Atomic-scale dispersed metal doped carbon nitride as well as preparation method and application thereof

Abstract

The invention relates to the technical field of catalysts, in particular to atomic-scale dispersed metal doped carbon nitride as well as a preparation method and application thereof. The preparation method of the atomic-scale dispersed metal doped carbon nitride comprises the following steps: carrying out hydrothermal reaction on cobalt salt, water and a nitrogen-containing organic solvent, washing the obtained solid, carrying out centrifugal separation, and drying to obtain a carbon nitride material. The atomic-scale dispersed metal-doped carbon nitride material is obtained by a hydrothermal reaction method, and the atomic-scale dispersed metal-doped carbon nitride material is remarkably different from conventional graphite-phase carbon nitride in crystal structure; the cobalt-doped carbon nitride material shows a clearer crystal structure, and shows significant difference in promoting hydrogen peroxide generation, and the hydrogen peroxide yield is high.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to atomic-level dispersed metal-doped carbon nitride and a preparation method and application thereof. Background Art

[0002] Single-atom electrocatalysts (SAECs) have attracted much attention in energy technology fields such as fuel cells, water electrolysis, and metal-air batteries due to their high surface area to volume ratio and uniformly distributed atomic active sites. In particular, carbon-supported SAECs, such as metal-nitrogen composite carbon materials (MNCs), can effectively utilize each atom due to their good conductivity and unique metal-ligand interactions, showing excellent catalytic activity and selectivity.

[0003] Although SAECs are excellent in catalytic performance and application potential, their preparation process usually requires high-temperature treatment of metal salts, nitrogen sources, and carbon sources (e.g., pyrrole, sodium alginate, dopamine, etc.), which may lead to metal aggregation problems, thus affecting the quality and stability of the material.

[0004] To solve these problems, researchers have begun to widely use metal organic frameworks (MOFs) pre-embedded with metal atom sites as precursors of SAECs. However, the commonly used ligands of MOFs are usually expensive and toxic, such as 2-methylimidazole and 2,2'-bipyridine, which hinders the large-scale production and practical application of SAECs [Energy & Environmental Science. A general route via formamide condensation to prepare atomically dispersed metal-nitrogen-carbon electrocatalysts for energy technologies. 2019, 12, 1317].

[0005] Therefore, in order to achieve its commercialization and large-scale industrial application in the energy field, problems such as high preparation cost, use of toxic substances and metal aggregation must be solved. Summary of the invention

[0006] The purpose of the present invention is to address the above-mentioned deficiencies in the prior art and to provide an atomically dispersed metal-doped carbon nitride and a preparation method and application thereof.

[0007] The invention discloses a method for preparing atomic-level dispersed metal-doped carbon nitride, comprising the steps of subjecting a cobalt salt, water and a nitrogen-containing organic solvent to a hydrothermal reaction, washing and centrifuging the obtained solid, and drying the solid to obtain the carbon nitride material.

[0008] Furthermore, the hydrothermal synthesis reaction temperature is 150~230℃, and the reaction time is 6~18 h.

[0009] Furthermore, the washing is performed by washing with deionized water and anhydrous ethanol for several times until the solution is clear.

[0010] Furthermore, the cobalt salt is one or more of cobalt sulfate and cobalt nitrate.

[0011] Furthermore, the mass volume ratio of the cobalt salt, water, and nitrogen-containing organic solution is 0.005-3.0 g: 0.5-3 mL: 5-100 mL.

[0012] Furthermore, the nitrogen-containing organic solution is any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylpropionamide, formamide, dimethylformamide, dimethylacetamide, N,N-diethylformamide, etc.

[0013] Atomically dispersed metal-doped carbon nitride is obtained by using the above preparation method.

[0014] An application of the atomically dispersed metal-doped carbon nitride as described above is used for the preparation of hydrogen peroxide, CO2 reduction, and water electrolysis.

[0015] The present invention obtains atomically dispersed metal-doped carbon nitride materials through a hydrothermal reaction method, which has significant differences in crystal structure from conventional graphite phase carbon nitride; the cobalt-doped carbon nitride material exhibits a more clear crystal structure, shows significant differences in promoting the generation of hydrogen peroxide, and has a high hydrogen peroxide yield.

[0016] The preparation method of the present invention has low raw material cost, short synthesis time, low synthesis temperature, simple steps, little impact on the environment, no toxicity, low energy consumption, higher yield, and is conducive to large-scale industrial production, and has good development prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The X-ray powder diffraction patterns of atomically dispersed metal-doped carbon nitride of Example 1, Example 5 and Comparative Example 1, Comparative Example 2 are shown.

[0018] Figure 2 This is a SEM image of the atomically dispersed metal-doped carbon nitride powder of Example 1.

[0019] Figure 3 It is a bar graph of the hydrogen peroxide selectivity and the electron transfer number of Example 1 and Comparative Examples 1-3.

[0020] Figure 4 Yield diagram of atomically dispersed metal-doped carbon nitride powders of Examples 1-4 at different temperatures. DETAILED DESCRIPTION

[0021] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0022] The present invention provides a method for preparing atomically dispersed metal-doped carbon nitride, comprising the following steps: S1: adding a metal salt having a mass content of 3-22% to 0.5 mL to 3 mL of water and 5 to 100 mL of a nitrogen-containing organic solution to obtain a catalyst precursor; S2: Pour the catalyst precursor into the liner, and place the liner in a reactor at 150-230°C for 6-18h, cool to room temperature, wash with ethanol 3-9 times, dry at 30-120°C for 3-15h, and grind into powder to obtain metal-doped atomically dispersed carbon nitride.

[0023] In the above step S1, the nitrogen-containing organic solution in the reactant is any one of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylpropionamide, formamide, dimethylformamide, dimethylacetamide, N,N-diethylformamide (not limited to the listed nitrogen-containing organic solutions). The metal salt can be any one of ferrous sulfate, ferric sulfate, ferric nitrate, cobalt sulfate, cobalt nitrate, cerium sulfate, cerium nitrate, nickel nitrate, manganese sulfate, nickel sulfate, etc. (but not limited to the listed metal salts). The catalyst precursor is obtained by mixing the solutions.

[0024] In the above step S2, the reaction temperature in the reactor can be 150-230° C., and the reaction time can be 6-18 hours. Through the regulation based on different temperatures, metal-doped atomically dispersed carbon nitride with different yields can be finally obtained.

[0025] The atomically dispersed metal-doped carbon nitride prepared in the embodiments of the present application can be used in the fields of hydrogen peroxide preparation, CO2 reduction, water electrolysis, etc.

[0026] A method for preparing atomically dispersed metal-doped carbon nitride according to an embodiment of the present application is described below by way of a number of specific embodiments.

[0027] Example 1 Embodiment 1 of the present application provides a method for preparing atomically dispersed metal-doped carbon nitride, comprising the following steps: Step 1: Add 0.02 g of cobalt nitrate hexahydrate into 1 mL of water and 40 mL of formamide to obtain a catalyst precursor; Step 2: Pour the catalyst precursor into a 100 mL liner, place the liner in a reactor and react at 180°C for 12 hours, cool to room temperature, wash with ethanol 4 times, dry at 80°C for 5 hours, and grind into powder to obtain carbon nitride.

[0028] Example 2 Embodiment 2 of the present application provides a method for preparing atomically dispersed metal-doped carbon nitride, comprising the following steps: Step 1: Add 0.02 g of cobalt nitrate hexahydrate into 1 mL of water and 40 mL of formamide to obtain a catalyst precursor; Step 2: Pour the catalyst precursor into a 100 mL liner, place the liner in a reactor and react at 190°C for 12 hours, cool to room temperature, wash with ethanol 4 times, dry at 80°C for 5 hours, and grind into powder to obtain carbon nitride.

[0029] Example 3 Embodiment 3 of the present application provides a method for preparing atomically dispersed metal-doped carbon nitride, comprising the following steps: Step 1: Add 0.02 g of cobalt nitrate hexahydrate into 1 mL of water and 40 mL of formamide to obtain a catalyst precursor; Step 2: Pour the catalyst precursor into a 100 mL liner, place the liner in a reactor and react at 200°C for 12 hours, cool to room temperature, wash with ethanol 4 times, dry at 80°C for 5 hours, and grind into powder to obtain carbon nitride.

[0030] Example 4 Embodiment 4 of the present application provides a method for preparing atomically dispersed metal-doped carbon nitride, comprising the following steps: Step 1: Add 0.02 g of cobalt nitrate hexahydrate into 1 mL of water and 40 mL of formamide to obtain a catalyst precursor; Step 2: Pour the catalyst precursor into a 100 mL liner, place the liner in a reactor at 210°C for 12 hours, cool to room temperature, wash with ethanol 4 times, dry at 80°C for 5 hours, and grind into powder to obtain carbon nitride.

[0031] Figure 2 The SEM image of the carbon nitride prepared in Example 1 clearly reveals that it presents a crystalline structure similar to a blooming flower. This unique petal-like appearance is vividly named "flower structure".

[0032] Comparative Example 1 Comparative Example 1 of the present application provides a method for preparing atomically dispersed metal-doped carbon nitride, comprising the following steps: Step 1: Add 0.02 g of ferric nitrate nonahydrate into 1 mL of water and 40 mL of formamide to obtain a catalyst precursor; Step 2: Pour the catalyst precursor into a 100 mL liner, place the liner in a reactor and react at 180°C for 12 hours, cool to room temperature, wash with ethanol 4 times, dry at 80°C for 5 hours, and grind into powder to obtain carbon nitride.

[0033] Comparative Example 2 Embodiment 1 of the present application provides a method for preparing atomically dispersed metal-doped carbon nitride, comprising the following steps: Step 1: Add 0.02 g of nickel nitrate hexahydrate into 1 mL of water and 40 mL of formamide to obtain a catalyst precursor; Step 2: Pour the catalyst precursor into a 100 mL liner, place the liner in a reactor and react at 180°C for 12 hours, cool to room temperature, wash with ethanol 4 times, dry at 80°C for 5 hours, and grind into powder to obtain carbon nitride.

[0034] Comparative Example 3 Comparative Example 3 of the present application prepared a commercial g-C3N4 material, and the preparation process is as follows: Step 1: Weigh 10 g of urea into an alumina crucible, place it in a tube furnace, heat it to 550 °C at a rate of 5 °C / min in a N2 atmosphere and keep it for 4 h; Step 2: After cooling, take it out, grind it, wash it with anhydrous ethanol, centrifuge it and dry it at 80 °C to obtain the commercial g-C3N4 catalyst.

[0035] Figure 1 The X-ray diffraction patterns of the carbon nitride powders of Example 1 and Comparative Examples 1-3 are shown. It can be clearly observed that there are significant differences in the crystal structure between atomically dispersed metal-doped carbon nitride and conventional graphite phase carbon nitride. Specifically, the metal-doped sample shows that the in-plane repeating unit is shifted to the left, which indicates that the lattice parameters or atomic positions have changed, showing the effect of metal doping on the crystal structure. At the same time, compared with conventional carbon nitride, the atomically dispersed metal-doped carbon nitride prepared in Example 1 exhibits a more clear crystalline structure, which may reflect the higher crystallinity or better lattice order of the crystal.

[0036] Figure 3 The bar graphs of Example 1 and Comparative Examples 1-3 are shown, respectively showing the hydrogen peroxide selectivity and the number of electron transfers. Apparently, atomically dispersed metal-doped carbon nitrides show significant differences in promoting hydrogen peroxide generation. Specifically, cobalt-doped carbon nitrides show higher hydrogen peroxide yields, while iron-doped carbon nitrides have lower hydrogen peroxide yields.

[0037] In addition, compared with commercial carbon nitride, the carbon nitride proposed in this application shows obvious advantages in the production of hydrogen peroxide. This phenomenon may be attributed to the structural changes of carbon nitride caused by different metal doping, which directly affect its ability to produce hydrogen peroxide in the catalytic reaction. Cobalt doping helps to form a carbon nitride structure that is more conducive to the generation of hydrogen peroxide, while iron doping may limit the generation of hydrogen peroxide, thus showing lower selectivity. Nickel-doped carbon nitride is between the two, and its hydrogen peroxide yield is not much different from that of conventional carbon nitride.

[0038] Figure 4 The yield graph of the product after the reaction of carbon nitride in Example 1-4 shows that as the temperature increases, the carbon nitride reaction product shows a significant increasing trend. The reason for this phenomenon is that the reaction rate increases under high temperature conditions, and the collision frequency and reaction rate constant between the reaction molecules will also increase significantly, thereby significantly improving the yield. This temperature-dependent reaction characteristic reveals the key role of temperature in the reaction, which may lead to changes in thermodynamic and kinetic parameters. Especially at high temperatures, it helps to reduce the activation energy of the reaction, making the reaction more inclined to produce carbon nitride. In addition, high temperature may also increase the stability of the reaction intermediates, further promoting the formation of carbon nitride.

[0039] The above are only some embodiments of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. Equivalent changes made based on the claims of the present invention still fall within the scope covered by the present invention.

[0040] For matters not mentioned above, the prior art applies.

[0041] Although some specific embodiments of the present invention have been described in detail through examples, those skilled in the art should understand that the above examples are for illustration only and are not intended to limit the scope of the present invention. Those skilled in the art to which the present invention belongs may make various modifications or supplements to the specific embodiments described or replace them in a similar manner, but they will not deviate from the direction of the present invention or exceed the scope defined by the attached claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing atomically dispersed metal-doped carbon nitride, characterized in that: The cobalt salt, water and nitrogen-containing organic solvent are subjected to hydrothermal reaction, and the obtained solid is washed and centrifuged, and then dried to obtain the carbon nitride material.

2. The preparation method according to claim 1, characterized in that The hydrothermal synthesis reaction temperature is 150-230°C and the reaction time is 6-18h.

3. The preparation method according to claim 1, characterized in that: The washing is performed by washing with deionized water and anhydrous ethanol for several times until the solution is clear.

4. The preparation method according to claim 1, characterized in that: The cobalt salt is one or more of cobalt sulfate and cobalt nitrate.

5. The preparation method according to claim 1, characterized in that: The mass volume ratio of the cobalt salt, water and nitrogen-containing organic solution is 0.005-3.0 g: 0.5-3 mL: 5-100 mL.

6. The preparation method according to claim 1, characterized in that: The nitrogen-containing organic solution is any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylpropionamide, formamide, dimethylformamide, dimethylacetamide, N,N-diethylformamide, etc.

7. An atomically dispersed metal-doped carbon nitride, characterized in that: The preparation method is obtained by any one of claims 1 to 6.

8. The use of atomically dispersed metal-doped carbon nitride as claimed in claim 7, characterized in that: Used for preparation of hydrogen peroxide, CO2 reduction, and water electrolysis.

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