Cerium-iron hetero-metal organic framework material, and preparation method and application thereof

Abstract

The application discloses a cerium-iron heterometallic organic framework material and a preparation method and application thereof, and relates to the technical field of MOF materials, and specifically discloses a cerium-iron heterometallic organic framework material, a preparation method and application thereof.The cerium-iron heterometallic organic framework material comprises a sheet-shaped Ce MOF and a nanoparticle-shaped Fe MOF loaded on the sheet-shaped Ce MOF, and is a MOF on MOF structure.The preparation method comprises the following steps: adding an organic metal salt and fumaric acid into an organic solvent, uniformly stirring and mixing, and then continuously stirring to obtain a mixed solution; transferring the mixed solution into a sealed container to perform a heating reaction; carboxylate ions ionized from the organic metal salt control the coordination rate of Fe and Ce ions and fumaric acid, so that the Ce MOF is first generated, and then the granular Fe MOF is in-situ grown on the surface of the Ce MOF to obtain a reaction product; and cooling, separating, washing and drying the reaction product to obtain the cerium-iron heterometallic organic framework material.The cerium-iron heterometallic organic framework material prepared by the application can adsorb fluoride ions through surface complexation, electrostatic adsorption, ligand exchange and ion exchange, and has excellent fluoride ion adsorption performance.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, and specifically relates to a cerium-iron heterogeneous metal-organic framework material, its preparation method, and its application in defluorination. Background Technology

[0002] my country's "Standards for Drinking Water Quality" (GB5749-2022) clearly stipulates that the fluoride content in drinking water should be less than 1.0 mg / L; the World Health Organization (WHO) standards for drinking water stipulate that the fluoride content should not exceed 1.5 mg / L. Due to the wide range of fluoride pollution, the fragmented nature of polluted areas, the complexity of the environment, the difficulty and high cost of treatment, the problem of fluoride pollution in my country's drinking water has attracted much attention.

[0003] Traditional technologies for removing fluoride ions from drinking water include coagulation and sedimentation, adsorption, membrane separation, ion exchange, and electrochemical methods. Among these, adsorption is considered one of the most effective methods for removing fluoride from water due to its low cost, simple operation, and mature development. Common adsorption materials include metal-organic frameworks (MOFs), metal oxides, layered bimetallic hydroxides (LDHs), and porous carbon materials. MOFs are crystalline composite materials formed by the coordination of metal ions or metal clusters with organic ligands. They have attracted widespread attention due to their extremely large specific surface area, numerous functional groups on their surface, and excellent stability. This has led to the widespread use of common single-metal organic frameworks such as Fe, La, and Ce in fluoride ion removal research. Although Fe is an abundant and inexpensive metal element, its low affinity for fluoride ions limits its adsorption effect. Rare earth metals such as La and Ce have large ionic radii and numerous extranuclear electron orbitals, giving them unique affinity for fluoride. However, rare earth elements are scarce and expensive, making them uneconomical. Meanwhile, single metal-organic frameworks are limited by the number of adsorption sites and specific surface area, resulting in a small adsorption capacity.

[0004] MOF-on-MOF heterostructured metal-organic frameworks can improve the specific surface area, number of active sites, and stability of single-metal MOFs. Therefore, it is necessary to leverage the advantages of MOF-on-MOF heterostructured metal-organic frameworks, providing a feasible solution to overcome the limitations of low adsorption capacity of iron-based metal-organic frameworks and the high cost of rare-earth metal Ce. However, the Fe... 3+ With Ce 3+ The competitive coordination problem can easily lead to disordered crystal phase and uneven composition in the final material. Summary of the Invention

[0005] To address the shortcomings and deficiencies of existing technologies, the present invention aims to provide a cerium-iron heterogeneous metal-organic framework material (Fe MOF on Ce MOF), its preparation method, and its applications. This material can significantly increase the number and activity of surface groups on the adsorbent. The interaction between Fe and Ce sites causes electron transfer or shift, modulating the distribution of electrons outside the Fe and Ce nuclei, thereby enhancing the coordination ability of fluoride ions. This solves the problems of small adsorption capacity, low adsorption rate, and narrow pH range for fluoride ions in traditional single metal-organic frameworks. Furthermore, the preparation method is simple and easy to implement.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first objective of this invention is to provide a cerium-iron heterogeneous metal-organic framework material, comprising sheet-like CeMOF and nanoparticle-like Fe MOF loaded on it, which is a MOF on MOF structure.

[0007] In a further embodiment, the specific surface area of ​​the cerium-iron heterogeneous metal-organic framework material is greater than 109 m² / g.

[0008] The second objective of this invention is to provide a method for preparing the aforementioned cerium-iron heterostructure metal-organic framework material, which includes the following steps: S1. Add the organometallic salt and fumaric acid to the organic solvent, stir and mix evenly, and then continue stirring to obtain a mixture; the organometallic salt is a mixture of organoferric salt and organocerium salt containing carboxyl functional groups; S2. The mixture is transferred to a sealed container for heating and reaction. The carboxylate ions ionized from the organometallic salt regulate the coordination rate of Fe and Ce ions with fumaric acid, thereby first generating Ce MOF, and then growing particulate Fe MOF in situ on the Ce MOF surface to obtain the reactants. S3. The reactants are cooled, separated, washed, and dried to obtain cerium-iron heterogeneous metal-organic framework materials.

[0009] In a further embodiment, the organic iron salt is one of ferric acetate, ferric benzoate, ferric oxalate hexahydrate, and ferric citrate; The organic cerium salt is one of cerium acetate, cerium tribenzoate, and cerium oxalate hydrate; The organic solvent is at least one of N,N-dimethylformamide, methanol, acetone, and ethanol.

[0010] In a further embodiment, the molar ratio of the organometallic salt to fumaric acid in the mixture is 1:1; The molar concentrations of both the organometallic salt and fumaric acid in the mixed solution were 0.1-0.2 mol / L. The molar ratio of the organic iron salt to the organic cerium salt is 0.67-1.5.

[0011] In a further embodiment, the continued stirring refers to stirring continuously at a speed of 120-180 rpm for 0.5-1 h.

[0012] In a further embodiment, the heating reaction is carried out at a temperature of 120-140°C for a duration of 12-18 hours.

[0013] In a further embodiment, the separation is performed by centrifugation; The washing is performed using N,N-dimethylformamide or a methanol and ethanol solution, respectively. The drying temperature is 60-80℃.

[0014] The third objective of this invention is to provide an application of a cerium-iron heterogeneous metal-organic framework material for removing fluoride ions from fluoride-containing wastewater.

[0015] A further approach involves adding cerium-iron heterogeneous metal-organic framework material to fluoride-containing wastewater, stirring for 5-30 minutes, and then separating the mixture to reduce the fluoride ion concentration in the wastewater to less than 1 mg / L.

[0016] In a further embodiment, the pH value of the fluoride-containing wastewater is 3-10, and the fluoride ion concentration is 5-20 mg / L; The amount of the cerium-iron heterogeneous metal-organic framework material added is 0.2-0.5 g / L, based on the volume of fluoride-containing wastewater.

[0017] The cerium-iron heterostructure metal-organic framework (Fe MOF on Ce MOF) fluoride removal material prepared in this invention possesses a large specific surface area (greater than 10⁹ m² / g), abundant adsorption sites, and stronger stability. Its surface active sites, including iron, cerium, and carboxyl groups, can adsorb fluoride ions through surface complexation, electrostatic adsorption, ligand exchange, and ion exchange, thus exhibiting excellent fluoride ion adsorption performance. More importantly, this cerium-iron heterostructure metal-organic framework material achieves enhanced fluoride ion coordination by introducing abundant and inexpensive iron elements into the synthesis process of the relatively expensive and fluoride-loving cerium metal-organic framework, forming a MOF on MOF structure. The interaction between Fe and Ce sites modulates the electron distribution of Fe and Ce, enhancing the fluoride ion coordination ability, improving fluoride removal performance, and reducing raw material costs. Furthermore, this cerium-iron heterostructure metal-organic framework material is environmentally friendly, producing no harmful substances during fluoride ion adsorption, making it a highly efficient and green water treatment material.

[0018] The reaction principle of this invention is as follows: This invention uses an organometallic salt containing a carboxylate functional group as the central metal and fumaric acid as the connecting ligand. An organic solvent is used to dissolve and disperse the metal salt and the organic ligand. At the same time, the carboxylate ions dissolved and ionized from the organometallic salt act as a regulator, which can adjust the coordination rate between the central metal ion and the ligand.

[0019] This invention utilizes a heating reaction to induce fumaric acid to bond with a central metal, forming a metal-organic framework network. Due to the different coordination abilities of Ce, Fe, and fumaric acid, and under the regulation of carboxylate ions, Ce preferentially binds to fumaric acid, thus first forming a Ce MOF. Fe then interacts with the Ce-O structure on the Ce MOF surface, forming a Ce-O-Fe structure. Subsequently, the Fe in the Ce-O-Fe structure coordinates with fumaric acid, generating particulate Fe MOFs in situ on the Ce MOF surface. After washing and drying, a cerium-iron heterogeneous metal-organic framework material (Fe MOF on Ce MOF) can be obtained.

[0020] The cerium-iron heterostructure metal-organic framework material prepared in this invention exhibits a larger specific surface area, more adsorption sites, and stronger stability compared to single-component Fe MOFs and Ce MOFs. Fe MOF on Ce MOF can adsorb fluoride ions through surface complexation, electrostatic adsorption, ligand exchange, and ion exchange, demonstrating excellent fluoride ion adsorption performance. Furthermore, the interaction between Fe and Ce sites modulates their outer electron distribution through electron transfer or shift, making the outer electron distribution of Fe and Ce more closely match the F 2p orbitals, thus enhancing the coordination ability of fluoride ions and resulting in better adsorption effect and higher adsorption capacity. It also exhibits excellent fluoride ion removal performance over a wider pH range (3-10).

[0021] Adding the cerium-iron heterogeneous metal-organic framework material prepared in this invention to fluoride-containing wastewater can reduce the initial fluoride ion concentration from approximately 5-20 mg / L to below 1 mg / L within 5-30 minutes, meeting the drinking water hygienic standards. Furthermore, no harmful substances are generated during the fluoride removal process, making it a novel, highly efficient, and green water treatment material.

[0022] The preparation method of the present invention is simple and easy to operate, requiring only stirring and heating to produce the product, making it suitable for large-scale industrial production. Attached Figure Description

[0023] Figure 1 Here is a SEM image of the cerium-iron heterostructure metal-organic framework material prepared in Example 1; Figure 2 The elemental distribution diagram of the cerium-iron heterostructure metal-organic framework material prepared in Example 1 is shown below. Figure 3The BET curves are shown for the cerium-iron heterostructure metal-organic framework material prepared in Example 1 and the Fe MOF and CeMOF materials prepared in Comparative Examples 1 and 2. Figure 4 This is a schematic diagram comparing the adsorption and removal efficiency of fluoride ions by the cerium-iron heterostructure metal-organic framework material prepared in Example 1 and the Fe MOF and CeMOF materials prepared in Comparative Examples 1 and 2. Figure 5 This is a schematic diagram comparing the adsorption effects of the cerium-iron heterostructure metal-organic framework material prepared in Example 1 with the Fe MOF and CeMOF materials prepared in Comparative Examples 1 and 2 at different pH values. Figure 6 The X-ray photoelectron spectroscopy (XPS) spectra of the materials prepared in Example 1, Comparative Examples 1 and 2 are shown. Figure 7 This is a schematic diagram showing the change in the fluoride ion adsorption capacity of the materials prepared in Examples 1-5 and Comparative Examples 1 and 2 as a function of the fluoride ion concentration in the solution. Detailed Implementation

[0024] The present invention will be further described below with reference to embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0025] Unless otherwise defined, 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 invention pertains. The terminology used herein in the description of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0026] In the following embodiments, the sealed container is a hydrothermal / solvothermal synthesis reactor, which means that the mixture is transferred to a polytetrafluoroethylene inner liner, then to a high-pressure reactor shell, and finally placed in an oven for heating and reaction.

[0027] In each embodiment, after the cerium-iron heterogeneous metal-organic framework material is added to the fluoride-containing wastewater and stirred, it needs to be separated to separate the adsorbed cerium-iron heterogeneous metal-organic framework material from the wastewater. Generally, centrifugal separation or filter cartridge filtration is used. The separated cerium-iron heterogeneous metal-organic framework material is used as filter bed packing material for defluorination.

[0028] Example 1: A method for preparing a cerium-iron heterostructure metal-organic framework material includes the following steps: S1. Ferric acetate (0.96 g, 0.005 mol), cerium acetate (1.59 g, 0.005 mol), fumaric acid (1.16 g, 0.01 mol) and 50 mL of N,N-dimethylformamide solution are stirred and mixed in a beaker to obtain mixed solution A; S2. Stir mixture A continuously at 120 rpm for 1 h; S3. Transfer the stirred mixture A to a high-pressure reactor and react at 140℃ for 12 h. The carboxylate ions ionized from the organometallic salt regulate the coordination rate of Fe and Ce ions with fumaric acid, thereby first generating Ce MOF, and then growing particulate Fe MOF in situ on the Ce MOF surface to obtain the reactant. S4. After cooling the product obtained after the reaction, separate it and wash it three times with N,N-dimethylformamide solution and ethanol solution respectively. Then dry it at 60°C to obtain the cerium-iron heterostructure metal-organic framework material.

[0029] The morphology and elemental distribution of the cerium-iron heterostructure metal-organic framework material prepared in Example 1 were characterized by scanning electron microscopy, as shown in the figure. Figure 1 , 2 As shown, from Figure 1 It can be seen that the prepared material is an irregularly shaped nanoparticle Fe MOF supported on a sheet-like Ce MOF, which is a MOF-on-MOF structure. And from... Figure 2 The elemental distribution diagram shows that the prepared material contains Fe, Ce, C, and O elements.

[0030] from Figure 3 The BET curve shows that the specific surface area of ​​the cerium-iron heterogeneous metal-organic framework material prepared in Example 1 is 109.57 m² / g.

[0031] By adding 0.2g of cerium-iron heterogeneous metal-organic framework material to 500mL of fluoride-containing wastewater (F... - After stirring for 5 minutes (at a concentration of approximately 20 mg / L), a sample was taken, and the fluoride ion concentration was measured and calculated using a fluoride ion electrode. The experimental results show that adding cerium-iron heterostructured metal-organic framework material at a dosage of 0.4 g / L can reduce the initial fluoride concentration of 20 mg / L to 0.48 mg / L, meeting drinking water standards.

[0032] The cerium-iron heterostructure metal-organic framework material has an adsorption capacity of 48.8 mg / g for fluoride ions.

[0033] Similarly, 500 mL of fluoride-containing wastewater with different initial fluoride ion concentrations (10, 20, 50, 100, 150, 200 mg / L) were prepared, and then 0.2 g of cerium-iron heterogeneous metal-organic framework material was added. Fluoride ion adsorption experiments were then conducted under the same conditions. The results were then obtained as follows: Figure 7 The diagram shows the change in fluoride ion adsorption capacity as a function of fluoride ion concentration in the solution.

[0034] Then from Figure 7 It can be concluded that the maximum adsorption capacity of the cerium-iron heterostructure metal-organic framework material prepared in Example 1 for fluoride ions is 148.77 mg / g.

[0035] Example 2: A method for preparing a cerium-iron heterostructure metal-organic framework material includes the following steps: S1. Ferric benzoate (2.52 g, 0.006 mol), cerium tribenzoate (2.01 g, 0.004 mol), fumaric acid (1.16 g, 0.01 mol) and 50 mL of methanol solution are stirred and mixed in a beaker to obtain mixed solution A; S2. Stir mixture A continuously at 160 rpm for 0.8 h; S3. Transfer the stirred mixture A to a high-pressure reactor and react at 130°C for 12 h. The carboxylate ions ionized from the organometallic salt regulate the coordination rate of Fe and Ce ions with fumaric acid, thereby first generating Ce MOF, and then growing particulate Fe MOF in situ on the Ce MOF surface to obtain the reactant. S4. After cooling the product obtained after the reaction, separate it and wash it three times with methanol solution and ethanol solution respectively. Then dry it at 80°C to obtain the cerium-iron heterogeneous metal-organic framework material.

[0036] The cerium-iron heterostructure metal-organic framework material synthesized in Example 2 was tested on a fluoride-containing water sample. Specifically: 0.2 g of cerium-iron heterostructured metal-organic framework material was added to 500 mL of actual fluoride-containing wastewater (F - After stirring for 5 minutes (at a concentration of approximately 20 mg / L), a sample was taken, and the fluoride ion concentration was measured and calculated using a fluoride ion electrode. The experimental results showed that a dosage of 0.4 g / L of cerium-iron heterostructured metal-organic frame material could reduce the initial fluoride concentration of 20 mg / L to 0.31 mg / L, meeting drinking water standards.

[0037] Same as in Example 1, by Figure 7 It can be concluded that the maximum adsorption capacity of the cerium-iron heterostructure metal-organic framework material prepared in Example 2 for fluoride ions is 161.29 mg / g.

[0038] Example 3: A method for preparing a cerium-iron heterostructure metal-organic framework material includes the following steps: S1. Ferric oxalate hexahydrate (2.42 g, 0.005 mol), cerium oxalate nonahydrate (3.53 g, 0.005 mol), fumaric acid (0.01 mol) and 50 mL of acetone are stirred and mixed in a beaker to obtain mixed solution A; S2. Stir mixture A continuously at 180 rpm for 0.5 h; S3. Transfer the stirred mixture A to a high-pressure reactor and react at 140℃ for 16 h. The carboxylate ions ionized from the organometallic salt regulate the coordination rate of Fe, Ce ions and fumaric acid, thereby first generating Ce MOF, and then growing particulate Fe MOF in situ on the Ce MOF surface to obtain the reactant. S4. After cooling the product obtained after the reaction, separate it and wash it three times with N,N-dimethylformamide solution and ethanol solution respectively. Then dry it at 60°C to obtain the cerium-iron heterostructure metal-organic framework material.

[0039] The cerium-iron heterostructure metal-organic framework material synthesized in Example 3 was tested on a fluoride-containing water sample, specifically as follows: 0.2 g of cerium-iron heterostructured metal-organic framework material was added to 500 mL of actual fluoride-containing wastewater (F - After stirring for 5 minutes (at a concentration of approximately 20 mg / L), a sample was taken, and the fluoride ion concentration was measured and calculated using a fluoride ion electrode. The experimental results showed that a dosage of 0.4 g / L of cerium-iron heterostructured metal-organic framework material could reduce the initial fluoride concentration of 20 mg / L to 0.37 mg / L, meeting drinking water standards.

[0040] Same as in Example 1, by Figure 7 It can be concluded that the maximum adsorption capacity of the cerium-iron heterostructure metal-organic framework material prepared in Example 3 for fluoride ions is 153.24 mg / g.

[0041] Example 4: A method for preparing a cerium-iron heterostructure metal-organic framework material includes the following steps: S1. Ferric citrate (0.98 g, 0.004 mol), cerium acetate (1.91 g, 0.006 mol), fumaric acid (0.01 mol) and 50 mL of ethanol solution are stirred and mixed in a beaker to obtain mixed solution A; S2. Stir mixture A continuously at 120 rpm for 1 h; S3. Transfer the stirred mixture A to a high-pressure reactor and react at 120°C for 18 h. The carboxylate ions ionized from the organometallic salt regulate the coordination rate of Fe and Ce ions with fumaric acid, thereby first generating Ce MOF, and then growing particulate Fe MOF in situ on the Ce MOF surface to obtain the reactants. S4. After cooling the product obtained after the reaction, separate it and wash it three times with methanol solution and ethanol solution respectively. Then dry it at 60°C to obtain the cerium-iron heterogeneous metal-organic framework material.

[0042] The cerium-iron heterostructure metal-organic framework material synthesized in Example 4 was tested on a fluoride-containing water sample, specifically as follows: 0.2 g of cerium-iron heterostructured metal-organic framework material was added to 500 mL of actual fluoride-containing wastewater (F - After stirring for 5 minutes (at a concentration of approximately 20 mg / L), a sample was taken, and the fluoride ion concentration was measured and calculated using a fluoride ion electrode. The experimental results showed that a dosage of 0.4 g / L of cerium-iron heterostructured metal-organic framework material could reduce the initial fluoride concentration of 20 mg / L to 0.43 mg / L, meeting drinking water standards.

[0043] Same as in Example 1, by Figure 7 It can be concluded that the maximum adsorption capacity of the cerium-iron heterostructure metal-organic framework material prepared in Example 4 for fluoride ions is 149.79 mg / g.

[0044] Example 5: A method for preparing a cerium-iron heterostructure metal-organic framework material includes the following steps: S1. Ferric acetate (0.48 g, 0.0025 mol), cerium acetate (0.79 g, 0.0025 mol), fumaric acid (0.58 g, 0.005 mol) and 50 mL of N,N-dimethylformamide solution are stirred and mixed in a beaker to obtain mixed solution A; S2. Stir mixture A continuously at 180 rpm for 0.5 h; S3. Transfer the stirred mixture A to a high-pressure reactor and react at 140℃ for 16 h. The carboxylate ions ionized from the organometallic salt regulate the coordination rate of Fe, Ce ions and fumaric acid, thereby first generating Ce MOF, and then growing particulate Fe MOF in situ on the Ce MOF surface to obtain the reactant. S4. After cooling the product obtained after the reaction, separate it and wash it three times with N,N-dimethylformamide solution and ethanol solution respectively. Then dry it at 60°C to obtain the cerium-iron heterostructure metal-organic framework material.

[0045] The cerium-iron heterostructure metal-organic framework material synthesized in Example 5 was tested on a fluoride-containing water sample, specifically as follows: 0.2 g of the cerium-iron heterostructure metal-organic framework material prepared in this embodiment was added to 500 mL of fluoride-containing wastewater (F - Samples were taken after stirring for 5 minutes (at a concentration of approximately 20 mg / L), and the fluoride ion concentration was measured and calculated using a fluoride ion electrode. The experimental results showed that a dosage of 0.4 g / L of cerium-iron heterostructured metal-organic framework defluorinating material could reduce the fluoride concentration from an initial 20 mg / L to 0.29 mg / L, meeting drinking water standards.

[0046] Same as in Example 1, by Figure 7 It can be concluded that the maximum adsorption capacity of the cerium-iron heterostructure metal-organic framework material prepared in Example 5 for fluoride ions is 158.67 mg / g.

[0047] Comparative Example 1: A method for preparing Fe MOF material includes the following steps: S1. Ferric acetate (1.91 g, 0.01 mol), fumaric acid (1.16 g, 0.01 mol), and 50 mL of N,N-dimethylformamide solution are mixed in a beaker to obtain mixed solution A. S2. Stir mixture A continuously at 180 rpm for 0.5 h; S3. Transfer the stirred mixture A to a high-pressure reactor and react at 140°C for 12 h. S4. After cooling following the reaction, the product is separated, washed three times with N,N-dimethylformamide solution and ethanol solution, and dried at 60℃ to obtain the Fe MOF material. Figure 3 According to the BET curve, its specific surface area is 36.178 m² / g.

[0048] The Fe MOF material prepared in Comparative Example 1 was tested on a fluoride-containing water sample. Specifically, the Fe MOF material was added at a dosage of 0.4 g / L and adsorbed for 30 min, which reduced the fluoride concentration from an initial concentration of 20 mg / L to 10.75 mg / L.

[0049] Same as in Example 1, by Figure 7 It can be concluded that the maximum adsorption capacity of the Fe MOF material prepared in Comparative Example 1 for fluoride ions is 64.35 mg / g. Its fluoride removal effect is significantly lower than that of the cerium-iron heterostructure metal-organic framework materials prepared in Examples 1-5. This is because the cerium-iron heterostructure metal-organic framework fluoride removal materials have a larger specific surface area and more active sites.

[0050] Comparative Example 2: A method for preparing Ce MOF material includes the following steps: S1, cerium acetate (3.17 g, 0.01 mol), fumaric acid (1.16 g, 0.01 mol), and 50 mL of N,N-dimethylformamide solution were mixed in a beaker to obtain mixed solution A; S2. Stir mixture A continuously at 120 rpm for 1 h; S3. Transfer the stirred mixture A to a high-pressure reactor and react at 130°C for 18 h. S4. After cooling following the reaction, the product is separated and washed three times with N,N-dimethylformamide solution and ethanol solution, then dried at 80℃ to obtain Ce MOF material. Figure 3 According to the BET curve, its specific surface area is 45.82 m² / g.

[0051] The Ce MOF material prepared in Comparative Example 2 was tested on a fluoride-containing water sample. Specifically, the Ce MOF material was added at a dosage of 0.4 g / L and adsorbed for 30 min, reducing the fluoride concentration from an initial concentration of 20 mg / L to 6.87 mg / L.

[0052] Same as in Example 1, by Figure 7 It can be concluded that the Ce MOF material prepared in Comparative Example 1 has a maximum adsorption capacity of fluoride ions of 79.54 mg / g. Its fluoride removal effect is lower than that of the cerium-iron heterostructure metal-organic framework materials prepared in Examples 1-5. This is because the cerium-iron heterostructure metal-organic framework material has a larger specific surface area, more active sites, and the introduction of iron forms a bimetallic synergistic effect, which enhances the fluoride ion adsorption performance.

[0053] The fluoride ion removal efficiency of the Fe MOF on Ce MOF material prepared in Example 1 is compared with that of the Fe MOF and Ce MOF materials prepared in Comparative Examples 1 and 2, as follows: Figure 4 As shown, this indicates that the adsorption performance of the Fe MOF on CeMOF material prepared in Example 1 of this application is significantly better than that of single Fe MOF and Ce MOF.

[0054] Figure 5 This comparison shows the fluoride ion removal efficiency of the Fe MOF on Ce MOF material prepared in Example 1 compared with that of the Fe MOF and Ce MOF materials prepared in Comparative Examples 1 and 2 at different pH values ​​(pH range 2-12). This demonstrates that the Fe MOF on Ce MOF material prepared in Example 1 exhibits excellent fluoride removal performance over a wider pH range, indicating that the MOF on MOF structure possesses greater stability.

[0055] Figure 6 The X-ray photoelectron spectroscopy (XPS) spectra (Fe 2p and Ce 3d) of the materials prepared in Examples 1, 1, and 2 show that, compared to single-metal MOF materials, the Fe 2p peak shifts towards higher binding energies, while the Ce 3d peak shifts towards lower binding energies. This indicates that electron shifts or transfers occur between the Fe and Ce sites, resulting in a better match between the Fe and Ce electrons and the F 2p orbitals, which is beneficial for the adsorption of fluoride ions.

[0056] Comparative Example 3: A Fe MOF on Ce MOF material includes the following steps: S1. Mix ferric nitrate nonahydrate (2.02 g), cerium nitrate hexahydrate (2.17 g), fumaric acid (1.16 g) with 50 mL of N,N-dimethylformamide solution in a beaker to obtain mixed solution A; S2. Stir mixture A continuously at 120 rpm for 1 h; S3. Transfer the stirred mixture A to a high-pressure reactor and react at 140°C for 12 h. S4. After cooling the product obtained after the reaction, separate it, wash it three times with N,N-dimethylformamide solution and ethanol solution, and dry it at 60°C to obtain the iron-cerium bimetallic organic framework material.

[0057] The iron-cerium bimetallic organic framework material synthesized in Comparative Example 3 was tested on a fluoride-containing water sample. With an addition of 0.4 g / L and adsorption for 30 min, the fluoride concentration was reduced from an initial concentration of 20 mg / L to 3.08 mg / L.

[0058] Similar to Example 1, the maximum adsorption capacity of fluoride ions is 93.27 mg / g. The fluoride removal effect is significantly lower than that of the cerium-iron heterostructure metal-organic framework materials prepared in Examples 1-5. This is because, in Comparative Example 3, an inorganic metal salt was used as the metal source, resulting in competition for ligands between the two metals. This is not conducive to the formation of the MOF on MOF structure, thus weakening the bimetallic synergistic effect and reducing the fluoride removal effect.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cerium-iron heterogeneous metal-organic framework material, characterized in that: This includes sheet-like Ce MOFs and Fe MOFs supported on them, forming a MOF-on-MOF structure.

2. The cerium-iron heterogeneous metal-organic framework material according to claim 1, characterized in that: The specific surface area of ​​the cerium-iron heterogeneous metal-organic framework material is greater than 109 m² / g.

3. The method for preparing a cerium-iron heterogeneous metal-organic framework material as described in claim 1 or 2, characterized in that: Includes the following steps: S1. Add the organometallic salt and fumaric acid to the organic solvent, stir and mix evenly, and then continue stirring to obtain a mixture; the organometallic salt is a mixture of organoferric salt and organocerium salt containing carboxyl functional groups; S2. The mixture is transferred to a sealed container for heating and reaction. The carboxylate ions ionized from the organometallic salt regulate the coordination rate of Fe and Ce ions with fumaric acid, thereby first generating Ce MOF, and then growing particulate Fe MOF in situ on the Ce MOF surface to obtain the reactants. S3. The reactants are cooled, separated, washed, and dried to obtain cerium-iron heterogeneous metal-organic framework materials.

4. The preparation method according to claim 2, characterized in that: The organic iron salt is one of ferric acetate, ferric benzoate, ferric oxalate hexahydrate, and ferric citrate; and / or, The organic cerium salt is one of cerium acetate, cerium tribenzoate, and cerium oxalate hydrate; and / or, The organic solvent is at least one of N,N-dimethylformamide, methanol, acetone, and ethanol.

5. The preparation method according to claim 3, characterized in that: The molar ratio of the organometallic salt to fumaric acid in the mixture is 1:1; and / or, The molar concentrations of both the organometallic salt and fumaric acid in the mixed solution are 0.1-0.2 mol / L; and / or, The molar ratio of the organic iron salt to the organic cerium salt is 0.67-1.

5.

6. The preparation method according to claim 3, characterized in that: The continued stirring refers to stirring continuously at a speed of 120-180 rpm for 0.5-h; and / or, The heating reaction is carried out at a temperature of 120-140℃ for 12-18 hours.

7. The preparation method according to claim 3, characterized in that: The separation is performed by centrifugation; and / or, The washing is performed using N,N-dimethylformamide or a solution of methanol and ethanol, respectively; and / or, The drying temperature is 60-80℃.

8. The application of a cerium-iron heterogeneous metal-organic framework material as described in claim 1 or 2, characterized in that: It is used to remove fluoride ions from fluoride-containing wastewater.

9. The application according to claim 8, characterized in that: Cerium-iron heterogeneous metal-organic framework material is added to fluoride-containing wastewater, stirred for 5-30 minutes, and then separated to make the fluoride ion concentration in the wastewater less than 1 mg / L.

10. The application according to claim 8, characterized in that: The fluoride-containing wastewater has a pH value of 3-10 and a fluoride ion concentration of 5-20 mg / L; The amount of the cerium-iron heterogeneous metal-organic framework material added is 0.2-0.5 g / L, based on the volume of fluoride-containing wastewater.

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