KR101511588B1 - Layered Polymorph of Rare Earth Hydroxide and Process for Preparing the Same - Google Patents

Abstract

The present invention relates to a lamellar structure of rare earth hydroxides capable of forming a stable aqueous colloid solution and stable in a physiological environment at low pH, and a stable aqueous colloid solution containing the same, which can be easily, economically and environmentally friendly ≪ / RTI >

Description

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a layered structure of rare earth hydroxides,

More particularly, the present invention relates to a layered structure of rare earth hydroxide capable of forming a stable aqueous colloid solution, and a method for easily and easily producing the layered structure of rare earth hydroxide. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a layered structure of rare earth hydroxides, .

BACKGROUND OF THE INVENTION Rare earth compounds are known to be usefully used as high performance magnets, light emitting devices, catalysts, and other functional materials due to their unique electronic, optical, and magnetic properties. In recent years, the relatively low toxicity of rare earth ions compared to other heavy metals and the highly sensitive 4f-4f transition in in vitro and in vivo biosolids have led to the development of rare-earth nanostructures such as emission markers, probes and sensors for immunoassay and high sensitivity imaging Interest in biomedical applications is increasing.

Among these classes of compounds, conventional rare earth hydroxides, RE (OH) ₃ (RE = rare earth element), are known to crystallize into a close-packed structure. The nanostructures of the close-packed RE (OH) ₃ (h-RE (OH) ₃ ) are hydrothermal, microwave, wet-chemical, solvothermal and complex- and composite-hydroxide-mediated techniques. However, these methods are often difficult to commercialize due to their small, vigorous, or complex synthetic pathways. To date, the main types of h-RE (OH) ₃ nanostructures have been nanotubes, nanowires, nanorods, and nanospheres.

On the other hand, rare-earth hydroxycloride (RE ₂ (OH) ₅ Cl mH ₂ O) nanosheets and their surface-modified forms can be used for the visual detection and separation of thiols and disulfides, magnetic resonance Applications [Korean Patent Publication Nos. 2010-0052726 and 2011-0021148]. However, the above materials have a poor stability in low pH physiological environment, have no organic anion for biomedical applications, and develop pure rare earth hydroxides stable in a low pH environment because they have unnecessary and toxic Cl ^- anions Has been desperately required.

The inventors of the present invention have conducted intensive research to develop a pure rare earth hydroxide nano-sheet and a method for producing the same. As a result, they have found that rare earth hydroxides such as rare earth hydroxides (RE ₂ (OH) ₅ Cl mH ₂ O) It has been found that the layered structure of hydroxides (RE (OH) ₃ .mH ₂ O) has the form of nanosheet, is capable of producing a stable aqueous colloidal solution, and is stable in a low pH environment, thereby completing the present invention .

It is therefore an object of the present invention to provide a layered structure of pure rare earth hydroxides.

Another object of the present invention is to provide a method for easily and easily producing the layered structure of the rare earth hydroxides.

It is another object of the present invention to provide an aqueous colloidal solution containing rare earth hydroxide nanosheets.

It is another object of the present invention to provide a method for producing an aqueous colloid solution containing rare earth hydroxide nanosheets.

On the other hand, the present invention relates to a layered structure of rare earth hydroxides of the following formula (I).

_{RE (OH) 3 · nH 2} O (I)

In this formula,

RE is a rare earth, preferably Sm, Eu, Gd, Tb, Dy, Er or Y,

n is from 0.5 to 2, preferably from 1 to 1.5.

The layered structure of the rare earth hydroxide of the present invention is a typical layered structure having interlayer water molecules, In the form of nanosheets with a thickness of a few nanometers and a width of tens to hundreds of nanometers.

On the other hand, the present invention relates to a process for preparing a layered structure of rare earth hydroxides of the formula (I), wherein the process comprises reacting a rare earth hydroxychloride of the formula (II) .

RE ₂ (OH) ₅ Cl mH ₂ O (II)

In this formula,

RE is a rare earth, preferably Sm, Eu, Gd, Tb, Dy, Er or Y,

m is from 0.5 to 4, preferably from 1 to 3.

The rare earth hydroxychloride of the formula (II) can be prepared according to the method disclosed in Korean Patent Publication No. 2010-0052726, in which rare-earth hydroxide cation layers and charge anion exchangeable chloride anion layers are alternately laminated.

The basic aqueous solution is preferably an aqueous solution of sodium hydroxide or potassium hydroxide and preferably has a pH of about 13 for RE = Sm, Eu, Gd or Tb and preferably has a pH of about 14 for RE = Dy and Er or Y.

The layered structure of the rare earth hydroxide of the present invention can be dispersed well in water to form a stable colloidal solution.

Thus, on the other hand, the present invention relates to an aqueous colloidal solution containing rare earth hydroxide nanosheets.

The aqueous colloidal solutions according to the invention exhibit excellent stability in physiological environments at low pH.

On the other hand, the present invention relates to a process for producing an aqueous colloidal solution containing a rare earth hydroxide nano-sheet,

(i) Recl ₃ pH ₂ O (p = 4-8) was added to the first basic aqueous solution and reacted at room temperature to obtain a slurry of RE ₂ (OH) ₅ Cl mH ₂ O (m = 0.5-4) step;

(ii) reacting the RE ₂ (OH) ₅ Cl mH ₂ O slurry in a second basic aqueous solution at room temperature to obtain a layered RE (OH) ₃ .nH ₂ O (n = 0.5-2) slurry ; And

(iii) dispersing the layered RE (OH) ₃ .nH ₂ O slurry in water.

Preferably, the first and second basic aqueous solutions are aqueous solutions of sodium hydroxide or potassium hydroxide and the second basic solution has a pH of about 13 for RE = Sm, Eu, Gd or Tb, and RE = Dy, Er or Y It is preferable that the pH is about 14.

According to the production method of the present invention, a stable aqueous colloidal suspension containing rare-earth hydroxide nanosheets can be mass-produced simply at room temperature and atmospheric pressure.

The layered RE (OH) ₃ .nH ₂ O according to the present invention can decompose at a low temperature (< 500 ° C) to produce RE ₂ O ₃ and can be used for thin film deposition of rare earth oxides. By performing a layer-by-layer deposition process using a colloid solution containing the pure RE (OH) ₃ .nH ₂ O nanosheets and producing RE ₂ O ₃ at low temperatures, the high- k gate Can be used to produce high quality thin films for optoelectronic devices such as dielectrics, waveguides and high resolution X-ray image detectors at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically showing the structure of a layered structure of (a) conventional h-RE (OH) ₃ and (b) RE (OH) ₃ .nH ₂ O according to an embodiment of the present invention.

As shown in FIG. 1, the hexagonal structure of the rare earth hydroxides including h-Gd (OH) ₃ is composed of metal atoms that are tri-capped trigonal prism bonded by hydroxide ions, The crystal is perpendicular to the hexagonal axis. On the other hand, the structure of RE (OH) ₃ · nH ₂ O generated after a topotactic exchange reaction between Cl ^- and OH ^- ions occurs in the interlayer gallery of RE ₂ (OH) ₅ Cl · mH ₂ O, (I. E., A typical layered structure with intercalated water molecules). Due to the close structural relationship, the 8 (green) - and 9 (blue) -coordinated polyhedra in the layer are connected by an intra-layer μ ₃ -OH group. The inter-OH group can be stabilized by hydrogen bonding to the hydroxide layers.

The layered structure of rare earth hydroxides according to the present invention is well dispersed in water and stable in low pH physiological suspension and can be used for biomedical applications such as contrast agents and imaging agents, Can also be used. In addition, according to the production method of the present invention, a stable aqueous colloidal solution containing a rare earth hydroxide nanosheet can be produced at room temperature in a simple, economical, and environmentally friendly manner.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically showing the structure of a layered structure of (a) conventional h-RE (OH) ₃ and (b) RE (OH) ₃ .nH ₂ O according to an embodiment of the present invention.
FIG. 2 is a graph showing the results of (a) Gd ₂ (OH) ₅ Cl mH ₂ O and pH = (b) 8, (c) 9, Gd ₂ in an aqueous solution (OH) ₅ Cl · mH ₂ O after the reaction of the product and (h) close political Gd (OH) ₃ is the XRD pattern.
Figure 3 is a XRD pattern of the _{RE 2 (OH) 5 Cl ·} mH RE 2 eseo ₂ O and an aqueous solution of different pH (OH) ₅ Cl · mH product after the ₂ O reaction (RE = (a) Sm, (b) Eu, (c) Tb, (d) Dy, (e) Er and (f) Y).
Figure 4 shows the reaction product of (a) Gd ₂ (OH) ₅ Cl · mH ₂ O, (b) Gd ₂ (OH) ₅ Cl · mH ₂ O in aqueous solution with pH = 13 and (c) h- OH) ₃ .
Figure 5 _{(a) Gd 2 (OH)} 5 Cl · 1.5H 2 O , and (b) of the layered structure, Gd (OH) ₃ · SEM image of H ₂ O and (c) of the layered structure Gd (OH) ₃ · H ₂ O.
Figure 6 _{(a) Gd 2 (OH)} 5 Cl · 1.5H 2 O, (b) a layered structure of _{Gd (OH) 3 · H 2} O , and (c) FT-IR spectrum of the close political Gd (OH) ₃ to be.
7 is an XRD pattern of a slurry of (a) Gd ₂ (OH) ₅ Cl _1.5 H ₂ O and (b) layered Gd (OH) ₃ .H ₂ O slurry.
Figure 8 is an FE-SEM image of a slurry of (a) Gd ₂ (OH) ₅ Cl _1.5 H ₂ O and (b) layered Gd (OH) ₃ .H ₂ O slurry.
9 is a photograph of a Gd (OH) ₃ .H ₂ O slurry having a layered structure dispersed in a phthalate buffer having pH = 3 and irradiated with laser after 1 hour, 2 hours, 4 hours and 12 hours.
10 is a photograph (RE = (a) Sm, (b) Eu, (c) Tb (c)) of a layered RE (OH) ₃ .H ₂ O slurry dispersed in water and irradiated with laser after one month , (d) Dy, (e) Er and (f) Y).

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are for illustrative purpose only and that the scope of the present invention is not limited to these embodiments.

Production Example 1: RE ₂ (OH) ₅ Cl · mH ₂ Preparation of O (RE = Sm, Eu, Gd, Tb, Dy, Er or Y)

RECl ₃ 6H ₂ O (10 mmol) and KOH (20 mmol) were dissolved in deionized water (40 mL), respectively. The KOH solution was then added dropwise to the RECl ₃ .6H ₂ O solution with vigorous stirring at room temperature. The resulting mixture (80 mL) was placed in a 100 mL stainless steel autoclave lined with Teflon at room temperature. The autoclave was then sealed and held at 130-150 [deg.] C for 12 hours. The solution was continuously stirred during the hydrothermal treatment. After the reaction was completed, the RE ₂ (OH) ₅ Cl · mH ₂ O solid product was collected by filtration, washed with distilled water and dried at 40 ° C. for one day.

Example 1: Preparation of layered RE (OH) ₃ · NH ₂ Preparation of O (RE = Sm, Eu, Gd, Tb, Dy, Er or Y)

Solutions of pH = 8, 9, 10, 11, 12, 13 and 14 were prepared by dissolving NaOH in water. The RE ₂ (OH) ₅ Cl · mH ₂ O crude powder obtained in Production Example 1 was dispersed in an aqueous solution at a different pH. After the mixture was stirred at room temperature for 12 hours, the resulting precipitate was collected by filtration, washed with a sufficient amount of water to remove the residual salt, and dried at 40 DEG C for a day.

Experimental Example 1: X-ray diffraction analysis

X-ray diffraction (XRD) experiments were conducted to demonstrate the conversion of RE ₂ (OH) ₅ Cl · mH ₂ O in a high pH aqueous solution.

(A) Gd ₂ (OH) ₅ Cl mH ₂ O obtained in Production Example 1 and the pH obtained in Example 1 = (b) 8, (c) 9, f) The XRD pattern for the reaction product of Gd ₂ (OH) ₅ Cl · mH ₂ O in aqueous solutions of 12 and (g) 13 and (h) the Gd (OH) ₃ (Alfa-Aesar Co.) Respectively.

Further, the reaction product of RE ₂ (OH) ₅ Cl · mH ₂ O in an aqueous solution of another RE ₂ (OH) ₅ Cl · mH ₂ O obtained in Production Example 1 and an aqueous solution of another pH obtained in Example 1, XRD The pattern is shown in Fig. In FIG. 3, RE = (a) Sm, (b) Eu, (c) Tb, (d) Dy, (e) Er and (f) Y.

A strong (00 l) reflection (reflection) of a _{Gd 2 (OH) 5 Cl ·} mH 2 O precursor obtained in Production Example 1 is that a typical layer structure of 8.76 Å basic interval. As shown in Figures 2 (a) -2 (e), the XRD pattern of Gd ₂ (OH) ₅ Cl · mH ₂ O did not change after the reaction at pH = 8-11. When the pH of the aqueous solution reached about 12, the intensity of the (00 l ) reflection began to decrease, while a new reflection peak appeared at about 2? = 11.4 占 (Fig. 2 (f)). The (00 l ) reflections of Gd ₂ (OH) ₅ Cl · mH ₂ O ultimately disappeared at pH = 13 (FIG. 2 (g)). Instead, a significant change in the diffraction pattern in a strong increase, and higher angle peak at 11.4 ° was generated a new set of (00 l) reflection, which suggests the formation of a distinct layered structure of the ~ 7.75 Å distance between layers. This new phase XRD pattern obtained at pH = 13 was significantly different from that of h-Gd (OH) ₃ (Fig. 2 (h)).

A similar change in RE ₂ (OH) ₅ Cl mH ₂ O was consistently observed at pH = 13 for RE = Sm-Tb and at RE = Dy for Er = Y and at pH = 14 for Y (FIG. Complete or partial deformation to the h-RE (OH) ₃ phase was not induced in a high pH aqueous solution at room temperature.

From the above results, it was confirmed that the formation of the layered structure of RE (OH) ₃ .nH ₂ O and the interlayer spacing change due to the exchange reaction between Cl ^- and OH ^- anions.

Experimental Example 2: Ion Chromatography and Thermogravimetric Analysis

The ion chromatography (IC) on the product after reaction in the high pH solution obtained in Example 1 showed substantially no Cl ^- (<10 ^-4 M / g). If the Cl ^- ion is completely exchanged by OH ^- ions in the gallery of Gd ₂ (OH) ₅ Cl · mH ₂ O, the formula for the product obtained at pH = 13 is Gd (OH) ₃ · nH ₂ O (ie Gd ₂ (OH) ₅ OH 2nH ₂ O).

In order to analyze the difference in composition between Gd ₂ (OH) ₅ Cl · mH ₂ O obtained in Production Example 1 and Gd (OH) ₃ · nH ₂ O obtained in Example 1, a thermogravimetric (TG) Lt; RTI ID = 0.0 &gt; 1100 C. &lt; / RTI &gt; (a) Gd ₂ (OH) ₅ Cl mH ₂ O, (b) the product obtained after the reaction of Gd ₂ (OH) ₅ Cl · mH ₂ O in an aqueous solution of pH = 13 and (c) h- ₃ is shown in Fig.

The weight loss of 6.27 and 7.30% observed at less than 200 ° C in Figures 4 (a) and 4 (b) is Gd ₂ (OH), respectively, considering water and variable amounts of intercalated water that may be adsorbed on the particle surface. ₅ · 1.5H ₂ O and from Cl _{Gd (OH) 3 · H 2} O ( _{i.e., Gd 2 (OH) 5 OH} · 2.0H 2 O) dehydration Gd ₂ (OH) ₅ Cl and to Gd (OH) ₃ in Which is similar to the calculated loss of 5.85 and 7.96%. The total ignition loss of 22.05% and 20.20% observed were similar to the calculated losses of 21.54 and 19.90%, respectively, and were consistent with the above compositions, as the Gd ₂ O ₃ oxide was formed when the product was heated above 500 ° C.

Experimental Example 3: Scanning Electron Microscopy and Electron Diffraction Analysis

(a) Preparation by Gd ₂ obtained in _{1 (OH) 5 Cl · 1.5H} 2 O precursor and (b) Gd embodiment of the layer structure obtained in 1 (OH) ₃ · Scanning electron microscopy analysis of the H ₂ O ( scanning electron microscopy (SEM) image and (c) electron diffraction (ED) patterns of the layered structure Gd (OH) ₃ .H ₂ O obtained in Example 1 are shown in FIG.

The SEM images of Figures 5 (a) and 5 (b) show that while the plate morphology is maintained after the conversion of Gd ₂ (OH) ₅ Cl · 1.5H ₂ O to Gd (OH) ₃ · H ₂ O, , And particle size reduction may be due to breakage by ion exchange in the interlayer gallery.

As shown in FIG. 5 (c), the ED pattern of Gd (OH) ₃ .H ₂ O shows distinct diffraction points suggesting a rectangular ab -plane arrangement in the reciprocal lattice. This provides evidence that the _{Gd (OH) 3 · H 2} O in the layer structure has a layered structure similar to the _{Gd 2 (OH) 5 Cl ·} 1.5H 2 O precursor of orthorhombic symmetry, which is the precursor hydroxy chloride Meaning that the structural skeleton is retained after the exchange reaction at high pH. 400, 200 and (040) lattice parameters of a = 12.83 (3) Å and b = 7.24 (9) Å calculated from the characteristic points corresponding to the diffraction of more that is observed in the XRD pattern (hkl) So that the reflection can be indexed.

Experimental Example 4: Infrared spectroscopic analysis

To further determine the structural similarities between a layer structure of the _{Gd (OH) 3 · H 2} O obtained in Production Example 1 Gd ₂ (OH) obtained in the embodiment ₅ Cl · 1.5H ₂ O Example 1, their FT- The IR spectrum is shown in Fig. 6 in comparison with the closely packed Gd (OH) ₃ .

Generally, since the stretching vibration mode of the hydroxyl group is observed at 3000-4000 cm ^-1 in the inorganic medium, a wide band composed of fine structures near 3000-3700 cm ^-1 is formed by the intramolecular hydroxyl groups and intermolecular water molecules OH stretching vibration. Based on the structural considerations of Gd ₂ (OH) ₅ Cl mH ₂ O, the three bands (~ 3611, 3574 and 3494 cm ^-1 ) and the broad band near 3335 cm ^-1 in Figure 6 Were assigned to stretching vibrations of μ ₃ -OH bonds and hydrogen-bonded intercalated water molecules in layers of different environments, respectively. In Fig. 6 (b), the layered Gd (OH) ₃ .H ₂ O shows a similar three-branched band and the fine structure was observed at slightly higher wavenumbers, ~ 3650, 3611 and 3547 cm ^-1 . In addition, a broad band centered at 3335 cm ^-1 was observed, consistent with the presence of interlayer water molecules.

On the other hand, the FT-IR spectrum of h-Gd (OH) ₃ shown in FIG. 6 (c) is completely different from Gd (OH) ₃ .H ₂ O according to the present invention. The strong and sharp band at 3611 cm ^-1 corresponds to fingerprint OH vibrations of hexagonal rare-earth hydroxides. A fine structure was not observed near the band, and a band associated with interlayer water molecules was not observed near 3335 cm ^-1 .

IR spectrum of the _{Gd (OH) 3 · H 2} O according to the invention was similar to the h-Gd (OH) ₃ and different from one _{Gd 2 (OH) 5 Cl ·} 1.5H 2 O, which for Gd (OH) ₃ Thereby supporting the layered structure.

Example 2: Preparation of the colloidal solution containing a layered structure _{RE (OH) 3 · n H} 2 O

KOH solution was added dropwise with (0.1 M) the RECl ₃ · stirred vigorously at room temperature for 6H ₂ O solution (0.05 M) and recovered by After stirring for 12 hours, the centrifugation precipitate (4000 rpm) and washed with water several times . The resulting slurry of RE ₂ (OH) ₅ Cl · mH ₂ O (10 g / L) was sonicated in aqueous NaOH (1.0 M) and maintained at room temperature for 12 hours with vigorous stirring. The layered RE (OH) ₃ .nH ₂ O slurry was recovered by repeated centrifugation (4000 rpm) and washed several times with water to completely remove Na ⁺ and Cl ^- ions.

Experimental Example 5: X-ray diffraction analysis

Example 2 exhibited a Gd ₂ (OH) XRD pattern of ₅ Cl · 1.5H ₂ O slurry and the layer structure _{Gd (OH) 3 · H 2} O in the slurry obtained in the FIG. The XRD pattern of the Gd ₂ (OH) ₅ Cl 1.5H ₂ O slurry compared to the bulk powder prepared in the hydrothermal conditions of Preparation Example 1 (see FIG. 2) is broad due to the preferred orientation of the nanosheets synthesized in a room temperature aqueous solution (00 l ) reflections and non-(00 l ) reflections. After the reaction in aqueous solution of NaOH (1.0 M) (00 l) reflection is larger diffraction is that each move as a whole similar to the case of the bulk powder which is manufactured by hydrothermal conditions, Gd (OH) of the layer structure ₃ · H ₂ therefrom O slurry could be confirmed.

Experimental Example 6: Scanning Electron Microscopy Analysis

Example 2 A layered structure Gd (OH) ₃ · H ₂ O slurry of Gd (OH) ₃ · the shape and size of the field emission scanning electron microscopy of H ₂ O of the obtained in (field emission scanning electron microscopy: FE -SEM) Lt; / RTI &gt; Figure 8 shows that the lateral size of the irregular Gd (OH) ₃ .H ₂ O nanosheet is less than 100 nanometers. Compared to the 100-200 nanometer Gd ₂ (OH) ₅ Cl _1.5 H ₂ O precursor slurry, the reduced lateral size is due to breakage or cracking of the sheet during the hydroxide ion exchange process.

Experimental Example 7: Evaluation of stability of aqueous colloid solution

A vigorous shaking of the aqueous solution containing the layered Gd (OH) ₃ .H ₂ O slurry obtained in Example 2 produced a translucent suspension which was similar to the Gd ₂ (OH) ₅ Cl 1.5H ₂ O slurry . As shown in Fig. 9, laser irradiation of the suspension showed a tin-dal effect, which supports the presence of abundant nanosheets dispersed in water.

The 1.0 g / L aqueous colloidal solution was stable for more than one month. When the suspension was diluted to 0.5 g / L, precipitation was not detected even after 2 months.

A, embodiments Gd ₂ obtained in _{2 (OH) 5 Cl · Gd} (OH) 3 · nH 2 O The slurry (20 mg) of mH ₂ O, and the layered structure in order to test the stability of the colloidal suspension in acidic solutions each pH = 2, 3, 5, 6 phthalate buffer (20 mL) and stirred at room temperature. After 1 hour, a small amount of suspension was collected and centrifuged to remove Gd ₂ (OH) ₅ Cl mH ₂ O and Gd (OH) ₃ .nH ₂ O solids. The amount of Gd in the supernatant was measured by inductively coupled plasma (ICP) analysis.

The slurries did not show an identifiable dissolution at pH > 6 but were readily dissolved as soon as mixed at pH ~ 2.

In addition, about 50% of Gd ³⁺ ions were released from Gd ₂ (OH) ₅ Cl 1.5H ₂ O within 1 hour by dissolving at pH = 3. On the other hand, Gd (OH) ₃ · colloidal solution of H ₂ O slurry was emitting Gd ³⁺ ions of less than 15% within one hour at pH = 3.0.

As shown in Figure 9, a strong tin-dal effect was observed after 4 hours at pH = 3, which means improved stability in low pH environments compared to Gd ₂ (OH) ₅ Cl _1.5 H ₂ O colloid.

10, this stability of the aqueous colloid solution is similar for RE (OH) ₃ .nH ₂ O slurries containing other rare earths other than Gd (RE = Sm, Eu, Tb, Dy, Er or Y) Respectively.

Claims (10)

A layered structure of rare earth hydroxides of the formula (I)
_{RE (OH) 3 · nH 2} O (I)
In this formula,
RE is rare earth,
n is from 0.5 to 2. The compound according to claim 1, wherein RE is Sm, Eu, Gd, Tb, Dy, Er or Y, n is 1 to 1.5 &Lt; / RTI &gt; the layered structure of rare earth hydroxides. The layered structure of rare earth hydroxide according to claim 1, wherein the layered structure of rare earth hydroxide is a layered structure having intercalated water molecules. A process for preparing a layered structure of rare earth hydroxide represented by the following formula (I) comprising reacting a rare earth hydroxychloride of the following formula (II) in a basic aqueous solution at a room temperature:
RE ₂ (OH) ₅ Cl mH ₂ O (II)
_{RE (OH) 3 · nH 2} O (I)
In this formula,
RE is rare earth,
m is from 0.5 to 4,
n is from 0.5 to 2. 5. The process according to claim 4, wherein the basic aqueous solution is an aqueous solution of sodium hydroxide or potassium hydroxide. The process according to claim 4, wherein the pH of the basic aqueous solution is 13 for RE = Sm, Eu, Gd or Tb, and 14 for RE = Dy, Er or Y. An aqueous colloidal solution containing a layered structure of rare earth hydroxides according to any one of claims 1 to 3. (i) Recl ₃ pH ₂ O (p = 4-8) was added to the first basic aqueous solution and reacted at room temperature to obtain a slurry of RE ₂ (OH) ₅ Cl mH ₂ O (m = 0.5-4) step;
(ii) reacting the RE ₂ (OH) ₅ Cl mH ₂ O slurry in a second basic aqueous solution at room temperature to obtain a layered RE (OH) ₃ .nH ₂ O (n = 0.5-2) slurry ; And
(iii) method of an aqueous colloidal solution containing a rare-earth hydroxide nanosheet comprising the steps of dispersing the _{RE (OH) 3 · nH 2} O slurry of the layered structure in the water. The process according to claim 8, wherein the first and second basic aqueous solutions are aqueous solutions of sodium hydroxide or potassium hydroxide. The process according to claim 8, wherein the pH of the second basic aqueous solution is 13 for RE = Sm, Eu, Gd or Tb and 14 for RE = Dy, Er or Y.

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