Method for in-situ construction of high electromagnetic shielding nanocomposite membrane based on COFs catalytic preparation of nano starch

Abstract

The present invention discloses a method for in-situ construction of a high electromagnetic shielding nanocomposite membrane based on the catalytic preparation of nanostarch by COFs. The catalytic action of COFs is used to hydrolyze the amorphous region of starch to form nanostarch. The COFs also act as a crosslinking agent to form hydrogen bonds with the nanostarch, thereby constructing the nanocomposite membrane in situ. The unique nanopore structure of COFs and the abundant sulfonic acid groups in the pores act as proton transfer groups to promote the high-speed transfer of protons, giving the nanocomposite membrane high proton conductivity, thereby effectively shielding electromagnetic radiation and having significant electromagnetic shielding performance. The present invention achieves a one-step, efficient preparation of nanostarch and its nanocomposite membrane, with simple operating steps, a high yield of nanostarch, and excellent electromagnetic shielding performance of the nanocomposite membrane.

Description

Technical Field

[0001] The invention belongs to the field of natural polymer materials, and particularly relates to a method for in-situ construction of a high electromagnetic shielding nanocomposite film by preparing nano starch based on COFs catalysis. Background Art

[0002] Currently, the main methods for preparing nano starch include hydrolysis, mechanical grinding, ultrasonication, high-pressure homogenization, cross-linking precipitation, and self-assembly. However, there are still some problems that need to be solved, which limits the large-scale preparation of nano starch. For example, the hydrolysis method is time-consuming, has low yields, and the product particle size is difficult to control; the mechanical grinding method will destroy the morphological structure of the nano starch and reduce the crystallinity; the high energy of ultrasonic waves will destroy the crystal structure of starch granules, causing the crystallinity of nano starch to decrease; the cross-linking precipitation method has high concentration requirements for starch solution; and the self-assembly method requires the selection of appropriate molecular structure and reaction conditions. Therefore, the development of green and efficient nano starch preparation methods is currently a difficult problem in research.

[0003] Covalent organic frameworks (COFs) are highly ordered crystalline network structures connected by chemical bonds within the crystal plane and stacked vertically through a π-π system, forming unique one-dimensional nanochannels in the vertical direction. The unique nanopore structure and highly controllable pore chemistry within COFs crystals enable high-speed proton transport. Introducing strongly acidic proton carrier sulfonic acid groups into the COFs pores not only enhances the catalytic performance of COFs but also increases the efficiency of proton transfer within the COFs pores. Therefore, using COFs for starch hydrolysis is expected to provide a green and efficient way to prepare nanostarch, promoting the large-scale production and application of nanostarch. Alternatively, by directly organically combining the COFs in the reaction system with the formed nanostarch without separation, a nanocomposite membrane can be constructed in a single step. The high proton conductivity of the COFs imparts electromagnetic shielding properties to the nanocomposite membrane. Summary of the Invention

[0004] To address the shortcomings of existing nanostarch preparation methods and the performance of their nanocomposite film materials, the present invention provides a method for in-situ construction of a high-electromagnetic-shielding nanocomposite film using COFs as catalyst and crosslinker. Using COFs as a catalyst and crosslinker, the nanostarch and high-electromagnetic-shielding nanocomposite film are efficiently prepared in a single step. The process is simple, eliminating the need for product separation. The nanocomposite film is constructed directly in situ within the reaction system, enabling simultaneous nanostarch preparation and nanocomposite film construction. This method results in a high nanostarch yield and excellent electromagnetic-shielding performance for the nanocomposite film.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The method for in-situ construction of a high electromagnetic shielding nanocomposite film based on COFs catalytic preparation of nano starch comprises the following steps:

[0007] (1) The octanoic acid solution of 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde was slowly added dropwise to the upper layer of the 2,5-diamino-1,4-benzenedisulfonic acid aqueous solution, and the mixture was placed in a constant temperature and humidity chamber and reacted at 60% humidity and 40°C for 48 hours. The upper octanoic acid solution was removed by oil-water separation, and the lower aqueous solution was dialyzed with deionized water to obtain a covalent organic framework (COF) aqueous solution with two sulfonic acid groups.

[0008] (2) adding the starch raw material to the COFs aqueous solution obtained in step (1), placing the mixture in a planetary ball mill, ball milling the mixture for a certain period of time, collecting the reaction product, and ultrasonically dispersing the mixture to form a uniform COFs / nanostarch mixed solution;

[0009] (3) The COFs / nano starch mixed solution obtained in step (2) is formed into a film by vacuum filtration and placed in a constant temperature and humidity chamber for drying to form a nanocomposite film.

[0010] Furthermore, in step (1), the molar ratio of 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde to 2,5-diamino-1,4-benzenedisulfonic acid is 1:2-1:3.

[0011] Furthermore, the concentration of the COFs aqueous solution obtained in step (1) is 1.5 mg / mL.

[0012] Furthermore, the starch raw material in step (2) is any one of corn starch, cassava starch, and wheat starch, and the solid-liquid ratio of the starch raw material to the COFs aqueous solution is 1:60-1:100 g / mL; the ball milling time is 3-5 h, and the ball milling speed is 500-800 rpm.

[0013] Furthermore, in step (3), the drying temperature is 60° C. and the humidity is 50%.

[0014] Significant advantages of the present invention

[0015] (1) The present invention efficiently prepares nano starch based on the catalytic effect of COFs, and constructs a nano composite membrane with high electromagnetic shielding performance in situ based on the cross-linking effect and high proton conductivity of COFs;

[0016] (2) The present invention has simple operation steps and does not require separation of reaction products. It realizes the simultaneous preparation of nano starch and construction of nano composite membrane. The yield of nano starch is high and the electromagnetic shielding performance of nano composite membrane is good.

[0017] (3) The present invention discloses a method for in situ construction of a high electromagnetic shielding nanocomposite membrane based on the catalytic preparation of nanostarch by COFs. The catalytic effect of COFs is used to hydrolyze the amorphous region of starch to form nanostarch. COFs also act as a crosslinking agent to form hydrogen bonds with the nanostarch, thereby in situ constructing a nanocomposite membrane. The unique nanopore structure of COFs and the abundant sulfonic acid groups in the pores act as proton transfer groups to promote the high-speed transfer of protons, giving the nanocomposite membrane high proton conductivity, thereby effectively shielding electromagnetic radiation and having significant electromagnetic shielding performance. The present invention achieves a one-step, efficient preparation of nanostarch and its nanocomposite membrane, with simple operating steps, high nanostarch yield, and good electromagnetic shielding performance of the nanocomposite membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a transmission electron microscope image of the nano starch prepared in the present invention;

[0019] Figure 2 This is a scanning electron microscope image of the nanocomposite film prepared in the present invention. DETAILED DESCRIPTION

[0020] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0021] Example 1

[0022] (1) A solution of 0.5 mol of 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde in octanoic acid was slowly added dropwise to the upper layer of an aqueous solution containing 1 mol of 2,5-diamino-1,4-benzenedisulfonic acid. The mixture was reacted in a constant temperature and humidity chamber at 60% humidity and 40°C for 48 h. The upper layer of octanoic acid solution was removed, and the lower aqueous solution was dialyzed with deionized water to obtain a COFs aqueous solution with a concentration of 1.5 mg / mL.

[0023] (2) 2 g corn starch was added to 150 mL COFs aqueous solution and ball milled in a planetary ball mill at 600 rpm for 4 h. The reaction product was collected and ultrasonically dispersed to form a uniform COFs / nanostarch mixed solution;

[0024] (3) The COFs / nanostarch mixed solution was vacuum filtered to form a membrane, and then dried in a constant temperature and humidity chamber at 60°C and 50% humidity to form a nanocomposite membrane.

[0025] The obtained nano starch is spherical with a diameter of 50-100nm and a yield of 50%. Figure 1 shown.

[0026] Example 2

[0027] (1) A solution of 1 mol of 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde in octanoic acid was slowly added dropwise to the upper layer of an aqueous solution containing 2.5 mol of 2,5-diamino-1,4-benzenedisulfonic acid. The mixture was reacted in a constant temperature and humidity chamber at 60% humidity and 40°C for 48 h. The upper layer of octanoic acid solution was removed, and the lower aqueous solution was dialyzed against deionized water to obtain a COFs aqueous solution with a concentration of 1.5 mg / mL.

[0028] (2) 2 g of cassava starch was added to 200 mL of COFs aqueous solution and ball-milled at 800 rpm for 5 h. The reaction product was collected and ultrasonically dispersed to form a uniform COFs / nanostarch mixed solution.

[0029] (3) The COFs / nanostarch mixed solution was vacuum filtered to form a membrane, and then dried in a constant temperature and humidity chamber at 60°C and 50% humidity to form a nanocomposite membrane.

[0030] The obtained nano starch is spherical with a diameter of 40-80nm and a yield of 56%. The scanning electron microscope image of the formed nano composite film is shown in FIG. Figure 2 shown.

[0031] Comparative Example 1

[0032] (1) 2 g corn starch was added to 150 mL of 3.2 mol / L sulfuric acid solution and ball milled in a planetary ball mill at 600 rpm for 4 h. The reaction product was collected and ultrasonically dispersed to form a uniform nano-starch solution.

[0033] (2) The nano starch solution was vacuum filtered to form a film, and then dried in a constant temperature and humidity chamber at 60°C and 50% humidity to form a nano composite film.

[0034] The obtained nano starch is spherical with a diameter of 70-120 nm and a yield of 29%.

[0035] Comparative Example 2

[0036] (1) A solution of 0.5 mol of 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde in octanoic acid was slowly added dropwise to the upper layer of 1 mol of phenylenediamine aqueous solution. The reaction was carried out in a constant temperature and humidity chamber at 60% humidity and 40°C for 48 h. The upper layer of octanoic acid solution was removed, and the lower aqueous solution was dialyzed with deionized water to obtain a 1.5 mg / mL aqueous solution of ordinary COFs without sulfonic acid groups.

[0037] (2) 2 g corn starch was added to 150 mL of ordinary COFs aqueous solution and ball milled in a planetary ball mill at 600 rpm for 4 h. The reaction product was collected and ultrasonically dispersed to form a uniform ordinary COFs / nanostarch mixed solution;

[0038] (3) The ordinary COFs / nanostarch mixed solution was vacuum filtered to form a membrane, and then dried in a constant temperature and humidity chamber at 60°C and 50% humidity to form a nanocomposite membrane.

[0039] The obtained nano starch is spherical with a diameter of 60-110 nm and a yield of 33%.

[0040] The properties of the nanocomposite films prepared in the examples and comparative examples were tested, and the results are shown in Table 1.

[0041] Table 1 Performance test of different nanocomposite films

[0042]

[0043] As shown in Table 1, the conductivity and electromagnetic shielding effectiveness of the nanocomposite film obtained in the embodiment are significantly better than those of comparative examples 1 and 2. This is mainly because the one-dimensional nanopores of the COFs in the nanocomposite film in the embodiment provide a fast channel for proton transfer, and the sulfonic acid groups in the pores can promote efficient proton transfer, so that the nanocomposite film has high conductivity. Excellent conductivity is the key to achieving high electromagnetic shielding, so the electromagnetic shielding effectiveness of the nanocomposite film in the embodiment is high. Compared with the embodiment, comparative example 1 uses sulfuric acid as a catalyst to prepare nano starch. Under the same reaction conditions as the embodiment, the sulfuric acid hydrolysis efficiency is low, the nano starch yield is low, and the formed nanocomposite film does not contain substances with proton conductivity and proton carrier groups. Therefore, the conductivity of the nanocomposite film is low, the conductivity is poor, and the electromagnetic shielding effectiveness is low; in comparative example 2, the COFs do not contain sulfonic acid groups, which cannot improve the catalytic performance of the COFs and cannot promote efficient proton transfer. Therefore, the nano starch yield and the conductivity and electromagnetic shielding effectiveness of the nanocomposite film are lower than those of the embodiment.

[0044] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for in-situ construction of a high electromagnetic shielding nanocomposite film using COFs-catalyzed nanostarch preparation, characterized by: The following steps are involved: (1) The octanoic acid solution of 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde was slowly added dropwise to the upper layer of the 2,5-diamino-1,4-benzenedisulfonic acid aqueous solution, and the mixture was placed in a constant temperature and humidity chamber and reacted at 60% humidity and 40°C for 48 hours. The upper octanoic acid solution was removed by oil-water separation, and the lower aqueous solution was dialyzed with deionized water to obtain a covalent organic framework (COF) aqueous solution with two sulfonic acid groups. (2) adding the starch raw material to the COFs aqueous solution obtained in step (1), placing the mixture in a planetary ball mill, ball milling the mixture for a certain period of time, collecting the reaction product, and ultrasonically dispersing the mixture to form a uniform COFs / nanostarch mixed solution; (3) The COFs / nano starch mixed solution obtained in step (2) is formed into a film by vacuum filtration and placed in a constant temperature and humidity chamber for drying to form a nanocomposite film.

2. The method for in-situ construction of a high electromagnetic shielding nanocomposite film based on COFs catalytic preparation of nano starch according to claim 1, characterized in that: In step (1), the molar ratio of 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde to 2,5-diamino-1,4-benzenedisulfonic acid is 1:2-1:

3.

3. The method for in-situ construction of high electromagnetic shielding nanocomposite membrane based on COFs catalytic preparation of nano starch according to claim 1, characterized in that: The concentration of the COFs aqueous solution obtained in step (1) is 1.5 mg / mL.

4. The method for in-situ construction of a high electromagnetic shielding nanocomposite film based on COFs catalytic preparation of nano starch according to claim 1, characterized in that: The starch raw material in step (2) is any one of corn starch, cassava starch, and wheat starch, and the solid-liquid ratio of the starch raw material to the COFs aqueous solution is 1:60-1:100 g / mL.

5. The method for in-situ construction of high electromagnetic shielding nanocomposite membrane based on COFs catalytic preparation of nano starch according to claim 1, characterized in that: In step (2), the ball milling time is 3-5 h, and the ball milling speed is 500-800 rpm.

6. The method of in-situ construction of high electromagnetic shielding nanocomposite membrane based on COFs catalytic preparation of nano starch according to claim 1, characterized in that: In step (3), the drying temperature is 60° C. and the humidity is 50%.

7. A high electromagnetic shielding nanocomposite film prepared by the method according to any one of claims 1 to 6.

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