Nanometer montmorillonite hollow microspheres, and preparation method and application thereof

Abstract

The application relates to a nano-montmorillonite hollow microsphere and a preparation method and application thereof. The method is characterized in that nano-montmorillonite is used as raw material, a sodium metasilicate aqueous solution and prepared nano-montmorillonite powder are fully reacted under the conditions of mechanical stirring and water bath heating; and the obtained montmorillonite suspension is subjected to spray drying, so that the nano-montmorillonite hollow microsphere is prepared. The application aims at the problems of many chemical reagents, complex preparation process and great difficulty in the current montmorillonite microsphere preparation technology, and provides a method for preparing the montmorillonite hollow microsphere by adding a small amount of sodium metasilicate to nano-montmorillonite. The preparation process is simple, the reaction condition is mild, the prepared montmorillonite hollow microsphere is uniform in size, good in dispersity, high in sphere forming rate and good in sphericity, the microsphere has a cavity inside, and the adsorption and loading capacity of the montmorillonite microsphere is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of nanometer montmorillonite preparation nanometer montmorillonite hollow microsphere preparation method and application, belong to montmorillonite forming field. BACKGROUND

[0002] Montmorillonite is a natural layered non-metallic clay mineral, belongs to monoclinic system, is made of hydrous silicate. Its unit layer structure is by the middle Al-O octahedral layer through oxygen atom by covalent bond connecting upper and lower two Si-O tetrahedral layer, forms 2:1 type " sandwich " layered structure.

[0003] Montmorillonite has special nanometer interlamination, high specific surface area, strong cation exchange and strong adsorption / desorption force characteristics make it have very strong surface / interface reactivity, can simultaneously with many guest substances occur intercalation, physical and chemical adsorption and ion exchange reaction, simultaneously due to its good swelling, suspensibility, cohesiveness and stable non-toxicity etc. characteristics, can be used as slow-release drug carrier, catalyst carrier, pollutant adsorbent etc., is widely used in chemical industry, medicine, environmental protection and many other fields. Montmorillonite's drug loading, slow release and adsorption performance and its structural properties, such as specific surface area, interlamination, porosity and pore size distribution, hydrophilicity and ion exchange capacity are closely related. In practical application, montmorillonite structure and surface properties are usually processed and modified to achieve the most ideal application effect. Montmorillonite microspheres because of its spherical morphology, make its specific surface area, porosity, adsorption performance etc. greatly improve compared with natural montmorillonite, thus gradually become the focus of research.

[0004] Yang Jianhong et al. (Preparation of Chitin / Montmorillonite Composite Microspheres and Its Adsorption of Cu2+ [J]. Journal of Changzhou University, 2016, 28 (6) : 78-85) chitin is suspended in 8% NaOH / 4% CO (NH2) 2 aqueous solution, after freezing at-20℃ for 12h under stirring, repeat freezing, stirring multiple times until chitin completely dissolves, then vacuum degassing 2% chitin solution is prepared, then add montmorillonite blend, the obtained solution is dropped into 10% HCl drop by drop, and chitin / montmorillonite microspheres are prepared. The preparation method is relatively complex, and the reaction time is long, which is not conducive to industrial production. And the prepared chitin / montmorillonite microspheres only have certain adsorption performance for heavy metal ions, and the function is relatively single.

[0005] CN 103961319 A discloses a preparation method of chitosan and montmorillonite composite drug-loaded microspheres. Chitosan acetic acid solution and montmorillonite suspension are mixed to prepare a chitosan / montmorillonite mixed solution by mechanical stirring. After adjusting the pH value, sodium pyrophosphate solution is added in a microwave reactor for crosslinking to prepare a chitosan / montmorillonite composite microsphere solution. Centrifugation, washing and freeze-drying obtain the chitosan / montmorillonite composite drug-loaded microspheres. The microspheres prepared by the method have obvious layered structure, wrinkles, increased specific surface area, and are beneficial to drug loading. However, the microspheres have large particle size, poor sphericity, and obvious agglomeration, which is not conducive to the dispersion and transportation of drugs in the body.

[0006] The existing related literature reports on the preparation of montmorillonite microspheres mostly need montmorillonite to be compounded with other materials, involve multiple chemical reagents, and have problems of complex preparation process and great difficulty. The prepared composite montmorillonite microspheres have relatively single and fixed functions. At present, there is no preparation technology for directly constructing the morphology of nanometer montmorillonite into a hollow microsphere by modification. SUMMARY

[0007] The purpose of the present application is to prepare nanometer montmorillonite hollow microspheres by using nanometer montmorillonite and spray drying technology under the condition of adding a small amount of sodium metasilicate as a binder. In view of the problems of the current montmorillonite microsphere preparation technology, such as involving multiple chemical reagents, complex preparation process and great difficulty, a method is provided for adding only a small amount of sodium metasilicate, modifying montmorillonite by using the hydrolysis product thereof, and constructing a hollow microsphere. The method has the characteristics of simple process and mild reaction conditions. The prepared nanometer montmorillonite hollow microspheres have uniform size, good dispersibility, high sphere formation rate, good sphericity, and a large number of pores on the surface of the sphere wall, which are connected with the internal cavity of the microsphere. The pore diameter is about 100-500 nm. The macromolecular substances can smoothly pass through the pores and enter and store in the internal cavity of the montmorillonite microsphere. The mass transfer and adsorption performance of the montmorillonite microsphere is greatly improved.

[0008] To achieve the above-mentioned purpose of the application, the following technical solutions are adopted in the present application:

[0009] In a first aspect, the present application provides a nanometer montmorillonite hollow microsphere, which is prepared by the following method:

[0010] S1: dispersing sodium-based montmorillonite in deionized water, fully dispersing and swelling, standing and stratifying, taking the middle layer (colloid part) for separation treatment to obtain nanometer montmorillonite;

[0011] S2: adding the nanometer montmorillonite in step S1 into 0.1-0.5 mmol·L -1 (0.4 mmol·L -1) in a sodium metasilicate aqueous solution, under mechanical stirring, at 30-50°C (preferably in a thermostatic water bath at 50°C) for 2-10h (preferably 4h), to obtain a nanometer-sized montmorillonite suspension;

[0012] S3: spray-drying the nanometer-sized montmorillonite suspension of step S2 to obtain the nanometer-sized montmorillonite hollow microspheres.

[0013] Further, the mass ratio of the sodium-based montmorillonite to the deionized water in step S1 is 1:50-150 (preferably 1:50).

[0014] In an embodiment of the present application, the dispersing and swelling in step S1 is performed by simultaneously ultrasonicating and mechanically stirring the montmorillonite in water at room temperature for 12-24h (preferably 24h).

[0015] In an embodiment of the present application, the standing and layering in step S1 is performed for 5-7 days (preferably 7 days).

[0016] Further, the separation treatment in step S1 is centrifuging the intermediate layer, washing the obtained precipitate with deionized water, and drying (vacuum drying in an oven at 60-80°C, preferably 80°C, for 24-36h, preferably 24h) to obtain the nanometer-sized montmorillonite.

[0017] Further, the volume of the sodium metasilicate aqueous solution in step S2 is 67-200mL / g (preferably 200mL / g) based on the mass of the nanometer-sized montmorillonite.

[0018] Further, the spray-drying in step S3 is performed under the following conditions: the nozzle diameter is 0.5-2.0mm (preferably 0.7mm), the feed flow rate is 200-1000mL·h -1 (preferably 1000mL·h -1 ), and the inlet temperature is 160-200°C (preferably 180°C).

[0019] The present application particularly recommends that the nanometer-sized montmorillonite hollow microspheres are prepared by the following method:

[0020] S1: dispersing sodium-based montmorillonite in deionized water, fully dispersing and swelling, standing and layering, taking the intermediate layer for separation treatment to obtain nanometer-sized montmorillonite;

[0021] S2: adding the nanometer-sized montmorillonite of step S1 into a 0.4mmol·L -1 sodium metasilicate aqueous solution, mechanically stirring at 50°C in a thermostatic water bath for 4h to obtain a nanometer-sized montmorillonite suspension;

[0022] S3: the nanometer montmorillonite suspension prepared in step S2 is spray dried to obtain the nanometer montmorillonite hollow microspheres; the spray drying conditions are as follows: nozzle diameter is 0.7 mm, feed flow rate is 1000 mL·h -1 , and inlet temperature is 180℃.

[0023] In a second aspect, the present application further provides the use of the nanometer montmorillonite hollow microspheres in the preparation of a sustained-release carrier.

[0024] The preferred conditions are obtained by orthogonal experiment and variance analysis.

[0025] Compared with the prior art, the present application has the following characteristics and beneficial effects:

[0026] (1) In the present application, the original sodium-based montmorillonite is nanometerized by ultrasonic and water swelling, and then the morphology of the nanometer montmorillonite powder is constructed by modification under mild conditions (30-50℃ under normal pressure), and the nanometer montmorillonite hollow microspheres are prepared by means of spray drying and other process means. The reaction process involves less chemical reagents, is green and environmentally friendly, and does not require post-treatment.

[0027] (2) The preparation process is simple and easy to operate, the raw materials used are non-toxic, have huge reserves and are low in price, the nanometer montmorillonite hollow microspheres prepared after nanometerization are uniform in size, good in sphericity, high in yield, have good dispersibility and excellent structural properties, and are suitable for industrial production.

[0028] (3) The nanometer montmorillonite hollow microspheres prepared have high specific surface area, strong cation exchange property and strong adsorption / desorption capacity, like traditional montmorillonite microspheres, and can load more macromolecular substances due to their unique hollow structure, so they can be used as drug sustained-release microcapsules, catalyst carriers, pollutant adsorbents, etc., and are widely used in the fields of environment, chemical industry and medicine. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a SEM image of the nanometer montmorillonite powder.

[0030] Figure 2 is a SEM image of the nanometer montmorillonite hollow microspheres prepared in Example 1.

[0031] Figure 3 is a SEM image of the nanometer montmorillonite hollow microspheres prepared in Example 2.

[0032] Figure 4 is a SEM image of the nanometer montmorillonite hollow microspheres prepared in Example 3.

[0033] Figure 5 is a SEM image of the nanometer montmorillonite hollow microspheres prepared in Example 4.

[0034] Figure 6 SEM image of the nano-montmorillonite hollow microspheres prepared in Example 5.

[0035] Figure 7 FT-IR image of the nano-montmorillonite hollow microspheres prepared in Example 5.

[0036] Figure 8 Nitrogen adsorption-desorption image of the nano-montmorillonite hollow microspheres prepared in Example 5.

[0037] Figure 9 Variation graph of the slow release of chlorine dioxide by the nano-montmorillonite hollow microspheres prepared in Example 5.

[0038] Figure 10 SEM image of the nano-montmorillonite hollow microspheres prepared in the comparative example. (The binder is a. ammonia water; b. aluminum hydroxyl chloride; c. trimethoxysilane; d. 3-aminopropyl triethoxysilane) DETAILED DESCRIPTION

[0039] The application will be further described in conjunction with specific embodiments, but the scope of protection of the application is not limited to this:

[0040] Example 1:

[0041] Sodium-based montmorillonite (Xinhan Mining Products Co., Ltd., analytical pure AR) and deionized water were mixed in a mass ratio of 1:50, and the montmorillonite was fully dispersed and expanded in water under simultaneous ultrasonic and mechanical stirring for 24 h at room temperature. After that, it was allowed to stand for 7 days to stratify, and the middle colloid part was centrifuged and washed with deionized water. The obtained precipitate was placed in a vacuum oven at 80°C and vacuum dried for 24 h to obtain nano-montmorillonite. Sodium metasilicate was weighed, and deionized water was measured to prepare a sodium metasilicate aqueous solution with a concentration of 0.1 mmol·L -1 -1. The 10.0 g of nano-montmorillonite powder was added to 2 L of the sodium metasilicate aqueous solution, and mechanical stirring was performed under the condition of a constant temperature water bath at 40°C for 4 h. The obtained montmorillonite suspension was dried by a spray drying device, the nozzle aperture was 0.7 mm, the feed flow rate was 1000 mL·h -1 -1, and the inlet temperature was 180°C. Thus, nano-montmorillonite hollow microspheres were prepared.

[0042] Figure 1 SEM image of the nano-montmorillonite powder, as Figure 1 can be seen, the nano-montmorillonite powder before reaction showed a dispersed sheet structure, the sheet edges were slightly curled, and the structure was relatively loose. The surface morphology analysis of the sample was observed by a ZEISS Gemini 500 field emission scanning electron microscope, and the results are shown in Figure 2 Figure 2 ​As can be seen in A, the sample particles exhibit spherical morphology, mainly sub-spherical and spherical, but the sphericity and sphericity are poor, with a large number of unformed fragments present. The sample particles also show significant agglomeration and poor dispersion. Figure 2 A. The diagonal and midline sampling method was used to measure the microsphere size, and the statistical data of the particle size results in Table 1 were obtained. The particle size distribution of the microsphere samples was plotted. Figure 2 B. From Table 1 and Figure 2 According to B, the particle size distribution range of the microsphere sample is approximately 2000–12000 nm, and the average particle size is D. 50 (50% of the particle size) is 6000 nm. Figure 2 C represents a complete microsphere sample with a secondary particle size of approximately 5600 nm. It can be seen that the microspheres are composed of many montmorillonite sheets stacked in a tortuous manner, and there are a large number of wrinkles and pores on the surface of the spheres. Figure 2 D is a broken microsphere sample, and its internal hollow structure can be clearly observed. The thickness of the sphere wall is about 1000 nm, and there are a large number of pores and cracks on both the inner and outer surfaces of the sphere wall.

[0043] Table 1. Statistical results of the particle size of the nano-montmorillonite hollow microspheres prepared in Example 1.

[0044]

[0045] Example 2:

[0046] Sodium-based montmorillonite (Xincheng Mineral Products Co., Ltd., analytical grade AR) and deionized water were mixed at a mass ratio of 1:50. The mixture was simultaneously ultrasonically and mechanically stirred at room temperature for 24 hours to allow the montmorillonite to fully disperse and swell in the water. After standing for 7 days to allow for stratification, the intermediate colloidal fraction was collected, centrifuged, washed with deionized water, and the resulting precipitate was vacuum-dried in an 80℃ oven for 24 hours to obtain nano-sized montmorillonite. Sodium metasilicate and deionized water were weighed to prepare a solution with a concentration of 0.2 mmol·L⁻¹. -1 10.0 g of nano-montmorillonite powder was added to 2 L of sodium metasilicate aqueous solution, and the reaction was carried out under mechanical stirring at a constant temperature water bath of 45 °C for 6 h. The resulting montmorillonite suspension was dried using a spray dryer with a nozzle diameter of 0.7 mm and a feed flow rate of 1000 mL·h. -1 Nano-montmorillonite hollow microspheres can be prepared by using an inlet temperature of 180℃.

[0047] Figure 1 SEM images of nano-montmorillonite powder, by Figure 1 It can be seen that the unreacted nano-montmorillonite powder exhibits a dispersed, plate-like structure with slightly curled edges, indicating a relatively loose structure. The surface morphology of the sample was analyzed using a ZEISS Gemini 500 field emission scanning electron microscope, and the results are as follows: Figure 3The results are shown in Table 1. Figure 3 As can be seen from Table 1, the spherical morphology appears in the sample particles, mainly sub-circular and circular spheres, but the spheroidization rate and sphericity are poor, and a large amount of unformed fragments exist in the sample; the sample particles have obvious agglomeration phenomenon, and the dispersion degree is poor. The sample particles are dispersed by ultrasonic dispersion, and the particle size is measured by the diagonal and midline point method. Figure 3 A, the particle size distribution of the microsphere sample is obtained by plotting the particle size statistical data in Table 2 Figure 3 B. As can be seen from Table 2 and Figure 3 B, the particle size distribution range of the microsphere sample is about 3000-13000 nm, and the average particle size D 50 (50% passing particle size) is 6500 nm. Figure 3 C is a complete microsphere sample, and the secondary particle size is about 6800 nm. It can be seen that the microsphere is formed by many montmorillonite layers stacked in a zigzag manner, and a large number of wrinkles and pores exist on the surface of the sphere. Figure 3 D is a broken microsphere sample, and its internal hollow structure can be clearly observed. The thickness of the sphere wall is about 1000 nm, and a large number of pores and cracks exist on the inner and outer surfaces of the sphere wall.

[0048] Table 2 Particle size statistical results of nanometer montmorillonite hollow microspheres prepared in Example 2

[0049]

[0050] Example 3:

[0051] Sodium montmorillonite (Xinhan Mining Products Co., Ltd., analytical pure AR) and deionized water were mixed in a mass ratio of 1:50, and the montmorillonite was fully dispersed and expanded in water under ultrasonic and mechanical stirring for 24 h at room temperature. After that, it was left to stand for 7 days to make it stratify, and the middle colloid part was centrifuged and washed with deionized water. The obtained precipitate was placed in a 80℃ oven for vacuum drying for 24 h to obtain nanometer montmorillonite. Sodium metasilicate was weighed, and deionized water was measured to prepare a sodium metasilicate aqueous solution with a concentration of 0.3 mmol·L -1 -1. 10.0 g of nanometer montmorillonite powder was added to 2 L of sodium metasilicate aqueous solution, and mechanical stirring was carried out under the condition of a constant temperature water bath at 35℃ for 10 h. The montmorillonite suspension obtained by the reaction was dried by a spray drying device, the nozzle aperture was 0.7 mm, the feed flow rate was 1000 mL·h -1 -1, the inlet temperature was 180℃, and nanometer montmorillonite hollow microspheres were prepared.

[0052] Figure 1 SEM image of nanometer montmorillonite powder, which is Figure 1It can be seen that the nano-montmorillonite powder before reaction has a dispersed sheet structure, the edges of the sheet layer are slightly curled, and the structure is relatively loose. The surface morphology of the sample was observed using a ZEISS Gemini500 field emission scanning electron microscope, and the results are shown in Figure 4 A. Figure 4 As can be seen from A, spherical morphology appears in the sample particles, mainly sub-circular and circular spheres, and the circularity is slightly improved compared with the above two samples, but the balling rate is still poor, and there are still some unformed fragments in the sample; the sample particles do not have obvious agglomeration, and the dispersion is good. The Figure 4 A was measured by the diagonal and midline point method, and the particle size statistical data of the sample are shown in Table 3, and the particle size distribution of the microsphere sample is plotted Figure 4 B. From Table 3 and Figure 4 B, it can be seen that the particle size distribution range of the microsphere sample is about 4000-13000 nm, and the average particle size D 50 (50% passing particle size) is 7000 nm. Figure 4 C is a complete microsphere sample, and the secondary particle size is about 6500 nm. It can be seen that the surface of the microsphere is composed of many small montmorillonite sheet layers tightly packed, and the surface is slightly rough, and there are a large number of small pores on the surface of the ball wall. Figure 4 D is a broken microsphere sample, and its internal hollow structure can be clearly observed. The thickness of the ball wall is about 800 nm, and there are a large number of small pores on the inner and outer surfaces of the ball wall.

[0053] Table 3 Statistical results of the particle size of the nano-montmorillonite hollow microspheres prepared in Example 3

[0054]

[0055] Example 4:

[0056] Sodium-based montmorillonite (Xinhan Mining Products Co., Ltd., analytical pure AR) and deionized water were mixed in a mass ratio of 1:50, and the montmorillonite was fully dispersed and expanded in water under ultrasonic and mechanical stirring at room temperature for 24 h. After that, it was left to stand for 7 days to separate the layers, and the middle colloidal part was centrifuged and washed with deionized water. The obtained precipitate was placed in a 80℃ oven for vacuum drying for 24 h to obtain nano-montmorillonite. Sodium metasilicate was weighed, and deionized water was measured to prepare a sodium metasilicate aqueous solution with a concentration of 0.5 mmol·L -1 -1. 10.0 g of nano-montmorillonite powder was added to 2 L of sodium metasilicate aqueous solution, and mechanical stirring was carried out under the condition of a 30℃ constant temperature water bath for 6 h. The montmorillonite suspension obtained by the reaction was dried by a spray drying device, the nozzle diameter was 0.7 mm, the feed flow rate was 1000 mL·h -1 -1, the inlet temperature was 180℃, and nano-montmorillonite hollow microspheres were prepared.

[0057] Figure 1 SEM image of the nanometer montmorillonite powder, which is shown in Figure 1 It can be seen that the nanometer montmorillonite powder before reaction has a dispersed flaky structure, the edges of the flaky layers are slightly curled, and the structure is relatively loose. The surface morphology of the sample was observed using a ZEISS Gemini 500 field emission scanning electron microscope, and the results are shown in Figure 5 As can be seen from Figure 5 A, spherical morphologies appear in the sample particles, mainly sub-circular and circular spheres, the sphere rate and sphericity are general, the sample particles are relatively large and irregular block particles appear; the sample particles have a relatively obvious agglomeration phenomenon and poor dispersibility. The Figure 5 A was measured by the diagonal and midline point method, and the particle size result statistical data of Table 4 was obtained, and the particle size distribution Figure 5 B of the microsphere sample was plotted. From Table 4 and Figure 5 B, it can be seen that the particle size distribution interval of the microsphere sample is about 4000-13000 nm, and the average particle size D 50 (50% passing particle size) is 7500 nm. Figure 5 C is a complete microsphere sample, and the secondary particle size is about 8700 nm. It can be seen that the surface of the microsphere is formed by the close accumulation of many small montmorillonite layers, and the surface is slightly rough, and there are a large number of small pores on the surface of the sphere wall. Figure 5 D is a broken microsphere sample, and its internal hollow structure can be clearly observed. The thickness of the sphere wall is about 1500 nm, and there are a large number of small pores on the inner and outer surfaces of the sphere wall.

[0058] Table 4 Statistical results of the spherical particle size of the nanometer montmorillonite hollow microspheres prepared in Example 4

[0059]

[0060] Example 5:

[0061] Sodium montmorillonite (Xinhan Mining Products Co., Ltd., analytical pure AR) and deionized water were mixed in a mass ratio of 1:50, and the montmorillonite was fully dispersed and expanded in water under ultrasonic and mechanical stirring at room temperature for 24 h. Then it was left to stand for 7 days to separate the layers, and the middle colloidal part was centrifuged and washed with deionized water. The obtained precipitate was placed in a 80℃ oven for vacuum drying for 24 h to obtain nanometer montmorillonite. Sodium metasilicate was weighed, and deionized water was measured to prepare a sodium metasilicate aqueous solution with a concentration of 0.4 mmol·L -1 . 10.0 g of nanometer montmorillonite powder was added to 2 L of sodium metasilicate aqueous solution, and mechanical stirring was carried out under the condition of a 50℃ constant temperature water bath for 4 h. The montmorillonite suspension obtained by the reaction was dried by a spray drying device, the nozzle aperture was 0.7 mm, and the feeding flow rate was 1000 mL·h -1, the import temperature is 180℃, and the nano-montmorillonite hollow microspheres can be prepared.

[0062] Figure 1 SEM image of the nano-montmorillonite powder, wherein Figure 1 It can be seen that the nano-montmorillonite powder before reaction has a dispersed sheet structure, the sheet edges are slightly curled, and the structure is relatively loose. The surface morphology analysis of the sample is observed by using a ZEISS Gemini500 field emission scanning electron microscope, and the results are shown in Figure 6 It can be seen from Figure 6 A that the spherical morphology appears in the sample particles, mainly circular spheres, and the circularity is better than the above-mentioned sample, the balling rate and sphericity are good, and only a small amount of unformed fragments exist in the sample; the sample particles do not have obvious agglomeration phenomenon, and the dispersity is good. The Figure 6 A is measured by using the diagonal and midline point method, and the particle size result statistical data of table 5 is obtained, and the particle size distribution Figure 6 B of the microsphere sample is plotted. It can be seen from table 5 and Figure 6 B that the particle size distribution interval of the microsphere sample is about 3000-13000nm, and the average particle size D 50 (50% passing particle size) is 6000nm. Figure 6 C is the complete microsphere sample, and the secondary particle size is about 7500nm. It can be seen that the surface of the microsphere is formed by the close accumulation of many small montmorillonite sheet layers, the surface is slightly rough, and a large number of small pores exist on the surface of the ball wall. Figure 6 D is the broken microsphere sample, and the internal hollow structure can be obviously observed. The ball wall thickness is about 600nm, and a large number of small pores exist on the inner and outer surfaces of the ball wall. Figure 7 is the infrared result of the nano-montmorillonite after the microsphere construction using a sodium metasilicate solution, wherein a is the nano-montmorillonite, and b is the montmorillonite microsphere. It can be seen that the nano-montmorillonite hollow microsphere has multiple montmorillonite characteristic peaks (such as the -OH vibration peak at 1635.4cm-1, the Si-O-Si vibration peak at 1037.7cm-1, and the Si-O-Al vibration peak at 520.2cm-1, etc.). At the same time, the -OH vibration peak at 1429.3cm-1 is broadened. This is because the construction of the microsphere form provides structural stability for one or more covalent bonds corresponding to the intramolecular hydroxyl group, thereby reducing the vibration energy transfer rate, thereby increasing the peak width of the hydroxyl group. Figure 8The adsorption isotherm of the nanometer montmorillonite hollow microspheres is of type IV, which is a typical isotherm type of mesoporous materials. At a low relative pressure, monolayer adsorption occurs; at a high relative pressure, multilayer adsorption occurs first, and then capillary condensation of the adsorbate occurs. The steeper the capillary condensation segment, the more uniform the mesopore distribution, the larger the pore size of the mesopores, and the greater the pressure at which capillary condensation occurs. After all the pores condense, adsorption only occurs on the outer surface far smaller than the surface area, and the curve is flat. At a relative pressure close to 1, adsorption occurs on the large pores, and the curve rises. The desorption isotherm is not coincident with the adsorption isotherm, and the desorption isotherm is above the adsorption isotherm, resulting in an adsorption hysteresis and forming an "adsorption hysteresis ring". The hysteresis ring is related to the shape and size of the pores. As can be seen from the figure, the nanometer montmorillonite hollow microspheres have a H2-type hysteresis ring, which is caused by a more complex pore structure, which may include typical "ink bottle" pores, tubular pores with uneven pore size distribution, and interstitial pores between densely packed spherical particles. Combined with the pore size distribution graph, it can be seen that the nanometer montmorillonite hollow microspheres have the largest proportion of pores with a pore size of about 3 nm, followed by pores with a pore size of 6 nm.

[0063] 10g of solid chlorine dioxide powder was mixed with 20g of montmorillonite microspheres, and the slow release of chlorine dioxide gas under sealed and dark conditions was detected. Figure 9 For the slow release of chlorine dioxide gas under sealed and dark conditions, as can be seen from the figure, without using nanometer montmorillonite hollow microspheres as a slow release carrier, the chlorine dioxide gas was consumed almost completely on the 8th day, and after using nanometer montmorillonite hollow microspheres as a slow release carrier, the release time of chlorine dioxide gas can be extended to 18 days.

[0064] Table 5 Nanometer montmorillonite hollow microspheres prepared in Example 5

[0065]

[0066] The orthogonal experiment is carried out on the morphology construction of the montmorillonite hollow microspheres by taking the sodium metasilicate concentration, the reaction temperature and the reaction time as the main factors. The best reaction condition is obtained by variance analysis, which is described in the example 5. Since the number of experimental groups is too large, not all of them are listed, only 5 groups of examples are selected for description. From the SEM images of the above 5 examples, it can be roughly known that among the three reaction conditions affecting the construction of the montmorillonite hollow microspheres, the sodium metasilicate concentration and the reaction temperature have the most obvious influence on the microsphere morphology. With the increase of the sodium metasilicate concentration and the reaction temperature, the accumulation of the montmorillonite layers becomes more and more compact, the sphere forming rate, the sphericity and the dispersion degree are better, the particle size of the sample is more uniform, the microsphere wall thickness is thinner, the cavity capacity in the microsphere is larger, and the pore size on the microsphere wall surface is more ideal, which is beneficial to the adsorption, storage and slow release of macromolecular substances. However, when the sodium metasilicate concentration is too high, the montmorillonite layers will be excessively accumulated to form irregular blocky particles with large size, at the same time, the microsphere wall thickness increases and the cavity capacity in the microsphere decreases, resulting in the reduction of the adsorption and loading performance of the microsphere.

[0067] Comparative example 1

[0068] The sodium-based montmorillonite (Xinhan Mining Products Co., Ltd., analytical pure AR) and deionized water are mixed in a mass ratio of 1:50, and the montmorillonite is fully dispersed and expanded in water under simultaneous ultrasonic and mechanical stirring for 24 h at room temperature. Then it is allowed to stand for 7 days to stratify, and the middle colloidal part is centrifuged and washed with deionized water. The obtained precipitate is vacuum dried in an oven at 80℃ for 24 h to obtain nanometerized montmorillonite. Ammonia water and deionized water are measured and prepared to prepare an ammonia water solution with a concentration of 0.4 mmol·L -1 -1. The 10.0 g of nanometer montmorillonite powder is added into 2 L of the ammonia water solution, and mechanical stirring is carried out under the condition of a constant temperature water bath at 50℃ for 4 h. The obtained montmorillonite suspension is dried by a spray drying device, the nozzle aperture is 0.7 mm, the feeding flow rate is 1000 mL·h -1 -1, and the inlet temperature is 180℃, so as to obtain the nanometer montmorillonite hollow microspheres.

[0069] Comparative example 2

[0070] The sodium-based montmorillonite (Xinhan Mining Products Co., Ltd., analytical pure AR) and deionized water are mixed in a mass ratio of 1:50, and the montmorillonite is fully dispersed and expanded in water under simultaneous ultrasonic and mechanical stirring for 24 h at room temperature. Then it is allowed to stand for 7 days to stratify, and the middle colloidal part is centrifuged and washed with deionized water. The obtained precipitate is vacuum dried in an oven at 80℃ for 24 h to obtain nanometerized montmorillonite. Ammonia water and deionized water are measured and prepared to prepare an ammonia water solution with a concentration of 0.4 mmol·L -1To prepare an aqueous solution of aluminum hydroxide chloride, 10.0 g of nano-montmorillonite powder was added to 2 L of aluminum hydroxide chloride aqueous solution, and the reaction was carried out under mechanical stirring at a constant temperature of 50 °C for 4 h. The resulting montmorillonite suspension was dried using a spray dryer with a nozzle diameter of 0.7 mm and a feed flow rate of 1000 mL·h. -1 Nano-montmorillonite hollow microspheres can be prepared by using an inlet temperature of 180℃.

[0071] Comparative Example 3:

[0072] Sodium-based montmorillonite (Xincheng Mineral Products Co., Ltd., analytical grade AR) and deionized water were mixed at a mass ratio of 1:50. The mixture was simultaneously ultrasonically and mechanically stirred at room temperature for 24 hours to allow the montmorillonite to fully disperse and swell in the water. After standing for 7 days to allow for stratification, the intermediate colloidal fraction was collected, centrifuged, washed with deionized water, and the resulting precipitate was vacuum-dried in an 80℃ oven for 24 hours to obtain nano-sized montmorillonite. Trimethoxysilane and deionized water were weighed to prepare a solution with a concentration of 0.4 mmol·L⁻¹. -1 A montmorillonite nanoparticle powder was added to 2 L of a trimethoxysilane aqueous solution and reacted under mechanical stirring at a constant temperature of 50 °C for 4 h. The resulting montmorillonite suspension was dried using a spray dryer with a nozzle diameter of 0.7 mm and a feed flow rate of 1000 mL·h. -1 Nano-montmorillonite hollow microspheres can be prepared by using an inlet temperature of 180℃.

[0073] Comparative Example 4:

[0074] Sodium-based montmorillonite (Xincheng Mineral Products Co., Ltd., analytical grade AR) and deionized water were mixed at a mass ratio of 1:50. The mixture was simultaneously ultrasonically and mechanically stirred at room temperature for 24 hours to allow the montmorillonite to fully disperse and swell in the water. After standing for 7 days to allow for stratification, the intermediate colloidal fraction was collected, centrifuged, washed with deionized water, and the resulting precipitate was vacuum-dried in an 80℃ oven for 24 hours to obtain nano-sized montmorillonite. 3-Aminopropyltriethoxysilane and deionized water were weighed to prepare a solution with a concentration of 0.4 mmol·L⁻¹. -1 A 3-aminopropyltriethoxysilane aqueous solution was prepared by adding 10.0 g of nano-montmorillonite powder to 2 L of 3-aminopropyltriethoxysilane aqueous solution and reacting under mechanical stirring at a constant temperature of 50 °C for 4 h. The resulting montmorillonite suspension was dried using a spray dryer with a nozzle diameter of 0.7 mm and a feed flow rate of 1000 mL·h. -1 Nano-montmorillonite hollow microspheres can be prepared by using an inlet temperature of 180℃.

[0075] Figure 1 SEM images of nano-montmorillonite powder, by Figure 1It can be seen that the nano-montmorillonite powder before reaction has a dispersed sheet structure, the sheet edges are slightly curled, and the structure is relatively loose. The surface morphology analysis of the comparative sample was observed using a ZEISS Gemini 500 field emission scanning electron microscope, and the results are shown in Figure 10 As shown. Spherical morphology appears in the sample particles, mainly sub-circular and circular-like spheres, but the balling rate and sphericity of the microsphere samples formed by the four binders are extremely poor, and a large number of unformed fragments exist in the sample; the sample particles have a relatively obvious agglomeration phenomenon, poor dispersity, and the sample particle size is extremely uneven.

Claims

1. A type of nano-montmorillonite hollow microsphere, characterized in that... The nano-montmorillonite hollow microspheres were prepared according to the following method: S1: Disperse sodium-based montmorillonite in deionized water, allow it to fully disperse and expand, let it stand and separate into layers, take the middle layer and separate it to obtain nano-sized montmorillonite; S2: Add the nano-sized montmorillonite described in step S1 to 0.1~0.5 mmol·L⁻¹ -1 A nano-montmorillonite suspension was obtained by mechanically stirring the sodium metasilicate aqueous solution at 30–50 °C for 2–10 h. S3: The nano-montmorillonite suspension obtained in step S2 is spray-dried to obtain the nano-montmorillonite hollow microspheres; The volume of the sodium metasilicate aqueous solution in step S2 is 67-200 mL / g based on the mass of the nano-sized montmorillonite.

2. The nano-montmorillonite hollow microspheres as described in claim 1, characterized in that: The mass ratio of sodium-based montmorillonite to deionized water in step S1 is 1:50 to 150.

3. The nano-montmorillonite hollow microspheres as described in claim 1, characterized in that: The dispersion expansion described in step S1 is performed as follows: simultaneous ultrasonic and mechanical stirring at room temperature for 12–24 h; The settling time for stratification in step S1 is 5 to 7 days.

4. The nano-montmorillonite hollow microspheres as described in claim 1, characterized in that: The separation process in step S1 is as follows: the intermediate layer is centrifuged, the resulting precipitate is washed with deionized water and dried to obtain the nano-sized montmorillonite.

5. The nano-montmorillonite hollow microspheres as described in claim 1, characterized in that: The concentration of the sodium metasilicate aqueous solution in step S2 is 0.4 mmol·L⁻¹. -1 .

6. The nano-montmorillonite hollow microspheres as described in claim 1, characterized in that: The temperature of the mechanical stirring reaction in step S2 is 50°C.

7. The nano-montmorillonite hollow microspheres as described in claim 1, characterized in that: The spray drying conditions described in step S3 are: nozzle diameter of 0.5–2.0 mm and feed flow rate of 200–1000 mL·h. -1 The inlet temperature is 160–200 ℃.

8. The nano-montmorillonite hollow microspheres as described in claim 1, characterized in that: The nano-montmorillonite hollow microspheres were prepared according to the following method: S1: Disperse sodium-based montmorillonite in deionized water, allow it to fully disperse and expand, let it stand and separate into layers, take the middle layer and separate it to obtain nano-sized montmorillonite; S2: Add the nano-sized montmorillonite described in step S1 to 0.4 mmol·L⁻¹ -1 A nano-montmorillonite suspension was obtained by mechanically stirring the sodium metasilicate aqueous solution at 50 °C for 4 h. S3: The nano-montmorillonite suspension obtained in step S2 is spray-dried to obtain the nano-montmorillonite hollow microspheres; the spray-drying conditions are: nozzle diameter of 0.7 mm and feed flow rate of 1000 mL·h. -1 The inlet temperature is 180 ℃.

9. The application of the nano-montmorillonite hollow microspheres as described in any one of claims 1-8 in the preparation of sustained-release carriers.

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