JP5283077B2 - photocatalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photocatalyst which is added to water together with a sacrificial electron donor, a photosensitizer and an electron transfer substance, and can efficiently proceed a decomposition reaction of the water (hydrogen generation reaction) when the water is irradiated with light. <P>SOLUTION: The photocatalyst comprises an organic ruthenium compound having a given structure, specifically, any one selected among an acetic acid ruthenium chloride, an acetic acid ruthenium tetrafluoroboronic salt, ruthenium terephthalate, ruthenium terephthalate chloride; ruthenium tetrafluoroboronic salt terephthalate, ruthenium hexafluorophosphorus terephthalate, and ruthenium bromide terephthalate. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a photocatalyst, and more particularly to a photocatalyst that promotes a hydrogen generation reaction that decomposes water to generate hydrogen molecules when the water is irradiated with light.

  Hydrogen does not generate warming gas or polluted gas only by generating water even if it is burned. For this reason, hydrogen has been attracting attention as a so-called clean fuel.

  As is well known, hydrogen is hardly contained in the atmosphere. Therefore, in order to use hydrogen as a fuel, it is necessary to generate hydrogen in advance. As one technique, it has been studied to decompose water under the catalytic action of a photocatalyst. This is because a large amount of water exists in nature, so that a large amount of hydrogen can be produced at low cost.

  For example, Non-Patent Document 1 discloses a sacrificial electron donor such as ethylenediamine-N, N, N ′, N′-tetraacetic acid disodium salt (EDTA-2Na), tris (2,2-bipyridyl) ruthenium ion. A photocatalyst is added to water together with a photosensitizer such as 1, and an electron transfer material such as 1,1′-dimethyl-4,4′-biperidium, and the water is irradiated with visible light. . As the photocatalyst, colloidal Pt, Pt (II) ion or Rh complex is selected.

  According to a report in Non-Patent Document 1, the hydrogen generation reaction proceeds efficiently in the presence of such a photocatalyst.

J. of the American Chemical Society 2006 Vol. 128, pp. 4926 to 4927 “A Photo-Hydrogen-Evolving Molecular Device Driving Visible-Light-Induced EDTA-Reduction of Water into Molecular Hydrogen "by Hironobu Ozawa, Masaaki Haga, Ken Sakai

  In order to solve problems such as global warming in recent years, further attempts have been made to use hydrogen combustion. In order to cope with this, in order to produce a large amount of hydrogen for fuel, there is a demand for a more efficient hydrogen production reaction from water.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a photocatalyst that allows the hydrogen generation reaction to proceed more efficiently.

In order to achieve the above object, the present invention provides a photocatalyst that is added to water together with a sacrificial electron donor, a photosensitizer, and an electron transfer material, and promotes a hydrogen generation reaction when the water is irradiated with light. Because
Terephthalic acid ruthenium chloride and terephthalic acid ruthenium tetrafluoroborate salt, terephthalic acid ruthenium hexafluorophosphate, characterized in that it consists of one selected from the group of terephthalic acid ruthenium bromide.

  The photocatalyst according to the present invention has a high turnover number and quantum efficiency, which are indices indicating superiority or inferiority as a photocatalyst. For this reason, when light is irradiated to water, the hydrogen production | generation reaction which decomposes | disassembles this water and obtains a hydrogen molecule can be advanced efficiently. For this reason, a large amount of hydrogen can be easily obtained in a short time.

  Examples of the sacrificial electron donor include EDTA-2Na, EDTA-tetraacetic acid tetrasodium salt, L-ascorbic acid (vitamin C), and alcohols such as methanol and ethanol. Photosensitizers , Tris (2,2′-bipyridyl) ruthenium (II) ion, tetra-p-sulfonate porphyrin zinc, tri (1,10-phenanthroline) ruthenium (II) salt, poly (bipyridine) ruthenium derivative, water-soluble metal porphyrin derivative Is exemplified.

  Furthermore, preferable examples of the electron transfer substance include alkyl viologens such as methyl viologen, ethyl viologen, and propyl viologen, and N, N'-dimethyl-diazapyrenium.

During the photocatalyst as described above, terephthalic acid ruthenium chloride, ruthenium terephthalic acid boron tetrafluoride salt, ruthenium hexafluorophosphate and terephthalic acid ruthenium bromide terephthalic acid is a complex formed by a plurality of molecules are coupled to each other Preferably there is. In this case, it shows particularly excellent performance as a photocatalyst.

  In this type of complex, cavities are formed between constituent molecules, in particular, between diphenyl bonds. This cavity is presumed to contribute to the activation of the photocatalyst.

  According to the present invention, an organic ruthenium compound having a predetermined structure is employed as a photocatalyst. When this photocatalyst is added to water together with a sacrificial electron donor, a photosensitizer, and an electron transfer material, and further irradiated with light, the water is efficiently decomposed to generate hydrogen. That is, the hydrogen production reaction for obtaining hydrogen molecules can be efficiently advanced.

2 is a schematic structural diagram schematically showing the structure of the reaction product obtained in Example 1. FIG. FIG. 3 is a schematic structural diagram schematically showing a theoretical structure of Ru ₂ (CH ₃ COO) ₄ Cl. 3 is a schematic structural diagram schematically showing the structure of a reaction product obtained in Example 2. FIG. 3 is a schematic structural diagram schematically showing the structure of a reaction product obtained in Example 3. FIG. 6 is a schematic structural diagram schematically showing the structure of a reaction product obtained in Example 4. FIG. 6 is a schematic structural diagram schematically showing the structure of a reaction product obtained in Example 5. FIG. 6 is a schematic structural diagram schematically showing the structure of a reaction product obtained in Example 6. FIG. 6 is a schematic structural diagram schematically showing the structure of a reaction product obtained in Example 7. FIG. It is a graph in which the amount of hydrogen generated from the start of the light irradiation until the lapse of 4 hours is plotted every hour for the reaction liquid using the photocatalyst (reaction product) of Examples 1 to is there. It is a graph which shows the turnover number of the photocatalyst (reaction product) of Examples 1-7.

  Hereinafter, a plurality of examples of the photocatalyst according to the present invention will be described and described in detail with reference to the accompanying drawings. In addition, the following examples are illustrations for understanding the present invention, and it is needless to say that the present invention is not limited to the respective examples.

Ruthenium acetate; Ru ₂ (CH ₃ COO) ₄ Cl In order to synthesize Ru ₂ (CH ₃ COO) ₄ Cl, 36 ml of acetic anhydride and 108 ml of acetic acid were introduced into a 300 ml eggplant flask, and 5 g each of RuCl ₃ · nH ₂ O and LiCl were added. did. While this mixed solution was vigorously stirred, the mixed solution was bubbled with oxygen. While continuing the above stirring and bubbling, the synthesis reaction was advanced by refluxing at 130 ° C. Note that bubbling was performed so that two to three oxygen bubbles having a diameter of about 1 mm were generated per second.

  As the reaction product was generated, the mixed solution became reddish brown. It was observed that the reaction product was precipitated 24 hours after the start of the reflux, and the reflux was stopped at this point.

  The obtained reaction product (precipitate) was collected on a sintered glass filter and then washed with ether. Furthermore, the reaction product was dried by performing vacuum drying for 1 hour.

This reaction product was subjected to structural analysis by FT-IR analysis, CHN elemental analysis, and magnetic susceptibility measurement. As a result, a complex of Ru ₂ (CH ₃ COO) ₄ Cl having the structure schematically shown in FIG. 1 as a repeating unit. It turned out to be. Note that the structure shown in FIG. 1 actually includes a double bond, but the double bond is omitted for convenience of explanation. The same applies to the following.

Here, the theoretical structure of Ru ₂ (CH ₃ COO) ₄ Cl is shown in FIG. As can be understood from the structural formulas shown in FIGS. 1 and 2, in the obtained reaction product, Cl in the ruthenium acetate chloride is arranged so as to bridge two ruthenium acetate molecules. Are linked. In other words, ruthenium acetate molecules are connected in a straight line via coordinated Cl to form a complex. That is, in this case, the reaction product is a two-dimensional chain complex.

Ruthenium acetate tetrafluoroborate; Ru ₂ (CH ₃ COO) ₄ BF ₄ was synthesized by introducing 40 ml of tetrahydrofuran into a 100 ml eggplant flask, and then adding 1 g of Ru ₂ (CH ₃ COO) ₄ Cl, 0 Each of .41 g of AgBF ₄ was added and further stirred for 24 hours. The solution was filtered through celite, and a filtrate remained on the celite. As a result of identifying this filtrate, it was confirmed to be AgCl.

  On the other hand, the filtrate was concentrated and extracted with ether. When this extract was passed through a sintered glass filter, powder remained on the sintered glass filter. The powder was dried by vacuum drying for 1 hour.

The powder after drying was subjected to structural analysis by FT-IR analysis, Raman spectrum analysis, CHN elemental analysis and powder X-ray diffraction measurement. As a result, Ru ₂ (CH ₃ COO) whose structure is schematically shown in FIG. It turned out to be ₄ BF ₄ .

Next, synthesis of ruthenium terephthalate (II, II); [Ru ₂ (p-BDC) ₂ ] _n was attempted. Note that p-BDC is an abbreviation meaning 1,4-benzenedicarboxylate, and the same applies to the following.

First, 30 ml of N, N′-dimethylformamide was introduced into a 100 ml volumetric flask, and then 0.1 g of Ru ₂ (CH ₃ COO) ₄ BF ₄ and 0.0592 g of 1,4-benzenedicarboxylic acid ( p-BDCA) was added. This mixed solution was refluxed at 170 ° C. for 24 hours under an argon atmosphere.

  Next, after cooling to room temperature, the precipitate was collected on a sintered glass filter. The collected precipitate was washed with acetone and then with methanol, and further dried by vacuum drying for 4 hours.

This precipitate was subjected to structural analysis by FT-IR analysis, Raman spectrum analysis, diffuse reflection ultraviolet-visible (DR-UV-Vis) spectrum analysis, CHN elemental analysis, specific surface area pore size distribution measurement, and XPS analysis. [Ru ₂ (p-BDC) ₂ ] _n complex having a structure schematically represented by

  That is, this complex has a form in which Ru is a central metal and a two-dimensional chain complex having a structure in which p-BDC is coordinated with Ru as a repeating unit is laminated via a diphenyl bond. Eventually, the complex has a three-dimensional structure.

  As can be seen from FIG. 4, in this complex, a cavity 10 is formed at the center of the cyclic bond. Due to the presence of the cavity 10, the complex forms a porous body in which pores are formed in the structure.

  When the SEM observation was performed on the precipitate, it was found that the precipitate had a relatively large polyhedral shape, and part of the corners of the polyhedral shape had an acute pointed shape.

Furthermore, synthesis of ruthenium terephthalate (II, III) chloride; [Ru ₂ (p-BDC) ₂ Cl] _n was attempted.

First, 30 ml of a mixed solvent of methanol / water mixed at a volume ratio of 1: 1 is introduced into an eggplant flask having a volume of 100 ml, and then 0.05 g of Ru ₂ (CH ₃ COO) ₄ Cl, 0.035 g Of p-BDCA and 0.045 g of LiCl were added. This mixed solution was refluxed at 100 ° C. for 6 hours under an argon atmosphere.

  Next, after cooling to room temperature, the precipitate was collected on a sintered glass filter. The collected precipitate was washed with acetone and then with methanol, and further dried by vacuum drying for 2 hours.

This precipitate was subjected to structural analysis by FT-IR analysis, Raman spectrum analysis, DR-UV-Vis spectrum analysis, CHN elemental analysis, specific surface area pore size distribution measurement, and XPS analysis. The structure is schematically shown in FIG. As a result, [Ru ₂ (p-BDC) ₂ Cl] _n complex represented by the formula (1) was obtained.

  As shown in FIG. 5, this complex is a two-dimensional structure in which Ru is a central metal and a coordinated bond in which p-BDC is coordinated to Ru and bonded via Cl. Has a chain complex. Then, self-organization occurs through the Cl, and the two-dimensional chain complex is thereby laminated through a diphenyl bond. As a result, this complex also has a three-dimensional structure.

  Also in this complex, the cavity 10 is formed at the center of the ring-shaped bond, thereby forming a pore in the structure of the complex. That is, the complex forms a porous body.

  As a result of SEM observation of the precipitate, it was found that the precipitate has a shape that can be approximately approximated to a rectangular parallelepiped shape.

Furthermore, ruthenium terephthalate (II, III) boron tetrafluoride salt; [Ru ₂ (p-BDC) ₂ BF ₄ ] _n was synthesized.

Specifically, first, 40 ml of tetrahydrofuran was introduced into an eggplant flask having a capacity of 100 ml, and 0.1 g of Ru ₂ (CH ₃ COO) ₄ BF ₄ and 0.0592 g of p-BDCA were then added. This mixed solution was refluxed at 100 ° C. for 6 hours under an argon atmosphere.

  Next, after cooling to room temperature, the precipitate was collected on a sintered glass filter. The collected precipitate was washed with acetone and then with methanol, and further dried by vacuum drying for 2 hours.

The precipitate was subjected to structural analysis by FT-IR analysis, Raman spectrum analysis, DR-UV-Vis spectrum analysis, CHN elemental analysis, specific surface area pore size distribution measurement, and XPS analysis. The structure of [Ru ₂ (p-BDC) ₂ BF ₄ ] _n determined by the obtained results is schematically shown in FIG. Also in this case, the result of being a complex was obtained.

As shown in FIG. 6, this complex has Ru as a central metal and a structure in which one BF ₄ ion is coordinated per one structure in which p-BDC is coordinated to Ru. Has a two-dimensional chain complex. The two-dimensional chain complexes are stacked through diphenyl bonds by self-organization. As a result, this complex also has a three-dimensional structure.

  Also in this complex, the cavity 10 is formed at the center of the cyclic bond. From this, this complex is also defined as a porous body.

  In addition, as a result of performing SEM observation about the said deposit, this deposit was substantially spherical shape.

Furthermore, ruthenium terephthalate (II, III) bromide; [Ru ₂ (p-BDC) ₂ Br] _n was synthesized.

That is, first, 30 ml of a mixed solvent of methanol / water mixed at a volume ratio of 1: 1 is introduced into a 100 ml volumetric flask and then 0.05 g of Ru ₂ (CH ₃ COO) ₄ BF ₄ , 0 0.0296 g p-BDCA and 0.091 g NaBr were added. This mixed solution was refluxed at 100 ° C. for 6 hours under an argon atmosphere.

Thereafter, the same operation as in Example 5 was performed, and the collected precipitate was dried. Thereafter, the structure of the precipitate was analyzed based on the above. The structure of [Ru ₂ (p-BDC) ₂ Br] _{n based on} the analysis result is schematically shown in FIG.

As shown in FIG. 7, in this case, Ru is a central metal, and a two-dimensional chain having a coordinated bond in which structures in which p-BDC is coordinated to Ru are bonded via Br is a repeating unit. A complex. And self-organization takes place via the Br, and the two-dimensional chain complex is thereby laminated. That is, this [Ru ₂ (p-BDC) ₂ Br] _n complex also has a three-dimensionally developed three-dimensional structure.

  Also in this complex, the cavity 10 exists in the center of the cyclic bond. That is, this complex is also a porous body.

Furthermore, ruthenium terephthalate (II, III) hexafluorophosphate salt: [Ru ₂ (p-BDC) ₂ PF ₆ ] _n was synthesized.

In this case, first, 40 ml of tetrahydrofuran was introduced into an eggplant flask having a capacity of 100 ml, and then 0.05 g of Ru ₂ (CH ₃ COO) ₄ BF ₄ , 0.0296 g of p-BDCA and 0.216 g of NH ₄ PF _6. Was added. This mixed solution was refluxed at 100 ° C. for 6 hours under an argon atmosphere.

Thereafter, the same operation as in Examples 5 and 6 was performed, and the collected precipitate was dried. Thereafter, the structure of the precipitate was analyzed based on the above. A structure based on this analysis result is schematically shown in FIG. Also in this case, it was recognized that [Ru ₂ (p-BDC) ₂ PF ₆ ] _n formed a complex.

As understood from FIG. 8, this complex has a structure in which Ru is a central metal and a structure in which one PF ₆ ion is coordinated per structure in which p-BDC is coordinated to Ru. It has a two-dimensional chain complex. The two-dimensional chain complexes are stacked through diphenyl bonds by self-organization, and as a result, this complex also expands three-dimensionally to form a three-dimensional structure.

  Also in this complex, a cavity 10 is formed at the center of the cyclic bond. That is, this complex is also a porous body.

First, Ru (bpy) ₃ Cl ₂ as a photosensitizer, methyl viologen as an electron transfer material, and EDTA-2Na as a reducing agent were introduced into a 10 ml volumetric flask. Thereafter, pure water was introduced until the 10 ml index line of the volumetric flask was reached, and Ru (bpy) ₃ Cl ₂ , methyl viologen and EDTA-2Na were dissolved to obtain an aqueous solution. The introduction amounts were adjusted so that the concentrations of Ru (bpy) ₃ Cl ₂ , methyl viologen, and EDTA-2Na were 0.1 mmol / liter, 5 mmol / liter, and 150 mmol / liter, respectively. Thereafter, this aqueous solution was transferred to a Schlenk tube, and oxygen was removed from the aqueous solution by freeze deaeration.

  Next, the aqueous solution from which oxygen was removed was transferred to a reaction cell in a glove box. Here, in the reaction cell, the final products (photocatalysts) of Examples 1 to 7 obtained as described above are preliminarily accommodated in an amount of 0.01 mmol. A photocatalyst was added to the aqueous solution along with the liquid operation. This obtained the reaction liquid.

  Although the photocatalysts of Examples 1 and 2 were dissolved in the aqueous solution, the photocatalysts of Examples 3 to 7 were not dissolved in the aqueous solution. That is, the reaction liquid according to Examples 1 and 2 was an aqueous solution, while the reaction liquid according to Examples 3 to 7 was a mixed solution or a dispersion solution.

  The reaction cell containing the above reaction solution was attached to a closed system circulation device. Then, the vacuum pump which comprises this closed system circulation apparatus was energized, and the reaction liquid was deaerated. After degassing, argon was supplied from an argon cylinder through a standard sample reservoir so that the pressure in the closed system circulation device was 100 Torr.

  Next, while vigorously stirring the reaction solution with a magnetic stirrer, visible light having a wavelength longer than 420 nm was irradiated from the outside of the reaction cell. A 500 W xenon lamp was used as the light source.

  It was recognized that gas was generated from the reaction solution with this light irradiation. This gas was identified and quantified by gas chromatography (column carrier = molecular sieve 5A, carrier gas = argon) constituting a closed system circulation apparatus. As a result, it was found that the gas was hydrogen. From this, it is clear that the hydrogen generation reaction in which water as a solvent of the reaction solution is decomposed to generate hydrogen molecules is in progress.

  In addition, the quantitative result by gas chromatography is shown in FIG. 9 as the amount of hydrogen generated every hour after the start of light irradiation. From this result, it can be understood that the reaction products of Examples 1 to 7 function as a photocatalyst.

  Separately from this, the turnover number (TON) with respect to the amount of hydrogen generated 4 hours after the light irradiation was determined. The results are shown in FIG. Note that TON is well known as one of the performance indicators of a photocatalyst, and the larger the value, the higher the performance as a photocatalyst.

  As can be understood from FIG. 10, the reaction products obtained in Examples 1 to 7 all exhibit sufficiently high TON. From this, it is clear that these reaction products function as excellent photocatalysts.

  In particular, the reaction products of Examples 3-7 show a particularly high TON. The reason for this is that these reaction products form a three-dimensional structure, and are porous complexes in which cavities 10 are formed in the structure. Therefore, the porous property contributes to the activity as a photocatalyst. This is presumed to be due to this.

  Moreover, the photocatalysts of Examples 3 to 7 are insoluble in water which is a solvent for the reaction solution. For this reason, if it isolate | separates from a reaction liquid after performing hydrogen production reaction, it can also be reused as a photocatalyst.

For comparison, a hydrogen generation reaction was allowed to proceed in the same manner as described above except that anatase TiO ₂ was used. However, in this case, the amount of hydrogen generated 4 hours after the start of light irradiation was only about 1/14 compared to Example 3.

  The quantum yield was determined for each reaction product of Examples 3, 4, and 5. The quantum yield is also well known as one of the performance indexes of the photocatalyst, and in this case, the quantum yield indicates the rate at which the light energy incident on the photocatalyst is consumed in the hydrogen generation reaction. Therefore, the larger the quantum yield value, the higher the performance as a photocatalyst. Incidentally, most of this type of photocatalyst has a quantum yield of about 0.1%, and the photocatalyst described in Non-Patent Document 1 is 2%.

  When determining the quantum yield, the reaction cell attached to the above closed system circulation device is provided with a filter on a 500 W xenon lamp, irradiated with 450 nm single wavelength light for 1 hour, and hydrogen generated at this time. Was quantified, and the number of generated hydrogen molecules was determined. For this determination, gas chromatography was used as described above.

  Meanwhile, the output of the xenon lamp was converted to the number of photons. For this conversion, a photodiode PM3 (trade name) manufactured by Coherent was used.

From the number of hydrogen molecules and the number of photons determined as described above, the quantum yield (%) was determined according to the following equation (1).
Quantum yield = [(number of generated hydrogen molecules × 2) / number of photons] × 100 (1)

  As a result, the quantum yields of the reaction products of Examples 3, 4, and 5 were 4.82%, 0.711%, and 2.36%, respectively. That is, a quantum yield significantly higher than that of a general photocatalyst was obtained.

  In particular, each reaction product of Examples 3 and 5 shows a quantum yield exceeding the photocatalyst described in Non-Patent Document 1. From this, it can be said that these reaction products function as an excellent photocatalyst.

10 ... Cavity

Claims (2)

A photocatalyst that is added to water together with a sacrificial electron donor, a photosensitizer, and an electron transfer material to promote a hydrogen generation reaction when the water is irradiated with light,
Terephthalic acid ruthenium chloride, terephthalic acid ruthenium tetrafluoroborate salt, terephthalic acid ruthenium hexafluorophosphate, photocatalyst, characterized in that it consists of one selected from the group of terephthalic acid ruthenium bromide. In the photocatalyst of claim 1, terephthalic acid ruthenium chloride, terephthalic acid ruthenium tetrafluoroborate salt, a photocatalyst, wherein the terephthalic acid ruthenium hexafluorophosphate, terephthalic acid ruthenium bromide is complex.

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