Method for preparing covalent organic framework nanosheet by microemulsion method

Abstract

The invention provides a method for preparing a covalent organic framework nanosheet by a microemulsion method, which comprises the following steps: dissolving an aldehyde group monomer in an oil phase, adding into water, and carrying out ultrasonic treatment to prepare an oil-in-water emulsion; dissolving an amino monomer and a catalyst in water to prepare a water phase solution; and fully mixing the oil-in-water emulsion and the aqueous phase solution according to the equivalence ratio of the amino group to the aldehyde group of 1: 1, and standing for reaction to obtain the covalent organic framework nanosheet homogeneous phase dispersion liquid. Different from a traditional interfacial polymerization method (an interfacial nucleation-interfacial growth mechanism) and a phase transfer polymerization method (a bulk phase nucleation-bulk phase growth mechanism), the micro-emulsion method provided by the invention has the advantages that the mechanism is interfacial nucleation-bulk phase growth, and accurate regulation and control on the nucleation and growth processes of the nanosheets can be realized. The method disclosed by the invention has the characteristics of high efficiency, controllability, universality and the like, large-scale preparation of the covalent organic framework nanosheets with multiple functional groups is realized, the obtained nanosheets have high crystallinity and uniform size, and the controllability and practicability of preparation of the covalent organic framework nanosheets are improved.

Description

Technical Field

[0001] The present invention belongs to the field of porous two-dimensional materials, and in particular relates to a method for synthesizing covalent organic framework nanosheets by a microemulsion method. Background Art

[0002] Covalent organic frameworks (COFs), a class of crystalline porous materials with designable structures and tunable pores, hold enormous potential for applications in material separation, drug delivery, energy storage, catalytic conversion, sensing, and other fields. COF nanosheets, due to their unique two-dimensional morphology (combining large lateral dimensions with nanometer-scale thickness), ordered nanochannels, and customizable pore chemistry, are ideal building blocks for high-precision separation membranes.

[0003] Currently, there are two main methods for the direct synthesis of COF nanosheets: interfacial polymerization and phase transfer polymerization. Both methods involve nucleation and growth processes. Interfacial polymerization involves dissolving two reactive monomers in an aqueous phase and an oil phase, respectively. The two monomers nucleate and grow at the interface, resulting in COF nanosheets. In phase transfer polymerization, a monomer is transferred from one phase to another across the interface, where the COF nanosheets nucleate and grow in the bulk phase. The main difference between these two methods lies in the different locations of nucleation and growth, and they have gradually developed into the two most commonly used methods for preparing COF nanosheets.

[0004] However, the above two synthesis methods face two major challenges: first, the synthesis efficiency of COF nanosheets is low, and the static reaction time is usually at least 3 days, which cannot meet the needs of mass production; second, it is impossible to intervene in the nucleation and growth processes separately, making it difficult to precisely control the size and structure of COF nanosheets. Summary of the Invention

[0005] To address these challenges, it is necessary to develop a universal and efficient method for preparing high-quality COF nanosheets. This method aims to achieve high-yield synthesis, ensure uniform nanosheet size, be applicable to a wide range of COF systems, and facilitate industrial scale-up. This approach will directly advance COF nanosheets from laboratory research to practical applications, particularly in membrane separation and electrochemical devices, where large-area uniform materials are required. The present invention provides a universal microemulsion method for preparing covalent organic framework nanosheets, featuring a simple and efficient preparation process and effective control of nanosheet size.

[0006] To this end, the present invention proposes a method for preparing covalent organic framework nanosheets by a microemulsion method, comprising:

[0007] Step 1) preparing reaction phase I: dissolving an aldehyde monomer in an oil phase to prepare an oil phase solution, adding the oil phase solution to water and sonicating the solution to obtain an oil-in-water emulsion as the reaction phase I;

[0008] Step 2) preparing reaction phase II: dissolving the amino monomer and the catalyst in water to prepare an aqueous solution as the reaction phase II;

[0009] Step 3) The reaction phase I and the reaction phase II are fully mixed to obtain a mixed solution, wherein the equivalent ratio of the amino group to the aldehyde group is 1:1. The mixed solution is allowed to react to obtain a homogeneous dispersion of covalent organic framework nanosheets, wherein the covalent organic framework nanosheets are two-dimensional covalent organic framework nanosheets.

[0010] Furthermore, the preparation method of the present invention, wherein:

[0011] In step 1), the aldehyde monomer is dissolved in the oil phase at a molar volume concentration of 100-500 mmol / L to obtain an oil phase solution; the oil phase solution is fully mixed with water at a volume ratio of 1:10-100, and ultrasonically crushed for 10-300 seconds to obtain the reaction phase I.

[0012] In the present invention, the oil phase is an oil phase that can be configured with an aqueous solution to form an oil-in-water emulsion, preferably mesitylene; in the oil phase solution, by adjusting the water volume, the concentration of the aldehyde monomer diffused in the aqueous phase is further regulated to regulate the growth rate of the nanosheets. The molar volume ratio of the aldehyde monomer to the oil phase is preferably 200 mmol / L, and the volume ratio of the oil phase solution to water is preferably 1:25. During the ultrasonic crushing process, the size of the oil droplets is adjusted by adjusting the ultrasonic crushing time, the interface area between the oil phase and the aqueous phase is regulated, and then the nucleation rate of the nanosheets is regulated. The preferred ultrasonic crushing time is 100 s.

[0013] In step 2), acetic acid is used as a catalyst to prepare an aqueous acetic acid solution with a molar volume concentration of 6 mol / L, and the amino monomer is fully dissolved in the aqueous acetic acid solution at a molar volume concentration of 4-20 mmol / L to obtain an aqueous phase solution as reaction phase II.

[0014] The amino monomers are diaminobenzenesulfonic acid (Pa-SO3H), 4,4'-diamino-3,3'-biphenyldisulfonic acid (Bd-(SO3H)2) and triaminoguanidine hydrochloride (TG Cl )

[0015] Preferably, the molar volume concentration of the amino monomer and the acetic acid aqueous solution is 12 mmol / L.

[0016] In step 3), the mixed solution is allowed to react at 10-60° C. for 2-24 hours. During the reaction, the size of the nanosheets is adjusted by adjusting the reaction time. Preferably, the reaction temperature is 25° C. for 2 hours.

[0017] Compared with the prior art, the significant effects of the present invention are mainly reflected in:

[0018] The preparation method of the present invention is a highly efficient method for producing high-quality covalent organic framework nanosheets. It proposes an "interfacial nucleation-bulk growth" mechanism. By increasing the interfacial area through an emulsion, rapid interfacial nucleation of the nanosheets is achieved (with a static reaction time of only 2-24 hours). Furthermore, a three-dimensional radial diffusion network is used to achieve uniform diffusion of monomers, directly yielding highly crystalline, uniformly sized COF nanosheets. By adjusting the size of the oil droplets (by controlling the ultrasonic disruption time in step 1), the monomer diffusion process can be effectively controlled, resulting in the efficient production of uniformly sized nanosheets.

[0019] The preparation method of the present invention has the characteristics of high efficiency, controllability, simplicity and universality, and realizes the batch preparation of multiple types of covalent organic framework nanosheets, including sulfonic acid functional groups and guanidine functional groups, but is not limited to these. It can also be other functional groups, such as: carboxylic acid (diaminophenylcarboxylic acid), phosphoric acid (diaminophenylphosphoric acid), etc., providing a new technical means for the large-scale and controllable preparation of covalent organic framework nanosheets. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a transmission electron micrograph of the COF nanosheet TpPa-SO3H-1 prepared in Example 1;

[0021] Figure 2 The atomic force microscope images of the COF nanosheets TpPa-SO3H-1 prepared in Example 1 are shown, where the left image is a magnified image of a single nanosheet and the right image is an overview of multiple nanosheets.

[0022] Figure 3 This is an atomic force microscope image of the COF nanosheet TpBd-(SO3H)2-2 prepared in Example 2;

[0023] Figure 4 This is an atomic force microscope image of the COF nanosheet TpTG-3 prepared in Example 3;

[0024] Figure 5 This is a transmission electron microscopy image of the COF nanosheet TpPa-SO3H-20min prepared in Comparative Example 1;

[0025] Figure 6 This is a transmission electron microscopy image of the COF nanosheet TpPa-SO3H-1h prepared in Comparative Example 2;

[0026] Figure 7 This is the size distribution diagram of COF nanosheets TpPa-SO3H-1 prepared in Example 1;

[0027] Figure 8This is the size distribution diagram of COF nanosheets TpPa-SO3H-2 prepared in Example 2;

[0028] Figure 9 This is the size distribution diagram of COF nanosheets TpTG-3 prepared in Example 3;

[0029] Figure 10 This is the size distribution diagram of COF nanosheets TpPa-SO3H-4 prepared in Example 4;

[0030] Figure 11 This is the size distribution diagram of COF nanosheets TpPa-SO3H-5 prepared in Example 5.

[0031] Figure 12 This is the size distribution diagram of the oil droplets after ultrasonic crushing of the microemulsion for 10 seconds in step 1) of Example 4;

[0032] Figure 13 This is a size distribution diagram of oil droplets after ultrasonic crushing of the microemulsion for 100 seconds in step 1) of Example 1-3;

[0033] Figure 14 This is the size distribution diagram of the oil droplets after ultrasonic crushing the microemulsion for 300 seconds in step 1) of Example 5. DETAILED DESCRIPTION

[0034] The present invention proposes a microemulsion method for preparing covalent organic framework nanosheets. The design concept is to propose an "interfacial nucleation-bulk growth" mechanism to successfully prepare highly uniform and well-crystalline COF nanosheets. The microemulsion system encapsulates aldehyde monomers in oil phase droplets and distributes amine monomers in the water phase, forming a water-oil interface with a large total interfacial area. Figure 12-14 , calculated by mathematical integration, the total interfacial area of ​​the microemulsion method is 3-4 orders of magnitude higher than that of the traditional two-phase system. The microemulsion method proposed in the present invention can precisely control the nucleation process, monomer diffusion kinetics and crystal nucleus growth behavior: first, explosive nucleation occurs at the microemulsion interface; then, the crystal nuclei located at the curved oil droplet interface migrate to the bulk phase for subsequent growth; at the same time, the monomers enriched in the oil droplets are uniformly released through a three-dimensional radial diffusion path, causing the crystal nuclei to grow into large-sized COF nanosheets. This method has dual advantages: on the one hand, the orders of magnitude larger interfacial area significantly accelerates the nucleation initiation and monomer diffusion rate, achieving efficient preparation (yield >90% within 2 hours); on the other hand, the microemulsion system gives the monomers three-dimensional radial diffusion characteristics, which not only achieves uniform distribution of monomers in the aqueous phase and constructs a homogeneous reaction environment, but also synchronizes the nanosheet growth process, ultimately obtaining COF nanosheets with both high crystallinity and size uniformity.

[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the following embodiments are by no means intended to limit the present invention in any way.

[0036] Example 1: Preparation of monosulfonic acid two-dimensional covalent organic framework nanosheets (TpPa-SO3H), the steps are as follows:

[0037] Step 1) 1 mmol of trialdehyde phloroglucinol (Tp) was added to 5 mL of mesitylene and fully dissolved to form an oil phase solution; the oil phase solution was added to 125 mL of water and ultrasonically crushed for 100 s to obtain an oil-in-water emulsion, which was reaction phase I. Figure 13 The size distribution of the oil droplets is shown; in Example 1, the molar volume concentration of the oil phase solution is 200 mmol / L, and the volume ratio of the oil phase solution to water is 1:25.

[0038] Step 2) 1.5 mmol of diaminobenzenesulfonic acid (Pa-SO3H) was added to 125 mL of 6 mol / L acetic acid aqueous solution to form reaction phase II. In Example 1, the molar volume concentration of the amino monomer and the acetic acid aqueous solution was 12 mmol / L.

[0039] Step 3) Reaction phase I and reaction phase II are fully mixed to obtain a mixed solution, which is reacted at 25°C for 2 hours to obtain a dispersion of monosulfonic acid-type two-dimensional covalent organic framework nanosheets (denoted as TpPa-SO3H-1); in this Example 1, the equivalent ratio of amino group to aldehyde group is 1:1.

[0040] like Figure 1 As shown, transmission electron microscopy test shows that the product has a flake morphology. Figure 7 The size distribution of the nanosheets prepared in this embodiment is shown in FIG. , which is about 2 to 3 μm in size; Figure 2 As shown, atomic force microscopy tests show that the product has uniform size and a thickness of about 3.8 nm.

[0041] Example 2, Preparation of bissulfonic acid type two-dimensional covalent organic framework nanosheets (TpBd-(SO3H)2). Compared with Example 1, the preparation process is different only in that: in step 2), 1.5mmol Pa-SO3H is replaced with 1.5mmol 4,4'-diamino-3,3'-biphenyldisulfonic acid (Bd-(SO3H)2); in step 3), the static reaction time is changed from 2h to 24h; finally, a dispersion of bissulfonic acid type two-dimensional covalent organic framework nanosheets (denoted as TpBd-(SO3H)2-2) is obtained. Figure 3 As shown, the atomic force microscope test shows that the product has a flake morphology. Figure 8 The nanosheets prepared in this example have a size distribution of about 2 to 6 μm.

[0042] Example 3, Preparation of guanidine-type two-dimensional covalent organic framework nanosheets (TpTG), compared with Example 1, the preparation process is different only: in step 2), 1.5mmol Pa-SO3H is replaced by 1.5mmol triaminoguanidine hydrochloride (TG Cl ); in step 3), the static reaction time was changed from 2h to 24h; finally, a dispersion of guanidine-type two-dimensional covalent organic framework nanosheets (denoted as TpTG-3) was obtained. Figure 4 As shown, the atomic force microscope test shows that the product has a flake morphology. Figure 9 The nanosheets prepared in this example have a size distribution of about 1 to 2 μm.

[0043] Example 4, Preparation of Monosulfonic Acid Two-Dimensional Covalent Organic Framework Nanosheets (TpPa-SO3H). Compared with Example 1, the preparation process is different only in that in step 1), the ultrasonic crushing time is changed from 100s to 10s. Figure 12 The size distribution of the oil droplets is shown; finally, a dispersion of monosulfonic acid-type two-dimensional covalent organic framework nanosheets (denoted as TpPa-SO3H-4) was obtained. Figure 10 The size distribution of the nanosheets prepared in this example is shown, and the size thereof is about 0.2 to 5 μm.

[0044] Example 5, Preparation of Monosulfonic Acid Two-Dimensional Covalent Organic Framework Nanosheets (TpPa-SO3H). Compared with Example 1, the preparation process is different only in that: in step 1), the ultrasonic crushing time is changed from 100s to 300s. Figure 14 The size distribution of the oil droplets is shown; finally, a dispersion of monosulfonic acid-type two-dimensional covalent organic framework nanosheets (denoted as TpPa-SO3H-5) is obtained. Figure 11 The nanosheet size distribution prepared in this example is shown, and the size thereof is about 0.02 to 2 μm.

[0045] Comparative Example 1, Preparation of monosulfonic acid type two-dimensional covalent organic framework nanosheets (TpPa-SO3H). The preparation process is basically the same as that in Example 1, except that the reaction time in step 3) is changed from 2h to 20min, and finally a sulfonic acid type two-dimensional covalent organic framework nanosheet (denoted as TpPa-SO3H-20min) dispersion is obtained. Figure 5 Transmission electron microscopy showed that the product had a flake-like morphology and a size of about 50 nm.

[0046] Comparative Example 2, Preparation of monosulfonic acid type two-dimensional covalent organic framework nanosheets (TpPa-SO3H). The preparation process is basically the same as that in Example 1, except that the reaction time in step 3) is changed from 2h to 1h, and finally a sulfonic acid type two-dimensional covalent organic framework nanosheet (denoted as TpPa-SO3H-1h) dispersion is obtained. Figure 6Transmission electron microscopy tests show that the product has a flake-like morphology and a size of about 1 to 2 μm.

[0047] By comparing Examples 1 to 5 and Comparative Examples 1-2, it can be concluded that the microemulsion method for preparing uniform covalent organic framework nanosheets has universal applicability and high efficiency, and the prepared nanosheets have good size uniformity. By comparing Examples 1-5 and Comparative Examples 1-2, it can be concluded that in the preparation of reaction phase I, after the oil phase solution is added to water, as the ultrasonic crushing time increases, the oil droplets in the water-in-oil emulsion become smaller, but this does not mean that the smaller the oil droplets, the smaller the size of the prepared nanosheets. Figure 7-14 As shown. The size of the oil droplet determines the nucleation of the reaction monomer at the interface, as well as the diffusion rate of the aldehyde monomer from the aqueous phase to the oil phase, that is, the growth rate of the nanosheet. If the oil droplet size is too large, it will lead to too little nucleation at the interface and a low diffusion rate of the aldehyde monomer. If the oil droplet size is too small, it will lead to excessive nucleation at the interface and consume most of the reaction monomer, which is not conducive to the later growth process of the nanosheet. Therefore, in the present invention, the preferred ultrasonic crushing time is 100s, and the preferred static reaction time is 2h. In order to ensure the quality of the synthesized nanosheets, the reaction time can also be extended, and the reaction time range is 2-24h. The mixed solution formed by fully mixing reaction phase I and reaction phase II, as the static reaction time increases, the size of the resulting nanosheet increases, as shown Figures 7 to 11 .

[0048] In summary, the present invention has developed a microemulsion-based method for synthesizing covalent organic framework (COF) nanosheets and revealed its unique mechanism of "interfacial nucleation-bulk growth." This method confines aldehyde monomers to oil-phase droplets and distributes amine monomers in the aqueous phase to construct a microemulsion system with an extremely large interfacial area. This increases the water-oil contact area by 3-4 orders of magnitude compared to traditional two-phase systems, thereby achieving precise control of the nucleation, diffusion, and growth processes. This method overcomes the limitations of traditional methods in nanosheet uniformity, crystallinity, and preparation efficiency, laying a solid foundation for the large-scale preparation and functional application of COF nanomaterials.

[0049] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many improvements and changes without departing from the purpose of the present invention, which are all protected by the present invention.

Claims

1. A method for preparing covalent organic framework nanosheets by a microemulsion method, comprising: Step 1) dissolving an aldehyde monomer in an oil phase to prepare an oil phase solution, adding the oil phase solution to water and sonicating the mixture to obtain an oil-in-water emulsion, which is designated as reaction phase I; Step 2) dissolving the amino monomer and the catalyst in water to prepare an aqueous phase solution, which is referred to as reaction phase II; Step 3) The reaction phase I and the reaction phase II are fully mixed to obtain a mixed solution, wherein the equivalent ratio of the amino group to the aldehyde group is 1:

1. The mixed solution is allowed to react to obtain a homogeneous dispersion of covalent organic framework nanosheets, wherein the covalent organic framework nanosheets are two-dimensional covalent organic framework nanosheets.

2. The preparation method according to claim 1, characterized in that In step 1), the aldehyde monomer is dissolved in the oil phase at a molar volume concentration of 100-500 mmol / L to obtain an oil phase solution; the oil phase solution is fully mixed with water at a volume ratio of 1:10-100, and ultrasonically crushed for 10-300 seconds to obtain the reaction phase I.

3. The preparation method according to claim 1 or 2, characterized in that In step 1), the oil phase is an oil phase that can be configured with an aqueous solution to form an oil-in-water emulsion.

4. The preparation method according to claim 3, characterized in that In step 1), the aldehyde monomer is trialdehyde phloroglucinol (Tp), and the oil phase is mesitylene; in the oil phase solution, the molar volume ratio of the aldehyde monomer to the oil phase is 200 mmol / L; the volume ratio of the oil phase solution to water is 1:25, and the ultrasonic crushing time is 100 s.

5. The preparation method according to claim 1, characterized in that In step 2), acetic acid is used as a catalyst to prepare an aqueous acetic acid solution with a molar volume concentration of 6 mol / L, and the amino monomer is fully dissolved in the aqueous acetic acid solution at a molar volume concentration of 4-20 mmol / L to obtain an aqueous phase solution as reaction phase II.

6. The preparation method according to claim 5, characterized in that In step 2), the amino monomer is one of diaminobenzenesulfonic acid (Pa-SO3H), 4,4'-diamino-3,3'-biphenyldisulfonic acid (Bd-(SO3H)2) and triaminoguanidine hydrochloride (TG).

7. The preparation method according to claim 5 or 6, characterized in that: The molar volume concentration of the amino monomer and the acetic acid aqueous solution is 12 mmol / L.

8. The preparation method according to claim 1, characterized in that In step 3), the mixed solution is allowed to react at 10-60° C. for 2-24 hours.

9. The preparation method according to claim 1 or 8, characterized in that The reaction temperature was 25° C. and the reaction time was 2 h.

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