Preparation method of a Fe₃O₄@fluorine-containing organic framework core-shell structure material for water-oil separation

Abstract

The present invention belongs to the technical field of functional materials, and specifically provides a preparation method of a Fe₃O₄@fluorinated organic framework core-shell structure material, realizing the dual-functional integration of the magnetic property of the core and the lipophilic property of the shell. By optimizing the types of functional groups X on the benzene ring of terephthalic acid (H₂BDC), the present invention regulates the nucleation and growth behaviors of MOFs during the reaction of Al ions with the H₂BDC-X organic ligand, and obtains a core-shell structure material with uniform dispersion and uniform coating. The present invention for the first time explores the influence mechanism of the functional groups of fluorinated organic ligands on the heterogeneous nucleation of the MOF shell on the surface of metal oxides, enriching the types of MOF shells; the core-shell structure material with both magnetic and lipophilic properties obtained by the present invention exhibits excellent performance in oil-water separation.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and particularly relates to a preparation method of a Fe₃O₄@fluorinated organic framework core-shell structure material for water-oil separation. Background Art

[0002] Industrial and domestic oily sewage and oil spills not only cause serious environmental problems but also lead to waste of resources. Therefore, efficient water-oil separation has attracted great interest. Common methods for water-oil separation include centrifugation, gravity separation, adsorption, flotation, biological oxidation, and chemical methods, etc. Among them, metal-organic frameworks (MOFs) have become excellent water-oil separation materials due to their structural advantages such as high specific surface area and high porosity. Especially in fluorinated MOFs materials, the fluorocarbon chain chemical bond is stable and has strong lipophilicity, making the oil phase easy to diffuse and penetrate in them. Therefore, it has recently attracted the attention of scientists. Compared with traditional MOF membrane materials, directly using MOF powders for water-oil separation, although the separation effect is good, there are problems such as poor powder reusability and difficulty in recovering oil products.

[0003] To achieve the reuse of water-oil separation materials, magnetic substances can be introduced into the water-oil separation materials. Among common magnetic materials, Fe₃O₄ has become one of the most widely used magnetic materials due to its low price. However, how to compound Fe₃O₄ with fluorinated MOF materials and achieve a Fe₃O₄@fluorinated MOF core-shell structure water-oil separation material with integrated magnetic and lipophilic dual functions through a simple and mild strategy still poses a great challenge. Summary of the Invention

[0004] Aiming at the potential application of MOF-based core-shell structure materials with both magnetic and lipophilic properties in water-oil separation, the present invention provides a preparation method of a Fe₃O₄@fluorinated organic framework core-shell structure material. By mixing Fe₃O₄, aluminum salts, and fluorinated organic ligands, without any sacrificial template or prior surface modification of Fe₃O₄ particles, a Fe₃O₄@fluorinated organic framework core-shell structure material with both magnetic and lipophilic properties is prepared by regulating the types of fluorinated organic ligands.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A preparation method of a Fe₃O₄@fluorinated organic framework core-shell structure material, comprising the following steps:

[0007] Ultrasonically disperse Fe₃O₄, aluminum salts, and fluorinated organic ligands in a mixed solvent, carry out the reaction under mechanical stirring, and then cool, centrifuge, wash, and dry to obtain the Fe₃O₄@fluorinated organic framework core-shell structure material.

[0008] The iron tetraoxide is nano-spherical particles with a particle size of 200-400 nm.

[0009] The aluminum salt is Al(NO 3 ) 3 ·9H 2 O.

[0010] The fluorine-containing organic ligand is one of 2-fluoroterephthalic acid and 2,5-bis(trifluoromethyl)terephthalic acid.

[0011] The mass ratio of the aluminum salt to the fluorine-containing organic ligand is 1 / 5-3 / 5.

[0012] The mass ratio of the fluorine-containing organic ligand to the iron tetraoxide is 1 / 10-1 / 2.

[0013] The mass-volume ratio of the fluorine-containing organic ligand to the mixed solvent is 0.5-2.5 mg / mL.

[0014] The mixed solvent is a mixed solvent of water and N,N-dimethylformamide. Among them, the volume ratio of N,N-dimethylformamide to water is less than 3, preferably 1 / 4-1. When the content of N,N-dimethylformamide is too large, the deprotonation ability changes, resulting in the homogeneous nucleation of MOFs.

[0015] The stirring rate of the mechanical stirring is 100-500 rpm, preferably 200 rpm;

[0016] The mechanical stirring time is 4-24 h, preferably 8 h;

[0017] The reaction temperature is 60-90 °C, preferably 60 °C.

[0018] Considering the types of organic ligand functional groups, especially the strong electron-withdrawing fluorine in the fluorine-containing organic ligand, which has a great influence on the nucleation and growth behavior of MOFs, there are still huge challenges in synthesizing the iron tetraoxide@fluorine-containing organic framework core-shell structure material. The present invention studies the influence of the functional group types on the heterogeneous nucleation of fluorine-containing MOFs on the surface of iron tetraoxide by regulating the functional groups of the fluorine-containing organic ligand; by regulating the content of N,N-dimethylformamide in the mixed solvent, the influence of the solvent composition on the nucleation kinetics of MOFs is explored; finally, appropriate reaction conditions and organic ligands are determined, so as to prepare the iron tetraoxide@fluorine-containing organic framework core-shell structure material.

[0019] Beneficial effects:

[0020] 1. The present invention first prepares the iron tetraoxide@fluorine-containing organic framework core-shell structure material with both magnetic and lipophilic bifunctionalities, and proposes the influence of the functional groups of the fluorine-containing organic ligand on the heterogeneous nucleation of the MOFs shell layer, enriching the types of metal oxides coated with MOFs on the surface.

[0021] 2. The Fe₃O₄@fluorinated organic framework core-shell structure material prepared by the present invention has excellent oil-water separation performance due to the oil-loving fluorinated MOFs in the core-shell structure material; in addition, using magnetic Fe₃O₄ as the inner core is beneficial to the recovery of the core-shell structure material. Description of the Drawings

[0022] Figure 1 Transmission electron microscopy image of the Fe₃O₄@fluorinated organic framework core-shell structure material prepared in Example 1;

[0023] Figure 2 Transmission electron microscopy image of the Fe₃O₄@fluorinated organic framework core-shell structure material prepared in Example 2;

[0024] Figure 3 Oil-loving property comparison diagram and magnetic property diagram of the Fe₃O₄@fluorinated organic framework core-shell structure material prepared in Example 2;

[0025] Figure 4 Transmission electron microscopy image of the Fe₃O₄@fluorinated organic framework core-shell structure material prepared in Example 3;

[0026] Figure 5 Transmission electron microscopy image of the Fe₃O₄@fluorinated organic framework core-shell structure material prepared in Comparative Example 1;

[0027] Figure 6 Transmission electron microscopy image of the Fe₃O₄@fluorinated organic framework core-shell structure material prepared in Comparative Example 2. Detailed Description of the Invention

[0028] The present invention will be further described below in conjunction with the drawings and embodiments. These embodiments are only used to illustrate the present invention by way of example and do not constitute any limitation to the scope of the present invention. Unless otherwise specified, the raw materials used in the following embodiments and comparative examples are all commercially available.

[0029] In the following embodiments and comparative examples, the Fe₃O₄ nanoparticles are obtained by hydrothermal reaction of ethylene glycol and ferric chloride. By changing the amounts of the regulating agents sodium acetate anhydrous and polyethylene glycol, the size of the Fe₃O₄ nanoparticles can be changed. The particle size of the Fe₃O₄ used in the following embodiments and comparative examples is 400 nm.

[0030] Example 1

[0031] Mix 50 mg of Fe₃O₄, 8 mg of Al(NO 3 ) 3 ·9H 2 O, and 20 mg of 2-fluoroterephthalic acid (H 2BDC-F) was ultrasonically dispersed in a mixed solution of 20 mL of deionized water and N,N-dimethylformamide (where the volume ratio of deionized water to N,N-dimethylformamide was 1:1), mechanically stirred at 60 °C with a stirring rate of 200 rpm for 8 h, cooled to room temperature, centrifuged, washed with DMF and ethanol respectively, and then dried under vacuum at 80 °C overnight to obtain the Fe₃O₄@Al-BDC-F core-shell structure material.

[0032] Figure 1 It is a low-magnification transmission electron micrograph of the Fe₃O₄@Al-BDC-F core-shell structure material. It can be seen from the figure that the Al-BDC-F shell uniformly coats the surface of the Fe₃O₄ particles, and the shell material shows a serrated shape.

[0033] Example 2

[0034] This example is the same as Example 1, except that the functional group in the organic ligand is changed from F to two CF 3 , that is, 2,5-bis(trifluoromethyl)terephthalic acid is used as the fluorinated organic ligand, and other conditions remain unchanged to prepare the Fe₃O₄@Al-BDC-2CF 3 core-shell structure material.

[0035] Figure 2 It shows a low-magnification transmission electron micrograph of the Fe₃O₄@Al-BDC-2CF 3 core-shell structure material. It can be seen from the figure that the MOFs material uniformly coats the surface of the Fe₃O₄ particles, and the serrated shape on the shell surface is more obvious than that of the Fe₃O₄@Al-BDC-F core-shell structure material prepared in Example 1.

[0036] As Figure 3 shown is the comparison diagram of the lipophilic properties of Fe₃O₄ and the Fe₃O₄@Al-BDC-2CF 3 core-shell structure material and the magnetic diagram of the Fe₃O₄@Al-BDC-2CF 3 core-shell structure sample. It can be seen from the figure that Fe₃O₄ is dispersed in the aqueous phase, while the Fe₃O₄@Al-BDC-2CF 3 core-shell structure material is enriched in the oil phase. Compared with Fe₃O₄ particles, the lipophilic property of the Fe₃O₄@Al-BDC-2CF 3 core-shell structure material prepared in this example is significantly improved, and the material can be easily recovered by applying an external magnet, showing great potential in oil-water separation applications.

[0037] Example 3

[0038] This example is the same as Example 2, except that the volume ratio of the deionized water and N,N-dimethylformamide mixed solution is 3:1, and other conditions remain unchanged, to prepare Fe₃O₄@Al-BDC-2CF 3 core-shell structure material.

[0039] Figure 4 It shows that when the volume ratio of the deionized water and N,N-dimethylformamide mixed solution is 3:1, the obtained Fe₃O₄@Al-BDC-2CF 3 low-magnification transmission electron microscopy image of the core-shell structure material. It can be seen from the figure that the MOFs material is uniformly coated on the surface of the Fe₃O₄ particles.

[0040] Example 4

[0041] This example is the same as Example 2, except that the volume ratio of the deionized water and N,N-dimethylformamide mixed solution is 10:0, and other conditions remain unchanged, to prepare Fe₃O₄@Al-BDC-2CF 3 core-shell structure material.

[0042] Comparative Example 1

[0043] This comparative example is the same as Example 1, except that the organic ligand is 2-trifluoromethyl terephthalic acid, and other reaction conditions remain unchanged. The low-magnification transmission electron microscopy image of the sample morphology prepared after the reaction is as Figure 5 shown. The MOFs is not uniformly coated on the surface of the Fe₃O₄ particles. Considering that the electron-withdrawing effect of the functional group 2-trifluoromethyl is between H and 2,5-bis(trifluoromethyl), both terephthalic acid and 2,5-bis(trifluoromethyl) terephthalic acid as organic ligands can form a core-shell structure, while 2-trifluoromethyl as an organic ligand cannot form a core-shell structure, which may be due to the different electron-withdrawing abilities of the two carboxyl groups on the benzene ring, resulting in symmetry destruction, thus causing different nucleation and growth behaviors.

[0044] Comparative Example 2

[0045] This comparative example is the same as Example 1, except that the organic ligand is 2,3,5,6-tetrafluoroterephthalic acid, and other reaction conditions remain unchanged. The transmission electron microscopy image of the sample prepared after the reaction is as Figure 6 shown. The MOFs is not uniformly coated on the surface of the Fe₃O₄ particles, which may be due to the too strong electron-withdrawing effect of the four F atoms connected to the benzene ring, affecting the nucleation and growth of the MOFs on the surface of the Fe₃O₄ particles.

[0046] Comparative Example 3

[0047] This comparative example is the same as Example 1, except that the volume ratio of water to N,N-dimethylformamide in the mixed solvent is 1:3. The low-magnification transmission electron microscopy image of the sample morphology prepared after the reaction shows that the MOFs did not coat on the surface of the magnetite particles but nucleated and grew independently. The reason is that too much N,N-dimethylformamide changed the growth kinetics of the MOFs.

Claims

1. A method for preparing ferroferric oxide @ fluorine-containing organic skeleton core-shell structure material for water-oil separation, characterized in that: The steps include: The ferroferric oxide, aluminum salt and fluorine-containing organic ligand are ultrasonically dispersed in a mixed solvent, mechanically stirred for reaction, and then cooled, centrifuged, washed and dried to obtain the ferroferric oxide@fluorine-containing organic skeleton core-shell structure material; The fluorine-containing organic ligand is one of 2-fluoroterephthalic acid and 2,5-bis(trifluoromethyl)terephthalic acid; The mixed solvent is a mixed solvent of water and N,N-dimethylformamide; The volume ratio of N,N-dimethylformamide to water is less than 3; The mass ratio of the fluorine-containing organic ligand to ferrosoferric oxide is 1 / 10 to 1 / 2; The mass ratio of the aluminum salt to the fluorine-containing organic ligand is 1 / 5 to 3 / 5; The reaction temperature is 60-90°C.

2. The method for preparing the ferroferric oxide@fluorine-containing organic skeleton core-shell structure material for water-oil separation according to claim 1, characterized in that: The aluminum salt is Al(NO3)3·9H2O.

3. The method for preparing the ferroferric oxide@fluorine-containing organic skeleton core-shell structure material for water-oil separation according to claim 1, characterized in that: The mass volume ratio of the fluorine-containing organic ligand to the mixed solvent is 0.5-2.5 mg / mL.

4. The method for preparing the ferroferric oxide@fluorine-containing organic skeleton core-shell structure material for water-oil separation according to claim 1, characterized in that: The volume ratio of the N,N-dimethylformamide to water is 1 / 4 to 1.

5. The method for preparing the ferroferric oxide@fluorine-containing organic skeleton core-shell structure material for water-oil separation according to claim 1, characterized in that: The ferrosoferric oxide is a nano-spherical particle with a particle size of 200-400nm.

6. The method for preparing the ferroferric oxide@fluorine-containing organic skeleton core-shell structure material for water-oil separation according to claim 1, characterized in that: The stirring rate of the mechanical stirring is 100-500 rpm; The mechanical stirring time is 4 to 24 hours.

Images