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The phosphate-addition induced improvement of the synthesis yield of fumarate from CO2 and pyruvate in an aqueous medium using a multi-biocatalytic system of ME from Sulfobus tokodaii and FUM from porcine heart in the presence of NADH was demonstrated.

Bioelectrocatalytic methanol production from formaldehyde with alcohol dehydrogenase from Saccharomyces cerevisiae was developed toward establishing a method for synthesizing CO2 to methanol.

The utilization of the light-harvesting and electron-transferring function of chlorophylls (Chls) has received attention for visible-light driven hydrogen production. In this work, a series of Chl derivatives based on pyropheophorbide-a (Pyro-a) conjugated with a viologen moiety, including a Pyro-a methyl ester directly bonded with the viologen at the 3-position 1, its 31-methylene analog 2 and Pyro-a connected with the viologen in the 17-substituent 3, were synthesized from chemical modification of naturally occurring Chl-a and characterized in terms of their photochemical and photophysical properties. As the photoexcited singlet state of the Pyro-a moiety was strongly quenched by the viologen moiety in a molecule, the effective photoinduced intramolecular electron transfer from Pyro-a to the bonded viologen moiety occurred. Moreover, these molecules were applied as a photosensitizer in the system for visible-light driven hydrogen production with platinum nanoparticles via intramolecular reduction of the bonded viologen moiety. Efficient photoreduction of external methyl viologen and successive hydrogen production on platinum nanoparticles were achieved using the synthetic conjugate of Pyro-a with the viologen moiety as a photosensitizer. In particular, effective visible-light driven hydrogen production was accomplished using 3 and platinum nanoparticles via the reduction of external methyl viologen.

Selective hydrogen production from formic acid with platinum nano-cluster dispersed by various protective polymer based agents polyvinylpyrrolidone (Pt-PVP) or polyacrylic acid (Pt-PAA) is attempte...

1. Introduction Photocatalytic and photoelectrochemical (PEC) CO2 reductions using semiconductor materials under solar light have attracted significant attention. The development of CO2-reduction systems operating under visible-light irradiation is essential for the practical use of solar energy because visible light takes up almost half of the solar radiation spectrum. Most metal sulfides, such as CdS, have suitable conduction band levels for CO2 reduction and narrow bandgaps, enabling visible-light absorption. However, most metal sulfides are unstable in aqueous solution under photoirradiation due to the occurrence of self-oxidative deactivation (photocorrosion) by photogenerated holes (e.g., CdS + 2h+ → Cd2+ + S). CO2 reduction in an aqueous solution competes with H2 evolution because the CO2 reduction potential is more negative compared to the water reduction potential. Therefore, the catalysts that can selectively reduce CO2 have been utilized. Enzymes are biocatalysts that only act on specific substrates. For example, formate dehydrogenase (FDH) can reduce CO2 to formate with 100% selectivity by accepting electrons from coenzyme NADH. We have recently reported PEC reduction of CO2 to formate using a sacrificial reagent-free system consisting of a TiO2 photoanode and FDH.1 However, this system cannot utilize visible light owing to the wide bandgap of TiO2. In this study, we attempted to fabricate stable CdS photoanode and construct a hybrid system consisting of the CdS photoanode, NADH, and FDH for the reduction of CO2 to formate under visible-light irradiation. 2. Experimental The CdS photoanode was fabricated by the chemical bath deposition (CBD) method according to a previous report.2 The CdS electrode was calcined in N2 flow at 200, 300, and 400 °C for 30 min. The electrochemical cell used for photocurrent measurements comprised a prepared electrode, a counter electrode (Pt wire), an Ag/AgCl reference electrode, and a borate buffer solution (pH 8) containing K4[Fe(CN)6]•3H2O. The electrodes were irradiated using a 300 W Xe lamp fitted with an L-42 cut-off filter. CO2 reduction was carried out using two-electrode system (counter electrode: carbon paper) in phosphate buffer solution (pH 7) under CO2 bubbling. Rh complex [Cp*Rh(bpy)(H2O)]2+,3 NAD+, and FDH was added in the counter side. 3. Results and discussion The stabilities of the photocurrents of the CdS electrodes were evaluated at a fixed potential (–0.5 V vs. Ag/AgCl) under continuous visible light irradiation. As shown in Fig. 1a, for CdS electrodes with and without calcination at 200 and 300 °C, the photocurrent densities gradually decreased with the start of light irradiation. After the reaction, large cubic particles with a particle size of approximately 100–300 nm, reflecting the crystal structure of K2Cd[Fe(CN)6], were observed on the electrodes. XRD analysis also confirmed the formation of K2Cd[Fe(CN)6]. As previously reported, K2Cd[Fe(CN)6] forms spontaneously on the CdS surface during photoirradiation by reaction of dissolved Cd2+ cations via photocorrosion and [Fe(CN)6]4− anions in the solution.4 Therefore, this gradual decrease in photocurrent density was mainly due to the photocorrosion of CdS. In contrast, calcination at 400 °C positively influenced the CdS electrode, gradually increasing the photocurrent density. The number of electrons passing through the outer circuit for over 1 h (19.7 C, corresponding to 205 μmol) exceeded the number of moles of CdS (approximately 22 μmol) in the electrode. Although large K2Cd[Fe(CN)6] particles were observed on the CdS electrode after the reaction, the amount was significantly lower than that observed on the other electrodes. Instead, fine particles of K2Cd[Fe(CN)6] (particle size ~10 nm) were densely formed on the CdS surface. Therefore, fine K2Cd[Fe(CN)6] particles generated on the surface effectively scavenged photogenerated holes in CdS and enabled the oxidation of [Fe(CN)6]4− to [Fe(CN)6]3−.4 Reduction of NAD+ to NADH using [Cp*Rh(bpy)(H2O)]2+ as an electron mediator was examined in two-electrode system consisting of the CdS photoanode (calcined at 400 °C) and a carbon paper counter electrode with no applied bias (0 V). Relatively stable photocurrent (0.2 mA cm–2) was observed for 60 min. UV-vis spectroscopy and liquid chromatography analyses revealed that the amount of 1,4-NADH, which functions as a coenzyme, was increased with progression of reaction by reduction of NAD+ over the carbon electrode accepting electrons from CdS photoanode. The PEC reduction of CO2 to formate was attempted by introducing FDH in the system. As shown in Fig. 1b, the amount of produced formate was increased with the increasing irradiation time and reached 1285 nmol, which exceeded that of FDH (64 nmol). Ishibashi, M. Higashi, S. Ikeda, Y. Amao, ChemCatChem, 2019, 11, 6227. Ikeda, T. et al, ChemSusChem, 2011, 4, 262. Ruppert, et al, Tetrahedron Lett., 1987, 28, 6583. Shirakawa, M. Higashi, O. Tomita, R. Abe, Sustain. Energy Fuels, 2017, 1, 1065. Figure 1

Visible-light-driven CO

Effective light-driven conversion of CO2 to formic acid with a hybrid system consisting of photocatalyst TiO2 nanoparticle (P25), methylviologen (MV2+) as an electron mediating molecule and biocata...

From the view point of green chemistry, CO2 utilization technologies with solar energy including the photoredox system have been received a lot of attention. As one of them, photoredox system containing a photosensitizer and a catalyst catalyzing a reaction of a carbon–carbon bond formation from CO2 as a feed stock were constructed. In a recent study, we reported the visible light-induced malate (C4 compound) production from pyruvate (C3 compound) and CO2 due to carbon–carbon bond formation with the system consisting an electron donor, a photosensitizer, diphenylviologen (PV2+) derivative as an electron mediator in the presence of malic enzyme (ME). However, the interaction between a photosensitizer and PV2+ derivative has not been clarified yet. In this study, water-soluble PV2+ derivative, 1,1′-bis(p-sulfonatophenyl)-4,4′-bipyridinium salt (PSV2+) was synthesized, and its electro-, photochemical properties were evaluated. Moreover, the photoredox properties of PSV2+ with water-soluble Zn porphyrin were studied using fluorescence spectroscopy and steady state irradiation. The fluorescence of Zn porphyrin was quenched by PSV2+ and the two-electron reduced form of PSV2+ were produced with Zn porphyrin with steady state irradiation. In addition, reaction solution containing triethanolamine, tetraphenylporphyrin tetrasulfonate, pyruvate, ME, Mg2+ and PSV2+ in CO2 saturated bis-tris buffer (pH 7.4) was irradiated with visible light, the oxaloacetate and malate were produced. This result indicates that PSV2+ is an efficient electron mediator in the visible light-induced redox system for carbon–carbon bond formation with ME from CO2 as a feedstock.

Carbon dioxide, CO2 reduction and utilization for organic compounds synthesis are the potential technologies in environmental science and technology. In order to establish efficient CO2 utilization technologies, an effective catalyst for CO2 reduction and utilization is necessary. Among various catalysts, the biocatalyst is one of promising catalysts because it has excellent selectivity for the reaction and substrate. In this review, focusing on biocatalyst “formate dehydrogenase FDH” catalyzing CO2 reduction to formic acid, representative examples of properties, types, structure of active-site of FDH and, reaction mechanism of formic acid oxidation and CO2 reduction with FDH are outlined. A genetic engineering modified FDH and FDH immobilized various support for improving CO2 reduction catalytic activity also are introduced. Moreover, chemical and electrochemical system of CO2 reduction to formic acid with FDH, aqueous homogenous system of visible-light driven CO2 reduction to formic acid with FDH and device for visible-light driven CO2 reduction to formic acid with FDH are also introduced as an application of FDH.

Photochemical and enzymatic production of methanol from CO2 was investigated with the system formate (FDH), aldehyde (AldDH) and alcohol (ADH) dehydrogenases, and methylviologen (MV2+) photoreduction by the visible light photosensitization of organo-photocatalyst, water-soluble porphyrin, tetraphenylporphyrin tetrasulfonate (H2TPPS) in the presence of triethanolamine (TEOA) as an electron donating reagent. To improve the methanol production from CO2, the kinetic parameters for methanol production with ADH and dithionite-reduced MV2+ were clarified. When the sample solution consisting of H2TPPS (100 μM), MV2+ (2.0 mM), TEOA (0.3 M), FDH (2.0 μM), AldDH (2.0 μM) and ADH (2.0 μM) in CO2 saturated 50 mM sodium pyrophosphate buffer was irradiated, continuous methanol production from CO2 was observed and methanol concentration produced was estimated to be 6.8 μM after 100 min irradiation.

Formate dehydrogenase (FDH) is an attractive biocatalyst for converting CO 2 to formic acid in ambient conditions. FDH is applied to the catalyst for the visible-light induced CO 2 – formic acid conversion system consisting of an electron donor, a photosensitizaer and an electron carrier. For improvement of the formic acid production efficiency with this system, the enhancement of electron relay processes among a photosensitizer, an electron carrier and FDH has been needed. We aimed to solve this problem by developing novel electron carrier based on the viologen derivative instead of methylviologen (MV), widely used as an electron carreir. In this study, viologen derivatives with carbamoyl group, 1,1′-dicarbamoylmethyl-4,4′-bipyridinium diiodide (CV) and 1-carbamoylmethyl-1′-methyl-4,4′-bipyridinium diiodide (CMV) were synthesized and applied to the electron carrier for photoinduced CO 2 -formic acid conversion system consisting of triethanolamine, water-soluble zinc porphyrin and FDH. By using CV and CMV, the effective formic acid production in the system of water-soluble zinc porphyrin and FDH was improved compared with that of MV.

Singlet and triplet excited states dynamics of the photosynthetic pigment chlorophyll a in various solvents have been investigated by sub-ns pump-probe spectroscopic measurements with a sub-ns time resolution and a temporal window up to 400 μs. The singlet and triplet lifetimes of chlorophyll a were determined respectively to be 5.2–7.0 ns and 1.2–12 μs, depending on solvents. On a basis of a global analysis of time-resolved spectroscopic data, we estimated an yield of the intersystem crossing from the singlet to triplet excited states chlorophyll a to be about 30% depending not on surrounding environments. The value is much lower than the previously reported values.

Molecular conversion reaction system containing a dye and a biocatalyst catalyzing a reaction of a carbon–carbon bond formation from CO2 as a feedstock were constructed. For example, NADP-malic enzyme (ME, EC1.1.1.40) catalyzes the reaction of introducing CO2 as a carboxy group to pyruvate (C3 compound) to form malate (C4 compound) via oxaloacetate in the presence of natural co-enzyme NADPH. In a recent study, visible light-induced oxaloacetate production from pyruvate and CO2 with the system consisting an electron donor, a photosensitizer, diphenylviologen (PV2+) derivative as an electron mediator and ME was reported. However, the visible light-induced reduction properties of PV2+ with water-soluble Zn porphyrin have not been clarified. In this study, chemical and photo-redox properties of PV2+ were studied. In addition, to produce malate, CO2 saturated reaction solution containing triethanolamine, tetraphenylporphine tetrasulfonate (H2TPPS), pyruvate, PV2+ and ME in the presence of Mg2+, co-factor for ME was irradiated with visible-light, the oxaloacetate and malate were produced.

The effect of the functional ionic group of 4,4′-bipyridinium salt derivatives (4,4′-BPs) as the electron carrier on the visible-light driven conversion of CO2 to formic acid with the system consisting of water-soluble zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS) and formate dehydrogenase (FDH) in the presence of triethanolamine (TEOA) as an electron donor was investigated. 1,1′-Diaminoethyl- (DAV), 1-aminoethyl-1′-methyl- (AMV), 1-carboxymethyl-1′-methyl- (CMV) and 1,1′-dicarboxymethyl-4,4′-bipyridinium salt (DCV) were prepared as the 4,4′-BPs with the functional ionic group. Irradiation of a CO2 saturated buffer solution containing TEOA, ZnTPPS, 4,4′-BP and FDH with visible light irradiation resulted in the production of formic acid. By using 4,4′-BPs with the cationic aminoethyl-group, DAV or AMV as an electron carrier, the effective visible-light driven formic acid production based on the CO2 reduction was observed compared to the 4,4′-BPs with the anionic carboxymethyl-group, CMV or DCV. The formic acid production rate with DAV was approximately 3.2 times higher than that of the system with DCV.

In this review, the recent studies on 1) the visible-light-induced reduction of CO2 to formic acid catalyzed by formate dehydrogenase (FDH) via the reduction of a 4,4′- or 2,2′-bipyridinium salt (BP2+) by a photosensitizer, 2) the electrochemical properties of BP2+, and 3) the enzymatic kinetic properties of the interaction between the reduced forms of BP2+ and FDH are reviewed. Moreover, visible-light-induced biocatalytic C–C bond formation using CO2 as a feedstock via photoreduction of the phenylviologen derivative is introduced.

Visible-light-driven CO2 reduction to formate with a system consisting of water-soluble zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS), formate dehydrogenase from Candida boidinii (CbFDH) and methylviologen (MV) in the presence of triethanolamine (TEOA) as an electron donor in an ionic liquid, 1-ethyl-3-methylimidazolium dimethyl phosphate ([EMlm][Me2PO4])/aqueous media was investigated. The catalytic activity of CbFDH for formate oxidation to CO2 and CO2 reduction to formate did not decrease significantly even in [EMlm][Me2PO4]/aqueous media, compared with that in aqueous media. The visible-light-driven MV reduction by the photosensitization of ZnTPPS in [EMlm][Me2PO4]/aqueous media proceeds more efficiently than in the aqueous media system. In the visible-light-driven CO2 reduction to formate system of ZnTPPS, MV and CbFDH with [EMlm][Me2PO4]/aqueous media, moreover, the formate production concentration after 180 min decreased by only 20% as compared with the system in aqueous media.

Acid phosphatase (APase) was immobilized in discrete mesospaces of an assembly of silica nanoparticles (SiO2NPA) to be used as a heterogeneous catalyst for the hydrolysis of organophosphates often found as pesticide residues in agricultural products. APase immobilized in SiO2NPA exhibited higher catalytic activity than APase supported on conventional porous supports for the hydrolysis of p-nitrophenyl phosphate (p-NPP) with quantitative yield of p-nitrophenol below pH 5.5 due to the efficient diffusion of substrates in the SiO2NPA. Especially, a heterogeneous catalyst prepared by the co-accumulation method, in which silica nanoparticles (SiO2NPs) dispersion containing APase was simply dried to assemble a composite catalyst (APase/SiO2NPA), exhibited four times faster rate for the hydrolysis of p-NPP than the catalyst prepared by the equilibrium adsorption of APase in pre-assembled SiO2NPA. The catalytic stability of immobilized APase above pH 6.0 was enhanced by surface modification of SiO2NPs with 3-aminopropyltriethoxysilane (APase/SiO2NPA-NH2) due to the strong electrostatic interaction between APase and the protonated amino groups at the pH condition. Such stability enhancement was hardly obtained by cross-linking treatment of SiO2NPA to improve the robustness. These results suggest that electrostatic interaction between APase and SiO2NPs is crucial to enhance catalytic stability in the wide range of pH as well as preparation methods for the stable encapsulation.

Formate dehydrogenase (FDH) is an attractive catalyst for the reduction of CO2 because CO2 is converted to formic acid by FDH at room temperature under normal pressure in neutral aqueous solution. The reduced form of methylviologen acts as an artificial co-enzyme for FDH in the conversion of CO2 to formic acid. To improve the catalytic activity of FDH in reducing CO2, viologen derivatives with ionic groups were synthesized as effective artificial co-enzymes for FDH. We used enzyme kinetic analysis to assess the effect of the ionic amino or carboxyl functional groups in the reduced form of the viologen derivatives on the catalytic activity of FDH with respect to the reduction of CO2. By using 1,1′-diaminoethyl-4,4′-bipyridinium salt, which is the reduced form of a viologen derivative with two amino groups, we optimized the reduction of CO2 to formic acid with FDH. The catalytic efficiency value (kcat/Km) of the reduced form of 1,1′-diaminoethyl-4,4′-bipyridinium salt was estimated to be more than 560 times larger than that of the natural co-enzyme NADH. From the analysis result, the CO2 reduction was influenced by the ionic group of the viologen derivative.

Photochemical synthesis of ethanol from acetate was investigated with the system aldehyde (AldDH) and alcohol (ADH) dehydrogenases from Yeast, and methylviologen (MV2+) photoreduction by the visible light photosensitization of chlorophyll derivative, chlorin-e6 of zinc complex (ZnChl-e6) in the presence of NADPH as an electron donating reagent. Irradiation of a solution containing NADPH, ZnChl-e6, MV2+, AldDH, ADH and sodium acetate with visible light resulted in ethanol synthesis. The concentration of ethanol produced was 1.4 mM after 150 min irradiation under the condition of NADPH (3.3 mM), ZnChl-e6 (100 μM), MV2+ (12 mM), AldDH (0.22 μM), ADH (6.7 nM) and sodium acetate (30 mM) in 50 mM of sodium pyrophosphate buffer pH 7.4).

Effect of chemical structures of some 2,2′-bipyridinium salts (BP2+) as the electron carrier molecules on the visible-light induced conversion of CO2 to formic acid with the system consisting of water-soluble zinc tetraphneylporphyrin tetrasulfonate (ZnTPPS) and formate dehydrogenase (FDH) in the presence of triethanolamine (TEOA) as an electron donor molecule was investigated. Irradiation of a CO2 saturated solution containing TEOA, ZnTPPS, BP2+ and FDH with visible light resulted in production of formic acid. By using 1,1′-ethylene-2,2′-bipyridinium dibromide (DB2+) as an electron carrier molecule, the effective formic acid production was observed compared with the other 2,2′-bipyridinium salt derivatives.

Zinc chlorophyll a derivatives were synthesised for use as photosensitizers. Herein, we report a system for photoinduced hydrogen production with colloidal platinum via photoreduction of methylviologen (MV2+) using the photosensitization of a Zn pyropheophorbide a (ZnPyOH) dimer connected by lysine (ZnPy-K(ZnPy)OH) as a special pair model in the photosynthetic reaction centre in the presence of NADPH as an electron donor.

Formate dehydrogenase (FDH) is an attractive biocatalyst for CO2 reduction. The reduced form of methylviologen acts as an artificial coenzyme for FDH. For further improvement in the CO2 reduction catalytic activity of FDH, a viologen derivative with two amino groups, 1,1′-diaminoethyl-4,4′-bipyridinium salt (DA2+), was synthesized as the effective artificial coenzyme for FDH. By enzyme kinetic analysis, the catalytic efficiency, i.e., kcat/Km value of the reduced form of DA2+ was estimated to be more than 560 times larger than that of NADH, the natural coenzyme for FDH.

The kinetic properties of the conversion of CO2 to formic acid with formate dehydrogenase (FDH) using some dithionite-reduced 2,2′-bipyridinium salts (1,1′-ethylene-2,2′-bipyridinium dibromide diquat and 1,1′-dimethyl-2,2′-bipyridinium dichloride) as an artificial coenzyme were studied. By using the reduced form of diquat, the effective CO2 reduction to formic acid with FDH is accomplished. The catalytic efficiency, the kcat/Km value of the reduced form of diquat was ca. 126 times larger than that of NADH.

Anti-Stokes fluorescence from chlorophyll a molecules dispersed in diethyl ether has been observed. From the excitation power dependence of the fluorescence spectrum, it is concluded that the anti-Stokes fluorescence appears via the linear optical process. To consider the relationship between the observed spectral shape and vibrational modes, the model spectral density has been determined based on the Raman spectrum and real-time coherent vibrational oscillation signals. The absorption spectrum observed in the experiment was well reproduced by the calculation, indicating the validity of the model spectral density. The involvement of the low-frequency vibrational modes in the anti-Stokes fluorescence process is discussed.

Nonlinear optical responses of β-carotene were investigated upon excitation using chirped pulses. We especially focus on spectrally resolved transient grating (TG) signals to discuss the influence of the spectral chirp over a wide spectral range. A significant change in the TG signal was observed when negatively chirped pulses were used. The experimental results were qualitatively reproduced by employing the Brownian oscillator model. The relationship between the wave packet motion in the excited state and spectral chirp is discussed. It is concluded that the third order nonlinear optical response reflects the competition between the spectral chirp and the energy separation of the potential curves.

Photosynthesis dye chlorophyll derivative chlorin-e 6 , viologen (electron carrier) and platinum nano-particle immobilized onto silica gel based thin layer substrate is for photoinduced hydrogen production is developed. When the chlorin-e6, viologen and platinum nano-particle immobilized onto substrate is irradiated with 100 mWcm -2 visible light in the presence of NADPH as an electron donor, the hydrogen production is observed. After 2 h irradiation, 6.0×10 -8 mol of hydrogen is produced.

To develop the visible light-induced hydrogen and oxygen production based on the water photolysis, 2,6-dichloroindophenol (DCIP) reduction based on the photoinduced water oxidation with oxygen evolved centre (OEC) of PSII in photosynthesis organ, grana from spinach was studied. It noted that manganese–calcium (4Mn–Ca) cluster consisted of four manganese and one calcium ions in OEC, and the role and effect of manganese (III) and calcium ions on the DCIP reduction were investigated. By addition of manganese (III) acetate up to 80 μmol dm −3 , the concentration of the reduced DCIP with irradiation was increased compared with the system in the absence of manganese (III) acetate. The activity of DCIP reduction in the presence of 80 μmol dm −3 manganese (III) acetate was 4.7 times higher than that in the absence of manganese (III) acetate. This result shows that the DCIP photoreduction with grana was promoted by addition of manganese (III) ion. In contrast, the activity of DCIP reduction in the presence of 120 μmol dm −3 manganese (III) acetate was 1.5 times higher than that in the absence of manganese (III) acetate, indicating that photoreduction of DCIP activity of grana was inhibited under higher concentration of manganese (III) ion or acetate anion. By addition of 80 μmol dm −3 calcium chloride, on the other hand, 5.9 μmol dm −3 of reduced DCIP was produced and the reduction ratio of the reduced DCIP to DCIP was 8.6% after 240 min irradiation. The activity of DCIP reduction in the presence of 80 μmol dm −3 calcium chloride was almost the same in the absence of calcium chloride. This result shows the no effect on the DCIP photoreduction based on the water oxidation with grana by addition of calcium ion.

We studied the photochemical and enzymatic synthesis of methanol from HCO3− using formate dehydrogenase (FDH) isolated from Candida boidinii, aldehyde dehydrogenase (AldDH) and alcohol dehydrogenase (ADH) isolated from yeast, and the photoreduction of methyl viologen (MV2+) by the visible-light sensitization using zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS) in the presence of triethanolamine (TEOA). When a sample solution containing ZnTPPS, MV2+, FDH, AldDH, ADH, TEOA, and NaHCO3 in potassium phosphate buffer solution (pH 8) was irradiated, the amount of methanol produced increased with the irradiation time. After irradiation for 3 h, 4.5 μmol dm−3 of methanol was produced from 100 μmol dm−3 NaHCO3. The conversion ratio of HCO3− to methanol was approximately 4.5%. This result indicates that a system for the photochemical synthesis of methanol from HCO3− can be developed by using three dehydrogenases (FDH, AldDH, and ADH) and for the photoreduction of MV2+ through the photosensitization of ZnTPPS in aqueous media.

To develop the visible light induced hydrogen and oxygen production based on the water photolysis, 2,6-dichloroindophenol (DCIP) reduction based on the photoinduced water oxidation with oxygen evolved centre (OEC) of PSII in photosynthesis organ, grana from spinach was studied. It noted that manganese cluster consisted of four manganese ions in OEC, and the role and effect of manganese(II) and (III) ions on the DCIP reduction were investigated. By addition of manganese(III) acetate up to 80 μmol dm −3 , the concentration of the reduced DCIP with irradiation was increased compared with the system in the absence of manganese(III) acetate. The activity of DCIP reduction in the presence of 80 μmol dm −3 manganese(III) acetate was 4.7 times higher than that in the absence of manganese(III) acetate. In contrast, the concentration of the reduced DCIP with irradiation was increased by addition of manganese(II) acetate up to 40 μmol dm −3 compared with the system in the absence of manganese(II) acetate. These results show that the DCIP photoreduction with grana was promoted by addition of manganese(III) or (II) ion.

Photoinduced biohydrogen production systems, coupling saccharaides biomass such as sucrose, maltose, cellobiose, cellulose, or saccharides mixture hydrolysis by enzymes and glucose dehydrogenase (GDH), and hydrogen production with platinum colloid as a catalyst using the visible light-induced photosensitization of Mg chlorophyll-a (Mg Chl-a) from higher green plant or artificial chlorophyll analog, zinc porphyrin, are introduced.

Here, we developed a photoinduced biohydrogen production system coupling saccharide hydrolysis with hydrogen production. A mixture of three different saccharides (sucrose, maltose, and cellobiose) was hydrolyzed by three enzymes (invertase, glucoamylase, and cellulase) and glucose dehydrogenase (GDH). Hydrogen production was performed with colloidal platinum as a catalyst, using visible light-induced photosensitization of Mg chlorophyll a (Mg Chl a ). Irradiation of the sample solution containing the saccharides, enzymes, GDH, NAD + , Mg Chl a , methyl viologen (MV 2+ ), and colloidal platinum resulted in continuous hydrogen production. Approximately 2.9 μmol hydrogen was produced after 2 h of irradiation, and the total yield was approximately 8.8%.

Visible light and enzymatic induced synthesis of malic acid from pyruvic acid and HCO 3 - with malic enzyme (ME) and NADP+ photoreduction by the visible light photosensitization of chlorophyll derivative, zinc chlorin-e6 (Zn Chl-e6) in the presence of NADH as an electron-donating reagent was investigated. When the sample solution containing NADH, Zn Chl-e6, methylviologen (MV2+), pyruvic acid, NaHCO3, NADP+, ferredoxine-NADP+-reductase (FNR) and ME was irradiated with visible light (>390 nm), malic acid was produced. The produced malic acid was 0.65 mmol dm−3 after 3 h visible light irradiation.

Photovoltaic conversion using zinc chlorin-e6 (ZnChl-e6), which is zinc chlorophyll-a derivative, and fatty acid (myristic acid or cholic acid) co-adsorbed nanocrystalline TiO2 layer onto ITO glass (OTE) electrode is developed. The maximum peaks of photocurrent action spectrum of the ZnChl-e6 adsorbed TiO2 layer onto OTE (ZnChl-e6/TiO2) are 400, 660 and 800 nm, respectively. Especially the IPCE value at 800 nm (7.5%) is larger than that of 660 nm (6.9%). This result indicates that ZnChl-e6 molecules is aggregated or formed dimer on a nanocrystalline TiO2 layer onto OTE and the absorption band is shifted to near IR region. The photocurrent action spectrum of ZnChl-e6 and cholic acid adsorbed TiO2 layer onto OTE (ZnChl-e6–Cho/TiO2) is similar to that of the UV–vis absorption spectrum in methanol solution, and IPCE values at 400 and 660 nm (8.1%) increase and the IPCE value at 800 nm (4.1%) decreases, indicating that the aggregation of ZnChl-e6 molecules on the TiO2 is suppressed by cholic acid. By using ZnChl-e6–Cho/TiO2, the short-circuit photocurrent density and open-circuit photovoltage also increase compared with that of ZnChl-e6 adsorbed nanocrystalline TiO2 electrode.

Photochemical and enzymatic synthesis of malic acid from pyruvic acid and HCO3- was studied with malic enzyme (ME) and NADP+ photoreduction with ferredoxin-NADP+-reductase (FNR) by visible light photo-sensitization of the chlorophyll derivative, zinc chlorin-e6 (ZnChl-e6), in the presence of NADH as an electron-donating reagent and methylviologen (MV2+) as an electron-relay reagent. NADPH was produced by irradiation of the reactant solution containing NADH, ZnChl-e6, MV2+, NADP+ and FNR in Bis-Tris buffer (pH 8.0). After 180-min irradiation, 8.3 mmol·dm-3 NADPH was produced under the optimum conditions with 10 mmol·dm-3 of NADP+. The reduction ratio of NADP+ to NADPH was about 83%. Malic acid was produced by irradiation with visible light (>390 nm) of the reactant solution containing NADH, ZnChl-e6, methylviologen (MV2+), pyruvic acid, NaHCO3, NADP+, ferredoxin-NADP+-reductase (FNR) and ME. Malic acid production was 2.0 mmol·dm-3 after 3-h irradiation under the optimum conditions with NADH, ZnChl-e6, MV2+, FNR, pyruvic acid, NaHCO3, NADP+ and ME. The ratio of HCO3- and pyruvic acid to malic acid was about 20% under the optimum conditions.

Zn chlorophyll- a derivative, Zn chlorin-e 6 (ZnChl-e 6 ) and carotenoid derivative, crocetin (Cro) adsorbed onto a nanocrystalline TiO 2 film (ZnChl-e 6 -Cro/TiO 2 ) electrode was prepared and the photovoltaic properties of ZnChl-e 6 -Cro/TiO 2 electrode were studied. Incident photon to current efficiency (IPCE) value at 640 nm in photocurrent action spectrum of ZnChl-e 6 -Cro/TiO 2 electrode was ca. 2.50%. In contrast, IPCE value at 640 nm in ZnChl-e 6 /TiO 2 electrode was ca. 1.27%. Thus, the IPCE value increases by co-adsorbed crocetin and ZnChl-e 6 onto TiO 2 film electrode. From the results of photocurrent responses with light intensity of 100 mW cm −2 irradiation, generated photocurrents in the ZnChl-e 6 -Cro/TiO 2 and ZnChl-e 6 /TiO 2 electrodes are 380 and 180 μA cm −2 , respectively. Photocurrent increases using ZnChl-e 6 -Cro/TiO 2 electrode compared with that of ZnChl-e 6 /TiO 2 electrode.

Photoinduced hydrogen production with Mg chlorophyll- a (MgChl- a ) from spirulina as a visible-light photosensitizer by use of three component system consisting of NADH as an electron donor, methylviologen (MV 2+ ) as electron relay reagent and colloidal platinum as hydrogen production catalyst in cationic surfactant, alkyltrimethyl bromide with different methylene chain length (CH 3 (CH 2 ) n N + (CH 3 ) 3 ·Br − ; n = 9, 13 and 15) micellar media is investigated. Consequently, the effective MV 2+ photoreduction and hydrogen production system is accomplished using MgChl- a in CH 3 (CH 2 ) 15 N + (CH 3 ) 3 ·Br − micellar media.

Photochemical and enzymatic formic acid synthesis from CO 2 gas system with the combination of formate dehydrogenase (FDH) from Saccharomyces cerevisiae and methylviologen (MV 2+ ) reduction by the visible light photosensitisation of Mg chlorophyll- a (Mg Chl- a ) is developed. Photochemical formic acid produced from CO 2 by adding FDH to the MV 2+ photoreduction system using photosensitisation of Mg Chl- a in the presence of NADPH as an electron donating reagent, and 56 μM of formic acid from CO 2 gas is produced after 4 h irradiation (1.0 M = 1.0 mol dm −3 ).

Photochemical synthesis of methanol from formaldehyde was evaluated with alcohol dehydrogenase (ADH) from Saccharomyces cerevisiae and NAD + photoreduction by the visible light photosensitization of zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS) in the presence of triethanolamine (TEOA) as an electron-donating reagent. Irradiation of a solution containing ZnTPPS, methylviologen (MV 2+ ), NAD + , diaphorase (5 units) and TEOA in potassium phosphate buffer with visible light resulted in formation of NADH increasing with time. NADH was not formed in the absence of any one of the five components, TEOA, ZnTPPS, MV 2+ , diaphorase and NAD + . The reduction ratio of NAD + to NADH reached about 60% after 180 min irradiation. Irradiation of a solution containing formaldehyde. ZnTPPS, MV 2+ , ADH, diaphorase and TEOA with visible light resulted in formation of methanol. The formaldehyde concentration decreased with formation of methanol. This result indicates that the photochemical synthesis of methanol from formaldehyde depends on ADH and NADH produced by the photosensitization of ZnTPPS. The concentration of methanol was 0.38 μmol · dm -3 after 3 h irradiation under conditions of ZnTPPS (1.0 μmol·dm -3 ), MV 2+ (0.1 mmol·dm -3 ), NAD + (0.1 mmol·dm -3 ), diaphorase (5 units), TEOA (0.3 mol·dm -3 ), formaldehyde (16 μmol·dm -3 ) and ADH (25 units).

Carbon-coated TiO2 were prepared by a simple heat treatment of the powder mixtures of anatase-type TiO2 (ST-01) with carbon precursor, poly (vinyl alcohol) (PVA), hydroxyl propyl cellrose (HPC) and poly (ethylene telephtalate) (PET) etc., at a temperature of 700 to 900°C. Diffuse optical reflectance spectra for carbon-coated TiO2 clearly showed the absorption edge for anatase-type structure, overlapping with absorption due to coated carbon over all wavelength of 220-850nm. Photocatalytic activity of carbon-coated TiO2 was evaluated through the determination of rate constant k for the decomposition of four model pollutants in water, methylene blue (MB), reactive black 5 (RB-5), phenol (Ph) and iminoctadine triacetate (IT), under UV irradiation. For MB most of carbon-coated TiO2 showed higher activity than the pristine anatase powder, but for others carbon-coated anatase gave either comparable or smaller rate constant for their photodecomposition. Photocatalytic activity defined by rate constant k for pollutants decomposition was found to depend strongly on crystallinity of anatase phase, which was evaluated by full width at half maximum intensity (FWHM) of 101 diffraction line; a maximum of k at an apparent FWHM of about 0.6° in 2θ (CuKα) for four pollutants. Adsorptivity of carbon-coated TiO2 photocatlysts was determined and discussed on the relations to BET surface area, amount of carbon coated and also rate constant k for the decomposition of MB, RB5, Ph and IT. Adsorptivity of carbon-coated catalysts depends strongly on the adsorbate (pollutant) but also on the surface nature of carbon layer on TiO2 particles. The relations between adsorptivity and rate constant k for four pollutants looked similar, suggesting that the pollutant adsorbed in the larger amount being decomposed with the higher rate. In order to check cyclic performance of carbon-coated TiO2, the photocatalysts were repeatedly used either in powder or fixed on one side of double-sided organic adhesive tape. It was proven that the carbon-coated TiO2 could be resisted to the multiple usage without marked deterioration in rate constant. The merits and demerits of carbon coating on photocatalyst TiO2 particles were discussed.

Various carbon coating TiO2 reduction phase (C-TinO2n-1) were synthesized by changing the mixing ratio of rutile-type TiO2 and polyvinyl alcohol (PVA) which is the carbon precursor, in order to examine Photocatalytic-activity from the photodegradation behavior under visible light. C-Tin-O2n-1 was synthesized by mixing with PVA and rutile-type TiO2 at the optional ratio under the Ar gas atmosphere, and it was introduced the oxgen defect. Photocatalytic-activity under visible light was examined from the photodegradation behavior under it of iminoctadine tri-acetate (IT) which was the disinfectant pesticide using it. The amount of carbon coating increased by increasing of amount of the PVA, and the specific surface also increased as the result. And, all of the rutile phase of TiO2 was transferred to the reduction phase. It became clear that to control specific surface and crystal phase of the TiO2 was possible by amount of the PVA as this result. The reduction phase of carbon coating TiO22 had shown the photocatalytic-activity under visible irradiation, that is it became clear that it had visible photocatalytic-activity. And, it became clear that decomposition efficiency improved by conducting the carbon coating to the TiO2 reduction phase. Carbon layer on the TiO2 reduction phase increased not only but also many products for decomposition fixed on the surface layer, it was made to concentrate that on carbon layer of the catalyst particles, and the decomposition effinciency could be increased, too.

A dye-sensitized solar cell using the visible light sensitization of chlorophyll-a derivative, chlorine-e 6 (Chl-e 6 ) immobilized on TiO 2 film was developed. From fluorescence spectrum of Chl-e 6 immobilized on TiO 2 film, the emission of Chl-e 6 was effectively quenched by TiO 2 , indicating that the effective electron injection from the excited singlet state of Chl-e 6 into the conduction band of TiO 2 occurred. The short-circuit photocurrent density ( I SC ), the open-circuit photovoltage ( V OC ), and the fill factor (FF) of solar cell consisting of Chl-e 6 immobilized on TiO 2 film electrode and platinum-coated substrate electrode were estimated to be 1.47 mA cm −2 , 425 mV, and 57.0%, respectively. IPCE values were reached a maximum around the wavelength of absorption maximum (11.0% at 400 nm, 4.7% at 541 nm and 7.9% at 661 nm), indicating that the dye-sensitized solar cell using visible light sensitization of TiO 2 film by Chl-e 6 was developed.