JP5696334B2 - Photocatalyst composition and method for producing photocatalyst composition - Google Patents
Photocatalyst composition and method for producing photocatalyst composition Download PDFInfo
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- 239000011941 photocatalyst Substances 0.000 title claims description 203
- 239000000203 mixture Substances 0.000 title claims description 47
- 238000004519 manufacturing process Methods 0.000 title claims description 12
- 239000001257 hydrogen Substances 0.000 claims description 125
- 229910052739 hydrogen Inorganic materials 0.000 claims description 125
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 122
- 229910052760 oxygen Inorganic materials 0.000 claims description 100
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 96
- 239000001301 oxygen Substances 0.000 claims description 96
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 93
- 239000000126 substance Substances 0.000 claims description 19
- 238000002156 mixing Methods 0.000 claims description 8
- 239000000463 material Substances 0.000 claims description 4
- 239000004065 semiconductor Substances 0.000 description 41
- 238000000354 decomposition reaction Methods 0.000 description 21
- 239000000523 sample Substances 0.000 description 21
- 238000011156 evaluation Methods 0.000 description 16
- 239000003795 chemical substances by application Substances 0.000 description 13
- 238000010586 diagram Methods 0.000 description 13
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 11
- 238000001878 scanning electron micrograph Methods 0.000 description 11
- 238000005304 joining Methods 0.000 description 10
- 230000003647 oxidation Effects 0.000 description 10
- 238000007254 oxidation reaction Methods 0.000 description 10
- 238000001228 spectrum Methods 0.000 description 10
- 238000006243 chemical reaction Methods 0.000 description 9
- 239000002265 redox agent Substances 0.000 description 9
- 239000003054 catalyst Substances 0.000 description 8
- 239000012153 distilled water Substances 0.000 description 8
- 239000002803 fossil fuel Substances 0.000 description 7
- 239000007789 gas Substances 0.000 description 7
- 238000004544 sputter deposition Methods 0.000 description 6
- 229910010413 TiO 2 Inorganic materials 0.000 description 5
- 150000002500 ions Chemical class 0.000 description 5
- 238000005259 measurement Methods 0.000 description 5
- 239000002245 particle Substances 0.000 description 5
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical group [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- 229910052786 argon Inorganic materials 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 238000000227 grinding Methods 0.000 description 4
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 230000001590 oxidative effect Effects 0.000 description 4
- 238000010298 pulverizing process Methods 0.000 description 4
- 230000006798 recombination Effects 0.000 description 4
- 238000005215 recombination Methods 0.000 description 4
- 230000002829 reductive effect Effects 0.000 description 4
- 229910052724 xenon Inorganic materials 0.000 description 4
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000002485 combustion reaction Methods 0.000 description 3
- 230000007613 environmental effect Effects 0.000 description 3
- 150000002431 hydrogen Chemical class 0.000 description 3
- 230000001678 irradiating effect Effects 0.000 description 3
- 230000033116 oxidation-reduction process Effects 0.000 description 3
- 230000001699 photocatalysis Effects 0.000 description 3
- 229910052697 platinum Inorganic materials 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 3
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 description 3
- 241000282414 Homo sapiens Species 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 230000005284 excitation Effects 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 230000008676 import Effects 0.000 description 2
- 239000003345 natural gas Substances 0.000 description 2
- 230000007935 neutral effect Effects 0.000 description 2
- 238000013032 photocatalytic reaction Methods 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 239000012488 sample solution Substances 0.000 description 2
- 229910052709 silver Inorganic materials 0.000 description 2
- 238000000629 steam reforming Methods 0.000 description 2
- 239000010936 titanium Substances 0.000 description 2
- 239000002028 Biomass Substances 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 241000284156 Clerodendrum quadriloculare Species 0.000 description 1
- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 description 1
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
- 238000003915 air pollution Methods 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 238000002453 autothermal reforming Methods 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 229910003460 diamond Inorganic materials 0.000 description 1
- 239000010432 diamond Substances 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000002019 doping agent Substances 0.000 description 1
- 238000005868 electrolysis reaction Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 229910052733 gallium Inorganic materials 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 229910052736 halogen Inorganic materials 0.000 description 1
- 125000005843 halogen group Chemical group 0.000 description 1
- 239000000383 hazardous chemical Substances 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 238000006386 neutralization reaction Methods 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 125000004430 oxygen atom Chemical group O* 0.000 description 1
- 238000010979 pH adjustment Methods 0.000 description 1
- 230000036961 partial effect Effects 0.000 description 1
- 230000008447 perception Effects 0.000 description 1
- 230000001443 photoexcitation Effects 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
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- 238000000985 reflectance spectrum Methods 0.000 description 1
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- 239000011856 silicon-based particle Substances 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
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- 238000003756 stirring Methods 0.000 description 1
- 150000003464 sulfur compounds Chemical class 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 238000001665 trituration Methods 0.000 description 1
- 238000010792 warming Methods 0.000 description 1
- 150000003736 xenon Chemical class 0.000 description 1
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
- B01J35/39—Photocatalytic properties
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
- B01J37/0027—Powdering
- B01J37/0036—Grinding
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
- C01B13/02—Preparation of oxygen
- C01B13/0203—Preparation of oxygen from inorganic compounds
- C01B13/0207—Water
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
- C01B3/04—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of inorganic compounds, e.g. ammonia
- C01B3/042—Decomposition of water
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
- B01J23/24—Chromium, molybdenum or tungsten
- B01J23/30—Tungsten
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
- B01J23/72—Copper
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
- B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/84—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
- B01J23/85—Chromium, molybdenum or tungsten
- B01J23/888—Tungsten
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
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Description
本発明は、光エネルギーにより水を分解して酸素と水素を発生させる光触媒組成物及び光触媒組成物の製造方法に関し、特に可視光線または可視光線よりも波長の長い光のエネルギーにより水を分解して酸素と水素とを発生させる光触媒組成物及び光触媒組成物の製造方法に関する。 The present invention relates to a photocatalyst composition that decomposes water with light energy to generate oxygen and hydrogen, and a method for producing the photocatalyst composition, and in particular, decomposes water with energy of visible light or light having a longer wavelength than visible light. The present invention relates to a photocatalyst composition that generates oxygen and hydrogen and a method for producing the photocatalyst composition.
人口増加による世界のエネルギー消費量は年々増加しており、人類の生活はエネルギー資源なしでは成り立たない。現在主力のエネルギー源として石油、天然ガス、石炭などの化石燃料が使用されており、これらを利用した内燃機関は工業的利用や広く一般へ普及されている。しかしながら、その依存度の高さ故に、人類は大気汚染や地球温暖化などの環境問題、化石燃料の枯渇によるエネルギー問題など様々な問題に直面している。 The world's energy consumption due to population growth is increasing year by year, and human life cannot be achieved without energy resources. At present, fossil fuels such as oil, natural gas, and coal are used as main energy sources, and internal combustion engines using these are widely used for industrial use and widely. However, due to its high dependence, human beings are faced with various problems such as environmental problems such as air pollution and global warming, and energy problems due to depletion of fossil fuels.
有限の資源であり近い将来枯渇することが懸念されている石油に関しては、我が国では国内消費量全体の99.7％を輸入に頼っており、さらにそのうち90％以上を中東地域からの輸入に依存している。中東地域が政治的に不安定であることも考慮するとエネルギーの安定供給や持続的な経済発展という観点から石油依存への認識を改める必要がある。 Regarding oil, which is a limited resource and is expected to be depleted in the near future, Japan relies on imports for 99.7% of the total domestic consumption, and more than 90% of that depends on imports from the Middle East. Yes. Considering the political instability in the Middle East region, it is necessary to change the perception of dependence on oil from the viewpoint of stable energy supply and sustainable economic development.
一方、太陽光エネルギーは無限に降り注ぐエネルギーであるため、化石燃料の代替エネルギーとして注目されている。太陽光エネルギーの大気上層部での強度は太陽定数と呼ばれ、年間を通してほぼ一定の1.40 kW/m2である。地球全体に毎時入射する太陽光エネルギーはこれと地球の断面積との積である1.73×1017W、年間では5.5×1024 Jとなる。大気層において吸収反射により約半分のエネルギーが失われることを加味しても、１時間あたりに地表に到達する太陽エネルギーは人類が１年間に消費するエネルギー総量を十分に上回る。On the other hand, solar energy has been attracting attention as an alternative energy to fossil fuel because it is an infinite amount of energy. The intensity of solar energy in the upper atmosphere is called the solar constant and is approximately constant 1.40 kW / m 2 throughout the year. The solar energy incident on the entire earth every hour is 1.73 x 10 17 W, which is the product of this and the cross-sectional area of the earth, and 5.5 x 10 24 J per year. Even taking into account that about half of the energy is lost due to absorption and reflection in the atmosphere, the solar energy that reaches the earth's surface per hour is well above the total energy consumed by mankind in a year.
また、クリーンなエネルギー源として水素が注目されている。例えば、燃料電池においては燃料として水素と酸素を使用し、生成物は水のみである。化石燃料の燃焼時に見られるCO2などの環境負荷物質を生成しないという点で水素エネルギーの利用は環境問題に対応するエネルギーシステムである。In addition, hydrogen is attracting attention as a clean energy source. For example, in a fuel cell, hydrogen and oxygen are used as fuel, and the product is only water. The use of hydrogen energy is an energy system that responds to environmental problems in that it does not produce environmentally hazardous substances such as CO 2 that are found during the combustion of fossil fuels.
現在の主な水素製造方法は、化石燃料使用によるものと非化石資源使用によるものに大別できる。非化石燃料を使用するものに関しては、実証レベルでバイオマス転換法や熱化学分解の技術開発が進んでいる。化石燃料を使用するものに関しては、水蒸気改質法、部分酸化法、自己熱改質法などがある。この中でも天然ガスの水蒸気改質は世界的に広く実用化されており、全水素生産の約50％を占めている。しかし、化石燃焼利用の水素製造法は、副生成物のCO2を排出するという問題がある。The current main hydrogen production methods can be broadly divided into those using fossil fuels and those using non-fossil resources. For those using non-fossil fuels, technological development of biomass conversion methods and thermochemical decomposition is progressing at the demonstration level. As for those using fossil fuel, there are a steam reforming method, a partial oxidation method, an autothermal reforming method and the like. Among them, steam reforming of natural gas is widely used worldwide and accounts for about 50% of total hydrogen production. However, the hydrogen production method using fossil combustion has a problem of emitting CO 2 as a by-product.
CnHm + n H2O → n CO + (m/2 + n) H2
CO + H2O → CO2 + H2
光触媒は太陽光エネルギーを化学エネルギーに変換する触媒である。1972年Natureにて陽極に酸化チタンを、陰極に白金を用いた電気化学セルにおいて、酸化チタン電極へ紫外線を照射することにより水分解反応が起こり、酸化チタン電極から酸素が白金電極から水素が発生する現象が報告された。この現象は発見者の名前をとって本多−藤嶋効果と呼ばれている。この反応系では白金極へ0.5 Vほどのバイアス電圧を印加しているが、水の電気分解に必要な電位差1.23 Vより十分に低いことから水分解反応には光子エネルギーが使われていることがわかる。CnHm + n H2O → n CO + (m / 2 + n) H 2
CO + H 2 O → CO 2 + H 2
A photocatalyst is a catalyst that converts solar energy into chemical energy. In 1972 Nature, in an electrochemical cell using titanium oxide as the anode and platinum as the cathode, a water splitting reaction occurred by irradiating the titanium oxide electrode with ultraviolet light, generating oxygen from the titanium oxide electrode and hydrogen from the platinum electrode. A phenomenon that was reported. This phenomenon is called the Honda-Fujishima effect in the name of the discoverer. In this reaction system, a bias voltage of about 0.5 V is applied to the platinum electrode, but since the potential difference required for water electrolysis is sufficiently lower than 1.23 V, photon energy is used in the water decomposition reaction. Recognize.
このように、光触媒を用いて太陽光と水から直接水素を製造できれば、上述の環境問題やエネルギー問題を解決するための究極のクリーンエネルギーシステムとなる。 Thus, if hydrogen can be directly produced from sunlight and water using a photocatalyst, it becomes the ultimate clean energy system for solving the above-mentioned environmental problems and energy problems.
しかしながら、太陽光スペクトル中で、波長380nm以下の紫外光は、太陽光線中にわずか３％しか含まれておらず、紫外光領域しか使用しない光触媒では、太陽光の使用効率が極めて悪いものであった。 However, in the sunlight spectrum, ultraviolet light with a wavelength of 380 nm or less contains only 3% in the sunlight, and the photocatalyst that uses only the ultraviolet light region has extremely poor use efficiency of sunlight. It was.
そこで、近年、太陽光スペクトル全体の４０％以上を占める波長400nm〜760nmの可視光領域を使用して水を分解できる光触媒の研究開発が行われている。例えば、特許文献１に記載された光触媒は、助触媒なしにおいてもより活性な水素生成反応を示し、長波長の可視光で水分解活性を有するＺｎＳを用いた光触媒を提供することを目的として、（ＺｎＳ）１−Ｙ（ＣｕＸ）Ｙ（ここでＹは０．０１≦Ｙ≦０．２であり、Ｘはハロゲン元素である）の組成の太陽光照射下で還元剤を含む水溶液の光水分解により水素を生成する活性を有する固溶体からなることを特徴にしている。これにより、硫黄化合物を犠牲薬とする水素生成光触媒活性の高い光触媒が得られるとしている。Therefore, in recent years, research and development of photocatalysts capable of decomposing water using a visible light region having a wavelength of 400 nm to 760 nm, which occupies 40% or more of the entire solar spectrum, has been performed. For example, the photocatalyst described in Patent Document 1 exhibits a more active hydrogen generation reaction without a cocatalyst, and for the purpose of providing a photocatalyst using ZnS having water splitting activity with visible light having a long wavelength, (ZnS) 1-Y (CuX) Y (where Y is 0.01 ≦ Y ≦ 0.2 and X is a halogen element) It is characterized by comprising a solid solution having an activity of generating hydrogen by decomposition. As a result, a photocatalyst with high hydrogen generation photocatalytic activity using a sulfur compound as a sacrificial agent is obtained.
また、Ｚスキームと呼ばれる２段階励起を利用した光触媒が知られている。これは、可視光線により水を分解して酸素を発生させる酸素発生触媒と、可視光線により水を分解して水素を発生させる水素発生触媒と、酸化還元媒体と、を組み合わせた触媒である。これにより、酸素発生触媒で水の還元に寄与しない電子が、酸化還元媒体を還元し、この還元された酸化還元媒体は、水素発生触媒で水の酸化に寄与しない正孔により酸化されて還元される前の酸化還元媒体に戻る、というサイクルを繰り返すことにより、水の完全分解（水素：酸素＝２：１（量論比））が出来るとしている。このようなＺスキームについては、例えば、非特許文献１に記載されている。 In addition, a photocatalyst using two-stage excitation called a Z scheme is known. This is a catalyst in which an oxygen generating catalyst that decomposes water with visible light to generate oxygen, a hydrogen generating catalyst that decomposes water with visible light to generate hydrogen, and a redox medium. As a result, electrons that do not contribute to the reduction of water in the oxygen generating catalyst reduce the redox medium, and the reduced redox medium is oxidized and reduced by holes that do not contribute to the oxidation of water in the hydrogen generating catalyst. It is said that complete decomposition of water (hydrogen: oxygen = 2: 1 (stoichiometric ratio)) can be achieved by repeating the cycle of returning to the oxidation-reduction medium before being discharged. Such a Z scheme is described in Non-Patent Document 1, for example.
しかしながら、特許文献１及び非特許文献１に記載された光触媒は、酸化還元剤や犠牲剤が必要であった。また、電子や正孔の受け渡し効率が、酸化還元剤の場合良好ではないので、水の分解に寄与しない電子や正孔により、水の分解に寄与する正孔や電子の活動が阻害され、それにより水の分解効率も良好なものにならなかった。 However, the photocatalyst described in Patent Literature 1 and Non-Patent Literature 1 requires a redox agent and a sacrificial agent. In addition, since the efficiency of transferring electrons and holes is not good in the case of a redox agent, the activities of holes and electrons that contribute to water decomposition are hindered by electrons and holes that do not contribute to water decomposition. As a result, the water decomposition efficiency was not improved.
本発明は、かかる実情に鑑み、酸化還元剤や犠牲剤を必要とすることなく、かつ、水の分解に寄与しない電子、正孔を効率的に処理して、水の分解効率を良好なものにすることの出来る光触媒組成物及び光触媒組成物の製造方法を提供しようとするものである。 In view of such circumstances, the present invention efficiently treats electrons and holes that do not contribute to the decomposition of water without requiring a redox agent or a sacrificial agent, and has a good water decomposition efficiency. It is intended to provide a photocatalyst composition that can be prepared and a method for producing the photocatalyst composition.
本発明の光触媒組成物は、対標準水素電極電位において伝導帯の下端が０Ｖよりも負である物質であり、かつ、３．０ｅＶ以下のバンドギャップエネルギーを持つ物質で構成された、光が照射されることにより水を分解して水素を発生させる水素発生光触媒と、対標準水素電極電位において価電子帯の上端が１．２３Ｖよりも低エネルギー正である物質であり、かつ、３．０ｅＶ以下のバンドギャップエネルギーを持つ物質で構成された、光が照射されることにより水を分解して酸素を発生させる酸素発生光触媒と、を接合して構成され、対標準水素電極電位で比較すると、前記酸素発生光触媒のフェルミ準位よりも前記水素発生光触媒のフェルミ準位のほうが負側もしくは同等であることを主要な特徴としている。 The photocatalyst composition of the present invention is a substance having a conduction band lower than 0 V at a potential relative to a standard hydrogen electrode and composed of a substance having a band gap energy of 3.0 eV or less. And a hydrogen generating photocatalyst that decomposes water to generate hydrogen, a substance having a positive energy lower than 1.23 V at the upper end of the valence band at a standard hydrogen electrode potential, and 3.0 eV or less It is composed of a substance having a band gap energy of, and is formed by joining an oxygen generating photocatalyst that decomposes water and generates oxygen when irradiated with light. The main feature is that the Fermi level of the hydrogen generating photocatalyst is negative or equivalent to the Fermi level of the oxygen generating photocatalyst.
これにより、前記酸素発生光触媒のフェルミ準位よりも前記水素発生光触媒のフェルミ準位のほうが負側もしくは同等であるので、酸素発生光触媒と水素発生光触媒とは、その接合面がオーミック接合になり、水素発生光触媒で水の酸化に寄与しない正孔と、酸素発生光触媒で水の還元に寄与しない電子がこのオーミック接合部分で再結合して消滅する。このため、水の分解反応を効率的に進めることが出来る。 Thereby, since the Fermi level of the hydrogen generation photocatalyst is more negative or equivalent to the Fermi level of the oxygen generation photocatalyst, the junction surface between the oxygen generation photocatalyst and the hydrogen generation photocatalyst becomes an ohmic junction, Holes that do not contribute to the oxidation of water by the hydrogen generation photocatalyst and electrons that do not contribute to the reduction of water by the oxygen generation photocatalyst recombine at this ohmic junction and disappear. For this reason, the decomposition reaction of water can be advanced efficiently.
また、犠牲剤も、酸化還元剤（レドックス）も不要で、更に、水のpH調節も不要でありながら、可視光線またはそれよりも長波長の光を吸収して、水を酸素と水素に分解することが出来る。 In addition, no sacrificial agent, no redox agent (redox), and no pH adjustment of water, but absorbs visible light or light having a longer wavelength and decomposes water into oxygen and hydrogen. I can do it.
また、本発明の光触媒組成物は、前記水素発生光触媒が、Ｓｉ（i型またはn型）であり、前記酸素発生光触媒がＷＯ３であることを主要な特徴としている。これにより、本発明の光触媒組成物の中でも、効率的に、性能良く水を分解することが出来る。The photocatalytic composition of the present invention is mainly characterized in that the hydrogen generating photocatalyst is Si (i-type or n-type) and the oxygen generating photocatalyst is WO 3 . Thereby, water can be decomposed | disassembled efficiently and efficiently among the photocatalyst compositions of this invention.
更に、本発明の光触媒組成物の製造方法は、前記水素発生光触媒と、前記酸素発生光触媒とをボールミルで混合する工程を備えたことを主要な特徴としている。これにより、水素発生光触媒と、酸素発生光触媒とを接合することができる。 Furthermore, the production method of the photocatalyst composition of the present invention is mainly characterized by comprising a step of mixing the hydrogen generation photocatalyst and the oxygen generation photocatalyst with a ball mill. Thereby, a hydrogen generation photocatalyst and an oxygen generation photocatalyst can be joined.
本発明の光触媒組成物及び光触媒組成物の製造方法によれば、酸化還元剤、犠牲剤不要で、可視光線またはそれよりも長波長の光を吸収して、水を酸素と水素に分解することが出来る光触媒組成物を提供することが出来る。 According to the photocatalyst composition and the production method of the photocatalyst composition of the present invention, no redox agent or sacrificial agent is required, visible light or light having a longer wavelength is absorbed, and water is decomposed into oxygen and hydrogen. Can be provided.
以下、添付図面を参照しながら、本発明を実施するための形態を詳細に説明する。本明細書中で、数値範囲を“ 〜 ”を用いて表す場合は、“ 〜 ”で示される上限、下限の数値も数値範囲に含むものとする。 Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the present specification, when the numerical range is expressed using “˜”, the upper and lower numerical values indicated by “˜” are also included in the numerical range.
＜光触媒組成物の構成＞
本発明の光触媒組成物は、可視光線を吸収し水を分解して酸素を発生させる酸素発生光触媒と、可視光線を吸収し水を分解して水素を発生させる水素発生光触媒と、を接合して構成され、対標準水素電極電位で比較すると、前記酸素発生光触媒のフェルミ準位よりも前記水素発生光触媒のフェルミ準位のほうが負側もしくは同等であることを特徴としている。<Configuration of photocatalyst composition>
The photocatalyst composition of the present invention comprises joining an oxygen-generating photocatalyst that absorbs visible light and decomposes water to generate oxygen, and a hydrogen-generating photocatalyst that absorbs visible light and decomposes water to generate hydrogen. When compared with the potential of a standard hydrogen electrode, the Fermi level of the hydrogen generating photocatalyst is more negative or equivalent to the Fermi level of the oxygen generating photocatalyst.
本発明の光触媒組成物に含まれる酸素発生光触媒（以下、単に酸素発生光触媒と称する。）と、本発明の光触媒組成物に含まれる水素発生光触媒（以下、単に水素発生光触媒と称する。）とは、それぞれ３．０ｅＶ以下のバンドギャップエネルギーを持つ物質で構成されている。ここで、可視光線またはそれよりも長波長の光線を吸収するために必要なバンドギャップエネルギーは、Ｅｇ＝３．０ｅＶ以下なので、酸素発生光触媒と、水素発生光触媒は、可視光線またはそれよりも長波長の光線を吸収することが出来る。 The oxygen generating photocatalyst (hereinafter simply referred to as oxygen generating photocatalyst) contained in the photocatalyst composition of the present invention and the hydrogen generating photocatalyst (hereinafter simply referred to as hydrogen generating photocatalyst) included in the photocatalyst composition of the present invention. , Each of which has a band gap energy of 3.0 eV or less. Here, since the band gap energy necessary for absorbing visible light or light having a wavelength longer than that is Eg = 3.0 eV or less, the oxygen-generating photocatalyst and the hydrogen-generating photocatalyst are visible light or longer. It can absorb light of wavelength.
また、酸素発生光触媒と、水素発生光触媒とは、バンドギャップエネルギーが、それぞれ１．０ｅＶ〜３．０ｅＶの範囲である物質で構成されても良い。この場合は、酸素発生光触媒と、水素発生光触媒は、可視光線のみを吸収することが出来る。 In addition, the oxygen generation photocatalyst and the hydrogen generation photocatalyst may be made of materials having band gap energies in the range of 1.0 eV to 3.0 eV, respectively. In this case, the oxygen generating photocatalyst and the hydrogen generating photocatalyst can absorb only visible light.
次に、図１を参照して説明する。図１は、種々の半導体のバンド構造と水の酸化還元電位を表す図である。図１には、物質ごとに、伝導帯の下端と、価電子帯の上端と、バンドギャップエネルギーの値と、が示されている。酸素発生光触媒は、価電子帯の上端が酸素発生電位である１．２３Ｖよりも正である（図１の縦軸の下方向）物質で構成されている。これにより、水を酸化して酸素を発生させることが出来る。 Next, a description will be given with reference to FIG. FIG. 1 is a diagram showing various semiconductor band structures and water redox potentials. FIG. 1 shows the lower end of the conduction band, the upper end of the valence band, and the value of the band gap energy for each substance. The oxygen generation photocatalyst is made of a material whose upper end of the valence band is more positive than 1.23 V which is an oxygen generation potential (downward in the vertical axis in FIG. 1). Thereby, oxygen can be generated by oxidizing water.
また、水素発生光触媒は、伝導帯の下端が水素発生電位である０Ｖよりも負である（図１の縦軸の上方向）物質で構成されている。これにより、水を還元して水素を発生させることが出来る。 Further, the hydrogen generation photocatalyst is composed of a substance whose lower end of the conduction band is more negative than 0 V which is a hydrogen generation potential (upward in the vertical axis in FIG. 1). Thereby, water can be reduced and hydrogen can be generated.
図１中において、上述したバンドギャップエネルギー、伝導帯の下端位置、価電子帯の上端位置の条件を満たすものは、GaP, ZrO2, Si, CdSc, TiO2, Fe2O3, WO3がある。よって、これらは、光触媒組成物を構成しうるものであるが、更に、以下の条件を満たす必要がある。ここで、図１中に記載された物質中で、本発明を構成しうるものを示したが、図１に記載された物質に、本発明の範囲が限定されるわけではない。In FIG. 1, those satisfying the above-mentioned conditions of the band gap energy, the lower end position of the conduction band, and the upper end position of the valence band are GaP, ZrO 2 , Si, CdSc, TiO 2 , Fe 2 O 3 , and WO 3. is there. Therefore, these can constitute a photocatalyst composition, but it is further necessary to satisfy the following conditions. Here, the substances that can constitute the present invention are shown among the substances described in FIG. 1, but the scope of the present invention is not limited to the substances described in FIG.
水素発生光触媒と、酸素発生光触媒とは、対標準水素電極電位で比較した場合、酸素発生光触媒のフェルミ準位よりも水素発生光触媒のフェルミ準位のほうが負側になるように、もしくは同じフェルミ準位になるように構成され、さらに水素発生光触媒と酸素発生光触媒とは、互いに接合されて構成される。なお、本発明の説明において酸素発生光触媒のフェルミ準位と、水素発生光触媒のフェルミ準位とを比較する場合、全て耐標準水素電極電位で比較した場合の正側、負側について示している。 When comparing the hydrogen generation photocatalyst and the oxygen generation photocatalyst with reference to the standard hydrogen electrode potential, the Fermi level of the hydrogen generation photocatalyst is more negative than the Fermi level of the oxygen generation photocatalyst, or the same Fermi level. Further, the hydrogen generation photocatalyst and the oxygen generation photocatalyst are configured to be joined to each other. In the description of the present invention, when comparing the Fermi level of the oxygen-generating photocatalyst and the Fermi level of the hydrogen-generating photocatalyst, the positive side and the negative side when all are compared with the standard hydrogen electrode potential are shown.
これにより、水素発生光触媒と酸素発生光触媒とは、オーミック接合されるので、水を分解することに寄与しない、水素発生光触媒中の正孔と酸素発生光触媒中の電子とが、このオーミック接合により互いに結合する。よって、従来のＺスキームでは、酸化還元剤により処理する必要があった水分解に寄与しない正孔と電子を、酸化還元剤を必要とすることなく容易に処理することが可能になった。 As a result, since the hydrogen generating photocatalyst and the oxygen generating photocatalyst are ohmic-bonded, the holes in the hydrogen-generating photocatalyst and the electrons in the oxygen-generating photocatalyst that do not contribute to the decomposition of water are mutually connected by this ohmic junction. Join. Therefore, in the conventional Z scheme, it has become possible to easily treat holes and electrons that do not contribute to water decomposition, which had to be treated with a redox agent, without requiring a redox agent.
更に、酸化還元剤を使用した場合、正孔と電子の授受効率が良くなかったため、水の分解に寄与できる電子と正孔とが、水の分解に寄与しない正孔と電子とに、それぞれの触媒中で再結合し水分解に寄与できなくなってしまい、水の分解効率が良くなかった。しかしながら、本発明においては、水素発生光触媒と酸素発生光触媒とをオーミック接合しているため、水分解に寄与しない正孔と電子を処理する効率が高く触媒中に水分解に寄与しない正孔と電子がほとんど存在しないので、水の分解が阻害されることなく、水の分解効率が良好になった。 Furthermore, when the redox agent was used, the transfer efficiency of holes and electrons was not good, so that electrons and holes that can contribute to water decomposition are converted into holes and electrons that do not contribute to water decomposition, respectively. The recombination in the catalyst could not contribute to water decomposition, and the water decomposition efficiency was not good. However, in the present invention, since the hydrogen generating photocatalyst and the oxygen generating photocatalyst are ohmic-bonded, holes and electrons that do not contribute to water splitting are highly efficient in treating the holes and electrons that do not contribute to water splitting. Since water is hardly present, water decomposition efficiency is improved without inhibiting water decomposition.
＜オーミック接合について＞
次に、水素発生光触媒と、酸素発生光触媒とのオーミック接合について図２を参照して更に詳しく説明する。図２は、半導体接合及び光照射によるバンドの変化を表した図である。図２は、酸素発生光触媒として用いられるｎ型半導体と、水素発生光触媒として用いられるｐ型半導体を接合させたときのバンド状態を表している。図中の、Evac、ECBM、EF、EVBMは、それぞれ真空準位、伝導帯下端、フェルミ準位、価電子帯上端を示す。ここで、図２においては、酸素発生光触媒としてｎ型半導体、水素発生光触媒としてｐ型半導体を例にとって説明しているが、本発明は、この組み合わせに限定されるものではない。<About ohmic bonding>
Next, the ohmic junction between the hydrogen generation photocatalyst and the oxygen generation photocatalyst will be described in more detail with reference to FIG. FIG. 2 is a diagram showing a band change due to semiconductor junction and light irradiation. FIG. 2 shows a band state when an n-type semiconductor used as an oxygen generation photocatalyst and a p-type semiconductor used as a hydrogen generation photocatalyst are joined. In the figure, E vac , E CBM , E F , and E VBM represent a vacuum level, a conduction band lower end, a Fermi level, and a valence band upper end, respectively. In FIG. 2, an n-type semiconductor is described as an example of an oxygen generation photocatalyst and a p-type semiconductor is used as an example of a hydrogen generation photocatalyst. However, the present invention is not limited to this combination.
図２の左側は、酸素発生光触媒（ｎ型半導体）と水素発生光触媒（ｐ型半導体）についてのバンドの状態を表している。図２の左側に示すように、酸素発生光触媒（ｎ型半導体）のフェルミ準位よりも水素発生光触媒（ｐ型半導体）のフェルミ準位の方が正側（図２において縦軸の下側）にある。これは、整流性ｐｎ接合として知られた状態であり、酸素発生光触媒（ｎ型半導体）と水素発生光触媒（ｐ型半導体）の接合界面は、空乏層になる。 The left side of FIG. 2 represents the band states for the oxygen generating photocatalyst (n-type semiconductor) and the hydrogen generating photocatalyst (p-type semiconductor). As shown on the left side of FIG. 2, the Fermi level of the hydrogen generating photocatalyst (p-type semiconductor) is more positive than the Fermi level of the oxygen generating photocatalyst (n-type semiconductor) (lower side of the vertical axis in FIG. 2). It is in. This is a state known as a rectifying pn junction, and the junction interface between the oxygen generating photocatalyst (n-type semiconductor) and the hydrogen generating photocatalyst (p-type semiconductor) becomes a depletion layer.
光照射中は、価電子帯の電子が励起されて伝導帯に移動するが、電子はエネルギー的に安定な状態になるべく、図２の左側である酸素発生光触媒（ｎ型半導体）に移動し、価電子帯の電子が励起されて伝導帯に移動することによって生じた価電子帯の正孔は、エネルギー的に安定な状態になるべく図２の右側である水素発生光触媒（ｐ型半導体）に移動する。このため、酸素発生光触媒は、正孔が不足して水を酸化する力が不足し、水素発生光触媒は、電子が不足して水を還元する力が不足する。さらに、水素発生光触媒側に移動した正孔は酸化力が低下し、水を酸化する力が不足し、酸素発生光触媒側に移動した電子は還元力が低下し、水を還元する力が不足する。 During light irradiation, electrons in the valence band are excited and move to the conduction band, but the electrons move to the oxygen generation photocatalyst (n-type semiconductor) on the left side of FIG. The holes in the valence band generated by the excitation of the electrons in the valence band to the conduction band move to the hydrogen generation photocatalyst (p-type semiconductor) on the right side of FIG. 2 so as to be in an energetically stable state. To do. For this reason, the oxygen generating photocatalyst has insufficient holes to oxidize water, and the hydrogen generating photocatalyst has insufficient electrons to reduce water. Furthermore, the holes that have moved to the hydrogen generating photocatalyst have a low oxidizing power and the ability to oxidize water is insufficient, and the electrons that have moved to the oxygen generating photocatalyst have a reducing power that is insufficient to reduce water. .
また、Ｚスキームにおいては酸素発生光触媒（ｎ型半導体）と水素発生光触媒（ｐ型半導体）は、接合されていないので、酸素発生光触媒、水素発生光触媒の間で電子、正孔の移動は発生しない。そのため、Ｚスキームにおいては、酸化還元剤を使用して、酸素発生光触媒（ｎ型半導体）側で水の還元に寄与しない電子と、水素発生光触媒（ｐ型半導体）で水の酸化に寄与しない正孔とを中和している。 In the Z scheme, since the oxygen generating photocatalyst (n-type semiconductor) and the hydrogen generating photocatalyst (p-type semiconductor) are not joined, no movement of electrons and holes occurs between the oxygen generating photocatalyst and the hydrogen generating photocatalyst. . Therefore, in the Z scheme, an oxidation-reduction agent is used, and an electron that does not contribute to the reduction of water on the oxygen generation photocatalyst (n-type semiconductor) side and a positive that does not contribute to the oxidation of water on the hydrogen generation photocatalyst (p-type semiconductor). Neutralizes the pores.
図２の右側は、本発明の酸素発生光触媒（ｎ型半導体）と水素発生光触媒（ｐ型半導体）についてのバンドの状態を表している。図２の右側に示すように、酸素発生光触媒（ｎ型半導体）のフェルミ準位よりも水素発生光触媒（ｐ型半導体）のフェルミ準位の方が負側（図２において縦軸の上側）にある。 The right side of FIG. 2 represents the band state for the oxygen generating photocatalyst (n-type semiconductor) and the hydrogen generating photocatalyst (p-type semiconductor) of the present invention. As shown on the right side of FIG. 2, the Fermi level of the hydrogen generating photocatalyst (p-type semiconductor) is more negative on the negative side (upper side of the vertical axis in FIG. 2) than the Fermi level of the oxygen generating photocatalyst (n-type semiconductor). is there.
これにより、酸素発生光触媒（ｎ型半導体）と水素発生光触媒（ｐ型半導体）を接合すると、図２に示すように接合界面はオーミック接合になり、電子と正孔の移動が可能になる。ここで、フェルミ準位が上記条件を満たすｎ型半導体とｐ型半導体であるIn2O3とCu2Oを接合するとオーミック接合になることが、H. Tanaka et al, Thin Solid Films, 469-470, 80-85(2004)に記載されている。このように、オーミック接合になることによって、酸化還元剤を使用しなくても、酸素発生光触媒（ｎ型半導体）側で水の還元に寄与しない電子と、水素発生光触媒（ｐ型半導体）で水の酸化に寄与しない正孔とを直接中和させることが出来る。As a result, when the oxygen generating photocatalyst (n-type semiconductor) and the hydrogen generating photocatalyst (p-type semiconductor) are joined, the joining interface becomes an ohmic junction as shown in FIG. 2, and electrons and holes can move. Here, when In 2 O 3 and Cu 2 O, which are n-type semiconductors and p-type semiconductors whose Fermi level satisfies the above conditions, are joined, an ohmic junction is formed. H. Tanaka et al, Thin Solid Films, 469- 470, 80-85 (2004). Thus, by forming an ohmic junction, an electron that does not contribute to the reduction of water on the oxygen generation photocatalyst (n-type semiconductor) side without using a redox agent and water with a hydrogen generation photocatalyst (p-type semiconductor). It is possible to directly neutralize holes that do not contribute to oxidation.
また、図２に示すように、酸素発生光触媒（ｎ型半導体）側で余った電子は、エネルギー的に安定な状態になるために水素発生光触媒（ｐ型半導体）との接合部に移動し、水素発生光触媒（ｐ型半導体）で余った正孔は、エネルギー的に安定な状態になるために酸素発生光触媒（ｎ型半導体）との接合部に移動する。そして、接合部においてこれら水の還元と酸化に寄与しない電子と正孔は再結合で消滅する。このように、水の還元と酸化に寄与しない電子と正孔との中和を効率良く行うことが出来る。 In addition, as shown in FIG. 2, the surplus electrons on the oxygen generation photocatalyst (n-type semiconductor) side move to the junction with the hydrogen generation photocatalyst (p-type semiconductor) in order to become stable in energy, The surplus holes in the hydrogen generating photocatalyst (p-type semiconductor) move to the junction with the oxygen generating photocatalyst (n-type semiconductor) in order to become stable in terms of energy. Then, electrons and holes that do not contribute to the reduction and oxidation of water disappear at the junction by recombination. Thus, neutralization of electrons and holes that do not contribute to the reduction and oxidation of water can be performed efficiently.
このため、酸素発生光触媒（ｎ型半導体）側には、水の還元に寄与しない電子（伝導帯電子）が存在しないため、水を酸化して酸素を発生させるための正孔（価電子帯正孔）が、この伝導帯電子と再結合し消滅することがほとんど無いので、正孔が多く存在し、水を分解して酸素を発生させる効率がよい。同様に、水素発生光触媒（ｐ型半導体）側には、水の酸化に寄与しない正孔（価電子帯正孔）が存在しないため、水を還元して水素を発生させるための電子が、この価電子帯正孔と再結合して消滅することがほとんど無いので、電子が多く存在し、水を還元して水素を発生させる効率がよい。 For this reason, since there are no electrons (conduction band electrons) that do not contribute to the reduction of water on the oxygen generation photocatalyst (n-type semiconductor) side, positive holes for generating oxygen by oxidizing water (valence band positive) Hole) is recombined with the conduction band electrons and hardly disappears, so that there are many holes, and the efficiency of generating oxygen by decomposing water is good. Similarly, since there are no holes (valence band holes) that do not contribute to the oxidation of water on the hydrogen generation photocatalyst (p-type semiconductor) side, electrons for reducing water to generate hydrogen Since there is almost no annihilation due to recombination with valence band holes, there are many electrons, and the efficiency of reducing water to generate hydrogen is good.
更に、図２の光照射中の図に示されるように、本発明においては、従来のｐｎ接合で発生する伝導帯での電子の酸素発生光触媒（ｎ型半導体）側への移動、価電子帯での正孔の水素発生光触媒（ｐ型半導体）側への移動が発生しないため、酸素発生光触媒（ｎ型半導体）での正孔の酸化力の低下、水素発生光触媒（ｐ型半導体）での電子の還元力の低下が発生しない。これにより、水の分解効率の低下を防ぐことが出来る。 Furthermore, as shown in the diagram during light irradiation in FIG. 2, in the present invention, electrons move to the oxygen generation photocatalyst (n-type semiconductor) side in the conduction band generated in the conventional pn junction, the valence band. Since no movement of holes to the hydrogen generation photocatalyst (p-type semiconductor) side occurs, the oxidation power of holes in the oxygen generation photocatalyst (n-type semiconductor) decreases, and in the hydrogen generation photocatalyst (p-type semiconductor) The reduction of electron reducing power does not occur. Thereby, the fall of the decomposition efficiency of water can be prevented.
ここで、酸素発生光触媒と水素発生光触媒のフェルミ準位が同じであっても、上述したのと同様であるので説明は省略するが、上述したのと同様にオーミック接合になり、同様の作用効果を得ることが出来る。ただし、酸素発生光触媒と水素発生光触媒のフェルミ準位が同じ場合よりも、水素発生光触媒（ｐ型半導体）が、酸素発生光触媒のフェルミ準位より負側にある場合の方が、バンドの湾曲が正孔・電子の拡散の駆動力になるため、正孔・電子の移動に有利である。このため、水の還元と酸化に寄与しない電子と正孔を効率よく再結合で消滅させることが出来るので、酸素発生光触媒と水素発生光触媒のフェルミ準位が同じ場合よりも、水素発生光触媒が、酸素発生光触媒のフェルミ準位より負側にある場合の方が水を分解して酸素と水素を発生させる効率が良好になる。 Here, even if the oxygen generation photocatalyst and the hydrogen generation photocatalyst have the same Fermi level, the description is omitted because it is the same as described above. Can be obtained. However, the curvature of the band is more when the hydrogen generating photocatalyst (p-type semiconductor) is on the negative side than the Fermi level of the oxygen generating photocatalyst than when the Fermi level of the oxygen generating photocatalyst is the same as that of the hydrogen generating photocatalyst. This is a driving force for the diffusion of holes and electrons, which is advantageous for the movement of holes and electrons. For this reason, since electrons and holes that do not contribute to the reduction and oxidation of water can be efficiently annihilated by recombination, the hydrogen generation photocatalyst is more than the case where the Fermi levels of the oxygen generation photocatalyst and the hydrogen generation photocatalyst are the same. When the oxygen generation photocatalyst is on the negative side of the Fermi level, the efficiency of generating oxygen and hydrogen by decomposing water is improved.
＜水分解反応機構＞
次に、光触媒組成物の水分解機構について、図３を参照して更に詳しく説明する。図３は、光触媒組成物の水分解反応機構を説明する説明図である。図３の縦軸は、標準水素電極電位を基準にした電位ポテンシャルである。<Water splitting reaction mechanism>
Next, the water splitting mechanism of the photocatalyst composition will be described in more detail with reference to FIG. FIG. 3 is an explanatory diagram for explaining the water splitting reaction mechanism of the photocatalyst composition. The vertical axis in FIG. 3 is a potential potential based on the standard hydrogen electrode potential.
図３に示すように、酸素発生光触媒は、価電子帯の上端が１．２３Ｖよりも正の電位（図３の縦軸では、下側が正の電位）である物質で構成されている。これにより、水を分解して酸素を発生することができる。また、水素発生光触媒は、伝導帯の下端が０Ｖより負の電位（図３の縦軸では、上側が負の電位）である物質で構成されている。これにより、水を分解して水素を発生することが出来る。 As shown in FIG. 3, the oxygen-generating photocatalyst is composed of a substance whose upper end of the valence band is more positive than 1.23 V (on the vertical axis in FIG. 3, the lower side is positive). Thereby, oxygen can be generated by decomposing water. Further, the hydrogen generation photocatalyst is composed of a substance whose lower end of the conduction band has a negative potential from 0 V (the vertical axis in FIG. 3 has a negative potential on the upper side). Thereby, water can be decomposed | disassembled and hydrogen can be generated.
この酸素発生光触媒と水素発生光触媒とを接合することにより、バンド構造が変化して、接合界面は、図３に示すようにオーミック接合になる。この互いに接合された酸素発生光触媒と水素発生光触媒とに可視光線を照射することにより、酸素発生光触媒の価電子帯の電子が励起されて、価電子帯に正孔が発生し、この正孔が水を酸化して酸素を発生させ、水素発生光触媒の価電子帯の電子が励起されて伝導帯に移動し、伝導帯に移動した電子が水を還元して水素を発生させる。酸素発生光触媒の伝導帯に発生した電子と、水素発生光触媒の価電子帯に発生した正孔は、オーミック接合部分で再結合して消滅する。 By joining the oxygen generating photocatalyst and the hydrogen generating photocatalyst, the band structure is changed, and the joining interface becomes an ohmic junction as shown in FIG. By irradiating visible light to the oxygen-generating photocatalyst and the hydrogen-generating photocatalyst bonded to each other, electrons in the valence band of the oxygen-generating photocatalyst are excited, and holes are generated in the valence band. Oxygen is generated by oxidizing water, and electrons in the valence band of the hydrogen generating photocatalyst are excited to move to the conduction band, and the electrons moved to the conduction band reduce water to generate hydrogen. The electrons generated in the conduction band of the oxygen generating photocatalyst and the holes generated in the valence band of the hydrogen generating photocatalyst are recombined at the ohmic junction and disappear.
次に、本発明の光触媒組成物を構成する酸素発生光触媒、水素発生光触媒の一例を図４に示す。図４は、本発明の光触媒組成物を構成する物質の例を表す図である。図４においては、各物質ごとに価電子帯の下端、伝導帯の上端、バンドギャップエネルギーの値が示されている。また、縦軸は、標準水素電極電を基準にした電位ポテンシャルを示している。図中に、水素と酸素の電位ポテンシャルの位置を点線で表している。 Next, an example of the oxygen generation photocatalyst and the hydrogen generation photocatalyst constituting the photocatalyst composition of the present invention is shown in FIG. FIG. 4 is a diagram showing examples of substances constituting the photocatalyst composition of the present invention. In FIG. 4, the lower end of the valence band, the upper end of the conduction band, and the value of the band gap energy are shown for each substance. The vertical axis shows the potential potential with reference to the standard hydrogen electrode power. In the figure, the position of the potential potential of hydrogen and oxygen is indicated by a dotted line.
図４に示すように、ここに示された物質は、TiO2を除いてバンドギャップエネルギーは、３．０ｅＶ以下なので、可視光線を吸収して価電子帯の電子が伝導帯に励起する。また、Fe2O3、WO3、In2O3、は、価電子帯の下端が酸素の電位ポテンシャルである１．２３Ｖよりも正の電位（図４の縦軸の下側）なので、酸素発生光触媒になりうる。Cu2O、Siは、伝導帯の下端が水素の電位ポテンシャルである０Ｖよりも負の電位（図４の縦軸の上側）なので、水素発生光触媒になりうる。ここで、TiO2は、バンドギャップエネルギーが３．２ｅＶですこし３．０ｅＶよりも大きい。よって、可視光より少し短波長の光を吸収することになるが、それを容認するならば本発明の酸素発生光触媒または水素発生光触媒として用いることも可能である。As shown in FIG. 4, the material shown here has a band gap energy of 3.0 eV or less except for TiO 2 , so that it absorbs visible light and excites electrons in the valence band to the conduction band. Fe 2 O 3 , WO 3 , and In 2 O 3 have oxygen atoms at the lower end of the valence band that are more positive than the oxygen potential of 1.23 V (below the vertical axis in FIG. 4). Can be a generated photocatalyst. Cu 2 O and Si can be a hydrogen generation photocatalyst because the lower end of the conduction band is a negative potential (upper side of the vertical axis in FIG. 4) than 0 V, which is the potential potential of hydrogen. Here, TiO 2 has a band gap energy of 3.2 eV, which is larger than 3.0 eV. Therefore, although it absorbs light having a wavelength slightly shorter than visible light, it can be used as the oxygen-generating photocatalyst or hydrogen-generating photocatalyst of the present invention if it is acceptable.
＜本発明の光触媒組成物評価＞
本発明の光触媒組成物について、可視光線を用いた水の分解について評価を行うための評価を行った。光触媒組成物は、以下に記載するように、水素発生光触媒と酸素発生光触媒を混合し、接合させることによって作製した。<Evaluation of the photocatalyst composition of the present invention>
The photocatalyst composition of the present invention was evaluated for evaluating the decomposition of water using visible light. The photocatalyst composition was prepared by mixing and joining a hydrogen generating photocatalyst and an oxygen generating photocatalyst as described below.
（１）準備及び評価方法
ここで準備したものは、これから記載する評価に使用される。試料は、スターバーストミニ（HJP025001、スギノマシン製）を用いて粉砕し、微粒子化した。試料の接合（酸素発生光触媒と水素発生光触媒の接合）前後の形状観察は、走査型電子顕微鏡（SEM、S-4500、日立製）を用いて行った。光を照射する光源には、林時計工業製のキセノンランプ（LA-410UV）を使用した。このキセノンランプの照射光のスペクトルを図５に示す。水分解装置としては、幕張理化学硝子製作所製のCLS-1370-PSWGを用いた。水分解により発生した酸素、水素は、ガスクロマトグラフ（GC-8A、島津製作所製）を用いて分析を行った。(1) Preparation and evaluation method What was prepared here is used for evaluation described from now on. The sample was pulverized using a Starburst Mini (HJP025001, manufactured by Sugino Machine) to make fine particles. The shape observation before and after the joining of the sample (joining of the oxygen generating photocatalyst and the hydrogen generating photocatalyst) was performed using a scanning electron microscope (SEM, S-4500, manufactured by Hitachi). A xenon lamp (LA-410UV) manufactured by Hayashi Clock Industry was used as the light source. FIG. 5 shows the spectrum of the irradiation light of this xenon lamp. As the water splitting device, CLS-1370-PSWG manufactured by Makuhari Chemical Chemical Glass Works was used. Oxygen and hydrogen generated by water splitting were analyzed using a gas chromatograph (GC-8A, manufactured by Shimadzu Corporation).
水素発生光触媒としては、Si（４N、>９９．９９％、関東化学製）、Cu2O（３N、>９９．９９％、関東化学製）を用い、酸素発生光触媒としては、WO3（２N、>９９％、関東化学製）、In2O3（３N、>９９．９９％、関東化学製）を用いた。Cu2Oは、粉砕、微粒子化せずに使用した。Siは、粉砕の程度によって2種類の試料（Si-1、Si-2）を準備した。最終的な光触媒組成物は、SiとWO3を接合することにより調製した。接合は、遊星ボールミル（セラミックボール６０ｇ）を用いて、SiとWO3を５０rpmで１０分間混合することにより行った。As the hydrogen generation photocatalyst, Si (4N,> 99.99%, manufactured by Kanto Chemical Co., Inc.) and Cu 2 O (3N,> 99.99%, manufactured by Kanto Chemical Co., Ltd.) were used, and as the oxygen generation photocatalyst, WO 3 (2N ,> 99%, manufactured by Kanto Chemical Co., Ltd.), In 2 O 3 (3N,> 99.99%, manufactured by Kanto Chemical Co., Ltd.). Cu 2 O was used without being pulverized or finely divided. Si prepared two types of samples (Si-1, Si-2) according to the degree of grinding. The final photocatalyst composition was prepared by joining the Si and WO 3. Bonding was performed by mixing Si and WO 3 at 50 rpm for 10 minutes using a planetary ball mill (ceramic ball 60 g).
試料粉砕前後の各試料の粒径をレーザ回折／散乱式粒度分布測定装置LA-910W型を用いて測定した。測定結果を図６に示す。図６は、試料粉砕前後の各試料の粒径を示す表である。また、試料の粉砕前後のSEM画像を図７、図８に、試料の接合後のSEM画像を図９に示す。図７は、Siの粉砕前後のSEM画像と、WO3の粉砕後のSEM画像である。図８は、In2O3とFe2O3の粉砕前後のSEM画像である。図９は、Si-2とWO3をwt%で、Si-2：WO3＝1：6になるように混合し接合した試料のSEM画像である。図９のSEM画像から、Si粒子上にWO3粒子が担持されていることが分かる。The particle size of each sample before and after sample crushing was measured using a laser diffraction / scattering particle size distribution analyzer LA-910W. The measurement results are shown in FIG. FIG. 6 is a table showing the particle size of each sample before and after sample crushing. 7 and 8 show SEM images before and after pulverization of the sample, and FIG. 9 shows SEM images after bonding of the sample. FIG. 7 shows SEM images before and after the pulverization of Si and an SEM image after the pulverization of WO 3 . FIG. 8 is SEM images of In 2 O 3 and Fe 2 O 3 before and after grinding. FIG. 9 is an SEM image of a sample obtained by mixing and bonding Si-2 and WO 3 at wt% so that Si-2: WO 3 = 1: 6. From the SEM image of FIG. 9, it can be seen that WO 3 particles are supported on the Si particles.
（２）事前評価（拡散反射スペクトル測定）
事前評価として、SiとWO3の拡散反射スペクトルを測定した。測定結果を図１０に示す。図１０は、SiとWO3の拡散反射スペクトルを示す図である。この図において、横軸は、波長（nm）を表し、左側の縦軸は、１から反射率を引いたもの（吸収率）を、右側の縦軸は、光の波長を表す。この拡散反射スペクトルから次のようにしてSiとWO3の吸収光子数の比を求めた。(2) Prior evaluation (diffuse reflection spectrum measurement)
As a prior evaluation, the diffuse reflection spectra of Si and WO 3 were measured. The measurement results are shown in FIG. FIG. 10 is a diagram showing diffuse reflection spectra of Si and WO 3 . In this figure, the horizontal axis represents the wavelength (nm), the left vertical axis represents 1 minus the reflectance (absorption rate), and the right vertical axis represents the wavelength of light. From this diffuse reflection spectrum, the ratio of the number of absorbed photons of Si and WO 3 was determined as follows.
照射光の波長1 nm毎に対して光強度が分かっているので、照射光の波長1 nm毎に対する照射光子数を計算した。照射光子数に対してSiとWO3の吸収率が図１０の拡散反射スペクトルから求まっているため、それぞれの波長1 nm毎の吸収光子数を次式によって求めた。Since the light intensity is known for each wavelength of irradiated light, the number of irradiated photons for each wavelength of irradiated light was calculated. Since the absorption rates of Si and WO 3 are obtained from the diffuse reflection spectrum of FIG. 10 with respect to the number of irradiated photons, the number of absorbed photons for each wavelength of 1 nm was obtained by the following equation.
（波長1 nm毎の吸収光子数）＝（照射光の波長1 nm毎に対する照射光子数）×（吸収率）
波長1 nm毎の吸収光子数を積分することによって、SiとWO3の吸収光子数が算出し、SiとWO3の吸収光子数の比を求めた。(Number of absorbed photons per wavelength 1 nm) = (Number of irradiated photons per 1 nm wavelength of irradiated light) x (Absorptance)
By integrating the number of absorbed photons for each wavelength of 1 nm, the number of absorbed photons of Si and WO 3 was calculated, and the ratio of the number of absorbed photons of Si and WO 3 was obtained.
このようにして求めたSiとWO3の吸収光子数の比は、Si：WO3＝２：１である。よって、キセノンランプのスペクトルに対して吸収光子数を同じにするためには、光触媒組成物を構成するSiとWO3の体積比は、Si：WO3＝１：２になることが必要である。ここで、Si：WO3の密度はそれぞれ、２．３３g/cm3、７．１６g/cm3なのでSi/WO3接合系の試料調製の割合を質量比１：６と見積もった。このようにして求められた１：６（Si：WO3）の質量比で、（１）準備及び評価方法で記載したように、SiとWO3をボールミルで混合して光触媒組成物を作製した。このとき、Siは、試料Si-2を用いた。The ratio of the number of absorbed photons between Si and WO 3 obtained in this way is Si: WO 3 = 2: 1. Therefore, in order to make the number of absorbed photons the same as the spectrum of the xenon lamp, the volume ratio of Si and WO 3 constituting the photocatalyst composition needs to be Si: WO 3 = 1: 2. . Here, Si: each density of WO 3 is, 2.33g / cm 3, 7.16g / cm 3 since Si / WO 3 junctions mass ratio the ratio of the sample preparation 1: 6 and estimated. A photocatalyst composition was prepared by mixing Si and WO 3 with a ball mill at a mass ratio of 1: 6 (Si: WO 3 ) thus obtained, as described in (1) Preparation and Evaluation Method. . At this time, sample Si-2 was used as Si.
（３）本発明の光触媒組成物を構成する触媒の個別評価
水素発生光触媒と酸素発生光触媒を混合することなく、個別に犠牲剤（HCHO及びAg+、Fe3+）の存在下で光照射による水の分解評価を行った。水素発生光触媒としては、Si（Si-1）、Cu2Oを用い、酸素発生光触媒としては、WO3、In2O3を用いた。(3) Individual evaluation of the catalyst constituting the photocatalyst composition of the present invention By light irradiation in the presence of a sacrificial agent (HCHO and Ag + , Fe 3+ ) individually without mixing the hydrogen generating photocatalyst and the oxygen generating photocatalyst Water decomposition was evaluated. Si (Si-1) and Cu 2 O were used as the hydrogen generation photocatalyst, and WO 3 and In 2 O 3 were used as the oxygen generation photocatalyst.
この評価は、水素発生光触媒については、犠牲剤としてHCHOaqを添加した蒸留水12ml中で、酸素発生光触媒については、犠牲剤としてFe3+（WO3）またはAg+（In2O3）を添加した蒸留水12ml中で、試料60mgをマグネチックスターラーと撹拌子を用いて撹拌させながら光源から光を試料に向かって照射し、発生する気体の種類、量を測定することにより行った。また、光触媒反応は、蒸留水中の残留気体除去のため、反応容器中の試料溶液を真空引きし、アルゴンガス（50kPa）で置換後に行った。In this evaluation, for hydrogen generation photocatalyst, 12 ml of distilled water with HCHOaq added as a sacrificial agent was added. For oxygen generation photocatalyst, Fe 3+ (WO 3 ) or Ag + (In 2 O 3 ) was added as a sacrificial agent. In 12 ml of distilled water, 60 mg of the sample was stirred with a magnetic stirrer and a stirrer while irradiating light from the light source toward the sample and measuring the type and amount of the generated gas. The photocatalytic reaction was performed after the sample solution in the reaction vessel was evacuated and replaced with argon gas (50 kPa) in order to remove residual gas in distilled water.
結果を図１１、図１２に示す。図１１は、水素発生光触媒に光を照射したときの水素発生量を示す図である。図１１の横軸は、光照射時間を示し、縦軸は、水素発生光触媒の単位重量あたりの水素発生量（μmol/g）を示す。図１２は、酸素発生光触媒に光を照射したときの酸素発生量を示す図である。図１２の横軸は、光照射時間を示し、縦軸は、酸素発生光触媒の単位重量あたりの酸素発生量（μmol/g）示す。 The results are shown in FIGS. FIG. 11 is a diagram showing the amount of hydrogen generation when the hydrogen generation photocatalyst is irradiated with light. The horizontal axis in FIG. 11 indicates the light irradiation time, and the vertical axis indicates the hydrogen generation amount (μmol / g) per unit weight of the hydrogen generation photocatalyst. FIG. 12 is a diagram showing the amount of oxygen generated when the oxygen generating photocatalyst is irradiated with light. The horizontal axis in FIG. 12 indicates the light irradiation time, and the vertical axis indicates the oxygen generation amount (μmol / g) per unit weight of the oxygen generation photocatalyst.
図１１、図１２に示されるように、Si（Si-1）、Cu2Oは、水を分解して水素を発生させた。また、WO3、In2O3は、水を分解して酸素を発生させた。Siの水素発生量は、直線的に増加し、Cu2Oは、カーブを描く傾向を示した。WO3においては、酸素発生が２時間経過以降減衰しているが、これは投入したFe3+濃度を考えると、犠牲剤が全て消費されたため、即ち、犠牲剤であるFe3+がすべて還元されてFe2+になったためと考えられる。As shown in FIGS. 11 and 12, Si (Si-1) and Cu 2 O decomposed water to generate hydrogen. WO 3 and In 2 O 3 decomposed water to generate oxygen. The hydrogen generation amount of Si increased linearly, and Cu 2 O showed a tendency to draw a curve. In WO 3 , oxygen generation has attenuated after the lapse of 2 hours. This is because all of the sacrificial agent has been consumed considering the concentration of Fe 3+ charged , that is, all of the sacrificial Fe 3+ has been reduced. This is thought to be due to Fe 2+ .
（４）本発明の光触媒組成物の評価
上述したように、Si（Si-2）とWO3を混合して作製した光触媒組成物は、蒸留水12ml中で、光触媒組成物60mgをマグネチックスターラーと撹拌子を用いて撹拌させながら光源から光を試料に向かって照射し、発生する気体の種類、量を測定することにより行った。また、光触媒反応は、蒸留水中の残留気体除去のため、反応容器中の試料溶液を真空引きし、アルゴンガス（50kPa）で置換後に行った。(4) Evaluation of the photocatalyst composition of the present invention As described above, a photocatalyst composition prepared by mixing Si (Si-2) and WO 3 was obtained by adding 60 mg of the photocatalyst composition to a magnetic stirrer in 12 ml of distilled water. The sample was irradiated with light from a light source while being stirred using a stir bar, and the kind and amount of the generated gas were measured. The photocatalytic reaction was performed after the sample solution in the reaction vessel was evacuated and replaced with argon gas (50 kPa) in order to remove residual gas in distilled water.
結果を図１３に示す。図１３は、光触媒組成物に光を照射したときの水素発生量と酸素発生量を示す図である。図１３の横軸は、光照射時間を示し、縦軸は、光触媒組成物の単位重量あたりの水素発生量（μmol/g）示す。 The results are shown in FIG. FIG. 13 is a diagram showing the hydrogen generation amount and the oxygen generation amount when the photocatalyst composition is irradiated with light. The horizontal axis of FIG. 13 indicates the light irradiation time, and the vertical axis indicates the amount of hydrogen generation (μmol / g) per unit weight of the photocatalyst composition.
図１３に示されるように、光触媒組成物は、犠牲剤を添加することなく、水を分解して酸素と水素を発生させた。ここで、使用した水は、蒸留水のみでありpH調製なども行っていない。 As shown in FIG. 13, the photocatalytic composition decomposed water to generate oxygen and hydrogen without adding a sacrificial agent. Here, the water used was only distilled water, and the pH was not adjusted.
水素と酸素の発生量は、化学量論的には２：１になるはずであるが、２：１になっていない。これは、以下の理由からである。図１３に示すように、WO3のみでは、蒸留水中（犠牲剤無し）で酸素は発生しない。Siのみの場合は、蒸留水中（犠牲剤無し）で水素が発生することを実験において確認した。これより、遊星ボールミルを用いた接合では、部分的にSiとWO3は、分離していると考えられ、分離したSi、即ちWO3と接合していないSiは、それ単独でも水素を発生させるが、分離したWO3、即ちSiと接合していないWO3は、酸素を発生しないため化学量論比よりも水素が多く発生していると考えられる。これは、遊星ボールミルでの接合条件が最適化されていないためであると考えられる。The amount of hydrogen and oxygen generated should be 2: 1 stoichiometrically, but not 2: 1. This is for the following reason. As shown in FIG. 13, with WO 3 alone, oxygen is not generated in distilled water (no sacrificial agent). In the case of Si alone, it was confirmed in an experiment that hydrogen is generated in distilled water (no sacrificial agent). From this, it can be considered that Si and WO 3 are partially separated in bonding using a planetary ball mill, and separated Si, that is, Si not bonded to WO 3 generates hydrogen alone. However, it is considered that separated WO 3 , that is, WO 3 not bonded to Si does not generate oxygen and thus generates more hydrogen than the stoichiometric ratio. This is considered to be because the joining conditions in the planetary ball mill are not optimized.
＜オーミック特性評価＞
次にオーミック特性評価について説明する。この評価は、Si（i型、p型）とWO3を接合し、電流電圧特性を測定することによりオーミック接合されているか否かを評価するものである。<Ohm characteristic evaluation>
Next, the ohmic characteristic evaluation will be described. In this evaluation, Si (i-type, p-type) and WO 3 are joined, and current-voltage characteristics are measured to evaluate whether or not they are ohmic joined.
（１）サンプル作成
Siとして、i型のSiウエハとp型のSiウエハとを準備し、それぞれのウエハをRCA洗浄し、その後にスパッタでWO3膜を成膜した。スパッタ条件を、下記の表1に示す。(1) Sample creation
As Si, an i-type Si wafer and a p-type Si wafer were prepared, each wafer was RCA cleaned, and then a WO 3 film was formed by sputtering. The sputtering conditions are shown in Table 1 below.
・プレスパッタ Ar100% 5min → Ar60％ O240%
・本スパッタ Ar60％ O240% 16min
成膜は、膜厚200nmを目標にして、成膜レートが12.6nm/minなので、16min本スパッタを行った。
・ Pre-sputtering Ar100% 5min → Ar60% O 2 40%
・ Sputter Ar60% O 2 40% 16min
Film formation was performed for 16 minutes since the film formation rate was 12.6 nm / min with a target film thickness of 200 nm.
（２）電流電圧特性評価
成膜後のSiウエハ表面と、Siウエハに成膜されたWO3膜表面に電極としてPtを25minスパッタした。このサンプルについて図１４を用いて更に説明する。図１４は、オーミック特性評価用サンプルの概略側面図である。(2) Evaluation of current-voltage characteristics Pt was sputtered for 25 min as an electrode on the Si wafer surface after film formation and on the WO 3 film surface formed on the Si wafer. This sample will be further described with reference to FIG. FIG. 14 is a schematic side view of a sample for evaluating ohmic characteristics.
スライドガラス１０の上には、Siウエハ２０が貼付されている。Siウエハ２０の一部には、WO3膜３０が成膜されており、WO3膜３０上には、Pt膜４０が形成されている。また、Si膜３０上には、Pt膜５０が形成されている。On the slide glass 10, the Si wafer 20 is stuck. Some of the Si wafer 20, WO 3 and film 30 is deposited, on the WO 3 film 30, Pt film 40 is formed. A Pt film 50 is formed on the Si film 30.
Pt膜４０とPt膜５０には、それぞれ銀ペースト６０、７０によって、Cu線８０、９０が接続されている。Cu線８０にプラス端子、Cu線９０にマイナス端子を接続し、オートマチックポラリゼーションシステム（HSV-110、北斗電工株式会社）を用いて電流電圧特性を測定した。電流電圧特性の測定は、光がSiウエハに当たらないように暗い状態（以下、暗時と称する。）での測定と、光をSiウエハに照射しながら（以下、照射時と称する。）の測定と、を行った。 Cu wires 80 and 90 are connected to the Pt film 40 and the Pt film 50 by silver pastes 60 and 70, respectively. A positive terminal was connected to the Cu wire 80 and a negative terminal was connected to the Cu wire 90, and current-voltage characteristics were measured using an automatic polarization system (HSV-110, Hokuto Denko Co., Ltd.). The current-voltage characteristics are measured in a dark state (hereinafter referred to as dark) so that light does not strike the Si wafer, and while the light is irradiated onto the Si wafer (hereinafter referred to as irradiation). Measurement was performed.
（３）評価結果
測定結果を図１５、図１６に示す。図１５は、WO3を成膜したi型Siウエハの電流電圧特性を示した図であり、図１６は、WO3を成膜したp型Siウエハの電流電圧特性を示した図である。図１５、図１６いずれも、横軸が電圧を示し、縦軸が電流を示す。(3) Evaluation results The measurement results are shown in Figs. FIG. 15 is a diagram showing current-voltage characteristics of an i-type Si wafer formed with WO 3 , and FIG. 16 is a diagram showing current-voltage characteristics of a p-type Si wafer formed with WO 3 . In both FIG. 15 and FIG. 16, the horizontal axis represents voltage, and the vertical axis represents current.
図１５に示すように、WO3を成膜したi型Siウエハにおいては、暗時、照射時とも電流-電圧の関係は直線になっており、WO3とi型Siを接合するとオーミック接合されることが分かる。また、暗時よりも照射時の方が、電流が大きくなっている。これは、電子が光励起によって生成し、電流増加に寄与しているということを示す。As shown in FIG. 15, in the i-type Si wafer on which WO 3 is formed, the current-voltage relationship is linear both in the dark and at the time of irradiation. When WO 3 and i-type Si are joined, ohmic junction is formed. I understand that In addition, the current is larger during irradiation than during darkness. This indicates that electrons are generated by photoexcitation and contribute to an increase in current.
また、図１６に示すように、WO3を成膜したp型Siウエハにおいては、電圧を正側に印加したときには電流が流れにくく、負側に印加したとき電流が流れることから、整流性があることが分かる。即ち、WO3とp型Siを接合するとオーミック接合にはならない。この理由は、ｐ型Siのフェルミ準位よりもWO3のフェルミ準位の方が負側にあるためと考えられる。In addition, as shown in FIG. 16, in the p-type Si wafer formed with WO 3 , current hardly flows when voltage is applied to the positive side, and current flows when voltage is applied to the negative side. I understand that there is. That is, when WO 3 and p-type Si are joined, an ohmic junction is not obtained. This is probably because the Fermi level of WO 3 is on the negative side than the Fermi level of p-type Si.
なお、この評価では実施しなかったが、WO3とｎ型Ｓｉとを接合するとオーミック接合になると考えられる。その理由は、ｎ型Siのフェルミ準位よりもWO3のフェルミ準位の方が正側だからである。Although not carried out in this evaluation, it is considered that an ohmic junction is formed when WO 3 and n-type Si are joined. This is because the Fermi level of WO 3 is more positive than the Fermi level of n-type Si.
＜本発明の光触媒組成物を構成する酸素発生光触媒と水素発生光触媒＞
酸素発生光触媒と水素発生光触媒は、これまでに述べた条件を満たすものであれば、本発明の光触媒組成物を構成することが出来るが、以下に、その例を挙げる。<Oxygen generating photocatalyst and hydrogen generating photocatalyst constituting the photocatalyst composition of the present invention>
The oxygen-generating photocatalyst and the hydrogen-generating photocatalyst can constitute the photocatalyst composition of the present invention as long as the conditions described so far are satisfied. Examples thereof are given below.
（１）水素発生光触媒
Si、DLC（ダイヤモンドライクカーボン）、Cu2O、ZnRh2O4、ABO2ただし、A = Cu, Ag (1価イオン), B = Al, Ga, In, Fe, Cr, Co (3価イオン)
（２）酸素発生光触媒
Fe2O3、WO3、In2O3、A, BドープTiO2ただし、A=W6+, Mo6+, V5+、B=Al3+, Ga3+
ここで、Aイオンは、TiO2の伝導帯下端を正側の電位にシフトするものである。また、Ti4+であるため、電気的中性条件を満足するようにカウンタードーパントとしてBイオンが選択されるものとする。また、電気的中性条件はTi3+の生成でもよいので、Bイオンがなくてもよい。(1) Hydrogen generation photocatalyst
Si, DLC (Diamond Like Carbon), Cu 2 O, ZnRh 2 O 4 , ABO 2 where A = Cu, Ag (monovalent ion), B = Al, Ga, In, Fe, Cr, Co (trivalent ion) )
(2) Oxygen generation photocatalyst
Fe 2 O 3 , WO 3 , In 2 O 3 , A, B-doped TiO 2 where A = W 6+ , Mo 6+ , V 5+ , B = Al 3+ , Ga 3+
Here, the A ions shift the lower end of the conduction band of TiO 2 to a positive potential. Further, since it is Ti 4+ , B ions are selected as the counter dopant so as to satisfy the electrical neutral condition. Further, since the electrical neutral condition may be the production of Ti 3+ , there may be no B ions.
以上列挙したものは、例であって、本発明の範囲はこれにより限定されるものではない。 The above list is an example, and the scope of the present invention is not limited thereby.
Claims (4)
対標準水素電極電位において価電子帯の上端が１．２３Ｖよりも正の電位をもつ物質であり、かつ、３．０ｅＶ以下のバンドギャップエネルギーを持つ物質で構成された、光が照射されることにより水を分解して酸素を発生させる酸素発生光触媒と、
を接合して構成され、
対標準水素電極電位で比較すると、前記酸素発生光触媒のフェルミ準位よりも前記水素発生光触媒のフェルミ準位のほうが負側もしくは同等である光触媒組成物。When the light is irradiated, water is formed by a substance having a lower end of the conduction band at a potential lower than 0 V at a standard hydrogen electrode potential and a substance having a band gap energy of 3.0 eV or less. A hydrogen generation photocatalyst that decomposes to generate hydrogen;
Irradiation with light composed of a material having a positive potential higher than 1.23 V at the upper end of the valence band at a potential relative to the standard hydrogen electrode and a band gap energy of 3.0 eV or less. An oxygen-generating photocatalyst that decomposes water to generate oxygen,
Composed of
A photocatalyst composition in which the Fermi level of the hydrogen-generating photocatalyst is negative or equivalent to the Fermi level of the oxygen-generating photocatalyst as compared with the standard hydrogen electrode potential.
請求項１に記載の光触媒組成物。The hydrogen generating photocatalyst is i-type Si or n-type Si, and the oxygen generating photocatalyst is WO 3 .
The photocatalyst composition according to claim 1.
前記水素発生光触媒と、前記酸素発生光触媒とをボールミルで混合する工程を備えた、
光触媒組成物の製造方法。It is a manufacturing method of the photocatalyst composition of Claim 1 or 2, Comprising:
A step of mixing the hydrogen generating photocatalyst and the oxygen generating photocatalyst with a ball mill;
A method for producing a photocatalyst composition.
可視光線または可視光線よりも波長の短い光を吸収して水を分解し、水素を発生させる水素発生光触媒と、
を接合して構成され、
対標準水素電極電位で比較すると、前記酸素発生光触媒のフェルミ準位よりも前記水素発生光触媒のフェルミ準位のほうが負側もしくは同等である、
光触媒組成物。An oxygen-generating photocatalyst that absorbs visible light or light having a shorter wavelength than visible light to decompose water and generate oxygen;
A hydrogen generation photocatalyst that absorbs visible light or light having a shorter wavelength than visible light to decompose water and generate hydrogen;
Composed of
When compared with the standard hydrogen electrode potential, the Fermi level of the hydrogen generating photocatalyst is more negative or equivalent to the Fermi level of the hydrogen generating photocatalyst.
Photocatalyst composition.
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