Heteroatom-doped porous graphene as well as preparation method and application thereof

Abstract

The invention belongs to the field of carbon materials, and provides heteroatom-doped porous graphene as well as a preparation method and application thereof. The preparation method of the heteroatom-doped porous graphene comprises the following steps: carrying out hydrothermal reaction on a reaction solution containing graphene oxide, an organic nitrogen source, an organic boron source and water to obtain reduced graphene oxide hydrogel; carrying out first drying on the reduced graphene oxide hydrogel to obtain reduced graphene oxide aerogel; and feeding the reduced graphene oxide aerogel into a rotary furnace, carrying out gradient heating treatment, washing, and carrying out secondary drying to obtain the nitrogen-boron co-doped porous graphene. According to the preparation method disclosed by the invention, the micropore proportion in the porous graphene and the anchoring capability to heteroatoms can be improved, the wastage rate of the heteroatoms is reduced, and the heteroatom-doped porous graphene with a high specific surface area is obtained.

Description

Technical Field

[0001] This application belongs to the field of carbon materials. Specifically, it provides a heteroatom-doped porous graphene, a preparation method thereof, and an application thereof. Background Art

[0002] Graphene is a new type of carbon material with a two-dimensional honeycomb structure formed by tightly packing single-layer carbon atoms. It has good mechanical properties and chemical stability. However, due to its high surface energy, the van der Waals force and π-π bond between the sheets cause it to be difficult to disperse during use, and it is prone to agglomeration and stacking, resulting in a reduction in the effective specific surface area and electron conduction ability of graphene, and affecting the performance of graphene. Porous graphene is a graphene material with a large number of void structures. Compared with ordinary graphene, porous graphene has characteristics such as low density and large effective specific surface area, and is suitable for use in fields such as conductive materials and catalyst preparation; further doping with heteroatoms is expected to improve the conductivity of porous graphene and application characteristics such as stability during catalyst preparation.

[0003] CN105833893A provides a preparation method of a doped graphene support, including ultrasonic dispersion of boric acid and graphene oxide in water, followed by a low-temperature hydrothermal reaction to obtain boron-doped graphene, and then mixing it with ammonia water, followed by a high-temperature hydrothermal reaction and calcination to obtain a B-N co-doped graphene support. In this method, the stability of the catalyst and the dispersion and utilization rate of the active component Pd metal particles can be improved by B-N co-doping the graphene support. Although this prior art successfully prepared B-N co-doped graphene by a two-step method, after graphene oxide is mixed with boric acid and ammonia water, operations such as filtration are carried out, resulting in the loss of boron source and nitrogen source, low B / N doping rate, and difficulty in regulating the internal pore size distribution.

[0004] CN110540196A discloses a preparation method of a doped porous graphene, including: first, using water vapor accompanied by Ar gas to react with graphene to generate nanopores to prepare 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 B-N co-doped porous graphene. This method uses water activation to obtain porous graphene, and then performs B-N co-doping by a two-step method. However, boric acid is dry-mixed with nitrogen-doped graphene, resulting in uneven mixing, difficulty in fixing the B element site, and difficulty in regulating the pore size distribution. The specific surface area of this doped porous graphene is also not high (<1000m 2 / g). Summary of the Invention

[0005] In view of the above problems existing in the prior art, the purpose of the present application is to provide a heteroatom-doped porous graphene, a preparation method thereof and an application thereof. The preparation method of the present application can increase the proportion of micropores in the porous graphene and the anchoring ability for heteroatoms, reduce the loss rate of heteroatoms, and obtain heteroatom-doped porous graphene with a high specific surface area.

[0006] In a first aspect, the present application provides a preparation method of heteroatom-doped porous graphene, comprising:

[0007] (1) Hydrothermally reacting 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) Performing a first drying on the reduced graphene oxide hydrogel to obtain a reduced graphene oxide aerogel;

[0009] (3) Feeding the reduced graphene oxide aerogel into a rotary furnace for gradient temperature increase treatment, then washing and performing a second drying to obtain nitrogen and boron co-doped porous graphene; wherein, the gradient temperature increase treatment is carried out in the presence of an inert gas and includes a first stage and a second stage carried out in sequence,

[0010] First stage: Introducing an inert gas into the rotary furnace, heating to a first temperature T1, and maintaining the temperature at the first temperature T1 for 0.5 to 5 h;

[0011] Second stage: Heating to a second temperature T2, maintaining the temperature at the second temperature T2 for 0.5 to 2 h, then introducing water vapor for a first activation treatment, and then introducing carbon dioxide for a second activation treatment; wherein,

[0012] T2 and T1 satisfy the relationship: T2 - T1 ≥ 200 °C, and T1 is 400 to 700 °C.

[0013] In the preparation method provided by the present application, the oxygen-containing groups on the surface of graphene oxide (GO) have an electrostatic effect, which can effectively anchor the organic boron source and the organic nitrogen source and fix the doping sites of B and N elements; during the gradient temperature increase process, first, low-temperature sintering can cause the boron source and the nitrogen source to generate small molecules and overflow, initially form a pore structure and realize in-situ doping of GO, increase the doping amounts of N and B, and then co-activate the doped graphene with water vapor and CO2 under high-temperature conditions. During the activation process, further pore formation is carried out: using boron oxide generated by the organic boron source as a hard template and the organic nitrogen source as a soft template to adjust the pore structure in the graphene, improve the activation efficiency and the proportion of micropores in the pore structure; thus, heteroatom-doped porous graphene with both a high specific surface area and a high heteroatom content can be successfully prepared.

[0014] In some embodiments of the present application, the sheet diameter of the graphene oxide is 1-20 μm, the thickness is 1-5 nm, and the oxygen content is 30%-60%.

[0015] In some embodiments of the present application, the organic boron source is selected from at least one of phenylboronic acid, 2-hydroxybenzeneboronic acid, 3-hydroxybenzeneboronic acid, 4-hydroxybenzeneboronic acid, 3-hydroxymethylbenzeneboronic acid, and 4-hydroxymethylbenzeneboronic acid.

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

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

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

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

[0020] Disperse the graphene oxide in water to obtain a graphene oxide dispersion;

[0021] Add an organic boron source or a methanol solution of the organic boron source to the graphene oxide dispersion, and perform a first stirring, then add the organic nitrogen source and perform a second stirring to obtain the reaction solution.

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

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

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

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

[0026] In some embodiments of the present application, in step (3), the rotation speed of the rotary furnace is 0.3-2 r / min.

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

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

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

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

[0031] In a second aspect, the present application provides heteroatom - doped porous graphene prepared by the preparation method described in the first aspect of the present application.

[0032] In some embodiments of the present application, the specific surface area of the heteroatom - doped porous graphene is ≥ 1500 m 2 / g, the micropore proportion is ≥ 60%, the mass content of nitrogen atoms is 3% - 3.5%, and the mass content of boron atoms is 1% - 1.5%.

[0033] In a third aspect, the present application provides the application of the heteroatom - doped porous graphene described in the second aspect of the present application in electronic devices or catalysts.

[0034] The additional aspects and advantages of the present application will be partially given in the following description, partially become apparent from the following description, or be understood through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The above - mentioned and / or additional aspects and advantages of the present application will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, where:

[0036] Figure 1 is a schematic flow chart of a preparation method of heteroatom - doped porous graphene according to an embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The embodiments of the present application will be described in detail below. The described embodiments are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application.

[0038] The "ranges" disclosed in this application are defined in the form of lower limits and / or upper limits. A given range is defined by selecting a lower limit and / or an upper limit. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily. That is, any lower limit can be combined with any upper limit to form a range not explicitly recorded, and any lower limit can be combined with other lower limits to form a range not explicitly recorded. Similarly, any upper limit can be combined with any other upper limit to form a range not explicitly recorded. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recorded.

[0039] If there is no special description, all the embodiments and optional embodiments of this application can be combined with each other to form a new technical solution, and such a technical solution 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, including:

[0041] (1) Subjecting a reaction solution containing graphene oxide, organic nitrogen source, organic boron source and water to a hydrothermal reaction to obtain a reduced graphene oxide hydrogel;

[0042] (2) Performing a first drying on the reduced graphene oxide hydrogel to obtain a reduced graphene oxide aerogel;

[0043] (3) Feeding the reduced graphene oxide aerogel into a rotary furnace for gradient temperature rise treatment, followed by washing and a second drying to obtain nitrogen and boron co-doped porous graphene.

[0044] In this application, the sheet diameter of the graphene oxide can be 1 to 20 μm, such as 1 μm, 2 μm, 3 μm, 5 μm, 7 μm, 8 μm, 12 μm, 15 μm, 20 μm, etc.; the thickness of the graphene oxide can be 1 to 5 nm, such as 1 nm, 2 nm, 3 nm, 5 nm, etc.; the oxygen content of the graphene oxide can be 30% to 60%, such as 30%, 32%, 35%, 40%, 43%, 45%, 50%, 60%, etc. The graphene oxide can be obtained by commercial purchase or prepared by methods well known in the art, such as prepared from various graphites by the Hummers method.

[0045] In the present application, the organic nitrogen source may be selected from various organic compounds having an amino group (-NH2), such as various amino acids. Compared with the inorganic nitrogen source, the amino group in the structure of the organic nitrogen source can crosslink with the oxygen-containing functional groups in graphene oxide to fix the N element sites, thereby further hindering the aggregation of graphene. 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 doping amount of N atoms, preferably, the mass ratio of the organic nitrogen source to the graphene oxide is (1-5):1, such as 1:1, 2:1, 2.5:1, 3:1, 4:1, 5:1, etc.

[0046] In the present application, the organic boron source may be selected from various organic compounds having a boronic acid group (-B(OH)2), such as various arylboronic acids, arylboronic acids having a hydroxyl group (-OH). The hydroxyl group can crosslink with the oxygen-containing functional groups in graphene oxide to fix the B element sites and hinder the aggregation of graphene. As some embodiments, the organic boron source is selected from at least one of phenylboronic acid, 2-hydroxybenzeneboronic acid, 3-hydroxybenzeneboronic acid, 4-hydroxybenzeneboronic acid, 3-hydroxymethylbenzeneboronic acid, and 4-hydroxymethylbenzeneboronic acid. Generally, the mass ratio of the organic boron source to the graphene oxide may be (2-20):1, such as 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 further reduce the mesopore ratio while increasing the doping amount of B atoms, preferably, the 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 a water-containing solvent. The reaction solution is usually a suspension. The water-containing solvent may be water or a mixed solvent of water and an alcohol. Specific examples of the alcohol include, but are not limited to, methanol and ethanol. The mixing methods include, but are not limited to, ultrasonic dispersion and magnetic stirring.

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

[0049] Disperse graphene oxide in water to obtain a graphene oxide dispersion; wherein, the concentration of the graphene oxide dispersion can be 1-20 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 organic boron source or a methanol solution of an organic boron source is added to the graphene oxide dispersion liquid, and first stirring is carried out. Then, an organic nitrogen source is added, and second stirring is carried out to obtain the reaction liquid. In the methanol solution of the organic boron source, the mass concentration of the organic boron source can be, for example, 5% to 40%.

[0051] This application has no special requirements for the ways of the first stirring and the second stirring, as long as the organic boron source and the organic nitrogen source can be evenly distributed in the graphene oxide dispersion liquid respectively. As some specific examples, the speed of the first stirring can be 300 to 700 rpm, and the stirring time can be 0.5 to 2 h; the speed of the second stirring can be 100 to 500 rpm, and the stirring time can be 0.1 to 1 h.

[0052] According to this application, during the hydrothermal reaction process, the graphene oxide (GO) in the reaction liquid forms hydrogen bonds with water by using the oxygen-containing functional groups (such as hydroxyl groups and carboxyl groups) on its surface, enabling GO to self-assemble in water to form a gel structure. Moreover, the amino group provided by the organic nitrogen source has reducibility and can partially reduce GO to obtain a reduced graphene oxide hydrogel. The hydrothermal reaction can be carried out in a high-pressure reaction kettle.

[0053] In some embodiments, the temperature of the hydrothermal reaction can be 150 to 250 °C, such as 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 to 24 h, such as 6 h, 8 h, 9.5 h, 10 h, 12 h, 15 h, 16 h, 17 h, 18 h, 20 h, 22 h, 24 h, etc. Preferably, the temperature of the hydrothermal reaction is 160 to 200 °C, and the reaction time is 10 to 24 h.

[0054] According to this application, in step (2), the first drying aims to quickly remove the moisture in the hydrogel to form an aerogel with a certain porosity. Preferably, the way of the first drying is freeze-drying, and the freeze-drying time can be 15 to 30 h, such as 15 h, 18 h, 20 h, 21 h, 22 h, 23 h, 24 h, 25 h, 26 h, 27 h, 28 h, 30 h.

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

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

[0057] First stage (low-temperature sintering): An inert gas is introduced into the rotary furnace, heated to a first temperature T1 (400 - 700 °C), and held at the first temperature T1 for 0.5 - 5 h. By calcining at a low temperature in an inert gas, small molecules can overflow, realizing pore formation and effective doping of heteroatoms (B and N).

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

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

[0060] Second stage (high-temperature activation): The rotary furnace is heated to a second temperature T2 (T2 - T1 ≥ 200 °C), held at the second temperature T2 for 0.5 - 2 h, then steam 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 °C < T2 - T1 ≤ 500 °C. To further increase the proportion of micropores, it is preferred that the second temperature T2 is 800 - 1000 °C, such as 800 °C, 850 °C, 880 °C, 900 °C, 910 °C, 920 °C, 930 °C, 950 °C, 960 °C, 980 °C, 1000 °C, etc.

[0062] In the second stage, it is preferred to heat the rotary furnace to the second temperature T2 at a heating rate of 5 - 20 °C / min. Before introducing steam, holding at the second temperature T2 for 0.5 - 2 h (such as 0.5 h, 1 h, 1.5 h, 2 h, etc.) can stabilize the internal temperature of the graphene and improve the uniformity of subsequent activation. In the activation treatment, 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. Combining with the pore formation in the first stage, these gases generated inside the graphene can be used to continue pore formation, increasing the specific surface area.

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

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

[0065] In step (3), preferably, the rotation speed of the rotary furnace is maintained at 0.3 - 2 r / min, such as 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 preferred to wash with water or an alcohol solvent (such as ethanol, methanol) to remove impurities such as excessive boron oxide in the gradient temperature rise treatment.

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

[0068] According to some specific embodiments, the preparation process of the porous graphene is as Figure 1 described:

[0069] Disperse graphene oxide in water to obtain a graphene oxide dispersion;

[0070] Disperse the graphene oxide dispersion, the organic boron source and the organic nitrogen source uniformly, and obtain a reduced graphene oxide hydrogel through a hydrothermal reaction;

[0071] Freeze-dry the reduced graphene oxide hydrogel to obtain a reduced graphene oxide aerogel;

[0072] Perform gradient temperature rise treatment on the reduced graphene oxide aerogel, and successively wash and vacuum dry to obtain boron and nitrogen co-doped porous graphene.

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

[0074] In some embodiments, the specific surface area of the heteroatom-doped porous graphene ≥ 1500 m 2 / g, the micropore proportion ≥ 60%, the mass content of nitrogen atoms is 3% - 3.5%, and the mass content of boron atoms is 1% - 1.5%.

[0075] In the third aspect, the present application provides the application of the heteroatom-doped porous graphene described in the second aspect of the present application in electronic devices or catalysts.

[0076] As described above, the heteroatom-doped porous graphene of the present application simultaneously has a high heteroatom doping amount and specific surface area. On the one hand, the heteroatom-doped porous graphene has a high conductivity and can be used in the preparation of electronic devices with requirements for electrical conductivity. On the other hand, the heteroatoms can improve the stability of the porous graphene, and the material also has a high specific surface area, which can be used as a catalyst support to effectively composite metal active components and improve the performance of the catalyst.

[0077] Embodiments of the present application will be described below. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation of the present application.

[0078] Example 1

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

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

[0081] After transferring the reaction solution into a high-pressure reaction kettle, it was reacted at 180 °C for 18 h to obtain a reduced graphene oxide (rGO) hydrogel B1;

[0082] The hydrogel B1 was soaked and washed until neutral, and then transferred to a freeze dryer for 24 h to obtain an rGO aerogel C1;

[0083] 40 g of the aerogel C1 was transferred into a rotary furnace, the furnace tube rotation speed was 0.5 r / min, and gradient heating was carried out under nitrogen protection, the nitrogen flow rate was 2 L / min. The temperature in the first stage: heated to 550 °C at a rate of 2 °C / min and held for 2 h; the temperature in the second stage: heated to 900 °C at a rate of 5 °C / 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, then carbon dioxide was introduced at a flow rate of 0.2 L / min and held for 1 h; finally, it was cooled to room temperature to obtain a dry powder D1;

[0084] The dry powder D1 was placed in ethanol for cleaning and vacuum dried at 80 °C for 24 h to obtain a nitrogen and boron co-doped porous graphene powder, denoted as PG-1.

[0085] Example 2

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

[0087] 4-Hydroxymethylphenylboronic acid was added to dispersion A2, and the mixture was stirred at 300 rpm for 90 min. Then glycine was added, and stirring was continued for 60 min to obtain a reaction solution; wherein, the mass ratio of 4-hydroxymethylphenylboronic acid, glycine to GO in dispersion A2 was 10:4:1;

[0088] After transferring the reaction solution into a high-pressure reactor, it was reacted at 200 °C for 12 h to obtain reduced graphene oxide (rGO) hydrogel B2;

[0089] The hydrogel B2 was soaked and washed with water until neutral, and then transferred to a freeze dryer for treatment for 24 h to obtain rGO aerogel C2;

[0090] 40 g of the aerogel C2 was transferred into a rotary furnace, the rotational speed of the furnace tube was 0.8 r / min, and gradient heating was carried out under nitrogen protection, the nitrogen flow rate was 2 L / min. The temperature in the first stage: heated to 600 °C at a rate of 2 °C / min and held for 1.5 h; the temperature in the second stage: heated to 950 °C at a rate of 5 °C / min and held for 1 h, then water vapor was introduced, the flow rate was 0.3 L / min, and held for 2 h, then carbon dioxide was introduced, the flow rate was 0.2 L / min, and held for 1.5 h; cooled to room temperature to obtain dry powder D2;

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

[0092] Example 3

[0093] Graphene oxide (GO, sheet diameter 3 μm, thickness 2 nm, oxygen content 50%) 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 25 wt%) was added to dispersion A3, and the mixture was stirred at 500 rpm for 90 min. Then dicyandiamide was added, and stirring was continued for 60 min to obtain a reaction solution; wherein, the mass ratio of 4-hydroxyphenylboronic acid, dicyandiamide to GO in dispersion A3 was 8:5:1;

[0095] After transferring the reaction solution into a high-pressure reactor, it was reacted at 160 °C for 24 h to obtain reduced graphene oxide (rGO) hydrogel B3;

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

[0097] Transfer 80 g of aerogel C3 into a rotary furnace with a furnace tube rotation speed of 0.3 r / min. Gradually increase the temperature under nitrogen protection with a nitrogen flow rate of 2 L / min. For the first-stage temperature: increase the temperature to 500 °C at a rate of 1 °C / min and hold for 2 h. For the second-stage temperature: increase the temperature to 950 °C at a rate of 10 °C / min, hold for 1 h, then introduce water vapor with a flow rate of 1 L / min and hold for 2 h. Then introduce carbon dioxide with a flow rate of 0.3 L / min and hold for 1 h. Cool down to room temperature to obtain dry powder D3.

[0098] Place the dry powder D3 in ethanol for cleaning and vacuum dry at 80 °C for 24 h to obtain a nitrogen and boron co-doped porous graphene powder, denoted as PG-3.

[0099] Example 4

[0100] Prepare nitrogen and boron co-doped porous graphene according to the method of Example 1, except that 2-hydroxybenzeneboronic acid is replaced with an equal mass of benzeneboronic acid. The prepared nitrogen and boron co-doped porous graphene is denoted as PG-4.

[0101] Example 5

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

[0103] Comparative Example 1

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

[0105] Add a methanol solution of 2-hydroxybenzeneboronic acid (concentration 25 wt%) to the dispersion A1, stir at 500 rpm for 60 min, then add phenylalanine and continue stirring for 60 min to obtain a reaction solution. Among them, the mass ratio of 2-hydroxybenzeneboronic acid, phenylalanine to GO in the dispersion A1 is 8:4:1.

[0106] Transfer the reaction solution into a high-pressure reaction kettle and react at 180 °C for 18 h to obtain a reduced graphene oxide (rGO) hydrogel B1.

[0107] Soak the hydrogel B1 and wash it to neutral, then transfer it to a freeze dryer and process for 24 h to obtain rGO aerogel C1.

[0108] Transfer 40 g of aerogel C1 into a rotary furnace with a furnace tube rotation speed of 0.5 r / min. Conduct high-temperature treatment under nitrogen protection with a nitrogen flow rate of 2 L / min. Heat up to 900 °C at a rate of 5 °C / min, hold for 1 h, then introduce water vapor with a flow rate of 0.5 L / min and hold for 1.5 h. Then introduce carbon dioxide with a flow rate of 0.2 L / min and hold for 1 h. Finally, cool down to room temperature to obtain dry powder D-11;

[0109] Place the dry powder D-11 in ethanol for cleaning and vacuum dry at 80 °C for 24 h to obtain a nitrogen and boron co-doped porous graphene powder, denoted as PG-d1.

[0110] Comparative Example 2

[0111] Disperse graphene oxide (GO, sheet diameter 2 μm, thickness 2 nm, oxygen content 40%) in water to prepare a GO dispersion A1 with a concentration of 5 mg / mL;

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

[0113] Transfer the reaction solution into a high-pressure reactor and react at 180 °C for 18 h to obtain a reduced graphene oxide (rGO) hydrogel B-21;

[0114] Soak the hydrogel B-21 and wash it with water until neutral, then transfer it to a freeze dryer for treatment for 24 h to obtain rGO aerogel C-21;

[0115] Transfer 40 g of aerogel C-21 into a rotary furnace with a furnace tube rotation speed of 0.5 r / min. Conduct gradient heating under nitrogen protection with a nitrogen flow rate of 2 L / min. First-stage temperature: Heat up to 550 °C at a rate of 2 °C / min and hold for 2 h, controlling the nitrogen flow rate at 2 L / min; Second-stage temperature: Heat up to 900 °C at a rate of 5 °C / min, hold for 1 h, then introduce water vapor with a flow rate of 0.5 L / min and hold for 1.5 h. Then introduce carbon dioxide with a flow rate of 0.2 L / min and hold for 1 h. Finally, cool down to room temperature to obtain dry powder D-21;

[0116] Place the dry powder D-21 in ethanol for cleaning and vacuum dry at 80 °C for 24 h to obtain a nitrogen and boron co-doped porous graphene powder, denoted as PG-d2.

[0117] Comparative Example 3

[0118] Disperse graphene oxide (GO, sheet diameter 2 μm, thickness 2 nm, oxygen content 40%) in water to prepare a GO dispersion A1 with a concentration of 5 mg / mL;

[0119] Add a methanol solution of 2-hydroxybenzeneboronic acid (concentration: 25 wt%) to dispersion A1, stir at 500 rpm for 60 min, then add ammonia water with a mass concentration of 25%, and continue stirring for 60 min to obtain a reaction solution; wherein, the mass ratio of 2-hydroxybenzeneboronic acid, ammonia water to GO in dispersion A1 is 8:16:1;

[0120] After transferring the reaction solution into a high-pressure reactor, react at 180 °C for 18 h to obtain reduced graphene oxide (rGO) hydrogel B-31;

[0121] Soak hydrogel B-31 and wash it with water until neutral, then transfer it to a freeze dryer and process for 24 h to obtain rGO aerogel C-31;

[0122] Transfer 40 g of aerogel C-31 into a rotary furnace, with the furnace tube rotation speed of 0.5 r / min, carry out gradient heating under nitrogen protection, the nitrogen flow rate is 2 L / min, first-stage temperature: heat up to 550 °C at a rate of 2 °C / min, keep warm for 2 h, control the nitrogen flow rate at 2 L / min; second-stage temperature: heat up to 900 °C at a rate of 5 °C / min, keep warm for 1 h, then introduce water vapor with a flow rate of 0.5 L / min, keep warm for 1.5 h, then introduce carbon dioxide with a flow rate of 0.2 L / min, keep warm for 1 h; finally cool down to room temperature to obtain dry powder D-31;

[0123] Wash the dry powder D-31 with ethanol and vacuum dry at 80 °C for 24 h to obtain nitrogen and boron co-doped porous graphene powder, denoted as PG-d3.

[0124] Test Example

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

[0126] 1. Use a specific surface area and pore size analyzer (ASAP2460 type) to measure the gas isothermal adsorption / desorption curve by the static method, and use the BET method and BJH method to obtain the specific surface area and pore size distribution. The test results are shown in Table 1.

[0127] 2. Use a GM-I type multifunctional powder resistivity automatic measuring instrument to test the powder resistivity. The test results are shown in Table 1.

[0128] 3. Use XPS method (instrument model Thermo VG Scientific ESCALAB 250, using Mg Ka ray) to analyze the element composition. The results are shown in Table 2.

[0129] Table 1

[0130]

[0131] Table 2

[0132] Material number C / wt% O / wt% N / wt% B / wt% 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] Combining Table 1 and Table 2, it can be seen that when comparing Examples 1-5 with Comparative Examples 1-3, the micropores of the porous graphene prepared in Examples 1-5 account for a relatively high proportion, with a large specific surface area and a relatively high proportion of B and N atoms, making the product also have relatively high conductivity.

[0134] When comparing Example 1 with Comparative Examples 1-3 respectively, it can be seen that in Comparative Example 1, one-step temperature rise will cause the internal small molecules to overflow too fast, the mesopore proportion to increase, the specific surface area to decrease, and at the same time affect the doping effect and increase the resistance; in Comparative Example 2, doping is carried out with an inorganic boron source (boron trioxide), resulting in a small B doping amount. The reason is that most of the boron trioxide acts as a hard template to regulate (increase) the mesoporous structure; when ammonia water is used as the nitrogen source in Comparative Example 3, it is easy to volatilize and the N content is not easy to control, resulting in a decrease in the N doping amount.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be covered within the scope of the claims and the description of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed in the text, 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) subjecting a reaction solution comprising graphene oxide, an organic nitrogen source, an organic boron source and water to a hydrothermal reaction to obtain a reduced graphene oxide hydrogel; (2) performing a first drying on the reduced graphene oxide hydrogel to obtain a reduced graphene oxide aerogel; (3) sending the reduced graphene oxide aerogel into a rotary kiln for gradient temperature treatment, and then washing and second drying to obtain nitrogen-boron co-doped porous graphene; wherein the gradient temperature treatment is carried out in the presence of an inert gas and includes a first stage and a second stage carried out in sequence, The first stage: introducing the inert gas into the rotary kiln, heating the rotary kiln to a first temperature T1, and maintaining the first temperature T1 for 0.5 to 5 hours; The second stage: heating to the second temperature T2, keeping the temperature at the second temperature T2 for 0.5 to 2 hours, then introducing water vapor for the first activation treatment, and then introducing carbon dioxide for the second activation treatment; wherein, T2 and T1 satisfy the relationship: T2-T1≥200°C, and T1 is 400~700°C.

2. The preparation method according to claim 1, characterized in that: The sheet diameter of the graphene oxide is 1-20 μm, the thickness is 1-5 nm, and the oxygen content is 30%-60%.

3. The preparation method according to claim 1 or 2, characterized in that: The organic boron source is selected from at least one of phenylboric acid, 2-hydroxyphenylboric acid, 3-hydroxyphenylboric acid, 4-hydroxyphenylboric acid, 3-hydroxymethylphenylboric acid and 4-hydroxymethylphenylboric acid; Preferably, the mass ratio of the organic boron source to the graphene oxide is (5-15):

1.

4. The preparation method according to any one of claims 1 to 3, characterized in that The organic nitrogen source is selected from at least one of dicyandiamide, glycine, urea, alanine and phenylalanine; Preferably, the mass ratio of the organic nitrogen source to the graphene oxide is (1-5):

1.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The reaction solution is obtained by the following method: dispersing graphene oxide in water to prepare a graphene oxide dispersion; Adding an organic boron source or a methanol solution of an organic boron source to the graphene oxide dispersion, and performing a first stirring, and then adding an organic nitrogen source, and performing a second stirring to obtain the reaction solution; Preferably, the concentration of the graphene oxide dispersion is 1 to 20 mg / mL; Preferably, 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.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The temperature of the hydrothermal reaction is 150-250° C., and the reaction time is 6-24 hours.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The first drying method is freeze drying, and the freeze drying time is 15 to 30 hours.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The rotating speed of the rotary kiln is 0.3-2 r / min; Preferably, the inert gas is nitrogen; Preferably, for every 30 to 100 g of the reduced graphene oxide aerogel, the flow rate of water vapor is 0.2 to 1 L / min, the time of 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 of the second activation treatment is 1 to 3 h; Preferably, the second temperature T2 is 800-1000°C; Preferably, water or an alcohol solvent is used for the washing, and the second drying method is vacuum drying.

9. Heteroatom-doped porous graphene prepared by the preparation method according to any one of claims 1 to 8; Preferably, the specific surface area of ​​the heteroatom-doped porous graphene is ≥1500m 2 / g, the proportion of micropores is ≥60%, the mass content of nitrogen atoms is 3% to 3.5%, and the mass content of boron atoms is 1% to 1.5%.

10. Use of the heteroatom-doped porous graphene according to claim 9 in electronic devices or catalysts.

Images