Efficient, controllable and low-cost black phosphorus crystal preparation method

Abstract

The invention discloses an efficient, controllable and low-cost black phosphorus crystal preparation method. The method comprises the following steps: firstly, at normal temperature and normal pressure, weighing a yellow phosphorus raw material and an inorganic porous medium, placing in a temperature-controlled and pressure-controlled container, sealing the container, controlling the temperature to fully melt yellow phosphorus, and controlling the pressure to fully adsorb molten yellow phosphorus by the porous medium; then cooling to normal temperature to quickly solidify yellow phosphorus and slowly recover to normal pressure to obtain a yellow phosphorus raw material coated with the porous medium; the phosphorus raw material, the catalyst and the transport agent are weighed and placed in a closed reactor, the reactor is subjected to a heating reaction through an optimized temperature control program, and after the reaction is finished, the high-quality black phosphorus crystal is finally prepared. By adopting the yellow phosphorus raw material coated with the porous medium, the melting, diffusion and volatilization rate of the phosphorus raw material can be accurately controlled only by regulating and controlling the parameters of the medium material, and the catalyst deactivation caused by material accumulation is avoided; meanwhile, other impurities are not additionally introduced into the inorganic porous medium in the reaction process, and the porous structure does not affect the chemical vapor transport process of the material.

Description

Technical Field

[0001] The present invention belongs to the technical field of two-dimensional materials, and specifically relates to a method for preparing black phosphorus crystals that is efficient, controllable and low-cost. Background Art

[0002] In 2014, black phosphorus emerged as a new star in the field of two-dimensional materials, and quickly attracted widespread attention from the scientific and industrial communities at home and abroad. From the initial transistors to the later optoelectronic devices, and then to catalysis, energy, biomedicine and many other fields, black phosphorus has shown great application prospects.

[0003] Black phosphorus crystals were first synthesized by Nobel Prize winner Bridgman in 1914 using a high-pressure method. Over the past century, researchers have been constantly trying to break through the technology for preparing black phosphorus crystals. Currently, there are several main methods for preparing black phosphorus crystals. The first is the high-pressure method, which uses yellow phosphorus or red phosphorus as raw materials and uses a high-pressure anvil cell to prepare black phosphorus crystals under GPa-level high pressure. This method is limited by complex reaction equipment, harsh preparation conditions and extremely low yields. This method is only suitable for laboratory-level scientific research. The second is the mercury-catalyzed method and the bismuth-catalyzed (Bismuth-flux) method, which uses yellow phosphorus or red phosphorus as raw materials and molten mercury or bismuth as a medium for high-temperature heating reaction to prepare black phosphorus crystals. Due to the low yield, heavy metal pollution and toxicity issues, this method is also difficult to promote effectively. The third is the high-energy ball milling method, which uses red phosphorus as the raw material and uses high-energy ball milling equipment to perform in-situ conversion to prepare black phosphorus crystals; the fourth is the solvent thermal method, which uses yellow phosphorus or red phosphorus as the raw material and uses alcohol or amine organic solvents as the medium to perform high-temperature heating reaction to prepare black phosphorus crystals. Although these two methods have the prospect of industrial scale-up, they are not conducive to large-scale controllable preparation due to their difficulties in controlling the reaction process and poor crystal quality. The fifth is the Chemical Vapor Transmission (CVT) method, which uses yellow phosphorus or red phosphorus as the raw material, selects suitable catalysts and transport agents, and prepares black phosphorus crystals through high-temperature and high-pressure reactions. Because of its simple process, good reproducibility, and high crystal quality, it has become the most widely used preparation method.

[0004] In recent years, researchers have also carried out a series of work on the optimization of chemical vapor transport systems, including the screening of catalytic systems, the regulation of reaction processes, and the design of reaction devices, but there are few reports on the direct optimization of the reaction raw material system. Patent CN110938867B discloses a method for efficiently preparing two-dimensional black phosphorus crystals, using red phosphorus raw materials with gradient ratios according to particle size and mass to prepare black phosphorus crystals. Compared with the use of ordinary red phosphorus raw materials, this method can more efficiently control the volatilization rate and system pressure of red phosphorus raw materials, and is more conducive to the precise control of the nucleation and growth process of black phosphorus crystals. Although this method is simple and efficient, it is limited to red phosphorus raw materials with controllable morphology and requires material screening. It is not suitable for yellow phosphorus raw materials with difficult morphology control and lower production costs. Patent CN113559886A discloses a method for efficiently synthesizing black phosphorus catalysts, mixing and grinding phosphorus iodine tin powder and carbon material additives, and then pressing them into tablets, and then encapsulating them in a quartz tube for high-temperature treatment to obtain a catalyst containing additives after curing, and finally using it for the preparation of black phosphorus. The addition of carbon material additives can greatly improve the mechanical properties and thermal conductivity of the catalyst, thereby increasing the conversion rate and cycle number of the catalyst to prepare black phosphorus. Patent CN116550349A discloses a supported black phosphorus catalyst and its preparation method, which 24 P 19.3 The I8 ternary complex is loaded on a carrier, and then subjected to high-temperature heat treatment to prepare a supported black phosphorus catalyst. This catalyst solves the problem of powder catalyst stacking and mixing with red phosphorus raw materials to cover the active sites, improves the catalytic activity, and is easily separated from raw materials and by-products, can be reused, and is suitable for the continuous preparation of black phosphorus. Although the catalysts in the above two methods have high catalytic efficiency and are easy to reuse, the cumbersome and pre-synthesis steps and complex post-treatment processes limit its large-scale production, and this method cannot effectively reduce the amount of catalyst and transport agent used, the production cost is high, and it is not suitable for the large-scale preparation of black phosphorus crystals.

[0005] In short, the current optimization process, whether for phosphorus raw materials or catalysts, is often limited to complex and cumbersome processing processes and high production costs. Therefore, developing an efficient, controllable, and low-cost method for preparing black phosphorus crystals and realizing large-scale controllable preparation of black phosphorus crystals is of great value to broaden the application of black phosphorus materials in many fields such as optoelectronic devices, energy catalysis, and biomedicine. Summary of the invention

[0006] The present invention uses yellow phosphorus coated with a porous medium as a phosphorus raw material, and performs a heating reaction through an optimized temperature control program, thereby successfully realizing the efficient and controllable preparation of black phosphorus crystals. This method can achieve precise control of the melting, diffusion and volatilization rate of the phosphorus raw material only by adjusting the parameters of the medium material, thereby effectively improving the material contact state and heat transfer, avoiding the catalyst deactivation caused by material accumulation, greatly reducing the amount of catalyst and transport agent introduced, and reducing production costs; at the same time, the inorganic porous medium does not introduce other impurities during the reaction process, and the porous structure does not affect the chemical vapor transport process of the material, and is more conducive to the adsorption of reaction by-products, thereby effectively improving the yield and quality of black phosphorus crystals, and facilitating the realization of industrial-scale preparation.

[0007] To achieve the above object, the technical solution adopted by the present invention is: A highly efficient, controllable and low-cost method for preparing black phosphorus crystals comprises the following steps: (1) At room temperature and pressure, weigh yellow phosphorus raw material and inorganic porous medium and place them in a temperature-controlled and pressure-controlled container. After the container is sealed, the temperature is controlled to fully melt the yellow phosphorus, and the pressure is controlled to fully absorb the molten yellow phosphorus by the porous medium. (2) cooling to room temperature to allow the yellow phosphorus to solidify rapidly and then slowly returning to normal pressure to obtain a yellow phosphorus raw material coated with a porous medium; (3) weighing the phosphorus raw material, the catalyst and the transport agent and placing them at the raw material end of the closed reactor, and heating the reactor for reaction through an optimized temperature control program; (4) After the reaction is completed, black phosphorus crystals are finally prepared at the nucleation end.

[0008] The following are preferred technical solutions of the present invention, but are not intended to be limitations of the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0009] In the above scheme, the inorganic porous medium is any one or a combination of two of aluminum oxide, silicon carbide, and zirconium oxide that are resistant to high temperatures (above 800° C.).

[0010] In the above scheme, the pore size range of the inorganic porous medium is 10~100 ppi.

[0011] Preferably, the pore size range of the inorganic porous medium is 10-60 ppi.

[0012] In the above scheme, the mass ratio of the yellow phosphorus raw material to the inorganic porous medium is 10:1~10; When the inorganic porous medium is alumina, the mass ratio of the yellow phosphorus raw material to the alumina is 10:1-4; When the inorganic porous medium is silicon carbide, the mass ratio of yellow phosphorus raw material to aluminum oxide is silicon carbide 10:2-6; When the inorganic porous medium is zirconium oxide, the mass ratio of the yellow phosphorus raw material to the aluminum oxide is 10:4-10 to zirconium oxide.

[0013] Preferably, when the inorganic porous medium is alumina, the mass ratio of the yellow phosphorus raw material to alumina is 10:2-3; When the inorganic porous medium is silicon carbide, the mass ratio of yellow phosphorus raw material to aluminum oxide is 10:3-5 for silicon carbide; When the inorganic porous medium is zirconium oxide, the mass ratio of the yellow phosphorus raw material to aluminum oxide is 10:6-8 to zirconium oxide.

[0014] In the above scheme, after the temperature-controlled and pressure-controlled container is sealed, the temperature is controlled to 80-100°C to fully melt the yellow phosphorus, and the pressure is controlled to -0.1 to -1 MPa to allow the porous medium to fully absorb the molten yellow phosphorus.

[0015] Preferably, after the temperature- and pressure-controlled container is sealed, the temperature is controlled to 80-100° C. to fully melt the yellow phosphorus, and the pressure is controlled to -0.5 to -0.8 MPa to allow the porous medium to fully absorb the molten yellow phosphorus.

[0016] In the above scheme, the yellow phosphorus is rapidly solidified by cooling to room temperature and then slowly restored to normal pressure within 2 to 12 hours to obtain a yellow phosphorus raw material coated with a porous medium.

[0017] Preferably, the cooling to room temperature causes the yellow phosphorus to solidify rapidly and then slowly returns to normal pressure within 4 to 10 hours to obtain a yellow phosphorus raw material coated with a porous medium.

[0018] In the above scheme, the catalyst is any one of Sn, Bi, In, Pb, Cd or a combination of at least two of them, or an alloy containing any one of Sn, Bi, In, Pb, Cd or a combination of at least two of them, and the purity of the catalyst is above 98%.

[0019] Preferably, the catalyst is any one of Sn, Bi, In, Pb or a combination of at least two of them, or an alloy containing any one of Sn, Bi, In, Pb or a combination of at least two of them, and the purity of the catalyst is above 99%.

[0020] In the above scheme, the transport agent is any one of I2, SnI4, SnI2, PbI2, NH4I, BiI3, PI3, SnCl2, SnBr2, or a combination of at least two thereof, and the purity of the transport agent is above 98%.

[0021] Preferably, the transport agent is any one of I2, SnI4, SnI2, PbI2, BiI3, PI3 or a combination of at least two thereof. The purity of the transport agent is above 99%.

[0022] In the above scheme, the mass feed ratio of the phosphorus raw material to the catalyst is 100:1-5; the mass feed ratio of the catalyst to the transport agent is 10:1-5.

[0023] In the above scheme, the temperature control program is as follows: under room temperature, the temperature of the raw material end is raised to 500-550°C in 1-2 hours, kept at this temperature for 6-12 hours, and then dropped to room temperature in 6-10 hours; the temperature of the nucleation end is raised to 480-520°C in 1-2 hours, kept at this temperature for 6-12 hours, and then dropped to room temperature in 6-10 hours. The temperature control programs of the raw material end and the nucleation end are carried out synchronously, and the temperature of the raw material end is always 10-40°C higher than that of the nucleation end.

[0024] Preferably, the temperature control program is as follows: at room temperature, the temperature of the raw material end is raised to 510-540°C in 1-2 hours, kept at this temperature for 8-10 hours, and then dropped to room temperature in 8-10 hours; the temperature of the nucleation end is raised to 490-510°C in 1-2 hours, kept at this temperature for 8-10 hours, and then dropped to room temperature in 8-10 hours. The temperature control programs of the raw material end and the nucleation end are carried out synchronously, and the temperature of the raw material end is always 20-30°C higher than the temperature of the nucleation end.

[0025] The present invention uses yellow phosphorus coated with a porous medium as the phosphorus raw material, and performs a heating reaction through an optimized temperature control program, thereby successfully achieving efficient and controllable preparation of black phosphorus crystals. Compared with the prior art, the present invention has the following beneficial effects: 1) In the present invention, the porous medium is made to fully absorb the molten yellow phosphorus through simple temperature and pressure control conditions, and the yellow phosphorus raw material coated with the porous medium can be obtained after rapid solidification. The processing process is efficient and convenient, and the porous medium used is simple, easy to obtain and can be reused, which is more conducive to the practical application of industrial-scale preparation.

[0026] 2) Compared with the traditional reaction method of directly using yellow phosphorus or red phosphorus as the phosphorus raw material, the present invention only adjusts the pore size parameters of the dielectric material and utilizes the hysteresis of the material in the adsorption and desorption process of the porous material to achieve precise control of the melting (40~120℃), diffusion (120~280℃) and volatilization (280~540℃) rates of the yellow phosphorus raw material as the temperature increases during the reaction.

[0027] 3) The melting point range of the metal catalyst used in the reaction process is between 200 and 350 °C (Sn: 231.96 °C, Bi: 271.5 °C, In: 156.51 °C, Pb: 327.46 °C, Cd: 321 °C. Generally, the melting point of an alloy is lower than that of the pure metal that makes it up). This temperature range coincides with the temperature range of the yellow phosphorus raw material melting (40 to 120 °C), diffusion (120 to 280 °C) and volatilization (280 to 540 °C). Based on the precise control in 2), the material contact state and heat transfer can be effectively improved, the catalyst deactivation caused by material accumulation can be avoided, the amount of catalyst and transport agent introduced can be greatly reduced, and the production cost can be reduced.

[0028] 4) In the present invention, the porous medium used is a high-temperature resistant inorganic material, does not participate in the reaction process of the original preparation system, does not introduce other impurities, and the porous structure does not affect the chemical vapor transport process of the material, but is more conducive to the adsorption of reaction by-products, thereby effectively improving the yield and quality of black phosphorus crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The figure is a flow chart of the preparation process of yellow phosphorus raw material coated with porous medium.

[0030] Figure 2 This is a physical picture of the inorganic porous medium (alumina, 10 ppi) used in Example 1.

[0031] Figure 3 This is a physical picture of the black phosphorus crystals prepared in Example 1.

[0032] Figure 4 This is the X-ray diffraction spectrum of the black phosphorus crystals prepared in Example 2.

[0033] Figure 5 This is a physical picture of the experimental product prepared in Comparative Example 1.

[0034] Figure 6 This is a physical picture of the experimental product prepared in Comparative Example 2.

[0035] Figure 7 This is a physical picture of the experimental product prepared in Comparative Example 3. DETAILED DESCRIPTION

[0036] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with specific embodiments and drawings, but the content of the present invention is not limited to the following embodiments.

[0037] Figure 1The present invention is a flow chart of the preparation process of the yellow phosphorus raw material coated with porous medium. First, at room temperature and pressure, the yellow phosphorus raw material and the inorganic porous medium are weighed and placed in a temperature-controlled and pressure-controlled container. After the container is sealed, the temperature is controlled to fully melt the yellow phosphorus, and the pressure is controlled to fully absorb the molten yellow phosphorus. Then, the temperature is lowered to room temperature to allow the yellow phosphorus to solidify rapidly and then slowly restored to normal pressure to obtain the yellow phosphorus raw material coated with porous medium. The yellow phosphorus raw materials coated with porous medium used in Examples 1 to 3 are all prepared using this process flow.

[0038] Example 1 An efficient, controllable and low-cost method for preparing black phosphorus crystals, the specific preparation steps are as follows: (1) At room temperature and pressure, weigh 10 kg of yellow phosphorus raw material and 1 kg of inorganic porous medium (alumina, 10 ppi) and place them in a temperature- and pressure-controlled container. After the container is sealed, the temperature is controlled to 80°C to fully melt the yellow phosphorus, and the pressure is controlled to -0.1 MPa to allow the porous medium to fully absorb the molten yellow phosphorus. (2) cooling to room temperature to allow the yellow phosphorus to solidify rapidly and then slowly returning to normal pressure within 2 hours to obtain a yellow phosphorus raw material coated with a porous medium; (3) Weigh the phosphorus raw material, 100 g of catalyst Sn with a purity of 98%, and 10 g of transport agent I2 with a purity of 98%, and place them at the raw material end of the closed reactor. Heat the reactor through an optimized temperature control program. The specific temperature increase program is as follows: at room temperature, the temperature at the raw material end is raised to 500 °C in 1 h, kept at this temperature for 6 h, and then dropped to room temperature in 6 h; the temperature at the nucleation end is raised to 480 °C in 1 h, kept at this temperature for 6 h, and then dropped to room temperature in 6 h. The temperature control programs at the raw material end and the nucleation end are carried out simultaneously, and the temperature at the raw material end is always 20 °C higher than the temperature at the nucleation end; (4) After the reaction was completed, 9.362 kg of black phosphorus crystals were finally prepared at the nucleation end, with an overall yield of 93.62%.

[0039] Figure 2 This is a physical picture of the inorganic porous medium (alumina, 10 ppi) used in Example 1. Figure 3 This is a physical picture of the black phosphorus crystals prepared in Example 1. As can be seen from the figure, the sample is a block crystal with a metallic luster, with a mass of 9.362 kg and a comprehensive yield of 93.62%.

[0040] Example 2 An efficient, controllable and low-cost method for preparing black phosphorus crystals, the specific preparation steps are as follows: (1) At room temperature and pressure, weigh 10 kg of yellow phosphorus raw material and 4 kg of inorganic porous medium (silicon carbide, 40 ppi) and place them in a temperature- and pressure-controlled container. After the container is sealed, the temperature is controlled to 90 °C to fully melt the yellow phosphorus, and the pressure is controlled to -0.6 MPa to allow the porous medium to fully absorb the molten yellow phosphorus. (2) cooling to room temperature to allow the yellow phosphorus to solidify rapidly and then slowly returning to normal pressure within 6 hours to obtain a yellow phosphorus raw material coated with a porous medium; (3) The phosphorus raw material, 200 g of 99% pure catalyst Bi and 40 g of 99% pure transport agent SnI4 were weighed and placed at the raw material end of the closed reactor. The reactor was heated by an optimized temperature control program. The specific temperature increase program was as follows: at room temperature, the temperature at the raw material end was raised to 525 °C in 2 h, kept at this temperature for 8 h, and then dropped to room temperature in 8 h; the temperature at the nucleation end was raised to 500 °C in 2 h, kept at this temperature for 8 h, and then dropped to room temperature in 8 h. The temperature control programs at the raw material end and the nucleation end were carried out synchronously, and the temperature at the raw material end was always 25 °C higher than that at the nucleation end.

[0041] (4) After the reaction was completed, 9.547 kg of black phosphorus crystals were finally prepared at the nucleation end, with an overall yield of 95.47%.

[0042] Figure 4 This is the X-ray diffraction spectrum of the black phosphorus crystal prepared in Example 2. As can be seen from the figure, the sample presents typical black phosphorus characteristic peaks, and no other impurity peaks appear, which indicates that the prepared black phosphorus crystal has good crystallinity and high purity. The three strong characteristic peaks correspond to the (020), (040), and (060) crystal planes of the black phosphorus crystal.

[0043] Example 3 An efficient, controllable and low-cost method for preparing black phosphorus crystals, the specific preparation steps are as follows: (1) At room temperature and pressure, weigh 10 kg of yellow phosphorus raw material and 10 kg of inorganic porous medium (zirconia, 100 ppi) and place them in a temperature- and pressure-controlled container. After the container is sealed, the temperature is controlled to 100 °C to fully melt the yellow phosphorus, and the pressure is controlled to -1 MPa to allow the porous medium to fully absorb the molten yellow phosphorus. (2) cooling to room temperature to allow the yellow phosphorus to solidify rapidly and then slowly returning to normal pressure within 12 hours to obtain a yellow phosphorus raw material coated with a porous medium; (3) Weigh the phosphorus raw material, 500 g of 99% pure catalyst In and 250 g of 99% pure transport agent SnI2 and place them at the raw material end of the closed reactor. Heat the reactor through the optimized temperature control program. The specific temperature program is as follows: at room temperature, the temperature of the raw material end is raised to 550 °C in 2 h, kept at this temperature for 12 h, and then dropped to room temperature in 10 h; the temperature of the nucleation end is raised to 520 °C in 2 h, kept at this temperature for 12 h, and then dropped to room temperature in 10 h. The temperature control programs of the raw material end and the nucleation end are carried out synchronously, and the temperature of the raw material end is always 30 °C higher than that of the nucleation end. (4) After the reaction was completed, 9.448 kg of black phosphorus crystals were finally prepared at the nucleation end, with an overall yield of 94.48%.

[0044] Comparative Example 1 A method for preparing black phosphorus crystals directly using yellow phosphorus as a phosphorus raw material, the specific preparation steps are as follows: (1) At room temperature and pressure, 10 kg of yellow phosphorus raw material, 100 g of catalyst Sn with a purity of 98%, and 10 g of transport agent I2 with a purity of 98% were weighed and placed at the raw material end of the closed reactor. The reactor was heated by an optimized temperature control program. The specific temperature increase program was as follows: at room temperature, the temperature at the raw material end was raised to 500 °C in 1 h, kept at this temperature for 6 h, and then dropped to room temperature in 6 h; the temperature at the nucleation end was raised to 480 °C in 1 h, kept at this temperature for 6 h, and then dropped to room temperature in 6 h. The temperature control programs at the raw material end and the nucleation end were carried out simultaneously, and the temperature at the raw material end was always 20 °C higher than that at the nucleation end; (2) No black phosphorus crystals are produced in the final reaction.

[0045] Figure 5 This is a physical picture of the experimental product prepared in Comparative Example 1. It can be seen from the figure that no black phosphorus crystals are generated in the reaction, and the products are red phosphorus raw materials that are not completely reacted and severely hardened, and tin phosphorus and tin iodine phosphorus compounds.

[0046] Comparative Example 2 A method for preparing black phosphorus crystals directly using yellow phosphorus as a phosphorus raw material, the specific preparation steps are as follows: (1) At room temperature and pressure, 10 kg of yellow phosphorus raw material, 500 g of catalyst Sn with a purity of 98%, and 250 g of transport agent I2 with a purity of 98% were weighed and placed at the raw material end of the closed reactor. The reactor was heated by an optimized temperature control program. The specific temperature increase program was as follows: at room temperature, the temperature at the raw material end was raised to 500 °C in 1 h, kept at this temperature for 6 h, and then dropped to room temperature in 6 h; the temperature at the nucleation end was raised to 480 °C in 1 h, kept at this temperature for 6 h, and then dropped to room temperature in 6 h. The temperature control programs at the raw material end and the nucleation end were carried out simultaneously, and the temperature at the raw material end was always 20 °C higher than that at the nucleation end; (2) The reaction ultimately produces only a small amount of black phosphorus crystals, with an overall yield of about 10%.

[0047] Figure 6 This is a physical picture of the experimental product prepared in Comparative Example 2. It can be seen from the figure that only a small amount of black phosphorus crystals are generated in the reaction, and the black phosphorus crystals are accompanied by unreacted and severely hardened red phosphorus raw materials and tin phosphorus and tin iodine phosphorus compounds, and the utilization rate is low, and the overall yield is about 10%.

[0048] Comparative Example 3 A method for preparing black phosphorus crystals directly using yellow phosphorus as a phosphorus raw material, the specific preparation steps are as follows: (1) At room temperature and pressure, 10 kg of yellow phosphorus raw material, 1 kg of catalyst Sn with a purity of 98%, and 500 g of transport agent I2 with a purity of 98% were weighed and placed at the raw material end of the closed reactor. The reactor was heated by an optimized temperature control program. The specific temperature increase program was as follows: at room temperature, the temperature at the raw material end was raised to 500 °C in 1 h, kept at this temperature for 6 h, and then dropped to room temperature in 6 h; the temperature at the nucleation end was raised to 480 °C in 1 h, kept at this temperature for 6 h, and then dropped to room temperature in 6 h. The temperature control programs at the raw material end and the nucleation end were carried out simultaneously, and the temperature at the raw material end was always 20 °C higher than that at the nucleation end; (2) After the reaction was completed, 7.270 kg of black phosphorus crystals were finally prepared at the nucleation end, with an overall yield of 72.70%.

[0049] Figure 7 This is a physical picture of the experimental product prepared in Comparative Example 2. It can be seen from the figure that a large amount of unreacted red phosphorus and tin phosphorus and tin iodine phosphorus by-products are attached to the surface of the sample, the crystal quality is poor, the post-processing is difficult, the mass is 7.270 kg, and the comprehensive yield is 72.70%.

[0050] The only difference between Comparative Example 1 and Example 1 is that no yellow phosphorus raw material coated with a porous medium is used, so during the reaction temperature rise process, the melting (40-120 ° C), diffusion (120-280 ° C) and volatilization (280-540 ° C) rates of the yellow phosphorus raw material cannot be effectively controlled. In the early stage of the reaction, a large amount of yellow phosphorus raw material directly covers the catalyst and the transport agent, resulting in the inability to efficiently contact the phosphorus raw material during the reaction, and the heat cannot be transferred between the materials in time, resulting in the deactivation of the catalyst, and the reaction ultimately does not generate black phosphorus crystals.

[0051] In order to improve the material contact state and heat transfer in Comparative Example 1, the amount of catalyst and transport agent introduced in Comparative Example 2 was increased by 5 times based on that in Comparative Example 1, reaching the maximum amount of introduction specified in the claims of the present invention. However, the degree of improvement is very limited. In the end, only a small amount of black phosphorus crystals are generated in the reaction, with a comprehensive yield of about 10%. In addition, the black phosphorus crystals are associated with unreacted and severely hardened red phosphorus raw materials and tin-phosphorus and tin-iodine-phosphorus compounds, and the crystal quality is poor and the utilization rate is low.

[0052] Furthermore, in Comparative Example 3, the amount of catalyst and transport agent introduced was increased 10 times on the basis of Comparative Example 1, far exceeding the maximum amount of introduction specified in the claims of the present invention. The degree of improvement this time is more obvious. The reaction finally prepared 7.270 kg of black phosphorus crystals at the nucleation end, with a comprehensive yield of 72.70%, but the overall yield is still lower than 93.62% in Example 1, and due to the lack of efficient adsorption of by-products by the porous medium during the reaction, a large amount of unreacted red phosphorus and tin phosphorus, tin iodine phosphorus compounds are attached to the surface of the sample, the crystal quality is poor, and the post-processing is difficult.

[0053] In summary, compared with the traditional reaction method of directly using yellow phosphorus or red phosphorus as the phosphorus raw material, the yellow phosphorus raw material coated with the porous medium can achieve precise control of the melting, diffusion and volatilization rate of the phosphorus raw material only by adjusting the medium material parameters, thereby effectively improving the material contact state and heat transfer, avoiding catalyst deactivation caused by material accumulation, greatly reducing the amount of catalyst and transport agent introduced, and reducing production costs; at the same time, the inorganic porous medium does not introduce other impurities during the reaction process, and the porous structure does not affect the chemical vapor transport process of the material, but is more conducive to the adsorption of reaction by-products, thereby effectively improving the yield and quality of black phosphorus crystals, which is conducive to the realization of industrial-scale preparation.

Claims

1. A highly efficient, controllable and low-cost method for preparing black phosphorus crystals, characterized in that: The steps include: (1) At room temperature and pressure, weigh yellow phosphorus raw material and inorganic porous medium and place them in a temperature-controlled and pressure-controlled container. After the container is sealed, the temperature is controlled to fully melt the yellow phosphorus, and the pressure is controlled to fully absorb the molten yellow phosphorus by the porous medium. (2) cooling to room temperature to allow the yellow phosphorus to solidify rapidly and then slowly returning to normal pressure to obtain a yellow phosphorus raw material coated with a porous medium; (3) weighing the phosphorus raw material, the catalyst and the transport agent and placing them at the raw material end of the closed reactor, and heating the reactor for reaction through an optimized temperature control program; (4) After the reaction is completed, black phosphorus crystals are finally prepared at the nucleation end.

2. The method for preparing black phosphorus crystals according to claim 1, characterized in that: The inorganic porous medium in step (1) includes any one of aluminum oxide, silicon carbide, and zirconium oxide, or a combination of two thereof.

3. The method for preparing black phosphorus crystals according to claim 1, characterized in that: The pore size range of the inorganic porous medium in step (1) is 10-100 ppi; the mass ratio of the yellow phosphorus raw material to the inorganic porous medium is 10:1-10.

4. The method for preparing black phosphorus crystals according to claim 3, characterized in that: When the inorganic porous medium is alumina, the mass ratio of the yellow phosphorus raw material to the alumina is 10:1-4; When the inorganic porous medium is silicon carbide, the mass ratio of yellow phosphorus raw material to aluminum oxide is silicon carbide 10:2-6; When the inorganic porous medium is zirconium oxide, the mass ratio of the yellow phosphorus raw material to the aluminum oxide is 10:4-10 to zirconium oxide.

5. The method for preparing black phosphorus crystals according to claim 1, characterized in that: After the temperature-controlled and pressure-controlled container described in step (1) is sealed, the temperature is controlled to 80-100°C to fully melt the yellow phosphorus, and the pressure is controlled to -0.1-1 MPa to allow the porous medium to fully absorb the molten yellow phosphorus.

6. The method for preparing black phosphorus crystals according to claim 1, characterized in that: The cooling to room temperature in step (2) allows the yellow phosphorus to solidify rapidly and then slowly return to normal pressure within 2 to 12 hours, thereby obtaining a yellow phosphorus raw material coated with a porous medium.

7. The method for preparing black phosphorus crystals according to claim 1, characterized in that: The catalyst described in step (3) is any one of Sn, Bi, In, Pb, Cd or a combination of at least two thereof, or an alloy containing any one of Sn, Bi, In, Pb, Cd or a combination of at least two thereof, and the purity of the catalyst is above 98%.

8. The method for preparing black phosphorus crystals according to claim 1, characterized in that: The transport agent described in step (3) is any one of I2, SnI4, SnI2, PbI2, NH4I, BiI3, PI3, SnCl2, SnBr2, or a combination of at least two thereof, and the purity of the transport agent is above 98%.

9. The method for preparing black phosphorus crystals according to claim 1, characterized in that: The mass feed ratio of the phosphorus raw material to the catalyst in step (3) is 100:1-5; the mass feed ratio of the catalyst to the transport agent is 10:1-5.

10. The method for preparing black phosphorus crystals according to claim 1, characterized in that: The temperature control program described in step (3) is specifically as follows: under room temperature conditions, the temperature of the raw material end is increased to 500-550°C over 1-2 hours, kept at this temperature for 6-12 hours, and then decreased to room temperature over 6-10 hours; the temperature of the nucleation end is increased to 480-520°C over 1-2 hours, kept at this temperature for 6-12 hours, and then decreased to room temperature over 6-10 hours; the temperature control programs of the raw material end and the nucleation end are carried out synchronously, and the temperature of the raw material end is always 10-40°C higher than the temperature of the nucleation end.

Images