A MOFs composite film rich in nitrogen atoms, and a preparation method and application thereof

Abstract

The application belongs to the technical field of membrane and adsorption separation material preparation, and particularly relates to a MOFs composite film rich in nitrogen atoms and a preparation method and application thereof. The preparation method comprises the following steps: firstly, synthesizing UiO-66-NH2, introducing aldehyde groups on the surface of the UiO-66-NH2 through a condensation reaction, then performing amino functionalization, and finally mixing and crosslinking to obtain the MOFs film rich in nitrogen atoms. The MOFs composite film prepared by the application has good uniformity, high mechanical strength and good flexibility, and is simple and convenient to form into a film, can be used as a separation membrane for adsorbing and removing heavy metal ions in water, and can also be used for enriching and recycling rare and precious metals in metallurgical wastewater. The MOFs composite film prepared by the application has high selectivity and large adsorption capacity for molybdenum ions, and has very significant application value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of membrane and adsorption separation material preparation, and particularly relates to a MOFs composite film rich in nitrogen atoms and a preparation method and application thereof. BACKGROUND

[0002] Adsorption separation is a very important link in industrial production. Metal-organic framework (MOFs) materials have been widely used in gas phase, liquid phase adsorption and separation and other fields due to their advantages such as porosity, adjustable porosity, variable structure, easy modification and good thermal stability. However, due to the limitation of the powder form of MOFs, there are many problems in actual processing, portability and recycling. Therefore, it is of great significance to convert the powder form of MOFs into a film or other forms through a chemical method to improve its actual use performance. Membrane separation technology has the advantages of high separation efficiency and good portability, so it is of great practical value to prepare a high-performance MOFs separation film.

[0003] The preparation methods of MOFs films include in-situ growth, deposition and matrix mixing. Among them, the in-situ growth method has high requirements for the substrate, and the mechanical strength of the film obtained by the deposition method is poor, while the MOFs film prepared by the matrix mixing method has more obvious advantages, and this method is simple to operate and can greatly play the main role of MOFs. However, there is a contradiction between the MOFs loading and the mechanical strength of the composite film. In order to ensure the stability and mechanical strength of the film, a large amount of polymer is often required. This leads to a decrease in the content of MOFs in the film and a decrease in the overall adsorption separation efficiency. In addition, too much matrix polymer often leads to the blockage of the pores of MOFs, affecting the liquid flux and ion mass transfer rate of the film, further reducing the utilization efficiency of MOFs, and leading to the decline of the comprehensive performance of the composite film. Therefore, the matrix polymer is very crucial to the performance of the composite film.

[0004] Grafting a polymer on the surface of MOFs particles to obtain modified MOFs with a core-shell structure, and then obtaining a film through solvent processing can overcome the disadvantages of uneven particle distribution in simple blending. The obtained film generally has a high MOFs content and good mechanical strength, and is an ideal method. However, most of the films currently have poor hydrophilicity, and when used for metal ion adsorption and separation in an aqueous phase, the rate is slow and the mass transfer efficiency is low, and its performance needs to be further improved. By introducing nitrogen atoms into the composite film, the hydrophilicity of the material can be improved by using the electronic properties of nitrogen atoms, and the selectivity and adsorption capacity of the material for ions can also be improved by coordination ability. Therefore, it is of great significance to prepare a MOFs film rich in nitrogen atoms to improve the ion adsorption and separation efficiency, and it is worth further studying. SUMMARY

[0005] In view of the problems in the prior art, the application provides a preparation method of a MOFs composite film rich in nitrogen atoms.

[0006] To achieve the above object, the technical scheme of the application is as follows:

[0007] A MOFs composite film rich in nitrogen atoms is composed of UiO-66-NH2 with amino groups and a polymer matrix rich in nitrogen atoms.

[0008] The polymer matrix rich in nitrogen atoms is polyethylene polyamine or polyethylene imine.

[0009] Preferably, the molecular weight of the polyethylene imine is 70000.

[0010] The central metal of the UiO-66-NH2 with amino groups is one or more tetravalent metal ions.

[0011] Preferably, the tetravalent metal ion is Zr 4+ , Ti 4+ or Ce 4+ .

[0012] The ligand of the UiO-66-NH2 with amino groups is one or more amino dicarboxylic acids.

[0013] The preparation method of the MOFs composite film rich in nitrogen atoms has the characteristics that it comprises the following steps:

[0014] 1) 0.5-1g of UiO-66-NH2 with amino groups is mixed with 6.86-13.72g of 50% glutaraldehyde aqueous solution in 30-50mL anhydrous methanol, heated to reflux at 80℃ for 12-24h, and the obtained product is washed with anhydrous methanol and dried to obtain modified MOFs containing aldehyde groups, named as U-G;

[0015] 2) 0.5-1g of U-G obtained in step 1) is mixed with 0.2-2g of 50% polyethylene imine aqueous solution in 30-50mL anhydrous methanol, heated to reflux at 80℃ for 12-24h, centrifuged, washed and dried to obtain modified MOFs rich in nitrogen atoms, named as U-GP;

[0016] 3) U-GP obtained in step 2) is mixed with glutaraldehyde in a mass ratio of 40:1-40:5 in methanol, ultrasonicated after ice water bath, poured into a plastic culture dish, and heated at 80℃ for 1-2h to obtain the MOFs composite film rich in nitrogen atoms.

[0017] Further, the preparation method of the above-mentioned UiO-66-NH2 with amino groups is as follows: 1.1013 g of zirconium tetrachloride and 0.9438 g of 2-amino terephthalic acid are weighed and dissolved in 50 mL of DMF, and the solution after ultrasonic treatment is placed in a 100 mL reaction kettle and reacted at 393 K for 24 h, and after cooling to room temperature, washed with DMF and methanol; anhydrous methanol is added and aged for 72 h, and vacuum dried at 80 DEG C for 6 h to obtain UiO-66-NH2 with amino groups.

[0018] The application of the MOFs composite film rich in nitrogen atoms in adsorbing Mo(Ⅵ) according to any one of the above-mentioned.

[0019] Further, the application method is as follows: the MOFs composite film rich in nitrogen atoms is added to a Mo(Ⅵ) solution with a concentration of 50-2000 mg·L -1 , the pH of the solution is adjusted to 1-7, and the solution is oscillated and adsorbed at 30 DEG C and 180 r / min for 12-24 h.

[0020] Preferably, the application method is as follows: the pH of the solution is adjusted to 1-4.

[0021] The beneficial effects of the present application are:

[0022] 1. The MOFs composite film provided by the present application has a simple and easy-to-operate preparation method, uniform material structure, high mechanical strength, good flexibility and good hydrophilicity.

[0023] 2. The MOFs composite film provided by the present application contains a large number of nitrogen atoms, and the film is easily protonated to carry a positive charge, which is conducive to the combination of anions through electrostatic action. In addition, the nitrogen atoms can also be combined with metal ions through coordination action, and can be used for the removal of heavy metal pollutants.

[0024] 3. The MOFs composite film provided by the present application contains a large number of Schiff base structures due to covalent crosslinking by glutaraldehyde during preparation, has a high recognition and combination capacity for Mo(Ⅵ), has a large adsorption capacity, and has practical application value.

[0025] 4. The MOFs composite film provided by the present application has good adsorption effect on Mo(Ⅵ) under acidic conditions (pH 1-4).

[0026] 5. The MOFs composite film provided by the present application can be used as a separation membrane for the adsorption and removal of heavy metal ions in water, and can also be used for the enrichment and recovery of rare and precious metals in metallurgical wastewater. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1The infrared spectra of U6N, UG, U-GP and MU-GP materials in Example 1 are shown.

[0028] Figure 2 SEM images of the upper and lower surfaces of a nitrogen-rich MOF composite film, where a and b represent the upper and lower surfaces, respectively.

[0029] Figure 3 The graph shows the adsorption performance of nitrogen-rich MOF composite films for Mo(VI) under different acidity conditions.

[0030] Figure 4 The adsorption isotherm of Mo(VI) on a nitrogen-rich MOF composite film is shown.

[0031] Figure 5 The adsorption kinetics curves are for nitrogen-rich MOF composite films.

[0032] Figure 6 This is a schematic diagram of the overall synthesis pathway for nitrogen-rich MOF composite films. Detailed Implementation

[0033] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0034] Example 1: Preparation of a nitrogen-rich MOF composite film

[0035] The overall synthesis pathway of nitrogen-rich MOF composite films is as follows: Figure 6 .

[0036] 1) Synthesis of UiO-66-NH2

[0037] 1.1013 g of zirconium tetrachloride and 0.9438 g of 2-aminoterephthalic acid were weighed and dissolved in 50 mL of N,N-dimethylformamide (DMF). The solution was sonicated for 10 min, and then placed in a 100 mL reaction vessel. The reaction was carried out at 393 K for 24 h. After cooling to room temperature, the solution was washed with DMF and methanol. Anhydrous methanol was added, and the mixture was aged for 72 h and then dried under vacuum at 80 °C for 6 h to obtain an amino-containing MOF, UiO-66-NH2, which was named U6N.

[0038] like Figure 1 The U6N curve in the infrared spectrum is shown in the range of 3300–3500 cm⁻¹. -1 The appearance of the -NH2 symmetric stretching vibration peak proves that UiO-66-NH2 was successfully synthesized.

[0039] 2) UG Synthesis

[0040] 1g UiO-66-NH2, 6.86g 50% mass fraction glutaraldehyde (GA) aqueous solution were mixed in 50mL anhydrous methanol, heated to reflux at 80℃ for 24h, and the obtained product was washed with anhydrous methanol and dried to obtain the modified MOFs containing aldehyde groups, named as U-G.

[0041] Figure 1 The U-G curve in the infrared spectrum shown in the figure, 2800~2950cm -1 corresponding to the characteristic peak of C-H bond, which proves that the modification of UiO-66-NH2 is successful.

[0042] 3) Synthesis of U-GP

[0043] 1g U-G, 2g 50% mass fraction polyethyleneimine (PEI with a molecular weight of 70000) aqueous solution were mixed in 50mL anhydrous methanol, heated to reflux at 80℃ for 24h, centrifuged, washed and dried to obtain the modified MOFs rich in nitrogen atoms, and the obtained product was named as U-GP.

[0044] Figure 1 The enhancement of C-N bond in the U-GP curve in the figure proves that PEI successfully reacts with U-G.

[0045] 4) Preparation of MOFs composite film

[0046] 4mL 0.1g / mL U-GP and 3mL 0.01g / mL glutaraldehyde methanol solution were mixed after ice water bath and ultrasonic, poured into a plastic culture dish, and dried at 80℃ for 1h to obtain the MOFs composite film rich in nitrogen atoms, named as M-U-GP.

[0047] Figure 1 The M-U-GP curve in the infrared spectrum shown in the figure, after crosslinking of U-GP with glutaraldehyde, obvious N-H absorption peak was observed, and the absorption peak of C-N became obviously sharp, which proves the successful preparation of the film.

[0048] Figure 2 The SEM images shown in the figure a and b are the upper and lower sides of the MOFs composite film rich in nitrogen atoms, and it can be seen that the composite film adsorbent surface is uniform and smooth, and the MOFs particles are uniformly dispersed in the film without obvious defects.

[0049] Example 2 Application of MOFs composite film rich in nitrogen atoms in adsorbing Mo(Ⅵ)

[0050] 1) Adsorption effect of MOFs composite film rich in nitrogen atoms on Mo(Ⅵ) under different acidity

[0051] Take 5 mg of the MOFs composite film rich in nitrogen atoms prepared in Example 1, respectively, and add to 5 mL of Mo(Ⅵ) solution with a concentration of 50, 250, 500 mg·L -1 , respectively, adjust the pH of the solution to 1-7, and oscillate adsorption in a constant temperature oscillation box at 30℃ and 180 r / min for 24 h.

[0052] The adsorption results are shown in Figure 3 . Overall, the MOFs composite film has a very high adsorption efficiency for Mo(Ⅵ) at pH 2, and the adsorption rate can reach 97.43% when the concentration of Mo(Ⅵ) is 500 ppm.

[0053] 2) Adsorption isotherm of the MOFs composite film rich in nitrogen atoms for Mo(Ⅵ)

[0054] Prepare Mo(Ⅵ) solution with a concentration of 50-2000 mg·L -1 , adjust the pH to 2, take 5 mg of the MOFs composite film rich in nitrogen atoms prepared in Example 1, add to 5 mL of the above-prepared Mo(Ⅵ) solution with different concentrations, and oscillate adsorption in a constant temperature oscillation box at 30℃ and 180 r / min for 24 h.

[0055] The results are shown in Figure 4 . The linear correlation coefficient R 2 value is the largest for the Langmuir adsorption isotherm model, R 2 is 0.96, which indicates that the adsorption of the composite film for Mo(Ⅵ) belongs to monolayer adsorption, and the maximum saturation adsorption capacity of the composite film for Mo(Ⅵ) at pH 2 is 1302.47 mg·g -1 , which is fitted according to the Langmuir adsorption isotherm model.

[0056] 3) Kinetic determination of the MOFs composite film rich in nitrogen atoms for Mo(Ⅵ)

[0057] Take 5 mg of the MOFs composite film rich in nitrogen atoms prepared in Example 1, add to 5 mL of Mo(Ⅵ) solution with a concentration of 100 mg·L -1 and pH 2, and perform adsorption at temperatures of 303 K, 313 K, and 323 K, respectively, and measure the residual Mo(Ⅵ) concentration every certain time, for a continuous monitoring of 12 hours.

[0058] The test results are shown in Figure 5 . The composite film can basically reach adsorption equilibrium at 2 h.

Claims

1. A nitrogen-rich MOFs composite thin film, characterized in that, The MOFs composite film is composed of UiO-66-NH2 with amino groups and a nitrogen-rich polymer matrix; the nitrogen-rich polymer matrix is ​​polyethyleneimine. The method for preparing the nitrogen-rich MOFs composite film includes the following steps: 1) Mix 0.5-1 g of amino-containing UiO-66-NH2 with 6.86-13.72 g of 50% glutaraldehyde aqueous solution in 30-50 mL of anhydrous methanol, heat at 80℃ under reflux for 12-24 h, wash the product with anhydrous methanol and dry it to obtain aldehyde-modified MOFs, named UG; 2) Mix 0.5-1 g of UG obtained in step 1) with 0.2-2 g of 50% polyethyleneimine aqueous solution in 30-50 mL of anhydrous methanol, heat under reflux at 80°C for 12-24 h, centrifuge, wash and dry to obtain nitrogen-rich modified MOFs, named U-GP; 3) Mix the U-GP obtained in step 2) with glutaraldehyde in methanol at a mass ratio of 40:1 to 40:5, sonicate in an ice-water bath, pour into a plastic petri dish, and heat at 80°C for 1-2 hours to obtain a nitrogen-rich MOFs composite film.

2. The nitrogen-rich MOFs composite thin film according to claim 1, characterized in that, The central metal of the amino-containing UiO-66-NH2 is one or more tetravalent metal ions.

3. The nitrogen-rich MOFs composite film according to claim 2, characterized in that, The tetravalent metal ion is Zr. 4+ Ti 4+ or Ce 4+ .

4. The nitrogen-rich MOFs composite film according to claim 1, characterized in that, The ligand of the amino group UiO-66-NH2 is one or more amino dicarboxylic acids.

5. The nitrogen-rich MOFs composite film according to claim 1, characterized in that, The molecular weight of the polyethyleneimine is 70,000.

6. A nitrogen-rich MOFs composite thin film according to claim 1, characterized in that, The preparation method of the amino-containing UiO-66-NH2 is as follows: Weigh 1.1013 g of zirconium tetrachloride and 0.9438 g of 2-aminoterephthalic acid, dissolve them in 50 mL of DMF, sonicate for 10 min, put the sonicated solution into a 100 mL reaction vessel, react at 393 K for 24 h, cool to room temperature, wash with DMF and methanol, add anhydrous methanol and age for 72 h, and vacuum dry at 80 °C for 6 h to obtain amino-containing UiO-66-NH2.

7. The application of the nitrogen-rich MOFs composite film according to any one of claims 1-5 in the adsorption of Mo(VI).

8. The application according to claim 7, characterized in that, The method is as follows: Nitrogen-rich MOF composite films are added to solutions with concentrations of 50-2000 mg·L⁻¹. -1 In a Mo(VI) solution, the pH of the solution was adjusted to 1-7, and the solution was shaken and adsorbed for 12-24 h at 30℃ and 180 r / min.

9. The application according to claim 8, characterized in that, Adjust the pH of the solution to 1-4.

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