Rare earth-polyacid-based compound, preparation method and application thereof

Abstract

The application belongs to the technical field of functional crystalline compound synthesis, and discloses a rare earth-polyacid-based compound and a preparation method and application thereof. 12 O 40 ] and the cell parameter is: the preparation method is as follows: H3[PMo 12 O 40 ] solution is used as a lower solution, an organic solvent is used as an intermediate buffer layer solution, a mixed solution of Dy(NO3)3.6H2O and 4-hydroxy azobenzene-2-carboxylic acid is used as an upper solution C, which is sequentially added to a container, a layered state is maintained, and the container is left to stand until crystal particles appear in the middle layer, and the crystal particles are the rare earth-polyacid-based compound. The compound has excellent electrocatalytic properties and can be applied to nitrite detection and redox.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of synthesis of functional crystalline compounds, and particularly relates to a rare earth-polyacid-based compound and a preparation method and application thereof. BACKGROUND

[0002] Nitrite is not only harmful to human health, but also a major water pollutant. Electro-catalytic reduction of nitrite is not only conducive to reducing the pollution of nitrite to the environment, but also can synthesize a chemical with high utilization value, ammonia (NH3). However, the reduction of nitrite is a complex process involving multiple electron and proton transfers, and the reaction path is: *NO2→*NO→*N→*NH→*NH2→*NH3, wherein the N=O chemical bond has a large bond energy (236 kJ / mol), making it difficult to dissociate the *NO intermediate. The complex reaction process and the large dissociation energy of the intermediate result in low activity and poor selectivity of electro-catalytic reduction of nitrite to synthesize ammonia, and it is a great challenge to develop a catalytic system with high selectivity for catalytic reduction of nitrite to synthesize ammonia.

[0003] Polyoxometalates (referred to as polyoxometalates) have reversible redox properties and strong electron accepting and transferring ability, and are ideal candidate materials for supercapacitors and electro-catalysts. Rare earth metals have high coordination number and oxygen affinity, and the introduction of rare earth ions into polyoxometalates can change the spatial arrangement of polyoxometalate anions, change the Bronsted basicity of polyoxometalate ions, and thus improve the catalytic activity. At the same time, after coordination, the redox point of the rare earth element can be changed, thereby changing the catalytic activity. However, due to the easy hydrolysis of rare earth ions and the strong reaction activity between rare earth ions and polyoxometalates, it is easy to precipitate and difficult to crystallize, and in addition to the coordination competition between different metal ions and polyoxometalates, the design and synthesis of rare earth-polyacid-based compounds are difficult. Therefore, the design and synthesis of rare earth-polyacid-based compounds is also a great challenge. SUMMARY

[0004] The present application aims to at least partially solve the above technical problems, and aims to provide a rare earth-polyacid-based organic-inorganic hybrid compound and a preparation method and application thereof, which has excellent electro-catalytic performance and can be applied to the detection and reduction of nitrite.

[0005] In a first aspect of the present application, a rare earth-polyacid-based compound is provided, and the chemical formula of the rare earth-polyacid-based compound is [Dy(DMF)8][PMo 12 O 40 ], and the unit cell parameters are:

[0006] The second aspect of the present application provides a preparation method of the rare earth-polyacid-based compound, which comprises: sequentially adding a lower solution A, an intermediate buffer layer solution B and an upper solution C into a container, maintaining a layered state, and standing until crystal particles appear in the intermediate layer of the container, wherein the crystal particles are the rare earth-polyacid-based organic-inorganic hybrid compound [Dy(DMF) 8] [PMo 12 O 40 ]; the lower solution A is a H 3 [PMo 12 O 40 ] solution; the intermediate buffer layer solution B is an organic solvent; and the upper solution C is a mixed solution of Dy(NO 3 ) 3 ·6H 2 O and 4-hydroxyazobenzene-2-carboxylic acid.

[0007] In some embodiments of the present application, the preparation method of the lower solution A comprises: dissolving H 3 [PMo 12 O 40 ] in a mixed solution of N,N-dimethylformamide and ethylene glycol.

[0008] In some embodiments of the present application, the ratio of the amount of H 3 [PMo 12 O 40 ] to the mixed solution of N,N-dimethylformamide and ethylene glycol is (0.1-0.3) g:(5-15) mL.

[0009] In some embodiments of the present application, the volume ratio of N,N-dimethylformamide to ethylene glycol in the mixed solution of N,N-dimethylformamide and ethylene glycol is 1:3.

[0010] In some embodiments of the present application, the intermediate buffer layer solution B is a mixed solution of N,N-dimethylformamide and ethylene glycol.

[0011] In some embodiments of the present application, the volume ratio of N,N-dimethylformamide to ethylene glycol in the intermediate buffer layer solution B is 1:1.

[0012] In some embodiments of the present application, the preparation method of the upper solution C comprises: dissolving Dy(NO 3 ) 3 ·6H 2 O in DMF, adding 4-hydroxyazobenzene-2-carboxylic acid, stirring at room temperature for 20-40 min, and forming an orange-red upper solution C.

[0013] In some embodiments of the present application, the ratio of the amount of Dy(NO 3 ) 3 ·6H 2 O, 4-hydroxyazobenzene-2-carboxylic acid and DMF is 0.18 g:(0-0.30) g:8 mL.

[0014] In some embodiments of the present application, the ratio of the amount of H 3 [PMo 12 O 40The mass ratio of the rare earth element and Dy(NO3)3·6H2O is 1:1.

[0015] In a third aspect of the present application, the rare earth-polyacid-based compound provided above or prepared by the preparation method provided above is applied to detection of nitrite or electrocatalytic reduction of nitrite.

[0016] In some embodiments of the present application, the nitrite is potassium nitrite or sodium nitrite.

[0017] In a fourth aspect of the present application, a method for electrocatalytic reduction of sodium nitrite is provided, which comprises: preparing the rare earth-polyacid-based compound provided above or prepared by the preparation method provided above into a carbon paste electrode, taking the carbon paste electrode as a working electrode, taking an Ag / AgCl electrode as a reference electrode, and taking a platinum electrode as a counter electrode to form a three-electrode system, and placing the three-electrode system in a sulfuric acid solution containing NaNO2 to perform an electrocatalytic reduction reaction.

[0018] The rare earth-polyacid-based compound and the preparation method and application thereof according to the embodiments of the present application have at least one of the following advantages:

[0019] (1) The rare earth element has a unique 4f electron structure and chemical property, the doping of the rare earth ion increases the number of surface active sites and improves the charge transfer, thereby effectively adjusting the electronic structure and electrocatalytic performance of the catalyst, and the rare earth ion Dy 3+ is coordinated with N,N-dimethylformamide to form a stable complex, so that the rare earth ion exists stably in the polyacid system.

[0020] (2) The rare earth complex forms a stable structure with the polyacid PMo 12 through electrostatic attraction, and based on a large number of hydrogen bonds, forms a 3D supramolecular structure, and the rich hydrogen bond network promotes reversible electron and proton transfer, thereby improving the electrocatalytic efficiency.

[0021] (3) The rare earth-polyacid-based compound prepared by the present application has excellent electrocatalytic properties, and can be applied to detection and redox of nitrite.

[0022] (4) The preparation method provided by the present application is simple in process and easy to promote in industry. BRIEF DESCRIPTION OF DRAWINGS

[0023] These and / or other aspects and advantages of the present application will become apparent and readily understood from the following description, taken in connection with the accompanying drawings, in which:

[0024] Figure 1 The rare earth-polyacid-based compound [Dy(DMF)8][PMo 12 O40 Molecular structure diagram of the compound [Dy(DMF)8][PMo

[0025] Figure 2 The rare earth-molybdophosphoric acid-based compound [Dy(DMF)8][PMo 12 O 40 3D supramolecular structure diagram of the compound [Dy(DMF)8][PMo

[0026] Figure 3 The rare earth-molybdophosphoric acid-based compound [Dy(DMF)8][PMo 12 O 40 Infrared spectrum of the compound [Dy(DMF)8][PMo

[0027] Figure 4 The rare earth-molybdophosphoric acid-based compound [Dy(DMF)8][PMo 12 O 40 Ultraviolet spectrum of the compound [Dy(DMF)8][PMo

[0028] Figure 5 Cyclic voltammograms of the compound [Dy(DMF)8][PMo

[0029] Figure 6 Cyclic voltammograms of the compound [Dy(DMF)8][PMo 12 O 40 Cyclic voltammograms of the compound [Dy(DMF)8][PMo DETAILED DESCRIPTION

[0030] The technical solutions of the present application will be further described below by way of examples in conjunction with the accompanying drawings. In the description, identical or similar reference numerals indicate identical or similar components. The following description of the embodiments of the present application with reference to the accompanying drawings is intended to explain the general inventive concept of the present application, and should not be construed as limiting the present application in any way.

[0031] The H3[PMo 12 O 40 ] used in the embodiments of the present application is prepared by the following method:

[0032] 1. 10.5 g of Na2MoO4·2H2O is weighed and dissolved in 21 mL of distilled water, and stirred until completely dissolved. 1 mL of concentrated H3PO4 is added, followed by 10 mL of concentrated HCl, and stirred for 40 min.

[0033] 2. The solution is transferred to a 250 mL separatory funnel, and 15 mL of ether is measured and manually shaken for 30 min until the solution is completely mixed. After cooling and standing for 20 min, the solution is separated into two layers, and the lower layer is separated.

[0034] 3. To the lower solution obtained in step 2, 10 mL of distilled water was added, shaken for 3 min, then 8 mL of ether was added, shaken for 30 min, left to stand, the solution was separated into two layers, and the lower layer was separated.

[0035] 4. To the lower solution obtained in step 3, 2 mL of distilled water was added, a blue color appeared in the solution, concentrated HNO3 was slowly added until it turned yellow, and it was left to stand in a water bath at 80°C for 30 min, a large amount of yellow solid was produced, which was separated and dried to obtain the pure product H3[PMo 12 O 40 ].

[0036] Example 1

[0037] Step 1: 0.05 g of H3[PMo 12 O 40 ] was dissolved in a mixed solution of 8 mL of N,N-dimethylformamide and ethylene glycol (V:V = 1:3) to form a clear light yellow solution A, which was used as the lower layer of the test tube;

[0038] Step 2: a mixed solution B of 3 mL of N,N-dimethylformamide and ethylene glycol (V:V = 1:1) was prepared as the middle buffer layer;

[0039] Step 3: 0.18 g of Dy(NO3)3·6H2O was dissolved in 8 mL of N,N-dimethylformamide, then 0.24 g of 4-hydroxyazobenzene-2-carboxylic acid was added, and the solution was stirred at room temperature for 30 min to form an orange-red solution C as the upper layer;

[0040] Step 4: solutions A, B, and C were placed in the test tube as the lower, middle, and upper layers, respectively, and left to stand for 24 h, and crystal particles appeared in the middle layer of the test tube.

[0041] Example 2

[0042] Step 1: 0.18 g of H3[PMo 12 O 40 ] was dissolved in a mixed solution of 8 mL of N,N-dimethylformamide and ethylene glycol (V:V = 1:3) to form a clear light yellow solution A, which was used as the lower layer of the test tube;

[0043] Step 2: a mixed solution B of 3 mL of N,N-dimethylformamide and ethylene glycol (V:V = 1:1) was prepared as the middle buffer layer;

[0044] Step 3: 0.18 g of Dy(NO3)3·6H2O was dissolved in 8 mL of N,N-dimethylformamide, then 0.24 g of 4-hydroxyazobenzene-2-carboxylic acid was added, and the solution was stirred at room temperature for 30 min to form an orange-red solution C as the upper layer;

[0045] Fourth step: Put solution A, B, C as lower, middle, upper layer into the test tube in turn, stand for 24h, the middle layer of test tube appears crystal particles.

[0046] Example 3

[0047] First step: Dissolve 0.18g of H3[PMo 12 O 40 ] in 8ml N,N-dimethylformamide and ethylene glycol (V:V = 1:3) mixed solution to form a clear light yellow solution A, and the solution A is used as the lower layer of the test tube;

[0048] Second step: Prepare 3ml of N,N-dimethylformamide and ethylene glycol (V:V = 1:1) mixed solution B as the middle buffer layer;

[0049] Third step: Dissolve 0.18g of Dy(NO3)3·6H2O in 8ml N,N-dimethylformamide, stir at room temperature for 30min to form an orange red solution C as the upper layer;

[0050] Fourth step: Put solution A, B, C as lower, middle, upper layer into the test tube in turn, stand for 24h, the middle layer of test tube appears precipitate.

[0051] Examples 1 and 2 are different H3[PMo 12 O 40 ] mass effects on the reaction, both examples 1 and 2 can get crystals, but the crystal of example 1 grows badly, which may be due to the low concentration of polyacid, and the reaction with rare earth ions is not suitable for matching, resulting in poor crystal quality. In example 3, no 4-hydroxyazobenzene-2-carboxylic acid is added, and no compound is obtained, only precipitate, indicating that 4-hydroxyazobenzene-2-carboxylic acid is important for synthesis.

[0052] Test example 1

[0053] The high-quality single crystal selected from the crystal prepared in example 2 is used for structure determination, as follows:

[0054] The single crystal is tested and all diffraction data are collected by Bruker APEX-II CCD at 296K and by Bruker D8 VENTURE PHOTONII single crystal diffractometer at 150K, and the radiation source is Mo Kα ray of graphite monochromator The hydrogen atom coordinates on the water molecule are obtained by difference Fourier synthesis method, all non-hydrogen atom coordinates are obtained by direct method, and are optimized by anisotropic thermal parameter correction and matrix least square method, and the hydrogen atoms are directly added to the molecular formula. The crystallographic data and structure parameters are shown in table 1, and the compound structure diagram and 3D supramolecular structure diagram are respectively as Figure 1 and 2As shown.

[0055] The infrared and ultraviolet spectra of the compound are as follows: Figure 3 and Figure 4 As shown. In the infrared spectrum of the compound, it appears in the 1200-1800 cm⁻¹ range. -1 The peaks in the wavenumber range were assigned to the characteristic vibrational peaks of the ligand DMF. A redshift was also observed in the characteristic vibrational peak of the C=O bond, from 1678 cm⁻¹. -1 (Free DMF molecules) migrated to 1654 cm⁻¹ -1 The wavenumbers near the specified values ​​indicate that the rare earth ions are coordinated with the O atoms on the C=O axis in the DMF. The compound exhibits four characteristic peaks of the Keggin structure, at 1061, 956, 877, and 803 cm⁻¹. –1 They are respectively classified as PO a Stretching vibration of the bond, Mo-O d The stretching vibration of Mo-O c stretching vibration and Mo-O d The stretching vibration peak, of which O a O d O b and O c These represent bridging oxygen atoms within the Keggin structure, at the ends, between different groups of MoO6 octahedra, and between octahedra within the same group. 3532cm -1 The peak at 3000 cm⁻¹ is attributed to intermolecular hydrogen bonds. -1 The absorption bands on the left and right belong to the -CH stretching vibration of the methyl group on the DMF molecule.

[0056] Table 1

[0057]

[0058] Test Example 2

[0059] Weigh 0.01g of each rare earth-polyacid compound [Dy(DMF)8][PMo] 12 O 40 0.10g of graphite is placed in an agate mortar and ground for 30 minutes to ensure thorough mixing. 1mL of liquid paraffin is added and stirred until homogeneous. The mixture is then sealed in a polytetrafluoroethylene tube with an inner diameter of 3mm and a length of 5cm containing a copper rod. The tube is gently pressed and the surface is polished to a smooth finish to form a carbon paste electrode of the compound.

[0060] The carbon paste electrode is used as a working electrode, the Ag / AgCl electrode is used as a reference electrode, and the platinum electrode is used as a counter electrode to form a three-electrode system, and the cyclic voltammograms are obtained in the potential range of 1.6 to-0.6 V in 0.1 mol / L H2SO4 solution at different scanning rates (0.01, 0.02, 0.04, 0.06, 0.08, 0.10, 0.15 V / s), as shown in Figure 5 . Figure 5 It can be seen that the symmetry of the image is good with the increase of the scanning rate, and the electrocatalytic reversibility is good.

[0061] The carbon paste electrode is used as a working electrode, the Ag / AgCl electrode is used as a reference electrode, and the platinum electrode is used as a counter electrode to form a three-electrode system, and the cyclic voltammograms are obtained in the potential range of 1.6 to-0.6 V in 0.1 mol / L H2SO4 solution at different scanning rates (0.01, 0.02, 0.04, 0.06, 0.08, 0.10, 0.15 V / s), as shown in Figure 6 . With the increase of the concentration of the NaNO2 solution, all the reduction peak currents increase, and the corresponding oxidation peak currents significantly decrease, indicating that the rare earth-polyacid-based compound [Dy(DMF)8][PMo 12 O 40 ] has electrocatalytic activity to NaNO2.

[0062] The rare earth-polyacid-based compound and the preparation method and application thereof according to the embodiments of the present application have at least one of the following advantages:

[0063] (1) The rare earth element has a unique 4f electron structure and chemical property, the doping of the rare earth ion increases the number of surface active sites and improves the charge transfer, thereby effectively adjusting the electronic structure and electrocatalytic performance of the catalyst, and the patent coordinates the easily hydrolyzed rare earth ion Dy 3+ with N,N-dimethylformamide to form a stable complex, so that the rare earth ion exists stably in the polyacid system.

[0064] (2) The rare earth complex forms a stable structure with the polyacid PMo 12 through electrostatic attraction, and a 3D supramolecular structure is constructed based on a large number of hydrogen bonds, and the rich hydrogen bond network promotes reversible electron and proton transfer, thereby improving the electrocatalytic efficiency.

[0065] (3) The rare earth-polyacid-based compound prepared by the present application has excellent electrocatalytic properties and can be applied to the detection and redox of sodium nitrite.

[0066] (4) The preparation method provided by the present application is simple and easy to promote.

Claims

1. A method for producing a rare earth-polyacid-based compound, characterized by, The preparation method comprises: sequentially adding a lower layer solution A, an intermediate buffer layer solution B and an upper layer solution C into a container, maintaining a layered state, and standing until crystal particles appear in the intermediate layer of the container, wherein the crystal particles are a rare earth-polyacid-based organic-inorganic hybrid compound [Dy(DMF)8][PMo 12 O 40 ] The preparation method of the lower layer solution A is: dissolving H3[PMo 12 O 40 ] in a mixed solution of N,N-dimethylformamide and ethylene glycol to obtain; The intermediate buffer layer solution B is a mixture of N,N-dimethylformamide and ethylene glycol; The preparation method of the upper layer solution C is: dissolving Dy(NO3)3·6H2O in DMF, then adding 4-hydroxyazobenzene-2-carboxylic acid, stirring at room temperature for 20-40 min, and forming an orange-red upper layer solution C; wherein the mass ratio of H3[PMo 12 O 40 ] to Dy(NO3)3-6H2O is 1:

1.

2. The production method according to claim 1, characterized by, H3[PMo 12 O 40 The use amount ratio of the mixed solution of the H3[PMo12O40] and the N,N-dimethylformamide and ethylene glycol is (0.1-0.3) g:(5-15) mL.

3. The preparation method according to claim 1, characterized in that, The ratio of the use amounts of Dy(NO3)3·6H2O, 4-hydroxyazobenzene-2-carboxylic acid and DMF is 0.18 g:(0-0.30) g:8 ml.

4. A rare earth-polyacid-based compound prepared according to the preparation method of any one of claims 1-3, having a chemical formula of [Dy(DMF)8][PMo 12 O 40 ], with a unit cell parameter of a = 13.4660(15) Å, b = 18.500(2) Å, c = 26.960(3) Å, V = 6683.9(13) Å 3 .

5. The application of the rare earth-polyacid-based compound prepared by the preparation method in any one of claims 1-3 or the rare earth-polyacid-based compound in claim 4 in electrocatalytic reduction of nitrite.

6. A method of electrocatalytically reducing sodium nitrite, characterized in that The method is: preparing the rare earth-polyacid-based compound prepared by the preparation method in any one of claims 1-3 or the rare earth-polyacid-based compound in claim 4 into a carbon paste electrode, taking the carbon paste electrode as a working electrode, taking an Ag / AgCl electrode as a reference electrode, and taking a platinum electrode as a counter electrode to form a three-electrode system, and placing the three-electrode system in a sulfuric acid solution containing sodium nitrite to perform an electrocatalytic reduction reaction.

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