Visible light responsive composition and photoelectrode, photocatalyst, optical sensor prepared using the same

The present invention relates to a visible light responsive composition and a photoelectrode, photocatalyst, and photosensor using the same.

In recent years, photoelectrodes for using solar energy, photocatalysts that decompose and remove environmental pollutants with sunlight, hydrogen production by the decomposition reaction of water using both, and photoelectric conversion element type for quantitative measurement of light. Optical sensors are attracting attention, and various semiconductors are being researched and developed as materials for them. Titanium oxide is a typical example, and is most often used practically. However, since this titanium oxide has a large band gap, it does not absorb the visible light region that occupies most of the sunlight, and the sunlight cannot be effectively used. In addition, titanium oxide does not function in indoor light or automobile interior light, which has extremely weak absorbing ultraviolet light region. As a countermeasure for this, in order to develop a newly available visible light responsive composition, improved research such as slightly doping an existing composition such as titanium oxide with a trace amount of other elements and a completely new visible light responsiveness Research is being conducted to search for compositions (for example, Non-Patent Documents 1 and 2). However, since the number of combinations of compositions containing various elements in different proportions is enormous, it takes a lot of time and effort to synthesize a new composition and evaluate its visible light responsiveness. Research and development has not made much progress so far. Therefore, the present inventors have newly developed a thin film automatic synthesizer having a composition containing various elements in various ratios and an automatic evaluation device for photocurrent responsiveness to light irradiation of the thin film, and have developed visible light responsiveness. We have been conducting high-speed search research on novel compositions that are promising as photoelectrodes, photocatalysts, and photosensor materials (Patent Document 1). In the process, the present inventors focused on the composition of Fe-Zr system and Fe-Ti system and proceeded with research and development, and Fe was 20% to 80%, Zr was 20% to 50%, and Ti was 0%. Visible light responsive composite oxide in the range of 30% (Patent Document 2), Fe is 50% to 85%, Zr is 8% to 48%, and M (Al, Zn, In, Sn, Ta) is 0. Visible light responsive composite oxide in the range of 01% to 29% (Patent Document 3), Fe 87% to 90%, Ti 9% to 10%, M (Si, Ba, Y) 0.1 Visible light responsive composite oxide in the range of% to 3% (Patent Document 4), Fe is 85% to 97%, Ti is 1% to 10%, and M (La, Sr) is 0.1% to 7 Visible light responsive composite oxide in the range of% (Patent Document 5), Fe in the range of 81% to 90%, Ti in the range of 9% to 10%, and M (Ca, Bi) in the range of 0.1% to 10%. Visible light responsive composite oxide (Patent Document 6), Fe in the range of 89% to 92%, Ti in the range of 1% to 10%, Zn in the range of 0.1% to 10%. A thing (Patent Document 7) was found. However, research and development has not yet progressed so much for compositions other than Fe-Zr and Fe-Ti.

<p><patcit num="1"><text>Japanese Unexamined Patent Publication No. 2006-300812</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 2009-73708</text></patcit><patcit num="3"><text>Japanese Unexamined Patent Publication No. 2010-264351</text></patcit><patcit num="4"><text>Japanese Unexamined Patent Publication No. 2010-277823</text></patcit><patcit num="5"><text>Japanese Unexamined Patent Publication No. 2010-274186</text></patcit><patcit num="6"><text>Japanese Unexamined Patent Publication No. 2010-274187</text></patcit><patcit num="7"><text>Japanese Unexamined Patent Publication No. 2010-275145</text></patcit></p>

<p><nplcit num="1"><text>"Photocatalyst Standard Research Method", Tokyo Tosho, January 2005</text></nplcit><nplcit num="2"><text>Chemistry of Materials, Vol. 20, No. 12, pp. 3803-3805 (2008)</text></nplcit></p>

<p num="0005"> Against the above background, the present invention further develops the studies by the inventors so far, and advances a wide range of studies on the compositions of the system which have not been studied at all in the past. A new composition that has current responsiveness and can be used as a photoelectrode material, photocatalyst material, and photosensor material, a new photoelectrode, photocatalyst, and photosensor composed of these, and a new water decomposition method using these photoelectrodes and photocatalysts. The challenge is to provide.</p>

<p num="0006"> The present inventors have diligently studied in order to solve the above-mentioned problems, and as a result of exploratory research on a novel visible light-responsive composition using the apparatus described in Patent Document 1 described above, even for visible light irradiation. We have discovered a novel composition as a material for a photoelectrode, a photocatalyst, and a photosensor that exhibits photocurrent responsiveness, and have completed the present invention. It was found that it was very effective at a specific ratio of three or more kinds of elements other than oxygen, and it is a special composition that was hardly found by manual search.</p><p num="0007"> That is, the present invention is characterized by the following. (1) A composition composed of Ti, Bi, Cu, and oxygen, wherein the element content ratio (molar ratio) is Ti: 50 to 70% and Bi: 15 when the total of Ti, Bi, and Cu is 100%. A visible light responsive composition, characterized in that it is in the range of ~ 45%, Cu: 5-15%. (2) An optical electrode composed of the above visible light responsive composition. (3) A photocatalyst composed of the above visible light responsive composition. (4) An optical sensor composed of the above visible light responsive composition. (5) The method for water decomposition using the photoelectrode according to (2) above and / or the photocatalyst according to (3) above.</p><p num="0008"> The present invention can also have the following aspects. (6) The visible light responsive composition according to (1) above, wherein the element content ratio (molar ratio) is in the range of Ti: 60 to 70%, Bi: 25 to 35%, Cu: 5 to 15%. Stuff. (7) The visible light responsive composition according to (1) or (6) above, which is a granular body, a thin film, a sintered body, or a laminated body. (8) The visible light responsive composition according to (1), (6), or (7) above, which is formed on a substrate or a substrate. (9) Visible light responsiveness according to any one of (1), (6) to (8) above, which is formed by a thermal decomposition method, a sintering method, or a vapor phase film forming method. Composition. (10) An optical electrode composed of the visible light responsive composition according to any one of (6) to (9) above. (11) A photocatalyst composed of the visible light responsive composition according to any one of (6) to (9) above. (12) An optical sensor composed of the visible light responsive composition according to any one of (6) to (9) above. (13) The method for water decomposition using the photoelectrode according to (10) above and / or the photocatalyst according to (11) above.</p>

<p num="0009"> The photocurrent indicates the performance when used as a photoelectrode material, and also indicates the degree of charge separation for the photocatalyst to function . Since the composition of the present invention causes charge separation by irradiation with visible light to generate a photocurrent, it can be used as a material for a visible light responsive photoelectrode or a visible light responsive photocatalyst. These can be used to reduce water to generate hydrogen and convert light energy into hydrogen. Further, as an optical sensor only in a specific wavelength region, it is possible to provide a material of an optical sensor having spectral sensitivity only in the visible light region.</p>

The visible light responsive composition of the present invention contains four elements of Ti, Bi, Cu and oxygen as essential elements. Here, the element content ratio (molar ratio) when the total of Ti, Bi, and Cu is 100% is in the range of Ti: 50 to 70%, Bi: 15 to 45%, and Cu: 5 to 15%. .. Preferably, it is in the range of Ti: 60 to 70%, Bi: 25 to 35%, and Cu: 5 to 15%. The visible light responsive composition of the present invention is basically composed of the above four elements, but does not attempt to exclude the inclusion of other elements as long as the visible light responsiveness is not significantly reduced. Moreover, even if other elements are contained, the other elements are excluded from the content ratio and are not added to the total.

When the optical electrode is constructed using the composition of the present invention, charge separation occurs due to visible light irradiation within the range of the above-mentioned element content ratio (molar ratio), and a large photocurrent is generated.

The composition of the present invention can be produced by various methods such as a thermal decomposition method, a mixed powder sintering method, an electrodeposition method, a vapor deposition method such as sputtering, and the like. Among them, thermal decomposition is possible. It is preferably produced by the method. For example, the case of producing a thin film shape (coating thermal decomposition method) will be described in detail in Examples. In this pyrolysis method, a solution containing each element (in some cases, a colloidal solution, a suspension, etc.) is well mixed to prepare a raw material solution, and the raw material solution is calcined to prepare a composition. In the thermal decomposition method, the element content ratio (molar ratio) can be accurately controlled, a uniform composition can be produced because it is mixed with a solution, and in the case of forming a thin film (coating thermal decomposition method), coating and firing are repeated. There is an advantage that a precise product can be manufactured by laminating. The thermal decomposition method used in the present invention may be any method as long as it is a method of mixing and firing a liquid containing each element, and examples thereof include a sol-gel method, a complex polymerization method, and an organometallic decomposition method. Polymers and organic substances such as polyethylene glycol and ethyl cellulose may be added to the solution in order to control the porosity of the thin film and the viscosity of the solution.

The composition of the present invention may be a composite oxide having a uniform composition or a doping compound. Further, a plurality of compounds may exist in a mixed state. When the present composition is synthesized by firing in oxygen or air, an oxide having the most stable composition is usually obtained, but a composition other than the oxide may be synthesized by controlling the atmospheric gas. For example, NH₃And H₂S, CH₄A composition containing a part of N, S, and C can be synthesized by synthesizing while flowing a gas. When used as an optical electrode or an optical sensor, the composition of the present invention is fixed on a conductive substrate. For example, a solution containing each element is applied onto a heat-resistant conductive substrate such as conductive glass or metal to form a film by a thermal decomposition method.

When this composition is used as a light electrode, it is desirable that the composition is strongly bonded to the substrate and is porous. When used as a photocatalyst, it is desirable that the surface area is relatively high and the crystallinity is high.

Then, according to the present invention, a photoelectrode, a photocatalyst and a photosensor using the above composition will be provided.

<p> Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.</p><p> (Examples 1 to 13, Comparative Examples 1 to 14) A ternary thin film library of Ti-Bi-Cu was synthesized by a coating pyrolysis method using an automatic composition thin film synthesizer (Patent Document 1). This thin film library is prepared by forming thin films having compositions having different content ratios of each element on a single conductive glass substrate at intervals. The element content was changed as shown in Table 1.</p><p> The raw material solution to be applied is obtained by diluting an organic complex solution of Ti, Bi, and Cu manufactured by Symmetrics with butyl acetate so that the molar concentration becomes 0.2 M, and mixing them by changing their volume ratios. The molar ratio of content was adjusted. To these solutions, an equal amount of a butyl acetate solution of 10% by weight ethyl cellulose was added as a thickener in an equal volume ratio and mixed. A laminated film was synthesized by repeating the process of applying each solution to a predetermined position on a conductive glass substrate and firing it four times. The firing was carried out in air at 550 ° C. for 0.5 hours and at 700 ° C. for an additional 0.5 hours. These were designated as (Examples 1 to 13 and Comparative Examples 1 to 14).</p><p> The visible light responsiveness of the composition was evaluated by measuring the photocurrent. Photocurrent is a measure of the charge separation ability and visible light reactivity of a composition, and the larger the value, the higher the performance. The thin film library of the prepared composition was placed in a 0.1 M sodium dihydrogen phosphate solution adjusted to pH 7.0 with sodium hydroxide, and a 300 W Xe lamp equipped with a filter that cuts wavelengths shorter than 420 nm was used. The photocurrent was measured at 1 V (vs. Ag / AgCl) while irradiating at 3.2 mW through a hole slit having a diameter of 1 mm. Platinum is used for the counter electrode, and hydrogen corresponding to the current value is generated on it. Table 1 shows the measurement results of the photocurrent. As for titanium oxide, a thin film library was synthesized and the photocurrent was measured in the same manner as in the examples of the present invention, but almost no photocurrent was generated (0 μA).</p><p><tables num="1"></tables></p><p> As is clear from Table 1, when Ti and Bi and Cu as the third component are selected and their compositions are Ti: 50 to 70%, Bi: 15 to 45%, and Cu: 5 to 15%. Showed a significantly larger photocurrent value than the comparative examples, and in all of them, the visible light responsiveness far exceeded that of titanium oxide.</p>

When the optical electrode is constructed by the composition of the present invention, the absorption and utilization of visible light is promoted, and more efficient utilization of sunlight by the optical electrode such as hydrogen production by decomposition of water becomes possible. In addition, even in places where ultraviolet light is weak, such as inside a building or in a car, the photocatalyst composed of the composition of the present invention uses room light or car interior light to remove environmental pollutants, deodorize, antibacterial, antivirus, etc. Enables anti-mold, anti-fouling, anti-fog, etc. Further, it is possible to provide a material for an optical sensor that reacts only to light in the visible light region.