Heteroatom-doped porous graphene and methods of making and using the same

Abstract

The application belongs to the field of carbon materials, and provides a kind of heteroatom doped porous graphene and its preparation method and application.The preparation method of the heteroatom doped porous graphene of the application comprises: making a reaction solution containing graphene oxide, organic nitrogen source, organic boron source and water to carry out hydrothermal reaction, to obtain reduced graphene oxide hydrogel;The reduced graphene oxide hydrogel is subjected to first drying to obtain reduced graphene oxide aerogel;The reduced graphene oxide aerogel is sent into a rotary furnace for gradient temperature treatment, and then washed, secondly dried to obtain nitrogen and boron co-doped porous graphene.The preparation method of the application can improve the micropore ratio in the porous graphene and the anchoring ability to heteroatoms, reduce the loss rate of heteroatoms, and obtain heteroatom doped porous graphene with high specific surface area.

Description

Technical Field

[0001] This application belongs to the field of carbon materials, specifically, it provides a heteroatom-doped porous graphene, its preparation method, and its application. Background Technology

[0002] Graphene is a novel carbon material with a two-dimensional honeycomb structure composed of a single layer of tightly packed carbon atoms. It possesses excellent mechanical properties and chemical stability. However, its high surface energy and the van der Waals forces and π-π bonds between its layers make it difficult to disperse during use, leading to agglomeration and stacking. This reduces its effective specific surface area and electronic conductivity, affecting its performance. Porous graphene, on the other hand, is a graphene material with a large number of pores. Compared to ordinary graphene, porous graphene has lower density and a larger effective specific surface area, making it suitable for use as a conductive material and in catalyst preparation. Further doping with heteroatoms is expected to improve the conductivity and stability of porous graphene in catalyst preparation.

[0003] CN105833893A discloses a method for preparing a doped graphene support, comprising ultrasonically dispersing boric acid and graphene oxide in water, followed by a low-temperature hydrothermal reaction to obtain boron-doped graphene, then mixing it with ammonia, followed by a high-temperature hydrothermal reaction and calcination to obtain a BN co-doped graphene support. In this method, BN co-doping of the graphene support can improve the stability of the catalyst and the dispersibility and utilization rate of the active component Pd metal particles. Although this prior art successfully prepares BN co-doped graphene through a two-step method, the mixing of graphene oxide with boric acid and ammonia involves filtration and other operations, leading to the loss of boron and nitrogen sources, a low B / N doping ratio, and difficulty in controlling the internal pore size distribution.

[0004] CN110540196A discloses a method for preparing doped porous graphene, comprising: firstly, reacting graphene with water vapor accompanied by Ar gas to generate nanopores, thus preparing porous graphene; then, heating the porous graphene in an NH3 / Ar mixed atmosphere to prepare nitrogen-doped porous graphene; and finally, co-heating it with boric acid in a protective atmosphere to prepare BN co-doped porous graphene. This method uses water activation to obtain porous graphene, followed by a two-step BN co-doping process. However, the dry mixing of boric acid and nitrogen-doped graphene leads to uneven mixing, making it difficult to fix the B element sites. Furthermore, the pore size distribution is difficult to control, and the specific surface area of ​​the doped porous graphene is not high (<1000 μm²). 2 / g). Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, the purpose of this application is to provide heteroatom-doped porous graphene, its preparation method, and its applications. The preparation method of this application can increase the micropore ratio and the anchoring ability of heteroatoms in porous graphene, reduce the heteroatom loss rate, and obtain heteroatom-doped porous graphene with a high specific surface area.

[0006] In a first aspect, this application provides a method for preparing heteroatom-doped porous graphene, comprising:

[0007] (1) A hydrothermal reaction is carried out on a reaction solution containing graphene oxide, an organic nitrogen source, an organic boron source and water to obtain a reduced graphene oxide hydrogel.

[0008] (2) The reduced graphene oxide hydrogel is first dried to obtain reduced graphene oxide aerogel.

[0009] (3) The reduced graphene oxide aerogel is fed into a rotary kiln for gradient heating treatment, followed by washing and a second drying to obtain nitrogen-boron co-doped porous graphene; wherein the gradient heating treatment is carried out in the presence of an inert gas and includes a first stage and a second stage performed sequentially.

[0010] First stage: Inert gas is introduced into the rotary kiln, the temperature is raised to a first temperature T1, and the temperature is maintained at the first temperature T1 for 0.5 to 5 hours;

[0011] The second stage involves raising the temperature to a second temperature T2, maintaining this temperature for 0.5–2 hours, then introducing steam for the first activation treatment, followed by introducing carbon dioxide for the second activation treatment.

[0012] T2 and T1 satisfy the following relationship: T2-T1≥200℃, and T1 is 400~700℃.

[0013] In the preparation method provided in this application, the oxygen-containing groups on the surface of graphene oxide (GO) have electrostatic effects, which can effectively anchor organic boron sources and organic nitrogen sources, and fix the doping sites of B and N elements. During the gradient heating process, the boron and nitrogen sources are first used to generate small molecules and overflow by low-temperature sintering, initially forming a porous structure and realizing in-situ doping of GO, increasing the doping amount of N and B. Then, the doped graphene is co-activated by water vapor and CO2 under high temperature conditions. During the activation process, pores are further formed: boron oxide generated by the organic boron source is used as a hard template and organic nitrogen source is used as a soft template to adjust the pore structure in graphene, improve the activation efficiency and the proportion of micropores in the pore structure. In this way, heteroatom-doped porous graphene with both high specific surface area and high heteroatom content can be successfully prepared.

[0014] In some embodiments of this application, the graphene oxide sheet has a diameter of 1–20 μm, a thickness of 1–5 nm, and an oxygen content of 30%–60%.

[0015] In some embodiments of this application, the organoboron source is selected from at least one of phenylboronic acid, 2-hydroxyphenylboronic acid, 3-hydroxyphenylboronic acid, 4-hydroxyphenylboronic acid, 3-hydroxymethylphenylboronic acid, and 4-hydroxymethylphenylboronic acid.

[0016] In some embodiments of this application, the mass ratio of the organic boron source to the graphene oxide is (5-15):1.

[0017] In some embodiments of this application, the organic nitrogen source is selected from at least one of dicyandiamide, glycine, urea, alanine, and phenylalanine.

[0018] In some embodiments of this application, the mass ratio of the organic nitrogen source to the graphene oxide is (1-5):1.

[0019] In some embodiments of this application, in step (1), the reaction solution is obtained by the following method:

[0020] Graphene oxide was dispersed in water to prepare a graphene oxide dispersion.

[0021] An organic boron source or a methanol solution of an organic boron source is added to the graphene oxide dispersion, and the mixture is stirred for the first time. Then an organic nitrogen source is added, and the mixture is stirred for the second time to obtain the reaction solution.

[0022] Furthermore, the concentration of the graphene oxide dispersion is 1–20 mg / mL.

[0023] Furthermore, the first stirring speed is 300-700 rpm and the stirring time is 0.5-2 h; the second stirring speed is 100-500 rpm and the stirring time is 0.1-1 h.

[0024] In some embodiments of this application, in step (1), the temperature of the hydrothermal reaction is 150-250°C and the reaction time is 6-24 hours.

[0025] In some embodiments of this application, in step (2), the first drying method is freeze drying, and the freeze drying time is 15 to 30 hours.

[0026] In some embodiments of this application, in step (3), the rotational speed of the rotary kiln is 0.3 to 2 r / min.

[0027] In some embodiments of this application, in step (3), the inert gas is nitrogen.

[0028] In some embodiments of this application, in step (3), the flow rate of water vapor is 0.2 to 1 L / min relative to every 30 to 100 g of the reduced graphene oxide aerogel, the time for the first activation treatment is 1 to 2 h, the flow rate of carbon dioxide is 0.2 to 1 L / min, and the time for the second activation treatment is 1 to 3 h.

[0029] In some embodiments of this application, in step (3), the second temperature T2 is 800 to 1000°C.

[0030] In some embodiments of this application, in step (3), the washing is performed using water or an alcohol solvent, and the second drying method is vacuum drying.

[0031] Secondly, this application provides heteroatom-doped porous graphene prepared by the preparation method described in the first aspect of this application.

[0032] In some embodiments of this application, the specific surface area of ​​the heteroatom-doped porous graphene is ≥1500 m². 2 / g, micropore ratio ≥60%, nitrogen atom mass content 3%~3.5%, boron atom mass content 1%~1.5%.

[0033] Thirdly, this application provides the application of heteroatom-doped porous graphene as described in the second aspect of this application in electronic devices or catalysts.

[0034] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0035] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, wherein:

[0036] Figure 1 This is a schematic flowchart of a method for preparing heteroatom-doped porous graphene according to one embodiment. Detailed Implementation

[0037] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0038] The "scope" disclosed in this application is defined in the form of a lower limit and / or an upper limit, whereby a given scope is defined by selecting a lower limit and / or an upper limit. This type of scope may or may not include endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form an undefined scope, and any lower limit can be combined with other lower limits to form an undefined scope, similarly, any upper limit can be combined with any other upper limit to form an undefined scope. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and can be combined with any other point or single value, or with other lower or upper limits, to form an undefined scope.

[0039] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0040] The first aspect of this application provides a method for preparing heteroatom-doped porous graphene, comprising:

[0041] (1) A hydrothermal reaction is carried out on a reaction solution containing graphene oxide, an organic nitrogen source, an organic boron source and water to obtain a reduced graphene oxide hydrogel.

[0042] (2) The reduced graphene oxide hydrogel is first dried to obtain reduced graphene oxide aerogel.

[0043] (3) The reduced graphene oxide aerogel is fed into a rotary kiln for gradient heating treatment, then washed and dried to obtain nitrogen-boron co-doped porous graphene.

[0044] In this application, the graphene oxide sheet diameter can be 1–20 μm, for example, 1 μm, 2 μm, 3 μm, 5 μm, 7 μm, 8 μm, 12 μm, 15 μm, 20 μm, etc.; the graphene oxide thickness can be 1–5 nm, for example, 1 nm, 2 nm, 3 nm, 5 nm, etc.; the oxygen content of the graphene oxide can be 30%–60%, for example, 30%, 32%, 35%, 40%, 43%, 45%, 50%, 60%, etc. The graphene oxide can be commercially available or prepared by methods well known in the art, such as the Hummers process using various graphite as raw materials.

[0045] In this application, the organic nitrogen source can be selected from various organic compounds containing amino groups (-NH2), such as various amino acids. Compared with inorganic nitrogen sources, the amino groups in the structure of organic nitrogen sources can crosslink with oxygen-containing functional groups in graphene oxide, fixing N element sites and thus further hindering graphene aggregation. As some embodiments, the organic nitrogen source is selected from one or more of dicyandiamide, glycine, urea, alanine, and phenylalanine. In order to increase the micropore ratio while increasing the N atom doping amount, preferably, the mass ratio of the organic nitrogen source to the graphene oxide is (1-5):1, for example, 1:1, 2:1, 2.5:1, 3:1, 4:1, 5:1, etc.

[0046] In this application, the organoboron source can be selected from various organic compounds having a boric acid group (-B(OH)2), such as various arylboronic acids and arylboronic acids having a hydroxyl group (-OH). The hydroxyl group can crosslink with the oxygen-containing functional groups in graphene oxide, fixing the B element sites and hindering graphene aggregation. As some embodiments, the organoboron source is selected from at least one of phenylboronic acid, 2-hydroxyphenylboronic acid, 3-hydroxyphenylboronic acid, 4-hydroxyphenylboronic acid, 3-hydroxymethylphenylboronic acid, and 4-hydroxymethylphenylboronic acid. Typically, the mass ratio of the organoboron source to the graphene oxide can be (2-20):1, for example, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 15:1, 16:1, 18:1, 20:1, etc. In order to increase the amount of boron doping while further reducing the proportion of mesopores, the preferred mass ratio of the organic boron source to the graphene oxide is (5-15):1.

[0047] In step (1), the reaction solution can be prepared by uniformly mixing graphene oxide, an organic nitrogen source, and an organic boron source in an aqueous solvent. The reaction solution is typically a suspension. The aqueous solvent can be water or a mixture of water and an alcohol, including but not limited to methanol and ethanol. The mixing method includes, but is not limited to, ultrasonic dispersion and magnetic stirring.

[0048] In some embodiments, the reaction solution can be obtained by the following method:

[0049] Graphene oxide is dispersed in water to prepare a graphene oxide dispersion; wherein the concentration of the graphene oxide dispersion can be 1 to 20 mg / mL, such as 1 mg / mL, 3 mg / mL, 5 mg / mL, 8 mg / mL, 10 mg / mL, 12 mg / mL, 15 mg / mL, 18 mg / mL, 20 mg / mL, etc.

[0050] An organoboron source or a methanol solution of an organoboron source is added to the graphene oxide dispersion, and the mixture is stirred for the first time. Then, an organonitrogen source is added, and the mixture is stirred for the second time to obtain the reaction solution. The mass concentration of the organoboron source in the methanol solution can be, for example, 5% to 40%.

[0051] This application does not have any special requirements for the methods of the first and second stirring, as long as the organic boron source and the organic nitrogen source are uniformly distributed in the graphene oxide dispersion. As some specific examples, the speed of the first stirring can be 300-700 rpm, and the stirring time can be 0.5-2 h; the speed of the second stirring can be 100-500 rpm, and the stirring time can be 0.1-1 h.

[0052] According to this application, during the hydrothermal reaction, graphene oxide (GO) in the reaction solution forms hydrogen bonds with water using its surface oxygen-containing functional groups (such as hydroxyl and carboxyl groups), causing GO to self-assemble into a gel structure in water. Furthermore, the amino groups provided by the organic nitrogen source have reducing properties, enabling partial reduction of GO to obtain a reduced graphene oxide hydrogel. The hydrothermal reaction can be carried out in a high-pressure reactor.

[0053] In some embodiments, the temperature of the hydrothermal reaction can be 150–250°C, for example, 150°C, 160°C, 165°C, 170°C, 172°C, 175°C, 180°C, 190°C, 193°C, 200°C, 210°C, 220°C, 235°C, 240°C, etc.; the time of the hydrothermal reaction can be 6–24 hours, for example, 6 hours, 8 hours, 9.5 hours, 10 hours, 12 hours, 15 hours, 16 hours, 17 hours, 18 hours, 20 hours, 22 hours, 24 hours, etc. Preferably, the temperature of the hydrothermal reaction is 160–200°C, and the reaction time is 10–24 hours.

[0054] According to this application, in step (2), the first drying aims to rapidly remove moisture from the hydrogel to form an aerogel with a certain porosity. Preferably, the first drying method is freeze-drying, and the freeze-drying time can be 15 to 30 hours, for example, 15 hours, 18 hours, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, 25 hours, 26 hours, 27 hours, 28 hours, or 30 hours.

[0055] Preferably, step (2) further includes: washing the reduced graphene oxide hydrogel before the first drying, for example, soaking the reduced graphene oxide hydrogel in water for 12 to 48 hours and then washing it with water until it is neutral.

[0056] According to this application, in step (3), the gradient heating process is carried out in the presence of an inert gas and includes a first stage and a second stage performed sequentially. The inert gas can be selected from various gases that do not participate in the reaction, such as argon, nitrogen, etc., and is preferably nitrogen.

[0057] First stage (low-temperature sintering): Inert gas is introduced into the rotary furnace, and the temperature is raised to a first temperature T1 (400-700℃), and held at the first temperature T1 for 0.5-5 hours. By calcining at low temperature in inert gas, small molecules can be allowed to escape, achieving pore formation and effective doping of heteroatoms (B and N).

[0058] As some specific examples, the first temperature T1 can be 400℃, 420℃, 430℃, 450℃, 470℃, 500℃, 520℃, 530℃, 550℃, 560℃, 580℃, 600℃, 650℃, 700℃, etc., and the holding time at the first temperature T1 can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 4h, 5h, etc.

[0059] In the first stage, it is preferable to heat the rotary kiln to the first temperature T1 at a heating rate of 1 to 5 °C / min. The low-speed heating can promote the gradual overflow of small molecules and reduce the proportion of mesopores in porous graphene.

[0060] The second stage (high temperature activation): The rotary kiln is heated to the second temperature T2 (T2-T1≥200℃), and held at the second temperature T2 for 0.5-2 hours. Then, water vapor is introduced for the first activation treatment, and then carbon dioxide is introduced for the second activation treatment.

[0061] In some embodiments, the second temperature T2 and the first temperature T1 satisfy the following relationship: 200℃ < T2 - T1 ≤ 500℃. To further increase the micropore ratio, the second temperature T2 is preferably 800-1000℃, such as 800℃, 850℃, 880℃, 900℃, 910℃, 920℃, 930℃, 950℃, 960℃, 980℃, 1000℃, etc.

[0062] In the second stage, the rotary kiln is preferably heated to the second temperature T2 at a heating rate of 5–20 °C / min. Before introducing steam, the temperature is held at the second temperature T2 for 0.5–2 hours (e.g., 0.5 h, 1 h, 1.5 h, 2 h, etc.) to stabilize the internal temperature of the graphene and improve the uniformity of subsequent activation. During the activation process, the carbon (C) provided by the graphene reacts with steam (H2O) to form gases H2 and CO, and reacts with CO2 to form gas CO. Combined with the pore-forming process in the first stage, these gases can be used to continue creating pores inside the graphene, increasing the specific surface area.

[0063] In some embodiments, the flow rate of water vapor is 0.2 to 1 L / min relative to each 30 to 100 g of the reduced graphene oxide aerogel, the time for the first activation treatment is 1 to 2 h, the flow rate of carbon dioxide is 0.2 to 1 L / min, and the time for the second activation treatment is 1 to 3 h.

[0064] In some embodiments, during the first and second stages, the flow rate of the inert gas can be 1 to 5 L / min relative to every 30 to 100 g of the reduced graphene oxide aerogel.

[0065] In step (3), it is preferable that the rotational speed of the rotary kiln is maintained at 0.3 to 2 r / min, for example 0.3 r / min, 0.5 r / min, 0.8 r / min, 1 r / min, 2 r / min, etc.

[0066] In step (3), it is preferable to use water or alcohol solvents (such as ethanol or methanol) for washing to remove excess impurities such as boron oxide from the gradient heating process.

[0067] In step (3), preferably, the second drying method is vacuum drying.

[0068] According to some specific implementation methods, the preparation process of the porous graphene is as follows: Figure 1 The following is stated:

[0069] Graphene oxide was dispersed in water to prepare a graphene oxide dispersion.

[0070] A reduced graphene oxide hydrogel was prepared by uniformly dispersing graphene oxide dispersion, organic boron source and organic nitrogen source and then undergoing hydrothermal reaction.

[0071] Reduced graphene oxide aerogel was prepared by freeze-drying the reduced graphene oxide hydrogel.

[0072] Reduced graphene oxide aerogel was subjected to gradient heating, followed by washing and vacuum drying to obtain boron-nitrogen co-doped porous graphene.

[0073] The second aspect of this application provides heteroatom-doped porous graphene prepared by the preparation method described in the first aspect of this application.

[0074] In some embodiments, the specific surface area of ​​the heteroatom-doped porous graphene is ≥1500 m². 2 / g, micropore ratio ≥60%, nitrogen atom mass content 3%~3.5%, boron atom mass content 1%~1.5%.

[0075] Thirdly, this application provides the application of heteroatom-doped porous graphene as described in the second aspect of this application in electronic devices or catalysts.

[0076] As described above, the heteroatom-doped porous graphene of this application possesses both high heteroatom doping amount and high specific surface area. On one hand, this heteroatom-doped porous graphene exhibits high conductivity, making it suitable for use in the fabrication of electronic devices requiring high conductivity. On the other hand, the heteroatoms improve the stability of the porous graphene, and the material also possesses a high specific surface area, enabling it to serve as a catalyst support for the effective composite of metal active components, thereby enhancing catalyst performance.

[0077] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0078] Example 1

[0079] Graphene oxide (GO, 2 μm in diameter, 2 nm in thickness, and 40% oxygen content) was dispersed in water to prepare a GO dispersion A1 with a concentration of 5 mg / mL.

[0080] A methanol solution of 2-hydroxyphenylboronic acid (concentration of 25 wt%) was added to dispersion A1 and stirred at 500 rpm for 60 min. Then phenylalanine was added and stirred for another 60 min to obtain the reaction solution. The mass ratio of 2-hydroxyphenylboronic acid, phenylalanine and GO in dispersion A1 was 8:4:1.

[0081] After the reaction solution was transferred to a high-pressure reactor, it was reacted at 180°C for 18 hours to obtain reduced graphene oxide (rGO) hydrogel B1.

[0082] Hydrogel B1 was soaked and washed with water until neutral, and then transferred to a freeze dryer for 24 hours to obtain rGO aerogel C1.

[0083] 40g of aerogel C1 was transferred into a rotary kiln at a rotation speed of 0.5 r / min. Under nitrogen protection, a gradient heating process was performed at a nitrogen flow rate of 2 L / min. The first temperature stage involved heating to 550℃ at a rate of 2℃ / min and holding for 2 hours. The second temperature stage involved heating to 900℃ at a rate of 5℃ / min and holding for 1 hour. Then, steam was introduced at a flow rate of 0.5 L / min and held for 1.5 hours. Next, carbon dioxide was introduced at a flow rate of 0.2 L / min and held for 1 hour. Finally, the mixture was cooled to room temperature to obtain dry powder D1.

[0084] Dry powder D1 was washed in ethanol and then vacuum dried at 80°C for 24 hours to obtain nitrogen-boron co-doped porous graphene powder, denoted as PG-1.

[0085] Example 2

[0086] Graphene oxide (GO, 5 μm in diameter, 3 nm in thickness, and 40% oxygen content) was dispersed in water to prepare a GO dispersion A2 with a concentration of 8 mg / mL.

[0087] Add 4-hydroxymethylphenylboronic acid to dispersion A2, stir at 300 rpm for 90 min, then add glycine and continue stirring for 60 min to obtain the reaction solution; wherein, the mass ratio of 4-hydroxymethylphenylboronic acid, glycine and GO in dispersion A2 is 10:4:1;

[0088] After the reaction solution was transferred to a high-pressure reactor, it was reacted at 200℃ for 12 hours to obtain reduced graphene oxide (rGO) hydrogel B2.

[0089] Hydrogel B2 was soaked and washed with water until neutral, and then transferred to a freeze dryer for 24 hours to obtain rGO aerogel C2.

[0090] 40g of aerogel C2 was transferred into a rotary kiln at a rotation speed of 0.8 r / min. Under nitrogen protection, a gradient heating process was performed at a nitrogen flow rate of 2 L / min. The first temperature stage involved heating to 600℃ at a rate of 2℃ / min and holding for 1.5 h. The second temperature stage involved heating to 950℃ at a rate of 5℃ / min and holding for 1 h. Water vapor was then introduced at a flow rate of 0.3 L / min and held for 2 h. Carbon dioxide was then introduced at a flow rate of 0.2 L / min and held for 1.5 h. The mixture was then cooled to room temperature to obtain dry powder D2.

[0091] The dry powder D2 was washed in ethanol and then vacuum dried at 80°C for 24 hours to obtain nitrogen-boron co-doped porous graphene powder, denoted as PG-2.

[0092] Example 3

[0093] Graphene oxide (GO, 3 μm in diameter, 2 nm in thickness, and 50% oxygen content) was dispersed in water to prepare a GO dispersion A3 with a concentration of 10 mg / mL.

[0094] A methanol solution of 4-hydroxyphenylboronic acid (concentration of 25 wt%) was added to dispersion A3 and stirred at 500 rpm for 90 min. Then, dicyandiamide was added and the mixture was stirred for another 60 min to obtain the reaction solution. The mass ratio of 4-hydroxyphenylboronic acid, dicyandiamide and GO in dispersion A3 was 8:5:1.

[0095] After the reaction solution was transferred to a high-pressure reactor, it was reacted at 160℃ for 24 hours to obtain reduced graphene oxide (rGO) hydrogel B3.

[0096] Hydrogel B3 was soaked and washed with water until neutral, and then transferred to a freeze dryer for 24 hours to obtain rGO aerogel C3;

[0097] 80g of aerogel C3 was transferred into a rotary kiln at a rotation speed of 0.3 r / min. Gradual heating was performed under nitrogen protection at a nitrogen flow rate of 2 L / min. The first temperature stage involved heating to 500℃ at a rate of 1℃ / min and holding for 2 hours. The second temperature stage involved heating to 950℃ at a rate of 10℃ / min and holding for 1 hour. Water vapor was then introduced at a flow rate of 1 L / min and held for 2 hours. Carbon dioxide was then introduced at a flow rate of 0.3 L / min and held for 1 hour. The mixture was then cooled to room temperature to obtain dry powder D3.

[0098] The dry powder D3 was washed in ethanol and then vacuum dried at 80°C for 24 hours to obtain nitrogen-boron co-doped porous graphene powder, denoted as PG-3.

[0099] Example 4

[0100] Nitrogen-boron co-doped porous graphene was prepared according to the method in Example 1, except that 2-hydroxyphenylboronic acid was replaced with an equal mass of phenylboronic acid. The prepared nitrogen-boron co-doped porous graphene was designated as PG-4.

[0101] Example 5

[0102] Nitrogen-boron co-doped porous graphene was prepared according to the method in Example 1, except that the temperature of the first stage was adjusted to 450°C and the temperature of the second stage was adjusted to 800°C. The prepared nitrogen-boron co-doped porous graphene is denoted as PG-5.

[0103] Comparative Example 1

[0104] Graphene oxide (GO, 2 μm in diameter, 2 nm in thickness, and 40% oxygen content) was dispersed in water to prepare a GO dispersion A1 with a concentration of 5 mg / mL.

[0105] A methanol solution of 2-hydroxyphenylboronic acid (concentration of 25 wt%) was added to dispersion A1 and stirred at 500 rpm for 60 min. Then phenylalanine was added and stirred for another 60 min to obtain the reaction solution. The mass ratio of 2-hydroxyphenylboronic acid, phenylalanine and GO in dispersion A1 was 8:4:1.

[0106] After the reaction solution was transferred to a high-pressure reactor, it was reacted at 180°C for 18 hours to obtain reduced graphene oxide (rGO) hydrogel B1.

[0107] Hydrogel B1 was soaked and washed with water until neutral, and then transferred to a freeze dryer for 24 hours to obtain rGO aerogel C1.

[0108] 40g of aerogel C1 was transferred into a rotary kiln at a furnace speed of 0.5 r / min and subjected to high-temperature treatment under nitrogen protection at a nitrogen flow rate of 2 L / min. The temperature was increased to 900℃ at a rate of 5℃ / min and held for 1 h. Then, water vapor was introduced at a flow rate of 0.5 L / min and held for 1.5 h. Next, carbon dioxide was introduced at a flow rate of 0.2 L / min and held for 1 h. Finally, the temperature was lowered to room temperature to obtain dry powder D-11.

[0109] The dry powder D-11 was washed in ethanol and then vacuum dried at 80°C for 24 hours to obtain nitrogen-boron co-doped porous graphene powder, denoted as PG-d1.

[0110] Comparative Example 2

[0111] Graphene oxide (GO, 2 μm in diameter, 2 nm in thickness, and 40% oxygen content) was dispersed in water to prepare a GO dispersion A1 with a concentration of 5 mg / mL.

[0112] Add boron trioxide to dispersion A1 and stir at 500 rpm for 60 min. Then add phenylalanine and continue stirring for 60 min to obtain the reaction solution. The mass ratio of boron trioxide, phenylalanine and GO in dispersion A1 is 8:4:1.

[0113] After the reaction solution was transferred to a high-pressure reactor, it was reacted at 180℃ for 18 hours to obtain reduced graphene oxide (rGO) hydrogel B-21.

[0114] Hydrogel B-21 was soaked and washed with water until neutral, and then transferred to a freeze dryer for 24 hours to obtain rGO aerogel C-21;

[0115] 40g of aerogel C-21 was transferred into a rotary kiln at a rotation speed of 0.5 r / min. Gradual heating was performed under nitrogen protection at a nitrogen flow rate of 2 L / min. The first stage involved heating to 550℃ at a rate of 2℃ / min and holding for 2 hours, with the nitrogen flow rate controlled at 2 L / min. The second stage involved heating to 900℃ at a rate of 5℃ / min and holding for 1 hour, followed by the introduction of steam at a rate of 0.5 L / min for 1.5 hours, then the introduction of carbon dioxide at a rate of 0.2 L / min for 1 hour. Finally, the mixture was cooled to room temperature to obtain dry powder D-21.

[0116] The dry powder D-21 was washed in ethanol and then vacuum dried at 80°C for 24 hours to obtain nitrogen-boron co-doped porous graphene powder, denoted as PG-d2.

[0117] Comparative Example 3

[0118] Graphene oxide (GO, 2 μm in diameter, 2 nm in thickness, and 40% oxygen content) was dispersed in water to prepare a GO dispersion A1 with a concentration of 5 mg / mL.

[0119] A methanol solution of 2-hydroxyphenylboronic acid (concentration of 25 wt%) was added to dispersion A1 and stirred at 500 rpm for 60 min. Then, ammonia water with a mass concentration of 25% was added and stirred for another 60 min to obtain the reaction solution. The mass ratio of 2-hydroxyphenylboronic acid, ammonia water and GO in dispersion A1 was 8:16:1.

[0120] After the reaction solution was transferred to a high-pressure reactor, it was reacted at 180°C for 18 hours to obtain reduced graphene oxide (rGO) hydrogel B-31.

[0121] Hydrogel B-31 was soaked and washed with water until neutral, and then transferred to a freeze dryer for 24 hours to obtain rGO aerogel C-31;

[0122] 40g of aerogel C-31 was transferred into a rotary kiln at a rotation speed of 0.5 r / min. Gradual heating was performed under nitrogen protection at a nitrogen flow rate of 2 L / min. The first stage involved heating to 550℃ at a rate of 2℃ / min and holding for 2 hours, with the nitrogen flow rate controlled at 2 L / min. The second stage involved heating to 900℃ at a rate of 5℃ / min and holding for 1 hour, followed by the introduction of steam at a flow rate of 0.5 L / min for 1.5 hours, then the introduction of carbon dioxide at a flow rate of 0.2 L / min for 1 hour. Finally, the mixture was cooled to room temperature to obtain dry powder D-31.

[0123] The dry powder D-31 was washed in ethanol and then vacuum dried at 80°C for 24 hours to obtain nitrogen-boron co-doped porous graphene powder, denoted as PG-d3.

[0124] Test case

[0125] The test examples are used to illustrate the characterization and performance testing of the nitrogen-boron co-doped porous graphenes PG-1 to PG-5 and PG-d1 to PG-d3 prepared in the above embodiments and comparative examples.

[0126] 1. The gas isothermal adsorption / desorption curves were measured using a specific surface area and pore size analyzer (ASAP2460 model) by static method. The specific surface area and pore size distribution were obtained by BET method and BJH method. The test results are shown in Table 1.

[0127] 2. The resistivity of the powder was tested using a GM-I type multifunctional automatic powder resistivity tester. The test results are shown in Table 1.

[0128] 3. The elemental composition was analyzed using XPS (Thermo VG Scientific ESCALAB 250 instrument, using Mg Ka-rays), and the results are shown in Table 2.

[0129] Table 1

[0130]

[0131] Table 2

[0132] PG-1 86.81 8.87 3.25 1.07 PG-2 87.84 7.65 3.15 1.36 PG-3 87.53 7.96 3.36 1.15 PG-4 87.01 8.54 3.23 1.22 PG-5 86.74 8.91 3.27 1.08 PG-d1 87.91 8.92 2.66 0.51 PG-d2 88.65 8.24 2.98 0.13 PG-d3 88.57 8.07 2.23 1.13

[0133] As can be seen from Tables 1 and 2, compared with Comparative Examples 1-3, the porous graphene prepared in Examples 1-5 has a higher proportion of micropores, a larger specific surface area, and a higher proportion of boron and nitrogen, which also gives the product higher conductivity.

[0134] Comparing Example 1 with Comparative Examples 1-3, it can be seen that the one-step heating in Comparative Example 1 leads to the rapid overflow of internal small molecules, an increase in the proportion of mesopores, a decrease in specific surface area, and an impact on the doping effect, resulting in increased resistance. Comparative Example 2 uses an inorganic boron source (boron trioxide) for doping, resulting in a low amount of boron doping. This is because boron trioxide mostly acts as a hard template, regulating (improving) the mesoporous structure. When ammonia is used as the nitrogen source in Comparative Example 3, it is easily volatile, and the N content is difficult to control, leading to a decrease in the amount of N doping.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing heteroatom-doped porous graphene, characterized in that, include: (1) A hydrothermal reaction is carried out on a reaction solution containing graphene oxide, an organic nitrogen source, an organic boron source, and water to obtain a reduced graphene oxide hydrogel, wherein, The mass ratio of the organic nitrogen source to the graphene oxide is (1~5):

1. The organic boron source is selected from at least one of phenylboronic acid, 2-hydroxyphenylboronic acid, 3-hydroxyphenylboronic acid, 4-hydroxyphenylboronic acid, 3-hydroxymethylphenylboronic acid, and 4-hydroxymethylphenylboronic acid, and the mass ratio of the organic boron source to the graphene oxide is (5~15):1; (2) The reduced graphene oxide hydrogel is first dried to obtain reduced graphene oxide aerogel; (3) The reduced graphene oxide aerogel is fed into a rotary kiln for gradient heating treatment, followed by washing and a second drying to obtain nitrogen-boron co-doped porous graphene; wherein the gradient heating treatment is carried out in the presence of an inert gas and includes a first stage and a second stage performed sequentially. First stage: Inert gas is introduced into the rotary kiln, the temperature is raised to a first temperature T1, and the temperature is maintained at the first temperature T1 for 0.5~5 hours; The second stage involves raising the temperature to a second temperature T2, maintaining this temperature for 0.5–2 hours, then introducing steam for the first activation treatment, followed by introducing carbon dioxide for the second activation treatment. T2 and T1 satisfy the following relationship: T2-T1≥200℃, and T1 is 400~700℃.

2. The preparation method according to claim 1, characterized in that, The graphene oxide has a sheet diameter of 1~20μm, a thickness of 1~5nm, and an oxygen content of 30%~60%.

3. The preparation method according to claim 1 or 2, characterized in that, The organic nitrogen source is selected from at least one of dicyandiamide, glycine, urea, alanine, and phenylalanine.

4. The preparation method according to claim 1 or 2, characterized in that, The reaction solution was obtained by the following method: Graphene oxide was dispersed in water to prepare a graphene oxide dispersion. An organic boron source or a methanol solution of an organic boron source is added to the graphene oxide dispersion, and the mixture is stirred for the first time. Then an organic nitrogen source is added, and the mixture is stirred for the second time to obtain the reaction solution.

5. The preparation method according to claim 4, characterized in that, The concentration of the graphene oxide dispersion is 1~20 mg / mL.

6. The preparation method according to claim 4, characterized in that, The first stirring speed is 300~700 rpm, and the stirring time is 0.5~2h; the second stirring speed is 100~500 rpm, and the stirring time is 0.1~1h.

7. The preparation method according to claim 1 or 2, characterized in that, The hydrothermal reaction is carried out at a temperature of 150~250℃ for 6~24h.

8. The preparation method according to claim 1 or 2, characterized in that, The first drying method is freeze drying, and the freeze drying time is 15-30 hours.

9. The preparation method according to claim 1 or 2, characterized in that, The rotary kiln rotates at a speed of 0.3~2 r / min.

10. The preparation method according to claim 1 or 2, characterized in that, The inert gas is nitrogen.

11. The preparation method according to claim 1 or 2, characterized in that, For every 30-100g of the reduced graphene oxide aerogel, the flow rate of water vapor is 0.2-1L / min, the first activation treatment time is 1-2h, the flow rate of carbon dioxide is 0.2-1L / min, and the second activation treatment time is 1-3h.

12. The preparation method according to claim 1 or 2, characterized in that, The second temperature T2 is 800~1000℃.

13. The preparation method according to claim 1 or 2, characterized in that, The washing is performed using water or an alcohol solvent, and the second drying method is vacuum drying.

14. Heteroatom-doped porous graphene prepared by the preparation method according to any one of claims 1-13.

15. The heteroatom-doped porous graphene according to claim 14, characterized in that, The heteroatom-doped porous graphene has a specific surface area ≥1500 m². 2 / g, micropores account for ≥60%, nitrogen atoms have a mass content of 3%~3.5%, and boron atoms have a mass content of 1%~1.5%.

16. The use of heteroatom-doped porous graphene according to claim 14 or 15 in electronic devices or catalysts.

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