A method for improving the thermoelectric properties of PEDOT:PSS thin films prepared by ethanol gel film formation method through acid-base treatment

Abstract

The present invention relates to a method for improving the thermoelectric performance of a PEDOT:PSS thin film prepared by an ethanol gel film forming method through acid-base treatment. The method comprises the following steps: step 1, slowly and uniformly adding a PEDOT:PSS aqueous solution into anhydrous ethanol to form a PEDOT:PSS thin film through gel film formation; step 2, drying the PEDOT:PSS thin film obtained in step 1 on a 100°C-130°C hot plate; step 3, immersing the film dried in step 2 in a 5ml-10ml H2SO4 solution for 10-20 minutes; step 4, rinsing the film in step 3 with deionized water to remove residual H2SO4 solution; step 5, immersing the film obtained in step 4 in a 5ml-10ml KOH solution for 10-20 minutes; step 6, rinsing the film in step 5 with deionized water 3-5 times; and step 7, drying on a hot plate to obtain the PEDOT:PSS thin film. The present invention adopts an ethanol gel film forming method, which improves the thermoelectric performance during the film forming process, and further acid-base treatment is added to obtain a PEDOT:PSS film with higher thermoelectric performance.

Description

Technical Field

[0001] The present invention relates to a method for improving thermoelectric properties, and specifically to a method for forming a film using ethanol gel, wherein the thermoelectric properties of the film are improved during the film forming process, and further acid-base treatment is performed to obtain a PEDOT:PSS film with higher thermoelectric properties. The present invention relates to a method for improving the thermoelectric properties of a PEDOT:PSS film prepared by the ethanol gel film forming method through acid-base treatment. Background Art

[0002] In recent years, the problems of environmental degradation and depletion of fossil energy have become increasingly prominent. Therefore, it is urgent to find a clean and efficient new energy source. Thermoelectric (TE) materials are functional materials that use the migration of carriers inside solid materials to directly convert thermal energy and electrical energy. Their principles are mainly based on the Seebeck effect and the Peltier effect. One of the uses of thermoelectric materials is thermoelectric power generation devices, which have the advantages of no transmission parts, no noise, and high reliability. However, the performance of organic thermoelectric materials is not significant at present, which has become the main bottleneck restricting its development. Improving the performance of thermoelectric materials is one of the most important ways to promote their application.

[0003] Poly(3,4-ethylenedioxythiophene:polystyrene sulfonate) (PEDOT:PSS) is one of the most common organic TE materials, and the highest thermoelectric figure of merit reported so far is 0.75. The inherent thermal conductivity of PEDOT:PSS is lower than that of traditional TE materials (about 2W / mK), at about 0.17W / mK. Compared with other organic TE materials, PEDOT:PSS has the advantages of good thermal stability, low thermal conductivity, high electrical conductivity and strong mechanical flexibility. However, the thermoelectric performance of untreated PEDOT:PSS is not very high and cannot achieve the effect that can be applied. Generally, various acid treatments including organic acids and inorganic acids are used to increase the conductivity of PDOT:PSS films by several orders of magnitude. At the same time, alkali treatment can also adjust its oxidation level, thereby optimizing its PF value. For example, Kim et al. treated PEDOT:PSS with concentrated sulfuric acid to achieve a conductivity of up to 4380 S / cm. Treating the PEDOT:PSS film with concentrated sulfuric acid only took 10 minutes, and the structure rearranged to form highly ordered crystalline PEDOT:PSS nanofibers. Furthermore, the effective removal of insulating PSS, the increase in the vertical stacking direction (edge-on) content of PEDOT, and the reduction in its π-π stacking spacing all facilitated carrier transport, significantly improving conductivity and thermoelectric performance. Furthermore, Chen et al. improved the thermoelectric properties of PEDOT:PSS by adjusting the stacking structure and oxidation level. They used a triple post-treatment of formamide, concentrated sulfuric acid, and sodium borohydride to obtain a flexible PEDOT:PSS thermoelectric film. By changing the stacking structure and adjusting the oxidation level to optimize the PF value, σ and S at room temperature were 1786 S / cm and 28.1 μV / K, respectively, and the PF reached 141 μW / mK. 2 Furthermore, the flexible PEDOT:PSS film was used to prepare a thermoelectric device with an output power density of 1μW / cm 2 Alternatively, a combination of acid and alkali treatment can be used, that is, first using concentrated sulfuric acid to remove excess PSS, significantly improving conductivity, and then performing alkali reduction treatment to change the carrier type and increase the Seebeck coefficient, thereby ultimately achieving the goal of improving the PF value.

[0004] In summary, developing a simple and effective method to improve the thermoelectric properties of PEDOT:PSS has very important theoretical significance and practical value. Summary of the Invention

[0005] In response to the above problems, the main purpose of the present invention is to provide a method for film formation using ethanol gel, which improves its thermoelectric properties during the film formation process, and further acid-base treatment is combined to obtain a PEDOT:PSS film with higher thermoelectric properties. The acid-base treatment is a method for improving the thermoelectric properties of PEDOT:PSS films prepared by the ethanol gel film formation method.

[0006] The present invention solves the above technical problems through the following technical solutions: a method for improving the thermoelectric properties of a PEDOT:PSS film prepared by an ethanol gel film forming method through acid and alkali treatment, characterized in that: the method adopts an ethanol gel film forming method to prepare a PEDOT:PSS film, which is achieved through one acid treatment and one alkali treatment;

[0007] The method comprises the following steps:

[0008] Step 1: slowly and uniformly add a PEDOT:PSS aqueous solution into anhydrous ethanol to form a PEDOT:PSS film through gel formation;

[0009] Step 2: Dry the PEDOT:PSS film obtained in step 1 on a hot plate at 100°C-130°C for 10-20 minutes;

[0010] Step 3: Immerse the film dried in step 2 in 5ml-10ml H2SO4 solution for 10min-20min;

[0011] Step 4: Rinse the film in step 3 with deionized water 3-5 times to remove the residual H2SO4 solution;

[0012] Step 5: Immerse the film obtained in step 4 in 5ml-10ml KOH solution for 10min-20min;

[0013] Step 6: Rinse the film in step 5 with deionized water 3-5 times to remove the residual KOH solution;

[0014] Step 7: Dry on a hot plate at 100° C.-130° C. for 10 min-20 min to obtain a PEDOT:PSS film.

[0015] In a specific embodiment of the present invention, the PEDOT:PSS is Clevios PH1000 model.

[0016] In a specific embodiment of the present invention, the temperature of the heating plate is 50-100° C., and the film forming time is 20-25 minutes.

[0017] In a specific embodiment of the present invention, the thickness of the obtained film is 2-6 microns.

[0018] The positive progress of the present invention is that the method provided by the present invention for improving the thermoelectric properties of PEDOT:PSS thin films prepared by the ethanol gel film forming method through acid-base treatment has the following advantages: The greatest advantage of the present invention is that the thermoelectric properties of the film have been improved during the film forming process by adopting the ethanol gel film forming method, and further acid-base treatment is added to obtain a PEDOT:PSS film with higher thermoelectric performance. In this method, a novel and simple method for preparing PEDOT:PSS thin films is adopted. By post-treating the PEDOT:PSS film with H2SO4 solution and KOH solution, the TE performance of the PEDOT:PSS film is successfully improved. Compared with the prepared PEDOT:PSS, the power factor after treatment is significantly improved. The oxidation level that affects the TE performance of the PEDOT:PSS film can also be well adjusted by controlling the experimental conditions during the basic treatment. When the H2SO4 concentration is 15M (mol / l) and the KOH solution concentration is 1M (mol / l), the optimal thermoelectric power of the film is 37.1μW / mK 2 The conductivity and Seebeck coefficient of the PEDOT:PSS film were 314 S / cm and 34.0 μV / K, respectively. Compared to the untreated PEDOT:PSS film, its thermoelectric performance was enhanced by 68%. This improvement in TE performance is attributed to the synergistic effect of the high charge mobility achieved by the acid treatment and the optimal oxidation level adjusted by the base treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] To further illustrate the specific technical content, the present invention is described in detail below with reference to the accompanying drawings and embodiments, wherein:

[0020] Figure 1 It is a schematic diagram of each reaction step of the preparation method of the present invention.

[0021] Figure 2-1 This is a graph showing how acid and alkali treatment improves the thermoelectric properties of PEDOT:PSS films prepared by the ethanol gel film formation method (a curve showing the change in electrical conductivity of PEDOT:PSS films treated with different acid concentrations versus measurement temperature).

[0022] Figure 2-2 This is a graph showing how acid and alkali treatment improves the thermoelectric properties of PEDOT:PSS films prepared by the ethanol gel film formation method (a curve showing the change of the Seebeck coefficient of PEDOT:PSS films treated with different acid concentrations as a function of the measurement temperature).

[0023] Figure 2-3 This is a graph showing how acid and alkali treatment improves the thermoelectric performance of PEDOT:PSS films prepared by the ethanol gel film formation method (a curve showing the change in power factor of PEDOT:PSS films treated with different acid concentrations as a function of measurement temperature).

[0024] Figure 2-4This is a graph showing the improvement of the thermoelectric properties of PEDOT:PSS films prepared by the ethanol gel film formation method through acid and alkali treatment (the curve of the change of the electrical conductivity of the PEDOT:PSS film treated with H2SO4-KOH as a function of the measurement temperature).

[0025] Figure 2-5 This is a graph showing the improvement of the thermoelectric performance of PEDOT:PSS film prepared by the ethanol gel film formation method by acid and alkali treatment (curve of the Seebeck coefficient of PEDOT:PSS film treated with H2SO4-KOH versus measurement temperature).

[0026] Figure 2-6 This is a graph showing the improvement of the thermoelectric performance of PEDOT:PSS film prepared by the ethanol gel film formation method by acid and alkali treatment (the power factor of the PEDOT:PSS film treated with H2SO4-KOH changes with the measurement temperature).

[0027] Figure 3-1 This is the XRD pattern of PEDOT:PSS film prepared by acid-base treatment to enhance ethanol gel film formation (XRD pattern of acid-treated PEDOT:PSS film).

[0028] Figure 3-2 This is the XRD pattern of the PEDOT:PSS film prepared by the acid-base treatment to enhance the ethanol gel film formation method (the XRD pattern of the PEDOT:PSS film treated with H2SO4-KOH).

[0029] Figure 4 This is the XPS graph of the PEDOT:PSS film prepared by the ethanol gel film formation method after acid and alkali treatment. Among them: XPS is X-ray photoelectron spectroscopy analysis DETAILED DESCRIPTION

[0030] The preferred embodiments of the present invention are given below in conjunction with the accompanying drawings to illustrate the technical solutions of the present invention in detail.

[0031] See also Figure 1 As shown, the present invention provides a method for improving the thermoelectric properties of a PEDOT:PSS film prepared by an ethanol gel film forming method by acid-base treatment, comprising the following steps:

[0032] Step 1: Slowly and uniformly add 500 μL of PEDOT:PSS aqueous solution into anhydrous ethanol, and gel to form a PEDOT:PSS film after 20-25 minutes;

[0033] Step 2: Dry the PEDOT:PSS film obtained in step 1 on a hot plate at 100°C for 10 min;

[0034] Step 3: Immerse the dried film in 5 ml of H2SO4 solution for 10 min;

[0035] Step 4: Rinse the film three times with deionized water to remove the residual H2SO4 solution;

[0036] Step 5: Immerse the film obtained in step 4 in 5 ml of KOH solution for 10 minutes;

[0037] Step 6: Rinse the film three times with deionized water to remove the residual KOH solution;

[0038] Step 7: Dry on a hot plate at 100 °C for 10 min to obtain a PEDOT:PSS film.

[0039] Example 1

[0040] Use a pipette to slowly and evenly add 500 μL of the PEDOT:PSS solution to a beaker containing 10 mL of anhydrous ethanol. After 20–25 minutes, a PEDOT:PSS film forms on the bottom of the beaker. Remove the film and dry it on a hotplate at 100°C for 10 minutes. After drying, add 5 mL of a 1 M H₂SO₄ solution and continue drying for 10 minutes. Rinse the film three times with deionized water to remove any residual H₂SO₄ solution, then dry it on a hotplate at 100°C for 10 minutes to obtain a PEDOT:PSS film.

[0041] The 1M in the above 1M H2SO4 solution represents 1 mol / l, and the M after the numbers in the following examples all represent mol / l.

[0042] Example 2

[0043] Use a pipette to slowly and evenly add 500 μL of the PEDOT:PSS solution to a beaker containing 10 mL of anhydrous ethanol. After 20–25 minutes, a PEDOT:PSS film forms on the bottom of the beaker. Remove the film and dry it on a hotplate at 100°C for 10 minutes. After drying, add 5 mL of a 3 M H₂SO₄ solution and continue drying for 10 minutes. Rinse the film three times with deionized water to remove any residual H₂SO₄ solution, then dry it on a hotplate at 100°C for 10 minutes to obtain a PEDOT:PSS film.

[0044] Example 3

[0045] Use a pipette to slowly and evenly add 500 μL of PEDOT:PSS solution to a beaker containing 10 mL of anhydrous ethanol. After 20–25 minutes, a PEDOT:PSS film forms on the bottom of the beaker. Remove the film and dry it on a glass dish on a hotplate at 100°C for 10 minutes. After drying, add 5 mL of a 5 M H₂SO₄ solution and continue drying for 10 minutes. Rinse the film three times with deionized water to remove any residual H₂SO₄ solution and then dry it on a hotplate at 100°C for 10 minutes to obtain a PEDOT:PSS film.

[0046] Example 4

[0047] Use a pipette to slowly and evenly add 500 μL of the PEDOT:PSS solution to a beaker containing 10 mL of anhydrous ethanol. After 20–25 minutes, a PEDOT:PSS film forms on the bottom of the beaker. Remove the film and dry it on a hotplate at 100°C for 10 minutes. After drying, add 5 mL of a 7 M H₂SO₄ solution and continue drying for 10 minutes. Rinse the film three times with deionized water to remove any residual H₂SO₄ solution and then dry it on a hotplate at 100°C for 10 minutes to obtain a PEDOT:PSS film.

[0048] Example 5

[0049] Use a pipette to slowly and evenly add 500 μL of PEDOT:PSS solution to a beaker containing 10 mL of anhydrous ethanol. After 20–25 minutes, a PEDOT:PSS film forms on the bottom of the beaker. Remove the film and dry it on a glass dish on a hotplate at 100°C for 10 minutes. After drying, add 5 mL of 10 M H₂SO₄ solution for 10 minutes. Rinse the film three times with deionized water to remove any residual H₂SO₄ solution and then dry it on a hotplate at 100°C for 10 minutes to obtain a PEDOT:PSS film.

[0050] Example 6

[0051] Use a pipette to slowly and evenly add 500 μL of the PEDOT:PSS solution to a beaker containing 10 mL of anhydrous ethanol. After 20–25 minutes, a PEDOT:PSS film forms on the bottom of the beaker. Remove the film and dry it on a 100°C hotplate for 10 minutes. After drying, add 5 mL of a 13 M H₂SO₄ solution for 10 minutes. Rinse the film three times with deionized water to remove any residual H₂SO₄ solution and then dry it on a 100°C hotplate for 10 minutes to obtain a PEDOT:PSS film.

[0052] Example 7

[0053] Use a pipette to slowly and evenly add 500 μL of the PEDOT:PSS solution to a beaker containing 10 mL of anhydrous ethanol. After 20–25 minutes, a PEDOT:PSS film forms on the bottom of the beaker. Remove the film and dry it on a hotplate at 100°C for 10 minutes. After drying, add 5 mL of a 15 M H₂SO₄ solution and continue drying for 10 minutes. Rinse the film three times with deionized water to remove any residual H₂SO₄ solution, then dry it on a hotplate at 100°C for 10 minutes to obtain a PEDOT:PSS film.

[0054] Example 8

[0055] Use a pipette to slowly and evenly add 500 μL of the PEDOT:PSS solution to a beaker containing 10 mL of anhydrous ethanol. After 20–25 minutes, a PEDOT:PSS film forms on the bottom of the beaker. Remove the film and dry it on a glass dish on a hotplate at 100°C for 10 minutes. After drying, add 5 mL of an 18 M H₂SO₄ solution and continue drying for 10 minutes. Rinse the film three times with deionized water to remove any residual H₂SO₄ solution and then dry it on a hotplate at 100°C for 10 minutes to obtain a PEDOT:PSS film.

[0056] Example 9

[0057] Use a pipette to slowly and evenly add 500 μL of PEDOT:PSS solution to a beaker containing 10 ml of anhydrous ethanol. After 20-25 minutes, a PEDOT:PSS film forms on the bottom of the beaker. Remove the film and dry it on a hotplate at 100°C for 10 minutes. After drying, add 5 ml of 15 M H2SO4 solution for 10 minutes. Rinse the film three times with deionized water to remove any remaining H2SO4 solution. Then, immerse the film in 5 ml of 0.1 M KOH solution for 10 minutes. Rinse the film three times with deionized water to remove any remaining KOH solution. Dry the film on a hotplate at 100°C for 10 minutes to obtain a PEDOT:PSS film.

[0058] Example 10

[0059] Use a pipette to slowly and evenly add 500μL of PEDOT:PSS solution to a beaker containing 10ml of anhydrous ethanol. After 20-25 minutes, a PEDOT:PSS film forms on the bottom of the beaker. Remove the film and dry it on a hotplate at 100°C for 10 minutes. After drying, add 5ml of 15M H2SO4 solution for 10 minutes. Rinse the film three times with deionized water to remove any residual H2SO4 solution. Then, immerse the film in 5ml of 0.5M KOH solution for 10 minutes. Rinse the film three times with deionized water to remove any residual KOH solution. Dry the film on a hotplate at 100°C for 10 minutes to obtain a PEDOT:PSS film.

[0060] Example 11

[0061] Use a pipette to slowly and evenly add 500 μL of PEDOT:PSS solution to a beaker containing 10 ml of anhydrous ethanol. After 20–25 minutes, a PEDOT:PSS film forms on the bottom of the beaker. Remove the film and dry it on a 100°C hotplate for 10 minutes. After drying, add 5 ml of a 15 M H2SO4 solution for 10 minutes. Rinse the film three times with deionized water to remove any remaining H2SO4. Then, immerse the film in 5 ml of a 1 M KOH solution for 10 minutes. Rinse the film three times with deionized water to remove any remaining KOH solution. Dry the film on a 100°C hotplate for 10 minutes to obtain a PEDOT:PSS film.

[0062] Example 12

[0063] Use a pipette to slowly and evenly add 500 μL of PEDOT:PSS solution to a beaker containing 10 ml of anhydrous ethanol. After 20-25 minutes, a PEDOT:PSS film forms on the bottom of the beaker. Remove the film and dry it on a hotplate at 100°C for 10 minutes. After drying, add 5 ml of 15 M H2SO4 solution for 10 minutes. Rinse the film three times with deionized water to remove any remaining H2SO4 solution. Then, immerse the film in 5 ml of 5 M KOH solution for 10 minutes. Rinse the film three times with deionized water to remove any remaining KOH solution. Dry the film on a hotplate at 100°C for 10 minutes to obtain a PEDOT:PSS film.

[0064] Figure 2-1 This is a graph showing how acid and alkali treatment improves the thermoelectric properties of PEDOT:PSS films prepared by the ethanol gel film formation method (a curve showing how the conductivity of PEDOT:PSS films treated with different acid concentrations changes with the measurement temperature). Figure 2-2 This is a graph showing how acid and alkali treatment improves the thermoelectric properties of PEDOT:PSS films prepared by the ethanol gel film formation method (a curve showing the change of the Seebeck coefficient of PEDOT:PSS films treated with different acid concentrations as a function of the measurement temperature). Figure 2-3 This is a graph showing how acid and alkali treatment improves the thermoelectric performance of PEDOT:PSS films prepared by the ethanol gel film formation method (a curve showing the change in power factor of PEDOT:PSS films treated with different acid concentrations as a function of measurement temperature). Figure 2-4 This is a graph showing the improvement of the thermoelectric properties of PEDOT:PSS films prepared by the ethanol gel film formation method through acid and alkali treatment (the curve of the change of the electrical conductivity of the PEDOT:PSS film treated with H2SO4-KOH as a function of the measurement temperature). Figure 2-5 This is a graph showing the improvement of the thermoelectric performance of PEDOT:PSS film prepared by the ethanol gel film formation method by acid and alkali treatment (curve of the Seebeck coefficient of PEDOT:PSS film treated with H2SO4-KOH versus measurement temperature). Figure 2-6 This is a graph showing how acid and alkali treatment improves the thermoelectric performance of PEDOT:PSS film prepared by the ethanol gel film formation method (the power factor of the H2SO4-KOH-treated PEDOT:PSS film changes with the measured temperature). As can be seen from the above figure: by post-treating the PEDOT:PSS film with H2SO4 solution, the TE performance of the PEDOT:PSS film is successfully improved. Compared with the prepared PEDOT:PSS, the power factor is significantly improved after treatment. The oxidation level that affects the TE performance of the PEDOT:PSS film can also be well adjusted by controlling the experimental conditions during the basic treatment. When the H2SO4 concentration is 15M and the KOH solution concentration is 1M, the optimal thermoelectric power of the film is 37.1μW / mK 2 , the electrical conductivity and Seebeck coefficient are 314 S / cm and 34.0 μV / K, respectively. The improvement in TE performance is attributed to the synergistic effect of high charge mobility due to acid treatment and optimal oxidation level adjusted by alkali treatment.

[0065] Figure 3-1 This is the XRD pattern of the PEDOT:PSS film prepared by the acid-base treatment-enhanced ethanol gel film formation method (XRD pattern of acid-treated PEDOT:PSS film). Where: XRD is X-ray diffraction. Figure 3-2 The following is an XRD pattern of a PEDOT:PSS film prepared by the ethanol gel film formation method, enhanced by acid and base treatment (XRD pattern of a PEDOT:PSS film treated with H₂SO₄-KOH). XRD stands for X-ray diffraction. The figure shows that after H₂SO₄ treatment, the first diffraction peak increases in intensity, indicating a decrease in the stacking distance and improved crystallinity. After KOH treatment, a decrease in the intensity of the diffraction peak is observed, indicating a loss of the quinone-like characteristic and a more compact conformation of the PEDOT chains.

[0066] Figure 4 This is the XPS graph of a PEDOT:PSS film prepared by the ethanol gel film formation method using acid and alkali treatment. XPS stands for X-ray photoelectron spectroscopy. Figure 4 It shows that after ethanol film formation, the S 2P The XPS intensity increased significantly, indicating that the mass ratio of PSS to PEDOT decreased. 2P The XPS intensity increased further and the mass ratio of PSS to PEDOT decreased further, proving that ethanol film formation and H2SO4 treatment could remove excess PSS particles. However, no further changes were detected after the subsequent KOH treatment, and the mass ratio of PSS to PEDOT did not change, proving that KOH treatment could not further remove excess PSS particles. 2P There is a slight shift in binding energy. This 0.2 eV shift to lower binding energy stems from a decrease in the average oxidation level.

[0067] The basic principles, main features and advantages of the present invention are shown and described above. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention, which is defined by the appended claims and their equivalents.

Claims

1. A method for improving the thermoelectric properties of a PEDOT:PSS thin film prepared by an ethanol gel film formation method by acid-base treatment, characterized in that: The method adopts an ethanol gel film forming method to prepare a PEDOT:PSS film, which is achieved by one acid treatment and one alkali treatment; The method comprises the following steps: Step 1: slowly and uniformly add a PEDOT:PSS aqueous solution into anhydrous ethanol to form a PEDOT:PSS film through gel formation; Step 2: Dry the PEDOT:PSS film obtained in step 1 on a hot plate at 100°C-130°C for 10-20 minutes; Step 3: Immerse the film dried in step 2 in 5ml-10ml H2SO4 solution for 10min-20min; Step 4: Rinse the film in step 3 with deionized water 3-5 times to remove the residual H2SO4 solution; Step 5: Immerse the film obtained in step 4 in 5ml-10ml KOH solution for 10min-20min; Step 6: Rinse the film in step 5 with deionized water 3-5 times to remove the residual KOH solution; Step 7: Dry on a hot plate at 100° C.-130° C. for 10 min-20 min to obtain a PEDOT:PSS film.

2. The method for improving the thermoelectric properties of a PEDOT:PSS thin film prepared by an ethanol gel film forming method by acid-base treatment according to claim 1, characterized in that: The PEDOT:PSS is the Clevios PH1000 model.

3. The method for improving the thermoelectric properties of a PEDOT:PSS thin film prepared by an ethanol gel film-forming method by acid-base treatment according to claim 1, characterized in that: The thickness of the obtained film is 2-6 microns.

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