JP2009184869A - Method for producing layered rare earth hydroxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a layered rare earth hydroxide simply and inexpensively. <P>SOLUTION: The method for producing the layered rare earth hydroxide is characterized by comprising a step to hydrolyze the salt of a rare earth element by decomposing hexamethylenetetramine (HMT) or urea in a mixed aqueous solution consisting of the salt of the rare earth element, hexamethylenetetramine (HMT) or urea and a solvent containing water. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a layered rare earth hydroxide.

  The layered material has a structure in which host layers spread in a two-dimensional direction through strong chemical bonds are stacked, and there are a wide variety of compounds. Further, it is known that the layered material exhibits reactivity (intercalation) for incorporating a different material (guest) between the layers.

  As such a layered substance, many natural and synthetic layered compounds having a cation exchange ability represented by clay mineral (smectite) and the like are known. On the other hand, layered substances having anion exchange ability are rare, and as a typical compound, layered double hydroxide (referred to as LDH) and a small number of basic salts are known ( For example, see Patent Document 1).

According to Patent Document 1, a layered double hydroxide not containing carbonate ions is obtained by a uniform precipitation method in which a mixed aqueous solution obtained by adding hexamethylenetetramine (C ₆ H ₁₂ N ₄ ) to an aqueous solution of a metal salt as a starting material is heated. Things are synthesized without using hydrothermal methods that require special high pressure equipment. The layered double hydroxide thus obtained is characterized by high crystallinity and large particle size.

Recently, a layered rare earth hydroxide has been reported as a layered material having an anion exchange ability different from that of LDH (see, for example, Non-Patent Document 1). According to Non-Patent Document 1, a layered rare earth hydroxide represented by a composition formula Ln ₂ (OH) ₅ NO ₃ .xH ₂ O (Ln = Y, Gd to Lu, x≈1.5) is a hydrothermal method. Is synthesized. Further, according to Non-Patent Document 1, nitrate ions in layered rare earth hydroxides undergo anion exchange with organic carboxylate and sulfonate ions, and Ln is weak in Tb and Dy but exhibits fluorescence. Is disclosed.

  However, the technique described in Patent Document 1 is specialized in the synthesis of LDH, and further application of the technique described in Patent Document 1 is expected. Further, the layered rare earth hydroxide described in Non-Patent Document 1 is limited to rare earth elements Ln, and it is desirable if a method for obtaining a layered rare earth hydroxide containing rare earth elements other than Y and Gd to Lu is developed. . In addition, the production of the layered rare earth hydroxide described in Non-Patent Document 1 requires a dedicated high-pressure device such as an autoclave, and the amount that can be produced at a time is limited. Not desirable for production. It would be advantageous if a layered rare earth hydroxide could be provided simply and at low cost.

JP 2005-335965 A McIntyre et al., Chem. Mater. , 20, 335-340 (2008)

  Accordingly, an object of the present invention is to provide a method for producing a layered rare earth hydroxide simply and inexpensively.

The method for producing the layered rare earth hydroxide according to the first aspect of the present invention includes the hexamethylenetetramine (HMT) in a mixed aqueous solution comprising a salt of a rare earth element, hexamethylenetetramine (HMT) or urea, and a solvent containing water. The method comprises the step of decomposing urea to hydrolyze the rare earth element salt.
Invention 2 is characterized in that, in Invention 1, the rare earth element salt is a nitrate of the rare earth element or a chloride of the rare earth element.
Invention 3 is characterized in that, in Invention 1, an alkali metal salt is further mixed in the mixed aqueous solution.
Invention 4 is characterized in that, in Invention 1, the mixed aqueous solution is prepared so that a molar ratio of the rare earth element salt to the hexamethylenetetramine (HMT) or urea is 0.75.
The invention 5 is characterized in that, in the invention 1, in the hydrolyzing step, the mixed aqueous solution is heated while stirring at a temperature of 70 ° C. or higher.
Invention 6 is the invention 1, wherein the layered rare earth hydroxide has a composition formula RE (OH) _2.5 Z _{(1/2 m)} · 0.125XH ₂ O (where RE is a rare earth element, and Z is the rare earth element). The anion generated from the salt of the element, m is represented by the valence of the anion, 6 <X <8).
Invention 7 is the invention 6, wherein the layered rare earth hydroxide is negatively charged with a positively charged [RE ₈ (OH) ₂₀ (H ₂ O) _x ] ⁴⁺ (RE is a rare earth element, 6 <X <8) layer. It has a laminated structure with an intermediate layer Z ^m− charged in a ^positive direction.

  The method for producing a layered rare earth hydroxide according to the present invention comprises the steps of preparing a mixed aqueous solution comprising a rare earth element salt, hexamethylenetetramine (HMT) or urea, and a water-containing solvent; Decomposing hexamethylenetetramine (HMT) or urea and hydrolyzing a salt of a rare earth element. Since it is only necessary to decompose HMT or urea in the mixed aqueous solution, a high-pressure apparatus necessary for the conventional hydrothermal method is unnecessary. As a result, since an existing apparatus can be used, the layered rare earth hydroxide can be provided simply and inexpensively.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
A process for producing a layered rare earth hydroxide according to the present invention will be described. The layered rare earth hydroxide according to the present invention decomposes hexamethylenetetramine (HMT) or urea in a mixed aqueous solution comprising a rare earth element salt, hexamethylenetetramine (HMT) or urea, and a solvent containing water. It is obtained by hydrolyzing a salt of a rare earth element. For convenience, the preparation of the mixed aqueous solution and the hydrolysis of the salt of the rare earth element will be described separately. This will be described in detail with reference to the flowchart.

  FIG. 1 is a flowchart showing steps for producing a layered rare earth hydroxide according to the present invention.

  This will be described in detail for each step.

  Step S110: A mixed aqueous solution containing a salt of a rare earth element (hereinafter simply referred to as RE), hexamethylenetetramine (hereinafter simply referred to as HMT) or urea, and a solvent containing water is prepared.

  In the present invention, RE means a lanthanoid from lanthanum (La) having an atomic number of 57 to lutetium (Lu) having an atomic number of 71, scandium (Sc) having an atomic number of 21, and yttrium having an atomic number of 39 ( Y) is intended, but among these, from La to Ho with atomic number 67 and Y are preferred. With these REs, the layered rare earth hydroxide of the present invention can be obtained without any special modification of the synthesis conditions. As will be described with reference to Examples 1 to 20 described later, since the layered rare earth hydroxide of the present invention can be obtained with almost all rare earth elements exhibiting similar properties, Er, Tm, Yb and Lu However, there is a great possibility that the target layered rare earth hydroxide can be obtained by modifying the synthesis conditions based on the production method of the present invention.

  Examples of RE salts include nitrates, halides, perhalogenates, carbonates and sulfates of RE. Of these, RE nitrates and chlorides are preferred because of their ease of synthesis, availability, and handling. Further, since the negatively charged intermediate layer (220 in FIG. 2), which will be described later, is produced from the salt of RE, when obtaining a layered rare earth hydroxide having high crystallinity, the nitrate and chloride of RE, Those which are not bulky are preferred.

  The solvent containing water may be water (for example, ultrapure water) alone, or a nonaqueous solvent such as ethanol may be used in addition to water, but at least water is sufficient. This is because the reaction is promoted by hydration of rare earth ions with water. Since at least water is sufficient, a RE salt hydrate may be used together with a solvent containing water.

Both HMT and urea function to increase the pH of the mixed aqueous solution after decomposition. Preferably, the molar ratio of the salt of RE to HMT or urea is 0.75. If this ratio is not satisfied, impurities such as RE (OH) ₃ and RE (OH) ₂ Cl may be generated.

The pH of the mixed aqueous solution is, for example, in the range of 5.5 to 6.5 when RE is an element selected from the group consisting of Nd, Eu, Gd, Tb, Dy, Ho, and Y. If it is this range, since pH of mixed aqueous solution will raise to 8-10 by step S120 mentioned later, and hydrolysis of the salt of RE accelerates | stimulates, a layered rare earth hydroxide can be obtained reliably. On the other hand, when RE is La, the pH of the mixed aqueous solution is preferably set to be lower than the above range and in the range of 4.5 or more and less than 5.5. This is because in the rare earth series, the basicity increases as the size increases, that is, toward the La side, and RE (OH) ₃ tends to be generated. In order to suppress this, it is effective to generate a layered hydroxide to set the pH lower. Incidentally, the adjustment of such pH, e.g., HCl, may be added suitably an acid such as HNO _3. The pH of the mixed aqueous solution is appropriately adjusted according to the RE selected in this way.

In step S110, an alkali metal salt may be further mixed into the mixed aqueous solution. Examples of the alkali metal salt include NaCl, NaNO ₃ , and KCl, but are not limited thereto. This facilitates synthesis even under conditions where the concentration of the RE salt is low. As a result, the morphology or crystallinity of the obtained layered rare earth hydroxide can be improved.

  Step S120: HMT or urea in the mixed aqueous solution obtained in step S110 is decomposed to hydrolyze the salt of RE.

  HMT and urea are decomposed to produce ammonia. Thereby, pH of mixed aqueous solution rises and it becomes alkaline. As a result, the salt of RE is hydrolyzed and precipitation of layered rare earth hydroxide occurs. Both HMT and urea (preferably by heating) produce ammonia slowly at a controlled rate, so there is no bias in nucleation and crystallization, and high quality layered rare earth water with uniform grain size and high crystallinity. An oxide is obtained.

  The decomposition of HMT and urea is carried out, for example, by stirring the mixed aqueous solution obtained in step S110 at room temperature for a long time. From the viewpoint of efficiency, it is preferable to heat at a temperature of at least 70 ° C. with stirring. . Thereby, since decomposition | disassembly of HMT and urea is accelerated | stimulated, a synthesis | combination advances efficiently. Crystal formation can be visually confirmed by heating for 30 minutes to 1 hour, but typically heating is performed for 6 hours to 10 hours. In particular, heating for 8 hours or more is preferable because the crystallinity of the layered rare earth hydroxide is improved. Moreover, although the upper limit of heating temperature changes with solvents to be used, it is the temperature which does not exceed 100 degreeC.

  Subsequent to step S120, the obtained layered rare earth hydroxide may be washed and dried at room temperature. This makes it possible to obtain a powdery layered rare earth hydroxide that is easy to handle. Washing is repeated several times with water and ethanol.

  As described above, according to the method of the present invention, a mixed aqueous solution containing a rare earth element salt, HMT or urea, and at least water is prepared in step S110, and the mixed aqueous solution is stirred or heated and stirred in step S120. Since only the elemental salt needs to be hydrolyzed, a dedicated high-pressure apparatus such as an autoclave is not required. Therefore, since a glass container such as a flask can be used, the layered rare earth hydroxide can be provided simply and inexpensively. Furthermore, since an existing apparatus can be used, the capacity is not particularly limited, and the layered rare earth hydroxide of the present invention can be produced in large quantities.

(Embodiment 2)
The structure of the layered rare earth hydroxide obtained by the production method according to the present invention will be described.

  FIG. 2 is a schematic diagram (A) and a crystal structure (B) of the layered rare earth hydroxide according to the present invention.

The layered rare earth hydroxide 200 according to the present invention has a composition formula RE (OH) _2.5 Z _{(1/2 m)} · 0.125XH ₂ O (where X satisfies 6 <X <8, Z is It is an anion that forms an intermediate layer 220 described later and is generated by the salt of RE described in Embodiment 1, and m is the valence of the anion. More specifically, the layered rare earth hydroxide 200 includes a positively charged [RE ₈ (OH) ₂₀ (H ₂ O) _X ] ⁴⁺ layer (also referred to as a host layer) 210 and a negatively charged intermediate layer Z. ^It has a laminated structure with ^m- 220. For example, when RE is Eu, Z is NO ₃ ^— , and X is 7, Eu (OH) _2.5 (NO ₃ ) _0.5 · 0.9H ₂ O is obtained.

In the [RE ₈ (OH) ₂₀ (H ₂ O) _X ] ⁴⁺ layer 210, RE is the rare earth element described in Embodiment 1. In addition, in the [RE ₈ (OH) ₂₀ (H ₂ O) _X ] ⁴⁺ layer 210, the number of water molecules slightly changes depending on the humidity, so that X has a range of 6 to 8, but in the complete state X = 7.

The negatively charged intermediate layer Z ^m- 220 is generated by the salt of RE used in the first embodiment. For example, in the case of using a nitrate RE as a salt of RE, the intermediate layer 220, NO ₃ ^- becomes the layer, in the case of using a chloride of RE as salts of RE, the intermediate layer 220 is Cl ^- layer It becomes. However, in either case, some carbonate ions are actually taken in from the air.

As shown in FIG. 2B, since the negatively charged intermediate layer Z ^m- 220 is not directly coordinated to the RE, the intermediate layer Z ^m- 220 can be easily exchanged with a different anion ( That is, the layered rare earth hydroxide 200 has anion exchange ability). For example, when the RE is Eu in the [RE ₈ (OH) ₂₀ (H ₂ O) _X ] ⁴⁺ layer 210 of the layered rare earth hydroxide 200 and the intermediate layer Z ^m− 220 is NO ₃ ⁻ , sulfate ions ( The above-described anion exchange occurs while maintaining the laminated structure of the layered rare earth hydroxide 200 only by bringing the layered rare earth hydroxide 200 into contact with the layered rare earth hydroxide 200 at room temperature.

Further, the morphology of the layered rare earth hydroxide 200 according to the present invention is a plate shape (also referred to as a small plate) reflecting the layered structure described above. Specifically, it is known that the shape of the platelet changes depending on the type of the intermediate layer Z ^m- 220 (that is, depending on the type of salt of RE selected in step S110 in FIG. 1). . The morphology of the layered rare earth hydroxide 200 is, for example, a rectangular plate shape when the intermediate layer Z ^m- 220 is halogen (Cl ⁻ , Br ⁻ ), and the intermediate layer Z ^m- 220 is NO ₃ ^— . Has a long hexagonal plate shape. Further, such morphology depends on the degree of crystallinity. When the crystallinity is good, the edge becomes sharp, and when the crystallinity is low, the edge tends not to be sharp.

Furthermore, the crystal system of the layered rare earth hydroxide 200 according to the present invention belongs to an orthorhombic system when the intermediate layer Z ^m- 220 is a chlorine ion, more specifically to a simple orthorhombic lattice, and to a monoclinic crystal with a nitrate ion. It is known that it belongs to the system. From the above morphology and crystal structure, whether or not the obtained product is a layered rare earth hydroxide is simply determined whether or not the platelet is confirmed by surface observation with an electron microscope. This can be determined by indexing the X-ray diffraction pattern of the product.

  In addition, RE is known to exhibit luminescent properties, magnetic properties and high catalytic activity. Also in the layered rare earth hydroxide 200 of the present invention, in addition to the anion exchange ability, the light emission characteristics based on the contained RE, the expression of magnetism and catalytic activity, and applications utilizing the same are expected.

  Next, examples will be described, but it should be noted that the present invention is not limited to the examples.

And EuCl ₃ · _6H 2 O as RE salt (5 mM), and HMT (3.75 mM), and NaCl (65 mM) were dissolved in ultrapure water 1000 ml, the final concentration was prepared a mixed aqueous solution of 5.65mM (Step S110 in FIG. 1). Here, although the rare earth element salt has six water molecules, it is known that the rare earth element salt is hygroscopic and varies between 6 and 7 depending on the environment. The same applies to the following embodiments. The pH of the mixed aqueous solution thus obtained was about 6. Next, the mixed aqueous solution was stirred with a magnetic stirrer and heated at a reflux temperature (about 100 ° C.) in nitrogen gas. Thereby, HMT was decomposed | disassembled (step S120 of FIG. 1). At this time, the pH of the mixed aqueous solution rose to about 8. These operations were performed using a two-necked flask equipped with a reflux condenser under a nitrogen flow.

  After 1 hour, white streamlines were observed in the mixed solution. This suggests that an anisotropic shaped crystal was formed. The product was then filtered, washed several times with water and ethanol, and dried at room temperature.

  The morphology and structure of the product thus obtained were observed using a scanning electron microscope SEM (JEOL, JSM-6700F) and a transmission electron microscope TEM (JEOL, JEM-1010). The observation results are shown in FIGS. 3 and 4 and will be described later. Moreover, the limited-field diffraction pattern (SAED) was obtained from the product put on the copper grid using TEM. The results are shown in FIG.

  The structural evaluation of the product was performed using X-ray diffraction. X-ray diffraction was measured with a Rigaku Rint-2000 diffractometer equipped with a Cu counter cathode (Cu-Kα ray) (λ = 1.5405 ＝). For further structural analysis, high-resolution synchrotron powder X-ray diffraction data was obtained using the beamline BL15 (λ = 0.65297Å) of the large synchrotron radiation facility (Spring 8). The respective results are shown in FIGS. 6 and 7 and will be described later.

Subsequently, structure determination was performed using the result of FIG. The structure was determined by the following procedure. First, the integrated intensity was extracted from the XRD pattern of FIG. 7 using the Le Bail method. The extracted integrated intensity was redistributed by the maximum entropy Patterson program ALBA to obtain a more reliable value. The obtained structural factors were directly introduced into the method program EXPO 2004, and the positions of rare earth atoms were determined. The positions of other atoms were obtained by electron density distribution analysis by MEM / Rietveld. Finally, the structure was refined using the Rietan-FP program. The electron density distribution was obtained by MEM using the structure factor F ₀ value obtained by the PRIMA program. If additional peaks were found in the electron density distribution, the structural model was modified and refinement was repeated until no further decrease in reliability factor (R factor) was visible. These results are shown in FIGS. 8 to 11 and Table 2 and will be described in detail.

  Elemental analysis of the product was performed. The amount of Eu was measured using an inductively coupled plasma (ICP) atomic emission spectrometry (Seiko SPS1700HVR) after dissolving the sample in an aqueous hydrochloric acid solution. The amount of OH in the product was determined by neutralizing titration with NaOH after dissolving a precisely weighed sample in sulfuric acid (0.1 mol). The amount of Cl in the product was determined by the ion electrode method. At this time, DKK IM-40S was used as a concentration meter, DKK CL-125B was used as an ion electrode, and DKK RE-2 was used as a reference electrode. The C content in the product was determined with a LECO RC-412 analyzer. The water content in the product was determined by thermogravimetric analysis. The results of elemental analysis of the obtained product will be described later with reference to FIGS.

  The emission characteristics of the product were examined. Excitation and emission spectra at room temperature were measured using a fluorescence spectrophotometer (Hitachi F-4500). The measurement results are shown in FIG.

Next, the anion exchange ability of the product was examined. A sample (0.2 g) was added to a NaNO ₃ aqueous solution (1 M, 200 cm ³ ), a Na ₂ SO ₄ aqueous solution (1 M, 200 cm ³ ), and a sodium dodecyl sulfate (C ₁₂ H ₂₅ OSO ₃ Na) aqueous solution (0.5 M, 200 cm). ³ ) Each was dispersed. The reaction vessel containing each mixed aqueous solution was sealed and shaken at room temperature for 2 days. Two days later, samples were collected from each reaction vessel.

  The structural evaluation of the collected samples was performed using X-ray diffraction. X-ray diffraction was measured with a Rigaku Rint-2000 diffractometer equipped with a Cu counter cathode (Cu-Kα ray) (λ = 1.5405 ＝). The results are shown in FIG. 13 and will be described later. The morphology of the collected sample was observed using SEM. The observation results are shown in FIGS.

The recovered sample was subjected to Fourier transform infrared spectroscopic analysis (FT-IR), and qualitative analysis was performed as to whether or not anion exchange was performed. The measurement was performed by the KBr pellet method using a Varian 7000e FT-IR spectrophotometer equipped with an MCT detector in a wave number range of 400 to 4000 cm ⁻¹ . The results are shown in FIG.

In Example 1, the product was obtained by the same procedure except that YCl ₃ · 6H ₂ O (5 mM) was used as the salt of RE. For the obtained product, XRD and SEM were measured in the same manner as in Example 1. The results are shown in FIGS. 18 and 19 and will be described later.

In Example 1, the product was obtained by the same procedure except that SmCl ₃ · 6H ₂ O (5 mM) was used as the salt of RE. For the obtained product, XRD and SEM were measured in the same manner as in Example 1. The results are shown in FIGS. 20 and 21 and will be described later.

In Example 1, the product was obtained by the same procedure except that GdCl ₃ · 6H ₂ O (5 mM) was used as the salt of RE. For the obtained product, XRD and SEM were measured in the same manner as in Example 1. The results are shown in FIGS. 22 and 23 and will be described later.

In Example 1, the product was obtained by the same procedure except that TbCl ₃ · 6H ₂ O (5 mM) was used as the salt of RE. For the obtained product, the XRD, SEM and excitation / emission spectrum were measured in the same manner as in Example 1. The results are shown in FIGS.

In Example 1, the product was obtained by the same procedure except that DyCl ₃ · 6H ₂ O (5 mM) was used as the salt of RE. For the obtained product, XRD and SEM were measured in the same manner as in Example 1. The results are shown in FIGS. 27 and 28 and will be described later.

In Example 1, except for using _{HoCl 3 · 6H 2 O (5mM} ) as a salt of the RE may obtain a product by the same procedure. For the obtained product, XRD and SEM were measured in the same manner as in Example 1. The results are shown in FIGS. 29 and 30 and will be described later.

In Example 1, the product was obtained by the same procedure except that NdCl ₃ · 6H ₂ O (5 mM) was used as the salt of RE. For the obtained product, XRD and SEM were measured in the same manner as in Example 1. The results are shown in FIGS. 31 and 32 and will be described later.

LaCl ₃ · 6H ₂ O (5 mM), HMT (3.75 mM), and NaCl (65 mM) as RE salts were dissolved in 1000 ml of ultrapure water to obtain a mixed aqueous solution. HCl (0.1 M) was further added to the mixed aqueous solution to prepare the mixed aqueous solution to have a pH of 5 (step S110 in FIG. 1). Next, the mixed aqueous solution was stirred with a magnetic stirrer and heated at a reflux temperature (about 100 ° C.) in nitrogen gas. Thereby, HMT was decomposed | disassembled (step S120 of FIG. 1). These operations were performed using a two-necked flask equipped with a reflux condenser under a nitrogen stream.

  After 1 hour, white streamlines were observed in the mixed solution. This suggests that an anisotropic shaped crystal was formed. The product was then filtered, washed several times with water and ethanol, and dried at room temperature. For the obtained product, XRD was measured in the same manner as in Example 1. The results are shown in FIG. 33 and will be described later.

In Example 5, a product was obtained by the same procedure except that NaCl was not used and the concentration of TbCl ₃ .6H ₂ O was changed to 5 mM, 10 mM, 15 mM, 25 mM, and 50 mM. For the products obtained from each concentration, XRD was measured in the same manner as in Example 5. The results are shown in FIG. 34 and will be described later.

  In Example 5, a product was obtained by the same procedure except that NaCl was not used and a mixed solvent of ethanol and water (ethanol: water = 9: 1) was used instead of ultrapure water. . For the obtained product, XRD was measured in the same manner as in Example 5. The results are shown in FIG. 35 and will be described later.

In Example 5, a product was obtained by the same procedure except that TbBr ₃ · 6H ₂ O (5 mM) and NaBr (65 mM) were used instead of TbCl ₃ · 6H ₂ O and NaCl, respectively. The XRD and SEM of the obtained product were measured in the same manner as in Example 5. The results are shown in FIGS. 36 and 37 and will be described later.

EuNO ₃ · 6H ₂ O (5 mM), HMT (3.75 mM), and NaNO ₃ (65 mM) as RE salts are dissolved in 1000 ml of ultrapure water to prepare a mixed aqueous solution with a final concentration of 5.65 mM. (Step S110 in FIG. 1). Next, the mixed aqueous solution was stirred with a magnetic stirrer and heated at a reflux temperature (about 100 ° C.) in nitrogen gas. Thereby, HMT was decomposed | disassembled (step S120 of FIG. 1). These operations were performed using a two-necked flask equipped with a reflux condenser under a nitrogen stream.

  After 1 hour, white streamlines were observed in the mixed solution. This suggests that an anisotropic shaped crystal was formed. The product was then filtered, washed several times with water and ethanol, and dried at room temperature.

  The XRD, SEM, and excitation / emission spectrum of the obtained product were measured in the same manner as in Example 1. The results are shown in FIGS. 38 to 40 and will be described later.

In Example 13, a product was obtained by the same procedure except that Sm (NO ₃ ) ₃ · 6H ₂ O (5 mM) was used as the salt of RE. For the obtained product, XRD and SEM were measured in the same manner as in Example 13. The results are shown in FIGS. 41 and 42 and will be described later.

In Example 13, a product was obtained by the same procedure except that Gd (NO ₃ ) ₃ · 6H ₂ O (5 mM) was used as the salt of RE. For the obtained product, XRD and SEM were measured in the same manner as in Example 13. The results are shown in FIGS. 43 and 44 and will be described later.

In Example 13, the product was obtained by the same procedure except that Tb (NO ₃ ) ₃ · 6H ₂ O (5 mM) was used as the salt of RE. For the obtained product, XRD and SEM were measured in the same manner as in Example 13. The results are shown in FIGS. 45 and 46 and will be described later.

In Example 13, a product was obtained by the same procedure except that Dy (NO ₃ ) ₃ · 6H ₂ O (5 mM) was used as the salt of RE. For the obtained product, XRD and SEM were measured in the same manner as in Example 13. The results are shown in FIGS. 47 and 48 and will be described later.

In Example 13, a product was obtained by the same procedure except that Ho (NO ₃ ) ₃ · 6H ₂ O (5 mM) was used as the salt of RE. For the obtained product, XRD and SEM were measured in the same manner as in Example 13. The results are shown in FIGS. 49 and 50 and will be described later.

In Example 13, a product was obtained by the same procedure except that Nd (NO ₃ ) ₃ · 6H ₂ O (5 mM) was used as the salt of RE. For the obtained product, XRD and SEM were measured in the same manner as in Example 13. The results are shown in FIGS. 51 and 52 and will be described later.

In Example 16, the product was obtained by the same procedure except that NaNO ₃ was not used. For the obtained product, XRD and SEM were measured in the same manner as in Example 16. The results are shown in FIGS. 53 and 54 and will be described later.

  Table 1 shows the experimental conditions and results of Examples 1 to 20 described above.

  Since the intensity (count value) of the XRD pattern, excitation spectrum, and emission spectrum varies depending on the measurement apparatus and conditions, the unit is an arbitrary unit. That is, it should be noted that the comparison can be made only within the present example measured under the same conditions.

  FIG. 3 is a SEM image of the product of Example 1.

  4 is a TEM image of the product of Example 1. FIG.

From FIG. 3 and FIG. 4, it was confirmed that the obtained product was a rectangular plate (platelet). Moreover, it turned out that it is a uniform magnitude | size over the whole product from FIG. From FIG. 4, the morphology (plate thickness) of the rectangular platelet was about 20 nm. In addition, the size of one rectangular small plate was about 2 μm in the longitudinal direction and about 1 μm in the short direction. These features, intermediate layer ^Z m-220 (Fig. 2) Cl ^- strongly suggests that the layered rare earth hydroxides is obtained is.

  FIG. 5 is a diagram showing the SAED pattern (A) of Example 1 and the relationship (B) between the basic unit cell and the superlattice.

FIG. 5A shows two sets of spot groups having different luminances. This suggests that a superlattice structure is formed. Specifically, the brighter spots forming the hexagons correspond to hexagonal symmetric elementary unit cells (a _f = 3.7Å). On the other hand, a darker spot to form a rectangle, rectangular superlattice _{(a s = 2√3Å, a f} = 13.1Å, b s = 2a f = 7.4Å) corresponds to. The relationship between these basic unit lattices and superlattices is schematically shown in FIG. The basic unit cell (hexagonal unit cell) indicates a hexagonal arrangement of rare earth atoms (here, Eu), and is a brucite type (Mg (OH) ₂ ) or a layered double hydroxide LDH type ([M ²⁺ _X M ³⁺ _1-X (OH) ₂ ] ^1-X ) implies a similarity to the host layer structure. It is considered that a rectangular superlattice is formed due to the deviation from the ideal brucite structure atomic position.

  6 is a diagram showing an XRD pattern of the product of Example 1. FIG.

  The XRD pattern is composed of a number of sharp diffraction peaks, indicating that the product is highly crystalline. In particular, the very strong peaks at about 10.6 ° and about 21.2 ° in the low angle region imply that the resulting product is a layered material. Next, the crystal structure of the product of Example 1 was examined in more detail.

  FIG. 7 is a high resolution synchrotron powder X-ray diffraction (XRD) pattern of the product of Example 1.

  The peaks seen in the XRD pattern in FIG. 7 were all orthorhombic, and more specifically, simple orthorhombic lattices could be indexed. In particular, the peak intensity of 001 reflection and 002 reflection was stronger than other peak intensities. It was confirmed that these peaks corresponded to the peaks at about 10.6 ° and about 21.2 ° in FIG. The lattice constants a, b and c of the simple orthorhombic lattice were a = 12.92 (1) Å, b = 7.38 (1) Å and c = 8.71 (1) Å, respectively. The ratio of a and b did not completely match √3. This suggests that the above-described hexagonal symmetric basic unit cell is not completely hexagonal symmetric as in an ideal bullsite structure.

  A and b obtained from FIG. 7 matched well with a and b obtained from the SAED pattern of FIG. This is because the platelets seen in FIG. 4 are located on the {001} crystal plane, and the SAED pattern of FIG. 5 (A) was taken along the [001] direction, that is, along the z-axis. It shows that.

As a result of the composition analysis, it was found that the elemental composition was Eu (OH) _2.36 Cl _0.51 (CO ₃ ) _0.065 · 0.87H ₂ O. From the results of indexing in the XRD pattern of FIG. 7, it was found that a series of peaks of h = 2n + 1 (in the case of h00) and k = 2n + 1 (in the case of 0k0) disappeared. This suggests that the product space group is P2 ₁ 2 ₁ 2. Further, as a result of intensity extraction by the Le Bail method, the space groups P2 ₁ 2 ₁ 2 matched best. From the above, it was concluded that the product space group was P2 ₁ 2 ₁ 2.

Next, as described with reference to FIG. 5, since eight Eu exist in the unit cell, Z = 8 and the unit formula is Eu ₈ (OH) _18.88 Cl _4.08 (CO _{3 0.52} · 6.96H ₂ O For simplicity, transferred charge of carbonate ion to hydroxide ion, the unit formula was _{Eu 8 (OH) 20 Cl 4} · 7.0H 2 O. First, the direct method using the program EXPO 2004 was applied to determine the atomic positions of 8 Eu. Other light element species (OH, H ₂ O, Cl) were determined by electron density distribution analysis employing MEM / Rietveld of the maximum entropy method. From this result, a layered crystal structure model was generated.

  FIG. 8 is a schematic diagram of a layered crystal structure model.

  The left diagram in FIG. 8 is a layered crystal structure model projected from the [001] direction, and the right diagram in FIG. 8 is a layered crystal structure model in the [010] direction. Based on these crystal structure models, the structural parameters were refined from the Rietan-FP program. The result is shown in FIG.

  FIG. 9 is a diagram showing a Rietveld pattern of the product in Example 1.

FIG. 9 shows experimental values, calculated values, and differences. Satisfactory pattern fitting was achieved as shown in FIG. The final confidence factor (R factor) is R _wp = 2.04% (S = 0.5167), R _p = 1.52%, R _I = 3.98% and R _F = 1.65%. It became. These extremely small R factors suggest that the layered structure model shown in FIG. 8 is valid. Table 2 shows the structural parameters obtained as a result of the refinement.

In Table 2, the numbers in parentheses are standard deviations. The space group is P2 ₁ 2 ₁ 2 and the lattice constants a, b and c are a = 12.9155 (3) Å, b = 7.3763 (1) Å and c = 8.70223 (3) （, respectively. Met. All temperature factors ( _Biso ) were fixed at 1.0 ² for the Eu site and 2.0 ² for the other species. In the final stage, the water molecule occupancy was fixed according to the elemental composition determined by elemental analysis. Further, the Eu3 site is a space group in which P2 ₁ 2 ₁ 2 does not have a symmetric center, and thus is fixed at a value obtained from the direct method.

  FIG. 10 is a diagram showing an electron density distribution.

According to the illustration of the result of the electron density distribution analysis of FIG. 10, the electron density distribution matched well with the layered crystal structure model of FIG. A remarkable feature is that the electron density corresponding to the intermediate layer Cl ⁻ exhibits a substantially spherical distribution. This is because Cl ⁻ is also well arranged between the layers, and has characteristics different from other layered double hydroxides in which intermediate layer anions are often arranged randomly.

From the above results, it was shown that the structure of the product obtained in Example 1 was the layered rare earth hydroxide described with reference to FIG. In particular, the layered rare earth _hydroxides, RE _{(OH) 2.5} meets Cl 0.5 · 0.9H ₂ O of composition formula, positively charged _{[Eu 8 (OH) 20 (} H 2 O) ₇ ] It consists of a ⁴⁺ layer and a negatively charged intermediate layer Cl ⁻ located between the layers. Thereby, the charge is compensated and stabilized.

  Next, coordination of Eu cation sites will be described. The Eu cation has an 8-coordinate, ie, 4c (0.2736, 0.2503, 0.9349) position with seven hydroxyl groups and one water molecule, and a nine-coordinate, ie, eight hydroxyl groups and one water molecule. There are three patterns with accompanying 2a (0, 0, 0.9194) sites or 2b (0, 0.5, 0.9324) positions.

  FIG. 11 is a diagram showing the coordination environment of Eu in the product in Example 1.

FIG. 11 schematically shows the coordination environment of the three different Eu sites described above. In any coordination, all the hydroxyl groups are bonded to Eu at a distance of 2.1 to 2.6. In addition, the distance between H ₂ O and Eu in 8-coordinate and 9-coordinate was 2.35 (2) Å, 2.65 (6), and 2.45 (5) Å, respectively. Eu coordinated with these hydroxyl groups and H ₂ O molecules are chained in a two-dimensional direction, and a layer parallel to the ab plane as shown by 210 in FIG. 2 is generated.

  The deviation of the Eu position from the ideal in-plane hexagonal arrangement was in good agreement with the SAED results. This is because although the hexagonal symmetrical basic unit cell is substantially recognized in the actual structure, the position of Eu undulates in the [001] direction, that is, the z-axis direction, and is also distorted in the ab plane. This is because the details are a simple orthorhombic superlattice. From the above, it has been found that the crystal system of the layered rare earth hydroxide containing Cl ions between the layers of the present invention belongs to orthorhombic crystal, and specifically has a simple orthorhombic superlattice structure.

  12 shows the excitation spectrum (A) and emission spectrum (B) of the product of Example 1. FIG.

12 (A) shows the observed emission wavelength 612 nm ^- a excitation spectrum when the ⁽⁵ _D 0 7 _{F 2} line), FIG. 12 (B) when excited with 395nm (intra-4f ⁶ direct excitation) Is an emission spectrum. The excitation spectrum showed multiple sharp peaks due to the intra-4f ⁶ transition in the Eu ³⁺ 4f ⁶ electron configuration. Emission spectra, 578.4nm, 594.6nm, 612.4nm, the 649.0nm and 696.8nm, typical ⁵ D ₀ - showed ⁷ F _{j (j} = ^0~4) transition. Fluorescence from higher excitation levels such as ⁵ D ₁ was not detected. This suggests that very efficiently non-radiative relaxation to ⁵ D ₀ level.

⁵ D ₀ in FIG. _{^{12 (B) - 7 F j}} (j = 0~4) emission peak intensity of the transition, and, by using the division of these emission peaks, were examined ^{Eu 3+} ions environment. According to FIG. 12 (B), ⁵ D ₀ to about 612 nm - showed the strongest emission peak of ⁷ F ₂ transition. Theoretically, ^{Eu 3+} If the the inversion symmetry in the crystal lattice, the magnetic dipole transition ⁵ D ₀ at about 590 nm - ⁷ F ₁ becomes a major emission peak, otherwise, at about 610nm~620nm electric dipole transition ⁵ D ₀ - ⁷ F ₂ becomes the major emission peak. This suggests that Eu ³⁺ in the layered rare earth hydroxide of Example 1 does not have inversion symmetry, that is, has no inversion center.

In addition, according to FIG. _{^{12 (B), 5 D 0}} - 7 F 1 transition and ⁵ D ₀ - ⁷ F ₂ emission peak by the transition, respectively, and the peak split into three and two. This suggests that the symmetry of the crystal field around Eu ³⁺ is low. These results were in good agreement with the crystal structure analysis results. As described with reference to FIG. 11, Eu ³⁺ has two local coordinations, namely an 8-coordinate 4c position in the point group C ₁ and a 9-coordinate 2a and 2b in the point group C _4ν . Both of the Eu ³⁺ coordinations (ie, the three positions) belong to low symmetry with no inversion center.

As described above, typical Eu ³⁺ emission (red emission) was confirmed from the excitation spectrum and emission spectrum of FIG. This suggests that RE (here, Eu) functions as a luminescent center in the product of the present invention, and is applicable to fluorescent materials and further to light emitting devices.

  FIG. 13 is a diagram showing an XRD pattern after anion exchange of the product of Example 1.

  FIG. 13 also shows an XRD pattern of a sample (including Cl ions between layers) before anion exchange for reference. The XRD pattern of the product after anion exchange showed a clear peak shift.

The interlayer distance before anion exchange was 8.63 mm. On the other hand, the interlayer distance of the product after anion exchange with sodium nitrate (NO ₃ ⁻ ), sodium sulfate (SO ₄ ²⁻ ), and sodium dodecyl sulfate (C ₁₂ H ₂₅ OSO ₃ ⁻ ) was 8.32 cm, 8 Changed to .94 cm and 23.6 cm.

  In addition, the XRD pattern of the product after anion exchange maintained a sharp diffraction peak, and it was found that high crystallinity was maintained by the process during anion exchange.

14 is a diagram showing an SEM image of the product after anion exchange with sodium nitrate (NO ₃ ⁻ ) in Example 1. FIG.

15 is a diagram showing an SEM image of the product after anion exchange with sodium sulfate (SO ₄ ²⁻ ) in Example 1. FIG.

16 is a diagram showing an SEM image of the product after anion exchange with sodium dodecyl sulfate (C ₁₂ H ₂₅ OSO ₃ ⁻ ) in Example 1. FIG.

  Comparing the SEM image of the product before the anion exchange of Example 1 in FIG. 3 with the SEM images of FIGS. 14 to 16, the product after the anion exchange is also a rectangular platelet in the product before the anion exchange. It was found to maintain the morphology of. This also shows that high crystallinity and crystal structure are maintained by the process during anion exchange.

  17 is a diagram showing an FT-IR absorption spectrum of the product after anion exchange in Example 1. FIG.

FIG. 17 also shows the FT-IR absorption spectrum (a) of the product before anion exchange for reference. Any spectrum (a) ~ (d) also, about 3500 cm ^-1, and an absorption band at about 1650 cm ^-1 and about 620 cm ^-1. The absorption band of about 3500 cm ⁻¹ is due to the O—H bond and the stretching vibration of ν (OH), and suggests that hydroxide ions due to the metal-OH layer exist in the crystal. The absorption band of about 1650 cm ⁻¹ is due to the expansion / contraction mode of water molecules. The absorption band of about 620 cm ⁻¹ is caused by Eu / O stretching / deformation vibration.

In addition, the FT-IR absorption spectrum of FIG. 17 also shows an absorption band due to the type of the intermediate layer Z ^m− . Specifically, the FT-IR absorption spectrum (b) of the product after anion exchange with sodium nitrate (NO ₃ ⁻ ) showed sharp and strong absorption at 1385 cm ⁻¹ and 1410 cm ⁻¹ . These are each, NO ₃ ^- anions _{D 3h,} [nu ₃ vibration mode, and, O-NO ₂ of _{C 2v,} due to _ν4 asymmetric stretching mode. These absorption bands were not found in the spectrum (a) before the reaction.

The FT-IR absorption spectrum (c) of the product after anion exchange with sodium sulfate (SO ₄ ²⁻ ) showed absorption at 1120 cm ⁻¹ due to SO ₄ ²⁻ . This absorption band was not seen in spectrum (a).

Sodium dodecyl sulfate ^{_{(C 12 H 25 OSO 3 -}} ) FT-IR absorption spectrum of the by product after anion exchange (d) is a strong absorption at 2920 cm ^-1 and 2850cm ^-1, 2958cm ^-1, 1470cm ^-1 and Relatively weak absorption was shown at 1300 cm ^{−1 to} 900 cm ⁻¹ . The absorptions at 2920 cm ⁻¹ and 2850 cm ⁻¹ are attributed to asymmetric CH ₂ stretching vibration and symmetric CH ₂ stretching vibration in the alkyl chain of dodecyl sulfate, respectively. Further, the relatively weak absorption at 2958 cm ⁻¹ is attributed to the stretching vibration of the CH ₃ group which is a hydrocarbon end group. The relatively weak absorption near 1470 cm ⁻¹ is due to the CH ₂ bending (or scissor) mode. ^Furthermore, a series of weak absorption in 1300cm ^-1 ~900cm -1 is sulfate ^- due to the expansion and contraction mode (OSO _3). These absorption bands were not found in spectrum (a).

Thus, it was found that the product of the present invention can be easily anion-exchanged at room temperature and maintain high crystallinity and crystal structure (layered structure) even after anion exchange. The above results indicate that the intermediate layer 220 (here, the Cl ⁻ layer) functions as a counter anion, as described with reference to FIG. When the product of the present invention is used as an anion exchange material, it is suggested that anion exchange can be performed with high efficiency at room temperature.

  18 is a diagram showing an XRD pattern of the product of Example 2. FIG.

The XRD pattern of FIG. 18 is similar to the XRD pattern of FIG. 6 in addition to strong peaks at about 10.6 ° and about 21.2 °, all other peaks are layered rare earth hydroxide (RE (OH) _{2 .5} Z _0.5 · 0.9 H ₂ O). From this, the product of Example 2 is a Y (OH) _2.5 Cl _0.5 · 0.9H ₂ O single phase, and in detail, [RE ₈ (OH) ₂₀ (H _This shows that a layered rare earth hydroxide in which RE is Y in the ₂ O) _X ] ⁴⁺ layer 210 and the intermediate layer Z ^m− 220 is Cl ⁻ is obtained.

  19 is a view showing an SEM image of the product of Example 2. FIG.

FIG. 19 shows a morphology in which rectangular platelets typical of layered rare earth hydroxides in which the intermediate layer Z ^m- 220 (FIG. 2) is Cl ⁻ are aggregated. This also suggests that a layered rare earth hydroxide was obtained.

  20 shows the XRD pattern of the product of Example 3. FIG.

The XRD pattern of FIG. 20 is similar to the XRD pattern of FIG. 6, in addition to the strong peaks at about 10.6 ° and about 21.2 °, all other peaks are layered rare earth hydroxide (RE (OH) _{2 .5} Z _0.5 · 0.9 H ₂ O). From this, the product of Example 3 is a single phase of Sm (OH) _2.5 Cl _0.5 · 0.9 H ₂ O, and in detail, [RE ₈ (OH) ₂₀ (H ₂ O) _X] RE in ⁴⁺ layer 210 is Sm, the intermediate layer ^Z m-220 is Cl ^- layered earth hydroxides it is indicated that the obtained a.

  21 is a SEM image of the product of Example 3. FIG.

From FIG. 21, the morphology of the product of Example 3 is similar to the morphology of the product of Example 1, the intermediate layer Z ^m-220 is Cl ^- typical rectangular layered rare earth hydroxide is Platelets were obtained uniformly throughout the product. This also suggests that the layered rare earth hydroxide was obtained in a single phase.

  22 shows the XRD pattern of the product of Example 4. FIG.

The XRD pattern of FIG. 22 is similar to the XRD pattern of FIG. 6 in addition to strong peaks at about 10.6 ° and about 21.2 °, all other peaks are layered rare earth hydroxide (RE (OH) _{2 .5} Cl _0.5 · 0.9 H ₂ O). From this, the product of Example 4 is a Gd (OH) _2.5 Cl _0.5 · 0.9H ₂ O single phase, and in detail, [RE ₈ (OH) ₂₀ (H ₂ O) _X] RE in ⁴⁺ layer 210 is Gd, intermediate layer ^Z m-220 is Cl ^- layered earth hydroxides it is indicated that the obtained a.

  23 is a view showing an SEM image of the product of Example 4. FIG.

FIG. 23 shows a morphology in which rectangular platelets typical of a layered rare earth hydroxide having an intermediate layer Z ^m- 220 of Cl ⁻ are aggregated. This also suggests that a layered rare earth hydroxide was obtained.

  FIG. 24 shows the XRD pattern of the product of Example 5.

The XRD pattern of FIG. 24 is similar to the XRD pattern of FIG. 6 in addition to the strong peaks at about 10.6 ° and about 21.2 °, all other peaks are layered rare earth hydroxide (RE (OH) _{2 .5} Cl _0.5 · 0.9 H ₂ O). From this, the product of Example 5 is a Tb (OH) _2.5 Cl _0.5 · 0.9H ₂ O single phase, and in detail, [RE ₈ (OH) ₂₀ (H ₂ O) _X] RE in ⁴⁺ layer 210 is Tb, the intermediate layer ^Z m-220 is Cl ^- layered earth hydroxides it is indicated that the obtained a.

  FIG. 25 is a view showing an SEM image of the product of Example 5.

FIG. 25 shows a morphology in which platelets typical of a layered rare earth hydroxide in which the intermediate layer Z ^m- 220 is Cl ⁻ are aggregated. This also suggests that a layered rare earth hydroxide was obtained.

  FIG. 26 shows the excitation / emission spectrum of the product of Example 5.

FIG. 26 shows an excitation spectrum when the observed emission wavelength is 543 nm and an emission spectrum when excited at 252 nm. Emission of a typical ^{Tb 3+} (green light emission) ^is, _{5 D} 4 ^- 7 _F 5 was confirmed to 543m by the transition. In the product of the present invention, RE (here, Tb) functions as an emission center, suggesting that it can be applied to fluorescent materials and further to light emitting devices.

  FIG. 27 is an XRD pattern of the product of Example 6.

The XRD pattern of FIG. 27 is similar to the XRD pattern of FIG. 6 in addition to strong peaks at about 10.6 ° and about 21.2 °, all other peaks are layered rare earth hydroxide (RE (OH) _{2 .5} Z _0.5 · 0.9 H ₂ O). From this, the product of Example 6 is a Dy (OH) _2.5 Cl _0.5 · 0.9H ₂ O single phase, and in detail, [RE ₈ (OH) ₂₀ (H ₂ O) _X] RE in ⁴⁺ layer 210 is Dy, intermediate layer ^Z m-220 is Cl ^- layered earth hydroxides it is indicated that the obtained a.

  28 is a SEM image of the product of Example 6. FIG.

FIG. 28 shows a morphology in which platelets typical of a layered rare earth hydroxide are aggregated although the size is not uniform. Moreover, the shape was partially broken, and the shape was rectangular. This also intermediate layer Z ^m-220 are Cl ^- be layered rare earth hydroxide obtained is suggesting.

  FIG. 29 is a diagram showing an XRD pattern of the product of Example 7. FIG.

The XRD pattern of FIG. 29 is similar to the XRD pattern of FIG. 6 in addition to the strong peaks at about 10.6 ° and about 21.2 °, all other peaks are layered rare earth hydroxide (RE (OH) _{2 .5} Z _0.5 · 0.9 H ₂ O). From this, the product of Example 7 is a Ho (OH) _2.5 Cl _0.5 · 0.9 H ₂ O single phase, and in detail, [RE ₈ (OH) ₂₀ (H ₂ O) _X] RE in ⁴⁺ layer 210 is Ho, intermediate layer ^Z m-220 is Cl ^- layered earth hydroxides it is indicated that the obtained a.

  30 is a SEM image of the product of Example 7. FIG.

FIG. 30 shows a morphology in which rectangular platelets typical of a layered rare earth hydroxide in which the intermediate layer Z ^m- 220 is Cl ⁻ are aggregated, although the shape is partially broken. This also suggests that a layered rare earth hydroxide was obtained.

  FIG. 31 shows the XRD pattern of the product of Example 8.

The XRD pattern of FIG. 31 is similar to the XRD pattern of FIG. 6 in that the layered rare earth hydroxide (RE (OH) _2.5 Z _{0 at} about 10.6 ° and about 21.2 ° is the same as in Example 1. _.5 · 0.9H ₂ O) showed a typical peak, but a part of the peak showing Nd (OH) ₃ was also observed. From this, it was found that the product of Example 8 was a mixture of Nd (OH) _2.5 Cl _0.5 · 0.9H ₂ O and Nd (OH) ₃ . As a result of structural refinement, it was found that the amount of Nd (OH) ₃ produced was 10% or less, and Nd (OH) _2.5 Cl _0.5 · 0.9H ₂ O was the main product.

  32 is a SEM image of the product of Example 8. FIG.

FIG. 32 shows a needle-like piece in addition to the morphology of platelets typical of layered rare earth hydroxide. In particular, the shape of the platelet was rectangular. This also indicates that the product of Example 8 is a mixture of Nd (OH) _2.5 Cl _0.5 · 0.9H ₂ O (rectangular platelet morphology) and Nd (OH) ₃ (acicular morphology). It is suggested that As described above, the layered rare earth hydroxide in which [RE ₈ (OH) ₂₀ (H ₂ O) _X ] ⁴⁺ layer 210 is RE in the [RE ₈ (OH) ₂₀ (H ₂ O) _X ] ⁴⁺ layer 210, and the intermediate layer Z ^m- 220 is Cl ⁻ , although not a complete simple substance It was found that was obtained.

  FIG. 33 is an XRD pattern of the product of Example 9.

According to FIG. 33, a peak corresponding to La (OH) ₃ was mainly detected, but a slight amount of layered rare earth hydroxide (RE (OH) _2.5 Z was observed at about 10.6 ° and about 21.2 °. _A typical peak was observed at _0.5 · 0.9H ₂ O). From this, it was found that the product of Example 9 was mainly La (OH) ₃ but also contained La (OH) _2.5 Cl _0.5 · 0.9H ₂ O. Although the layered rare earth hydroxide of the present invention is obtained in La, Nd (see Example 8), and Sm (see Example 3) among rare earth elements RE that are not completely simple elements, If Ce, Pr and Pm sandwiched between La and Sm are also employed, it is expected that a layered rare earth hydroxide will be obtained.

  FIG. 34 is an XRD pattern of the product of Example 10.

According to FIG. 34, all XRD patterns were the same XRD patterns as in Example 5 shown in FIG. From this, the product of Example 10 is a Tb (OH) _2.5 Cl _0.5 · 0.9H ₂ O single phase, and in detail, [RE ₈ (OH) ₂₀ (H ₂ O) _X ] It is suggested that a layered rare earth hydroxide in which RE is Tb in the ⁴⁺ layer 210 and the intermediate layer Z ^m− 220 is Cl ⁻ is obtained. From the above, it was shown that a layered rare earth hydroxide can be obtained without adding an alkali metal salt.

Furthermore, the peak intensity of the XRD pattern of the product obtained from 5 mM TbCl ₃ in FIG. 34 was found to be lower than the peak intensity of the XRD pattern shown in FIG. From this, it was shown that when the same TbCl ₃ molar concentration was used, crystallinity was improved by adding an alkali metal salt (NaCl in Example 5). However, it was confirmed that a high-quality layered rare earth hydroxide having good crystallinity can be obtained without adding an alkali metal salt when a high concentration salt of TbCl ₃ 10 mM or more is used. From the above, it is suggested that when a relatively low concentration salt of less than 10 mM is employed as the RE salt in step S110 of FIG. 1, it is desirable to add an alkali metal salt.

  FIG. 35 shows the XRD pattern of the product of Example 11.

The XRD pattern in FIG. 35 was the same XRD pattern as in Example 5 shown in FIG. From this, the product of Example 11 is a Tb (OH) _2.5 Cl _0.5 · 0.9H ₂ O single phase, and in detail, [RE ₈ (OH) ₂₀ (H ₂ O) _X ] It is suggested that a layered rare earth hydroxide in which RE is Tb in the ⁴⁺ layer 210 and the intermediate layer Z ^m− 220 is Cl ⁻ is obtained. From the above, it was shown that a layered rare earth hydroxide can be obtained without adding an alkali metal salt and using a mixed solvent of water and ethanol as a solvent.

  FIG. 36 shows the XRD pattern of the product of Example 12.

The XRD pattern in FIG. 36 was the same XRD pattern as in Example 5 shown in FIG. From this, the product of Example 12 is a Tb (OH) _2.5 Br _0.5 · 0.9H ₂ O single phase, and in detail, [RE ₈ (OH) ₂₀ (H ₂ O) _X ] It is suggested that a layered rare earth hydroxide in which RE is Tb in the ⁴⁺ layer 210 and the intermediate layer Z ^m− 220 is Br ⁻ is obtained.

  FIG. 37 is a SEM image of the product of Example 12.

FIG. 37 shows a morphology in which rectangular platelets typical of a layered rare earth hydroxide in which the intermediate layer Z ^m- 220 is Cl ⁻ are aggregated, although a portion showing a part of an amorphous shape is included. This also suggests that a layered rare earth hydroxide was obtained. From the above, it was shown that the layered rare earth hydroxide can be obtained even when bromide is used in place of chloride as the RE salt in step S110 of FIG. Moreover, it is suggested that the morphology of the layered rare earth hydroxide whose intermediate layer Z ^m- 220 is halogen is a rectangular plate shape.

  FIG. 38 shows the XRD pattern of the product of Example 13.

In the XRD pattern of FIG. 38, in addition to the strong peaks of 9.8 ° and 19.7 °, a large number of sharp diffraction lines were observed, similar to the XRD pattern of FIG. When this pattern was indexed, the compound was monoclinic and the lattice constants were a = 12.800 (7) Å, b = 7.692 (8) Å, c = 9.002 (9). Å and β = 94.65 (9) ° were obtained. The length of a-axis and b-axis chlorine type compound ^- since good agreement therewith very (i.e. the intermediate layer Z ^m-220 is Cl layered rare earth hydroxide is), the compound is the same as the chlorine-type compound It is strongly suggested to have a host layer. It is understood that the layering mode of the host layer changes due to the influence of the interlayer ions being changed to nitrate ions, and has a monoclinic structure. From this, the product of Example 13 is a single phase of Eu (OH) _2.5 (NO ₃ ) _0.5 · 0.9H ₂ O, and in detail, [RE ₈ (OH) ₂₀ (H It is suggested that a layered rare earth hydroxide in which RE is Eu in the ₂ O) _X ] ⁴⁺ layer 210 and the intermediate layer Z ^m− 220 is NO ₃ ⁻ is obtained.

  FIG. 39 shows the SEM image of the product of Example 13.

The product morphology of Example 13 was plate-like typical for layered rare earth hydroxides and was obtained uniformly throughout the product. This also suggests that the layered rare earth hydroxide was obtained in a single phase. The plate-like shape was an elongated hexagonal shape unlike the case where the intermediate layer Z ^m- 220 was halogen. From the above, it was shown that the layered rare earth hydroxide can be obtained even when nitrate is used in place of the halide as the RE salt in step S110 of FIG. Further, it is suggested that the crystal symmetry and the plate shape differ depending on the type of the intermediate layer Z ^m- 220.

  40 is a diagram showing an excitation / emission spectrum of the product of Example 13. FIG.

FIG. 40 shows an excitation spectrum when the observed emission wavelength is 612 nm and an emission spectrum when excited at 395 nm. As described with reference to FIG. 12, the emission of a typical ^{Eu 3+ is,} 5 _D 0 ^- confirmed to 543m by 7 _{F 2} transition. In the product of the present invention, even when the intermediate layer is NO ₃ ⁻ instead of Cl ⁻ , RE (Eu in this case) functions as the emission center, suggesting that it can be applied to a light emitting device.

  FIG. 41 is an XRD pattern of the product of Example 14.

Although the overall peak intensity is low, like the XRD pattern of FIG. 38, in addition to the strong peaks at 9.8 ° and 19.7 °, all other peaks are layered rare earth hydroxide (RE (OH) _{2 .5} Z _0.5 · 0.9 H ₂ O). From this, it was found that the product of Example 14 was a single phase of Sm (OH) _2.5 (NO ₃ ) _0.5 · 0.9H ₂ O.

  42 is a SEM image of the product of Example 14. FIG.

In FIG. 42, in addition to the morphology in which elongated hexagonal platelets typical of layered rare earth hydroxides in which the intermediate layer Z ^m- 220 is NO ₃ ^— are aggregated, some of the needle-like shapes considered to be impurities A small piece was confirmed. From the above, although there is a possibility of containing impurities, the layered rare earth in which [RE ₈ (OH) ₂₀ (H ₂ O) _X ] ⁴⁺ layer 210 has RE as Sm and intermediate layer Z ^m− 220 as NO ₃ ^−. It was found that the hydroxide was obtained almost in single phase.

  FIG. 43 is an XRD pattern of the product of Example 15.

The XRD pattern of FIG. 43 is similar to the XRD pattern of FIG. 38, in addition to the strong peaks at 9.8 ° and 19.7 °, all other peaks are layered rare earth hydroxide (RE (OH) _2.5 It coincided with the peak of Z _0.5 · 0.9 H ₂ O). From this, the product of Example 15 is a Gd (OH) _2.5 (NO ₃ ) _0.5 · 0.9H ₂ O single phase, and in detail, [RE ₈ (OH) ₂₀ (H _This shows that a layered rare earth hydroxide in which RE is Gd in the ₂ O) _X ] ⁴⁺ layer 210 and the intermediate layer Z ^m− 220 is NO ₃ ⁻ is obtained.

  44 is a SEM image of the product of Example 15. FIG.

For the product morphology of Example 15, elongated hexagonal platelets typical of layered rare earth hydroxides with intermediate layer Z ^m- 220 of NO ₃ ^— were obtained uniformly throughout the product. This also suggests that the layered rare earth hydroxide was obtained in a single phase.

  FIG. 45 is an XRD pattern of the product of Example 16.

The XRD pattern of FIG. 45 is similar to the XRD pattern of FIG. 38, in addition to the strong peaks at 9.8 ° and 19.7 °, all other peaks are layered rare earth hydroxide (RE (OH) _2.5 It coincided with the peak of Z _0.5 · 0.9 H ₂ O). From this, the product of Example 16 is a Tb (OH) _2.5 (NO ₃ ) _0.5 · 0.9H ₂ O single phase, and in detail, [RE ₈ (OH) ₂₀ (H _This shows that a layered rare earth hydroxide in which RE is Tb in the ₂ O) _X ] ⁴⁺ layer 210 and the intermediate layer Z ^m− 220 is NO ₃ ⁻ is obtained.

  46 is a SEM image of the product of Example 16. FIG.

For the product morphology of Example 16, elongated hexagonal platelets typical of layered rare earth hydroxides where the intermediate layer Z ^m- 220 is NO ₃ ^— were obtained uniformly throughout the product. This also suggests that the layered rare earth hydroxide was obtained in a single phase.

  47 is a diagram showing an XRD pattern of the product of Example 17. FIG.

The XRD pattern of FIG. 47 is similar to the XRD pattern of FIG. 38, in addition to the strong peaks at 9.8 ° and 19.7 °, all other peaks are layered rare earth hydroxide (RE (OH) _2.5 It coincided with the peak of Z _0.5 · 0.9 H ₂ O). From this, the product of Example 17 is a Dy (OH) _2.5 (NO ₃ ) _0.5 · 0.9H ₂ O single phase, and in detail, [RE ₈ (OH) ₂₀ (H _This shows that a layered rare earth hydroxide in which RE is Dy in the ₂ O) _X ] ⁴⁺ layer 210 and the intermediate layer Z ^m− 220 is NO ₃ ⁻ is obtained.
48 is a SEM image of the product of Example 17. FIG.

FIG. 48 shows a morphology in which elongated hexagonal platelets typical of layered rare earth hydroxides in which the intermediate layer Z ^m- 220 is NO ₃ ^— are aggregated. This also suggests that a layered rare earth hydroxide was obtained.

  FIG. 49 shows the XRD pattern of the product of Example 18.

The XRD pattern of FIG. 49 is similar to the XRD pattern of FIG. 38, in addition to the strong peaks at 9.8 ° and 19.7 °, all other peaks are layered rare earth hydroxide (RE (OH) _2.5 It coincided with the peak of Z _0.5 · 0.9 H ₂ O). From this, the product of Example 18 is Ho (OH) _2.5 (NO ₃ ) _0.5 · 0.9H ₂ O single phase, and in detail, [RE ₈ (OH) ₂₀ (H _This shows that a layered rare earth hydroxide in which RE is Ho in the ₂ O) _X ] ⁴⁺ layer 210 and the intermediate layer Z ^m− 220 is NO ₃ ⁻ is obtained.

  50 is a diagram showing an SEM image of the product of Example 18. FIG.

FIG. 50 shows a morphology in which elongated hexagonal platelets typical of layered rare earth hydroxides in which the intermediate layer Z ^m- 220 is NO ₃ ^— are aggregated. This also suggests that a layered rare earth hydroxide was obtained.

  51 is a diagram showing an XRD pattern of the product of Example 19. FIG.

According to FIG. 51, a peak corresponding to Nd (OH) ₃ was detected, but the layered rare earth hydroxide (RE (OH) _2.5 Z _0.5 · 0.9H _{2 was} slightly observed at 9.8 °. A typical peak was confirmed in O).

  52 is a diagram showing an SEM image of the product of Example 19. FIG.

According to FIG. 52, the product had an overall needle-like morphology. This indicates that the majority of the product of Example 19 is Nd (OH) ₃ . As mentioned above, although the product of Example 19 has Nd (OH) ₃ as the main product, it is slightly layered rare earth water of Nd (OH) _2.5 (NO ₃ ) _0.5 · 0.9H ₂ O. It is suggested that an oxide is obtained.

  53 shows the XRD pattern of the product of Example 20. FIG.

The XRD pattern shown in FIG. 53 was almost the same as the XRD pattern of Example 16 shown in FIG. From this, the product of Example 20 is a Tb (OH) _2.5 (NO ₃ ) _0.5 · 0.9H ₂ O single phase, and in detail, [RE ₈ (OH) ₂₀ (H _This shows that a layered rare earth hydroxide in which RE is Tb in the ₂ O) _X ] ⁴⁺ layer 210 and the intermediate layer Z ^m− 220 is NO ₃ ⁻ is obtained. From the above, it was shown that a layered rare earth hydroxide can be obtained without adding an alkali metal salt (NaNO _{3 in} Example 16).

  54 is a diagram showing an SEM image of the product of Example 20. FIG.

FIG. 54 shows the morphology of an elongated hexagonal platelet typical of a layered rare earth hydroxide in which the intermediate layer Z ^m- 220 is NO ₃ ^{—, although} it is not uniform. Comparing FIG. 54 and FIG. 46, it was found that the morphology of the product shown in FIG. 46 is a more uniform elongated hexagonal platelet compared to that of FIG. This indicates that when the same TbNO ₃ molar concentration is used, adding the alkali metal salt (NaNO _{3 in} Example 16) improves the product morphology.

The above examples have shown that layered rare earth hydroxides are synthesized for halides and nitrates of rare earth elements RE. In particular, according to Examples 1 to 7 and Examples 13 to 18, if the method of the present invention is employed, a salt of rare earth element RE (among others, Y, Sm, Eu, Gd, An element selected from the group consisting of Tb, Dy and Ho) and HMT are dissolved in ultrapure water, and the layered rare earth hydroxide of the present invention can be easily formed in a single phase simply by heating the resulting mixed aqueous solution It turns out that it is obtained. When the product contains a second phase such as RE (OH) ₃ , the layered rare earth hydroxide can be obtained in a single phase by adjusting the production conditions (pH, molar concentration, etc.). Moreover, the light emission characteristic and the anion exchange ability at room temperature of the layered rare earth hydroxide of the present invention were confirmed.

  According to the method of the present invention, a step of preparing a mixed aqueous solution containing a salt of a rare earth element, hexamethylenetetramine (HMT) or urea, and a solvent containing water, and hexamethylenetetramine (HMT) in the mixed aqueous solution are provided. Or a step of decomposing urea and hydrolyzing a salt of the rare earth element RE. Since it is only necessary to decompose HMT or urea in the mixed aqueous solution, a high-pressure apparatus necessary for the conventional hydrothermal method is unnecessary. As a result, since it can be synthesized using a glass apparatus such as a flask, a large amount of layered rare earth hydroxide can be provided easily and inexpensively. In addition, the layered rare earth hydroxide thus obtained is an anion exchange material based on a layered substance having a counter anion, a light emitting material based on a rare earth element, a magnetic material, a catalyst material, and a combination of these materials, Furthermore, it can be used for a device using these materials.

Flowchart showing steps for producing layered rare earth hydroxide according to the present invention. Schematic diagram (A) and crystal structure (B) of layered rare earth hydroxide according to the present invention The figure which shows the SEM image of the product of Example 1 The figure which shows the TEM image of the product of Example 1 The figure which shows the SAED pattern (A) of Example 1, and the relationship (B) of a basic unit cell and a superlattice. Figure showing the XRD pattern of the product of Example 1 FIG. 5 shows a high-resolution synchrotron powder X-ray diffraction (XRD) pattern of the product of Example 1 Schematic diagram of a layered crystal structure model The figure which shows the Rietveld pattern of the product of Example 1 Diagram showing electron density distribution The figure which shows the coordination environment of Eu in the product in Example 1 The figure which shows the excitation spectrum (A) and emission spectrum (B) of the product of Example 1 The figure which shows the XRD pattern after anion exchange of the product of Example 1 Shows an SEM image of the product after the anion exchange with _- sodium nitrate in Example 1 (NO ³⁾ Shows an SEM image of the product after anion exchange with sodium sulfate of Example 1 _(SO ^{4 2-)} It shows an SEM image of the product after the anion exchange with ^- sodium dodecyl sulfate of Example _{1 (C 12 H 25 OSO 3} ) The figure which shows the FT-IR absorption spectrum of the product after anion exchange of Example 1. Figure 4 shows the XRD pattern of the product of Example 2 The figure which shows the SEM image of the product of Example 2 Figure 3 shows the XRD pattern of the product of Example 3 The figure which shows the SEM image of the product of Example 3 Figure 4 shows the XRD pattern of the product of Example 4 The figure which shows the SEM image of the product of Example 4 Figure 5 shows the XRD pattern of the product of Example 5 The figure which shows the SEM image of the product of Example 5 FIG. 5 shows the excitation / emission spectrum of the product of Example 5 Figure 4 shows the XRD pattern of the product of Example 6 The figure which shows the SEM image of the product of Example 6 Figure 7 shows the XRD pattern of the product of Example 7 The figure which shows the SEM image of the product of Example 7 Figure 4 shows the XRD pattern of the product of Example 8 The figure which shows the SEM image of the product of Example 8 Figure 5 shows the XRD pattern of the product of Example 9 Figure 5 shows the XRD pattern of the product of Example 10 FIG. 11 shows the XRD pattern of the product of Example 11. Figure 4 shows the XRD pattern of the product of Example 12 The figure which shows the SEM image of the product of Example 12 Figure 4 shows the XRD pattern of the product of Example 13 The figure which shows the SEM image of the product of Example 13 FIG. 10 shows the excitation / emission spectrum of the product of Example 13. Figure 4 shows the XRD pattern of the product of Example 14 FIG. 10 is a diagram showing an SEM image of the product of Example 14. Figure 5 shows the XRD pattern of the product of Example 15 FIG. 10 is a diagram showing an SEM image of the product of Example 15. FIG. 11 shows the XRD pattern of the product of Example 16. FIG. 10 shows an SEM image of the product of Example 16. Figure 4 shows the XRD pattern of the product of Example 17 FIG. 11 is a SEM image of the product of Example 17 FIG. 11 shows the XRD pattern of the product of Example 18. FIG. 10 shows an SEM image of the product of Example 18 FIG. 10 shows the XRD pattern of the product of Example 19 FIG. 11 is a SEM image of the product of Example 19 FIG. 10 shows the XRD pattern of the product of Example 20 FIG. 5 is a SEM image of the product of Example 20.

Explanation of symbols

200 layered rare earth hydroxide 210 [RE ₈ (OH) ₂₀ (H ₂ O) _X ] ⁴⁺ layer or host layer 220 intermediate layer

Claims (7)

A method for producing a layered rare earth hydroxide comprising:
The hexamethylenetetramine (HMT) or urea in a mixed aqueous solution composed of a rare earth element salt, hexamethylenetetramine (HMT) or urea, and a solvent containing water is decomposed to hydrolyze the rare earth element salt. It is characterized by comprising the steps of:   2. The method according to claim 1, wherein the rare earth element salt is a nitrate of the rare earth element or a chloride of the rare earth element.   The method according to claim 1, wherein an alkali metal salt is further mixed in the mixed aqueous solution.   2. The method according to claim 1, wherein the mixed aqueous solution is prepared so that a molar ratio of the rare earth element salt to the hexamethylenetetramine (HMT) or urea is 0.75. .   The method according to claim 1, wherein the hydrolyzing step heats the mixed aqueous solution while stirring at a temperature of 70 ° C. or higher. 2. The method according to claim 1, wherein the layered rare earth hydroxide has a composition formula RE (OH) _2.5 Z _{(1/2 m)} · 0.125XH ₂ O (where RE is a rare earth element, and Z is the An anion generated from a salt of a rare earth element, m is represented by the valence of an anion, 6 <X <8). The method according to claim 6, wherein the layered rare earth hydroxide comprises a positively charged [RE ₈ (OH) ₂₀ (H ₂ O) _x ] ⁴⁺ (RE is a rare earth element, 6 <X <8) layer. It has a laminated structure with a negatively charged intermediate layer ^Zm- .