A zirconium-based MOF adsorbent containing fluorine and azo and a preparation method and application thereof

Abstract

The application provides a zirconium-based MOF adsorbent containing fluorine and azo and a preparation method and application thereof, and belongs to the technical field of new energy materials.The zirconium-based MOF adsorbent containing fluorine and azo is obtained by one-pot self-assembly of zirconium chloride and nitrogen benzene-3,3'-difluoro-4,4'-dicarboxylic acid as raw materials in N,N-dimethylformamide and acetic acid solvents.The zirconium-based MOF adsorbent containing fluorine and azo prepared by the application has the characteristics of large pore size and specific surface area, high thermal stability and chemical stability, and high benzene adsorption capacity in a steam adsorption instrument, and has good separation capacity detected by nuclear magnetic resonance, thereby providing a new idea for subsequent research and development, and having wide application prospects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy materials, and particularly relates to a zirconium-based MOF adsorbent containing fluorine and azo as well as a preparation method and application thereof. BACKGROUND

[0002] Light hydrocarbons (LHs, i.e. C1-C9 hydrocarbons) are basic raw materials for producing industrial commodities, which are mainly obtained from petrochemical products or natural gas processing. Traditional separation methods (such as distillation, extraction and absorption) have huge energy consumption, and from the perspective of energy sustainability and circular economy, the limitations of traditional separation methods are exacerbated by specialized equipment and high production costs. In order to meet the separation needs of the petrochemical industry while reducing energy consumption in the separation process, it is crucial to develop efficient and energy-saving gas separation and purification technology. In recent years, MOFs (metal-organic framework compounds) have been widely used in gas storage and separation due to their large specific surface area and adjustable pore size.

[0003] In the petrochemical industry, cyclohexane (Cy) is an important raw material for producing resins, nylon fibers and pharmaceutical intermediates, which is mainly produced by catalytic hydrogenation of benzene (Bz). However, the limited conversion rate in liquid-phase production leads to the easy miscibility of benzene and cyclohexane (C6H6 / C6H 12 ) products, so subsequent separation procedures are needed to obtain high-purity cyclohexane. C6H6 / C6H 12 Due to their very close boiling points and kinetic diameters, conventional distillation is generally insufficient to separate benzene and cyclohexane, while special distillation methods such as azeotropic distillation and extractive distillation have the problems of complex process and high energy requirement. Therefore, the application proposes a zirconium-based MOF adsorbent containing fluorine and azo as well as a preparation method and application thereof. SUMMARY

[0004] In order to solve the problems of difficult separation of benzene and cyclohexane and high energy consumption, the application proposes a zirconium-based MOF adsorbent containing fluorine and azo as well as a preparation method and application thereof. The application uses zirconium hexacule as a metal node and 3,3'-difluoro-4,4'-dicarboxylic acid as a coordination ligand. A MOF adsorbent material with a typical UiO structure is synthesized by one-pot self-assembly process in N,N-dimethylformamide solvent (DMF) and acetic acid solvent. The obtained adsorbent material has excellent benzene adsorption capacity and the ability to separate benzene and cyclohexane.

[0005] To achieve the above purpose, the application provides the following technical solutions:

[0006] One of the technical solutions of the application is:

[0007] A preparation method of a zirconium-based MOF adsorbent containing fluorine and azo, which comprises the following steps: taking zirconium chloride and nitrobenzene-3,3'-difluoro-4,4'-dicarboxylic acid as raw materials, and adding them into a mixed solvent of N,N-dimethylformamide (DMF) and acetic acid solvent to obtain a precursor solution through ultrasonic treatment; and adding the precursor solution into a high-pressure reaction kettle with a polytetrafluoroethylene lining to perform a hydrothermal reaction, and then performing centrifugation, washing and vacuum drying on the obtained solution to obtain the zirconium-based MOF adsorbent containing fluorine and azo.

[0008] Further, the preparation method of the zirconium-based MOF adsorbent containing fluorine and azo comprises the following steps:

[0009] The zirconium chloride and nitrobenzene-3,3'-difluoro-4,4'-dicarboxylic acid are added into a mixed solvent of N,N-dimethylformamide (DMF) and acetic acid solvent to obtain a precursor solution through ultrasonic treatment; the precursor solution is added into a high-pressure reaction kettle with a polytetrafluoroethylene lining to perform a hydrothermal reaction, and then the obtained solution is centrifuged, washed and vacuum dried to obtain the zirconium-based MOF adsorbent containing fluorine and azo.

[0010] Further, the molar ratio of the zirconium chloride and nitrobenzene-3,3'-difluoro-4,4'-dicarboxylic acid is 1:1.

[0011] Further, the volume ratio of the N,N-dimethylformamide (DMF) and acetic acid solvent is 25:3.

[0012] Further, the total amount of the zirconium chloride and nitrobenzene-3,3'-difluoro-4,4'-dicarboxylic acid added into the mixed solvent is 3.85 g / L.

[0013] Further, the hydrothermal reaction temperature is 120 DEG C, and the time is 3 days; and the cooling is performed at a rate of 2 DEG C / min.

[0014] Further, the temperature of the vacuum drying is 60 DEG C.

[0015] The second technical solution of the present application:

[0016] The zirconium-based MOF adsorbent containing fluorine and azo prepared by the preparation method, wherein a zirconium hexanuclear cluster is used as a metal node, and nitrobenzene-3,3'-difluoro-4,4'-dicarboxylic acid is used as a coordination ligand.

[0017] The third technical solution of the present application:

[0018] The zirconium-based MOF adsorbent containing fluorine and azo is used in the adsorption and separation of benzene and cyclohexane.

[0019] Further, the adsorption test of benzene and cyclohexane is performed in a steam adsorption instrument, and the separation performance of benzene and cyclohexane is evaluated through nuclear magnetic resonance.

[0020] The significant difference between benzene and cyclohexane is that a conjugated pi bond is formed on the benzene ring, and the aromatic ring on the organic ligand in the MOF adsorbent can form a pi-pi interaction with the guest molecule benzene, which provides a favorable structural basis for the specific recognition of benzene. Compared with cyclohexane, due to the presence of pi-pi interaction, benzene is more likely to form strong interaction forces with the framework of the MOF adsorbent, thereby selectively separating benzene from the mixed liquid, and the MOF adsorbent of the present application emphasizes the synergistic effect between the fluorine atom of the electrosorption group and the nitrogen atom with the conjugated pi-electron system, which makes the benzene ring plane of the benzene molecule parallel to the benzene ring plane of the framework while forming C-H-F and C-H-N interactions, thereby forming a more favorable pi-pi interaction, and therefore the interaction between fluorine and azo formed in the MOF adsorbent of the present application is the key to improving the benzene adsorption capacity of the MOF framework.

[0021] Compared with the prior art, the present application has the following advantages and technical effects:

[0022] (1) The zirconium-based MOF adsorbent containing fluorine and azo prepared by the present application has the characteristics of large pore size and specific surface area in structure, and is rich in micropores, thereby having high material adsorption capacity, and through fine design of the functional sites on the ligand, the adsorbent has excellent adsorption capacity and high separation selectivity.

[0023] (2) The zirconium-based MOF adsorbent containing fluorine and azo prepared by the present application has extremely high thermal stability and chemical stability, and exhibits high benzene adsorption capacity (8.03 mmol / g) in a steam adsorption instrument, and through nuclear magnetic detection, good separation capacity (76.73) is detected, which provides a new idea for subsequent research and development, and has wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0024] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and the schematic embodiments of the present application and their descriptions are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0025] Figure 1 SEM image of the zirconium-based MOF adsorbent material containing fluorine and azo prepared for Example 1;

[0026] Figure 2 BET image of the zirconium-based MOF adsorbent material containing fluorine and azo prepared for Example 1;

[0027] Figure 3 Pore size curve of the zirconium-based MOF adsorbent material containing fluorine and azo prepared for Example 1;

[0028] Figure 4Thermogravimetric curve of the fluorine and azo-containing zirconium-based MOF adsorbent material prepared in Example 1;

[0029] Figure 5 XRD pattern of the fluorine and azo-containing zirconium-based MOF adsorbent material prepared in Example 1; wherein a is the XRD pattern after soaking in different organic solvents for three days; b is the XRD pattern after soaking in aqueous solutions with different pH values for three days;

[0030] Figure 6 Steam adsorption curves of the fluorine and azo-containing zirconium-based MOF adsorbent material prepared in Example 1 and the MOF adsorbent material prepared in Comparative Example 1-2, wherein a is the steam adsorption curve of benzene; b is the steam adsorption curve of cyclohexane;

[0031] Figure 7 Comparison chart of the separation performance of benzene and cyclohexane in nuclear magnetic resonance of the fluorine and azo-containing zirconium-based MOF adsorbent material prepared in Example 1 and the MOF adsorbent material prepared in Comparative Example 1-2;

[0032] Figure 8 Structural model of the fluorine and azo-containing zirconium-based MOF adsorbent material prepared in the present application. DETAILED DESCRIPTION

[0033] The various illustrative embodiments of the present application will now be described in detail in connection with the following figures. This description is not to be taken in a limiting sense but is made merely for the purpose of providing a full and enabling disclosure of the application. The detailed description set forth below in connection with the appended drawings describes exemplary embodiments and does not represent the only embodiments in which the application can be practiced.

[0034] It should be understood that the terms used herein are for the purpose of describing particular embodiments and are not intended to limit the present application. Additionally, for a range of values of a variable being described, it is intended that every middle value of the range is also described. Each smaller range which falls within the larger ranges described herein is also a part of the present application. The upper and lower limits of these smaller ranges can independently be included or excluded in the range.

[0035] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice of the present application, the preferred methods and materials are described herein. All patents, patent applications, publications, and descriptions mentioned herein are incorporated by reference in their entirety for the disclosure and

[0036] Many modifications and variations to the illustrative embodiments described herein will be apparent to those of ordinary skill in the art from the foregoing description. Such variations may not depart from the scope of the present application. Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples given are exemplary only.

[0037] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", "contains", "containing", or variations thereof, are intended to be open-ended terms that mean inclusion, but not limited to, the listed material or list of materials.

[0038] The embodiment of the present application provides a preparation method of a zirconium-based MOF adsorbent containing fluorine and azo, which is prepared from zirconium chloride and nitrogen benzene-3,3'-difluoro-4,4'-dicarboxylic acid, and is obtained by one-pot self-assembly in a mixed solvent of N,N-dimethylformamide (DMF) and acetic acid, and specifically comprises the following steps:

[0039] The zirconium chloride and the nitrogen benzene-3,3'-difluoro-4,4'-dicarboxylic acid are added into the mixed solvent of the N,N-dimethylformamide solvent and the acetic acid solvent for ultrasonic treatment to obtain a precursor solution; the precursor solution is added into a high-pressure reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction, and after the reaction is completed, the temperature is lowered, and the obtained solution is centrifuged, washed and vacuum dried to obtain the zirconium-based MOF adsorbent containing fluorine and azo.

[0040] In the preferred embodiment of the present application, the molar ratio of the zirconium chloride and the nitrogen benzene-3,3'-difluoro-4,4'-dicarboxylic acid is 1:1.

[0041] In the preferred embodiment of the present application, the volume ratio of the N,N-dimethylformamide solvent and the acetic acid solvent is 25:3.

[0042] In the preferred embodiment of the present application, the total amount of the zirconium chloride and the nitrogen benzene-3,3'-difluoro-4,4'-dicarboxylic acid added into the mixed solvent is 3.85 g / L.

[0043] In the preferred embodiment of the present application, the hydrothermal reaction temperature is 120 DEG C, the time is 3 days, and the temperature lowering is at a rate of 2 DEG C / min.

[0044] In the preferred embodiment of the present application, the temperature of the vacuum drying is 60 DEG C.

[0045] The embodiment of the present application also provides the zirconium-based MOF adsorbent containing fluorine and azo prepared by the preparation method, which has a structure of zirconium hexanuclear metal node, nitrogen benzene-3,3'-difluoro-4,4'-dicarboxylic acid as a coordination ligand, and a structure similar to UiO.

[0046] Room temperature in the embodiments of the present application refers to "25±2℃".

[0047] The technical solutions of the present application are further illustrated by the following examples.

[0048] Example 1

[0049] A zirconium-based MOF adsorbent containing fluorine and azo is prepared by the following steps:

[0050] (1) 93.2 mg (0.4 mol) of zirconium chloride and 122.4 mg (0.4 mol) of 3,3'-difluoro-4,4'-dicarboxylic acid are added together into a mixed solvent composed of 50 mL of DMF solvent and 6 mL of acetic acid solvent, and ultrasonic treatment is performed for 20 min to obtain a precursor solution;

[0051] (2) The precursor solution is added into a 100 mL stainless steel reaction kettle with a polytetrafluoroethylene liner, and placed in a 120℃ oven for heating for 3 d, and then cooled to room temperature at a cooling rate of 2℃ / min;

[0052] (3) The solution obtained in step (2) is centrifuged to obtain a precipitate, the obtained precipitate is washed with DMF for three times, and dried in a vacuum drying box at 60℃ to obtain a zirconium-based MOF adsorbent containing fluorine and azo.

[0053] Comparative Example 1

[0054] A zirconium-based MOF adsorbent containing azo is prepared by the following steps:

[0055] (1) 60 mg of zirconium chloride and 68.9 mg of 4,4'-azobenzene dicarboxylic acid are added together into a mixed solvent composed of 20 mL of DMF solvent and 11 mL of acetic acid solvent, and ultrasonic treatment is performed for 20 min to obtain a precursor solution;

[0056] (2) The precursor solution is added into a 100 mL stainless steel reaction kettle with a polytetrafluoroethylene liner, and placed in a 120℃ oven for heating for 3 d, and then cooled to room temperature at a cooling rate of 5℃ / min;

[0057] (3) The solution obtained in step (2) is centrifuged to obtain a precipitate, the obtained precipitate is washed with DMF for three times, and dried in a vacuum drying box at 60℃ to obtain a zirconium-based MOF adsorbent containing azo.

[0058] Comparative Example 2

[0059] A zirconium-based MOF adsorbent not containing fluorine and azo is prepared by the following steps:

[0060] (1) 60 mg of zirconium chloride, 68.4 mg of 4,4'-stilbene dicarboxylic acid and 527 mg of L-proline were added into 20 mL of DMF solvent and ultrasonically treated for 20 min to obtain a precursor solution;

[0061] (2) The precursor solution was added into a 50 mL stainless steel reactor with a polytetrafluoroethylene liner and placed in a 120°C oven for heating for 3 d, and then cooled to room temperature at a rate of 5°C / min;

[0062] (3) The solution obtained in step (2) was centrifuged to obtain a precipitate, which was washed with DMF three times and dried in a vacuum drying oven at 60°C to obtain a zirconium-based MOF adsorbent free of fluorine and azo.

[0063] Performance test

[0064] The SEM image of the zirconium-based MOF adsorbent containing fluorine and azo prepared in Example 1 is shown in Figure 1 It can be seen that the zirconium-based MOF adsorbent containing fluorine and azo prepared in this example 1 has an octahedral structure.

[0065] The BET image of the zirconium-based MOF adsorbent containing fluorine and azo prepared in Example 1 is shown in Figure 2 It can be seen that the zirconium-based MOF adsorbent containing fluorine and azo prepared in this example 1 has a high nitrogen adsorption capacity.

[0066] The pore size curve of the zirconium-based MOF adsorbent containing fluorine and azo prepared in Example 1 is shown in Figure 3 It can be seen that the zirconium-based MOF adsorbent containing fluorine and azo prepared in this example 1 has a large pore size, and the pore size is (pore size less than 2 nm, is classified as micropore).

[0067] The thermogravimetric curve of the zirconium-based MOF adsorbent containing fluorine and azo prepared in Example 1 is shown in Figure 4 It can be seen that the zirconium-based MOF adsorbent containing fluorine and azo prepared in this example 1 has very high thermal stability.

[0068] The XRD image of the zirconium-based MOF adsorbent containing fluorine and azo prepared in Example 1 is shown in Figure 5 , wherein A is the XRD image of the MOF adsorbent after being soaked in different organic solvents for three days; b is the XRD image of the MOF adsorbent after being soaked in different pH aqueous solutions for three days; it can be seen that the zirconium-based MOF adsorbent containing fluorine and azo prepared in this example 1 has very high chemical stability.

[0069] The test was carried out at 298 K and 308 K, and before the adsorption test, the MOF adsorbent sample was soaked in acetone for 72 h, and the exchanged sample was activated at 120 DEG C for 10 h in vacuum. The single-component gas adsorption isotherm was measured on the ASAP 2460. The steam adsorption curves of the fluorine and azo-containing zirconium-based MOF adsorbent prepared in Example 1 and the MOF adsorbent prepared in Comparative Example 1-2 are shown in the following figure. Figure 6 Wherein a is the steam adsorption curve of benzene; b is the steam adsorption curve of cyclohexane (298K-1 represents the test result of the MOF adsorbent of Example 1 at 298 K, 298K-2 represents the test result of the MOF adsorbent of Comparative Example 1 at 298 K, and 298K-3 represents the test result of the MOF adsorbent of Comparative Example 2 at 298 K). It can be seen that the fluorine and azo-containing zirconium-based MOF adsorbent prepared in Example 1 has a higher benzene adsorption capacity and a lower cyclohexane adsorption capacity.

[0070] The fluorine and azo-containing zirconium-based MOF adsorbent prepared in Example 1 and the MOF adsorbent prepared in Comparative Example 1-2 were subjected to benzene and cyclohexane adsorption test in a steam adsorption instrument, and the separation performance of benzene and cyclohexane was evaluated by nuclear magnetic resonance. The comparison of the separation performance of benzene and cyclohexane of the fluorine and azo-containing zirconium-based MOF adsorbent prepared in Example 1 and the MOF adsorbent prepared in Comparative Example 1-2 detected by nuclear magnetic resonance is shown in the following figure. Figure 7 Wherein 1 represents Example 1, 2 represents Comparative Example 1, and 3 represents Comparative Example 2. It can be seen that the separation capacity of the fluorine and azo-containing zirconium-based MOF adsorbent prepared in Example 1 is 76.73, which has a better benzene and cyclohexane adsorption capacity, and is much higher than that of Comparative Example 1 and Comparative Example 2.

[0071] The fluorine and azo-containing zirconium-based MOF adsorbent prepared in Example 1 has a structure of zirconium hexamer as a metal node, nitrogen benzene-3,3'-difluoro-4,4'-dicarboxylic acid as a coordination linker, and a structure similar to UiO, and the structural model is shown in the following figure. Figure 8 It can be seen that the structure of the fluorine and azo-containing zirconium-based MOF adsorbent contains two different types of polyhedral cage cavities: octahedral cages sharing faces with 8 tetrahedral cages and octahedral cages sharing edges with 8 additional octahedral cages.

[0072] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method of preparing a zirconium-based MOF adsorbent containing fluorine and azo, characterized in that, The zirconium chloride and azobenzene-3,3'-difluoro-4,4'-dicarboxylic acid are added into a mixed solvent of N,N-dimethylformamide and acetic acid to obtain a precursor solution by ultrasonic treatment; the precursor solution is added into a high-pressure reactor with a polytetrafluoroethylene liner to perform a hydrothermal reaction, and after the reaction is completed, the temperature is lowered, and the obtained solution is centrifuged, washed and vacuum dried to obtain the zirconium-based MOF adsorbent containing fluorine and azo.

2. The method of making a zirconium-based MOF adsorbent containing fluorine and azo according to claim 1, characterized in that, The method comprises the following steps: The zirconium chloride and azobenzene-3,3'-difluoro-4,4'-dicarboxylic acid are added into a mixed solvent of N,N-dimethylformamide and acetic acid to obtain a precursor solution by ultrasonic treatment; the precursor solution is added into a high-pressure reactor with a polytetrafluoroethylene liner to perform a hydrothermal reaction, and after the reaction is completed, the temperature is lowered, and the obtained solution is centrifuged, washed and vacuum dried to obtain the zirconium-based MOF adsorbent containing fluorine and azo.

3. The method of making a zirconium-based MOF adsorbent containing fluorine and azo according to claim 2, characterized in that, The molar ratio of the zirconium chloride and azobenzene-3,3'-difluoro-4,4'-dicarboxylic acid is 1:

1.

4. The method of making a zirconium-based MOF adsorbent containing fluorine and azo according to claim 2, characterized in that, The volume ratio of the N,N-dimethylformamide and acetic acid is 25:

3.

5. The method of making a zirconium-based MOF adsorbent containing fluorine and azo according to claim 2, characterized in that, The total amount of the zirconium chloride and azobenzene-3,3'-difluoro-4,4'-dicarboxylic acid added into the mixed solvent is 3.85 g / L.

6. The method of making a zirconium-based MOF adsorbent containing fluorine and azo according to claim 2, characterized in that, The hydrothermal reaction temperature is 120 DEG C, the time is 3 days, and the temperature is lowered at a rate of 2 DEG C / min.

7. The method of making a zirconium-based MOF adsorbent containing fluorine and azo according to claim 2, characterized in that, The temperature of the vacuum drying is 60 DEG C.

8. A zirconium-based MOF adsorbent containing fluorine and azo groups, produced by the production method according to any one of claims 1 to 7, characterized in that, The zirconium hexanuclear cluster is used as a metal node, and azobenzene-3,3'-difluoro-4,4'-dicarboxylic acid is used as a coordination linker.

9. The zirconium-based MOF adsorbent containing fluorine and azo in claim 8 is applied to adsorption and separation of benzene and cyclohexane.

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