JP6578596B2 - Method for producing metal (X) -doped bismuth vanadate and metal (X) -doped bismuth vanadate - Google Patents

Description

  The present invention relates to a method for producing metal (X) -doped bismuth vanadate and metal (X) -doped bismuth vanadate.

  As one of the hydrogen production technologies, photocatalytic technology that uses solar energy to decompose water to produce hydrogen has attracted attention. Since this technology is a clean and sustainable hydrogen production technology that does not depend on fossil resources, it is very significant in terms of energy and environmental issues. In order to use solar energy in a wide wavelength range, it is important to develop a material that exhibits photocatalysis by absorbing visible light that occupies about half of the solar energy.

Bismuth vanadate (hereinafter sometimes abbreviated as “BiVO ₄ ”) in the monolite phase of the celite structure (hereinafter sometimes abbreviated as “sm phase”) absorbs solar energy up to 520 nm. Known as a possible photocatalyst. For example, a water decomposition reaction under pseudo-sunlight irradiation using a Z-scheme type photocatalyst combining Rh-doped strontium titanate (SrTiO ₃ : Rh) and sm phase BiVO ₄ has been reported (Non-Patent Document). 1). In this Z-scheme type photocatalyst, SrTiO ₃ : Rh plays a role of hydrogen generation, and sm phase BiVO ₄ plays a role of oxygen generation. In order to improve the water splitting reaction rate, the high performance of sm phase BiVO ₄ Is necessary.

As one of high-performance techniques for sm phase BiVO _4, a high-performance technique using metal doping is known (Non-patent Document 2). Here, the metal dope is a state where the metal is in a single ion state and exists in the lattice points or between the lattices of the BiVO ₄ crystal, or a metal compound such as a metal oxide is included in the inter-lattice of the BiVO ₄ crystal or other gaps. Mo, W, etc. are known as a kind of metal. The sm-phase BiVO ₄ doped with metal is produced under high temperature conditions by a solid phase method.

Control of the particle shape is also known as one of the techniques for improving the performance of sm phase BiVO ₄ (Non-patent Document 3). By this method, the sm phase BiVO ₄ can promote charge separation by making it into a particle shape having facets, and can have high performance. However, it is easily imagined that it is difficult to dope metal into the sm phase BiVO ₄ in the synthesis under the low temperature condition as in the prior art. Not achieved.

Yasuyoshi Sasaki, 3 others, “Solar water splitting using powder photocatalyst driven by Z-scheme interparticle electron transfer without electron mediation” Mediator), J. et al. Phys. Chem. C, 2009, 113, p. 17536-17542. Weifeng Yao, two others, "Effects of molybdenum substitution on the photocatalytic action of BiVO4" (Effects of the molecular catalytic on the photocatalytic of BiVO4, Tr. UK, 2008, p. 1426-1430. Akihiko Kudo and two others, “A novel aqueous process for preparing highly crystalline BiVO4 powder with controlled crystal form from vanadate having a layered structure at room temperature, its photocatalyst and photophysical properties” (A Novel Aqueous Process) for Preparation of Crystal Form-Controlled and Highly Crystalline BiVO4 Powder from Layered Vanadates at Rome Tempered and Its Photocatalyst. AM. Chem. Soc. , 1999, 121, p. 11459-11467.

However, since the solid-phase method is a synthesis method that is unsuitable for controlling the particle shape, particles having an irregular shape are generated, and when the sm phase BiVO ₄ is doped with metal, a high crystal having a facet is formed. Sex particles are not generated. As described above, examples of s-m-phase BiVO ₄ metal-doped with than conventional eased synthesis conditions yet without further example of s-m-phase BiVO ₄ doped with metal comprising particles having a faceted There is not yet. Thus, the metal doped sm phase BiVO ₄ having sufficient performance as a photocatalyst has not been completed.

The present invention has been made in view of the above, and an object thereof is to provide BiVO ₄ doped with a metal and a method for producing the same.

The present invention relates to BiVO ₄ doped with a metal and a method for producing the same. That is, the present invention relates to a photocatalyst considered to exhibit higher activity than a photocatalyst having a conventional BiVO ₄ structure.
As a result of various investigations of production conditions based on the liquid-solid phase method, the present inventors have succeeded in developing a method for producing metal-doped BiVO ₄ that can be controlled in particle morphology. This production method has led to the development of sm phase BiVO ₄ containing particles having facets and doped with metal.

  That is, the present invention includes the following matters.

[1] A metal (X containing a bismuth-forming step in which a vanadate doped with one or more metals (X) selected from elements included in Groups 2 to 15 of the periodic table is brought into contact with bismuth ions. ) Method for producing doped bismuth vanadate.
[2] The doping amount of the metal (X) is 0.01 as the ratio {X / (V + X)} of the number of moles of the metal (X) to the sum of the number of moles of vanadium (V) and the metal (X). The manufacturing method as described in [1] which is -1.0 mol%.
[2] The production method according to [1] or [2], wherein the bismuth ions are present in a liquid or an atmosphere including the bismuth ion supply source.
[4] The production according to any one of [1] to [3], further including an annealing step of annealing the metal (X) -doped bismuth vanadate in a temperature range in which the shape of the facet-containing particles is not broken. Method.
[5] The manufacturing method according to any one of [1] to [4], wherein the metal (X) -doped bismuth vanadate is a metal (X) -doped sealite structure monoclinic phase bismuth vanadate.
[6] The manufacturing method according to any one of [1] to [5], wherein the metal (X) is one or more elements selected from molybdenum or tungsten.

[7] Metal (X) -doped bismuth vanadate, which is doped with one or more metals (X) selected from elements included in Groups 2 to 15 of the periodic table and includes particles having facets.
[8] The metal (X) -doped bismuth vanadate according to [7], which has a photocatalytic function.
[9] The metal (X) -doped bismuth vanadate according to [7] or [8], wherein the metal (X) is one or more elements selected from molybdenum or tungsten.

[10] A photocatalyst containing the metal (X) -doped bismuth vanadate according to any one of [7] to [9].
[11] A photoelectrode containing the metal (X) -doped bismuth vanadate according to any one of [7] to [9].

According to the present invention, it is possible to provide a metal-doped BiVO ₄ having a higher photocatalytic activity than the conventionally obtained metal-doped sm phase BiVO ₄ and metal undoped sm phase BiVO ₄ .

Is an XRD measurement chart of _K 3 _V 5 _{O 14} obtained in Test Example 1-4. _{4 is} an XRD measurement chart of sm phase BiVO ₄ obtained in Test Examples 1 to 4 and Comparative Example 1. FIG. _{2 is} an electron microscope image of sm phase BiVO ₄ obtained in Test Examples 1 to 4 and Comparative Example 1. FIG. Is an XRD measurement chart of _K 3 _V 5 _{O 14} obtained in Test Example 5-8. 7 is an XRD measurement chart of sm phase BiVO ₄ obtained in Test Examples 5 to 8 and Comparative Example 2. It is an electron microscope image of sm phase BiVO ₄ obtained in Test Examples 5 to 8 and Comparative Example 2.

  Hereinafter, embodiments of the present invention will be described in detail.

The method for producing metal (X) -doped BiVO _{4 according to} the present invention comprises a vanadate salt doped with one or more metals (X) selected from elements included in Groups 2 to 15 of the periodic table. A bismuth-forming step to be brought into contact with.
The above-mentioned production method of the present invention is characterized in that one or more metals (X) selected from elements included in Groups 2 to 15 of the periodic table are pre-doped into vanadate and further contacted with bismuth ions. There is to make it. By pre-doping the metal (X) into the vanadate, the metal (X) -doped vanadate can be stabilized. Moreover, the particle shape of the obtained metal (X) -doped BiVO ₄ can also be controlled by the production method of the present invention. According to the present invention, BiVO ₄ containing particles having facets and doped with metal (X) can be obtained for the first time.

[Metal (X)]
The metal (X) doped into BiVO ₄ is one or more metal elements selected from elements included in Groups 2 to 15 of the periodic table. Examples of the metal (X) include alkaline earths. Metal elements and rare earth elements (lanthanoids) may be used, but group 4 of the periodic table such as Ti, Zr, Hf, etc .; group 5 of the periodic table such as Nb, Ta; and Mo, W, Cr, etc. One or more elements selected from Group 6 of the periodic table are preferable, one or more metal elements selected from the elements included in Groups 5 to 6 of the periodic table are more preferable, and Periodic Table One or more metal elements selected from elements included in Group 6 of the table are more preferable, and Mo and W are most preferable in that the electrical conductivity of BiVO ₄ can be increased.
The amount of metal (X) doped into BiVO ₄ is not particularly limited, but the ratio of the number of moles of metal (X) to the sum of the number of moles of vanadium (V) and metal (X) {X / (V + X) } Is preferably 0.01 to 1.0 mol%, more preferably 0.01 to 0.5 mol%, still more preferably 0.01 to 0.45 mol%, still more preferably 0.02 to 0.4 mol%, 0.02-0.3 mol% is most preferable.

  The raw material of the metal (X) is not particularly limited as long as it is a source of the metal (X). For example, the oxide of the metal (X); hydroxide; chloride; carbonate, nitrate, ammonium Salts such as salts; and the like, and metal (X) oxides and hydroxides are preferred.

[Vanadate doped with metal (X)]
In the present invention, as a vanadate used for synthesizing a vanadate doped with metal (X), a general vanadate capable of doping metal (X) is applicable. Examples of the vanadate include salts containing various vanadate ions such as V ₅ O ₁₄ ³⁻ , V ₃ O ₈ ¹⁻ , V ₄ O ₁₁ ²⁻ , and specifically, K ₃ V ₅ O ₁₄ , KV ₃ O ₈ , CsV ₃ O ₈ , Cs ₂ V ₄ O _{11 and the} like.
The raw material of vanadate is not particularly limited as long as it is a source of vanadium, and examples thereof include vanadium oxides; hydroxides; chlorides; carbonates, nitrates, ammonium salts and the like; An oxide of vanadium is preferable, and vanadium pentoxide is more preferable.
The vanadate doped with metal (X) is not particularly limited as long as the metal vanadate is doped with metal (X), but K ₃ V ₅ having a layered structure that easily reacts with bismuth ions. O ₁₄ or preferably those _KV 3 doped _{O 8} metal _(X), is more preferable doped with metal (X) to K ₃ V _{5 O 14.}

The method for synthesizing the vanadate doped with the metal (X) is not particularly limited, and any known method can be applied. For example, a specific example of the case where K ₃ V ₅ O ₁₄ doped with metal (X) is synthesized by a solid phase method is shown below.
Each raw material of potassium, vanadium, and metal (X) is mixed, and a solid phase reaction is caused by firing to obtain K ₃ V ₅ O ₁₄ doped with metal (X). The raw materials for potassium and vanadium are not particularly limited, and include potassium or vanadium oxides; hydroxides; chlorides; carbonates, nitrates, ammonium salts, and the like; and potassium salts such as potassium carbonate. Vanadium oxides such as vanadium pentoxide are preferred. The raw material of the metal (X) is not particularly limited, and examples thereof include metal (X) oxides; hydroxides; chlorides; carbonates, nitrates, ammonium salts and the like; Oxides and hydroxides are preferred, and oxides of metal (X) are more preferred. The amount of potassium, vanadium, and metal (X) is not particularly limited, but the ratio of the number of moles of potassium (K) charged to the sum of the moles of vanadium (V) and metal (X) {K / ( V / X)} is preferably K / (V + X) = 0.600 to 0.660 (mol / mol), more preferably 0.600 to 0.618 (mol / mol). The firing temperature is preferably 300 to 600 ° C, more preferably 400 to 500 ° C. The firing time is preferably 1 to 20 hours, more preferably 3 to 10 hours, and even more preferably 5 to 10 hours.

[Metal (X) doped BiVO ₄ ]
Metal-doped BiVO ₄ is obtained by a method including a step of contacting vanadate doped with metal (X) with bismuth ions (sometimes referred to as “bismuthization step” in the present specification and claims). Synthesize.
In the above step, the bismuth ions are preferably present in a liquid or atmosphere containing bismuth ions, specifically, may be present in a liquid or atmosphere containing a supply source of bismuth ions, Therefore, these liquids or atmospheres can be brought into contact with the vanadate doped with metal (X). In this specification, a method in which a vanadate salt doped with metal (X) is used as a solid phase and the solid phase is brought into contact with a liquid or atmosphere containing bismuth ions may be referred to as a “liquid solid phase method”.

  For example, in the case of a solution containing a bismuth ion source, the liquid containing the bismuth ion source can be prepared by dissolving the bismuth source in a solvent. The solvent is not particularly limited as long as the source of bismuth to be used is a soluble solvent. For example, water, any organic solvent, a mixed solvent of water and an organic solvent, and the like can be used. For adjustment, an acid such as nitric acid, hydrochloric acid or sulfuric acid may be contained. A preferable solvent is neutral water from the viewpoint of practical use.

The liquid containing the bismuth ion source may also be a suspension containing the bismuth ion source, and can be prepared by dispersing the bismuth source in a solvent.
The atmosphere containing the bismuth ion supply source can be prepared, for example, by placing the liquid containing the bismuth ion supply source at a temperature equal to or higher than its boiling point.

As the bismuth ion supply source, a known bismuth compound or bismuth simple substance can be used. Examples of the bismuth compound include bismuth salts such as bismuth nitrate, bismuth chloride, bismuth oxycarbonate, bismuth oxychloride, and bismuth hydroxide; Bismuth oxides such as bismuth trioxide; and the like, bismuth salts are preferred, and bismuth nitrate is more preferred.
The amount of bismuth ions brought into contact with the metal (X) -doped vanadate is not particularly limited, but the ratio of the number of moles of bismuth (Bi) to the sum of the moles of vanadium (V) and metal (X) { Bi / (V + X)} is preferably in the range of 0.9 to 1.0 (mol / mol), more preferably in the range of 0.95 to 1.0 (mol / mol).

  The conditions for bringing the vanadate doped with metal (X) into contact with bismuth ions are not particularly limited, but the preferred implementation temperature and embodiment differ depending on the type of solvent used. For example, in the case of water, the embodiment is not particularly limited at a temperature of 100 ° C. or lower, but hydrothermal treatment using a pressure vessel is preferable at a temperature of 100 ° C. or higher exceeding the boiling point. When water is used as a solvent, the temperature to be carried out is preferably in the range of 5 to 200 ° C, more preferably in the range of 5 to 100 ° C, still more preferably in the range of 40 to 80 ° C, and in the range of 40 to 70 ° C. Is more preferable. When water is used as a solvent, the contact time is not particularly limited, but is preferably 3 to 500 hours, and more preferably 3 to 100 hours. Moreover, when making it contact, you may implement, stirring the whole liquid using a stirring element or a stirring blade. About the case where a stirrer is used, it is although it does not specifically limit as a rotational speed, The range of 1-3000 rpm is preferable and the range of 1000-2000 rpm is more preferable.

When the vanadate doped with metal (X) is brought into contact with bismuth ions, oxygen in the liquid or atmosphere may be supplied, in which case, for example, oxygen is supplied to the vanadate ions. Sometimes.
Although it does not specifically limit as vanadate salt which doped metal (X), It is preferable to grind | pulverize and to contact with bismuth ion.

In the liquid solid phase method, metal (X) -doped BiVO ₄ is synthesized by ion exchange of bismuth ions eluted in a liquid or atmosphere with a base of vanadate (such as potassium ions). Therefore, a layered vanadate capable of allowing ion exchange to proceed more smoothly is preferable. Nevertheless, it is usually difficult to put ions such as molybdenum and tungsten between the layers of the layered vanadate because of the difference in charge and ion radius. On the other hand, potassium of the layered vanadate is easily ion-exchanged in a liquid or atmosphere, but vanadate ions are stably present in the liquid or atmosphere. The present invention makes it possible to synthesize a metal (X) -doped BiVO ₄ by previously doping the vanadate with a metal (X) by taking advantage of this characteristic. For example, vanadium of a layered vanadate It is possible to synthesize molybdenum-doped BiVO ₄ by previously doping the site with molybdenum.

As the metal (X) -doped BiVO ₄ , it is possible to obtain a metal having a molar ratio equivalent to or substantially equivalent to the molar ratio of vanadium and metal (X) in the above-mentioned charged amount. That is, the ratio {X / (V + X)} of the number of moles of metal (X) to the sum of moles of vanadium (V) and metal (X) contained in the metal (X) -doped BiVO ₄ is 0. 01-1.0 mol% is preferable, 0.01-0.5 mol% is more preferable, 0.01-0.45 mol% is still more preferable, 0.02-0.4 mol% is still more preferable, 0.02- 0.3 mol% is most preferable.
The molar ratio of vanadium (V) to metal (X) and {X / (V + X)} contained in the metal (X) -doped BiVO ₄ are inductively coupled plasma emission spectroscopy (ICP) defined in JIS K0116. -AES, Inductively coupled plasma (Atomic emission spectroscopy) can be quantitatively measured. In this specification, in the ICP-AES method, a sample solution prepared by adding concentrated nitric acid to a sample as a solution is injected into a plasma flame in a mist state, specified for vanadium with a specific wavelength of 292.403 nm, and specified for molybdenum A value obtained by quantifying the amount of each element in a sample from each emission intensity at a wavelength of 167.079 nm.

[Structure of metal (X) -doped BiVO ₄ ]
The metal (X) doped BiVO ₄ produced by the present invention is not particularly limited, metal (X) can also be prepared dope s-m-phase BiVO ₄ other than metal (X) doped BiVO _4, Solar Metal (X) -doped sm phase BiVO ₄ is preferable in that energy can be easily used in a wide wavelength range. As the metal (X) doped s-m phase BiVO ₄ has a s-m-phase BiVO ₄ equivalent of the crystal structure of the metal undoped, it can be determined by XRD measurements. BiVO ₄ has a plurality of crystal structures and crystal phases. Among them, a celite-structure monoclinic phase (sm phase) generally absorbs visible light and exhibits high photocatalytic activity. Diffraction lines characteristic of the sm phase are observed in the vicinity of 2θ = 15 °, 2θ = 28 °, and 2θ = 31 °. The vicinity here means ± 0.5 °.

In this specification, “metal (X) -doped BiVO ₄ ” means BiVO ₄ doped with metal (X), and unless otherwise specified as “sm phase” or the like, the sm phase BiVO ₄ other than those may be included. In addition to the sm phase, there are zircon tetragonal phases and the like. The content of s-m other than phase BiVO ₄ is, s-m and the area of the XRD peaks of the phase BiVO _4, occupying the sum of the areas of the XRD peaks of the s-m other than phase BiVO _4, the latter s-m The value calculated as the ratio of the area of the XRD peak of BiVO ₄ other than the phase is preferably 30% or less, and more preferably 10% or less.

The particle shape of the manufactured metal (X) -doped sm phase BiVO ₄ can be confirmed with an electron microscope such as a scanning electron microscope (SEM), and the particles having facets are confirmed by visual observation of an electron microscope image. Can do.

The facet means a crystal face on a particle where a crystal face of a certain extent is exposed like a single crystal surface. The particles having facets in the present invention are particles in which a region of 20% or more of the surface area of each particle viewed in plan is occupied by facets when the particles are viewed with an electron microscope image. Thus, it is a single crystal-like particle having a particle diameter of 100 nm or more (in the present specification, sometimes referred to as “faceted particle”). In this specification, when viewed with an electron microscope image, the area ratio of the area occupied by facets out of the area of the surface viewed in plan for each particle may be referred to as “facet occupation ratio”.
The facet occupancy on the particle surface is preferably 50% or more.

In the present invention, when expressed as metal (X) -doped bismuth vanadate containing faceted particles, 70% or more of the total number of particles in the field of view when observed with an electron microscope is occupied by the particles having facets. Means that
The ratio of the particles having facets to the total number of particles in the field of view is preferably 80% or more, more preferably 90% or more.

  The facets included in the particles contained in the metal (X) -doped bismuth vanadate of the present invention may have any crystal plane, but preferred crystal planes include (011) plane that serves as an oxidation reaction field, and ( 110) plane. In the photocatalytic reaction, since the oxidation reaction and the reduction reaction proceed simultaneously on the photocatalyst particles, it is more preferable that the (010) plane serving as the reduction reaction field is exposed on the particle surface in a well-balanced manner in addition to the oxidation reaction field.

[Annealing treatment]
For metal (X) -doped BiVO ₄ obtained by bringing vanadate doped with metal (X) into contact with bismuth ions, annealing treatment is performed if the particle shape having facets is not broken. Also good. The annealing temperature is preferably in the range of 100 to 550 ° C, more preferably in the range of 400 to 500 ° C. By performing the annealing treatment, the metal (X) -doped BiVO ₄ crystal tends to grow, and the crystallinity can be improved.

[Photocatalytic function]
The metal (X) -doped BiVO ₄ produced in the present invention has a photocatalytic function, and particularly has an excellent photocatalytic function for solar energy of 250 to 520 nm.
In the present specification, the “photocatalytic function” refers to exhibiting some catalytic function when irradiated with light of 250 to 520 nm. For example, evaluation can be performed according to the evaluation method of photocatalytic activity in Examples described later. it can. In the present specification, “photocatalytic function” is sometimes referred to as “photocatalytic activity”.

The embodiment of the case of using as manufactured metal (X) doped BiVO ₄ photocatalyst is not particularly limited, platinum, Ruthenium, ruthenium oxide, iridium, iridium oxide, gold, silver and copper, copper oxide, iron oxide, water Iron oxide, nickel, nickel oxide, gallium oxide, cobalt, cobalt oxide, manganese oxide, cobalt oxide-manganese oxide solid solution, etc. can be supported and used.

The manufactured metal (X) -doped BiVO ₄ can be used as a photoelectrode by being deposited on a conductive substrate, and the embodiment is not particularly limited. In this case, the metal (X) doped BiVO ₄ may be used alone, but the metal (X) doped BiVO ₄ is platinum, ruthenium, ruthenium oxide, iridium, iridium oxide, gold, silver, copper, copper oxide, iron oxide. Further, iron hydroxide oxide, nickel, nickel oxide, gallium oxide, cobalt, cobalt oxide, manganese oxide, cobalt oxide-manganese oxide solid solution, and the like can be supported and used.

Hereinafter, the metal of the present invention with reference to Examples (X) doped BiVO _4, and is specifically described for their photocatalytic activity, the present invention is not limited to these examples.

[Test Example 1]
K ₂ CO ₃ (1.0469 g), V ₂ O ₅ (2.2724 g), MoO ₃ (0 so that K / V / Mo = 3.03 / 4.9975 / 0.0025 (mol ratio). .0018g) and ethanol (10 mL) were mixed in a menor mortar for 30 minutes. The obtained mixture was put in a magnetic crucible and baked in an electric furnace at 450 ° C. for 5 hours in the atmosphere. After firing, the mixture was allowed to cool to room temperature and then crushed.

The result of XRD measurement of the obtained powder is shown in FIG. Since there was no impurity attributed to Mo species, it was confirmed to be a single phase of Mo-doped K ₃ V ₅ O ₁₄ . The obtained powder (2.3844 g) was mixed with 100 ml of water and Bi (NO ₃ ) ₃ · 5H ₂ so that Bi / V / Mo = 1.00 / 0.9995 / 0.0005 (mol ratio). The mixture was placed in a 300 mL Erlenmeyer flask containing O (9.702 g) and stirred at 1500 rpm using a stirrer at 70 ° C. for 10 hours. The obtained precipitate was collected by suction filtration, washed with water, and then dried with a dryer at 60 ° C. for 12 hours to obtain a powder sample.
The above molar ratio in Test Example 1 represents the amount charged.

The result of XRD measurement of the obtained powder sample is shown in FIG. Again, since there was no impurity attributed to the Mo species, it was confirmed to be a single phase of Mo-doped sm-phase BiVO ₄ . The XRD measurement was performed at room temperature using a powder X-ray diffractometer SmartLab (X-ray source: CuKα ray) manufactured by Rigaku. The conditions for the XRD measurement are the same in Test Examples 2 to 8 and Comparative Examples 1 and 2.
Moreover, the SEM photograph of the obtained powder sample is shown in FIG. Particles with clear facets were observed.
Furthermore, V / Mo (mol ratio) of the obtained powder sample was measured by ICP-AES method based on JIS K0116. The results are shown in Table 1.

[Test Examples 2 to 4]
A powder sample was obtained in the same manner as in Test Example 1 except that K / V / Mo (mol ratio) and Bi / V / Mo (mol ratio) were changed as shown in Table 1.
The results of XRD measurement before and after contacting with bismuth ions are shown in FIGS. 1 (b) to (d) and FIGS. 2 (b) to (d), and SEM photographs of the obtained powder samples are shown in FIGS. d).
Furthermore, V / Mo (mol ratio) of the obtained powder sample was measured by ICP-AES method based on JIS K0116. The results are shown in Table 1.

[Comparative Example 1]
Bi ₂ O ₃ (2.3298 g), NH ₄ VO ₃ (1.1686 g), and MoO ₃ so that the charged amount is Bi / V / Mo = 1.00 / 0.9990 / 0.0010 (mol ratio). (0.0014 g) was mixed in an alumina mortar for 30 minutes. The obtained mixture was put in an alumina crucible and baked in an electric furnace at 900 ° C. for 10 hours in the air. After firing, the mixture was allowed to cool to room temperature and crushed. An XRD measurement chart of the obtained powder sample is shown in FIG. It was confirmed to be a single phase of Mo-doped sm-phase BiVO ₄ without impurities. An SEM photograph of the obtained powder sample is shown in FIG. There were no facets and amorphous particles were observed.
The production conditions of Test Examples 1 to 4 and Comparative Example 1 are shown together with [V / Mo measured molar ratio] as [Table 1].

[Test Example 5]
K ₂ CO ₃ (1.0469 g), V ₂ O ₅ (2.2724 g) and WO ₃ (0 so that K / V / W = 3.03 / 4.9975 / 0.0025 (mol ratio). 0058 g) and ethanol (10 mL) were mixed in a menor mortar for 30 minutes. The obtained mixture was put in a magnetic crucible and baked in an electric furnace at 450 ° C. for 5 hours in the atmosphere. After firing, the mixture was allowed to cool to room temperature and then crushed.

The result of XRD measurement of the obtained powder is shown in FIG. Since there was no impurity attributed to the W species, it was confirmed to be a single phase of W-doped K ₃ V ₅ O ₁₄ . The obtained powder (2.3844 g) was mixed with 100 ml of water and Bi (NO ₃ ) ₃ · 5H ₂ so that Bi / V / W = 1.00 / 0.9995 / 0.0005 (mol ratio). The mixture was placed in a 300 mL Erlenmeyer flask containing O (9.702 g), and stirred at 1500 rpm using a stirrer at 70 ° C. for 72 hours. The obtained precipitate was collected by suction filtration, washed with water, and then dried with a dryer at 60 ° C. for 12 hours to obtain a powder sample.
The above molar ratio in Test Example 5 represents the amount charged.

The result of XRD measurement of the obtained powder sample is shown in FIG. Again, since there was no impurity attributed to the W species, it was confirmed to be a single phase of W-doped sm phase BiVO ₄ .
Moreover, the SEM photograph of the obtained powder sample is shown to Fig.6 (a). Particles with clear facets were observed.

[Test Examples 6 to 8]
A powder sample was obtained in the same manner as in Test Example 5 except that K / V / W (mol ratio) and Bi / V / W (mol ratio) were changed as shown in Table 2.
The results of XRD measurement before and after contacting with bismuth ions are shown in FIGS. 4B to 4D and FIGS. 5B to 5D, and SEM photographs of the obtained powder samples are shown in FIGS. d).

[Comparative Example 2]
Bi ₂ O ₃ (2.3298 g), NH ₄ VO ₃ (1.1636 g), WO ₃ so that the charged amount is Bi / V / W = 1.00 / 0.9950 / 0.0050 (mol ratio). (0.0116 g) was mixed in an alumina mortar for 30 minutes. The obtained mixture was put in an alumina crucible and baked in an electric furnace at 900 ° C. for 10 hours in the air. After firing, the mixture was allowed to cool to room temperature and crushed. An XRD measurement chart of the obtained powder sample is shown in FIG. It was confirmed that it was a single phase of W-doped sm phase BiVO ₄ without impurities. An SEM photograph of the obtained powder sample is shown in FIG. There were no facets and amorphous particles were observed.
The production conditions of Test Examples 5 to 8 and Comparative Example 2 are collectively shown as [Table 2].

[Evaluation of photocatalytic activity]
The photocatalytic activity was evaluated by oxygen generation reaction from an aqueous silver nitrate solution under simulated sunlight irradiation. For the evaluation, an upper irradiation type reaction cell connected to a closed circulation type reactor was used. 0.3 g of the catalyst powder obtained in Test Examples 1 to 8 and Comparative Examples 1 and 2 was suspended in 200 ml of 0.020 mol / L AgNO ₃ aqueous solution and stirred during evaluation with a magnetic stirrer. Pseudo sunlight was irradiated from the top of a Pyrex (registered trademark) glass window using a solar simulator (manufactured by Mitsunaga Electric Corporation; XES-40S2-CE). The generated oxygen was quantified by an online gas chromatograph (manufactured by Shimadzu Corporation; GC-8A, MS-5A, TCD, Ar carrier).

Table 3 shows the results of evaluating the presence or absence of Mo or W doping, the amount of facet particles, and the photocatalytic activity of the powder samples of sm phase BiVO ₄ obtained in Test Examples 1 to 8 and Comparative Examples 1 and 2. Show.
In Table 3, “O” in the column of “Mo-doped” or “W-doped” indicates that Mo or W was doped, and “x” indicates that Mo or W was not doped. ○ in the column of “Which facet particles are 70% or more” indicates that the ratio of the number of facet particles to the total number of particles in the field of view is 70% or more when the electron microscope image is visually confirmed. X indicates that the ratio is less than 70%.

As understood from Table 3, Mo dope or W manufactured by liquid solid phase method using K ₃ V ₅ O ₁₄ doped with 0.05 to 0.5% of Mo or W by a charge amount by solid phase method Doped sm phase BiVO ₄ (Test Examples 1 to 8) is a particle in which 70% or more of the whole particles seen in an electron microscopic image have facets, and Mo or W is preliminarily vanadized in Comparative Examples 1 and 2. It was more active than Mo-doped or W-doped sm phase BiVO ₄ synthesized by a solid phase method without doping into an acid salt.

Claims (11)

  A metal (X) -doped vanadium comprising a bismuth-forming step in which a vanadate salt doped with one or more metals (X) selected from elements included in Groups 2 to 15 of the periodic table is brought into contact with bismuth ions. Method for producing bismuth acid.   The amount of the metal (X) charged is 0.01 to 1. as the ratio {X / (V + X)} of the number of moles of the metal (X) to the sum of the number of moles of vanadium (V) and the metal (X). The production method according to claim 1, which is 0 mol%.   The manufacturing method according to claim 1, wherein the bismuth ions are present in a liquid or an atmosphere including a supply source of the bismuth ions.   Furthermore, the manufacturing method of any one of Claims 1-3 including the annealing process which anneals a metal (X) dope bismuth vanadate in the temperature range which the particle | grain shape which has a facet does not break.   5. The method according to claim 1, wherein the metal (X) -doped bismuth vanadate is a metal (X) -doped sealite structure monoclinic phase bismuth vanadate.   The manufacturing method according to any one of claims 1 to 5, wherein the metal (X) is one or more elements selected from molybdenum and tungsten.   Metal (X) -doped bismuth vanadate, which is doped with one or more kinds of metal (X) selected from elements included in Groups 2 to 15 of the periodic table, and includes particles having facets.   The metal (X) -doped bismuth vanadate according to claim 7 having a photocatalytic function.   The metal (X) -doped bismuth vanadate according to claim 7 or 8, wherein the metal (X) is one or more elements selected from molybdenum or tungsten.   The photocatalyst containing the metal (X) dope bismuth vanadate of any one of Claims 7-9.   The photoelectrode containing the metal (X) dope bismuth vanadate of any one of Claims 7-9.