Polyoxometallate containing rare earth neodymium as well as preparation method and application of polyoxometallate

Abstract

The invention discloses polyoxometallate containing rare earth neodymium as well as a preparation method and application of the polyoxometallate, and relates to the technical field of water treatment. According to the invention, reagents such as germanium dioxide, sodium metavanadate, potassium chloride, neodymium nitrate and the like are used as raw materials, and polyoxometallate K15Nd (GeW10VO39) 2. NH2O containing rare earth neodymium is synthesized. The prepared polyoxometallate containing rare earth neodymium has a remarkable degradation effect on reactive red X3B, and after ultraviolet irradiation is carried out for 40 min, the degradation rate of the reactive red X3B reaches 99.94%.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a polyoxometalate containing rare earth neodymium and a preparation method and application thereof. Background Art

[0002] Dyes are widely used in various industries, such as pigments, leather, cosmetics, textiles, plastics and electronics, etc. However, textile dye wastewater is discharged directly into rivers without treatment, which will cause serious pollution to water resources and seriously threaten the ecological environment and human health. Photocatalytic degradation of organic dyes has attracted much attention due to its green and environmentally friendly characteristics. In industry, Reactive Red X3B, Rhodamine B, etc. are commonly used for impregnation, roll dyeing and tie-dyeing of cotton, fiber, nylon, wool, etc., and as a monoazo reactive dye, it is difficult to decompose under natural conditions and difficult to remove by microorganisms. Therefore, Reactive Red X3B is a typical pollutant in printing and dyeing wastewater. The process of using polyoxometalates (POMs) as oxidation catalysts and acid catalysts has been industrialized. POMs can efficiently oxidize and decompose organic pollutants, converting them into CO2, H2O, N2, SO4 2- A series of environmentally friendly substances such as POMs have been widely used as photocatalysts for the degradation of dye wastewater. Among the various structures of POMs, the research and application of keggin-type polyoxometalates are the most extensive, and they can be used as oxidation-reduction type, acid type or bifunctional catalysts, photocatalysts in many catalytic reactions. However, as far as we know, there are few reports on the photocatalytic activity of vacancy-type polyoxometalates. Summary of the invention

[0003] The purpose of the present invention is to provide a polyoxometalate containing rare earth neodymium and a preparation method and application thereof, so as to solve the following technical problems: Existing polyoxometalates (POMs) have low efficiency in photocatalytic degradation of azo dyes.

[0004] The purpose of the present invention can be achieved through the following technical solutions: A method for preparing a polyoxometalate containing rare earth neodymium comprises the following steps: S1: Mix the sodium germanate solution and the sodium tungstate solution, adjust the pH to 5-6, control the temperature to 90-100℃, keep the temperature for 0.5-2h, filter and take the filtrate, add potassium chloride to the filtrate, control the temperature to 40-60℃, keep the temperature for reaction to produce a white precipitate, take the white precipitate and dry it to obtain K8[GeW 11 O 39 ]·13H2O; S2: K8[GeW 11 O 39Mix 13H₂O and water in a reaction kettle, add sodium metavanadate, adjust the pH of the solution to 2 - 3, control the temperature at 85 - 95 °C, keep the temperature for 1 - 3 h, cool to room temperature to obtain a reaction solution, and add ether to extract the reaction solution to obtain H₅GeW 11 VO 40 ; S3: Mix H₅GeW 11 VO 40 , distilled water, and neodymium nitrate, add potassium acetate to adjust the pH to 4 - 5.5, control the temperature at 70 - 90 °C, keep the temperature for 1 - 3 h, cool to room temperature and dry to obtain a rare earth neodymium-containing polyoxometalate.

[0005] As a further scheme of the present invention: In S1, add a 4 - 6 mol / L hydrochloric acid aqueous solution to adjust the pH to 5 - 6.

[0006] As a further scheme of the present invention: In S2, add a 4 - 6 mol / L hydrochloric acid aqueous solution to adjust the pH to 2 - 3.

[0007] As a further scheme of the present invention: The preparation method of sodium germanate solution is: Mix germanium dioxide and an aqueous sodium hydroxide solution to obtain a sodium germanate solution; the aqueous sodium hydroxide solution is a 3.8 - 4.2 mol / L aqueous sodium hydroxide solution; the mass ratio of germanium dioxide in the sodium germanate solution is 15 - 20%; The preparation method of sodium tungstate solution is: Mix 69 g of sodium tungstate and 90 mL of water, and dropwise add to adjust the pH value of the sodium tungstate solution to 6 - 6.5 to obtain a sodium tungstate solution; In S1, the mass ratio of sodium germanate to sodium tungstate is 1:19.42 - 21.36.

[0008] As a further scheme of the present invention: In the preparation method of sodium tungstate solution, use a 4 - 6 mol / L hydrochloric acid aqueous solution to adjust the pH value of the sodium tungstate solution to 6 - 6.5.

[0009] As a further scheme of the present invention: In S1, the mass ratio of potassium chloride to sodium germanate is 3.59:1.

[0010] As a further scheme of the present invention: In S2, the addition ratio of K₈[GeW 11 O 39 ·13H₂O, water, and sodium metavanadate is 22 g:60 mL:1 - 1.2 g.

[0011] As a further scheme of the present invention: In S3, the distilled water is distilled water at 60 - 80 °C; the addition ratio of H₅GeW 11 VO 40 , distilled water, and neodymium nitrate is 1.4 - 1.5 g:10 mL:0.1 g.

[0012] As a further embodiment of the present invention, the specific steps of ether extraction are: adding the reaction solution into a separatory funnel, adding ether, and dripping 10 mL / L sulfuric acid aqueous solution until no oil is produced, and drying the oil to obtain H5GeW 11 VO 40 .

[0013] As a further solution of the present invention, the specific steps of the drying treatment are: heating the light yellow oil in a water bath to remove ether, and then drying to obtain H5GeW 11 VO 40 .

[0014] A polyoxometalate containing rare earth neodymium, prepared by any one of the above preparation methods.

[0015] The rare earth neodymium-containing polyoxometalates mentioned above are used in the field of water treatment.

[0016] Beneficial effects of the present invention: The present invention adopts an ion exchange method to prepare a Keggin-type rare earth neodymium-containing vacancy polyoxometalate K 15 Nd(GeW 10 VO 39 )2·nH2O(NdGeW 10 VO); heteropoly anions can be degraded to obtain missing 11-tungsten, which can form 1:1 and 1:2 structures with transition metal or rare earth ions. The missing heteropoly anions can form mixed heteropoly complexes with rare earth ions through 4-8 dentate ligands. Due to the extranuclear electron configuration of rare earth elements, the 4f electrons that have multiple levels and are easily affected by external conditions to generate transitions can form a multi-electron configuration. The rare earth elements react with heteropoly acids to form clustered polyoxometalates, which changes the surface properties of heteropoly acids, thereby improving the optical, catalytic, electrical and other properties, and improving the redox properties of heteropoly acids, and ultimately improving the photocatalytic effect.

[0017] The polyoxometalate containing rare earth neodymium prepared in the present application degrades organic dyes such as azo dyes such as Reactive Red X-3B and Rhodamine B under ultraviolet light irradiation, and can effectively degrade 99.94% of Reactive Red X3B in 40 minutes under ultraviolet light irradiation. The present application doped rare earth neodymium in the polyoxometalate, which can significantly improve the photocatalytic activity of heteropolyacids. The polyoxometalate containing rare earth neodymium prepared in the present application has important applications in the fields of analysis, functional materials, and pharmaceuticals. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described below in conjunction with the accompanying drawings.

[0019] Figure 1 It is the NdGeW prepared in Example 1 of the present application. 10Absorbance change curve of the reaction solution during the catalytic degradation of X3B reaction solution with pH = 0.5 by VO; Figure 2 is NdGeW prepared in Example 1 of this application 10 Color change diagram at 0 min, 20 min, and 40 min during the catalytic degradation of X3B reaction solution with pH = 0.5 by VO; Figure 3 is H5GeW prepared in Comparative Example 1 of this application 11 VO 40 Absorbance change curve of the reaction solution during the catalytic degradation of X3B reaction solution with pH = 0.5 by VO; Figure 4 is NdGeW prepared in Example 1 of this application 10 VO and H5GeW prepared in Comparative Example 1 11 VO 40 Statistical broken line chart of decolorization rate detection data; Figure 5 is NdGeW prepared in Example 1 of this application 10 VO and H5GeW prepared in Comparative Example 1 11 VO 40 Infrared spectrum; Figure 6 is NdGeW prepared in Example 1 of this application 10 VO and H5GeW prepared in Comparative Example 1 11 VO 40 XRD pattern; Figure 7 is NdGeW prepared in Example 1 of this application 10 TG-DSC curve of VO; Figure 8 is the chemical reaction equation for preparing K8[GeW 11 O 39 ·13H2O; Figure 9 is the chemical reaction equation for preparing H5GeW 11 VO 40 ; Figure 10 is the chemical reaction equation for preparing K 15 Nd(GeW 10 VO 39 )2·nH2O. Detailed implementation manners

[0020] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0021] Example 1 The preparation method of the rare-earth neodymium-containing polyoxometalate includes the following steps: S1: Refer to Figure 1 , mix 82.9 g of 4 mol / L sodium hydroxide aqueous solution with 17.1 g of germanium dioxide to obtain a sodium germanate solution; Dissolve 69 g of sodium tungstate in 90 mL of water at 70 °C, and add 6 mol / L hydrochloric acid aqueous solution to adjust the pH value of the sodium tungstate solution to 6.5 to obtain a sodium tungstate solution; Add the sodium tungstate solution containing 205 g of sodium tungstate to the sodium germanate solution containing 10 g of sodium germanate, add 6 mol / L hydrochloric acid aqueous solution to adjust the pH value to 5.5, control the temperature at 95 °C, heat in a water bath for 1 h, cool and filter to obtain a filtrate. Add 35.9 g of potassium chloride to the filtrate and stir magnetically until dissolved, control the temperature at 50 °C, heat in a water bath until a white precipitate appears, take the precipitate and dry it in an oven at 50 °C to obtain K8[GeW 11 O 39 ·13H2O; S2: Refer to Figure 2 , mix 22 g of K8[GeW 11 O 39 ·13H2O and 60 mL of water, add 1.08 g of sodium metavanadate, add 6 mol / L hydrochloric acid aqueous solution to adjust the pH value of the solution to 2.5, control the temperature at 90 °C, heat in a water bath for 1.5 h, cool to room temperature, add ether for extraction, and add 0.01 vt% sulfuric acid aqueous solution dropwise to the separatory funnel during the extraction process. A yellow oily substance is formed and precipitated, and a glass rod is inserted into the separatory funnel to stir appropriately to make it completely precipitate; until no more oily substance is produced when adding 0.01 vt% sulfuric acid aqueous solution, collect the pale yellow oily substance and remove the remaining ether by heating in a water bath at 50 °C. After the solution is evaporated to dryness, transfer it to an oven at 50 °C for drying to obtain a yellow solid H5GeW 11 VO 40 ; S3: Refer to Figure 3 , at room temperature, mix and dissolve 1.4 g of H5GeW 11 VO 40 and 10 mL of distilled water at 70 °C, add 0.1 g of neodymium nitrate, adjust the pH value to 4 - 5.5 with potassium acetate, control the temperature at 80 °C, heat in a water bath for 2 h, cool to room temperature to obtain a yellow solid K15 Nd(GeW 10 VO 39 )2·nH2O (abbreviation: NdGeW 10 VO), namely polyoxometalate containing rare earth neodymium.

[0022] Example 2 The preparation method of polyoxometalate containing rare earth neodymium includes the following steps: S1: Please refer to Figure 1 , mix 82.9 g of 3.8 mol / L sodium hydroxide aqueous solution with 17.1 g of germanium dioxide to obtain sodium germanate solution; Dissolve 69 g of sodium tungstate in 90 mL of water at 70 °C, and add 6 mol / L hydrochloric acid aqueous solution to adjust the pH value of the sodium tungstate solution to 6.5 to obtain sodium tungstate solution; Add the sodium tungstate solution containing 194.2 g of sodium tungstate to the sodium germanate solution containing 10 g of sodium germanate, add 6 mol / L hydrochloric acid aqueous solution to adjust the pH value to 5, control the temperature at 95 °C, heat in a water bath for 1 h, cool and filter to obtain a filtrate. Add 35.9 g of potassium chloride to the filtrate and stir magnetically until dissolved, control the temperature at 50 °C, heat in a water bath until a white precipitate appears, take the precipitate and dry it in an oven at 50 °C to obtain K8[GeW 11 O 39 ·13H2O; S2: Please refer to Figure 2 , mix 22 g of K8[GeW 11 O 39 ·13H2O and 60 mL of water, add 1 g of sodium metavanadate, add 6 mol / L hydrochloric acid aqueous solution to adjust the pH value of the solution to 2, control the temperature at 85 °C, heat in a water bath for 1 h, cool to room temperature, add ether for extraction, and add 0.01 vt% sulfuric acid aqueous solution dropwise to the separatory funnel during the extraction process. A yellow oil substance is generated and precipitated, and use a glass rod to stir appropriately in the separatory funnel to make it completely precipitate; until no more oil substance is produced when adding 0.01 vt% sulfuric acid aqueous solution, collect the light yellow oil substance and remove the remaining ether by heating in a water bath at 50 °C. After the solution is evaporated to dryness, transfer it to an oven at 50 °C for drying to obtain a yellow solid H5GeW 11 VO 40 ; S3: Please refer to Figure 3 , at room temperature, dissolve 1.4 g of H5GeW 11 VO 40 and 10 mL of distilled water at 70 °C, add 0.1 g of neodymium nitrate, adjust the pH value to 4 with potassium acetate, control the temperature at 70 °C, heat in a water bath for 1 h, cool to room temperature to obtain a yellow solid K 15 Nd(GeW 10 VO 39) 2·nH2O (abbreviation: NdGeW 10 VO), that is, a polyoxometalate containing rare earth neodymium.

[0023] Example 3 The preparation method of the polyoxometalate containing rare earth neodymium includes the following steps: S1: Please refer to Figure 1 , blend 82.9 g of 4.2 mol / L sodium hydroxide aqueous solution with 17.1 g of germanium dioxide to obtain a sodium germanate solution; Dissolve 69 g of sodium tungstate in 90 mL of water at 70 °C, and add 6 mol / L hydrochloric acid aqueous solution to adjust the pH value of the sodium tungstate solution to 6.5 to obtain a sodium tungstate solution; Add the sodium tungstate solution containing 213.6 g of sodium tungstate to the sodium germanate solution containing 10 g of sodium germanate, add 6 mol / L hydrochloric acid aqueous solution to adjust the pH value to 5.5, control the temperature at 95 °C, heat in a water bath for 1 h, cool and filter to obtain a filtrate. Add 35.9 g of potassium chloride to the filtrate and stir magnetically until dissolved, control the temperature at 50 °C, heat in a water bath until a white precipitate appears, take the precipitate and dry it in an oven at 50 °C to obtain K8[GeW 11 O 39 ·13H2O; S2: Please refer to Figure 2 , blend 22 g of K8[GeW 11 O 39 ·13H2O and 60 mL of water, add 1.2 g of sodium metavanadate, add 6 mol / L hydrochloric acid aqueous solution to adjust the pH value of the solution to 3, control the temperature at 95 °C, heat in a water bath for 3 h, cool to room temperature, add ether for extraction, and add 0.01 vt% sulfuric acid aqueous solution dropwise to the separatory funnel during the extraction process. A yellow oily substance is formed and precipitated, and use a glass rod to stir appropriately in the separatory funnel to make it completely precipitate; until no more oily substance is produced when adding 0.01 vt% sulfuric acid aqueous solution, collect the pale yellow oily substance and remove the remaining ether by heating in a water bath at 50 °C. After the solution is evaporated to dryness, transfer it to an oven at 50 °C for drying to obtain a yellow solid H5GeW 11 VO 40 ; S3: Please refer to Figure 3 , at room temperature, dissolve 1.5 g of H5GeW 11 VO 40 and 10 mL of distilled water at 70 °C, add 0.1 g of neodymium nitrate, adjust the pH value to 5.5 with potassium acetate, control the temperature at 90 °C, heat in a water bath for 3 h, cool to room temperature to obtain a yellow solid K 15 Nd(GeW 10 VO 39 )2·nH2O (abbreviation: NdGeW 10 VO), that is, a polyoxometalate containing rare earth neodymium.

[0024] Comparative Example 1 The preparation method of the polyoxometalate includes the following steps: S1: Mix 82.9 g of 4 mol / L sodium hydroxide aqueous solution with 17.1 g of germanium dioxide to obtain a sodium germanate solution; Dissolve 69 g of sodium tungstate in 90 mL of water at 70 °C, and add 6 mol / L hydrochloric acid aqueous solution to adjust the pH value of the sodium tungstate solution to 6.5 to obtain a sodium tungstate solution; Add the sodium tungstate solution containing 205 g of sodium tungstate to the sodium germanate solution containing 10 g of sodium germanate, add 6 mol / L hydrochloric acid aqueous solution to adjust the pH value to 5.5, control the temperature at 95 °C, heat in a water bath for 1 h, cool and filter to obtain a filtrate. Add 35.9 g of potassium chloride to the filtrate and stir magnetically until dissolved. Control the temperature at 50 °C and heat in a water bath until a white precipitate appears. Take the precipitate and dry it in an oven at 50 °C to obtain K8[GeW 11 O 39 ·13H2O; S2: Please refer to Figure 2 , mix 22 g of K8[GeW 11 O 39 ·13H2O and 60 mL of water, add 1.08 g of sodium metavanadate, add 6 mol / L hydrochloric acid aqueous solution to adjust the pH value of the solution to 2.5, control the temperature at 90 °C, heat in a water bath for 1.5 h, cool to room temperature, add ether for extraction. During the extraction process, add 0.01 vt% sulfuric acid aqueous solution dropwise to the separatory funnel. A yellow oil substance is formed and precipitated. Insert a glass rod into the separatory funnel and stir appropriately to make it completely precipitate; until no more oil substance is produced when adding 0.01 vt% sulfuric acid aqueous solution. Collect the pale yellow oil substance and remove the remaining ether by heating in a water bath at 50 °C. After the solution is evaporated to dryness, transfer it to an oven at 50 °C and dry it to obtain a yellow solid H5GeW 11 VO 40 , that is, the polyoxometalate.

[0025] Performance detection (1) Decolorization rate detection ① Prepare the reaction solution: Take 100 mL of 2 mg / L reactive red X3B solution, and use 1 mol / L hydrochloric acid aqueous solution to adjust the pH value of the reaction solution to 0.5. Stir evenly for 5 min in the dark on a constant temperature magnetic stirrer.

[0026] ② Detection steps: Use an ultraviolet lamp as the light source. Take the test solution under different degrees of light every 10 min, and measure its absorbance using a double-beam ultraviolet spectrophotometer.

[0027] ③ Set up a blank control group: Take 100 mL of 2 mg / L reactive red X3B solution, adjust the pH value of the reaction solution to 0.5 with 1 mol / L hydrochloric acid aqueous solution, place it in a constant temperature under the irradiation of an ultraviolet lamp, and make the light radiation uniform through electromagnetic stirring. Measure the absorbance of the reactive red X3B solution at 540 nm, and calculate the decolorization rate according to the change of the absorbance values of the samples before and after the reaction.

[0028] ④ Calculate the decolorization rate: The maximum absorption wavelength of reactive red X3B is 540 nm. Measure the absorbance of the extracted sample at this wavelength with a UV-visible spectrophotometer; and calculate the decolorization rate (DC) according to the following formula: DC = [(A0 - A) / A0] × 100% In the formula: A0 - the absorbance of the solution at λ = 540 nm before light irradiation; A - the absorbance after light irradiation for a certain period of time. Use a 500 W medium-pressure mercury lamp as the light source, take samples for analysis after light irradiation for a certain period of time, record the absorbance data at the maximum wavelength, and process the recorded data with Oringinpro-8.0. The test results are shown in Table 1; Table 1: Statistical table of decolorization rate detection data As shown in Table 1 and Figure 1-2 shown, the rare earth neodymium-containing polyoxometalate (NdGeW 10 VO) prepared in Examples 1-3 of the present application degrades the reactive red X3B in the reaction solution. As the light irradiation time prolongs, the absorbance becomes flatter and flatter. When the reaction is 40 min, the decolorization rate is above 99%.

[0029] As shown in Table 1 and Figure 3 shown, the H5GeW 11 VO 40 prepared in Comparative Example 1 of the present application degrades the reactive red X3B in the reaction solution. As the light irradiation time prolongs, the absorbance becomes flatter and flatter. When the reaction is 40 min, the decolorization rate is 71.63%, and when the reaction is 60 min, the decolorization rate is 90.30%.

[0030] Please refer to Figure 4 , under the same reaction conditions, the rare earth neodymium-containing polyoxometalate (NdGeW 10 VO) prepared in Example 1 of the present application has better photocatalytic activity than the H5GeW 11 VO 40 prepared in Comparative Example 1.

[0031] The rare earth neodymium-containing polyoxometalate (NdGeW 10The (VO) contains rare earth elements. Rare earth elements have special electronic structures and strong coordination abilities. Their oxygenophilic ability and ligand field stabilization are very suitable for reacting with heteropolyacids to form polyoxometalates with structural changes. Moreover, due to the arrangement of the outer electrons of the rare earth elements, they have multi-level 4f electrons that are easily affected by external conditions and undergo transitions, and can form multi-electron configurations. Reacting rare earth elements with heteropolyacids can generate polyoxometalates with substituted saturated structures, sandwich structures, and cluster structures, changing the surface properties of the heteropolyacids and improving properties in aspects such as optics, catalysis, and electricity, and enhancing the redox property, thermal stability, catalytic activity, and selectivity of the heteropolyacids. The polyoxometalates formed by the complexation of heteropolyacids with rare earth neodymium ions enhance the redox effect and ultimately improve the catalytic effect. This shows that the introduction of rare earth elements in this application further improves the photocatalytic activity of the heteropolyacids.

[0032] (2)For the NdGeW prepared in the example 10 VO, the H5GeW prepared in Comparative Example 1 11 VO 40 Carry out infrared spectrum comparison Please refer to Figure 5 , the H5GeW prepared in Comparative Example 1 11 VO 40 has 4 peaks in the low wavenumber region, which conform to the 4 characteristic peaks of the Keggin-type structure heteropolyacid: 1033.6 cm -1 is the characteristic peak generated by the vibration of W-O d , 948.8 cm -1 is the characteristic peak generated by the vibration of W-O b , 850.4 cm -1 is the characteristic peak generated by the vibration of Ge-O a , 800.3 cm -1 is the characteristic peak generated by the vibration of W-O c vibration.

[0033] The NdGeW prepared in the example 10 VO and the H5GeW prepared in Comparative Example 1 11 VO 40 Compared, their infrared spectra are generally similar, which indicates that the structure of the heteropolyanion has not changed due to the addition of rare earth neodymium ions, that is, the neodymium ions have not entered the inner sphere of the heteropolyanion. Therefore, the synthesized rare earth neodymium-containing heteropolyacid salt still maintains the Keggin-type structure. However, after the rare earth ions are coordinated with the heteropolyanion, the force constant of the bond decreases and the bond distance increases, making the intensity of W-O d decrease, the frequency redshift, and the characteristic peak shift to the low wavenumber band. It can be seen from the infrared spectrum comparison that the neodymium ion coordination is successful.

[0034] (3)For the NdGeW prepared in the example 10VO, H5GeW prepared in Comparative Example 1 11 VO 40 Perform XRD comparison X-ray powder diffraction (XRD) is mainly used to study the arrangement of atoms in crystals. Through X-ray diffraction, the structure of the substance can be understood and the macroscopic properties of polyoxometalates can be explained. In this application, NdGeW prepared in the examples was measured at 10° ≤ 2θ ≤ 80° 10 VO, H5GeW prepared in Comparative Example 1 11 VO 40 XRD to determine its structural properties and grain size.

[0035] Please refer to Figure 6 , in the range of 10° ≤ 2θ ≤ 40°, both compounds have strong diffraction peaks. From the comparison chart of the diffraction peaks of NdGeW 10 VO and H5GeW 11 VO 40 , it can be seen that the intensity of the diffraction peaks changes and the strongest diffraction peak shifts. The spatial volume of neodymium ions is larger than that of hydrogen ions, resulting in the expansion of the entire Keggin structure unit, indicating that the neodymium ions are successfully complexed with the heteropolyacid anions.

[0036] (4) Thermogravimetric analysis The structural unit of NdGeW 10 VO prepared in this application consists of two [GeW 10 VO 39 9- anions, one Nd 3+ , 15 K + and 55 water molecules, that is, K 15 Nd(GeW 10 VO 39 )2·55H2O. In [GeW 10 VO 39 9- anion, Ge is the heteroatom, while V and W are coordination atoms that combine with O atoms to form an unsaturated Keggin structure. Nd 3+ is located in the middle of two vacant polyoxometalate anions [GeW 10 VO 39 9- , and forms a sandwich sandwich configuration with Nd 3+ through a double Keggin-type vacant polyoxometalate combined with O atoms. The rare earth Nd 3+ ions are connected to eight O atoms through a quadrilateral antiprism coordination mode, and each vacant anion [GeW 10 VO 39 9- provides 4 oxygen atoms. ​​​​

[0037] Please refer to Figure 7 , when the temperature is below 600 °C, the NdGeW prepared in Example 1 10 VO contains bound water and crystal water. These waters are mainly degraded in the following two steps: First, below 133.7 °C, 15 molecules of bound water are lost; second, between 133.7 °C and 364.6 °C, 40 molecules of crystal water are lost.

[0038] The above has described an embodiment of the present invention in detail, but the content described is only a preferred embodiment of the present invention and cannot be considered as defining the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of the application of the present invention should still fall within the scope covered by the patent of the present invention.

Claims

1. A preparation method of a rare-earth neodymium-containing polyoxometalate, characterized in that, It includes the following steps: S1: Blend sodium germanate solution and sodium tungstate solution, adjust the pH to 5 - 6, control the temperature at 90 - 100 °C, keep the temperature for reaction for 0.5 - 2 h, filter and take the filtrate. Add potassium chloride to the filtrate, control the temperature at 40 - 60 °C, keep the temperature for reaction until white precipitate appears. Take the white precipitate and dry it to obtain K8[GeW 11 O 39 ·13H2O; S2: Mix K8[GeW 11 O 39 ·13H2O and water in a reaction kettle, add sodium metavanadate, adjust the pH of the solution to 2 - 3, control the temperature at 85 - 95 °C, keep the reaction for 1 - 3 h, cool to room temperature to obtain a reaction solution, add ether to extract the reaction solution to obtain H5GeW 11 VO 40 ; S3: Blend H5GeW 11 VO 40 , distilled water, and neodymium nitrate, add potassium acetate to adjust the pH to 4 - 5.5, control the temperature at 70 - 90 °C, perform heat preservation treatment for 1 - 3 h, cool to room temperature, and dry to obtain a rare-earth neodymium-containing polyoxometalate.

2. The preparation method of a polyoxometalate containing rare earth neodymium according to claim 1, characterized in that The method for preparing sodium germanate solution is: mixing germanium dioxide and an aqueous sodium hydroxide solution to obtain a sodium germanate solution; the aqueous sodium hydroxide solution is an aqueous sodium hydroxide solution with a concentration of 3.8 - 4.2 mol / L; the mass ratio of germanium dioxide in the sodium germanate solution is 15 - 20%; The method for preparing sodium tungstate solution is: mixing 69 g of sodium tungstate and 90 mL of water, and adjusting the pH value of the sodium tungstate solution to 6 - 6.5 by dropping to obtain a sodium tungstate solution; The mass ratio of sodium germanate to sodium tungstate in S1 is 1:19.42 - 21.

36.

3. The preparation method of a polyoxometalate containing rare earth neodymium according to claim 1, characterized in that The mass ratio of potassium chloride to sodium germanate in S1 is 3.59:

1.

4. The preparation method of a polyoxometalate containing rare earth neodymium according to claim 1, characterized in that, K8[GeW 11 O 39 ·13H2O, water, and sodium metavanadate are added in a ratio of 22 g: 60 mL: 1 - 1.2 g.

5. The preparation method of a polyoxometalate containing rare earth neodymium according to claim 1, characterized in that, The distilled water in S3 is distilled water at 60-80 °C; H5GeW 11 VO 40 The addition ratio of distilled water, neodymium nitrate is 1.4-1.5 g: 10 mL: 0.1 g.

6. The preparation method of a polyoxometalate containing rare earth neodymium according to claim 1, characterized in that, The specific steps for extraction with ether are as follows: Add the reaction solution into a separating funnel, add ether, and dropwise add 0.01 vt% sulfuric acid aqueous solution until no more oily substances are produced. Dry the oily substances to obtain H5GeW 11 VO 40 .

7. The preparation method of a polyoxometalate containing rare earth neodymium according to claim 6, characterized in that, The specific steps of the drying treatment are as follows: The light yellow oily substance is heated in a water bath to remove ether and then dried to obtain H5GeW 11 VO 40 .

8. A polyoxometalate containing rare earth neodymium, characterized in that, It is made by the preparation method described in any one of claims 1 - 7.

9. The polyoxometalate containing rare earth neodymium according to claim 8 is applied in the field of water treatment.

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