Amorphous ZIF-8 film as well as preparation method and application thereof

Abstract

The invention provides an amorphous ZIF-8 membrane and a preparation method and application thereof, and belongs to the field of membrane materials.The preparation method of the amorphous ZIF-8 membrane comprises the following steps that S1, the ZIF-8 membrane is soaked in a DMF solution, one face of the ZIF-8 membrane faces upwards, and a reaction is conducted; and S2, after the reaction in the step S1 is completed, taking out the ZIF-8 membrane, and activating the ZIF-8 membrane by using a blast dryer to obtain the amorphous ZIF-8 membrane. The preparation method is mild and controllable in reaction condition, and the gas selectivity of the ZIF-8 membrane can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of membrane materials technology, and more specifically, to an amorphous ZIF-8 membrane, its preparation method, and its application. Background Technology

[0002] In the field of gas separation, inorganic membrane separation technology based on molecular sieve matrices (such as zeolite membranes and MOF membranes) is currently attracting attention. However, the industrial application of inorganic membranes is still limited. Taking ZIF-8 membrane as an example, the crystallographic pore size of ZIF-8 membrane is about 3.4 Å. Theoretically, gas molecules can be sieved through size exclusion effect. However, due to the dynamic flexibility of the crystal lattice, the rotational degree of freedom of the imidazole linkage in ordinary ZIF-8 membrane is large. Under external force expansion, the actual pore size will fluctuate greatly, which will affect the gas sieving performance of ZIF-8. Secondly, the quadrupole moment characteristics of many gas molecules (such as carbon dioxide and ammonia) cannot be effectively utilized by ZIF-8 membrane. At the same time, in practice, ZIF-8 also has the problem of significant competitive adsorption effect and large attenuation of separation selectivity in low concentration gas environments.

[0003] To address these issues, ZIF-8 membranes need to be modified. Amorphization is a commonly used method for ZIF-8 modification. This method disrupts the crystal order through thermal, mechanical, or other energy inputs. However, the energy input intensity often exceeds the mechanical and thermal tolerance thresholds of the ZIF-8 framework and support, which may cause distortion of the ZIF-8 lattice and framework collapse, leading to a deviation of the pore size distribution from the ideal size and compromising the precision of the molecular sieve. If mechanical energy input is used, the shear force generated by mechanical grinding will also damage the interfacial bonding between ZIF-8 and the support, forming cracks and ultimately impairing gas separation performance due to structural damage.

[0004] As can be seen from the above description, existing ZIF-8 modification technologies struggle to balance the contradiction between "selective enhancement" and "penetration rate maintenance," and existing modification processes pose a high risk of ZIF-8 structural damage. Summary of the Invention

[0005] The purpose of this invention is to provide a process for preparing amorphous ZIF-8 with mild reaction conditions that does not easily damage the ZIF-8 membrane structure.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing an amorphous ZIF-8 membrane, comprising the following steps: S1: Immerse the ZIF-8 membrane in DMF solution, with one side of the ZIF-8 membrane facing upwards during the reaction; S2: After the reaction in step S1 is completed, the ZIF-8 membrane is removed and activated using a blower dryer to obtain an amorphous ZIF-8 membrane.

[0007] Preferably, in step S1, the concentration of the DMF solution is at least 99%.

[0008] Preferably, in step S1, the reaction temperature is 10~35℃.

[0009] Preferably, in step S1, the reaction time is 6 to 18 hours.

[0010] Preferably, in step S1, the ZIF-8 has a support, which is any one of alumina, titanium dioxide, or polymer.

[0011] Preferably, in step S2, the activation temperature is 85~110℃.

[0012] Preferably, in step S2, the activation time is 1 to 3 hours.

[0013] In step S1 of the preparation method provided by the present invention, the ZIF-8 membrane is placed in a high concentration DMF solution at room temperature of 10~35°C. Under these mild conditions, DMF molecules can cause the crystal structure of the ZIF-8 membrane to transform into an amorphous state. This phase transition process avoids the mechanical damage to the membrane and support caused by traditional high temperature and high pressure modification, and simplifies the preparation process.

[0014] In the preparation method of the present invention, ZIF-8 with a support is used. On the one hand, the ZIF-8 film layer can be effectively fixed to prevent the ZIF-8 film layer from falling off. On the other hand, the support can react with the interface of the ZIF-8 film layer to improve the stability of the interface bonding.

[0015] A second aspect of the present invention provides an amorphous ZIF-8 membrane, wherein the amorphous ZIF-8 membrane is prepared by the preparation method described in the first aspect.

[0016] A third aspect of the present invention provides an application of an amorphous ZIF-8 membrane, the application comprising using the amorphous ZIF-8 membrane for the separation of a mixed gas, wherein the mixed gas is any one of a carbon dioxide / nitrogen mixture, a carbon dioxide / methane mixture, a carbon dioxide / propane mixture, a hydrogen / nitrogen mixture, a hydrogen / methane mixture, or a hydrogen / propane mixture.

[0017] The preparation method provided by this invention can cause a phase transition in the ZIF-8 crystal film, resulting in the reorganization of the pore structure within the film and the formation of finer and more uniform nanopores. This makes the amorphous ZIF-8 film prepared by this invention suitable for the separation of mixed gases, especially for the separation of carbon dioxide / nitrogen mixtures and hydrogen / nitrogen mixtures.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The method for preparing the amorphous ZIF-8 membrane provided by the present invention transforms the internal structure of ZIF-8 towards an amorphous direction by immersion in solution, thereby optimizing the separation performance of the ZIF-8 membrane: due to the transformation of the structure into an amorphous shape, the pores of the ZIF-8 membrane are reduced to a size suitable for the separation of mixed gases, thereby improving the selectivity of the ZIF-8 membrane. 2. The method for preparing amorphous ZIF-8 membrane provided by the present invention adopts a room temperature static soaking process. Only the reaction temperature and reaction time need to be controlled to achieve the modification of ZIF-8 membrane. No complicated equipment or solvents are required for post-treatment, which can effectively shorten the cost required for ZIF-8 membrane modification. 3. The operation method of the present invention is simple, the modification cost is low, and it is suitable for the large-scale preparation of amorphous ZIF-8 membranes; 4. The amorphous ZIF-8 membrane provided by this invention is suitable for separating CO2 / N2 mixed gases of low, medium and high concentrations, and can be used directly without pretreatment of the mixed gas, making it convenient to use. Attached Figure Description

[0019] Figure 1 The results are the single-component gas permeability test results of product M1 in Example 1 of this invention; Figure 2 The results of XRD analysis of product M1 in Embodiment 1 of this invention; Figure 3 The graph shows the CO2 permeability and CO2 / N2 separation performance results of products M1, M2, and M3 in the embodiments of the present invention. Figure 4 The graph shows the CO2 permeability and CO2 / N2 separation performance results of products M1, M4, and M5 in the embodiments of the present invention.

[0020] Figure 5 This is an AFM surface morphology diagram of product M1 in Embodiment 1 of the present invention; Figure 6 This is an AFM surface morphology diagram of product M6 in Comparative Example 1 of the present invention. Detailed Implementation

[0021] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the present invention.

[0022] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] As described in the background section, existing methods for modifying amorphous ZIF-8 suffer from drawbacks such as high thermal conversion temperatures, high pressures, and easy destruction of the ZIF-8 structure. Therefore, this invention provides a mild method for preparing amorphous ZIF-8 films, comprising the following steps: S1: Immerse the ZIF-8 membrane in DMF solution, with one side of the ZIF-8 membrane facing upwards during the reaction; S2: After the reaction in step S1 is completed, the ZIF-8 membrane is removed and activated using a blower dryer to obtain an amorphous ZIF-8 membrane.

[0024] In step S1 of the above embodiment, the concentration of the DMF solution is at least 99%.

[0025] In step S1 of the above embodiment, the reaction temperature is 10~35°C.

[0026] In step S1 of the above embodiment, the reaction time is 6 to 18 hours.

[0027] In step S1 of the above embodiment, the ZIF-8 has a support, which is any one of alumina, titanium dioxide, and polymer.

[0028] More specifically, in the above embodiments, the support is preferably an alumina support.

[0029] In step S2 of the above embodiment, the activation temperature is 85~110°C.

[0030] In step S2 of the above embodiment, the activation time is 1 to 3 hours.

[0031] The technical solutions of the present invention are further described below through specific embodiments. Unless otherwise defined, all terms, symbols, and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art. In some cases, terms with a conventional understanding are limited herein for clarification or ease of reference, and such limitations should not be construed as indicating a significant difference from the conventional understanding in the art. The technical methods described or referenced herein are generally well understood by those skilled in the art and have been adopted by conventional methods. Unless otherwise stated, the use of commercially available reagents and instruments shall be performed according to the manufacturer's instructions and parameters.

[0032] In the following examples, the DMF (N,N-dimethylformamide) was obtained from Sinopharm Shanghai Laboratory, and all DMFs were of analytical grade.

[0033] Example 1 Preparation of amorphous ZIF-8 membranes S1: Immerse the alumina-supported ZIF-8 membrane in 30 mL of DMF solution, with one side of the ZIF-8 membrane facing upwards during the reaction. The reaction temperature is 25 °C and the reaction time is 12 h. S2: After the reaction in step S1 is completed, the ZIF-8 membrane is removed, and the excess DMF solution on the surface is absorbed with filter paper. The ZIF-8 membrane is then activated using a blower dryer to obtain an amorphous ZIF-8 membrane. The activation temperature is 100℃ and the activation time is 1 day. The obtained amorphous ZIF-8 membrane is labeled as product M1.

[0034] The single-component gas permeability of product M1 was measured, and the results are as follows: Figure 1 As shown, by Figure 1 It is evident that product M1 prepared by the method provided by this invention has an effective size sieving effect for CO2 / N2.

[0035] XRD analysis was performed on the M1 and ZIF-8 films. The XRD diffraction patterns are as follows: Figure 2 As shown, by Figure 2 The results show that the ZIF-8 membrane structure, after being soaked in DMF solution at 25°C, has completely transformed from a crystalline state to an amorphous structure.

[0036] The CO2 / N2 separation selectivity and permeability of product M1 were tested, and the test results are shown in Table 1.

[0037] Table 1 As shown in Table 1, the CO2 / N2 mixed gas separation selectivity of product M1 is 26.57, and the propylene permeability is 133.6%. 10 -9mol m -2 s -1 Pa -1 This demonstrates that product M1 has effective separation performance for CO2 / N2.

[0038] Example 2 Effect of different reaction temperatures on amorphous ZIF-8 films S1: Immerse the alumina-supported ZIF-8 membrane in 30 mL of DMF solution, with one side of the ZIF-8 membrane facing upwards during the reaction. The reaction time is 12 h. One group of reactions is at a temperature of 10 °C, and the other group is at a temperature of 35 °C. S2: After the reaction in step S1 is completed, the ZIF-8 membrane is removed, and excess DMF solution on the surface is absorbed with filter paper. The ZIF-8 membrane is then activated using a blower dryer to obtain an amorphous ZIF-8 membrane. The activation temperature is 100℃, the activation time is 1 day, and the amorphous ZIF-8 membrane prepared under the reaction conditions of 10℃ is labeled as product M2. The amorphous ZIF-8 membrane prepared under the reaction conditions of 35℃ is labeled as product M3.

[0039] The CO2 / N2 separation selectivity and permeability of products M2 and M3 were tested, and the test results are shown in Table 2.

[0040] Table 2 The results of CO2 permeability and CO2 / N2 separation performance of products M1, M2, and M3 are shown in the figure below. Figure 3 As shown.

[0041] From Table 2 and Figure 3 The test results show that the amorphous ZIF-8 membranes prepared at different reaction temperatures all have good separation performance for CO2 / N2.

[0042] Example 4 Effect of different reaction times on amorphous ZIF-8 membranes S1: The alumina-supported ZIF-8 membrane was immersed in 30 mL of DMF solution, with one side of the ZIF-8 membrane facing upwards during the reaction. The reaction temperature was 25 °C. One group of reactions lasted for 6 hours, and the other group lasted for 18 hours. S2: After the reaction in step S1 is completed, the ZIF-8 membrane is removed, and the excess DMF solution on the surface is absorbed with filter paper. The ZIF-8 membrane is then activated using a blower dryer to obtain an amorphous ZIF-8 membrane. The activation temperature is 100℃ and the activation time is 1 day. The amorphous ZIF-8 membrane obtained with a reaction time of 6 hours is labeled as product M4, and the amorphous ZIF-8 membrane obtained with a reaction time of 18 hours is labeled as product M5.

[0043] The CO2 / N2 separation selectivity and permeability of products M4 and M5 were tested, and the test results are shown in Table 3.

[0044] Table 3 The results of CO2 permeability and CO2 / N2 separation performance of products M1, M4, and M5 are shown in the figure below. Figure 4 As shown.

[0045] From Table 3 and Figure 4 The test results show that the amorphous ZIF-8 membranes M4 and M5 prepared with different reaction times all have good separation performance for CO2 / N2.

[0046] Comparative Example 1 Effect of activation treatment on crystalline ZIF-8 films S1: The ZIF-8 membrane supported by alumina was directly activated at 100°C for 1 day, and the resulting ZIF-8 membrane was labeled as product M6.

[0047] The CO2 / N2 separation selectivity and permeability of product M6 were tested, and the test results are shown in Table 4.

[0048] Table 4 AFM surface morphology characterization of product M1 is as follows: Figure 5 As shown, the AFM surface morphology characterization results of product M6 are as follows: Figure 6 As shown.

[0049] From Table 4 and Figures 5-6 The test results show that the crystalline ZIF-8 membrane without DMF solvent treatment has low selectivity for CO2 / N2 separation. From... Figure 5 and Figure 6 As can be seen from the AFM surface morphology diagram, the surface roughness of the amorphous ZIF-8 film is reduced and the surface morphology is more uniform after DMF solvent treatment.

[0050] While the disclosure is as stated above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of this invention.

Claims

1. A method for preparing an amorphous ZIF-8 membrane, characterized in that, Includes the following steps: S1: Immerse the ZIF-8 membrane in DMF solution, with one side of the ZIF-8 membrane facing upwards with the horizontal plane as a reference; S2: After the reaction in step S1 is completed, the ZIF-8 membrane is removed and activated using a blower dryer to obtain an amorphous ZIF-8 membrane.

2. The preparation method according to claim 1, characterized in that, In step S1, the concentration of the DMF solution is not less than 99%.

3. The preparation method according to claim 1, characterized in that, In step S1, the reaction temperature is 10~35℃.

4. The preparation method according to claim 1, characterized in that, In step S1, the reaction time is 6 to 18 hours.

5. The preparation method according to claim 1, characterized in that, In step S1, the ZIF-8 has a support, which is any one of alumina, titanium dioxide, or polymer.

6. The preparation method according to claim 1, characterized in that, In step S2, the activation temperature is 85~110℃.

7. The preparation method according to claim 1, characterized in that, In step S2, the activation time is 1 to 3 hours.

8. An amorphous ZIF-8 membrane, characterized in that, The amorphous ZIF-8 membrane is prepared by any of the preparation methods described in claims 1 to 7.

9. An application of the amorphous ZIF-8 membrane according to claim 8, characterized in that, The application includes using the amorphous ZIF-8 membrane for the separation of mixed gases, wherein the mixed gas is any one of carbon dioxide / nitrogen mixture, carbon dioxide / methane mixture, carbon dioxide / propane mixture, hydrogen / nitrogen mixture, hydrogen / methane mixture, and hydrogen / propane mixture.

Images