A linear high-polysilane reinforced wear-resistant and anti-reflective coating and its preparation method

Abstract

This invention belongs to the field of coating technology, specifically relating to a linear high-polysilane-reinforced wear-resistant antireflective coating and its preparation method. Using tetraethyl orthosilicate and methyltriethoxysilane / methyltrimethoxysilane as co-precursors, an alkaline network silica sol is synthesized under alkaline conditions via a sol-gel method. Using poly(methylhydrosiloxane) as the silicon source, a linear high-polysiloxane sol is synthesized under the action of a catalyst. The two silica sols are then mixed, aged, and ammonia-removed to obtain a neutral mixed sol. A double-sided antireflective coating is then deposited on a borosilicate glass surface using an dip-coating method. Finally, the coating is calcined in a muffle furnace at 550°C for 2 hours to obtain the wear-resistant antireflective coating. The prepared antireflective coating exhibits high transmittance and good wear resistance. The preparation process avoids the use of acid, preventing corrosion of production equipment and environmental pollution, making the production operation green and environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a linear high-polysilane reinforced wear-resistant and anti-reflective coating and its preparation method. Background Technology

[0002] Mechanical stability is crucial for antireflective coatings during manufacturing, installation, maintenance, and cleaning. Generally, alkali-catalyzed silica coatings exhibit excellent transmittance, but because silica particles are randomly stacked only with point contact forces, they are susceptible to mechanical scratches, making them easy to remove.

[0003] On the other hand, acid-catalyzed silica antireflective coatings consist of strongly cross-linked linear chains, providing strong adhesion to the substrate. However, the linear chain structure results in low porosity, leading to high refractive index and poor transmittance. Therefore, neither base-catalyzed nor acid-catalyzed coatings can simultaneously provide excellent transmittance and high abrasion resistance.

[0004] The traditional solution combines the advantages of alkaline-catalyzed and acid-catalyzed antireflective coatings, providing good transmittance and mechanical stability.

[0005] Rubing Xi et al. prepared a coating with high mechanical stability (3H pencil scratch test) by dipping in a mixed suspension composed of acid-catalyzed silica sol and hydrophobic silica nanoparticles. The coating showed an average transmittance increase of 4.0% in the wavelength range of 400–800 nm, but the pH of the acid catalysis process was 1–2.

[0006] CN 108455872 B discloses a method for preparing a scratch-resistant hydrophobic antireflective coating. The hybrid sol is formed by cross-linking and hybridizing hydrophobically modified hollow spherical silica nanoparticles with a hydrophilic inorganic nano-binder. The transmittance curve of the prepared hydrophobic antireflective coating remains basically unchanged before and after 1000 cycles of rinsing test, but the pH value is 0.1 to 5 during the preparation process.

[0007] Chen Jinglei prepared acid-catalyzed silica sol and alkali-catalyzed silica sol by sol-gel method, and prepared acid-alkali composite catalyzed silica sol by mixing them in a volume ratio of 1:5. The antireflection coating prepared by dip-coating method had a maximum transmittance of about 99% in the visible light region. After repeatedly rubbing the coated glass with a cotton ball soaked in alcohol 100 times, the transmittance only decreased slightly (<1%). The pH of the acid sol was 2-3.

[0008] In addition, Fangting Chi et al. improved the mechanical durability of silica coatings through ammonia treatment. To obtain a nano-coating, they synthesized two different sizes of silica nanoparticles and then deposited them on a glass substrate. An ammonia atmosphere was generated by placing 50 mL of ammonia water in a 5 L sealed glass container. The hardness of the coating increased with increasing ammonia treatment time. The coating's average transmittance remained essentially unchanged after ammonia treatment, as demonstrated by the 2H pencil hardness test. However, the ammonia treatment process requires a large amount of ammonia water, which can also be harmful to the environment.

[0009] To enhance the mechanical stability of antireflective coatings, a traditional method involves mixing acid-catalyzed linear silica sol as a binder with an alkaline adhesive. However, the acid-catalyzed process requires large amounts of acids such as hydrochloric acid, which can corrode production equipment and pose significant environmental risks during industrial production. Therefore, developing a method for preparing robust antireflective coatings under neutral conditions is both desirable and challenging. Summary of the Invention

[0010] To address the technical problems identified in the background section, this invention provides a linear high-polysilane-reinforced wear-resistant and anti-reflective coating and its preparation method: An alkaline network silica sol is prepared via a sol-gel method. Using poly(methylhydrosiloxane) as the silicon source, a linear high-polysilane sol is synthesized under the action of a catalyst. The alkaline network silica sol and the linear high-polysilane sol are mixed according to the mass ratio of SiO2 in the alkaline sol to PMHS used in the linear high-polysilane sol. After aging, the linear high-polysilane sol and the network silica sol combine, crosslink, and fill the spaces between silica network nanoparticles. Then, a double-layer coating is simultaneously deposited on both sides of the glass using an dip-coating method. After calcination in a muffle furnace, the wear-resistant and anti-reflective coating is obtained.

[0011] The main steps of the preparation method are as follows:

[0012] (1) Using anhydrous ethanol (EtOH) as solvent, ammonia (NH4OH) as catalyst, and tetraethyl orthosilicate (TEOS) and methyltriethoxysilane (MTES) / methyltrimethoxysilane (MSDS) as silicon sources, an alkaline network silica sol was prepared by vigorous stirring in an oil bath at 60°C for 12 h using the sol-gel method, and then aged.

[0013] Among them, Si 总 The molar ratio of (TEOS / MTES), EtOH, NH4OH and H2O is 1:47.25:0.88:3.67, and the molar ratio of MTES to TEOS or MSDS is 0.25 to 0.75:1.

[0014] Linear high-polysilicon sol was prepared by using anhydrous ethanol (EtOH) as solvent, Karstedt as catalyst, and poly(methylhydrosiloxane) (PMHS) as silicon source, with stirring at 25°C for 5 min and ultrasonication in a water bath for 30 min.

[0015] The volumetric mass ratio of EtOH, Karstedt catalyst, and PMHS is 1:0.001:2.

[0016] (2) Alkaline network silica sol and linear high-polymer silica sol are mixed according to the mass ratio of SiO2 in the alkaline sol to PMHS used in the linear high-polymer silica sol; after aging for 4 days, the mixed sol is placed in an open fume hood and vigorously stirred to remove ammonia. After removing ammonia, the solvent is added until the mass is equal to that before removing ammonia.

[0017] The mass ratio of SiO2 in the alkaline network silica sol to PMHS used in the linear high-polymer silica sol is 1:1 to 1:5.

[0018] (3) The mixed sol was deposited onto the glass substrate by dip-coating method, and then placed in a muffle furnace at 550°C for 2 hours.

[0019] The impregnation and lifting speed of the mixed sol was 600–1000 μm / s, the impregnation time was 360 s, the impregnation was repeated twice, and the residence time was 120 s.

[0020] The advantages of this invention compared to the prior art are:

[0021] 1. The alkaline network silica sol is prepared by the sol-gel method. The preparation process is simple and easier to apply. Furthermore, the sol-gel method is carried out at room temperature and atmospheric pressure, and high-performance and low-cost coatings can be prepared without complicated equipment.

[0022] 2. The use of poly(methylhydrosiloxane) to form linear high polysilanes acts as a binder, avoiding the use of acid. The resulting mixed sol has a pH of 7, making the production operation environmentally friendly and preventing corrosion of production equipment and environmental pollution.

[0023] 3. The alkaline network nanoparticles provide high porosity for the coating, which is essential for antireflective coatings. Due to the large number of hydroxyl groups on the surface of the network silica nanoparticles, the side chain groups in the linear high-polysilicon sol will replace the hydroxyl groups on the surface of the network silica nanoparticles, increasing the degree of cross-linking between particles. When the concentration of the linear high-polysilicon sol increases to a certain level, the linear chain linear high-polysilicon sol and the network silica nanoparticles are fully cross-linked, which can improve the mechanical properties of the coating and increase its wear resistance.

[0024] 4. A double-layer coating was deposited on both sides of the glass substrate using the dip-coating method. The deposited coating surface was smooth and uniform. Experimental results showed that the coating of the mixed sol of alkaline network silica sol and linear high-polymer silica sol had an average light transmittance of 97.21% and had an anti-reflection effect.

[0025] 5. The coating obtained by this invention combines anti-reflective properties with wear resistance. Its average light transmittance can reach 97.21%. According to ISO158184 standard, when the coating is tested with a 3H pencil, no scratches are observed on the surface under a microscope. When tested with a 4H pencil, scratches are observed on the surface of the coating under a microscope, indicating that the coating hardness reaches 3H. After 1000 rubs with an alcohol cotton ball, the average light transmittance is still as high as 96.25%. Attached image description:

[0026] Figure 1 This is a transmission electron microscope image of the silica nanoparticles obtained in Example 2 of the present invention.

[0027] Figure 2 This is a scanning electron microscope cross-sectional image of the coating obtained in Example 2 of the present invention.

[0028] Figure 3 This is a microscopic image of the coating hardness obtained in Example 2 of the present invention after testing. Detailed Implementation

[0029] The present invention will be further described below with reference to embodiments, but is not limited thereto.

[0030] Example 1

[0031] (1) Using anhydrous ethanol as solvent, ammonia as catalyst, tetraethyl orthosilicate and methyltriethoxysilane as silicon sources, alkaline network silica sol was prepared by sol-gel method and vigorous stirring in an oil bath at 60°C for 12 hours.

[0032] Among them, Si 总 The molar ratio of (TEOS / MTES), EtOH, NH4OH and H2O is 1:47.25:0.88:3.67, of which the molar ratio of MTES to TEOS is 0.5:1;

[0033] Linear high-polysilicon sol was prepared by using anhydrous ethanol as solvent, Karstedt as catalyst, and poly(methylhydrosiloxane) as silicon source, with stirring at 25°C for 5 min and ultrasonication in a water bath for 30 min.

[0034] The volumetric mass ratio of EtOH, Karstedt catalyst, and PMHS is 1:0.001:2.

[0035] (2) The alkaline network silica sol and the linear high-polymer silica sol were mixed at a mass ratio of 1:1 between SiO2 in the alkaline sol and PMHS used in the linear high-polymer silica sol. After aging for 4 days, the sol was placed in an open fume hood and vigorously stirred to remove ammonia. After removing ammonia, the solvent was added until the mass was equal to that before removing ammonia, and a uniform and stable mixed sol was obtained. The pH of the mixed sol was measured to be 7.

[0036] (3) The coating was prepared by dip-coating method with a dipping speed of 900 μm / s, a dipping time of 360 s, and two dipping cycles with a dwell time of 120 s. The coating was then calcined in a muffle furnace at 550℃ for 2 h to obtain a wear-resistant anti-reflective coating. The average transmittance of the coating in the visible light range was measured to be 94.78%. According to ISO 158184 standard, when tested with an H pencil, no scratches were observed under a microscope. However, when tested with a 2H pencil, scratches were observed under a microscope, indicating that the coating hardness reached H. After 1000 rubs with an alcohol cotton ball, the average transmittance was 93.26%.

[0037] Example 2

[0038] (1) Using anhydrous ethanol as solvent, ammonia as catalyst, tetraethyl orthosilicate and methyltriethoxysilane as silicon sources, alkaline network silica sol was prepared by sol-gel method and vigorous stirring in an oil bath at 60°C for 12 hours.

[0039] Among them, Si 总 The molar ratio of (TEOS / MTES), EtOH, NH4OH and H2O is 1:47.25:0.88:3.67, of which the molar ratio of MTES to TEOS is 0.5:1;

[0040] Linear high-polysilicon sol was prepared by using anhydrous ethanol as solvent, Karstedt as catalyst, and poly(methylhydrosiloxane) as silicon source, with stirring at 25°C for 5 min and ultrasonication in a water bath for 30 min.

[0041] The volumetric mass ratio of EtOH, Karstedt catalyst, and PMHS is 1:0.001:2.

[0042] (2) The alkaline network silica sol and the linear high-polymer silica sol were mixed at a mass ratio of 1:4 between SiO2 in the alkaline sol and PMHS used in the linear high-polymer silica sol. After aging for 4 days, the sol was placed in an open fume hood and stirred vigorously to remove ammonia. After removing ammonia, the solvent was added until the mass was equal to that before removing ammonia, and a uniform and stable mixed sol was obtained. The pH of the mixed sol was measured to be 7.

[0043] (3) The coating was prepared using an dip-coating method with a dipping speed of 900 μm / s, a dipping time of 360 s, and two dipping cycles with a dwell time of 120 s. The coating was then calcined in a muffle furnace at 550℃ for 2 hours to obtain a wear-resistant and anti-reflective coating. The average transmittance of the coating in the visible light range was measured to be 97.21%. Figure 3 As shown, according to the ISO158184 standard, when the coating is tested with a 3H pencil, no scratches are observed on the surface under a microscope. When tested with a 4H pencil, scratches are observed on the surface of the coating under a microscope, indicating that the coating hardness reaches 3H. After 1000 rubs with an alcohol cotton ball, the average light transmittance is 96.25%.

[0044] Example 3

[0045] (1) Using anhydrous ethanol as solvent, ammonia as catalyst, tetraethyl orthosilicate and methyltriethoxysilane as silicon sources, alkaline network silica sol was prepared by sol-gel method and vigorous stirring in an oil bath at 60°C for 12 hours.

[0046] The molar ratio of total Si (TEOS / MTES), EtOH, NH4OH and H2O is 1:47.25:0.88:3.67, and the molar ratio of MTES to TEOS is 0.5:1.

[0047] Linear high-polysilicon sol was prepared by using anhydrous ethanol as solvent, Karstedt as catalyst, and poly(methylhydrosiloxane) as silicon source, with stirring at 25°C for 5 min and ultrasonication in a water bath for 30 min.

[0048] The volumetric mass ratio of EtOH, Karstedt catalyst, and PMHS is 1:0.001:2.

[0049] (2) The alkaline network silica sol and the linear high-polymer silica sol were mixed at a mass ratio of 1:5 between SiO2 in the alkaline sol and PMHS used in the linear high-polymer silica sol. After aging for 4 days, the sol was placed in an open fume hood and stirred vigorously to remove ammonia. After removing ammonia, the solvent was added until the mass was equal to that before removing ammonia, and a uniform and stable mixed sol was obtained. The pH of the mixed sol was measured to be 7.

[0050] (3) The coating was prepared by dip-coating method with a dipping speed of 900 μm / s and a dipping time of 360 s. The dipping was repeated twice with a dwell time of 120 s. The coating was then calcined in a muffle furnace at 550℃ for 2 h to obtain a wear-resistant and anti-reflective coating. The average transmittance of the coating in the visible light range was measured to be 96.53%. According to ISO158184 standard, the coating was tested with a 3H pencil, and no scratches were observed on the surface under a microscope. However, when tested with a 4H pencil, scratches were observed on the surface of the coating under a microscope, indicating that the coating hardness reached 3H. After 1000 rubs with an alcohol cotton ball, the average transmittance was 95.62%.

[0051] Example 4

[0052] (1) Using anhydrous ethanol as solvent, ammonia as catalyst, tetraethyl orthosilicate and methyltriethoxysilane as silicon sources, alkaline network silica sol was prepared by sol-gel method and vigorous stirring in an oil bath at 60°C for 12 hours.

[0053] Among them, Si 总 The molar ratio of (TEOS / MTES), EtOH, NH4OH and H2O is 1:47.25:0.88:3.67, of which the molar ratio of MTES to TEOS is 0.25:1;

[0054] Linear high-polysilicon sol was prepared by using anhydrous ethanol as solvent, Karstedt as catalyst, and poly(methylhydrosiloxane) as silicon source, with stirring at 25°C for 5 min and ultrasonication in a water bath for 30 min.

[0055] The volumetric mass ratio of EtOH, Karstedt catalyst, and PMHS is 1:0.001:2.

[0056] (2) The alkaline network silica sol and the linear high-polymer silica sol were mixed at a mass ratio of 1:4 between SiO2 in the alkaline sol and PMHS used in the linear high-polymer silica sol. After aging for 4 days, the sol was placed in an open fume hood and stirred vigorously to remove ammonia. After removing ammonia, the solvent was added until the mass was equal to that before removing ammonia, and a uniform and stable mixed sol was obtained. The pH of the mixed sol was measured to be 7.

[0057] (3) The coating was prepared by dip-coating method with a dipping speed of 900 μm / s and a dipping time of 360 s. The dipping was repeated twice with a dwell time of 120 s. The coating was then calcined in a muffle furnace at 550℃ for 2 h to obtain a wear-resistant and anti-reflective coating. The average transmittance of the coating in the visible light range was measured to be 96.37%. According to ISO158184 standard, the coating was tested with a 3H pencil, and no scratches were observed on the surface under a microscope. However, when tested with a 4H pencil, scratches were observed on the surface of the coating under a microscope, indicating that the coating hardness reached 3H. After 1000 rubs with an alcohol cotton ball, the average transmittance was 95.41%.

[0058] Example 5

[0059] (1) Using anhydrous ethanol as solvent, ammonia as catalyst, tetraethyl orthosilicate and methyltriethoxysilane as silicon sources, alkaline network silica sol was prepared by sol-gel method and vigorous stirring in an oil bath at 60°C for 12 hours.

[0060] Among them, Si 总 The molar ratio of (TEOS / MTES), EtOH, NH4OH and H2O is 1:47.25:0.88:3.67, of which the molar ratio of MTES to TEOS is 0.75:1;

[0061] Using anhydrous ethanol as solvent, Karstedt catalyst as catalyst, and poly(methylhydrosiloxane) as silicon source, a linear high-polysilicon sol was prepared by sol-gel method, stirring at 25℃ for 5 min and ultrasonication in a water bath for 30 min.

[0062] The volumetric mass ratio of EtOH, Karstedt catalyst, and PMHS is 1:0.001:2.

[0063] (2) The alkaline network silica sol and the linear high-polymer silica sol were mixed at a mass ratio of 1:4 between SiO2 in the alkaline sol and PMHS used in the linear high-polymer silica sol. After aging for 4 days, the sol was placed in an open fume hood and stirred vigorously to remove ammonia. After removing ammonia, the solvent was added until the mass was equal to that before removing ammonia, and a uniform and stable mixed sol was obtained. The pH of the mixed sol was measured to be 7.

[0064] (3) The coating was prepared by dip-coating method with a dipping speed of 900 μm / s, a dipping time of 360 s, and two dipping cycles with a dwell time of 120 s. The coating was then calcined in a muffle furnace at 550℃ for 2 h to obtain a wear-resistant anti-reflective coating. The average transmittance of the coating in the visible light range was measured to be 95.97%. According to ISO158184 standard, when tested with a 3H pencil, no scratches were observed under a microscope. However, when tested with a 4H pencil, scratches were observed under a microscope, indicating that the coating hardness reached 3H. After 1000 rubs with an alcohol cotton ball, the average transmittance was 94.82%.

[0065] Example 6

[0066] (1) Using anhydrous ethanol as solvent, ammonia as catalyst, tetraethyl orthosilicate and methyltrimethoxysilane as silicon sources, alkaline network silica sol was prepared by sol-gel method and vigorous stirring in an oil bath at 60°C for 12 hours.

[0067] Among them, Si 总 The molar ratio of (TEOS / MTES), EtOH, NH4OH and H2O is 1:47.25:0.88:3.67, of which the molar ratio of MTMS to TEOS is 0.5:1;

[0068] Using anhydrous ethanol as solvent, Karstedt catalyst as catalyst, and poly(methylhydrosiloxane) as silicon source, a linear high-polysilicon sol was prepared by sol-gel method, stirring at 25℃ for 5 min and ultrasonication in a water bath for 30 min.

[0069] The volumetric mass ratio of EtOH, Karstedt catalyst, and PMHS is 1:0.001:2.

[0070] (2) The alkaline network silica sol and the linear high-polymer silica sol were mixed at a mass ratio of 1:4 between SiO2 in the alkaline sol and PMHS used in the linear high-polymer silica sol. After aging for 4 days, the sol was placed in an open fume hood and stirred vigorously to remove ammonia. After removing ammonia, the solvent was added until the mass was equal to that before removing ammonia, and a uniform and stable mixed sol was obtained. The pH of the mixed sol was measured to be 7.

[0071] (3) The coating was prepared by dip-coating method with a dipping speed of 900 μm / s and a dipping time of 360 s. The dipping was repeated twice with a dwell time of 120 s. The coating was then calcined in a muffle furnace at 550℃ for 2 h to obtain a wear-resistant and anti-reflective coating. The average transmittance of the coating in the visible light range was measured to be 96.45%. According to ISO158184 standard, the coating was tested with a 3H pencil, and no scratches were observed on the surface under a microscope. However, when tested with a 4H pencil, scratches were observed on the surface of the coating under a microscope, indicating that the coating hardness reached 3H. After 1000 rubs with an alcohol cotton ball, the average transmittance was 95.51%.

[0072] Comparative Example 1

[0073] (1) The alkaline network silica sol was prepared in the same way as in Example 1. After aging for 2 days, the sol was placed in an open fume hood and stirred vigorously to remove ammonia. After removing ammonia, the solvent was added until the mass was equal to that before removing ammonia, and a uniform and stable mixed sol was obtained.

[0074] (2) The coating was prepared by dip-coating method with a dipping speed of 2000 μm / s and a dipping time of 360 s. Then, it was calcined in a muffle furnace at 550℃ for 2 h to obtain an anti-reflective coating. The average transmittance of the coating in the visible light range was measured to be 98.75%. According to ISO158184 standard, the coating was tested with a 5B pencil. Microscopic observation showed obvious scratches on the surface, indicating that the coating hardness was <5B. After three rubs with an alcohol cotton ball, the coating peeled off.

[0075] Comparative Example 2

[0076] (1) Using anhydrous ethanol as solvent, concentrated hydrochloric acid as catalyst, tetraethyl orthosilicate as silicon source, and deionized water, acidic silica sol was prepared by sol-gel method and aged.

[0077] The molar ratio of Si, EtOH, HCl, and H2O is 1:36:0.17:4.62, and the aging time is 4 days.

[0078] (2) The alkaline network silica sol (same as in Example 1) and the acidic silica sol were mixed at a SiO2 molar ratio of 8:2 and aged for 4 days to obtain a uniform and stable mixed sol. The pH of the mixed sol was measured to be 2.

[0079] (3) The coating was deposited using the dip-coating method with a dipping speed of 3000 μm / s and a dipping time of 360 s. It was then calcined in a muffle furnace at 550℃ for 2 h to obtain a wear-resistant and anti-reflective coating. The average transmittance of the coating in the visible light range was measured to be 98.29%. According to ISO 158184 standard, when tested with a 2H pencil, no scratches were observed under a microscope. However, when tested with a 3H pencil, scratches were observed under a microscope, indicating that the coating hardness reached 2H. After 1000 rubs with an alcohol cotton ball, the average transmittance was 95.36%.

[0080] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A linear high-polymer silane-reinforced wear-resistant and anti-reflective coating, characterized in that, The preparation method of the wear-resistant and anti-reflective coating is as follows: (1) Anhydrous ethanol (EtOH) was used as a solvent, ammonia (NH4OH) was used as a catalyst, and tetraethyl orthosilicate (TEOS) and methyltriethoxysilane (MTES) / methyltrimethoxysilane (MTMS) were used as silicon sources to prepare alkaline network silica sol by sol-gel method. Linear high-polysilicon sol was prepared by sol-gel method using anhydrous ethanol (EtOH) as solvent, Karstedt as catalyst, and poly(methylhydrosiloxane) PMHS as silicon source. (2) Weigh out alkaline network silica sol and linear high-polymer silica sol, mix them, age them, remove ammonia, and prepare a stable and uniform mixed sol; (3) The mixed sol obtained in step (2) is deposited onto the glass substrate by dip-coating method, and then placed in a muffle furnace for calcination to obtain a wear-resistant and anti-reflective coating.

2. The wear-resistant and anti-reflective coating as described in claim 1, characterized in that: In step (1), an alkaline network silica sol is prepared by vigorous stirring in an oil bath at 60°C for 12 hours.

3. The wear-resistant and anti-reflective coating as described in claim 1, characterized in that: In step (1), the linear high-polysilicon sol is prepared by stirring at 25°C for 5 min and then sonicating in a water bath for 30 min.

4. The wear-resistant and anti-reflective coating as described in claim 1, characterized in that: In step (2), the mass ratio of SiO2 in the alkaline network silica sol to PMHS used in the linear high-polymer silica sol is 1:1 to 1:

5.

5. The wear-resistant and anti-reflective coating as described in claim 1, characterized in that: In step (3), the impregnation and lifting speed of the mixed sol is 600-1000 μm / s, the impregnation time is 360s, the impregnation is repeated twice, the residence time is 120s, and the calcination is carried out in a muffle furnace at 550℃ for 2h.

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