Core-shell type porous silicon dioxide microsphere, preparation method thereof and application of core-shell type porous silicon dioxide microsphere in structural color

Abstract

The invention belongs to the technical field of chemical preparation of nano-porous materials, and relates to core-shell type porous silicon dioxide microspheres, a preparation method thereof and application of the core-shell type porous silicon dioxide microspheres in structural color. The preparation method comprises the following steps: (1) mixing absolute ethyl alcohol, ammonia water and deionized water to obtain alkaline hydrolysate; (2) mixing tetraethyl orthosilicate with organosilane to obtain a silane mixed solution; (3) simultaneously and respectively dropwise adding the alkaline hydrolysate and the silane mixed liquid into the silicon dioxide microsphere dispersion liquid under stirring, and reacting to obtain an intermediate; and (4) calcining the obtained intermediate at 550-650 DEG C to obtain the core-shell type porous silicon dioxide microspheres. The preparation method of the core-shell type porous silicon dioxide microspheres is simple, easy to operate and mild in condition. The raw materials are simple, easy to obtain, non-toxic and harmless, a surfactant and a template agent are not needed, and the cost is greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical preparation of nanoporous materials, and relates to core-shell porous silica microspheres, a preparation method thereof, and an application thereof in structural color. Background Art

[0002] According to different color development mechanisms, colors are roughly divided into pigment colors and structural colors. Structural color refers to the color generated by the interaction of incident light with micro-nano structures similar to the wavelength of visible light. Compared with pigment colors, it is more stable, adjustable, and environmentally friendly. Photonic crystals are an important material that can generate structural colors. They are artificial optical materials composed of periodically regular arrangements of media with different refractive indexes. Photonic crystals have the same periodic structure and bandgap structure as semiconductors, making it possible to control the flow of photons, and having broad application prospects in emerging fields such as filtering, optical fibers, sensing, display, anti-counterfeiting, and coatings.

[0003] Silica microspheres are one of the most common and widely used raw materials for preparing photonic crystals. Among them, porous silica microspheres are a kind of porous nanomaterial, which has high chemical stability and thermal stability, and also has a certain mechanical strength. The porous structure on the surface gives it a high specific surface area, and it has good application value and potential in fields such as specific adsorption separation, biomedicine, photonic crystals, sensors, and environmental monitoring.

[0004] At present, the preparation methods of porous silica microsphere materials are mostly template method and hydrothermal synthesis method. The former requires the consumption of a large amount of template agents and surfactants, greatly increasing the cost and the steps are relatively cumbersome; while the latter requires high-temperature and high-pressure experimental conditions, which are relatively dangerous and harsh, and it is difficult to control the reaction process. Summary of the Invention

[0005] In view of the above problems, the present invention provides a core-shell porous silica microsphere, a preparation method thereof, and an application thereof in structural color. In particular, the preparation method is simple to operate, the thickness of the porous shell layer can be adjusted, the cost is greatly reduced, and it can be applied to the formation of structural color of photonic crystals to realize the regulation of the color wavelength of structural color.

[0006] The first aspect of the present invention provides a preparation method of core-shell porous silica microspheres, characterized in that the preparation method includes the following steps: (1) Mix absolute ethanol, ammonia water and deionized water to obtain an alkaline hydrolysis solution; (2) Mix tetraethyl orthosilicate and organosilane to obtain a silane mixture; (3) Under stirring, simultaneously and separately drop the alkaline hydrolysis solution and the silane mixture into the silica microsphere dispersion and react to obtain an intermediate; (4) Calcinate the obtained intermediate at 550 - 650 °C to obtain the core - shell porous silica microspheres.

[0007] In the present invention, the organosilane undergoes hydrolysis and polycondensation under the condition of an alkaline hydrolysis solution, and the polycondensation rate is greater than the hydrolysis rate, which can directly coat a layer of organosilicon shell on the silica microspheres. After high - temperature calcination, the organic carbon chains in the shell react to generate gas and escape, forming pores in the original position, thereby preparing core - shell porous silica microspheres with adjustable shell thickness. The obtained core - shell porous silica microspheres have certain application prospects in regulating the color and wavelength of photonic crystal structural colors.

[0008] Preferably, in step (1): the content of absolute ethanol in the alkaline hydrolysis solution is 75 - 80 wt%, the content of ammonia water is 3 wt% - 7.5 wt%, and the rest is deionized water; and / or, the concentration of the ammonia water is 25 - 30 wt%.

[0009] Preferably, in step (2): the selected organosilane is one of octadecyltrimethoxysilane, octadecyltriethoxysilane, hexadecyltrimethoxysilane, and hexadecyltriethoxysilane; and / or, the mass ratio of tetraethyl orthosilicate to organosilane is (2 - 4):1; and / or, the purity of the organosilane ≥ 95%, and the purity of the tetraethyl orthosilicate is > 99%.

[0010] Preferably, in step (3): the dropping rate of the alkaline hydrolysis solution is 1.6 - 2.4 mL / h; and / or, the dropping rate of the silane mixture is 0.1 - 0.15 mL / h; and / or, the volume ratio of the alkaline hydrolysis solution to the silane mixture is (12 - 20):1, preferably (14 - 18):1.

[0011] Preferably, in step (3): the diameter of the monodisperse silica microspheres in the silica microsphere dispersion is 200 - 250 nm; and / or, the content of the monodisperse silica microspheres in the silica microsphere dispersion is 1.0 wt% - 1.5 wt%; and / or, the solvent of the silica microsphere dispersion is absolute ethanol; Preferably, the monodisperse silica microspheres are refluxed in hydrochloric acid for at least 24 hours to activate a large number of hydroxyl groups on the surface of the monodisperse silica microspheres.

[0012] Preferably, in step (3): the stirring is magnetic stirring, preferably at a rotation speed of 180 - 240 rpm; The temperature of the reaction is 40 - 60 °C; The time of the reaction is at least 6 hours; Preferably, after the reaction is completed, centrifugation, washing, and drying are carried out to obtain the intermediate.

[0013] Preferably, in step (4): the atmosphere for the calcination treatment is air; and / or, the time of the calcination treatment is at least 5 hours.

[0014] The second aspect of the present invention provides a core-shell porous silica microsphere, comprising: a silica microsphere, and a porous silica layer coated on the surface of the silica microsphere; the average pore diameter of the porous silica layer is 2-4 nm.

[0015] Preferably, the thickness of the porous silica layer is 15-50 nm.

[0016] Preferably, the diameter of the silica microsphere is 200-250 nm.

[0017] Preferably, the average particle size of the core-shell porous silica microsphere is 230-350 nm.

[0018] Preferably, the pore volume of the core-shell porous silica microsphere is 0.12-0.24 cm 3 / g.

[0019] Preferably, the specific surface area of the core-shell porous silica microsphere is 200-430 m 2 / g.

[0020] The third aspect of the present invention provides an application of the core-shell porous silica microsphere in structural color.

[0021] The fourth aspect of the present invention provides an application of the core-shell porous silica microsphere in the preparation of photonic crystals.

[0022] Advantages of the present invention: The preparation method of the core-shell porous silica microsphere of the present invention is simple and easy to operate, and the conditions are mild. The raw materials are simple and easy to obtain, non-toxic and harmless, and no surfactant and template agent are required, so the cost is greatly reduced. Description of the drawings

[0023] Figure 1 It is a scanning electron microscope image of the core-shell porous silica microsphere described in Example 1 at a magnification of 50,000 times; Figure 2 It is a transmission electron microscope image of the core-shell porous silica microsphere described in Example 1 at a magnification of 30,000 times; Figure 3Nitrogen adsorption - desorption isotherm diagram of the core - shell porous silica microspheres described in Example 1, where the abscissa is the relative pressure P / P0 (Relative Pressure), and the ordinate is the volume (Volume) @STO (cc / g); Figure 4 Pore size distribution diagram of the core - shell porous silica microspheres described in Example 1, where the abscissa is the pore width (nm), the left ordinate is the cumulative pore volume (cc / g), and the right ordinate is dV(d) (cc / nm / g); Figure 5 Digital photos of the structural colors prepared from the core - shell porous silica microspheres described in Examples 1 - 5; Figure 6 Digital photos of the structural colors prepared from the silica microspheres obtained in Comparative Example 1. Detailed implementation manners

[0024] The present invention will be further described below through the following implementation manners. It should be understood that the following implementation manners are only used to illustrate the present invention and do not limit the present invention.

[0025] The present disclosure provides a core - shell porous silica microsphere, its preparation method and application in structural colors, which can realize the regulation of photonic crystal structural colors.

[0026] The preparation method of the core - shell porous silica microspheres will be exemplarily described below.

[0027] The monodisperse silica microspheres and absolute ethanol are mixed and ultrasonically and uniformly dispersed in a three - necked flask to obtain a silica microsphere dispersion. Specifically, a certain mass of monodisperse silica microspheres is taken and added to a container (for example, a three - necked flask with a volume of, for example, 250 mL), and then a certain amount of absolute ethanol is added to the flask, and ultrasonic treatment is carried out for several minutes to make it uniformly dispersed, obtaining a silica microsphere dispersion. Among them, the diameter of the taken monodisperse silica is 200 - 250 nm (for example, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, etc.). The added absolute ethanol makes the solid content of silica be 1 wt% - 1.5 wt% (1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, etc.).

[0028] After mixing absolute ethanol, ammonia water, and deionized water evenly according to a certain mass ratio, an alkaline hydrolysis solution is obtained. The mass fraction of absolute ethanol in the alkaline hydrolysis solution is about 75%, and the mass fraction of ammonia water is 3% - 7.5% (for example, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 7.5wt%, etc.), and the rest is deionized water. Preferably, the alkaline hydrolysis solution can be injected into a syringe needle (such as 50 mL) for standby.

[0029] After mixing tetraethyl orthosilicate and organosilane evenly according to a certain mass ratio, a silane mixture is obtained. Preferably, the silane mixture can be injected into a syringe needle (such as 10 mL) for standby. Among them, the selected organosilane is one of octadecyltrimethoxysilane, octadecyltriethoxysilane, hexadecyltrimethoxysilane, and hexadecyltriethoxysilane. The mass ratio of tetraethyl orthosilicate to organosilane in the silane mixture is (2 - 4):1 (for example, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, etc.).

[0030] After injecting the prepared alkaline hydrolysis solution and silane mixture into two syringe needles, at a certain stirring speed (such as the magnetic stirring speed) and reaction temperature, using two syringe pumps, the two syringe needles are respectively pushed to drip the corresponding liquids into the flask at different dripping rates for the coating reaction. For example, the dripping rates of the syringe needles containing the alkaline hydrolysis solution and the silane mixture are controlled to be 1.6 - 2.4 mL / h and 0.1 - 0.15 mL / h respectively. During the coating reaction, the magnetic stirring rate is 180 - 240 rpm, and the reaction temperature is 40 - 60 °C. Among them, stirring, dripping, and coating reaction are started simultaneously, and the time used is the same, all more than 6 h (for example, 6 hours, 10 hours, 12 hours, 18 hours, 24 hours, 30 hours, etc.). The time can also be appropriately extended according to the required coating thickness. The volume ratio of the alkaline hydrolysis solution to the silane mixture is (12 - 20):1, preferably (14 - 18):1, and more preferably 16:1.

[0031] After reacting for a certain time, solid-liquid separation is carried out by centrifugation, and then washing and drying are carried out to obtain an intermediate. Specifically, after stopping after a certain time, the supernatant is removed by centrifugation, and the product is ultrasonically cleaned alternately with deionized water and absolute ethanol, and the supernatant is removed by centrifugation. Repeat this three times, and finally vacuum dry overnight to obtain the intermediate.

[0032] The intermediate is calcined to obtain core-shell porous silica microspheres. Specifically, the intermediate is placed in a muffle furnace, heated at a certain rate and maintained at a certain temperature for a certain period of time, and finally the core-shell porous silica microspheres are obtained. Specifically, when calcining the intermediate, the atmosphere used is air, and the heating rate is 3-5 °C / min. The calcination temperature is 550-650 °C, and the calcination time is at least 5 h.

[0033] As a detailed example of preparing core-shell porous silica microspheres, it includes: taking 0.5 g of monodisperse silica microspheres with a particle size of about 250 nm, adding them to a 250 mL three-necked flask, and then adding 50 mL of absolute ethanol to the flask, and ultrasonically treating for several minutes to make them evenly dispersed. After mixing absolute ethanol, ammonia water, and deionized water in a certain mass ratio evenly, an alkaline hydrolysis solution is obtained and injected into a 50 mL syringe needle. After mixing tetraethyl orthosilicate and a certain organosilane in a certain mass ratio evenly, a silane mixture is obtained and injected into a 10 mL syringe needle. At a magnetic stirring speed of 180-240 rpm and a reaction temperature of 40-60 °C, using two injection pumps, the 50 mL and 10 mL syringe needles are respectively pushed to drop the corresponding liquids into the flask at a dropping rate of 1.6-2.4 mL / h and 0.1-0.15 mL / h. After dropping for 6-24 h, stop, centrifuge at 8000 rpm for 4 min, remove the supernatant, ultrasonically clean the product alternately with deionized water and absolute ethanol, and centrifuge to remove the supernatant. Repeat this three times. After vacuum drying overnight at 60 °C, an intermediate is obtained. The intermediate is placed in a muffle furnace, heated to 600 °C at a heating rate of 5 °C / min in an air atmosphere, and maintained at this temperature for calcination for 5 h, and finally the core-shell porous silica microspheres are obtained. The monodisperse silica microspheres can be refluxed in hydrochloric acid for several hours before use to activate a large number of hydroxyl groups on the surface of the silica spheres. The mass fraction of the ammonia water solution is 25%-30%. The purity of the tetraethyl orthosilicate is >99%. The organosilane is one of octadecyltrimethoxysilane, octadecyltriethoxysilane, hexadecyltrimethoxysilane, and hexadecyltriethoxysilane, with a purity of 95%, and must be stored at 2-8 °C. The alkaline hydrolysis solution and the silane mixture must be filtered through a 0.22 μm nylon membrane after preparation to ensure no impurities and ensure the clarity of the solution. The needle of the 50 mL syringe must be closely attached to the inner wall of the three-necked flask, and the needle of the 10 mL syringe must be immersed below the liquid level.

[0034] The core-shell porous silica particles of the present invention are used to prepare photonic crystals and form structural colors.

[0035] Performance test method: The specific surface area, pore volume, and average pore diameter of the core-shell porous silica microparticles were calculated through nitrogen adsorption-desorption experiments; The average particle diameter and shell thickness of the core-shell porous silica microparticles were determined by a laser particle size analyzer; The experimental value of the wavelength was actually measured by a spectrophotometer; The theoretical value of the wavelength was calculated by the simplified Bragg-Snell equation λ = 2.2D.

[0036] The following further exemplifies embodiments to illustrate the present invention in detail. It should be understood that the following embodiments are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are also only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, rather than being limited to the specific values in the following examples.

[0037] Example 1 (1) Take 0.5 g of monodisperse silica microspheres with a particle size of about 250 nm and add them to a 250 mL three-necked flask. Then add 50 mL of absolute ethanol to the flask and ultrasonicate for several minutes to disperse them evenly to obtain a silica microsphere dispersion; (2) Mix absolute ethanol, ammonia water, and deionized water evenly according to a mass ratio of 10:1:2.25 to obtain an alkaline hydrolysis solution, and inject it into a 50 mL syringe needle; (3) Mix tetraethyl orthosilicate and octadecyltrimethoxysilane evenly according to a mass ratio of 3:1 to obtain a silane mixture, and inject it into a 10 mL syringe needle; (4) Under a magnetic stirring speed of 240 rpm and a reaction temperature of 60 °C, use two injection pumps to simultaneously push the 50 mL and 10 mL syringe needles to drop the corresponding liquids into the flask containing the silica microsphere dispersion at dropping rates of 2.4 mL / h and 0.15 mL / h, respectively. Stop dropping after 6 h, centrifuge at 8000 rpm for 4 min, remove the supernatant, alternately use deionized water and absolute ethanol to ultrasonically clean the product, and centrifuge to remove the supernatant. Repeat this three times. After vacuum drying overnight at 60 °C, an intermediate is obtained;

[0038] (5) Put the intermediate into a muffle furnace, and under an air atmosphere, raise the temperature to 600 °C at a heating rate of 5 °C / min and maintain it at this temperature for calcination for 5 h to finally obtain the core-shell porous silica microspheres.

[0039] The scanning electron microscope image of the core-shell porous silica microspheres described in Example 1 of the present invention at a magnification of 50,000 times is asFigure 1 As shown, its transmission electron microscope image at a magnification of 30,000 times is as Figure 2 shown, and its nitrogen adsorption - desorption isotherm is as Figure 3 shown, and its pore size distribution diagram is as Figure 4 shown. Observation Figures 1-4 , it can be significantly seen that the porous structure and core - shell structure of the silica spheres, with a specific surface area of about 200 m 2 / g, a total pore volume reaching more than 0.12 cc / g, and an average pore size of about 3 nm, belonging to narrow mesopores.

[0040] Example 2 (1) Take 0.5 g of monodisperse silica microspheres with a particle size of about 250 nm, add them to a 250 - mL three - necked flask, and then add 50 mL of anhydrous ethanol to the flask. Ultrasonic for several minutes to make it evenly dispersed, obtaining a silica microsphere dispersion; (2) Mix anhydrous ethanol, ammonia water, and deionized water evenly according to a mass ratio of 10:1:2.25 to obtain an alkaline hydrolysis solution, and inject it into a 50 - mL syringe needle; (3) Mix tetraethyl orthosilicate and octadecyltrimethoxysilane evenly according to a mass ratio of 2.5:1 to obtain a silane mixture, and inject it into a 10 - mL syringe needle; (4) At a magnetic stirring speed of 240 rpm and a reaction temperature of 60 °C, use two injection pumps to simultaneously push the 50 - mL and 10 - mL syringe needles at a dropping rate of 2.4 mL / h and 0.15 mL / h respectively to drop the corresponding liquids into the flask containing the silica microsphere dispersion. Stop dropping after 10 h, centrifuge at 8000 rpm for 4 min, then remove the supernatant. Alternately use deionized water and anhydrous ethanol to ultrasonically clean the product and centrifuge to remove the supernatant. Repeat this three times. After vacuum drying overnight at 60 °C, an intermediate is obtained;

[0041] (5) Put the intermediate into a muffle furnace, under an air atmosphere, raise the temperature to 600 °C at a heating rate of 5 °C / min, and maintain this temperature for calcination for 5 h to finally obtain the core - shell type porous silica microspheres.

[0042] Example 3 (1) Take 0.5 g of monodisperse silica microspheres with a particle size of about 250 nm, add them to a 250 - mL three - necked flask, and then add 50 mL of anhydrous ethanol to the flask. Ultrasonic for several minutes to make it evenly dispersed, obtaining a silica microsphere dispersion; (2) Mix anhydrous ethanol, ammonia water, and deionized water evenly according to a mass ratio of 20:1:5.5 to obtain an alkaline hydrolysis solution, and inject it into a 50 - mL syringe needle; (3) Mix tetraethyl orthosilicate and octadecyltrimethoxysilane evenly according to a mass ratio of 3:1 to obtain a silane mixture, and inject it into a 10 mL syringe needle; (4) At a magnetic stirring speed of 240 rpm and a reaction temperature of 60 °C, use two syringe pumps to simultaneously push a 50 mL and a 10 mL syringe needle at dropping rates of 2.4 mL / h and 0.15 mL / h respectively to drop the corresponding liquids into a flask containing a silica microsphere dispersion. Stop dropping after 12 h, centrifuge at 8000 rpm for 4 min, remove the supernatant, ultrasonically clean the product alternately with deionized water and absolute ethanol, and centrifuge to remove the supernatant. Repeat this three times. After vacuum drying overnight at 60 °C, obtain an intermediate;

[0043] (5) Put the intermediate into a muffle furnace, and under an air atmosphere, raise the temperature to 600 °C at a heating rate of 5 °C / min, and maintain the calcination at this temperature for 5 h to finally obtain the core-shell porous silica microspheres.

[0044] Example 4 (1) Take 0.5 g of monodisperse silica microspheres with a particle size of about 250 nm, add them to a 250 mL three-necked flask, and then add 50 mL of absolute ethanol to the flask. Ultrasonicate for several minutes to disperse them evenly to obtain a silica microsphere dispersion; (2) Mix absolute ethanol, ammonia water, and deionized water evenly according to a mass ratio of 10:1:2.25 to obtain an alkaline hydrolysis solution, and inject it into a 50 mL syringe needle; (3) Mix tetraethyl orthosilicate and octadecyltrimethoxysilane evenly according to a mass ratio of 3:1 to obtain a silane mixture, and inject it into a 10 mL syringe needle; (4) At a magnetic stirring speed of 180 rpm and a reaction temperature of 40 °C, use two syringe pumps to simultaneously push a 50 mL and a 10 mL syringe needle at dropping rates of 2.4 mL / h and 0.15 mL / h respectively to drop the corresponding liquids into a flask containing a silica microsphere dispersion. Stop dropping after 14 h, centrifuge at 8000 rpm for 4 min, remove the supernatant, ultrasonically clean the product alternately with deionized water and absolute ethanol, and centrifuge to remove the supernatant. Repeat this three times. After vacuum drying overnight at 60 °C, obtain an intermediate;

[0045] (5) Put the intermediate into a muffle furnace, and under an air atmosphere, raise the temperature to 600 °C at a heating rate of 5 °C / min, and maintain the calcination at this temperature for 5 h to finally obtain the core-shell porous silica microspheres.

[0046] Example 5 (1) Take 0.5 g of monodisperse silica microspheres with a particle size of about 250 nm and add them to a 250 mL three-necked flask. Then add 50 mL of absolute ethanol to the flask and ultrasonicate for several minutes to disperse them evenly, obtaining a silica microsphere dispersion; (2) Mix absolute ethanol, ammonia water, and deionized water evenly according to a mass ratio of 10:1:2.25 to obtain an alkaline hydrolysis solution, and inject it into a 50 mL syringe; (3) Mix tetraethyl orthosilicate and octadecyltrimethoxysilane evenly according to a mass ratio of 3:1 to obtain a silane mixture, and inject it into a 10 mL syringe; (4) At a magnetic stirring speed of 180 rpm and a reaction temperature of 40 °C, use two syringe pumps to simultaneously push the 50 mL and 10 mL syringes to drop the corresponding liquids into the flask containing the silica microsphere dispersion at dropping rates of 1.6 mL / h and 0.1 mL / h, respectively. After dropping for 24 h, stop, centrifuge at 8000 rpm for 4 min, remove the supernatant, ultrasonically clean the product alternately with deionized water and absolute ethanol, and centrifuge to remove the supernatant. Repeat this three times. After vacuum drying overnight at 60 °C, obtain an intermediate;

[0047] (5) Put the intermediate into a muffle furnace, and under an air atmosphere, heat it to 600 °C at a heating rate of 5 °C / min and maintain it at this temperature for calcination for 5 h to finally obtain the core-shell porous silica microspheres.

[0048] Comparative Example 1 (1) Take 0.5 g of monodisperse silica microspheres with a particle size of about 250 nm and add them to a 250 mL three-necked flask. Then add 50 mL of absolute ethanol to the flask and ultrasonicate for several minutes to disperse them evenly, obtaining a silica microsphere dispersion; (2) Mix absolute ethanol, ammonia water, and deionized water evenly according to a mass ratio of 10:1:2.25 to obtain an alkaline hydrolysis solution, and inject it into the silica microsphere dispersion and mix evenly; (3) Mix tetraethyl orthosilicate and octadecyltrimethoxysilane evenly according to a mass ratio of 3:1 to obtain a silane mixture, and inject it into a 10 mL syringe; (4) At a magnetic stirring speed of 180 rpm and a reaction temperature of 60 °C, use a syringe pump to push the 10 mL syringe to drop the silane mixture into the flask containing the silica microsphere dispersion and the alkaline hydrolysis solution at a dropping rate of 0.15 mL / h. After dropping for 14 h, stop, centrifuge at 8000 rpm for 4 min, remove the supernatant, ultrasonically clean the product alternately with deionized water and absolute ethanol, and centrifuge to remove the supernatant. Repeat this three times. After vacuum drying overnight at 60 °C, obtain an intermediate;

[0049] (5) Place the intermediate in a muffle furnace. Under an air atmosphere, raise the temperature to 600 °C at a heating rate of 5 °C / min, and maintain the calcination at this temperature for 5 h to finally obtain core-shell porous silica microspheres.

[0050] Comparative Example 2 (1) Take 0.5 g of monodisperse silica microspheres with a particle size of about 250 nm and add them to a 250 mL three-necked flask. Then add 50 mL of absolute ethanol to the flask and ultrasonicate for several minutes to disperse them evenly to obtain a silica microsphere dispersion; (2) Mix absolute ethanol, ammonia water, and deionized water evenly according to a mass ratio of 10:1:2.25 to obtain an alkaline hydrolysis solution; (3) Mix tetraethyl orthosilicate and octadecyltrimethoxysilane evenly according to a mass ratio of 3:1 to obtain a silane mixture; (4) At a magnetic stirring speed of 180 rpm and a reaction temperature of 60 °C, directly pour the alkaline hydrolysis solution and the silane mixture into the flask containing the silica microsphere dispersion. After reacting for 14 h, stop the reaction, centrifuge at 8000 rpm for 4 min, and then remove the supernatant. Alternately use deionized water and absolute ethanol to ultrasonically clean the product and centrifuge to remove the supernatant. Repeat this three times. After vacuum drying overnight at 60 °C, obtain the intermediate;

[0051] (5) Place the intermediate in a muffle furnace. Under an air atmosphere, raise the temperature to 600 °C at a heating rate of 5 °C / min, and maintain the calcination at this temperature for 5 h to finally obtain core-shell porous silica microspheres.

[0052] Applications of the core-shell porous silica microspheres prepared by the methods described in Examples 1-5 and Comparative Examples 1-2 in structural color. The main method is as follows: Take a glass slide that has been soaked in 30% hydrogen peroxide for more than 24 h in advance, perform ultrasonic cleaning and dry it for later use. Take 0.05 g of the core-shell porous silica microspheres obtained in Examples 1-5 and Comparative Examples 1-2, and add an absolute ethanol suspension containing 0.02% by mass of carbon black particles until the total weight is 1 g. Ultrasonicate strongly until it is completely dispersed evenly, then pour it into a spray gun, spray it evenly onto the surface of the glass slide at a certain constant pressure, and immediately place it in an oven to quickly volatilize the ethanol to obtain a structurally colored sample with saturated color. Finally, determine the wavelength corresponding to the color through the reflection spectrum in the visible light band of a UV-visible spectrophotometer.

[0053] The specific surface area, pore volume, average pore diameter, shell thickness, particle size, and wavelength corresponding to the structural color of the core-shell porous silica microspheres obtained in Examples 1-5 and Comparative Examples 1-2 of the present invention are shown in Table 1.

[0054] Table 1: <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Average pore diameter (nm) Average particle size (nm) Shell thickness (nm) Theoretical wavelength value (nm) Actual wavelength value (nm) Example 1 199 0.126 2.82 289.9 19.9 638 573 Example 2 309 0.172 2.70 305.7 27.8 673 595 Example 3 353 0.199 2.82 314.8 32.4 693 603 Example 4 375 0.217 3.18 321.1 35.5 706 618 Example 5 430 0.233 2.94 337.9 43.9 743 641 Comparative Example 1 295 0.177 3.07 311.1 / 193.3 30.5 684 / 425 None Comparative Example 2 125 0.082 2.58 None None None None It can be seen from Examples 1-5 in Table 1 that the preparation method of the present invention has a good effect, the coating layer and pore formation basically meet the expected requirements, and the specific surface area can reach 200-430 m 2 / g, and the total pore volume can reach 0.12~0.24 cm 3 / g, the average pore size is about 3 nm, which belongs to narrow mesopores, and the coating thickness also increases steadily over time. The actual value of the color corresponding to the wavelength is blue-shifted to a considerable extent compared with the corresponding theoretical value calculated according to the formula, indicating that a large number of pores in the silicon sphere can achieve the regulation of the structural color. This is mainly because a large number of holes introduce a large number of air holes, which reduces the overall refractive index of the material, thereby causing a blue shift. Comparing Example 4 with Comparative Example 1, it can be seen that the specific surface area and pore volume of Comparative Example 1 are reduced, and there are two distributions of the average particle size 311.1nm / 193.3nm. The inventors found through research that the existence of two particle size distributions is mainly because the actual reaction in Comparative Example 1 includes two parts: one part is that part of the tetraethyl orthosilicate and the organosilane raw materials undergo the coating reaction of the present invention on the surface of the silica microspheres, and the other part is that due to the sufficient alkaline hydrolysis solution, part of the tetraethyl orthosilicate and the organosilane raw materials undergo secondary nucleation (i.e., partial hydrolysis to form silica microspheres with smaller particle sizes), which results in the presence of two silica microspheres with different particle sizes in the silica microsphere dispersion, resulting in the presence of two particle size distributions of the obtained core-shell porous silica microspheres, i.e., poor monodispersity (poor uniformity of particle size). The disadvantage of poor monodispersity in Comparative Example 1 will result in the structural color saturation of the core-shell porous silica microspheres finally obtained being inferior to that of Examples 1-5, poor brightness, and dim color. Comparing Example 4 with Comparative Example 2, it can be seen that the specific surface area and pore volume of Comparative Example 2 are further reduced, indicating that more ethyl orthosilicate and organosilane raw materials have undergone secondary nucleation reactions, and less raw materials are used for coating reactions. In fact, after 3 to 4 hours of reaction, the silica microspheres will all sink to the bottom in the solution (rather than existing in the form of silica microsphere dispersion), indicating that the agglomeration and adhesion of the silica microspheres are very serious, which will cause the silica microspheres to stick together tightly and no longer have a complete spherical morphology, but an irregular shape (such as an ellipse, a gourd shape, etc.). At this time, the particle size measured by the instrument cannot represent the particle size of the microspheres themselves and the value will be larger, and the monodispersity will be worse, so the corresponding data in Table 1 are all filled in as None. At this time, the structural color prepared by the core-shell porous silica microspheres of Comparative Example 2 is the same as the structural color of Comparative Example 1, with poor brightness, and the color is darker than that of Examples 1-5 and the color will be uneven. In addition, the actual wavelength value "None" in Table 1 means that the tested structural color wavelength is in a very wide range, not a fixed value (the wavelength is generally determined by the position of the peak of the reflection spectrum curve. If the peak is very wide and flat, it is difficult to determine the wavelength).

[0055] In summary, the present invention provides a method for preparing core-shell porous silica microspheres and their application in structural color. The raw materials of the preparation method are common and easy to obtain, the operation is simple, no template agent and surfactant are required, the cost is greatly reduced, the thickness of the porous shell layer can be adjusted, and it can be applied to the formation of structural color of photonic crystals to achieve the regulation of the color wavelength of structural color.

Claims

1. A method for preparing core-shell porous silica microspheres, characterized in that: The preparation method comprises the following steps: (1) Mixing anhydrous ethanol, ammonia water and deionized water to obtain an alkaline hydrolyzate; (2) mixing tetraethyl orthosilicate and organosilane to obtain a silane mixed solution; (3) under stirring, simultaneously and separately adding the alkaline hydrolyzate and the silane mixture to the silica microsphere dispersion to react and obtain an intermediate; (4) The obtained intermediate is calcined at 550-650° C. to obtain the core-shell porous silica microspheres.

2. The preparation method according to claim 1, characterized in that: In step (1): the content of anhydrous ethanol in the alkaline hydrolyzate is 75-80wt%, the content of aqueous ammonia is 3wt%-7.5wt%, and the rest is deionized water; and / or the solubility of aqueous ammonia is 25-30wt%.

3. The preparation method according to claim 1 or 2, characterized in that: In step (2): the organosilane is one of octadecyltrimethoxysilane, octadecyltriethoxysilane, hexadecyltrimethoxysilane and hexadecyltriethoxysilane; And / or, the mass ratio of tetraethyl orthosilicate to organosilane is (2-4):1; And / or, the purity of the organosilane is ≥95%, and the purity of the tetraethyl orthosilicate is >99%.

4. The preparation method according to any one of claims 1 to 3, characterized in that In step (3): the dropping rate of the alkaline hydrolyzate is 1.6-2.4 mL / h; and / or, the dropping rate of the silane mixture is 0.1-0.15 mL / h; And / or, the volume ratio of the alkaline hydrolysis solution to the silane mixture is (12-20):1, preferably (14-18):

1.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In step (3): the diameter of the monodispersed silica microspheres in the silica microsphere dispersion is 200-250 nm; and / or, the content of monodisperse silica microspheres in the silica microsphere dispersion is 1.0wt% to 1.5wt%; And / or, the solvent of the silica microsphere dispersion is anhydrous ethanol; Preferably, the monodisperse silica microspheres are refluxed in hydrochloric acid for at least 24 hours.

6. The preparation method according to any one of claims 1 to 5, characterized in that In step (3): the stirring is magnetic stirring, preferably with a rotation speed of 180-240 rpm; The reaction temperature is 40-60°C; The reaction time is at least 6 hours; Preferably, after the reaction is completed, the product is centrifuged, washed and dried to obtain an intermediate.

7. The preparation method according to any one of claims 1 to 6, characterized in that In step (4): the calcination treatment atmosphere is air; and / or the calcination treatment time is at least 5 hours.

8. A core-shell porous silica microsphere, characterized in that: The core-shell porous silica microspheres include: silica microspheres, and a porous silica layer coated on the surface of the silica microspheres; the average pore size of the porous silica layer is 2-4 nm.

9. The core-shell porous silica microspheres according to claim 8, characterized in that: The thickness of the porous silica layer is 15-50 nm; and / or the diameter of the silica microspheres is 200-250 nm.

10. The core-shell porous silica microspheres according to claim 8 or 9, characterized in that: The average particle size of the core-shell porous silica microspheres is 230-350 nm; And / or, the pore volume of the core-shell porous silica microspheres is 0.12-0.24 cm 3 / g; And / or, the specific surface area of ​​the core-shell porous silica microspheres is 200-430 m 2 / g.

11. Use of the core-shell porous silica microspheres according to claim 8 in structural color.

12. Use of the core-shell porous silica microspheres according to claim 8 in preparing photonic crystals.

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