Inorganic nanosheet composite and method for manufacturing inorganic nanosheet composite

Abstract

To provide an inorganic nanosheet composite containing a metal complex that can be obtained by a relatively easy manufacturing method and can impart predetermined characteristics to the composite, and a method for manufacturing the inorganic nanosheet composite.SOLUTION: An inorganic nanosheet composite comprises a plurality of monodisperse inorganic nanosheets and cation species excluding simple metal ions and ammonium cations, in which the cation species are positioned between the monodisperse inorganic nanosheets in nanosheet-stacked nanofibers formed by stacking the plurality of monodisperse inorganic nanosheets, and an equivalent ratio of the cation species to the ion exchange capacity of the monodisperse inorganic nanosheets is an equivalent ratio in a range where the nanosheet-stacked nanofibers are formed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an inorganic nanosheet composite and a method for producing the inorganic nanosheet composite. In particular, the present invention relates to an inorganic nanosheet composite containing cationic species and a method for producing the inorganic nanosheet composite.

Background Art

[0002] Conventionally, an inorganic nanosheet laminate having a string-like structure composed of a plurality of stacked inorganic nanosheets is known (see, for example, Patent Document 1). When obtaining the inorganic nanosheet laminate described in Patent Document 1, first, by a bottom-up method, inorganic nanosheets having substantially uniform particle size and shape can be obtained from a raw material solution, and inorganic nanosheets with a very narrow particle size distribution can be obtained. Thereafter, a string-like structure can be formed by applying an attractive force between the inorganic nanosheets by a method such as concentration.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, in the production of the inorganic nanosheet laminate described in Patent Document 1, after mixing a predetermined ammonium salt and a predetermined metal alkoxide and then refluxing, a string-like structure of the inorganic nanosheet can be formed by a method such as concentration. However, the production of the inorganic nanosheet laminate described in Patent Document 1 requires a production method under somewhat limited conditions. In addition, it has not been easy to impart characteristics different from those of the inorganic nanosheets constituting the inorganic nanosheet laminate to the inorganic nanosheet laminate described in Patent Document 1.

[0005] Accordingly, an object of the present invention is to provide an inorganic nanosheet composite containing a cationic species that can be obtained by a relatively easy production method and can impart predetermined properties to the inorganic nanosheet composite, and a method for producing the inorganic nanosheet composite.

Means for Solving the Problems

[0006] The present invention provides an inorganic nanosheet composite including a plurality of monodisperse inorganic nanosheets and a cationic species other than a simple metal ion and an ammonium cation, wherein the cationic species is located between the monodisperse inorganic nanosheets in a nanosheet laminated nanofiber in which the plurality of monodisperse inorganic nanosheets are laminated, and the equivalent ratio of the cationic species to the ion exchange capacity of the monodisperse inorganic nanosheet is an equivalent ratio within a range in which the nanosheet laminated nanofiber is formed.

[0007] In the inorganic nanosheet composite, when the equivalent ratio is equal to or greater than a predetermined equivalent ratio, an aggregate of nanosheet laminated nanofibers may be included. In the inorganic nanosheet composite, the monodisperse inorganic nanosheet is selected from the group consisting of layered metal chalcogenides, layered metal oxides, layered metal oxyhalides, layered metal phosphates, clay minerals or layered silicates, and layered double hydroxides, and the cationic species may be selected from the group consisting of metal complexes, metal cluster ions, molecular ions, and polyelectrolytes. Further, the inorganic nanosheet composite may be an inorganic nanosheet composite for a visible light-responsive photocatalyst.

[0008] In addition, in order to achieve the above object, the present invention provides a method for producing an inorganic nanosheet composite, comprising: preparing a mixed solution by mixing an ammonium salt, a metal alkoxide, and a solvent; preparing a colloidal solution of monodisperse inorganic nanosheets synthesized by refluxing the mixed solution; and forming an inorganic nanosheet composite by mixing an aqueous solution containing cation species excluding single metal ions and ammonium cations with the colloidal solution, wherein cation species are located between each of the monodisperse inorganic nanosheets in a nanosheet laminated nanofiber in which a plurality of monodisperse inorganic nanosheets are laminated, and the equivalent ratio of the cation species to the ion exchange capacity of the monodisperse inorganic nanosheets is an equivalent ratio within the range in which the nanosheet laminated nanofiber is formed.

Effects of the Invention

[0009] According to the inorganic nanosheet composite and the method for producing the inorganic nanosheet composite of the present invention, an inorganic nanosheet composite containing cation species that can be obtained by a relatively easy production method and can impart predetermined characteristics to the inorganic nanosheet composite, and a method for producing the inorganic nanosheet composite can be provided.

Brief Description of the Drawings

[0010]

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[0011] [Conventional Knowledge Regarding Inorganic Nanosheet Complexes] In the conventional method for manufacturing inorganic nanosheets, since a delamination treatment step such as a step of intercalating a predetermined compound into a layered crystal and delaminating it or a step of delaminating by irradiating ultrasonic waves is required, irregular crushing of the layered crystal occurs, and it is impossible to substantially make the particle size and shape of the inorganic nanosheet uniform. That is, due to the delamination treatment step, not only are some of the inorganic nanosheets crushed and the shapes and particle sizes of the inorganic nanosheets not uniform, but also the shape and particle size cannot be controlled in the first place. Therefore, it is impossible to control the expression of a highly ordered structure (for example, a columnar phase, etc.) by the conventional method (so-called top-down method). For this reason, conventionally, only a liquid crystal state called a nematic liquid crystal phase or a swollen lamellar phase has been reported. Moreover, conventional DLVO theory, Onsager theory, etc. assume that the object is a stable colloid system dominated by repulsive forces and do not assume the use of gravity induction such as organic thermotropic liquid crystals. That is, conventionally, in the design of liquid crystals using inorganic materials, the viewpoint of gravity induction has been almost ignored. And since the particle sizes of the inorganic nanosheets obtained by the conventional method are uneven, it has also been impossible to optimize the physical property study with the particle size of the inorganic nanosheet as a parameter or a predetermined function (for example, catalytic activity function) by precise control of the aggregate structure of the inorganic nanosheet.

[0012] Therefore, the present inventors conducted studies aiming to precisely design a highly organized structure using inorganic nanosheet liquid crystals. As a result, they found that making the particle size distribution of the inorganic nanosheets extremely narrow, typically having substantially uniform particle sizes and shapes of the inorganic nanosheets, actually greatly contributes to the formation of a highly organized structure of the inorganic nanosheet liquid crystals. Specifically, the present inventors attempted to introduce precise control of the particle size and shape of the inorganic nanosheets and the viewpoint of attractive interactions into the synthesis of inorganic nanosheet liquid crystals, and proposed an inorganic nanosheet laminated structure having a string-like structure as reported in JP-A-2022-42584 (which may also be referred to as an "inorganic nanosheet laminated column"). In this proposal, inorganic nanosheets are directly synthesized by stirring a solution in which a predetermined metal alkoxide and a predetermined organic cation are mixed for a certain period of time. Further, in this proposal, by this synthesis method, monodisperse inorganic nanosheets having an extremely narrow particle size distribution and substantially uniform shapes are synthesized, and the concentration of the monodisperse inorganic nanosheets and the concentration of the coexisting salt are adjusted to control the interaction between the inorganic nanosheets, thereby obtaining an inorganic nanosheet laminated structure having a string-like structure.

[0013] Furthermore, in JP-A-2022-42584, the present inventors also proposed that when monodisperse inorganic nanosheets having a particle size of about 20 nm coexist with a predetermined organic cation, the inorganic nanosheets form an inorganic nanosheet laminated structure having a string-like structure like an organic supramolecular polymer (more easily formed when the monodisperse inorganic nanosheets and the predetermined organic cation coexist at high concentrations), and that the columnar nematic liquid crystal phase is expressed when this inorganic nanosheet laminated structure is oriented. This columnar structure can also be regarded as a very peculiar-shaped layered crystal having a major axis perpendicular to the laminated plane. Further, it was also proposed that the formation of the inorganic nanosheet laminated structure and the liquid crystal is reversible.

[0014] [New Findings Regarding Inorganic Nanosheet Composites] Here, in the inorganic nanosheet laminated structure reported in Japanese Patent Application Laid-Open No. 2022-42584, a step of adjusting the concentration of the inorganic nanosheet and the concentration of the ammonium salt to the concentration at which a plurality of inorganic nanosheets are laminated is required. That is, since it is necessary to adjust the concentration condition of a predetermined ammonium salt to a relatively high concentration, it is not easy to maintain the laminated structure without adjusting the salt concentration and to impart predetermined properties to the laminated structure, and it is desired to make the manufacturing method of the laminated structure itself easier. Therefore, the present inventor focused on the structure itself of the inorganic nanosheet laminated structure and tried to control the interaction between inorganic nanosheets by a principle different from that of ammonium salts. That is, the present inventor tried to control the interaction between inorganic nanosheets not by causing ammonium salts to exist around the inorganic nanosheets, that is, not by controlling with the salt concentration in a solution of the inorganic nanosheet and the ammonium salt, but by controlling with the structure itself of the inorganic nanosheet. Specifically, the present inventor controlled the bonding between inorganic nanosheets (that is, between layers) by using a predetermined cation species, and found that a predetermined laminated structure (hereinafter sometimes referred to as "nanosheet-laminated nanofiber") that can stably exist, that is, an inorganic nanosheet composite, can be synthesized by applying various compounds to the inorganic nanosheet.

[0015] That is, the present inventor obtained the knowledge that an inorganic nanosheet composite can be stably synthesized by introducing a cation species that exhibits an interaction (attractive force between inorganic nanosheets) that binds inorganic nanosheets (that is, layers) to each other, rather than controlling the bonding between inorganic nanosheets by causing ammonium salts to exist around the inorganic nanosheets. In addition, the present inventor also obtained the knowledge that by changing the equivalent ratio of the cation species to the ion exchange capacity of the inorganic nanosheet, the nanosheet-laminated nanofiber of the inorganic nanosheet and the aggregate of the nanosheet-laminated nanofibers can be selectively synthesized.

[0016] Specifically, the nanosheet-laminated nanofiber is formed by anionic inorganic nanosheets aggregating due to electrostatic interaction with a cation species. However, when the cation species is Na + , K+ , Ca 2+ In the case of simple small metal ions such as, since the charge / size ratio of the cation species is large, the electrostatic interaction is too strong, and the inorganic nanosheets are stacked into random aggregates without being aligned in the lateral position. On the other hand, when using organic cations (ammonium cations) such as alkylammonium cations or alkyltrimethylammonium cations, the charge / size ratio of the cation becomes small, and due to the electrostatic interaction that is not too strong, the inorganic nanosheets can adjust their lateral positions while aggregating, so that nanosheet - stacked nanofibers are formed. However, the nanosheet - stacked nanofibers formed by these organic cations are easily dissociated.

[0017] Therefore, from the viewpoint of increasing the degree of freedom in adjusting the cation size and valence, the present inventors attempted to use cation species that have not been studied so far (for example, metal complexes, metal cluster ions, molecular ions, polyelectrolytes). As a result, it was found that by using these cation species, it is possible to control the formation of nanosheet - stacked nanofibers and to adjust the stability of the nanosheet - stacked nanofibers. Furthermore, since various functions possessed by these cation species can be introduced into the nanosheet - stacked nanofibers, it was also found that it is possible to design materials capable of luminescence, magnetism, conductivity, redox, and / or selective substance adsorption. For example, in the experimental examples described later, nanosheet - stacked nanofibers using a ruthenium complex (Ru(bpy) 2+ ) will be described. In the nanosheet - stacked nanofibers into which the ruthenium complex is introduced, it was confirmed that the nanosheet - stacked nanofibers stably exist even when the ionic strength of the solution is reduced to 10 -2 . Also, it was confirmed that the fluorescence characteristics possessed by the ruthenium complex are imparted to the nanosheet - stacked nanofibers. The present invention is based on such findings.

[0018] Here, the following principles are assumed as the principles for stably synthesizing the inorganic nanosheet composite. First, from the perspective of strengthening the connection between inorganic nanosheets, it is conceivable to introduce a predetermined metal ion between the inorganic nanosheets. However, when using a simple metal ion (for example, a metal ion without a ligand such as Ca 2+ etc.), the connection between the inorganic nanosheets becomes too strong, and it is impossible to synthesize appropriate nanosheet laminated nanofibers as described above. Therefore, the inventor of the present invention considered from the perspective of stably synthesizing nanosheet laminated nanofibers, and while weakening the connection between inorganic nanosheets compared to metal ions, from the perspective of realizing a connection that can form a composite of inorganic nanosheets, a cationic species having a ligand or the like that exhibits steric hindrance compared to a simple metal ion is used. It was found that the connection between inorganic nanosheets can be adjusted within a range where nanosheet laminated nanofibers can stably exist. That is, the following principles are assumed.

[0019] a) Control of the interaction between monodisperse inorganic nanosheets by cationic species The interaction that binds monodisperse inorganic nanosheets by a predetermined cationic species is weaker than the interaction that binds monodisperse inorganic nanosheets by a simple metal ion. Therefore, when using a predetermined cationic species, random aggregation of monodisperse inorganic nanosheets can be suppressed, and nanosheet laminated nanofibers can be obtained. b) Improvement of the stability of the inorganic nanosheet composite by cationic species The interaction that binds monodisperse inorganic nanosheets by a predetermined cationic species is stronger than the interaction that binds monodisperse inorganic nanosheets by the conventionally used alkylammonium ion (for example, tetrabutylammonium, etc.). Therefore, it is possible to form a nanosheet laminated nanofiber that is difficult to decompose and has high stability. c) Control of the interaction between monodisperse inorganic nanosheets by the equivalent ratio By changing the equivalent ratio of the cationic species to the ion exchange capacity of the monodisperse inorganic nanosheets, the force of the interaction can be controlled. As a result, it becomes possible to selectively form the higher-order structure of the monodisperse inorganic nanosheets. d) Control of the formation of nanosheet - laminated nanofibers by valence, etc. When the cationic species is a metal complex, the valence of the central metal and the size of the ligand; when it is a molecular ion or a metal cluster ion, the valence and the cation size; and when it is a polyelectrolyte (polymeric cation), the degree of polymerization and the introduction amount of the cationic monomer can precisely control the attractive force between the monodisperse inorganic nanosheets and the cationic species to form nanosheet - laminated nanofibers. Metal complexes, molecular ions, metal cluster ions, and polyelectrolytes are all known compounds, and the valence of the central metal of the metal complex and the size of the ligand, the valence and the cation size of each of the molecular ion and the metal cluster ion, and the degree of polymerization of the polyelectrolyte and the introduction amount of the cationic monomer are also known. Therefore, from the known information, it is possible to estimate the attractive force between the monodisperse inorganic nanosheets and the cationic species within the range capable of forming nanosheet - laminated nanofibers.

[0020] By combining the above four principles and applying a predetermined cationic species to the monodisperse inorganic nanosheets, it is possible to form nanosheet - laminated nanofibers in which the cationic species are located between the monodisperse inorganic nanosheets (interlayer), and aggregates of the nanosheet - laminated nanofibers (hereinafter, may be referred to as "nanosheet - laminated nanofiber aggregates").

[0021] The present invention has been made based on the above findings and assumed principles. Hereinafter, the inorganic nanosheet composite according to this embodiment will be described in detail.

[0022] [Details of the inorganic nanosheet composite] In this embodiment, a predetermined cation species is positioned between a plurality of monodisperse inorganic nanosheets, and by controlling the equivalent ratio of the cation species to the ion exchange capacity of the monodisperse inorganic nanosheets, a string-shaped nanosheet laminated nanofiber in which the monodisperse inorganic nanosheets are laminated is formed. This nanosheet laminated nanofiber is one of the inorganic nanosheet composites. Further, by controlling the equivalent ratio of the cation species to the ion exchange capacity of the monodisperse inorganic nanosheets, a nanosheet laminated nanofiber and an aggregate of nanosheet laminated nanofibers in which the nanosheet laminated nanofibers are aggregated (this aggregate is also one of the inorganic nanosheet composites) can be selectively formed. That is, the inorganic nanosheet composite according to this embodiment is composed of a plurality of monodisperse inorganic nanosheets laminated at a predetermined interval and cation species positioned between the monodisperse inorganic nanosheets, and is a nanosheet laminated nanofiber having a string shape and / or an aggregate of nanosheet laminated nanofibers.

[0023] <Inorganic nanosheet> The monodisperse inorganic nanosheet according to this embodiment is a thin plate-shaped inorganic crystal as a unit structure obtained by synthesis using a predetermined compound (hereinafter, the "monodisperse inorganic nanosheet" may be simply referred to as the "inorganic nanosheet" for simplicity of explanation). For example, the monodisperse inorganic nanosheet is an anionic inorganic nanosheet obtained by reacting a predetermined ammonium salt with a predetermined metal alkoxide. The composition and shape of the inorganic nanosheet are determined according to the types and mixing ratios of the ammonium salt and the metal alkoxide used in the synthesis. Further, the particle size distribution of the inorganic nanosheet can be adjusted in the same manner. That is, the shape and thickness of the inorganic nanosheet reflect the crystallographic structure of the inorganic compound to be synthesized.

[0024] The inorganic nanosheets obtained by synthesis have, for example, a thickness of several nanometers (e.g., 0.75 nm in the case of lepidocrocite-type titanium oxide nanosheets) and a width of about a dozen to several tens of nanometers. As a result, the inorganic nanosheets have a highly anisotropic shape (i.e., a shape with a high aspect ratio). Here, the "particle size" of the inorganic nanosheets according to this embodiment is defined as follows.

[0025] The "particle size" of the inorganic nanosheets is substantially the lateral width of the inorganic nanosheets. That is, when the maximum width in the plan view of the inorganic nanosheets is taken as the lateral width w, the average value of this lateral width w is defined as the "particle size" in this embodiment. However, since the inorganic nanosheets are obtained by synthesis in this embodiment, they reflect the crystallographic structure of the inorganic compound to be synthesized, and the shape of the inorganic nanosheets becomes a substantially uniform predetermined shape (e.g., rectangular shape, rhombic shape, etc.). In this case, the "particle size" of the inorganic nanosheets is the lateral width of the said predetermined shape. For example, the lateral width in the case where the shape of the inorganic nanosheets is rectangular can be represented by the combination of the length of the short side and the length of the long side (or the length of the diagonal), and the lateral width in the case of a rhombic shape can be represented by the combination of the length of the major axis and the length of the minor axis. The "particle size" of the inorganic nanosheets can be measured and calculated using measurement means such as the dynamic light scattering method or an electron microscope. Also, the thickness t of the inorganic nanosheets is determined according to the crystal structure of the inorganic material to be synthesized. The thickness of the inorganic nanosheets can be measured by atomic force microscope observation or small-angle X-ray scattering measurement.

[0026] Also, there is no limitation on the particle size of the inorganic nanosheets according to this embodiment. However, from the viewpoint of highly organizing the inorganic nanosheets, it is preferably substantially monodisperse.

[0027] Here, in this embodiment, the inorganic nanosheets being "monodisperse" means the case where the following conditions are satisfied. (1) The particle shape observed by a transmission electron microscope is substantially uniform (for example, when the shape of the inorganic nanosheet observed by a transmission electron microscope is rhombic, the ratio of the short axis to the long axis of each rhombic inorganic nanosheet is 1.4:1, and the lateral widths of each inorganic nanosheet are substantially the same, it can be determined that the shape is substantially uniform.). (2) The particle size distribution measured by a transmission electron microscope or the like is approximated by a unimodal normal distribution function, and its standard deviation is less than 50% of the average particle size, and generally 40% or less (when this condition is satisfied, it can be determined that the particle size distribution is extremely narrow.).

[0028] In the case of inorganic nanosheets obtained by a conventional exfoliation method, the particle shape is amorphous, and the standard deviation of the particle size is about 50 to 200% of the average particle size, which can be clearly distinguished from the "monodisperse" inorganic nanosheets in the present embodiment. Further, by making the particle size distribution of the inorganic nanosheets into a predetermined narrow distribution, the formation of the higher-order ordered structure of the inorganic nanosheets can be controlled (that is, the lower-order control is performed for the higher-order ordered structure control). After making the inorganic nanosheets monodisperse, the interaction between the inorganic nanosheets (that is, attractive force, repulsive force) is adjusted and controlled by setting the equivalent ratio of the cation species to the ion exchange capacity of the inorganic nanosheets within a predetermined range, whereby a nanosheet laminated nanofiber and an aggregate of the nanosheet laminated nanofibers can be formed. If the repulsive force between the inorganic nanosheets is too strong, the inorganic nanosheets will disperse and no structure will be formed. If the attractive force is too strong, they will aggregate disorderly and irreversibly. However, these situations can be easily observed by using a polarized light microscope or the like. Even if the attractive force and the repulsive force between the inorganic nanosheets differ depending on the species and size of the inorganic nanosheets, the attractive force and the repulsive force of various inorganic nanosheets can be adjusted by setting the equivalent ratio of the cation species to the ion exchange capacity of the inorganic nanosheets within a predetermined range.

[0029] In addition, in this specification, "substantially uniform" does not mean that the particle size and shape of the inorganic nanosheets are exactly the same for each and every one of the inorganic nanosheets. Even when there are some inorganic nanosheets with different particle sizes and shapes, as long as the standard deviation of the particle size distribution is within a predetermined value and it exhibits a predetermined liquid crystal state or the like in a solution or colloidal state, it is considered to be in a state where the particle size and shape are uniform in terms of its content and essence. Also, "substantially monodisperse" has the same meaning.

[0030] The inorganic nanosheets are not particularly limited as long as they are inorganic nanosheets obtained by synthesis. That is, inorganic nanosheets that can form layered inorganic compounds, and there is no particular limitation as long as they are synthesizable inorganic nanosheets. Examples of the layered inorganic compounds include layered metal chalcogenides, layered metal oxides (e.g., titanium oxide, layered perovskite compounds, titanium niobates, molybdates, etc.), layered metal oxyhalides, layered metal phosphates (e.g., layered antimony phosphates, etc.), clay minerals or layered silicates (e.g., mica, smectite group (montmorillonite, saponite, hectorite, fluorohectorite, etc.), kaolin group (kaolinite, etc.), magadiite, kanemite, etc.), and layered double hydroxides, etc. For example, examples of the inorganic nanosheets include various oxide-based nanosheets such as silica nanosheets, titanium oxide nanosheets, niobium oxide nanosheets, cobalt oxide nanosheets, etc.

[0031] In this embodiment, for example, layered titanates can be synthesized and used. As an example of the layered titanates, it is a crystal having a layered structure formed by a chain of TiO6 octahedrons and having metal ions between its layers, such as the ramsdellite-type layered titanate (e.g., Cs x Ti 2-x / 4 O4 (where 0.5 ≦ x ≦ 1), A x Ti 2-x / 3Li x / 3 O4 (where A = K, Rb, Cs; 0.5 ≦ x ≦ 1), etc.). Specific examples of the ramsdellite-type layered titanate include K 0.8 Ti 1.73Li 0.27 O4, Rb 0.75 Ti 1.75 Li 0.25 O4, Cs 0.7 Ti 1.77 Li 0.23 O4, Cs 0.7 Ti 1.825 Examples include O4 and the like.

[0032] <Synthesis of Monodisperse Inorganic Nanosheets> Examples of the method for synthesizing monodisperse inorganic nanosheets include, for example, a method in which the synthesis method reported previously (E.L. Tae, et al., J.Am.Chem.Soc., 2008, 130, 6534) is improved. As an example, from the viewpoint of easy control of the particle size and shape of the inorganic nanosheets, a method of stirring or refluxing a mixed solution obtained by mixing raw materials in a predetermined solvent can be used. Specifically, a mixed solution obtained by adding a metal alkoxide to an alkaline solution, or a mixed solution obtained by adding a predetermined ammonium salt and a predetermined metal alkoxide to a predetermined solvent (for example, water) is prepared, and this mixed solution is stirred and / or refluxed to synthesize a colloid containing monodisperse inorganic nanosheets (hereinafter referred to as "monodisperse inorganic nanosheet colloid"). By synthesizing inorganic nanosheets using a mixed solution as in this embodiment, the particle size and shape can be precisely controlled, so that monodisperse inorganic nanosheets with a desired particle size and shape can be synthesized.

[0033] Note that the concentration of the inorganic nanosheets in the monodisperse inorganic nanosheet colloid can be adjusted according to the amount of each of a plurality of raw materials (for example, ammonium salt and metal alkoxide) mixed in the solvent, and / or the ratio of the plurality of raw materials (for example, the ratio of the amount of the metal alkoxide to the amount of the ammonium salt).

[0034] As an example, a monodisperse inorganic nanosheet colloid based on a rhabdocytetype layered titanate can be prepared by reacting a metal alkoxide with an ammonium salt and refluxing at a predetermined temperature for a predetermined time. Thereby, substantially monodisperse inorganic nanosheets are formed in the colloid.

[0035] (Ammonium salt) As the ammonium salt, an alkylammonium salt can be used. As the alkylammonium salt, for example, a quaternary ammonium compound can be used. As the quaternary ammonium compound, as an example, tetramethylammonium hydroxide (TMAOH), tetraethylammonium hydroxide (TEAOH), tetrapropylammonium hydroxide (TPAOH), tetrabutylammonium hydroxide (TBAOH), trimethyl-2-hydroxyethylammonium hydroxide, etc. can be mentioned.

[0036] Here, the alkylammonium salt can be used as a solution added to a predetermined solvent. For example, it can be used as an aqueous solution of the alkylammonium salt. In this case, the concentration of the alkylammonium salt in the aqueous solution of the alkylammonium salt is not particularly limited as long as it can synthesize monodisperse inorganic nanosheets. For example, from the viewpoint of facilitating the synthesis of monodisperse inorganic nanosheets, 0.1 M or more is preferable, 0.3 M or more is also preferable, and it may be 2 M or less.

[0037] (Metal alkoxide) Examples of the metal alkoxide include metal alkoxides represented by the following general formula (1).

[0038] M(OR)4 General formula (1)

[0039] In the general formula (1), M is a metal element, and R is an alkyl group having 1 or more and 10 or less carbon atoms, which may be the same or different. M is, for example, an element selected from the group consisting of Mg, Al, Si, Ca, V, Cr, Mn, Fe, Co, Ni, Zn, Ga, Ge, Sr, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Ba, Ta, W, Re, Os, Ir, Pb, La, Ce, Nd, Sm, Eu, Gd, Tb, and Dy, etc. Also, from the viewpoint of realizing an appropriate reaction rate, an alkyl group having 1 to 4 carbon atoms is preferable for R. For example, a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-propyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a ter-butyl group, etc. are preferable.

[0040] Specific metal alkoxides include, for example, aluminum triethoxide, aluminum triisopropoxide, aluminum tributoxide, aluminum tri-sec-butoxide, aluminum diisopropoxide sec-butoxide, aluminum diisopropoxide acetylacetonate, aluminum di-sec-butoxide acetylacetonate, aluminum diisopropoxide ethyl acetoacetate, aluminum di-sec-butoxide ethyl acetoacetate, aluminum trisacetylacetonate, aluminum trisethylacetoacetate, aluminum acetylacetonate bisethylacetoacetate, titanium tetraethoxide, titanium tetraisopropoxide, titanium tetrabutoxide, titanium diisopropoxide bisacetylacetonate, titanium diisopropoxide bisethylacetoacetate, titanium tetra-2-ethylhexoxide, titanium diisopropoxide bis(2-ethyl-1,3-hexanediolate), titanium dibutoxide bis(triethanolaminato), zirconium tetrabutoxide, zirconium tetraisopropoxide, zirconium tetramethoxide, zirconium tributoxide monoacetylacetonate, zirconium dibutoxide bisacetylacetonate, zirconium butoxide trisacetylacetonate, zirconium tetraacetylacetonate, zirconium tributoxide monoethylacetoacetate, zirconium dibutoxide bisethylacetoacetate, zirconium butoxide trisethylacetoacetate, zirconium tetraethylacetoacetate, etc. In addition, cyclic 1,3,5-triisopropoxycyclotrialuminoxane, etc. are also included.

[0041] In the synthesis of monodisperse inorganic nanosheets, by setting the alkylammonium concentration within a certain range, the pH is mainly set within a range appropriate for synthesis. Then, depending on the concentration of the metal alkoxide, the number of nuclei generated at the initial stage of inorganic nanosheet synthesis and the subsequent particle size are determined. For example, in the synthesis of the monodisperse inorganic nanosheets according to this embodiment, when the alkylammonium concentration is 0.3 M, the metal alkoxide concentration is preferably reacted at 0.1 M or more, more preferably reacted at 0.2 mol or more, and preferably reacted at 1 M or less. Note that by adjusting the amount of the metal alkoxide relative to the unit amount of the ammonium salt during the synthesis of the monodisperse inorganic nanosheets, the average particle size of the obtained inorganic nanosheets can be controlled.

[0042] (Stirring or reflux conditions) There are no particular limitations on the stirring or reflux conditions. The stirring conditions may be, for example, stirring in air (that is, under an atmospheric atmosphere) at room temperature (for example, 25 °C) for a predetermined time. Also, the conditions for refluxing may be, for example, a temperature exceeding room temperature (as an example, 40 °C or more or 70 °C or more and a predetermined temperature of 100 °C or less), and refluxing for a predetermined time under an atmospheric atmosphere. Note that the average particle size of the inorganic nanosheets can be controlled by the reflux time. That is, the average particle size of the inorganic nanosheets can be increased as the reflux time becomes longer.

[0043] (Solvent) As the solvent, an aqueous solvent, for example, pure water can be used.

[0044] <Cation species> The cationic species according to this embodiment can be introduced between the inorganic nanosheet layers, and the interaction between the inorganic nanosheets is weaker than that of the simple metal ions (and / or the interaction between the inorganic nanosheets is stronger than that of the alkylammonium ions), and there is no particular limitation as long as it can form nanosheet laminated nanofibers. Examples of the cationic species include cationic species excluding simple metal ions and ammonium cations such as alkylammonium cations and alkyltrimethylammonium cations, such as metal complexes, metal cluster ions, molecular ions, and polyelectrolytes (polymeric cations).

[0045] (Metal complex) A metal complex is a compound in which a predetermined ligand coordinates to a central metal. In this embodiment, the interaction between the inorganic nanosheets by the metal complex is weaker than the interaction between the inorganic nanosheets by the simple metal ions of the central metal. As long as an inorganic nanosheet composite (nanosheet laminated nanofibers and a nanosheet laminated nanofiber aggregate) can be stably formed, various metal complexes can be used. That is, as the metal complex, a metal complex in which the ratio of the valence of the central metal to the size of the ligand (valence / size) is within a range capable of forming nanosheet laminated nanofibers can be used.

[0046] For example, as the metal complex, one or more metals selected from the group consisting of Fe, Co, Ni, Mn, Zn, Cu, W, Ru, Pd, Pt, Ir, Rh, Os, Sm, Sc, Se, Re, Au, and Ag, and aqua (OH2), hydroxo (OH), hydride (H), chloro (Cl), carbonyl (CO), carboxyl (COOH), pyridine (py), 4-picoline (pic), isoquinoline (isoq), pentamethylcyclopentadienyl (Cp *Monodentate ligands such as ), and derivatives thereof, and polydentate ligands such as 2,2'-bipyridine (bpy), 2-phenylpyridine (ppy), 1,10-phenanthroline (phen), pyridine-2-thiolate (pyS), 1,2-benzenedithiolate (bdt), 2,2':6',2''-terpyridine (tpy), 2,6-bis(1-methylbenzimidazol-2-yl)pyridine (Mebimpy), 2,6-bis-(di-tert-butylphosphinomethyl)pyridine (PNPtBu), 1,4,8,11-tetraazacyclotetradecane (cyclam), porphyrin (por), and derivatives thereof, and one or more ligands selected from the group consisting of metal complexes formed therefrom.

[0047] As an example, ruthenium complexes, iron complexes, etc. can be used as the metal complex. As the ruthenium complex, tris(2,2'-bipyridine)ruthenium(II) complex ([Ru(bpy)3] 2+ ) can be mentioned, and as the iron complex, tris(2,2'-bipyridine)iron(II) complex ([Fe(bpy)3] 2+ ) and the like can be mentioned.

[0048] (Metal cluster ion) The metal cluster ion is an ion of an aggregate composed of several to several hundred or several thousand metal atoms. In the present embodiment, the interaction that binds inorganic nanosheets by metal cluster ions is weaker than the interaction that binds inorganic nanosheets by single metal ions. As long as an inorganic nanosheet complex can be stably formed, various metal cluster ions can be used. That is, as the metal cluster ion, a metal cluster ion in which the ratio of valence to cation size (valence / size) is in a range capable of forming a nanosheet stacked nanofiber can be used.

[0049] For example, as the metal cluster ion, a metal cluster cation having a Keggin structure can be mentioned. As an example of the Keggin-type cluster cation, the Keggin-type Al cluster cation [ε-Al 13 O4(OH)24 (H2O) 12 7+ include the following.

[0050] (Molecular ion) As the cation species, molecular ions can also be used. In this embodiment, compared with the interaction that binds inorganic nanosheets by a single metal ion, the interaction that binds inorganic nanosheets by molecular ions is weaker. As long as an inorganic nanosheet complex can be stably formed, various molecular ions can be used. That is, as the molecular ion, a molecular ion in which the ratio of valence to cation size (valence / size) is within the range capable of forming a nanosheet stacked nanofiber can be used.

[0051] As an example of the molecular ion, [Cr3O(OOCH)6(H2O)3] + include the following.

[0052] (Polymer electrolyte) As the cation species, polymer electrolytes can also be used. In this embodiment, compared with the interaction that binds inorganic nanosheets by a single metal ion, the interaction that binds inorganic nanosheets by polymer electrolytes is weaker. As long as an inorganic nanosheet complex can be stably formed, various polymer electrolytes can be used. That is, as the polymer electrolyte, a polymer electrolyte in which the degree of polymerization and the introduction amount of cation monomers are within the range capable of forming a nanosheet stacked nanofiber can be used.

[0053] As the polymeric cation, various polymers can be mentioned in consideration of the interaction with an anionic inorganic nanosheet. As the polymeric cation, as an example, chitosan, polyallylamine, polydiallyldimethylammonium, etc., which are cationic polymeric cations, can be mentioned.

[0054] <Inorganic nanosheet complex> ​The inorganic nanosheet composite according to this embodiment is composed of a plurality of monodisperse inorganic nanosheets and cation species (excluding simple metal ions and ammonium cations). Specifically, the inorganic nanosheet composite is composed of cation species located between a plurality of monodisperse inorganic nanosheets. That is, in the inorganic nanosheet composite, cation species are located between the monodisperse inorganic nanosheets in the nanosheet laminated nanofibers in which a plurality of monodisperse inorganic nanosheets are laminated. And the ratio of the equivalent amount (gram equivalent, that is, molecular weight / valence) of the cation species to the cation exchange capacity (CEC) of the monodisperse inorganic nanosheet (that is, equivalent amount of cation species / CEC) is adjusted to be the equivalent ratio within the range where the nanosheet laminated nanofibers are formed. When this equivalent ratio becomes equal to or greater than a predetermined equivalent ratio, an aggregate of nanosheet laminated nanofibers is formed. That is, nanosheet laminated nanofibers are formed in the range of the first equivalent ratio, and nanosheet laminated nanofibers and an aggregate of nanosheet laminated nanofibers are formed in the range of the second equivalent ratio different from the first equivalent ratio. Therefore, by changing the equivalent ratio, the structure of the inorganic nanosheet composite can be changed between nanosheet laminated nanofibers and an aggregate of nanosheet laminated nanofibers.

[0055] Here, the nanosheet laminated nanofibers according to this embodiment exhibit a string-like structure. Specifically, the nanosheet laminated nanofibers are formed by laminating the surfaces of monodisperse inorganic nanosheets (inorganic nanosheets with a substantially uniform particle shape) parallel to the short axis of the nanofibers and laminating the inorganic nanosheets in the long axis direction. Note that such a string-like structure is formed by self-organization of inorganic nanosheets with a substantially uniform particle shape, with the surfaces of the inorganic nanosheets laminated parallel to the short axis of the string (the laminated structure can be confirmed, for example, by a transmission electron microscope image). And since the particle shape of the inorganic nanosheet is substantially uniform, the width of the short axis of the string-like structure is substantially uniform.

[0056] In addition, as the cation species, the above various cation species can be used. And the characteristics of each cation species, that is, in the case of a metal complex, the valence of the central metal and the size of the ligand, in the case of a molecular ion or a metal cluster ion, the valence and the cation size, and in the case of a polyelectrolyte, the degree of polymerization and the introduction amount of the cation monomer are known. Therefore, for example, as shown in the examples described later, since an inorganic nanosheet composite according to this embodiment is formed using a predetermined cation species with clear valence and ligand size, etc., and the attractive force between the monodisperse inorganic nanosheet and the cation species can be precisely controlled, it is possible to estimate how much of a predetermined cation species should be used for a predetermined monodisperse inorganic nanosheet to form an inorganic nanosheet composite.

[0057] <Method for producing inorganic nanosheet composite> The method for preparing the inorganic nanosheet composite is not particularly limited. For example, a mixed solution (first mixed solution) prepared by adding a predetermined alkylammonium salt and a predetermined metal alkoxide to a predetermined solvent is refluxed to synthesize a monodisperse inorganic nanosheet colloidal solution. Then, the concentration of the inorganic nanosheets in the synthesized monodisperse inorganic nanosheet colloidal solution is adjusted to a predetermined concentration. On the other hand, a predetermined cation species is added to a predetermined solvent (for example, pure water, etc.) to prepare a cation species solution adjusted to a predetermined concentration. Then, a mixed solution (second mixed solution) obtained by mixing the monodisperse inorganic nanosheet colloidal solution with adjusted concentration and the cation species solution is stirred. After stirring, the second mixed solution is subjected to a desalting treatment to remove excess ammonium salts and the like. Note that the stirring conditions are not particularly limited, and the stirring conditions may be, for example, stirring in air (that is, under an atmospheric atmosphere) at room temperature (for example, 25 ° C) for a predetermined time.

[0058] Thereby, an inorganic nanosheet composite according to this embodiment, that is, a nanosheet laminated nanofiber, can be obtained. Here, by adjusting the ratio of the equivalent amount of the cation species to the ion exchange capacity of the inorganic nanosheets of the inorganic nanosheet composite within a range of a predetermined equivalent ratio when preparing the second mixed solution, a nanosheet laminated nanofiber or an aggregate of nanosheet laminated nanofibers can be selectively prepared.

[0059] In addition, as the desalting treatment, a method of centrifuging the second mixed solution using a centrifuge can be used. Further, as the desalting treatment, a method can also be used in which the second mixed solution is allowed to stand to phase-separate the precipitate and the supernatant, water is added to the precipitate after removing the supernatant, the mixture is stirred and then allowed to stand again for phase separation, and the supernatant is removed repeatedly. The inorganic nanosheet composite according to the present embodiment can stably maintain its shape even when subjected to desalting treatment. That is, even when the nanosheet laminated nanofiber as the inorganic nanosheet composite according to the present embodiment is subjected to desalting treatment, the shape of the nanofiber is stably maintained. This is because the cation species according to the present embodiment is less soluble in an aqueous solvent than a simple metal ion or an ammonium cation and easily maintains the interaction between inorganic nanosheets.

[0060] <Examples of application fields> The inorganic nanosheet composite according to the present embodiment can be used as a functional material applied to composite materials, catalysts, adsorption materials, separation membranes, electrode materials, etc. For example, the inorganic nanosheet composite can be applied to adsorption / separation (e.g., gas separation, water purification, removal of pollutants, etc.), functional thin films (e.g., antibacterial, transparent conductive films, etc.), solid ion conductors (e.g., fuel cells, soft actuators, etc.), high specific surface area electrodes (e.g., supercapacitors, etc.), photocatalysts, solar cells, etc. In particular, since the cation species that exhibits a predetermined function exists between the layers of the monodisperse inorganic nanosheets having a high aspect ratio and a large specific surface area in the inorganic nanosheet composite according to the present embodiment, various functions based on the cation species (as an example, the function of a visible light-responsive photocatalyst) can be exhibited. Therefore, an inorganic nanosheet composite that exhibits a desired function can be obtained by appropriately selecting the combination of the inorganic nanosheet and the cation species.

[0061] <Effects of the embodiment> The inorganic nanosheet composite according to this embodiment can form a nanosheet laminated nanofiber in which cation species are located between monodisperse inorganic nanosheets by complexing monodisperse inorganic nanosheets and a predetermined cation species. That is, by combining anionic monodisperse inorganic nanosheets and bulky cation species, the attractive force between monodisperse inorganic nanosheets is controlled within a range where the monodisperse inorganic nanosheets do not randomly aggregate, and nanofibers in which the monodisperse inorganic nanosheets are laminated can be formed. Furthermore, in the inorganic nanosheet composite according to this embodiment, by controlling the equivalent ratio of the cation species to the ion exchange capacity of the monodisperse inorganic nanosheets, a nanosheet laminated nanofiber and an aggregate of nanosheet laminated nanofibers can be selectively formed.

[0062] Here, when adopting the conventional method of controlling the salt concentration to form a laminated structure, when the solvent is removed from the nanosheet laminated nanofiber dispersion to make it solid, a large amount of salt remains, so a washing process is required, and when washing, the nanosheet laminated nanofiber may change to another structure (for example, the structure collapses). On the other hand, in the inorganic nanosheet composite according to this embodiment, since the interaction between monodisperse inorganic nanosheets is controlled by cation species, a large amount of salt does not remain. In addition, the characteristics inherent to the cation species can also be imparted to the nanosheet laminated nanofiber (the string-like structure of monodisperse inorganic nanosheets).

[0063] In the inorganic nanosheet composite according to this embodiment, various inorganic nanosheets can be used as the monodisperse inorganic nanosheets, and one cation species can be replaced with another cation species. Therefore, in the inorganic nanosheet composite using one cation species, the function based on the one cation species is exhibited, and in the inorganic nanosheet composite using another cation species, the function based on the other cation species is exhibited. Therefore, according to the inorganic nanosheet composite according to this embodiment, an inorganic nanosheet composite that exhibits a desired function can be easily designed.

[0064] Hereinafter, the inorganic nanosheet composite according to this embodiment will be specifically described using experimental examples.

[0065] [Experimental Example 1] <Synthesis of Monodisperse Inorganic Nanocheet Colloid> For the monodisperse inorganic nanosheet colloid, 33.4 mmol of titanium tetraisopropoxide (TIP) was added to 150 mL of a 0.273 mol / L aqueous solution of tetramethylammonium hydroxide (TMAOH), and the mixture was stirred at room temperature in an air atmosphere for 60 minutes and then refluxed at 80°C in an air atmosphere for 24 hours. Thereby, a monodisperse inorganic nanosheet colloid (monodisperse titania nanosheet colloid solution) was obtained. The concentration of the thus-obtained inorganic nanosheet colloid solution of monodisperse titania nanosheets was 1.7 wt%, and the TMA + concentration was 0.273 mol / L. The reagents used were as follows.

[0066] · TMAOH: 25% aqueous solution of tetramethylammonium hydroxide (TMAOH) (manufactured by Tokyo Chemical Industry Co., Ltd.) · TIP: titanium tetraisopropoxide (manufactured by Fujifilm Wako Pure Chemical Corporation)

[0067] <Preparation of Aqueous Solution Containing Metal Complex> As the aqueous solution containing a metal complex, an aqueous solution of a ruthenium complex was prepared. Specifically, 2.94 g of tris(2,2'-bipyridine)ruthenium(II) chloride hexahydrate and 47.1 g of water were mixed and stirred at 500 rpm for 60 minutes to prepare 50.0 mL of a 0.0779 mol / L [Ru(bpy)3] 2+ aqueous solution. Next, in order to adjust the ratio (equivalent ratio) of the equivalent (molar equivalent, that is, amount of substance / valence) of [Ru(bpy)3] 2+ to the ion exchange capacity (CEC) of the inorganic nanosheet, this [Ru(bpy)3] 2+The aqueous solution was diluted with water. The reagents used are as follows. Here, CEC is the amount of cations that can adsorb negatively charged inorganic nanosheets, which is the amount of cations per unit mass of the nanosheet, and the unit of CEC is meq / g. meq means milliequivalent, which is the amount of substance (mmol) divided by the valence of the ion. For example, the CEC of titania nanosheet is 4.63 meq / g. Here, since the CEC of divalent cations is calculated by multiplying the reciprocal of the valence, the adsorbable divalent [Ru(bpy)3] 2+ is calculated as 2.31 mmol / g by multiplying the CEC of the titania nanosheet by 1 / 2.

[0068] · Ruthenium complex: Tris(2,2´-bipyridine)ruthenium(II) chloride hexahydrate (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0069] More specifically, when controlling the equivalent ratio "Ru / CEC" of [Ru(bpy)3] 2+ to the ion exchange capacity of the inorganic nanosheet to, for example, "0.20", and preparing 1.0 g of an aqueous solution containing a metal complex of this ratio, since 0.20×(1 / 2)=0.10, 0.10 g of [Ru(bpy)3] 2+ aqueous solution (0.0779 mol / L) and 0.90 g of water are mixed, an aqueous solution containing [Ru(bpy)3] 2+ with "Ru / CEC" of 0.40 times equivalent can be prepared. Under such a principle, an aqueous solution of [Ru(bpy)3] 2+ with an equivalent ratio (Ru / CEC) of 0.2 times (0.2 times equivalent) to the ion exchange capacity (CEC) of the inorganic nanosheet was prepared to be 1.00 g. The concentration (mol / L) of [Ru(bpy)3 2+ is as shown in Table 1. 2+ is as shown in Table 1.

[0070] <Synthesis of inorganic nanosheet composite> (Preparation of inorganic nanosheet composite) [Ru(bpy)3] prepared to 0.20 times equivalent 2+1.00 g of an aqueous solution and 1.00 g of a monodisperse inorganic nanosheet colloid solution (monodisperse titania nanosheet colloid solution) with an inorganic nanosheet concentration (titania nanosheet [mNS] concentration) of 1.7 wt% and a TMA + concentration of 0.273 mol / L were mixed and stirred at 300 rpm for 30 minutes. As a result, a 2.00 g inorganic nanosheet composite (ruthenium titania nanosheet composite, sometimes referred to as "[Ru(bpy)3] + -mNS") containing solution with an inorganic nanosheet concentration of 1.10 wt% and a TMA 2+ concentration of 0.137 mol / L was prepared. The equivalent ratio ([Ru(bpy)3] 2+ / CEC) of [Ru(bpy)3] 2+ to the ion exchange capacity (CEC) of the inorganic nanosheets of this inorganic nanosheet composite is 0.20 times equivalent. Thereby, a sample of [Ru(bpy)3] 2+ -mNS according to Experimental Example 2 was obtained.

[0071] [Experimental Example 1, Experimental Examples 3 to 13, and Experimental Example 14] Also, using the monodisperse inorganic nanosheet colloid prepared in the same manner as in Experimental Example 2 and 1.00 g of an [Ru(bpy)3] 2+ aqueous solution prepared for each multiple equivalent, samples of [Ru(bpy)3] 2+ -mNS according to each experimental example with an equivalent ratio of [Ru(bpy)3] 2+ to the ion exchange capacity (CEC) of the inorganic nanosheets ranging from 0.10 times equivalent to 2.0 times equivalent were also prepared (Experimental Example 1, Experimental Examples 3 to 13). Furthermore, a sample without using the [Ru(bpy)3] 2+ aqueous solution ([Ru(bpy)3] 2+ / CEC = 0 "0 times equivalent" sample) was also prepared (Experimental Example 14). The equivalent ratio of [Ru(bpy)3] 2+ to the ion exchange capacity (CEC) of the inorganic nanosheets and the concentration (mol / L) of [Ru(bpy)3 2+ in each sample are as shown in Table 1.

[0072]

Table 1

[0073] Regarding the sample according to Experimental Example 9, an attempt was made to collect the nanosheet laminated nanofibers, which are the formed inorganic nanosheet composites, using the following washing method.

[0074] (Washing method) The salt was removed and the sample was washed from the prepared solution containing the inorganic nanosheet composite according to Experimental Example 9. As a result, the solid sample of Ru(bpy)3 2+ -mNS according to Experimental Example 9 was obtained. The method for removing the salt is as follows.

[0075] The prepared solution containing the inorganic nanosheet composite ([Ru(bpy)3] 2+ -mNS) was allowed to stand, phase-separated into a precipitate and a supernatant, and the supernatant was removed. Then, water was added to the precipitate so that the mass was the same as the mass after the preparation of the inorganic nanosheet composite, stirred, allowed to stand again until phase separation occurred, and after phase separation, the supernatant was removed. This operation was performed a total of 2 times.

[0076] [Characterization - Measurement method, etc.] (Visual observation - Crossed Nicol observation) After visual observation of each of the samples according to Experimental Examples 1 to 14, the presence or absence of stationary birefringence and flow birefringence was confirmed by crossed Nicol observation. The confirmation of stationary birefringence was performed by visually observing the sample enclosed in a 0.50 mm silicon spacer. Also, the confirmation of flow birefringence was performed by visually observing the sample placed in a screw tube under crossed Nicol conditions.

[0077] (Polarizing microscope (POM) observation) Regarding each of the samples according to Experimental Examples 1 to 14, the state and birefringence of the structure formed by [Ru(bpy)3] 2+ -mNS were observed using a polarizing microscope (POM: manufactured by OLYMPUS, BX51-P). Specifically, the sample was enclosed in a 0.50 mm silicon spacer, the enclosed sample was covered with a cover glass, and observed using a polarizing microscope.

[0078] (Ultraviolet-visible spectrophotometer (UV-Vis) measurement) To derive the wavelength range of light absorbed by the metal-ligand charge transfer state (MLCT) of [Ru(bpy)3] in the prepared ruthenium complex aqueous solution and the unknown concentration, an ultraviolet-visible spectrophotometer (manufactured by HITACHI, U-2910) was used to obtain an absorption spectrum by plotting the quantitative analysis in the solution sample and the absorbance for each wavelength of light. The titania nanosheet aqueous solution, the prepared ruthenium complex aqueous solution ([Ru(bpy)3] 2+ aqueous solution), and each sample of Experimental Examples 1 to 13 were measured. 2+

[0079] (Fluorescence spectrophotometer (FL) measurement) For each sample of Experimental Examples 1 to 14 and the ruthenium complex aqueous solution ([Ru(bpy)3] 2+ aqueous solution), the wavelength range in which the solution of the ruthenium titania nanosheet complex ([Ru(bpy)3] 2+ -mNS) emits fluorescence was measured using a fluorescence spectrophotometer (manufactured by HITACHI, F-2500).

[0080] (Fluorescence microscope (FM) observation) To confirm the formation of the nanosheet stacked nanofibers by [Ru(bpy)3] and mNS in the ruthenium titania nanosheet complex ([Ru(bpy)3] 2+ -mNS) in each of the sample of Experimental Example 8 and the mNS ethanol-water mixed solution, observation was carried out using a fluorescence microscope (manufactured by KEYENCE, BZ-X800). The fluorescence filter used for the observation was the BZ-X-GFP filter (excitation wavelength 470 ± 20 nm, dichroic mirror wavelength 495 nm or more, absorption wavelength 525 ± 25 nm), and the fluorescence emitted when the ruthenium complex was excited and relaxed to the ground state was observed. The observed fluorescence image was shown in orange to match the fluorescence emitted by the ruthenium complex. 2+

[0081] (Confocal laser scanning microscope (CLSM) observation) ​​For each of the samples according to Experimental Example 14, Experimental Example 1, Experimental Example 6, Experimental Example 7, Experimental Example 8, Experimental Example 9, Experimental Example 10, and Experimental Example 13, the presence or absence of nanosheet laminated nanofibers formed by the complex of monodisperse titania nanosheets and ruthenium complex ([Ru(bpy)3] 2+ ) was observed using a confocal laser microscope (manufactured by Nikon Instec Co., Ltd., A1R+). In a confocal laser microscope, an object can be observed using two types of lasers: a laser with a wavelength of 488 nm and a laser with a wavelength of 405 nm. In the observation using the laser with a wavelength of 405 nm, a scattered image can be obtained, so the structure of the object in the solution can be observed. On the other hand, in the observation using the laser with a wavelength of 488 nm, a fluorescence image can be obtained, so fluorescent dyes adsorbed on the object can be observed. Here, in order to observe the presence or absence of nanosheet laminated nanofibers, the fluorescence images of each sample were observed using a laser with a wavelength of 488 nm. Specifically, the sample was dropped onto the bottom surface of a glass-bottom dish, and the scattered image of the sample was observed using a confocal laser microscope.

[0082] (Small-angle / Wide-angle X-ray Scattering (SAXS / WAXS) Measurement) The structure of the monodisperse titania nanosheet colloid and the structure of the nanosheet laminated nanofibers of the ruthenium titania nanosheet complex ([Ru(bpy)3] 2+ -mNS) in each of the samples according to Experimental Examples 1 to 14 were measured using small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) (manufactured by Rigaku Corporation, NANOPIX, measurement conditions: camera length (720 mm), CuKα characteristic X-ray, 40 kV·30 mA, two-dimensional CCD detector). For the small-angle X-ray scattering measurement, the sample to be measured was enclosed in a capillary with an inner diameter of 2.0 mm (manufactured by WJM-Glas) and measured for 30 minutes. On the other hand, the wide-angle X-ray scattering measurement was performed for 90 minutes. In the small-angle / wide-angle X-ray scattering measurement, in a graph showing the scattering intensity I with respect to the scattering vector q, which is obtained by circularly integrating the two-dimensional pattern, when the power law of I~q -1 is observed, the presence of a rod-shaped structure is presumed, and when the power law of I~q -2 is observed, the presence of a disk-shaped structure is presumed.

[0083] (Atomic force microscopy (AFM) observation) The presence or absence of the formation of nanosheet stacked nanofibers of ruthenium titania nanosheet composite ([Ru(bpy)3] 2+ -mNS) in the sample according to Experimental Example 2 was observed using an atomic force microscope (AFM, manufactured by HITACHI, AFM5000II). Specifically, the sample according to Experimental Example 2 was diluted 50-fold, the diluted sample was dropped onto a mica substrate, dried, and then observed.

[0084] (Transmission electron microscopy (TEM) observation) The presence or absence of the formation of the structure of nanosheet stacked nanofibers of ruthenium titania nanosheet composite ([Ru(bpy)3] 2+ -mNS) in each of the samples according to Experimental Example 4, Experimental Example 7, and Experimental Example 13 was observed using a transmission electron microscope (TEM JEOL, JEM-1400). To obtain a high-contrast image, a tungsten filament was used as the electron source. Specifically, a grid (HRC-M10) with a carbon support film having a thickness of 15 nm was used, and each sample was measured at an acceleration voltage of 80 kV. The sample for TEM observation was prepared by diluting each sample 50-fold with pure water, dropping 1 μL of the diluted sample, holding it for 30 seconds, sucking up the moisture with filter paper, and drying it in a desiccator.

[0085] [Characterization - Measurement Results] Figure 1 shows the visual observation results of the samples according to Experimental Example 1 to Experimental Example 14. Specifically, Figure 1(a) shows the visual observation results of the samples according to Experimental Example 1 to Experimental Example 14 immediately after preparation, and Figure 1(b) shows the visual observation results of the samples according to Experimental Example 1 to Experimental Example 14 after standing for 24 hours after preparation. The numerical values described below each figure indicate the value of ([Ru(bpy)3] 2+ / CEC (equivalent ratio).

[0086] (Results of Visual Observation) First, the samples according to Experimental Example 1 to Experimental Example 14 ([Ru(bpy)3] 2+When visually observing the (-mNS-containing aqueous solution), as shown in Fig. 1(a), no turbidity was observed in the samples of Experimental Example 14 and Experimental Examples 1 to 6. On the other hand, turbidity began to be observed in the sample of Experimental Example 7 (the sample with the equivalent ratio of [Ru(bpy)3] to the ion exchange capacity (CEC) of the inorganic nanosheet being 0.80 times equivalent. Hereinafter, the equivalent ratio of [Ru(bpy)3] to the ion exchange capacity (CEC) of the inorganic nanosheet may be simply referred to as the "equivalent ratio"). Turbidity was observed in the samples from Experimental Example 7 to Experimental Example 13. That is, it was observed that when the equivalent ratio was 0.80 times equivalent or more, turbidity began to occur in the [Ru(bpy)3]-mNS-containing aqueous solution. 2+ sample with the equivalent ratio of [Ru(bpy)3] to the ion exchange capacity (CEC) of the inorganic nanosheet being 0.80 times equivalent. Hereinafter, the equivalent ratio of [Ru(bpy)3] to the ion exchange capacity (CEC) of the inorganic nanosheet may be simply referred to as the "equivalent ratio". 2+ to the ion exchange capacity (CEC) of the inorganic nanosheet may be simply referred to as the "equivalent ratio". 2+ -mNS-containing aqueous solution.

[0087] Furthermore, the samples according to Experimental Examples 1 to 14 were left standing at room temperature in an air atmosphere for 24 hours and then visually observed again. As a result, as shown in Fig. 1(b), it was observed that from the sample according to Experimental Example 9 (equivalent ratio: 1.0 times equivalent) to the sample according to Experimental Example 13 (equivalent ratio: 2.0 times equivalent), separation into supernatant and precipitate occurred. It is considered that the tendency of phase separation increases as the concentration of [Ru(bpy)3] 2+ becomes higher.

[0088] (Results of cross Nicol observation) Fig. 2 shows the results of cross Nicol observation of the samples according to Experimental Examples 1 to 14.

[0089] As can be seen by referring to Fig. 2, no birefringence was observed in the samples from the sample according to Experimental Example 14 (equivalent ratio: 0 times equivalent) to Experimental Example 5 (equivalent ratio: 0.60 times equivalent). On the other hand, flow birefringence was observed in the sample of Experimental Example 6 (equivalent ratio: 0.70 times equivalent), and steady birefringence was observed in the sample of Experimental Example 9 (equivalent ratio: 1.0 times equivalent). And no birefringence was observed in the samples from Experimental Example 9 (equivalent ratio: 1.0 times equivalent) to Experimental Example 13 (equivalent ratio: 2.0 times equivalent). In Experimental Examples 9 to 13, [Ru(bpy)3 2+It is considered that no birefringence was observed because the concentration was high. From these results, it was shown that flow birefringence was observed when the equivalent ratio was at least 0.70 times equivalent or more, and steady birefringence was observed when the equivalent ratio was 1.0 times equivalent or more.

[0090] (Results of polarized light microscopy observation) Figure 3 shows the results of polarized light microscopy observation of a sample in which conventional inorganic nanosheets are uniformly dispersed. Specifically, Fig. 3(a) shows the results in a previously reported polarized light microscopy observation of a sample in which inorganic nanosheets are uniformly dispersed, and Fig. 3(b) shows the results of polarized light microscopy observation of a sample of inorganic nanosheets without the introduction of a metal complex (inorganic nanosheets without a dye).

[0091] It has been reported that when conventional inorganic nanosheets are not laminated and are uniformly dispersed, the interference colors shown in Fig. 3(a) can be confirmed (N. Miyamoto and T. Nakato, Adv. Mater., 2002, 14, 1267). This is because when the interface with the sensitive color plate of the inorganic nanosheet is parallel, it shows blue, and when the interface with the sensitive color plate is perpendicular, it shows yellow. From this, it can be judged that there are parts where the titania nanosheets are arranged parallel to the interface of the sensitive color plate in a conventional monodisperse titania nanosheet colloidal solution.

[0092] Also, as shown in Fig. 3(b), when a sample without the introduction of the [Ru(bpy)3] 2+ complex ([TMA + is 2.2 M and the inorganic nanosheet concentration is 10 wt%) forms an elongated string-like structure (nanosheet laminated nanofiber), yellow was confirmed at the part where the interface with the sensitive color plate is parallel, and blue was confirmed at the part where the interface with the sensitive color plate is perpendicular. From this, it can be judged that when an elongated structure is formed without introducing the [Ru(bpy)3] 2+ complex, there are parts where the inorganic nanosheets are oriented perpendicular to the interface.

[0093] Figure 4 shows the results of polarized light microscopic observations of the samples according to Experimental Examples 1 to 14. The numerical values described in the parentheses after the text of the experimental examples in each figure indicate the value of [[Ru(bpy)3]] 2+ / CEC (equivalent ratio).

[0094] Then, as can be seen by referring to Figure 4, in the observation by a polarized light microscope (POM), nothing was observed up to the sample of Experimental Example 7 (equivalent ratio: 0.80 times equivalent), and in the samples of Experimental Examples 8 (equivalent ratio: 0.90 times equivalent) to Experimental Example 13 (equivalent ratio: 2.0 times equivalent), interference colors (orange and black) were confirmed at the interface of each sample with the spacer. This is considered that by introducing the [[Ru(bpy)3]] 2+ complex, yellow changed to orange and blue changed to black. From this, it was shown that when the [[Ru(bpy)3]] 2+ complex is introduced, if the interface with the sensitive color plate is parallel, orange is observed, and if it is perpendicular, black is observed. Therefore, it was confirmed that the elongated structure was maintained even after the introduction of the [[Ru(bpy)3]] 2+ complex.

[0095] (Results of UV-Vis measurement) Figure 5 shows the UV-vis measurement and calibration curve of the titania nanosheet, Figure 6 shows the UV-vis measurement and calibration curve of the ruthenium complex aqueous solution, and Figure 7 shows the UV-vis measurement results of the ruthenium titania nanosheet composite ([Ru(bpy)3]] 2+ -mNS).

[0096] For each sample of the titania nanosheet (mNS) aqueous solution (see Figure 5, Table 2), the ruthenium complex aqueous solution (aqueous solution of [[Ru(bpy)3]] 2+ in Experimental Examples 1 to 13) (see Figure 6, Table 3)), and the composite sample of [[Ru(bpy)3]] 2+ and titania nanosheet (mNS) in Experimental Examples 1 to 13 (see Table 4, Figure 7), the absorption spectrum was measured by UV-Vis measurement. The concentration of the mNS aqueous solution was 2.20×10 -4 wt% to 3.67×10 -4The range was set to wt%. The ruthenium complex aqueous solution ([Ru(bpy)3] 2+ aqueous solution) was in the range of 1.0×10 -5 M to 3.0×10 -5 M. The composite samples of titania nanosheets (mNS) (Experimental Examples 1 to 13) were diluted 800-fold and used for measurement. In the titania nanosheet (mNS) aqueous solution, as the nanosheet concentration increased in the ultraviolet region, the absorbance (band gap absorption) with a peak at 242 nm increased (Figure 5). In the aqueous solution of [Ru(bpy)3] 2+ , with the increase in the concentration of [Ru(bpy)3] 2+ , 242 nm (π-π * transition) and 452 nm (MLCT absorption) increased (Figure 6). Here, the increase in these concentrations followed the following Lambert-Beer equation.

[0097] A (λ) =ε (λ) Cl

[0098] Here, at a certain light wavelength λ, A (λ) is the absorbance, ε (λ) is the extinction coefficient (「L mol -1 cm -1 」 or [wt% -1 cm -1 , C ([mol / L] or [wt%]) is the concentration of the absorbing substance, and l (cm) is the optical path length of the cell container. In this experiment, the optical path length was 1 cm. In the mNS aqueous solution, from the calibration curve shown in the inset of Figure 5, ε (242nm) =774.54 [wt% -1 cm -1 , and also ε (452nm) =0 [wt% -1 cm -1 . In the aqueous solution of [Ru(bpy)3] 2+ , from the calibration curve shown in the inset of Figure 6, ε (242nm) =26746 [L mol -1 cm -1 , ε (452nm) =14432 [L mol -1 cm -1 . On the other hand, in the aqueous solution of [Ru(bpy)3] 2+In the composite sample with titania nanosheet (mNS), the spectrum obtained by adding the absorption of titania nanosheet (mNS) and [Ru(bpy)3] 2+ was obtained (Figure 7). From this, it was shown that the concentrations of mNS, Ru, and [Ru(bpy)3] 2+ in this composite system can be easily determined by UV-Vis measurement.

[0099]

Table 2

[0100]

Table 3

[0101]

Table 4

[0102] (Results of FL measurement) For each of the samples of Experimental Examples 1 to 13 and the aqueous solution of only the ruthenium complex ([Ru(bpy)3] 2+ aqueous solution, 2.5×10 -6 M to 5×10 -5 M), the fluorescence spectrum and fluorescence excitation spectrum of [Ru(bpy)3] 2+ were measured. In the FL measurement, the sample was irradiated with an excitation wavelength of 452 nm, and fluorescence peaks were observed at wavelengths from about 612 nm to 590 nm. In each sample in which titania nanosheet and [Ru(bpy)3] 2+ were complexed, as the ruthenium concentration increased, the peak shifted to the short wavelength side and the fluorescence intensity increased. In the aqueous solution of the ruthenium complex, a fluorescence peak was observed at a wavelength of about 589 nm.

[0103] Also, in the fluorescence excitation spectrum, fluorescence excitation intensity of peaks derived from the MLCT absorption band was observed at around 451 nm to 455 nm. A tendency for the fluorescence intensity to increase as the ruthenium concentration increased was confirmed.

[0104] From the above results, like the samples from Experimental Example 1 (equivalent ratio: 0.10 times equivalent) to Experimental Example 4 (equivalent ratio 0.50 times equivalent), [[Ru(bpy)3]] 2+ when the introduction amount is low, [[Ru(bpy)3]] 2+ is adsorbed on the nanosheet, and it is presumed that [[Ru(bpy)3]] 2+ the energy level of the electron orbit changes and the fluorescence wavelength shifts to a longer wavelength. [[Ru(bpy)3]] 2+ When the introduction amount is high (i.e., 1.0 times equivalent) in an aqueous solution, an excessive amount of [[Ru(bpy)3]] 2+ exists in the solution. Therefore, as a result of the increase in the concentration of [[Ru(bpy)3]] that is not complexed with mNS, 2+ the fluorescence wavelength is considered to approach that of an aqueous solution of [[Ru(bpy)3]] alone. 2+

[0105] (Results of FM observation) Figure 8 shows the results of FM observation. Specifically, Figures 8(a) and (b) show the results of FM observation of the mNS ethanol-water mixed solution, and Figures 8(c) and (d) show the results of FM observation of the sample according to Experimental Example 8.

[0106] In the FM observation, the sample according to Experimental Example 8 was compared with an mNS ethanol-water mixed solution prepared using a titania nanosheet (mNS) concentration of 0.50 wt%, a TMA + concentration of 0.080 mol / L, 70 wt% ethanol, and 30 wt% water. As a result, although a large number of elongated structures were observed with white light in the mNS ethanol-water mixed solution (see Figure 8(a)), nothing was observed in the fluorescence image (see Figure 8(b)). On the other hand, in the sample according to Experimental Example 8, an orange elongated structure was observed with white light (see Figure 8(c)), and an orange emitter was observed in the fluorescence image (see Figure 8(d)). Thus, in Experimental Example 8, it was confirmed that mNS and [[Ru(bpy)3]] 2+ were complexed to form a nanosheet stacked nanofiber.

[0107] (Results of confocal laser microscopy observation) Figure 9 shows the results of confocal laser microscopy observation of the samples according to Experimental Example 1, Experimental Example 6, Experimental Example 7, Experimental Example 8, Experimental Example 9, Experimental Example 10, Experimental Example 13, and Experimental Example 14.

[0108] As can be seen with reference to Figure 9, in the confocal laser microscope (CLSM) observation, nothing was observed up to the sample of Experimental Example 6 (equivalent ratio: 0.70 times equivalent), nano-sheet laminated nano-fibers were observed from Experimental Example 7 (equivalent ratio: 0.80 times equivalent), elongated string-like nano-sheet laminated nano-fibers and their aggregates were observed in the sample of Experimental Example 8 (equivalent ratio: 0.90 times equivalent), and aggregates of string-like nano-sheet laminated nano-fibers were observed in the sample of Experimental Example 13 (equivalent ratio: 2.0 times equivalent) and later, starting from Experimental Example 9 (equivalent ratio: 1.0 times equivalent). Therefore, it was confirmed that in the CLSM observation, elongated string-like nano-sheet laminated nano-fibers of a size not observable in the POM observation began to form from the sample of Experimental Example 7 (equivalent ratio: 0.80 times equivalent). That is, it was shown that nano-sheet laminated nano-fibers as an inorganic nano-sheet complex (a complex of titania nano-sheets and ruthenium complexes) were formed by controlling the equivalent ratio to at least 0.80 times equivalent or more, and aggregates of nano-sheet laminated nano-fibers were formed by setting the equivalent ratio to 1.0 times equivalent or more.

[0109] (Results of small angle / wide angle X-ray scattering measurement) Figure 10 shows the results of small angle / wide angle X-ray scattering measurement of the samples according to Experimental Example 1 to Experimental Example 14. Also, Figure 11 shows a conceptual diagram of ruthenium titania nano-sheet complex ([Ru(bpy)3] 2+ -mNS). The numerical values described in the parentheses after the text of each experimental example in Figure 10 indicate the value of ([Ru(bpy)3] 2+ / CEC (equivalent ratio).

[0110] For the samples according to Experimental Examples 1 to 14, small-angle / wide-angle X-ray scattering was used to measure the nanosheet laminated nanofibers of each sample. As can be seen by referring to FIG. 10, in the samples of Experimental Example 14 (equivalent ratio: 0-fold equivalent) and Experimental Example 1 (equivalent ratio: 0.10-fold equivalent), the graph of the scattering intensity I with respect to the scattering vector q shows that I~q in the region where q>0.4 nm -2 and on the small-angle side where q<0.4 nm, I became a constant value. The shape of this graph is similar to the shape factor function of a thin disk shape. Here, when fitting with the shape factor function of a thin disk shape, it was confirmed that the measurement results of the samples of Experimental Example 14 and Experimental Example 1 indicate the existence of an isotropic phase in which titania nanosheets with a side length of about 13 nm are dispersed.

[0111] Also, from the sample of Experimental Example 2 (equivalent ratio: 0.20-fold equivalent) to the sample of Experimental Example 8 (equivalent ratio: 0.90-fold equivalent), the graph of the scattering intensity I with respect to the scattering vector q shows a region with a slope of q -1 indicating the presence of a rod-like structure on the small-angle side, and multiple peaks were observed on the wide-angle side. As shown in FIG. 11, these multiple peaks are considered to be peaks derived from 1 / 2, 1 / 3, and 1 / 4 of the interlayer distance d (spacing between planes) of 2.6 nm when [Ru(bpy)3] 2+ is combined with the titania nanosheet. Note that FIG. 11 shows a conceptual diagram of a state in which the ruthenium complex 20 is located together with the hydration water 30 between the layers of the titania nanosheet 10. The thickness of the titania nanosheet 10 shown in FIG. 11 is 0.65 nm. Also, the particle size r of the ruthenium complex 20 in the state without the hydration water 30 is 1.01 nm, and the thickness t of the hydration water 30 is 0.47 nm. Therefore, from the sample of Experimental Example 2 (equivalent ratio: 0.20-fold equivalent) to the sample of Experimental Example 8 (equivalent ratio: 0.90-fold equivalent), nanosheet laminated nanofibers in which [Ru(bpy)3] 2+ is combined with the titania nanosheet are formed, and from Experimental Example 9 (equivalent ratio: 1.0-fold equivalent) to at least Experimental Example 12 (equivalent ratio: 1.6-fold equivalent), it is considered that aggregates of nanosheet laminated nanofibers in which [Ru(bpy)3] 2+ is combined with the titania nanosheet are formed.

[0112] Furthermore, in the graph of the scattering intensity I with respect to the scattering vector q on the small-angle side of the sample of Experimental Example 9 (equivalent ratio: 1.0-fold equivalent) to the sample of Experimental Example 13 (equivalent ratio: 2.0-fold equivalent), a region of the slope of q indicating the presence of larger objects that are not rod-shaped or nanosheet-shaped was observed. -3 Therefore, it is considered that an aggregate of nanosheet-laminated nanofibers was formed in the samples from Experimental Example 9 (equivalent ratio: 1.0-fold equivalent) to Experimental Example 13 (equivalent ratio: 2.0-fold equivalent), that is, in samples with an equivalent ratio of 1.0-fold equivalent or more.

[0113] That is, in small-angle / wide-angle X-ray scattering measurements, although not confirmed in POM measurements and CLSM measurements, by controlling the equivalent ratio to 0.20-fold equivalent or more, nanosheet-laminated nanofibers as an inorganic nanosheet complex (a complex of titania nanosheets and ruthenium complexes) began to form, and it was shown that an aggregate of nanosheet-laminated nanofibers was formed by setting the equivalent ratio to 1.0-fold equivalent or more.

[0114] (Result of TEM observation) Figure 12 shows the results of TEM observation of the samples according to Experimental Example 4, Experimental Example 7, and Experimental Example 13. The numerical values described in parentheses after the text of each experimental example in Figure 12 indicate the value of 2+ [Ru(bpy)3] / CEC (equivalent ratio).

[0115] Diluted samples were prepared by diluting the samples of Experimental Example 4 (equivalent ratio: 0.50 times equivalent), Experimental Example 7 (equivalent ratio: 0.80 times equivalent), and Experimental Example 13 (equivalent ratio: 2.0 times equivalent) 50-fold each. Then, each of the prepared diluted samples was observed using TEM. As a result, in the sample of Experimental Example 4, nanosheet laminated nanofibers with an interlayer distance of 1.6 nm to 1.7 nm were observed. As is clear from referring to the TEM image of Experimental Example 4 in Fig. 12, the width of the short axis of the string-like structure was almost uniform, and shading was observed at regular intervals in the direction parallel to the short axis. From this, it was confirmed that the monodisperse inorganic nanosheets were in a string-like structure laminated parallel to the short axis. In addition, as a result of small angle / wide angle X-ray scattering measurement, a peak indicating an interlayer distance of 2.6 nm was observed, which is different from the interlayer distance observed by TEM. This is presumably because in the small angle / wide angle X-ray scattering measurement, [Ru(bpy)3] between the layers 2+ is hydrated, but in the TEM observation, it is observed in a vacuum and is dehydrated. Also, in the sample of Experimental Example 7, string-like structures with a diameter of 20 nm and a length of about several hundred nm to several μm (typically about 100 nm) were observed on the grid. It was observed that the length of the structure in the sample of Experimental Example 7 was longer than that of the structure in the sample of Experimental Example 4, and the string-like structures were observed to be in contact with each other at multiple locations. Furthermore, in the sample of Experimental Example 13, rod-shaped giant particles (aggregates of nanosheet laminated nanofibers) were observed on the grid, and it was confirmed that the observed particles had a particle size similar to that of the particles observed by confocal laser microscopy. In the TEM image of the sample of Experimental Example 13, when the tip portion of the particle was magnified and observed, it was confirmed that the titania nanosheets were laminated along the long axis direction of the rod-shaped particle. As estimated from the results of small angle / wide angle X-ray scattering measurement, it is presumed that the titania nanosheets form nanosheet laminated nanofibers, and an aggregate structure is formed in which the formed nanosheet laminated nanofibers are further aggregated.

[0116] (Result of AFM observation) Fig. 13 shows the result of AFM observation of the sample according to Experimental Example 2. Fig. 14 shows an overview of the presumed nanosheet laminated nanofibers.

[0117] The sample obtained by diluting the sample of Experimental Example 2 (equivalence ratio: 0.20 times equivalent) 50-fold was observed. For this sample, the concentration of [Ru(bpy)3] 2+ was 0.000078 M, the concentration of TMA + was 0.00137 M, and the concentration of the titania nanosheet was 0.00110 wt%. In the AFM observation, the diluted sample was cast on a mica plate, and the sample dried for 1 day was observed. As a result, as shown in Fig. 13, an elongated structure with a thickness t3 of about 12 to 13 nm, a width w of about 18 nm, and a length l of 650 nm was observed. Since the particle size of the titania nanosheet obtained by preparation is about 12 nm, it is considered that a laminated column formed from the titania nanosheet and the ruthenium complex is formed. Specifically, it is considered that a nanosheet laminated nanofiber is formed by the ruthenium complex ([Ru(bpy)3] 2+ ) 20 being located and laminated between the titania nanosheets 10 on the mica plate 40 as shown in Fig. 14.

[0118] [Examination of sample washing] From the observation results of the sample according to Experimental Example 9 (equivalence ratio: 1.0 times equivalent) to the sample according to Experimental Example 11 (equivalence ratio: 2.0 times equivalent) in the visual observation, the tendency to separate into supernatant and precipitate is [Ru(bpy)3] 2+ is considered to be stronger as the concentration is higher. This is presumably because the nanosheet laminated nanofibers aggregated and precipitated, and the supernatant contained salts and the like that did not form nanosheet laminated nanofibers. Therefore, for the sample according to Experimental Example 9, an attempt was made to wash the sample using separation.

[0119] In addition, the concentrations of [Ru(bpy)3] 2+ contained in the sample according to Experimental Example 9 after two washings (hereinafter referred to as "washed sample"), the concentration of mNS, and the concentration of TMA + were calculated as follows. First, the washed sample was diluted 7,000-fold and adjusted to 50 mL, and the absorbance was measured using UV-vis. As a result, [Ru(bpy)3] in the prepared washed sample2+ The concentration of -2 is 1.1×10 2+ (mol / L), the mNS concentration is 0.16 (wt%), and compared with immediately after the preparation of [Ru(bpy)3] 2+ -mNS (the first sample), the concentration of [Ru(bpy)3] -3 was shown to have decreased only by 8×10 + (mol / L) and the mNS concentration by 0.94 (wt%). Since the absorption spectrum of TMA + was not confirmed, the concentration of TMA was calculated from the mass of the sample after washing. The TMA + concentration was calculated to be 0.0409 (mol / L) and was estimated to have decreased by 0.10 (mol / L).

[0120] Figure 15 shows the results of observing the sample after washing. Specifically, Figures 15(a) and 15(b) show CLSM images that differ only in magnification, and Figure 15(c) shows the results of visually observing the sample in the vial using crossed Nicols. Also, Figure 16 shows the results of small-angle / wide-angle X-ray scattering measurements of the sample of Experimental Example 9 (the upper is the sample after washing and the lower is the sample before washing).

[0121] When the sample after washing was observed using crossed Nicols, birefringence was observed (Figure 15(c)). Also, in the CLSM observation, an aggregate of elongated nanosheet-layered nanofibers was observed (Figure 15(b)).

[0122] Also, WAXS measurements were performed on each of the sample according to Experimental Example 9 (the sample before washing) and the sample after washing the sample according to Experimental Example 9 twice (Figure 16). As a result, peaks corresponding to interlayer distances of 2.6 nm, 1.3 nm, 0.85 nm, and 0.65 nm were observed in the sample after washing. Also, on the small-angle side, the slope of q -4 showing a spherical structure was confirmed. From these results, it was confirmed that the same layered structure as that of the sample before washing was maintained even after washing.

[0123] As described above, by controlling the equivalent ratio of the ruthenium complex to the ion exchange capacity of the titania nanosheet, an inorganic nanosheet complex ([Ru(bpy)3] 2+ -mNS) in which the ruthenium complex is located between each titania nanosheet in a nanosheet stacked nanofiber formed by stacking a plurality of titania nanosheets can be prepared. It was shown that the structure of the complex changes from a nanosheet stacked nanofiber to an aggregate of nanosheet stacked nanofibers as the equivalent ratio increases. Specifically, in the experimental example, when [Ru(bpy)3] 2+ / CEC (equivalent ratio) is 0.20 times equivalent or more, nanosheet stacked nanofibers begin to form, and when the equivalent ratio is controlled to 0.80 times equivalent or more, nanosheet stacked nanofibers are surely formed. When the equivalent ratio is 1.0 times equivalent or more, it was shown that an aggregate of nanosheet stacked nanofibers is formed.

[0124] That is, when [Ru(bpy)3] 2+ / CEC (equivalent ratio) is from 0.0 times equivalent to 0.10 times equivalent, an isotropic phase of a solution of titania nanosheets or a mixed solution of titania nanosheets and ruthenium complex is formed. When the equivalent ratio is from 0.20 times equivalent to 0.60 times equivalent, nanosheet stacked nanofibers are formed. When the equivalent ratio is from 0.70 times equivalent to 0.90 times equivalent, birefringence is observed as the nanosheet stacked nanofibers increase. When the equivalent ratio is 1.0 times equivalent or more, a stack of stacked columns and an aggregate of the stack of stacked columns are formed. When the equivalent ratio is 2.0 times equivalent, an aggregate of stacked columns is predominantly formed. Therefore, it was shown that the structure of the inorganic nanosheet complex can be controlled by controlling the equivalent ratio.

[0125] Note that when no cation species is added to the colloidal solution of the monodisperse inorganic nanosheets used in the experimental example (when only TMA is used), if the concentration of TMA + in the colloidal solution is about 1.5 M to 2.0 M, a string-like structure of the monodisperse inorganic nanosheets can be formed, but when the concentration is less than 1.5 M, the structure collapses (dissolves and the structure disappears). On the other hand, as shown in the experimental example, when a predetermined cation species is used, TMA+ even when the concentration is ~10 -2 M, the lamination peak of the inorganic nanosheet etc. was observed, and it was confirmed that it exists as a nanosheet laminated nanofiber. Further, since TMA is a strong alkali, it is preferable to perform desalting treatment in the application of the various materials of the inorganic nanosheet composite obtained in the experimental example.

[0126] Figure 17 shows the results of visual observation and cross-Nicol observation of an inorganic nanosheet composite in which each of an iron trisbipyridine complex (Fe(bpy)3 2+ ), a ruthenium tris(phenanthroline) complex (Ru(phen)3 2+ ), a potassium porphyrin (K(Por)), a potassium-incorporated crown ether (K(18C6)), and a cobaltocene (Co-Cp2) is combined with a titania nanosheet (mNS). Further, Figure 18 shows the results of SAXS / WAXS measurement of the laminated nanofibers by the inorganic nanosheet composite in which various metal complexes are combined with the titania nanosheet (mNS), compared with the results of Experimental Example 9.

[0127] Specifically, Figure 17(a) shows the observation results of an inorganic nanosheet composite prepared in the same manner as in Experimental Example 8 using Fe(bpy)3 2+ . The left side of Figure 17(a) is the result of visual observation, and the right side is the result of cross-Nicol observation. Figure 17(b) shows Ru(phen)3 2+The observation results of the inorganic nanosheet composites prepared in the same manner as in Experimental Example 8 using [the relevant substances] are shown. The left side of Fig. 17(b) is the result of visual observation, and the right side is the result of cross-polarized light observation. Also, Fig. 17(c) shows the observation results of the inorganic nanosheet composites prepared in the same manner as in Experimental Example 8 using K(Por). The left side of Fig. 17(c) is the result of visual observation, and the right side is the result of cross-polarized light observation. Furthermore, Fig. 17(d) shows the observation results of the inorganic nanosheet composites prepared in the same manner as in Experimental Example 8 using K(18C6). The left side of Fig. 17(d) is the result of visual observation, and the right side is the result of cross-polarized light observation. Also, Fig. 17(e) shows the observation results of the inorganic nanosheet composites prepared in the same manner as in Experimental Example 8 using Co-Cp2. The left side of Fig. 17(e) is the result of visual observation, and the right side is the result of cross-polarized light observation.

[0128] In any of the samples, as in Experimental Example 8 etc., since no visually observable particles were observed, it was shown that the inorganic nanosheets were not randomly aggregated. Furthermore, as in Experimental Example 8 etc., since flow birefringence was observed as a result of cross-polarized light observation, it was inferred that nanofibers or nanofiber bundles were formed. Also, as a result of SAXS measurement (Fig. 18), in the sample prepared using [Fe(bpy)3] 2+ peaks almost the same as those in the case of [Ru(bpy)3] 2+ were observed, and it was confirmed that a stacked structure of nanosheets with [Fe(bpy)3] 2+ inserted between the layers was formed. In the sample prepared using Ru(phen)3 2+ , peaks with d values of 2.84 nm and 1.42 nm appeared, and it was identified as a structure in which hydrated Ru(phen)3 2+ and mNS were alternately stacked. Compared with the system of [Ru(bpy)3] 2+ , the fact that the stacking interval is slightly larger means that the molecular size of Ru(phen)3 2+ is larger than that of [Ru(bpy)3] 2+It is reasonable considering it is larger. For K(Por) and K(18C6), a peak with a d value of 1.2 nm was observed. K(Por) and K(18C6) have a planar molecular structure, and the thickness of the molecule can be considered equivalent to about 0.3 nm, which is the ionic diameter of K ions, or about 0.5 nm, which is its hydrated ionic diameter, without any problem. Therefore, considering the thickness of the nanosheet of 0.65 nm, this interlayer distance of 1.2 nm is considered to indicate that a stacked structure was formed in which K(Por) or K(18C6) was inserted between the layers of mNS with the molecular plane parallel to the nanosheet. Note that for the nanofibers inserted with tetramethylammonium before introducing these substances, the d value was 1.7 nm. In any system, the d value has changed significantly, which also indicates that these molecules replaced tetramethylammonium and were incorporated into the stacked structure in the nanofibers. For Co-Cp2, a peak with a d value of 1.7 nm was observed. It is a reasonable value considering the molecular size of Co-Cp2, which is the same as the d value of the nanofibers inserted with tetramethylammonium.

[0129] Note that each cation species was prepared as follows.

[0130] (Preparation of aqueous solution of iron trisbipyridine complex) 0.117 g of iron(II) chloride tetrahydrate, 0.275 g of 2,2‘-bipyridyl, and 49.7 g of water were mixed and refluxed at 80 °C under an air atmosphere for 24 hours. In this way, an aqueous solution of [Fe(bpy)3] complex with 0.0117 mol / L of iron(II) chloride tetrahydrate and 0.0350 mol / L of 2,2’-bipyridyl 2+ ) was prepared.

[0131] (Aqueous solution of ruthenium dichlorotrisphenyl complex) 0.574 g of dichlorotris(1,10-phenanthroline)ruthenium(II) hydrate and 19.4 g of water were mixed and stirred at 500 rpm for 60 minutes, and 20.0 mL of an aqueous solution of [Ru(phen)3] with 0.03914 mol / L 2+ was prepared.

[0132] (Preparation of Aqueous Solution of Potassium Porphyrin Complex) 9.48 g of 0.273 M aqueous TMAOH solution and 0.0200 g of 5,10,15,20 - tetrakis(4 - hydroxyphenyl)porphyrin were mixed and stirred until dissolved to prepare 10 mL of an aqueous solution of potassium porphyrin complex (0.671 mol / L potassium chloride, 0.00295 mol / L crown ether).

[0133] (Preparation of Aqueous Solution of Potassium Crown Ether Complex) 1.50 g of crown ether, 1.50 g of KCl and 8.50 g of water were mixed and stirred until dissolved to prepare 10 mL of an aqueous solution of potassium crown ether complex (1.75 mol / L potassium chloride, 0.493 mol / L crown ether).

[0134] (Preparation of Aqueous Solution of Cobaltocene Complex) 0.0858 g of bis(cyclopentadienyl)cobalt(III) hexafluorophosphate cobaltocene hexafluorophosphate and 9.91 g of N,N - dimethylformamide (DMF) were mixed and stirred for 10 minutes to prepare 10 mL of an aqueous solution of cobaltocene DMF.

[0135] The reagents (metal complexes) used are as follows. · [Ru(phen)3] 2+ : Dichlorotris(1,10 - phenanthroline)ruthenium(II) Monohydrate (manufactured by Tokyo Chemical Industry Co., Ltd.) · Iron complex: Iron(II) chloride tetrahydrate (FeCl2 4H2O) (manufactured by Fujifilm Wako Pure Chemical Corporation), 2,2‘ - Bipyridyl (manufactured by Tokyo Chemical Industry Co., Ltd.) · Potassium polyphenylene complex: Potassium chloride (KCl) (FUJIFILM Wako Pure Chemical Corporation), 5,10,15,20-Tetrakis(4-hydroxyphenyl)porphyrin (Tokyo Chemical Industry Co., Ltd.) · Potassium crown ether system: Potassium chloride (KCl) (FUJIFILM Wako Pure Chemical Corporation), 18-Crown6-Ether (Tokyo Chemical Industry Co., Ltd.) · Cobaltocene complex: Bis(cyclopentadienyl)cobalt(III) Hexafluorophosphate (Tokyo Chemical Industry Co., Ltd.), N,N-Dimethylformamide (FUJIFILM Wako Pure Chemical Corporation)

[0136] The characteristics of these samples include that the inorganic nanosheets are not aggregated (not randomly aggregated), and flow birefringence or stationary birefringence is observed. Note that the observation of flow birefringence or stationary birefringence is a characteristic of the formation of nanofibers.

[0137] As described above, the embodiments and experimental examples of the present invention have been explained. However, the embodiments and experimental examples described above do not limit the invention according to the claims. Also, it should be noted that not all combinations of the features described in the embodiments and experimental examples are essential means for solving the problems of the invention.

[0138] Note that the inorganic nanosheet composite according to this embodiment and the method for manufacturing the inorganic nanosheet composite can also be mentioned in the following supplementary claims that should not be confused with the claims. (Supplementary Claim 1) A plurality of monodisperse inorganic nanosheets, Cation species (e.g., metal complexes, metal cluster ions, molecular ions, or polyelectrolytes) located between the plurality of monodisperse inorganic nanosheets and comprising an inorganic nanosheet complex in which the equivalent ratio of the cation species to the ion exchange capacity of the monodisperse inorganic nanosheet is within the range in which a nanosheet laminated nanofiber formed by laminating the plurality of monodisperse inorganic nanosheets is formed.

Explanation of Symbols

[0139] 10 Titania nanosheet 20 Ruthenium complex 30 Water of hydration 40 Mica plate

Claims

1. A plurality of monodisperse inorganic nanosheets, Cation species excluding simple metal ions and ammonium cations, and are included, wherein the cation species are located between the monodisperse inorganic nanosheets in the nanosheet laminated nanofibers in which the plurality of monodisperse inorganic nanosheets are laminated, An inorganic nanosheet composite in which the equivalent ratio of the cation species to the ion exchange capacity of the monodisperse inorganic nanosheet is the equivalent ratio in the range in which the nanosheet laminated nanofiber is formed.

2. The inorganic nanosheet composite according to claim 1, wherein when the equivalent ratio is equal to or more than a predetermined equivalent ratio, an aggregate of the nanosheet laminated nanofibers is included.

3. The monodisperse inorganic nanosheet is selected from the group consisting of layered metal chalcogenides, layered metal oxides, layered metal oxyhalides, layered metal phosphates, clay minerals or layered silicates, and layered double hydroxides, The inorganic nanosheet composite according to claim 1, wherein the cation species are selected from the group consisting of metal complexes, metal cluster ions, molecular ions, and polyelectrolytes.

4. The inorganic nanosheet composite according to claim 1, wherein the inorganic nanosheet composite is an inorganic nanosheet composite for a visible light-responsive photocatalyst.

5. A step of preparing a mixed solution by mixing an ammonium salt, a metal alkoxide, and a solvent, A step of preparing a colloidal solution of monodisperse inorganic nanosheets synthesized by refluxing the mixed solution, A step of forming an inorganic nanosheet composite by mixing an aqueous solution containing cation species excluding simple metal ions and ammonium cations and the colloidal solution, and wherein the cation species are located between the respective monodisperse inorganic nanosheets in the nanosheet laminated nanofibers in which the plurality of monodisperse inorganic nanosheets are laminated, A method for producing an inorganic nanosheet composite in which the equivalent ratio of the cation species to the ion exchange capacity of the monodisperse inorganic nanosheet is the equivalent ratio in the range in which the nanosheet laminated nanofiber is formed.

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