A sheet-like nano zinc oxide and its preparation method

Abstract

This invention relates to a sheet-like nano-zinc oxide and its preparation method. The method includes reacting a zinc salt with a precipitant to generate a precipitate under the action of a dispersant; wherein the dispersant includes trimethylolethane. The preparation method of the sheet-like nano-zinc oxide according to one embodiment of this invention is simple in procedure, does not require high-temperature hydrothermal treatment or calcination, and can obtain sheet-like nano-zinc oxide without the addition of complex morphology control agents. Furthermore, the product is easy to clean.

Description

Technical Field

[0001] This invention relates to nano zinc oxide, and more particularly to a sheet-like nano zinc oxide and its preparation method. Background Technology

[0002] The structure and morphology of nanomaterials have a significant impact on their performance and applications. Therefore, the preparation of nanomaterials with specific structures is of great academic and practical value for developing new areas of nanomaterial performance. Nano zinc oxide is a novel inorganic nanomaterial with high functionality and high added value. It possesses photosensitive, electrical, and magnetic properties not found in many other materials. It can absorb and scatter ultraviolet light and achieve catalytic effects, and has been applied in photocatalysis, thermistors, piezoelectric materials, gas sensing, sun protection, and antibacterial applications.

[0003] Flake-shaped nano-zinc oxide is a zinc oxide powder material with a special morphology. This powder is easy to disperse, has good transparency, feels good on the skin, exhibits minimal whitening, and provides good UV shielding, making it particularly advantageous for use in sunscreens. Furthermore, nano-zinc oxide itself has antibacterial properties, and the extremely thin flake-shaped nano-zinc oxide, with its sharp edges, can cut bacteria upon contact, thereby enhancing its antibacterial effect. Therefore, the controlled preparation of flake-shaped nano-zinc oxide is increasingly attracting the attention of researchers.

[0004] There are many existing methods for preparing nano-zinc oxide, commonly used methods include liquid-phase precipitation, microemulsion method, chemical vapor deposition, sol-gel method, and hydrothermal synthesis method. Methods for controlling the formation of sheet-like nano-zinc oxide can be broadly divided into two types: one is to prepare it by adding various organic / inorganic morphology control agents during the crystallization process of nano-zinc oxide; the problem with this method is that some morphology control agents are not easy to clean. The other method is to first synthesize a zinc compound precursor, and then obtain sheet-like nano-zinc oxide through hydrothermal or calcination methods; the problem with this method is that the process is complex and energy-intensive.

[0005] Specifically, for example, patent application CN105293567A discloses a method for preparing porous sheet-like nano-zinc oxide. This method requires adding sodium citrate as a template agent, using zinc salt and urea as reactants, generating a precursor under hydrothermal action, and then calcining it at 400-600℃ for 4-6 hours to obtain sheet-like zinc oxide. This preparation process is complex and energy-intensive. Another example is patent application CN101811727A, which discloses a method for low-temperature controlled synthesis of sheet-like nano-zinc oxide. This method uses alkyl polyoxyethylene ether, cyclohexane, n-octanol, and water to prepare a microemulsion, and then uses sodium hydroxide and zinc acetate as raw materials to prepare nano-zinc oxide within the microemulsion system. This method uses a large amount of template agent in the synthesis process, and the synthesized product is difficult to clean, easily leading to waste. Summary of the Invention

[0006] To overcome at least one of the defects of the prior art, one embodiment of the present invention provides a method for preparing sheet-like nano zinc oxide, comprising reacting zinc salt with a precipitant to generate a precipitate under the action of a dispersant; wherein the dispersant comprises trimethylolethane.

[0007] According to one embodiment of the present invention, the dispersant comprises diammonium hydrogen phosphate.

[0008] According to one embodiment of the present invention, the mass ratio of the diammonium hydrogen phosphate to the trimethylolpropane is 1:(3.5-5).

[0009] According to one embodiment of the present invention, the method includes:

[0010] Provide the first solution;

[0011] Adding a second solution dropwise to the first solution yields a third solution; and

[0012] The precipitant is added to the third solution;

[0013] The first solution comprises the zinc salt and trimethylolethane, and the second solution comprises diammonium hydrogen phosphate.

[0014] According to one embodiment of the present invention, in the first solution, the concentration of the zinc salt is 30-100 mM, and the mass content of the trimethylolethane is 1-5%.

[0015] According to one embodiment of the present invention, in the second solution, the concentration of the diammonium hydrogen phosphate is 20-25 mM; and / or,

[0016] After the precipitant is added to the third solution, the pH of the system is 8.5 to 9.5.

[0017] According to one embodiment of the present invention, the method includes freeze-drying the precipitate to obtain the sheet-like nano zinc oxide.

[0018] According to one embodiment of the present invention, the zinc salt comprises zinc acetate.

[0019] According to one embodiment of the present invention, the precipitant includes ammonia.

[0020] On the other hand, one embodiment of the present invention provides a sheet-like nano zinc oxide, which is prepared by the above-described method.

[0021] The method for preparing sheet-like nano zinc oxide according to one embodiment of the present invention is simple in steps, does not require high-temperature hydrothermal treatment or calcination, and can obtain sheet-like nano zinc oxide without adding complex morphology control agents. At the same time, the product is easy to clean.

[0022] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0023] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention.

[0024] in:

[0025] Figures 1A to 1C Here is a SEM image of the sheet-like zinc oxide nanoparticles from Example 1;

[0026] Figure 2 The image shows the XRD pattern of the sheet-like zinc oxide nanoparticles from Example 1.

[0027] Figure 3 The image shows the ultraviolet spectrum of the sheet-like zinc oxide nanoparticles from Example 1.

[0028] Figure 4 The infrared spectrum of the sheet-like zinc oxide nanoparticles in Example 1;

[0029] Figure 5 Here is a SEM image of the sheet-like zinc oxide nanoparticles from Example 2;

[0030] Figure 6A , 6B Here is a SEM image of the sheet-like zinc oxide nanoparticles from Example 3;

[0031] Figure 7 Here is a SEM image of the sheet-like zinc oxide nanoparticles from Example 4;

[0032] Figure 8 This is a SEM image of the sheet-like zinc oxide nanoparticles in Comparative Example 2.

[0033] Figure 9 The graph shows the bacterial growth of Escherichia coli and Staphylococcus aureus (hereinafter referred to as S. aureus) after 24 hours of incubation with aqueous solutions of different concentrations of the sheet-like nano zinc oxide used in Example 1.

[0034] Figure 10 The survival rate of bacteria after 24 hours of incubation of Escherichia coli and Staphylococcus aureus with aqueous solutions of different concentrations of the sheet-like nano zinc oxide used in Example 1.

[0035] Figure 11 SEM image of DXN-HQ20T sheet-like zinc oxide nanoparticles from Application Example 2;

[0036] Figure 12A This is a graph showing the bacterial growth of the zinc oxide sample prepared in Example 1 of Application Example 2;

[0037] Figure 12B This is a diagram showing the bacterial growth of the DXN-HQ20T sheet-like zinc oxide sample in Application Example 2. Detailed Implementation

[0038] The preferred embodiments of the present invention will be described in detail below. The accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0039] One embodiment of the present invention provides a method for preparing sheet-like nano zinc oxide, comprising reacting zinc salt with a precipitant under the action of a dispersant to generate zinc hydroxide precipitate, and the precipitate being dried to convert into zinc oxide; wherein the dispersant includes trimethylolethane.

[0040] In one embodiment, the dispersant includes diammonium hydrogen phosphate and trimethylolpropane. Further, the mass ratio of diammonium hydrogen phosphate to trimethylolpropane can be 1:(3.5-5), for example 1:3.8, 1:4, 1:4.2, 1:4.5, or 1:4.8.

[0041] In one embodiment, the mass ratio of zinc salt to trimethylolethane can be 1:(1.3 to 3), for example 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, or 1:2.8.

[0042] In one embodiment, the zinc salt may be one or more of zinc acetate, zinc chloride, zinc sulfate, and zinc nitrate.

[0043] In one embodiment, the precipitant may be ammonia water, and the molar ratio of ammonia water to zinc salt in the ammonia water is (4-10):1, for example 5:1, 6:1, 7:1, 8:1, or 9:1.

[0044] The method for preparing sheet-like nano zinc oxide according to one embodiment of the present invention includes:

[0045] Provide the first solution;

[0046] Adding the second solution dropwise to the first solution yields the third solution; and

[0047] Add the precipitant to the third solution;

[0048] The first solution comprises zinc salt and trimethylolethane, and the second solution comprises diammonium hydrogen phosphate.

[0049] In one embodiment, the solvents of the first solution, the second solution, and the third solution can all be water; for example, the second solution can be an aqueous solution of diammonium hydrogen phosphate.

[0050] In one embodiment, the concentration of the zinc salt in the first solution is 30–100 mM, for example 35 mM, 40 mM, 45 mM, 50 mM, 60 mM, 70 mM, 80 mM, 90 mM, or 95 mM; and the mass content of trimethylolethane is 1–5%, for example 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or 4.5%.

[0051] In one embodiment, the preparation process of the first solution includes: mixing a zinc salt or a zinc-containing solid with water to prepare a zinc salt aqueous solution; and

[0052] Trimethylolethane was added to an aqueous solution of zinc salt to prepare the first solution.

[0053] In one embodiment, the concentration of diammonium hydrogen phosphate in the second solution is 20–25 mmol / L, for example, 21 mmol / L, 22 mmol / L, 23 mmol / L, or 24 mmol / L.

[0054] In one embodiment, the reaction temperature between the zinc salt and the precipitant can be 18–20°C, for example 19°C; preferably, the reaction is carried out under ultrasonic treatment.

[0055] In one embodiment, the first solution is ultrasonically treated at 18–20°C. During the ultrasonic treatment, a second solution is added dropwise to the first solution to obtain a third solution. Then, ammonia is added dropwise to the third solution to adjust the pH of the system to 8.5–9.5, for example, 9. A pH range of 8.5–9.5 allows the prepared nano-zinc oxide to have better morphology and size, further enhancing the nano-size effect of the nano-zinc oxide particles.

[0056] In one embodiment, after adding the precipitant to the third solution, the system reacts at a temperature of 18–20°C for 1–12 hours, for example, 2 hours, 3 hours, 5 hours, 6 hours, 8 hours, or 10 hours. After the reaction is complete, the system can be allowed to stand and age for 3–24 hours, for example, 5 hours, 6 hours, 8 hours, 10 hours, 11 hours, 12 hours, 13 hours, 15 hours, 16 hours, 18 hours, 20 hours, or 22 hours. The continued reaction after adding the precipitant and the standing aging further ensure the complete growth of zinc hydroxide crystals.

[0057] In one embodiment, the precipitate obtained after the reaction is washed, for example by centrifugation, and then freeze-dried to obtain sheet-like zinc oxide nanoparticles. Centrifugation can remove residues on the zinc oxide nanoparticles after the reaction, and freeze-drying can remove moisture from the crystals while protecting the crystal structure of the nanoparticles.

[0058] In one embodiment, existing processes can be used for freeze drying, such as freezing at -30°C and vacuuming at -30°C for 60 hours.

[0059] One embodiment of the present invention further provides a sheet-like nano zinc oxide, which is prepared by the above method.

[0060] In one embodiment, the width of the sheet-like nano zinc oxide can be 1 to 2 μm, which refers to the length of a small dimension on a plane perpendicular to the thickness direction; the thickness can be less than 20 nm.

[0061] The method for preparing sheet-like nano zinc oxide according to one embodiment of the present invention is simple in steps, does not require high-temperature hydrothermal treatment or calcination, and can obtain sheet-like nano zinc oxide without adding complex morphology control agents. At the same time, the product is easy to clean.

[0062] The method for preparing sheet-like nano-zinc oxide according to one embodiment of the present invention uses a lower temperature during the reaction process to inhibit the excessive growth of zinc oxide crystals and reduce the size of zinc oxide crystals; in addition, the reaction is always carried out under ultrasonic conditions, which weakens the aggregation effect of zinc oxide nanoparticles.

[0063] The preparation of sheet-like nano zinc oxide according to an embodiment of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0064] Example 1

[0065] Preparation of the first solution: Add 1.83g of zinc acetate dihydrate powder to 250mL of water to prepare a 33.4mM zinc acetate salt solution; after the zinc acetate powder is completely dissolved, add 1wt% (percentage relative to the zinc acetate solution) of trimethylolethane to the zinc acetate solution.

[0066] Preparation of the second solution: Add 0.66g of diammonium hydrogen phosphate powder to 250mL of water to prepare a 20mM diammonium hydrogen phosphate solution.

[0067] Place the beaker containing the first solution into an ultrasonic bath at 18–20°C. Under ultrasonic power of 220W and mechanical stirring at 150r / min, slowly add the second solution dropwise to the first solution to obtain the third solution. Then, slowly add concentrated ammonia to the third solution to bring the pH of the reaction system to about 9. After the ammonia has been added, continue the ultrasonic-controlled reaction for 6 hours.

[0068] After the reaction was completed, the solution was allowed to stand for 12 hours, the supernatant was discarded, the precipitate was centrifuged, and then washed twice with deionized water by centrifugation. After freeze-drying for 36 hours, white flake-shaped nano zinc oxide powder was finally obtained.

[0069] The prepared sheet-like zinc oxide nanoparticles were characterized, and the specific results are shown in [reference needed]. Figures 1A to 4 . Figures 1A to 1C The image shows an SEM image of the sheet-like zinc oxide nanoparticles prepared in Example 1. As can be seen from the image, the width of the sheet-like zinc oxide nanoparticles is 1 to 2 μm. This width refers to the length of the small dimension on the plane perpendicular to the thickness direction, and the thickness is less than 20 nm.

[0070] Figure 2 , 3 The XRD pattern and UV spectrum of the sheet-like zinc oxide nanoparticles from Example 1 are shown respectively. The results show that the prepared zinc oxide nanoparticles have a zincite structure.

[0071] Figure 4 The image shows the infrared spectrum of the sheet-like zinc oxide nanoparticles from Example 1. As can be seen from the image, the sample contains a characteristic absorption peak of the Zn-O bond at 493.687. In addition, there are peaks related to hydrogen at 3427.368 and 1634.376. These characteristic peaks should belong to the stretching or bending vibration absorption peaks of hydroxyl groups or bridged hydroxyl groups on the ZnO surface.

[0072] Example 2

[0073] This embodiment uses the same raw materials and steps as Example 1 to prepare sheet-like nano zinc oxide, the only difference being that the amount of trimethylolethane added is 3wt%.

[0074] SEM images of the obtained products are shown below. Figure 5 As shown, Figure 5 and Figures 1A to 1C A comparison shows that the morphology and particle size of the nano-zinc oxide obtained in Example 2 are not significantly different from those in Example 1. Therefore, in the preparation of sheet-like nano-zinc oxide, a 3 wt% addition of trimethylolethane has a similar effect to a 1 wt% addition.

[0075] Example 3

[0076] This embodiment uses the same raw materials and steps as Example 1 to prepare sheet-like nano zinc oxide, the only difference being: ammonia water is added dropwise until the reaction pH is 11.

[0077] SEM images of the obtained products are shown below. Figure 6A , 6B As shown. From Figure 6A , 6B It can be seen that the nano zinc oxide product has a coarse flower cluster structure with fine particles attached to the surface. The particle size is much larger than that of the nano zinc oxide in Example 1, which weakens the nano size effect of the nano zinc oxide particles.

[0078] Example 4

[0079] This embodiment uses the same proportions and steps as Example 1 to prepare sheet-like nano zinc oxide, the only difference being that zinc chloride is used instead of zinc acetate as the zinc source.

[0080] SEM images of the obtained products are shown below. Figure 7 As shown in the figure, the morphology and particle size of the nano zinc oxide in Example 4 are not much different from those of the nano zinc oxide in Example 1.

[0081] Comparative Example

[0082] This example uses the same raw materials and steps as Example 1 to prepare sheet-like nano-zinc oxide, the only difference being that trimethylolethane is not added as a dispersant. The prepared zinc oxide is as follows: Figure 8 As shown in the figure, the prepared product does not have a fixed morphology, which is not conducive to stable production.

[0083] Application Example 1

[0084] 1. Preparation of bacterial suspension

[0085] Pick one or two standard bacterial strains cultured by streak plating with an inoculation loop, inoculate them into prepared MH broth medium (purchased from Guangdong Huankai Microbial Technology Co., Ltd.), stir gently, seal the centrifuge tube containing the medium with sealing film, and place it in a 36℃ constant temperature shaking incubator for 24 hours to obtain a bacterial suspension.

[0086] To use, centrifuge the tube containing the bacterial suspension at 5000 rpm for 5 minutes. Discard the supernatant and wash twice with 10 ml of PBS solution. Add another 10 ml of PBS solution to prepare the bacterial suspension for use. Dilute the bacterial suspension with a certain amount of PBS solution, and add 200 μL to a 96-well plate. When the concentrations of both Escherichia coli and Staphylococcus aureus are approximately 0.1, the bacterial suspension has a concentration of 1*10⁸ CFU / mL and should be used within 4 hours.

[0087] 2. Prepare zinc oxide aqueous solutions of different concentrations.

[0088] 10 mg of the nano-zinc oxide prepared in Example 1 was added to 10 ml of sterile water, shaken well, and sonicated at 210 W for 5 min to prepare an antibacterial solution with a concentration of 1000 μg / ml. Then, 2.5 ml of this solution was added to 2.5 ml of sterile water to prepare an antibacterial solution with a concentration of 500 μg / ml. Next, 2.5 ml of the 500 μg / ml antibacterial solution was added to 2.5 ml of sterile water to prepare a solution with a concentration of 250 μg / ml. Finally, 2.5 ml of the 250 μg / ml antibacterial solution was added to 2.5 ml of sterile water to prepare a solution with a concentration of 125 μg / ml.

[0089] 3. Inoculation solution

[0090] Add 2.5 mL of double-concentration nutrient broth (preparation method refers to the minimum inhibitory concentration test in "Disinfection Technical Specifications 2002") to the zinc oxide aqueous solutions of different concentrations in step 2. Set up a control group consisting of 2.5 mL of double-concentration nutrient broth and 2.5 mL of sterile water. Add 0.1 mL of the 1*10⁸ CFU / mL bacterial suspension prepared in step 1 to each of the above solutions. Seal the centrifuge tubes containing each group of samples with sealing film.

[0091] 4. Shaking cultivation

[0092] Place the centrifuge tubes containing the samples and bacterial culture into a 36°C constant temperature shaking incubator and incubate with shaking for 24 hours.

[0093] 5. Plate culture

[0094] Take 0.1 ml of the bacterial culture from step 4, after shaking and incubation for 24 hours, spread it onto nutrient agar medium, and incubate in a constant temperature and humidity incubator for 24 hours. Take photos to record the colony growth of each group. The results are as follows: Figure 9 As shown.

[0095] Bacterial survival rate was calculated based on the number of colonies on the plate, and the results are as follows: Figure 10 As shown. Wherein:

[0096] The formula for calculating bacterial survival rate is: Y = 1 - [(WQ) / W]

[0097] In the formula:

[0098] Y—Formula for calculating bacterial survival rate;

[0099] W—The concentration of viable bacteria (CFU / mL) in the conical flask after 24 hours of shaking contact with the control sample;

[0100] Q—The concentration of viable bacteria (CFU / mL) in the conical flask after 24 hours of shaking contact with the sample.

[0101] According to the Minimum Inhibitory Concentration (MIC) test (nutrient broth dilution method) in the "Disinfection Technical Specifications 2002", the MIC of the prepared nano zinc oxide was determined to be 250 ppm.

[0102] Application Example 2

[0103] The sheet-like zinc oxide sample prepared in Example 1 and the purchased DXN-HQ20T sheet-like zinc oxide sample were compared using SEM images as shown below. Figure 11 (As shown) Prepared an aqueous solution of 250 μg / mL, and tested its antibacterial properties according to the method in Application Example 1. The test results are as follows. Figure 12A , 12B As shown in the figure, no colonies grew on the zinc oxide sample plate prepared in Example 1. Figure 12A The purchased sample could not completely inhibit the growth of Escherichia coli at a concentration of 250 μg / mL. Figure 12B This indicates that the antibacterial effect of the sheet-like nano zinc oxide sample prepared in Example 1 is better than that of the purchased sheet-like nano zinc oxide sample.

[0104] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing sheet-like nano-zinc oxide, comprising reacting a zinc salt with a precipitant to generate a precipitate under the action of a dispersant, wherein the reaction temperature is 18-20℃, washing the precipitate by centrifugation with deionized water, and freeze-drying, wherein the width of the zinc oxide is 1-2 μm and the thickness is less than 20 nm; wherein, The dispersant comprises trimethylolethane and diammonium hydrogen phosphate, wherein the mass ratio of diammonium hydrogen phosphate to trimethylolethane is 1:(3.5-5), and the mass content of trimethylolethane is 1-5%; the precipitant is ammonia water, and the method specifically includes: Provide the first solution; Adding a second solution dropwise to the first solution yields a third solution; and The precipitant is added to the third solution; The first solution comprises the zinc salt and trimethylolethane, the second solution comprises diammonium hydrogen phosphate, and the pH of the system is 8.5–9.5 after the precipitant is added to the third solution.

2. The method according to claim 1, wherein, In the first solution, the concentration of the zinc salt is 30–100 mmol / L.

3. The method according to claim 1, wherein, In the second solution, the concentration of diammonium hydrogen phosphate is 20–25 mmol / L.

4. The method according to any one of claims 1 to 3, wherein, The zinc salt includes one or more of zinc acetate, zinc chloride, zinc sulfate, and zinc nitrate.

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