阅读说明：本技术 二硫化钼纳米片/氮化碳纳米片/石墨烯三维复合电极催化剂的制备方法 (Preparation method of molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst ) 是由 黄华杰 严敏敏 何海燕 姜全国 于 2019-09-27 设计创作，主要内容包括：本发明提供了一种二硫化钼纳米片/氮化碳纳米片/石墨烯三维复合电极催化剂的制备方法,涉及电极催化剂领域,以氮化碳、氧化石墨烯和二硫化钼通过超声剥离生成二维的单层或少层二硫化钼纳米片、氮化碳纳米片和氧化石墨烯纳米片,再制备二硫化钼纳米片、氮化碳纳米片和氧化石墨烯的混合溶液,严格控制三者之间的添加比例,采用水热反应使得二硫化钼纳米片、氮化碳纳米片和氧化石墨烯相互连结,自下而上组装成三维多孔气凝胶,构筑出具有银耳状的三维多孔自支撑结构,复合催化剂的比表面积大,催化活性位点数量多,循环稳定性好,具有优异的催化性能。(The invention provides a preparation method of a molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst, relates to the field of electrode catalysts, the method comprises the steps of ultrasonically stripping carbon nitride, graphene oxide and molybdenum disulfide to generate a two-dimensional single-layer or few-layer molybdenum disulfide nanosheet, a carbon nitride nanosheet and a graphene oxide nanosheet, preparing a mixed solution of the molybdenum disulfide nanosheet, the carbon nitride nanosheet and the graphene oxide, strictly controlling the addition ratio of the molybdenum disulfide nanosheet, the carbon nitride nanosheet and the graphene oxide, enabling the molybdenum disulfide nanosheet, the carbon nitride nanosheet and the graphene oxide to be mutually connected by adopting a hydrothermal reaction, assembling the molybdenum disulfide nanosheet, the carbon nitride nanosheet and the graphene oxide from bottom to top to form the three-dimensional porous aerogel, and constructing the three-dimensional porous self-supporting structure with the shape of a tremella.)

1. The preparation method of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst is characterized by comprising the following steps of:

s1, preparing a molybdenum disulfide nanosheet dispersion liquid, a carbon nitride nanosheet dispersion liquid and a graphene oxide dispersion liquid;

s2, mixing the molybdenum disulfide nanosheet dispersion liquid, the carbon nitride nanosheet dispersion liquid and the graphene oxide dispersion liquid obtained in the step S1, and uniformly stirring to obtain a molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene oxide ternary complex solution, wherein the addition amount of the molybdenum disulfide nanosheet and the carbon nitride nanosheet is 1-10: 1-10, wherein the addition amount of the binary composite of the graphene oxide and the molybdenum disulfide nanosheet/carbon nitride nanosheet is 1-10: 1-10;

s3, carrying out hydrothermal reaction on the ternary compound solution obtained in the step S2 to obtain a hydrogel-like product, then dialyzing, washing with water, and freeze-drying to obtain the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst.

2. The preparation method of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst according to claim 1, wherein in step S2, the addition amount of the molybdenum disulfide nanosheet and the carbon nitride nanosheet is 1-7: 1-4, wherein the addition amount of the binary composite of the graphene oxide and the molybdenum disulfide nanosheet/carbon nitride nanosheet is 1-4: 1 to 2.

3. The preparation method of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst as claimed in claim 2, wherein in step S2, the added amounts of the molybdenum disulfide nanosheet and the carbon nitride nanosheet are in a mass ratio of 7: 3, the addition amount of the binary composite of the graphene oxide and the molybdenum disulfide nanosheet/carbon nitride nanosheet is 1: 1.

4. the preparation method of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst of claim 1, wherein in step S1, the concentration of the molybdenum disulfide nanosheet dispersion is 0.1-5g/L, the concentration of the carbon nitride nanosheet dispersion is 0.1-5g/L, and the concentration of the graphene oxide dispersion is 0.1-5 g/L.

5. The preparation method of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst as defined in claim 1, wherein in step S2, the stirring conditions are: magnetic stirring at 0-60 deg.C for 10-60 min.

6. The preparation method of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst according to claim 1, wherein in step S3, the hydrothermal reaction conditions are as follows: the reaction time is 2-48h at 100 ℃ and 200 ℃.

7. The method for preparing the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst according to claim 1, wherein in step S3, the dialysis water washing time is 1-10d, and the drying pressure during freeze drying is 10-200 Pa.

8. The preparation method of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst as defined in any one of claims 1 to 7, wherein the preparation of the carbon nitride nanosheet dispersion liquid in step S1 specifically comprises the following steps:

p1, dispersing commercial carbon nitride powder in isopropanol solution, and carrying out ultrasonic treatment for 1-10 h;

p2, centrifuging the obtained dispersion liquid at 3000rpm for 5-60min, removing precipitates to obtain a light yellow dispersion liquid, and drying to obtain carbon nitride nanosheet powder;

and P3, placing the obtained carbon nitride nanosheet powder in 35% concentrated nitric acid to react for 0.1-1h at the temperature of 20-100 ℃, washing the obtained sample with water, drying, and re-dispersing in an aqueous solution to obtain a uniform carbon nitride nanosheet dispersion liquid.

Technical Field

The invention relates to a preparation method of an electrode catalyst, in particular to a preparation method of a molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst.

Background

Hydrogen, as an efficient, clean and environmentally friendly energy source, has attracted more and more scientists' eyes. The electro-catalytic hydrogen production has the advantages of high efficiency, no pollution and wide raw material water source, and is very suitable for the industrial preparation of hydrogen. In the traditional field of electrocatalytic hydrogen production, metal platinum is often used as an electrode catalyst material due to a special electronic structure and high catalytic activity, but the characteristics of high price and easy poisoning of platinum greatly prevent the large-scale commercial application of the platinum. Therefore, it is of great interest to develop new electrode catalysts that are efficient, environmentally friendly and capable of supporting commercial applications.

Molybdenum disulfide (MoS)₂) Is a typical layered transition metal compound, has a layered structure similar to graphite, has good electrocatalytic performance, and is widely used for research in the field of hydrogen evolution catalysis. Carbon nitride (C)₃N₄) The catalyst shows stronger oxidizing ability and photocatalytic organic matter decomposition ability under the irradiation of visible light, and simultaneously enters the field of scientists as a member of hydrogen production catalysts. Compared with the molybdenum disulfide and carbon nitride materials with the traditional block structures, the molybdenum disulfide nanosheets and the carbon nitride nanosheets can expose more active sites, so that the electrocatalytic performance is better. In addition, the molybdenum disulfide nanosheets and the carbon nitride nanosheets are poor in conductivity, and a high-conductivity carbon material is introduced to serve as a base material so as to reduce the charge transfer resistance of the composite catalyst, so that the method is an effective means for improving the electrocatalytic activity of a composite system. As a novel carbon material, graphene has the advantages of large specific surface area, high conductivity, electrochemical stability and the like, and can be used as an ideal conductive additive. Currently, in research hotspots of hydrogen production by electrocatalyst, molybdenum disulfide, graphene, carbon nitride and their modified derivatives are taken as representatives, and many researches are carried out to prepare binary hybrid catalyst by compounding molybdenum disulfide nanosheet or carbon nitride nanosheet with graphene for electrocatalytic hydrogen production (Tan X, Tahini HA, Smith SC, P-doped graphene/graphene carbon carbide n)(iii) upright hybrid electrocatalysts, wherein, irregular charge transfer mechanisms for enhanced hydrogen evolution reaction performance. ACS Catalysis 2016,6, 7071-7077; lee JE, Jung J, Ko TY, et al, catalytic synthesis effect of MoS2/reduced graphene oxide hybrids for a high affinity reaction, RSC Advance 2017,7, 5480-5487). The research on assembling the molybdenum disulfide nanosheet, the carbon nitride nanosheet and the graphene two-dimensional nanostructure into the three-dimensional composite catalyst is rarely reported.

Chinese patent No. CN109174149A discloses a visible light response type MoS₂/GO/g-C₃N₄Ternary composite photocatalytic material and preparation method thereof, wherein GO occupies MoS₂1-7% of total mass of/GO and MoS₂/GO occupies MoS₂/GO/g-C₃N₄The total mass of the ternary composite photocatalytic material is 1-5%, the prepared ternary composite catalyst can be used for photocatalytic degradation of RhB, but the scanning electron microscope image of the ternary composite photocatalyst shows that the ternary composite catalyst is similar to other two-dimensional lamellar materials in structure, GO and g-C₃N₄Large Van der Waals force exists between the sheets, and irreversible agglomeration and stacking phenomena occur in the preparation and use processes of the catalyst, so that partial reactive sites are covered to reduce the catalytic efficiency, and MoS₂The particles are dispersed among the lamella, and are easy to migrate, agglomerate and grow on the surface of the carrier in the using process, further reducing the active surface area of the catalyst and reducing the performance of the catalyst. Therefore, the development of a new preparation method, the reduction of the stacking of all the nanosheets in the composite system and the improvement of the photocatalytic activity of the composite material have important significance.

Disclosure of Invention

In order to solve the defects in the prior art, the invention provides a preparation method of a molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst.

The preparation method of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst comprises the following steps:

s1, preparing a molybdenum disulfide nanosheet dispersion liquid, a carbon nitride nanosheet dispersion liquid and a graphene oxide dispersion liquid;

s2, mixing the molybdenum disulfide nanosheet dispersion liquid, the carbon nitride nanosheet dispersion liquid and the graphene oxide dispersion liquid obtained in the step S1, and uniformly stirring to obtain a molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene oxide ternary complex solution, wherein the addition amount of the molybdenum disulfide nanosheet and the carbon nitride nanosheet is 1-10: 1-10, wherein the addition amount of the binary composite of the graphene oxide and the molybdenum disulfide nanosheet/carbon nitride nanosheet is 1-10: 1-10;

s3, carrying out hydrothermal reaction on the ternary compound solution obtained in the step S2 to obtain a hydrogel-like product, then dialyzing, washing with water, and freeze-drying to obtain the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst.

The invention uses carbon nitride, graphene oxide and molybdenum disulfide to generate two-dimensional single-layer or few-layer molybdenum disulfide nanosheets, carbon nitride nanosheets and graphene oxide nanosheets through ultrasonic stripping, then prepares a mixed solution of the molybdenum disulfide nanosheets, the carbon nitride nanosheets and the graphene oxide, strictly controls the addition ratio of the three, adopts hydrothermal reaction to combine the carbon nitride, the graphene oxide and the molybdenum disulfide, and adopts the hydrothermal reaction to combine the carbon nitride, the graphene oxide and the molybdenum disulfide, and the nanosheets which are arranged in disorder form mutual overlapping and disordered support, namely, the self-supporting nanosheets are used as building elements and are assembled into the three-dimensional porous aerogel from bottom to top, so as to build the three-dimensional self-supporting structure with the silver ear shape, and the gaps among the building elements which are overlapped are mutually communicated to form a microporous network, thereby not only promoting the dispersion among the nanosheets to expose more active sites, but also the external electrolyte can easily, meanwhile, smooth channels are provided for the transmission of electrons and the permeation of electrolyte into the catalyst, so that the active sites are ensured to be fully contacted with a reaction medium; the specific surface area of the catalyst is improved, the service life of a photon-generated carrier is prolonged, photon-generated electrons and holes are rapidly separated, the recombination of the photon-generated electrons and the holes is remarkably inhibited, and the electrocatalytic activity of the three-dimensional catalyst is enhanced.

Further, in step S2, the addition amount of the molybdenum disulfide nanosheet to the carbon nitride nanosheet is 1-7: 1-4, wherein the addition amount of the binary composite of the graphene oxide and the molybdenum disulfide nanosheet/carbon nitride nanosheet is 1-4: 1 to 2.

Further, in step S2, the addition amounts of the molybdenum disulfide nanosheets and the carbon nitride nanosheets are 7: 3, the addition amount of the binary composite of the graphene oxide and the molybdenum disulfide nanosheet/carbon nitride nanosheet is 1: 1.

further, in step S1, the concentration of the molybdenum disulfide nanosheet dispersion is 0.1-5g/L, the concentration of the carbon nitride nanosheet dispersion is 0.1-5g/L, and the concentration of the graphene oxide dispersion is 0.1-5 g/L.

Further, in step S2, the stirring conditions are: magnetic stirring at 0-60 deg.C for 10-60 min.

Further, in step S3, the hydrothermal reaction conditions are: the reaction time is 2-48h at 100 ℃ and 200 ℃.

Further, in step S3, the dialysis water washing time is 1-10d, and the drying pressure during freeze drying is 10-200 Pa.

Further, the step S1 of preparing the carbon nitride nanosheet dispersion specifically includes the steps of:

p1, dispersing commercial carbon nitride powder in isopropanol solution, and carrying out ultrasonic treatment for 1-10 h;

p2, centrifuging the obtained dispersion liquid at 3000rpm for 5-60min, removing precipitates to obtain a light yellow dispersion liquid, and drying to obtain carbon nitride nanosheet powder;

and P3, placing the obtained carbon nitride nanosheet powder in 35% concentrated nitric acid to react for 0.1-1h at the temperature of 20-100 ℃, washing the obtained sample with water, drying, and re-dispersing in an aqueous solution to obtain a uniform carbon nitride nanosheet dispersion liquid.

The invention achieves the following beneficial technical effects:

1. according to the preparation method of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst, the prepared electrode catalyst has a three-dimensional self-supporting structure in the shape of a silver ear, the specific surface area of the catalyst is large, the number of catalytic active sites is large, the circulation stability is good, and the catalytic performance of the composite electrode catalyst is excellent. The molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst prepared by the method has good application prospect and economic benefit in the fields of electrolytic hydrogen production and the like.

2. The two-dimensional nanosheets are assembled to form a three-dimensional structure, so that the problems of stacking and agglomeration among nanosheets are solved, the components tend to be uniformly dispersed in the composite catalyst, active sites can be effectively increased, and the transmission rate of electrons is higher.

3. MoS of the invention₂GO and C₃N₄The preparation method is simple and controllable, has good repeatability, is favorable for large-scale production, and has high practical value.

Drawings

FIG. 1 is a schematic flow diagram of the present invention;

fig. 2 is an X-ray diffraction (XRD) spectrum of a molybdenum disulfide nanosheet, a carbon nitride nanosheet, graphene oxide and a molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst prepared by the method of embodiment 3 of the present invention;

fig. 3 Atomic Force Microscope (AFM) spectra of molybdenum disulfide nanoplates (fig. A, B), carbon nitride nanoplates (fig. C, D), and graphene oxide (fig. E, F) prepared by the method of example 3 of the present invention;

fig. 4 is a field emission scanning electron microscope (FE-SEM) photograph of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst prepared by the method of example 3 (fig. a, fig. B) of the present invention and comparative examples 3, 4 (fig. C, fig. D);

fig. 5 is a Transmission Electron Microscope (TEM) photograph of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst prepared by the method of embodiment 3 of the present invention;

fig. 6 is a nitrogen adsorption and desorption graph of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst prepared by the method of embodiment 3 of the present invention;

fig. 7 shows a molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst (MoS) prepared by the method in embodiment 3 of the present invention₂-C₃N₄(G) and molybdenum disulfide nanosheet (MoS)₂) Carbon nitride nanosheet (C)₃N₄) And a comparison curve chart of linear scanning voltammetry (diagram A) and tafel slope (diagram B) of the reaction of the graphene (G) material on electrocatalytic hydrogen production;

fig. 8 is a cycle performance test chart of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst prepared by the method in embodiment 3 of the present invention.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1, a preparation method of a molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst comprises the following steps:

s1, respectively preparing a molybdenum disulfide nanosheet dispersion liquid, a carbon nitride nanosheet dispersion liquid and a graphene oxide dispersion liquid with the concentration of 0.1-5 g/L.

S2, mixing the molybdenum disulfide nanosheet dispersion liquid, the carbon nitride nanosheet dispersion liquid and the graphene oxide dispersion liquid obtained in the step S1, magnetically stirring for 10-60min at 0-60 ℃, and uniformly mixing to obtain a molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene oxide ternary compound solution; the addition amount of the molybdenum disulfide nanosheet and the carbon nitride nanosheet is 1-10: 1-10, wherein the addition amount of the binary composite of the graphene oxide and the molybdenum disulfide nanosheet/carbon nitride nanosheet is 1-10: 1-10;

s3, placing the ternary complex solution obtained in the step S2 at 100-200 ℃ for hydrothermal reaction for 2-48h to obtain a hydrogel-like product, dialyzing and washing for 1-10d, and freeze-drying under the drying pressure of 10-200Pa to obtain the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst.

The preparation of the carbon nitride nanosheet dispersion liquid in step S1 specifically includes the following steps:

p1, dispersing commercial carbon nitride powder in isopropanol solution, and carrying out ultrasonic treatment for 1-10 h;

p2, centrifuging the obtained dispersion liquid at 3000rpm for 5-60min, removing precipitates to obtain a light yellow dispersion liquid, and drying to obtain carbon nitride nanosheet powder;

and P3, placing the obtained carbon nitride nanosheet powder in 35% concentrated nitric acid to react for 0.1-1h at the temperature of 20-100 ℃, washing the obtained sample with water, drying, and re-dispersing in an aqueous solution to obtain a uniform carbon nitride nanosheet dispersion liquid.

The preparation method of the molybdenum disulfide nanosheet dispersion comprises the following steps: ultrasonically stripping molybdenum disulfide powder in a mixed solution of isopropanol and water at 0-60 ℃ for 0.5-10h to obtain a molybdenum disulfide nanosheet dispersion liquid; the preparation method of the graphene oxide dispersion liquid comprises the following steps: and ultrasonically stripping graphene oxide in water at 0-60 ℃ for 0.5-10h to obtain a graphene oxide dispersion liquid. Since the prior art has reported a lot of reports on the dispersion degree of the molybdenum disulfide nanosheets and the graphene oxide according to the ultrasonic temperature and time, no description is given in the present application, and ultrasonic stripping at 25 ℃ for 5 hours is preferred as the preparation condition of the present application, which is selected in the following embodiments.

Example 1

The preparation method of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst comprises the following steps:

s1, respectively preparing 0.1g/L of molybdenum disulfide nanosheet dispersion liquid, 0.1g/L of carbon nitride nanosheet dispersion liquid and 0.1g/L of graphene oxide dispersion liquid;

s2, mixing the molybdenum disulfide nanosheet dispersion liquid, the carbon nitride nanosheet dispersion liquid and the graphene oxide dispersion liquid obtained in the step S1, magnetically stirring for 10min at 0 ℃, and uniformly mixing to obtain a molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene oxide ternary compound solution; the addition amount of the molybdenum disulfide nanosheet and the carbon nitride nanosheet is 1: 10, the addition amount of the binary composite of the graphene oxide and the molybdenum disulfide nanosheet/carbon nitride nanosheet is 1: 10;

s3, placing the ternary complex solution obtained in the step S2 at 100 ℃ for hydrothermal reaction for 2 hours to obtain a hydrogel-like product, then dialyzing and washing for 1d, carrying out freeze drying at-80 ℃ under the drying pressure of 10Pa to obtain the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst.

The preparation of the carbon nitride nanosheet dispersion liquid in step S1 specifically includes the following steps:

p1, dispersing commercial carbon nitride powder in isopropanol solution, and carrying out ultrasonic treatment for 1 h;

p2, centrifuging the obtained dispersion liquid at 3000rpm for 5min, removing precipitates to obtain a light yellow dispersion liquid, and drying to obtain carbon nitride nanosheet powder;

and P3, placing the obtained carbon nitride nanosheet powder in 35% concentrated nitric acid to react for 0.1h at 20 ℃, washing the obtained sample with water, drying, and re-dispersing in an aqueous solution to obtain a uniform carbon nitride nanosheet dispersion liquid.

Example 2

The preparation method of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst comprises the following steps:

s1, respectively preparing 5g/L of molybdenum disulfide nanosheet dispersion liquid, 5g/L of carbon nitride nanosheet dispersion liquid and 5g/L of graphene oxide dispersion liquid;

s2, mixing the molybdenum disulfide nanosheet dispersion liquid, the carbon nitride nanosheet dispersion liquid and the graphene oxide dispersion liquid obtained in the step S1, magnetically stirring for 25min at 20 ℃, and uniformly mixing to obtain a molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene oxide ternary compound solution; the addition amount of the molybdenum disulfide nanosheet and the carbon nitride nanosheet is 1: 4, the addition amount of the binary composite of the graphene oxide and the molybdenum disulfide nanosheet/carbon nitride nanosheet is 1: 2;

s3, placing the ternary compound solution obtained in the step S2 at 200 ℃ for a hydrothermal reaction time of 48 hours to obtain a hydrogel-like product, then dialyzing and washing for 10 days, carrying out freeze drying at-10 ℃ under a drying pressure of 200Pa to obtain the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst.

The preparation of the carbon nitride nanosheet dispersion liquid in step S1 specifically includes the following steps:

p1, dispersing commercial carbon nitride powder in isopropanol solution, and carrying out ultrasonic treatment for 10 h;

p2, centrifuging the obtained dispersion liquid at 3000rpm for 10min, removing precipitates to obtain a light yellow dispersion liquid, and drying to obtain carbon nitride nanosheet powder;

and P3, placing the obtained carbon nitride nanosheet powder in 35% concentrated nitric acid to react for 0.5h at 70 ℃, washing the obtained sample with water, drying, and re-dispersing in an aqueous solution to obtain a uniform carbon nitride nanosheet dispersion liquid.

Example 3

The preparation method of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst comprises the following steps:

s1, respectively preparing 2g/L of molybdenum disulfide nanosheet dispersion liquid, 3g/L of carbon nitride nanosheet dispersion liquid and 2g/L of graphene oxide dispersion liquid;

s2, mixing the molybdenum disulfide nanosheet dispersion liquid, the carbon nitride nanosheet dispersion liquid and the graphene oxide dispersion liquid obtained in the step S1, magnetically stirring for 60min at 60 ℃, and uniformly mixing to obtain a molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene oxide ternary compound solution; the addition amount of the molybdenum disulfide nanosheet and the carbon nitride nanosheet is 7: 3, the addition amount of the binary composite of the graphene oxide and the molybdenum disulfide nanosheet/carbon nitride nanosheet is 1: 1;

s3, placing the ternary compound solution obtained in the step S2 at 180 ℃ for 24 hours of hydrothermal reaction to obtain a hydrogel-like product, then dialyzing and washing for 3 days, and carrying out freeze drying at-50 ℃ under the drying pressure of 15Pa to obtain the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst.

The preparation of the carbon nitride nanosheet dispersion liquid in step S1 specifically includes the following steps:

p1, dispersing commercial carbon nitride powder in isopropanol solution, and carrying out ultrasonic treatment for 10 h;

p2, centrifuging the obtained dispersion liquid at 3000rpm for 60min, removing precipitates to obtain a light yellow dispersion liquid, and drying to obtain carbon nitride nanosheet powder;

and P3, placing the obtained carbon nitride nanosheet powder in 35% concentrated nitric acid to react for 1h at 100 ℃, washing the obtained sample with water, drying, and dispersing in an aqueous solution again to obtain a uniform carbon nitride nanosheet dispersion liquid.

Example 4

Embodiment 4 differs from embodiment 3 in that, in step S2, the addition amounts of the molybdenum disulfide nanosheets and the carbon nitride nanosheets are 4: 1, the addition amount of the binary composite of the graphene oxide and the molybdenum disulfide nanosheet/carbon nitride nanosheet is 4: 1.

example 5

Embodiment 5 differs from embodiment 3 in that, in step S2, the molybdenum disulfide nanosheets and the carbon nitride nanosheets are added in an amount of 10: 1, the addition amount of the binary composite of the graphene oxide and the molybdenum disulfide nanosheet/carbon nitride nanosheet is 10: 1.

comparative example 1

Comparative example 1 differs from example 3 in that, in step S2, the addition amount of the molybdenum disulfide nanosheets to the carbon nitride nanosheets is 15: 1.

comparative example 2

Comparative example 2 differs from example 3 in that, in step S2, the addition amounts of the molybdenum disulfide nanosheets and the carbon nitride nanosheets are 1: 15.

comparative example 3

The difference between the comparative example 3 and the example 3 is that the addition amount of the graphene oxide and molybdenum disulfide nanosheet/carbon nitride nanosheet binary composite is 15: 1.

comparative example 4

The comparative example 4 is different from the example 3 in that the addition amount of the graphene oxide and molybdenum disulfide nanosheet/carbon nitride nanosheet binary composite is 1: 15.

application case Performance characterization

The molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst prepared by the method of embodiment 3 is taken as an example for performance characterization.

1) X-ray powder diffraction Pattern (XRD)

Fig. 2 is an X-ray powder diffraction pattern, i.e., XRD pattern, of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst prepared by the method of example 3, from which characteristic peaks of molybdenum disulfide and carbon nitride can be clearly seen, which indicates that the composite product contains the two components. In addition, the XRD spectrum does not have the characteristic peak of graphite oxide, but only has one peak at about 25 degrees, indicating that graphite oxide has been reduced to graphene.

2) Microscopic analysis

Fig. 3 is an atomic force microscope image of molybdenum disulfide nanosheets, carbon nitride nanosheets and graphene oxide, from which it can be seen that the molybdenum disulfide, carbon nitride and graphene oxide are in a distinct monolayer or few-layer lamellar structure;

fig. 4A and 4B are field emission scanning electron microscope images of a molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst, wherein fig. 4B is a partially enlarged view of fig. 4A. The catalyst has a very obvious three-dimensional porous network structure, the size of pores is distributed in the range from hundreds of nanometers to tens of micrometers, meanwhile, the molybdenum disulfide nanosheets, the carbon nitride nanosheets and the graphene components exist in the form of two-dimensional sheets, and the three components are overlapped with each other to construct a three-dimensional self-supporting structure with a silver ear shape. When the proportion of the graphene oxide is changed, a good three-dimensional porous network structure cannot be formed if the content of the graphene oxide is too high or too low; as shown in fig. 4C and 4D, when the content of graphene oxide is too high, sufficient space between sheets is not available to form a three-dimensional network structure, and a large amount of graphene is easily stacked and agglomerated to form a thicker carbon layer; when the content of the graphene oxide is too low, only sparse connection exists between the sheets, and the graphene component shows a typical two-dimensional shape and cannot form a three-dimensional network structure.

Fig. 5 is a transmission electron microscope image of a molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst. The ultrathin molybdenum disulfide nanosheets, the carbon nitride nanosheets and the graphene are effectively connected with one another, and the constructed three-dimensional composite catalyst well solves the problems of stacking and agglomeration of the materials of the traditional nanosheet layers.

The results show that the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst has an anti-stacking and anti-agglomeration three-dimensional porous network framework, and the components form good dispersion, have large specific surface area and more active sites, so that the catalyst has higher catalytic performance and electrochemical activity.

3) Nitrogen adsorption and desorption test

As can be seen from the adsorption and desorption test graph of FIG. 6, the specific surface area of the catalyst is 249.5m²g^-1The structure is rich in micropore and mesopore structures.

4) Electrochemical hydrogen production reaction test

The experimental method comprises the following steps: electrocatalytic hydrogen production reaction tests were performed on an electrochemical workstation (CHI 760E, shanghai chenhua instruments ltd). A standard three-electrode system is adopted, and a Pt wire, a Saturated Calomel Electrode (SCE) and a glassy carbon electrode (GCE, 3mm) coated with a three-dimensional composite catalytic material are respectively used as a counter electrode, a reference electrode and a working electrode. The working electrode was prepared using a typical method: 2mg of the three-dimensional composite catalytic material was dissolved in a mixed solution (475. mu.L of water, 45. mu.L of ethanol and 50. mu.L of 5% Nafion), sonicated for 30min, and then 5. mu.L of the above suspension was carefully dropped on the surface of the pretreated glassy carbon electrode (GCE, 3mm) and dried at room temperature. In the hydrogen evolution performance test, the hydrogen evolution performance is 0.5M H₂SO₄In aqueous solution, the potential of the scanning electrode is 0.242 to-0.658V (Vs RHE), and the potential scanning rate is 2mV s^-1Measure whenAnd obtaining a polarization curve. At room temperature, 2000 cycles at a potential of-0.258 to-0.338V (Vs RHE) with a sweep rate of 10mV s^-1。

As can be seen from fig. 7A, the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene three-dimensional composite electrode catalyst has the lowest reaction initiation potential and the highest current density, which indicates that the catalyst has good catalytic durability; as can be seen from fig. 7B, the Tafel (Tafel) slope of the molybdenum disulfide nanosheet/carbon nitride nanosheet/graphene composite electrode catalyst is the smallest, which indicates that the catalytic activity of the catalyst is the best. Meanwhile, as shown in fig. 8, the activity of the catalyst was hardly attenuated after 2000 cycles of the test, indicating that it had excellent cycle stability.

In addition, hydrogen production catalytic activity tests were performed on the three-dimensional composite electrode catalysts prepared by the methods of examples 1 to 5 and comparative examples 1 to 4, and the results are shown in table 1.

Table 1 performance index of catalysts prepared in examples 1 to 5 for hydrogen production reaction

As can be seen from Table 1, the catalysts prepared by the methods of examples 1-5 all had low overpotential, low Tafel slope and large exchange current density, and high catalytic activity. With the increase of the content of the molybdenum disulfide nanosheet in the binary composite of the molybdenum disulfide nanosheet/carbon nitride nanosheet, the active surface area and the exchange current density of the catalyst are increased, the overpotential and the Tafel slope are correspondingly reduced, but the addition amount of the molybdenum disulfide nanosheet is further increased, as seen in example 5, the performance of the catalyst is reduced in comparison with that of example 3 and example 4, and when the content of the molybdenum disulfide nanosheet is increased to the content of comparative example 1, the performance of the catalyst is sharply reduced; this is because of MoS₂The conductivity of the conductive paste is not good, and the electron transfer efficiency is reduced due to the large addition of the conductive paste; comparative example 2 compared toIn examples 1 to 5, the carbon nitride nanosheet content of the binary composite of molybdenum disulfide nanosheet/carbon nitride nanosheet is high, and a large number of active sites on the surface of the molybdenum disulfide nanosheet are covered with carbon nitride, which also reduces the catalytic activity. Suitable C₃N₄And MoS₂The addition proportion is beneficial to comprehensively exerting the catalytic performances of the two, and a synergistic effect is generated, so that high catalytic activity and catalytic stability are obtained.

The heterogeneous composite of the two-dimensional layered material forms a three-dimensional self-supporting network structure which has a larger contact interface than other dimensions such as two-dimensional or granular composite materials, so that the transfer of electrolyte ions and electrons at the interface can be accelerated, and the sufficient contact between a reaction medium and an active site is facilitated, thereby showing more ideal catalytic activity; and C₃N₄And MoS₂The graphene oxide carbon material can not form a three-dimensional network structure by itself, and needs to be supported by graphene oxide, so that a good three-dimensional network structure can be obtained only under a proper condition due to the addition of the graphene oxide, the addition of the graphene oxide is too high, and a large number of graphene sheets tend to be stacked together to form a thick carbon layer due to the strong hydrogen bonding effect among the graphene oxide sheets, as shown in comparative example 3; and the content of graphene oxide is low, see comparative example 4, the graphene sheets lack enough connection and cannot form effective carrier supporting function, and part C₃N₄And MoS₂The two-dimensional layered nanosheets directly stacked are tightly and compactly in two-dimensional structure, so that the rapid transmission of electrolyte ions in the material is greatly limited, and the catalytic performance of the material can be seriously reduced. Through a large number of experiments, the proportion of each component is determined, and the hydrogen production electric catalyst with good catalytic performance can be obtained only under the content of each component in the proportion.