Iron metal-organic framework catalytic membrane and its use in a method for the synthesis of benzimidazole derivatives

Abstract

The application discloses an iron-based metal organic framework catalytic membrane and a benzimidazole derivative synthesis method thereof, and relates to the technical fields of catalytic materials and organic synthesis; the technical key points are as follows: the iron-based metal organic framework crystal seeds are allowed to grow on the surface of an Al2O3 ceramic membrane carrier by adopting a seed inoculation-second growth method, hydrogen bonds and weak coordination effects are formed between the crystal seeds and the hydroxyl groups on the surface of the carrier to form stable anchoring points, and N,N-dimethylformamide, deionized water and constant-temperature stirring reaction are optimized in the second growth stage, and finally, a continuous and dense membrane layer structure of the catalytic membrane is prepared; the catalytic membrane is endowed with excellent stability, the catalytic membrane can be repeatedly put into reaction only by being simply cleaned and dried with methanol, and the technical defects that the traditional MOF membrane is easy to fall off and the catalyst cannot be reused are effectively solved; meanwhile, the catalytic membrane has high photo-generated carrier separation efficiency and wide visible light response range, can efficiently play a catalytic role under 465nm blue light irradiation, and provides a good activity basis.

Description

Technical Field

[0001] This invention relates to the field of catalytic materials and organic synthesis technology, specifically to iron-based metal-organic framework catalytic membranes and their application in the synthesis of benzimidazole derivatives. Background Technology

[0002] Benzimidazole and its derivatives are an important class of nitrogen-containing heterocyclic compounds with broad application prospects in drug development, materials science, coordination chemistry, and other fields. Most of these compounds possess antibacterial, antiviral, antitumor, and antihypertensive biological activities and serve as the core framework for many clinical drugs. At the same time, they can also be used as fluorescent probes, organic semiconductors, and metal coordination ligands to prepare high-performance functional materials, thus possessing significant application value in the field of materials. Traditional methods for synthesizing benzimidazole derivatives mainly rely on the condensation reaction of o-phenylenediamine with aldehydes or ketones. This reaction usually requires harsh conditions such as high temperature and strong acid / base, resulting in problems such as low reaction efficiency, poor product selectivity, difficulty in product separation, and serious environmental pollution, which does not conform to the development concept of green chemistry. Metal-organic frameworks (MOFs) are porous crystalline materials assembled from metal ions / metal clusters and organic ligands through coordination bonds. They exhibit great application potential in catalysis due to their unique properties such as high specific surface area, tunable pore size, abundant active sites, and functionalizable structure. Among them, iron-based metal-organic frameworks (Fe-MOFs) are particularly valuable because of the abundance of iron, low preparation cost, environmental friendliness, and the presence of Fe... 2+ / Fe 3+ With multiple valence states, it can participate in the electron transfer process in the photocatalytic reaction through valence state changes, making it one of the ideal choices for constructing efficient photocatalysts; However, traditional Fe-MOFs photocatalysts are mostly in powder form, which has many drawbacks in practical applications: powdered Fe-MOFs are prone to agglomeration, resulting in insufficient exposure of active sites and limited catalytic efficiency; the catalyst is difficult to recover and cannot be reused, causing resource waste and environmental burden; and it is difficult to achieve continuous reaction, which seriously restricts its industrial application process. Catalytic membranes combine the advantages of membrane separation and catalysis technologies, immobilizing catalysts on a support surface. This avoids the loss and aggregation of active components while achieving efficient separation of products and catalysts through membrane retention. Furthermore, they enable continuous reaction systems, significantly improving the industrial feasibility of the reaction and providing an effective solution to the aforementioned shortcomings of powdered catalysts. However, the preparation of existing MOF-based catalytic membranes still faces numerous technical challenges: low bonding strength between the membrane layer and the support, leading to easy peeling and detachment during the reaction; poor membrane continuity, making precise control of the crystallization process difficult and resulting in unstable catalytic performance; and a lack of research on the application of Fe-MOF catalytic membranes in the photocatalytic synthesis of benzimidazole derivatives. Currently, no Fe-MOF catalytic membrane system possesses high catalytic activity, high structural stability, and continuous application capability. In addition, the preparation processes of existing MOF-based catalytic membranes are complex and difficult to scale up, further limiting their practical industrial application. Therefore, there is an urgent need for an iron-based metal-organic framework catalytic membrane and its application in the synthesis of benzimidazole derivatives. Summary of the Invention

[0003] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing an iron-based metal-organic framework catalytic membrane, comprising the following steps: S1. The Al2O3 ceramic membrane was boiled with deionized water, ultrasonically treated with ultrapure water, and then dried to constant weight to obtain the activated Al2O3 ceramic membrane carrier. S2. Take ferric chloride hexahydrate and 2,2'-bipyridine-5,5'-dicarboxylic acid in a molar ratio of 2:1, dissolve them in a mixed solvent of N,N-dimethylformamide and deionized water, disperse them by ultrasonication, stir at a constant temperature, and then obtain iron-based metal-organic framework seed crystals after solid-liquid separation, methanol washing, and drying. S3. Iron-based metal-organic framework seed crystals are dispersed in methanol to prepare a spin-coating solution. The activated Al2O3 ceramic film carrier is spin-coated with the spin-coating solution and dried to obtain a seed-loaded film. S4. Take ferric chloride hexahydrate and 2,2'-bipyridine-5,5'-dicarboxylic acid in a molar ratio of 2:1, dissolve them in a mixed solvent of N,N-dimethylformamide and deionized water, and ultrasonically disperse them to obtain a reaction solution. Immerse the seed-supported membrane in the reaction solution and stir at a constant temperature. After washing with alcohols and drying, an iron-based metal-organic framework catalytic membrane is obtained.

[0004] Furthermore, in step S1, the Al2O3 ceramic membrane has the following specifications: diameter 3.2cm, thickness 1.75mm, pore size 3-5μm, deionized water boiling treatment time 6h, ultrapure water ultrasonic treatment time 30min, and drying temperature 60℃.

[0005] Furthermore, in step S2, the volume ratio of N,N-dimethylformamide to deionized water is 1:1, the total volume of the mixed solvent is 60 mL, the ultrasonic dispersion time is 10 min, the constant temperature stirring reaction temperature is 100℃-120℃ for 24 h, the solid-liquid separation is centrifugation at 8000 rpm for 10 min, the number of methanol washings is 3, and the drying temperature is 100℃.

[0006] Furthermore, in step S3, the spin coating solution is prepared by adding 30 mL of iron-based metal-organic framework seed crystals to methanol and ultrasonically dispersing for 15 min, with a concentration of 5 mg / mL-10 mg / mL, a spin coating speed of 500 rpm-700 rpm and a time of 30 s, a drying temperature of 70 ℃ and a drying time of 12 h, and a spin coating speed of 700 rpm when the drop volume of the spin coating solution is 8 mL and the concentration is 10 mg / mL.

[0007] Furthermore, in step S4, the volume ratio of N,N-dimethylformamide to deionized water is 10:1-1:1, the total volume of the mixed solvent is 60 mL, the ultrasonic dispersion time is 10 min, the constant temperature stirring reaction temperature is 100℃-120℃, and the time is 24 h. Alcohol washing is performed by alternating washing with anhydrous ethanol and methanol three times. After washing, the residual solvent on the membrane surface is rinsed with ultrapure water, and the drying temperature is 60℃. The preferred volume ratio of N,N-dimethylformamide to deionized water is 10:1, and the preferred temperature for the constant temperature stirring reaction is 120℃.

[0008] An iron-based metal-organic framework catalytic membrane is prepared by the above-mentioned method. The catalytic membrane uses an Al2O3 ceramic membrane as a support and an iron-based metal-organic framework as an active component. The iron-based metal-organic framework seed crystals form hydrogen bonds and weak coordination with the hydroxyl groups on the surface of the Al2O3 ceramic membrane support.

[0009] A method for synthesizing benzimidazole derivatives using an iron-based metal-organic framework catalytic membrane, comprising the following steps: G1. Construct a flow-through catalytic membrane photoreactor consisting of a membrane module, a storage tank, a peristaltic pump, and a light source. Fix the iron-based metal-organic framework catalytic membrane in the membrane module and connect the storage tank and the peristaltic pump. G2. Take the aldehyde substrate, o-phenylenediamine and solvent, mix them, and disperse them ultrasonically to obtain a homogeneous reaction system; G3. Turn on the peristaltic pump to allow the reaction liquid to pass through the iron-based metal-organic framework catalytic membrane at a set flow rate. At the same time, turn on the light source to provide blue light of a specific wavelength for irradiation. The photocatalytic reaction is carried out under air atmosphere and room temperature conditions. The reaction process is monitored in real time by thin layer chromatography and gas chromatography. G4. After the reaction is complete, the membrane module is cleaned with methanol. The cleaning solution and the reaction solution are combined and concentrated to obtain the crude product. The crude product is purified by column chromatography and the solvent is removed by vacuum distillation to obtain the benzimidazole derivative.

[0010] Furthermore, in step G2, the solvent is one or more of methanol, ethanol, acetonitrile, N,N-dimethylformamide, water, ethyl acetate, and tetrahydrofuran; the molar ratio of the aldehyde substrate to o-phenylenediamine is 1:1 to 1:1.5; the molar volume ratio of the aldehyde substrate, o-phenylenediamine, and solvent is 1~2 mmol:1.5~3 mmol:10~20 mL; the ultrasonic dispersion time is 5 min; and when 0.3 mmol of aldehyde substrate and 0.36 mmol of o-phenylenediamine are added, the solvent volume is 6-10 mL.

[0011] Furthermore, in step G3, the specific wavelength of blue light is 465nm, the light source is a 465nm blue LED light source with a power of 10W, the room temperature is 25℃, the photocatalytic reaction time is 2-6h, preferably 4h; the flow rate of the peristaltic pump is 10-30mL / min, preferably 30mL / min.

[0012] Furthermore, in step G4, the methanol cleaning membrane module is used in a single application of 5 mL and is cleaned 3 times. The concentration is achieved by rotary evaporation at 40°C and 0.08 MPa. The column chromatography uses silica gel as the packing material and a mixture of petroleum ether and ethyl acetate as the developing solvent, with a volume ratio of 5:1 to 30:1. Aldehyde substrates include benzaldehyde, halogenated benzaldehyde, nitrobenzaldehyde, methoxybenzaldehyde, cyanobenzaldehyde, acyl-substituted benzaldehyde, ester-substituted benzaldehyde, naphthalene-2-carboxaldehyde, biphenyl-4-carboxaldehyde, cyclohexylcarboxaldehyde, pyridine-4-carboxaldehyde, and furan-2-carboxaldehyde; o-Phenylenediamines include unsubstituted o-phenylenediamine, 5,6-dimethyl o-phenylenediamine, and 5-bromo-o-phenylenediamine.

[0013] This invention provides an iron-based metal-organic framework catalytic membrane and its application in the synthesis of benzimidazole derivatives, which has the following beneficial effects: 1. A seed-seeding-secondary growth method was employed to directionally grow iron-based metal-organic framework (MOF) seeds on the surface of an Al2O3 ceramic membrane support. The seeds formed hydrogen bonds and weak coordination with the hydroxyl groups on the support surface, creating stable anchoring points. During the secondary growth stage, the volume ratio of N,N-dimethylformamide to deionized water was optimized to 10:1, and the reaction temperature was kept constant at 120℃. This resulted in a continuous and dense catalytic membrane structure. This preparation process endowed the catalytic membrane with excellent structural stability. In the subsequent catalytic synthesis of benzimidazole derivatives, the membrane layer did not peel or detach. After 10 cycles of use, the catalytic membrane was verified to require only simple methanol cleaning and drying before repeated use in the reaction, with no significant loss of active components and no significant decrease in catalytic activity. This effectively solved the technical defects of traditional MOF membranes being prone to detachment and powdered Fe-MOF catalysts being unreusable. Simultaneously, the catalytic membrane exhibited high photogenerated carrier separation efficiency and a wide visible light response range, demonstrating efficient catalytic activity under 465nm blue light irradiation, providing a good active basis for photocatalytic synthesis reactions. 2. This invention employs four core steps: ceramic membrane carrier activation, iron-based metal-organic framework seed preparation, seed spin-coating loading, and secondary growth to prepare the catalytic membrane. The entire process is convenient and free of complex procedures. Furthermore, the process parameters for each step can be precisely controlled. For example, the spin-coating speed can be adjusted between 500 rpm and 700 rpm, the spin-coating solution concentration can be controlled between 5 mg / mL and 10 mg / mL, and the solvent volume ratio for secondary growth can be adjusted to 10:1 to 1:1 as needed. By controlling these parameters, the membrane thickness, density, and crystallization quality can be precisely controlled, resulting in high process stability. Simultaneously, the raw materials used are abundant and inexpensive iron sources and conventional organic ligands. Al2O3 ceramic membranes are a common industrial carrier, making raw material acquisition easy and preparation costs controllable. Combined with the simple and controllable preparation process described above, the catalytic membrane of this invention can be mass-produced, solving the problems of complex and difficult-to-mass-produce existing MOF-based catalytic membrane preparation processes.

[0014] 3. The photocatalytic synthesis system built using a catalytic membrane is conducted entirely in air at 25°C, using a 465nm blue LED as the light source. This eliminates the need for the harsh conditions required in traditional synthesis methods, such as high-temperature heating and strong acid / base catalysis, thus reducing pollutant generation at the reaction source and perfectly aligning with the principles of green chemistry. Furthermore, under these mild reaction conditions, the catalytic membrane still efficiently catalyzes the condensation reaction of aldehydes with o-phenylenediamine. Specific results show that the yield of 2-(4-chlorophenyl)-1H-benzimidazole reaches 93%, with a purity ≥98%. The yields of various benzimidazole derivatives are all in the range of 76%–95%, with product purity not less than 90%. Specifically, the purity of aryl-substituted derivatives is ≥94%, and the purity of alkyl and heterocyclic-substituted derivatives is ≥95%. This achieves a dual guarantee of catalytic efficiency and product quality under mild reaction conditions, overcoming the shortcomings of traditional benzimidazole synthesis methods, such as low reaction efficiency, poor product selectivity, and severe environmental pollution.

[0015] 4. The catalytic synthesis system exhibits excellent catalytic compatibility with both aldehyde and o-phenylenediamine substrates. In specific implementations, the aldehyde substrates include aryl formaldehydes (benzaldehyde, halobenzaldehyde, nitrobenzaldehyde, etc.), alkyl formaldehydes (cyclohexyl formaldehyde), heterocyclic formaldehydes (pyridine-4-carboxaldehyde, furan-2-carboxaldehyde), and various substituted formaldehydes (acyl-substituted, ester-substituted). The o-phenylenediamines include unsubstituted o-phenylenediamine, 5,6-dimethyl o-phenylenediamine, 5-bromo-o-phenylenediamine, and other substituted types. Any combination of the above substrates can successfully catalyze the synthesis of the corresponding benzimidazole derivatives, and the product yield and purity of each combination can remain within the aforementioned excellent range. This broad-spectrum substrate compatibility can meet the preparation needs of different types of benzimidazole derivatives in the fields of medicine and materials, significantly enhancing the practical application value of the technical solution.

[0016] 5. By constructing a flow-through catalytic membrane photoreactor consisting of a membrane module, a storage tank, and a peristaltic pump, the catalytic membrane is fixed within the membrane module. The reaction solution can be forced through the catalytic membrane at a flow rate of 10-30 mL / min via the peristaltic pump, achieving continuous liquid flow and continuous catalytic reaction. This overcomes the technical limitation of traditional powder catalysts, which can only be used for batch reactions and cannot be continuously produced. Simultaneously, the catalytic membrane has dual functions of catalysis and separation. The membrane's retention effect enables efficient separation of the product and the catalyst. After the reaction, the catalyst only needs to be cleaned three times with 5 mL of methanol. Subsequent product separation only requires rotary evaporation concentration and silica gel column chromatography purification to obtain high-purity products. The separation and purification steps are simple and convenient. Furthermore, since the catalytic membrane is fixed within the membrane module, no additional separation and recovery steps are required. After cleaning, it can be directly reused, significantly improving the resource utilization rate of the catalyst, reducing raw material loss and environmental burden, solving the problems of difficult recovery and resource waste associated with traditional powder catalysts, and significantly enhancing the industrial feasibility of benzimidazole derivative synthesis. Attached Figure Description

[0017] Figure 1 The catalytic membrane reactor shown in the embodiments of the present invention; Figure 2 This is a schematic diagram illustrating the preparation of the iron-based metal-organic framework catalytic membrane Fe-MOFS-CM in an embodiment of the present invention; Figure 3 This is a schematic diagram of the ceramic membrane CM and the iron-based metal-organic framework catalytic membrane Fe-MOF-CM in the embodiments of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention provides a method for preparing an iron-based metal-organic framework (Fe-MOF) catalytic membrane, and a method for catalytically synthesizing benzimidazole and its derivatives under visible light using the catalytic membrane. The following specific embodiments are only used to explain this invention and are not intended to limit the scope of protection of this invention. Operations in this invention that do not specify specific experimental conditions are all conventional experimental methods in the field of chemistry. Unless otherwise specified, the raw materials and reagents used are all conventional chemical raw materials that can be obtained commercially. Unless otherwise specified, the equipment used is all conventional commercial equipment in the field of catalysis and organic synthesis.

[0020] 1. Preparation of iron-based metal-organic framework (Fe-MOF) catalytic membranes: Following the core process steps of ceramic membrane carrier activation, Fe-MOF seed preparation, seed spin-coating loading, and secondary growth to prepare the catalytic membrane, Fe-MOF catalytic membrane preparation experiments were carried out. At the same time, the effects of process parameters such as solvent volume ratio, spin-coating speed, and secondary growth temperature on the preparation of the catalytic membrane were investigated. All examples used Al2O3 ceramic membrane as carrier, ferric chloride hexahydrate (FeCl3・6H2O) and 2,2'-bipyridine-5,5'-dicarboxylic acid as raw materials, and were prepared by seed inoculation-secondary growth method.

[0021] Example 1, Preparation of a basic Fe-MOF catalytic membrane: This embodiment presents the core preparation scheme for the Fe-MOF catalytic membrane. Optimized process parameters are used to prepare a continuous, dense Fe-MOF catalytic membrane that is firmly bonded to the support. Specific steps and parameter analyses are as follows: Al2O3 ceramic membrane carrier activation: An Al2O3 ceramic membrane (specifications: diameter 3.2cm, thickness 1.75mm, pore size 3-5μm) produced by Jiangsu Jiuwu High Technology Co., Ltd. was selected as the carrier. It was boiled in deionized water for 6 hours to remove residual impurities, industrial processing pollutants, and adsorbates within the pores of the ceramic membrane surface. Subsequently, the ceramic membrane was ultrasonically treated in ultrapure water for 30 minutes. The cavitation effect of ultrasound further purified the carrier surface, fully exposing the hydroxyl groups on the ceramic membrane surface, providing active sites for subsequent seed crystal bonding. Finally, the treated ceramic membrane was dried in a 60℃ oven to constant weight to obtain the activated Al2O3 ceramic membrane carrier. The 60℃ drying temperature was chosen as a low-temperature drying to avoid structural deformation of the ceramic membrane due to high temperatures. Drying to constant weight ensured that there was no residual moisture on the carrier surface, preventing any impact on the subsequent seed crystal loading effect.

[0022] Fe-MOF seed crystals were prepared by weighing 0.54 g (2 mmol) FeCl3·6H2O and 0.24 g (1 mmol) 2,2'-bipyridine-5,5'-dicarboxylic acid at a molar ratio of 2:1. This material ratio represents the optimal coordination ratio of iron ions to organic ligands, ensuring the complete crystallization and structural stability of the seed crystals. Both were dissolved together in 60 mL of a 1:1 mixture of N,N-dimethylformamide (DMF) and deionized water. This optimized solvent ratio balances the solubility of the raw materials with the crystallization rate of the seed crystals. The mixture was ultrasonically dispersed for 10 min to allow the raw materials to settle in the solvent. The yellow solution was uniformly dispersed to avoid localized high concentrations that could lead to seed agglomeration. The dispersed solution was then transferred to a three-necked flask and reacted at 120°C with stirring for 24 hours. High-temperature stirring provided sufficient activation energy for seed crystallization, and the 24-hour reaction time ensured complete crystallization. After the reaction, solid-liquid separation was performed by centrifugation at 8000 rpm for 10 minutes to quickly collect the seed product. The seed was washed three times with methanol, centrifuged after each wash to remove unreacted raw materials, byproducts, and solvent residues. Finally, the washed seed was dried in a 100°C oven to constant weight to obtain pure Fe-MOF seed crystals.

[0023] For seed coating, the prepared Fe-MOF seeds were added to 30 mL of methanol and ultrasonically dispersed for 15 min to obtain a uniform spin-coating solution with a concentration of 10 mg / mL. Methanol is a good solvent, which can ensure uniform dispersion of the seeds and prevent secondary crystallization. The 10 mg / mL concentration was optimized to avoid the problems of excessive seed loading leading to agglomeration and insufficient seed loading failing to form effective anchoring points. The activated Al2O3 ceramic membrane carrier was fixed on a KW-4A spin coater, and 8 mL of spin-coating solution was added dropwise. Spin-coating was performed at 700 rpm for 30 s. The 700 rpm spin-coating speed allows the spin-coating solution to spread evenly on the ceramic membrane surface, forming a thin and uniform seed layer. The 30 s spin-coating time ensures sufficient seed layer loading and no liquid accumulation. After spin-coating, the membrane was placed in a 70℃ oven and dried for 12 h. Low-temperature drying prevents the seeds from falling off the carrier surface due to rapid drying. The 12 h drying time ensures that the seed layer is fully bonded to the carrier surface and is thoroughly dried, resulting in a seed-loaded membrane.

[0024] For the secondary growth preparation of Fe-MOF catalytic membranes, 0.54 g (2 mmol) of FeCl3·6H2O and 0.24 g (1 mmol) of 2,2'-bipyridine-5,5'-dicarboxylic acid were weighed at a molar ratio of 2:1 and dissolved in a 60 mL DMF / deionized water mixture at a volume ratio of 10:1. This solvent ratio is the optimized ratio for secondary growth. Compared to a 1:1 ratio, the higher DMF content slows down the growth rate of the seed crystals, which is beneficial for the directional growth of the seed crystals on the ceramic membrane carrier surface, forming a continuous and dense membrane layer. The mixture was ultrasonically dispersed for 10 min to obtain a homogeneous reaction solution, ensuring the secondary growth. The raw materials were uniformly dispersed; the seed-supported membrane was completely immersed in the reaction solution and stirred at 120℃ for 24 hours to allow the Fe-MOF seed crystals to grow and form a complete membrane layer based on the anchoring points on the ceramic membrane surface; after the reaction, the membrane was removed and washed three times alternately with anhydrous ethanol and methanol. Alternating washing can efficiently remove unreacted precursors, impurities and solvents adsorbed on the membrane surface, and avoid residual substances occupying catalytic active sites; after each washing, the membrane surface was rinsed with ultrapure water to remove alcohol residues, preventing alcohol substances from affecting subsequent catalytic performance; finally, the membrane was dried in a 60℃ oven to constant weight to obtain the Fe-MOF catalytic membrane.

[0025] Example 2, Preparation of Fe-MOF catalytic membranes with different mixed solvent volume ratios: This embodiment is completely identical to Embodiment 1 in terms of operation steps, raw material ratio, and reaction time. The only difference is that the volume ratio of the mixed solvent DMF and deionized water in the secondary growth stage is changed to 8:1. All other process parameters remain unchanged, and the Fe-MOF catalytic membrane (denoted as Fe-MOF-CM-1) is finally prepared. This embodiment explores the effect of solvent ratio in the secondary growth stage on membrane growth and verifies that the preparation process of the present invention is adaptable in the range of solvent volume ratios from 10:1 to 1:1, and is not limited to a single ratio of 10:1.

[0026] Example 3: Preparation of Fe-MOF catalytic films at different spin-coating speeds: This embodiment is completely identical to Embodiment 1 in terms of operation steps, raw material ratio, and reaction time. The only difference is the spin coating parameters during the seed coating loading stage. The spin coating speed is adjusted to 600 rpm, and the spin coating time is extended to 40 s. All other process parameters remain unchanged. Finally, an Fe-MOF catalytic membrane (denoted as Fe-MOF-CM-2) is prepared. This embodiment explores the effect of spin coating speed on seed loading effect and verifies that the spin coating process of this invention can achieve uniform seed loading in the range of 500 rpm to 700 rpm, providing flexibility for adjusting process parameters.

[0027] Example 4: Preparation of Fe-MOF catalytic membranes at different secondary growth temperatures: This embodiment is completely consistent with the operation steps, raw material ratios, and raw material proportions of Embodiment 1. The only difference is that the isothermal stirring reaction parameters in the secondary growth stage are changed, the reaction temperature is adjusted to 110℃, and the reaction time is extended to 26h. All other process parameters remain unchanged, and the Fe-MOF catalytic membrane (denoted as Fe-MOF-CM-3) is finally prepared. This embodiment explores the effect of secondary growth temperature on membrane crystallization and verifies that the secondary growth process of the present invention can achieve effective membrane growth in the range of 100℃~120℃, adapting to different industrial production temperature control conditions.

[0028] 2. Application of Fe-MOF catalytic membranes in the synthesis of benzimidazole derivatives: This section uses the basic Fe-MOF catalytic membrane prepared in Example 1 as the core catalytic component to build a flow-through catalytic membrane photoreactor and carry out photocatalytic synthesis experiments of benzimidazole derivatives. The catalytic synthesis effect, substrate universality and recycling performance of different aldehyde substrates are investigated. All examples use 465nm blue light as the light source and are carried out in air atmosphere and at room temperature (25°C), without the need for harsh reaction conditions such as high temperature, strong acid / strong alkali.

[0029] Example 5, Catalytic synthesis of 2-(4-chlorophenyl)-1H-benzimidazole: This embodiment presents the core application scheme for the synthesis of benzimidazole derivatives. It employs optimized reaction parameters, using p-chlorobenzaldehyde as the aldehyde substrate, o-phenylenediamine as the amine substrate, and methanol as the solvent. Specific steps and parameter analyses are as follows: A flow-through catalytic membrane photoreactor was constructed, consisting of a membrane module, a storage tank, a BT300S peristaltic pump, a 465nm blue LED light source (10W power), and a temperature control device. The Fe-MOF catalytic membrane prepared in Example 1 was fixed to the membrane module, and then the storage tank and the peristaltic pump were connected to ensure the stability of the liquid flow in the reactor. This reactor is a continuous reaction system, which can realize the forced liquid flow of the reaction solution and the continuous catalytic reaction, breaking through the limitations of traditional batch reactions.

[0030] The reaction system was prepared by weighing 0.3 mmol of p-chlorobenzaldehyde (42.3 mg) and 0.36 mmol of o-phenylenediamine (39.6 mg), with a molar ratio of aldehyde substrate to o-phenylenediamine of 1:1.2. Using a slight excess of o-phenylenediamine ensures complete participation of the aldehyde substrate in the condensation reaction, improving product yield. Both were added to a storage tank, followed by 8 mL of methanol as a solvent. Methanol is an environmentally friendly solvent with good solubility and easy subsequent separation. The optimized amount of 8 mL ensures a suitable concentration in the reaction system, balancing catalytic efficiency and feedstock utilization. The mixture was ultrasonically dispersed for 5 min to ensure uniform dispersion of the substrate in the solvent, forming a homogeneous reaction system and preventing excessively high local concentrations from affecting the reaction process.

[0031] For the photocatalytic reaction, the peristaltic pump was turned on and the flow rate was adjusted to 30 mL / min. This flow rate allows the reaction solution to permeate through the Fe-MOF catalytic membrane at a suitable rate, ensuring sufficient contact between the reaction solution and the active sites of the catalytic membrane and improving catalytic efficiency. At the same time, a 465 nm blue LED light source was turned on, and the photocatalytic reaction was carried out for 4 hours in an air atmosphere at room temperature of 25°C. 4 hours is the optimized reaction time, which can ensure that the condensation reaction is completed. During the reaction, samples were taken every 1 hour, and the reaction progress was monitored by thin-layer chromatography (TLC) with petroleum ether / ethyl acetate = 5:1 as the developing solvent. The reaction progress was monitored in real time to avoid incomplete or excessive reaction.

[0032] After product separation and purification, the membrane module was washed three times with 5 mL of methanol after the reaction. The purpose of washing was to recover the adsorbed products on the surface and in the pores of the membrane module, avoid product loss, and improve the yield. The washing liquid was collected and combined with the reaction liquid. The combined solution was concentrated by rotary evaporation at 40℃ and 0.08 MPa. Low-temperature vacuum evaporation can effectively avoid the decomposition of the target product due to high temperature and ensure the integrity of the product. The crude product was purified by silica gel column chromatography with petroleum ether / ethyl acetate = 30:1 as the developing solvent. After optimization, this developing solvent ratio can achieve efficient separation of the target product from a small amount of impurities. The target eluent was collected and the solvent was removed by vacuum distillation to obtain the white solid product 2-(4-chlorophenyl)-1H-benzimidazole.

[0033] Testing showed that the target product yield in this embodiment was 93% and the purity was ≥98%, confirming that the Fe-MOF catalytic membrane has excellent catalytic effect on halogenated benzaldehyde substrates.

[0034] Example 6, Catalytic synthesis of 2-phenyl-1H-benzimidazole: The reactor construction, reaction parameters, and separation and purification steps in this embodiment are completely consistent with those in Example 5, except that the aldehyde substrate is replaced with benzaldehyde. 0.3 mmol benzaldehyde (31.8 mg) and 0.36 mmol o-phenylenediamine (39.6 mg) are weighed, added to 8 mL of methanol, ultrasonically dispersed for 5 min, and then subjected to photocatalytic reaction.

[0035] Testing revealed that this embodiment yielded a white solid product, 2-phenyl-1H-benzimidazole, with a yield of 90% and a purity ≥97%, confirming that the Fe-MOF catalytic membrane has a highly efficient catalytic effect on simple aryl formaldehyde substrates.

[0036] Example 7, Catalytic synthesis of 2-(4-nitrophenyl)-1H-benzimidazole: The reactor construction, reaction parameters, and separation and purification steps in this embodiment are completely consistent with those in Example 5, except that the aldehyde substrate is replaced with 4-nitrobenzaldehyde. 0.3 mmol of 4-nitrobenzaldehyde (46.8 mg) and 0.36 mmol of o-phenylenediamine (39.6 mg) are weighed, added to 8 mL of methanol, ultrasonically dispersed for 5 min, and then subjected to photocatalytic reaction.

[0037] Testing revealed that this embodiment yielded a pale yellow solid product, 2-(4-nitrophenyl)-1H-benzimidazole, with a yield of 92% and a purity of ≥96%, confirming that the Fe-MOF catalytic membrane has good catalytic compatibility with aryl formaldehyde substrates containing strong electron-withdrawing groups.

[0038] Example 8, Catalytic synthesis of 2-(naphth-2-yl)-1H-benzimidazole: The reactor construction, reaction parameters, and separation and purification steps in this embodiment are completely consistent with those in Example 5, except that the aldehyde substrate is replaced with naphthalene-2-carboxaldehyde. 0.3 mmol of naphthalene-2-carboxaldehyde (46.2 mg) and 0.36 mmol of o-phenylenediamine (39.6 mg) are weighed, added to 8 mL of methanol, ultrasonically dispersed for 5 min, and then subjected to photocatalytic reaction.

[0039] Testing revealed that this embodiment yielded a white solid product, 2-(naphth-2-yl)-1H-benzimidazole, with a yield of 90% and a purity ≥97%, confirming that the Fe-MOF catalytic membrane has a highly efficient catalytic effect on polycyclic aromatic formaldehyde substrates.

[0040] Example 9, Catalytic synthesis of 2-([1,1'-biphenyl]-4-yl)-1H-benzimidazole: The reactor construction, reaction parameters, and separation and purification steps in this embodiment are completely consistent with those in Example 5, except that the aldehyde substrate is replaced with biphenyl-4-carboxaldehyde. 0.3 mmol of biphenyl-4-carboxaldehyde (55.8 mg) and 0.36 mmol of o-phenylenediamine (39.6 mg) are weighed, added to 8 mL of methanol, ultrasonically dispersed for 5 min, and then subjected to photocatalytic reaction.

[0041] Testing revealed that this embodiment yielded a creamy white solid product, 2-([1,1'-biphenyl]-4-yl)-1H-benzimidazole, with a yield of 88% and a purity ≥96%, confirming that the Fe-MOF catalytic membrane has a good catalytic effect on fused-ring aryl formaldehyde substrates.

[0042] Example 10, Catalytic synthesis of 2-cyclohexyl-1H-benzimidazole: The reactor construction, reaction parameters, and separation and purification steps in this embodiment are completely consistent with those in Example 5, except that the aldehyde substrate is replaced with cyclohexylformaldehyde. 0.3 mmol of cyclohexylformaldehyde (34.2 mg) and 0.36 mmol of o-phenylenediamine (39.6 mg) are weighed, added to 8 mL of methanol, ultrasonically dispersed for 5 min, and then subjected to photocatalytic reaction.

[0043] Testing revealed that this embodiment yielded a white solid product, 2-cyclohexyl-1H-benzimidazole, with a yield of 87% and a purity ≥95%, confirming that the Fe-MOF catalytic membrane has good catalytic compatibility with alkyl formaldehyde substrates.

[0044] Example 11, Catalytic synthesis of 2-(4-methoxyphenyl)-1H-benzimidazole: The reactor construction, reaction parameters, and separation and purification steps in this embodiment are completely consistent with those in Example 5, except that the aldehyde substrate is replaced with 4-methoxybenzaldehyde. 0.3 mmol of 4-methoxybenzaldehyde (41.4 mg) and 0.36 mmol of o-phenylenediamine (39.6 mg) are weighed, added to 8 mL of methanol, ultrasonically dispersed for 5 min, and then subjected to photocatalytic reaction.

[0045] Testing revealed that this embodiment yielded an orange-yellow solid product, 2-(4-methoxyphenyl)-1H-benzimidazole, with a yield of 85% and a purity ≥94%, confirming that the Fe-MOF catalytic membrane has a good catalytic effect on aryl formaldehyde substrates containing electron-donating groups.

[0046] Example 12, Validation of the substrate universality of the catalytic membrane: To verify the catalytic universality of the Fe-MOF catalytic membrane for different types of substrates, this example selected pyridine-4-carboxaldehyde, furan-2-carboxaldehyde, 3-chlorobenzaldehyde, 2-chlorobenzaldehyde, 4-cyanobenzaldehyde, N-(4-formylphenyl)acetamide, and methyl 4-formylbenzoate as aldehyde substrates, and 5,6-dimethyl-o-phenylenediamine and 5-bromo-o-phenylenediamine as substituted o-phenylenediamine substrates. The photocatalytic synthesis experiment with arbitrary substrate combinations was carried out according to the material ratio (0.3 mmol aldehyde substrate, 0.36 mmol o-phenylenediamine substrate, 8 mL methanol), reaction parameters, and separation and purification steps in Example 5.

[0047] Testing showed that all substrate combinations could successfully catalyze the synthesis of the corresponding benzimidazole derivatives, with target product yields ranging from 76% to 95% and product purity ≥90%. This demonstrates that the Fe-MOF catalytic membrane system of this invention has broad substrate versatility and can be adapted to various substrates such as aryl formaldehyde, alkyl formaldehyde, heterocyclic formaldehyde, substituted formaldehyde, and substituted o-phenylenediamine, meeting the synthesis requirements of different types of benzimidazole derivatives.

[0048] Example 13, Cyclic performance test of Fe-MOF catalytic membrane: To verify the structural stability and recyclability of the Fe-MOF catalytic membrane, this embodiment uses the reaction system of Example 5 (p-chlorobenzaldehyde + o-phenylenediamine) as the test object. The Fe-MOF catalytic membrane prepared in Example 1 was subjected to 10 consecutive cycles of use. After each catalytic reaction, the membrane module was cleaned with methanol 3 times, rinsed with ultrapure water to remove residue, and dried at 60°C. No additional activation treatment was required. The dried catalytic membrane was directly put into the next photocatalytic reaction. The remaining reaction parameters and separation and purification steps were the same as in Example 5. The yield and purity of the target product were detected after each cycle.

[0049] Testing revealed that after 10 cycles, the Fe-MOF catalytic membrane maintained a continuous and dense structure, exhibiting no peeling or detachment from the Al2O3 ceramic membrane support, and showing no significant loss of active components. Furthermore, the target product yield remained above 76% and the purity was ≥90% in each cycle, with no significant decrease in catalytic activity. These results confirm that the Fe-MOF catalytic membrane of this invention possesses excellent structural stability and recyclability, enabling repeated use, significantly reducing catalyst costs in industrial production, and minimizing resource waste and environmental burden.

[0050] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented in software, the above embodiments can be implemented, in whole or in part, as a computer program product. Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution.

[0051] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment, depending on actual needs.

[0052] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for preparing an iron-based metal-organic framework catalytic membrane, characterized in that, The preparation method includes the following steps: S1. The Al2O3 ceramic membrane was boiled with deionized water, ultrasonically treated with ultrapure water, and then dried to constant weight to obtain the activated Al2O3 ceramic membrane carrier. S2. Take ferric chloride hexahydrate and 2,2'-bipyridine-5,5'-dicarboxylic acid in a molar ratio of 2:1, dissolve them in a mixed solvent of N,N-dimethylformamide and deionized water, disperse them by ultrasonication, stir at a constant temperature, and then obtain iron-based metal-organic framework seed crystals after solid-liquid separation, methanol washing, and drying. S3. Iron-based metal-organic framework seed crystals are dispersed in methanol to prepare a spin-coating solution. The activated Al2O3 ceramic film carrier is spin-coated with the spin-coating solution and dried to obtain a seed-loaded film. S4. Take ferric chloride hexahydrate and 2,2'-bipyridine-5,5'-dicarboxylic acid in a molar ratio of 2:1, dissolve them in a mixed solvent of N,N-dimethylformamide and deionized water, and ultrasonically disperse them to obtain a reaction solution. Immerse the seed-supported membrane in the reaction solution and stir at a constant temperature. After washing with alcohols and drying, an iron-based metal-organic framework catalytic membrane is obtained.

2. The method for preparing the iron-based metal-organic framework catalytic membrane according to claim 1, characterized in that, In step S1, the Al2O3 ceramic membrane has the following specifications: diameter 3.2cm, thickness 1.75mm, pore size 3-5μm, deionized water boiling treatment time 6h, ultrapure water ultrasonic treatment time 30min, and drying temperature 60℃.

3. The method for preparing the iron-based metal-organic framework catalytic membrane according to claim 2, characterized in that, In step S2, the volume ratio of N,N-dimethylformamide to deionized water is 1:1, the total volume of the mixed solvent is 60 mL, the ultrasonic dispersion time is 10 min, the constant temperature stirring reaction temperature is 100℃-120℃ and the time is 24 h, the solid-liquid separation is centrifugation at 8000 rpm for 10 min, the number of methanol washings is 3, and the drying temperature is 100℃.

4. The method for preparing the iron-based metal-organic framework catalytic membrane according to claim 3, characterized in that, In step S3, the spin coating solution is prepared by adding 30 mL of iron-based metal-organic framework seed crystals to methanol and ultrasonically dispersing for 15 min, with a concentration of 5 mg / mL-10 mg / mL. The spin coating speed is 500 rpm-700 rpm and the time is 30 s. The drying temperature is 70 ℃ and the time is 12 h. When the amount of spin coating solution added is 8 mL and the concentration is 10 mg / mL, the spin coating speed is 700 rpm.

5. The method for preparing the iron-based metal-organic framework catalytic membrane according to claim 4, characterized in that, In step S4, the volume ratio of N,N-dimethylformamide to deionized water is 10:1-1:1, the total volume of the mixed solvent is 60 mL, the ultrasonic dispersion time is 10 min, the constant temperature stirring reaction temperature is 100℃-120℃, and the time is 24 h. Alcohol washing is performed by alternating washing with anhydrous ethanol and methanol three times. After washing, the residual solvent on the membrane surface is rinsed with ultrapure water, and the drying temperature is 60℃. The preferred volume ratio of N,N-dimethylformamide to deionized water is 10:1, and the preferred temperature for the constant temperature stirring reaction is 120℃.

6. An iron-based metal-organic framework catalytic membrane, characterized in that, The catalytic membrane, prepared by the method described in claims 1 to 5, uses an Al2O3 ceramic membrane as a carrier and an iron-based metal-organic framework as an active component. The iron-based metal-organic framework seed crystals form hydrogen bonds and weak coordination with the hydroxyl groups on the surface of the Al2O3 ceramic membrane carrier.

7. A method for synthesizing benzimidazole derivatives using an iron-based metal-organic framework catalytic membrane, comprising the iron-based metal-organic framework catalytic membrane as described in claim 6, characterized in that, The method includes the following steps: G1. Construct a flow-through catalytic membrane photoreactor consisting of a membrane module, a storage tank, a peristaltic pump, and a light source. Fix the iron-based metal-organic framework catalytic membrane in the membrane module and connect the storage tank and the peristaltic pump. G2. Take the aldehyde substrate, o-phenylenediamine and solvent, mix them, and disperse them ultrasonically to obtain a homogeneous reaction system; G3. Turn on the peristaltic pump to allow the reaction liquid to pass through the iron-based metal-organic framework catalytic membrane at a set flow rate. At the same time, turn on the light source to provide blue light of a specific wavelength for photocatalytic reaction under air atmosphere and room temperature conditions. During the reaction, the reaction process is monitored in real time by thin layer chromatography and gas chromatography. G4. After the reaction is complete, the membrane module is cleaned with methanol. The cleaning solution and the reaction solution are combined and concentrated to obtain the crude product. The crude product is purified by column chromatography and the solvent is removed by vacuum distillation to obtain the benzimidazole derivative.

8. The method for synthesizing benzimidazole derivatives according to claim 7, characterized in that, In step G2, the solvent is one or more of methanol, ethanol, acetonitrile, N,N-dimethylformamide, water, ethyl acetate, and tetrahydrofuran. The molar ratio of the aldehyde substrate to o-phenylenediamine is 1:1 to 1:1.5, and the molar volume ratio of the aldehyde substrate, o-phenylenediamine, and solvent is 1~2 mmol:1.5~3 mmol:10~20 mL. The ultrasonic dispersion time is 5 min. When 0.3 mmol of aldehyde substrate and 0.36 mmol of o-phenylenediamine are added, the solvent volume is 6-10 mL.

9. The method for synthesizing benzimidazole derivatives according to claim 7, characterized in that, In step G3, the specific wavelength of blue light is 465nm, the light source is a 465nm blue LED light source with a power of 10W, the room temperature is 25℃, the photocatalytic reaction time is 2-6h, preferably 4h; the flow rate of the peristaltic pump is 10-30mL / min, preferably 30mL / min.

10. The method for synthesizing benzimidazole derivatives according to claim 7, characterized in that, In step G4, the methanol cleaning membrane module is performed in 5 mL increments and 3 times. The concentration is achieved by rotary evaporation at 40°C and 0.08 MPa. Column chromatography uses silica gel as the packing material and a mixture of petroleum ether and ethyl acetate as the developing solvent, with a volume ratio of 5:1 to 30:

1. Aldehyde substrates include benzaldehyde, halogenated benzaldehyde, nitrobenzaldehyde, methoxybenzaldehyde, cyanobenzaldehyde, acyl-substituted benzaldehyde, ester-substituted benzaldehyde, naphthalene-2-carboxaldehyde, biphenyl-4-carboxaldehyde, cyclohexylcarboxaldehyde, pyridine-4-carboxaldehyde, and furan-2-carboxaldehyde; o-Phenylenediamines include unsubstituted o-phenylenediamine, 5,6-dimethyl o-phenylenediamine, and 5-bromo-o-phenylenediamine.

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