MOFs cross-linked composite film as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of preparation of membrane materials and adsorption separation materials, and particularly relates to an MOFs / PVA cross-linked composite film as well as a preparation method and application thereof. The preparation method comprises the following steps: modifying MOFs with amino on the surface to enable the surface of the MOFs to have silicon hydroxyl, then mixing with polyvinyl alcohol (PVA), and heating and drying in a mold to obtain the MOFs / PVA cross-linked composite film. The cross-linked composite film provided by the invention is uniform and continuous, and the problem of poor dispersibility of the MOFs material in the mixed matrix film is solved. The film has good adsorption capacity on metal ions such as molybdate radicals, is high in hydrophilicity and still has a stable film structure in an acid environment, and an effective solution is provided for treatment of heavy metal pollution in industrial wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of membrane materials and adsorption separation materials, and particularly relates to a MOFs / PVA cross-linked composite film, a preparation method thereof, and an application thereof. Background Art

[0002] Metal-organic framework (MOFs) materials have the advantages of high porosity, large specific surface area, easy functionalization, etc., and have irreplaceable advantages in adsorption separation. However, MOFs are usually powders, and there are problems such as easy dispersion and aggregation, and difficult effective recycling in practical applications. Therefore, it has very important practical significance to convert MOFs powders into film forms for practical applications through certain methods.

[0003] At present, the common preparation methods of MOF mixed matrix membranes in the prior art mainly include solution casting method, phase inversion method, interfacial polymerization method, etc. Among them, the solution casting method is the most commonly used method. Its basic steps are to disperse MOFs particles into a polymer solution, and then cast it on a flat substrate to form a film through solvent evaporation. However, this type of method has significant limitations: First, due to the poor compatibility between MOFs particles and the polymer matrix, MOFs particles are prone to agglomeration in the polymer solution, resulting in uneven distribution of MOFs in the film and affecting the performance of the film. Second, interface defects such as voids or cracks are easily formed between MOFs particles and the polymer matrix, and these defects will become non-selective transmission channels for gas molecules, reducing the selectivity of the film. In addition, in order to obtain a continuous polymer matrix, the loading amount of MOFs is usually small. An excessive loading amount of MOFs will lead to a decrease in the mechanical properties of the film, and even a self-supporting film cannot be formed. Therefore, developing a simple, efficient, and scalable method for preparing high-performance MOF mixed matrix membranes is still a challenge.

[0004] By reasonably selecting organic ligands with active functional groups, modifiable active sites can be constructed on the surface of metal-organic framework materials (MOFs). Based on these active sites, chemical modification is carried out to form strong chemical bonds, which can significantly enhance the interfacial binding force between MOFs and the polymer matrix and effectively avoid the phase separation problem that easily occurs in traditional physical mixing. This covalent cross-linking network can inhibit the structural collapse of MOFs in humid or solvent environments. In addition, introducing hydrophilic polymers as cross-linking agents is also beneficial to improving the performance of composite films. On the one hand, it can effectively reduce the surface contact angle of the composite film and increase the permeation flux of water molecules or polar substances, which is particularly suitable for water treatment; on the other hand, it can effectively disperse MOFs particles and inhibit their agglomeration, while overcoming the defects of high brittleness and difficulty in forming independent films of traditional MOF materials. However, the composite process of MOFs and hydrophilic polymers involves multiple-step chemical reactions and fine structure regulation, and problems such as unsatisfactory mechanical strength and easy cracking of the final film often occur. Therefore, based on modified MOFs, realizing their controllable composite with hydrophilic polymers has important research significance. Obtaining hydrophilic MOF mixed matrix membranes with excellent structural stability can promote the development of related fields such as film preparation and ion adsorption separation, and has important application value. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention provides a MOFs / PVA cross-linked composite film and discloses its preparation method.

[0006] The technical solution adopted by the present invention is as follows: A MOFs / PVA cross-linked composite film, and the preparation method includes the following steps:

[0007] 1) Synthesize MOFs with amino groups by hydrothermal method;

[0008] 2) React the MOFs prepared in step 1) with an epoxy group silane coupling agent;

[0009] 3) Hydrolyze the product obtained in step 2) under acidic conditions to obtain MOFs with silanol groups on the surface;

[0010] 4) Mix the MOFs with silanol groups on the surface prepared in step 3) and the polymer PVA in a certain proportion, coat on the surface of the substrate, and obtain the MOFs / PVA cross-linked composite film after drying.

[0011] For the above-mentioned MOFs / PVA cross-linked composite film, in step 1), the central metal of the MOFs with amino groups is Zr 4+ , Ti 4+ , Ce 4+ , Zn 2+ , Co 2+ , Cu 2+ , Ni2+ One or more of them, and its ligand is one or more dicarboxylic acid ligands containing amino groups.

[0012] For one of the above-mentioned MOFs / PVA cross-linked composite films, in step 2), the epoxy group silane coupling agent is 3-glycidoxypropyltrimethoxysilane.

[0013] For one of the above-mentioned MOFs / PVA cross-linked composite films, in step 4), the molecular weight range of the PVA is 74000 - 80000, and the PVA is a single molecular weight or a mixture of several molecular weights.

[0014] For one of the above-mentioned MOFs / PVA cross-linked composite films, in step 4), the mass ratio range of the MOFs with silicon hydroxyl groups on the surface to PVA is 1:2 - 1:0.5.

[0015] Furthermore, for the above-mentioned MOFs / PVA cross-linked composite film, the optimal mass ratio of the MOFs with silicon hydroxyl groups on the surface to PVA with hydroxyl groups in the molecular chain is 1:0.8.

[0016] Furthermore, the preparation method of the above-mentioned MOFs / PVA cross-linked composite film includes the following steps:

[0017] 1) Using zirconium tetrachloride and 2-aminoterephthalic acid as raw materials, synthesize MOFs with amino groups (UiO-66-NH2) by hydrothermal method;

[0018] 2) Take 1 - 10 g of UiO-66-NH2 obtained in step 1), use a cell crusher to disperse it in 30 - 300 mL of anhydrous methanol, add 10 - 100 g of 3-glycidoxypropyltrimethoxysilane (GPTMS), and reflux and react for 24 - 48 h in an environment of 50 - 90 °C. After the reaction, wash and centrifuge the product with anhydrous methanol three times repeatedly, remove the supernatant, and obtain an intermediate product, named U6N-G;

[0019] 3) Take 1 - 10 g of U6N-G obtained in step 2), use a water bath ultrasonic machine to disperse it in 30 - 300 mL of 0.1 M HCl solution, and reflux and react for 24 - 48 h in an environment of 35 - 65 °C to obtain a hydrolyzed solution of modified MOFs with silicon hydroxyl groups on the surface, named U6N-G-OH;

[0020] 4) Add 2.5 - 5 g of PVA to 47.5 - 95 mL of water, and reflux and dissolve it for 3 - 6 h in an environment of 80 - 98 °C to obtain a 5% mass concentration PVA aqueous solution;

[0021] 5) Mix the hydrolyzed solution of the modified MOFs obtained in step 3) and the PVA aqueous solution obtained in step 4) in proportion, ultrasonically bath for 25 - 30 min, then pour it into a plastic petri dish and dry it in an oven at 45 - 60 °C for 6 h to obtain the MOFs / PVA crosslinked composite film.

[0022] The application of the above-mentioned MOFs / PVA crosslinked composite film in the field of adsorption and separation.

[0023] Furthermore, for the above application, the application of the above-mentioned MOFs / PVA crosslinked composite film in adsorbing Mo(Ⅳ).

[0024] Furthermore, for the above application, the method is as follows: Add the MOFs / PVA crosslinked composite film into the Mo(Ⅳ) solution for adsorption.

[0025] Furthermore, for the above application, the adsorption is carried out at a pH of 1 - 7, oscillating and adsorbing at 30 °C and 180 r / min for 24 h.

[0026] Furthermore, for the above application, the concentration of the Mo(Ⅳ) solution is 10 - 300 mg / L.

[0027] The beneficial effects of the present invention are as follows:

[0028] 1. The MOFs / PVA crosslinked composite film provided by the present invention has a rapid and simple preparation method, and the prepared MOFs / PVA crosslinked composite film is uniform and continuous, suitable for large-scale processing and production.

[0029] 2. In the MOFs / PVA crosslinked composite film prepared by the present invention, MOFs and PVA are connected by covalent bonds, and the MOFs in the film are fixed by PVA without falling off.

[0030] 3. The MOFs / PVA crosslinked composite film prepared by the present invention has good hydrophilicity and water stability, and can be applied to separation in an aqueous environment.

[0031] 4. The MOFs / PVA crosslinked composite film prepared by the present invention has the maximum adsorption rate at pH = 3 - 4. At this time, molybdenum in the solution mainly exists in the forms of H3Mo7O 24 3- 、H2Mo7O 24 4- 、HMo7O 24 5- 、Mo8O 26 4- The maximum adsorption amount of molybdenum by this film is 70.74 mg / g in an environment with a pH of 3. Description of the Drawings

[0032] Figure 1 Synthesis route diagram of the hydrolyzed solution of modified MOFs in Example 1.

[0033] Figure 2 Photo of the MOFs / PVA crosslinked composite film with modified MOFs:PVA = 1:0.8.

[0034] Figure 3 Infrared spectra of UiO-66-NH2, U6N-G, U6N-G-OH, and the MOFs / PVA crosslinked composite film with modified MOFs:PVA = 1:0.8 in Example 1.

[0035] Figure 4 Scanning electron micrographs of UiO-66-NH2 (a) and the MOFs / PVA crosslinked composite film with modified MOFs:PVA = 1:0.8 (b) in Example 1.

[0036] Figure 5 Analysis diagram of the adsorption performance of the MOFs / PVA crosslinked composite film with modified MOFs:PVA = 1:0.8 for Mo(Ⅳ) at different pH values.

[0037] Figure 6 Isothermal adsorption curve of the MOFs / PVA crosslinked composite film with modified MOFs:PVA = 1:0.8 for Mo(Ⅳ).

[0038] Figure 7 Pseudo-second-order kinetic fitting curve of the MOFs / PVA crosslinked composite film with modified MOFs:PVA = 1:0.8.

[0039] Figure 8 Adsorption thermodynamic fitting curve of the MOFs / PVA crosslinked composite film with modified MOFs:PVA = 1:0.8 for Mo(Ⅳ).

[0040] Figure 9 Analysis diagram of the maximum adsorption capacity of the MOFs / PVA crosslinked composite films with modified MOFs:PVA = 1:1, 1:0.8, and 1:0.6 for Mo(Ⅳ). Detailed implementation method

[0041] Preparation of the MOFs / PVA crosslinked composite film in Example 1

[0042] (I) Preparation method

[0043] 1) Measure 50 mL of N,N-dimethylformamide (DMF), add 1.4 mL of concentrated hydrochloric acid and stir evenly. Then add 0.9438 g of zirconium tetrachloride and 1.1013 g of 2-aminoterephthalic acid. Ultrasonically bath the solution at room temperature for 30 min, then transfer it to a 100 mL autoclave and react at 120 °C for 24 h. After the reaction, cool it to room temperature. Wash the product with DMF and methanol by centrifugation three times each, dry it in an oven at 60 °C for 10 h, and then vacuum dry it in an 80 °C environment for 6 h to obtain MOFs with amino groups, named UiO-66-NH2;

[0044] 2) Add 1 g of UiO-66-NH2 and 10 mL of anhydrous methanol to a sample bottle. After ultrasonically crushing the cells for 30 min, transfer it to a single-neck round-bottom flask. Then add 10 g of 3-glycidoxypropyltrimethoxysilane (GPTMS) and 20 mL of anhydrous methanol. After ultrasonically bathing in water for 10 min, reflux it in an electric heating mantle or oil bath at 80 °C for 24 h. Wash the obtained product with anhydrous methanol by centrifugation repeatedly three times to obtain MOFs with methoxysilyl groups on the surface, named U6N-G;

[0045] 3) Add 30 mL of 0.1 M HCl solution to U6N-G obtained in step 2), heat and stir it in an electric heating mantle or oil bath at 40 °C for 24 h. After centrifuging the obtained product to remove the supernatant, dissolve it in 4 mL of methanol to obtain a hydrolyzed solution of modified MOFs with silanol groups on the surface. Measure the solid content to be 0.21 g / mL, named U6N-G-OH; (The first three steps of the preparation method are as Figure 1 shown)

[0046] 4) Place 2.5 g of polyvinyl alcohol (PVA) and 47.5 g of deionized water in a 100 mL single-neck round-bottom flask and reflux it in an electric heating mantle or oil bath at 97 °C until completely dissolved to obtain a 5% mass concentration PVA solution;

[0047] 5) Use a pipette to take 0.6 mL of the hydrolyzed solution of modified MOFs into a sample bottle, add 1.9 mL of 5% mass concentration PVA solution, ultrasonically mix it in water bath for 25 min, then pour it into a mold and send it to an oven at 50 °C to dry, and then a cross-linked composite film of MOFs / PVA with a mass ratio of modified MOFs:PVA of 1:0.8 can be obtained. The film is as Figure 2 shown.

[0048] (II) Characterization

[0049] Figure 3 For the infrared spectra of UiO-66-NH2, U6N-G, U6N-G-OH, and the cross-linked composite film of MOFs / PVA with a mass ratio of modified MOFs:PVA of 1:0.8 in Example 1. In the figure, at 3390 cm -1The symmetric stretching vibration peak of -NH2 appearing on the left and right proves the successful synthesis of UiO-66-NH2; 765 cm -1 The peak appearing around corresponds to the C-Si bond, proving the successful modification of UiO-66-NH2 by GPTMS.

[0050] Figure 4 In, a is the scanning electron microscope image of UiO-66-NH2. It can be seen that UiO-66-NH2 is stacked in blocks; b is the scanning electron microscope image of the modified MOFs / PVA cross-linked composite film with a ratio of modified MOFs:PVA of 1:0.8 in Example 1, indicating that the modified MOFs are evenly and tightly distributed on the film surface and there are many pore structures.

[0051] Application of the MOFs / PVA cross-linked composite film in Example 2 for the adsorption of Mo(Ⅳ)

[0052] (I) Adsorption effect of the MOFs / PVA cross-linked composite film on Mo(Ⅳ) at different acidities

[0053] Method: Weigh 7 portions of 5 mg of the modified MOFs / PVA cross-linked composite film with a ratio of modified MOFs:PVA of 1:0.8 prepared in Example 1, and add them to 5 mL of Mo(Ⅳ) solution with a concentration of 20 mg / L respectively. Adjust the pH of the solution to 1, 2, 3, 4, 5, 6, 7, and oscillate and adsorb in an oscillation box at 30 °C and 180 r / min for 24 h.

[0054] The average adsorption rate results after three adsorption tests are as Figure 5 shown. It can be seen from the figure that the adsorption rate of this film for Mo(Ⅳ) is the largest at pH = 3, thus enabling the recovery of Mo(Ⅳ).

[0055] (II) Isothermal adsorption curve of the MOFs / PVA cross-linked composite film for the adsorption of Mo(Ⅳ)

[0056] Method: Prepare Mo(Ⅳ) solutions with concentrations of 10 mg / L, 20 mg / L, 50 mg / L, 80 mg / L, 100 mg / L, 120 mg / L, 150 mg / L, 180 mg / L, 200 mg / L, 250 mg / L, and 300 mg / L respectively, adjust the pH to 3, weigh 11 portions of 5 mg of the modified MOFs / PVA cross-linked composite film with a ratio of modified MOFs:PVA of 1:0.8 prepared in Example 1, and add them to 5 mL of the above-prepared Mo(Ⅳ) solutions with different concentrations respectively, and place them in an oscillation box at 30 °C and 180 r / min and oscillate for 24 h.

[0057] The results are as Figure 6 shown. The data fits well with the Langmuir isothermal adsorption model, and the linear correlation coefficient R 2It is 0.92, indicating that the adsorption of Mo(IV) by the MOFs / PVA crosslinked composite film belongs to monolayer adsorption, and the maximum adsorption capacity obtained by fitting with the Langmuir isothermal adsorption model is 70.74 mg / g.

[0058] (III) Determination of the adsorption kinetics of the MOFs / PVA crosslinked composite film

[0059] Method: Weigh 3 portions of 5 mg of the MOFs / PVA crosslinked composite film with a modified MOFs:PVA ratio of 1:0.8 prepared in Example 1, and add them to 5 mL of Mo(IV) solutions with concentrations of 20 mg / L, 50 mg / L, and 100 mg / L respectively. The pH of the solution is 3. Oscillate and adsorb in an oscillation box at 30 °C and 180 r / min, and measure the remaining Mo(IV) concentration at corresponding intervals for 24 hours continuously.

[0060] The results are as Figure 7 shown. The adsorption of the MOFs / PVA crosslinked composite film with a modified MOFs:PVA ratio of 1:0.8 conforms to the pseudo-second-order kinetic model.

[0061] (IV) Determination of the adsorption thermodynamics of the MOFs / PVA crosslinked composite film

[0062] Method: Weigh 5 mg of the MOFs / PVA crosslinked composite film with a modified MOFs:PVA ratio of 1:0.8 prepared in Example 1, and add it to 5 mL of a Mo(IV) solution with a concentration of 120 mg / L. The pH of the solution is 3. Oscillate and adsorb in an oscillation box at 180 r / min at 30 °C, 40 °C, and 50 °C for 24 h respectively.

[0063] The results of the adsorption thermodynamics fitting curve of this film for Mo(IV) are as Figure 8 shown. By analysis, the adsorption rate of this film increases with the increase in temperature. The enthalpy change of adsorption ΔH = 2.27 kJ / mol, and the entropy change ΔS = 28.8 J / (mol·K). The thermodynamic parameters are shown in Table 1.

[0064] Table 1 Thermodynamic parameters of the MOFs / PVA crosslinked composite film for the adsorption of Mo(IV)

[0065]

[0066] (V) Determination of the maximum adsorption capacity of different crosslinked composite films

[0067] According to the preparation method of Example 1, 2.4 mL and 1.4 mL of PVA solution with a mass concentration of 5% were respectively taken and mixed with 0.6 mL of the hydrolyzed solution of modified MOFs to prepare MOFs / PVA cross-linked composite films with a mass ratio of modified MOFs:PVA of 1:1 and 1:0.6, and the maximum adsorption capacity of the cross-linked composite films for Mo(Ⅳ) was measured respectively according to the experimental steps in (2) of Example 2.

[0068] The measurement results are compared as Figure 9 shown. It can be analyzed that the composite film has the best adsorption performance when the modified MOFs:PVA is 1:0.8.

Claims

1. A MOFs / PVA cross-linked composite film, characterized in that, The preparation method comprises the following steps: 1) Synthesize amino-functionalized MOFs by hydrothermal method; 2) React the MOFs prepared in step 1) with epoxy silane coupling agent; 3) Hydrolyze the product obtained in step 2) under acidic conditions to obtain MOFs with silanol groups on the surface; 4) Mix the MOFs with silanol groups on the surface prepared in step 3) and polymer PVA in a certain proportion, coat on the substrate surface, and obtain the MOFs / PVA cross-linked composite film after drying.

2. The MOFs / PVA crosslinked composite film according to claim 1, wherein In step 1), for the MOFs with amino groups, the central metal is Zr 4+ , Ti 4+ , Ce 4+ , Zn 2+ , Co 2+ , Cu 2+ , Ni 2+ or one or more of them, and the ligand is one or more dicarboxylic acid ligands containing amino groups.

3. The MOFs / PVA cross-linked composite film according to claim 1, wherein In step 2), the epoxy silane coupling agent is 3-glycidoxypropyltrimethoxysilane.

4. The MOFs / PVA cross-linked composite film according to claim 1, wherein In step 4), the molecular weight range of the PVA is 74000 - 80000, and the PVA is a single molecular weight or a mixture of several molecular weights.

5. A MOFs / PVA cross-linked composite film according to claim 1, wherein In step 4), the mass ratio of the MOFs with silanol groups on the surface to PVA ranges from 1:2 to 1:0.

5.

6. Application of a MOFs / PVA cross-linked composite film according to any one of claims 1 - 5 in the field of adsorption separation.

7. The application according to claim 6, characterized in that Application of the MOFs / PVA cross-linked composite film in adsorbing Mo(Ⅳ).

8. The application according to claim 7, wherein The method is as follows: Add the MOFs / PVA cross-linked composite film into the Mo(Ⅳ) solution for adsorption.

9. The application according to claim 8, characterized in that, The adsorption is carried out at pH 1 - 7, with oscillation adsorption at 30 °C and 180 r / min for 24 h.

10. The application according to claim 9, characterized in that, The concentration of the Mo(Ⅳ) solution is 10 - 300 mg / L.

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