JP6567278B2 - Photocatalyst production method, hydrogen generation method, and photocatalyst for hydrogen generation - Google Patents

Description

  The present invention relates to a photocatalyst, a production method thereof, and a hydrogen generation method using the photocatalyst. In particular, the present invention relates to a photocatalyst capable of generating hydrogen by decomposing water by irradiation with visible light, a method for producing the photocatalyst, and a hydrogen generation method using the photocatalyst.

  In recent years, there has been a growing interest in sustainable energy systems. This system needs to be driven with energy that is inexpensive, can be supplied in large quantities and easily. Hydrogen energy may be easily supplied in large quantities from water at low cost, and is one of the energies that can drive the system (Non-Patent Documents 1 to 5). One method for supplying hydrogen energy is to use a photocatalyst capable of generating hydrogen by decomposing water by visible light irradiation.

Such photocatalysts include niobium oxides such as SrTiO ₃ , HPb ₂ Nb ₃ O ₁₀ or Sn ₂ Nb ₂ O ₇ to which any of Ta, Rh and Ni is added, and transition metal oxynitrides such as TaON. And lanthanoid metal oxynitrides such as LaTiO ₂ N.
However, Pb is toxic, and Rh, Nb, Ta, La, etc. have low annual production, so none of these materials are suitable as photocatalysts.

Tong, H.C. Ouyang, S .; Bi, Y .; Umezawa, N .; Oshikiri, M .; Ye, J .; , Adv. Mater. 2012, 24, 229-251. Hoffmann, M.M. R. Martin, S .; T.A. Choi, W .; Y. Bahnemann, D .; W. , Chem. Rev. 1995, 95, 69-96. Osterloh, F.A. E. , Chem. Mater. 2008, 20, 35-54. Chen, X .; B. Shen, S .; H. Guo, L .; J. et al. Mao, S .; S. , Chem Rev. 2010, 110, 6503-6570. Kudo, A .; Miseki, Y .; , Chem. Soc. Rev. 2009, 38, 253-278. Nature 1967, 215, 955-956. White, T .; A. Moreno, M .; S. and Midgley, P.A. A. Z. Kristallogr. 2010, 225, 56-66. Seko, A .; Togo, A .; Oba, F .; and Tanaka, I .; Phys. Rev. Lett. 2008, 100, 045702. Berengue, O.M. M.M. Simon, R .; A. Chiquito, A .; J. et al. Dalmaschio, C .; J. et al. Leite, E .; R. Guerreiro, H .; A. and Guimarnaes, F.A. E. G. J. et al. Appl. Phys. 2010, 107, 033717. He, Y. Li, D .; Chen, J .; Yu, S .; Xian, J .; Zheng, X .; and Wang P.M. RSC Adv. , 2014, 4, 1266-1269.

  An object of the present invention is to provide a photocatalyst that is mainly composed of a material that is not toxic and has a high annual output, and that can generate hydrogen by decomposing water by irradiation with visible light.

In view of the above circumstances, material search was conducted and attention was focused on Sn and its oxide which are non-toxic and have a high annual production. Sn ₃ O ₄ , first reported as a substance in “Nature” in 1967, is a material such as a crystal structure (Non-Patent Documents 6 to 8), a photoelectron characteristic (Non-Patent Document 9), and a fading characteristic (Non-Patent Document 10). Although there were reports on properties, there were no reports on photocatalytic properties. As a result of synthesizing high-purity Sn ₃ O ₄ nanocrystals by hydrothermal synthesis and investigating their photocatalytic properties, it is possible to generate a sufficient amount of hydrogen from an aqueous alcohol solution by irradiation with visible light. And the present invention has been completed by finding that it can be used as a hydrogen energy source for a sustainable energy system.
The present invention has the following configuration.

(1) A photocatalyst characterized by being represented by the chemical formula Sn ₃ O ₄ , wherein two or more Sn having different valences are present in the crystal.
(2) The photocatalyst according to (1), wherein a structure composed of two Sn ²⁺ and Sn ⁴⁺ O ₆ octahedrons is regularly arranged.

(3) Dispersing raw materials and a surfactant in water to prepare a dispersion, adding an aqueous NaOH solution to the dispersion to prepare an alkaline dispersion, and heating the alkaline dispersion And a step of hydrothermally synthesizing the photocatalyst.
(4) The method for producing a photocatalyst according to (3), wherein the raw material is SnCl ₂ · 2H ₂ O.
(5) The method for producing a photocatalyst according to (3), wherein the surfactant is sodium citrate (Na ₃ C ₆ H ₅ O ₇ · H ₂ O).

(6) The method for producing a photocatalyst according to (3), wherein the water is ultrapure water.
(7) The method for producing a photocatalyst according to (3), wherein the heating temperature of the alkaline dispersion is 150 ° C. or higher and 200 ° C. or lower.
(8) A step of dispersing and stirring the photocatalyst described in (1) or (2) in an aqueous alcohol solution, and adding an H ₂ PtCl ₆ solution, a Pt promoter (also referred to as a cocatalyst) is applied to the photocatalyst. A hydrogen generation method using a photocatalyst, comprising: a step of depositing; and a step of generating hydrogen by irradiating light to an alcohol aqueous solution in which the photocatalyst on which the Pt promoter has been photodeposited is dispersed.

The photocatalyst of the present invention is a crystal represented by the chemical formula Sn ₃ O ₄ , and since there are two or more Sn having different valences in the crystal, Sn having different valences can be arranged adjacent to each other, Between the band gap capable of absorbing visible light and the energy value of the valence band and the conduction band, there can be a reference potential for efficiently changing H ⁺ in the aqueous alcohol solution to H _2. A photocatalyst capable of generating a large amount of hydrogen from an aqueous solution can be obtained. In addition, Sn, which is a non-toxic, high annual production amount and low-priced material, is used as a main component, so that a photocatalyst that is safe, inexpensive, and can be supplied in large quantities can be provided.

The method for producing a photocatalyst of the present invention includes a step of dispersing a raw material and a surfactant in water to prepare a dispersion, a step of adding an aqueous NaOH solution to the dispersion to prepare an alkaline dispersion, A step of hydrothermally synthesizing the photocatalyst by heating the alkaline dispersion, and a band gap capable of absorbing visible light based on Sn, which is a non-toxic material with high annual production, A photocatalyst capable of generating a large amount of hydrogen from an aqueous alcohol solution by irradiation with visible light can exist between the energy values of the valence band and the conduction band so that a reference potential for efficiently changing H ⁺ in the aqueous alcohol solution to H ₂ can be present. Can be manufactured easily and in large quantities.

The hydrogen generation method using the photocatalyst of the present invention includes a step of dispersing and stirring the photocatalyst described above in an alcohol aqueous solution, a step of adding a H ₂ PtCl ₆ solution to photoprecipitate a Pt promoter on the photocatalyst, And a step of generating hydrogen by irradiating the aqueous alcohol solution in which the photocatalyst having the Pt promoter photodeposited is dispersed to generate light, so that a large amount of hydrogen can be generated from the aqueous alcohol solution under visible light irradiation. it can.

It is the top view (a) and side view (b) which show an example of the photocatalyst which is embodiment of this invention. It is the structural model top view (a) and structural model side view (b) which show an example of the photocatalyst which is embodiment of this invention. Is a band diagram of the Sn ₃ O ₄ is a photocatalyst according to an embodiment of the present invention. For comparison, band diagrams of TiO ₂ , SnO ₂ , and SnO are also shown. Is a photograph showing the microscopic observation results of the photocatalytic _Sn 3 _{O 4.} Is a graph showing the EDS results of measurement of the photocatalytic _Sn 3 _{O 4.} It is a graph showing the measurement results of the pXRD and HX-PES photocatalyst _Sn 3 _{O 4.} The absorption spectrum of the photocatalyst _Sn 3 _{O 4.} It is the schematic of a photocatalyst characteristic measuring apparatus. It is a graph showing the results of measuring the amount of hydrogen generation photocatalyst Sn ₃ O _4. A pXRD profile photocatalyst _Sn 3 _{O 4} before and after irradiation and the hydrogen generation experiment 96 hours. Is a graph showing the results of the density of states by theoretical ^{calculation, Sn 2+ O (a),} Sn 4+ O 2 (b), a photocatalyst _Sn 3 _O 4 (c), of the photocatalytic _Sn 3 _{O 4} of ^{Sn 2+} and ^{Sn 4+} state It is the graph (d) which decomposed | disassembled the density. It is a graph showing the results of measuring the amount of hydrogen generation photocatalyst Sn ₃ O _4.

(photocatalyst)
First, the photocatalyst that is an embodiment of the present invention will be described.
FIG. 1 is a plan view (a) and a side view (b) showing an example of a photocatalyst according to an embodiment of the present invention.
As shown in FIGS. 1A and 1B, a photocatalyst 11 according to an embodiment of the present invention is a plate-like body having a substantially polygonal shape in plan view. The plate-like body is formed with a layered structure. Each face is a highly crystalline {100} face.
Diameter _{d 11} of the photocatalyst 11 is less than 1μm than 100 nm. The thickness _{t 11} is less than 100 nm. Since it is a nano-order crystal, it is a nanocrystal.

FIG. 2 is a structural model plan view (a) and a structural model side view (b) showing an example of a photocatalyst according to an embodiment of the present invention.
The photocatalyst 11 is a crystal represented by the chemical formula Sn ₃ O ₄ . As shown in FIG. 2, the photocatalyst 11 has a structure in which two Sn ²⁺ and Sn ⁴⁺ O ₆ octahedron (Octahedra) are regularly arranged, and (Sn ²⁺ ) ₂ (Sn ⁴⁺ ) O ₄ It is a crystal of the mixed valence Sn oxide represented.

FIG. 3 is a band diagram of Sn ₃ O ₄ which is a photocatalyst according to an embodiment of the present invention. For comparison, band diagrams of TiO ₂ , SnO ₂ , and SnO are also shown.
As shown in FIG. 3, Sn ₃ O ₄ which is a photocatalyst according to an embodiment of the present invention has an energy gap (band gap) between a valence band and a conduction band of 2. There is a reference potential that changes H ⁺ to H ₂ between the energy values of both bands. When the band gap is 2.5 eV, it is possible to absorb blue light having a wavelength shorter than about 500 nm and excite valence band electrons to the conduction band. Further, since the reference potential exists between the energy values of both bands, the excited electrons can be efficiently changed to H ₂ by reducing H ⁺ in the aqueous alcohol solution.

On the other hand, since the band gap of TiO ₂ is 3.4 eV, the valence band electrons can hardly be excited to the conduction band with visible light. Even if the electrons can be excited, the reference potential is almost the same as the energy value of the valence band. Therefore, even when energy is released, H ⁺ in the alcohol aqueous solution can hardly be effectively changed to H ₂ .
SnO ₂ is expressed as Sn ⁴⁺ O ₂ , but has a band gap of 3.1 eV, and therefore, visible light cannot efficiently excite electrons in the valence band to the conduction band. Even if electrons can be excited, since the reference potential is higher than the energy value of the valence band, even if energy is released, H ⁺ in the water molecule cannot be changed to H ₂ .
SnO can also be expressed as Sn ²⁺ O. However, since the position of the valence band is high and it is inappropriate for the oxidation of alcohol, H ⁺ in the water molecule cannot be changed to H ₂ .

(Photocatalyst production method)
Next, the manufacturing method of the photocatalyst which is embodiment of this invention is demonstrated.
The method for producing a photocatalyst that is an embodiment of the present invention includes a dispersion preparation step S1, an alkaline dispersion preparation step S2, and a hydrothermal synthesis step S3.

(Dispersion preparation step S1)
In this step, a raw material and a surfactant are dispersed in water to prepare a dispersion.
Examples of the raw material include SnCl ₂ .2H ₂ O. Further, as the surfactant, it may be mentioned sodium citrate _{(Na 3 C 6 H 5 O} 7 · H 2 O). By adding the surfactant, the raw material can be more uniformly dispersed.
It is preferable that the water is ultrapure water. By reducing the impurities, the purity of the nanocrystal can be improved.

(Alkaline dispersion preparation step S2)
In this step, an aqueous NaOH solution is added to the dispersion to prepare an alkaline dispersion. At this time, the NaOH concentration is preferably 0.2 M or less.

(Hydrothermal synthesis step S3)
In this step, the alkaline dispersion is heated to hydrothermally synthesize the photocatalyst.
The heating temperature of the alkaline dispersion is preferably 150 ° C. or higher and 200 ° C. or lower, and more preferably 170 ° C. or higher and 190 ° C. or lower. Moreover, it is preferable to hold | maintain at the said heating temperature for 5 hours or more and 19 hours or less, and it is more preferable to hold | maintain for 10 hours or more and 14 hours or less. Thereby, the production | generation efficiency of the nanocrystal by hydrothermal synthesis can be improved.
Through the above steps, the photocatalyst 11 according to the embodiment of the present invention can be easily produced in a short time and in large quantities.

(Method of generating hydrogen using photocatalyst)
Next, a hydrogen generation method using a photocatalyst that is an embodiment of the present invention will be described.
The method for producing a photocatalyst that is an embodiment of the present invention includes a photocatalyst dispersion / stirring step S11, a Pt cocatalyst photoprecipitation step S12, and a hydrogen generation step S13.
In the photocatalyst dispersion / stirring step S11, the photocatalyst 11 is dispersed / stirred in an alcohol aqueous solution. Examples of the alcohol include methanol and ethanol.
In the Pt cocatalyst photodeposition step S12, an H ₂ PtCl ₆ solution is added to photoprecipitate the Pt cocatalyst on the photocatalyst. Pt is formed in an island shape on the surface of the particulate photocatalyst.
In the hydrogen generation step S13, hydrogen is generated by irradiating the aqueous alcohol solution in which the photocatalyst on which the Pt promoter has been photodeposited is dispersed. The aqueous alcohol solution in which the photocatalyst on which the Pt cocatalyst is photodeposited is dispersed or in the form of a colloid.
By having the above structure, a large amount of hydrogen can be generated from an aqueous alcohol solution by irradiation with visible light.

The photocatalyst 11 according to an embodiment of the present invention is a crystal represented by Sn ₃ O ₄ and has two or more Sn having different valences in the crystal, and therefore Sn having different valences are arranged adjacent to each other. And a reference potential for efficiently converting H ⁺ in the aqueous alcohol solution into H ₂ can exist between the band gap capable of absorbing visible light and the energy values of the valence band and the conduction band. It can be set as the photocatalyst which can generate | occur | produce a large amount of hydrogen from alcohol aqueous solution by light irradiation. In addition, Sn, which is a non-toxic, high annual production amount and low-priced material, is used as a main component, so that a photocatalyst that is safe, inexpensive, and can be supplied in large quantities can be provided.

Since the photocatalyst 11 according to the embodiment of the present invention has a structure in which structures composed of two Sn ²⁺ and Sn ⁴⁺ O ₆ octahedrons are regularly arranged, Sn having different valences can be arranged adjacently, Between the band gap capable of absorbing visible light and the energy value of the valence band and the conduction band, there can be a reference potential for efficiently changing H ⁺ in the aqueous alcohol solution to H _2. A photocatalyst capable of generating a large amount of hydrogen from an aqueous solution can be obtained.

The method for producing a photocatalyst 11 according to an embodiment of the present invention includes a step of dispersing a raw material and a surfactant in water to prepare a dispersion, and an aqueous NaOH solution is added to the dispersion to prepare an alkaline dispersion. And the step of heating the alkaline dispersion and hydrothermally synthesizing the photocatalyst, it is composed of Sn, which is a non-toxic material with high annual production, and can absorb visible light. A reference potential for efficiently changing H ⁺ in alcohol aqueous solution to H ₂ between the energy value of valence band and valence band and conduction band, and a large amount of hydrogen from alcohol aqueous solution by visible light irradiation Can be produced easily and in large quantities.

  The method for producing a photocatalyst 11 according to an embodiment of the present invention includes a step of dispersing a raw material and a surfactant in water to prepare a dispersion, and an aqueous NaOH solution is added to the dispersion to prepare an alkaline dispersion. And a step of hydrothermally synthesizing the photocatalyst by heating the alkaline dispersion, so that the main component is Sn, which is a non-toxic material with a high annual production, and alcohol is irradiated with visible light. A photocatalyst capable of generating hydrogen from an aqueous solution can be produced easily and in large quantities.

The production method of the photocatalyst 11 according to an embodiment of the present invention is composed of SnCl ₂ .2H ₂ O as a raw material, and therefore has no toxicity, high annual production, and low-cost material Sn as a main component, A photocatalyst that is safe, inexpensive, and can be supplied in large quantities can be produced efficiently.

The method for producing the photocatalyst 11 according to the embodiment of the present invention has a configuration in which the surfactant is sodium citrate (Na ₃ C ₆ H ₅ O ₇ · H ₂ O), and thus has no toxicity and high annual production. Therefore, it is possible to efficiently produce a photocatalyst that is based on Sn, which is a low-priced material, and that can be supplied in large quantities safely and inexpensively.

  The method for producing the photocatalyst 11 according to an embodiment of the present invention is composed of the ultra pure water, so that it is not toxic, has a high annual production, and is based on Sn, which is a low-cost material, and is safe. An inexpensive photocatalyst that can be supplied in large quantities can be produced with high purity.

  The method for producing the photocatalyst 11 according to an embodiment of the present invention is a composition in which the heating temperature of the alkaline dispersion is 150 ° C. or higher and 200 ° C. or lower, and therefore is non-toxic, has a high annual output, and is an inexpensive material. It is possible to efficiently produce a photocatalyst that is safe, inexpensive, and can be supplied in large quantities.

The hydrogen generation method using a photocatalyst according to an embodiment of the present invention includes a step S11 of dispersing and stirring the photocatalyst 11 in an alcohol aqueous solution, and a step of adding a H ₂ PtCl ₆ solution to photoprecipitate the Pt promoter on the photocatalyst. S12 and the step S13 of generating hydrogen by irradiating the aqueous alcohol solution in which the photocatalyst having the Pt promoter photo-deposited is dispersed to generate hydrogen, so that a large amount of hydrogen is generated from the aqueous alcohol solution by visible light irradiation. Can do.

  The photocatalyst which is an embodiment of the present invention, a method for producing the photocatalyst, and a hydrogen generation method using the photocatalyst are not limited to the above-described embodiment, and are implemented with various modifications within the scope of the technical idea of the present invention. be able to. Specific examples of this embodiment are shown in the following examples. However, the present invention is not limited to these examples.

Example 1
(Hydrothermal synthesis of photocatalyst Sn ₃ O ₄ )
First, SnCl ₂ · 2H ₂ O (0.90 g, 4.0 mmol) was prepared as a raw material, and sodium citrate (Na ₃ C ₆ H ₅ O ₇ · H ₂ O) (0.294 g, 10 mmol) was prepared as a surfactant. These were dispersed in 10 ml of ultrapure water (Milli-Q water) and then stirred and uniformly dispersed to prepare a dispersion.

  Next, 10 ml of 0.2 M NaOH aqueous solution was added to the dispersion and stirred to prepare an alkaline dispersion.

Next, the alkaline dispersion was transferred to a 40 ml Teflon-lined stainless steel autoclave (autoclave).
Next, the autoclave was heated at 180 ° C. for 12 hours in an electric furnace and then returned to room temperature.
Next, after a precipitate was obtained by centrifugation, the precipitate was washed several times with ultrapure water (Milli-Q water) and acetone.
Through the above process, was obtained photocatalyst _Sn 3 _{O 4} (Example 1 Samples).

(Comparative Examples 1 and 2)
SnO was prepared as a comparative example 1 sample.
Moreover, SnO ₂ was prepared as a comparative example 2 sample.

(Characterization of photocatalyst Sn ₃ O ₄ )
First, the photocatalyst Sn ₃ O ₄ (Example 1 sample) was observed with a microscope using SEM (Scanning electron microscope, manufactured by Hitachi) and TEM (Transmission electron microscope, JEOL 2100-F).
A SEM equipped with FIB (Focused ion beam, manufactured by SII Nanotechnology Inc.) was used, and a TEM equipped with EDS (Energy-dispersion spectroscopy) was used.
A TEM sample was prepared by suspending a methanol suspension containing a photocatalyst Sn ₃ O ₄ (Example 1 sample) on a copper mesh and then drying the suspension.

FIG. 4 is a photograph showing the microscopic observation results of the photocatalyst Sn ₃ O ₄ , and includes an SEM image (a), an enlarged SEM image (b), a TEM image (c), an SAED pattern (c insertion photograph), and an enlarged TEM image ( d) A structural model (d inset).
As shown in FIGS. 4A and 4B, a plurality of plate-like materials having a substantially polygonal shape in plan view were obtained. The size was approximately 100 nm or more and less than 1 μm.

FIG. 4 (c inset photo) is a selected-area electron diffraction (SAED) pattern obtained by irradiating the central piece of material in FIG. 4C with a beam. 111, 002, [ 110] was obtained.
As shown in FIG. 4D, a regularly arranged crystal structure could be observed. From this crystal structure, it was found that d (111) was 0.33 nm or 0.35 nm. From this, a structural model (FIG. 4d inset) was obtained.

Next, EDS measurement was performed using EDS provided in the TEM.
FIG. 5 is a graph showing the EDS measurement result of the photocatalyst Sn ₃ O ₄ . From this, it was found that Sn: O = 3: 4.

Next, pXRD and HX-PES were measured.
FIG. 6 is a graph showing the measurement results of pXRD and HX-PES of the photocatalyst Sn ₃ O ₄ , and is a graph (a) showing the pXRD measurement results and a graph (b) showing the HX-PES measurement results. FIG. 6A shows a known pXRD pattern (calculated value), and FIG. 6B also shows SnO and SnO ₂ measurement results.
As shown in FIG. 6A, the peak position of the pXRD pattern almost coincided with the pXRD pattern (calculated value).
As shown in FIG. 6B, the Sn oxide d-orbital binding energy value was almost the same in the Sn oxide, but the SnO d-orbital energy value shifted to a lower energy side.

Next, the absorption spectrum was measured.
FIG. 7 is an absorption spectrum of the photocatalyst Sn ₃ O ₄ . For comparison, the absorption spectra of SnO ₂ and SnO are also shown. Further, in the inset, the spectrum with the horizontal axis as energy for the photocatalysts Sn ₃ O ₄ and SnO ₂ is shown.
The photocatalyst Sn ₃ O ₄ had an absorption peak in the vicinity of 390 nm, and absorption in which the field expanded to around 510 nm was observed. In fact, the photocatalyst Sn ₃ O ₄ is orange and absorbs blue light.
On the other hand, SnO ₂ has an absorption peak at 360 nm or less and hardly absorbs visible light at 400 nm or more. In addition, SnO exhibited uniform absorption over the entire range from ultraviolet to visible light, but the absorption intensity was lower than that of the photocatalyst Sn ₃ O ₄ .

(Photocatalytic property evaluation 1 of photocatalyst Sn ₃ O ₄ )
Next, using photocatalyst Sn ₃ O ₄ , hydrogen ions in the methanol aqueous solution were reduced to generate H _2, and the amount of H ₂ generated was measured to evaluate the photocatalytic characteristics.
FIG. 8 is a schematic view of a photocatalytic property measuring apparatus.
As shown in FIG. 8, this apparatus includes a Pyrex cell storing water in which a photocatalyst is dispersed, a xenon lamp arranged on one side of the container, and a light arranged between the xenon lamp and the container. The filter includes a filter, a rotary pump connected to the Pyrex cell through a pipe, and a gas chromatograph connected to the Pyrex cell through another pipe.

The inside of the apparatus is a gas-closed circulation system. The inside of the Pyrex cell can be depressurized by a rotary pump, and the amount of hydrogen generated in the Pyrex cell can be measured by a gas chromatograph.
In addition, the photocatalyst in methanol water in the Pyrex cell is irradiated with visible light emitted from a xenon lamp and made more than 400 nm with an optical filter, and hydrogen ions in the methanol water are reduced on the surface of the photocatalyst to generate hydrogen. Is possible.

Specifically, first, photocatalyst Sn ₃ O ₄ (0.3 g) was added to a CH ₃ OH aqueous solution (distilled water 220 mL + CH ₃ OH 50 mL) in a predetermined amount of Pyrex cell together with a predetermined amount of H ₂ PtCl ₆ solution. Then, it stirred with the magnetic stirring bar.
Next, using a Xe arc lamp light source (300 W: no filter), the above aqueous solution was irradiated with light to photo-deposit the Pt promoter 0.5 wt% on the surface of the photocatalyst Sn ₃ O ₄ . . After Pt cocatalyst photodeposition, visible light irradiation was performed with a Xe arc lamp light source equipped with an L42 cutoff filter (λ> 400 nm), and the amount of H ₂ generated from the aqueous solution was measured as a function of time.
The amount of H ₂ generation was measured using a gas chromatograph (GC-8A, manufactured by Shimadzu) equipped with a thermal conductivity detector (TCD).

FIG. 9 is a graph showing the measurement results of the hydrogen generation amount of the photocatalyst Sn ₃ O ₄ .
This is a result of measuring the amount of hydrogen generated during the period of four light repetitions after repeating light irradiation for 24 hours and then stopping light irradiation and depressurizing the inside of the container with a rotary pump.
With photocatalyst Sn ₃ O ₄ , when light irradiation was continued, hydrogen was generated at a considerably high rate in the initial stage, and after 10 hours, the ratio was almost constant until 96 hours.
On the other hand, SnO ₂ and SnO ₂ could hardly generate hydrogen.

Next, the pXRD profile of the photocatalyst Sn ₃ O ₄ after 96 hours of light irradiation was measured.
FIG. 10 is a pXRD profile of the photocatalyst Sn ₃ O ₄ before light irradiation and 96 hours after the hydrogen generation experiment. The bar graph represents the XRD peak position and intensity obtained from the database. The pXRD profile of the photocatalyst Sn ₃ O ₄ before light irradiation and a known pXRD pattern (calculated value) are also shown.
The pXRD profile of the photocatalyst Sn ₃ O ₄ hardly changed before and after the light irradiation.

(Theoretical calculation)
Next, theoretical calculation based on work function and band gap was performed.
FIG. 11 is a graph showing the result of the density of states by theoretical calculation. Sn ²⁺ O (a), Sn ⁴⁺ O ₂ (b), photocatalyst Sn ₃ O ₄ (c), Sn ^{2+ of} photocatalyst Sn ₃ O ₄ and It is the graph (d) which decomposed ^| disassembled the density of states of Sn4 ⁺ .
As shown in FIGS. 11C and 11D, in Sn ₃ O ₄ , there are a valence band caused by oxygen orbitals of −2 eV or less and a conduction band caused by tin orbitals of 2 eV or more. Meanwhile, another occupied band exists at −2 to 0 eV. This band is due to the coexistence of Sn ²⁺ and Sn ⁴⁺ and forms the top of the valence band. The band from the highest occupied band to the conduction band becomes a band gap, which absorbs visible photons and excites the electrons in the valence band to the conduction band. In addition, a band structure having a reference potential for reducing water to generate hydrogen between the valence band and the conduction band is formed.

On the other hand, as shown in FIG. 11A, in Sn ²⁺ O, a plurality of energy bands exist widely and the band gap is very small.
Further, as shown in FIG. 11B, the density of the conduction band is very small in Sn ⁴⁺ O ₂ .

(Photocatalytic property evaluation 2 of photocatalyst Sn ₃ O ₄ )
Next, the photocatalyst Sn ₃ O ₄ was used to reduce hydrogen ions in the aqueous alcohol solution in the same manner as in “Photocatalytic property evaluation 1 of photocatalyst Sn ₃ O ₄ ” except that an ethanol aqueous solution was used instead of the methanol aqueous solution. Then, H ₂ was generated and the amount of H ₂ generated was measured to evaluate the photocatalytic characteristics.

Specifically, first, photocatalyst Sn ₃ O ₄ (0.3 g) was dispersed in a C ₂ H ₅ OH aqueous solution (distilled water 220 mL + C ₂ H ₅ OH 50 mL) in a Pyrex cell, and stirred with a magnetic stirring bar.
Next, a predetermined amount of H ₂ PtCl ₆ solution was added to the reaction solution, and 0.5 wt% of Pt promoter was photo-deposited on the photocatalyst Sn ₃ O ₄ .
Next, light was irradiated to generate hydrogen, and the amount of hydrogen generated was measured.

FIG. 12 is a graph showing the measurement results of the hydrogen generation amount of the photocatalyst Sn ₃ O ₄ .
Light irradiation was continued for 6 hours, and the amount of hydrogen generated during that time was measured every hour.
After 6 hours, light irradiation was stopped and the inside of the container was depressurized with a rotary pump.
In FIG. 12, the result of the methanol aqueous solution of “photocatalytic property evaluation 1 of photocatalyst Sn ₃ O ₄ ” is also shown. Compared to the case of using an aqueous methanol solution, the amount of hydrogen generation per unit time (hydrogen generation efficiency) was slightly decreased in the case of using an aqueous ethanol solution, but almost the same efficiency was obtained.
In this photocatalyst, an occupied Sn band resulting from the coexistence of Sn ²⁺ and Sn ⁴⁺ is formed between the valence band and the conduction band, and visible photons are absorbed from this band through the band gap. Thus, whether the aqueous methanol solution or the aqueous ethanol solution is used, the occupied Sn band electrons can be excited to the conduction band at a substantially similar rate, and H ⁺ is reduced by this excited electron at approximately the same rate. Inferred that hydrogen could be generated.

  When the alcohol in the solution was consumed, the photocatalytic reaction stopped, and if water was decomposed, hydrogen: oxygen should come out at 2: 1, but in this reaction only hydrogen was present. Therefore, it was considered that the result of this experiment should not be related to water splitting but should be positioned as "hydrogen generation from alcohol aqueous solution".

  The photocatalyst of the present invention relates to a photocatalyst that is mainly composed of Sn, which is a non-toxic material and has a high annual output, and can generate hydrogen from an alcohol aqueous solution by visible light irradiation. The photocatalyst is only irradiated with visible light. Therefore, hydrogen can be generated easily and in large quantities from an aqueous alcohol solution, and hydrogen energy can be stably supplied, so there is a possibility that it can be put into practical use in a sustainable energy system. It can be used in the equipment and equipment industries.

11 ... photocatalyst, d _{11 ...} diameter, t _{11 ...} thickness.

Claims (8)

And SnCl ₂ · _{2H 2} O and a surfactant dispersed in water, preparing a dispersion liquid,
Adding an aqueous NaOH solution to the dispersion to prepare an alkaline dispersion;
And heating the alkaline dispersion, a photocatalyst possess a step of hydrothermal synthesis, wherein the photocatalyst is a represented by crystals by a chemical formula Sn ₃ O _4, different Sn is valences in the crystal A method for producing a photocatalyst, which is a photocatalyst present in two or more . The method for producing a photocatalyst according to claim 1, wherein the photocatalyst is formed by regularly arranging a structure composed of two Sn ²⁺ and Sn ⁴⁺ O ₆ octahedrons . Method for producing a photocatalyst according to claim 1 or 2, wherein the surfactant is sodium citrate _{(Na 3 C 6 H 5 O} 7 · H 2 O). The method for producing a photocatalyst according to any one of claims 1 to 3 , wherein the water is ultrapure water. The method for producing a photocatalyst according to any one of claims 1 to 4, wherein the heating temperature of the alkaline dispersion is 150 ° C or higher and 200 ° C or lower. Dispersing and stirring the photocatalyst produced by the method for producing a photocatalyst according to any one of claims 1 to 5 in an aqueous alcohol solution;
Adding a H ₂ PtCl ₆ solution to photoprecipitate a Pt promoter on the photocatalyst;
And a step of generating hydrogen by irradiating light to an aqueous alcohol solution in which the photocatalyst having the Pt promoter photodeposited is dispersed, to generate hydrogen using the photocatalyst. Chemical formula Sn ₃ O ₄ A photocatalyst for hydrogen generation, wherein two or more Sn having different valences exist in the crystal. 2 Sn ²⁺ And Sn ⁴⁺ O ₆ The photocatalyst for hydrogen generation according to claim 7, wherein the structure composed of octahedrons is regularly arranged.