Hierarchical porous silicon material and preparation method thereof

Abstract

The invention provides a hierarchical porous silicon material and a preparation method thereof, and belongs to the technical field of comprehensive utilization of fly ash. The preparation method of the hierarchical porous silicon material provided by the invention comprises the following steps: mixing fly ash and an activating agent, and calcining to obtain activated fly ash; the activating agent comprises at least one of sodium salt and potassium salt; and mixing the activated fly ash with hydrochloric acid, and carrying out acid etching to obtain the hierarchical porous silicon material. According to the invention, at least one of sodium salt and potassium salt is adopted to activate the fly ash, and at least one of Na < + > and K < + > in the activation process can promote the conversion of mullite in the fly ash to different mineral phase aluminosilicate, so that a nepheline structure of Na and / or K is formed; and then hydrochloric acid is adopted for acid etching, and the alumina component can be selectively etched, so that the hierarchical pore channel is constructed, the process is simplified, and template-free preparation of the hierarchical pore silicon material is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of comprehensive utilization of fly ash, and particularly relates to a hierarchical porous silicon material and a preparation method thereof. Background Art

[0002] Hierarchical porous silicon materials refer to composite materials with two or more pore structures, which have characteristics such as a large specific surface area, high thermal stability, excellent permeability and storage performance, and thus have wide applications in the fields of catalysis, chemical industry, biotechnology, and environmental energy.

[0003] At present, hierarchical porous silicon materials are mainly prepared by various templating methods. For example, fly ash is first activated with an activator, then extracted, and then a templating agent is added for crystallization. Such methods have complex preparation processes and are difficult to achieve large-scale production and application. Therefore, how to improve the method to simplify the process of preparing hierarchical porous silicon materials without a template has become an urgent technical problem in this field. Summary of the Invention

[0004] The purpose of the present invention is to provide a hierarchical porous silicon material and a preparation method thereof. The preparation method provided by the present invention can prepare hierarchical porous silicon materials without using a templating agent, and the process is simple.

[0005] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions: The present invention provides a preparation method of a hierarchical porous silicon material, comprising the following steps: (1) Mix fly ash and an activator, and perform calcination to obtain activated fly ash; the activator includes at least one of sodium salts and potassium salts; (2) Mix the activated fly ash obtained in step (1) with hydrochloric acid, and perform acid etching to obtain a hierarchical porous silicon material.

[0006] Preferably, when the activator in step (1) is a sodium salt and a potassium salt, the mass ratio of the sodium salt to the potassium salt is 1:3 to 3:1.

[0007] Preferably, the mixing in step (1) is ball milling.

[0008] Preferably, the ball milling includes self-rotation and revolution; the rotation speed of the self-rotation is 300 to 500 revolutions per minute; the rotation speed of the revolution is 150 to 200 revolutions per minute.

[0009] Preferably, the ball-to-material ratio of the ball milling is (5 to 8):1, and the ball milling time is 2 to 4 h.

[0010] Preferably, the calcination temperature in step (1) is 800 to 1100 °C, and the calcination time is 1 to 3 h.

[0011] Preferably, the mass concentration of hydrochloric acid in the step (2) is 10-30%.

[0012] Preferably, the mass ratio of the activated fly ash to the volume of hydrochloric acid in the step (2) is 1 g:(8-12) mL.

[0013] Preferably, the temperature of the acid etching in the step (2) is 80-100 °C, and the time of the acid etching is 0.5-8 h.

[0014] The present invention also provides a hierarchical porous silicon material prepared by the preparation method described in the above technical solution.

[0015] The present invention provides a preparation method of a hierarchical porous silicon material, comprising the following steps: mixing fly ash and an activator, and performing calcination to obtain activated fly ash; the activator includes at least one of a sodium salt and a potassium salt; mixing the activated fly ash with hydrochloric acid, and performing acid etching to obtain a hierarchical porous silicon material. The present invention uses at least one of a sodium salt and a potassium salt to activate fly ash. During the activation process, at least one of Na + and K + can promote the transformation of the mullite phase in fly ash into different mineral phase aluminosilicates, forming a nepheline structure; then, hydrochloric acid is used for acid etching, which can selectively etch the alumina component, thereby constructing hierarchical pores, simplifying the process, and realizing the template-free preparation of a hierarchical porous silicon material. Experimental results show that the pore diameter of the hierarchical porous silicon material prepared by the present invention is concentrated in the range of 3-4 nm, and according to the pore size distribution trend, there are some micropores (D<2 nm). Description of the Drawings

[0016] Figure 1 It is the N2 adsorption-desorption isotherm diagram of the hierarchical porous silicon materials prepared in Examples 1-4 and Comparative Examples 1-2; Figure 2 It is the BJH pore size distribution curve diagram of the hierarchical porous silicon materials prepared in Examples 1-4 and Comparative Examples 1-2; Figure 3 It is the nitrogen adsorption-desorption isotherm of the hierarchical porous silicon materials prepared in Examples 3, 5-6; Figure 4 It is the BJH pore size distribution curve of the hierarchical porous silicon materials prepared in Examples 3, 5-6; Figure 5 It is the SEM image of the hierarchical porous silicon material prepared in Example 3 magnified 1000 times; Figure 6 It is the SEM image of the hierarchical porous silicon material prepared in Example 3 magnified 5000 times; Figure 7 It is the SEM image of the hierarchical porous silicon material prepared in Example 5 magnified 1000 times; Figure 8 SEM image of the hierarchically porous silicon material prepared in Example 5 magnified 5000 times; Figure 9 SEM image of the hierarchically porous silicon material prepared in Example 6 magnified 1000 times; Figure 10 SEM image of the hierarchically porous silicon material prepared in Example 6 magnified 5000 times. Detailed implementation manners

[0017] The present invention provides a method for preparing a hierarchically porous silicon material, comprising the following steps: (1) Mix fly ash and an activator, and perform calcination to obtain activated fly ash; the activator includes at least one of sodium salts and potassium salts; (2) Mix the activated fly ash obtained in step (1) with hydrochloric acid, and perform acid etching to obtain a hierarchically porous silicon material.

[0018] The present invention has no special limitation on the sources of the respective raw materials, and commercially available products well-known to those skilled in the art can be used.

[0019] The present invention mixes fly ash and an activator, and performs calcination to obtain activated fly ash.

[0020] In the present invention, the particle size of the fly ash is preferably <75 μm; the fly ash is preferably pulverized coal furnace (PC) fly ash, and more preferably high-aluminum fly ash.

[0021] The present invention has no special limitation on the contents of the respective components in the high-aluminum fly ash, and high-aluminum fly ash well-known to those skilled in the art can be used.

[0022] As an implementation manner, the mass content of SiO2 in the high-aluminum fly ash can be 36.40%; the mass content of Al2O3 in the high-aluminum fly ash can be 35.00%.

[0023] In the present invention, the activator includes at least one of sodium salts and potassium salts. The present invention uses at least one of sodium salts and potassium salts to activate fly ash, and at least one of Na + and K + during the activation process can promote the transformation of the mullite phase in fly ash into different mineral-phase aluminosilicates, forming a nepheline structure of Na and / or K.

[0024] In the present invention, the sodium salt is preferably one of sodium carbonate (Na2CO3), sodium sulfate, and sodium sulfite; the potassium salt is preferably one of potassium carbonate (K2CO3), potassium sulfate, and potassium sulfite.

[0025] In the present invention, when the activator is a sodium salt and a potassium salt, the mass ratio of the sodium salt to the potassium salt is preferably 1:3 to 3:1, more preferably 1:2 to 2:1. Limiting the mass ratio of the sodium salt to the potassium salt within the above range in the present invention can further improve the activation effect.

[0026] In the present invention, the mass ratio of the fly ash to the activator is preferably (1.5 to 2.5):1, more preferably 2:1. Limiting the mass ratio of the fly ash to the activator within the above range in the present invention can further improve the activation effect; at the same time, it can also limit the content of the alumina component in the activated fly ash and further construct hierarchical pores during subsequent acid etching.

[0027] In the present invention, the mixing of the fly ash and the activator is preferably ball milling; the ball milling preferably includes self-rotation and revolution; the rotation speed of the self-rotation is preferably 300 to 500 revolutions per minute; the rotation speed of the revolution is preferably 150 to 200 revolutions per minute. As an implementation manner, the rotation speed of the self-rotation can be 350 to 450 revolutions per minute, and can also be 400 revolutions per minute; the rotation speed of the revolution can be 160 to 180 revolutions per minute.

[0028] In the present invention, the ball-to-material ratio of the ball milling is preferably (5 to 8):1; the time of the ball milling is preferably 2 to 4 h. As an implementation manner, the ball-to-material ratio of the ball milling can be (6 to 7):1; the time of the ball milling can be 3 h.

[0029] In the present invention, the temperature of the calcination is preferably 800 to 1100 °C; the time of the calcination is preferably 1 to 3 h. As an implementation manner, the temperature of the calcination can be 900 to 1000 °C; the time of the calcination can be 2 h. Limiting the temperature and time of the calcination within the above range in the present invention can further improve the activation effect.

[0030] After the calcination is completed, the present invention preferably cools the product obtained by the calcination to obtain activated fly ash.

[0031] The present invention has no special limitation on the operation of the cooling, and it can be cooled to room temperature by using the operations well-known to those skilled in the art.

[0032] After obtaining the activated fly ash, the present invention mixes the activated fly ash with hydrochloric acid and performs acid etching to obtain hierarchical pore silicon materials.

[0033] In the present invention, the mass concentration of the hydrochloric acid is preferably 10% to 30%, more preferably 15% to 25%, and even more preferably 20% to 25%; the mass ratio of the activated fly ash to the volume of the hydrochloric acid is preferably 1 g : (8 - 12) mL, and more preferably 1 g : 10 mL. Limiting the mass ratio of the activated fly ash to the volume of the hydrochloric acid within the above range in the present invention can further improve the degree of acid etching, thereby further obtaining a material with porous channels.

[0034] The present invention has no special limitation on the operation of mixing the activated fly ash and the hydrochloric acid, and a technical solution for preparing a mixed material well-known to those skilled in the art can be adopted.

[0035] In the present invention, the temperature of the acid etching is preferably 80°C to 100°C; the time of the acid etching is preferably 0.5 h to 8 h. As an implementation manner, the temperature of the acid etching can be 85°C, 90°C or 95°C; the time of the acid etching can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h or 7 h. Limiting the temperature and time of the acid etching within the above range in the present invention can further improve the degree of acid etching, thereby further obtaining a material with porous channels.

[0036] In the present invention, the acid etching is preferably carried out under stirring conditions. The present invention has no special limitation on the stirring rate, and a stirring operation well-known to those skilled in the art can be adopted.

[0037] After the acid etching is completed, the present invention preferably cools, separates the solid from the liquid, washes and dries the product obtained by the acid etching in sequence to obtain a hierarchical porous silicon material.

[0038] The present invention has no special limitation on the cooling operation, and a cooling operation well-known to those skilled in the art can be adopted.

[0039] The present invention has no special limitation on the solid-liquid separation operation, and a residue can be obtained by an operation well-known to those skilled in the art.

[0040] The present invention has no special limitation on the washing operation, and wash until Cl cannot be detected by using an AgNO3 solution. - That's all.

[0041] The present invention has no special limitation on the drying operation, and dry to a constant weight by an operation well-known to those skilled in the art.

[0042] The present invention activates fly ash by using at least one of a sodium salt and a potassium salt. During the activation process, Na + and K +At least one of them can promote the transformation of mullite phase in fly ash into aluminosilicates with different mineral phases, forming nepheline structures of Na and / or K; then acid etching is carried out with hydrochloric acid, which can selectively etch the alumina component, thereby constructing hierarchical pores, simplifying the process, and realizing the template-free preparation of hierarchical porous silicon materials.

[0043] The present invention has the advantages of simple process, low production cost, and no environmental pollution. It can not only solve the problems of complex process, high production cost, and toxic template agent in various template methods, but also solve the storage problem of bulk solid waste fly ash, improve its comprehensive utilization rate, and reduce environmental pollution. This method is of great significance for developing hierarchical porous silicon materials from fly ash through a simple process.

[0044] The present invention realizes the mineral phase transformation and pore structure regulation of fly ash through the fly ash mineral phase transformation-acid etching method, and finally obtains hierarchical porous silicon materials, effectively improving the transformation efficiency of mullite and quartz phases in fly ash, reducing the dosage of additives, and reducing the generation of by-products such as basic nepheline; at the same time, acid etching can also regulate the pore structure of hierarchical porous silicon materials, forming hierarchical pores, realizing the simple preparation of hierarchical porous silicon materials; at the same time, no template agent is used, reducing the cost, solving the problem that the competitive effect between different template agents is difficult to control, and the preparation process is also simpler.

[0045] The present invention also provides a hierarchical porous silicon material prepared by the preparation method described in the above technical solution.

[0046] The hierarchical porous silicon material provided by the present invention has hierarchical pores.

[0047] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0048] The fly ash used in the examples is pulverized coal furnace (PC) fly ash, which is high-aluminum fly ash, and its chemical composition is shown in Table 1: Table 1 Chemical composition of fly ash in the examples

[0049] Example 1 The preparation method of the hierarchical porous silicon material is as follows: (1) Grind fly ash with a particle size < 75 μm and an activator for 2 h, then calcine at 900 °C for 2 h, and then cool to room temperature to obtain activated fly ash; among them, the activator is K2CO3; the mass ratio of fly ash to the activator is 2:1; the ball milling is rotation and revolution; the rotation speed is 400 revolutions per minute; the revolution speed is 200 revolutions per minute; the ball-to-material ratio of ball milling is 6:1; (2) Mix the activated fly ash obtained in step (1) with 10 wt% hydrochloric acid, continuously stir and etch with acid at 80 °C for 2 h, then cool, then perform vacuum filtration, and then wash the filter residue with deionized water multiple times until Cl cannot be detected by AgNO3 solution - and then dry in an oven at 105 °C for 24 h to obtain a hierarchical porous silicon material KAlSiO4, denoted as 10% HCl; among them, the mass ratio of activated fly ash to the volume of hydrochloric acid is 1 g:10 mL.

[0050] Example 2 On the basis of Example 1, modify the mass concentration of hydrochloric acid to 15%, and keep other conditions unchanged to obtain a hierarchical porous silicon material, denoted as 15% HCl.

[0051] Example 3 On the basis of Example 1, modify the mass concentration of hydrochloric acid to 20%, and keep other conditions unchanged to obtain a hierarchical porous silicon material, denoted as 20% HCl.

[0052] Example 4 On the basis of Example 1, modify the mass concentration of hydrochloric acid to 30%, and keep other conditions unchanged to obtain a hierarchical porous silicon material, denoted as 30% HCl.

[0053] Comparative Example 1 On the basis of Example 1, modify the mass concentration of hydrochloric acid to 2.5%, and keep other conditions unchanged to obtain a hierarchical porous silicon material, denoted as 2.5% HCl.

[0054] Comparative Example 2 On the basis of Example 1, modify the mass concentration of hydrochloric acid to 5%, and keep other conditions unchanged to obtain a hierarchical porous silicon material, denoted as 5% HCl.

[0055] The N2 adsorption-desorption isotherms of the hierarchical porous silicon materials prepared in Examples 1 to 4 and Comparative Examples 1 to 2 are as Figure 1 shown; the BJH pore size distribution curves of the hierarchical porous silicon materials prepared in Examples 1 to 4 and Comparative Examples 1 to 2 are as Figure 2As shown; the test method is to use a specific surface area analyzer (BET) to test the nitrogen adsorption isotherm curve and the hysteresis loop of the hierarchical porous silicon material; using the Brunauer Emmett Teller test, in the relative equilibrium pressure range of 0.06 - 0.15, the specific surface area of the sample is determined according to the N2 adsorption isotherm; the Barrett Joyner Halenda method is used to determine the pore size from the adsorption branch of the isotherm. When the relative pressure P / P0 is greater than 0.99, the pores with an internal width less than 50 nm are completely covered by liquid nitrogen. Therefore, the pore volume (V) is regarded as the liquid nitrogen volume at x = 0.96.

[0056] Combined with Figures 1 - 2 it can be seen that the change in the degree of acid etching has a significant impact on the pore shape and pore size of the product.

[0057] Judged by the adsorption curve and the type of hysteresis loop in the International Union of Pure and Applied Chemistry (IUPAC), the order of pore shape change of the acid-leached product is: no mesopores, wedge-shaped, flat-shaped, ink-bottle-shaped, and wedge-shaped. With the increase in the degree of acid etching, the most probable pore size D BJH distribution changes from dispersed to concentrated.

[0058] Example 5 On the basis of Example 3, the mass ratio of Na2CO3 and K2CO3 was modified to 2:2, and other conditions remained unchanged, obtaining a hierarchical porous silicon material, denoted as MS-NK.

[0059] Example 6 On the basis of Example 3, the activator was modified to Na2CO3, and other conditions remained unchanged, obtaining a hierarchical porous silicon material, denoted as MS-N.

[0060] The N2 adsorption-desorption isotherms of the hierarchical porous silicon materials prepared in Examples 3, 5 - 6 are as Figure 3 shown; the BJH pore size distribution curves of the hierarchical porous silicon materials prepared in Examples 3, 5 - 6 are as Figure 4 shown ( Figure 3 and 4 where MS-K in

[0061] From Figure 3It can be seen that the hierarchical porous silicon materials obtained by acid etching of activated fly ash (hexagonal phase (Na, K)AlSiO4) in Example 5, the hierarchical porous silicon materials obtained by acid etching of activated fly ash (hexagonal phase KAlSiO4) in Example 3, and the hierarchical porous silicon materials obtained by acid etching of activated fly ash (hexagonal phase NaAlSiO4) in Example 6 exhibit a Type-IV N2 adsorption isotherm and an H4 hysteresis loop, indicating the formation of an ink-bottle-shaped mesoporous structure; the N2 adsorption isotherm of the hierarchical porous silicon material prepared in Example 5 is closer to the y-axis at low P / P0 (0-0.2), indicating the existence of a certain number of micropores.

[0062] It can be seen from Figure 4 that the hierarchical porous silicon materials prepared in Examples 3, 5-6 all produced uniform and concentrated mesoporous channels, the pore size distribution curves are similar, the pore sizes are concentrated in the range of 3-4 nm, and according to the trend of the pore size distribution, there are some micropores (D<2 nm).

[0063] Figure 5 Figure 9 is an SEM image of the hierarchical porous silicon material prepared in Example 3 magnified 1000 times; Figure 6 Figure 10 is an SEM image of the hierarchical porous silicon material prepared in Example 3 magnified 5000 times; Figure 7 Figure 11 is an SEM image of the hierarchical porous silicon material prepared in Example 5 magnified 1000 times; Figure 8 Figure 12 is an SEM image of the hierarchical porous silicon material prepared in Example 5 magnified 5000 times; Figure 9 Figure 13 is an SEM image of the hierarchical porous silicon material prepared in Example 6 magnified 1000 times; Figure 10 Figure 14 is an SEM image of the hierarchical porous silicon material prepared in Example 6 magnified 5000 times.

[0064] It can be seen from Figures 5 - 10 that the addition of sodium promoted the activation reaction of the crystal phase in the fly ash system, resulting in the aluminum silicate particles formed during the calcination process tending to agglomerate more, and the particle edge morphology being more regular, indicating good crystal crystallization state.

[0065] It can be seen from the above examples and comparative examples that the preparation method provided by the present invention can prepare hierarchical porous silicon materials without using a template agent, and the process is simple.

[0066] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a multi-level porous silicon material, comprising the following steps: (1) mixing fly ash and an activator, and calcining them to obtain activated fly ash; the activator comprises at least one of a sodium salt and a potassium salt; (2) The activated fly ash obtained in step (1) is mixed with hydrochloric acid and subjected to acid etching to obtain a multi-level porous silicon material.

2. The preparation method according to claim 1, characterized in that: When the activating agent in step (1) is sodium salt and potassium salt, the mass ratio of sodium salt to potassium salt is 1:3 to 3:

1.

3. The preparation method according to claim 1, characterized in that: The mixing in step (1) is performed by ball milling.

4. The preparation method according to claim 3, characterized in that: The ball mill includes rotation and revolution; the rotation speed is 300-500 rpm; the revolution speed is 150-200 rpm.

5. The preparation method according to claim 3, characterized in that: The ball-to-material ratio of the ball mill is (5-8):1, and the ball milling time is 2-4 hours.

6. The preparation method according to claim 1, characterized in that: In the step (1), the calcination temperature is 800-1100° C. and the calcination time is 1-3 hours.

7. The preparation method according to claim 1, characterized in that: The mass concentration of hydrochloric acid in step (2) is 10-30%.

8. The preparation method according to claim 1, characterized in that: In the step (2), the ratio of the mass of activated fly ash to the volume of hydrochloric acid is 1 g: (8-12) mL.

9. The preparation method according to claim 1, characterized in that: In the step (2), the acid etching temperature is 80-100° C., and the acid etching time is 0.5-8 h.

10. The multi-level porous silicon material prepared by the preparation method according to any one of claims 1 to 9.

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