Multistage precise pore channel carbon-based composite material and preparation method thereof

Abstract

According to the multistage precise pore channel carbon-based composite material and the preparation method thereof, the carbon-based composite material is prepared through preparation of tubular carbon nanofibers and directional induction of surface growth of MOF through carboxyl modification of the tubular carbon nanofibers, the pore size of the prepared carbon-based composite material is 0.35-0.77 nm, and the pore size of the prepared carbon-based composite material is 10-20 nm. By constructing a pore diameter which is more matched with the kinetic diameter (0.41 nm) of xenon, and meanwhile, through surface carboxylation modification of a carbon-based material and internal polarity regulation and control of an MOF coating layer, the synergistic effect of pore channel confinement and polarization induction is exerted, and the interaction force between the material and xenon is improved, so that krypton and xenon separation is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite materials, in particular to a multi-stage precise pore carbon-based composite material and a preparation method thereof. BACKGROUND

[0002] The application of krypton-xenon separation technology is mainly concentrated in the industrial demand field of high-purity rare gases. As rare gases, krypton and xenon are used as laser gases for photolithography process in semiconductor manufacturing, as high-efficiency gas discharge lamps in the lighting industry, as gas fillers for CT scanners in medical imaging, as working fluids for ion thrusters in the aerospace field, and also play an important role in nuclear reactor monitoring and scientific research experiments. With the progress of precision manufacturing and high-end technology, the requirements for krypton-xenon purity and separation efficiency continue to improve.

[0003] In the prior art, activated carbon is often used to adsorb krypton and xenon. Activated carbon has the advantages of large specific surface area, good stability, and low preparation cost, and has been widely used in the retention and capture of inert gases. The kinetic diameters of krypton and xenon are similar, being 0.36 nm and 0.41 nm, respectively. Due to its single and wide pore structure, the average pore size of micropores is greatly different from the kinetic diameter of inert gases, and cannot be precisely matched, resulting in a small difference in dynamic adsorption coefficient on activated carbon, limited separation efficiency, and the need for multi-stage adsorption or complex desorption temperature regulation, increasing the operation cost and energy consumption.

[0004] The above problems need to be solved. SUMMARY

[0005] The present application discloses a multi-stage precise pore carbon-based composite material and a preparation method thereof, aiming to solve the technical problems existing in the prior art.

[0006] The present application adopts the following technical solutions: According to a first aspect of the present application, a preparation method of a multi-stage precise pore carbon-based composite material is provided, which comprises the following preparation steps: preparation of tubular carbon nanofibers, dissolving monomers in a dispersant to form a dispersion solution, adding the dispersion solution to a continuous phase, then adding a catalyst solution, continuously reacting at 80-100 DEG C for 8-10 h, washing to obtain a solid, Soxhlet extracting the solid, and vacuum drying to obtain tubular carbon nanofibers; Preparation of carboxyl-modified tubular carbon nanofibers, adding the obtained tubular carbon nanofibers to an oxidizing agent for liquid-phase oxidation treatment at 100-120 DEG C for 3-5 h, washing and drying after cooling to room temperature to obtain carboxyl-modified tubular carbon nanofibers; Preparation of the carbon-based composite material, the obtained carboxyl-modified tubular carbon nanofiber is dispersed in an organic solvent to obtain a suspension, Zn(NO3)2·6H2O is added to the suspension, after stirring uniformly, 2-methyl imidazole solution is added, after stirring for 5-6 h, the precipitate is collected by centrifugation, and the carbon-based composite material is obtained after washing the precipitate.

[0007] In a possible implementation, the monomer includes any one of 1,4-p-dichlorobenzene, p-dibromobenzene, and m-dibromobenzene; the continuous phase is any one of polydimethylsiloxane, kerosene, liquid paraffin, and solid paraffin; and the dispersant is 1,2-dichloroethane.

[0008] In a possible implementation, the concentration of the monomer in the dispersion solution is 120 mg / mL.

[0009] In a possible implementation, the catalyst solution is a solution of a catalyst in 1,2-dichloroethane, the catalyst is anhydrous FeCl3, the concentration of the anhydrous FeCl3 in the catalyst solution is 75 mg / mL, and the volume ratio of the catalyst to the monomer is (1-1.6):(1.6-1).

[0010] In a possible implementation, during preparation of the tubular carbon nanofiber, 1,2-dichloroethane and anhydrous ethanol are used for cleaning, and vacuum drying is performed at a temperature of 650-800 ℃ for 4-6 h.

[0011] In a possible implementation, the oxidant is a mixed solution of H2O and HNO3, and the volume ratio of H2O to HNO3 in the mixed solution of H2O and HNO3 is 1:1.

[0012] In a possible implementation, during preparation of the carboxyl-modified tubular carbon nanofiber, after cooling to room temperature, the carboxyl-modified tubular carbon nanofiber is cleaned with deionized water and anhydrous ethanol, and drying is performed at a temperature of 60 ℃ for 6-8 h.

[0013] In a possible implementation, the 2-methyl imidazole solution is a solution of 2-methyl imidazole in methanol, and the concentration of 2-methyl imidazole in the 2-methyl imidazole solution is 0.016 g / mL.

[0014] In a possible implementation, the concentration of the carboxyl-modified tubular carbon nanofiber in the organic solvent is 0.004 g / mL, the molar ratio of the carboxyl-modified tubular carbon nanofiber to Zn(NO3)2·6H2O is 1:1, the Zn(NO3)2·6H2O is added to the suspension and stirred at a speed of 800-1000 r / min for 30-60 min, and the precipitate is washed with anhydrous ethanol.

[0015] According to a second aspect of the present application, the present application provides a multi-level precise pore carbon-based composite material, which is prepared by the preparation method described above, and the micropore diameter of the carbon-based composite material is 0.35-0.77nm.

[0016] The technical scheme adopted by the present application can achieve the following beneficial effects: The present application mainly provides a multi-level precise pore carbon-based composite material and a preparation method thereof. The present application prepares tubular carbon nanofibers and directionally induces surface growth of MOF through carboxyl modification of the tubular carbon nanofibers, and then prepares a carbon-based composite material. The pore diameter of the prepared carbon-based composite material is 0.35-0.77nm. By constructing a pore diameter that is more matched with the kinetic diameter (0.41nm) of xenon, and by regulating the polarity inside the MOF coating layer through carboxyl modification of the surface of the carbon-based material, the synergistic effect of "pore confinement and polarization induction" is achieved, the interaction force between the material and xenon is improved, and thus the separation of krypton and xenon is realized. The problem of weak interaction force between the activated carbon material and krypton and xenon gas is solved. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows, which form a part of the present application. The schematic embodiments of the present application and the description and explanation thereof do not constitute an improper limitation on the present application. In the drawings: Figure 1 A scanning electron microscope image of the carbon-based composite material provided for Embodiment 1 of the present application; Figure 2 A pore size distribution graph of the carbon-based composite material provided for Embodiment 1 of the present application; Figure 3 A pore size distribution graph of the carbon-based composite material provided for Embodiment 2 of the present application; Figure 4 A pore size distribution graph of the carbon-based composite material provided for Embodiment 3 of the present application; Figure 5 A pore size distribution graph of the carbon-based composite material provided for Embodiment 4 of the present application; Figure 6 A pore size distribution graph of the carbon-based composite material provided for Embodiment 5 of the present application; Figure 7 A pore size distribution graph of the carbon-based composite material provided for Embodiment 6 of the present application; Figure 8 A pore size distribution graph of the carbon-based composite material provided for Embodiment 7 of the present application. DETAILED DESCRIPTION

[0018] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in combination with specific embodiments of the present application and corresponding drawings. In the description of the present application, it should be noted that the term "or" is generally used in the sense of including "and / or" unless the context clearly indicates otherwise.

[0019] Example 1 Preparation of tubular carbon nanofiber: Weigh 36 g of 1,4-p-dichlorobenzene and dissolve it in 300 mL of 1,2-dichloroethane, and then add it to a three-necked flask containing 3 L of polydimethylsiloxane under stirring. Then, add 200 mL of 1,2-dichloroethane solution containing 15 g of anhydrous FeCl3 to it, and then continuously react at 100℃ for 10 h. After that, clean it with 1,2-dichloroethane and anhydrous ethanol respectively until the filtrate is colorless and transparent, and then obtain a reddish-brown solid. Soxhlet extract the obtained solid with anhydrous ethanol, and then vacuum dry and cool to room temperature to obtain a tubular polymer nanofiber. The temperature of vacuum drying is 800℃, and the calcination time is 6 h.

[0020] Preparation of carboxyl-modified tubular carbon nanofiber: Select H2O / HNO3 mixed solution (volume ratio of 1:1) as the oxidant to perform liquid phase oxidation treatment on the tubular carbon nanofiber. Under magnetic stirring, add the tubular carbon nanofiber to a three-necked flask containing the H2O / HNO3 mixed solution. The system is reacted at 100~120℃ for 3~5 h. After the solution is cooled to room temperature, clean it with deionized water and anhydrous ethanol respectively until the solution is neutral. Dry the product in a vacuum oven at 60℃ for 8 h, and finally obtain the carboxyl-modified tubular carbon nanofiber.

[0021] Preparation of carbon-based composite material: Disperse the carboxyl-modified tubular carbon nanofiber in 500 mL of methanol and ultrasonically treat for 30 min, and then add 3 g of Zn(NO3)2·6H2O to the above suspension and magnetically stir at a rotation speed of 800~1000 r / min for 60 min. Then, add 8 g of 2-methylimidazole to 500 mL of methanol, and then quickly add it to the stirring suspension, and then stir at room temperature for 6 h. Finally, centrifugally collect the precipitate, and then wash it with anhydrous ethanol to obtain the carbon-based composite material (carboxylated tubular carbon nanofiber / MOF composite material).

[0022] Place the prepared carbon-based composite material under a field emission scanning electron microscope (SEM, Germany-ZEISS-Gemini SEM360) to observe its morphology, Figure 1 The scanning electron microscope image of the carbon-based composite material provided for Example 1 of the present application; as Figure 1As shown, the long strip structure is a carboxylated tubular carbon nanofiber, and the spherical structure is a MOF metal organic framework, which is grown on the tubular carbon nanofiber. Figure 1 It can be seen that the preparation method produces a carboxylated tubular carbon nanofiber / MOF composite, i.e., a carbon-based composite material.

[0023] The prepared carbon-based composite material is prepared into uniform granular. Then, the carbon-based composite material is pretreated in vacuum at 150 DEG C for 12 h, and then, a BET full-automatic specific surface area analyzer is used to perform gas adsorption and desorption testing on the sample under the condition of liquid nitrogen at 77 K. After the instrument is analyzed, an isothermal adsorption and desorption curve is obtained. Finally, according to HK model data processing, the pore diameter of the carbon-based composite material is obtained. Figure 2 The pore diameter distribution of the carbon-based composite material provided for Example 1 of the present application is shown in the figure. The pore diameter of the carbon-based composite material prepared according to the preparation method of Example 1 is 0.4607 nm.

[0024] Example 2 The implementation of Example 2 is the same as that of Example 1, except that: The addition ratio of the catalyst to the monomer is 1:1.6.

[0025] Figure 3 The pore diameter distribution of the carbon-based composite material provided for Example 2 of the present application is shown in the figure. The pore diameter of the carbon-based composite material prepared according to the preparation method of Example 2 is 0.3910 nm.

[0026] Example 3 The implementation of Example 3 is the same as that of Example 1, except that: The monomer is p-dibromobenzene, Figure 4 The pore diameter distribution of the carbon-based composite material provided for Example 3 of the present application is shown in the figure. The pore diameter of the carbon-based composite material prepared according to the preparation method of Example 3 is 0.3535 nm.

[0027] Example 4 The implementation of Example 4 is the same as that of Example 1, except that: The monomer is m-dibromobenzene, Figure 5 The pore diameter distribution of the carbon-based composite material provided for Example 4 of the present application is shown in the figure. The pore diameter of the carbon-based composite material prepared according to the preparation method of Example 4 is 0.3583 nm.

[0028] Example 5 The implementation of Example 5 is the same as that of Example 1, except that: The continuous phase is kerosene, Figure 6The pore size distribution of the carbon-based composite material provided in Embodiment 5 of the present application is 0.7437 nm.

[0029] Embodiment 6 Embodiment 6 is implemented in the same manner as Embodiment 1, except that: the continuous phase is liquid paraffin, Figure 7 The pore size distribution of the carbon-based composite material provided in Embodiment 6 of the present application is 0.7679 nm.

[0030] Embodiment 7 Embodiment 7 is implemented in the same manner as Embodiment 1, except that: the continuous phase is solid paraffin, Figure 8 The pore size distribution of the carbon-based composite material provided in Embodiment 7 of the present application is 0.7547 nm.

[0031] Table 1 Comparison of results of Embodiments 1-7

[0032] The pore size distribution of the carbon-based composite material prepared by the preparation method of the present application is close to the kinetic diameter of xenon, and the pore size is close to the kinetic diameter of krypton and xenon, which are 0.36 nm and 0.41 nm, respectively. By increasing the interaction with xenon, krypton-xenon separation is achieved.

[0033] Embodiments 2, 3, and 4 use 1,4-p-dichlorobenzene, p-dibromobenzene, and m-dibromobenzene as monomers, and the ratio of catalyst to monomer in Embodiment 2 is 1:1.6. The pore size distribution of the carbon-based composite material prepared in Embodiments 2, 3, and 4 is less than 0.41, although krypton-xenon separation can be achieved, the interaction with xenon is slightly poor, and the effect is not as good as the separation effect of Embodiment 1.

[0034] Embodiments 5, 6, and 7 use kerosene, liquid paraffin, and solid paraffin as the continuous phase, respectively, to prepare carbon-based composite materials with a pore size distribution greater than 0.41, although krypton-xenon separation can be achieved, the interaction with xenon is slightly poor, and the effect is not as good as the separation effect of Embodiment 1.

[0035] Therefore, when the monomer 1,4-p-dichlorobenzene is selected, the continuous phase is polydimethylsiloxane, the catalyst is FeCl3, and the addition ratio of catalyst to monomer is 1.6:1, the pore size distribution of the prepared carbon-based composite material is greater than and closest to the kinetic diameter of xenon, krypton-xenon separation is achieved by increasing the interaction with xenon, and the effect is best.

[0036] The embodiments of the present application are described above with reference to the accompanying drawings, but the present application is not limited to the above-described specific embodiments, and the above-described specific embodiments are merely illustrative, but not restrictive, and a person of ordinary skill in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims, and all of them belong to the protection of the present application.

Claims

1. A method for preparing a multi-level precision porous carbon-based composite material, characterized in that, The preparation steps include the following: The preparation of tubular carbon nanofibers involves dissolving monomers in a dispersant to form a dispersion solution, adding the dispersion solution to a continuous phase, then adding a catalyst solution, and continuing the reaction at 80-100℃ for 8-10 h. After washing, a solid is obtained, which is then subjected to Soxhlet extraction and vacuum drying to obtain tubular carbon nanofibers. The preparation of carboxyl-modified tubular carbon nanofibers involves adding the obtained tubular carbon nanofibers to an oxidant and reacting them at 100-120℃ for 3-5 h for liquid-phase oxidation treatment. After cooling to room temperature, the fibers are washed and dried to obtain carboxyl-modified tubular carbon nanofibers. The carbon-based composite material was prepared by dispersing the obtained carboxyl-modified tubular carbon nanofibers in an organic solvent to obtain a suspension, adding Zn(NO3)2·6H2O to the suspension, stirring evenly, adding 2-methylimidazole solution, stirring for 5-6 hours, centrifuging to collect the precipitate, washing the precipitate to obtain the carbon-based composite material.

2. The preparation method according to claim 1, characterized in that, The monomer includes any one of p-dichlorobenzyl, p-dibromobenzyl, and m-dibromobenzyl; the continuous phase is any one of polydimethylsiloxane, kerosene, liquid paraffin, and solid paraffin; and the dispersant is 1,2-dichloroethane.

3. The preparation method according to claim 1, characterized in that, The concentration of the monomer in the dispersion solution is 120 mg / mL.

4. The preparation method according to claim 2, characterized in that, The catalyst solution is prepared by dissolving the catalyst in 1,2-dichloroethane solution. The catalyst is anhydrous FeCl3, and the concentration of the anhydrous FeCl3 in the catalyst solution is 75 mg / mL. The volume ratio of the catalyst to the monomer is (1.6-1):(1-1.6).

5. The preparation method according to claim 1, characterized in that, In the preparation of the tubular carbon nanofibers, 1,2-dichloroethane and anhydrous ethanol are used for cleaning, vacuum drying is carried out at a temperature of 650~800℃, and calcination is carried out for 4~6 h.

6. The preparation method according to claim 1, characterized in that, The oxidant is a mixed solution of H2O and HNO3, wherein the volume ratio of H2O to HNO3 in the mixed solution is 1:

1.

7. The preparation method according to claim 1, characterized in that, In the preparation process of the carboxyl-modified tubular carbon nanofibers, the process involves cooling to room temperature and then washing with deionized water and anhydrous ethanol, drying at 60°C, and drying for 6-8 hours.

8. The preparation method according to claim 2, characterized in that, The organic solvent is methanol; the 2-methylimidazole solution is 2-methylimidazole dissolved in methanol, and the concentration of 2-methylimidazole in the 2-methylimidazole solution is 0.016 g / mL.

9. The preparation method according to claim 8, characterized in that, The concentration of the carboxyl-modified tubular carbon nanofibers in the organic solvent is 0.004 g / mL, and the molar ratio of the carboxyl-modified tubular carbon nanofibers to the Zn(NO3)2·6H2O is 1:1; the Zn(NO3)2·6H2O is added to the suspension and the mixture is magnetically stirred at 800~1000 r / min for 30~60 min; the precipitate is washed with anhydrous ethanol.

10. A multi-level precision-channel carbon-based composite material, characterized in that, The carbon-based composite material is prepared by the preparation method according to any one of claims 1-9, and the micropore size of the carbon-based composite material is 0.35-0.77 nm.

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