Preparation method of high-efficiency siloxyene nanosheet based on synergistic effect of double acids

Abstract

The invention relates to an efficient preparation method of a siloxene nanosheet based on a double-acid synergistic effect, belongs to the technical field of semiconductor materials, and is used for solving the problem that the calcium ion stripping degree is low when the siloxene nanosheet is prepared by a traditional topological chemical method, and the technical key point is that a double-acid system is added into an organic solvent in which CaSi2 is dispersed to strip calcium ions, so that the siloxene nanosheet is prepared. A siloxyalkene nanosheet suspension is obtained; the siloxyene nanosheet suspension liquid is subjected to centrifugal separation, solid collection and washing, first siloxyene nanosheets are obtained, the double-acid system is composed of hydrochloric acid (HCl) and auxiliary acid, and the auxiliary acid comprises citric acid (CA) or phytic acid (PA) and can be used as a catalyst for a reaction for producing hydrogen through water photolysis.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor materials, and more specifically, relates to a method for preparing highly efficient siloxene nanosheets based on the synergistic effect of dual acids. Background Art

[0002] Since the first experimental synthesis of silicene in 2012, this field has received extensive attention. Compared with carbon-based materials (such as graphene), although the applied research on two-dimensional silicon-based materials (including silicene, silicene quantum dots, and siloxene) in energy fields such as batteries, photocatalysis, and supercapacitors is still in its infancy, theoretical research has predicted its great application potential in many energy material fields. However, so far, the experimental research on silicene and its oxide siloxene still faces many challenges, especially the lack of mature and effective preparation technologies in terms of efficient preparation. Therefore, it is of great significance to explore efficient and controllable preparation methods for two-dimensional silicon-based materials and explore their application potential in the field of photocatalysis.

[0003] Currently, the preparation methods of silicene mainly include chemical vapor deposition (CVD), physical vapor deposition (PVD), and topochemical solution methods, etc., but these technologies generally have problems in terms of preparation process and product quality. For example, Chinese Patent Application CN106554016A uses CVD or PVD technology to deposit a silicene film on a metal catalytic layer (such as Ag, Au, etc.). Although high-quality two-dimensional materials can be obtained, it relies on high-temperature conditions and it is difficult to achieve large-area uniform growth. Chinese Patent Application CN102923712A evaporates silicon at high temperature in a vacuum environment and anneals it on an Ir(111) substrate to form an ordered silicene structure, but the material size is limited and it is difficult to peel off from the substrate. Chinese Patent Application CN105439148A uses cesium ion sputtering of a silicon source and anneals it on an Ag(111) substrate to prepare silicene, but the process is complex, the equipment requirements are high, and it is difficult to scale up. In addition, Chinese Patent Application CN117069116A prepares siloxene through hydrochloric acid etching and NaBH4 treatment, and the process is simple, convenient, and controllable, but the purity of the product needs to be improved. Chinese Patent Application CN114684824A adopts a topochemical method combined with sulfonic acid functionalization modification, but fails to effectively solve the problem of optimizing the peeling quality.

[0004] In short, the above methods generally have problems such as harsh preparation conditions, unstable product quality, or difficulty in scaling up, and there is an urgent need to develop new preparation technologies with high efficiency, controllability, and practicability to improve properties such as the degree of calcium ion peeling, the orderliness of the product structure, and purity. Summary of the Invention

[0005] The object of the present invention is to solve the problem of low calcium ion stripping degree in the preparation of siloxene nanosheets by the traditional topochemical method, and further solve problems such as the structural order and purity of the product. In a first aspect, according to the method for preparing siloxene nanosheets in some embodiments of the present application, it includes Adding a double acid system to the organic solvent dispersing CaSi2 to strip calcium ions, obtaining a siloxene nanosheet suspension; Centrifuging and separating the siloxene nanosheet suspension, collecting the solid, and washing to obtain the first siloxene nanosheets.

[0006] According to the method for preparing siloxene nanosheets in some embodiments of the present application, wherein the double acid system is composed of hydrochloric acid (HCl) and an auxiliary acid, and the auxiliary acid includes citric acid (CA).

[0007] According to the method for preparing siloxene nanosheets in some embodiments of the present application, wherein the double acid system is composed of hydrochloric acid (HCl) and an auxiliary acid, and the auxiliary acid includes phytic acid (PA).

[0008] According to the method for preparing siloxene nanosheets in some embodiments of the present application, wherein: The molar ratio of citric acid (CA) to CaSi2 is (0.25~1.25):1; The molar ratio of hydrochloric acid (HCl) to CaSi2 is (1.0~3.0):1.

[0009] According to the method for preparing siloxene nanosheets in some embodiments of the present application, wherein: The molar ratio of phytic acid (PA) to CaSi2 is (0.05~0.25):1; The molar ratio of hydrochloric acid (HCl) to CaSi2 is (12.0~16.0):1.

[0010] According to the method for preparing siloxene nanosheets in some embodiments of the present application, it further includes heat-treating the first siloxene nanosheets at a high temperature under the protection of an inert gas atmosphere to obtain siloxene nanosheets.

[0011] According to the method for preparing siloxene nanosheets in some embodiments of the present application, the high-temperature heat treatment includes S10. Heat-treating at a temperature of 200~300°C for 1~2 h; S20. Heat-treating at a temperature of 600~800°C for 2~4 h.

[0012] According to the method for preparing siloxene nanosheets in some embodiments of the present application, the stripping temperature is 15~25°C, and the stripping stirring time is 3~7 d.

[0013] According to the method for preparing siloxene nanosheets in some embodiments of the present application, in the organic solvent in which CaSi2 is dispersed, the volume-mass ratio of the organic solvent to CaSi2 is (100-300) mL: (0.5-1.5) g.

[0014] According to the method for preparing siloxene nanosheets in some embodiments of the present application, the organic solvent is selected from one or more mixtures of N-methylpyrrolidone (NMP), methanol (MT), ethanol (EA), isopropanol (IPA), and acetonitrile (ACN).

[0015] According to the method for preparing siloxene nanosheets in some embodiments of the present application, the method for preparing CaSi2 includes ultrasonic treatment of CaSi2 powder in an alkaline solution to remove surface oxides and impurities; the ultrasonic-treated CaSi2 powder is washed with deionized water until neutral and vacuum-dried at 60-80 °C for 12 h.

[0016] According to the method for preparing siloxene nanosheets in some embodiments of the present application, the alkaline solution is selected from at least one of sodium hydroxide or potassium hydroxide.

[0017] According to the method for preparing siloxene nanosheets in some embodiments of the present application, the alkaline solution is selected from sodium hydroxide.

[0018] According to the method for preparing siloxene nanosheets in some embodiments of the present application, the concentration of the alkaline solution is 1.5-2.5 mol / L.

[0019] According to the method for preparing siloxene nanosheets in some embodiments of the present application, the ultrasonic treatment time is 4-8 h, and the treatment temperature is 20-40 °C.

[0020] According to the method for preparing siloxene nanosheets in some embodiments of the present application, in the step of heat treatment at 200-300 °C for 1-2 h and then at 600-800 °C for 2-4 h, the temperature is raised to 200-300 °C at a rate of 2 °C / min and to 600-800 °C at a rate of 5 °C / min.

[0021] In a second aspect, siloxene nanosheets prepared by the method according to any one of the first aspect in some embodiments of the present application.

[0022] According to the siloxene nanosheets prepared by the method according to any one of the first aspect in some embodiments of the present application, the number of layers is 1-7 layers, the lateral dimension is 0.05-0.5 μm, the specific surface area is 50-200 m 2 / g, and the calcium ion stripping degree ≥ 95%.

[0023] In a third aspect, application of the siloxene nanosheets according to the second aspect in some embodiments of the present application in the photocatalytic water splitting for hydrogen production reaction.

[0024] The present invention has the following beneficial effects: In the first aspect, the present invention prepares siloxene nanosheets. By adding phytic acid or citric acid as an assistant to hydrochloric acid during the topochemical exfoliation process, hydrochloric acid can quickly etch the interlayer calcium ions of CaSi2, and the phosphoric acid groups / polycarboxylic groups of phytic acid / citric acid chelate the residual calcium ions. The two acids synergistically improve the exfoliation degree. Experiments show that the exfoliation degrees of the two-acid system for calcium ions are 97.20% and 98.30%, which are significantly higher than the exfoliation degree of 80.84% of the single hydrochloric acid system.

[0025] In the second aspect, the two-acid system composed of hydrochloric acid and citric acid in the present invention is combined with a high-temperature post-treatment step to reconstruct the crystal lattice. Experiments show that it can effectively improve the structural order and product purity. However, experiments also show that the two-acid system composed of hydrochloric acid and phytic acid in the present invention, combined with the high-temperature post-treatment step, does not significantly improve the structural order and product purity. It can be seen that the two-acid system composed of hydrochloric acid and citric acid in the present invention can synergistically cooperate with the high-temperature post-treatment step to achieve the effect of improving the structural order and product purity.

[0026] In the third aspect, the siloxene nanosheets prepared by the present invention show good performance in the photocatalytic water splitting for hydrogen production reaction, with good hydrogen production rate and stability, laying an important experimental foundation for the application of siloxene nanosheets in the field of photoelectrocatalysis and expanding the application scope of two-dimensional silicon-based materials.

[0027] In the fourth aspect, experiments show that the two-acid system of phytic acid can only produce hydrogen without rate decay within 5 h after annealing, while the two-acid system of citric acid can produce hydrogen without rate decay within 5 h regardless of whether there is an annealing step. It can be seen that the two-acid system of citric acid is beneficial to the stability of the hydrogen production rate. Description of the Drawings

[0028] Figure 1 XPS full-spectrum diagrams of siloxene nanosheet D2 (SN) of Comparative Example 2, siloxene nanosheet A2 (SN-PA) of Example 2, and A6 (SN-CA) of Example 6.

[0029] Figure 2 XRD spectra of siloxene nanosheet A6 sample (aSN-14.4-1-CA-EA) of Example 6 and siloxene nanosheet A7 sample (SN-14.4-1-CA-EA) of Example 7.

[0030] Figure 3 XRD spectra of siloxene nanosheet D1 sample (aSN-2.4-0.1-PA-ACN) of Comparative Example 1 and siloxene nanosheet A2 sample (SN-2.4-0.1-PA-ACN) of Example 2. Detailed Embodiments

[0031] The present invention will be further described below with reference to specific examples, but the present invention is not limited thereto in any way.

[0032] Terminology Notes: Citric acid (CA): also known as citric acid, with the molecular formula C6H8O7, is an important organic weak acid. It is a colorless crystal, odorless, easily soluble in water, and its solution is acidic.

[0033] Phytic acid (PA): also known as inositol hexaphosphate, cyclohexane hexaphosphate, molecular formula C6H 18 O 24 P6 is an organophosphorus compound.

[0034] The present invention proposes a strategy for preparing siloxane nanosheets based on the synergistic effect of double acids. From the perspective of adding auxiliary agents to assist in exfoliation, the topological reaction kinetics is promoted, and efficient exfoliation of calcium silicide in air is achieved to obtain high-quality few-layer nanosheet structures. Subsequently, the structure and properties of the nanosheets are further optimized in combination with post-processing processes, thereby enhancing their stability during application.

[0035] Specifically, the method for preparing siloxane nanosheets based on the synergistic effect of bis(acids) provided by the present invention comprises the following steps: S1. Precursor purification: Place CaSi2 powder in an alkaline solution, remove surface oxides and impurities by ultrasonic treatment, then wash with deionized water until neutral, and dry in a vacuum drying oven at 60-80°C for 12 hours; S2, acid-assisted exfoliation: The purified CaSi2 is dispersed in an organic solvent, and a double acid system consisting of hydrochloric acid (HCl) and phytic acid (PA) or citric acid (CA) is added. The exfoliation temperature is controlled at 15-25°C, and the reaction is stirred in air for 3-7 days to obtain a suspension of siloxane nanosheets. S3, separation and preliminary purification: centrifuging the siloxane nanosheet suspension obtained in step S2 at 6000-9000 rpm for 5-20 min, collecting the solid, and washing with deionized water to remove residual organic solvent and acid; S4, high temperature post-treatment: After the product obtained in step S3 is vacuum dried at 60°C, it is first heat-treated at 200-300°C for 1-2 hours to remove surface adsorbents, and then the lattice is reconstructed at 600-800°C for 2-4 hours. The entire process is carried out under the protection of an inert gas atmosphere.

[0036] Preferably, the ultrasonic treatment time in step S1 is 4 to 8 hours, and the treatment temperature is maintained at 20 to 40°C. Preferably, the alkaline solution in step S1 is selected from at least one of sodium hydroxide or potassium hydroxide, and the concentration is 1.5-2.5 mol / L.

[0037] Preferably, in step S2, the volume-to-mass ratio of the organic solvent to the purified CaSi2 is (100-300) mL:(0.5-1.5) g.

[0038] Preferably, the organic solvent in step S2 is selected from one or more of N-methylpyrrolidone (NMP), methanol (MT), ethanol (EA), isopropanol (IPA), and acetonitrile (ACN).

[0039] Preferably, in step S2, the dual-acid system: When citric acid is used, control the molar ratio of CA / CaSi2 to be 0.25-1.25 and the molar ratio of HCl / CaSi2 to be 1.0-3.0; When phytic acid is used, control the molar ratio of PA / CaSi2 to be 0.05-0.25 and the molar ratio of HCl / CaSi2 to be 12.0-16.0.

[0040] Preferably, in step S3, the temperature gradient of the lattice reconstruction is controlled as follows: rise to 200-300 °C at a rate of 2 °C / min, and then rise to 600-800 °C at a rate of 5 °C / min.

[0041] The operation of the present invention is simple and the conditions are mild: the entire preparation process does not require extreme temperatures, high pressures, or special equipment, reducing the operation difficulty and cost, while ensuring the high quality and excellent performance of the siloxene nanosheets.

[0042] The present invention improves the exfoliation efficiency and degree: the exfoliation efficiency specifically refers to two aspects, namely the exfoliation degree and the yield. By adding phytic acid or citric acid as an auxiliary agent in the topochemical exfoliation process, hydrochloric acid rapidly etches the calcium ions between the CaSi2 layers, and phytic acid / citric acid chelates the residual calcium ions through phosphate groups / polycarboxyl groups, synergistically enhancing the calcium ion exfoliation degree. The yield of the present invention is increased from about 0.2 g to about 0.4 g (under the condition that the initial calcium silicide is 1 g).

[0043] The present invention optimizes the exfoliation effect: optimizing the exfoliation conditions according to the type of auxiliary agent and promoting the lattice order reconstruction by gradient heat treatment, realizing the unity of high exfoliation efficiency and excellent crystal structure, providing a new idea for the controllable preparation of siloxene.

[0044] Example 1: Preparation of siloxene nanosheets A1: 1 g of CaSi2 powder was added to 200 mL of 2 mol / L sodium hydroxide solution, and ultrasonic treatment was carried out at 25 °C for 4 h; it was washed with deionized water until neutral and dried at 60 °C for 12 h. The dried CaSi2 was dispersed in 200 mL of ACN, 4 mL of 6 mol / L hydrochloric acid and 0.5 mL of 15 mol / L phytic acid were added successively, and the reaction was carried out at 20 °C for 6 d. After the reaction, centrifugal separation was carried out at a speed of 9000 rpm for 5 min, and it was washed with deionized water until neutral to obtain siloxene nanosheets with 1 - 7 layers, a lateral size of 0.05 - 0.5 μm, a specific surface area of 50 - 70 m 2 / g, and a calcium ion stripping degree of 95%. The prepared siloxene nanosheets were used as photocatalysts for photocatalytic water splitting to produce hydrogen under visible light. The hydrogen production rate measured within 1 h was 910 μmol·g -1 ·h -1 , and it decayed to 695 μmol·g -1 ·h -1 after 3 h.

[0045] Example 2: Preparation of siloxene nanosheets A2: 1 g of CaSi2 powder was added to 200 mL of 2 mol / L sodium hydroxide solution, and ultrasonic treatment was carried out at 25 °C for 8 h; it was washed with deionized water until neutral and dried at 60 °C for 12 h. The dried CaSi2 was dispersed in 200 mL of ACN, 4 mL of 6 mol / L hydrochloric acid and 0.5 mL of 15 mol / L phytic acid were added successively, and the reaction was carried out at 20 °C for 6 d. After the reaction, centrifugal separation was carried out at a speed of 9000 rpm for 5 min, and it was washed with deionized water until neutral to obtain siloxene nanosheets with 1 - 4 layers, a lateral size of 0.05 - 0.5 μm, a specific surface area of 70 - 100 m 2 / g, and a calcium ion stripping degree of 98.3%. The prepared siloxene nanosheets were used as photocatalysts for photocatalytic water splitting to produce hydrogen under visible light. The hydrogen production rate measured within 1 h was 2389 μmol·g -1 ·h -1 , and it decayed to 1279 μmol·g -1 ·h -1 after 3 h.

[0046] Example 3: Preparation of siloxene nanosheets A3: 1 g of CaSi2 powder was added to 200 mL of 2 mol / L potassium hydroxide solution, and ultrasonic treatment was carried out at 25 °C for 8 h; it was washed with deionized water until neutral and dried at 60 °C for 12 h. The dried CaSi2 was dispersed in 200 mL of ACN, 4 mL of 6 mol / L hydrochloric acid and 0.5 mL of 15 mol / L phytic acid were added successively, and the reaction was carried out at 20 °C for 6 d. After the reaction, centrifugal separation was carried out at a speed of 9000 rpm for 5 min, and it was washed with deionized water until neutral to obtain siloxene nanosheets with 1 - 7 layers, a lateral size of 0.05 - 0.5 μm, a specific surface area of 50 - 70 m 2 / g, and a calcium ion stripping degree of 95.0%. The prepared siloxene nanosheets were used as photocatalysts for photocatalytic water splitting to produce hydrogen under visible light. The hydrogen production rate measured within 1 h was 461 μmol·g -1 ·h -1 , and it decayed to 390 μmol·g -1 ·h -1 .

[0047] Example 4: Preparation of siloxene nanosheets A4: 1 g of CaSi2 powder was added to 200 mL of 2 mol / L sodium hydroxide solution, and ultrasonic treatment was carried out at 25 °C for 8 h; it was washed with deionized water until neutral and dried at 60 °C for 12 h. The dried CaSi2 was dispersed in 200 mL of ACN, 4 mL of 6 mol / L hydrochloric acid and 1.3 mL of 15 mol / L phytic acid were added successively, and the reaction was carried out at 20 °C for 6 d. After the reaction, centrifugal separation was carried out at a speed of 9000 rpm for 5 min, and it was washed with deionized water until neutral to obtain siloxene nanosheets with 1 - 4 layers, a lateral size of 0.05 - 0.5 μm, a specific surface area of 50 - 70 m 2 / g, and a calcium ion stripping degree of 98.0%. The prepared siloxene nanosheets were used as photocatalysts for photocatalytic water splitting to produce hydrogen under visible light. The hydrogen production rate measured within 1 h was 1389 μmol·g -1 ·h -1 , and it decayed to 814 μmol·g -1 ·h -1 .

[0048] Example 5: Preparation of siloxene nanosheets A5: 1 g of CaSi2 powder was added to 200 mL of 2 mol / L sodium hydroxide solution, and ultrasonically treated at 25 °C for 8 h; washed with deionized water until neutral, and dried at 60 °C for 12 h. The dried CaSi2 was dispersed in 200 mL of MT, and 4 mL of 6 mol / L hydrochloric acid and 0.5 mL of 15 mol / L phytic acid were added successively, and reacted at 20 °C for 6 d. After the reaction, centrifuged at 9000 rpm for 5 min, washed with deionized water until neutral, to obtain siloxene nanosheets with 1 - 4 layers, lateral size of 0.05 - 0.5 μm, specific surface area of 90 - 110 m 2 / g, and calcium ion stripping degree of 96.0%. The prepared siloxene nanosheets were used as photocatalysts for photocatalytic water splitting to produce hydrogen under visible light, and the hydrogen production rate was measured to be 1071 μmol·g -1 ·h -1 , and attenuated to 661 μmol·g -1 ·h -1 .

[0049] Comparative Example 1: Preparation of siloxene nanosheets D1: 1 g of CaSi2 powder was added to 200 mL of 2 mol / L sodium hydroxide solution, and ultrasonically treated at 25 °C for 8 h; washed with deionized water until neutral, and dried at 60 °C for 12 h. The dried CaSi2 was dispersed in 200 mL of ACN, and 4 mL of 6 mol / L hydrochloric acid and 0.5 mL of 15 mol / L phytic acid were added successively, and reacted at 20 °C for 6 d. After the reaction, centrifuged at 9000 rpm for 5 min, washed with deionized water until neutral, to obtain siloxene nanosheets with 1 - 4 layers, lateral size of 0.05 - 0.5 μm, specific surface area of 70 - 100 m 2 / g, and calcium ion stripping degree of 98.3%. It was heated to 200 °C at 2 °C / min to remove surface adsorbed substances, and then heated to 800 °C at 5 °C / min for lattice reconstruction. The lattice - reconstructed siloxene nanosheets were used as photocatalysts for photocatalytic water splitting to produce hydrogen under visible light, and the hydrogen production rate was measured to be 560 μmol·g -1 ·h -1 , and no attenuation was observed within 5 h.

[0050] Comparative Example 2: Preparation of siloxene nanosheets D2: Add 1 g of CaSi2 powder into 200 mL of 2 mol / L sodium hydroxide solution, and ultrasonically treat it at 25 °C for 8 h; wash it with deionized water until neutral, and dry it at 60 °C for 12 h. Disperse the dried CaSi2 in 200 mL of ACN, add 4 mL of 6 mol / L hydrochloric acid in sequence, and react at 20 °C for 6 d. After the reaction is completed, centrifuge and separate at a speed of 9000 rpm for 5 min, wash it with deionized water until neutral, to obtain siloxene nanosheets with 1 - 4 layers, a lateral size of 0.05 - 0.5 μm, a specific surface area of 70 - 100 m 2 / g, and a calcium ion stripping degree of 80.8%. Use the prepared siloxene nanosheets as a photocatalyst to carry out a hydrogen production reaction by photocatalytic water splitting under visible light, and the measured hydrogen production rate is 1850 μmol·g -1 ·h -1 , and it decays to 1089 μmol·g -1 ·h -1 after 3 h.

[0051] Example 6: Preparation of siloxene nanosheets A6: Add 1 g of CaSi2 powder into 200 mL of 2 mol / L sodium hydroxide solution, and ultrasonically treat it at 25 °C for 8 h; wash it with deionized water until neutral, and dry it at 60 °C for 12 h. Disperse the dried CaSi2 in 200 mL of EA, add 24 mL of 12 mol / L hydrochloric acid and 2 g of citric acid in sequence, and react at 20 °C for 6 d. After the reaction is completed, centrifuge and separate at a speed of 9000 rpm for 5 min, wash it with deionized water until neutral, to obtain siloxene nanosheets with 1 - 4 layers, a lateral size of 0.05 - 0.5 μm, a specific surface area of 70 - 100 m 2 / g, and a calcium ion stripping degree of 97.2%. Raise the temperature to 200 °C at a rate of 2 °C / min to remove surface adsorbates, and then raise the temperature to 800 °C at a rate of 5 °C / min for lattice reconstruction. Use the prepared siloxene nanosheets as a photocatalyst to carry out a hydrogen production reaction by photocatalytic water splitting under visible light, and the measured hydrogen production rate is 1318 μmol·g -1 ·h -1 , and there is no attenuation within 5 h.

[0052] Example 7: Preparation of siloxene nanosheets A7: Add 1 g of CaSi2 powder into 200 mL of 2 mol / L sodium hydroxide solution, and ultrasonically treat it at 25 °C for 8 h; wash it with deionized water until neutral, and dry it at 60 °C for 12 h. Disperse the dried CaSi2 in 200 mL of EA, add 24 mL of 12 mol / L hydrochloric acid and 2 g of citric acid in sequence, and react at 20 °C for 6 d. After the reaction, centrifuge and separate it at a speed of 9000 rpm for 5 min, and wash it with deionized water until neutral to obtain siloxene nanosheets with 1 - 4 layers, a lateral size of 0.05 - 0.5 μm, a specific surface area of 70 - 100 m 2 / g, and a calcium ion stripping degree of 97.2%. Use the prepared siloxene nanosheets as a photocatalyst to carry out the photocatalytic water splitting for hydrogen production reaction under visible light, and the measured hydrogen production rate is 263 μmol·g -1 ·h -1 , and no attenuation is seen within 5 h.

[0053] Example 8: Preparation of siloxene nanosheets A8: Add 1 g of CaSi2 powder into 200 mL of 2 mol / L sodium hydroxide solution, and ultrasonically treat it at 25 °C for 8 h; wash it with deionized water until neutral, and dry it at 60 °C for 12 h. Disperse the dried CaSi2 in 200 mL of EA, add 24 mL of 12 mol / L hydrochloric acid and 1 g of citric acid in sequence, and react at 20 °C for 6 d. After the reaction, centrifuge and separate it at a speed of 9000 rpm for 5 min, and wash it with deionized water until neutral to obtain siloxene nanosheets with 1 - 4 layers, a lateral size of 0.05 - 0.5 μm, a specific surface area of 70 - 100 m 2 / g, and a calcium ion stripping degree of 98.2%. Raise the temperature to 200 °C at a rate of 2 °C / min to remove surface adsorbates, and then raise the temperature to 800 °C at a rate of 5 °C / min for lattice reconstruction. Use the prepared siloxene nanosheets as a photocatalyst to carry out the photocatalytic water splitting for hydrogen production reaction under visible light, and the measured hydrogen production rate is 1011 μmol·g -1 ·h -1 , and no attenuation is seen within 5 h.

[0054] Example 9: Preparation of siloxene nanosheets A9: Add 1 g of CaSi2 powder into 200 mL of 2 mol / L sodium hydroxide solution, and ultrasonically treat it at 25 °C for 8 h; wash it with deionized water until neutral, and dry it at 60 °C for 12 h. Disperse the dried CaSi2 in 200 mL of IPA, and successively add 24 mL of 12 mol / L hydrochloric acid and 2 g of citric acid, and react at 20 °C for 6 d. After the reaction is completed, centrifuge and separate it at a speed of 9000 rpm for 5 min, and wash it with deionized water until neutral to obtain siloxene nanosheets with 1 - 4 layers, a lateral size of 0.05 - 0.5 μm, a specific surface area of 150 - 200 m2 / g, and a calcium ion stripping degree of 97.0%. Heat it to 200 °C at a rate of 2 °C / min to remove surface adsorbed substances, and then heat it to 800 °C at a rate of 5 °C / min for lattice reconstruction. Use the prepared siloxene nanosheets as a photocatalyst for photocatalytic water splitting to produce hydrogen under visible light, and the measured hydrogen production rate is 323 μmol·g-1·h-1, and there is no attenuation within 5 h.

[0055] Example 10: Preparation of siloxene nanosheets A10: Add 1 g of CaSi2 powder into 200 mL of 2 mol / L sodium hydroxide solution, and ultrasonically treat it at 25 °C for 8 h; wash it with deionized water until neutral, and dry it at 60 °C for 12 h. Disperse the dried CaSi2 in 200 mL of NMP, and successively add 24 mL of 12 mol / L hydrochloric acid and 2 g of citric acid, and react at 20 °C for 6 d. After the reaction is completed, centrifuge and separate it at a speed of 9000 rpm for 5 min, and wash it with deionized water until neutral to obtain siloxene nanosheets with 1 - 4 layers, a lateral size of 0.05 - 0.5 μm, a specific surface area of 70 - 100 m 2 / g, and a calcium ion stripping degree of 98.2%. Heat it to 200 °C at a rate of 2 °C / min to remove surface adsorbed substances, and then heat it to 800 °C at a rate of 5 °C / min for lattice reconstruction. Use the prepared siloxene nanosheets as a photocatalyst for photocatalytic water splitting to produce hydrogen under visible light, and the measured hydrogen production rate is 2495 μmol·g -1 ·h -1 , and there is no attenuation within 5 h.

[0056] Experimental Example 1: Calculate the Ca content in CaSi2 before and after stripping, and calculate the stripping degree Table 1 is a statistical table of the Ca content of the siloxene nanosheets D2 (SN) of Comparative Example 2, the siloxene nanosheets A2 (SN-PA) of Example 2, and A6 (SN-CA) of Example 6.

[0057] Table 1 Among them, the calcium ion stripping degree The calculation method is as follows: Among them, nb(Ca 2+ ), and na(Ca 2+ ) represent the molar masses of calcium in the initial CaSi2 and the silicon oxyene sample after exfoliation, respectively.

[0058] It can be seen therefrom that the exfoliation degrees of the double - acid system for calcium ions are 97.20% and 98.30%, which are significantly higher than the exfoliation degree of 80.84% of the single - hydrochloric - acid system.

[0059] Figure 1 The XPS full - spectrum diagrams of the silicon oxyene nanosheets D2(SN) of Comparative Example 2, the silicon oxyene nanosheets A2(SN - PA) of Example 2, and A6(SN - CA) of Example 6 are shown. It can be Figure 1 seen that in the XPS full - spectrum diagrams of the silicon oxyene nanosheets D2(SN) treated only with hydrochloric acid in Comparative Example 2, the silicon oxyene nanosheets A2(SN - PA) treated with hydrochloric acid and phytic acid in Example 2, and the silicon oxyene nanosheets A6(SN - CA) treated with hydrochloric acid and citric acid in Example 6, the Ca2p characteristic peak at 347.3 eV can be seen in the spectrum of D2(SN), while it disappears in the spectra of A2(SN - PA) and A6(SN - CA). This further indicates that highly efficient exfoliation of calcium ions is achieved under the synergistic action of the double acid.

[0060] Figure 2 The XRD patterns of the silicon oxyene nanosheet A6 sample (aSN - 14.4 - 1 - CA - EA) of Example 6 and the silicon oxyene nanosheet A7 sample (SN - 14.4 - 1 - CA - EA) of Example 7 are shown. Among them, Example 6 and Example 7 have the same preparation steps, and the double - acid system is hydrochloric acid and citric acid. The difference is that Example 6 also has a high - temperature heat treatment (annealing) step. It can be Figure 2It can be seen that, compared with the sample SN-14.4-1-CA-EA of Example 7, the intensity of the broad peak of the sample aSN-14.4-1-CA of Example 6 between 2θ = 15° - 30° is significantly reduced; obvious peaks appear at 2θ = 28°, 33°, 47° and 56°, corresponding to the (111), (200), (220) and (311) crystal planes of the cubic silicon structure respectively. These diffraction peaks are narrow and sharp, without obvious amorphous scattering, indicating a high degree of atomic order in the sample and an improvement in crystallinity. Compared with the sample SN-14.4-1-CA-EA of Example 7, the FeSi2 characteristic peaks of the sample aSN-14.4-1-CA of Example 6 at 2θ = 17.4° and 37.8° disappear, confirming that the impurities have been removed. It can be seen that for the sample aSN-14.4-1-CA-EA of Example 7 obtained by annealing the sample SN-14.4-1-CA-EA of Example 7, it can effectively improve the structural order and purity of the material. It can be seen that the double acid system of Example 6 is hydrochloric acid and citric acid, and the annealing step achieves the purpose of effectively improving the structural order and purity of the material.

[0061] Figure 3 XRD patterns of the siloxene nanosheet D1 sample (aSN-2.4-0.1-PA-ACN) of Comparative Example 1 and the siloxene nanosheet A2 sample (SN-2.4-0.1-PA-ACN) of Example 2, where Comparative Example 1 and Example 2 have the same preparation steps, and the double acid system is hydrochloric acid and phytic acid, the difference being that Comparative Example 1 also has a high-temperature heat treatment (annealing) step. From Figure 3 It can be seen that for the sample aSN-2.4-0.1-PA-ACN of Comparative Example 1 obtained by annealing the sample (SN-2.4-0.1-PA-ACN) of Example 2, the positions and relative intensities of the XRD diffraction peaks of the sample before and after annealing basically remain the same, without obvious phase transformation or change in crystallinity, indicating that annealing does not improve the structural order and purity of the material. It can be seen that for Comparative Example 1 with a double acid system of hydrochloric acid and phytic acid, the annealing step cannot achieve the purpose of effectively improving the structural order and purity of the material.

[0062] Thus, it can be seen that only the double acid system composed of hydrochloric acid and citric acid can cooperate with the annealing step to achieve the purpose of effectively improving the structural order and purity of the material, and the double acid system composed of hydrochloric acid and phytic acid cannot cooperate with the annealing step to achieve this purpose for material optimization.

[0063] The difference between Example 1 and Example 2 lies in the different ultrasonic treatment times, which however leads to differences in the hydrogen production rate and hydrogen production stability. It can be seen that for the hydrogen production rate and hydrogen production stability, the ultrasonic treatment time has a certain influence. The difference between Example 2 and Example 3 lies in the different alkaline solutions, which however leads to differences in the hydrogen production rate and hydrogen production stability. It can be seen that for the hydrogen production rate and hydrogen production stability, the alkaline solution has a certain influence. The difference between Example 4 and Example 2 lies in the different amounts of phytic acid used, which however leads to differences in the hydrogen production rate and hydrogen production stability. It can be seen that for the hydrogen production rate and hydrogen production stability, the amount of phytic acid used has a certain influence. The difference between Example 5 and Example 2 lies in the different organic solvents, which however leads to differences in the hydrogen production rate and hydrogen production stability. It can be seen that for the hydrogen production rate and hydrogen production stability, the organic solvent has a certain influence. The difference between Example 8 and Example 6 lies in the different amounts of citric acid used, which however leads to differences in the hydrogen production rate and hydrogen production stability. It can be seen that for the hydrogen production rate and hydrogen production stability, the amount of citric acid used has a certain influence. Examples 9 and 10 also illustrate that for the hydrogen production rate and hydrogen production stability, the organic solvent has a certain influence.

[0064] The dual-acid system of Examples 1-5 consists of hydrochloric acid and phytic acid and does not have an annealing step. The prepared siloxene nanosheets have a decaying rate within 3 h of hydrogen production.

[0065] The dual-acid system of Comparative Example 1 consists of hydrochloric acid and phytic acid and has an annealing step. The prepared siloxene nanosheets have no decaying rate within 5 h of hydrogen production.

[0066] The dual-acid systems of Examples 6, 8-10 consist of hydrochloric acid and citric acid and have an annealing step. The prepared siloxene nanosheets have no decaying rate within 5 h of hydrogen production.

[0067] The dual-acid system of Example 7 consists of hydrochloric acid and citric acid and does not have an annealing step. The prepared siloxene nanosheets have no decaying rate within 5 h of hydrogen production.

[0068] It can be seen from this that only through annealing can the dual-acid system of phytic acid have no decaying rate within 5 h of hydrogen production, while the dual-acid system of citric acid can have no decaying rate within 5 h of hydrogen production regardless of whether it has an annealing step. It can be seen that the dual-acid system of citric acid is beneficial to the stability of the hydrogen production rate.

[0069] In summary, the prepared siloxene nanosheets in the embodiments of the present invention have excellent performance in hydrogen production by photocatalytic water splitting. This is mainly attributed to the successful and efficient preparation of high-quality siloxene nanosheets: the addition of additives improves the exfoliation efficiency and degree of calcium silicide; the exfoliation conditions are optimized according to the type of additives, and gradient heat treatment promotes the ordered reconstruction of the crystal lattice, realizing the unity of high exfoliation efficiency, low oxidation degree and excellent crystal structure.

[0070] As described above, it is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. A method for preparing siloxene nanosheets, characterized in that, including adding a double acid system to an organic solvent dispersing CaSi2 to strip calcium ions to obtain a suspension of siloxene nanosheets; centrifuging and separating the suspension of siloxene nanosheets, collecting the solid, and washing to obtain the first siloxene nanosheets.

2. The preparation method of the siloxene nanosheet according to claim 1, wherein, The double acid system consists of hydrochloric acid (HCl) and an auxiliary acid, and the auxiliary acid includes citric acid (CA).

3. The preparation method of the siloxene nanosheet according to claim 1, wherein, The double acid system consists of hydrochloric acid (HCl) and an auxiliary acid, and the auxiliary acid includes phytic acid (PA).

4. The preparation method of the siloxene nanosheet according to claim 2, wherein Wherein: the molar ratio of citric acid (CA) to CaSi2 is (0.25 - 1.25):1; the molar ratio of hydrochloric acid (HCl) to CaSi2 is (1.0 - 3.0):

1.

5. The method for preparing the siloxene nanosheet according to claim 3, wherein Wherein: the molar ratio of phytic acid (PA) to CaSi2 is (0.05 - 0.25):1; the molar ratio of hydrochloric acid (HCl) to CaSi2 is (12.0 - 16.0):

1.

6. The method for preparing siloxene nanosheets according to claim 1 further includes heat-treating the first siloxene nanosheets at a high temperature under the protection of an inert gas atmosphere to obtain siloxene nanosheets.

7. The preparation method of the siloxene nanosheet according to claim 6, characterized in that, The high-temperature heat treatment includes S10. heat-treating at a temperature of 200 - 300 °C for 1 - 2 h; S20. heat-treating at a temperature of 600 - 800 °C for 2 - 4 h.

8. The preparation method of the siloxene nanosheet according to claim 1, characterized in that The stripping temperature is 15 - 25 °C, and the stripping stirring time is 3 - 7 d; Preferably, in the organic solvent dispersing CaSi2, the volume-to-mass ratio of the organic solvent to CaSi2 is (100 - 300) mL:(0.5 - 1.5) g; Preferably, the organic solvent is selected from one or more mixtures of N-methylpyrrolidone (NMP), methanol (MT), ethanol (EA), isopropanol (IPA), and acetonitrile (ACN); Preferably, the method for preparing CaSi2 includes ultrasonic treatment of CaSi2 powder in an alkaline solution to remove surface oxides and impurities; the ultrasonic-treated CaSi2 powder is washed with deionized water until neutral and vacuum-dried at a temperature of 60 - 80 °C for 12 h; Preferably, the alkaline solution is selected from at least one of sodium hydroxide or potassium hydroxide; More preferably, the alkaline solution is selected from sodium hydroxide; More preferably, the concentration of the alkaline solution is 1.5 - 2.5 mol / L; Preferably, the ultrasonic treatment time is 4 - 8 h, and the treatment temperature is 20 - 40 °C; Preferably, in the step of heat-treating at a temperature of 200 - 300 °C for 1 - 2 h and then at 600 - 800 °C for 2 - 4 h, the temperature is raised to 200 - 300 °C at a rate of 2 °C / min and to 600 - 800 °C at a rate of 5 °C / min.

9. A siloxene nanosheet prepared by the method according to any one of claims 1 - 8; Preferably, the number of layers of the siloxene nanosheets is 1 to 7 layers, the lateral size is 0.05 to 0.5 μm, the specific surface area is 50 to 200 m 2 / g, and the calcium ion stripping degree is ≥95%.

10. An application of the siloxene nanosheet according to claim 9 in a photocatalytic water splitting for hydrogen production reaction.

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