阅读说明：本技术 Yolk-Shell结构的催化剂、制备方法及应用 (Catalyst with Yolk-Shell structure, preparation method and application ) 是由 孙阳艺 李嘉 戚栋明 祝强韬 张成宇 何梦瑶 于 2021-08-13 设计创作，主要内容包括：本发明提供了一种Yolk-Shell结构的催化剂、制备方法及应用,涉及纳米材料制备技术领域。本发明的Yolk-Shell结构的催化剂,包括内核和包覆在内核外的壳层,其中,内核为贵金属纳米粒子,壳层为介孔有机硅。在该介孔有机硅的协助下,可以使得该贵金属纳米粒子的分散性好,不易团聚,具有较好的催化特性。制备方法可以包括：向乙醇与醋酸水溶液的混合液中加入表面活性剂并进行搅拌,得到第一反应液；向第一反应液中加入硅烷偶联剂,水解得到第二反应液；将贵金属纳米粒子分散在乙醇水溶液中,升温至40～60℃后加入碱催化剂得到第三反应液；将第二反应液加入到第三反应液中反应得到Yolk-Shell结构的催化剂。本发明的制备方法的原料易得,操作过程简单,反应条件温和,能耗低。(The invention provides a catalyst with a Yolk-Shell structure, a preparation method and application thereof, and relates to the technical field of nano material preparation. The catalyst with the Yolk-Shell structure comprises an inner core and a Shell layer coated outside the inner core, wherein the inner core is a noble metal nano particle, and the Shell layer is mesoporous organic silicon. With the help of the mesoporous organic silicon, the noble metal nano particles have good dispersibility, are not easy to agglomerate and have better catalytic property. The preparation method can comprise the following steps: adding a surfactant into a mixed solution of ethanol and an acetic acid aqueous solution, and stirring to obtain a first reaction solution; adding a silane coupling agent into the first reaction liquid, and hydrolyzing to obtain a second reaction liquid; dispersing noble metal nanoparticles in an ethanol aqueous solution, heating to 40-60 ℃, and adding an alkali catalyst to obtain a third reaction solution; and adding the second reaction solution into the third reaction solution for reaction to obtain the catalyst with the Yolk-Shell structure. The preparation method has the advantages of easily available raw materials, simple operation process, mild reaction conditions and low energy consumption.)

1. The catalyst with the Yolk-Shell structure is characterized by comprising an inner core and a Shell layer coated outside the inner core, wherein the inner core is a noble metal nanoparticle, and the Shell layer is mesoporous organic silicon; the noble metal nanoparticles can have good dispersibility and stability in an alkaline solution.

2. The catalyst of Yolk-Shell structure according to claim 1, wherein,

the noble metal nano particles are selected from one or two of gold nano particles, silver nano particles or platinum nano particles.

3. The catalyst of Yolk-Shell structure according to claim 1, wherein,

the particle size of the noble metal nano particles is 10 nm-60 nm.

4. A method for preparing a catalyst of Yolk-Shell structure according to any one of claims 1 to 3, comprising:

adding a surfactant into a mixed solution of ethanol and an acetic acid aqueous solution, and stirring to obtain a first reaction solution;

adding a silane coupling agent into the first reaction liquid, and hydrolyzing at 20-40 ℃ for 5-60 min to obtain a second reaction liquid;

dispersing noble metal nanoparticles in an ethanol aqueous solution, heating to 40-60 ℃, and adding an alkali catalyst to obtain a third reaction solution;

and adding the second reaction solution into the third reaction solution, and stirring for reaction to obtain the catalyst with the Yolk-Shell structure.

5. The method for preparing a catalyst of Yolk-Shell structure according to claim 4,

the volume ratio of the ethanol to the acetic acid aqueous solution in the mixed solution of the ethanol and the acetic acid aqueous solution is 1-7: 1; the pH value of the acetic acid aqueous solution is 4-7;

optionally, the surfactant is selected from at least one of cetyltrimethyl-p-toluenesulfonium, cetyltrimethyl-ammonium bromide or cetyltrimethyl-ammonium chloride.

6. The method for preparing a catalyst of Yolk-Shell structure according to claim 4 or 5,

the organosilane coupling agent is at least one selected from 1, 2-di (triethoxysilyl) ethane and bis- [ gamma- (triethoxysilyl) propyl ] -tetrasulfide or a mixture of at least one selected from 1, 2-di (triethoxysilyl) ethane and bis- [ gamma- (triethoxysilyl) propyl ] -tetrasulfide and Tetraethoxysilane (TEOS);

optionally, the mass ratio of the surfactant to the organosilane coupling agent to the mixed solution of ethanol and acetic acid aqueous solution is 1: 2-8: 300-400.

7. The method for preparing a catalyst of Yolk-Shell structure according to claim 4,

the noble metal nanoparticles are at least one of gold nanoparticles, silver nanoparticles or platinum nanoparticles, and the noble metal nanoparticles can have good dispersibility and stability in an alkaline solution;

optionally, the particle size of the noble metal nanoparticles is 10nm to 60 nm;

optionally, the base catalyst is selected from at least one of ammonia, triethylamine or triethanolamine;

optionally, the volume ratio of ethanol to water in the ethanol aqueous solution is 1: 1 to 10.

8. The method for preparing a catalyst of Yolk-Shell structure according to claim 4 or 7,

the mass ratio of the noble metal nanoparticles to the second reaction solution to the ethanol aqueous solution to the base catalyst is (1-6): 20-50: 20-50: 1.

9. the application of the catalyst with the Yolk-Shell structure prepared by the preparation method of the catalyst with the Yolk-Shell structure as defined in any one of claims 4 to 8 in catalytic reduction of 4-nitrophenol.

10. The application of the catalyst with the Yolk-Shell structure prepared by the preparation method of the catalyst with the Yolk-Shell structure according to claim 9 in the catalytic reduction of 4-nitrophenol,

the step of catalyzing and reducing 4-nitrophenol by using the catalyst with the Yolk-Shell structure comprises the following steps:

4-nitrophenol is reacted with NaBH₄Mixing according to a preset molar ratio; wherein the preset molar ratio is 3: 40;

adding a catalyst with a Yolk-Shell structure prepared by a preparation method for utilizing the catalyst with the Yolk-Shell structure in advance into the mixed solution, and stirring;

and monitoring the solution after the reaction by using an ultraviolet spectrum to obtain the reduction reaction time of the 4-nitrophenol.

Technical Field

The invention relates to the technical field of nano material preparation, in particular to a catalyst with a Yolk-Shell structure, a preparation method and application thereof.

Background

As noble metal materials such as Au, Ag, Pt and the like are excellent catalysts, the catalyst has wide application in the fields of catalysis and chemical industry. Among them, Ag is attracting attention because of its excellent optical, electronic and catalytic properties. From the catalytic point of view, reducing the size of the silver particles to the nanometer level, increasing the surface area and active sites thereof, can greatly increase the catalytic efficiency of the reaction. However, the silver particles used alone tend to agglomerate due to their high specific surface energy, resulting in a reduction in catalytic efficiency and secondary pollution at the end of the reaction. So that the Ag nanoparticles can achieve high catalytic efficiency in the reaction process usually with the aid of a support.

In the prior art, a nano reactor with a mesoporous silica shell layer loaded with a silver particle structure is disclosed, and due to the fact that a process of smashing nano silver particles on the surface under the action of laser irradiation exists in the reaction process, the appearance of the composite microsphere is easily damaged, and meanwhile, in the process, the microsphere tends to agglomerate, so that the catalytic effect is poor.

Disclosure of Invention

The invention aims to provide a catalyst with a Yolk-Shell structure, which solves the problem of unstable catalytic efficiency caused by easy agglomeration of single noble metal nano particles in the prior art.

An object of the second aspect of the present invention is to provide a preparation method of a catalyst with a Yolk-Shell structure, which solves the problem of complicated preparation method in the prior art.

Another object of the second aspect of the present invention is to solve the problem of poor catalytic effect of the microspheres prepared by the preparation method in the prior art.

The first aspect of the invention aims to provide application of a catalyst with a Yolk-Shell structure.

Particularly, the invention provides a catalyst with a Yolk-Shell structure, which comprises an inner core and a Shell layer coated outside the inner core, wherein the inner core is a noble metal nano particle, and the Shell layer is mesoporous organic silicon; the noble metal nanoparticles can have good dispersibility and stability in an alkaline solution.

Optionally, the noble metal nanoparticles are selected from one or two of gold nanoparticles, silver nanoparticles or platinum nanoparticles.

Optionally, the noble metal nanoparticles have a particle size of 10nm to 60 nm.

In particular, the present invention also provides a preparation method of the above-described catalyst of Yolk-Shell structure, comprising:

adding a surfactant into a mixed solution of ethanol and an acetic acid aqueous solution, and stirring to obtain a first reaction solution;

adding a silane coupling agent into the first reaction liquid, and hydrolyzing at 20-40 ℃ for 5-60 min to obtain a second reaction liquid;

dispersing noble metal nanoparticles in an ethanol aqueous solution, heating to 40-60 ℃, and adding an alkali catalyst to obtain a third reaction solution;

and adding the second reaction solution into the third reaction solution, and stirring for reaction to obtain the catalyst with the Yolk-Shell structure.

Optionally, the volume ratio of the ethanol to the acetic acid aqueous solution in the mixed solution of the ethanol and the acetic acid aqueous solution is 1-7: 1; the pH value of the acetic acid aqueous solution is 4-7;

optionally, the surfactant is selected from at least one of cetyltrimethyl-p-toluenesulfonium, cetyltrimethyl-ammonium bromide or cetyltrimethyl-ammonium chloride.

Optionally, the organosilane coupling agent is selected from at least one of 1, 2-bis (triethoxysilyl) ethane, bis- [ gamma- (triethoxysilyl) propyl ] -tetrasulfide or a mixture of at least one of 1, 2-bis (triethoxysilyl) ethane, bis- [ gamma- (triethoxysilyl) propyl ] -tetrasulfide and Tetraethoxysilane (TEOS);

optionally, the mass ratio of the surfactant to the organosilane coupling agent to the mixed solution of ethanol and acetic acid aqueous solution is 1: 2-8: 300-400.

Optionally, the noble metal nanoparticles are at least one of gold nanoparticles, silver nanoparticles or platinum nanoparticles, and the noble metal nanoparticles can have good dispersibility and stability in an alkaline solution;

optionally, the particle size of the noble metal nanoparticles is 10nm to 60 nm;

optionally, the base catalyst is selected from at least one of ammonia, triethylamine or triethanolamine;

optionally, the volume ratio of ethanol to water in the ethanol aqueous solution is 1: 1 to 10.

Optionally, the mass ratio of the noble metal nanoparticles to the second reaction liquid to the ethanol aqueous solution to the base catalyst is 1-6: 20-50: 20-50: 1.

particularly, the invention also provides application of the catalyst with the Yolk-Shell structure prepared by the preparation method of the catalyst with the Yolk-Shell structure in catalytic reduction of 4-nitrophenol.

Alternatively, the step of catalytically reducing 4-nitrophenol with the catalyst of the Yolk-Shell structure comprises:

4-nitrophenol is reacted with NaBH₄Mixing according to a preset molar ratio; wherein the preset molar ratio is 3: 40;

adding a catalyst with a Yolk-Shell structure prepared by a preparation method for utilizing the catalyst with the Yolk-Shell structure in advance into the mixed solution, and stirring;

and monitoring the solution after the reaction by using an ultraviolet spectrum to obtain the reduction reaction time of the 4-nitrophenol.

The morphology and dispersion of the noble metal nanoparticles are decisive for the catalytic efficiency. The Yolk-Shell structure is a structure with a special cavity, the existence of the cavity is beneficial to the dispersion and transmission of substances, the loading capacity of the carrier can be increased, and the agglomeration of noble metal nano particles is avoided, so that the catalytic efficiency of the noble metal nano particles is improved. The catalyst with the Yolk-Shell structure is characterized in that the inner core is provided with precious metal nano particles, the Shell layer is provided with mesoporous organic silicon, the mesoporous organic silicon is equivalent to a carrier of the precious metal nano particles, and the problems of high reduction of catalytic efficiency and unstable catalytic activity of the catalyst caused by agglomeration of the precious metal nano particles can be solved with the help of the mesoporous organic silicon.

Mesoporous organosilicon compared with inorganic SiO₂Has good biological affinity, controllable hydrophilic and hydrophobic property and excellent thermal stability. In the process of loading the noble metal nano particles, the contact between the noble metal nano particles and the noble metal nano particles can be isolated, and the shape and the chemical property of the noble metal nano particles are stabilized by utilizing the confinement effect of the silicon dioxide shell, so that the phenomena of agglomeration, size change and the like in the reaction process are avoided. In addition, the mesoporous organic silicon has a mesoporous structure, so that the mesoporous organic silicon provides a reaction channel for the noble metal nanoparticles in the catalytic reduction process, and a good catalytic effect can be achieved.

The preparation method of the catalyst with the Yolk-Shell structure has the advantages of easily obtained raw materials, simple operation process, mild reaction conditions and low energy consumption. And by utilizing the preparation method, the target product can be obtained in one pot, and the method is suitable for industrial production.

The catalyst with the Yolk-Shell structure prepared by the preparation method has the advantages of adjustable particle size, regular shape, good dispersibility and multiple catalytic active sites.

The Yolk-Shell structure noble metal-mesoporous organic silicon catalyst prepared by the method has the advantages that noble metal nanoparticles are not easy to agglomerate due to the Yolk-Shell structure, the catalytic activity is high, the catalytic performance is stable, the catalyst has a good effect in the process of catalytic reduction of 4-nitrophenol, and the catalyst has a strong application prospect.

The above and other objects, advantages and features of the present invention will become more apparent to those skilled in the art from the following detailed description of specific embodiments thereof, taken in conjunction with the accompanying drawings.

Drawings

Some specific embodiments of the invention will be described in detail hereinafter, by way of illustration and not limitation, with reference to the accompanying drawings. The same reference numbers in the drawings identify the same or similar elements or components. Those skilled in the art will appreciate that the drawings are not necessarily drawn to scale. In the drawings:

FIG. 1 is a schematic flow diagram of a method of preparing a catalyst of the Yolk-Shell structure according to one embodiment of the present invention;

FIG. 2 is a transmission electron micrograph of a catalyst of a Yolk-Shell structure prepared according to example 1 of the present invention;

FIG. 3 is a transmission electron micrograph of a catalyst of the Yolk-Shell structure prepared according to example 2 of the present invention;

FIG. 4 is a transmission electron micrograph of a catalyst of the Yolk-Shell structure prepared according to example 3 of the present invention;

FIG. 5 is a transmission electron micrograph of a catalyst of the Yolk-Shell structure prepared according to example 4 of the present invention;

FIG. 6 is a transmission electron micrograph of a catalyst of the Yolk-Shell structure prepared according to example 5 of the present invention;

FIG. 7 is a transmission electron micrograph of a product according to comparative example 1 of the present invention;

FIG. 8 is a transmission electron micrograph of a product made according to comparative example 2 of the present invention;

FIG. 9 is a transmission electron micrograph of a product made according to comparative example 3 of the present invention;

FIG. 10 is a graph showing the time-dependent change of the ratio of the concentration of 4-nitrophenol to the original concentration in the catalytic reduction process of 4-nitrophenol in the products prepared in examples 1 to 5 and comparative examples 1 to 3 according to the present invention;

FIG. 11 is a graph showing the change of the ratio of the concentration of 4-nitrophenol to the original concentration obtained by catalyzing 4-nitrophenol a plurality of times using the silver nanoparticles of comparative example 4 as a catalyst for 4-nitrophenol with time;

FIG. 12 is a graph showing the change of the ratio of the concentration of 4-nitrophenol to the original concentration with time, obtained by catalyzing 4-nitrophenol with a catalyst of a Yolk-Shell structure prepared in example 1 several times.

Detailed Description

As a specific embodiment of the present invention, this embodiment provides a catalyst with a Yolk-Shell structure, where the catalyst with a Yolk-Shell structure may include an inner core and a Shell layer coated outside the inner core, where the inner core is a noble metal nanoparticle, and the Shell layer is mesoporous organosilicon; the noble metal nanoparticles can have good dispersibility and stability in an alkaline solution.

The morphology of the noble metal nanoparticles plays a decisive role in their catalytic efficiency. The Yolk-Shell structure is a structure with a special cavity, the existence of the cavity is beneficial to the dispersion and the transmission of substances, and the loading capacity of a carrier can be increased, so that the catalytic efficiency of the noble metal nano-particles is improved. Since the catalyst with the Yolk-Shell structure in the embodiment is the catalyst with the noble metal nano-particles as the inner core and the mesoporous organosilicon as the Shell layer, the mesoporous organosilicon is equivalent to the carrier of the noble metal nano-particles, and the agglomeration of the noble metal nano-particles can be reduced with the help of the mesoporous organosilicon, thereby ensuring the catalytic stability.

Furthermore, mesoporous silicones are compared to inorganic SiO₂Has good biological affinity, controllable hydrophilic and hydrophobic property and excellent thermal stability. In the process of uniformly coating the noble metal nano particles, the contact between the noble metal nano particles and the outside can be isolated, and the domain limiting effect of the silicon dioxide shell is utilized to stabilize the appearance and shape of the noble metal nano particlesChemical property, and avoids the phenomena of agglomeration, size change and the like in the reaction process. In addition, the mesoporous organic silicon has a mesoporous structure, so that the mesoporous organic silicon provides a reaction channel for the noble metal nanoparticles in the catalytic reduction process, and a good catalytic effect can be achieved.

As a specific example of the present invention, the noble metal nanoparticles of the present embodiment are selected from one or two of gold nanoparticles, silver nanoparticles, or platinum nanoparticles.

Specifically, the noble metal nanoparticles may have a particle diameter of 10nm to 60 nm. For example, the noble metal nanoparticles may be 10nm, 20nm, 50nm, or 60 nm. The noble metal nanoparticles are not easy to coat with organic silicon when the particle size is too high, and the catalytic efficiency is possibly reduced when the particle size is too small and the noble metal nanoparticles are easy to agglomerate. The nano silver particles under the particle size scale are more suitable for organic silicon coating.

Fig. 1 is a schematic flow chart of a preparation method of a catalyst of Yolk-Shell structure according to one embodiment of the present invention. As a specific example of the present invention, as shown in fig. 1, this example provides a preparation method of the above catalyst of Yolk-Shell structure, which may include:

step S100, adding a surfactant into a mixed solution of ethanol and an acetic acid aqueous solution, and stirring to obtain a first reaction solution;

step S200, adding a silane coupling agent into the first reaction liquid, and hydrolyzing at 20-40 ℃ for 5-60 min to obtain a second reaction liquid;

step S300, dispersing the noble metal nanoparticles in an ethanol water solution, heating to 40-60 ℃, and adding an alkali catalyst to obtain a third reaction solution;

and S400, adding the second reaction solution into the third reaction solution, and stirring for reaction to obtain a catalyst with a Yolk-Shell structure.

The preparation method of the catalyst with the Yolk-Shell structure has the advantages of easily available raw materials, simple operation process, mild reaction conditions and low energy consumption. And by utilizing the preparation method of the embodiment, a target product can be obtained in one pot, and the method is suitable for industrial production.

The catalyst with the Yolk-Shell structure prepared by the preparation method of the embodiment has the advantages of adjustable particle size, regular shape, good dispersibility and multiple catalytic active sites.

In step S100, an acetic acid aqueous solution is prepared in advance, and the pH value of the acetic acid aqueous solution is 4-7. Specifically, the mixed solution of ethanol and acetic acid aqueous solution also needs to be mixed in advance, and the volume ratio of the ethanol to the acetic acid aqueous solution can be 1-7: 1. for example, the volume ratio to the aqueous acetic acid solution may be 1: 1. 5: 1 or 7: 1.

in step S100, the surfactant is selected from at least one of cetyltrimethyl-p-toluenesulfonyl ammonium, cetyltrimethyl ammonium bromide or cetyltrimethyl ammonium chloride. Preferably, when the surfactant is cetyltrimethylammonium bromide, the surfactant is more effectively combined with the silane precursor.

In step S200, the organosilane coupling agent is selected from at least one of 1, 2-bis (triethoxysilyl) ethane and bis- [ gamma- (triethoxysilyl) propyl ] -tetrasulfide or a mixture of at least one of 1, 2-bis (triethoxysilyl) ethane and bis- [ gamma- (triethoxysilyl) propyl ] -tetrasulfide and Tetraethoxysilane (TEOS).

Preferably, the organosilane coupling agent can be a mixture of 1, 2-bis (triethoxysilyl) ethane and bis- [ gamma- (triethoxysilyl) propyl ] -tetrasulfide, and the volume ratio of the two can be 1-10: 1, for example, may be 1: 1. 5: 1 or 10: 1. the noble metal nanoparticles are exemplified as silver nanoparticles. Specifically, the silicon source forms copolycondensated oligomer through prehydrolysis, and then is deposited on the surface of Ag particles by utilizing the interaction of Ag-S bonds. The coating mode of the organic silicon on the Ag particles is controlled by regulating the proportion of the two organosilane coupling agents, the dosage proportion of the Ag/organosilane coupling agent and the concentration of the alkali catalyst, so that a Yolk-Shell structure is obtained, and the uniformity of coating and the dispersibility of particles are ensured.

As a specific example of the present invention, the mass ratio of the surfactant, the organosilane coupling agent, and the mixed solution of ethanol and the acetic acid aqueous solution in the present example may be 1: 2-8: 300-400. Specifically, the mass ratio of the surfactant, the organosilane coupling agent, and the mixed solution of ethanol and the acetic acid aqueous solution may be 1: 2: 300. 1: 6: 300. 1: 6: 400. 1: 8: 300. 1: 8: 350 or 1: 8: 400.

as a preferred embodiment, the volume ratio of ethanol to acetic acid aqueous solution in the mixed solution of ethanol and acetic acid aqueous solution is 2-5: 1, the mass ratio of the surfactant to the organic silane coupling agent to the mixed solution of ethanol and acetic acid aqueous solution is 1: 2-5: 310-360 hours, in the mixed solution of ethanol/dilute acetic acid with proper proportion, the organosilane coupling agent can be completely hydrolyzed, and simultaneously, the organosilane coupling agent and the surfactant achieve good combination effect.

As a specific example of the present invention, in step S300 of this embodiment, the noble metal nanoparticles are at least one of gold nanoparticles, silver nanoparticles or platinum nanoparticles, and the noble metal nanoparticles need to have good dispersibility and stability in an alkaline solution. The particle size of the noble metal nano particles is 10 nm-60 nm. For example, the noble metal nanoparticles may be 10nm, 20nm, 50nm, or 60 nm. The catalyst is not easy to coat by organic silicon when the particle size is too high, and is easy to agglomerate and reduce the catalytic efficiency when the particle size is too small. Under the particle size scale, the obtained nano silver particles are more suitable for organic silicon coating. Preferably, the noble metal nanoparticles of the present embodiment may be silver nanoparticles.

Specifically, the alkali catalyst is at least one selected from ammonia, triethylamine or triethanolamine. Preferably aqueous ammonia. In the embodiment, only a trace amount of alkali catalyst needs to be added into the reaction system to adjust the pH in the reaction system, so that the hydrolysis and co-condensation are promoted, meanwhile, the alkalinity of the ammonia water is not easy to be too large, and the particles cannot be stably dispersed in the ammonia water dispersion liquid to agglomerate due to the too strong alkalinity.

Optionally, the volume ratio of ethanol to water in the ethanol aqueous solution is 1: 1 to 10. For example, the volume ratio of ethanol to water in the ethanol aqueous solution of the embodiment may be 1: 1. 1: 4. 1: 8 or 1: 10. the ratio of ethanol to water has an important influence on the morphology of the synthesized noble metal-mesoporous organosilicon, because the ratio of ethanol to water can influence the interfacial tension in the system, thereby having a great influence on the growth mode of the organosilane coupling agent.

In step S300, the steps of dispersing the noble metal nanoparticles in an ethanol aqueous solution, heating to 40 to 60 ℃, and adding an alkali catalyst to obtain a third reaction solution include:

dispersing the noble metal nano particles in an ethanol water solution by an ultrasonic dispersion method; wherein the ultrasonic dispersion conditions comprise ultrasonic temperature of 0-20 ℃, ultrasonic time of 5-40 min and ultrasonic power of 50-500W;

stirring the ethanol aqueous solution dispersed with the noble metal nano particles, heating the ethanol aqueous solution for 10min to 40min until the temperature is between 40 and 60 ℃, and adding an alkali catalyst to obtain a third reaction solution.

The ultrasonic temperature, the ultrasonic time, the ultrasonic power and the stirring temperature rise time have great influence on the dispersity of the noble metal nanoparticles, so that the subsequent synthesis reaction is influenced, and finally the morphology of the composite particles is changed. The mass ratio of the noble metal nanoparticles to the second reaction liquid to the ethanol aqueous solution to the base catalyst is 1-6: 20-50: 20-50: 1. for example, the ratio may be 1: 20: 20: 1. 2: 30: 30: 1 or 6: 50: 50: 1.

in a reaction system, the shape of the catalyst with the Yolk-Shell structure is influenced by the dosage proportion of the noble metal nano particles and the organosilane coupling agent and the dosage of the alkali catalyst, and the thickness of a Shell layer is increased with the proper increase of the dosage of the organosilane coupling agent or the alkali catalyst.

As a preferred example, under the reaction conditions: the volume ratio of ethanol to water in the ethanol/water mixed solution is 1: 1-5, the ultrasonic temperature is 0-10 ℃, the ultrasonic time is 25-40 min, and the ultrasonic power is 200-500W. Stirring and heating for 10-25 min, wherein the mass ratio of the noble metal nanoparticles to the second reaction solution to the ethanol aqueous solution to the base catalyst is 1-4: 25-40: 25-40: 1, under the condition, the obtained catalyst with the Yolk-Shell structure has the best catalytic activity.

The invention will be further described with reference to specific examples, but the scope of the invention is not limited thereto.

Example 1

(1) Adding 0.05g of hexadecyl trimethyl ammonium bromide into a mixed solution of 15mL of ethanol and 5mL of dilute acetic acid, and uniformly stirring to obtain a first reaction solution;

(2) adding 0.4mL of 1, 2-bis (triethoxysilyl) ethane and 0.1mL of a mixture of bis- [ gamma- (triethoxysilyl) propyl ] -tetrasulfide into the first reaction liquid, and hydrolyzing at 40 ℃ for 50min to obtain a second reaction liquid;

(3) adding 1g of Ag nano-particle dispersion liquid into a mixed solution of 6mL of ethanol and 12mL of water, performing ultrasonic dispersion uniformly (the ultrasonic temperature is 0 ℃, the ultrasonic time is 10min, and the ultrasonic power is 300W), stirring and heating for 15min to 60 ℃, and adding 1.0mL of ammonia water to obtain a third reaction liquid.

(4) And (5) quickly adding 5mL of second reaction solution into the third reaction solution after 5min, and stirring for reaction to obtain the catalyst with the Yolk-Shell structure.

FIG. 2 is a transmission electron micrograph of a catalyst of a Yolk-Shell structure prepared in example 1. As can be seen from fig. 2, the catalyst product with the Yolk-Shell structure is prepared in this embodiment, and the overall particle size of the catalyst with the Yolk-Shell structure is 460nm to 490nm, the thickness of the mesoporous organosilicon Shell layer is 60nm, the Ag nanoparticles and the silica are well combined, and the dispersibility of the composite material is good. Specifically, the particle size of the Yolk-Shell structured catalyst may be 460nm, 500nm or 600 nm.

Example 2

Compared with the example 1, the catalyst with the Yolk-Shell structure, which has the advantages of small organosilicon grain diameter and thin Shell layer thickness, is obtained by only changing the dosage of the ammonia water and adding 0.5mL of the ammonia water with the same other steps.

FIG. 3 is a transmission electron micrograph of a catalyst of a Yolk-Shell structure prepared in example 2. As can be seen from fig. 3, the catalyst product with the Yolk-Shell structure prepared in this embodiment has good dispersibility, the overall particle size is 250nm-300nm, and the thickness of the mesoporous organosilicon Shell layer is 28 nm.

Example 3

Compared with the example 1, the catalyst with the Yolk-Shell structure, which has larger organosilicon grain diameter and increased Shell layer thickness, is obtained by only changing the dosage of the ammonia water and adding 2.0mL of ammonia water in the same steps.

FIG. 4 is a transmission electron micrograph of a catalyst of a Yolk-Shell structure prepared in example 3. As can be seen from FIG. 4, the catalyst product with the Yolk-Shell structure is prepared in the embodiment, and the catalyst with the Yolk-Shell structure has good dispersibility, the overall particle size is 550nm-600nm, and the thickness of the mesoporous organosilicon Shell layer is 80 nm. As can be seen from examples 1 to 3, the amount of ammonia used can vary the Shell thickness and the overall particle size of the resulting catalyst having a Yolk-Shell structure. The method is characterized in that when the using amount of ammonia water is reduced, the Shell layer of the catalyst with the Yolk-Shell structure obtained by the reaction is thinned, and the whole grain size is reduced. When the amount of ammonia water becomes large, the Shell layer of the Yolk-Shell structure obtained by the reaction becomes thick, and the overall particle size becomes large.

Example 4

Compared with example 1, the catalyst with the Yolk-Shell structure, in which the particle size of the organosilicon is increased and the Shell thickness is increased, is obtained by adding 7.5mL of the second reaction solution only by changing the dosage of the second reaction solution, and the other steps are the same.

FIG. 5 is a transmission electron micrograph of a catalyst of the Yolk-Shell structure prepared in example 4. As can be seen from FIG. 5, the catalyst product with the Yolk-Shell structure is prepared in the embodiment, and the catalyst with the Yolk-Shell structure has good dispersibility, the overall particle size is 550nm-600nm, and the thickness of the organosilicon Shell layer is 66 nm.

Example 5

Compared with the example 1, the catalyst with the Yolk-Shell structure, which has the increased organosilicon particle size and the increased Shell thickness, is obtained by only changing the dosage of the second reaction solution and adding 10mL of the second reaction solution in the same other steps.

FIG. 6 is a transmission electron micrograph of a catalyst of a Yolk-Shell structure prepared in example 5. As can be seen from FIG. 6, the catalyst product with the Yolk-Shell structure is obtained in the embodiment, and the catalyst with the Yolk-Shell structure has good dispersibility, the overall particle size is 600nm-640nm, and the thickness of the organosilicon Shell layer is 96 nm.

It can also be seen from examples 1, 4 and 5 that the amount of the second reaction solution used can affect the thickness of the Shell layer and the size of the overall particle diameter of the catalyst having a Yolk-Shell structure, in particular, when the amount of the second reaction solution is increased, the thickness of the Shell layer is increased, and the overall particle diameter is increased.

Comparative example 1

Compared with the example 1, the core-shell noble metal nano particle-mesoporous organic silicon is obtained by only changing the dosage of the ethanol and the water, adding 12mL of the ethanol and 6mL of the water and the other steps are the same.

FIG. 7 is a transmission electron micrograph of the product obtained in comparative example 1. As can be seen from FIG. 7, the catalyst product with the Yolk-Shell structure is not prepared in this example, and the finally prepared product has a core-Shell structure, the overall particle size is 120nm-140nm, and the thickness of the organosilicon Shell layer is 38 nm.

As can be seen from fig. 7, the volume ratio of ethanol to water has an influence on the morphology of the final Yolk-Shell structured catalyst, and in this embodiment, since the volume of ethanol is greater than the volume of water, the product structure obtained in the present application is core-Shell noble metal-mesoporous organosilicon, that is, the mesoporous organosilicon obtained in the present application is directly coated outside the noble metal nanoparticles, and cannot form a Yolk-Shell structure. Compared with a Yolk-Shell structure, the formed core-Shell noble metal nano particle-mesoporous organic silicon has very low catalytic activity.

Comparative example 2

Compared with the embodiment 1, only the steps (3) and (4) are needed, the organosilane coupling agent is directly added into the steps (3) and (4), and other steps are the same, so that the core-shell-shaped noble metal nanoparticle-mesoporous organosilicon is obtained.

FIG. 8 is a transmission electron microscope image of the product prepared in comparative example 2. it can be seen from FIG. 8 that the catalyst product with the Yolk-Shell structure is not prepared in this example, and the finally prepared product has a core-Shell structure and some floccules, the overall particle size is 120nm to 150nm, and the thickness of the organosilicon Shell layer is 30 nm.

Comparative example 3

Compared with the example 1, the steps (3) and (4) are not present, the obtained organic silicon spheres are not coated with Ag particles, and the other steps are the same, so that the simple mesoporous organic silicon is obtained.

FIG. 9 is a transmission electron micrograph of the product obtained in comparative example 3. As can be seen in fig. 9, the product produced in this example had an irregular granular structure.

As a specific example of the present invention, this embodiment further provides an application of the catalyst with the Yolk-Shell structure prepared by the preparation method of the catalyst with the Yolk-Shell structure in catalytic reduction of 4-nitrophenol.

The step of using the catalyst of the Yolk-Shell structure for catalytic reduction of 4-nitrophenol may comprise:

4-nitrophenol is reacted with NaBH₄Mixing according to a preset molar ratio; wherein the preset molar ratio is 3: 40;

adding the catalyst with the Yolk-Shell structure prepared by the preparation method of the catalyst with the Yolk-Shell structure into the mixed solution and stirring;

and monitoring the solution after the reaction by using an ultraviolet spectrum to obtain the reduction reaction time of the 4-nitrophenol.

The Yolk-Shell structure noble metal-mesoporous organic silicon catalyst prepared by the method has high catalytic activity due to the Yolk-Shell structure, has a good effect in the process of catalytic reduction of 4-nitrophenol (4-NP), and has a strong application prospect.

Specifically, in this example, catalytic reduction of 4-NP was performed in a 1cm quartz cuvette and monitored in real time using ultraviolet spectroscopy (UV-Vis). 0.15mL of 4-NP solution (0.01mol/L) was reconstituted with 1.0mL of NaBH₄(0.2M) solution is mixed, added into the solution of the embodiment 1-4 and the comparative example 1-2 and stirred uniformly, then deionized water is added until the total amount of the solution is fixed at 3.0mL, and the solution is subjected to UV-Vis in-situ monitoring at intervals to finally evaluate the catalytic performance of the solution.

Comparative example 4

4-nitrophenol (4-NP) is directly reduced by silver nano-particle catalysis, and the solution after reaction is monitored by ultraviolet spectrum to obtain the reduction reaction time of the 4-nitrophenol.

FIG. 10 is a graph showing the time-dependent change of the ratio of the concentration of 4-nitrophenol to the original concentration in the catalytic reduction process of 4-nitrophenol in the products prepared in examples 1 to 5 and comparative examples 1 to 4 of the present invention. As can be seen from FIG. 10, the catalysts of the Yolk-Shell structure obtained in examples 1 to 3 all have very good catalytic activity for 4-nitrophenol (4-NP), wherein, the catalyst with the Yolk-Shell structure prepared in the example 2 has the strongest catalytic activity on 4-nitrophenol (4-NP), only needs about 10min from the reaction to the end, the catalyst with the Yolk-Shell structure prepared in the example 1 has the second catalytic activity on 4-nitrophenol (4-NP), only needs about 17min from the reaction to the end, the catalyst with the Yolk-Shell structure prepared in example 3 has the lowest catalytic activity on 4-nitrophenol (4-NP) compared with examples 1 to 2, and requires about 28min from the reaction to the end. It can also be seen that the amount of ammonia in this example affects the Shell thickness and the overall particle size of the catalyst with the Yolk-Shell structure, and thus may affect the catalytic activity of the catalyst with the Yolk-Shell structure. The specific expression is that the thinner the Shell layer thickness of the catalyst with the Yolk-Shell structure is, the smaller the whole grain diameter is, and the higher the catalytic activity is.

Specifically, as can be seen from fig. 10, the catalysts of Yolk-Shell structure prepared in examples 4 and 5 also have good catalytic activity on 4-nitrophenol (4-NP). Since the amount of the second reaction solution was gradually increased in examples 4 and 5, it was shown in both examples 4 and 5 that the Shell thickness of the resulting catalyst having a Yolk-Shell structure was increased, the overall particle size was increased, and finally, the catalytic activity was gradually decreased. For example, in example 4, the end time of the reduction of 4-nitrophenol (4-NP) by the catalyst of the Yolk-Shell structure is approximately 20 min. In example 5, the end time of the reduction of 4-nitrophenol (4-NP) by the catalyst of the Yolk-Shell structure was about 35 min.

In addition, as can be seen from fig. 10, the core-shell-shaped noble metal nanoparticle-mesoporous organosilicon obtained in both comparative example 1 and comparative example 2 has almost no catalytic activity for the reduction reaction of 4-nitrophenol (4-NP). Comparative example 1 illustrates that the volume ratio of ethanol to water is very important to form the Yolk-Shell structure of this example, which in turn is very important for catalytic activity. When the volume ratio of ethanol to water is more than 1, a product with a Yolk-Shell structure cannot be prepared, so that the catalytic activity of the 4-nitrophenol is influenced. Comparative example 2 illustrates that when an organosilane coupling agent is directly reacted without being treated, a product having a Yolk-Shell structure cannot be obtained, thereby affecting the catalytic activity of 4-nitrophenol.

As can be seen from fig. 10, the pure mesoporous organosilicon obtained in comparative example 3 also showed almost no catalytic activity for 4-nitrophenol (4-NP).

As can be seen from fig. 10, the pure silver nanoparticles in comparative example 4 have strong catalytic activity on 4-nitrophenol (4-NP), but are agglomerated during the catalytic reduction of 4-nitrophenol (4-NP), so that the catalytic efficiency of the silver nanoparticles after later agglomeration for catalytic reduction of 4-nitrophenol (4-NP) is reduced.

FIG. 11 is a graph showing the change of the ratio of the concentration of 4-nitrophenol to the original concentration with time obtained by catalyzing 4-nitrophenol (4-NP) a plurality of times using the silver nanoparticles of comparative example 4 as a catalyst for 4-nitrophenol. As can be seen from fig. 11, the silver nanoparticles alone in comparative example 4 substantially lost the catalytic activity in the late stage of the first catalytic reduction of 4-nitrophenol. Substantially incapable of catalytically reducing 4-nitrophenol during the subsequent second to fifth catalytic reduction of 4-nitrophenol.

FIG. 12 is a graph showing the change of the ratio of the concentration of 4-nitrophenol to the original concentration with time, obtained by catalyzing 4-nitrophenol (4-NP) several times with the catalyst of the Yolk-Shell structure prepared in example 1. As can be seen from fig. 12, although the initial catalytic activity of the catalyst with the Yolk-Shell structure obtained in the comparative example 1 is not as good as that of a pure silver nanoparticle, the dispersibility of the catalyst is good, so that the silver nanoparticle is not easy to agglomerate, the stability of the catalyst with the Yolk-Shell structure is good, the catalyst can maintain high catalytic activity after the 4-nitrophenol is reduced by multiple times of catalytic reduction, and the catalyst has a very strong application value.

Thus, it should be appreciated by those skilled in the art that while a number of exemplary embodiments of the invention have been illustrated and described in detail herein, many other variations or modifications consistent with the principles of the invention may be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be understood and interpreted to cover all such other variations or modifications.