Method for selectively intercalating layered oxide into interlayers, method for synthesizing layered compound structure, and layered compound structure
By selectively intercalating organic species into layered ruthenic acid 0.5 hydrate, the method addresses the challenge of creating new layered compound structures with detachable sites, enabling the production of multi-layered nanosheets with improved properties.
Patent Information
- Application Number
- JP2023161558
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-09-25
- Publication Date
- 2025-04-07
AI Technical Summary
Existing methods for obtaining nanosheets from layered compounds require intercalation of organic species to reduce electrostatic interactions, but they lack the ability to selectively intercalate organic species, limiting the creation of new layered compound structures with selectively detachable sites.
A method involving the synthesis of layered ruthenic acid 0.5 hydrate by desorbing intercalation water from layered ruthenic acid 0.9 hydrate every other layer, followed by selective intercalation of organic species, such as CTA cations, at sites where interlayer water is not desorbed, maintaining the stage structure and enabling selective detachment.
This method allows for the creation of a new layered compound structure with selectively detachable sites, making it an effective precursor for obtaining multi-layered nanosheets with enhanced properties.
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Abstract
Description
[Technical field]
[0001] The present invention relates to a method for selectively intercalating between layers of a layered oxide, a method for synthesizing a layered compound structure by said method, and a layered compound structure obtained by said synthesis method. [Background technology]
[0002] Nanosheets, which correspond to one layer of a layered compound, can be obtained by peeling off the layered compound. They are two-dimensional nanomaterials that exhibit high anisotropy, with atomic-level thickness and lateral dimensions of micrometers. All constituent atoms of nanosheets are exposed on the surface, and there are many atoms that can participate in reactions. Taking advantage of these structural characteristics, research is being conducted on nanosheets for applications such as thermal materials, magnetic materials, gas sensors, photocatalysts, and electrode catalysts. To peel off nanosheets from layered compounds, bulky organic species must be intercalated between the layers. The presence of the intercalated organic species between the layers weakens the electrostatic interaction between the layers, allowing the formation of nanosheets.
[0003] It is known that the layered compounds used to obtain nanosheets all have the same interlayer environment, but Non-Patent Document 1 reports that by converting layered ruthenium oxide with a K-type structure to an H-type by acid treatment and then drying under appropriate conditions, a structure can be formed in which every other layer has a different hydration environment. [Prior art documents] [Non-patent literature]
[0004] [Non-Patent Document 1] K. Fukuda, H. Kato, J. Sato, W. Sugimoto and Y. Takasu, Swelling, intercalation, and exfoliation behavior of layered ruthenate derived from layered potassium ruthenate, J. Solid State Chem., 182, 2997(2009). Summary of the Invention [Problem to be solved by the invention]
[0005] The above-mentioned Non-Patent Document 1 reports that layered ruthenium oxide can be converted to a structure in which every other layer has a different hydration environment by treating it with an acid. If it is possible to selectively induce intercalation of an organic species so as to change the interlayer structure in a layered compound in which all interlayer environments are the same, it will be possible to obtain a new layered compound structure in which sites that are easy to exfoliate are selectively present.
[0006] The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for selectively intercalating between layers of a layered oxide, a method for synthesizing a layered compound structure synthesized by the method, and a layered compound structure obtained by the synthesis method. [Means for solving the problem]
[0007] (1) The method according to the present invention is a method for selectively intercalating between layers of a layered oxide, and is characterized in that it comprises synthesizing layered ruthenic acid 0.5-hydrate by removing interlayer water from layered ruthenic acid 0.9-hydrate from every other layer, and intercalating an organic species into sites of the layered ruthenic acid 0.5-hydrate from which interlayer water has not been removed (intercalation step).
[0008] According to this invention, organic species can be intercalated at the sites of layered ruthenic acid 0.5 hydrate where interlayer water has not been removed. Such intercalation can be achieved while maintaining the layered oxide structure (also called stage structure) in which water is introduced in a different way. The layered ruthenium oxide structure thus obtained is a new layered compound structure in which sites that are easily exfoliated are selectively present, and is therefore extremely promising as a precursor for obtaining any multilayer nanosheet.
[0009] In the method according to the invention, the organic species is preferably a CTA cation.
[0010] According to this invention, it is possible to intercalate a CTA cation into the site where the interlayer water has not been released. The CTA cation is a cation constituting cetyltrimethylammonium bromide (CTAB), which is a quaternary ammonium cation.
[0011] In the method according to the invention, the intercalation is preferably carried out in an aqueous solution of cetyltrimethylammonium bromide.
[0012] (2) The method for producing layered ruthenium oxide according to the present invention is characterized in that the layered ruthenium oxide structure obtained by the method according to the present invention is exfoliated to produce a multilayer nanosheet containing two ruthenium oxide nanosheets.
[0013] According to the present invention, the above-mentioned method provides a layered ruthenium oxide structure in which easily exfoliated portions are selectively present, and by exfoliating the easily exfoliated portions, a multilayer nanosheet containing two ruthenium oxide nanosheets can be obtained.
[0014] (3) The ruthenium oxide nanosheet according to the present invention is characterized in that it is obtained by the above-mentioned method for producing layered ruthenium oxide according to the present invention.
[0015] According to the present invention, the above-mentioned method for producing layered ruthenium oxide makes it possible to obtain a multilayer nanosheet having a new structure containing two ruthenium oxide nanosheets, which is expected to lead to the development and application of properties that have not previously existed. Effect of the Invention
[0016] According to the method of the present invention for selectively intercalating between layers of a layered oxide, organic species can be intercalated at sites in layered potassium ruthenate 0.5-hydrate where interlayer water has not been removed. The resulting layered ruthenium oxide structure is a new layered compound structure in which sites that are easily exfoliated are selectively present, and is therefore extremely promising as a precursor for obtaining any multilayer nanosheet.
[0017] According to the method for producing layered ruthenium oxide of the present invention, a layered ruthenium oxide structure is obtained in which easily exfoliated portions are selectively present, and thus a multilayer nanosheet containing two ruthenium oxide nanosheets can be obtained by exfoliating the easily exfoliated portions.
[0018] According to the ruthenium oxide nanosheet of the present invention, a multilayer nanosheet having a new structure containing two ruthenium oxide nanosheets can be obtained, and this is expected to lead to the development and application of properties that have not previously existed. [Brief description of the drawings]
[0019] [Figure 1] FIG. 2 is a schematic diagram for explaining synthesis of a stage structure (staging), intercalation of an organic species while maintaining the stage structure, and peeling at the site where the organic species has been intercalated. [Diagram 2] (1) is a model in which layered ruthenic acid 0.9 hydrate (S1-HRO) is staged to form layered ruthenic acid 0.5 hydrate (S2-HRO), and (2) is a model in which the CTA cation is intercalated while maintaining the stage structure. [Diagram 3]This shows XRD patterns before and after the reaction when S2-HRO was reacted with CTAB so that CTA cations / protons = 5. [Figure 4] FIG. 1 is a schematic diagram of a double-layered ruthenic acid nanosheet obtained by exfoliating a layered ruthenic acid structure (S2-CTA-HRO) after intercalation with CTA cations. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The method for selective intercalation between layers of a layered oxide, the method for synthesizing a layered compound structure, and the layered compound structure according to the present invention will be described in detail below, but the present invention is not limited to the following description within the technical scope of the present invention.
[0021] The present inventor foresaw the possibility of selectively intercalating organic species by changing the hydration environment between specific layers of a layered oxide to a different structure, and completed the present invention through continued research. Specifically, as shown in Figures 1 and 2, the present invention first changes the hydration structure of layered ruthenium oxide by selectively removing interlayer water from layered ruthenic acid, and then realizes selective intercalation of organic species by intercalating organic species into the site in layered ruthenic acid where interlayer water has not been removed. Note that, as will be described in the experimental examples below, the organic species is a CTA cation, and the CTA cation is a cation constituting cetyltrimethylammonium bromide (CTAB).
[0022] That is, the method according to the present invention is a method for selectively intercalating between layers of a layered oxide, and is characterized by synthesizing layered potassium ruthenate 0.5-hydrate in which interlayer water contained in layered ruthenic acid 0.9-hydrate has been removed from every other layer (synthesis step), and intercalating an organic species into sites in the layered potassium ruthenate 0.5-hydrate from which interlayer water has not been removed (intercalation step).
[0023] In the present invention, organic species can be intercalated at sites where interlayer water has not been removed in layered potassium ruthenate 0.5 hydrate. In other words, the present invention is a method for synthesizing or preparing layered oxides with different water-entering methods (hydration environments) and selectively intercalating organic species at specific sites (sites where interlayer water has not been removed) where organic species are likely to intercalate among the sites with different water-entering methods. Such intercalation can be achieved while maintaining the structure of the layered oxides with different water-entering methods (also called "stage structure") as shown in Figures 1 and 2. The layered ruthenium oxide structure thus obtained is a new layered compound structure in which sites that are likely to peel off are selectively present, and is therefore extremely promising as a precursor for obtaining any multilayer nanosheet.
[0024] The obtained layered compound structure can be peeled off at the site of the intercurant selectively present between the layers. If the site of the intercurant is present in every other layer, it becomes a two-layered oxide nanosheet, and if it is present in every third layer, it becomes a three-layered oxide nanosheet.
[0025] Each component will be described.
[0026] [Layered oxide, staging] Although layered ruthenic acid will be used as an example of the layered oxide below, any layered oxide that causes staging and intercalation by a similar mechanism is not limited to layered ruthenic acid. Note that "staging" refers to a reaction or process in which the interlayer environment is transformed into a structure that changes at an arbitrary period, "intercalation" refers to a reaction or process in which a compound or element penetrates between layers of a layered oxide, and "intercalant" refers to a compound or element that penetrates between layers of a layered oxide by intercalation.
[0027] In the present invention, the hydrate of layered ruthenic acid shown in Fig. 1 and Fig. 2 is staged to synthesize a structure having a different water content (also called a "stage structure"), or layered ruthenic acid having such a stage structure is prepared in advance. Such a process may be called a synthesis or preparation process. As an example will be shown in the experimental example described later, the layered ruthenic acid hydrate before staging may be layered ruthenic acid 0.9 hydrate, and the stage structure after staging may be layered ruthenic acid 0.5 hydrate.
[0028] Layered ruthenic acid 0.9 hydrate (H 0.2 RuO 2.1 0.9H 2 The synthesis of layered potassium ruthenate 0.7 hydrate (K 0.2 RuO 2.1 0.7H 2 O) is synthesized. In this synthesis, the starting materials ruthenium oxide and potassium carbonate are weighed out and mixed in a solvent, the solvent is removed, and the dried mixture is pelletized, then calcined. The calcined pellets are crushed and washed to obtain layered potassium ruthenate 0.7 hydrate. The obtained layered potassium ruthenate 0.7 hydrate is acid-treated in an aqueous hydrochloric acid solution to obtain layered ruthenate 0.9 hydrate (referred to as "Stage 1-HRO" or "S1-HRO"). (Reference 1: K. Fukuda, H. Kato, J. Sato, W. Sugimoto and Y. Takasu, Swelling, intercalation, and exfoliation behavior of layered ruthenate derived from layered potassium ruthenate, J. Solid State Chem., 182, 2997 (2009) 10.1016 / j.jssc.2009.08.012.)
[0029] The layered ruthenic acid 0.5 hydrate is a stage structure after staging called "Stage 2-HRO" or "S2-HRO". It can be obtained by adding ultrapure water to layered ruthenic acid 0.9 hydrate and drying it in an appropriate environment. As shown in Figs. 1 and 2, the obtained layered ruthenic acid 0.5 hydrate has a stage structure in which a portion where interlayer water is removed and a portion where interlayer water is not removed are alternately present for each layer. In the method according to the present invention, the layered ruthenic acid 0.5 hydrate may be obtained by synthesis as described above or may be prepared in advance.
[0030] [Organic species, intercalation] The organic species penetrates between the layers by intercalation. In the present invention, as exemplified in the experimental examples described later, the organic species intercalating into the layered ruthenic acid 0.5 hydrate is CTA cation (CTA + The CTA cation is present in an aqueous solution of cetyltrimethylammonium bromide as a cation constituting cetyltrimethylammonium bromide (CTAB), which is a quaternary ammonium cation.
[0031] In the intercalation, protons (H + It is preferable to adjust the ratio of the organic species to be ion-exchanged, add a CTAB aqueous solution, and shake. In the present invention, intercalation can be achieved while maintaining the stage structure. Since such a layered ruthenium oxide structure is a new layered compound structure in which easily exfoliated sites are selectively present, it is highly promising as a precursor for obtaining any multilayer nanosheet.
[0032] Figure 3 shows the XRD patterns before and after the reaction when S2-HRO was reacted with cetyltrimethylammonium bromide (CTAB) so that the CTA cation / proton ratio was 5. When CTA cations are intercalated into S2-HRO while maintaining the stage structure, the basal plane spacing is in the range of 2.01 nm to 3.33 nm, but a periodic structure of d = 3.10 nm can be clearly confirmed from the XRD pattern after the reaction. From this, it can be said that CTA cations are intercalated into S2-HRO while maintaining the stage structure.
[0033] [Peeling] Figure 4 is a schematic diagram of a two-layer ruthenium oxide nanosheet obtained by exfoliating a layered ruthenium oxide structure (referred to as "S2-CTA-HRO") after intercalation with CTA cations. Exfoliation can be performed by dispersing the resulting layered compound structure (S2-CTA-HRO) in a solvent. The exfoliation process can produce a multilayer nanosheet with a new structure containing two ruthenium oxide nanosheets, as shown in Figure 4. EXAMPLES
[0034] The present invention will now be described in more detail with reference to experimental examples.
[0035] [Experiment 1] Layered ruthenic acid 0.9 hydrate (H 0.2 RuO 2.1 0.9H 2 The synthesis of layered potassium ruthenate 0.7 hydrate (K 0.2 RuO 2.1 0.7H 2 The synthesis is carried out by converting the starting materials ruthenium oxide and potassium carbonate into RuO 2 :K 2 CO 3The mixture was weighed out so that the ratio was 8:5, mixed in an acetone solvent, the solvent was removed, the dried mixture was pelletized, and then calcined at 850°C for 12 hours. The calcined pellets were crushed and washed with ultrapure water to obtain layered potassium ruthenate 0.7-hydrate. The obtained layered potassium ruthenate 0.7-hydrate was subjected to an acid treatment in a 1M aqueous hydrochloric acid solution to obtain layered ruthenic acid 0.9-hydrate (S1-HRO).
[0036] Layered ruthenic acid 0.5 hydrate was obtained by adding ultrapure water to layered ruthenic acid 0.9 hydrate and drying it in an appropriate environment.
[0037] The organic species was CTA cation, and layered ruthenic acid 0.5 hydrate was intercalated in cetyltrimethylammonium bromide (CTAB). This intercalation was carried out by adding an aqueous solution of CTAB to layered ruthenic acid 0.5 hydrate (S2-HRO) so that the ratio of CTA cation to be ion-exchanged with protons was 5, and then shaking. After the reaction was completed, the sample was collected by suction filtration and air-dried to obtain the layered ruthenic acid structure (S2-CTA-HRO).
Claims
1. A method for selectively intercalating between layers of a layered oxide, comprising synthesizing layered ruthenic acid 0.7-hydrate by removing interlayer water from layered ruthenic acid 0.9-hydrate at every other layer, and intercalating an organic species at a site in the layered ruthenic acid 0.5-hydrate where the interlayer water has not been removed.
2. The method of claim 1 , wherein the organic species is a CTA cation.
3. 3. The method according to claim 1 or 2, wherein the intercalation is carried out in an aqueous solution of cetyltrimethylammonium bromide.
4. A method for producing layered ruthenium oxide, comprising exfoliating the layered ruthenium oxide structure obtained by the method according to claim 1 to produce a multilayer nanosheet containing two ruthenium oxide nanosheets.
5. A layered ruthenium oxide nanosheet, which is obtained by the method according to claim 4 .