An ultrathin two-dimensional aza-graphene and a preparation method and a supported metal atomic catalyst thereof
Patent Information
- Application Number
- CN202211049645.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-08-30
- Publication Date
- 2026-09-25
- Estimated Expiration
- 2042-08-30
AI Technical Summary
这两类方法不但需要借助金属催化剂作为基底，而且所需的条件也十分严苛，不利于生成超薄二维氮杂石墨烯及氮杂石墨烯的量产
[0024]本发明通过一种简单地制备方法，合成了具有高比表面积的超薄二维氮杂石墨烯。通常来说，三聚氰胺存在热挥发的问题，在碳化温度下难以得到产物或得到产物较少，且碳化后的三聚氰胺氮掺杂位点少，不易形成均匀的氮杂石墨烯。因此，本发明区别于其他已知的氮掺杂方法，采用三聚氰胺为模板，通过在三聚氰胺体系中引入共轭双键，改变了三聚氰胺的结构，引入的共轭双键C＝C降低了碳源的损耗，实现了三聚氰胺自身提供碳源和氮源，且通过化学反应引入的碳碳双键可保证三聚氰胺体系中碳和氮分布的有序性，避免了额外复合杂质的产生。本发明所提供的制备方法实现了超薄二维氮杂石墨烯的制备，且制备条件温和，不需要额外的处理及碳源即可得到高比表面积的超薄二维氮杂石墨烯。
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of nitrogen-based graphene technology, specifically relating to an ultrathin two-dimensional nitrogen-based graphene, its preparation method, and a supported metal atom catalyst. Background Technology
[0002] Graphene, a novel nanomaterial composed of a single layer of carbon atoms, possesses numerous properties and application potential, such as high specific surface area, high thermal conductivity, and strong Young's modulus. All of these factors contribute to its broad application prospects in energy conversion and storage, electrocatalysis, sensors, and electronics. To meet diverse application needs, researchers have studied graphene, modifying its morphology and structure to prepare various graphene materials, such as two-dimensional graphene nanoribbons, one-dimensional graphene nanorods, graphene quantum dots, and the more widely used graphene oxide in recent years. However, despite being a zero-bandgap material, graphene still has limitations in practical applications. In the field of catalysis, researchers have been actively exploring alternatives to noble metal catalysts and two-dimensional single-atom catalyst supports. However, pure graphene lacks sufficient active sites and is difficult to use as a support for complexing metal atoms. To overcome the defects of graphene and expand its applications, researchers have proposed a nitrogen-doping method to modify graphene. The resulting nitrogen-doped graphene possesses a band gap that makes it a candidate material for semiconductor devices, and it shows great promise as a catalyst and supported single-atom catalyst. In addition, nitrogen-doped graphene can also be used in batteries, sensors, and supercapacitors. Nitrogen doping has significantly broadened the application range of graphene.
[0003] Generally, there are two main methods for chemically doping graphene: (1) adsorbing gases, metals, and organic molecules onto the graphene surface to form doping; and (2) substitution doping, introducing heteroatoms such as nitrogen and boron atoms into the carbon lattice of graphene to form doping. Both of these methods not only require metal catalysts as substrates, but also require very harsh conditions, which are not conducive to the generation of ultrathin two-dimensional nitrogen-doped graphene and the mass production of nitrogen-doped graphene. Research on the preparation of nitrogen-doped graphene using melamine as a template has encountered challenges. Due to the thermal volatilization of melamine, it is difficult to obtain products or only a small amount of products at the carbonization temperature. Furthermore, carbonized melamine has few nitrogen doping sites, making it difficult to form uniform nitrogen-doped graphene. Therefore, most current methods use melamine as the nitrogen source and introduce additional carbon sources to achieve nitrogen doping. This not only creates impurities in the composite nitrogen source but also results in excessively high reaction temperatures and harsh reaction conditions, requiring precise control of the reaction steps and even the use of additional hazardous gases. Therefore, there is an urgent need to develop a method for preparing ultrathin two-dimensional nitrogen-doped graphene that is mild, simple in steps, and produces uniform products. Summary of the Invention
[0004] To address the problems existing in the prior art, the present invention aims to provide an ultrathin two-dimensional nitrogen-containing graphene, its preparation method, and a supported metal atom catalyst. The preparation method is simple, the preparation conditions are mild, and high specific surface area ultrathin two-dimensional nitrogen-containing graphene can be obtained without additional treatment or carbon source. It can be used as a support for supporting single-atom and diatomic catalysts.
[0005] This invention is achieved through the following technical solution:
[0006] A method for preparing ultrathin two-dimensional nitrogen-containing graphene includes the following steps:
[0007] Step 1: Mix melamine, glyoxal, and anhydrous ethanol to obtain a mixture;
[0008] Step 2: Stir the mixture under heating conditions to obtain the precursor solution;
[0009] Step 3: Wash the precursor solution and then recover the precipitate to obtain the precursor;
[0010] Step 4: The precursor is heat-treated at 400-600℃ under a protective atmosphere, and then heat-treated at 600-900℃ to obtain ultrathin two-dimensional nitrogen-based graphene.
[0011] Preferably, in step 2, the heating condition is to heat to 60-100℃.
[0012] Preferably, in step 4, the protective atmosphere is nitrogen.
[0013] Preferably, in step 4, the heat treatment time is 2-4 hours at 400-600℃ and 2-4 hours at 600-900℃.
[0014] Ultrathin two-dimensional nitrogen-containing graphene obtained using the preparation method described above.
[0015] The metal atom catalyst supported on the ultrathin two-dimensional nitrogen-doped graphene is described above.
[0016] Preferably, the metal atom catalyst is a Pd single-atom catalyst or an Ag-Pd diatomic catalyst.
[0017] The method for preparing the ultrathin two-dimensional nitrogen-supported metal atom catalyst includes:
[0018] Step 1: Dissolve the metal salt in water to form a metal salt solution;
[0019] Step 2: Add the ultrathin two-dimensional nitrogen-containing graphene to a metal salt solution and stir to form a homogeneous metal atom catalyst precursor solution;
[0020] Step 3: Freeze-dry the homogeneous metal atom catalyst precursor liquid to obtain metal atom precursor powder;
[0021] Step 4: Heat-treat the metal atom precursor powder at 400-600℃ under a protective atmosphere, and then heat-treat it at 600-900℃ to obtain an ultrathin two-dimensional nitrogen-containing graphene-supported metal atom catalyst.
[0022] Preferably, the metal salt is palladium nitrate, or it is a mixture of palladium nitrate and silver nitrate.
[0023] Compared with the prior art, the present invention has the following beneficial effects:
[0024] This invention synthesizes ultrathin two-dimensional nitrogen-doped graphene with high specific surface area through a simple preparation method. Melamine typically suffers from thermal volatilization, making it difficult to obtain products or yielding limited products at carbonization temperatures. Furthermore, carbonized melamine has few nitrogen-doped sites, hindering the formation of uniform nitrogen-doped graphene. Therefore, this invention differs from other known nitrogen-doping methods by using melamine as a template. By introducing conjugated double bonds into the melamine system, the structure of melamine is altered. The introduced C=C conjugated double bonds reduce carbon source loss, allowing melamine to provide both carbon and nitrogen sources. Moreover, the carbon-carbon double bonds introduced through a chemical reaction ensure the ordered distribution of carbon and nitrogen in the melamine system, avoiding the generation of additional composite impurities. The preparation method provided by this invention achieves the preparation of ultrathin two-dimensional nitrogen-doped graphene under mild conditions, requiring no additional treatment or carbon source to obtain ultrathin two-dimensional nitrogen-doped graphene with high specific surface area.
[0025] Furthermore, the molar ratio of melamine to glyoxal is 0.4:1. This ratio limits the introduction of conjugated double bonds to the maximum extent, which means that each aldehyde group will fully react with an amine group. Other ratios will lead to an excess of one side, resulting in the generation of byproducts.
[0026] Furthermore, the heating condition is to heat to 60-100℃, which allows the chemical reaction to proceed at a suitable temperature.
[0027] The ultrathin two-dimensional nitrogen-containing graphene prepared by this invention has a large specific surface area, which can be used as a support for single-atom or diatomic catalysts. The metal complexation of nitrogen atoms and the large specific surface area in nitrogen-containing graphene can provide more active sites for single-atom and diatomic catalysts, which is beneficial to improving the utilization rate of single-atom and diatomic catalysts. In addition, the unique structure of nitrogen-containing graphene has great application prospects in catalysis and other fields. Attached Figure Description
[0028] Figure 1TEM image of the ultrathin two-dimensional nitrogen-doped graphene prepared in Example 1;
[0029] Figure 2 TEM image of the ultrathin two-dimensional nitrogen-doped graphene prepared in Example 2;
[0030] Figure 3 The elemental distribution diagram of the ultrathin two-dimensional nitrogen-containing graphene prepared in Example 2;
[0031] Figure 4 The Raman spectrum of the ultrathin two-dimensional nitrogen-doped graphene prepared in Example 2;
[0032] Figure 5 TEM image of the ultrathin two-dimensional nitrogen-doped graphene prepared in Example 3;
[0033] Figure 6 TEM image of palladium single atoms prepared in Example 4;
[0034] Figure 7 The Raman spectrum of the palladium single atom prepared in Example 4;
[0035] Figure 8 The graph shows the hydrogen production performance of palladium single atoms in formic acid prepared in Example 4.
[0036] Figure 9 TEM image of the silver-palladium diatomic array prepared in Example 5;
[0037] Figure 10 The Raman spectrum of the silver-palladium diatomic array prepared in Example 5;
[0038] Figure 11 The graph shows the hydrogen production performance of the silver-palladium diatomic formic acid prepared in Example 5. Detailed Implementation
[0039] To further understand the present invention, the present invention will be described below with reference to embodiments. These descriptions are only for further explaining the features and advantages of the present invention and are not intended to limit the claims of the present invention.
[0040] The preparation method of the ultrathin two-dimensional nitrogen-containing graphene of the present invention includes the following steps:
[0041] Step 1: Weigh a certain amount of melamine into a round-bottom flask, add a certain amount of anhydrous ethanol, and stir and reflux in an oil bath at 60-100℃ to obtain a melamine dispersion.
[0042] Step 2: Weigh a certain amount of glyoxal and add it to the melamine dispersion. Stir and reflux in an oil bath at 60-100℃ for 2-4 hours to obtain the precursor solution.
[0043] Step 3: Centrifuge and wash the precursor solution and recover the precipitate to obtain the precursor;
[0044] Step 4: A certain amount of precursor is heat-treated in a nitrogen atmosphere at 400-600℃, and then further heat-treated at 600-900℃ to obtain ultrathin two-dimensional nitrogen-based graphene.
[0045] The preparation method of Pd single-atom catalyst includes the following steps:
[0046] Step 1: Dissolve palladium nitrate in ultrapure water to form a palladium nitrate solution;
[0047] Step 2: Take ultrathin two-dimensional nitrogen-containing graphene powder, add it to palladium nitrate solution, and stir at room temperature for 12-24 hours to form a homogeneous palladium single-atom catalyst precursor solution;
[0048] Step 3: Freeze-dry the homogeneous palladium single-atom catalyst precursor liquid for 12-24 hours to remove the water in the precursor liquid and obtain palladium single-atom precursor powder.
[0049] Step 4: Take palladium single-atom precursor powder in a ceramic boat and heat-treat it at 400-600℃ under a nitrogen atmosphere, and then heat-treat it at 600-900℃ to obtain ultrathin two-dimensional nitrogen-containing graphene-supported Pd single atoms.
[0050] The preparation method of Ag-Pd diatomic catalyst includes the following steps:
[0051] Step 1: Dissolve palladium nitrate and silver nitrate in ultrapure water to form a mixed solution of silver nitrate and palladium nitrate;
[0052] Step 2: Take ultrathin two-dimensional nitrogen-containing graphene powder, add it to a mixed solution of silver nitrate and palladium nitrate, and stir at room temperature for 12-24 hours to form a homogeneous silver-palladium diatomic catalyst precursor solution.
[0053] Step 3: Freeze-dry the homogeneous silver-palladium diatomic catalyst precursor solution for 12-24 hours to remove water from the precursor solution and obtain silver-palladium diatomic catalyst precursor powder.
[0054] Step 4: Place the silver-palladium diatomic catalyst precursor powder in a ceramic boat and heat-treat it at 400-600℃ under a nitrogen atmosphere, followed by heat treatment at 600-900℃ to obtain ultrathin two-dimensional nitrogen-containing graphene-supported silver-palladium diatomic catalyst.
[0055] Example 1
[0056] Step 1: Weigh 0.08 mol of melamine into a round-bottom flask, add 50 ml of anhydrous ethanol, and stir and reflux in an oil bath at 80 °C to obtain a melamine dispersion.
[0057] Step 2: Weigh 0.2 mol of glyoxal and add it to the melamine dispersion. Stir and reflux in an oil bath at 80°C for 2 hours to obtain the precursor solution.
[0058] Step 3: Centrifuge and wash the precursor solution and recover the precipitate to obtain the precursor;
[0059] Step 4: The precursor is heat-treated at 550°C in a nitrogen atmosphere for 2 hours, and then further heat-treated at 600°C for 2 hours to obtain ultrathin two-dimensional nitrogen-containing graphene.
[0060] TEM image of the nitrogen-containing graphene obtained in Example 1 of this invention is shown below. Figure 1 As shown, from Figure 1 It can be seen that nitrogen-containing graphene is a two-dimensional material.
[0061] Example 2
[0062] Step 1: Weigh 0.08 mol of melamine into a round-bottom flask, add 50 ml of anhydrous ethanol, and stir and reflux in an oil bath at 80 °C to obtain a melamine dispersion.
[0063] Step 2: Weigh 0.2 mol of glyoxal and add it to the melamine dispersion. Stir and reflux in an oil bath at 80°C for 2 hours to obtain the precursor solution.
[0064] Step 3: Centrifuge and wash the precursor solution and recover the precipitate to obtain the precursor;
[0065] Step 4: The precursor is heat-treated at 550°C for 3 hours in a nitrogen atmosphere, and then further heat-treated at 700°C for 3 hours to obtain ultrathin two-dimensional nitrogen-containing graphene.
[0066] TEM image of the nitrogen-containing graphene obtained in Example 2 of this invention is shown below. Figure 2 As shown, from Figure 2 It can be seen that nitrogen-containing graphene is a two-dimensional material. Elemental analysis of ultrathin two-dimensional nitrogen-containing graphene is as follows: Figure 3 As shown, from Figure 3 It can be seen that carbon and nitrogen elements are uniformly distributed on the ultrathin two-dimensional nitrogen-containing graphene. Raman spectra are as follows... Figure 4 As shown, from Figure 4 The presence of D and G peaks in the Raman spectrum confirms the successful synthesis of nitrogen-doped graphene. Furthermore, the D and G peaks of nitrogen-doped graphene show changes with nitrogen doping.
[0067] Example 3
[0068] Step 1: Weigh 0.08 mol of melamine into a round-bottom flask, add 50 ml of anhydrous ethanol, and stir and reflux in an oil bath at 80 °C to obtain a melamine dispersion.
[0069] Step 2: Weigh 0.2 mol of glyoxal and add it to the melamine dispersion. Stir and reflux in an oil bath at 80°C for 2 hours to obtain the precursor solution.
[0070] Step 3: Centrifuge and wash the precursor solution and recover the precipitate to obtain the precursor;
[0071] Step 4: The precursor is heat-treated at 550°C in a nitrogen atmosphere for 4 hours, and then further heat-treated at 800°C for 4 hours to obtain ultrathin two-dimensional nitrogen-containing graphene.
[0072] TEM image of the nitrogen-containing graphene obtained in Example 3 of this invention is shown below. Figure 5 As shown, from Figure 5 It can be seen that nitrogen-containing graphene is an ultrathin two-dimensional material.
[0073] Example 4
[0074] Step 1: Weigh 0.4 mmol of palladium nitrate and dissolve it in 5 ml of ultrapure water to form a palladium nitrate solution;
[0075] Step 2: Weigh 4g of the ultrathin two-dimensional nitrogen-containing graphene powder prepared in Example 2, add it to the palladium nitrate solution, and stir at room temperature for 12h to form a homogeneous palladium single-atom catalyst precursor solution.
[0076] Step 3: Freeze-dry the homogeneous palladium single-atom catalyst precursor liquid for 12 hours to remove the water in the precursor liquid and obtain palladium single-atom precursor powder.
[0077] Step 4: Palladium single-atom precursor powder is placed in a ceramic boat and heat-treated at 550°C under a nitrogen atmosphere, followed by heat treatment at 700°C to obtain an ultrathin two-dimensional nitrogen-containing graphene-supported Pd single-atom catalyst.
[0078] TEM images of palladium single atoms supported on ultrathin two-dimensional nitrogen-doped graphene obtained in Example 4 of this invention are shown below. Figure 6 As shown, from Figure 6 It can be seen that the palladium single atoms supported on the ultrathin two-dimensional nitrogen-containing graphene are ultrathin two-dimensional materials, and there are no lattice fringes characteristic of Pd nanomaterials in the field of view, proving that Pd exists in an atomically dispersed form. Raman spectra are as follows... Figure 7 As shown, from Figure 7 The presence of D and G peaks in the Raman spectrum confirms the successful synthesis of nitrogen-containing graphene. The intensity of the D and G peaks changes after loading Pd atoms, which is attributed to the effect of Pd atom loading. The hydrogen production performance of palladium single-atom formic acid is shown in the figure below. Figure 8 As shown in the figure, 10 mg of palladium single-atom catalyst with a 3% loading can produce about 2 ml of hydrogen gas in 10 min at 50 °C, which confirms that its atomically dispersed palladium catalyst has the ability to produce hydrogen from formic acid.
[0079] Example 5
[0080] Step 1: Weigh 0.2 mmol palladium nitrate and 0.2 mmol silver nitrate and dissolve them in 5 ml of ultrapure water to form a mixed solution of silver nitrate and palladium nitrate;
[0081] Step 2: Weigh 4g of the ultrathin two-dimensional nitrogen-containing graphene powder prepared in Example 2, add it to a mixed solution of silver nitrate and palladium nitrate, and stir for 12h at room temperature to form a homogeneous silver-palladium diatomic catalyst precursor solution.
[0082] Step 3: Freeze-dry the homogeneous silver-palladium diatomic catalyst precursor solution for 12 hours to remove water from the precursor solution and obtain silver-palladium diatomic catalyst precursor powder.
[0083] Step 4: Place the silver-palladium diatomic catalyst precursor powder in a ceramic boat and heat-treat it at 550°C under a nitrogen atmosphere, followed by heat-treating it at 700°C to obtain an ultrathin two-dimensional nitrogen-containing graphene-supported silver-palladium diatomic catalyst.
[0084] TEM images of silver-palladium diatomic atoms supported on ultrathin two-dimensional nitrogen-doped graphene obtained in Example 5 of this invention are shown below. Figure 9 As shown, from Figure 9 It can be seen that the silver-palladium diatomic support on the ultrathin two-dimensional nitrogen-containing graphene is an ultrathin two-dimensional material, and there are no lattice fringes characteristic of Ag and Pd nanomaterials in the field of view, proving that Ag and Pd exist in an atomically dispersed form. Raman spectroscopy is as follows... Figure 10 As shown, from Figure 10 The presence of D and G peaks in the Raman spectrum confirms the successful synthesis of nitrogen-containing graphene. The intensity of the D and G peaks changes after loading with Ag and Pd diatoms, which is attributed to the influence of the Ag and Pd diatoms. The hydrogen production performance of silver-palladium diatomic formic acid is shown in the figure below. Figure 11 As shown in the figure, 10 mg of silver-palladium diatomic catalyst with a 3% loading can produce about 10 ml of hydrogen gas in 20 min at 50 °C, which confirms that the atomically dispersed silver-palladium catalyst has the ability to produce hydrogen from formic acid.
Claims
1. A method for preparing ultrathin two-dimensional nitrogen-based graphene, characterized in that, include: Step 1: Mix melamine, glyoxal, and anhydrous ethanol to obtain a mixture; Step 2: Stir the mixture under heating conditions to obtain the precursor solution; Step 3: Wash the precursor solution and then recover the precipitate to obtain the precursor; Step 4: The precursor is heat-treated at 400-600℃ under a protective atmosphere, and then heat-treated at 600-900℃ to obtain ultrathin two-dimensional nitrogen-based graphene.
2. The method for preparing ultrathin two-dimensional nitrogen-containing graphene according to claim 1, characterized in that, In step 1, the molar ratio of melamine to glyoxal is 0.4:
1.
3. The method for preparing ultrathin two-dimensional nitrogen-doped graphene according to claim 1, characterized in that, In step 2, the heating condition is to heat to 60-100℃.
4. The method for preparing ultrathin two-dimensional nitrogen-doped graphene according to claim 1, characterized in that, In step 4, the protective atmosphere is nitrogen.
5. The method for preparing ultrathin two-dimensional nitrogen-doped graphene according to claim 1, characterized in that, In step 4, the heat treatment time is 2-4 hours at 400-600℃ and 2-4 hours at 600-900℃.
6. Ultrathin two-dimensional nitrogen-containing graphene obtained by the preparation method according to any one of claims 1-5.
7. The ultrathin two-dimensional nitrogen-supported metal atom catalyst according to claim 6, characterized in that, The metal atom catalyst is supported on the ultrathin two-dimensional nitrogen-containing graphene as described in claim 6.
8. The ultrathin two-dimensional nitrogen-supported metal atom catalyst according to claim 7, characterized in that, The metal atom catalyst is a Pd single-atom catalyst or an Ag-Pd diatomic catalyst.
9. The method for preparing the ultrathin two-dimensional nitrogen-supported metal atom catalyst according to claim 7, characterized in that, include: Step 1: Dissolve the metal salt in water to form a metal salt solution; Step 2: Add the ultrathin two-dimensional nitrogen-containing graphene as described in claim 6 to the metal salt solution and stir to form a homogeneous metal atom catalyst precursor solution; Step 3: Freeze-dry the homogeneous metal atom catalyst precursor liquid to obtain metal atom precursor powder; Step 4: Heat-treat the metal atom precursor powder at 400-600℃ under a protective atmosphere, and then heat-treat it at 600-900℃ to obtain an ultrathin two-dimensional nitrogen-containing graphene-supported metal atom catalyst.
10. The method for preparing the ultrathin two-dimensional nitrogen-supported metal atom catalyst according to claim 9, characterized in that, The metal salt is palladium nitrate, or, palladium nitrate and silver nitrate.