Preparation and application of a hierarchical porous iron-manganese bimetallic organic framework gel

Abstract

The present invention provides a preparation and application of a multi-level porous iron-manganese bimetallic organic framework gel, which belongs to the field of new materials for advanced oxidation catalysts. The preparation method comprises the following steps: (1) dissolving ferric nitrate nine hydrate and manganese nitrate four hydrate in a mixture of ethanol and N,N-dimethylformamide; dissolving an organic ligand trimesic acid in a mixture of ethanol and N,N-dimethylformamide, and then mixing the two evenly; (2) transferring the mixture to a closed reaction vessel and placing it in a forced air drying oven to heat it into a gel to obtain a gel-like substance; (3) washing the gel-like substance with ethanol, and then drying the product to obtain the multi-level porous iron-manganese bimetallic organic framework gel. The bimetallic organic framework gel of the present invention has a multi-level porous structure of micropores, mesopores and macropores, and the block morphology is not easy to agglomerate and is convenient to recycle, which is more conducive to promoting the mass transfer process of the catalytic degradation reaction, and is a more ideal advanced oxidation catalyst form.

Description

Technical Field

[0001] The present invention relates to the field of new materials for advanced oxidation catalysts, and in particular to a bimetallic organic framework gel material for catalyzing the efficient degradation of ofloxacin by peracetic acid, and a preparation method and use method thereof. Background Art

[0002] Metal-organic frameworks (MOFs) have attracted significant attention from researchers both domestically and internationally due to their rich microporous structures, large surface areas, structural and functional tunability, and designability in areas such as gas storage and separation, catalysis, sensing, drug loading, and environmental applications. In particular, MOFs, as catalysts with abundant reactive sites, hold broad application prospects in the advanced oxidation degradation of antibiotics.

[0003] However, MOFs as advanced oxidation catalysts still have certain defects in the application of antibiotic degradation, such as The molecular size is mainly micropores (less than )’s MOF pore structure limits the mass transfer efficiency and reduces the catalytic degradation effect; MOFs materials are usually macroscopic powders, which are easy to agglomerate, resulting in a decrease in catalytic performance and poor recycling effect, and are not conducive to recycling.

[0004] Researchers have begun combining MOFs with traditional porous materials with mesopores or macropores, such as mesoporous silicon, macroporous polymers, and three-dimensional foams, to form hierarchical porous composite materials to address these issues. However, the synthesis steps of such composite materials are complex and prone to raw material loss during the synthesis process, making them unsuitable for practical production needs. For example, CN112961650A provides a tri-metal organic framework-derived iron-nickel alloy / porous carbon ultrathin absorber and its preparation method. The method used is to perform high-temperature carbonization using MOF as a template. The resulting carbonized product is in powder form and does not have the original MOF structure.

[0005] In recent years, metal-organic framework (MOF) gels, a class of bulk materials derived from MOFs and prepared by the sol-gel method with a hierarchical porous structure, have attracted much attention. These materials are formed by the coordination of organic ligands and metal ions and can be directly synthesized in a "one-pot" method with high yield. However, the capillary forces caused by the violent evaporation of the solvent during the drying process can cause the macropores and mesopores in the gel structure to collapse. Using mild and slow activation methods such as supercritical carbon dioxide or freeze-drying can enable the activated gel to retain the original macropore and mesoporous structure, ultimately forming a gel material with high specific surface area, low density, high porosity, a hierarchical porous structure, and macroscopic plasticity. However, the harsh activation conditions limit the practical application of metal-organic framework gels.

[0006] CN115232325A provides a preparation method and application of a low-crystalline iron-manganese bimetallic organic framework material. The synthesized low-crystalline iron-manganese bimetallic organic framework material has superior physical and chemical properties compared to its high-crystalline counterpart. Compared with its high-crystalline counterpart, the crystal structure undergoes significant changes, with long-range disorder and short-range order. The surface functional groups of the material remain essentially unchanged, and the material's apparent morphology changes from irregular to regular octahedral, with a reduced particle size. However, the change in crystallinity is not necessarily related to the formation of a multi-level pore structure, and the product synthesized in the above patent is still a powder material and cannot be macro-shaped into a gel state.

[0007] In order to solve the defects of MOFs materials as advanced oxidation catalysts in the application of antibiotic degradation and further simplify the synthesis method of multi-level porous metal organic framework gels to promote their practical application, the present invention is specially proposed. Summary of the Invention

[0008] To address the aforementioned issues in the prior art, the present invention provides the preparation and application of a hierarchically porous iron-manganese bimetallic organic framework gel. The bimetallic organic framework gel exhibits a hierarchical microporous-mesoporous-macroporous structure, resulting in a block morphology that resists agglomeration and facilitates recycling. This facilitates mass transfer during catalytic degradation reactions, making it an ideal form of advanced oxidation catalyst.

[0009] The technical solutions of the present invention are as follows:

[0010] A method for preparing a hierarchical porous iron-manganese bimetallic organic framework gel comprises the following steps:

[0011] (1) dissolving ferric nitrate nonahydrate and manganese nitrate tetrahydrate in a mixture of ethanol and N,N-dimethylformamide to prepare solution A;

[0012] The organic ligand trimesic acid is dissolved in a mixture of ethanol and N,N-dimethylformamide to prepare solution B, and then solution A and solution B are mixed evenly;

[0013] (2) transferring the mixed solution obtained in step (1) into a sealed reaction vessel, and heating it in a forced air drying oven to form a gel to obtain a gel-like substance;

[0014] (3) washing the colloidal substance obtained in step (2) with ethanol, and then drying the product to obtain the multi-level porous iron-manganese bimetallic organic framework gel.

[0015] The specific surface area of ​​the multi-level porous iron-manganese bimetallic organic framework gel prepared by the present invention is 616-982m 2 / g, the average pore diameter calculated according to the BJH method is 1.84-5.27nm, and it has a micropore-mesopore-macroporous ternary pore structure, in which the volume ratio of micropores, mesopores and macropores is 1:0.9-6.5:0.01-0.2.

[0016] The iron and manganese elements in the bimetallic organic framework gel structure are coordinated with the carboxyl group in trimesic acid. The molar ratio of the metal elements, i.e., the sum of iron and manganese, to the organic ligand trimesic acid in the bimetallic organic framework gel is 2.8-3.2:1.7-2.3, preferably 3:2.

[0017] Preferably, the molar ratio of the ferric nitrate nonahydrate to the manganese nitrate tetrahydrate in step (1) is 1:0.3-3.

[0018] Preferably, the volume ratio of ethanol to N,N-dimethylformamide in step (1) is 1:0.25-1 respectively.

[0019] Preferably, the sealed reaction vessel in step (2) is a sealed glass reaction bottle with a polytetrafluoroethylene gasket, or a polytetrafluoroethylene-lined reactor.

[0020] Preferably, the heating temperature of the blast drying oven in step (2) is 100-120° C., and the heating time is 12-24 hours.

[0021] Preferably, the ethanol washing times in step (3) are no less than 3 times, and the drying process is ventilation drying at room temperature.

[0022] The present invention also provides an application of the bimetallic organic framework gel obtained by the preparation method, that is, the gel is used as an advanced oxidation catalyst for degrading ofloxacin.

[0023] Preferably, the gel is used to degrade ofloxacin in sewage; peracetic acid is added as an oxidant during degradation, and the gel catalyzes the peracetic acid to produce oxidative active substances, thereby degrading ofloxacin in sewage.

[0024] More preferably, the dosage of the peracetic acid is 26-105 mg / L, the concentration of ofloxacin is 1-5 mg / L; and the concentration of the bimetallic organic framework gel is 50-150 mg / L.

[0025] The beneficial technical effects of the present invention are:

[0026] 1. The multi-level porous bimetallic organic framework gel prepared by the present invention has two important advances compared to powdered MOFs. First, the product of the present invention is in a macroscopic gel state, and the macroscopic block structure can effectively avoid the problems of active site agglomeration and deactivation and catalyst recycling during the catalytic process; second, the product of the present invention has three pore structures, micropores less than 2nm, mesopores of 2-50nm, and macropores greater than 50nm; among them, the macropores and mesopores can further improve the mass transfer efficiency of the catalytic reaction, and the electron transfer between the iron and manganese elements can further accelerate the catalytic reaction cycle and thus improve the advanced oxidation degradation performance. In addition, the microscopic morphology crystals of the gel prepared by the present invention are spherical particles less than 50nm, and the particle size is smaller than that of CN115232325A.

[0027] 2. Compared with the existing technology, the present invention does not involve the use of complex activation methods such as supercritical carbon dioxide or freeze drying, and does not require the addition of additional pore-forming agents or compounding with other materials. A one-step room-temperature drying and activation method can synthesize a bimetallic organic framework gel material with a multi-level pore structure and macroscopic block morphology. The synthesis method is simple and the product yield is extremely high.

[0028] 3. The bimetallic organic framework gel of the present invention has the advantages of low preparation cost, wide source of raw materials, simple operation, good repeatability, mass production, and easy transformation of results. It avoids the complex steps and raw material loss problems in the synthesis process of composite materials. It can be obtained by "one-pot" synthesis and drying at room temperature. It has potential application value in the fields of water quality, air purification, soil remediation, etc.

[0029] 4. The formation of the multi-level pores of the present invention is not achieved by changing the type of salt to change the pore structure of the product as used in the prior art, but is related to the introduction of Mn ions and salt concentration. The salts used in the present invention are all nitrates, and the change in the pore structure ratio in the multi-level pores is achieved by adjusting the ratio of metal salts. The inventors found through comparative experiments that after replacing the raw materials with ferric chloride hexahydrate and manganese chloride tetrahydrate, although gelation can also be achieved, the higher solubility of chloride salts than nitrates causes the metal ions and organic ligands to coordinate too quickly, accelerating the gelation process so that the gel pore structure is smaller, and the pore structure of the final product is mainly micropores, which has an adverse effect on the degradation kinetics.

[0030] Furthermore, the formation process of the hierarchical porous structure of the present invention places strict demands on the synthesis solvent, metal salt type, metal salt concentration, and synthesis temperature. By adjusting the reactant concentrations, the product transitions from a liquid to a gel state during the reaction, forming a network gel structure with macropores and mesopores. Simultaneously, controlling the synthesis temperature promotes coordination between metal ions and ligands, increasing product crystallinity and forming micropores.

[0031] 5. The product obtained by the present invention can catalyze the degradation of ofloxacin with peracetic acid and can be used to treat ofloxacin-containing wastewater. For antibiotic-contaminated water with an ofloxacin concentration of 5 mg / L, the degradation rate exceeds 80% and the degradation time is 1 hour. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention and the solutions of the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. The drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 This is a transmission electron micrograph of the iron-manganese bimetallic organic framework gel obtained in Example 1;

[0034] Figure 2 This is the nitrogen adsorption-desorption isotherm of the iron-manganese bimetallic organic framework gel obtained in Example 1;

[0035] Figure 3 This is the pore size distribution diagram of the iron-manganese bimetallic organic framework gel obtained in Example 1;

[0036] Figure 4 The catalytic degradation effect of ofloxacin by the iron-manganese bimetallic organic framework gel obtained in Example 1 was compared with that of the iron-based metal organic framework gel. DETAILED DESCRIPTION

[0037] The present invention is described in detail below with reference to the accompanying drawings and embodiments. It is apparent that the embodiments described are only a portion of the embodiments of the present invention, rather than all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0038] Example 1:

[0039] (1) Dissolve 3.75 mmol of ferric nitrate nonahydrate and 11.25 mmol of manganese nitrate tetrahydrate in 20 mL of a mixture of ethanol and N,N-dimethylformamide (volume ratio 1:0.5) to obtain solution A;

[0040] Take another 20 mL of a mixture of ethanol and N,N-dimethylformamide (volume ratio 1:0.5) and dissolve 0.01 mol of trimesic acid in it to obtain Solution B;

[0041] (2) The two solutions were then mixed and transferred into a sealed pressure-resistant reaction vessel, which was then placed in a 120° C. forced air drying oven for 24 hours to obtain a gel-like substance.

[0042] (3) The colloidal substance was washed three times with ethanol and then dried at room temperature in a fume hood to obtain an Fe-Mn bimetallic organic framework gel.

[0043] The transmission electron microscopy image of the iron-manganese bimetallic organic framework gel prepared by the above method is as follows: Figure 1 As shown in the figure, the product is a cross-linked network structure with mesopores and macropores, among which the micropores are too small to be seen from the electron microscope image; the nitrogen adsorption-desorption isotherm is shown in Figure 2 As shown in the figure, it can be seen that the nitrogen adsorption-desorption isotherm of the sample is a typical type IV curve. The rapid increase of nitrogen adsorption in the low pressure section indicates the presence of micropores in the structure, and the presence of a hysteresis loop in the high pressure section indicates the presence of mesopores in the structure. The pore size distribution calculated according to the BJH method is shown in Figure 3 As shown, there are micropores, mesopores and macropores in the structure, V 微孔 :V 介孔 :V 大孔 =1:6.5:0.2.

[0044] Example 2:

[0045] Dissolve 11.25 mmol of ferric nitrate nonahydrate and 3.75 mmol of manganese nitrate tetrahydrate in 20 mL of a 1:1 volume ratio of ethanol and N,N-dimethylformamide. Dissolve 0.01 mol of trimesic acid in another 20 mL of a 1:1 volume ratio of ethanol and N,N-dimethylformamide. The two solutions are then transferred to a sealed pressure-resistant reaction vessel. The sealed pressure-resistant reaction vessel is placed in a 120°C forced air drying oven for 24 hours to obtain the product, which is then washed three times with ethanol and dried in a fume hood at room temperature.

[0046] The prepared iron-manganese bimetallic organic framework gel has a specific surface area of ​​982 m 2 / g, the average pore size calculated by BJH method is 1.99nm, with a multi-level pore structure, V 微孔 :V 介孔 :V 大孔 =1:0.92:0.012.

[0047] Example 3:

[0048] Dissolve 7.5 mmol of ferric nitrate nonahydrate and 7.5 mmol of manganese nitrate tetrahydrate in 20 mL of a mixture of ethanol and N,N-dimethylformamide (volume ratio of 1:0.25). Dissolve 0.01 mol of trimesic acid C in another 20 mL of a mixture of ethanol and N,N-dimethylformamide (volume ratio of 1:0.25). The two solutions are then mixed and transferred to a sealed pressure-resistant reaction vessel. The sealed pressure-resistant reaction vessel is placed in a 120°C forced air drying oven for 24 hours to obtain the product, which is then washed three times with ethanol and dried at room temperature in a fume hood.

[0049] The prepared Fe-Mn bimetallic organic framework gel has a specific surface area of ​​622 m 2 / g, the average pore size calculated by BJH method is 1.84nm, with a multi-level pore structure, V 微孔 :V 介孔 :V 大孔 =1:1.18:0.057.

[0050] Test Example 1:

[0051] The catalytic performance of the iron-manganese bimetallic organic framework gel obtained in Example 1 in the degradation of ofloxacin with peracetic acid was compared with that of the iron-based metal-organic framework gel. The preparation method of the iron-based metal-organic framework gel was based on the paper "Metal-organic framework (MOF) aerogels with high micro- and macroporosity" (Lohe MR, Rose M., Kaskel S.. Chemical Communications, 2009, Vol. 40: 6056-6058).

[0052] The degradation experimental process is as follows:

[0053] Experimental water was prepared to a concentration of 5 mg / L ofloxacin, and the pH was adjusted to 7.0 with HCl and NaOH. 10 mg each of the iron-manganese bimetallic organic framework gel catalyst and the iron-based metal-organic framework gel catalyst prepared in Example 1 were placed in 100 mL of experimental water. Subsequently, 1.034 mM PAA was added to initiate the catalytic degradation reaction.

[0054] During the reaction, the solution was stirred at 400 r / min with a magnetic stirrer for 1 h and a reaction temperature of 298 K. 1 mL of sample was taken with a syringe at reaction times of 0, 2.5, 5, 10, 15, 20, 30, 45, and 60 min, and the water sample was filtered with a 0.22 μm aqueous filter. 10 μL of 100 mM Na2S2O8 was then added to the water sample to quench the reaction, and the ofloxacin concentration in the sample was determined by liquid chromatography.

[0055] The results are as follows Figure 4 As shown in the figure, it can be seen that the degradation rate and degradation efficiency of the iron-manganese bimetallic organic framework gel are better than those of the iron-based metal-organic framework gel.

[0056] Test Example 2:

[0057] A spiked experiment was conducted using Dianshan Lake water samples. The water was prepared with Dianshan Lake raw water at a concentration of 5 mg / L ofloxacin. 10 mg of the iron-manganese bimetallic organic framework gel catalyst prepared in Example 1 was added to 100 mL of this water. Subsequently, 1.034 mM PAA was added to initiate the catalytic degradation reaction. The results showed that the degradation rate of ofloxacin in the Dianshan Lake water sample (at a spiked concentration of 5 mg / L) exceeded 80%, demonstrating the applicability of this catalytic degradation system to real-world wastewater.

[0058] Comparative Example 1: Effect of Changing the Type of Metal Salt on the Product

[0059] Based on Example 3, the ferric nitrate nonahydrate and manganese nitrate tetrahydrate were replaced with ferrous sulfate heptahydrate and manganese sulfate, and the obtained product was a turbid liquid, not a gel.

[0060] Comparative Example 2: Effect of Changing Metal Salt Concentration on the Product

[0061] Based on Example 3, the concentrations of the metal salt and the ligand were diluted 15 times, and the obtained product was a turbid liquid, not a gel.

[0062] Based on Example 3, the concentrations of the metal salt and the ligand were diluted 20 times, and the obtained product was a turbid liquid, not a gel.

[0063] Based on Example 3, the concentrations of the metal salt and ligand were diluted 25 times, and the obtained product was a clear liquid.

[0064] Comparative Example 3: Effect of Changing Synthesis Temperature on the Product

[0065] Based on Example 3, the sealed pressure-resistant reaction vessel was placed at room temperature for reaction. The obtained product was in a gel state. The nitrogen adsorption-desorption isotherm was a typical type I curve. There were only a few micropores in the structure. The small amount of nitrogen adsorption indicated that the coordination degree between the metal ion and the ligand was low and the pore structure was small. Its specific surface area was 2.99 m 2 / g.

[0066] Based on Example 3, the sealed pressure-resistant reaction vessel was placed in a 40°C forced air drying oven for 24 hours. The obtained product was in a gel state, and the nitrogen adsorption-desorption isotherm was a typical type I curve. There were only a few micropores in the structure. The small amount of nitrogen adsorption indicated that the coordination degree between the metal ion and the ligand was low, and the pore structure was small. Its specific surface area was 0.06 m 2 / g.

[0067] Based on Example 3, the sealed pressure-resistant reaction vessel was placed in a forced air drying oven at 80°C for 24 hours. The obtained product was in a gel state, and the nitrogen adsorption-desorption isotherm was a typical type I curve. There were only a few micropores in the structure. The small amount of nitrogen adsorption indicated that the coordination degree between the metal ion and the ligand was low, and the pore structure was small. Its specific surface area was 47.14 m 2 / g.

[0068] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, for those of ordinary skill in the art, various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A method for preparing a hierarchical porous iron-manganese bimetallic organic framework gel, characterized in that: The following steps are involved: (1) Dissolving ferric nitrate nonahydrate and manganese nitrate tetrahydrate in a mixture of ethanol and N,N-dimethylformamide to prepare solution A; The organic ligand trimesic acid is dissolved in a mixture of ethanol and N,N-dimethylformamide to prepare solution B, and then solution A and solution B are mixed evenly; (2) transferring the mixed solution obtained in step (1) into a sealed reaction vessel, and heating the mixture in a forced air drying oven to form a gel to obtain a gel-like substance; (3) washing the colloidal substance obtained in step (2) with ethanol, and then drying the product to obtain the hierarchical porous iron-manganese bimetallic organic framework gel; The iron and manganese elements in the bimetallic organic framework gel structure are coordinated with the carboxyl group in trimesic acid, and the molar ratio of the metal elements, i.e., the sum of iron and manganese, to the organic ligand trimesic acid in the bimetallic organic framework gel is 2.8-3.2:1.7-2.3; The molar ratio of the ferric nitrate nine hydrate to the manganese nitrate tetrahydrate in step (1) is 1:0.3-3; The volume ratio of ethanol and N,N-dimethylformamide in step (1) is 1:0.25-1 respectively; The heating temperature of the blast drying oven in step (2) is 100-120° C., and the heating time is 12-24 hours.

2. The preparation method according to claim 1, characterized in that The bimetallic organic framework gel has a micropore-mesopore-macroporous ternary pore structure, wherein the volume ratio of micropores, mesopores and macropores is 1:0.9-6.5:0.01-0.

2.

3. The preparation method according to claim 1, characterized in that The sealed reaction vessel in step (2) is a sealed glass reaction bottle with a polytetrafluoroethylene gasket, or a polytetrafluoroethylene-lined reactor.

4. The preparation method according to claim 1, characterized in that In step (3), the ethanol washing is performed for no less than 3 times, and the drying process is performed by drying under ventilation at room temperature.

5. An application of a bimetallic organic framework gel obtained by the preparation method according to any one of claims 1 to 4, characterized in that: The gel serves as an advanced oxidation catalyst for degrading ofloxacin.

6. The use according to claim 5, characterized in that The gel is used for degrading ofloxacin in sewage; during degradation, peracetic acid is added as an oxidant, and the gel catalyzes the peracetic acid to produce oxidative active substances, thereby degrading the ofloxacin in the sewage.

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