Preparation method and application of high-nitrogen-content nitrogen-doped porous carbon with multiple nitrogen-rich units

Abstract

This invention discloses a method for preparing high-nitrogen-content nitrogen-doped porous carbon with multiple nitrogen-rich units and its applications, belonging to the field of porous carbon materials. This invention uses a triazine containing a triyne group as the crosslinking center and a pyrazine containing a diazid group as the crosslinking arm. The two react via click chemistry to form a triazole structure, constructing a nitrogen-doped porous polymer with multiple nitrogen-rich units. The nitrogen content is controllable, high, and uniformly distributed, and the nitrogen-containing structure exhibits high stability, resulting in a higher residual nitrogen content after activation and carbonization, thereby improving the CO2 adsorption selectivity of the porous carbon. The nitrogen-doped porous polymer, through activation and carbonization, yields high-nitrogen-content nitrogen-doped porous carbon with multiple nitrogen-rich units, exhibiting high yield, adsorption capacity, selectivity, and reusability, and has broad application prospects in adsorption, catalysis, and membrane separation.

Description

Technical Field

[0001] This invention belongs to the field of porous adsorbents, and specifically relates to a method for preparing and applying a nitrogen-doped porous carbon with high nitrogen content and multiple nitrogen-rich units. Background Technology

[0002] The excessive consumption of fossil fuels has led to massive CO2 emissions, causing serious environmental problems. CO2 capture, utilization, and storage are crucial strategies for mitigating the threat of global warming. Among these, CO2 capture is the most indispensable step. Amine-based solvent adsorbents are currently the most mature industrialized CO2 capture technology; however, the amine washing process is not only energy-intensive but also produces harmful byproducts. Therefore, it is necessary to develop alternative CO2 capture technologies and prepare highly efficient CO2 capturing materials.

[0003] Currently, many solid adsorbents that promise to replace amine solvents have been developed. Among them, biomass porous carbon is abundant, has high specific surface area and pore volume, easily adjustable pore structure, and good thermal stability, making it beneficial for CO2 capture. However, the structure and pore size of these biomass porous carbons are unpredictable, and the type of nitrogen content is also uncertain. For porous carbon adsorbents, the porous structure, pore volume, and surface properties all affect the ability to capture CO2. Introducing nitrogen atoms into porous carbon can effectively improve its adsorption capacity, enhance surface polarity and alkalinity, and improve its reaction with CO2.

[0004] Therefore, to address the issues of insufficient nitrogen content, CO2 adsorption capacity, and selectivity in existing nitrogen-doped porous carbons, this paper proposes a method to introduce nitrogen atoms by modifying the introduction of azide units and introducing pyrazine units, thus constructing a nitrogen-doped porous carbon with multiple nitrogen-rich units, without affecting the overall performance of the carbon material. Achieving controllable and uniform nitrogen content, improving char yield, and thus further enhancing the CO2 adsorption selectivity of the porous carbon are particularly important. Summary of the Invention

[0005] In view of the technical problems existing in the prior art, the purpose of this invention is to propose a method for preparing high-nitrogen-content nitrogen-doped porous carbon with multiple nitrogen-rich units and its application.

[0006] To achieve the above objectives and effects, this invention employs the following technical solution: Pyrazine containing a bis(azide) group serves as the crosslinking arm. The two groups form a triazole structure through a click chemical reaction of alkynyl and azide groups. After crosslinking, activation and carbonization are performed to construct a nitrogen-doped porous carbon with multiple nitrogen-rich units. N atoms can act as framework builders, with controllable and high N content and more uniform distribution, further improving the CO2 adsorption selectivity of the porous carbon. By controlling the carbonization temperature and time, the pore size of the carbon material is concentrated within the microporous-mesoporous range. Changing the type and ratio of activator adjusts the pore volume of the porous carbon, thereby achieving effective control over the microporous structure and nitrogen atom doping. Specifically, the following steps are included:

[0007] (1) Preparation of pyrazines containing diazid groups:

[0008] Potassium azide and pyrazine chloride were dissolved in DMF and stirred at 60°C for 24 hours. After cooling to room temperature, the reaction mixture was poured into deionized water, filtered, washed, dissolved in chloroform, dried over magnesium sulfate, filtered, and the solvent was evaporated to obtain pyrazine containing diazid groups.

[0009] Furthermore, the mass ratio of potassium azide to pyrazine chloride is 1:0.5-1.

[0010] Furthermore, the pyrazine chloride is 2,6-dichloropyrazine, 3,6-dichloropyrazine, or 2,4-dichloropyrimidine.

[0011] (2) Preparation of triazines containing triyne groups:

[0012] (1) After mixing cyanuric chloride, PdCl2(PPh3)2, CuI and triethylamine evenly, trimethylethynylsilane was added under N2 atmosphere and stirred at 80°C for 24 h. Then, dichloromethane was added for dilution, and the mixture was filtered through diatomaceous earth. The filtrate was extracted with CH2Cl2 and water, washed with saturated NaCl, dried with anhydrous Na2SO4, and evaporated to dryness to obtain compound 1.

[0013] (2) Compound 1 was dissolved in methanol, then K2CO3 was added, and the mixture was stirred at room temperature for 4 hours. The mixture was then evaporated to dryness, and the organic phase was extracted with water and CH2Cl2. The mixture was washed with saturated NaCl, dried with anhydrous Na2SO4, and evaporated to dryness to obtain triazine containing triyne groups.

[0014] Furthermore, the mass ratio of cyanochloroethylene, PdCl2(PPh3)2, CuI, triethylamine, and trimethylethynylsilane is 1:0.1-1:0.05-0.5:1-2:2-10.

[0015] (3) Preparation of multiple nitrogen-rich porous organic polymers:

[0016] Triazine containing triyne, pyrazine containing diazide group, Pd(PPh3)4, CuI, and i-Pr2NH were mixed in a mass ratio of 1:1.5-3:1-2:0.5-2:1-5 and dissolved in THF. The mixture was reacted at 60-120℃ under N2 atmosphere for 6-24 h. After cooling to room temperature, the reaction mixture was poured into ethyl acetate. The organic layer was washed successively with 5wt% HCl, saturated NaHCO3, and saturated NaCl solutions, dried with MgSO4, filtered, and the solvent was evaporated under reduced pressure to obtain a multi-nitrogen-rich porous organic polymer.

[0017] (4) Preparation of high-nitrogen-content nitrogen-doped porous carbon with multiple nitrogen-rich units:

[0018] After mixing multiple nitrogen-rich porous organic polymers with an activator, the mixture was dried under vacuum at 80°C for 12 hours, then carbonized under a N2 atmosphere. After cooling to room temperature, the mixture was washed with 5 mol / L HCl and deionized water until the pH of the filtrate was 7. After drying, nitrogen-doped porous carbon with multiple nitrogen-rich units was obtained.

[0019] Furthermore, the mass ratio of the multiple nitrogen-rich porous organic polymer to the activator is 1:1-3; the activator is one or a mixture of potassium hydroxide (KOH), zinc chloride (ZnCl2), and ferric chloride (FeCl3).

[0020] Furthermore, the carbonization treatment temperature is 600-800℃, and the heating rate is 2-5℃ / min.

[0021] Application of high-nitrogen-content nitrogen-doped porous carbon materials with multiple nitrogen-rich units prepared by the above method in CO2 adsorption and separation.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention uses a triazine containing a triyne group as the crosslinking center and a pyrazine containing a diazid group as the crosslinking arm. The two crosslink through a click chemical reaction of the yne and diazid groups to form a triazole structure, thus constructing a nitrogen-doped porous polymer with multiple nitrogen-rich units. The nitrogen content is controllable, high, and uniformly distributed, and the nitrogen-containing structure has high stability. This results in a higher residual nitrogen content after activation and carbonization, thereby improving the CO2 adsorption selectivity of the porous carbon. By using activation and carbonization to improve the pore structure of the nitrogen-doped porous polymer, a high-nitrogen-content nitrogen-doped porous carbon with multiple nitrogen-rich units is obtained. This gives it a high specific surface area and a well-developed microporous structure. The synergistic effect of the high nitrogen content and the porous carbon results in high adsorption capacity, selectivity, and reusability, showing broad application prospects in adsorption, catalysis, and membrane separation.

[0024] The nitrogen-doped porous polymers with multiple nitrogen-rich units prepared by this invention have a yield of 61-85%, with pore sizes concentrated in the range of 0.5-2.5 nm and a specific surface area as high as 1100-2200 m². 2 With a nitrogen content of 8.24–15.18 wt% and a CO2 adsorption capacity of 2.5–3.7 mmol / g, it has broad application prospects in adsorption, catalysis and membrane separation. Attached image description:

[0025] The accompanying drawings, which are provided to further illustrate the invention and constitute a part of this invention, are illustrative embodiments and descriptions of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention.

[0026] Figure 1 The reaction formulas are those for POP-CDP prepared in Examples 1-5;

[0027] Figure 2 It refers to the POP-CDP prepared in Examples 1-5, its corresponding raw materials, and compounds 1, 2, and 3 in each step. 1 H NMR spectrum;

[0028] Figure 3 These are FTIR images of POP-CDP prepared in Examples 1-5, its corresponding raw materials, and compounds 1, 2, and 3 in each step;

[0029] Figure 4 These are SEM images of POP-CDP (a) and POP-CDP-KOH-800 (b), and a TEM image (c) of POP-CDP-KOH-800.

[0030] Figure 5 The N2 isotherm and CO2 adsorption curves of the high-nitrogen-content nitrogen-doped porous carbon with multiple nitrogen-rich units prepared in Examples 1-5 are shown.

[0031] Figure 6 These are XPS curves of nitrogen-doped porous carbon with multiple nitrogen-rich units prepared in Examples 1-5;

[0032] Figure 7 These are the CO2 isotherm adsorption curves and breakthrough curves of POP-CDP-KOH-600 prepared in Example 1. Detailed Implementation

[0033] The present invention will be further described below with reference to embodiments, comparative examples, and accompanying drawings, so that those skilled in the art can implement it based on the description. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods, and the reagents and materials described are commercially available.

[0034] Example 1

[0035] (1) Melamine chloride (1 g, 5.42 mmol), PdCl2(PPh3)2 (165 mg, 0.325 mmol), CuI (22.2 mg, 0.169 mmol), and triethylamine (10 mL) were mixed thoroughly. Then, trimethylethynylsilane (2.39 g, 24.33 mmol) was added under a N2 atmosphere, and the mixture was stirred at 80 °C for 24 h. The reaction mixture was diluted with dichloromethane (50 mL) and filtered through diatomaceous earth. The filtrate was extracted with CH2Cl2 and water, washed with saturated NaCl, dried over anhydrous Na2SO4, and evaporated to dryness to obtain compound 1.

[0036] (2) Compound 1 (1 g, 2.71 mmol) was dissolved in methanol (150 mL), and then K2CO3 (1.49 g, 8.13 mmol) was added. The mixture was stirred at room temperature for 4 h. The reaction mixture was evaporated to dryness, the organic phase was extracted with water and CH2Cl2, washed with saturated NaCl, dried over anhydrous Na2SO4, and evaporated to dryness to give a triazine containing a triyne group, denoted as compound 2.

[0037] (3) Potassium azide (0.82 g, 10.10 mmol) and 2,6-dichloropyrazine (1.50 g, 10.06 mmol) were dissolved in DMF (200 mL) and stirred at 60 °C for 24 h. After cooling to room temperature, the reaction mixture was poured into (200 mL) of water. The mixture was filtered, washed with water (250 mL), and the solid residue was dissolved in chloroform. After drying with magnesium sulfate and filtering, the solvent was evaporated to obtain a pyrazine containing a diazide group, denoted as compound 3.

[0038] (4) Compound 2 (1.0 g, 6.57 mmol), compound 3 (3.20 g, 19.73 mmol), Pd(PPh3)4 (429 mg, 0.989 mmol), CuI (70.8 mg, 0.989 mmol), and i-Pr2NH (10 mL) were dissolved in THF (30 mL) and reacted at 80 °C under N2 for 22 h. After cooling to room temperature, the reaction mixture was poured into ethyl acetate (200 mL). The organic layer was washed with 5% HCl (200 mL), saturated NaHCO3 (100 mL), and saturated NaCl solution (100 mL). The organic layer was dried with MgSO4 and filtered. The solvent was evaporated under reduced pressure to obtain a multiple nitrogen-rich porous organic polymer, denoted as POP-CDP, with a yield of 90%.

[0039] (5) The obtained POP-CDP was mixed with KOH at a ratio of 1:2 and dried under vacuum at 80℃ for 12 h. Under N2, the temperature was increased to 600℃ at 5℃ / min and held for 2 h. After cooling to room temperature, it was washed with 5 mol / L HCl and water until the filtrate was neutral. It was then dried under vacuum at 80℃ for 24 h to obtain nitrogen-doped porous carbon with high nitrogen content and multiple nitrogen-rich units, denoted as POP-CDP-KOH-600, with a yield of 85%.

[0040] Through FTIR and 1 H NMR characterized the structures of POP-CDP and its corresponding starting materials, as well as compounds 1, 2, and 3 in each step (see [link to H NMR]). Figure 2 and Figure 3 ),exist Figure 2 In compound a, the proton peak on the trimethylethynylsilynyl group is at 2.38 ppm, the proton peak on the methyl group is at 0.2 ppm, and the peak at 7.26 ppm is the proton peak of the solvent CDCl3. In compound 1, the proton peak on the methyl group adjacent to silicon is at 0.08 ppm, the peak at 2.66 ppm is the solvent peak of DMSO, the peak at 3.67 ppm is the water peak with DMSO as the solvent, and the remaining peaks are impurity peaks of cyanuric chloride. In compound 2, the proton peak on the ynyl group is at 4.05 ppm, the peak at 2.57 ppm is the solvent peak of DMSO, the peak at 3.52 ppm is the water peak with DMSO as the solvent, and the remaining peaks are impurity peaks of cyanuric chloride. Figure 2 In compound b, the proton peak at N=CC in 2,6-dichloropyrazine is at 8.86 ppm, while the proton peak at N=CC in compound 3 is at 8.23 ​​ppm; Figure 2 In C, the 7.50 ppm peak in POP-CDP represents the proton peak of the carbon atom in the triazole structure, while the peaks at 8.02 and 8.19 ppm represent the proton peaks of the pyrazine ring. Combined with FTIR and 1 The H NMR results confirmed the successful preparation of POP-CDP.

[0041] Example 2

[0042] The difference between Example 2 and Example 1 is that the carbonization temperature in step (5) is 700℃, while the rest is the same as in Example 1.

[0043] The nitrogen-doped porous carbon with multiple nitrogen-rich units prepared in Example 2 is designated as POP-CDP-KOH-700, with a yield of 75%.

[0044] Example 3

[0045] The difference between Example 3 and Example 1 is that the carbonization temperature in step (5) is 800℃, while the rest is the same as in Example 1.

[0046] The nitrogen-doped porous carbon with multiple nitrogen-rich units prepared in Example 3 is designated as POP-CDP-KOH-800, with a yield of 61%.

[0047] Depend on Figure 4 It is known that POP-CDP has relatively small pore size and porosity before carbonization, but the porosity increases after carbonization and activation. TEM results further show that POP-CDP exhibits increased porosity and microporous characteristics after carbonization and activation.

[0048] Example 4

[0049] The difference between Example 4 and Example 1 is that KOH is replaced with ZnCl2 in step (5), otherwise it is the same as Example 1.

[0050] The nitrogen-doped porous carbon with multiple nitrogen-rich units prepared in Example 4 is designated as POP-CDP-ZnCl2-700, with a yield of 81%.

[0051] Example 5

[0052] The difference between Example 5 and Example 1 is that KOH is replaced with FeCl3 in step (5), otherwise it is the same as Example 1.

[0053] The nitrogen-doped porous carbon with multiple nitrogen-rich units prepared in Example 4 is designated as POP-CDP-FeCl3-700, with a yield of 79%.

[0054] Table 1. BET data, nitrogen content, CO2 adsorption capacity, and CO2 / N2 selectivity of the porous carbon materials prepared in Examples 1-5

[0055]

[0056]

[0057] a Total pore volume when relative pressure P / P0 = 0.99;

[0058] b The cumulative micropore volume (in cm³) for pore sizes smaller than 0.8 nm was calculated using the NLDFT model. 3 / g;

[0059] c Calculate specific surface area using the BET method;

[0060] d Aperture calculated using the BJH method;

[0061] e The test conditions were 25℃ and 780mmHg.

[0062] The nitrogen-doped porous carbon materials with multiple nitrogen-rich units prepared in Examples 1-5 of this invention were characterized by N2 adsorption-desorption tests. The pore structure parameters, specific surface area, nitrogen content, CO2 adsorption capacity, and CO2 / N2 selectivity data for each example and comparative example are shown in Table 1 and... Figure 5-7 As shown, the specific surface area of ​​the obtained nitrogen-doped porous carbon material is as high as 2198 m². 2 With a nitrogen content as high as 15.18% per gram, it exhibits high selectivity and can effectively improve CO2 adsorption performance. At 25℃, the CO2 adsorption capacity is 2.52-3.72 mmol / g. It is a carbon material with high specific surface area and high nitrogen content, and can be applied to CO2 capture.

[0063] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing high-nitrogen-content nitrogen-doped porous carbon with multiple nitrogen-rich units, characterized in that, Includes the following steps: After the multiple nitrogen-rich porous organic polymers and the activator are mixed evenly, they are placed at 80°C. o After vacuum drying for 12 h, carbonization was carried out under N2 atmosphere. After cooling to room temperature, the carbon was washed with 5 mol / L HCl and deionized water until the pH of the filtrate was 7. After drying, nitrogen-doped porous carbon with multiple nitrogen-rich units with high nitrogen content was obtained. The multiple nitrogen-rich porous organic polymer is formed by a click chemistry reaction of a triazine containing a triyne group and a pyrazine containing a diazid group to form a triazole structure; the chemical formula of the triyne-containing triazine is: ; The chemical formula of the pyrazine containing the diazid group is: ; The activator is potassium hydroxide, zinc chloride, or ferric chloride; Application of high-nitrogen-content nitrogen-doped porous carbon materials with multiple nitrogen-rich units in CO2 adsorption and separation.

2. The method for preparing high-nitrogen-content nitrogen-doped porous carbon material with multiple nitrogen-rich units according to claim 1, characterized in that, The specific preparation method of the aforementioned nitrogen-rich porous organic polymer is as follows: Triazine containing a triyne group, pyrazine containing a diazide group, Pd(PPh3)4, CuI, and i-Pr2NH were mixed in a mass ratio of 1:1.5-3:1-2:0.5-2:1-5 and dissolved in THF. The mixture was then dissolved in THF under a N2 atmosphere at 60-120 °C. o After reacting at C for 6-24 h, the mixture was cooled to room temperature and poured into ethyl acetate. The organic layer was washed successively with 5wt% HCl, saturated NaHCO3 and saturated NaCl solutions, dried with MgSO4 and filtered. The solvent was evaporated under reduced pressure to obtain a multi-nitrogen-rich porous organic polymer.

3. The method for preparing high-nitrogen-content nitrogen-doped porous carbon material with multiple nitrogen-rich units as described in claim 2, characterized in that, The specific preparation method of the triazine containing the triyne group is as follows: (1) After mixing melamine chloride, PdCl2(PPh3)2, CuI and triethylamine evenly, trimethylethynylsilane is added under N2 atmosphere and heated to 80°C. o The reaction was stirred at C for 24 h, then diluted with dichloromethane, filtered through diatomaceous earth, the filtrate was extracted with CH2Cl2 and water, washed with saturated NaCl, dried over anhydrous Na2SO4, and evaporated to dryness to obtain compound 1. (2) Compound 1 was dissolved in methanol, then K2CO3 was added, and the mixture was stirred at room temperature for 4 h. The mixture was then evaporated to dryness, and the organic phase was extracted with water and CH2Cl2. The mixture was washed with saturated NaCl, dried with anhydrous Na2SO4, and evaporated to dryness to obtain triazine containing triyne groups.

4. The method for preparing high-nitrogen-content nitrogen-doped porous carbon material with multiple nitrogen-rich units as described in claim 3, characterized in that, The mass ratio of cyanochloroethylene, PdCl2(PPh3)2, CuI, triethylamine, and trimethylethynylsilane is 1:0.1-1:0.05-0.5:1-2:2-10.

5. The method for preparing high-nitrogen-content nitrogen-doped porous carbon material with multiple nitrogen-rich units as described in claim 2, characterized in that, The specific preparation steps of the pyrazine containing the bisazide group are as follows: Potassium azide and pyrazine chloride were dissolved in DMF at 60 °C. o After stirring at C for 24 h, the mixture was cooled to room temperature and poured into deionized water. After filtration and washing, it was dissolved in chloroform, dried over magnesium sulfate, filtered, and the solvent was evaporated to obtain pyrazine containing a diazid group.

6. The method for preparing high-nitrogen-content nitrogen-doped porous carbon material with multiple nitrogen-rich units according to claim 5, characterized in that, The mass ratio of potassium azide to pyrazine chloride is 1:0.5-1; the pyrazine chloride is 2,6-dichloropyrazine, 3,6-dichloropyrazine, or 2,4-dichloropyrimidine.

7. The method for preparing high-nitrogen-content nitrogen-doped porous carbon material with multiple nitrogen-rich units according to claim 1, characterized in that, The carbonization temperature is 600-800°C. o C, heating rate is 2-5 o C / min.

8. The method for preparing high-nitrogen-content nitrogen-doped porous carbon material with multiple nitrogen-rich units according to claim 1, characterized in that, The mass ratio of the multiple nitrogen-rich porous organic polymers to the activator is 1:1-3.

Images