Metal-organic monoacid framework material, coating composite film and preparation method of metal-organic monoacid framework material

Abstract

The invention relates to the field of metal-organic framework materials, in particular to a metal-organic monoacid framework material, a coating composite film and a preparation method of the coating composite film. The metal-organic monoacid framework material is formed by metal ions, an organic ligand and a monoacid modifier through coordination, the metal ions are Zn < 2 + >, the organic ligand is 2-methylimidazole, and the monoacid modifier is oleic acid. The core composition of the metal-organic monoacid framework material is limited, and the metal-organic monoacid framework material is defined to be formed by specific metal ions, organic ligands and monoacid modifiers through coordination. According to the technical scheme, metal ions, organic ligands and monoacid modifiers which are specifically combined are selected, and a novel framework structure is constructed through the synergistic coordination effect of the metal ions, the organic ligands and the monoacid modifiers. The introduced monoacid modifier not only participates in coordination to form a stable skeleton, but also can endow the material with hydrophobic property through the structural characteristics of the monoacid modifier.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metal-organic framework materials, in particular to a metal-organic monobasic acid framework material, a coated composite membrane and a preparation method thereof. BACKGROUND

[0002] As a class of crystalline materials with high porosity and structural flexibility, metal-organic frameworks (MOFs) have shown broad application prospects in sensing, catalysis, energy storage and separation due to their unique chemical versatility. With the rise of low-dimensional material research, 2D MOF nanosheets have become a research hotspot in the field of MOFs due to their high specific surface area and abundant accessible active sites; while 1D MOF nanostructures are expected to further expand the application boundaries by combining the characteristics of 2D materials with their unique physical and chemical properties. However, the preparation of existing 1D MOF nanostructures faces many challenges. Traditional template methods require complex template design and removal processes, which are tedious to operate and not conducive to industrial scaling; template-free methods have poor structure controllability and insufficient product uniformity, which limit the practical application of 1D MOF materials.

[0003] Despite the significant progress made in the study of MOFs materials, their inherent defect of poor water stability has always been a key bottleneck restricting their industrialization. Most traditional MOFs materials are sensitive to water or humidity and are prone to structural collapse or performance degradation in water environments, while water / humidity is ubiquitous in industrial production and daily life, making it difficult for MOFs materials to meet the needs of practical application scenarios. In terms of application expansion, the preparation of functional composite membranes by compounding MOFs materials with porous substrates is an important way to realize their practical application in the field of separation. Traditional MOF composite membrane preparation methods often rely on complex processes such as vacuum filtration and in-situ growth, which have problems such as tedious operation process, insufficient stability of MOF materials and substrates, and difficulty in large-scale preparation. At the same time, existing composite membranes often fail to balance high separation efficiency and good service stability, and the introduction of fluorine-containing reagents in the hydrophobic modification process further limits their environmental compatibility. SUMMARY

[0004] Based on the technical problems existing in the prior art, the present application provides a metal-organic monobasic acid framework material, a coated composite membrane and a preparation method thereof.

[0005] A metal-organic monobasic acid framework material, a coated composite membrane and a preparation method thereof adopt the following technical solutions: In a first aspect, the present application discloses a metal-organic monobasic acid framework material adopting the following technical solutions: A metal-organic monobasic acid framework material, the material is formed by coordination of metal ions, organic ligands and monobasic acid modifiers, the metal ions are Zn2+ The organic ligand is 2-methylimidazole, and the monobasic acid modifier is oleic acid.

[0006] By the technical solution, the core composition of the metal-organic monobasic acid framework material is defined, and it is clear that the material is formed by the coordination of specific metal ions, organic ligands and monobasic acid modifiers. The technical solution is innovative in selecting the specific combination of metal ions, organic ligands and monobasic acid modifiers to construct a new framework structure through synergistic coordination. Unlike traditional MOFs which only rely on the coordination of metal ions and organic ligands, the monobasic acid modifier introduced in the application not only participates in the coordination to form a stable framework, but also endows the material with hydrophobic properties through its structural characteristics, without the need for additional fluorine-containing modification reagents, thus solving the environmental and cost problems caused by fluorine-containing reagents from the source.

[0007] Further, the metal-organic monobasic acid framework material is a 2D sheet or a 1D nanoroll / nanotube, and the 1D nanoroll / nanotube is formed by self-rolling of the 2D sheet, and the self-rolling is prepared by temperature regulation.

[0008] By the technical solution, the structure and formation method of the material are further defined. The technical solution is innovative in that the material can present two morphologies of 2D sheet and 1D nanoroll / nanotube, and the 1D structure is formed by self-rolling of the 2D sheet, and the self-rolling process is realized only by temperature regulation. The preparation of traditional 1D MOF structure often needs template guidance or complex crystal growth regulation, while the application can trigger the self-rolling transformation of the 2D sheet by temperature, a simple and easy-to-control parameter, without the need for additional templates or complex process adjustment, thus simplifying the preparation process of the 1D structure. At the same time, the controllability of the 2D and 1D structures makes the material adapt to the needs of different application scenarios, solving the problem of single structure and insufficient adaptability of traditional MOF materials.

[0009] In a second aspect, the application provides a preparation method of a metal-organic monobasic acid framework material, which adopts the following technical solution: The preparation method of the metal-organic monobasic acid framework material comprises the following steps: A Zn(NO3)2 aqueous solution is added to a container as a bottom liquid, and a 2-methylimidazole solution dissolved in oleic acid is taken as a top liquid and added dropwise to the surface of the bottom liquid; The two-phase mixture is aged at 45-55℃ for 12-48h to make the 2D metal-organic monobasic acid framework material sheet self-roll into a 1D nanoroll / nanotube; The aged product is treated by centrifugation, washing and drying to obtain a metal-organic monobasic acid framework material.

[0010] By the above technical solution, the oil / water interface assembly preparation method of the metal-organic monobasic acid framework material is optimized. The existing 1DMOF material preparation process is complicated and has poor controllability. The oil / water interface assembly strategy is innovatively adopted. The bottom layer liquid and the upper layer liquid are arranged in layers. The material is guided to grow in a directional manner to form a 2D sheet by using the characteristics of the two-phase interface. The self-rolling conversion of the 1D structure is realized by mild temperature regulation. Unlike the traditional template method which requires complex template preparation and removal steps, and unlike the existing template-free method which has poor structure controllability, the method realizes the preparation of the 2D sheet and the conversion of the 1D structure in one step by the combination of interface assembly and temperature regulation. The process flow is simple and easy to operate, and no special equipment is required.

[0011] Further, the Zn(NO3)2:2-methylimidazole:oleic acid:methanol is 1:(1.1-1.2):(1.2-1.3):(145-150).

[0012] By the above technical solution, the molar ratio range of the raw materials is further limited. The technical solution determines the specific molar ratio range of the raw materials through a large number of experiments. The ratio range is not a routine choice of those skilled in the art, but is accurately determined based on the coordination reaction characteristics of metal ions, organic ligands and monobasic acid modifiers, as well as the requirements for material structure formation and performance realization. Within the ratio range, the three can fully coordinate to ensure the formation of a stable structure and uniform performance framework material, and to ensure the smooth conversion of the 2D sheet to the 1D structure. If the ratio range is deviated, it may lead to insufficient coordination reaction, material structure defects, and decreased hydrophobicity and water stability.

[0013] Further, the centrifugal speed is 4500-5500 rpm, the centrifugal time is 8-12 min, the washing reagent is methanol, and the drying temperature is 45-55℃.

[0014] By the technical solution, the post-treatment parameters in the preparation method are limited, including the centrifugal speed, centrifugal time, washing reagent and drying temperature. The technical solution is aimed at the problem that the unreasonable post-treatment process of the existing MOF material leads to low product purity and easy destruction of the structure, and the specific post-treatment parameters are optimized and determined in combination with the structural characteristics and composition characteristics of the material. The selection of the centrifugal parameters can ensure efficient separation of the product, avoid collapse of the material structure due to too high speed or too long time, or incomplete separation of the product due to too low speed or insufficient time; the selection of the washing reagent is adapted to the chemical properties of the material, which can effectively remove unreacted raw materials and impurities without affecting the skeleton structure of the material; and the limitation of the drying temperature avoids the destruction of the material structure caused by high temperature, and ensures sufficient drying of the product. The technical solution is further improved, and the practicality and creativity of the application are enhanced.

[0015] In a third aspect, the application provides a metal-organic monobasic acid framework material coated composite membrane.

[0016] By the technical solution, the core composition of the metal-organic monobasic acid framework material coated composite membrane is limited, and the metal-organic monobasic acid framework material with excellent water stability and hydrophobicity is used as a coating material to form a composite membrane with a porous substrate. Unlike the traditional MOF material used in existing composite membranes, the coating material of the application has good hydrophobicity without additional hydrophobic modification, and has strong water stability, which can maintain stable structure and performance in actual separation environment; at the same time, the 2D or 1D structure of the material is beneficial to form a uniform and dense coating on the surface of the substrate, and improves the separation efficiency of the composite membrane. The existing MOF composite membrane mostly uses conventional MOF material, and the insufficient water stability and hydrophobicity limit the application range of the composite membrane.

[0017] In a fourth aspect, the application provides a preparation method of a metal-organic monobasic acid framework material coated composite membrane, which adopts the following technical solution: A preparation method of a metal-organic monobasic acid framework material coated composite membrane, comprising the following preparation steps: immersing the porous substrate in a Zn(NO3)2 aqueous solution, and then casting the Zn(NO3)2 aqueous solution on the surface of the immersed porous substrate; aging the casted porous substrate at 45-55℃ for 10-14h to obtain a metal-organic monobasic acid framework material coated composite membrane.

[0018] By the technical scheme, the preparation method of the composite membrane is optimized, the simple sequential drop casting method is adopted, and the preparation of the composite membrane is completed through three core steps of soaking, casting and aging. The pretreatment step can make the porous substrate surface adsorb metal ions, providing sites for the formation of the subsequent coating material; the casting step is simple to operate, without the need for complex equipment such as vacuum filtration and in-situ growth, which is conducive to large-scale production; and the aging step promotes the stable formation and combination of the coating material on the substrate surface through temperature regulation. Unlike the existing composite membrane preparation process which needs to strictly control the reaction conditions and rely on complex equipment, the preparation method of the present application is simple and convenient to operate, and can ensure the firm combination of the coating and the substrate, and avoid the performance degradation of the composite membrane caused by the peeling of the coating. The simple and efficient composite membrane preparation method.

[0019] Further, the porous substrate is a nylon membrane with a diameter of 45-49 mm and a pore size of 180-220 nm.

[0020] Through the above technical scheme, the type, size and pore size parameters of the porous substrate are further limited. In view of the problem that unreasonable selection of the existing composite membrane substrate leads to poor combination of the coating and poor separation performance, the specific type, size and pore size of the porous substrate are accurately selected in combination with the structural characteristics of the coating material and the separation application requirements of the composite membrane. The pore size of the selected substrate can be adapted to the structure of the coating material, which not only ensures the smooth passage of the fluid during separation, but also provides stable support and attachment sites for the coating material; the size parameters of the substrate are adapted to the use requirements of the conventional separation equipment, improving the practicality of the composite membrane; and the specific type of substrate has good chemical stability and mechanical strength, which can synergize with the coating material to ensure the structural stability of the composite membrane during use. These limitations of substrate parameters are not the routine selection of those skilled in the art, but a targeted design based on the characteristics of the coating material and the application scenarios of the composite membrane, which can maximize the performance advantages of the coating material and solve the problem of insufficient compatibility between traditional substrates and MOF coatings.

[0021] In summary, the present application has the following advantages: First, the metal-organic monobasic acid framework material of the present application realizes excellent hydrophobic performance without fluorine-containing reagents through the synergistic coordination of specific metal ions, organic ligands and monobasic acid modifiers, significantly improves the water stability and chemical stability of the material, solves the core problems of traditional MOFs materials such as water sensitivity and dependence on high environmental risk fluorine-containing reagents for hydrophobic modification; and the material can be flexibly adjusted to 2D sheet or 1D nanoroll / nanotube, and the structural diversity enables it to adapt to the application requirements of multiple fields such as sensing, catalysis and separation.

[0022] Secondly, both the oil / water interface assembly and the solvothermal synthesis of the two preparation methods of the application do not require template assistance, and the self-transformation from 2D to 1D structure can be realized by simple temperature regulation, and the process flow is simple, convenient to operate and the reaction conditions are mild; the sequential drop-casting preparation method of the composite film does not require complex equipment, and can be completed by only three steps of soaking, casting and aging, effectively reducing the production difficulty and cost, avoiding the problems of traditional 1D MOF preparation and MOF composite film coating process being complicated and difficult to scale up, and adapting to the needs of industrial production.

[0023] Thirdly, the coated composite film formed by the metal-organic monobasic acid framework material and the porous substrate has excellent hydrophobic performance, structural stability and separation performance, and can adapt to the separation and other practical application scenarios in water environment without additional modification; the material and the composite film have good environmental compatibility, avoiding the environmental hidden danger brought by fluorine-containing reagents, and further expanding the application boundary of MOF materials in industrial production, daily life and other fields, which has significant practical value and market prospect. DETAILED DESCRIPTION

[0024] The application will be further described in detail below in combination with examples.

[0025] Example 1 A preparation method of a metal-organic monobasic acid framework material, comprising the following steps: Preparation of the bottom layer liquid: 4 mL of 0.8 M Zn(NO3)2·6H2O aqueous solution was taken and added to a 55 mm diameter culture dish, and the liquid surface was kept flat after standing for 5 min; Preparation and dropwise addition of the upper layer liquid: 2-methylimidazole was weighed and dissolved in oleic acid to prepare a 0.3 M 2-methylimidazole oleic acid solution, 0.8 mL of the solution was taken and slowly added to the surface of the bottom layer liquid in the culture dish along the inner wall of the culture dish using a pipette to avoid damaging the two-phase interface; Aging treatment: the culture dish containing the two-phase mixture was placed in an oven and aged at 45°C for 12 h, during which the 2D metal-organic monobasic acid framework material sheet gradually self-rolled to form 1D nanorolls / nanotubes; Centrifugal separation: the aged mixture was transferred to a centrifuge tube and placed in a centrifuge at a speed of 4500 rpm for 8 min, and the bottom precipitate was collected; Washing and purification: 10 mL of methanol was added to the centrifuge tube, the precipitate was dispersed by shaking, and then centrifuged at 4500 rpm for 8 min again, and the supernatant was discarded; the washing-centrifugation operation was repeated for 3 times to remove unreacted raw materials and impurities; Drying treatment: the washed precipitate was transferred to a drying dish and placed in a 45°C oven for constant temperature drying for 12 h to obtain the metal-organic monobasic acid framework material.

[0026] Example 2 A method for preparing a metal-organic monobasic acid framework material, comprising the following steps: Preparation of the bottom layer liquid: take 5 mL of a 1.0 M aqueous solution of Zn(NO3)2·6H2O, and add it to a petri dish with a diameter of 60 mm, and let it stand for 5 min to keep the liquid surface flat; Preparation and dropwise addition of the upper layer liquid: take 2-methylimidazole, dissolve it in oleic acid to prepare a 0.4 M 2-methylimidazole oleic acid solution, take 1.0 mL of the solution, and slowly drop it along the inner wall of the petri dish to the surface of the bottom layer liquid in step 1 using a pipette, avoiding the destruction of the two-phase interface; Aging treatment: place the petri dish containing the two-phase mixture in an oven, and keep it at a constant temperature of 50°C for 30 h, during which the 2D metal-organic monobasic acid framework material sheet gradually self-rolls to form 1D nanorolls / nanotubes; Centrifugal separation: transfer the aged mixture to a centrifuge tube, and place it in a centrifuge, and centrifuge it at a speed of 5000 rpm for 10 min, and collect the bottom precipitate; Washing and purification: add 10 mL of methanol to the centrifuge tube, shake and disperse the precipitate, and centrifuge it again at 5000 rpm for 10 min, and discard the supernatant; repeat the washing and centrifugation operation 3 times to remove unreacted raw materials and impurities; Drying treatment: transfer the washed precipitate to a drying dish, and place it in an oven at a constant temperature of 50°C for 15 h, and obtain the metal-organic monobasic acid framework material.

[0027] Example 3 A method for preparing a metal-organic monobasic acid framework material, comprising the following steps: Preparation of the bottom layer liquid: take 6 mL of a 1.2 M aqueous solution of Zn(NO3)2·6H2O, and add it to a petri dish with a diameter of 65 mm, and let it stand for 5 min to keep the liquid surface flat; Preparation and dropwise addition of the upper layer liquid: take 2-methylimidazole, dissolve it in oleic acid to prepare a 0.5 M 2-methylimidazole oleic acid solution, take 1.2 mL of the solution, and slowly drop it along the inner wall of the petri dish to the surface of the bottom layer liquid in step 1 using a pipette, avoiding the destruction of the two-phase interface; Aging treatment: place the petri dish containing the two-phase mixture in an oven, and keep it at a constant temperature of 55°C for 48 h, during which the 2D metal-organic monobasic acid framework material sheet fully self-rolls to form a 1D nanotube structure; Centrifugal separation: transfer the aged mixture to a centrifuge tube, and place it in a centrifuge, and centrifuge it at a speed of 5500 rpm for 12 min, and collect the bottom precipitate; Washing and purification: 10 mL of methanol was added into the centrifuge tube, and the precipitate was dispersed by shaking. After centrifugation at 5500 rpm for 12 min, the supernatant was discarded. The washing and centrifugation operation was repeated for 3 times to remove the unreacted raw materials and impurities. Drying treatment: the washed precipitate was transferred to a drying dish and placed in an oven at 55°C for constant temperature drying for 18 h to obtain the metal-organic monobasic acid framework material.

[0028] Example 4 A preparation method of a metal-organic monobasic acid framework material coated composite film, comprising the following preparation steps: Substrate pretreatment: a nylon film with a diameter of 45 mm and a pore size of 180 nm was selected as the porous substrate. The surface impurities were first washed with deionized water, and then soaked in anhydrous ethanol for 15 min for degreasing treatment. After taking out, it was air-dried at room temperature for standby use. Soaking treatment: a 1M Zn(NO3)2·6H2O aqueous solution was prepared, and the pretreated nylon film was completely immersed in the aqueous solution for 30 min to ensure that the surface and pores of the film were fully adsorbed with Zn 2+ ; Casting coating: the soaked nylon film was taken out, and the excess aqueous solution on the surface was drained. The film was placed on a clean glass slide, and a 0.8 mL 1M Zn(NO3)2·6H2O aqueous solution was taken by a pipette and slowly cast onto the surface of the film along the edge of the film. A clean glass rod was used to gently scrape and coat the solution evenly to ensure that the solution completely covered the effective area of the film. Aging and solidification: the cast nylon film was placed in an oven together with the glass slide, and aged at 45°C for 10 h. During this period, the adsorbed Zn²⁺ on the surface of the film coordinated with the subsequently generated metal-organic monobasic acid framework material to form a dense coating. Post-treatment: after aging, the composite film was taken out, and the unbound impurities on the surface were washed with deionized water. After air-drying at room temperature, a metal-organic monobasic acid framework material coated composite film was obtained.

[0029] Example 5 A preparation method of a metal-organic monobasic acid framework material coated composite film, comprising the following preparation steps: Substrate pretreatment: a nylon film with a diameter of 47 mm and a pore size of 200 nm was selected as the porous substrate. The surface attached dust and impurities were removed by ultrasonic cleaning with deionized water for 10 min, and then degreased by soaking in anhydrous ethanol for 15 min. After taking out, it was placed in a 30°C oven for drying for 15 min for standby use. Soaking treatment: a 1M Zn(NO3)2·6H2O aqueous solution was prepared, and the pretreated nylon film was immersed in the aqueous solution for 30 min to ensure that the pore structure and surface of the film were fully loaded with Zn 2+ ; Casting coating: Take out the nylon film, gently press to remove excess surface moisture, and lay it on a clean loading platform placed horizontally. Use a pipette to draw 1.0 mL of 1M Zn(NO3)2·6H2O aqueous solution and slowly cast it onto the film surface in a circular path, ensuring that the solution penetrates evenly and covers the entire film surface without missing or piling up; Aging and curing: Place the loading platform together with the nylon film into the oven and age it at 50℃ for 12h, allowing the metal-organic monobasic acid framework material to grow and firmly bond in situ on the film surface and pores, forming a uniform and dense composite coating; Post-processing: After aging is completed, rinse the composite film surface with deionized water 2-3 times to remove free unbound components, and then dry it in a 40℃ oven for 20min to obtain a metal-organic monobasic acid framework material coated composite film.

[0030] Example 6 A method for preparing a metal-organic monobasic acid framework material coated composite film, comprising the following preparation steps: Substrate pretreatment: Select a nylon film with a diameter of 49mm and a pore size of 220nm as the porous substrate, ultrasonically clean it with deionized water for 15min to remove impurities on the film surface and in the pores, then immerse it in anhydrous ethanol for 20min for deep degreasing, and air dry it at room temperature to ensure that there is no residual oil on the film surface; Soaking treatment: Prepare a 1M Zn(NO3)2·6H2O aqueous solution, and immerse the pretreated nylon film in the solution for 30min, allowing Zn 2+ to be fully adsorbed on the surface and internal pore walls of the film; Casting coating: Take out the nylon film, drain the surface moisture, and lay it on a clean quartz plate. Use a pipette to draw 1.2mL of 1M Zn(NO3)2·6H2O aqueous solution, and evenly drop and slowly cast it along the radial direction of the film. Use a clean polytetrafluoroethylene scraper to gently scrape it flat, ensuring that the coating thickness is uniform with no bubbles or cracks; Aging and curing: Place the quartz plate together with the nylon film into the oven and age it at 55℃ for 14h to promote the firm bonding of the metal-organic monobasic acid framework material with the substrate, forming a structurally stable coating; Post-processing: After aging is completed, gently rinse the surface of the composite film with deionized water to remove unreacted raw materials and impurities, and then dry it in a 45℃ oven for 30min to obtain a metal-organic monobasic acid framework material coated composite film.

[0031] Performance testing Water contact angle: Test according to GB / T 30693-2014 "Determination of contact angle of plastics - Films and sheets"; Water stability: refer to GB / T 19341-2015 "activated carbon for water treatment" stability test method; Coating adhesion: tested according to ASTM D3359-2017 "standard test method for adhesion by tape test"; Dye interception rate: tested according to GB / T 32360-2015 "ultrafiltration membrane test method"; The results are shown in Table 1-2 below: Table 1 Example 1-3 performance test table

[0032] Table 2 Example 4-6 performance test table

[0033] From the above examples 1-6 combined with Table 1-2 test results, it can be found that: In combination with the technical solutions of examples 1-3, the technical solutions of the present application optimize the oil / water interface assembly preparation method of the metal-organic monobasic acid framework material. Through the combination of interface assembly and temperature regulation, the preparation of 2D sheet and the conversion of 1D structure are realized in one step. Unlike traditional MOFs which only rely on the coordination of metal ions and organic ligands, the monobasic acid modifier introduced in the present application not only participates in the coordination to form a stable framework, but also can impart hydrophobic properties to the material through its own structural characteristics.

[0034] In combination with the performance data of examples 4-6, it is shown that the technical solutions of the present application use metal-organic monobasic acid framework material with excellent water stability and hydrophobic properties as coating material, and composite with porous substrate to form composite membrane. Unlike traditional MOF materials used in existing composite membranes, the coating material of the present application can have good hydrophobic properties without additional hydrophobic modification, and has strong water stability, which can maintain stable structure and performance in actual separation environment; at the same time, the 2D or 1D structure of the material is beneficial to form a uniform and dense coating on the surface of the substrate, and improves the separation efficiency of the composite membrane.

[0035] The present application has been described in detail in the above in combination with specific embodiments and exemplary examples, but these descriptions cannot be understood as limitations of the present application. Those skilled in the art understand that various equivalent substitutions, modifications or improvements can be made to the technical solutions and embodiments of the present application without departing from the spirit and scope of the present application, and these all fall within the scope of the present application. The protection scope of the present application is subject to the appended claims.

[0036] All publications, patent applications, patents, and other references mentioned in this specification are herein incorporated by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict between the definitions in this specification and that of any incorporated reference, the definition in this specification prevails.

[0037] When the specification states that a material, substance, method, step, apparatus or component etc. is "known to those of ordinary skill in the art," that material, substance, method, step, apparatus or component etc. is known to the skilled artisan at the time that this application is filed, but can or can not have been published or otherwise become known in this art before the filing date of this application.

[0038] In the context of this specification, except as otherwise explicitly indicated, any matter or item not mentioned is directly applicable without any change to those known in the art.

Claims

1. A metal-organic monocarboxylic acid framework material, characterized in that, The material is formed by coordination of metal ions, organic ligands, and a monobasic acid modifier, wherein the metal ions are Zn. 2+ The organic ligand is 2-methylimidazole, and the monocarboxylic acid modifier is oleic acid.

2. The metal-organic monocarboxylic acid framework material according to claim 1, characterized in that, The metal-organic monocarboxylic acid framework material is a 2D sheet or a 1D nanoroll / nanotube. The 1D nanoroll / nanotube is formed by self-rolling the 2D sheet, and the self-rolling is prepared by temperature control.

3. The method for preparing a metal-organic monocarboxylic acid framework material according to claim 1 or 2, characterized in that, Includes the following steps: Add the Zn(NO3)2 aqueous solution as the bottom layer to the container, and then take the 2-methylimidazole solution dissolved in oleic acid as the top layer and drop it onto the surface of the bottom layer. The two-phase mixture is aged at 45~55℃ for 12~48h to allow the 2D metal-organic monocarboxylic acid framework material sheet to self-roll into 1D nanorolls / nanotubes. The aged product was centrifuged, washed, and dried to obtain a metal-organic monocarboxylic acid framework material.

4. The method for preparing a metal-organic monocarboxylic acid framework material according to claim 3, characterized in that, The ratio of Zn(NO3)2:2-methylimidazolium:oleic acid:methanol is 1:(1.1-1.2):(1.2-1.3):(145-150).

5. The method for preparing a metal-organic monocarboxylic acid framework material according to claim 3, characterized in that, The centrifugation speed is 4500~5500 rpm, the centrifugation time is 8~12 min, the washing reagent is methanol, and the drying temperature is 45~55℃.

6. A metal-organic monocarboxylic acid framework material coated composite film, characterized in that, Includes a metal-organic monocarboxylic acid framework material as described in claim 1 or 2.

7. The method for preparing a metal-organic monocarboxylic acid framework material coated composite film according to claim 6, characterized in that, The preparation steps include the following: The porous substrate was immersed in a Zn(NO3)2 aqueous solution, and then the Zn(NO3)2 aqueous solution was cast onto the surface of the immersed porous substrate. The porous substrate after casting is aged at 45~55℃ for 10~14h to obtain a metal-organic monocarboxylic acid framework material coated composite film.

8. The method for preparing a metal-organic monocarboxylic acid framework material coated composite film according to claim 7, characterized in that, The porous substrate is a nylon membrane with a diameter of 45~49mm and a pore size of 180~220nm.

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