Hydrogen peroxide production method

Abstract

It is found that a layer comprising a thiophene polymer that is a pure organic material can serve as a light absorber and a catalyst which are extremely highly efficient and enable the production of hydrogen peroxide from water and dissolved air (oxygen) when the thiophene polymer is irradiated with light, and that the thiophen polymer can act even in alkaline water in which a general-purpose and inexpensive water oxidation catalyst layer that is a counter electrode of the thiophene polymer can act effectively. This finding leads to the accomplishment of the present invention. The present invention provides a hydrogen peroxide production method which is environment-friendly, simple and extremely highly efficient, the method comprising combining a water oxidation catalyst with a light-absorbable and oxygen-reducing catalyst layer comprising a thiophene polymer, immersing the resultant combined product in alkaline water, and irradiating the light-absorbable and oxygen-reducing catalyst layer with light.

Description

[Technical field]

[0001] The present invention relates to a method for producing hydrogen peroxide, etc. More specifically, the present invention relates to a conductive combination in which a light absorbing and oxygen reducing catalyst layer (hereinafter referred to as a light absorbing oxygen reducing catalyst layer) is combined with a water oxidation catalyst (hereinafter referred to as a water oxidation catalyst) under light irradiation; a conductive thin plate having a thiophene polymer layer formed on its surface as the light absorbing oxygen reducing catalyst layer, and a conductive thin plate having a water oxidation catalyst layer (hereinafter referred to as a water oxidation catalyst layer) formed on its surface are connected by a conductor; a thin plate formed by sandwiching the light absorbing oxygen reducing catalyst layer and the water oxidation catalyst layer via a conductive thin plate; fine particles having water oxidation catalytic activity coated with the light absorbing oxygen reducing catalyst layer; and a method for producing hydrogen peroxide using the combination, the thin plate, or the fine particles. [Background technology]

[0002] Hydrogen peroxide is widely used industrially as a bleaching agent in the paper and pulp industry, as a treatment agent in the environmental field such as wastewater, and as an oxidizing agent in the chemical industry (Non-Patent Document 1), and its usage is increasing year by year on a global scale (projected to be 6 Mt / year in 2024, Non-Patent Document 2), making it an extremely important compound industrially. In addition, compared to hydrogen, it has recently been studied and tested as a clean energy source and fuel for fuel cells (Non-Patent Document 3), and some of it is in practical use. For example, 3% hydrogen peroxide water is widely used in everyday products such as disinfectants and as an oxidizing agent for organic synthesis.

[0003] There are several methods for producing hydrogen peroxide, including the direct synthesis method in which hydrogen and oxygen are reacted under pressure, and the electrolytic reduction method of oxygen, but the autoxidation method using anthraquinone is currently the most widely used industrial method. However, it is not necessarily an advantageous production method now or in the future, as it requires an organic solvent used in the reaction with benzene, a process for extracting the hydrogen peroxide produced, high-pressure hydrogen and its catalyst, and the raw material for hydrogen is a fossil resource (Non-Patent Document 1).

[0004] There have been several reports on the generation of hydrogen peroxide by reducing oxygen dissolved in water through light irradiation of a catalyst, which is an ideal method that is simple and environmentally friendly. For example, melam, tungsten (IV) oxide, and graphite carbon nitride have been used as catalysts for light absorption and oxygen reduction, and the generation of hydrogen peroxide under light irradiation has been measured (Non-Patent Documents 4, 5, 6). However, these reports have been conducted using ultraviolet light irradiation of 400 nm or less and pure oxygen injection, and the catalysts that account for the majority of the technology are not environmentally friendly. In addition, the generation of hydrogen peroxide is extremely slow (10 μg hydrogen peroxide / mg catalyst / hour), and the current situation is that it is far from a method for producing hydrogen peroxide from water in air under light irradiation.

[0005] Meanwhile, the present inventors have been conducting research on the photoelectrochemical decomposition of water and hydrogen generation for many years (Non-Patent Document 7), and recently reported that a highly pure thiophene polymer layer was obtained by a unique polymerization method using iodine vapor, and that when this was immersed in water and irradiated with light, hydrogen gas was generated by the decomposition of water with an applied voltage of about 0.5 V (or even without application of voltage, although the reaction rate was low) (Non-Patent Documents 8 and 9). [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Campos-Martin, JM, et al., Angew. Chem. Int. Ed. 45, 6962-6984 (2006) [Non-Patent Document 2] Global Industry Analysts, Inc., "Hydrogen peroxide", A Global strategic business report, MCP-2080, https: / / www.strategyr.com / pressMCP-2080.asp [Non-Patent Document 3] Fukuzumi, S., et al., Electrochim. Acta 82, 493-511 (2012) [Non-Patent Document 4] Jin, Z., et al., Appl. Catal. B 205, 569-575 (2017) [Non-Patent Document 5] Shiraishi, Y., et al., Angew. Chem. Int. Ed. 53, 13454-13459 (2014) [Non-Patent Document 6] Wei, Z., et al., Energy Environ. Sci. 11, 2581-2589 (2018)) [Non-Patent Document 7] CH Ng, O. Winther-Jensen, et al., J. Mater. Chem. A, 2015, 3, 11358. [Non-Patent Document 8] Oka, K., et al., Energy Environ. Sci. 11, 1335-1342 (2018). [Non-Patent Document 9] Oka, K., et al., Adv. Energy Mater. 9, 1803286, (2019). Summary of the Invention [Problem to be solved by the invention]

[0007] The objective of this study is to find an organic polymer compound that has a catalytic energy level and band gap (i.e., the difference between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)) suitable for absorbing light, has a LUMO level suitable for reducing oxygen to produce oxygen peroxide, and has a HOMO level suitable for oxidizing and regenerating a catalyst for the reaction that oxidizes water to produce oxygen, which is a compensatory reaction that pairs with the oxygen reduction reaction, and to establish simple conditions under which this compound can operate in the above reaction, thereby providing a new, environmentally friendly, and extremely efficient method for producing hydrogen peroxide. [Means for solving the problem]

[0008] Based on the pioneering knowledge of water decomposition by light irradiation that the above-mentioned inventors of the present invention have pioneered both in Japan and overseas, and on their original method for forming a thiophene polymer layer, they have conducted intensive research aimed at the development of a completely new method for easily producing hydrogen peroxide from water by light irradiation. As a result, they have discovered that a layer of a thiophene polymer, which is a purely organic substance, becomes a light absorption and oxygen reduction catalyst that produces hydrogen peroxide from water and oxygen with extremely high efficiency even in water under air, when irradiated with light, and that this catalyst works even at high pH levels where general-purpose, inexpensive water oxidation catalyst layers are effective, thus completing the present invention.

[0009] Specifically, the present invention provides a method for producing hydrogen peroxide, which comprises combining a light-absorbing and oxygen-reducing catalyst layer (hereinafter referred to as a light-absorbing oxygen-reducing catalyst layer) made of a thiophene polymer with a water oxidation catalyst (hereinafter referred to as a water oxidation catalyst), immersing the combined layer in alkaline water, and irradiating the light-absorbing oxygen-reducing catalyst layer with light.

[0010] In the method for producing hydrogen peroxide of the present invention, the thiophene polymer may be a copolymer of thiophene and an aromatic compound having a structural unit represented by the following formula (I) (hereinafter, referred to as a thiophene copolymer): [ka] however, A represents a structural unit derived from an aromatic compound, x and 1-x represent the composition ratio of the structural units of the copolymer, 0 <x≦1である。

[0011] In the method for producing hydrogen peroxide of the present invention, the conductive thin plate having the light absorbing oxygen reduction catalyst layer formed on its surface may be connected with a conductive thin plate having the hydroxide oxidation catalyst layer formed on its surface by a conductor, immersed in alkaline water, and exposed to light.

[0012] In the method for producing hydrogen peroxide of the present invention, the conductive thin plate having the light absorbing oxygen reducing catalyst layer formed on its surface may be a transparent conductive thin plate.

[0013] In the method for producing hydrogen peroxide of the present invention, a plurality of conductive thin plates having the light absorbing oxygen reducing catalyst layer formed on the surface thereof may be connected together.

[0014] The method for producing hydrogen peroxide of the present invention may include immersing a thin plate having the light absorbing oxygen reduction catalyst layer formed on one side and the hydroxide oxidation catalyst layer formed on the other side of a conductive thin plate in alkaline water and irradiating it with light.

[0015] The method for producing hydrogen peroxide of the present invention may include immersing fine particles of a hydroxide catalyst, the majority of whose surface is coated with a thiophene copolymer, in alkaline water and irradiating the fine particles with light.

[0016] In the method for producing hydrogen peroxide of the present invention, in order to obtain the thiophene copolymer, a dimer or trimer of thiophene and an aromatic compound represented by the following general formula (II) or (III) may be synthesized in advance, and then polymerized to obtain a copolymer of thiophene and an aromatic compound: [ka] [ka] Here, B and C represent aromatic compounds.

[0017] In the method for producing hydrogen peroxide of the present invention, the hydroxide catalyst may be composed of manganese oxide, cobalt oxide or ruthenium oxide.

[0018] In the method for producing hydrogen peroxide of the present invention, sunlight, simulated sunlight, or ultraviolet or visible light may be used as the light source for the light irradiation.

[0019] The present invention also provides a method for preparing a light-absorbing oxygen-reducing catalyst layer, which comprises coating the synthesized dimer or trimer on a conductive thin plate and exposing it to iodine vapor to obtain the thiophene copolymer.

[0020] Furthermore, the present invention provides a thin plate for producing hydrogen peroxide, which comprises a conductive thin plate having a light absorbing oxygen reduction catalyst layer on one side and a water oxidation catalyst layer on the other side.

[0021] The present invention also provides fine particles for producing hydrogen peroxide, which have a light-absorbing oxygen-reducing catalyst layer formed on the surface of a water oxidation catalyst having water oxidation catalytic activity.

[0022] The present invention also provides a conductive thin plate combination for producing hydrogen peroxide, which is formed by combining a conductive thin plate having a light absorbing oxygen reduction catalyst layer formed on its surface with a conductive thin plate having a water oxidation catalyst layer formed on its surface, and connecting these with a conductive wire. Effect of the Invention

[0023] The present invention provides a novel, environmentally friendly and highly efficient method for producing hydrogen peroxide. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is an energy level diagram required for a method of producing hydrogen peroxide from alkaline water by light irradiation, comprising the use of a thiophene polymer as a light absorption and oxygen reduction catalyst in combination with a water oxidation catalyst according to the present invention. [Diagram 2] This method involves connecting a thin plate (preferably a transparent thin plate) having a light absorption and oxygen reduction catalyst layer formed on its surface, which is made of a copolymer of thiophene and an aromatic compound, to a thin plate having a water oxidation catalyst layer formed thereon with a conductive wire, immersing the plate in alkaline water, and irradiating the plate with light to produce hydrogen peroxide. [Diagram 3] This shows a simple reaction vessel under light irradiation, which is made by placing a thin plate in water, with a conductive thin plate sandwiched between a light absorption and oxygen reduction catalyst layer and a water oxidation catalyst layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] 1.How hydrogen peroxide is produced One embodiment of the present invention is a method for producing hydrogen peroxide.

[0026] More specifically, the method for producing hydrogen peroxide includes a step of combining a light-absorbing and oxygen-reducing catalyst layer (hereinafter referred to as a light-absorbing oxygen-reducing catalyst layer) made of a thiophene polymer with a water oxidation catalyst (hereinafter referred to as a water oxidation catalyst), immersing the combined layer in alkaline water, and irradiating the light-absorbing oxygen-reducing catalyst layer with light.

[0027] In this specification, the term "consisting of" is used in the sense of "formed from," and is not used in the sense of "consisting only of." In other words, "consisting of a thiophene polymer" means "formed from a thiophene polymer," and does not mean "consisting only of a thiophene polymer."

[0028] In addition, in this specification, the light-absorbing oxygen-reducing catalyst layer means a layer made of a material having both light-absorbing activity and oxygen-reducing catalytic activity, and does not include a layer formed by layering or mixing a material having light-absorbing activity with another material having oxygen-reducing activity.

[0029] Hereinafter, the method for producing hydrogen peroxide by light irradiation according to the present invention will be described in detail with reference to the accompanying drawings.

[0030] FIG. 1 shows the energy levels required for the method of the present invention for producing hydrogen peroxide from alkaline water by light irradiation, which comprises using a thiophene polymer as a light-absorbing oxygen-reducing catalyst in combination with a hydroxide catalyst.

[0031] Let's start from the right side of Figure 1. The potential at which oxygen dissolved in water is reduced (i.e., two electrons are donated) to produce hydrogen peroxide is expressed by the reaction formula O2 + 2H2O + 2e - → H2O2+ 2OH -(neutral), the redox potential is -0.21 V with a silver / silver chloride electrode as the reference electrode (hereafter referred to as silver / silver chloride), or the reaction formula that produces hydrogen peroxide anion, which is the precursor of hydrogen peroxide, is O2+ H2O + 2e - → HO2 - + OH - (alkaline) is - 0.15 V vs. silver / silver chloride. Hydrogen peroxide anions are neutralized in the air by the reaction formula HO2 - + H + →H2O2 automatically becomes hydrogen peroxide.

[0032] The most important component of the present invention is the organic polymer layer in the second column on the right side of Figure 1, which absorbs light, separates charges, and catalytically serves to reduce oxygen with excited electrons. To achieve this, the layer is made of a π-conjugated organic polymer, and the requirements are that the layer must (1) have a high light absorption coefficient and (2) have a conjugated organic polymer with a lowest unoccupied molecular orbital (LUMO) level that is moderately higher than the reduction potential of oxygen. For (1), it is desirable that the band gap be approximately 2.0 eV. In addition, the layer must also have (3) charge transport properties that allow electrons and holes generated by charge separation to diffuse to the left and right interfaces, and (4) a moderately low highest occupied molecular orbital (HOMO) level that allows holes to be injected into the water oxidation catalyst. Furthermore, (5) a high efficiency of electron injection into oxygen, or in other words, catalytic activity, is required. In addition, (6) it is desirable that this catalytic activity be maintained regardless of the pH of water, for example, even in an alkaline environment where the water oxidation catalyst operates efficiently.

[0033] The water oxidation catalysts in the third row on the right side of Figure 1 receive holes from the organic polymer layer under light irradiation and catalytically oxidize water. Manganese oxide is a typical example of a general-purpose, inexpensive, and highly active catalyst, and these catalysts work with alkaline water. The potential to oxidize water in the fourth row (i.e., extract four electrons) to produce oxygen is expressed by the reaction formula 4OH - → O2+ 2H2O + 4e -(Alkaline water) is +0.32 V vs silver / silver chloride. The potential of manganese oxide is +0.5 V vs silver / silver chloride. However, if the HOMO level of the conjugated organic polymer is approximately +1.0 V vs silver / silver chloride, an ideal cascade in which the transfer of electrons (or holes) operates in series is established.

[0034] Hereinafter, the components in the hydrogen peroxide production method of the present invention will be specifically described.

[0035] Examples of the thiophene polymer serving as the light-absorbing oxygen reduction catalyst layer include copolymers having a structural unit represented by the following general formula (I) (hereinafter referred to as thiophene copolymers). [Chemical formula] However, A represents a structural unit derived from an aromatic compound, x and 1 - x represent the composition ratio of the structural units of the copolymer, 0 < x ≤ 1, preferably 1 / 2 ≤ x ≤ 2 / 3, and more preferably x = 2 / 3.

[0036] The preferred degree of polymerization of the thiophene copolymer is in the range of 2 to 30, more preferably in the range of 4 to 15, and the preferred average molecular weight is in the range of 500 to 7500, more preferably in the range of 1000 to 4000.

[0037] Examples of aromatic compounds that combine with thiophene to form thiophene polymers include benzene, naphthalene, anthracene, furan, thiophene, fluorothiophene, 3,4-difluorothiophene, 3,4-dimethylthiophene, pyrrole, pyrazole, imidazole, pyridine, pyridazine, pyrimidine, pyrazine, toluene, ethylbenzene, cumene, phenol, benzyl alcohol, anisole, benzaldehyde, benzoic acid, acetophenone, benzenesulfonic acid, nitrobenzene, aniline, thiophenol, benzonitrile, styrene, xylene, cresol, catechol, resorcinol, hydroquinone, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, and toluidine.

[0038] The thiophene and thiophene derivatives used to obtain the thiophene polymer are represented by the following general formula (II) or (III). [ka] [ka] Here, B and C represent aromatic compounds.

[0039] Examples of the thiophene derivatives include 2-phenylthiophene, terthiophene, 3,4-ethylenedioxythiophene, 1,4-di(2-thienyl)benzene, 1,4-di(2-thienyl)pyrrole, 1,4-di(2-thienyl)pyridine, 1,4-di(2-thienyl)biperidin, 1,4-di(2-thienyl)naphthalene, 1,4-di(2-thienyl)-2-fluorobenzene, and 3-phenyl-terthiophene. Many of them have electron-withdrawing π-conjugated molecules compared to thiophene, and the HOMO, LUMO, and band gap, which is the difference between the two, of the resulting thiophene polymer satisfy the above-mentioned functions. In addition, as a catalyst layer that operates in contact with water, it is preferable that it can be given hydrophilicity. In addition, the conditions are also the solvent solubility, melting point, and thin layer forming ability suitable for the reactivity and polymerization conditions during polymerization described later.

[0040] Examples of methods for obtaining thiophene polymers include gas-phase polymerization, electrolytic polymerization, and chemical oxidation polymerization (Society of Polymer Science, Polymer Synthesis and Reactions (2) Synthesis of Condensation Polymers, New Polymer Experiments 3, Kyoritsu Publishing Co., Ltd., 1996). A representative example is iodine gas-phase polymerization, which has the following advantages over other polymerization methods: (1) no metal catalyst is used, so no residues are left, (2) a simple polymerization vessel, (3) an easy purification process, and (4) it is easy to scale up.

[0041] Examples of thin plates on which the light absorbing catalyst layer can be formed include glassy carbon, carbon paper, conductive glass (e.g., transparent glass surface-coated with ITO (indium tin oxide)), and conductive transparent plastic films (e.g., polyethylene terephthalate film surface-coated with PEDOT (poly(3,4-ethylenedioxythiophene)) doped with conductive PSS (poly(4-styrenesulfonic acid)).

[0042] Examples of water oxidation catalysts include manganese oxide, iridium, iridium and ruthenium oxide, and nickel / cobalt / iron. A representative manganese oxide is prepared by electrochemical oxidation of manganese acetate in an ionic liquid (Zhou, F., et al, Advanced Energy Materials 2, 1013-1021, (2012)).

[0043] The pH of the reaction solution is neutral to alkaline, preferably alkaline, and the reaction solution is, for example, alkaline water having a pH of 8 or higher, more preferably a pH of 11 or higher, and further preferably a pH of about 12. Examples of alkaline water include an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, and a phosphate buffer solution.

[0044] The light source for irradiating the light may be any that provides ultraviolet or visible light, with sunlight being the most effective in terms of cost and efficiency, and pseudo-sunlight may also be used.

[0045] A thin plate (preferably a transparent thin plate) having a light-absorbing oxygen-reducing catalyst layer formed on its surface, which is made of a copolymer of thiophene and an aromatic compound, is connected to a thin plate having a water oxidation catalyst layer formed thereon by a conductor, and hydrogen peroxide is produced by immersing the plate in alkaline water and irradiating the plate with light (see Figure 2). It is preferable to use multiple transparent thin plates having a light-absorbing oxygen-reducing catalyst layer formed on their surface.

[0046] Alternatively, a thin conductive plate is immersed in alkaline water and hydrogen peroxide is produced by irradiating it with light, with a light-absorbing oxygen-reduction catalyst layer made of a copolymer of thiophene and an aromatic compound formed on one side and a hydroxide catalyst layer formed on the other side (see Figure 3).

[0047] As the conductive wire, a commonly used conductive wire can be used, for example, a copper wire.

[0048] Furthermore, the present invention can produce hydrogen peroxide by a production method including immersing fine particles of a hydroxide catalyst, the majority of whose surface is coated with a thiophene copolymer, in alkaline water and irradiating the fine particles with light.

[0049] The fine particles in this case are, for example, manganese oxide fine particles (preferably with a particle size of 0.1 to 1 μm) whose surfaces are partially coated with a thiophene polymer by chemical oxidation polymerization.

[0050] 2. Preparation method of the light-absorbing oxygen-reduction catalyst layer Another embodiment of the present invention is a method for preparing a light-absorbing oxygen-reducing catalyst layer.

[0051] More specifically, in obtaining the thiophene copolymer described in "1. Method for producing hydrogen peroxide" above, a dimer or trimer of thiophene represented by general formula (II) or (III) and an aromatic compound is synthesized in advance, the resultant is applied onto a conductive thin plate, and the resultant is exposed to iodine vapor to obtain the thiophene copolymer. This is a method for preparing a light-absorbing oxygen-reducing catalyst layer.

[0052] More specifically, the method can be carried out by the method described in "1. Method for producing hydrogen peroxide" above and in the Examples below.

[0053] 3. Sheet metal for hydrogen peroxide production Another embodiment of the present invention is a sheet for producing hydrogen peroxide.

[0054] More specifically, the present invention relates to a thin plate for producing hydrogen peroxide, which has a light absorbing oxygen reduction catalyst layer formed on one side and a water oxidation catalyst layer formed on the other side of a conductive thin plate.

[0055] The types of conductive thin plate, the method for manufacturing the light absorbing oxygen reduction catalyst layer, the method for manufacturing the hydroxide catalyst layer, the method for manufacturing the thin plate for hydrogen peroxide production, and the method for producing hydrogen peroxide using them were described in detail in the above "Method for producing hydrogen peroxide." In addition, examples of actual implementation are described in the following examples.

[0056] Therefore, based on the description in "1. Method for producing hydrogen peroxide" above and the following examples, a thin plate for producing hydrogen peroxide can be produced and used for producing hydrogen peroxide.

[0057] 4. Microparticles for hydrogen peroxide production Another embodiment of the present invention is a microparticle for the production of hydrogen peroxide.

[0058] More specifically, the microparticles are for producing hydrogen peroxide, in which a light absorbing oxygen reducing catalyst layer is formed on the surface of a water oxidation catalyst having water oxidation catalytic activity.

[0059] The types and sizes of the fine particles of the hydroxide catalyst having hydroxide catalytic activity used in this embodiment, the method for producing the light absorbing oxygen reduction catalyst layer, the method for forming the light absorbing oxygen reduction catalyst layer on the surface of the hydroxide catalyst, and the method for producing hydrogen peroxide using the fine particles are described above in "1. Method for producing hydrogen peroxide", and specific examples of these are described in the Examples below.

[0060] Therefore, based on the description in "1. Method for producing hydrogen peroxide" above and the following examples, fine particles for producing hydrogen peroxide can be produced and used for producing hydrogen peroxide.

[0061] 5. Conductive thin plate assembly for hydrogen peroxide production Another embodiment of the present invention is a conductive sheet combination for producing hydrogen peroxide.

[0062] More specifically, it is a conductive thin plate combination for producing hydrogen peroxide, which is formed by combining a conductive thin plate having a light absorbing oxygen reduction catalyst layer formed on its surface with a conductive thin plate having a water oxidation catalyst layer formed on its surface, and connecting these with a conductive wire.

[0063] A method for producing hydrogen peroxide in which a conductive thin plate having a light absorbing oxygen reduction catalyst layer formed on its surface is combined with a conductive thin plate having a hydroxide oxidation catalyst layer formed on its surface and connected with a conductor has been described above in "1. Method for producing hydrogen peroxide", and a specific example of an actual implementation is described in the following Examples.

[0064] Therefore, based on the description in "1. Method for Producing Hydrogen Peroxide" above and the following examples, a conductive thin plate combination for producing hydrogen peroxide can be produced and used for producing hydrogen peroxide.

[0065] All documents mentioned herein are incorporated by reference in their entirety. The examples described herein are illustrative of embodiments of the invention and should not be construed as limiting the scope of the invention. EXAMPLES

[0066] <Production of hydrogen peroxide using poly(1,4-di(2-thienyl)benzene) as a thiophene polymer and glassy carbon as a conductive thin plate> A thin glassy carbon plate was coated with 1,4-di(2-thienyl)benzene, a trimer in which thiophene is bonded to the 1,4-positions of benzene (C in the following formula (III) is a 1,4-benzene group), which was polymerized with iodine vapor (described in detail below) to form a light absorption and oxygen reduction catalyst layer. The plate was then connected with a conductor to another thin glassy carbon plate on which a water oxidation catalyst layer was formed. The plate was then immersed in alkaline water and exposed to light to produce hydrogen peroxide.

[0067] [ka]

[0068] This is explained in detail below.

[0069] (1) Synthesis of 1,4-di(2-thienyl)benzene 1,4-Di(2-thienyl)benzene was synthesized according to the following reaction scheme.

[0070] [ka]

[0071] 1,4-Dibromobenzene (Tokyo Chemical Industry Co., Ltd., product code: D0170) 1.18 g, 2-thiopheneboronic acid pinacol (Tokyo Chemical Industry Co., Ltd., product code: T2924) 2.36 g, potassium carbonate (Tokyo Chemical Industry Co., Ltd., product code: P1748) 1.55 g, [1,1′-bis(diphenylphosphino)ferrocene]dichloropalladium(II) (Tokyo Chemical Industry Co., Ltd., product code: B2064) 0.204 g were dissolved in a mixed solvent of 25 mL of tetrahydrofuran and 3.5 mL of water, and refluxed at 60°C for 24 hours under a nitrogen gas atmosphere. The mixture was separated into ethyl acetate / water, and the ethyl acetate solution was taken out and 1,4-di(2-thienyl)benzene was separated using a silica gel packed column (toluene, elution solvent). Recrystallization from toluene gave 0.957 g of 1,4-di(2-thienyl)benzene as yellow crystals. The crystals were soluble in chloroform, dichloromethane, THF, toluene, etc. Melting point: 206°C. 1 H-NMR(CD2Cl2, 500 MHz, ppm): δ = 7.64 (s, 4H), 7.37 (d, J = 4.0 Hz, 2H), 7.32 (d, J = 5.2 Hz, 2H), 7.11 (dd, J = 4.4, 3.2 Hz, 2H), Mass spectrometry value m / z = 242.2, (calculated value)m / z = 242.4

[0072] (2) Polymerization of 1,4-di(2-thienyl)benzene on a glassy carbon plate with iodine vapor 100 mg of 1,4-di(2-thienyl)benzene was dissolved in 10 mL of chlorobenzene, and 4 mL of the solution was spin-coated (3 seconds at 1500 rpm, then 20 seconds and 3 seconds) onto a 10 cm square glassy carbon thin plate (manufactured by ALLIANCE Biosystems Inc.). This was placed in a bell jar, sealed together with 0.5 g of iodine placed on a separate petri dish, and heated at 70°C for 2 hours. The 1,4-di(2-thienyl)benzene-coated surface of the thin plate was washed three times with 200 mL of acetonitrile. [ka]

[0073] The UV-Vis-IR absorption of the coating layer showed a strong absorption band in the light wavelength range of 300-600 nm. There was no absorption in the near infrared range, indicating that it was a pure undoped thiophene polymer. MALDI-TOF mass spectrometry revealed that it was a high molecular weight substance with a maximum molecular weight of about 3,400, and the molecular weight and degree of polymerization of the main component were 962 and 4, respectively. Raman spectroscopy (excitation wavelengths of 532 and 785 nm) showed a peak at 1222 cm -1 The strong absorption at the nucleus supported the formation of a linear polymer. Measurements using a general-purpose multi-function X-ray diffractometer (RINT-Ultima III, Rigaku Corporation) (measurements at 4° with the oblique incidence parallel method) showed a broad spectrum indicating the formation of an amorphous polymer.

[0074] Using a 0.1 M tetrabutylammonium perchlorate in acetonitrile solution as the electrolyte, the highest occupied molecular orbital level was calculated to be -5.5 eV from the thin layer cyclic voltammogram (sweep rate 50 mV / s). Furthermore, the lowest unoccupied molecular orbital level was calculated to be -3.3 eV from the band gap calculated from the ultraviolet absorption spectrum.

[0075] (3) Formation of a thin manganese oxide layer on a glassy carbon plate Manganese oxide thin layers were prepared according to a procedure described in a published literature (Zhou, F., et al., Advanced Energy Materials 2, 1013-1021, doi:10.1002 / aenm.201100783 (2012)). Briefly, ethylammonium nitrate was prepared by neutralizing 200 mL of ethylamine with 4 M dilute nitric acid, followed by removing water under reduced pressure using a rotary evaporator at 70 °C for 2 h. The electrolyte was prepared by dissolving 0.2 g of manganese acetate in 100 mL of a 1:9 water:ethylammonium nitrate mixture. 0.25 mL of 4 M dilute nitric acid was added to make it acidic. A 10 cm square glassy carbon thin plate was placed in the electrolyte, and platinum was used as the counter electrode, and the current was measured at 200 μA / cm. 2A constant current density of 10 ...

[0076] (4) Production of hydrogen peroxide by light irradiation A thiophene polymer obtained by polymerization of the 1,4-di(2-thienyl)benzene with iodine vapor was used, and a 10 cm square glassy carbon plate coated with a thin layer of the thiophene polymer and a 10 cm square glassy carbon plate coated with a thin layer of manganese oxide were connected with copper wires. The glassy carbon plate coated with the thin layer of the thiophene polymer was placed in a water tank with a width of 12 cm, a depth of 10 cm, and a depth of 0.3 cm (inner dimensions) as the irradiation surface, and the tank was filled with 30 mL of a sodium hydroxide aqueous solution of pH 12. The tank was then irradiated with light (simulated sunlight, 1000 W / m as irradiance). 2 (manufactured by Asahi Spectroscopy Co., Ltd.).

[0077] The amount of hydrogen peroxide was quantified according to a conventional method (Naga, A. et al., Anal. Chim. Acta, 204, 349-353 (1988)). Briefly, this method quantifies hydrogen peroxide by forming a copper(I) complex through reduction of copper(II) ions by hydrogen peroxide in the presence of excess 2,9-dimethyl-1,10-phenanthroline. 1 g of neocuproine was dissolved in 100 cm 3 A solution of 2,9-dimethyl-1,10-phenanthroline in ethanol was prepared by dissolving it in 10 cm 3 In a measuring flask, add 1 cm of 0.01 M copper(II) sulfate solution and 1 cm of 2,9-dimethyl-1,10-phenanthroline in ethanol. 3 The hydrogen peroxide sample solution was added to 8 cm 3 was added. Quantification was performed from the absorption intensity at the maximum absorption wavelength of 454 nm for the copper(I)-DMP complex. A calibration curve was created at five points from 0 to 120 μM using a commercially available 35 wt% hydrogen peroxide solution (Tokyo Chemical Industry Co., Ltd., product code: H1222) standard solution. The aqueous solution containing hydrogen peroxide was adjusted to pH 9 by diluting a dilute aqueous sulfuric acid solution with distilled water.

[0078] Approximately 30 mL of hydrogen peroxide solution with a concentration of 0.9 wt% was obtained 10 hours after the start of light irradiation. Furthermore, approximately 30 mL of hydrogen peroxide solution with a concentration of 2.0 wt% was obtained 24 hours after the start of light irradiation. The production rate of hydrogen peroxide 10 hours after light irradiation was 1.1 mg hydrogen peroxide / mg catalyst / hour, which exceeded the known values by more than two digits in a similar method.

Example

[0079] <Production of Hydrogen Peroxide Using a Conductive Thin Plate Coated with PEDOT / PSS> A glass thin plate surface-coated with conductive PSS (PEDOT (poly(3,4-ethylenedioxythiophene)) doped with poly(4-styrenesulfonic acid), hereinafter abbreviated as PEDOT / PSS) was prepared as follows. A PEDOT / PSS aqueous dispersion (Aldrich-Sigma Inc., product code: 483095) was spin-coated (1000 rpm, 60 sec) on the glass thin plate and dried by heating at 120 °C for 15 minutes to coat with PEDOT / PSS. The PEDOT / PSS-coated plate was fixed with acid-resistant tape and immersed in sulfuric acid (Junsei Chemical Co., Ltd., product code: 83010-2550) at room temperature for 1 minute. After washing twice with ultrapure water, it was dried by heating at 90 °C for 10 minutes and acid-treated. When the surface resistance of this thin plate was measured, the sheet resistance, layer thickness, and conductivity were 89 Ω / sq, 110 nm, and 1048 S / cm, respectively.

[0080] According to Example 1(2) above, a thiophene polymer layer was formed on a glass thin plate surface-coated with PEDOT / PSS. Two of these thin plates were connected, and further connected to a glassy carbon thin plate coated with a manganese oxide thin layer with a copper wire (see Figure 2).

[0081] When hydrogen peroxide was produced in the same manner as in Example 1, approximately 30 mL of hydrogen peroxide solution with a concentration of 0.7 wt% was obtained 5 hours after the start of light irradiation. Approximately 30 mL of hydrogen peroxide solution with a concentration of 1.9 wt% was obtained 18 hours after the start of light irradiation.

Example

[0082] <Production of hydrogen peroxide using poly(1,4-di(2-thienyl)naphthalene) as a thiophene polymer> A thin layer of manganese oxide was formed as a hydroxide catalyst layer on one side of a glassy carbon thin plate by electrolytic oxidation. On the other side of the plate, a trimer of thiophene and 1,4-naphthalene, 1,4-di(2-thienyl)naphthalene, was polymerized with iodine vapor to form poly(1,4-di(2-thienyl)naphthalene) as a light absorbing oxygen reduction catalyst layer. The resulting plate was immersed in alkaline water and irradiated with light to produce hydrogen peroxide. The polymerization method using iodine vapor was carried out according to Example 1. The HOMO and LUMO levels of the polymer layer made of the trimer were both 0.1 eV lower than those of the polymer of 1,4-di(2-thienyl)benzene.

[0083] Hydrogen peroxide was produced in the same manner as in Example 1, and about 30 mL of aqueous hydrogen peroxide solution with a concentration of 3.1 wt % was obtained 18 hours after the start of light irradiation. EXAMPLES

[0084] <Production of hydrogen peroxide using poly(2-fluoro-1,4-di(2-thienyl)benzene) as a thiophene polymer> As in Example 3, a thin layer of manganese oxide was formed as a hydroxide catalyst layer on one side of a glassy carbon thin plate by electrolytic oxidation. On the opposite side of the plate, a trimer of thiophene and fluorobenzene (2-fluoro-1,4-di(2-thienyl)benzene) was polymerized with iodine vapor to form poly(2-fluoro-1,4-di(2-thienyl)benzene) as a light absorbing oxygen reduction catalyst layer.

[0085] Hydrogen peroxide was produced in the same manner as in Example 3, and about 30 mL of aqueous hydrogen peroxide solution with a concentration of 1.6 wt % was obtained 24 hours after the start of light irradiation. EXAMPLES

[0086] <Production of Hydrogen Peroxide Using Polyterthiophene as Thiophene Polymer> A thin layer of manganese oxide was formed as a hydroxide oxidation catalyst layer on one side of a glassy carbon thin plate by electrolytic oxidation in the same manner as in Example 3. A polyterthiophene was formed as a light absorbing oxygen reduction catalyst layer on the opposite side of the plate by polymerizing thiophene trimer terthiophene with iodine vapor.

[0087] Hydrogen peroxide was produced in the same manner as in Example 3, and about 30 mL of aqueous hydrogen peroxide solution with a concentration of 1.2 wt % was obtained 24 hours after the start of light irradiation. EXAMPLES

[0088] <Production of hydrogen peroxide by modifying the formation method of poly(1,4-di(2-thienyl)benzene)> In Example 1, poly(1,4-di(2-thienyl)benzene) was obtained by electrolytic polymerization. That is, 100 mg of 1,4-di(2-thienyl)benzene was dissolved in 10 mL of 0.1 M tetrabutylammonium perchlorate in acetonitrile. A glassy carbon thin plate was immersed in the solution and subjected to one cycle of cyclic voltammogram (sweep rate 50 mV / s) at 0-1.2 V vs. silver / silver ion to form a poly(1,4-di(2-thienyl)benzene) thin layer. Residues could be removed by exposing the plate to ethanol or acetonitrile.

[0089] This was filled in a tank of 30 mL of a sodium hydroxide solution at pH 12 in the same manner as in Example 1, and irradiated with light (pseudo solar light, irradiance of 1000 W / m 2 When the sample was collected using a 2.1 wt % hydrogen peroxide solution (manufactured by Asahi Spectroscopy Co., Ltd.), approximately 30 mL of hydrogen peroxide solution was obtained 24 hours after the start of light irradiation. EXAMPLES

[0090] <Method of producing hydrogen peroxide using fine particles as a hydroxide oxidation catalyst layer> Manganese oxide fine particles (particle size: 50 μm) were partially coated with thiophene polymer by chemical oxidation polymerization, and the fine particles were dispersed in alkaline water and hydrogen peroxide was produced by light irradiation. The details are explained below.

[0091] (1) Formation of a poly(1,4-di(2-thienyl)benzene) layer on the surface of manganese oxide particles Manganese(II,III) oxide (Aldrich-Sigma Inc., product code: 377473-100G), 200 mg, was dispersed in a flask containing 50 ml of chlorobenzene and 1,4-di(2-thienyl)benzene (500 mg), then added to a 200 ml flask, and the mixture was treated in an ultrasonic bath for 20 minutes to ensure sufficient dispersion. Anhydrous iron(III) chloride (7.8 g), an oxidizing agent, was dissolved in 50 ml of chlorobenzene and added dropwise to the mixture at room temperature. Stirred at room temperature for 24 hours. The dark grey precipitate was collected by filtration and extracted with methanol for 24 hours to remove residual iron(III) chloride. After washing with methanol several times and drying by heating in a vacuum oven, manganese oxide with a poly(1,4-di(2-thienyl)benzene) layer on the surface was obtained.

[0092] (2) Production of hydrogen peroxide by light irradiation Add 50 mg of the microparticles prepared in (1) to a 500 mL beaker, fill it with 100 mL of a sodium hydroxide solution with a pH of 12, and irradiate with light (simulated sunlight: irradiance of 1000 W / m 2 (manufactured by Asahi Spectroscopy Co., Ltd.).

[0093] Nine hours after the start of light irradiation, approximately 100 mL of hydrogen peroxide solution with a concentration of 1.8 wt % was obtained.

[0094] From the above results, the method for producing hydrogen peroxide according to the present invention has the following characteristics: (1) It is activated by light irradiation. This is due to the discovery of a thiophene polymer that satisfies the energy levels of both the light absorbing oxygen reduction catalyst layer and the water oxidation catalyst layer, enabling it to function as a compensatory water oxidation catalyst, by using it as a copolymer with an aromatic compound. (2) The rate of hydrogen peroxide production is sufficiently high (>0.1 mg hydrogen peroxide / mg catalyst / hour, more than two orders of magnitude higher than the known rate for similar methods). This is because the LUMO level is sufficiently high to reduce oxygen to produce hydrogen peroxide, providing a strong driving force, and the sites of the thiophene polymer, especially the copolymer with aromatic compounds, may act as catalytic active sites. As a result, the method works sufficiently with water in the air, without the need to use water with an increased oxygen concentration by blowing oxygen into it. (3) It operates in neutral water or alkaline water (preferably alkaline water), for example, at a pH of 8 or higher, more preferably at a pH of 11 or higher. This is the optimum pH condition for the operation of general-purpose inexpensive manganese oxide, cobalt oxide, ruthenium oxide, and the like in the hydroxide oxidation catalyst layer, which is the compensation reaction in the present invention, and is generally an inappropriate condition for known light-absorbing oxygen reduction catalysts; however, the thiophene polymer discovered in the present invention has made this possible for the first time. (4) A conductive thin plate on which a light-absorbing oxygen-reduction catalyst has been formed and a conductive thin plate on which a water-oxidation catalyst layer has been formed are connected by a conductor (Figure 2), or a conductive thin plate is sandwiched between the light-absorbing oxygen-reduction catalyst and the water-oxidation catalyst layer (Figure 3), or the surface of fine particles is coated with another material. By placing or suspending these in water, a simple reaction tank under light irradiation can be created.

Claims

1. A method for producing hydrogen peroxide, comprising combining a water oxidation catalyst (hereinafter referred to as a water oxidation catalyst) with a light absorbing and oxygen reducing catalyst layer (hereinafter referred to as a light absorbing oxygen reducing catalyst layer) made of a thiophene polymer, immersing the combined layer in alkaline water, and irradiating the light absorbing oxygen reducing catalyst layer with light.

2. The method according to claim 1, wherein the thiophene polymer is a copolymer of thiophene and an aromatic compound having a structural unit represented by the following formula (I) (hereinafter, referred to as a thiophene copolymer): 【Chemistry 1】 however, A represents a structural unit derived from an aromatic compound; x and 1-x represent the composition ratio of the structural units of the copolymer, 0<x≦1.

3. 3. The method according to claim 1, further comprising connecting the conductive thin plate having the light absorbing oxygen reduction catalyst layer formed on its surface to a conductive thin plate having the water oxidation catalyst layer (hereinafter referred to as water oxidation catalyst layer) formed on its surface with a conductor, immersing the plate in alkaline water, and irradiating the plate with light.

4. 3. The method according to claim 1, further comprising immersing a thin plate having the light absorbing oxygen reduction catalyst layer formed on one side and the water oxidation catalyst layer formed on the other side of a conductive thin plate in alkaline water and irradiating the thin plate with light.

5. 3. The method according to claim 1, further comprising immersing fine particles of a hydroxide catalyst, the majority of the surface of which is coated with a thiophene copolymer, in alkaline water and irradiating the fine particles with light.

6. The method according to any one of claims 2 to 5, characterized in that, in obtaining the thiophene copolymer, a dimer or trimer of thiophene and an aromatic compound represented by the following general formula (II) or (III) is synthesized in advance, and the dimer or trimer is polymerized to obtain a copolymer of thiophene and an aromatic compound: 【Chemistry 2】 【Chemistry 3】 Here, B and C represent aromatic compounds.

7. The method according to any one of claims 1 to 6, wherein the hydroxide catalyst is composed of manganese oxide, cobalt oxide or ruthenium oxide.

8. The method according to any one of claims 1 to 7, wherein sunlight, simulated sunlight, or ultraviolet or visible light is used as a light source for the light irradiation.

9. A method for preparing a light absorbing oxygen reducing catalyst layer, comprising the steps of: applying the dimer or trimer synthesized in claim 6 onto a conductive thin plate; and exposing the plate to iodine vapor to obtain the thiophene copolymer.

10. A thin plate for producing hydrogen peroxide, comprising a conductive thin plate having a light absorbing oxygen reduction catalyst layer made of a thiophene polymer formed on one side and a hydroxide oxidation catalyst layer formed on the other side.

11. A fine particle for producing hydrogen peroxide, comprising a light absorbing oxygen reducing catalyst layer made of a thiophene polymer formed on the surface of a hydroxide catalyst having a hydroxide catalytic activity.

12. A conductive thin plate combination for producing hydrogen peroxide, comprising a conductive thin plate having a light absorbing oxygen reduction catalyst layer formed on its surface, which is made of a thiophene polymer, and a conductive thin plate having a hydroxide oxidation catalyst layer formed on its surface, and these are connected by a conductor.

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