Zn and Co bimetallic organic framework doped organic silicon composite film and preparation method and application thereof

Abstract

This application discloses an organosilicon composite membrane doped with Zn and Co bimetallic organic frameworks, its preparation method and application, including the steps: Zn / Co-ZIF Under electric stirring, Zn(COOCH3)2 and Co(COOCH3)2·4H2O are dissolved in N,N-dimethylformamide solution to obtain solution A; 2,5-dihydroxyterephthalic acid is dissolved in N,N-dimethylformamide solution to obtain solution B; salicylic acid is dissolved in N,N-dimethylformamide solution to obtain solution C; when the solution is stirred until clear, solution A is slowly added dropwise to solution B, and then solution C is added dropwise thereto, and stirring is continued, and then left to stand, and the supernatant is discarded, and the precipitate is centrifuged and washed with N,N-dimethylformamide and methanol respectively; the cleaned product is dispersed in methanol, and the product is centrifuged and washed with methanol, and then activated to obtain ZnCo-ZIF; the dried Zn / CO-ZIF is dispersed in polydimethylsiloxane coating solution to form a coating solution to be coated; the coating solution to be coated is cured on a polyvinylidene fluoride substrate membrane to prepare an organosilicon composite membrane for highly separating CO2 / N2 gas.

Description

Technical Field

[0001] The invention belongs to the technical field of composite films, and relates to an organosilicon composite film doped with a Zn and Co bimetallic organic framework, and a preparation method and application thereof. Background Art

[0002] In order to solve environmental problems such as global warming, CO 2 Capture technology has received increasing attention. 2 The membrane separation technology has environmental and economic advantages such as reproducibility, continuous operation, and low energy consumption, and has become a CO 2 One of the most promising directions in capture technology.

[0003] Membrane separation is a rapidly developing energy-saving CO 2 Separation technology is a relatively new physical separation method without phase change. It has the advantages of simple equipment, small footprint, easy operation, high separation efficiency, low energy consumption, environmental friendliness and easy integration with other methods. This makes the research and development of this technology a hot spot for competition in the field of high-tech among countries around the world. However, at present, organic membrane materials are expensive, easily contaminated and blocked, and have a short service life. Gas separation is limited by the Robeson upper limit. In order to overcome this limitation, a mixed matrix membrane has been developed, which has the specific function of a microporous molecular sieve, can provide a favorable transport pathway, and has better mechanical properties.

[0004] Metal-Organic Frameworks (MOFs) have the advantages of structural diversity, high porosity, and adjustable pore size. As a hybrid material, MOFs materials themselves contain organic components, so they are considered to be more conducive to improving their compatibility with organic membrane materials. Therefore, after filling, the permeability and selectivity of the entire separation membrane can be improved. Compared with other MOF materials, the metal-linker-metal bonding angle (-145°) in ZIF materials ZIF-67 (Co(II)) and ZIF-8 (Zn(II)) is similar to the bonding angle of TOT in zeolite, forming a zeolite topological structure with excellent solvent resistance and thermal and chemical stability. It has good adsorption of carbon dioxide, but MOF materials are easy to aggregate at the nanoscale size and are easily consumed in practical applications, which reduces their service life. Therefore, the mixed matrix membrane synthesized based on MOF fillers can enhance the selectivity, permeability and mechanical strength of gases by taking advantage of the advantages of MOF and membrane separation technology. Summary of the invention

[0005] The technical problem to be solved by the present invention is to address the deficiencies of the prior art. In view of the deficiencies of the prior art, the method described in the present invention combines the synthesis of bimetallic Zn / Co-ZIF and polydimethylsiloxane materials, and mixes Zn / Co-ZIF into polydimethylsiloxane to prepare a mixed matrix membrane, so as to achieve the complementary advantages of multiple materials, further improve the separation performance of polydimethylsiloxane membrane, and apply it to the separation of carbon dioxide. The chemical-physical synergistic force in the polymer-induced interface ordered self-assembly process is used to regulate the orderly self-assembly of each component on the active organic interface layer to achieve the combination of metal organic skeleton and matrix membrane. The new bimetallic organic silicon matrix membrane synthesized by this method increases the free volume in the membrane, improves the adsorption performance of carbon dioxide, and achieves CO 2 / N 2 The permeability and selectivity of the separation membrane material are improved simultaneously. 2 / N 2 Gas separation performance, when the temperature is room temperature and the pressure is 0.15Mpa, the permeability of carbon dioxide is 5218Barrer, and its selectivity is 35. In addition, the method described in the present invention is simple and suitable for scale-up for industrial production.

[0006] In order to achieve the above advantages, the present invention provides a method for preparing a Zn and Co bimetallic organic framework doped organic silicon composite film, the method comprising the following steps:

[0007] Under electric stirring, Zn(COOCH 3 ) 2 and Co(COOCH 3 ) 2 ·4H 2 O is dissolved in N,N-dimethylformamide solution to obtain solution A;

[0008] Dissolving 2,5-dihydroxyterephthalic acid in N,N-dimethylformamide solution to obtain solution B;

[0009] Dissolving salicylic acid in N,N-dimethylformamide solution to obtain solution C;

[0010] After the solution is stirred until it is clear, solution A is slowly added dropwise to solution B. After the addition is complete, stirring is continued, and solution C is then added dropwise thereto, stirring is continued. After stirring is stopped, the supernatant is discarded, and the precipitate is centrifuged and washed with N,N-dimethylformamide and methanol, respectively;

[0011] The cleaned product was dispersed in methanol, transferred into a high-pressure reactor, kept at 110°C-130°C for a predetermined time, and after reaching room temperature, the product was centrifugally washed with methanol, and then placed in a vacuum drying oven for activation to obtain ZnCo-ZIF;

[0012] Dispersing the dried Zn / CO-ZIF in a polydimethylsiloxane coating liquid and performing ultrasonic dispersion to form a coating liquid;

[0013] The coating liquid is coated on the polyvinylidene fluoride base film, and the coating is completely cured by heating to obtain a Zn / Co-ZIF / polydimethylsiloxane / polyvinylidene fluoride mixed matrix film.

[0014] According to one embodiment of the present invention, the amount of Zn / CO-ZIF in 1 kg of the coating liquid is between 0.01 wt % and 3 wt %.

[0015] According to one embodiment of the present invention, the amount of Zn / CO-ZIF in 1 kg of the coating liquid is between 0.1 wt % and 3 wt %.

[0016] According to one embodiment of the present invention, the method further comprises preparing a polyvinylidene fluoride ultrafiltration base membrane:

[0017] Weigh polyvinylidene fluoride, triethyl phosphate, N-methylpyrrolidone, and polyvinylpyrrolidone, put them into a flask, heat and stir in a water bath, set the stirring at a predetermined temperature, shake the casting liquid thoroughly, then take out the casting liquid, and place it in an oven to stand and degas.

[0018] According to one embodiment of the present invention, the method further comprises preparing a polydimethylsiloxane coating liquid:

[0019] An appropriate amount of polydimethylsiloxane is dissolved in 900 grams of n-hexane solution, wherein the content of the polydimethylsiloxane is between 5wt% and 15wt%. The solution is stirred with a stirrer to make the polydimethylsiloxane evenly dispersed.

[0020] The present invention also provides a Zn and Co bimetallic organic framework doped organic silicon composite film, which is prepared by any of the above methods.

[0021] The present invention also provides a use of a Zn and Co bimetallic organic framework doped organic silicon composite film prepared by the preparation method of any of the above Zn and Co bimetallic organic framework doped organic silicon composite films, for CO 2 / N 2 Gas separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 shows the SEM image of Zn / Co-ZIF;

[0023] Figure 2 shows the SEM image of Zn / Co-ZIF / polydimethylsiloxane mixed matrix membrane;

[0024] Figure 3 shows the XRD pattern of Zn / Co-ZIF;

[0025] Figure 4 Adhesion strength test graphs are shown, wherein (a) is a polydimethylsiloxane / polyvinylidene fluoride test graph; (b) is a Zn / Co-ZIF / polydimethylsiloxane / polyvinylidene fluoride test graph;

[0026] Figure 5 A Zn / Co-ZIF adsorption graph is shown. DETAILED DESCRIPTION

[0027] The preferred embodiments described below are for example only, and those skilled in the art may think of other obvious variations. The basic principles of the present invention defined in the following description may be applied to other embodiments, variations, improvements, equivalents, and other technical solutions that do not deviate from the spirit and scope of the present invention.

[0028] In order to achieve at least one of the above advantages, the present invention provides a technical problem to be solved by the present invention. In view of the shortcomings of the prior art, the present invention provides a method for preparing an organosilicon composite film doped with a Zn and Co bimetallic organic framework. The method comprises the following steps:

[0029] Zn / Co-ZIF was stirred by electric stirring to obtain Zn(COOCH 3 ) 2 and Co(COOCH 3 ) 2 ·4H 2 O is dissolved in N,N-dimethylformamide solution to obtain solution A;

[0030] Dissolving 2,5-dihydroxyterephthalic acid in N,N-dimethylformamide solution to obtain solution B;

[0031] Dissolving salicylic acid in N,N-dimethylformamide solution to obtain solution C;

[0032] After the solution is stirred until it is clear, solution A is slowly added dropwise to solution B. After the addition is complete, stirring is continued, and solution C is then added dropwise thereto, stirring is continued. After stirring is stopped, the supernatant is discarded, and the precipitate is centrifuged and washed with N,N-dimethylformamide and methanol, respectively;

[0033] The cleaned product is dispersed in methanol, transferred into a high-pressure reactor, maintained at 110°C-130°C for a predetermined period of time, and after reaching room temperature, the product is centrifugally washed with methanol, and then placed in a vacuum drying oven for activation to obtain ZnCo-ZIF;

[0034] Dispersing the dried Zn / CO-ZIF in a polydimethylsiloxane coating liquid and performing ultrasonic dispersion to form a coating liquid;

[0035] The coating liquid is coated on the polyvinylidene fluoride base film, and the coating is completely cured by heating to obtain a Zn / Co-ZIF / polydimethylsiloxane / polyvinylidene fluoride mixed matrix film.

[0036] Example 1

[0037] The method comprises step 1: preparation of ZnCo-ZIF, which comprises:

[0038] S1001, under electric stirring, 1.5 mmol Zn(COOCH 3 ) 2 and 0.3 mmol Co(COOCH 3 ) 2 4H 2 O was dissolved in 20 mL N,N-dimethylformamide solution to obtain solution A; ensure that Zn(COOCH 3 ) 2 With Co(COOCH 3 ) 2 The molar mass ratio between them is 5:1. Different Zn / Co ratios will affect the structure and pore characteristics of ZIFs. In this experiment, a ratio of 5:1 was used to obtain the best pore size, porosity and material stability while maintaining the best adsorption performance.

[0039] S1002, dissolve 0.5 mmol 2,5-dihydroxyterephthalic acid in 20 mL N,N-dimethylformamide solution to obtain solution B;

[0040] S1003, dissolve 0.4 mmol salicylic acid in 5 mL N,N-dimethylformamide solution to obtain solution C;

[0041] S1004, after the solution is stirred until it is clear, the A solution is slowly added dropwise to the B solution. After the addition is completed, the stirring is continued, usually for 5-10 min, and in this embodiment, the stirring is for 5 min. Then, the C solution is added dropwise thereto, and the stirring is continued, usually for 15-30 min, and in this embodiment, the stirring is for 15 min. After stopping the stirring, the solution is allowed to stand for a period of usually 30-60 min, and in this embodiment, the solution is allowed to stand for 30 min. The supernatant is discarded, and the precipitate is centrifugally washed 3-5 times with N,N-dimethylformamide and methanol, respectively, and in this embodiment, the solution is washed 3 times.

[0042] S1005, the cleaned product was dispersed in 35 mL of methanol, transferred into a 50 mL high-pressure reactor, maintained at 120°C for 36 h, and after reaching room temperature, the product was centrifuged and washed three times with methanol, and then placed in a vacuum drying oven and activated at 150°C for 24 h to obtain ZnCo-ZIF.

[0043] Preferably, the method comprises step 2: preparation of polyvinylidene fluoride ultrafiltration base membrane.

[0044] S1006, weigh polyvinylidene fluoride, triethyl phosphate, N-methylpyrrolidone, and polyvinylpyrrolidone, put them into a flask, heat and stir in a water bath, set the temperature to 80°C, the speed to 500 rpm, stir for 12 hours, shake the casting liquid thoroughly, then take out the casting liquid, place it in a 60°C oven to stand and degas for 12 hours for use.

[0045] Preferably, after the casting liquid is prepared, the above-mentioned coating agent is used to coat the substrate, and the coating thickness is set to 200μm. The phase inversion method is used for coating. After the casting liquid is evenly coated on the non-woven fabric, it quickly invades the deionized water coagulation bath to cause the polyvinylidene fluoride to undergo phase transformation into a membrane. During the preparation process, the thickness and pore size of the membrane (0.2-0.4μm) must be strictly controlled. The thickness and pore size of the base membrane will directly affect the separation performance of the membrane. Temperature control is also very critical during the production of polyvinylidene fluoride membranes. It affects the evaporation rate of the solvent and the phase transformation of polyvinylidene fluoride. The experimental temperature is room temperature 20-30°C.

[0046] Preferably, the method comprises step three: preparing a polydimethylsiloxane coating liquid.

[0047] S1007, a proper amount of polydimethylsiloxane is dissolved in n-hexane solution. Preferably, the content of polydimethylsiloxane in every 900 grams of n-hexane solution is preferably between 5wt% and 15wt%, and in this embodiment it is 11wt%. The solution is stirred with a stirrer for 1-3 hours to evenly disperse the polydimethylsiloxane, and 1kg of solution is obtained for use.

[0048] The method comprises step 4:

[0049] Disperse the dried Zn / CO-ZIF in the solution of step 3, and ultrasonicate for 2-4 hours to prepare a uniformly dispersed solution of Zn / Co-ZIF / polydimethylsiloxane for use. Put the prepared solution on a coating machine and coat it on the polyvinylidene fluoride base film by roller coating, and heat to completely cure the coating to obtain a Zn / Co-ZIF / polydimethylsiloxane / polyvinylidene fluoride mixed matrix membrane.

[0050] Evidence: Adsorption strength

[0051] Preferably, in step 4, the amount of Zn / CO-ZIF dispersed in the 1 kg solution of the standby solution of step 3 is between 0.01wt% and 3wt%, the optimal amount is between 0.1wt% and 3wt%, the curing temperature is between 40 and 200°C, and the optimal temperature is between 60 and 150°C.

[0052] It is worth mentioning that ultrasound can prevent the aggregation of Zn / CO-ZIF to the greatest extent and make it evenly dispersed in the solution.

[0053] Comparative Example 1

[0054] Except for step 4, the other steps are the same as those in Example 1. In this comparative example, the prepared polydimethylsiloxane coating liquid is placed on a coating machine and coated on a polyvinylidene fluoride base film by a roll coating method, and the coating is heated to completely cure to obtain a polydimethylsiloxane / polyvinylidene fluoride film. The prepared polydimethylsiloxane / polyvinylidene fluoride film is experimentally tested as a comparative example. By XU GS, YAO JF, WANG K, et al. Preparation of ZIF-8 membranessupported on ceramic hollow fibers from a concentrated synthesis gel[J].Journal of Membrane Science, 2011, 385: 187-193, formed.

[0055] Comparative Example 2

[0056] Except for step 4, the other steps are the same as in Example 1. In this comparative example, the prepared polydimethylsiloxane coating liquid is placed on a coating machine and coated on a polyvinylidene fluoride base film by a roll coating method, and the coating is heated to completely cure to obtain a polydimethylsiloxane / polyvinylidene fluoride film. The polydimethylsiloxane / polyvinylidene fluoride film is experimentally tested as a comparative example. Formed by HOU JM, WEI YY, ZHOU S, et al. Highly efficient H2 / CO2separation via an ultrathin metal-organic framework membrane[J]. ChemicalEngineering Science, 2018, 182: 180-188.

[0057] Comparative Example 3: Reference Fu WJ, Zhang L et al. Ceramic-based composite membranes decorated by incorporating ZIF-8 and polydimethylsiloxane for highly efficient CO2 / N2 separation[J]. Journal of Membrane Science, 2014, 459: 244-255, to make ZIF-8 / polydimethylsiloxane.

[0058] Zn / Co-ZIF / polydimethylsiloxane mixed matrix membrane performance test:

[0059] Depend on Figure 1 SEM images and Figure 3 The XRD graph shows that the Zn / Co-ZIF bimetallic material was successfully synthesized. The polyvinylidene fluoride substrate is loose and porous, and its pore size is much larger than the molecular dynamic diameter of carbon dioxide gas, and it does not have the function of separating carbon dioxide. After compounding it with polydimethylsiloxane, the surface of the composite membrane becomes very dense and smooth, and there is no cracking phenomenon, indicating that the membrane synthesis is very successful. After compounding Zn / Co-ZIF with it to synthesize a mixed matrix membrane, SEM Figure 2 It can be seen that Zn / Co-ZIF is evenly dispersed on the membrane, indicating that the Zn / Co-ZIF / polydimethylsiloxane mixed matrix membrane was successfully prepared in the experiment.

[0060] As can be seen from Table 1, the organic membrane loaded with Zn / Co-ZIF in this experiment has a significant effect on CO 2 The permeability coefficient and selectivity of the synthesized ZIF were significantly improved, which can be attributed to the abundant N sites in the synthesized ZIF skeleton, which can 2 Produces a strong adsorption effect, and its pore size is in the range of CO 2 and N 2 The kinetic diameter of CO 2 / N 2 It has a good screening effect. Figure 5 The adsorption curves show that Zn / Co-ZIF shows type I N 2The adsorption isotherm proves that it has a microporous structure. At the same time, the good interaction and compatibility between the various components enhance the free volume of the membrane and reduce the transmission resistance of carbon dioxide in the membrane. It can also be seen from the comparative example that the introduction of Co in the bimetallic ZIF has higher permeability and separation effect than the monometallic ZIF-8 material. The main reason is that the bimetallic Zn / Co-ZIF exhibits better thermal stability than the monometallic ZIF, which allows it to maintain structural integrity and optimal adsorption performance over a wider temperature range. At the same time, the zinc metal and cobalt metal centers can produce a synergistic effect, which can enhance the adsorption capacity of gas molecules, especially the adsorption performance of carbon dioxide.

[0061] The introduction of bimetallic also increases the wear resistance of the membrane surface and the adhesion strength between the membrane and the base membrane. The adhesion strength test uses the same tape to tear the membrane surface. The same tape is attached to the membrane surface and the membrane surface is torn under the same conditions. The experiment shows that the adhesion of the polydimethylsiloxane / polyvinylidene fluoride membrane without bimetallic ZIF modification is very poor. After modification, the Zn / Co-ZIF / polydimethylsiloxane / polyvinylidene fluoride membrane has no change and has good adhesion. Figure 4 .

[0062] membrane Adhesion strength to non-woven fabrics Carbon dioxide permeability coefficient (at 30°C) / Barrer CO2 / N2 selectivity Polydimethylsiloxane / polyvinylidene fluoride weak 2100 8.5 Zn / Co-ZIF / polydimethylsiloxane / polyvinylidene fluoride This experiment powerful 5218 35 Comparative Example 1 - 358 12.9 Comparative Example 2 - 40 - Comparative Example 3 (ZIF-8 / polydimethylsiloxane) 3050 10.7

[0063] Table 1: Performance test of different organic films Note: 1 Barrer = 1×10 –10 (STP) cm 3 cm / (cm 2 ·s·cm Hg)

[0064] Comparative Examples 1, 2, and 3 respectively compared ZIF-8 (Zn-ZIF) hollow fiber membrane, ZIF-8 / gC 3 N 4 Membranes, CO2 separation by ZIF-8 / polydimethylsiloxane mixed matrix membranes.

[0065] It should be understood by those skilled in the art that the embodiments of the present invention described above are only examples and do not limit the present invention. The purpose of the present invention has been fully and effectively achieved. The functional and structural principles of the present invention have been demonstrated and explained in the embodiments, and the embodiments of the present invention may be modified or altered in any way without departing from the principles.

Claims

1. A method for preparing a Zn and Co bimetallic organic framework doped organic silicon composite film, characterized in that: The method comprises the following steps: dissolving Zn(COOCH3)2 and Co(COOCH3)2·4H2O in N,N-dimethylformamide solution under electric stirring to obtain solution A, wherein the molar mass ratio of Zn(COOCH3)2 to Co(COOCH3)2 is 5:1; Dissolving a predetermined amount of 2,5-dihydroxyterephthalic acid in N,N-dimethylformamide solution to obtain solution B; Dissolving a predetermined amount of salicylic acid in N,N-dimethylformamide solution to obtain solution C; After the solution is stirred until it is clear, solution A is slowly added dropwise to solution B. After the addition is complete, stirring is continued, and solution C is then added dropwise thereto, stirring is continued. After stirring is stopped, the supernatant is discarded, and the precipitate is centrifuged and washed with N,N-dimethylformamide and methanol, respectively; The cleaned product was dispersed in methanol, transferred into a high-pressure reactor, kept at 110°C-130°C for a predetermined time, cooled to room temperature, and then centrifuged and washed with methanol, and then placed in a vacuum drying oven for activation to obtain Zn / Co-ZIF; Dispersing the dried Zn / Co-ZIF in a polydimethylsiloxane coating liquid and performing ultrasonic dispersion to form a coating liquid, wherein the polydimethylsiloxane coating liquid is composed of a n-hexane solution and polydimethylsiloxane, wherein the content of the polydimethylsiloxane in every 900 grams of the n-hexane solution is between 5wt% and 15wt%; The coating liquid is coated on the polyvinylidene fluoride base film, and the coating is completely cured by heating to obtain a Zn / Co-ZIF / polydimethylsiloxane / polyvinylidene fluoride mixed matrix membrane. In 1 kg of the coating liquid, the amount of Zn / Co-ZIF is between 0.01wt% and 3wt%.

2. The method for preparing the Zn and Co bimetallic organic framework doped organic silicon composite film according to claim 1, characterized in that: In 1 kg of the coating solution, the amount of Zn / Co-ZIF is between 0.1 wt% and 3 wt%.

3. The method for preparing the Zn and Co bimetallic organic framework doped organic silicon composite film according to claim 1, characterized in that: The method also includes the preparation of a polyvinylidene fluoride ultrafiltration base membrane: weighing polyvinylidene fluoride, triethyl phosphate, N-methylpyrrolidone, and polyvinylpyrrolidone, placing them in a flask for heating and stirring in a water bath, setting the stirring at a predetermined temperature, shaking the casting liquid thoroughly, then taking out the casting liquid, and placing it in an oven for standing and degassing.

4. The method for preparing the Zn and Co bimetallic organic framework doped organic silicon composite film according to any one of claims 1 to 3, characterized in that: The method also includes the preparation of polydimethylsiloxane coating liquid: polydimethylsiloxane is dissolved in 900 grams of n-hexane solution, the content of polydimethylsiloxane is between 5wt% and 15wt%, and the solution is stirred with a stirrer to make the polydimethylsiloxane evenly dispersed.

5. Zn and Co bimetallic organic framework doped organic silicon composite film, characterized in that: It is produced by the method according to any one of claims 1 to 4.

6. Use of a Zn and Co bimetallic organic framework doped organosilicon composite membrane prepared by the method for preparing a Zn and Co bimetallic organic framework doped organosilicon composite membrane according to any one of claims 1 to 4, characterized in that: Used for CO2 / N2 gas separation.

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