E. Enzymatic biohydrogen production. Nature 2000, 405, 1014-1015. (7) Inoue, T.; Kumar, S. N.; Kamachi, T.; Okura, I. Hydrogen evolution from glucose with the combination of glucose dehydrogenase and hydrogenase from A. eutrophus H16. Chem. Lett. 1999, 147-148. (8) Woodward, J.; Mattingly, S. M.; Danson, M.; Hough, D.; Ward, N.; Adams, M. In vitro hydrogen production by glucose dehydrogenase and hydrogenase. Nature Biotechnol. 1996, 14, 872-874. (9) Darwent, J. R.; Douglas, P.; Harriman, A.; Porter, G.; Richoux, M. C. Metal phthalocyanines and porphyrins as photosensitizers for reduction of water to hydrogen. Coord. Chem. Rev. 1982, 44, 93-126. (10) Okura, I. Hydrogenase and its application for photoinduced hydrogen evolution. Coord. Chem. Rev. 1985, 68, 53-99.

photosensitizer in photosynthesis in green plants,11 and methyl viologen (MV2+) are useful as a photosensitizer and electron carrier, respectively.12,13 Especially platinum nanoparticles are a suitable catalyst for the hydrogen production.9,14,15 In photoinduced hydrogen production with the system consisting of an electron donor, photosensitizer, an electron carrier, and catalyst, the photoexcited photosensitizer reacts with the electron carrier to form the reduced electron relay and hydrogen gas is produced by reduction of proton with the catalyst and then the oxidized photosensitizer is reduced by an electron-donating reagent such as reduced nicotinamide adenine denucleotide (NADH). Thus, the electron donor, NADH, is a sacrificial reagent and the oxidized electron donor, NAD+, is consumed in the reaction system. However, NADH can be regenerated, and the photoinduced hydrogen production system would be accomplished without NAD+ consumption. Since GDH uses NAD+ as a cofactor, a photoinduced hydrogen production can be developed using the combination of two reactions. One is the NADH regeneration with GDH, and the other one is a hydrogen production system with photosensitizer, electron relay reagent, and catalyst. We have previously reported the enzymatic photoinduced hydrogen production from sucrose and maltose as a renewable bio-resources using the photosensitization of Mg Chl-a.16,17 However, the photoinduced hydrogen production from polysaccharide, such as cellulose, im(11) Scheer, H. Chlorophylls. CRC Press: London, 1991. (12) Tomonou, Y.; Amao, Y. Visible light induced hydrogen production with Mg chlorophyll-a from Spirulina and colloidal platinum. Biometals 2002, 15, 391-395 (13) Tomonou, Y.; Amao, Y. Visible and near-IR light induced hydrogen production with Mg chlorophyll-a from Spirulina and colloidal platinum. Biometals 2003, 16, 419-424. (14) Brugger, P. A.; Cuendet, P.; Gra¨tzel, M. Ultrafine and specific catalysts affording efficient hydrogen evolution from water under visible light illumination. J. Am. Chem. Soc. 1981, 103 (3), 2923-2927. (15) Kiwi, J.; Gra¨tzel, M.; Protection size factors, and reaction dynamics of colloidal redox catalysis mediating light induced hydrogen evolution from water. J. Am. Chem. Soc. 1979, 101, 7214-7217.

10.1021/ef034006w CCC: $25.00 © 2003 American Chemical Society Published on Web 10/31/2003

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Himeshima and Amao

Scheme 1. Visible Light-Induced Hydrogen Production System Coupling Methylcellulose Hydrolysis with Cellulase and GDH and Hydrogen Production with Platinum Nanoparticles via MV2+ Photoreduction Using Sensitization of Mg Chl-a

portant renewable bio-resources, using the photosensitization of Mg Chl-a, has not been accomplished. In this paper we describe the photoinduced hydrogen production system by coupling the cellulose derivative, methylcellulose, hydrolysis with cellulase and GDH, and hydrogen production with platinum nanoparticles via the photoreduction of MV2+ using the sensitization of Mg Chl-a as shown in Scheme 1. Experimental Section 2.1. Materials. Mg Chl-a from Spilurina, GDH from Bacillus sp., and methylcellulose (average molecular weight 41 000) were purchased from Wako Pure Chemical Industry Co. Ltd. Methyl viologen dichloride (MV2+) and cetyltrimethylammonium bromide (CTAB) were obtained from Tokyo Kasei Co. Ltd. NAD+ and NADH were purchased from Oriental Yeast Co. Ltd. Cellulase from Aspergillus niger was obtained from Sigma. Hydrogen hexachloplatinate hexahydrate and sodium citrate dihydrate were obtained from Kanto Chemical Co. Ltd. The other chemicals were analytical grade or the highest grade available. Mg Chl-a was solubilized with 10 mmol dm-3 of CTAB, since Mg Chl-a is insoluble in aqueous solution. 2.2. Enzyme Activity. One unit of GDH activity was defined as the amount of enzyme required to reduce 1.0 µmol NAD+ to NADH per min in the presence of glucose. One unit of cellulase activity was defined as the amount of enzyme required to reduce 1.0 µmol methylcellulose to 6-methylglucose by per min. 2.3. Preparation of Platinum Nanoparticles. A suspension of platinum nanoparticles was prepared by refluxing hydrogen hexachloplatinate(IV) hexahydrate and sodium citrate.14 A solution of 400 mL of water containing 30 mg of hydrogen hexachloplatinate hexahydrate was heated to boiling using a heater mantle and a magnetic stirrer for 1.5 h and then a solution of 30 mL of water containing 600 mg of sodium citrate dihydrate was added and refluxed at 100 °C for 4 h. The particle size was estimated to be 1.5 nm. The prepared platinum nanoparticles has the ability to release 0.7 µmol of hydrogen in the reaction system of 10 µL platinum nanoparticles, 1.2 × 10-5 mmol MV2+, and 7.7 × 10-5 mmol sodium dithionite in 4 mL of 50 mmol dm-3 Tris/HCl buffer (pH 7.4) at 30 °C for 10 min. One unit of platinum nanoparticles activity was defined as release of 1.0 µmol of hydrogen per min. 2.4. NADH Formation with Methylcellulose, Cellulase, and GDH. The reaction was started by adding NAD+ (0.175 mmol dm-3) to a solution containing methylcellulose (0.38 mmol dm-3), cellulase, and GDH (5 units) in phosphate buffer (16) Saiki, Y.; Amao, Y. Visible light induced biohydrogen production from sucrose using the photosensitization of Mg chlorophyll-a. Bioconjugate Chem. 2002, 13, 898-901. (17) Himeshima, N.; Amao, Y. H2 production from maltose derived from starch using the visible light photosensitization of Mg chlorophyll-a from Spirulina. Biotechnol. Lett. 2002, 24, 1647-1650

(pH 7.0) (processes A and B in Scheme 1). The reduction of NAD+ to NADH by GDH was determined by following the specific absorption at 340 nm assuming a molar extinction coefficient of 6.3 × 103 mol-1 dm3 cm-1. To investigate the effect of cellulase activity on the NADH reduction, cellulase activity was changed from 2 to 16 units. 2.5. Photoreduction of MV2+. Photoreduction of MV2+ was tested in a reaction mixture containing NAD+, methylcellulose (20 mmol dm-3 monomer concentration), cellulase (4 units) and GDH (5 units), Mg Chl-a (9.0 µmol dm-3), and MV2+ (0.4 mmol dm-3) in 3.0 mL of 10 mmol dm-3 potassium phosphate buffer (pH 7.0) (processes A, B, and C in Scheme 1). The solution was deaerated by repeated freeze-pump-thaw cycles and irradiated with a 200 W tungsten lamp at a distance of 3.0 cm. Wavelengths less than 390 nm were removed with a Toshiba L-39 cutoff filter. The light intensity was measured by the potassium ferrioxalate actinometry method.18 Reduction of MV2+ was monitored using an UV-vis spectrophotometer set at 605 nm assuming a molar extinction coefficient of 1.3 × 104 mol-1 dm3 cm-1.19 To investigate the effect of NAD+ concentration on the MV2+ reduction, NAD+ concentration was changed from 2.5 to 10 mmol dm-3. 2.6. Photoinduced Hydrogen Production. Photoinduced hydrogen production was tested in a reaction mixture containing methylcellulose (20 mmol dm-3 monomer concentration), cellulase (4 units), GDH (5 units), NAD+ (5 mmol dm-3), Mg Chl-a (9.0 µmol dm-3), MV2+ (0.4 mmol dm-3), and platinum nanoparticles (0.5 unit) in 3.0 mL of 10 mmol dm-3 potassium phosphate buffer (pH 7.0). The solution was deaerated by freeze-pump-thaw cycle for 6 times, and flushed with argon gas. The amount of hydrogen produced and the other produced gases were measured with a Shimadzu GC-14B gas chromatography (detector: TCD, column temperature: 40 °C, column: active charcoal with the particle size 60-80 mesh, carrier gas: nitrogen gas, carrier gas flow rate: 24 mL min-1).

Results and Discussion 3.1. NADH Formation with Methylcellulose, Cellulase, and GDH. The time dependence of NADH forming in a solution containing methylcellulose, cellulase, GDH, and NAD+ is shown in Figure 1. The initial rate of NADH formation was determined by the amount of NADH after incubation for 10 min. The rate of formation increased with the concentration of cellulase up to 4 units and then became constant value. In contrast, no formation of NADH was observed in a (18) Hatchard, C. G.; Parker, C. A. A new sensitive chemical actinometer. II. Potassium ferrioxalate as a standard chemical actinometer. Proc. R. Soc. 1956, A235, 518-536. (19) Watanabe, T.; Honda, K. Measurement of the extinction coefficient of the methyl viologen cation radical and the efficiency of its formation by semiconductor photocatalysis. J. Phys. Chem. 1982, 86, 2617-2619.

Photoinduced H2 Production from Cellulose Derivative

Figure 1. Time dependence of NADH formation with methylcellulose (0.38 mmol dm-3), cellulase, NAD+ (0.175 mmol dm-3) ,and GDH (5 units) in in 3.0 mL of 10 mmol dm-3 phosphate buffer (pH 7.0). Cellulase (open circle): 2, (closed square): 4 (open square): 8, and (closed circle): 16 units; (closed triangle): without cellulase.

Figure 2. The time dependence of the reduced MV2+ concentration under steady-state irradiation with visible light using a 200 W tungsten lamp at a distance of 3.0 cm. The sample solution consisting of NAD+, methylcellulose (20 mmol dm-3), cellulase (4 units), GDH (5 units), Mg Chl-a (9.0 µmol dm-3), and MV2+ (0.4 mmol dm-3) in 3.0 mL of 10 mmol dm-3 potassium phosphate buffer (pH 7.0). NAD+ (closed square): 2.5, (closed circle): 5.0, (open square): 7.5, and (open circle): 10 mmol dm-3; (closed triangle): without NAD+.

solution containing methylcellulose, GDH and NAD+. Thus, NADH was formed via methylcellulose hydrolysis with cellulase. Four units of cellulase, formed 0.173 mmol dm-3 NADH after 40 min. The yield of conversion of NAD+ to NADH in this system was almost 100%. 3.2. Photoreduction of MV2+. Time dependence of the MV.+ concentration in the system containing methylcellulose, cellulase, GDH, NAD+, Mg Chl-a, and MV2+ with visible light irradiation is shown in Figure 2. The absorbance at 605 nm, absorption band of MV.+, increased with irradiation time. In all cases of NAD+ concentrations, ca. 0.1 mmol dm-3 of reduced MV2+ was produced and the yield of MV2+ to MV.+ was estimated to be ca. 25% after 50 min irradiation. The quantum yield was 2.0% by the potassium ferrioxalate actinometry method. The photoreduction rate was independent

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Figure 3. Time dependence of hydrogen production under steady-state irradiation with visible light using a 200 W tungsten lamp at a distance of 3.0 cm. The sample solution consisting of NAD+ (5.0 mmol dm-3), methylcellulose (20 mmol dm-3), cellulase (4 units), GDH (5 units), Mg Chl-a (9.0 µmol dm-3), MV2+ (0.4 mmol dm-3), and platinum nanoparticles (0.5 unit) in 3.0 mL of 10 mmol dm-3 potassium phosphate buffer (pH ) 7.0). (open circle): without NAD+. The reaction temperature: (closed triangle): 20 °C, (closed square): 30 °C, (closed circle): 40 °C.

of the concentrations of NAD+, methylcellulose, cellulase, and GDH. In contrast, the reduction rate depends on the concentrations of Mg Chl-a and MV2+. Thus, the rate-limiting step in the MV2+ reduction (processes A, B, and C in Scheme 1) is the electron-transfer process from the photoexcited Mg Chl-a (*Mg Chl-a) to MV2+ (process C in Scheme 1). On the other hand, MV2+ was not reduced without NAD+ in the above system (open triangle). Thus, the MV2+ photoreduction proceeded by coupling the methylcellulose hydrolysis with cellulase and GDH (processes A and B in Scheme 1) and MV2+ reduction using the photosensitization of Mg Chl-a (process C in Scheme 1). 3.3. Photoinduced Hydrogen Production. Figure 3 shows the time dependence of the photoinduced hydrogen production in the system containing methylcellulose, cellulase, GDH, NAD+, Mg Chl-a, MV2+, and platinum nanoparticles by the visible light. From the result of gas analysis in the gaseous phase using chromatography, hydrogen and argon gases were detected and the other gases were not detected. Carbon dioxide gas also was not detected. The byproduct formation in the reaction mixture was analyzed using HPLC with an electrical conductivity detector (Shimadzu CDD10AVP) (column temperature: 40 °C, column: polystyrene sulfonate column Shimadzu SCR-H, elutant: ptoluenesulfonic acid, and flow rate: 0.8 mL min-1). 6-Methylgluconic acid was produced as byproduct. 6-Methylgluconic acid was formed by oxidation of 6-methylglucose (formed by methylcellulose hydrolysis with cellulase) with GDH as shown in steps A and B of Scheme 1. Thus, the visible light-induced hydrogen production proceeded by coupling the methylcellulose hydrolysis with cellulase and GDH and the hydrogen production with platinum nanoparticles using the photosensitization of Mg Chl-a as shown in Scheme 1. By irradiation, hydrogen was produced continuously for

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more than 4 h. The amount of hydrogen production was estimated to be 12 µmol after 4 h irradiation (closed square). The quantum yield was 2.0% by the potassium ferrioxalate actinometry method. It indicated that 24 µmol of proton, that was 8000 times the amount of Mg Chl-a (3.0 nmol) in the sample solution, was reduced to hydrogen molecules. Therefore, the Mg Chl-a appeared to serve as the system for transferring electrons from NADH, which was formed from methylcellulose, to a more reductive hydrogen molecule. On the other hand, the hydrogen also was not evolved in the absence of NAD+ in the above system (open circle). These results strongly suggest that the visible light-induced hydrogen production proceeded by coupling the methylcellulose hydrolysis with cellulase and GDH (processes A and B in Scheme 1) and the hydrogen production with platinum nanoparticles using the photosensitization of Mg Chl-a (processes C and D in Scheme 1). Next let us focus on the effect of reaction temperature on the photoinduced hydrogen production. Figure 3 also shows the time dependence of the photoinduced hydrogen production in the system containing methylcellulose, cellulase, GDH, NAD+, Mg Chl-a, MV2+, and platinum nanoparticles irradiated under visible light under various reaction temperatures. The amount of

Himeshima and Amao

hydrogen produced was maximum at 30 °C and then decreased with increasing temperature, indicating that the enzyme activity may be decreased at 40 °C. In conclusion, a hydrogen production system coupling methycellulose hydrolysis with cellulase and GDH and hydrogen production with platinum nanoparticles via MV2+ photoreduction using light-induced sensitization of Mg Chl-a was developed and the continuous hydrogen gas was achieved. 6-Methylgluconic acid only was produced as a byproduct and no carbon dioxide gas was evolved in the present reaction system. For example, in renewable bio-resources utilization, carbon dioxide is evolved in the methanol production from cellulose by alcohol fermentation. In contrast, no carbon dioxide is evolved in our photoinduced hydrogen production system. Thus, renewable bio-resources have been effectively used to produce hydrogen gas through an environmentally clean process. Acknowledgment. This work was partially supported by a Special Fund from The Iwatani Naoji Foundation. EF034006W