A method for preparing porous silicon

Abstract

The present invention provides a method for preparing porous silicon, belonging to the technical field of porous silicon preparation. The present invention uses graphite as an etching catalyst, the electronegativity of graphite is 2.55, which is greater than the electronegativity of silicon 1.90, and has high chemical stability. The high electronegativity enables graphite to take electrons from Si, and holes are injected into Si, Si is oxidized, and the chemical stability (chemical inertness) enables graphite to maintain its morphology and properties during the reaction process, so that it can replace precious metals as etching catalysts to obtain porous silicon, without the use of precious metals, and at a lower cost.

Description

Technical Field

[0001] The invention belongs to the technical field of porous silicon preparation, and in particular relates to a method for preparing porous silicon. Background Art

[0002] Porous silicon has a large specific surface area and a high theoretical specific capacity (4200 mAh / g), which makes it widely used in catalysis, sensors, optoelectronics, bioimaging and energy batteries.

[0003] At present, the preparation method of porous silicon is mainly metal-assisted chemical etching, which uses noble metals as catalysts to assist etching, thereby preparing porous silicon. However, the high cost of noble metals limits their application. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing porous silicon. The present invention uses graphite as a catalyst, does not need to use precious metals, and has low cost.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing porous silicon, comprising the following steps:

[0007] Mixing silicon, graphite, a solvent and an etching solution for etching to obtain porous silicon, wherein the etching solution includes hydrogen fluoride, hydrogen peroxide and water;

[0008] The ratio of the amount of hydrogen fluoride in the etching solution to the total amount of hydrogen fluoride and hydrogen peroxide is 0.75 to 0.9;

[0009] The silicon, graphite, solvent and etching solution are mixed in the following manner: silicon and part of the solvent are mixed to obtain a mixed solution A, graphite and the remaining solvent are mixed to obtain a mixed solution B, the mixed solution A and the mixed solution B are then mixed to obtain a suspension, and the suspension is then mixed with the etching solution; or silicon and graphite are mixed, and then a solvent is added to obtain a suspension, and the suspension is then mixed with the etching solution.

[0010] Preferably, the average particle size of the silicon is 5-45 μm.

[0011] Preferably, the average particle size of the graphite is 1-8 μm.

[0012] Preferably, the mass ratio of silicon to graphite is 1:(0.1~1).

[0013] Preferably, the mass ratio of the silicon to the volume of the solvent is 1 g: (10-30) mL.

[0014] Preferably, the mass of silicon and the volume ratio of the etching solution are 1 g: (1-10) mL.

[0015] Preferably, the etching temperature is 20-60° C., and the etching time is 0.5-8 h.

[0016] The present invention provides a method for preparing porous silicon. The present invention uses graphite to assist etching. The electronegativity of graphite is 2.55, which is greater than the electronegativity of silicon, 1.90. At the same time, it has high chemical stability. The high electronegativity allows graphite to take electrons from Si, and holes are injected into Si, and Si is oxidized. The chemical stability (chemical inertness) allows graphite to maintain its morphology and properties during the reaction process, so that it can replace precious metals as etching catalysts to obtain porous silicon without using precious metals, and the cost is lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a SEM image of the porous silicon prepared in Example 1 at a magnification of 1900;

[0018] Figure 2 This is a SEM image of the porous silicon prepared in Example 1 at a magnification of 5300;

[0019] Figure 3 XRD pattern of porous silicon prepared in Example 1;

[0020] Figure 4 This is a SEM image of the porous silicon prepared in Example 2;

[0021] Figure 5 This is a SEM image of the porous silicon prepared in Example 3;

[0022] Figure 6 This is a SEM image of the porous silicon prepared in Example 4;

[0023] Figure 7 This is a SEM image of the porous silicon prepared in Example 5;

[0024] Figure 8 This is a SEM image of the porous silicon prepared in Example 6;

[0025] Fig. 9 This is a SEM image of the porous silicon prepared in Example 7;

[0026] Fig.10 This is a SEM image of the porous silicon prepared in Example 8;

[0027] Fig.11 This is a SEM image of the porous silicon prepared in Example 9;

[0028] Fig.12 This is a SEM image of the porous silicon prepared in Example 10;

[0029] Fig.13This is a SEM image of the porous silicon prepared in Example 11;

[0030] Fig.14 This is the SEM image of the porous silicon prepared in Comparative Example 1. DETAILED DESCRIPTION

[0031] The present invention provides a method for preparing porous silicon, comprising the following steps:

[0032] Silicon, graphite, a solvent and an etching solution are mixed and etched to obtain porous silicon, wherein the etching solution includes hydrogen fluoride, hydrogen peroxide and water.

[0033] Unless otherwise specified, the present invention has no particular limitation on the sources of the raw materials, and commercially available products known to those skilled in the art may be used.

[0034] In the present invention, the average particle size of the silicon is preferably 5 to 45 μm. In an embodiment of the present invention, the average particle size of the silicon may be specifically 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm or 45 μm. In the present invention, the silicon is preferably metal silicon powder (polycrystalline silicon).

[0035] In the present invention, the average particle size of the graphite is preferably 1-8 μm. In an embodiment of the present invention, the average particle size of the graphite may be specifically 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm or 8 μm.

[0036] In the present invention, the mass ratio of silicon to graphite is preferably 1:(0.1-1). In an embodiment of the present invention, the mass ratio of silicon to graphite may be specifically 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1. The present invention controls the mass ratio of silicon to graphite within the above range, so that silicon can be fully etched to form a porous structure.

[0037] In the present invention, the solvent preferably includes water and ethanol.

[0038] In the present invention, the volume ratio of water to ethanol is preferably 1:(0.5-1.5), more preferably 1:1.

[0039] In the present invention, the mass of silicon and the volume ratio of the solvent are preferably 1 g: (10-30) mL, more preferably 1 g: (15-25) mL, and further preferably 1 g: 20 mL. The present invention controls the type of solvent, the mass of silicon and the volume ratio of the solvent within the above range, so that silicon and graphite can be more fully and evenly dispersed in the solvent.

[0040] In the present invention, the etching solution includes hydrogen fluoride, hydrogen peroxide and water.

[0041] In the present invention, the ratio of the amount of hydrogen fluoride in the etching solution to the total amount of hydrogen fluoride and hydrogen peroxide is 0.75 to 0.9. In an embodiment of the present invention, the ratio of the amount of hydrogen fluoride in the etching solution to the total amount of hydrogen fluoride and hydrogen peroxide can be specifically 0.75, 0.8 or 0.9. The present invention controls the ratio of the amount of hydrogen fluoride in the etching solution to the total amount of hydrogen fluoride and hydrogen peroxide within the above range, which can make etching more sufficient.

[0042] In the present invention, the etching solution is preferably prepared by mixing hydrofluoric acid and hydrogen peroxide solution to obtain the etching solution.

[0043] The present invention has no particular limitation on the concentrations of the hydrofluoric acid and hydrogen peroxide solutions, as long as the ratio of the amount of hydrogen fluoride in the mixed etching solution to the total amount of hydrogen fluoride and hydrogen peroxide is within the above range.

[0044] The present invention has no special limitation on the mixing operation of the hydrofluoric acid and hydrogen peroxide solution, and a technical solution for mixing materials well known to those skilled in the art may be adopted.

[0045] In the present invention, the mass ratio of the silicon to the volume of the etching solution is preferably 1 g: (1-10) mL. In an embodiment of the present invention, the mass ratio of the silicon to the volume of the etching solution can be specifically 1 g: 1 mL, 1 g: 5 mL or 1 g: 10 mL.

[0046] In the present invention, the silicon, graphite, solvent and etching solution are mixed in the following manner: silicon and part of the solvent are mixed to obtain a mixed solution A, graphite and the remaining solvent are mixed to obtain a mixed solution B, and then the mixed solution A and the mixed solution B are mixed to obtain a suspension, and then the suspension is mixed with the etching solution; or silicon and graphite are mixed, and then a solvent is added to obtain a suspension, and then the suspension is mixed with the etching solution.

[0047] In the present invention, the mixing preferably includes stirring, grinding or ultrasound; the mixing time is preferably 5 to 40 minutes. In the present invention, the grinding does not substantially change the particle size of silicon and graphite.

[0048] The present invention has no special limitation on the stirring mode, speed, ultrasonic power and grinding operation, and the technical solutions well known to those skilled in the art can be adopted.

[0049] In the present invention, the etching temperature is preferably 20-60° C. In an embodiment of the present invention, the etching temperature may be specifically 20° C., 30° C., 40° C., 50° C. or 60° C.

[0050] In the present invention, the etching time is preferably 0.5 to 8 hours. In an embodiment of the present invention, the etching time can be specifically 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours.

[0051] In the present invention, the etching is preferably carried out under stirring conditions. The present invention has no particular limitation on the stirring mode and rate, and the stirring mode and rate well known to those skilled in the art can be used. The present invention controls the etching temperature and time within the above ranges, so that the etching can be fully carried out.

[0052] After etching is completed, the present invention preferably mixes the etched system with water, performs solid-liquid separation after centrifugation, and then dries the obtained solid to obtain porous silicon.

[0053] The present invention has no special limitation on the amount of water used, and the technical solutions well known to those skilled in the art can be adopted.

[0054] In the present invention, the number of centrifugation is preferably 2 to 5 times. In the present invention, the rotation speed of a single centrifugation is preferably 2500 to 4500 rpm; and the time of a single centrifugation is preferably 3 to 8 minutes.

[0055] The present invention has no special limitation on the solid-liquid separation operation, and the technical solutions well known to those skilled in the art can be adopted.

[0056] In the present invention, the drying temperature is preferably 40-60° C.; the drying time is preferably 6-12 hours.

[0057] The present invention adopts graphite-assisted etching to obtain porous silicon, does not need to use precious metals, has lower costs, and controls various process parameters to make the porous silicon have a higher specific surface area.

[0058] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0059] Example 1

[0060] The preparation method of porous silicon is:

[0061] (1) 1 g of silicon (average particle size of 30 μm) was mixed with 5 mL of water and 5 mL of anhydrous ethanol, and magnetically stirred for 10 min to obtain a mixed solution A; 0.1 g of graphite (average particle size of 1.6 μm) was mixed with 5 mL of water and 5 mL of anhydrous ethanol, and magnetically stirred for 10 min to obtain a mixed solution B; mixed solution A and mixed solution B were mixed and stirred for 10 min to obtain a suspension, in which the mass ratio of silicon to graphite was 1:0.1, and the mass ratio of silicon to solvent was 1 g:20 mL;

[0062] (2) mixing hydrofluoric acid having a mass concentration of 40% and hydrogen peroxide solution having a mass concentration of 30% to obtain an etching solution, wherein the ratio of the amount of hydrogen fluoride in the etching solution to the total amount of hydrogen fluoride and hydrogen peroxide is 0.75;

[0063] (3) Mix the suspension in step (1) and the etching solution in step (2) in a ratio of silicon mass to etching solution volume of 1 g:5 mL. Etch at 50° C. for 6 h under stirring. Pour the etched solution into a centrifuge tube and add purified water for three centrifuges. The speed of each centrifugation is 4500 rpm and the time of each centrifugation is 5 min. Then separate the solid and liquid, and dry the solid in a 50° C. forced air drying oven for 12 h to obtain porous silicon.

[0064] Example 2

[0065] The preparation method of porous silicon is:

[0066] (1) Place 1 g of silicon (average particle size 30 μm) and 0.1 g of graphite (average particle size 1.6 μm) in a beaker, then add 10 mL of water and 10 mL of anhydrous ethanol, mix, and stir magnetically for 10 min to obtain a suspension. The mass ratio of silicon to graphite is 1:0.1, and the mass ratio of silicon to solvent is 1 g:20 mL.

[0067] (2) mixing hydrofluoric acid having a mass concentration of 40% and hydrogen peroxide solution having a mass concentration of 30% to obtain an etching solution, wherein the ratio of the amount of hydrogen fluoride in the etching solution to the total amount of hydrogen fluoride and hydrogen peroxide is 0.75;

[0068] (3) Mix the suspension in step (1) and the etching solution in step (2) in a ratio of silicon mass to etching solution volume of 1 g:5 mL. Etch at 50° C. for 6 h under stirring. Pour the etched solution into a centrifuge tube and add purified water for three centrifuges. The speed of each centrifugation is 4500 rpm and the time of each centrifugation is 5 min. Then separate the solid and liquid, and dry the solid in a 50° C. forced air drying oven for 12 h to obtain porous silicon.

[0069] Example 3

[0070] The preparation method of porous silicon is:

[0071] (1) Grind 1 g of silicon (average particle size 30 μm) and 0.1 g of graphite (average particle size 1.6 μm) in a mortar for 30 min, then add 10 mL of water and 10 mL of anhydrous ethanol to obtain a suspension. The mass ratio of silicon to graphite is 1:0.1, and the volume ratio of silicon mass to solvent is 1 g:20 mL.

[0072] (2) mixing hydrofluoric acid having a mass concentration of 40% and hydrogen peroxide solution having a mass concentration of 30% to obtain an etching solution, wherein the ratio of the amount of hydrogen fluoride in the etching solution to the total amount of hydrogen fluoride and hydrogen peroxide is 0.75;

[0073] (3) Mix the suspension in step (1) and the etching solution in step (2) in a ratio of silicon mass to etching solution volume of 1 g:5 mL. Etch at 50° C. for 6 h under stirring. Pour the etched solution into a centrifuge tube and add purified water for three centrifuges. The speed of each centrifugation is 4500 rpm and the time of each centrifugation is 5 min. Then separate the solid and liquid, and dry the solid in a 50° C. forced air drying oven for 12 h to obtain porous silicon.

[0074] Example 4

[0075] The preparation method of porous silicon is:

[0076] (1) Place 1 g of silicon (average particle size of 30 μm) and 0.1 g of graphite (average particle size of 1.6 μm) in a beaker, then add 10 mL of water and 10 mL of anhydrous ethanol, mix, and ultrasonically disperse for 10 min to obtain a suspension. The mass ratio of silicon to graphite is 1:0.1, and the mass ratio of silicon to solvent is 1 g:20 mL.

[0077] (2) mixing hydrofluoric acid having a mass concentration of 40% and hydrogen peroxide solution having a mass concentration of 30% to obtain an etching solution, wherein the ratio of the amount of hydrogen fluoride in the etching solution to the total amount of hydrogen fluoride and hydrogen peroxide is 0.75;

[0078] (3) Mix the suspension in step (1) and the etching solution in step (2) in a ratio of silicon mass to etching solution volume of 1 g:5 mL. Etch at 50° C. for 6 h under stirring. Pour the etched solution into a centrifuge tube and add purified water for three centrifuges. The speed of each centrifugation is 4500 rpm and the time of each centrifugation is 5 min. Then separate the solid and liquid, and dry the solid in a 50° C. forced air drying oven for 12 h to obtain porous silicon.

[0079] Example 5

[0080] The amount of graphite in step (1) of Example 1 was replaced with 1 g. At this time, the mass ratio of silicon to graphite was 1:1. The other parameters were the same as those in Example 1.

[0081] Example 6

[0082] The ratio of the amount of hydrogen fluoride to the total amount of hydrogen fluoride and hydrogen peroxide in the etching solution in step (2) of Example 1 is replaced by 0.25, and the other parameters are the same as those in Example 1.

[0083] Example 7

[0084] The ratio of the amount of hydrogen fluoride to the total amount of hydrogen fluoride and hydrogen peroxide in the etching solution in step (2) of Example 1 is replaced by 0.5, and the other parameters are the same as those in Example 1.

[0085] Example 8

[0086] The ratio of the amount of hydrogen fluoride to the total amount of hydrogen fluoride and hydrogen peroxide in the etching solution in step (2) of Example 1 is replaced by 0.9, and the other parameters are the same as those in Example 1.

[0087] Example 9

[0088] The etching time in step (3) of Example 1 was replaced with 2 h, and the other parameters were the same as those of Example 1.

[0089] Example 10

[0090] The etching time in step (3) of Example 1 was replaced with 4 h, and the other parameters were the same as those of Example 1.

[0091] Embodiment 11

[0092] The etching time in step (3) of Example 1 was replaced with 8 h, and the other parameters were the same as those of Example 1.

[0093] Comparative Example 1

[0094] The ratio of the amount of hydrogen fluoride to the total amount of hydrogen fluoride and hydrogen peroxide in the etching solution in step (2) of Example 1 is replaced by 0.99, and the other parameters are the same as those in Example 1.

[0095] The porous silicon prepared in Example 1 was observed using a scanning electron microscope, and the SEM images obtained at a magnification of 1900 and a magnification of 5300 were as follows: Figure 1~2 As shown. Figure 1~2 It can be seen that a uniform pore structure is produced on the prepared porous silicon surface.

[0096] The XRD pattern of the porous silicon prepared in Example 1 is as follows: Figure 3 As shown. Figure 3It can be seen that porous silicon has no other impurities.

[0097] The porous silicon prepared in Example 2 was observed using a scanning electron microscope, and the SEM image obtained with a magnification of 6900 was as follows: Figure 4 The porous silicon prepared in Example 3 was observed using a scanning electron microscope, and the SEM image obtained with a magnification of 5500 is as shown in FIG. Figure 5 The porous silicon prepared in Example 4 was observed using a scanning electron microscope, and the SEM image obtained with a magnification of 2500 is as shown in FIG. Figure 6 As shown. Figure 1 , Figures 4 to 6 It can be seen that the mixing mode of silicon and graphite has a certain influence on the etching of porous silicon, and different mixing modes have an influence on the adhesion between silicon and graphite. The specific surface areas of porous silicon prepared in Examples 1 to 4 are 2.911 m 2 g -1 , 2.0774m 2 g -1 ,4.3311m 2 g -1 and 2.176m 2 g -1 Example 1: Silicon and graphite are mixed separately and then mixed again, so that the adhesion effect is better and the holes are denser and more uniform during etching.

[0098] The porous silicon prepared in Example 5 was observed using a scanning electron microscope, and the SEM image obtained with a magnification of 12000 was as follows: Figure 7 As shown. Figure 1 and Figure 7 It can be seen that the amount of graphite has an impact on the etching effect. When the mass ratio of silicon to graphite increases from 1:0.1 to 1:1, the etching is more complete, the holes are larger, and the etching rate is faster.

[0099] The porous silicon prepared in Example 6 was observed using a scanning electron microscope, and the SEM image obtained with a magnification of 5000 was as follows: Figure 8 The porous silicon prepared in Example 7 was observed using a scanning electron microscope, and the SEM image obtained with a magnification of 5000 is as shown in FIG. Fig. 9 The porous silicon prepared in Example 8 was observed using a scanning electron microscope, and the SEM image obtained with a magnification of 6000 is as shown in FIG. Fig.10 As shown. Figure 1 , Figures 8-10 It can be seen that different etching solution compositions also affect the etching effect. When the ratio of the amount of hydrogen fluoride in the etching solution to the total amount of hydrogen fluoride and hydrogen peroxide is 0.75, the etching is more sufficient, the holes are denser and more uniform, and the proportion of silicon etched is greater.

[0100] The porous silicon prepared in Example 9 was observed using a scanning electron microscope, and the SEM image obtained with a magnification of 2800 was as follows: Fig.11 The porous silicon prepared in Example 10 was observed using a scanning electron microscope, and the SEM image obtained with a magnification of 16000 is as shown in FIG. Fig.12 The porous silicon prepared in Example 11 was observed using a scanning electron microscope, and the SEM image obtained with a magnification of 12000 is as shown in FIG. Fig.13 As shown. Figure 1 and Figures 11 to 13 It can be seen that the etching time has an important influence on the etching effect. When the etching time is short, the etching marks on the surface of the silicon particles are shallow and the etching is incomplete. If the etching time is too long, the small holes etched on the silicon surface will merge and the structure of the holes on the silicon surface will be damaged. The morphology and density of the holes etched on the silicon surface can be controlled by the etching time. In general, the etching degree is positively correlated with the etching time.

[0101] The porous silicon prepared in Comparative Example 1 was observed using a scanning electron microscope, and the SEM image obtained with a magnification of 6000 was as follows: Fig.14 As shown. Figure 1 and Fig.14 It can be seen that when the etching solution composition exceeds the scope of the present invention, such as when the ratio of the amount of hydrogen fluoride to the total amount of hydrogen fluoride and hydrogen peroxide in the comparative example is 0.99, the etched area is small and the etching is insufficient.

[0102] In summary, the present invention uses graphite to assist in etching porous silicon, which has lower costs.

[0103] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing porous silicon, comprising the following steps: Mixing silicon, graphite, a solvent and an etching solution to perform etching to obtain porous silicon, wherein the etching solution includes hydrogen fluoride, hydrogen peroxide and water; The ratio of the amount of hydrogen fluoride in the etching solution to the total amount of hydrogen fluoride and hydrogen peroxide is 0.75; The silicon, graphite, solvent and etching solution are mixed in the following manner: silicon and part of the solvent are mixed to obtain a mixed solution A, graphite and the remaining solvent are mixed to obtain a mixed solution B, mixed solution A and mixed solution B are then mixed to obtain a suspension, and the suspension is then mixed with the etching solution; The mass ratio of silicon to graphite is 1:(0.1-1); the volume ratio of the mass of silicon to the etching solution is 1 g:(1-10) mL; the etching temperature is 20-60° C., and the etching time is 0.5-8 h.

2. The preparation method according to claim 1, characterized in that The average particle size of the silicon is 5-45 μm.

3. The preparation method according to claim 1, characterized in that The average particle size of the graphite is 1-8 μm.

4. The preparation method according to claim 1, characterized in that The mass ratio of the silicon to the volume of the solvent is 1 g: (10-30) mL.

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