Method for preparing a coating using diatom frustules and applications thereof

Abstract

The application provides a method for preparing a coating layer by using diatom shells and application, comprising the following steps: 1, adding distilled water into diatom mud or diatom dry powder, adjusting pH value by using strong acid, and then standing to obtain precipitate, centrifuging and washing the obtained precipitate to obtain primary diatom shells; 2, digesting or calcining the primary diatom shells to remove organic matter to obtain inorganic diatom shells; 3, mixing the inorganic diatom shells or the primary diatom shells with anhydrous ethanol and ammonia water to obtain diatom shell sol; and 4, coating the diatom shell sol on the surface of a substrate and heat treating to obtain a coating layer. The application utilizes the porous structure, large specific surface area and high light trapping efficiency of diatom shells, and prepares diatom shell sol by using diatom mud or diatom dry powder as raw material to form a coating layer on a substrate, without the need of complex pretreatment and modification steps, so that the coating layer has high light transmittance, hydrophobic characteristics, good antireflection effect, and is widely applied to solar cells, automobile, greenhouse and building glass.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, specifically to a method for preparing coatings using diatom shells and its application. Background Technology

[0002] Diatoms are a type of single-celled microorganism with chloroplasts. As primary producers in aquatic bodies, they are widely distributed and abundant in rivers, lakes, and oceans. The diatom shell is highly siliceous, possessing a nanoporous structure and a large specific surface area, making it a type of natural biomineralized silicon material. Diatom shells are currently the only known naturally produced nanomaterial; their structure is complex and precise, with silicon dioxide as its basic component. Diatom shells possess the strength of glass, and combined with their porous, pore-within-pore nanostructure, they exhibit excellent toughness and elasticity.

[0003] In recent years, numerous developments and applications of diatomaceous earth shells have emerged, but most remain in the laboratory stage due to complex processes. Patent CN201910976417.4 discloses a system and method for the industrial production of diatomaceous earth shells, laying the foundation for the widespread application of this new material. Patents CN202211622325.4 and CN201810658576.5 respectively disclose methods for using modified diatomaceous earth shells as adsorbents to separate and purify bioactive substances, and methods for rapidly coagulating red blood cells. These applications are all based on the porous structure of diatomaceous earth shells, which offer high adsorption capacity and separation efficiency. However, due to the complexity of pretreatment and modification processes in these applications, large-scale application is not yet feasible.

[0004] It is worth noting that, based on the porous structure of diatom shells, diatom cells can efficiently capture light energy even in deep water, providing energy for cell reproduction. Based on the principle of biomimicry, biomineralized silicon derived from diatoms, i.e., diatom shells, has an inherent advantage in efficiently capturing light energy, making it a promising substrate for anti-reflective coatings. Currently, anti-reflective and anti-reflective coatings play a significant role in improving the solar energy utilization efficiency of photovoltaic panels and are a research hotspot. Existing technologies mostly use industrially produced silica nanoparticles to prepare anti-reflective and anti-reflective coatings. Patents CN201110250081.7 and 201210562795.6 disclose anti-reflective and anti-reflective coatings prepared using solid and hollow industrial silica nanoparticles, respectively, achieving good results. Compared with industrially produced silica nanoparticles, diatom shells have a complex porous structure and a large specific surface area, clearly giving them an advantage in efficiently capturing light. The use of diatom shells for coating preparation is currently a technological gap. Therefore, there is a need for a diatomaceous earth shell material that can meet the application requirements of efficiently capturing light energy when applied to the surface of substrates such as glass. Summary of the Invention

[0005] This invention provides a method and application for preparing a coating using diatom shells. The preparation method is simple and can be applied on a large scale in industry. The coating prepared using diatom shells has high light transmittance and is inherently hydrophobic, with strong anti-reflective and anti-transmittance properties.

[0006] This invention provides a method for preparing a coating using diatom shells, comprising the following steps:

[0007] Step 1: Add distilled water to diatom cell mud or dried diatom cell powder to obtain a first turbid liquid with a concentration of 0.01-0.05 g / ml; adjust the pH of the first turbid liquid with strong acid, let it stand for 5-12 h, centrifuge and wash the obtained first precipitate, collect and dry it to obtain primary diatom shells.

[0008] Step 2: Digest or calcine the primary diatom shells to remove organic matter and obtain inorganic diatom shells;

[0009] Step 3: Mix inorganic diatom shells or primary diatom shells with anhydrous ethanol to obtain a second turbid liquid with a concentration of 0.02-0.05 g / ml. Mix ammonia water with the second turbid liquid evenly to obtain diatom shell sol.

[0010] Step 4: Apply diatomaceous earth sol to the surface of the substrate and heat-treat at 60-150℃ for 5-15 hours to obtain the coating.

[0011] Specifically, the diatom cell slurry or dried diatom cell powder mentioned in step 1 is prepared from any one of the following: photosynthetically cultured *Phaeodactylum tricornutum*, *Cyclocarya paliurus*, *Rhomboidella*, or *Cyclocarya circinata*.

[0012] Specifically, the strong acid mentioned in step 1 is any one of hydrochloric acid, sulfuric acid, or phosphoric acid; the pH adjustment is to adjust the pH value to 1.8-2.3.

[0013] Specifically, in step 2, the digestion process involves adding nitrohydrochloric acid to the primary diatom shell to obtain a first composite solution with a concentration of 0.05-0.15 g / ml. The first composite solution is then heated in an oven at 120-160°C for 0.2-4 hours to produce a second precipitate. The second precipitate is then washed and dried to obtain inorganic diatom shells.

[0014] Specifically, in step 2, the calcination process involves placing the primary diatom shells in a calcination furnace and calcining them at a temperature of 500℃-1200℃ for 1-4 hours to obtain inorganic diatom shells.

[0015] Specifically, in step 3, ammonia water and the second turbid liquid are mixed at a volume ratio of (3-5):100.

[0016] Specifically, the diatomaceous earth sol obtained in step 3 is further modified by heating the diatomaceous earth sol to 60°C in a fume hood to remove ammonia, thereby obtaining a second composite liquid. Tetraethyl orthosilicate and the second composite liquid are mixed at a volume ratio of (2-3):100 and stirred at 60°C for 12 hours to obtain the modified diatomaceous earth sol.

[0017] Specifically, the substrate mentioned in step 4 is either glass or a solar panel.

[0018] The present invention also provides an application of the coating obtained by the above method in solar cells, automobiles, and buildings.

[0019] The beneficial effects of this invention are as follows:

[0020] (1) This invention makes full use of the natural porous structure, large specific surface area and efficient light-trapping characteristics of diatom shells. Diatom shell sol is prepared by using diatom cell mud or dried diatom cell powder as raw materials and forming a coating on the substrate by spraying. This preparation method does not require complicated pretreatment and modification steps and can be applied on a large scale in industry, thus broadening the large-scale application of diatom biomineralized silicon.

[0021] (2) The coating prepared by the present invention has high light transmittance and has hydrophobic properties. The coating has good anti-reflection effect and can be applied to solar cells, automobiles, greenhouses and building windows to effectively improve the light-catching effect of the glass. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art are within the scope of protection of the present invention.

[0023] Example 1

[0024] Dried diatom cell powder was obtained from 3μm rhomboid algae cultured using photosynthetic polyculture. 1g of the dried diatom powder was added to 100ml of distilled water to obtain a first turbid solution. The pH of the first turbid solution was adjusted to 2.1 using hydrochloric acid. After stirring for 1 hour and standing for 8 hours, the resulting precipitate was centrifuged and washed. The precipitate was collected and dried to obtain primary diatom shells. 0.5g of primary diatom shells were mixed with 10ml of anhydrous ethanol, and 0.5ml of ammonia was added and mixed thoroughly to obtain diatom shell sol. The diatom shell sol was sprayed onto the surface of a clean borosilicate glass slide measuring 2.5cm × 2.5cm and heat-treated at 120℃ for 8 hours to obtain coating a.

[0025] The method for cleaning borosilicate glass slides is as follows: Cut a glass slide of 2.5cm × 2.5cm, immerse it in a 0.5wt% sodium hydroxide solution and ultrasonically clean it for 30 minutes. Then, rinse it three times with glass cleaner to remove stains from the glass surface. Finally, rinse it with deionized water until no water streams remain or water droplets form. Finally, dry the glass slide with nitrogen gas for later use, obtaining a clean borosilicate glass slide.

[0026] Example 2

[0027] Diatom cell slurry was obtained from photosynthetically autotrophic culture of rhomboid algae with a cell size of 3 μm. 5 g of dried diatom cell slurry was added to 100 ml of distilled water to obtain a first turbid liquid. The pH of the first turbid liquid was adjusted to 2 using hydrochloric acid. After stirring for 1 h, the mixture was allowed to stand for 12 h. The resulting precipitate was centrifuged and washed, collected, and dried to obtain primary diatom shells. The primary diatom shells were placed in a calcination furnace and calcined at 800 °C to obtain inorganic diatom shells. 3 g of inorganic diatom shells were mixed with 100 ml of anhydrous ethanol, and then 4 ml of ammonia was added and mixed thoroughly to obtain a diatom shell sol. The diatom shell sol was sprayed onto the surface of a clean borosilicate glass slide measuring 2.5 cm × 2.5 cm and heat-treated at 150 °C for 6 h to obtain coating b.

[0028] Example 3

[0029] Diatom cell slurry was obtained from photosynthetically autotrophic culture of *Nyctaginosa* with a cell size of 3 μm. 4 g of dried diatom cell slurry was added to 100 ml of distilled water to obtain a first turbid liquid. The pH of the first turbid liquid was adjusted to 1.8 using hydrochloric acid. After stirring for 1 h and standing for 5 h, the resulting precipitate was centrifuged and washed. The precipitate was collected and dried to obtain primary diatom shells. 2 g of primary diatom shells were added to 15 ml of nitrohydrochloric acid and heated in an oven at 140 °C for 2 h. The precipitate was repeatedly washed with water and then dried to obtain... To obtain inorganic diatomaceous earth shells; mix 3g of inorganic diatomaceous earth shells with 100ml of anhydrous ethanol, then add 3ml of ammonia water and mix evenly to obtain diatomaceous earth shell sol; place the diatomaceous earth shell sol in a fume hood and heat to 50℃ to remove ammonia, then quickly add 3ml of tetraethyl orthosilicate to the mixed solution, maintain the temperature and stir for 12h to obtain modified diatomaceous earth shell sol; spray the modified diatomaceous earth shell sol onto the surface of a clean borosilicate glass sheet with dimensions of 2.5cm×2.5cm, and heat treat at 120℃ for 13h to obtain coating c.

[0030] Example 4

[0031] Dried diatom cell powder was obtained from 3μm rhomboid algae cultured using photosynthetic polyculture. 2g of the dried diatom powder was added to 100ml of distilled water to obtain a first turbid solution. The pH of the first turbid solution was adjusted to 2.3 using hydrochloric acid. After stirring for 1 hour, the solution was allowed to stand for 10 hours. The resulting precipitate was centrifuged and washed, collected, and dried to obtain primary diatom shells. 10ml of nitrohydrochloric acid was added to 2g of primary diatom shells, and the solution was heated at 120℃ for 4 hours. The resulting precipitate was repeatedly washed with water and dried to obtain inorganic diatom shells. 1 Inorganic diatom shells were mixed with 100 ml of anhydrous ethanol, and then 3 ml of ammonia was added and mixed evenly to obtain a diatom shell sol. The diatom shell sol was placed in a fume hood and heated to 70°C to remove ammonia. Then, 2.5 ml of tetraethyl orthosilicate was quickly added to the mixed solution, and the mixture was stirred for 12 h while maintaining the temperature to obtain a modified diatom shell sol. The surface of the diatom shell sol was further modified with a low surface energy substance. The modified diatom shell sol was sprayed onto the surface of a clean borosilicate glass slide with dimensions of 2.5 cm × 2.5 cm and heat-treated at 80°C for 8 h to obtain the d coating.

[0032] Example 5

[0033] Dry diatom cell powder was obtained from 2μm cells of *Cyclocarya scoparia* obtained through photosynthetic co-culture. 100ml of distilled water was added to 1g of the dried diatom powder to obtain a first turbid solution. The pH of the first turbid solution was adjusted to 2.1 using hydrochloric acid. After stirring for 1 hour and standing for 8 hours, the resulting precipitate was centrifuged and washed. The precipitate was collected and dried to obtain primary diatom shells. 0.5g of primary diatom shells were mixed with 10ml of anhydrous ethanol, and 0.5ml of ammonia was added and mixed thoroughly to obtain diatom shell sol. The diatom shell sol was sprayed onto the surface of a clean borosilicate glass slide measuring 2.5cm × 2.5cm and heat-treated at 120℃ for 8 hours to obtain the e-coating.

[0034] Example 6

[0035] Diatom cell slurry was obtained from photosynthetically autotrophic culture of *Cyclocarya scoparia* with a cell size of 2 μm. 5 g of dried diatom cell slurry was added to 100 ml of distilled water to obtain a first turbid liquid. The pH of the first turbid liquid was adjusted to 2 using hydrochloric acid. After stirring for 1 h and standing for 12 h, the resulting precipitate was centrifuged and washed. The precipitate was collected and dried to obtain primary diatom shells. The primary diatom shells were placed in a calcination furnace and calcined at 800 °C to obtain inorganic diatom shells. 3 g of inorganic diatom shells were mixed with 100 ml of anhydrous ethanol, and then 4 ml of ammonia was added and mixed thoroughly to obtain diatom shell sol. The diatom shell sol was sprayed onto the surface of a clean borosilicate glass slide measuring 2.5 cm × 2.5 cm and heat-treated at 150 °C for 6 h to obtain the f coating.

[0036] Example 7

[0037] Diatom cell slurry was obtained from photosynthetically autotrophic culture of *Cyclocarya scoparia* with a cell size of 2 μm. 4 g of dried diatom cell slurry was added to 100 ml of distilled water to obtain a first turbid liquid. The pH of the first turbid liquid was adjusted to 1.8 using hydrochloric acid. After stirring for 1 h, the mixture was allowed to stand for 5 h. The resulting precipitate was centrifuged and washed, and the precipitate was collected and dried to obtain primary diatom shells. 2 g of primary diatom shells were added to 15 ml of nitrohydrochloric acid and heated in an oven at 140 °C for 2 h. The precipitate was repeatedly washed with water and then dried to obtain... To obtain inorganic diatomaceous earth shells; mix 3g of inorganic diatomaceous earth shells with 100ml of anhydrous ethanol, then add 3ml of ammonia water and mix evenly to obtain diatomaceous earth shell sol; place the diatomaceous earth shell sol in a fume hood and heat to 50℃ to remove ammonia, then quickly add 3ml of tetraethyl orthosilicate to the mixed solution, maintain the temperature and stir for 12h to obtain modified diatomaceous earth shell sol; spray the modified diatomaceous earth shell sol onto the surface of a clean borosilicate glass sheet with dimensions of 2.5cm×2.5cm, and heat treat at 120℃ for 13h to obtain g coating.

[0038] Example 8

[0039] Dry diatom cell powder was obtained from *Cyclocarya scoparia* with a cell size of 2 μm obtained through photosynthetic co-culture. 2 g of the dried diatom powder was added to 100 ml of distilled water to obtain a first turbid solution. The pH of the first turbid solution was adjusted to 2.3 using hydrochloric acid. After stirring for 1 h and standing for 10 h, the resulting precipitate was centrifuged and washed. The precipitate was collected and dried to obtain primary diatom shells. 10 ml of nitrohydrochloric acid was added to 2 g of primary diatom shells, and the mixture was heated at 120 °C for 4 h in an oven. The resulting precipitate was repeatedly washed with water and dried to obtain inorganic diatom shells. 1 Inorganic diatom shells were mixed with 100 ml of anhydrous ethanol, and then 3 ml of ammonia was added and mixed evenly to obtain a diatom shell sol. The diatom shell sol was placed in a fume hood and heated to 70°C to remove ammonia. Then, 2.5 ml of tetraethyl orthosilicate was quickly added to the mixed solution, and the mixture was stirred for 12 h while maintaining the temperature to obtain a modified diatom shell sol. The surface of the diatom shell sol was further modified with a low surface energy substance. The modified diatom shell sol was sprayed onto the surface of a clean borosilicate glass slide with dimensions of 2.5 cm × 2.5 cm and heat-treated at 80°C for 8 h to obtain the h coating.

[0040] Comparative Example 1

[0041] Industrial hollow silica of the same size as the primary diatom shells prepared in Example 1 was selected as raw material to prepare a SiO2 coating. The specific steps are as follows: 3g of SiO2 particles were mixed with 100ml of anhydrous ethanol, and then 4ml of ammonia water was added and mixed evenly to obtain SiO2 sol; the SiO2 sol was sprayed onto the surface of a clean borosilicate glass sheet with a size of 2.5cm×2.5cm, and heat-treated at 150℃ for 6h to obtain the SiO2 coating.

[0042] Comparative Example 2

[0043] Cut a 2.5cm x 2.5cm glass slide, clean it thoroughly, and you will get a clean borosilicate glass slide with no coating.

[0044] Performance testing

[0045] The contact angle was measured using a KrussEasydrop DSA 20 optical video contact angle meter (Germany); the visible light transmittance was measured using a Specord plus UV meter (Germany) manufactured by Jena Instruments (Germany).

[0046] -Measured by a visible spectrophotometer.

[0047] Contact angle test: Water droplets were dropped onto the glass surfaces with diatomaceous earth coatings of Examples 1-8, respectively. Water droplets were also dropped onto the SiO2-coated glass surface of Comparative Example 1 and the uncoated glass surface of Comparative Example 2. The contact angle of the water droplets was tested at at least three different locations, and the average value was taken as the contact angle value of the glass surface.

[0048] Transmittance test: The transmittance of the glass substrate with the anti-reflection and anti-reflection superhydrophobic coating was determined using the transmittance mode, with a scanning range of 200-2500 nm.

[0049] The test results are shown in the table below:

[0050] Table 1. Contact angle and transmittance of glass slide surfaces in different embodiments / comparative examples.

[0051] Examples / Comparative Examples Diatom types Coating type Contact angle (°) Transmittance (%) Example 1 Nitzschia Primary diatom shell coating 153 92 Example 2 Nitzschia Inorganic diatom shell coating 135 95 Example 3 Nitzschia Modified diatom shell coating 150 93 Example 4 Nitzschia Modified diatom shell coating 157 96 Example 5 Round sieve algae Primary diatom shell coating 155 95 Example 6 Round sieve algae Inorganic diatom shell coating 158 94 Example 7 Round sieve algae Modified diatom shell coating 140 98 Example 8 Round sieve algae Modified diatom shell coating 160 95 Comparative Example 1 - Silica coating 125 90 Comparative Example 2 - Uncoated 45 83

[0052] As can be seen from the table above, the coatings prepared in Examples 1-8 all exhibit transparency exceeding 90%, with a maximum transmittance of 98% and a water contact angle exceeding 150°, reaching a maximum of 96%. This demonstrates excellent transparency and superhydrophobicity, possessing anti-reflective and anti-reflective properties, and efficiently capturing light energy. Compared to glass with silica coatings and uncoated glass, their hydrophobicity and light transmittance are significantly improved. Furthermore, the coating preparation method in this invention is simple, effective, and easy to apply to large-area substrates. These advantages allow diatomaceous earth coatings to be widely used in automotive glass, solar panels, greenhouses, and windows of tall buildings.

[0053] The above are merely embodiments of this application and are not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing a coating using diatomaceous earth shells, comprising the following steps: Step 1: Add distilled water to diatom cell slurry or dried diatom cell powder to obtain a first turbid solution with a concentration of 0.01-0.05 g / ml; After adjusting the pH of the first turbid liquid with strong acid, let it stand for 5-12 hours, centrifuge and wash the resulting first precipitate, collect and dry it to obtain primary diatom shells. Step 2: Digest or calcine the primary diatom shells to remove organic matter and obtain inorganic diatom shells; Step 3: Mix inorganic diatom shells or primary diatom shells with anhydrous ethanol to obtain a second turbid liquid with a concentration of 0.02-0.05 g / ml. Mix ammonia water with the second turbid liquid evenly to obtain diatom shell sol. Step 4: Apply diatomaceous earth sol to the surface of the substrate and heat-treat at 60-150℃ for 5-15 hours to obtain the coating. In step 1, the diatom cell slurry or dried diatom cell powder is prepared from any one of the following: photosynthetically cultured *Phaeodactylum tricornutum*, *Cyclophora microphylla*, *Rhomboidella*, or *Cyclophora circinata*. The strong acid mentioned in step 1 is any one of hydrochloric acid, sulfuric acid, or phosphoric acid; the pH adjustment is to adjust the pH value to 1.8-2.3; In step 3, ammonia water and the second turbid liquid are mixed at a volume ratio of (3-5):

100.

2. The method according to claim 1, characterized in that, In step 2, the digestion process involves adding nitrohydrochloric acid to the primary diatom shell to obtain a first composite solution with a concentration of 0.05-0.15 g / ml. The first composite solution is then heated in an oven at 120-160℃ for 0.2-4 hours to produce a second precipitate. The second precipitate is then washed and dried to obtain inorganic diatom shells.

3. The method according to claim 1, characterized in that, In step 2, the calcination process involves placing the primary diatom shells in a calcination furnace and calcining them at a temperature of 500℃-1200℃ for 1-4 hours to obtain inorganic diatom shells.

4. The method according to claim 1, characterized in that, The diatomaceous earth sol obtained in step 3 is further modified by heating the diatomaceous earth sol to 60°C in a fume hood to remove ammonia, thereby obtaining a second composite liquid. Tetraethyl orthosilicate and the second composite liquid are mixed at a volume ratio of (2-3):100 and stirred at 60°C for 12 hours to obtain the modified diatomaceous earth sol.

5. The method according to claim 1, characterized in that, The substrate mentioned in step 4 can be either glass or a solar panel.

6. An application of a coating obtained by the method of claim 1 in solar cells, automobiles, and buildings.