Alkali metal-rare earth carbonate functional material as well as preparation method and application thereof

Abstract

The invention discloses an alkali metal-rare earth carbonate functional material as well as a preparation method and application thereof. The inorganic rare earth carbonate functional material is prepared through a normal-temperature soaking method, hydrothermal conditions such as high temperature and high pressure are not needed, additives are not needed, the production cost is low, the number of preparation procedures is small, the production efficiency is greatly improved, and the purity of the prepared functional material is high. The inorganic rare earth carbonate functional material obtained by the invention has nonlinear optical performance and has a second harmonic effect with certain strength. The inorganic rare earth carbonate functional material obtained by the invention is a fibrous whisker, and has high length-diameter ratio and flexibility. The functional material can be used for fluorescence detection, anti-counterfeiting, phosphate adsorption removal, papermaking or filler for high polymer materials.

Description

Technical Field

[0001] The present invention belongs to the field of inorganic materials, and in particular relates to an alkali metal-rare earth carbonate functional material and a preparation method and application thereof. Background Art

[0002] Rare earth (Ln) ions may exist in the form of various complex ions in alkali metal carbonate solutions, such as LnCO3 + 、Ln(CO3) 2- 、Ln(CO3)3 3- or Ln(CO3)4 5- Therefore, when carbonate precipitation is generated, a variety of rare earth carbonate materials may be formed, such as Ln2(CO3)3·xH2O, NaLn(CO3)2·xH2O, or Na4Ln2(CO3)5. Among them, the alkali metal-rare earth carbonate Na3Ln(CO3)3·6H2O is a potential nonlinear optical crystal material due to its non-centrosymmetric space group.

[0003] The structure of the rare earth element yttrium-containing Na3Ln(CO3)3·6H2O compound, Na3Y(CO3)3·6H2O, has been reported. Na3Y(CO3)3·6H2O was first discovered as a mineral and named Adamsite-(Y). In 2004, Amor Ben Ali et al. (Hydrothermal synthesis, crystal structure, thermal behavior, IR and Raman spectroscopy of Na3Y(CO3)3·6H2O", Comptes Rendus Chimie (2004), 6-7 (2004): 661-668) reported a hydrothermal synthesis method for the alkali metal-rare earth yttrium carbonate Na3Y(CO3)3(H2O)6. This method uses Na2CO3\YF3\H2O with a molar ratio of 25:1:55 as raw materials and undergoes high-temperature hydrothermal growth at 220°C for 120 hours to prepare Na3Y(CO3)3(H2O)6. This method has high requirements for reaction energy consumption and equipment. On the other hand, apart from the rare earth element yttrium, alkali metal-rare earth carbonates Na3Ln(CO3)3(H2O)6 of other rare earth elements have not been reported.

[0004] Currently, the preparation of other reported alkali metal-rare earth carbonates (such as Na8Lu2(CO3)6F2 and Na4La2(CO3)5) is similar to that of Na3Y(CO3)3·6H2O, requiring a long (120 hours) high-temperature hydrothermal reaction (220°C). Furthermore, the preparation of some alkali metal-rare earth carbonates requires the addition of fluoride, resulting in impurities in the final product and difficulty in purification. In summary, existing alkali metal-rare earth carbonate preparation methods have disadvantages such as harsh reaction conditions, high equipment requirements, and uncontrollable product purity. Summary of the Invention

[0005] In order to improve the above technical problems, the present invention provides a method for preparing alkali metal-rare earth carbonate functional material Na3Ln(CO3)3·xH2O by immersion method under normal temperature and normal pressure conditions. The method has mild reaction conditions and does not require special equipment. It can be used to prepare a single-phase alkali metal-rare earth carbonate functional material Na3Ln(CO3)3·xH2O, which has nonlinear optical properties and second harmonic effect, and can be used in fluorescence detection, anti-counterfeiting, adsorption and removal of phosphate and other fields.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing an alkali metal-rare earth carbonate functional material, comprising the following steps:

[0008] 1) Preparing a soaking solution: preparing an alkali metal carbonate solution as a soaking solution;

[0009] 2) Raw material pretreatment: The raw material is rare earth carbonate hydrate or alkali metal rare earth dicarbonate powder, and the pretreatment includes drying the raw material;

[0010] 3) Reaction: soaking the pretreated raw material obtained in step 2) in the soaking solution of step 1), ultrasonically dispersing, standing and reacting to obtain the alkali metal-rare earth carbonate functional material.

[0011] According to an embodiment of the present invention, in step 1), the concentration of the alkali metal carbonate solution (in terms of carbonate ion concentration) is 0.5 to 3.0 mol / L, exemplified by 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L or 3.0 mol / L.

[0012] In the present invention, when the concentration of the alkali metal carbonate solution is within the range of 0.5 to 3.0 mol / L, an excess of alkali metal carbonate is ensured to remain after the system is completely precipitated, thereby promoting the reaction toward the formation of the alkali metal-rare earth carbonate functional material. Furthermore, the concentration of the alkali metal carbonate solution determines the morphology of the functional material: when a low concentration of the alkali metal carbonate solution is used, the resulting alkali metal-rare earth carbonate whiskers have a large radius, short length, and a low aspect ratio; whereas, when a high concentration of the alkali metal carbonate solution is used, the resulting alkali metal-rare earth carbonate whiskers have a small radius, long length, and a high aspect ratio.

[0013] According to an embodiment of the present invention, in step 1), the alkali metal is Li, Na, K or Rb; specifically, the alkali metal is Na.

[0014] According to an embodiment of the present invention, in step 1), the solvent in the alkali metal carbonate solution is water.

[0015] According to an embodiment of the present invention, in step 2), the chemical structural formula of the rare earth carbonate hydrate is Ln2(CO3)3·xH2O; wherein Ln represents a rare earth element, for example, at least one of samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), and yttrium (Y); and x represents the amount of water of crystallization, for example, it can be 2.

[0016] According to an embodiment of the present invention, in step 2), the rare earth carbonate hydrate may be prepared by mixing a rare earth salt with a carbonate solution for precipitation.

[0017] According to an embodiment of the present invention, in step 2), the chemical structural formula of the alkali metal rare earth bicarbonate is (MLn(CO3)2·xH2O; wherein, M represents an alkali metal such as Li, Na, K or Rb, preferably Na; Ln represents a rare earth element, for example, it can be at least one of samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), and yttrium (Y); x represents the amount of water of crystallization, for example, 6.

[0018] According to an embodiment of the present invention, in step 2), the alkali metal rare earth dicarbonate can be prepared by reacting a rare earth salt with an alkali metal carbonate.

[0019] In one embodiment of the present invention, the rare earth salt is selected from rare earth hydrochlorides, for example, it can be the hydrochloride of at least one of samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), and yttrium (Y).

[0020] Specifically, the alkali metal in the alkali metal carbonate is, for example, Li, Na, K or Rb, preferably Na.

[0021] In one embodiment of the present invention, the rare earth hydrochloride and the alkali metal carbonate are reacted in a solvent. For example, a rare earth salt solution and an alkali metal carbonate solution are first prepared separately, and then the two solutions are mixed.

[0022] In one embodiment of the present invention, the concentration of the rare earth salt solution is 0.5 to 3 mol / L, exemplified by 0.5 mol / L, 1 mol / L, 2 mol / L, and 3 mol / L.

[0023] In one embodiment of the present invention, the concentration of the alkali metal carbonate solution is 0.5 to 3 mol / L, exemplified by 0.5 mol / L, 1 mol / L, 2 mol / L, and 3 mol / L.

[0024] In one embodiment of the present invention, the mixing volume ratio of the rare earth salt solution to the alkali metal carbonate solution is 1:(1-3), exemplified by 1:1, 1:2, and 1:3.

[0025] In one embodiment of the present invention, the preparation method of the alkali metal rare earth bicarbonate is carried out under stirring conditions. For example, the stirring time can be 1 to 24 hours, exemplified by 1 hour, 2 hours, 6 hours, 10 hours, 12 hours, 18 hours, 20 hours, or 24 hours; the stirring temperature is 15 to 60°C, exemplified by 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or 60°C.

[0026] In one embodiment of the present invention, the method for preparing the alkali metal rare earth bicarbonate further comprises allowing the stirred reaction solution to stand. For example, the standing time can be 1 to 24 hours, exemplified by 1 hour, 2 hours, 6 hours, 10 hours, 12 hours, 18 hours, 20 hours, or 24 hours; and the standing temperature can be 15 to 60°C, exemplified by 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or 60°C.

[0027] In one embodiment of the present invention, the method for preparing the alkali metal rare earth dicarbonate further comprises performing solid-liquid separation on the reaction system after the reaction is completed to obtain the alkali metal rare earth dicarbonate. For example, the solid-liquid separation can be performed by methods known in the art, such as filtration.

[0028] In one embodiment of the present invention, the method for preparing the alkali metal rare earth bicarbonate further comprises washing the reaction product obtained by solid-liquid separation.

[0029] According to an embodiment of the present invention, in step 2), the solvents in the various solutions are the same or different, and can be independently selected from water, for example.

[0030] According to an embodiment of the present invention, in step 2), the drying temperature is 60-90°C, preferably 70-80°C, and exemplified by 60°C, 70°C, 80°C, and 90°C. Furthermore, the drying time is 12-24 hours, preferably 15-20 hours, and exemplified by 12 hours, 16 hours, 18 hours, 20 hours, 21 hours, and 24 hours. The purpose of pre-treating the raw materials is to remove free water molecules that may be contained in the raw materials to reduce weighing errors in subsequent steps.

[0031] According to an embodiment of the present invention, in step 3), the mass volume ratio of the raw material to the soaking liquid is (0.1-2) g:20 mL, exemplified by 0.1 g:20 mL, 0.2 g:20 mL, 0.25 g:20 mL, 0.5 g:20 mL, 0.8 g:20 mL, 1 g:20 mL, 1.5 g:20 mL or 2 g:20 mL. The inventors have found through a large number of experimental studies that when the mass volume ratio of the raw material to the soaking liquid is less than 0.1 g:20 ml, the alkali metal-rare earth carbonate functional material product obtained is too small; and when the mass volume ratio of the raw material to the soaking liquid exceeds 2 g:20 ml, the sample purity of the obtained alkali metal-rare earth carbonate functional material will be reduced. Within the above preferred mass volume ratio range, a high-purity alkali metal-rare earth carbonate functional material can be prepared.

[0032] According to an embodiment of the present invention, in step 3), the standing time is 1 to 30 days, exemplified by 2 days, 7 days, 15 days, and 30 days. The inventors have found through extensive experimental research that, under the premise of a certain mass volume ratio of raw materials to soaking liquid, the higher the concentration of the soaking liquid, the shorter the standing reaction time required.

[0033] According to an embodiment of the present invention, in step 3), the standing temperature is 15-60°C, exemplified by 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C or 60°C.

[0034] According to an embodiment of the present invention, step 3) further comprises: after the reaction is completed, performing solid-liquid separation on the reaction system to obtain the alkali metal-rare earth carbonate functional material. For example, the solid-liquid separation can be performed by means known in the art, such as filtration.

[0035] According to an embodiment of the present invention, in step 3), after solid-liquid separation, the reaction product obtained by solid-liquid separation is further subjected to a washing treatment. For example, the washing solvent may be acetone. For another example, the washing may be performed once, twice, or more times, preferably three times.

[0036] According to an embodiment of the present invention, step 3) further includes drying the washed reaction product. For example, the drying temperature is 60-90°C, preferably 70-80°C, and exemplified by 60°C, 70°C, 80°C, and 90°C. Furthermore, the drying time is 12-24 hours, preferably 15-20 hours, and exemplified by 12 hours, 15 hours, 18 hours, 20 hours, 21 hours, and 24 hours.

[0037] According to an embodiment of the present invention, the chemical formula of the alkali metal-rare earth carbonate functional material is M3Ln(CO3)3·xH2O, wherein M represents an alkali metal such as Li, Na, K or Rb; preferably Na; Ln represents a rare earth element, for example, it can be at least one of samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), and yttrium (Y); x represents the amount of crystal water, for example, it can be 6.

[0038] According to an embodiment of the present invention, the alkali metal-rare earth carbonate functional material is a whisker, specifically a fibrous whisker. The aspect ratio of the whisker-shaped alkali metal-rare earth carbonate functional material prepared by the present invention is adjustable.

[0039] According to an embodiment of the present invention, the alkali metal-rare earth carbonate functional material has nonlinear optical properties.

[0040] According to an embodiment of the present invention, the alkali metal-rare earth carbonate functional material has a second harmonic effect.

[0041] The present invention also provides the use of the alkali metal-rare earth carbonate functional material in fluorescence detection, anti-counterfeiting, adsorption and removal of phosphates, papermaking or fillers for polymer materials.

[0042] According to an embodiment of the present invention, the alkali metal-rare earth carbonate functional material can be used for nonlinear optical crystals, phosphors (for fluorescence detection or anti-counterfeiting); or, by controlling the product morphology, rare earth carbonate whiskers can be prepared for functional polymer fillers (mechanical enhancement, luminescence); or, for selective adsorption of phosphate; or, for enhancing paper strength (specifically, it can be used in combination with other organic fibers); and the like.

[0043] Beneficial effects of the present invention:

[0044] (1) The present invention adopts a room temperature immersion method to prepare the inorganic rare earth carbonate functional material, which has mild reaction conditions, simple preparation process, controllable operating conditions, and can be produced on a large scale.

[0045] (2) The present invention does not require hydrothermal conditions such as high temperature and high pressure, and does not require additives. It has low production costs and fewer preparation steps, which greatly improves production efficiency, and the prepared samples have high purity.

[0046] (3) The inorganic rare earth carbonate functional material with nonlinear optical properties that can be obtained by the present invention exhibits a second harmonic effect of a certain intensity.

[0047] (4) The inorganic rare earth carbonate functional material obtained by the present invention is a fibrous whisker with a high aspect ratio and flexibility. When Eu (europium) is used as a rare earth element, it appears white in sunlight and produces red fluorescence under ultraviolet light, thus being useful for anti-counterfeiting. It can also be used in combination with other organic fibers to effectively improve paper strength during papermaking.

[0048] (5) In addition to being used as a nonlinear optical crystal, the alkali metal-rare earth carbonate functional material Na3Ln(CO3)3·6H2O of the present invention can also be added to composite materials as whiskers. This is attributed to the fact that the naturally generated and artificially synthesized Na3Y(CO3)3(H2O)6 both have fibrous morphologies and a relatively large aspect ratio, making them suitable as alkali metal-rare earth carbonate whiskers. The alkali metal-rare earth carbonate functional material Na3Ln(CO3)3·6H2O whiskers of the present invention are widely used for filling composite materials, which can not only improve the strength and toughness of the material, but also improve the wear resistance and heat resistance of the composite material. At the same time, since rare earth ions have fluorescent properties, the alkali metal-rare earth carbonate functional material Na3Ln(CO3)3·6H2O whiskers containing rare earth elements of the present invention can also be used for fluorescence detection of substances, thereby further expanding the application range of the whiskers. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 These are the X-ray diffraction patterns of the inorganic rare earth carbonate functional materials obtained in Examples 1, 2, and 3.

[0050] Figure 2 The second harmonic effect intensity of the inorganic rare earth carbonate functional material prepared in Example 2.

[0051] Figure 3 (a) and (b) are photos of the inorganic rare earth carbonate functional material prepared in Example 3 under visible light irradiation; Figure 3 (c) is a photograph of the inorganic rare earth carbonate functional material prepared in Example 3 under ultraviolet light.

[0052] Figure 4 This is a field emission scanning electron microscope photograph of the inorganic rare earth carbonate functional material prepared in Example 1.

[0053] Figure 5This is a field emission scanning electron microscope photograph of the inorganic rare earth carbonate functional material prepared in Example 2.

[0054] Figure 6 This is a field emission scanning electron microscope photograph of the inorganic rare earth carbonate functional material prepared in Example 3. DETAILED DESCRIPTION

[0055] The technical solutions of the present invention will be described in further detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection that the present invention is intended to protect.

[0056] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0057] Example 1

[0058] A method for preparing an inorganic rare earth carbonate functional material using rare earth carbonate hydrate (Y2(CO3)3·xH2O) as a raw material, specifically comprising the following steps:

[0059] (1) Preparation of soaking solution: Prepare 3 mol / L Na2CO3 solution.

[0060] (2) Pretreatment of raw materials: The rare earth carbonate hydrate (Y2(CO3)3·xH2O) raw material was placed in a vacuum drying oven at 60°C and dried for 4 h.

[0061] (3) Preparation reaction process. Weigh 0.5 g of the rare earth carbonate hydrate (Y2(CO3)3·xH2O) pretreated in step (2) into a 20 mL sample bottle, then add 20 mL of the 3 mol / L sodium carbonate solution prepared in step (1), and sonicate for 5 minutes to disperse the bulk powder solid.

[0062] (4) After the sample bottle was left to stand at 45°C for 3 days, it was filtered, rinsed with acetone three times, and dried at 60°C for 24 hours to obtain the inorganic rare earth carbonate functional material Na3Y(CO3)3·6H2O.

[0063] Example 2

[0064] A method for preparing an inorganic rare earth carbonate functional material using rare earth carbonate hydrate (Ln2(CO3)3·xH2O) as a raw material, specifically comprising the following steps:

[0065] (1) Preparation of soaking solution: Prepare 1 mol / L Na2CO3 solution.

[0066] (2) Pretreatment of raw materials: The raw material of rare earth carbonate hydrate (Tb2(CO3)3·xH2O) was dried in a vacuum drying oven at 60°C for 4 h.

[0067] (3) Preparation reaction process. Weigh 0.25 g of the rare earth carbonate hydrate (Tb2(CO3)3·xH2O) pretreated in step (2) into a 20 mL sample bottle, then add 20 mL of the 1 mol / L sodium carbonate solution prepared in step (1) and sonicate for 5 minutes to disperse the bulk powder solid.

[0068] (4) After the sample bottle was left to stand at room temperature for 7 days, it was filtered, rinsed with acetone three times, and dried at 90°C for 12 hours to obtain the inorganic rare earth carbonate functional material Na3Tb(CO3)3·6H2O.

[0069] Example 3

[0070] A method for preparing an inorganic rare earth carbonate functional material using alkali metal rare earth bicarbonate hydrate (NaLn(CO3)2·xH2O) as a raw material accelerates the reaction rate by reducing the reaction process, ultimately producing a fibrous inorganic rare earth carbonate functional material with a high aspect ratio. Specifically, the method includes the following steps:

[0071] (1) Preparation of raw materials. Alkali metal-rare earth double carbonate hydrate (NaEu(CO3)2·xH2O) raw materials were prepared by controlling the reaction ratio of rare earth carbonate and sodium carbonate.

[0072] 100 mL of a 0.5 mol / L rare earth chloride EuCl3 solution and 200 mL of a 0.5 mol / L sodium carbonate solution were prepared respectively, and the prepared sodium carbonate solution was added to the rare earth chloride EuCl3 solution, stirred for 24 h, allowed to stand for 24 h, filtered, washed, and dried to obtain an alkali metal rare earth dicarbonate hydrate (NaEu(CO3)2·xH2O) raw material.

[0073] (2) Preparation of soaking solution: Prepare 1 mol / L sodium carbonate solution.

[0074] (3) Preparation reaction process. Weigh 0.5 g of dried alkali metal rare earth dicarbonate hydrate (NaEu(CO3)2·xH2O) into a 20 mL sample bottle, then add 20 mL of the 1 mol / L sodium carbonate solution prepared in step (2) and sonicate for 5 minutes to disperse the bulk powder solid.

[0075] (4) After the sample bottle was left to stand at room temperature for 5 days, it was filtered, rinsed with acetone three times, and dried at 80° C. for 16 h to obtain an inorganic rare earth carbonate functional material.

[0076] Figure 1The XRD patterns of the inorganic rare earth carbonate functional materials obtained in Examples 1, 2, and 3 are shown. As can be seen from the figures, the present invention utilizes simple room temperature reaction conditions, using only rare earth carbonates or alkali metal rare earth dicarbonates as raw materials to obtain high-purity alkali metal-rare earth carbonate functional materials through soaking. The reaction process eliminates the need for additives, modifiers, surfactants, and other additives that can easily introduce impurities, and also avoids the use of high-temperature, high-pressure hydrothermal conditions.

[0077] Figure 2 The second harmonic effect intensity of the inorganic rare earth carbonate functional material prepared in Example 2. As can be seen from the figure, the present invention utilizes rare earth carbonates that lack second harmonic effect intensity to prepare the alkali metal-rare earth carbonate Na3Tb(CO3)3·6H2O functional material through an in-situ soaking reaction. Its second harmonic effect intensity is 0.5 times that of the standard sample KDP.

[0078] Figure 3 (a) and (b) are actual pictures of the inorganic rare earth carbonate functional material sample prepared in Example 3 under visible light conditions. It can be seen from the pictures that the inorganic rare earth carbonate functional material is white under visible light. Figure 3 (c) is a sample picture of the inorganic rare earth carbonate functional material prepared in Example 3 under a 254nm ultraviolet lamp. It can be seen from the picture that the inorganic rare earth carbonate functional material emits red fluorescence under ultraviolet light.

[0079] Figure 4 、 5 Figures 6 and 7 are field emission scanning electron micrographs of the inorganic rare earth carbonate functional materials prepared in Examples 1, 2, and 3, respectively. Comparison reveals that by controlling the conditions and raw material types in the preparation method, alkali metal-rare earth carbonate materials with different aspect ratios can be obtained. Therefore, the controllable preparation of alkali metal rare earth carbonate whiskers with different aspect ratios can be achieved by regulating the conditions and parameters in the preparation method.

[0080] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A method for preparing an alkali metal-rare earth carbonate functional material, characterized in that: The method comprises the following steps: 1) Preparing a soaking solution: preparing an alkali metal carbonate solution as a soaking solution; 2) Raw material pretreatment: The raw material is rare earth carbonate hydrate or alkali metal rare earth dicarbonate powder, and the pretreatment includes drying the raw material; 3) Reaction: soaking the pretreated raw material obtained in step 2) in the soaking solution of step 1), ultrasonically dispersing, standing and reacting to obtain the alkali metal-rare earth carbonate functional material.

2. The preparation method according to claim 1, wherein In step 1), the concentration of the alkali metal carbonate solution is 0.5 to 3 mol / L; Preferably, in step 1), the alkali metal is Li, Na, K or Rb.

3. The preparation method according to claim 1 or 2, wherein In step 2), the drying temperature is 60-90° C.; preferably, the drying time is 12-24 hours.

4. The preparation method according to any one of claims 1 to 3, characterized in that: In step 2), the chemical formula of the rare earth carbonate hydrate is Ln2(CO3)3·xH2O; wherein Ln represents a rare earth element, preferably at least one of samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), and yttrium (Y); and x represents the amount of crystal water; Alternatively, in step 2), the chemical structural formula of the alkali metal rare earth bicarbonate is MLn(CO3)2·xH2O; wherein M represents an alkali metal such as Li, Na, K or Rb; Ln represents a rare earth element, preferably at least one of samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), and yttrium (Y); and x represents the amount of water of crystallization.

5. The preparation method according to any one of claims 1 to 4, characterized in that In step 2), the rare earth carbonate hydrate is prepared by mixing a rare earth salt with a carbonate solution and precipitating the mixture; Alternatively, the alkali metal rare earth dicarbonate is prepared by reacting a rare earth salt with an alkali metal carbonate.

6. The preparation method according to any one of claims 1 to 5, characterized in that In step 3), the mass volume ratio of the raw material to the soaking liquid is (0.1-2) g:20 mL. Preferably, in step 3), the standing time is 1 to 30 days. Preferably, in step 3), the standing temperature is 15-60°C.

7. An alkali metal-rare earth carbonate functional material, which is prepared by the preparation method according to any one of claims 1 to 6.

8. The alkali metal-rare earth carbonate functional material according to claim 7, characterized in that: The chemical formula of the alkali metal-rare earth carbonate functional material is M3Ln(CO3)3·xH2O, wherein M represents an alkali metal such as Li, Na, K or Rb; Ln represents a rare earth element, such as at least one of samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), and yttrium (Y); and x represents the amount of crystal water, such as 6. Preferably, the alkali metal-rare earth carbonate functional material is a whisker, specifically, a fibrous whisker.

9. Use of the alkali metal-rare earth carbonate functional material according to claim 7 or 8 in fluorescence detection, anti-counterfeiting, adsorption and removal of phosphates, papermaking, or fillers for polymer materials.

10. The use according to claim 9, characterized in that The alkali metal-rare earth carbonate functional material is used for nonlinear optical crystals, phosphors (for fluorescence detection or anti-counterfeiting); or, by controlling the product morphology, rare earth carbonate whiskers can be prepared for use as functional polymer fillers (mechanical enhancement, luminescence); or, for selective adsorption of phosphate; or, for enhancing paper strength (specifically, can be used in combination with other organic fibers).

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