Two-dimensional transition metal compound and preparation method and application thereof

Abstract

The application belongs to the technical field of two-dimensional material preparation, and relates to a two-dimensional transition metal compound and a preparation method and application thereof, and the preparation method comprises the following steps: 1) grinding molybdenite into micron-sized mineral powder; 2) mixing the micron-sized mineral powder with a chlorine salt, and performing high-temperature molten salt reaction under a reaction atmosphere and then cooling to room temperature to obtain a reaction product; and 3) washing and drying the reaction product to obtain molybdenum nitride or molybdenum phosphide. The application realizes efficient conversion from a bulk layered transition metal sulfide to a two-dimensional transition metal compound nanosheet by using the fluxing, intercalation and exfoliation effects of molten chlorine salt; different two-dimensional molybdenum-based nitrides or phosphides of different phases can be selectively prepared by adjusting the reaction temperature and chlorine salt composition; the method has simple synthesis process, controllable cost and high production efficiency, and the by-product salt after the reaction is easy to recycle and reuse, and belongs to a green and industrialized two-dimensional material preparation process, and has wide popularization and application prospects.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional material preparation technology, and relates to a two-dimensional transition metal compound, its preparation method and application. Background Technology

[0002] Two-dimensional materials, due to their unique quantum confinement and surface effects, show broad application prospects in fields such as electronic devices, catalysis, and energy storage. Researchers are continuously exploring novel two-dimensional materials with superior electrical, catalytic, and mechanical properties, building upon graphene and transition metal sulfides (such as MoS2). Molybdenum-based nitrides and phosphides possess metal-like high conductivity, high hardness, and excellent catalytic activity in their bulk state; preparing them in two-dimensional form is expected to further amplify these properties, making them highly promising candidate materials.

[0003] However, unlike the widely studied layered MoS2, two-dimensional molybdenum-based nitrides and phosphides are non-layered materials, with strong chemical bonds connecting them in all three dimensions. These cannot be obtained through simple liquid-phase exfoliation, posing a fundamental challenge to their preparation. On the one hand, this structural characteristic results in extremely demanding requirements for precursors and reaction conditions. While existing methods such as chemical vapor deposition (CVD), topological transformation, and MAX phase-selective etching can attempt preparation, they all suffer from limitations such as high cost, cumbersome procedures, or unsatisfactory product quality. On the other hand, many molybdenum nitride and phosphide phases exhibit poor stability at high temperatures, easily decomposing or undergoing phase transitions, further limiting the application of traditional high-temperature synthesis methods.

[0004] Specifically, chemical vapor deposition (CVD) places a molybdenum source (such as MoO3) on one side of a substrate and a phosphorus source (such as red phosphorus) or a nitrogen source (such as urea). High-temperature evaporation causes the precursor to react on the substrate surface to generate a two-dimensional material. However, this method involves complex equipment and high costs, making large-scale production difficult. Topological transformation utilizes structurally stable layered precursors, retaining the layered framework through solid-phase or gas-phase atomic substitution reactions. However, it has stringent requirements for the precursor, making it difficult to obtain the target product directly from commercial raw materials. Selective etching uses the MAX phase as a precursor, selectively etching A-layer atoms (such as Al, Ga, etc.) to prepare accordion-shaped two-dimensional metal carbides or nitrides (MXenes). This method requires large amounts of highly corrosive HF or LiF-HCl mixed solutions, which does not align with the direction of green large-scale development; the resulting two-dimensional carbides or nitrides contain numerous defects such as hydroxyl groups, oxygen-containing functional groups, or fluorine terminals on their surfaces, resulting in poor stability in air and water. Furthermore, this method is mainly applicable to the preparation of carbide MXene, while nitride MXene is limited to a few systems such as Mo2N, V2N, Ti4N3 and Ti2N. There are currently no reports on phosphide MXene.

[0005] In summary, existing methods for preparing two-dimensional transition metal compounds, molybdenum-based nitrides and phosphides, suffer from problems such as complex processes, high costs, or unsatisfactory product quality. There is an urgent need to develop an efficient, low-cost, and easy-to-operate preparation process to meet the needs of their practical applications. Summary of the Invention

[0006] The main objective of this invention is to overcome the problems of complex preparation processes, high costs, and difficulty in scaling up existing two-dimensional transition metal compounds, such as molybdenum-based nitrides and phosphides, and to provide a two-dimensional transition metal compound, its preparation method, and its application.

[0007] To achieve the above objectives, the specific technical solution is as follows: This invention provides a method for preparing a two-dimensional transition metal compound, wherein the two-dimensional transition metal compound is two-dimensional molybdenum nitride or molybdenum phosphide, comprising the following steps: 1) Grind molybdenum concentrate into micron-sized mineral powder; 2) The micron-sized mineral powder is mixed with chloride salt, heated to above the chloride salt melting temperature under a reaction atmosphere to carry out a high-temperature molten salt reaction, and then cooled to room temperature to obtain the reaction product; the reaction atmosphere is ammonia or phosphine. 3) The reaction product is washed with water and dried to obtain two-dimensional molybdenum nitride or molybdenum phosphide.

[0008] This invention utilizes molten chloride salt as a flux and salt intercalation agent to bring bulk molybdenum disulfide into a eutectic state at high temperature. The molten salt penetrates and intercalates into the interlayer, achieving physical exfoliation and forming ultrathin nanosheets isolated by the salt. This process provides pre-support for the structural stability of the nanosheets in subsequent reactions, effectively preventing high-temperature sintering. The active components generated by the decomposition of NH3 or PH3 on the surface of the molten salt film further penetrate the molten salt layer and react with molybdenum disulfide, constructing a gas-liquid-solid three-phase reaction interface. At this interface, the molybdenum disulfide nanosheets undergo topological transformation, with sulfur atoms gradually replaced by nitrogen or phosphorus atoms, preserving the two-dimensional morphology. After the reaction, the soluble mixed salt template is removed by simple water washing, yielding independent two-dimensional molybdenum nitride or molybdenum phosphide nanosheets.

[0009] Further, in step 1), the particle size of the molybdenite concentrate is 10-100 µm; the particle size of the micron-sized mineral powder is ≤10 µm, preferably 1-10 µm.

[0010] This invention grinds molybdenum disulfide concentrate into micron-sized mineral powder of 1-10 µm, which significantly increases its specific surface area, thereby providing more reactive sites for subsequent high-temperature molten salt reactions. This promotes the penetration and intercalation of molten chloride salts, which is beneficial for improving the exfoliation efficiency of molybdenum disulfide and the uniformity of the reaction, thus enhancing the quality and yield of the final product, two-dimensional molybdenum nitride or molybdenum phosphide nanosheets. If the powder particle size is too large, the molten salt may not be able to fully penetrate into the bulk, affecting the thoroughness of exfoliation and reaction. While a particle size that is too small theoretically results in higher reactivity, excessively fine powder may easily agglomerate during processing, which is detrimental to subsequent operations and the smooth progress of the reaction. A particle size range of 1-10 µm can better balance reaction efficiency and operational feasibility.

[0011] Further, the chloride salt is selected from one or more of KCl, NaCl, LiCl, MgCl2, and CaCl2; preferably KCl, or a mixture of KCl and NaCl, or a mixture of KCl and LiCl.

[0012] The advantage of using the above-mentioned chloride salt in this invention is that it has a suitable melting point, can form a good polar environment, and is conducive to the replacement of nitrogen and phosphorus atoms and the formation of lamellar layers.

[0013] Further, in step 2), the molar ratio of the micron-sized mineral powder to the chloride salt is 1:1-12, preferably 1:1-4.

[0014] The above-mentioned mass ratio range used in this invention ensures that chloride salts, in a high-temperature molten state, fully encapsulate and penetrate into the micron-sized mineral powder, providing sufficient reaction medium for the stripping of molybdenum disulfide and subsequent nitriding / phosphating reactions. If the chloride salt ratio is too low, the amount of molten salt may be insufficient, failing to effectively achieve uniform dispersion and full penetration of the mineral powder, thus affecting the stripping efficiency and the thoroughness of the reaction. On the other hand, if the chloride salt ratio is too high, it will increase the difficulty of subsequent water washing and separation, as well as water consumption, resulting in resource waste. Furthermore, excessive chloride salts may introduce unnecessary impurities into the reaction system, adversely affecting the purity of the final product.

[0015] Further, in step 2), the flow rate of the ammonia gas is 50-300 sccm.

[0016] The ammonia flow rate of this invention is controlled within the range of 50-300 sccm, which can provide a suitable nitrogen source atmosphere for the nitriding reaction. When the ammonia flow rate is too low, there is insufficient nitrogen source in the reaction system, making it difficult to ensure the full progress of the nitriding reaction, which may lead to a low nitrogen content in the product and affect the performance of molybdenum nitride; while if the flow rate is too high, it will not only waste ammonia and increase production costs, but may also cause product particle agglomeration or structural defects due to an overly vigorous reaction.

[0017] Furthermore, in step 2), the phosphine is generated by heating sodium hypophosphite with hydrogen.

[0018] The phosphine produced in this invention is generated by the thermal decomposition of sodium hypophosphite. This method has the advantages of simple operation and stable and controllable gas production. It can avoid the storage, transportation and safety risks caused by directly using highly toxic phosphine gas. At the same time, by controlling the heating temperature and rate of sodium hypophosphite, the production rate and amount of phosphine can be effectively adjusted to ensure that the phosphating reaction is carried out under stable phosphorus source supply conditions, which is conducive to obtaining molybdenum phosphide products with uniform composition and excellent performance.

[0019] Further, in step 2), when the chloride salt is selected from KCl, the molar ratio of the micron-sized mineral powder to the chloride salt is 1:(2-6); the reaction temperature is 850-950℃, and the reaction time is 2-8h.

[0020] Further, in step 2), when the chloride salt is selected from a mixture of KCl and NaCl, the molar ratio of the micron-sized mineral powder to KCl and NaCl is 1:(2-6):(2-6); the reaction temperature is 700-950℃, and the reaction time is 2-8h.

[0021] Further, in step 2), when the chloride salt is selected from a mixture of KCl and LiCl, the molar ratio of the micron-sized mineral powder to KCl and LiCl is 1:(0-6):(2-6), preferably 1:(1-6):(2-6); the reaction temperature is 650-850℃, and the reaction time is 2-8h.

[0022] Furthermore, in step 3), the filtrate after water washing is distilled to recover chloride salts, thereby achieving the recycling of chloride salts.

[0023] In one specific embodiment of the present invention, a method for preparing a two-dimensional transition metal compound, wherein the two-dimensional transition metal compound is MoN, includes the following steps: 1) Grind molybdenum concentrate to obtain micron-sized mineral powder; 2) The micron-sized mineral powder is mixed with a mixed salt of sodium chloride and potassium chloride, heated to 700-950℃ under an ammonia atmosphere, reacted for 2-8 hours, and then cooled to room temperature to obtain the reaction product; the molar ratio of the micron-sized mineral powder to sodium chloride and potassium chloride is 1:(2-6):(2-6). 3) The reaction product is washed with water and dried to obtain MoN.

[0024] In one specific embodiment of the present invention, a method for preparing a two-dimensional transition metal compound, wherein the two-dimensional transition metal compound is Mo3N2, includes the following steps: 1) Grind molybdenum concentrate to obtain micron-sized mineral powder; 2) The micron-sized mineral powder is mixed with sodium chloride monosalt, heated to 850-1050℃ under ammonia atmosphere, reacted for 2-8 hours, and then cooled to room temperature to obtain the reaction product; the molar ratio of the micron-sized mineral powder to potassium chloride is 1:(2-6). 3) The reaction product was washed with water and dried to obtain Mo3N2.

[0025] In one specific embodiment of the present invention, a method for preparing a two-dimensional transition metal compound, wherein the two-dimensional transition metal compound is Mo5N6, includes the following steps: 1) Grind molybdenum concentrate to obtain micron-sized mineral powder; 2) The micron-sized mineral powder is mixed with a mixed salt of lithium chloride and potassium chloride, and heated to 650℃-850℃ under an ammonia atmosphere for 2-8 hours. After cooling to room temperature, the reaction product is obtained. The molar ratio of the micron-sized mineral powder to lithium chloride and potassium chloride is 1:(2-6):(0-6); preferably 1:(2-6):(1-6). 3) The reaction product was washed with water and dried to obtain Mo5N6.

[0026] In one specific embodiment of the present invention, a method for preparing a two-dimensional transition metal compound, wherein the two-dimensional transition metal compound is MoP, includes the following steps: 1) Grind molybdenum concentrate to obtain micron-sized mineral powder; 2) The micron-sized mineral powder is mixed with a mixed salt of sodium chloride and potassium chloride, with sodium hypophosphite placed upstream. Argon gas containing 5-10% hydrogen is introduced, and the mixture is heated to 700-950℃. After reacting for 2-8 hours, the mixture is cooled to room temperature to obtain the reaction product. The molar ratio of the micron-sized mineral powder to lithium chloride and potassium chloride is 1:(2-6):(2-6); the mass ratio of the micron-sized mineral powder to sodium hypophosphite is 1:10. 3) The reaction product is washed with water and dried to obtain MoP.

[0027] The present invention also provides a two-dimensional transition metal compound, which is prepared by the above-described method for preparing two-dimensional transition metal compounds.

[0028] This invention further provides the application of the above-mentioned two-dimensional transition metal compounds in the preparation of electronic devices, catalytic materials, and energy storage materials.

[0029] Compared with the prior art, the present invention has the following significant advantages: (1) This invention utilizes the molten salt assisted effect to successfully inherit the two-dimensional layered structure of the precursor into the product, realizing the efficient conversion from bulk layered transition metal sulfides to two-dimensional transition metal compound nanosheets, obtaining ultrathin, large specific surface area two-dimensional molybdenum nitride or molybdenum phosphide nanosheets, avoiding the defect of easily forming dense bulk products when directly nitriding or phosphating bulk raw materials.

[0030] (2) By rationally controlling the reaction temperature and the composition of the mixed chloride salt, this invention can selectively prepare high-purity two-dimensional molybdenum-based nitrides or phosphides (such as MoN, Mo3N) of different phases. 2、 Mo5N6, MoP, etc.

[0031] (3) The chloride salts used in this invention are inexpensive and readily available. They can be completely removed by washing with water after the reaction. The post-treatment is simple, safe, and extremely low in cost. Furthermore, the mixed chloride salts in the filtrate can be recovered and recycled by distillation.

[0032] (4) This invention does not require the use of highly corrosive etching agents (such as HF) or metal catalysts, thus avoiding the discharge of harmful waste liquids and product pollution, and meets the requirements of green chemistry and sustainable development.

[0033] (5) The raw materials of the present invention are widely available. Commercial molybdenum concentrate can be used directly as the starting material without the need to synthesize special precursors in advance, which greatly reduces the raw material cost and production threshold.

[0034] (6) The “molten salt-assisted topological transformation” strategy of the present invention can be extended to the transformation of other layered transition metal sulfides / selenides (such as WS2, MoSe2, NbS2, etc.) into their corresponding nitrides (WN, MoN, NbN), providing a general platform for the preparation of a series of two-dimensional transition metal nitrides and phosphides. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the process for preparing molybdenum nitride and molybdenum phosphide according to the present invention; Figure 2 This is a scanning electron microscope image of the molybdenite concentrate used in this invention at a magnification of 2000x. Figure 3 The image shows the XRD pattern of the molybdenite concentrate used in this invention. Figure 4This is a scanning electron microscope image of the molybdenum concentrate used in this invention after ball milling, under a magnification of 2000x. Figure 5 This is a scanning electron microscope image of MoN prepared in Example 1 of the present invention at a magnification of 20000x. Figure 6 XRD images of MoN were prepared for Example 1 of the present invention; Figure 7 AFM height morphology image of MoN prepared in Example 1 of this invention; Figure 8 AFM height profile of MoN prepared in Example 1 of this invention; Figure 9 This is a scanning electron microscope image of Mo5N6 prepared in Example 2 of the present invention at a magnification of 20000x. Figure 10 XRD images of Mo5N6 were prepared for Example 2 of the present invention; Figure 11 This is a scanning electron microscope image of MoP prepared in Example 3 of the present invention at a magnification of 20000x. Figure 12 XRD images of MoP were prepared for Example 3 of this invention; Figure 13 This is a scanning electron microscope image of MoN prepared in Comparative Example 1 of this invention at a magnification of 20000x. Figure 14 XRD images of MoN were prepared for Comparative Example 1 of this invention; Figure 15 This is a scanning electron microscope image of the product prepared in Comparative Example 2 of the present invention at a magnification of 20000x. Figure 16 The image shows the XRD pattern of the product prepared in Comparative Example 2 of this invention. Figure 17 This is a scanning electron microscope image of the product prepared in Comparative Example 3 of the present invention at a magnification of 20000x. Figure 18 The image shows the XRD pattern of the product prepared in Comparative Example 3 of this invention. Figure 19 This is a scanning electron microscope image at 20000x magnification of the Mo3N2 and MoN mixed phase prepared in Comparative Example 4 of this invention. Figure 20 XRD images of a Mo3N2 / MoN mixed phase prepared for Comparative Example 4 of this invention; Figure 21 This is a scanning electron microscope image at 20000x magnification of the MoN and Mo5N6 mixed phase prepared in Comparative Example 5 of the present invention. Figure 22XRD images of the MoN and Mo5N6 mixed phase were prepared for Comparative Example 5 of this invention; Figure 23 This is a scanning electron microscope image at 20000x magnification of the MoP and MoP2 mixed phase prepared in Comparative Example 6 of this invention. Figure 24 XRD images of a mixture of MoP and MoP2 were prepared for Comparative Example 6 of this invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0038] Unless otherwise specified in the embodiments of the present invention, the techniques or conditions described in the literature in this field or the product instructions shall be followed; if the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be purchased through legitimate channels.

[0039] The bulk molybdenum disulfide used in the embodiments and comparative examples of this invention is commercially available molybdenite concentrate powder with a size of 0.5~100 μm.

[0040] The technical roadmap adopted in this invention is as follows: Figure 1 As shown, when NH3 is used as the reaction atmosphere, two-dimensional molybdenum nitride is obtained, and when PH3 is used as the reaction atmosphere, two-dimensional molybdenum phosphide is obtained. Example 1

[0041] A method for preparing two-dimensional molybdenum nitride nanosheets, such as Figure 1 As shown, the specific preparation method includes the following steps: 1) Weigh 1 g of molybdenum concentrate and place it in a ball mill jar. Ball mill at 400 rpm (5 min working / 1 min interval, 72 cycles, repeated once after inversion). Wash the resulting powder with water for 15 min, filter three times, and freeze dry for more than 24 h to obtain micron-sized molybdenum disulfide powder.

[0042] 2) Weigh the above molybdenum disulfide powder and the mixed salt of sodium chloride and potassium chloride (the molar ratio of sodium chloride to potassium chloride is 1:1), wherein the total molar ratio of molybdenum disulfide to the mixed salt is 1:3. Grind them thoroughly and transfer them to a crucible.

[0043] 3) Place the crucible in a tube furnace and heat it to 850°C at a heating rate of 5°C / min under an ammonia atmosphere, then hold it at that temperature for 6 hours. The ammonia flow rate is 200 sccm. Finally, cool it to room temperature.

[0044] 4) After annealing, the mixture was washed with deionized water for 5 minutes and then filtered. It was then freeze-dried for more than 24 hours to finally obtain dried two-dimensional nitride nanosheets.

[0045] The morphology and XRD of the molybdenum disulfide powder used in this embodiment are as follows: Figures 2-4 As shown, the results indicate that molybdenite has high purity and large size, with a particle size of about 50 μm. After ball milling, the particle size is mostly below 10 μm.

[0046] Figure 5 and Figure 6 The images shown are the scanning electron microscope (SEM) image and XRD pattern of the final product in this embodiment. Figure 7 and Figure 8 The image shows the AFM pattern of the final product. The two-dimensional nanosheets obtained by the above method of the present invention have good dispersion and thin thickness. The size of the nanosheets is about 1-5 μm and the thickness is about 4 nm. The diffraction peak positions of the obtained product are basically consistent with those of the standard card MoN-PDF#01-074-4265, indicating that the final product obtained after molten salt nitriding is a high-purity two-dimensional MoN nanosheet. Example 2

[0047] A method for preparing two-dimensional Mo5N6 nanosheets includes the following steps: 1) Weigh 1 g of molybdenum disulfide concentrate and place it in a ball mill jar. Ball mill at 400 rpm (5 min working time / 1 min interval, 72 cycles, repeated once after inversion). Wash the resulting powder with water for 15 min, filter three times, and freeze-dry for more than 24 h to obtain micron-sized molybdenum disulfide powder.

[0048] 2) Weigh out a mixture of molybdenum disulfide powder, lithium chloride, and potassium chloride (the molar ratio of lithium chloride to potassium chloride is 1:1), wherein the total molar ratio of molybdenum disulfide to the mixed salt is 1:3. Grind the mixture thoroughly and transfer it to a crucible.

[0049] 3) Place the crucible in a tube furnace and heat it to 750°C at a heating rate of 5°C / min under an ammonia atmosphere, then hold it at that temperature for 6 hours at a flow rate of 200 sccm. Finally, cool it to room temperature.

[0050] 4) After annealing, the mixture was washed with deionized water for 5 minutes and then filtered. It was then freeze-dried for more than 24 hours to finally obtain dry two-dimensional nitride nanosheets.

[0051] Figure 10 and Figure 11The images shown are the scanning electron microscope (SEM) image and XRD pattern of the final product in this embodiment. The diffraction peak positions of the obtained product are basically consistent with those of the standard card Mo5N6-PDF#01-076-3748, indicating that the final product obtained after molten salt nitriding is a high-purity two-dimensional Mo5N6 nanosheet. Example 3

[0052] A method for preparing two-dimensional molybdenum phosphide nanosheets specifically includes the following steps: 1) Weigh 1 g of molybdenum disulfide concentrate and place it in a ball mill jar. Ball mill at 400 rpm (5 min working time / 1 min interval, 72 cycles, repeated once after inversion). Wash the resulting powder with water for 15 min, filter three times, and freeze-dry for more than 24 h to obtain micron-sized molybdenum disulfide powder.

[0053] 2) Weigh out a mixture of molybdenum disulfide powder, sodium chloride, and lithium chloride (the molar ratio of sodium chloride to potassium chloride is 1:1), wherein the total molar ratio of molybdenum disulfide to the mixed salt is 1:3. Grind the mixture thoroughly and transfer it to a crucible. Weigh out 2g of sodium hypophosphite and place it in another crucible.

[0054] 3) Place the crucible in a tube furnace, place the sodium hypophosphite at the top air outlet 15 cm away from the sample, heat to 850 °C at a heating rate of 5 °C / min in an argon atmosphere containing 7% hydrogen, hold for 6 h at a flow rate of 50 sccm, and finally cool to room temperature.

[0055] 4) After annealing, the mixture was washed with deionized water for 5 minutes and then filtered. It was then freeze-dried for more than 24 hours to finally obtain dry two-dimensional phosphide nanosheets.

[0056] Figure 12 and Figure 13 The images shown are the scanning electron microscope (SEM) image and XRD pattern of the final product of this embodiment. The diffraction peak positions of the obtained product are basically consistent with those of the standard card MoP-PDF#00-024-0771, indicating that the final product obtained after molten salt nitriding is a high-purity two-dimensional MoP nanosheet.

[0057] Comparative Example 1 A method for preparing two-dimensional molybdenum nitride nanosheets is provided, which is largely the same as that in Example 1, except that chloride salts are not used. The method specifically includes the following steps: 1) Weigh 1 g of molybdenum disulfide concentrate and place it in a ball mill jar. Ball mill at 400 rpm (5 min working time / 1 min interval, 72 cycles, repeated once after inversion). Wash the resulting powder with water for 15 min, filter three times, and freeze-dry for more than 24 h to obtain micron-sized molybdenum disulfide powder (particle size <10 μm).

[0058] 2) Weigh out the molybdenum disulfide powder, grind it thoroughly and evenly, and transfer it to a crucible.

[0059] 3) Place the crucible in a tube furnace and heat it to 850°C at a heating rate of 5°C / min under an ammonia atmosphere. Hold the temperature for 6 hours at a flow rate of 200 sccm. Finally, cool it to room temperature.

[0060] 4) After annealing, the mixture was washed with deionized water for 5 minutes and then filtered. It was then freeze-dried for more than 24 hours to finally obtain dry two-dimensional nitride nanosheets.

[0061] Figure 14 and Figure 15 The images shown are the scanning electron microscope (SEM) image and XRD pattern of the final product in this embodiment. The diffraction peak positions of the obtained product are basically consistent with those of the standard card MoN-PDF#01-074-4265. However, the material does not have an obvious two-dimensional structure, indicating that only bulk MoN can be obtained without molten salt nitriding.

[0062] Comparative Example 2 A method for preparing two-dimensional molybdenum nitride nanosheets is provided, which is largely the same as that in Example 1, except that the annealing temperature is lower than the nitriding temperature. The method specifically includes the following steps: 1) Weigh 1 g of molybdenum disulfide concentrate and place it in a ball mill jar. Ball mill at 400 rpm (5 min working time / 1 min interval, 72 cycles, repeated once after inversion). Wash the resulting powder with water for 15 min, filter three times, and freeze-dry for more than 24 h to obtain micron-sized molybdenum disulfide powder (particle size <10 μm).

[0063] 2) Weigh the above molybdenum disulfide powder and the mixed salt of sodium chloride and potassium chloride (the molar ratio of sodium chloride to potassium chloride is 1:1), wherein the total molar ratio of molybdenum disulfide to the mixed salt is 1:3. Grind them thoroughly and transfer them to a crucible.

[0064] 3) Place the crucible in a tube furnace and heat it to 650°C at a heating rate of 5°C / min under an ammonia atmosphere, then hold it at that temperature for 6 hours. The flow rate is 200 sccm. Finally, cool it to room temperature.

[0065] 4) After annealing, the mixture was washed with deionized water for 5 minutes and then filtered. It was then freeze-dried for more than 24 hours to finally obtain dry two-dimensional nitride nanosheets.

[0066] Figure 16 and Figure 17 The images shown are the scanning electron microscope (SEM) image and XRD pattern of the final product in this embodiment. The diffraction peak positions of the obtained product are basically consistent with those of the standard card MoS2 PDF#01-077-1716. Moreover, the material does not have an obvious two-dimensional structure, indicating that MoN cannot be obtained without reaching the nitriding temperature, nor can a layered structure be obtained.

[0067] Comparative Example 3 A method for preparing two-dimensional molybdenum nitride nanosheets is generally the same as that in Example 1, except that magnesium chloride single salt is used. The method specifically includes the following steps: 1) Weigh 1 g of molybdenum disulfide concentrate and place it in a ball mill jar. Ball mill at 400 rpm (5 min working time / 1 min interval, 72 cycles, repeated once after inversion). Wash the resulting powder with water for 15 min, filter three times, and freeze-dry for more than 24 h to obtain micron-sized molybdenum disulfide powder.

[0068] 2) Weigh out molybdenum disulfide powder and magnesium chloride monosalt, wherein the molar ratio of molybdenum disulfide to magnesium chloride is 1:5, grind them thoroughly and evenly and transfer them to a crucible.

[0069] 3) Place the crucible in a tube furnace and heat it to 850°C at a heating rate of 5°C / min under an ammonia atmosphere. Hold the temperature for 6 hours at a flow rate of 200 sccm. Finally, cool it to room temperature.

[0070] 4) After annealing, the mixture was washed with deionized water for 5 minutes and then filtered. It was then freeze-dried for more than 24 hours to finally obtain dry two-dimensional nitride nanosheets.

[0071] Figure 18 and Figure 19 The images shown are the scanning electron microscope (SEM) image and XRD pattern of the final product of this embodiment. In addition to the peaks of the standard card MoN-PDF#01-074-4265, the diffraction peaks of the obtained product also contain peaks of MgO and Mg impurities. This is because molten magnesium chloride corrodes the corundum crucible, and after nitriding with magnesium chloride single salt, a two-dimensional layered MoN containing MgO and Mg impurities is obtained.

[0072] Comparative Example 4 A method for preparing two-dimensional molybdenum nitride nanosheets is generally the same as that in Example 1, except that potassium chloride monosalt is used. The method specifically includes the following steps: 1) Weigh 1 g of molybdenum concentrate and place it in a ball mill jar. Ball mill at 400 rpm (5 min working time / 1 min interval, 72 cycles, repeated once after inversion). Wash the obtained powder with water for 15 min, filter three times, and freeze dry for more than 24 h to obtain micron-sized molybdenum disulfide powder.

[0073] 2) Weigh out a mixture of molybdenum disulfide powder and potassium chloride, wherein the molar ratio of molybdenum disulfide to potassium chloride is 1:3, grind it thoroughly and evenly and transfer it to a crucible.

[0074] 3) Place the crucible in a tube furnace and heat it to 850°C at a heating rate of 5°C / min under an ammonia atmosphere. Hold the temperature for 6 hours at a flow rate of 200 sccm. Finally, cool it to room temperature.

[0075] 4) After annealing, the mixture was washed with deionized water for 5 minutes and then filtered. It was freeze-dried for more than 24 hours to finally obtain dry two-dimensional nitride nanosheets.

[0076] Figure 19 and Figure 20 The images shown are the scanning electron microscope (SEM) and XRD pattern of the final product in this embodiment. The diffraction peaks of the obtained product are present at the standard card MoN-PDF#01-074-4265 and a small amount of Mo3N2-PDF#01-089-3712, indicating that single-salt nitriding can also yield two-dimensional sheet molybdenum nitride.

[0077] Comparative Example 5 A method for preparing two-dimensional molybdenum nitride nanosheets is largely the same as that in Example 2, except that a mixed salt of sodium chloride and potassium chloride is used, and includes the following steps: 1) Weigh 1 g of molybdenum disulfide concentrate and place it in a ball mill jar. Ball mill at 400 rpm (5 min working time / 1 min interval, 72 cycles, repeated once after inversion). Wash the resulting powder with water for 15 min, filter three times, and freeze-dry for more than 24 h to obtain micron-sized molybdenum disulfide powder.

[0078] 2) Weigh out a mixture of molybdenum disulfide powder, sodium chloride, and potassium chloride (the molar ratio of sodium chloride to potassium chloride is 1:1), wherein the total molar ratio of molybdenum disulfide to the mixed salt is 1:3. Grind the mixture thoroughly and transfer it to a crucible.

[0079] 3) Place the crucible in a tube furnace and heat it to 750°C at a heating rate of 5°C / min under an ammonia atmosphere, then hold it at that temperature for 6 hours at a flow rate of 200 sccm. Finally, cool it to room temperature.

[0080] 4) After annealing, the mixture was washed with deionized water for 5 minutes and then filtered. It was then freeze-dried for more than 24 hours to finally obtain dry two-dimensional nitride nanosheets.

[0081] Figure 21 and Figure 22 The images shown are the scanning electron microscope (SEM) and XRD patterns of the final product in this embodiment. The diffraction peaks of the obtained product include those of the standard card MoN-PDF#01-074-4265 and Mo5N6-PDF#01-076-3748, indicating that without selecting the correct molten salt for nitriding, the final product is a mixed-phase nanosheet of MoN and Mo5N6, and a pure phase cannot be obtained.

[0082] Comparative Example 6 A method for preparing two-dimensional molybdenum phosphide nanosheets is largely the same as that in Example 6, except that the atmosphere is changed to a pure argon atmosphere, and includes the following steps: 1) Weigh 1 g of molybdenum disulfide concentrate and place it in a ball mill jar. Ball mill at 400 rpm (5 min working time / 1 min interval, 72 cycles, repeated once after inversion). Wash the resulting powder with water for 15 min, filter three times, and freeze-dry for more than 24 h to obtain micron-sized molybdenum disulfide powder (particle size <10 μm).

[0083] 2) Weigh out a mixture of molybdenum disulfide powder, sodium chloride, and lithium chloride (the molar ratio of sodium chloride to potassium chloride is 1:1), wherein the total molar ratio of molybdenum disulfide to the mixed salt is 1:3. Grind the mixture thoroughly and transfer it to a crucible. Weigh out 2g of sodium hypophosphite and place it in another crucible.

[0084] 3) Place the crucible in a tube furnace, place the sodium hypophosphite at the top air outlet 15 cm away from the sample, heat to 850 °C at a heating rate of 5 °C / min under a pure argon atmosphere, hold for 6 h at a flow rate of 50 sccm, and finally cool to room temperature.

[0085] 4) After annealing, the mixture was washed with deionized water for 5 minutes and then filtered. It was then freeze-dried for more than 24 hours to finally obtain dry two-dimensional phosphide nanosheets.

[0086] Figure 23 and Figure 24 The images shown are the scanning electron microscope (SEM) image and XRD pattern of the final product of this embodiment. The diffraction peaks of the obtained product include the standard card MoP-PDF#00-024-0771 and MoP2-PDF#00-016-0499, indicating that two-dimensional MoP and MoP2 mixed-phase nanosheets were obtained after molten salt phosphating in the absence of H2.

[0087] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a two-dimensional transition metal compound, characterized in that, Includes the following steps: 1) Grind molybdenum concentrate into micron-sized mineral powder; 2) The micron-sized mineral powder is mixed with chloride salt, heated to above the chloride salt melting temperature under a reaction atmosphere to carry out a high-temperature molten salt reaction, and then cooled to room temperature to obtain the reaction product; the reaction atmosphere is ammonia or phosphine. 3) The reaction product is washed with water and dried to obtain two-dimensional molybdenum nitride or molybdenum phosphide.

2. The method for preparing a two-dimensional transition metal compound according to claim 1, characterized in that, In step 1), the particle size of the molybdenite concentrate is 10-100 µm; the particle size of the micron-sized mineral powder is ≤10 µm, preferably 1-10 µm.

3. The method for preparing a two-dimensional transition metal compound according to claim 1 or 2, characterized in that, The chloride salt is selected from one or more of KCl, NaCl, LiCl, MgCl2, and CaCl2; preferably KCl, or a mixture of KCl and NaCl, or a mixture of KCl and LiCl.

4. The method for preparing the two-dimensional transition metal compound according to claim 3, characterized in that, In step 2), the molar ratio of the micron-sized mineral powder to the chloride salt is 1:1-12, preferably 1:1-4.

5. The method for preparing a two-dimensional transition metal compound according to claim 1 or 2, characterized in that, In step 2), the flow rate of ammonia is 50-300 sccm; the phosphine is generated by heating sodium hypophosphite and hydrogen.

6. The method for preparing a two-dimensional transition metal compound according to claim 3, characterized in that, In step 2), when the chloride salt is selected from KCl, the molar ratio of the micron-sized mineral powder to the chloride salt is 1:(2-6); the reaction temperature is 850-950℃, and the reaction time is 2-8h.

7. The method for preparing a two-dimensional transition metal compound according to claim 3, characterized in that, In step 2), when the chloride salt is selected from a mixture of KCl and NaCl, the molar ratio of the micron-sized mineral powder to KCl and NaCl is 1:(2-6):(2-6); the reaction temperature is 700-950℃, and the reaction time is 2-8h.

8. The method for preparing a two-dimensional transition metal compound according to claim 3, characterized in that, In step 2), when the chloride salt is selected from a mixture of KCl and LiCl, the molar ratio of the micron-sized mineral powder to KCl and LiCl is 1:(0-6):(2-6); the reaction temperature is 650-850℃, and the reaction time is 2-8h.

9. A two-dimensional transition metal compound, characterized in that, It is prepared by the method for preparing two-dimensional transition metal compounds according to any one of claims 1 to 8.

10. The application of the two-dimensional transition metal compound as described in claim 9 in the preparation of electronic devices, catalytic materials, and energy storage materials.

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