Rare earth boride nanometer material and preparation method and application thereof

Abstract

The invention discloses a rare earth boride nano material as well as a preparation method and application thereof. The phase state of the rare earth boride nano material is REB6 or REB4; the preparation method comprises the following steps: S1, respectively weighing a compound raw material containing an RE element and a compound raw material containing a B element; s2, adding an additive, and fully grinding; s3, reacting under the protection of inert gas; s4, after the reaction is finished, excessive methanol is added, centrifugal separation is performed after no bubbles emerge, and a precipitate A is reserved; s5, adding diluted hydrochloric acid for soaking, and performing centrifugal separation again to reserve a precipitate B; and S6, washing the precipitate B with deionized water, and drying to obtain the rare earth boride nano material. According to the preparation method disclosed by the invention, a normal-pressure and low-temperature preparation method is adopted, the pure-phase rare earth hexaboride nanocrystal can be obtained at normal pressure and the temperature as low as 300 DEG C, and no active metal elementary substance needs to be introduced in the preparation process.

Description

Technical Field

[0001] The present invention relates to a rare earth boride nanomaterial, a preparation method thereof and an application thereof, belonging to the technical field of nanomaterials. Background Art

[0002] Rare earth (RE) refers to 17 elements such as scandium (Sc), yttrium (Y) and lanthanide series. Its unique electronic structure endows it with rich optical, electrical and magnetic properties. Rare earth boride (REB 6 or REB 4 ) is a special type of rare earth compound, which has attracted extensive attention due to its unique properties such as high melting point, high hardness, chemical stability, magnetism, high-efficiency thermionic emission and surface plasmon resonance. The excellent properties of rare earth borides stem from their unique crystal structure, which consists of rare earth metal atoms embedded in a stable boron octahedron network, and there is a coexistence state of covalent bonds, ionic bonds and metallic bonds inside. However, although this structure endows the material with excellent properties such as high melting point and high hardness, it also greatly increases the difficulty of its preparation and regulation.

[0003] Patent CN113582190A discloses a multi-component rare earth boride nanopowder and a preparation method thereof, including the following steps: S1, using La 2 O 3 , RE 2 O 3 , B 2 O 3 and Ca as raw materials, mixing them evenly and pre-pressing them into blocks to obtain a block blank;

[0004] S2, placing the block blank in S1 in a vacuum or inert atmosphere for heating, with a predetermined heating temperature of 800-1000 °C, to prepare a multi-component rare earth boride reaction product; S3, washing the multi-component rare earth boride reaction product in S2 with acid and repeatedly washing it with pure water until it is neutral, filtering and drying it in vacuum to obtain a multi-component rare earth boride La 1-x RE x B 6 nanopowder, where 0 < X < 1. The calciothermic reduction process in the present invention reduces the formation probability of La 1-x RE x BO 3 compounds, improves the yield of rare earth hexaboride, and simplifies the purification process in the preparation of rare earth hexaboride by the magnesiothermic reduction method, improving the production efficiency. However, the above method has a high reaction temperature, high energy consumption, high requirements for equipment, and is not suitable for industrial production.

[0005] Traditional preparation methods usually require extremely high temperatures (over 1500°C) and high pressures, or the introduction of active metal elements as reducing agents and high temperatures. The reaction process consumes a lot of energy and is highly dangerous, and also places higher demands on the reaction equipment and post-processing processes. In addition, due to the extremely high hardness of rare earth borides, the crushing process of the materials becomes extremely difficult, and an effective method for preparing their nanomaterials has not yet been found. Therefore, the preparation of rare earth boride nanomaterials still faces huge challenges.

[0006] In view of the above problems, this application is specially filed. Summary of the invention

[0007] In view of the shortcomings of the prior art, the first object of the present invention is to provide a method for preparing rare earth boride nanomaterials.

[0008] The second object of the present invention is to provide rare earth boride nanomaterials prepared by the above method.

[0009] The third object of the present invention is to provide applications of the rare earth boride nanomaterials.

[0010] In order to achieve the first object, the present invention is implemented by the following technical scheme: a method for preparing a rare earth boride nanomaterial, wherein the phase state of the rare earth boride nanomaterial is REB 6 or REB 4 , wherein RE is selected from one of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; and the preparation method thereof comprises the following steps:

[0011] S1: Weighing a compound raw material containing the RE element and a compound raw material containing the B element respectively, with a molar ratio of 1:4-12, to obtain a mixed raw material;

[0012] S2: adding additives to the mixed raw material obtained in step S1, grinding thoroughly to obtain a mixture A, and then transferring the mixture A to a three-necked flask or a porcelain boat;

[0013] S3: reacting the mixture A obtained in step S2 under the protection of an inert gas, heating it with a heating jacket or a tubular furnace, controlling the reaction temperature to be 300-800° C., and the reaction time to be 6 hours, to obtain a mixture B;

[0014] S4: After the reaction is completed, excess methanol is added to the mixture B obtained in step S3, and centrifugation is performed after no bubbles emerge, and the precipitate A is retained;

[0015] S5: adding dilute hydrochloric acid to the precipitate A obtained in step S4 and soaking for 12 hours, and centrifuging again to retain the precipitate B;

[0016] S6: Wash the precipitate B obtained in step S5 with deionized water and dry it to obtain rare earth boride nanomaterials.

[0017] Preferably, the compound raw material containing RE element in step S1 includes anhydrous rare earth halide, and the compound raw material containing B element is alkali metal borohydride.

[0018] Preferably, the additive in step S2 is alkali metal halide, and the molar ratio of the additive to the mixed raw materials is 1:1.

[0019] Preferably, in step S3, the inert gas is nitrogen or argon, and the pressure of the system is one atmosphere.

[0020] Preferably, the concentration of the dilute hydrochloric acid in step S5 is 0.6 mol / L, and its purpose is to remove the oxides in the precipitate A.

[0021] Preferably, the centrifugation conditions in steps S4 and S5 are: rotation speed 8000 rpm, time 3 - 7 min.

[0022] Adopting the above technical solution, an excessive amount of methanol is added in step S4, and its purpose is to remove the active metals generated in the reaction; deionized water is used for washing in step S6, effectively removing soluble salts such as alkali metal halides. By adding molten salt, the chemical bonds in the boron source precursor can be weakened, so that the synthesis of rare earth borides can be carried out under mild conditions.

[0023] To achieve the second object, the present invention is realized through the following technical solution: A rare earth boride nanomaterial, whose phase state is REB 6 or REB 4 , the color is black or dark brown, the morphology is nearly spherical or cubic, and the diameter is less than 20 nm.

[0024] Adopting the above technical solution, the rare earth boride nanomaterial has local surface plasmon resonance characteristics and has good light absorption properties in the ultraviolet - visible - near infrared region. At the same time, the rare earth boride nanomaterial also has excellent photothermal properties, antibacterial properties and dye degradation properties.

[0025] The third object of the present invention is: The application of rare earth boride nanomaterials in heat insulation coatings, photocatalysis and solar water evaporation fields.

[0026] Preferably, the solar water evaporation includes seawater desalination, treatment of bacteria-containing wastewater and treatment of high-salt dye wastewater.

[0027] The beneficial effects of the present invention:

[0028] (1) The preparation conditions of the present invention are mild, requiring only normal pressure, and the reaction temperature is much lower than that of the traditional method; it has good universality and is applicable to all rare earth elements, and the product size can be controlled.

[0029] (2) The rare earth boride nanomaterial of the present invention has localized surface plasmon resonance properties, good light absorption properties in the ultraviolet-visible-near infrared region, and excellent photothermal properties, antibacterial properties and dye degradation properties, indicating that the material has the potential to be used as a photocatalyst and a light absorber in a solar water evaporation system.

[0030] (3) The preparation method provided by the present invention has the advantages of being simple, efficient, low energy consumption, low pollution, high yield, safe and reliable, and the prepared material has excellent performance. It can provide a reliable raw material supply for the application of rare earth functional materials related to optoelectronics, energy, and environmental protection, and has certain practical significance.

[0031] (4) The present invention adopts a normal pressure and low temperature preparation method, which can obtain pure phase rare earth hexaboride nanocrystals at normal pressure and a temperature as low as 300°C, and the preparation process does not require the introduction of any active metal element. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a transmission electron microscope photograph of the sample in Example 1 of the present invention;

[0033] Figure 2 is the X-ray powder diffraction pattern of the sample in Example 1 of the present invention;

[0034] Figure 3 is the UV-visible-near infrared absorption spectrum of the sample in Example 1 of the present invention;

[0035] Figure 4 is the X-ray powder diffraction pattern of the sample in Example 2 of the present invention;

[0036] Figure 5 is the X-ray powder diffraction pattern of the sample in Example 3 of the present invention;

[0037] Figure 6 is the X-ray powder diffraction pattern of the sample in Example 4 of the present invention;

[0038] Figure 7 is the X-ray powder diffraction pattern of the sample in Example 5 of the present invention;

[0039] Figure 8 is the X-ray powder diffraction pattern of the sample in Example 6 of the present invention;

[0040] Figure 9 is the X-ray powder diffraction pattern of the sample in Example 7 of the present invention;

[0041] Figure 10 is the X-ray powder diffraction pattern of the sample in Example 8 of the present invention;

[0042] Figure 11 is the X-ray powder diffraction pattern of the sample in Example 9 of the present invention;

[0043] Figure 12 is the transmission electron microscope photograph of the sample in Example 9 of the present invention;

[0044] Figure 13 is the X-ray powder diffraction pattern of the sample in Example 10 of the present invention;

[0045] Figure 14 is the transmission electron microscope photograph of the sample in Example 10 of the present invention;

[0046] Figure 15 is the photothermal conversion performance curve of the sample in Example 1 of the present invention;

[0047] Figure 16 is the solar evaporation performance curve of the sample in Example 1 of the present invention;

[0048] Figure 17 is the dye degradation performance curve of the sample in Example 1 of the present invention;

[0049] Figure 18 is the antibacterial performance photograph of the sample in Example 1 of the present invention. Detailed implementation manners

[0050] To make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific implementation manners.

[0051] Example 1 Preparation of rare earth boride nanomaterial LaB 6 of

[0052] S1: Mix 1 mmol of anhydrous lanthanum chloride and 8 mmol of sodium borohydride to obtain a mixed raw material;

[0053] S2: Add the mixed raw material to 9 mmol of alkali metal halide (the specific components and ratios are: LiI:LiCl:KI = 57.3:2.6:40.1), and grind thoroughly to obtain mixture A;

[0054] S3: Transfer mixture A to a three-necked flask, seal it, and heat it to 350 °C under the protection of N at one atmosphere 2 for 6 h to obtain mixture B;

[0055] S4: After cooling, add excessive methanol to mixture B. After no bubbles emerge, conduct centrifugation at 8000 rpm for 5 min, and retain precipitate A.

[0056] S5: Add dilute hydrochloric acid to precipitate A and soak for 12 h, then conduct centrifugation again to retain precipitate B.

[0057] S6: Wash precipitate B three times with deionized water and then dry it to obtain rare earth boride LaB 6 nanomaterials.

[0058] Use a transmission electron microscope to conduct morphology analysis on the obtained product. As Figure 1 shown, the prepared material has a near-spherical morphology with a diameter of 3 - 4 nm. Use an X-ray powder diffractometer to conduct phase and structure characterization on the obtained product. As Figure 2 shown, the X-ray powder diffraction peaks of the prepared material coincide with the diffraction peaks corresponding to the LaB 6 standard PDF card. The above characterization results indicate that the rare earth boride nanomaterial LaB 6 is successfully prepared. According to the Scherrer formula, its particle size is calculated to be 4.2 nm, corresponding to the result of the transmission electron microscope.

[0059] Use an ultraviolet-visible-near-infrared spectrometer to test the optical properties of the above sample. As Figure 3 shown, the sample has absorption in the ultraviolet-visible-near-infrared region and has strong absorption in the near-infrared region, indicating that it is a good light absorption material.

[0060] Example 2 Preparation of rare earth boride nanomaterial CeB 6 of

[0061] S1: Mix 1 mmol of anhydrous cerium chloride and 8 mmol of sodium borohydride to obtain a mixed raw material.

[0062] S2 - S6: The same as Example 1.

[0063] Use an X-ray powder diffractometer to conduct phase and structure characterization on the obtained product. As Figure 4 shown, the X-ray powder diffraction peaks of the prepared material coincide with the diffraction peaks corresponding to the CeB 6 standard PDF card. The above characterization results indicate that the rare earth boride nanomaterial CeB 6 is successfully prepared.

[0064] Example 3 Preparation of rare earth boride nanomaterial PrB 6 of

[0065] S1: Mix 1 mmol of anhydrous praseodymium chloride and 8 mmol of potassium borohydride to obtain a mixed raw material.

[0066] S2 - S6: The same as in Example 1.

[0067] The obtained product was characterized for its phase and structure using an X - ray powder diffractometer, as Figure 5 shown. The X - ray powder diffraction peaks of the prepared material match those corresponding to the PrB 6 standard PDF card. The above characterization results indicate that the rare - earth boride nanomaterial PrB 6 was successfully prepared.

[0068] Example 4 Preparation of rare - earth boride nanomaterial NdB 6

[0069] S1: 1 mmol of anhydrous neodymium chloride and 8 mmol of sodium borohydride were mixed to obtain a mixed raw material;

[0070] S2 - S6: The same as in Example 1.

[0071] The obtained product was characterized for its phase and structure using an X - ray powder diffractometer, as Figure 6 shown. The X - ray powder diffraction peaks of the prepared material match those corresponding to the NdB 6 standard PDF card. The above characterization results indicate that the rare - earth boride nanomaterial NdB 6 was successfully prepared.

[0072] Example 5 Preparation of rare - earth boride nanomaterial EuB 6

[0073] S1: 1 mmol of anhydrous europium chloride and 8 mmol of lithium borohydride were mixed to obtain a mixed raw material;

[0074] S2 - S6: The same as in Example 1.

[0075] The obtained product was characterized for its phase and structure using an X - ray powder diffractometer, as Figure 7 shown. The X - ray powder diffraction peaks of the prepared material match those corresponding to the EuB 6 standard PDF card. The above characterization results indicate that the rare - earth boride nanomaterial EuB 6 was successfully prepared.

[0076] Example 6 Preparation of rare - earth boride nanomaterial ErB 6

[0077] S1: 1 mmol of anhydrous erbium chloride and 8 mmol of sodium borohydride were mixed to obtain a mixed raw material;

[0078] S2: The same as in Example 1;

[0079] ​​​S3: Transfer mixture A to a porcelain boat and place it in a tube furnace. Under a nitrogen atmosphere of one atmosphere, heat it to 800 °C and react for 6 h to obtain mixture B; 2 Protect and heat to 800 °C for 6 h to obtain mixture B;

[0080] S4 - S6: The same as in Example 1.

[0081] Use an X - ray powder diffractometer to characterize the phase and structure of the obtained product. As Figure 8 shown, the X - ray powder diffraction peaks of the prepared material coincide with the diffraction peaks corresponding to the ErB 6 standard PDF card. The above characterization results indicate that the rare - earth boride nanomaterial ErB 6 is successfully prepared.

[0082] Example 7 Preparation of rare - earth boride nanomaterial YbB 6 of

[0083] S1: Mix 1 mmol of anhydrous ytterbium chloride and 8 mmol of sodium borohydride to obtain a mixed raw material;

[0084] S2 - S6: The same as in Example 6.

[0085] Use an X - ray powder diffractometer to characterize the phase and structure of the obtained product. As Figure 9 shown, the X - ray powder diffraction peaks of the prepared material coincide with the diffraction peaks corresponding to the YbB 6 standard PDF card. The above characterization results indicate that the rare - earth boride nanomaterial YbB 6 is successfully prepared.

[0086] Example 8 Preparation of rare - earth boride nanomaterial LuB 4 of

[0087] S1: Mix 1 mmol of anhydrous lutetium chloride and 12 mmol of potassium borohydride to obtain a mixed raw material

[0088] S2 - S6: The same as in Example 6.

[0089] Use an X - ray powder diffractometer to characterize the phase and structure of the obtained product. As Figure 10 shown, the X - ray powder diffraction peaks of the prepared material coincide with the diffraction peaks corresponding to the LuB 4 standard PDF card. The above characterization results indicate that the rare - earth boride nanomaterial LuB 4 is successfully prepared.

[0090] Example 9 Preparation of rare - earth boride nanomaterial LaB 6 of

[0091] S1: Mix 1 mmol of anhydrous lanthanum chloride and 8 mmol of sodium borohydride to obtain a mixed raw material;

[0092] S2 - S6: The same as in Example 6.

[0093] Use a transmission electron microscope to analyze the morphology of the obtained product. As Figure 11 shown, the prepared material has a cubic morphology with a size of 8 - 10 nm. Use an X-ray powder diffractometer to characterize the phase and structure of the obtained product. As Figure 12 shown, the X-ray powder diffraction peaks of the prepared material coincide with the diffraction peaks corresponding to the LaB 6 standard PDF card. The above characterization results indicate that the rare earth boride nanomaterial LaB 6 is successfully prepared. According to the Scherrer formula, its particle size is calculated to be 8.2 nm, corresponding to the result of the transmission electron microscope. The above results show that this method has good controllability for the size of the product.

[0094] Example 10 Preparation of rare earth boride nanomaterial LaB 6

[0095] S1: Mix 1 mmol of anhydrous lanthanum chloride and 8 mmol of sodium borohydride to obtain a mixed raw material;

[0096] S2: The same as in Example 6;

[0097] S3: Transfer mixture A to a porcelain boat and place it in a tube furnace. Heat it to 1000 °C under the protection of one atmosphere of N 2 and react for 6 h;

[0098] S4 - S6: The same as in Example 6.

[0099] Use a transmission electron microscope to analyze the morphology of the obtained product. As Figure 13 shown, the prepared material has a cubic morphology with a size of 18 - 20 nm. Use an X-ray powder diffractometer to characterize the phase and structure of the obtained product. As Figure 14 shown, the X-ray powder diffraction peaks of the prepared material coincide with the diffraction peaks corresponding to the LaB 6 standard PDF card. The above characterization results indicate that the rare earth boride nanomaterial LaB 6 is successfully prepared. According to the Scherrer formula, its particle size is calculated to be 17.0 nm, corresponding to the result of the transmission electron microscope. The above results show that this method has good controllability for the size of the product.

[0100] Test Example 1

[0101] Test group: The sample obtained in Example 1;

[0102] ​Test method: The sample obtained in Example 1 was used as the photothermal material of the photothermal layer of the solar thermal interface evaporator, and the test conditions were as follows: LaB 6 The loading amount of the nanomaterial was 1 mg / cm 2 , the substrate of the solar thermal evaporator was a 3*3*3 cm wood sponge, the test environment was set to a constant temperature and humidity chamber at 25°C and 45%, the light source was a xenon lamp solar simulator of Solar-500Q, and the light intensity was set to 1 kW / m 2 , and the illumination time was 300 s;

[0103] Test results: As Figure 15 shown, after the wood solar evaporator with a LaB 6 nanomaterial loading of 1 mg / cm 2 was illuminated for 60 s, the interface temperature rose to 76.2°C, and the maximum temperature stabilized at 80.5°C, showing excellent photothermal conversion performance.

[0104] Test Example 2

[0105] Test group: The sample obtained in Example 1;

[0106] Test method: The wood solar evaporator with a LaB 6 nanomaterial loading of 1 mg / cm 2 was applied to the field of seawater desalination, and the test conditions were as follows: The light source was a xenon lamp solar simulator of Solar-500Q, the light intensity was set to 1 kW / m 2 , the water source was a 3.5% NaCl salt solution simulating seawater concentration, and the evaporation time was 120 s;

[0107] Test results: As Figure 16 shown, with the extension of the illumination time, the water evaporation rate increased, and the maximum value of the water evaporation rate reached 3.12 kg / m 2 / h 1 , which is a sustainable clean fresh water production platform with a high water evaporation rate.

[0108] Test Example 3

[0109] Test group: Example 1;

[0110] Test method: The sample obtained in Example 1 was used as the catalyst for the degradation of organic dyes, and the test conditions were as follows: The concentration of the LaB 6 nanomaterial was 0.1 mg / mL, the concentration of methyl orange dye was 20 ppm, the volume of the dye solution for the degradation reaction was 100 ml, the reaction was carried out at room temperature, the reaction vessel was a self-made quartz tube, the light source was a xenon lamp of Solar-500Q, and the reaction was irradiated with a xenon lamp at a light intensity of 1 kW / m 2 for 120 min;

[0111] Test results: As Figure 17 shown, under the catalytic condition of 0.1 mg / mL LaB 6 nanoparticles, the degradation rate of methyl orange dye reaches 98.2%, and LaB 6 nanomaterials exhibit potential catalytic performance in degrading organic pollutants in wastewater under sunlight.

[0112] Test Example 4

[0113] Test group: Example 1;

[0114] Test method: The antibacterial performance of the sample obtained in Example 1 was tested. The antibacterial activity of different doses of LaB 6 nanomaterials against Gram-negative bacterium E. coli was studied through the spread plate experiment. The experimental conditions are as follows: The preserved E. coli strain was amplified before the experiment and stored in a 4°C refrigerator for later use. The LaB 6 nanomaterials were sterilized. Different amounts of nanomaterials were added to test tubes containing bacterial suspension (4.0×10 5 CFU / mL) and PBS. The concentrations of nanomaterials were 0 μg / ml (as the blank control group), 100 μg / mL, 200 μg / mL, and 300 μg / mL. The co-culture condition was a constant temperature shaker at 37°C and oscillation at 160 rpm for 12 h to allow the bacteria to fully contact with the nanomaterials. After co-culturing for 12 h, the bacterial suspension in the test tube was diluted 10 4 times with sterile PBS. 80 μL of the diluted solution was taken and evenly spread on the agar plate. After the bacterial solution was completely absorbed, the plate was inverted and incubated in a biochemical incubator at 37°C for 15 h, and then the results were photographed and recorded;

[0115] Test results: As Figure 18 shown, compared with the control group, as the dose of sample nanoparticles increased, the survival rate of E. coli decreased, and the antibacterial performance reached nearly 100% at a concentration of 300 μg / ml. The results indicate that LaB 6 nanomaterials exhibit significantly enhanced antibacterial activity.

[0116] The rare earth boride nanomaterials of the present invention have excellent photothermal properties, antibacterial properties, and dye degradation properties; they can be applied to the field of thermal insulation coatings, as well as the fields of photocatalysis and solar water evaporation, including application scenarios such as seawater desalination, treatment of bacteria-containing wastewater, and treatment of high-salt dye wastewater. The atmospheric pressure and low-temperature preparation method of the present invention is simple, efficient, safe, and reliable, has good controllability and universality, is suitable for large-scale industrial production, and the obtained samples have good performance and can be applied to fields such as catalysis, antibacterial, and seawater desalination.

[0117] The foregoing has shown and described the basic principles, main features and advantages of the present invention. For a person skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and without departing from the spirit or basic features of the present invention, the present invention can be implemented in other specific forms. Therefore, in whatever aspect, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to embrace all changes that fall within the meaning and scope of the equivalent elements of the claims in the present invention.

[0118] In addition, it should be understood that although this specification is described according to the embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. A person skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by a person skilled in the art.

Claims

1. A method for preparing a rare earth boride nanomaterial, characterized in that: The phase state of the rare earth boride nanomaterial is REB6 or REB4, wherein RE is selected from one of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; and the preparation method thereof comprises the following steps: S1: Weighing a compound raw material containing the RE element and a compound raw material containing the B element respectively, with a molar ratio of 1:4-12, to obtain a mixed raw material; S2: Add additives to the mixed raw material obtained in step S1, and grind thoroughly to obtain a mixture A; S3: reacting the mixture A obtained in step S2 under the protection of an inert gas, controlling the reaction temperature to be 300-800° C., and the reaction time to be 6 h, to obtain a mixture B; S4: After the reaction is completed, excess methanol is added to the mixture B obtained in step S3, and centrifugation is performed after no bubbles emerge, and the precipitate A is retained; S5: adding dilute hydrochloric acid to the precipitate A obtained in step S4 and soaking for 12 hours, and centrifuging again to retain the precipitate B; S6: Wash the precipitate B obtained in step S5 with deionized water, and dry it to obtain a rare earth boride nanomaterial.

2. The method for preparing a rare earth boride nanomaterial according to claim 1, characterized in that: The compound raw material containing the RE element in step S1 includes anhydrous rare earth halides, and the compound raw material containing the B element is an alkali metal borohydride.

3. The method for preparing a rare earth boride nanomaterial according to claim 1, characterized in that: The additive in step S2 is an alkali metal halide, and the molar ratio of the additive to the mixed raw material is 1:

1.

4. The method for preparing a rare earth boride nanomaterial according to claim 1, characterized in that: In step S3, the inert gas is nitrogen or argon, and the pressure of the system is one atmosphere.

5. The method for preparing a rare earth boride nanomaterial according to claim 1, characterized in that: The concentration of the dilute hydrochloric acid in step S5 is 0.6 mol / L.

6. The method for preparing a rare earth boride nanomaterial according to claim 1, characterized in that: The centrifugation conditions in steps S4 and S5 are: rotation speed 8000 rpm, time 3-7 min.

7. The rare earth boride nanomaterial prepared by the method according to any one of claims 1 to 6, characterized in that: Its phase state is REB6 or REB4, its color is black or dark brown, its morphology is nearly spherical or cubic, and its diameter is less than 20nm.

8. Use of the rare earth boride nanomaterial as claimed in claim 7 in the fields of thermal insulation coating, photocatalysis and solar water evaporation.

9. The use of a rare earth boride nanomaterial as claimed in claim 8, characterized in that: The solar water evaporation includes seawater desalination, bacteria-containing wastewater treatment and high-salt dye wastewater treatment.

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