Organometallic structures containing titanium as a metallic element and methods for manufacturing the same

Abstract

The objective is to provide a method for manufacturing an organometallic structure that can exhibit sufficient catalytic efficiency to be suitable for use as a photocatalyst utilizing solar energy, without requiring post-processing or multiple steps. [Solution] A method for manufacturing an organometallic structure, A step of dissolving an acid compound having terephthalic acid as its main molecular structure, polyacrylic acid, and a silver-containing compound to obtain intermediate A, The process involves mixing a titanium-containing metal oxide cluster with the aforementioned intermediate A to obtain intermediate B. The process involves heating the intermediate B to obtain intermediate C, which is a solid component. The process involves repeatedly dissolving and centrifuging the intermediate C to obtain an organometallic structure. It is characterized by including.

Description

【Technical Field】 【0001】 The present invention relates to an organometallic structure having titanium (Ti) as a metal element and a method for producing the same, and is suitably used for decomposing water as a photocatalyst to generate hydrogen by introducing and promoting a heterometallic compound. 【Background Art】 【0002】 Hydrogen is developing greatly as a clean energy that does not generate carbon dioxide gas. Currently, there are mainly three methods for producing hydrogen. A method of reacting hydrocarbons such as methane contained in petroleum and natural gas with steam to separate them into hydrogen and carbon dioxide, a method of roasting coal to produce coal gas of hydrogen and carbon monoxide, and a method of electrolyzing water by passing an electric current through it. However, in these methods, there are significant problems with respect to the environment and cost, such as generating carbon dioxide gas in the process and consuming a large amount of electric power to generate hydrogen in the electrolysis process. Therefore, it is important to supply environmentally friendly and low-cost hydrogen in the future. As a technology for this, the reaction of decomposing water into hydrogen and oxygen by a photocatalyst utilizing solar energy is being actively researched and developed as a cutting-edge technology. Currently, metal oxides such as barium titanate and strontium titanate have achieved high quantum efficiency as photocatalysts. On the other hand, an organometallic structure (MOF) is a material expected to have a surface area effect due to its microporous and dense structure, and is highly expected in catalysts, and active research and development are being carried out. In photocatalysts, research has also been conducted on an organometallic structure having a titanium element as a cluster as a photocatalyst. Currently, the research challenge in using organometallic structures as photocatalysts is to improve their catalytic efficiency. Published results include research by Yanghe Fu et al. at Fuzhou University, who increased visible light absorption by adding amines to the linker constituting the organometallic structure (Non-Patent Document 1), and research by Horiuchi et al. at Osaka Metropolitan University, who increased light absorption by inducing structural defects (Non-Patent Document 2). Furthermore, Horiuchi et al. at Osaka Metropolitan University have further improved efficiency by supporting a co-catalyst within the organometallic structure (Non-Patent Document 3). Other examples of introducing co-catalysts include synthesizing an organometallic structure by coordinating a co-catalyst metal to the linker (Patent Document 1), adsorbing a nitrogen compound containing a co-catalyst onto a pre-fabricated organometallic structure (Patent Document 2), and immersing a pre-fabricated organometallic structure in an inorganic salt solution to exchange cations (Patent Document 3). [Prior art documents] [Patent Documents] 【0003】 [Patent Document 1] Special Publication 2022-527963 [Patent Document 2] Special Publication 2007-534651 [Patent Document 3] Special Publication 2023-519686 [Non-patent literature] 【0004】 [Non-Patent Document 1] Angewandte Chemie International Edition(IF16.6) Pub Date:2012-02-22 [Non-Patent Document 2] Journal of Catalysis 392(2020)119-125 [Non-Patent Document 3] Journal of the Japan Society for Smart Process Engineering, Vol. 2, No. 6 (November 2013), pp. 287-292 [Non-Patent Document 4] Electronic origins of photocatalytic activity in d0 metal organic frame-works, Sci.Rep.6(2016)23676 [Overview of the Initiative] [Problems that the invention aims to solve] 【0005】 However, conventional technologies as described above involve post-processing measures to improve catalyst efficiency after manufacturing the organometallic structure, which leads to increased production costs due to the multi-step process, and also presents problems in achieving uniformity in the processed and added state. Furthermore, when introducing compounds containing co-catalysts to support the co-catalysts, it is not easy to introduce them into the interior of the organometallic structure in solution, and they tend to concentrate near the surface of the structure, resulting in a problem of a reduced region with high catalytic effect. For these reasons, organometallic structures could not fully exhibit their inherent properties when used as catalysts, and their application to reactions such as the decomposition of water into hydrogen and oxygen using photocatalysis powered by solar energy was difficult. Therefore, the object of the present invention is to provide an organometallic structure that can exhibit sufficient catalytic efficiency to be suitably used as a photocatalyst utilizing solar energy, and a method for manufacturing the organometallic structure that does not require post-treatment or multiple steps. [Means for solving the problem] 【0006】 The present invention relates to an organometallic structure of MIL-125, The present invention relates to an organometallic structure characterized in that a silver-containing compound is present inside the organometallic structure. Furthermore, the present invention relates to a method for manufacturing an organometallic structure, A step of dissolving an acid compound having terephthalic acid as its main molecular structure, polyacrylic acid, and a silver-containing compound to obtain intermediate A, The process involves mixing a titanium-containing metal oxide cluster with the aforementioned intermediate A to obtain intermediate B. A step of heating the intermediate B to obtain the intermediate C which is a solid content, A step of repeatedly performing dissolution and centrifugation on the intermediate C to obtain an organometallic structure, It relates to a method for producing an organometallic structure, characterized by including the above steps. 【Advantages of the Invention】 【0007】 According to the present invention, for a titanium-based organometallic structure, structural defects can be efficiently increased, and in the process of synthesizing the organometallic structure, a silver compound as a cocatalyst is incorporated, so that the cocatalyst can be uniformly introduced into the interior of the organometallic structure. 【Brief Description of the Drawings】 【0008】 [Figure 1] It is a flowchart showing the outline of the method for producing the organometallic structure of the present invention. [Figure 2] It is a diagram showing the SEM observation results of an organometallic structure synthesized by adding only polyacrylic acid. [Figure 3] It is a graph showing the X-ray diffraction measurement results of a normally synthesized product, a product synthesized by adding polyacrylic acid, and the organometallic structure related to the present invention. [Figure 4] It is a graph showing the X-ray diffraction measurement results of a comparative example sample. [Figure 5] It is a diagram showing the formulation and observation results of an example. [Figure 6] It is a graph showing the X-ray diffraction measurement results of an example. [Figure 7] It is a comparison graph of the background intensity value / peak intensity value (Ib / I) between an example and a comparative example. 【Modes for Carrying Out the Invention】 【0009】 <Organometallic Structure (MOF)> The titanium-based organometallic structure (Ti-MOF) is a part of the MOF family, and MIL-125 is a Ti-based MOF derived from Ti metal ions and organic ligands. 【0010】 The organometallic structure of the present invention is this MIL-125-based organometallic structure, characterized in that a silver-containing compound is present inside the organometallic structure. 【0011】 In the organometallic structure of the present invention, due to the presence of a silver-containing compound that functions as a cocatalyst inside the skeleton of the organometallic structure, the catalytic effect is enhanced, and it can be expected that water can be decomposed more efficiently than before as a photocatalyst. 【0012】 The MIL-125-based organometallic structure can be synthesized from an organic linker and a metal oxide cluster having titanium. 【0013】 The organic linker is an acid compound having terephthalic acid as the main molecular structure. As the acid compound having terephthalic acid as the main molecular structure, for example, a terephthalic acid derivative can be used. The terephthalic acid derivative preferably has an amino group from the viewpoint of increasing light absorption in the visible region, and the terephthalic acid derivative having an amino group is, for example, 2-amino-terephthalic acid and its derivatives. 【0014】 The metal oxide cluster containing titanium is not particularly limited. As the organic titanate which is a metal oxide cluster containing titanium, for example, titanium(IV) isopropoxide, titanium(IV) butoxide, tetrabutyl orthotitanate can be used. Among them, the metal oxide cluster containing titanium is preferably tetrabutyl orthotitanate. 【0015】 The silver-containing compound is not particularly limited. For example, silver benzoate, silver carbonate, silver chloride, silver bromide, silver acetate can be used. Among them, the silver-containing compound is preferably silver benzoate. 【0016】 The organometallic structure of the present invention preferably contains polyacrylic acid, and as will be described in detail in the later manufacturing method and examples of the organometallic structure, the presence of polyacrylic acid can induce defects in the organometallic structure. 【0017】 On the other hand, in the present invention, the presence of a silver-containing compound that functions as a co-catalyst "inside" the skeleton of the organometallic structure is due to the induction and increase of defects in the organometallic structure by the method for producing the organometallic structure of the present invention, which will be described below, and the introduction and promotion of a heterometallic compound (silver-containing compound) that acts as a co-catalyst into the gaps created by the defects. Furthermore, in the 2θ-θ measurement of X-ray diffraction with a measurement wavelength of 1.5418 Å of the obtained organometallic structure powder, the ratio of the background intensity Ib to the peak intensity I at 2θ = 6.74 degrees (Ib / I) is 0.1 or more, indicating that gaps due to defects in the organometallic structure have been created that allow the silver-containing compound to be present inside the skeleton of the organometallic structure. The (Ib / I) is preferably 0.3 or more, more preferably 0.5 or more. 【0018】 <Method for manufacturing organometallic structures> Figure 1 is a flowchart illustrating the method for manufacturing the organometallic structure of the present invention. 【0019】 First, in the step of obtaining intermediate A, intermediate A is obtained by dissolving the above-mentioned constituent components: an acid compound having terephthalic acid as its main molecular structure, polyacrylic acid, and a silver-containing compound. Specifically, 2-aminoterephthalic acid is dissolved in dimethylformamide solvent as the acid compound having terephthalic acid as its main molecular structure, and then polyacrylic acid and silver benzoate are mixed in. This mixed solution is then mixed with a mixed solution of methanol solvent and silver benzoate in a glove box air-purged with nitrogen, and the mixture is stirred thoroughly to obtain intermediate A. 【0020】 Here, it is necessary to dissolve and mix these components simultaneously. Polyacrylic acid induces structural disruption of the MIL-125 organometallic structure, and simultaneously, the silver-containing compound increases structural defects, causing the silver-containing compound to be present inside the organometallic structure. 【0021】 Next, intermediate A is mixed with the above-mentioned titanium-containing metal oxide cluster, such as titanium isopropoxide, to obtain intermediate B. 【0022】 Furthermore, the intermediate B can be transferred to an autoclave and heated to obtain intermediate C, which is a solid component. By repeatedly dissolving and centrifuging the obtained intermediate C, the desired organometallic structure can be obtained. 【0023】 The manufacturing process for the organometallic structure of the present invention is as described above. Below, a specific example of the "method for manufacturing an organometallic structure of Ti clusters" is shown, and based on this specific example, the "method for manufacturing an organometallic structure by adding and synthesizing only polyacrylic acid" and the "method for manufacturing an organometallic structure related to the present invention" were used to perform structural analysis of the organometallic structures obtained by SEM observation and X-ray diffraction. 【0024】 (Method for manufacturing organometallic structures of Ti clusters) The manufacturing method was carried out according to Non-Patent Document 4 by MANasalevich et al. The organometallic structure dealt with in this proposal is denoted as MIL-125(Ti)-NH2. Its manufacturing method is as follows. Note that the amino group is not necessarily required. (1) Dissolve 2.86 g (15.8 mol) of 2-aminoterephthalic acid in a mixture of 40 mL of dimethylformamide (DMF) and 10 mL of dry methanol (MEOH). (2) Then, add 2.86 ml (9.7 mol) of titanium isopropoxide and transfer to an autoclave. (3) The autoclave is sealed and heated at 110°C for 72 hours. (4) Filter the yellow product, wash the product with fresh dimethylformamide, and stir overnight with 50 mL of dimethylformamide per gram of product. This removes any excess linker. (5) Repeat (4) twice with methanol to replace dimethylformamide with methanol. (6) Dry the product at 100°C. 【0025】 The structure of the dried product (a conventionally synthesized MOF) was analyzed by X-ray diffraction, and the results are shown in Figure 3 (line A in Figure 3). A peak similar to that reported in Non-Patent Document 4 appears, indicating that the structure as an MOF has been established. 【0026】 (Method for producing organometallic structures by adding only polyacrylic acid during synthesis) The following describes the case where polyacrylic acid (PAA) is added in the process described in (1) above. Figure 2 shows SEM images of the organometallic structure when polyacrylic acid (molecular weight 5000, manufactured by Wako Pure Chemical Industries, Ltd.) is added to the solvent at concentrations of 0.6 g / L, 3.0 g / L, and 9.0 g / L, respectively. It can be seen that as the amount of polyacrylic acid increases, the shape of the organometallic structure changes from a regular octahedron shape to a cocoon shape. 【0027】 Furthermore, regarding the case where the above polyacrylic acid concentration of 9.0 g / L was added, the results of structural analysis by X-ray diffraction are shown in Figure 3 (line B in Figure 3). Compared to the above conventionally synthesized MOF, the peak intensity of the sample that changed into a cocoon-like structure was weaker, but it showed the reflection peak characteristic of MIL-125(Ti)-NH2, indicating that the dense structure of the organometallic structure was generally maintained. 【0028】 (Method for manufacturing an organometallic structure related to the present invention) The manufacturing method in the present invention involves dissolving and mixing polyacrylic acid and silver benzoate together with 2-aminoterephthalic acid in step (1) of the above method for manufacturing an organometallic structure of Ti clusters, and then proceeding with steps (2) and beyond. The concentration of polyacrylic acid relative to the solvent is 8.57 g / L (approximately the same amount as in the above example where a polyacrylic acid concentration of 9.0 g / L is added), and silver benzoate (manufactured by Tokyo Chemical Industry Co., Ltd.) is added in a molar amount of 20% relative to the 2-aminoterephthalic acid. 【0029】 Line C in Figure 3 shows the analysis results of the generated sample by X-ray diffraction. As previously mentioned, polyacrylic acid plays a role in inducing structural breakdown of the MIL-125 organometallic structure, and the structural defects in the MIL-125 organometallic structure induced by polyacrylic acid make it easier for silver-containing compounds to exist inside the organometallic structure. However, in this manufacturing method, the reflection peak characteristic of MIL-125(Ti)-NH2 is considerably weaker. Therefore, it can be seen that adding silver benzoate along with polyacrylic acid further increased the structural defects. In addition, the background is larger at diffraction angles (2θ) below 10 degrees, indicating an increase in scattering due to the structure. [Examples] 【0030】 The present invention will be further described below with reference to comparative examples and embodiments of the present invention. 【0031】 [Comparative Example] This study investigates the effects of different solvent formulations on MIL-125(Ti)-NH2 without additives (polyacrylic acid and silver benzoate). Table 1 shows the formulations. In Table 1, the linker is 2-aminoterephthalic acid (manufactured by Tokyo Chemical Industries, Ltd.), the metal oxide cluster is tetrabutyl orthotitanate (manufactured by Tokyo Chemical Industries, Ltd.), solvent 1 is dimethylformamide (manufactured by Tokyo Chemical Industries, Ltd.), and solvent 2 is dry methanol (manufactured by Hayashi Pure Chemical Industries, Ltd.). The "standard recipe" follows the usual synthesis method for the above MOF. 【0032】 [Table 1] 【0033】 Figure 4 shows the X-ray diffraction results for each example in Table 1 with different formulations. The X-ray diffraction results in Figure 4 show that simply changing the formulations of the basic materials and solvent does not significantly increase the background (the Ib / I ratio does not change much). Specifically, when the amount of metal clusters in Experiment 1 was doubled, synthesis failed, and no reflection peaks appeared at all (line b in Figure 4). Furthermore, the normally synthesized product (line a in Figure 4) has a high yield of MIL-125(Ti)-NH2, while the others (Experiments 2, 3, and 4) have formulations deviating from the standard, resulting in lower yields and thus a difference in background size compared to the normally synthesized product. 【0034】 [Examples 1-5] The synthesis of organometallic structures with added polyacrylic acid and silver benzoate was carried out in each of Examples 1 to 5 using the formulations shown in Figure 5. Since it is known that the pH value of the synthesis solution affects the degree of octahedral particle shape of MIL-125(Ti)-NH2, the pH value was also adjusted. 【0035】 The results are shown in Figures 5 and 6. Figure 5 shows the formulation and pH, along with SEM observation results of samples encapsulated in resin and cross-sectionally processed. Figure 6 shows the reflectance measurement results using an X-ray diffractometer. All samples show differences in the intensity of the characteristic reflectance peak of MIL-125(Ti)-NH2, indicating that the degree to which the original structure is maintained in the organometallic structure differs. 【0036】 Here, the results of the comparative example and Examples 1-5 were compared using the background intensity Ib / peak intensity I at a diffraction angle of 6.74 degrees, which yields a large reflection peak. The X-ray diffractometer used was the Rigaku Ultima IV. The diffraction pattern was acquired using this X-ray diffractometer by 2θ-θ measurement. A Cu tube was used, and the measurement wavelength λ was 1.5418 Å. The tube voltage was 40 kV, and the tube current was 40 mA. The temperature was 23°C ± 2°C. The 2θ range was from 5° to 55°, the sampling width was 0.02°, and the speed was 2° / min (2 integrations). The slits were set as follows: exit / entry solar slit 5°, divergent slit 1 / 4, height-limited slit 10 mm, receiving slit open, and scattering slit 2 / 3. The background value was calculated using the value analyzed by the Data Analysis Software PDXL2 attached to the instrument. 【0037】 Figure 7 shows the results of the comparison, with "BG / PEAK" on the vertical axis representing background intensity Ib / peak intensity I. "MOF linker doubling" is from experiment 2 in the comparative example, "MOF solvent 1x" is from experiment 4 in the comparative example, and "MOF solvent 2x" is from experiment 3 in the comparative example. Experiment 1 in the comparative example is not shown in Figure 7 because the synthesis was unsuccessful. 【0038】 As shown in Figure 7, there was a clear difference in the values ​​between the comparative sample, which had a modified basic material composition without the addition of polyacrylic acid and silver benzoate, and the example sample, which had polyacrylic acid and silver benzoate added. Furthermore, it was confirmed that whether structural anisotropy increased and enough gaps due to defects in the organometallic structure were created to allow the silver-containing compound to exist inside the framework of the organometallic structure could be determined from the data of Examples 1 to 5 in Figure 7, particularly Example 2, by the ratio of background intensity Ib to peak intensity I (Ib / I) at 2θ of 6.74 degrees under the above measurement conditions being 0.1 or higher. 【0039】 <Configuration included in the embodiment of the present invention> This embodiment includes the following configuration. (Configuration 1) An organometallic structure of MIL-125, An organometallic structure characterized in that a silver-containing compound is present inside the organometallic structure. (Configuration 2) The organometallic structure according to Configuration 1, wherein in a 2θ-θ measurement of X-ray diffraction measurement with a powder measurement wavelength of 1.5418 Å, the ratio of the background intensity Ib to the peak intensity I at 2θ = 6.74 degrees (Ib / I) is 0.1 or more. (Configuration 3) The organometallic structure according to Configuration 1 or 2, wherein the organometallic structure contains polyacrylic acid. (Configuration 4) The organometallic structure according to any one of Configurations 1 to 3, wherein the silver-containing compound is silver benzoate. (Configuration 5) The organometallic structure according to any one of Configurations 1 to 4, wherein the organometallic structure is used as a photocatalyst to decompose water and generate oxygen and / or hydrogen. (Configuration 6) A method for manufacturing an organometallic structure, A step of dissolving an acid compound having terephthalic acid as its main molecular structure, polyacrylic acid, and a silver-containing compound to obtain intermediate A, The process involves mixing a titanium-containing metal oxide cluster with the aforementioned intermediate A to obtain intermediate B. The process involves heating the intermediate B to obtain intermediate C, which is a solid component. The process involves repeatedly dissolving and centrifuging the intermediate C to obtain an organometallic structure. A method for producing an organometallic structure, characterized by containing [the specified ingredient]. (Configuration 7) The method for producing an organometallic structure according to Configuration 6, wherein the step of obtaining the intermediate A is to simultaneously dissolve the acid compound having terephthalic acid as its main molecular structure, the polyacrylic acid, and the silver-containing compound. (Configuration 8) A method for producing an organometallic structure according to Configuration 6 or 7, wherein the acid compound having terephthalic acid as its main molecular structure has an amino group. (Configuration 9) A method for producing an organometallic structure according to any one of Configurations 6 to 8, wherein the silver-containing compound is silver benzoate. (Configuration 10) A method for producing an organometallic structure according to any one of Configurations 6 to 9, wherein the titanium-containing metal oxide cluster is tetrabutyl orthotitanate. (Configuration 11) A method for producing an organometallic structure according to any one of Configurations 6 to 10, wherein the silver-containing compound is present inside the obtained organometallic structure. (Configuration 12) A method for producing an organometallic structure according to any one of Configurations 6 to 11, wherein in a 2θ-θ measurement of X-ray diffraction of the obtained organometallic structure powder with a measurement wavelength of 1.5418 Å, the ratio of the background intensity Ib to the peak intensity I at 2θ = 6.74 degrees (Ib / I) is 0.1 or more. [Industrial applicability] 【0040】 The present invention's method for producing organometallic structures allows for the uniform introduction of a silver compound as a co-catalyst into the organometallic structure. Therefore, the resulting organometallic structure can be suitably used in a hydrogen production method, which utilizes solar energy-based photocatalysis to decompose water into hydrogen and oxygen, and is attracting attention as a clean energy source.

Claims

[Claim 1] A metal-organic structure of MIL-125, An organometallic structure characterized in that a silver-containing compound is present inside the organometallic structure. [Claim 2] The organometallic structure according to claim 1, wherein in a 2θ-θ measurement of X-ray diffraction with a powder measurement wavelength of 1.5418 Å, the ratio of the background intensity Ib to the peak intensity I at 2θ = 6.74 degrees (Ib / I) is 0.1 or more. [Claim 3] The organometallic structure according to claim 1 or 2, wherein the organometallic structure contains polyacrylic acid. [Claim 4] The organometallic structure according to claim 1 or 2, wherein the silver-containing compound is silver benzoate. [Claim 5] The organometallic structure according to claim 1 or 2, wherein the organometallic structure is used as a photocatalyst to decompose water and generate oxygen and / or hydrogen. [Claim 6] A method for manufacturing an organometallic structure, A step of dissolving an acid compound having terephthalic acid as its main molecular structure, polyacrylic acid, and a silver-containing compound to obtain intermediate A, The process involves mixing a titanium-containing metal oxide cluster with the aforementioned intermediate A to obtain intermediate B. The process involves heating the intermediate B to obtain intermediate C, which is a solid component. The intermediate C is subjected to repeated dissolution and centrifugation to obtain an organometallic structure. A method for producing an organometallic structure, characterized by containing [the specified ingredient]. [Claim 7] The method for producing an organometallic structure according to claim 6, wherein the step of obtaining the intermediate A involves simultaneously dissolving the acid compound having terephthalic acid as its main molecular structure, the polyacrylic acid, and the silver-containing compound. [Claim 8] A method for producing an organometallic structure according to claim 6 or 7, wherein the acid compound having terephthalic acid as its main molecular structure has an amino group. [Claim 9] A method for producing an organometallic structure according to claim 6 or 7, wherein the silver-containing compound is silver benzoate. [Claim 10] The method for producing an organometallic structure according to claim 6 or 7, wherein the titanium-containing metal oxide cluster is tetrabutyl orthotitanate. [Claim 11] The method for producing an organometallic structure according to claim 6 or 7, wherein the silver-containing compound is present inside the obtained organometallic structure. [Claim 12] A method for producing an organometallic structure according to claim 6 or 7, wherein in a 2θ-θ measurement of X-ray diffraction of the obtained organometallic structure powder with a measurement wavelength of 1.5418 Å, the ratio of the background intensity Ib to the peak intensity I at 2θ = 6.74 degrees (Ib / I) is 0.1 or more.

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