Preparation method and application of critical wetting diatom shale-based antibacterial and mildew-proof material

Abstract

The present application relates to the field of inorganic building material surface functionalization, and specifically discloses a method for preparing a critical-wetting diatomite shale-based antibacterial and mildew-resistant material and applications thereof. The method controls the metal salt solution and diatomite shale carrier to a critical-wetting state, so that the system is in a state of no visible free liquid phase and overall uniform wetting. Capillary action is used to drive metal ions into the carrier pores and achieve enrichment and deposition in the confined space. Subsequently, low-temperature calcination treatment in an air atmosphere generates metal oxides or elemental active phases in situ in the carrier pores and surface. The resulting material has uniformly dispersed active components, firm interface bonding, and excellent antibacterial and mildew-resistant performance, with an antibacterial rate of 100% for both gram-negative and gram-positive bacteria. The method has simple process, low cost, and good potential for large-scale production, and is suitable for the preparation of antibacterial and mildew-resistant coatings for the surfaces of building systems such as wood, engineered wood, wall materials, and decorative materials.

Description

Technical Field

[0001] This invention belongs to the field of surface functionalization of inorganic building materials, and relates to a method for preparing and applying a critically wettable diatomaceous earth-based antibacterial and antifungal material. Background Technology

[0002] As interior building materials develop towards green and functional directions, wood, engineered wood, and wall materials are prone to bacterial and mold growth in humid environments. This not only affects the mechanical properties and service life of the materials but may also release harmful metabolites, posing a potential threat to human health. Therefore, developing functional coating materials that combine long-term stability with highly effective antibacterial and anti-mold properties has become an important research direction in the field of building materials.

[0003] Currently, common antibacterial and antifungal strategies mainly rely on introducing inorganic components with antibacterial activity (such as zinc oxide, copper oxide, and nano-silver) into the matrix system. The choice of carrier material has a decisive influence on the dispersion state of the active components and the overall performance of the material. Commonly used porous carriers in existing technologies include diatomaceous earth and activated carbon. However, although diatomaceous earth has a naturally porous structure, it has a high impurity content and small, unevenly distributed pore size, which easily leads to the accumulation or even blockage of active components at the pore openings during loading. Therefore, it usually requires multiple pretreatment steps such as acid washing, ball milling, and high-temperature calcination to obtain clean pores (such as the diatomaceous earth-based formaldehyde-removing ceramic tile prepared by patent CN116751076A), resulting in complex processes, high energy consumption, and increased environmental burden. Furthermore, its mechanical strength is low, and it is prone to pulverization during processing and use, exhibiting insufficient stability. While activated carbon boasts a high specific surface area, its predominantly microporous pores hinder the effective loading and uniform distribution of nano-antibacterial particles. Furthermore, its dark appearance limits its application in light-colored coatings, and its production cost is relatively high. Therefore, finding a porous carrier with suitable pore size, stable structure, and controllable cost is a crucial issue that urgently needs to be addressed in this field. Diatomaceous earth shale, a natural porous mineral material formed from diatomite through long-term diagenesis, not only retains a rich, ordered pore structure but also possesses higher mechanical strength and thermal stability. Its pore size distribution, dominated by mesopores and macropores, is conducive to the uniform loading and spatially confined distribution of antibacterial active components. In addition, the surface of diatomaceous earth shale is rich in silanol groups, exhibiting good wettability and interfacial compatibility, making it an ideal alternative to traditional carriers such as diatomite and activated carbon.

[0004] In terms of specific implementation methods, existing technologies mostly employ impregnation, mechanical mixing, or calcination methods to introduce metal precursors or nanoparticles into porous carrier materials. For example, patent CN105494429A prepares a composite antibacterial and antifungal agent by mixing antibacterial metal salts, diatomaceous earth, and organic antifungal components, followed by centrifugation, filtration, dehydration, and grinding; patent CN105838158A uses a high-speed disperser to mechanically mix various additives, diatomaceous earth, zeolite powder, etc.; and patent CN105967641A prepares insect-resistant hollow clay bricks by calcining diatomaceous earth with calcium-magnesium slag and other materials at high temperatures through multiple steps. Although the above methods can achieve the loading of active components, they essentially rely on simple physical mixing or impregnation processes lacking controllability, making it difficult to effectively control the distribution of active substances in the carrier's pore structure. Specifically: Traditional impregnation methods typically rely on excess solution to saturate the carrier for adsorption. During solvent evaporation, metal ions tend to migrate with the solvent to the outer surface of the carrier, becoming concentrated and unable to penetrate the pores for spatially confined distribution. This leads to particle agglomeration during subsequent drying or calcination, reducing the utilization rate of active sites. Mechanical mixing methods only achieve physical stacking, lacking effective interfacial bonding between the active phase and the carrier. This results in easy detachment or migration during use, affecting the long-term stability of the material. High-temperature calcination (typically >1000℃) not only easily causes agglomeration and crystal transformation of active components, weakening antibacterial and antifungal activity, but also has high energy consumption, making it unsuitable for heat-sensitive organic-inorganic coating systems. Research shows that the spatial distribution of active components is controlled by the wetting behavior between the solution and the carrier. However, current research largely focuses on material selection, lacking effective control mechanisms for the key processes of how metal ions enter the carrier pores and achieve uniform distribution: when the solvent is excessive, a free liquid phase easily forms, leading to surface agglomeration; when the solvent is insufficient, uneven distribution occurs. For example, while the adsorption catalyst proposed in patent CN120438000A can effectively improve the catalytic conversion rate and waste gas absorption rate by loading inorganic non-metallic nanoparticles and metal oxide catalysts, the saturated adsorption formed by impregnation leads to complex post-treatment steps and easy particle agglomeration and uneven distribution. In contrast, the system under critical wetting conditions does not have a free liquid phase and maintains uniform wetting, which can effectively prevent solute from migrating to the outer surface of the support with the solvent. Therefore, how to achieve uniform distribution and stable loading of active components in the pore structure of the support while ensuring process simplicity is a technical problem that urgently needs to be solved in this field.

[0005] In view of this, the inventors of this application intend to provide a method for preparing and applying a critically wettable diatomaceous earth-based antibacterial and antifungal material. Summary of the Invention

[0006] The purpose of this invention is to address the problems existing in the prior art, and to provide a method for preparing and applying a critically wettable diatomaceous earth-based antibacterial and antifungal material. This method achieves a uniform and confined distribution of active components within the pores of the carrier by controlling the wetting state between the solution and the carrier, and generates a stable antibacterial active phase during subsequent heat treatment, thereby significantly improving the antibacterial and antifungal properties and durability of the material.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing and applying a critically wettable diatomaceous earth shale-based antibacterial and antifungal material, characterized by comprising the following steps:

[0009] Step 1: Dissolve the metal salt in deionized water and stir until it is fully dissolved to form a homogeneous solution, thus obtaining the metal salt solution.

[0010] Step 2: The metal salt solution is added dropwise to the diatom shale while continuously stirring to control the system to a critical wetting state, so that the solution is adsorbed by the carrier, the system has no visible free liquid phase, and the whole system is uniformly wetted; then the drying process is carried out to obtain the composite particle precursor.

[0011] Step 3: The composite particle precursor is calcined in a low-temperature air atmosphere to obtain diatomaceous earth shale-based antibacterial and antifungal material.

[0012] Furthermore, in step one, the metal salt has cations selected from one or more of zinc, copper, silver, manganese, cobalt, and magnesium, and anions selected from one or more of nitrate and chloride ions.

[0013] Furthermore, in step two, the mesh size of the diatom shale is 3000-20000 mesh.

[0014] Furthermore, the critical wetting state in step two is: the system has no visible free liquid phase, the whole system is uniformly wetted, and no macroscopic liquid flow occurs.

[0015] Furthermore, in step three, the low-temperature calcination temperature is not lower than 400℃, and the calcination time is 0.5-2h.

[0016] Furthermore, in order to make the system reach the critical wetting state, the ratio of metal salt, diatom shale and water is (5-10) g: (80-100) g: (30-50) mL.

[0017] The present invention also provides the use of a critically wettable diatomaceous earth shale-based antibacterial and antifungal material for the preparation of antibacterial and antifungal coatings on the surfaces of building systems such as wood, engineered wood, wall materials, and decorative materials.

[0018] The beneficial effects of this invention are as follows:

[0019] (1) This invention regulates the critical wetting state between the metal salt solution and diatomaceous earth shale, utilizing capillary action to drive the selective entry of metal ions into the pores of the carrier, thereby achieving spontaneous enrichment and confined distribution of active metal ions within the pores and preventing the accumulation of the solution on the outer surface of the carrier. This spatial confinement effect effectively inhibits the agglomeration of metal oxides or elemental active phases during drying and calcination, ensuring a high degree of dispersion of active particles, thus significantly improving the specific surface area of ​​the material and the utilization rate of antibacterial active sites.

[0020] (2) This invention uses a heat treatment process to transform the metal components in situ into metal oxides or elemental active phases within the carrier channels and on the surface. Since the active phase grows within the channels and is tightly bonded to the silica framework, this anchoring structure greatly enhances the chemical stability and mechanical durability of the material. In actual building environments, the antibacterial components are less prone to detachment, migration, or loss, overcoming the shortcomings of poor stability and short lifespan inherent in physical mixing methods, thus ensuring the long-term antifungal performance of the material.

[0021] (3) The diatomaceous earth shale used in this invention has porous adsorption properties, which can adsorb moisture in the air and promote the enrichment of microorganisms on the material surface, thereby enhancing the contact efficiency between the antibacterial active components and microorganisms. Combined with a uniformly loaded broad-spectrum antibacterial metal oxide or elemental active phase (such as zinc oxide, nano silver, etc.), a synergistic effect mechanism is formed. Experimental tests show that the obtained material has broad-spectrum antibacterial properties, with an antibacterial rate of 100% against both Gram-negative and Gram-positive bacteria; after being coated on the wood surface, it can still reach the highest level (level 0) anti-mildew standard under 28-day long-term culture conditions, showing potential for industrial application.

[0022] (4) The preparation process of this invention is simple and efficient, requiring only stirring and conventional calcination, without the need for additional reducing agents, surfactants, or complex pretreatment steps. The raw materials are widely available and inexpensive, the production process is environmentally friendly, and the cost is controllable. This facilitates the application of the material in existing building material production lines such as interior coatings and board processing, and it has good industrial application prospects and potential for large-scale production. Attached Figure Description

[0023] Figure 1 Scanning electron microscope images of the surface morphology of the diatomaceous earth antibacterial and antifungal materials prepared in Example 1 and Comparative Example 1. (a) is a morphology image of the material obtained in Comparative Example 1, and (b) is a morphology image of the material obtained in Example 1.

[0024] Figure 2 The images show the energy dispersive spectral distribution of the diatomaceous earth shale antibacterial and antifungal material prepared in Example 1. (a) is the elemental distribution diagram of Zn, and (b) is the elemental distribution diagram of Cu.

[0025] Figure 3 The X-ray diffraction patterns are those of the diatomaceous earth antibacterial and antifungal materials prepared in Example 1 and Comparative Example 2.

[0026] Figure 4 The figures show the experimental results of the antibacterial and antifungal properties of the diatomaceous earth antibacterial and antifungal materials prepared in Example 1 and Control Example 1. (a) is a photograph of a bacterial culture agar plate, (b) is the calculated antibacterial efficiency, (c) is a picture of the antifungal properties of the coated plate after 7 days of culture, and (d) is a picture of the antifungal properties of the coated plate after 28 days of culture. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings. The following embodiments are all implemented based on the technical solution of the present invention, and detailed implementation methods are given. However, the protection scope of the present invention is not limited to the following embodiments. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention. Unless otherwise specified, the raw materials and reagents in the embodiments have not undergone special treatment and are all commercially available products that can be used directly; all characterization equipment uses the instrument parameters recommended by the manufacturer.

[0028] Example 1: A method for preparing a critically wettable diatomaceous earth shale-based antibacterial and antifungal material, comprising the following steps:

[0029] S1: Weigh 4g Zn(NO3)2 and 4g Cu(NO3)2, add 40mL of deionized water and stir until completely dissolved to obtain a metal salt solution.

[0030] S2: The above metal salt solution was slowly added dropwise to 100g of diatomaceous earth shale while continuously stirring until the system reached the critical wetting state (i.e., no visible free liquid phase exists, the whole system is uniformly wetted, and there is no macroscopic liquid flow). The system was then dried overnight at 60℃ to obtain the composite particle precursor.

[0031] S3: The above composite particle precursor was calcined in air at 400°C for 30 minutes to obtain diatomaceous earth antibacterial and antifungal material loaded with ZnO-CuO.

[0032] Example 2: A method for preparing a critically wettable diatomaceous earth shale-based antibacterial and antifungal material, comprising the following steps:

[0033] S1: Weigh 2g AgNO3, 4g Zn(NO3)2 and 4g Cu(NO3)2, add 30mL of deionized water and stir until completely dissolved to obtain a metal salt solution.

[0034] S2: The above metal salt solution was slowly added dropwise to 80g of diatomaceous earth shale while continuously stirring until the system reached the critical wetting state. It was then dried overnight at 60℃ to obtain the composite particle precursor.

[0035] S3: The above composite particle precursor was calcined in air at 600°C for 60 min to obtain diatomaceous earth antibacterial and antifungal material loaded with Ag-ZnO-CuO.

[0036] Example 3: A method for preparing a critically wettable diatomaceous earth shale-based antibacterial and antifungal material, comprising the following steps:

[0037] S1: Weigh 3g CuCl2, add 25mL of deionized water and stir until completely dissolved to obtain metal salt solution 1.

[0038] S2: The above metal salt solution 1 was slowly added dropwise to 80g of diatomaceous earth shale while continuously stirring until the system reached the critical wetting state. It was then dried overnight at 60℃ to obtain composite particle precursor 1.

[0039] S3: Weigh 2g of AgNO3, add 25mL of deionized water and stir until completely dissolved to obtain metal salt solution 2.

[0040] S4: The above metal salt solution 2 is slowly added dropwise to the composite particle precursor 1 while continuously stirring until the system reaches the critical wetting state. Then, it is dried overnight at 60°C to obtain the composite particle precursor 2.

[0041] S5: The above composite particle precursor was calcined in air at 400°C for 120 min to obtain diatomaceous earth antibacterial and antifungal material loaded with Ag-CuO.

[0042] Verification experiments showed that Examples 1-3 can achieve confined load and antibacterial and antifungal properties under critical wetting conditions.

[0043] Compare with Example 1:

[0044] Diatom shale was calcined in air at 400℃ for 30 min to obtain a diatom shale control sample without active components.

[0045] Compare with Example 2:

[0046] (1) Weigh 4g Zn(NO3)2 and 4g Cu(NO3)2, add 40mL of deionized water and stir until completely dissolved. Dry overnight at 60℃ to obtain particulate precursor.

[0047] (2) The above-mentioned particulate precursor was calcined in air at 400°C for 30 min to obtain a ZnO-CuO antibacterial and antifungal material control sample.

[0048] Performance tests were conducted on Examples 1-3 and Comparative Examples 1-2, and the results are shown in Table 1:

[0049] 1. Antibacterial performance test

[0050] The antibacterial properties of the material were tested according to the standard "Test Method for Antibacterial Properties of Nano-Inorganic Materials (GB / T 21510-2024)". Escherichia coli (Gram-negative bacterium) and Staphylococcus aureus (Gram-positive bacterium) were selected to evaluate the antibacterial properties of the material.

[0051] (1) Test steps

[0052] Weigh 500 mg of the diatomaceous earth antibacterial and antifungal material prepared in Example 1 and Control Example 1 into Erlenmeyer flasks respectively, and add 5 mL of bacterial solution (concentration of 1×10⁻⁶). 5 Add CFU / mL and 95 mL of PBS to the conical flask and mix well. Incubate at 37°C for 4 hours. Then dilute the solution and plate it. Incubate the plate upside down on a shaker at 37°C overnight. Finally, count the colonies and calculate the antibacterial rate.

[0053] (2) Analysis of experimental results

[0054] The results are as follows Figure 4 As shown in (ab), compared with the blank control group and the materials prepared in Example 1, the antibacterial and antifungal material of diatomaceous earth prepared in Example 1 of the present invention achieved an antibacterial rate of 100% against Escherichia coli and Staphylococcus aureus.

[0055] 2. Anti-mildew performance test

[0056] The actual anti-mildew performance of the material was tested according to the standard "Test Method for Anti-mildew Resistance of Coating Film (GB / T 1741-2020)".

[0057] (1) Test steps

[0058] Preparation of coated panels: 10g of the diatomaceous earth shale antibacterial and antifungal materials prepared in Example 1 and Control Example 1 were weighed and placed in beakers. 5mL of deionized water and 2mL of white glue were added and stirred to initially obtain a viscous and uniform mixed coating. Subsequently, the coating was evenly applied to a 5×5cm dry sterile wooden board using a sterile brush and then dried.

[0059] Mold culture and apparatus setup: Mold plaques were collected and cultured on potato dextrose agar to extract spores and prepare a spore suspension. Then, 200 mL of saturated Na₂CO₃ solution was poured into a 500 mL beaker, and a foam plate ring was placed on top of the suspension to construct the anti-mold performance testing system.

[0060] Test procedure: A spore suspension was sprayed onto both sides of the coated board in a fume hood after UV sterilization. The coated board sprayed with mold spores was then placed in a pre-assembled device and incubated at 37 ℃. The mold growth on the coated board was recorded every 7 days.

[0061] (2) Analysis of experimental results

[0062] The results are as follows Figure 4 As shown in (cd), compared to fresh, sterile coated panels, the coated panels prepared with the material of Comparative Example 1 showed a large number of mold hyphae on the surface after 7 and 28 days, and the paint film color deteriorated. However, the coated panels coated with the diatomaceous earth antibacterial and antifungal material prepared in Example 1 of this invention showed no traces of mold growth on the surface, the paint film had an intact appearance, and the color and texture were consistent with the state without mold, meeting the 0-level evaluation requirements of GB / T 1741-2020, and exhibiting excellent antifungal performance.

[0063] In the embodiments and comparative examples of this invention:

[0064] Figure 1 The images show scanning electron microscope (SEM) images of the diatomaceous earth antibacterial and antifungal materials prepared in Example 1 and Comparative Example 1. As shown in the figures, compared to pure diatomaceous earth powder, the particles loaded under critical wetting confinement exhibit a clear pore distribution on their surface, and the nanoparticles are uniformly loaded. Figure 2 The image shown is an energy dispersive spectroscopy (EDS) image of the diatomaceous earth antibacterial and antifungal material prepared in Example 1, demonstrating the successful loading and uniform distribution of metal ions on the surface of the diatomaceous earth shale.

[0065] Figure 3 The X-ray diffraction (XRD) patterns of the antibacterial and antifungal materials prepared in Example 1 and Comparative Example 2 are shown. Due to the low content and high dispersion of the active component loaded on diatomaceous earth shale, only crystal faces belonging to diatomaceous earth shale were observed in Example 1, and no obvious characteristic diffraction peaks of ZnO and CuO were observed. Further analysis of the metal presence form in Comparative Example 2 revealed that the positions of the diffraction peaks in the patterns matched the standard cards for CuO (00-048-1548) and ZnO (00-036-1451), indicating the presence of the active metal oxide phase.

[0066] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing and applying a critically wettable diatomaceous earth shale-based antibacterial and antifungal material, characterized in that, Includes the following steps: Step 1: Dissolve the metal salt in deionized water and stir until it is fully dissolved to form a homogeneous solution, thus obtaining the metal salt solution; Step 2: The metal salt solution is added dropwise to the diatom shale while continuously stirring to control the system to a critical wetting state, so that the solution is adsorbed by the carrier, the system has no visible free liquid phase, and the whole system is uniformly wetted; then the drying process is carried out to obtain the composite particle precursor. Step 3: The composite particle precursor is calcined in a low-temperature air atmosphere to obtain diatomaceous earth shale-based antibacterial and antifungal material.

2. The method for preparing a critically wettable diatomaceous earth-based antibacterial and antifungal material according to claim 1, characterized in that, In step one, the metal salt has cations selected from one or more of zinc, copper, silver, manganese, cobalt, and magnesium, and anions selected from one or more of nitrate and chloride ions.

3. The method for preparing a critically wettable diatomaceous earth-based antibacterial and antifungal material according to claim 1, characterized in that, In step two, the diatomaceous earth shale has a mesh size of 3,000-20,000.

4. The method for preparing a critically wettable diatomaceous earth-based antibacterial and antifungal material according to claim 1, characterized in that, The critical wetting state in step two is: the system has no visible free liquid phase, the whole system is uniformly wetted, and no macroscopic liquid flow occurs.

5. The method for preparing a critically wettable diatomaceous earth-based antibacterial and antifungal material according to claim 1, characterized in that, In step three, the low-temperature calcination temperature is not lower than 400℃, and the calcination time is 0.5-2h.

6. The method for preparing a critically wettable diatomaceous earth-based antibacterial and antifungal material according to claim 1, characterized in that, The ratio of the metal salt, diatom shale and water used is (5-10) g: (80-100) g: (30-50) mL.

7. A critically wettable diatomaceous earth-based antibacterial and antifungal material according to any one of claims 1-6, characterized in that, Metal oxides or elemental active phases are uniformly distributed in the pores and surface of the support, and selectively enriched inside the pores to form a confined distribution structure.

8. The use of a critically wettable diatomaceous earth-based antibacterial and antifungal material according to any one of claims 1-7, characterized in that, The material is used to prepare antibacterial and antifungal coatings for building systems such as wood, engineered wood, wall materials, and decorative materials.

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