Preparation method of hydrotalcite-like nanosheet

Abstract

The invention provides a preparation method of hydrotalcite-like nanosheets, and relates to the technical field of layered mineral materials.The preparation method comprises the steps that carbonate type magnesium-aluminum hydrotalcite-like master batch and a polypeptide solution with the first concentration are mixed, and a pre-product is obtained after a heating reaction; and putting the pre-product into a polypeptide solution with a second concentration, and obtaining the hydrotalcite-like nanosheet under the action of a high-energy ultrasonic probe, wherein the polypeptide solution with the first concentration is a saturated solution, and the first concentration is greater than the second concentration. According to the invention, a saturated polypeptide solution is used, a heating reaction is used for assisting a high-energy ultrasonic probe to directly realize delamination of the micron-sized carbonate type magnesium-aluminum hydrotalcite, and the whole preparation process avoids using an organic solvent, strong acid, strong alkali and the like, avoids high-temperature calcination, accords with the concepts of low carbon, energy conservation, environmental protection and the like, and is suitable for industrial production. And the magnesium-aluminum hydrotalcite nanosheet with a high length-diameter ratio can also be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of layered mineral materials, and particularly relates to a preparation method of hydrotalcite-like nanosheets. BACKGROUND

[0002] In recent years, hydrotalcite-like, i.e. synthetic layered double hydroxides (LDHs), have attracted extensive attention as gas barrier materials, and magnesium-aluminum hydrotalcite-like has been certified as a food packaging barrier material. An effective strategy to enhance the gas barrier properties of polymer films using hydrotalcite-like is to construct a highly ordered "brick-mortar" layered structure in the polymer matrix and to use high aspect ratio hydrotalcite-like nanosheets. At present, the main factor restricting the industrialization of magnesium-aluminum hydrotalcite-like based gas barrier films is that the technology for low-cost and efficient large-scale preparation of high aspect ratio hydrotalcite-like nanosheets is not mature. Therefore, whether a method for large-scale preparation of high aspect ratio hydrotalcite-like nanosheets can be developed is a key problem that determines whether hydrotalcite-like based high gas barrier films can be industrialized.

[0003] Two requirements need to be met to obtain high aspect ratio hydrotalcite-like nanosheets: preparation of large particle size hydrotalcite-like particles and delamination of hydrotalcite-like. Common methods for preparing LDHs are coprecipitation (constant pH method, variable pH method, nucleation-crystallization isolation method, urea method, etc.) and calcination-rehydration method. The constant pH method and the variable pH method can only obtain small particle size hydrotalcite-like particles (diameter < 200 nm), and the urea method is usually used to prepare micron-sized large particle size LDH particles. The LDHs obtained by the urea method are usually CO3 2- LDHs. Then, high aspect ratio LDH nanosheets can be prepared by delaminating the CO3 2- LDHs matrix. The preparation of LDH nanosheets mainly includes "bottom-up" and "top-down" strategies. The methods for preparing LDH nanosheets using the "bottom-up" strategy include one-step synthesis, nucleation-crystallization isolation, reverse microemulsion, etc. These methods use growth inhibitors, strengthen mixing, or create confined spaces to prepare LDH nanosheets. In general, the "bottom-up" method for directly synthesizing high aspect ratio LDH nanosheets usually uses a low concentration of reactants and is sensitive to the concentration of reactants. When the concentration of reactants used is higher than the threshold value, the thickness of the obtained LDHs is usually larger, resulting in a low aspect ratio. At the same time, the use of low concentration limits the yield and is not conducive to large-scale preparation. The "top-down" strategy is to delaminate the layered matrix directly using methods such as large ion intercalation, mechanical force, and water-soluble solvent treatment. Among the common interlayer anions, CO3 2- has the largest affinity for LDHs, and CO3 2-The largest particles of the LDHs are the most difficult to exfoliate. The existing "top-down" exfoliation method basically needs to replace CO32- 2- with other anions with weaker affinity first, and then use shear force (ultrasound, shaking, stirring, etc.) in a solvent with a large dielectric constant (such as formamide) to realize exfoliation, which has the disadvantages of many steps, long time consumption, etc. Recently, the use of plasma to exfoliate LDHs has attracted widespread attention. This method can efficiently prepare LDHs nanosheets with rich defect sites, which are effective oxygen evolution catalysts, but the exfoliation scale is small. Although there have been attempts in recent years to directly exfoliate CO32- 2- LDHs in liquid phase, but the thickness of the prepared LDHs nanosheets is relatively large, and the aspect ratio is small. At present, there is a gap in the method of efficiently, time-saving and large-scale preparation of LDHs nanosheets with high aspect ratio. SUMMARY

[0004] In view of the defects in the prior art, the technical problem solved by the present application is to provide a preparation method of hydrotalcite-like nanosheets, which has simple process, low requirement for equipment, is easy to industrialize, and the prepared hydrotalcite-like nanosheets have high aspect ratio.

[0005] To achieve the above purpose, the present application provides a preparation method of hydrotalcite-like nanosheets, which comprises: mixing a carbonate type magnesium aluminum hydrotalcite masterbatch with a polypeptide solution of a first concentration, and obtaining a pre-product after heating reaction; placing the pre-product in a polypeptide solution of a second concentration to obtain the hydrotalcite-like nanosheets under the action of a high-energy ultrasonic probe; wherein the polypeptide solution of the first concentration is a saturated solution, and the first concentration is greater than the second concentration.

[0006] Preferably, the heating reaction temperature is 100-150℃.

[0007] Preferably, the heating reaction time is 1-5h.

[0008] Preferably, the first concentration is 0.5-4mol / L.

[0009] Preferably, the second concentration is 0.1-2mol / L.

[0010] Preferably, the action time of the high-energy ultrasonic probe is 15-60s.

[0011] Preferably, the preparation method of the carbonate type magnesium aluminum hydrotalcite masterbatch comprises the following steps: mixing a magnesium salt, an aluminum salt and urea in deionized water to obtain a mixed solution, and heating the mixed solution to obtain the carbonate type magnesium aluminum hydrotalcite masterbatch.

[0012] Preferably, the molar ratio of the magnesium salt, aluminum salt, and urea is (2~4):1:6.

[0013] Preferably, the diameter of the carbonate-type magnesium aluminum hydrotalcite masterbatch is 4μm-5μm.

[0014] Preferably, the aspect ratio of the hydrotalcite-like nanosheets is greater than 400.

[0015] Compared with the prior art, the advantages of the present invention are as follows: The present invention uses a saturated polypeptide solution and uses a heating reaction to assist a high-energy ultrasonic probe to directly exfoliate micron-sized carbonate-type magnesium aluminum hydrotalcite. The entire preparation process avoids the use of organic solvents, strong acids and alkalis, and high-temperature calcination, which is in line with the concepts of low carbon, energy saving and environmental protection. It can also obtain magnesium aluminum hydrotalcite nanosheets with high aspect ratio. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 The X-ray diffraction pattern of the carbonate-type magnesium aluminum hydrotalcite masterbatch prepared in Example 1 of this invention; Figure 2 This is a SEM image of the carbonate-type magnesium aluminum hydrotalcite masterbatch prepared in Example 1 of the present invention; Figure 3 The X-ray diffraction pattern of the hydrotalcite-like nanosheets prepared in Example 1 of this invention; Figure 4 This is a SEM image of the hydrotalcite-like nanosheets prepared in Example 1 of this invention; Figure 5 The X-ray diffraction pattern is shown for the product prepared in Comparative Example 1 of this invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention provides a method for preparing hydrotalcite-like nanosheets. The method uses a saturated peptide solution and a heating reaction assisted by a high-energy ultrasonic probe to directly exfoliate micron-sized carbonate-type magnesium aluminum hydrotalcite in a short time. This solves the technical problem in the prior art that it is impossible to prepare high aspect ratio hydrotalcite-like nanosheets efficiently, time-savingly and on a large scale.

[0020] To achieve the above-mentioned technical effects, the overall concept of this invention is as follows: On one hand, the present invention provides a method for preparing hydrotalcite-like nanosheets, the method comprising: The carbonate-type magnesium aluminum hydrotalcite masterbatch was mixed with a polypeptide solution of the first concentration and heated to react to obtain the preproduct. The preproduct was placed in a polypeptide solution of a second concentration, and the hydrotalcite-like nanosheets were obtained under the action of a high-energy ultrasonic probe. Wherein, the polypeptide solution of the first concentration is a saturated solution, and the first concentration is greater than the second concentration.

[0021] The applicant, through extensive experimental research and analysis, has determined the following delamination mechanism in the preparation method of this invention: The layers of carbonate-type magnesium aluminum hydrotalcite are positively charged, and the delamination occurs through interlayer anions (carbonate ions (CO3-)). 2- To maintain electroneutrality, the insertion of polypeptide molecules into the interlayer of magnesium aluminum bimetallic hydroxides can be accelerated by heating in the solution, thereby expanding the interlayer spacing. A saturated polypeptide solution can enable more polypeptide molecules to intercalate into LDHs, further increasing the interlayer spacing. Although the heating reaction can enable polypeptide molecules to intercalate, it is not enough to cause the layers to peel off. The instantaneous destructive force generated by high-energy ultrasound can cause the peeling between the stretched layers to occur.

[0022] Therefore, this invention creatively uses a saturated polypeptide solution and high-energy ultrasound to directly exfoliate micron-sized carbonate-type magnesium aluminum hydrotalcite in a short time through heating reaction. The entire preparation process avoids the use of organic solvents, strong acids and bases, and high-temperature calcination, which is in line with the concepts of low carbon, energy saving and environmental protection. It can also obtain magnesium aluminum hydrotalcite nanosheets with high aspect ratio.

[0023] Preferably, the heating reaction temperature of the present invention is 100~150℃, and the heating reaction time is 1~5h.

[0024] Under the above heating conditions, the present invention can enable sufficient polypeptide molecules to intercalate into the interlayer of magnesium-aluminum hydrotalcite, with short heating time, low energy consumption, low cost, low equipment requirements, and easy industrial production.

[0025] Preferably, the first concentration of the present invention is 0.5-4 mol / L, that is, the concentration of the saturated polypeptide solution used in the present invention is 0.5-4 mol / L. The polypeptide solution of this concentration can open up the layers of LDHs, providing favorable conditions for subsequent exfoliation by high-energy ultrasound.

[0026] A saturated polypeptide solution is prepared as follows: Weigh out the appropriate mass of polypeptide and the corresponding volume of deionized water according to the concentration of 0.5-4 mol / L. Under the condition of 80-150℃, add the polypeptide to the deionized water and stir for about one minute until the polypeptide is completely dissolved.

[0027] Preferably, the second concentration is 0.1~2 mol / L. The pre-product after polypeptide molecule intercalation is added to a polypeptide solution of the above concentration, and exfoliation of carbonate-type magnesium-aluminum hydrotalcite can be achieved in a short time under the action of high-energy ultrasound.

[0028] Preferably, the action time of the high-energy ultrasonic probe is 15-60 seconds. The high-energy ultrasonic probe can generate instantaneous destructive force, which causes the separated layers to peel apart. If the ultrasonic time is too long, the nanosheets will be damaged, which is not conducive to the formation of hydrotalcite-like nanosheets with a large aspect ratio.

[0029] Preferably, the polypeptide used in this invention is a polypeptide commonly used in the art, such as diglycinate, triglycinate, etc.

[0030] Preferably, the preparation method of the carbonate-type magnesium-aluminum hydrotalcite masterbatch includes the following steps: mixing magnesium salt, aluminum salt, and urea in deionized water to obtain a mixed solution, and heating the mixed solution to obtain the carbonate-type magnesium-aluminum hydrotalcite masterbatch. The masterbatch obtained by the above preparation method of the present invention has good crystallinity, uniform particles, and a diameter of 4μm-5μm. Using the above-mentioned well-crystallized masterbatch with uniform particles and a diameter of 4μm-5μm as raw material for exfoliation can lay the foundation for subsequently obtaining nanosheets with high aspect ratios.

[0031] Preferably, the heating temperature in the preparation method of the carbonate-type magnesium aluminum hydrotalcite masterbatch is 100-150℃, and the heating time is 1-2 days.

[0032] Preferably, the molar ratio of the magnesium salt, aluminum salt, and urea is (2-4):1:6.

[0033] Preferably, the magnesium salt is a common magnesium salt in the art, such as magnesium chloride, magnesium nitrate, etc., and the aluminum salt is a common aluminum salt in the art, such as aluminum chloride, aluminum nitrate, aluminum sulfate, etc.

[0034] Preferably, the preparation method of the carbonate-type magnesium-aluminum hydrotalcite masterbatch further includes: after the reaction is completed, the reaction product is successively washed, dried, and ground to obtain powdered carbonate-type magnesium-aluminum hydrotalcite masterbatch. The reaction product is washed with deionized water until the pH value is neutral. The present invention uses drying at 70-80℃ for 12-24 hours. Since magnesium-aluminum hydrotalcite nanosheets are commonly used in the food industry, solvents should be avoided during the preparation process.

[0035] Preferably, the diameter of the carbonate-type magnesium-aluminum hydrotalcite masterbatch is 4μm-5μm. Exfoliating the carbonate-type magnesium-aluminum bimetallic hydroxide masterbatch with a diameter of 4μm-5μm is beneficial for improving exfoliation efficiency and obtaining nanosheets with a high aspect ratio.

[0036] Preferably, the aspect ratio of the hydrotalcite-like nanosheets is greater than 400.

[0037] Preferably, after the heating reaction, the preproduct is further subjected to centrifugation and washing. The preproduct after the reaction still contains unreacted polypeptide molecules. This invention uses centrifugation to separate the preproduct from the remaining polypeptides. During centrifugation, deionized water is continuously used for washing to obtain a relatively pure preproduct.

[0038] Preferably, after the high-energy ultrasonic probe treatment, the product obtained after the reaction is further subjected to centrifugation and washing. After the reaction, the excess polypeptides are washed away with deionized water to obtain impurity-free magnesium-aluminum hydrotalcite nanosheets.

[0039] In this embodiment of the invention, a method for preparing a hydrotalcite-like nanosheet specifically includes the following steps: (1) Preparation of carbonate-type magnesium aluminum hydrotalcite masterbatch: S1. Mix magnesium salt, aluminum salt, and urea in deionized water at a molar ratio of (2-4):1:6 to obtain the first mixed solution; S2. React the first mixed solution obtained in step S1 at 100-150℃ for 1-2 days to obtain the reaction mixture; S3. Wash the reaction mixture with ethanol and deionized water until the pH value is neutral, filter, dry in an oven at 70-80℃ for 12-24 hours, and then grind into a fine powder to obtain carbonate-type magnesium aluminum hydrotalcite masterbatch.

[0040] (2) Preparation of hydrotalcite-like nanosheets by exfoliation reaction: S4. The above carbonate-type magnesium-aluminum hydrotalcite masterbatch is mixed with a saturated polypeptide solution to obtain a second mixed solution, and the mixed solution is reacted at 100-150℃ for 1-5 hours. S5. After the reaction is complete, cool to room temperature and obtain the preproduct by centrifugation and washing. S6. Place the preproduct in a peptide solution and sonicate it for 15-60 seconds using a 200-700W high-energy ultrasonic probe. S6. After ultrasonication, hydrotalcite-like nanosheets are obtained by centrifugation and washing.

[0041] Secondly, the present invention also provides a hydrotalcite-like nanosheet, which is prepared using the preparation method of the first aspect.

[0042] The hydrotalcite-like nanosheets prepared by the above method have a thickness of about 1 nm and an aspect ratio greater than 400. They have a high aspect ratio, can be scaled up, and are easy to store for a long time.

[0043] Thirdly, this invention also provides an application of hydrotalcite-like nanosheets. The hydrotalcite-like nanosheets prepared by the method in the first aspect of this invention are magnesium-aluminum hydrotalcite nanosheets. The entire preparation process avoids the use of organic solvents, strong acids, and strong alkalis, resulting in magnesium-aluminum hydrotalcite nanosheets with a large aspect ratio. Applying this invention to the food packaging field will break through the barriers of existing technologies and realize the industrialization of magnesium-aluminum hydrotalcite-based gas barrier films.

[0044] The following specific embodiments illustrate a method for preparing hydrotalcite-like nanosheets according to the present invention.

[0045] Example 1 (1) Preparation of carbonate-type magnesium aluminum hydrotalcite masterbatch: S1. Add 6.25g aluminum nitrate nonahydrate, 8.55g magnesium nitrate hexahydrate, and 6.01g urea to 100mL of deionized water and mix evenly to obtain a mixture; S2. Place the mixture obtained in step S1 into a reaction vessel, heat it to 100°C under an air atmosphere, react for 24 hours, and then allow it to cool naturally. S3. Wash the obtained reaction mixture with deionized water until the pH value is neutral, then dry it at 70°C for 12 hours, and then grind it into a fine powder to obtain carbonate-type magnesium aluminum hydrotalcite masterbatch.

[0046] (2) Preparation of magnesium-aluminum hydrotalcite nanosheets by exfoliation reaction: S4. Take 30 mg of the above magnesium-aluminum hydrotalcite masterbatch and 2.83 g of triglycinate water and mix them into 10 mL of deionized water to obtain a mixed solution. Allow the mixed solution to react fully at 100°C for 5 h. S5. After the reaction is complete, cool to room temperature and wash away the remaining triglycines with deionized water to obtain the preproduct. S6. Then place the preproduct in 10 ml of 0.35 mol / L triglycine aqueous solution and sonicate for 30 s using a 500 W high-energy ultrasonic probe. S7. After ultrasound, the remaining triglycines were washed away with deionized water to obtain magnesium-aluminum hydrotalcite nanosheet gel.

[0047] Example 2 The difference between Example 2 and Example 1 is as follows: S4. Take 30 mg of the above magnesium-aluminum hydrotalcite masterbatch and 5 g of diglycinate water and mix them into 10 mL of deionized water to obtain a mixed solution. Allow the mixed solution to react fully at 100°C for 1.5 h. S6. Then place the preproduct in 10 ml of 0.35 mol / L diglycinate aqueous solution and sonicate for 60 s using a 500 W high-energy ultrasonic probe. Comparative Example 1 The difference between Comparative Example 1 and Example 2 is that ultrasound is not used after the reaction, i.e.: S4. Take 30 mg of the above magnesium-aluminum hydrotalcite masterbatch and 5 g of diglycinate water and mix them into 10 mL of deionized water to obtain a mixed solution. Allow the mixed solution to react fully at 100°C for 1.5 h. S5. After the reaction is complete, cool to room temperature and wash away the remaining diglycinate with deionized water to obtain the product.

[0048] The carbonate-type magnesium aluminum layered double hydroxide masterbatch and magnesium aluminum layered double hydroxide nanosheets obtained in Example 1 were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results are as follows: Figures 1-4 As shown.

[0049] Figure 1 The X-ray diffraction pattern of the carbonate-type magnesium aluminum hydrotalcite masterbatch from Example 1 of this invention is shown below. Figure 1 It can be seen that the 003 peak at 11.8° is a typical first peak of carbonate-type LDHs. The results show that no other impurity peaks appeared, indicating that the carbonate-type magnesium aluminum hydrotalcite masterbatch was prepared in Example 1 of this invention.

[0050] Figure 2 This is a SEM image of the carbonate-type magnesium-aluminum hydrotalcite masterbatch from Example 1 of the present invention. Figure 2 It can be seen that the carbonate-type magnesium aluminum hydrotalcite masterbatch sample has good crystallization, with uniform particles and a diameter of 4-5 μm.

[0051] Figure 3 The X-ray diffraction pattern of the magnesium-aluminum hydrotalcite nanosheets prepared in Example 1 of this invention is shown below. Figure 3 It can be seen that there are obvious double peaks at diffraction angles of 3.56° and 7.2°, and no obvious characteristic peaks of hydrotalcite masterbatch. This indicates that the carbonate-type magnesium aluminum hydrotalcite masterbatch has achieved delamination, and the nanosheets after delamination are attached with polypeptide macromolecules, which causes the stacking peaks to shift to smaller angles.

[0052] Figure 4 This is a SEM image of the magnesium-aluminum hydrotalcite nanosheets from Example 1 of the present invention. Figure 4 As can be seen, the nanosheets are very thin compared to the SEM image of the masterbatch, about 1 nm thick. Some nanosheets are connected into a film, with an average particle size of about 410 nm. According to the ratio of the aspect ratio to the average particle size of the nanosheets and the thickness of the nanosheets, the aspect ratio of the nanosheets obtained in Example 1 is about 410.

[0053] Preliminary calculations show that the aspect ratio of the nanosheets obtained in Example 2 of this invention is approximately 460.

[0054] Figure 5 The X-ray diffraction pattern of the product of Comparative Example 1 of this invention shows that the 003 peak (around 11.6°) of the masterbatch is still very obvious. There is a small, indistinct peak below 10°, which is presumably intercalation or partial delamination. This indicates that without the use of high-energy ultrasound, it is impossible to obtain nanosheets that have been successfully delaminated.

[0055] It should be noted that, in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0056] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and refinements without departing from the principles of this invention, and these improvements and refinements are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A method for preparing hydrotalcite-like nanosheets, characterized in that, The preparation method includes: The carbonate-type magnesium aluminum hydrotalcite masterbatch was mixed with a polypeptide solution of the first concentration and heated to react to obtain the preproduct. The preproduct was placed in a polypeptide solution of a second concentration, and the hydrotalcite-like nanosheets were obtained under the action of a high-energy ultrasonic probe. Wherein, the polypeptide solution of the first concentration is a saturated solution, and the first concentration is greater than the second concentration.

2. The method for preparing hydrotalcite-like nanosheets as described in claim 1, characterized in that, The temperature of the heating reaction is 100~150℃.

3. The method for preparing hydrotalcite-like nanosheets as described in claim 1, characterized in that, The heating reaction time is 1 to 5 hours.

4. The method for preparing hydrotalcite-like nanosheets as described in claim 1, characterized in that, The first concentration is 0.5-4 mol / L.

5. The method for preparing hydrotalcite-like nanosheets as described in claim 1, characterized in that, The second concentration is 0.1~2 mol / L.

6. The method for preparing hydrotalcite-like nanosheets as described in claim 1, characterized in that, The action time of the high-energy ultrasonic probe is 15-60s.

7. The method for preparing hydrotalcite-like nanosheets as described in claim 1, characterized in that, The preparation method of the carbonate-type magnesium-aluminum hydrotalcite masterbatch includes the following steps: mixing magnesium salt, aluminum salt, and urea in deionized water to obtain a mixed solution, and heating the mixed solution to obtain the carbonate-type magnesium-aluminum hydrotalcite masterbatch.

8. The method for preparing hydrotalcite-like nanosheets as described in claim 7, characterized in that, The molar ratio of the magnesium salt, aluminum salt, and urea is (2~4):1:

6.

9. The method for preparing hydrotalcite-like nanosheets as described in claim 1, characterized in that, The diameter of the carbonate-type magnesium-aluminum hydrotalcite masterbatch is 4μm-5μm.

10. The method for preparing hydrotalcite-like nanosheets as described in claim 1, characterized in that, The aspect ratio of the hydrotalcite-like nanosheets is greater than 400.

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