A natural polyphenol hydrogel with microwave absorption function and a preparation method thereof

Abstract

The application discloses a natural polyphenol hydrogel with microwave absorption function and a preparation method thereof, and the method comprises the following steps: dissolving the natural polyphenol in deionized water, and performing ultrasonic dispersion and stirring to obtain a natural polyphenol aqueous solution; adding a graphene oxide aqueous dispersion into the natural polyphenol aqueous solution, adding sodium hydroxide to adjust the pH value to 8.5, heating and stirring to obtain a natural polyphenol / graphene oxide mixed solution; adding dilute hydrochloric acid into the natural polyphenol / graphene oxide mixed solution to adjust the pH value to 7, performing heat treatment under a sealed condition, and then performing washing to obtain the natural polyphenol hydrogel. The natural polyphenol hydrogel prepared by the application has good microwave absorption function, and the microwave absorption performance can be controlled by the amount of graphene oxide; meanwhile, the natural polyphenol hydrogel has a microwave absorption intelligent switching function; with the increase of temperature, the hydrogen bond action is weakened, the Pi interaction is enhanced, the electronic transmission capacity is also enhanced, and the microwave absorption performance is significantly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyphenol application, and particularly relates to a natural polyphenol hydrogel with microwave absorption function and a preparation method thereof. BACKGROUND

[0002] Electromagnetic wave technology has become the basis of the communication field and the remote sensing and telemetry field, and has made outstanding contributions in the application aspects of 5G communication and radar detection. Due to the wide and complex application scenarios of electromagnetic wave technology, electromagnetic wave interference and pollution have brought many problems such as electromagnetic radiation / leakage / failure and equipment exposure, and therefore, a wave-absorbing material capable of effectively absorbing electromagnetic waves is the key to realizing accurate and efficient application of electromagnetic technology.

[0003] In recent years, with the deep development of electromagnetic technology, its application environment and conditions are increasingly variable, and the demand for considering electromagnetic interference and effective communication function is increasingly urgent. In view of this problem, at present, people usually use a secret and less interfered wave band as their own communication wave band to avoid the conflict between shielding interference demand and communication. However, with the increasing difficulty of expanding to high frequency, and the inevitable security problem of communication wave band leakage, the demand for intelligent microwave absorbing materials capable of adjusting the microwave absorption performance according to the use demand and working environment is imminent.

[0004] Graphene oxide has excellent electrical conductivity and dielectric properties and is widely used in microwave absorption, but the local destruction of hydrogen bonds caused by the functional groups of the oxidized state destroys the Pi conjugation conducive to electron conduction, and therefore, secondary reduction is often needed to ensure its electrical properties. Natural polyphenol compounds exist widely in nature and play a crucial role in various ecological systems of animals, plants, bacteria and fungi. They have similar structures and forces to graphene oxide and have been widely used as good structural and functional units in the design and construction of various functional materials. Although many construction methods have been proposed and applied in recent years, complex purification, additional additives and complicated construction routes are still the main challenges limiting the potential application of polyphenol functional materials. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the present application aims to prepare a composite hydrogel capable of effectively absorbing microwaves by simply mixing a plurality of polyphenol molecules with graphene oxide and controlling the temperature and pH value, and to realize variable control of microwave absorption performance through the dynamic change of the force between polyphenol and graphene oxide.

[0006] To achieve the above-mentioned purpose, according to one aspect of the present application, a preparation method of a natural polyphenol hydrogel with microwave absorption function is provided, comprising the following steps:

[0007] S1: dissolve the natural polyphenol in deionized water, and perform ultrasonic dispersion and stirring to obtain a natural polyphenol aqueous solution;

[0008] S2: add a graphene oxide aqueous dispersion to the natural polyphenol aqueous solution, and add sodium hydroxide to adjust the pH value to 8.5, and then perform heating and stirring to obtain a natural polyphenol / graphene oxide mixed solution;

[0009] S3: add dilute hydrochloric acid to the natural polyphenol / graphene oxide mixed solution to adjust the pH value to 7, perform heat treatment under sealed conditions, and then perform washing to obtain a natural polyphenol hydrogel.

[0010] Further, the natural polyphenol is any one of quercetin, caffeic acid, gallic acid, ellagic acid, apigenin, emodin, luteolin, and tannic acid.

[0011] Further, the concentration of the natural polyphenol aqueous solution in S1 is 5-15 mg / mL.

[0012] Further, the heating temperature in S2 is 80℃, and the stirring time is 2 h.

[0013] Further, the dosage of the graphene oxide aqueous dispersion and the natural polyphenol aqueous solution is 1:1.

[0014] Further, the addition amount of the graphene oxide in the graphene oxide aqueous dispersion in S2 is 1:1-1:2 of the mass ratio of the natural polyphenol and the graphene oxide.

[0015] Further, the heat treatment temperature in S3 is 70-90℃, and the heat treatment time is 16-48 h.

[0016] According to another aspect of the present application, a natural polyphenol hydrogel with microwave absorption function is provided, which is prepared according to the preparation method as described above.

[0017] Compared with the prior art, the present application can achieve the following beneficial effects:

[0018] 1. The natural polyphenol hydrogel prepared by the present application has good microwave absorption function, and the microwave absorption performance can be easily adjusted by adjusting the amount of graphene oxide; at the same time, the hydrogel has a significant microwave absorption intelligent switching function, as the temperature rises, the hydrogen bond interaction in the composite hydrogel weakens, the Π interaction force strengthens, the electronic transmission capacity of the composite hydrogel is further enhanced, and better impedance matching is brought, so that the microwave absorption performance that can change with temperature is realized.

[0019] 2. The natural polyphenol and graphene oxide used in the synthesis process of the present application are common reagents with standard production specifications, which are very convenient to use and make the method have good repeatability.

[0020] 3、The method adopted by the present application is very simple, and the polyphenol hydrogel can be successfully prepared through simple temperature rising and lowering and PH value adjustment, avoiding complex purification, additional additives and complicated construction route.

[0021] 4、The method adopted by the present application has high efficiency, repeatability and scalability, and has good industrialization prospect. Compared with the traditional polyphenol functional material preparation method, the process is simple, and the size can be easily enlarged according to the demand, which has great advantages in actual application.

[0022] 5、The preparation method provided by the present application has good adjustability, and the microwave absorption function can be controlled by the amount of graphene oxide. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a scanning electron microscope graph of the polyphenol hydrogel of embodiment 1 of the present application;

[0024] Figure 2 It is an X-ray diffraction graph of the polyphenol hydrogel of embodiment 1 of the present application;

[0025] Figure 3 It is an element proportion distribution graph of the polyphenol hydrogel of embodiment 1 of the present application;

[0026] Figure 4 It is a conductivity statistical graph of the polyphenol hydrogel obtained by different kinds of polyphenols in embodiments 1 and 2;

[0027] Figure 5 It is a microwave absorption performance statistical graph of the polyphenol hydrogel of embodiment 1 of the present application at different temperatures;

[0028] Figure 6 It is a microwave absorption performance statistical graph of the polyphenol hydrogel obtained by different concentrations of polyphenol aqueous solution in embodiment 3 of the present application;

[0029] Figure 7 It is a microwave absorption performance statistical graph of the polyphenol hydrogel obtained by different amounts of graphene oxide in embodiment 4 of the present application;

[0030] Figure 8 It is a microwave absorption performance statistical graph of the polyphenol hydrogel obtained by different heat treatment temperatures in embodiments 1 and 5 of the present application. DETAILED DESCRIPTION

[0031] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0032] The present application utilizes the hydrogen bonding and Π interaction of natural polyphenol and graphene oxide to realize excellent intercalation, and then weakens the hydrogen bonding and strengthens the Π interaction by temperature treatment to form hydrogel, and further improves the conductivity of the hydrogel. With the increase of temperature, the hydrogen bonding in the composite hydrogel is weakened, the Π force is strengthened, the electron transport capacity of the composite hydrogel is further enhanced, and the impedance matching is better, so that the microwave absorption performance which can be changed with temperature is realized.

[0033] The present application provides a preparation method of natural polyphenol hydrogel with microwave absorption function, comprising the following steps:

[0034] S1: one of quercetin, caffeic acid, gallic acid, ellagic acid, apigenin, emodin, luteolin, tannic acid and other natural polyphenols is dissolved in deionized water, and ultrasonic dispersion treatment is carried out for 3-10 minutes, and then it is fully stirred at room temperature for 10 minutes to obtain a uniform transparent natural polyphenol aqueous solution, and the concentration of the natural polyphenol aqueous solution is 5-15 mg / mL.

[0035] S2: slowly add graphene oxide aqueous dispersion to the natural polyphenol aqueous solution, the dosage of the graphene oxide aqueous dispersion and the natural polyphenol aqueous solution is 1:1, the added amount of graphene oxide in the graphene oxide aqueous dispersion is 1:1-1:2 based on the mass ratio of natural polyphenol and graphene oxide, then add sodium hydroxide to adjust the pH value to 8.5, heat to 80℃, and maintain uniform stirring speed for 2h to obtain a natural polyphenol / graphene oxide mixed solution.

[0036] In this process, the present application reduces the protonation of phenolic hydroxyl and carboxyl groups by adjusting the pH value to enhance the hydrogen bonding, and realizes the excellent intercalation of natural polyphenol and graphene oxide.

[0037] S3: add dilute hydrochloric acid to the natural polyphenol / graphene oxide mixed solution to adjust the pH value to 7, place it in a 70-90℃ oven under sealed conditions for heat treatment for 16-48h, and then wash it with deionized water to obtain a natural polyphenol hydrogel.

[0038] In the process, the application utilizes the hydrogen bond and Π interaction of natural polyphenol and graphene oxide to realize excellent intercalation, and then through heat treatment and reducing pH value to increase the atomic distance in the hydrogen bond and to enhance the difficulty of protonation to form hydrogen bond, weaken the hydrogen bond and strengthen the Π interaction and form hydrogel, further improve the conductivity of the hydrogel. With the increase of temperature, the hydrogen bond in the composite hydrogel is weakened, the Π interaction is strengthened, the electron transmission capacity of the composite hydrogel is further enhanced, and better impedance matching is brought, so that the microwave absorption performance changing with temperature is realized.

[0039] According to another aspect of the application, a natural polyphenol hydrogel with microwave absorption function is provided, which is prepared according to the preparation method as described above.

[0040] Example 1

[0041] A preparation method of a natural polyphenol hydrogel with microwave absorption function, comprising the following steps:

[0042] S1: Dissolve quercetin in deionized water and perform ultrasonic dispersion treatment for 10 minutes, and then fully stir at room temperature for 10 minutes to obtain a uniform transparent natural polyphenol aqueous solution, and the concentration of the natural polyphenol aqueous solution is 10 mg / mL.

[0043] S2: Slowly add graphene oxide aqueous dispersion to the natural polyphenol aqueous solution, the dosage of the graphene oxide aqueous dispersion and the polyphenol aqueous solution is 1:1, the added amount of graphene oxide in the graphene oxide aqueous dispersion is 1:1.5 based on the mass ratio of natural polyphenol and graphene oxide, and then add sodium hydroxide to adjust the pH value to 8.5, heat to 80℃, and maintain uniform stirring speed for stirring for 2h to obtain a natural polyphenol / graphene oxide mixed solution.

[0044] S3: Add dilute hydrochloric acid to the natural polyphenol / graphene oxide mixed solution to adjust the pH value to 7, and then place it in a 80℃ oven for heat treatment under sealed conditions for 24h, and then wash it with deionized water to obtain a natural polyphenol hydrogel.

[0045] Example 2

[0046] As shown in Table 1, the quercetin in S1 of Example 1 is replaced by one of coffee acid, gallic acid, ellagic acid, apigenin, emodin, luteolin and tannic acid, i.e. different types of polyphenols are selected to prepare a natural polyphenol hydrogel.

[0047] Example 3

[0048] The concentration of the natural polyphenol aqueous solution in S1 of Example 1 was adjusted to 5 mg / mL, 7 mg / mL, 9 mg / mL, 11 mg / mL, 13 mg / mL, and 15 mg / mL, respectively, to prepare the natural polyphenol hydrogel.

[0049] Example 4

[0050] The mass ratio of the natural polyphenol and graphene oxide in S2 of Example 1 was adjusted to 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, and 1:2, respectively, to prepare the natural polyphenol hydrogel.

[0051] Example 5

[0052] The temperature of the heat treatment in S3 of Example 1 was adjusted to 70°C and 90°C, respectively, to prepare the natural polyphenol hydrogel.

[0053] Table 1 Preparation parameters of natural polyphenol hydrogel in each example

[0054]

[0055] To better understand the performance of the natural polyphenol hydrogel prepared in the above examples, the natural polyphenol hydrogel was tested and characterized, and the results are as follows:

[0056] 1. Characterization of natural polyphenol hydrogel - morphology

[0057] The polyphenol hydrogel obtained in each example was freeze-dried and then tested by table scanning electron microscopy to observe the microstructure of the obtained sample. The specific operation method is as follows: freeze the polyphenol hydrogel with liquid nitrogen, dry it in a vacuum low-temperature environment, and then observe it after drying and gold spraying. The scanning electron microscopy image of the polyphenol hydrogel of Example 1 after freeze-drying is shown in Figure 1 From the scanning electron microscopy image, it can be observed that the obtained sample has a clear layered structure, which verifies the significant layer-by-layer stacking structure formed by the Π interaction between the polyphenol and graphene oxide. Figure 1

[0058] 2. Characterization of natural polyphenol hydrogel - structure

[0059] The polyphenol hydrogel obtained in each example was freeze-dried and then characterized by X-ray diffraction and X-ray photoelectron spectroscopy for its chemical structure and physical structure.

[0060] The X-ray diffraction pattern of the polyphenol hydrogel of Example 1 after freeze-drying is shown in Figure 2 From the X-ray diffraction pattern, it can be observed that the obtained sample has a clear layered structure, which verifies the significant layer-by-layer stacking structure formed by the Π interaction between the polyphenol and graphene oxide. Figure 2 ​The sharp peak appeared at 20-25°, which corresponds to the interlayer spacing of 0.33-0.4 nm of the π interaction accumulation, verifying that there is a significant ordered π stacking structure between the polyphenol and graphene oxide.

[0061] The polyphenol hydrogel obtained in Example 1 was freeze-dried and characterized by X-ray photoelectron spectroscopy to test the element ratio distribution, as shown in Figure 3 The element ratio distribution is shown in the figure, wherein the O element ratio is 25.99%, which is significantly lower than the O element ratio of 29.93% in the graphene oxide before the reaction, which indicates that the natural polyphenol can reduce the graphene oxide during the reaction, thereby constructing a more complete and continuous conjugated structure, which is beneficial to the improvement of the electrical performance of the hydrogel.

[0062] 3. Characterization of natural polyphenol hydrogel - conductivity

[0063] The conductivity of the natural polyphenol hydrogel prepared by different types of polyphenol in Examples 1 and 2 was tested by a four-probe conductivity tester, and the specific operation method was as follows: a 5mm thick polyphenol hydrogel was prepared in a circular mold with a diameter of 2cm, and the conductivity was measured by a four-probe conductivity tester, and the measurement results are shown in Figure 4 As can be seen from Figure 4 , different types of polyphenol showed different conductivity results, which may be due to the difference in force and solubility of different polyphenols.

[0064] 4. Characterization of natural polyphenol hydrogel - microwave absorption efficiency

[0065] The microwave absorption efficiency of the natural polyphenol hydrogel was measured by a vector network analyzer, and the specific operation method was as follows: a 1mm thick polyphenol hydrogel was prepared in a circular ring mold with an inner diameter of 3.04mm and an outer diameter of 7mm, and the microwave absorption efficiency in the range of 2-18GHz was measured by a vector network analyzer.

[0066] The natural polyphenol hydrogel prepared in Example 1 was placed in an oven at 20℃, 40℃, 60℃ and 80℃ for 10 minutes, and the electromagnetic wave shielding efficiency in the range of 2-18GHz was measured. The measurement results are shown in Figure 5 As can be seen from the figure, with the increase of temperature, the microwave absorption efficiency of the natural polyphenol hydrogel gradually increases, which is because with the increase of temperature, the hydrogen bond interaction in the composite hydrogel is weakened, the π interaction is enhanced, and the electronic transmission ability of the composite hydrogel is further enhanced, which brings better impedance matching, thereby realizing the temperature-variable microwave absorption performance.

[0067] The electromagnetic wave shielding efficiency in the range of 2-18GHz of the natural polyphenol hydrogel prepared by different concentrations of polyphenol in Example 3 was measured. The measurement results are shown in Figure 6As shown, the electromagnetic shielding performance is optimal when the polyphenol concentration is close to 10 mg / mL, because the excellent dispersion of graphene oxide is difficult to achieve when the polyphenol concentration is too low, and the agglomeration of polyphenols due to the limitation of solubility greatly reduces the electromagnetic shielding performance.

[0068] The electromagnetic wave shielding performance of the natural polyphenol hydrogel prepared in Example 4 in the range of 2-18 GHz was determined, and the influence of different amounts of graphene oxide on the electromagnetic wave shielding performance of the natural polyphenol hydrogel was analyzed. The determination results are shown in Table 2. Figure 7 As shown, with the increase of the amount of graphene oxide, the electromagnetic wave shielding performance shows a trend of first increasing and then decreasing. The optimal mass ratio of natural polyphenol to graphene oxide is 1:1.5, because at this ratio, the best effect of in-situ polymerization of natural polyphenol intercalated graphene oxide can be achieved, and when the amount of graphene oxide is too low or too high, the uniform aggregation and distribution of the two may occur, thereby the optimal interaction effect cannot be achieved.

[0069] The electromagnetic wave shielding performance of the natural polyphenol hydrogel prepared in Example 1 and Example 5 in the range of 2-18 GHz was determined, and the influence of different heat treatment temperatures on the electromagnetic wave shielding performance of the natural polyphenol hydrogel was analyzed. The determination results are shown in Table 3. Figure 8 As shown, the optimal performance is achieved under the condition of heat treatment at 80℃, because too high temperature will cause further weakening of hydrogen bonds, thereby resulting in too low degree of gel hydration, thereby causing large impedance change.

[0070] The above examples only express the embodiments of the present application, which are described in more detail and in detail, but should not be understood as limiting the scope of the patent of the present application. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for preparing a natural polyphenol hydrogel having a microwave absorption function, characterized by, The method comprises the following steps: S1: dissolving natural polyphenol in deionized water, and performing ultrasonic dispersion and stirring to obtain a natural polyphenol aqueous solution; S2: adding a graphene oxide aqueous dispersion into the natural polyphenol aqueous solution, and adding sodium hydroxide to adjust the pH value to 8.5, and then heating and stirring, wherein the heating temperature is 80℃, to obtain a natural polyphenol / graphene oxide mixed solution; S3: adding dilute hydrochloric acid into the natural polyphenol / graphene oxide mixed solution to adjust the pH value to 7, and then performing heat treatment under a sealed condition, wherein the heat treatment temperature is 70-90℃, and then washing to obtain a natural polyphenol hydrogel.

2. The method for preparing a natural polyphenol hydrogel with microwave absorption function according to claim 1, characterized in that, The natural polyphenol is any one of quercetin, caffeic acid, gallic acid, ellagic acid, apigenin, emodin, luteolin, and tannic acid.

3. The method for preparing a natural polyphenol hydrogel with microwave absorption function according to claim 1, characterized in that, The concentration of the natural polyphenol aqueous solution in S1 is 5-15 mg / mL.

4. The method for preparing a natural polyphenol hydrogel with microwave absorption function according to claim 1, characterized in that, The stirring time in S2 is 2 h.

5. The method for preparing a natural polyphenol hydrogel with microwave absorption function according to claim 1, characterized in that, The dosage of the graphene oxide aqueous dispersion and the natural polyphenol aqueous solution in S2 is 1:

1.

6. The method for preparing a natural polyphenol hydrogel with microwave absorption function according to claim 1, characterized in that, The added amount of graphene oxide in the graphene oxide aqueous dispersion in S2 is 1:1-1:2 of the mass ratio of natural polyphenol to graphene oxide.

7. The method for preparing a natural polyphenol hydrogel with microwave absorption function according to claim 1, characterized in that, The heat treatment time in S3 is 16-48 h.

8. A natural polyphenol hydrogel having a microwave absorption function, characterized by, The natural polyphenol hydrogel is prepared according to the preparation method in any one of claims 1-7.

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