JP2005144210A - Catalyst for decomposing water comprising galium nitride solid solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photocatalyst for decomposing water improving spectrum characteristic and photoactivity of a system including Ga element. <P>SOLUTION: The photocatalyst for decomposing water comprises the solid solution of ZnO and GaN of (ZnO)<SB>X</SB>(GaN)<SB>1-X</SB>(wherein X is in the range of 0.03≤X≤0.3). Further, the photocatalyst for decomposing water is obtained by combining the catalyst and a co-catalyst. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a photocatalyst for water splitting, particularly a photocatalytic water splitting catalyst comprising a solid solution mainly composed of GaN, particularly a solid solution with a ZnO component, or having a promoter made of a metal oxide supported thereon.

Since fossil resources cannot be said to be inexhaustible, it is preferable to allocate them to chemical raw materials from the viewpoint of effective use of resources. In addition, from the viewpoint of environmental problems such as global warming, conversion to clean energy without generating CO ₂ is eagerly desired. Further, it is said that not only the generation of CO ₂ but also the generation of fluorine from a compound contained in the coal as muscovite when the coal is burned. The nuclear power generation technology that has emerged as a non-problematic energy supply means is also concerned about the destruction of the world order due to the use of substances produced in the process of manufacturing fuel materials and the processing after use as weapons. This led to a big problem. Under such circumstances, development of energy resources that are environmentally friendly, high in safety, and relatively low in equipment costs is desired. Recently, many investments have been directed to wind power generation because of its infinite use of energy resources and relatively low equipment costs. In addition, since solar cells produce clean and highly usable energy, they have been put into practical use, and many studies have been conducted for further improving efficiency and supplying stable energy. In addition, as an energy conversion technology using sunlight, there is an interest in water photolysis using a photocatalyst. The photocatalyst active in the photolysis reaction of water used here is an advanced photofunctional material having functions such as light absorption, charge separation, and surface oxidation-reduction reaction, and many have been proposed. .

Journal of the Ceramic Society of Japan, 109 (6) S81-S88 (2001), especially item 7. Surface, Vol.36, No.12, 625-645 (1998), especially item 4. And Section 7.2. J. Sato, N. Saito, H. Nishiyama, and Y. Inoue, J. Phys. Chem. B, Vol. 105, No. 26, p6061-6063, 2001. MATERIAL STAGE Vol.2, No2, (2002), 27-32, 3.4 Ga oxide, pages 30-31 (K. Ikarashi, N. Saito, H. Nishiyama, and Y. Inoue, Submitted to J. Phys.Chem. Kazunari Domen, Nitrides, oxynitrides and oxysulfides as photocatalysts for water splitting under visible light irradiation.Anais do 12 Congresso Brasilelio de Catalise, 1141-1144, http: //www.12cbcat.com.br/trabalhos/M021.pdf,

On the other hand, since H ₂ is clean energy used for fuel cells and the like, development of an efficient and clean manufacturing process is desired. Kudo explains the principle of water photolysis catalyst for the purpose of producing hydrogen using light energy up to that point in Non-Patent Documents 1 and 2, and the photo-water decomposition catalyst used for this. Yes. Reference 7 above. , The photocatalytic activity of oxides such as metal ions in the d ⁰ electronic state, for example, Ti ⁴⁺ , Zr ⁴⁺ , Nb ⁵⁺ and Ta ⁵⁺ , and the photocatalytic activity of oxides of the metal ions in the d ¹⁰ and / or s2 electronic states, etc. doing. Further, in FIG. 6 on page 629 of the above-mentioned document 2, Ga is cited as an element on the periodic table used for producing the photohydrolysis catalyst. Further, in page 640, line 10 from the bottom right column to page 641, left column, the β-Ga ₂ O ₃ structure forms a solid solution with the d ¹⁰ metal In oxide, in particular, so that photocatalytic activity is increased. Suggests that
Furthermore, Inoue et al. In the above-mentioned documents 3 and 4, MGa ₂ O ₄ (M = Zn, Ca), MIn ₂ O ₄ (M = Ca, Sr), NaSbO ₃ containing typical metal ions in the d ¹⁰ electronic state, M ₂ SnO ₄ (M = Sr, Ca, Ba), Zn ₂ GeO ₄ , M ₂ Sb ₂ O ₇ (M = Ca, Sr), and MSb ₂ O ₆ carry RuO ₂ to completely photodecompose water. It is reported to have high activity against the reaction. In Non-Patent Document 5, Domen refers to nitrogenization, oxynitride formation, and oxysulfide formation of an oxide photocatalyst in the design of a visible light active photowater decomposition catalyst. However, no mention is made of a photohydrolysis catalyst that can use visible light containing a Ga element.

The subject of this invention is providing the photocatalyst decomposition catalyst containing Ga element which extended the active wavelength range to visible light. The present inventors have prepared a material obtained by solid solution the d ¹⁰ metal ZnO as the compound containing Ga elements including nitride structure, was examined its photocatalytic activity, also water degradable in the light of a wavelength longer than 400nm As a result, it was confirmed that the present invention has a good activity, and the above-mentioned problems were solved.

The first of the present invention is (1) (ZnO) _X (GaN) _1-X , wherein X is a photo-water decomposition catalyst comprising a solid solution of ZnO and GaN in the range of 0.03 ≦ X ≦ 0.3. It is. Preferably, (2) the photo-water splitting catalyst according to (1), wherein NiO, NiO and Cr ₂ O ₃ or RuO ₂ are supported as a co-catalyst. In the second aspect of the present invention, (3) a mixed powder having a molar ratio of ZnO and Ga ₂ O ₃ of 0.5-2: 1 is supplied with NH ₃ within a flow rate of 50-1000 mL / min, It is a photo-water decomposition catalyst comprising a ZnO-GaN solid solution compound obtained by firing for 1 to 20 hours in the range of 750 ° C to 950 ° C. Preferably, (4) the photohydrolysis catalyst according to (3), wherein NiO, NiO and Cr ₂ O ₃ or RuO ₂ are supported as promoters.

As an effect of the invention, the developed compound consisting of a solid solution of ZnO and GaN exhibits the characteristic of absorbing visible light up to 470 nm, and in particular, the one carrying NiO and Cr ₂ O ₃ is water with a wavelength longer than 400 nm. It can be mentioned that it functions effectively as a catalyst for completely decomposing.

The solid solution of A, ZnO and GaN is a mixture of ZnO and Ga ₂ O ₃ in a molar ratio of 0.5 to 2: 1 in an ammonia stream with a flow rate of 50 to 1000 mL / min. Firing and nitriding in the range of 1 ° C. for 1 to 20 hours.
B, Water-splitting photocatalytic activity was confirmed in the solid solution of ZnO and GaN represented by (ZnO) _X (GaN) _1-X , where 0.03 ≦ X ≦ 0.3.
C. The Zn—Ga oxynitride solid solution compound is prepared, for example, as follows. It is natural from chemical engineering experience that various design changes can be made when scaling up.
An alumina board with 1 to 3 g of precursor powder is placed in the center of a nitriding device consisting of an alumina tube with a length of 80 to 100 cm and an inner diameter of 2 to 3 cm. From an ammonia cylinder (purity of 99.8% or more) to a stainless steel tube Ammonia gas is passed through the alumina tube at a flow rate of 50 to 1000 mL / min through (1/8 inch). At this time, the flow rate is adjusted by a mass flow controller (manufactured by STEC, SEC-E440J). The center of the alumina tube, that is, the vicinity where the sample is placed, is heated to a predetermined temperature by a tubular electric furnace (30 cm wide). The degree of nitridation was observed by (XRD, elemental analysis) to obtain the desired oxynitride compound.

D. The XRD pattern of the obtained Zn-Ga oxynitride solid solution compound was measured by an X-ray diffractometer (manufactured by Rigak, Geigerflex RAD-B), and the UV (ultraviolet) -Vis (visible) absorption spectrum was manufactured by Jasco. It was measured by trade name V-560.
E. (ZnO) _X (GaN) _1-X in an aqueous solution containing Ni, Cr, and a plurality of nitrates of the metal in a predetermined amount to be the final oxide promoter amount, or in a tetrahydrofuran (THF) solution of Ru ₃ (CO) ₁₂ However, impregnation in the range of 0.03 ≦ X ≦ 0.3, and then supporting the promoter composed of the metal oxide by firing in air at 300 ° C. for 1 hour or 400 ° C. for 3 hours. Can do.

A mixture of ZnO and Ga ₂ O ₃ in a molar ratio of 2: 1 is baked and nitrided at 950 ° C. for 10 hours in an ammonia stream of 2.5 × 10 ⁵ mm ³ / min. As a result, a material represented by a composition of Zn _0.05 Ga _0.95 O _0.05 N _0.95 is obtained. From the X-ray diffraction (XRD) pattern, it was confirmed that a solid solution of ZnO and GaN was formed. A part of the zinc component volatilizes at the time of firing, and a compound having a zinc ratio smaller than that of the starting material is obtained. The photocatalytic activity of the obtained solid solution was examined. For comparison, Ga ₂ O ₃ alone was baked and nitrided at 950 ° C. for 10 hours in an ammonia stream of 2.5 × 10 ⁵ mm ³ / min to produce GaN, and the activity and the like were compared. In the photocatalytic reaction, 0.3 g of Zn _0.05 Ga _0.95 O _0.05 N _0.95 each carrying NiO (1 wt%) + Cr ₂ O ₃ (0.5 wt%) was added to pure water. And irradiated with light having a wavelength longer than 190 nm by a 450 W high pressure mercury lamp. As shown in FIG. 1, GaN exhibits little activity, whereas Zn _0.05 Ga _0.95 O _0.05 N _0.95 can decompose water to generate hydrogen and oxygen. It was confirmed that it functions as a photocatalyst. By entering Zn, water can be completely decomposed.

FIG. 2 shows absorption spectra of the solid solution obtained in Example 1 having a composition of Zn _0.05 Ga _0.95 O _0.05 N _0.95 and GaN using the above-described measuring apparatus. From FIG. 2, GaN obtained by nitriding Ga ₂ O ₃ has absorption in the ultraviolet region up to 380 nm, whereas Zn ₀ obtained by nitriding by mixing ZnO and Ga ₂ O _{3. .05} Ga _0.95 O _0.05 N _0.95 was confirmed to have absorption in the visible light region up to 470 nm. FIG. 3 shows the XRD pattern (a) and diffraction peak shift (b) of the (100) plane of GaN and Zn _0.05 Ga _0.95 O _0.05 N _0.95 . From these measurement results, a solid solution structure of ZnO in GaN can be estimated. Further, 0.3 g of a catalyst supporting NiO (1 wt%) + Cr ₂ O ₃ (0.5 wt%) on Zn _0.05 Ga _0.95 O _0.05 N _0.95 was suspended in pure water. The photocatalytic activity was examined by irradiating light with a wavelength longer than 400 nm through a sodium nitrite solution filter using a 450 W high pressure mercury lamp as a light source. As shown in FIG. 4, Zn _0.05 Ga _0.95 O _0.05 N _0.95 was found to function as a photocatalyst capable of decomposing water by visible light irradiation to generate hydrogen and oxygen. .

NiO (1.5 wt%) + Cr ₂ O ₃ (0.5 wt%) was supported on the solid solution with the composition of Zn _0.05 Ga _0.95 O _0.05 N _0.95 obtained in Example 1. Then, 0.3 g of the catalyst was suspended in 420 mL of pure water, and photocatalytic activity was measured by irradiating light having a wavelength longer than 290 nm through a Pyrex jacket using a 450 W high pressure mercury lamp. FIG. 5 shows the generation characteristics of hydrogen and oxygen.

In 420 mL of pure water, 0.3 g of a catalyst in which NiO (1.5 wt%) was supported on the solid solution having the composition of Zn _0.05 Ga _0.95 O _0.05 N _0.95 obtained in Example 1 was used. The photocatalytic activity was measured by suspending and irradiating light having a wavelength longer than 290 nm through a Pyrex jacket using a 450 W high pressure mercury lamp.
FIG. 6 shows the generation characteristics of hydrogen and oxygen.

A mixture of ZnO and Ga ₂ O ₃ at a molar ratio of 2: 1 is baked and nitrided at 950 ° C. for 10 hours in an ammonia stream of 2.5 × 10 ⁵ mm ³ / min. As a result, a material represented by a composition of Zn _0.05 Ga _0.95 O _0.05 N _0.95 is obtained. The material is immersed in a solution of Ru ₃ (CO) ₁₂ in several mL of tetrahydrofuran (THF) and evaporated to dryness in a hot water bath. This is calcined in air at 400 ° C. for 3 hours to carry RuO ₂ . At this time, the loading amount is 1% by weight. 0.3 g of the material carrying 1% by weight of the synthesized RuO ₂ was suspended in 420 dm ³ of pure water, and a 450 W high-pressure mercury lamp was used as a light source to transmit light having a wavelength longer than 290 nm through a quartz jacket. Irradiated to measure photocatalytic activity. As shown in FIG. 7, simultaneous generation of hydrogen and oxygen was observed.

(ZnO) _x (GaN) _1-x obtained by setting the calcination temperatures in the nitriding treatment to 750 ° C. and 950 ° C., where X is 0.3 (750 ° C.) or 0.03 (950 ° C.) The X-ray diffraction (XRD) pattern of the compound is shown in FIG. 8, and the absorption spectra are shown in FIGS. 9 (750 ° C.) and 10 (950 ° C.). In addition, 0.3 g of NiO supported on each light water splitting catalyst is suspended in 420 mL of pure water, and a 450 W high-pressure mercury lamp is used as a light source, passing through a Pyrex jacket, a wavelength longer than 290 nm. The water photocatalytic activity was measured. FIG. 11 (firing at 750 ° C.) and FIG. 12 (firing at 950 ° C.) show the generation characteristics of hydrogen and oxygen.

Comparative example

Comparative Example 1
A mixture of ZnO and Ga ₂ O ₃ in a molar ratio of 2: 1 is fired in air at 950 ° C. for 10 hours. Thereby, a material represented by a composition of ZnGa ₂ O ₄ is obtained. As shown in FIG. 13, there is no absorption in the visible light region. Naturally, it does not show photocatalytic activity under visible light irradiation. From this, it can be presumed that the visible light responsiveness of the present invention is produced by incorporating nitrogen into the oxide containing Zn and Ga.

  The photo-hydrolysis catalyst of the present invention can generate hydrogen and oxygen using light energy in the visible light region without requiring a sacrificial agent, thus enabling a practical hydrogen production system design by photo-hydrolysis. To do.

Hydrogen using Zn _0.05 Ga _0.95 O _0.05 N _0.95 supporting NiO (1 wt%) + Cr ₂ O ₃ (0.5 wt%) of Example 1 as a photo-water splitting catalyst (●) and oxygen (◆) generation characteristics The UV (ultraviolet) -Vis (visible) absorption spectrum of Zn _0.05 Ga _0.95 O _0.05 N _0.95 prepared in Example 1. GaN absorption spectrum for comparison. The XRD pattern (a) and diffraction peak shift (b) of (100) plane of GaN and Zn _0.05 Ga _0.95 O _0.05 N _0.95 prepared in Example 1 are shown. Zn _0.05 Ga _0.95 O _0.05 N _0.95 carrying NiO (1% by weight) + Cr ₂ O ₃ (0.5% by weight) of Example 1 was used as a photowater decomposition catalyst, and 400 nm. Generation characteristics of hydrogen (●) and oxygen (◆) by longer wavelength light NiO (1.5 wt%) + Cr ₂ O ₃ (0.5 wt%) was supported on the solid solution having the composition of Zn _0.05 Ga _0.95 O _0.05 N _0.95 obtained in Example 1. Production characteristics of hydrogen (●) and oxygen (♦) using light longer than 290nm of photo-hydrolysis catalyst Hydrogen using light having a wavelength longer than 290 nm of a photohydrolysis catalyst in which NiO (1.5 wt%) is supported on a solid solution having a composition of Zn _0.05 Ga _0.95 O _0.05 N _0.95 (● ) And oxygen (◆) formation characteristics Hydrogen (●) and oxygen (light) having a wavelength longer than 290 nm of the photohydrolysis catalyst having RuO ₂ supported on Zn _0.05 Ga _0.95 O _0.05 N _0.95 prepared in Example 1 ◆) Generation characteristics (ZnO) _X (GaN) _1-X obtained by setting the firing temperature in the nitriding treatment of Example 6 to 750 ° C. and 950 ° C., where X is 0.3 (750 ° C.) or 0.03 (950 ° C.) X-ray diffraction (XRD) pattern (ZnO) _X (GaN) _1-X obtained at a firing temperature of 750 ° C. in Example 6, where X is a UV (ultraviolet) -Vis (visible) absorption spectrum of 0.3 (ZnO) _X (GaN) _1-X obtained at a firing temperature of 950 ° C. in Example 6, where X is 0.03 UV (ultraviolet) -Vis (visible) absorption spectrum Production characteristics of hydrogen (●) and oxygen (♦) using light having a wavelength longer than 290 nm, although 1.5% by weight of NiO was supported on the photohydrolysis catalyst having a firing temperature of 750 ° C. in Example 6 Production characteristics of hydrogen (●) and oxygen (♦) using light having a wavelength longer than 290 nm, although 1.5% by weight of NiO is supported on the photohydrolysis catalyst having a firing temperature of 950 ° C. in Example 6 Absorption spectrum of comparative example ZnGa ₂ O ₄

Claims (4)

(ZnO) _X (GaN) _1-X , wherein X is a photohydrolysis catalyst comprising a solid solution of ZnO and GaN in the range of 0.03 ≦ X ≦ 0.3. The photo-water decomposition catalyst according to claim 1, wherein NiO, NiO and Cr ₂ O ₃ or RuO ₂ are supported as a co-catalyst. In a mixed powder having a molar ratio of ZnO to Ga ₂ O ₃ of 0.5 to 2: 1, NH ₃ is supplied at a flow rate of 50 to 1000 mL / min, and the temperature is 750 ° C. or higher and 950 ° C. or lower. A photohydrolysis catalyst comprising a ZnO-GaN solid solution compound obtained by firing for 1 to 20 hours. The photo-water decomposition catalyst according to claim 3, wherein NiO, NiO and Cr ₂ O ₃ or RuO ₂ are supported as a co-catalyst.

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