阅读说明：本技术 一种利用体相层状过渡金属硫化物制备非层状二维过渡金属化合物的方法 (Method for preparing non-lamellar two-dimensional transition metal compound by using bulk phase lamellar transition metal sulfide ) 是由 霍开富 宋豪 张旭明 任玉磊 于 2021-07-26 设计创作，主要内容包括：本发明公开了一种利用体相层状过渡金属硫化物制备非层状二维过渡金属化合物的方法,首先将体相层状过渡金属硫化物依次与碳酸钠、尿素研磨混合均匀；然后在辅助气氛下进行保温反应,再经酸洗、洗涤干燥等处理制备非层状二维过渡金属化合物纳米片。本发明利用熔盐辅助法实现体相层状过渡金属硫化物高效制备二维过渡金属化合物纳米片,并首次提出利用尿素作为碳源(或氮源),通过调控反应气氛实现二维碳化物或二维氮化物纳米片的选择性制备；涉及的合成工艺简单、成本较低、生产效率高,反应后副产物盐易除去,属于一种绿色、易工业化的二维材料制备工艺路线,适合推广和工业应用。(The invention discloses a method for preparing a non-lamellar two-dimensional transition metal compound by using a bulk phase lamellar transition metal sulfide, which comprises the following steps of firstly, sequentially grinding and uniformly mixing the bulk phase lamellar transition metal sulfide with sodium carbonate and urea; then carrying out heat preservation reaction under the auxiliary atmosphere, and preparing the non-layered two-dimensional transition metal compound nanosheet through acid washing, drying and other treatment. According to the invention, a fused salt auxiliary method is utilized to realize efficient preparation of two-dimensional transition metal compound nanosheets from bulk phase layered transition metal sulfides, urea is firstly proposed to be used as a carbon source (or a nitrogen source), and selective preparation of two-dimensional carbide or two-dimensional nitride nanosheets is realized by regulating and controlling reaction atmosphere; the related synthesis process is simple, the cost is low, the production efficiency is high, the byproduct salt is easy to remove after the reaction, the method belongs to a green and easily-industrialized two-dimensional material preparation process route, and the method is suitable for popularization and industrial application.)

1. A method for preparing a non-lamellar two-dimensional transition metal compound by using a bulk lamellar transition metal sulfide is characterized by comprising the following steps:

1) grinding and uniformly mixing the bulk phase layered transition metal sulfide and sodium carbonate; then adding urea, grinding for the second time and mixing uniformly;

2) heating the mixture obtained in the step 1) in an auxiliary atmosphere to perform heat preservation reaction, and cooling;

3) and (3) carrying out acid washing on the reaction product obtained in the step 2), washing with water to be neutral, filtering and drying to obtain the nano flaky non-laminar two-dimensional transition metal compound.

2. The method of claim 1, wherein the bulk layered transition metal sulfide is bulk molybdenum disulfide or bulk tungsten disulfide on a scale of 0.5 to 100 μ ι η.

3. The method of claim 1, wherein the non-layered transition metal compound is a transition metal nitride or a transition metal carbide.

4. The method according to claim 1, wherein the auxiliary atmosphere is an inert atmosphere or an auxiliary atmosphere of a hydrogen-containing atmosphere; wherein, inert atmosphere is adopted to obtain a two-dimensional transition metal nitride product, and auxiliary atmosphere containing hydrogen is adopted to obtain a two-dimensional transition metal carbide product.

5. The method of claim 4, wherein the inert atmosphere is argon or nitrogen; in the auxiliary atmosphere containing hydrogen, the volume percentage of the hydrogen is 3-80%.

6. The method according to claim 2, wherein when bulk molybdenum disulfide is selected as the bulk layered transition metal sulfide, the molar ratio of molybdenum disulfide to sodium carbonate is 1 (2.0-6.0); the molar ratio of the urea to the molybdenum disulfide is (15-50): 1.

7. The method according to claim 2, wherein when bulk tungsten disulfide is selected as bulk layered transition metal sulfide, the molar ratio of tungsten disulfide to sodium carbonate is 1 (3.0-6.5); the molar ratio of the urea to the tungsten disulfide is (10-100): 1.

8. The method as claimed in claim 2, wherein when bulk layered transition metal sulfide is bulk molybdenum disulfide, the temperature of the heat preservation reaction in step 2) is 600-950 ℃, and the heat preservation time is 1-5 h.

9. The method as claimed in claim 2, wherein when bulk layered transition metal sulfide is bulk tungsten disulfide, the temperature of the step 2) is 700-950 ℃, and the holding time is 2-8 h.

10. The method of claim 1, wherein the acid wash is performedStep (2) adopts HCl and H₂SO₄One or more of acetic acid and formic acid.

Technical Field

The invention belongs to the technical field of two-dimensional material preparation processes, and particularly relates to a method for preparing a non-layered two-dimensional transition metal compound nanosheet from a bulk-phase layered transition metal sulfide.

Background

The carbon and nitride of Mo and W-based transition metal is a gap type compound. Because the d orbitals of metal atoms and the s and p orbitals of C atoms (or N atoms) are hybridized, the d-charged electronic structures of carbon and nitride of Mo and W metals are widened, so that the Pt-like electronic structures are shown, and the Pt-like electronic structures have high conductivity and high electrocatalytic activity, and are widely applied to the fields of catalysis and electrochemical energy storage. In addition, compared with bulk phase materials, the two-dimensional Mo and W transition metal carbide (or nitride) has a high-activity surface induced by a large amount of unsaturated dangling bonds exposed on the surface, and meanwhile, the ultrathin thickness causes the formation of a unique electronic state, so that the electrocatalytic performance and the energy storage performance are enhanced, and the two-dimensional Mo and W transition metal carbide (or nitride) has a better application prospect in the field of electrochemical energy conversion. Unlike layered sulfide, Mo and W metal carbide (nitride) is a non-layered material, and crystal lattices are connected through strong three-dimensional chemical bonds, which means that the conventional layered two-dimensional material preparation method of peeling from bottom to top is difficult to prepare the two-dimensional Mo and W metal carbide (nitride), so that the development of a method with simple process, high production efficiency and easy scale production to prepare the two-dimensional Mo and W transition metal compound nanosheet is a difficult problem which needs to be solved urgently at present.

At present, the method for synthesizing Mo and W based two-dimensional carbide (or two-dimensional nitride) at home and abroad mainly comprises the following steps: 1) a selective etching method, wherein a graphene-like two-dimensional metal carbide (or nitride) MXene material is prepared by selectively etching A layer atoms (such as Al, Ga and the like) in MAX; the method needs a large amount of strong corrosive HF or LiF-HCl mixed solution, is not in line with the development direction of green scale, and the two-dimensional carbide (or nitride) obtained by chemical etching has a large amount of defects (hydroxyl or oxygen-containing functional groups or fluorine-containing terminals are linked on the surface), and has poor stability in water and air. In addition, the method is mainly used for preparing the carbide MXene material, and the nitride MXene material is limited to Ti₄N₃、Ti₂N、V₂N and Mo₂N, no W-based MXene material is reported; 2) a topological transformation method for preparing a two-dimensional carbide (or nitride) by carbonizing a two-dimensional oxide or sulfide precursor synthesized in advance; the method has a certain application prospect, but the method is low in cost, high in efficiency and capable of preparing the two-dimensional MoO in a large scale₃Or MoS₂And two-dimensional WO₃Or WS₂The precursor is still a challengeTitle to be obtained; 3) chemical vapor deposition method, which comprises depositing and growing Mo and W-based two-dimensional carbide (or two-dimensional nitride) by selecting proper substrate; the method has low yield, extremely high temperature and high cost; 4) molten salt assisted exfoliation, e.g. the document "Chang H Q, Zhang G H, Chou K C₂C)via Na₂CO₃-Assited carbothermal reduction of 2H–MoS₂[J]Materials Chemistry and Physics,2020,244:122713 ", will bulk MoS₂Powder and Na₂CO₃And mixing the activated carbon according to a certain proportion, calcining in an argon atmosphere, and washing off a molten salt reaction byproduct to prepare the two-dimensional molybdenum carbide. The prepared two-dimensional molybdenum carbide utilizes activated carbon as a carbon source, so that more activated carbon is difficult to remove, and the prepared two-dimensional molybdenum carbide is easy to accumulate; such as the document "Sun G D, Chang H Q, Zhang G H, et al.A low-cost and effective path for preparation of 2D MoN nanosheets via Na₂CO₃-assisted nitridation of MoS₂ with NH₃[J]Journal of the American Ceramic Society, 2019, 102(12):7178-₂[J]In Ceramics International 2020,46(3):4024-₂Taking powder as precursor and CaO and Na₂CO₃Grinding and mixing the salt uniformly in NH₃Calcining in the atmosphere, using molten salt as an auxiliary agent, and then cleaning off by-products to obtain two-dimensional molybdenum nitride; although the method can obtain a large amount of two-dimensional molybdenum nitride product, the two-dimensional molybdenum nitride product is easy to be aggregated into a spherical shape and is not easy to be dispersed, and NH is utilized₃As a nitrogen source, an additional ammonia gas absorption device is needed, the synthesis cost is increased, and the large-scale preparation is difficult. In addition, the synthesis method has no report of W-based two-dimensional carbide (or two-dimensional nitride) nanosheets. Comparative MoS₂The tungsten-based sulfide has higher melting point and stable chemical property, and further increases the difficulty of preparing the two-dimensional carbide (nitride) of the tungsten-based sulfide.

Therefore, the method further explores the preparation process of the Mo and W-based two-dimensional carbide or two-dimensional nitride material with high efficiency, low cost and simple and convenient operation, and has important research and application significance.

Disclosure of Invention

The invention mainly aims to provide a method for preparing a two-dimensional transition metal compound nanosheet by using bulk phase layered transition metal sulfide, wherein urea is used as an auxiliary stripping agent and a carbon source (or nitrogen source) to realize efficient selective conversion from a layered transition metal sulfide object phase material to a two-dimensional nitride nanosheet (or a two-dimensional carbide nanosheet); and the preparation method is simple, convenient to operate and suitable for industrial popularization and application.

In order to achieve the purpose, the invention adopts the technical scheme that:

a method for preparing a two-dimensional transition metal compound nanosheet using a bulk layered (micron-sized) transition metal sulfide, comprising the steps of:

1) grinding and uniformly mixing bulk phase layered transition metal sulfide particles and sodium carbonate; then adding urea, grinding for the second time and mixing uniformly;

2) heating the mixture obtained in the step 1) in an auxiliary atmosphere to perform heat preservation reaction, and cooling;

3) and (3) carrying out acid washing on the reaction product obtained in the step 2), washing with water to be neutral, filtering and drying to obtain the two-dimensional transition metal compound nanosheet.

In the above scheme, the transition metal is molybdenum or tungsten; the bulk lamellar transition metal sulfide is bulk phase molybdenum disulfide or tungsten disulfide.

In the scheme, the block molybdenum disulfide can be selected from commercially available molybdenum disulfide powder or molybdenite concentrate powder; the bulk tungsten disulfide can be selected from commercially available tungsten disulfide powder and the like, and the size of the bulk tungsten disulfide is 500nm-100 mu m.

In the above aspect, the transition metal compound is a transition metal nitride or a transition metal carbide.

In the above scheme, the auxiliary atmosphere is an inert atmosphere or a hydrogen-containing atmosphere; wherein, inert atmosphere is adopted to obtain a two-dimensional transition metal nitride product, and auxiliary atmosphere containing hydrogen is adopted to obtain a two-dimensional transition metal carbide product; the selective preparation of two-dimensional transition metal nitride products and carbide products is realized by adjusting the reaction atmosphere.

In the above scheme, the inert atmosphere may be argon or nitrogen.

Preferably, in the auxiliary atmosphere containing hydrogen, the volume percentage of hydrogen is 3-80%; the auxiliary atmosphere other than hydrogen is argon, nitrogen, or the like.

Preferably, when the bulk phase layered transition metal sulfide is blocky molybdenum disulfide, the molar ratio of the molybdenum disulfide to the sodium carbonate is 1 (2.0-6.0); the molar ratio of the urea to the molybdenum disulfide is (15-50): 1.

Preferably, when the bulk phase layered transition metal sulfide is blocky tungsten disulfide, the molar ratio of the tungsten disulfide to the sodium carbonate is 1 (3.0-6.5); the molar ratio of the urea to the tungsten disulfide is (10-100): 1.

Preferably, when the bulk layered transition metal sulfide is bulk molybdenum disulfide, the temperature of the heat preservation reaction in the step 2) is 600-950 ℃, and the heat preservation time is 1-5 h.

Preferably, when the bulk layered transition metal sulfide is bulk tungsten disulfide, the temperature of the heat preservation reaction in the step 2) is 700-950 ℃, and the heat preservation time is 2-8 h.

In the scheme, the heating rate adopted in the step 2) is 1-15 ℃/min.

In the scheme, HCl and H are adopted in the acid washing step₂SO₄One or more of acetic acid and formic acid, and when the block lamellar transition metal sulfide is selected from block molybdenum disulfide, the concentration of the adopted acid solution is 0.5-5 mol/L; when the blocky layered transition metal sulfide is blocky tungsten disulfide, the adopted acid solution is 0.5-6 mol/L.

In the above scheme, the drying step may adopt a freeze-drying means.

The principle of the invention is as follows:

the invention adopts Na₂CO₃The low-cost urea is used as an auxiliary stripping agent and a carbon source (or a nitrogen source) to realize phase lamination for molten saltThe method comprises the following steps of efficiently converting transition metal sulfide into two-dimensional transition metal compound nanosheets, and simultaneously realizing selective preparation of two-dimensional carbide and two-dimensional nitride by regulating and controlling molten salt reaction time and reaction atmosphere: under the auxiliary atmosphere of argon or nitrogen, the decomposition product NH of urea₃The catalyst can preferentially participate in a nitridation reaction to further obtain a nitride product, and the activity of carbon-containing gas of a urea decomposition product can be improved and participate in the reaction under the hydrogen-assisted atmosphere, so that the carbide forming temperature is reduced, and further a two-dimensional carbide product is obtained; further, during the heating, Na₂CO₃And bulk MoS₂Form a low eutectic molten salt, Na₂CO₃In situ decomposition into sodium oxide and CO₂Gas, make molybdenum sulfide or tungsten sulfide slice layer swell and strip; urea enters the interlayer of bulk molybdenum sulfide or tungsten sulfide together in the high-temperature heating process, the molybdenum sulfide or tungsten sulfide is converted into two-dimensional carbide (or two-dimensional nitride) in situ, and on the other hand, a large amount of gas (CO and NH) is generated by in-situ decomposition₃、CO₂Etc.) preventing the nanosheets from agglomerating and stacking; and finally, removing by-product salt by acid washing to obtain the two-dimensional carbide nanosheet or two-dimensional nitride nanosheet with good dispersibility.

According to the invention, urea is used as a carbon source (or a nitrogen source) and an auxiliary stripping agent simultaneously, the obtained two-dimensional carbide or nitride has good dispersibility, and the synthesized two-dimensional carbide or nitride has high crystallinity and high purity; and the related synthesis process is simple, the production efficiency is high, and the large-scale preparation in batches is facilitated.

Compared with the prior art, the invention has the beneficial effects that:

1) the invention provides a low cost, commercial molybdenite concentrate (MoS)₂) Bulk phase powder is used as a raw material, easily-decomposable alkaline salt is used as an auxiliary agent, and a two-dimensional Mo-based nanosheet is not needed as a precursor, so that the cost is low; low cost, commercial WS₂Bulk phase powder is used as a raw material, a tungsten-based compound nanosheet prepared by a molten salt auxiliary method is provided for the first time, the preparation process is simple, and the cost is low;

2) the urea is selectively used as a nitrogen source or a carbon source for the first time, so that the toxic ammonia gas is prevented from being introduced for a long time or the activated carbon is prevented from being introduced, and the synthesis cost is effectively reduced; the introduced urea can synchronously play the role of an auxiliary stripping agent in the heating reaction process, the urea and sodium oxide cooperatively promote the generation of two-dimensional nitrides or carbides, and the intermediate product sodium sulfide is embedded between nanosheet layers, so that the two-dimensional carbides or nitride nanosheets with good dispersibility and relatively uniform size and morphology are obtained;

3) the selective preparation of two-dimensional nitride or two-dimensional carbide can be realized by regulating and controlling the reaction atmosphere;

4) the related synthesis process is simple, the production efficiency is high, and the byproduct salt is easy to remove after the reaction, so that the method is a green and easily-industrialized two-dimensional material preparation process route;

5) the two-dimensional nitride or two-dimensional carbide obtained by the invention has the advantages of less defects, easy dispersion, high purity, high crystallinity, lower synthesis cost and environmental friendliness, and can provide a new thought for low-cost and batch preparation of the two-dimensional nitride or two-dimensional carbide.

Drawings

FIG. 1 shows a commercial MoS phase used in example 1 of the present invention₂XRD pattern of the powder;

FIG. 2 shows a commercial MoS phase used in example 1 of the present invention₂Scanning electron microscope topography of the powder;

FIG. 3 is an XRD pattern of a two-dimensional molybdenum nitride nanosheet prepared in example 1 of the present invention;

FIG. 4 is a topography of a two-dimensional molybdenum nitride nanosheet prepared in example 1 of the present invention under (a)40000x and (b)80000x magnification conditions;

fig. 5 is (a) a topography 80000x and (b) an XRD pattern of a two-dimensional molybdenum nitride nanosheet prepared in example 2 of the present invention;

FIG. 6 is a comparative XRD pattern of the products obtained in example 1 of the present invention and comparative examples 1 and 2;

FIG. 7 is a scanning electron micrograph of a product obtained in comparative example 3 of the present invention;

fig. 8 is (a) a topography 80000x and (b) an XRD pattern of a two-dimensional molybdenum nitride nanosheet prepared in example 3 of the present invention;

fig. 9 is an XRD pattern of a two-dimensional molybdenum carbide nanosheet prepared in example 4 of the present invention;

fig. 10 is a topography of two-dimensional molybdenum carbide nanosheets prepared according to example 4 of the present invention under (a)40000x and (b)80000x magnification conditions;

FIG. 11 is an XRD pattern of the product of comparative example 4 of the present invention;

FIG. 12 is a two-dimensional molybdenum carbide XRD pattern obtained from example 5 of the present invention;

fig. 13 is (a) a topography 80000x and (b) an XRD pattern of a prepared two-dimensional molybdenum carbide nanosheet prepared in example 6 of the present invention;

fig. 14 is an XRD pattern of a two-dimensional molybdenum carbide nanosheet prepared in example 7 of the present invention;

fig. 15 is (a) a morphology map 80000x and (b) an XRD pattern of a prepared two-dimensional molybdenum carbide nanosheet prepared in example 8 of the present invention.

FIG. 16 shows commercially available bulk WS that was used in example 9 of the present invention₂XRD pattern of the powder;

FIG. 17 shows commercially available bulk WS that was used in example 9 of the present invention₂A scanning electron microscope topography of the powder under (a)10000x and (b)100000x magnification conditions;

FIG. 18 is a two-dimensional tungsten nitride XRD pattern obtained from preparation of example 9 of the present invention;

FIG. 19 is a two-dimensional tungsten nitride nanosheet topography prepared according to example 9 of the present invention;

FIG. 20 is an XRD pattern of a sample prepared according to comparative example 5 of the present invention;

FIG. 21 is an XRD pattern of a sample prepared according to comparative example 6 of the present invention;

FIG. 22 is a topographical view of a sample prepared in comparative example 7 of the present invention;

FIG. 23 is a two-dimensional tungsten nitride XRD pattern obtained from preparation of example 10 in accordance with the invention;

FIG. 24 is a two-dimensional tungsten carbide XRD pattern obtained from preparation of example 11 in accordance with the invention;

FIG. 25 is a two-dimensional tungsten carbide nanosheet topography prepared according to example 11 of the present invention;

fig. 26 shows (a) a morphology pattern and (b) an XRD pattern of a two-dimensional tungsten carbide nanosheet prepared according to example 12 of the present invention;

FIG. 27 is a two-dimensional tungsten carbide nanosheet topography prepared according to example 13 of the present invention;

figure 28 is a two-dimensional tungsten carbide XRD pattern obtained from example 14 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In the following examples, the bulk molybdenum disulfide used is commercial molybdenite concentrate powder, the size of which is 0.5-100 μm; the adopted block tungsten disulfide is commercially available tungsten disulfide powder, and the size of the tungsten disulfide powder is 0.5-50 mu m.

Example 1

A method for preparing a two-dimensional molybdenum nitride nanosheet by using bulk molybdenum disulfide comprises the following steps:

1) mixing commercial molybdenite concentrate (MoS)₂) Weighing the powder and anhydrous sodium carbonate according to the molar ratio of 1:2, and then fully and uniformly grinding the powder and the anhydrous sodium carbonate in a mortar; then weighing urea according to the requirement that the molar ratio of the urea to the molybdenum disulfide is 25:1, adding the urea, further grinding and uniformly mixing, and transferring the mixture into a crucible;

2) putting the crucible in the step 1) into a tube furnace, heating to 700 ℃ at a heating rate of 5 ℃/min under the protective atmosphere of argon, preserving heat for 3h, and cooling to room temperature;

3) adding the reaction product obtained in the step 2) into 1M HCl solution, washing and stirring for 2h, then repeatedly washing with deionized water until the pH value is 7, performing suction filtration, and finally performing vacuum drying for 12h to obtain the two-dimensional molybdenum nitride nanosheet with good dispersibility.

In this example, MoS was used₂Bulk phase powder is commercial molybdenite concentrate (MoS)₂) The XRD pattern and the micro-topography pattern of the powder are respectively shown in figure 1 and figure 2; the results show that commercial molybdenite concentrate (MoS) was used₂) Diffraction peak of powder and standard card MoS₂The positions of the diffraction peaks of PDF #37-1492 are basically consistent, which indicates that the purity is higher; the characterization results of the low-magnification and high-magnification scanning electron microscope in FIG. 2 show thatCommercial molybdenite concentrate (MoS)₂) The powder has larger size and good layered structure.

The product obtained in the example was subjected to X-ray diffraction analysis, and the results are shown in FIG. 3, which shows that the diffraction peak position of the product obtained is substantially consistent with that of MoN PDF #89-5024 standard card, and no other redundant diffraction peaks exist, thus demonstrating that MoS can be obtained by adopting the above-mentioned scheme of the present invention₂Completely converted to two-dimensional MoN.

FIG. 4 is a scanning electron micrograph of the product obtained in this example, which shows that the bulk MoS is obtained by the method of the present invention₂The obtained MoN nano-sheet basically has no overlapping and good dispersibility, the thickness of the nano-sheet is thin, and the size of the nano-sheet is basically about 1-2 μm.

Example 2

A method for preparing a two-dimensional molybdenum nitride nanosheet by using bulk molybdenum disulfide comprises the following steps:

1) mixing commercial molybdenite concentrate (MoS)₂) Weighing the powder and anhydrous sodium carbonate according to the molar ratio of 1:2, and then fully and uniformly grinding the powder and the anhydrous sodium carbonate in a mortar; then weighing urea according to the requirement that the molar ratio of the urea to the molybdenum disulfide is 15:1, adding the urea, further grinding and uniformly mixing, and transferring the mixture into a crucible;

2) putting the crucible in the step 1) into a tube furnace, heating to 700 ℃ at a heating rate of 5 ℃/min under the protective atmosphere of argon, preserving heat for 3h, and cooling to room temperature;

3) adding the reaction product obtained in the step 2) into 1M HCl solution, washing and stirring for 2h, then repeatedly washing with deionized water until the pH value is 7, performing suction filtration, and finally performing vacuum drying for 12h to obtain the two-dimensional molybdenum nitride nanosheet with good dispersibility.

FIG. 5 is an SEM topography and XRD pattern for example 1 under otherwise unchanged conditions but with the urea to molybdenum disulfide powder molar ratio decreasing from 25:1 to 15:1, showing that: the two-dimensional nanosheet with the phase of MoN can be obtained by properly reducing the proportion of urea.

Comparative example 1

A method for preparing a two-dimensional molybdenum nitride nanosheet by using bulk molybdenum disulfide is substantially the same as that in embodiment 1, except that: commercial molybdenite concentrate (MoS)₂) Powder and anhydrous sodium carbonateThe molar ratio is 1: 1.

Comparative example 2

A method for preparing a two-dimensional molybdenum nitride nanosheet by using molybdenum disulfide is substantially the same as that in example 1, except that: in the step 1), the commercial molybdenite concentrate (MoS) is directly added without adding anhydrous sodium carbonate₂) The powder and urea were placed in a mortar at a molar ratio of 1:25 and ground thoroughly and homogeneously and transferred to a crucible (commercially available MoS)₂The mol ratio of the powder to the anhydrous sodium carbonate is 1: 0).

Comparative example 3

A method for preparing a two-dimensional molybdenum nitride nanosheet by using bulk molybdenum disulfide is substantially the same as that in embodiment 1, except that: the urea consumption is molybdenite concentrate (MoS)₂) The mol ratio of the powder to the urea is 1: 10.

Fig. 6 is a XRD comparison of the products obtained in example 1 and comparative examples 1 and 2, showing that: no Na₂CO₃When salt-assisted, urea is essentially unable to nitridize MoS₂The resulting product substantially retains MoS₂The phase of (a); when the 1:1 ratio requirement is adopted, part of MoS is still present₂Not completely converted into MoN; when Na is present₂CO₃Increasing to 1:2, the resulting product was substantially converted to MoN.

FIG. 7 is a scanning electron micrograph of the product obtained in comparative example 3, showing that the urea content and MoS are the same₂When the molar ratio of the powder is reduced to 10:1, the obtained reaction product cannot keep a good nanosheet shape, which shows that the content of urea adopted by the invention can slow down the MoS (sodium oxide) by virtue of sodium oxide₂The corrosion and synchronization of the molybdenum nitride and the molybdenum nitride can play a role of an auxiliary stripping agent and maintain the 2D appearance of the molybdenum nitride.

Example 3

A method for preparing a two-dimensional molybdenum nitride nanosheet by using bulk molybdenum disulfide comprises the following steps:

1) mixing commercial molybdenite concentrate (MoS)₂) Weighing the powder and anhydrous sodium carbonate according to the molar ratio of 1:3, and then fully and uniformly grinding the powder and the anhydrous sodium carbonate in a mortar; then weighing urea according to the requirement that the molar ratio of the urea to the molybdenum disulfide is 25:1, adding the urea, further grinding and uniformly mixing, and transferring the mixture into a crucible;

2) putting the crucible in the step 1) into a tube furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under the protective atmosphere of argon, preserving heat for 3h, and cooling to room temperature;

3) adding the reaction product obtained in the step 2) into 1M HCl solution, washing and stirring for 2h, then repeatedly washing with deionized water until the pH value is 7, performing suction filtration, and finally performing vacuum drying for 12h to obtain the two-dimensional molybdenum nitride nanosheet with good dispersibility.

FIG. 8 is a schematic representation of example 1A commercial MoS₂And (3) when the molar ratio of the powder to the anhydrous sodium carbonate is increased to 1:3 and the temperature is increased to 800 ℃, an SEM morphology graph and an XRD graph show that the morphology and the phase of the MoN nanosheet still remain.

Example 4

A method for preparing a two-dimensional molybdenum carbide nanosheet by using bulk molybdenum disulfide comprises the following steps:

1) mixing commercial molybdenite concentrate (MoS)₂) Weighing the powder and anhydrous sodium carbonate according to the molar ratio of 1:3, and then fully and uniformly grinding the powder and the anhydrous sodium carbonate in a mortar; then weighing urea according to the requirement that the molar ratio of the urea to the molybdenum disulfide is 25:1, adding the urea, further grinding and uniformly mixing, and transferring the mixture into a crucible;

2) putting the crucible in the step 1) into a tube furnace, heating to 700 ℃ at a heating rate of 5 ℃/min under the atmosphere of mixed gas of 93 vol% argon and 7 vol% hydrogen for heat preservation reaction for 3h, and cooling to room temperature;

3) adding the reaction product obtained in the step 2) into 1M HCl solution, washing and stirring for 2h, then repeatedly washing with deionized water until the pH value is 7, performing suction filtration, and finally performing vacuum drying for 12h to obtain the two-dimensional molybdenum carbide nanosheet with good dispersibility.

The product obtained in the example is subjected to X-ray diffraction analysis, and the result is shown in figure 9, and the result shows that the diffraction peak position of the obtained product is basically consistent with that of MoC PDF #65-6664 of a standard card and has no MoS₂Diffraction peaks indicating that MoS can be converted using the above protocol of the present invention₂Complete conversion to two-dimensional MoC.

FIG. 10 is a scanning electron micrograph of the product obtained in this example, which shows that the bulk MoS is obtained by the above method of the present invention₂The obtained molybdenum carbide nanosheet is basically non-overlapped and has good dispersibility, and the size of the nanosheet are smallThe particle size is about 1-2 μm.

Comparative example 4

A method for preparing a two-dimensional molybdenum carbide nanosheet by using bulk molybdenum disulfide is substantially the same as that in embodiment 4, except that: the reaction temperature adopted in step 2) was 550 ℃.

The XRD pattern of the product obtained in this comparative example is shown in FIG. 11, which shows that a large amount of MoS still remains under the reaction condition of 550 deg.C₂Not converted to MoC.

Example 5

A method for preparing a two-dimensional molybdenum carbide nanosheet by using bulk molybdenum disulfide comprises the following steps:

1) mixing commercial molybdenite concentrate (MoS)₂) Weighing the powder and anhydrous sodium carbonate according to the molar ratio of 1:3, and then fully and uniformly grinding the powder and the anhydrous sodium carbonate in a mortar; then weighing urea according to the requirement that the molar ratio of the urea to the molybdenum disulfide is 25:1, adding the urea, further grinding and uniformly mixing, and transferring the mixture into a crucible;

2) putting the crucible in the step 1) into a tube furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under the atmosphere of mixed gas of 93 vol% argon and 7 vol% hydrogen for heat preservation reaction for 3h, and cooling to room temperature;

3) adding the reaction product obtained in the step 2) into 1M HCl solution, washing and stirring for 2h, then repeatedly washing with deionized water until the pH value is 7, performing suction filtration, and finally performing vacuum drying for 12h to obtain the two-dimensional molybdenum carbide nanosheet with good dispersibility.

The XRD pattern of the product obtained in this example is shown in FIG. 12, which shows that the product obtained in this example is pure phase MoC, and no other transformation of the MoC phase occurs when the reaction temperature reaches 800 ℃.

Example 6

A method for preparing a two-dimensional molybdenum carbide nanosheet by using bulk molybdenum disulfide comprises the following steps:

1) mixing commercial molybdenite concentrate (MoS)₂) Weighing the powder and anhydrous sodium carbonate according to the molar ratio of 1:2, and then fully and uniformly grinding the powder and the anhydrous sodium carbonate in a mortar; then weighing urea according to the requirement that the molar ratio of the urea to the molybdenum disulfide is 25:1, adding the urea, further grinding and uniformly mixing, and transferring the mixture into a crucible;

2) putting the crucible in the step 1) into a tubular furnace, heating to 950 ℃ at a heating rate of 5 ℃/min under the atmosphere of mixed gas of 93 vol% argon and 7 vol% hydrogen for heat preservation reaction for 3h, and cooling to room temperature;

3) adding the reaction product obtained in the step 2) into 1M HCl solution, washing and stirring for 2h, then repeatedly washing with deionized water until the pH value is 7, performing suction filtration, and finally performing vacuum drying for 12h to obtain the two-dimensional molybdenum carbide nanosheet with good dispersibility.

The morphology and XRD pattern of the product obtained in this example are shown in FIG. 13(950 ℃ corresponding curve), and the result shows that the product obtained in this example is also pure-phase MoC, and when the reaction temperature reaches 950 ℃, the phase of MoC does not undergo other transformations, and the morphology of the nanosheet does not change much.

Example 7

A method for preparing a two-dimensional molybdenum carbide nanosheet by using bulk molybdenum disulfide comprises the following steps:

1) mixing commercial molybdenite concentrate (MoS)₂) Weighing the powder and anhydrous sodium carbonate according to the molar ratio of 1:3, and then fully and uniformly grinding the powder and the anhydrous sodium carbonate in a mortar; then weighing urea according to the requirement that the molar ratio of the urea to the molybdenum disulfide is 50:1, adding the urea, further grinding and uniformly mixing, and transferring the mixture into a crucible;

2) placing the crucible in the step 1) into a tubular furnace, heating to 700 ℃ at a heating rate of 5 ℃/min under an atmosphere of a mixed gas of 20 vol% argon and 80 vol% hydrogen (argon-hydrogen mixed gas is always introduced in the reaction process, and the flow is controlled to be 5Sccm), carrying out heat preservation reaction for 3h, and cooling to room temperature;

3) adding the reaction product obtained in the step 2) into 1M HCl solution, washing and stirring for 2h, then repeatedly washing with deionized water until the pH value is 7, performing suction filtration, and finally performing vacuum drying for 12h to obtain the two-dimensional molybdenum carbide nanosheet with good dispersibility.

The XRD patterns of the products obtained in this example are shown in FIG. 14, which shows that the products obtained in this example are also pure phase MoC, indicating that no other transformation of the MoC phase occurs when the urea proportion and the volume concentration of hydrogen are increased.

Example 8

A method for preparing a two-dimensional molybdenum carbide nanosheet by using bulk molybdenum disulfide comprises the following steps:

1) mixing commercial molybdenite concentrate (MoS)₂) Weighing the powder and anhydrous sodium carbonate according to the molar ratio of 1:6, and then fully and uniformly grinding the powder and the anhydrous sodium carbonate in a mortar; then weighing urea according to the requirement that the molar ratio of the urea to the molybdenum disulfide is 50:1, adding the urea, further grinding and uniformly mixing, and transferring the mixture into a crucible;

2) putting the crucible in the step 1) into a tubular furnace, heating to 600 ℃ at a heating rate of 5 ℃/min under the atmosphere of mixed gas of 93 vol% argon and 7 vol% hydrogen for heat preservation reaction for 3h, and cooling to room temperature;

3) adding the reaction product obtained in the step 2) into 1M HCl solution, washing and stirring for 2h, then repeatedly washing with deionized water until the pH value is 7, performing suction filtration, and finally performing vacuum drying for 12h to obtain the two-dimensional molybdenum carbide nanosheet with good dispersibility.

The morphology and XRD pattern of the product obtained in this example are shown in FIG. 15, and the result shows that the product obtained in this example is also pure-phase MoC, and when the molar ratio of sodium carbonate to molybdenum sulfide is increased from 1:3 to 1:6, the reaction temperature is reduced to 600 ℃, the MoC phase is not subjected to other transformation, and the morphology of the nanosheet is not greatly changed.

Example 9

A method for preparing a two-dimensional tungsten nitride nanosheet by using bulk tungsten disulfide comprises the following steps:

1) will market WS₂Weighing the powder and anhydrous sodium carbonate according to the molar ratio of 1:3.5, and then fully and uniformly grinding the powder in a mortar; then weighing urea according to the requirement that the molar ratio of the urea to the tungsten disulfide is 50:1, adding the urea, further grinding and uniformly mixing, and transferring the mixture into a crucible;

2) putting the crucible in the step 1) into a tube furnace, heating to 750 ℃ at a heating rate of 5 ℃/min under the protective atmosphere of argon, preserving heat for 3h, and cooling to room temperature;

3) adding the reaction product obtained in the step 2) into 1M HCl solution, washing and stirring for 2h, then repeatedly washing with deionized water until the pH value is 7, performing suction filtration, and finally performing vacuum drying for 12h to obtain the two-dimensional tungsten nitride nanosheet with good dispersibility.

In this embodiment, WS is used₂Bulk phase powder is commercially available WS₂Powder, its XRD pattern andthe micro-topography is shown in fig. 16 and 17, respectively; the results show the commercial WS employed₂Diffraction peak of powder and standard card WS₂The positions of the diffraction peaks of PDF #84-1398 are basically consistent, which shows that the purity is higher; FIG. 17 shows the low power and high power scanning electron microscopy characterization of the commercially available WS₂The powder has larger size and good layered structure.

The product obtained in this example was subjected to X-ray diffraction analysis, and the results are shown in FIG. 18, which shows that the diffraction peak position of the product obtained is substantially consistent with WN PDF #89-4754 of the standard card, and no other redundant diffraction peaks exist, indicating that the solution of the present invention can be used to separate WS in bulk phase₂Completely translated into two dimensions WN.

FIG. 19 is a scanning electron microscope image of the product obtained in the present embodiment, which shows that WN prepared by using urea-assisted sodium carbonate molten salt basically maintains a relatively uniform two-dimensional nanosheet structure, the nanosheets are relatively thin, and the size of each nanosheet is approximately 200-500 nm.

Comparative example 5

A method for preparing a two-dimensional tungsten nitride nanosheet by using bulk tungsten disulfide is substantially the same as that in embodiment 9, except that: the reaction temperature adopted in the step 2) is 650 ℃.

The XRD pattern of the product obtained in this comparative example is shown in FIG. 20, and it can be seen that there is a large amount of WS when the reaction temperature of 650 ℃ is used₂Not converted to WN; when the reaction temperature reached 750 ℃, the WN pure phase had been completely transformed.

Comparative example 6

A method for preparing a two-dimensional tungsten nitride nanosheet by using bulk tungsten disulfide is substantially the same as that in embodiment 9, except that: commercially available WS₂The molar ratio of the powder to the anhydrous sodium carbonate is 1: 2.5.

The XRD pattern of the product obtained in this comparative example is shown in FIG. 21, when WS is commercially available₂When the molar ratio of the powder to the anhydrous sodium carbonate is 1:2.5, part of WS still remains₂Not completely converted to WN.

Comparative example 7

Method for preparing two-dimensional tungsten nitride nanosheet by using block tungsten disulfide, and preparation method and application thereofExample 9 is the same except that: commercially available WS₂The molar ratio of the powder to the urea is 1: 5.

The product obtained in this comparative example has a morphology as shown in FIG. 22, when WS is commercially available₂When the molar ratio of the powder to the urea is 1:5, only a part of WN nanosheets are generated.

Example 10

A method for preparing a two-dimensional tungsten nitride nanosheet by using bulk tungsten disulfide comprises the following steps:

1) will market WS₂Weighing the powder and anhydrous sodium carbonate according to the molar ratio of 1:3.5, and then fully and uniformly grinding the powder in a mortar; then weighing urea according to the requirement that the molar ratio of the urea to the tungsten disulfide is 10:1, adding the urea, further grinding and uniformly mixing, and transferring the mixture into a crucible;

2) putting the crucible in the step 1) into a tube furnace, heating to 750 ℃ at a heating rate of 5 ℃/min under the protective atmosphere of argon, preserving heat for 3h, and cooling to room temperature;

3) adding the reaction product obtained in the step 2) into a 1M HCl solution, washing and stirring for 2h to remove the intermediate by-product Na₂And S, repeatedly washing with deionized water until the pH value is 7, performing suction filtration, and finally performing vacuum drying for 12 hours to obtain the two-dimensional tungsten nitride nanosheet with good dispersibility.

The XRD pattern of the product obtained in this example is shown in FIG. 23, which shows that: when the molar ratio of the urea to the tungsten disulfide powder is reduced to 10:1, the WN phase is not changed at all.

Example 11

A method for preparing a two-dimensional tungsten carbide nanosheet by using bulk tungsten disulfide comprises the following steps:

1) will market WS₂Weighing the powder and anhydrous sodium carbonate according to the molar ratio of 1:3.5, and then fully and uniformly grinding the powder in a mortar; then weighing urea according to the requirement that the molar ratio of the urea to the tungsten disulfide is 50:1, adding the urea, further grinding and uniformly mixing, and transferring the mixture into a crucible;

2) putting the crucible in the step 1) into a tubular furnace, heating to 750 ℃ at a heating rate of 5 ℃/min for 3h under an argon-hydrogen mixed gas atmosphere (wherein the hydrogen accounts for 7% by volume, the argon-hydrogen mixed gas is always introduced in the reaction process, and the flow is controlled to be 300Sccm), and cooling to room temperature;

3) adding the reaction product obtained in the step 2) into a 1M HCl solution, washing and stirring for 2h to remove the intermediate by-product Na₂And S, repeatedly washing with deionized water until the pH value is 7, performing suction filtration, and finally performing vacuum drying for 12 hours to obtain the two-dimensional tungsten carbide nanosheet with good dispersibility.

The XRD pattern of the product obtained in this example is shown in FIG. 24, which shows that: introducing argon-hydrogen atmosphere, using urea as carbon source, and making WS in bulk phase₂The product is basically consistent with standard card WC PDF #65-4539 in diffraction peak position and has no WS₂Diffraction peak, description of WS₂WC has been entirely transformed.

The scanning electron micrograph of the product obtained in this example is shown in FIG. 25, and the result shows that: slave volume phase WS₂The size of the obtained WC nano-sheet is basically about 500nm, and the appearance is similar to that of the WN nano-sheet.

Example 12

A method for preparing a two-dimensional tungsten carbide nanosheet by using bulk tungsten disulfide comprises the following steps:

1) will market WS₂Weighing the powder and anhydrous sodium carbonate according to the molar ratio of 1:3.0, and then fully and uniformly grinding the powder in a mortar; then weighing urea according to the requirement that the molar ratio of the urea to the tungsten disulfide is 50:1, adding the urea, further grinding and uniformly mixing, and transferring the mixture into a crucible;

2) putting the crucible in the step 1) into a tubular furnace, heating to 950 ℃ at a heating rate of 5 ℃/min for heat preservation for 3h under an argon-hydrogen mixed gas atmosphere (wherein the hydrogen accounts for 7% by volume, the argon-hydrogen mixed gas is always introduced in the reaction process, and the flow is controlled to be 300Sccm), and cooling to room temperature;

3) adding the reaction product obtained in the step 2) into a 1M HCl solution, washing and stirring for 2h to remove the intermediate by-product Na₂And S, repeatedly washing with deionized water until the pH value is 7, performing suction filtration, and finally performing vacuum drying for 12 hours to obtain the two-dimensional tungsten carbide nanosheet with good dispersibility.

The scanning electron micrograph and XRD pattern of the product obtained in this example are shown in FIG. 26, and the results show that: as commercially available WS₂The molar ratio of the powder to the anhydrous sodium carbonate1:3.0, and raising the reaction temperature to 950 ℃, wherein the obtained product still maintains the two-dimensional nanosheet structure and the WC phase of the product is not changed.

Example 13

A method for preparing a two-dimensional tungsten carbide nanosheet by using bulk tungsten disulfide comprises the following steps:

1) will market WS₂Weighing the powder and anhydrous sodium carbonate according to the molar ratio of 1:3.5, and then fully and uniformly grinding the powder in a mortar; then weighing urea according to the requirement that the molar ratio of the urea to the tungsten disulfide is 80:1, adding the urea, further grinding and uniformly mixing, and transferring the mixture into a crucible;

2) putting the crucible in the step 1) into a tubular furnace, heating to 750 ℃ at a heating rate of 5 ℃/min for 3h under an argon-hydrogen mixed gas atmosphere (wherein the hydrogen accounts for 80% by volume, the argon-hydrogen mixed gas is always introduced in the reaction process, and the flow is controlled to be 5Sccm), and cooling to room temperature;

3) adding the reaction product obtained in the step 2) into a 1M HCl solution, washing and stirring for 2h to remove the intermediate by-product Na₂And S, repeatedly washing with deionized water until the pH value is 7, performing suction filtration, and finally performing vacuum drying for 12 hours to obtain the two-dimensional tungsten carbide nanosheet with good dispersibility.

The scanning electron micrograph of the product obtained in this example is shown in FIG. 27, and the result shows that: when the molar ratio of urea content to tungsten disulfide was increased from 50:1 to 80:1 and the hydrogen volume concentration was increased to 80%, the resulting product still maintained a two-dimensional nanosheet structure.

Example 14

A method for preparing a two-dimensional tungsten carbide nanosheet by using bulk tungsten disulfide comprises the following steps:

1) will market WS₂Weighing the powder and anhydrous sodium carbonate according to the molar ratio of 1:6.5, and then fully and uniformly grinding the powder in a mortar; then weighing urea according to the requirement that the molar ratio of the urea to the tungsten disulfide is 80:1, adding the urea, further grinding and uniformly mixing, and transferring the mixture into a crucible;

2) putting the crucible in the step 1) into a tubular furnace, heating to 700 ℃ at a heating rate of 5 ℃/min for heat preservation for 3h under an argon-hydrogen mixed gas atmosphere (wherein the hydrogen accounts for 7% by volume, the argon-hydrogen mixed gas is always introduced in the reaction process, and the flow is controlled to be 300Sccm), and cooling to room temperature;

3) adding the reaction product obtained in the step 2) into a 1M HCl solution, washing and stirring for 2h to remove the intermediate by-product Na₂And S, repeatedly washing with deionized water until the pH value is 7, performing suction filtration, and finally performing vacuum drying for 12 hours to obtain the two-dimensional tungsten carbide nanosheet with good dispersibility.

The XRD pattern of the product obtained in this example is shown in FIG. 28, which shows that: when the molar ratio of the content of the anhydrous sodium carbonate to the tungsten disulfide is increased from 3.5:1 to 6.5:1, and 700 ℃ is adopted as the reaction temperature, the obtained WC product is still pure-phase WC.

The above embodiments are merely examples for clearly illustrating the present invention and do not limit the present invention. Other variants and modifications of the invention, which are obvious to those skilled in the art and can be made on the basis of the above description, are not necessary or exhaustive for all embodiments, and are therefore within the scope of the invention.