WO2023065375A1 - Metal organic framework derived carbon material, preparation method therefor and application thereof - Google Patents

Abstract

A metal organic framework (MOF) derived carbon material, a preparation method therefor and an application thereof, relating to the technical field of radioactive gas adsorption and removal. The MOF derived carbon material is obtained by heating and carbonizing a zeolite imidazole framework precursor in an inert gas environment. The MOF derived carbon material inherits the inherent network connection of a precursor MOFs material, and compared with traditional activated carbon materials, the MOF derived carbon material has the characteristic that the pore structure is adjustable, greatly improving adsorption selectivity of radioactive gas radon. Meanwhile, high-temperature carbonization is carried out by means of a proper path, thereby increasing the effective pore volume of the material, increasing the adsorption capacity of the material to radon, and also improving adsorption efficiency of the material.

Description

Metal-organic framework-derived carbon materials and their preparation methods and applications technical field

The invention relates to the technical field of radioactive gas adsorption and removal, in particular to a metal-organic framework-derived carbon material and its preparation method and application.

Background technique

Metal-organic frameworks (MOFs)-derived carbon materials, as an emerging porous carbon material, have attracted extensive attention because they inherit some unique properties of the precursor MOFs. It not only inherits the inherent network connection structure of MOFs materials, but also exhibits excellent structural stability, and is widely used in the fields of gas adsorption separation and catalysis. At present, there are few reports on the design and synthesis of MOF-derived carbon materials for the adsorption and separation of radioactive gases. Zeolitic imidazole frameworks (ZIFs), as a class of metal-organic frameworks with zeolite-like structures, have shown excellent performance in the adsorption and separation of gases. However, due to the limited pore volume, low adsorption capacity, and poor thermal and chemical stability of such materials, it is difficult to achieve sustainable operation.

The radioactive gas radon ( ²²² Rn) and its progeny are the main sources of natural radiation exposure to human beings, and they are widely present in soil, rock, water and air. Radon and its progeny enter the human body along with the air, exposing the human body to internal radiation, which in turn induces lung cancer, leukemia and respiratory diseases. Protection technologies against radon, a radioactive gas, mainly include forced ventilation, shielding and adsorption. Adsorption is a method based on the adsorption of radioactive gas radon and its progeny inside or on the surface of porous materials, thereby reducing the concentration of radon in the environment. However, activated carbon materials, which are traditional radon-absorbing materials, have disadvantages such as poor adsorption selectivity and low adsorption efficiency.

At present, among all materials for the adsorption of radioactive radon, activated carbon materials are favored in the field of radon adsorption and separation due to their large specific surface area and developed micropore volume. However, in the actual application process of this material, due to its wide pore size distribution, the adsorption specificity to radon is poor, the adsorption capacity is limited, the adsorption efficiency is low, and the adsorption process is greatly affected by temperature and humidity.

Contents of the invention

In order to solve the above technical problems, the present invention provides a metal-organic framework-derived carbon material and its preparation method and application. The purpose of the present invention is to prepare a MOF-derived carbon material with specific and selective adsorption and high adsorption capacity for radon. Furthermore, the present invention is an environmentally friendly adsorption material due to the inherent low toxicity properties of carbon-based materials.

The first object of the present invention is to provide a method for preparing a metal-organic framework-derived carbon material, comprising the following steps:

The zeolite imidazole framework precursor is heated and carbonized in an inert gas environment to obtain the metal organic framework derived carbon material; the zeolite imidazole framework precursor is ZIF-7, ZIF-8, ZIF-11, ZIF-12 and One or more of ZIF-67.

In one embodiment of the present invention, the zeolite imidazole framework precursor is synthesized by a solvothermal synthesis method.

In one embodiment of the present invention, the inert gas is nitrogen or argon, and the gas flow rate is 50-100 mL/min.

In one embodiment of the present invention, the rate of temperature increase is 2-5° C./min.

In one embodiment of the present invention, the carbonization is carbonization at 750-950° C. for 2-4 hours.

In one embodiment of the present invention, after the temperature-rising carbonization, cooling treatment is also included, and the temperature after cooling is 20-40°C.

The second object of the present invention is to provide a metal-organic framework-derived carbon material prepared by the preparation method.

The third object of the present invention is to provide an application of the metal-organic framework-derived carbon material in the adsorption of radioactive gas radon.

In one embodiment of the present invention, the radon concentration of the radioactive gas is ≥300Bq/m ³ .

In one embodiment of the present invention, the radon is ²²² Rn.

Compared with the prior art, the technical solution of the present invention has the following advantages:

(1) The MOF-derived carbon material of the present invention uses a metal-organic framework as a template, removes metal or non-metal elements in the framework by selective etching, and retains the framework relatively intact. Narrow pore size distribution and adjustable pore structure are the advantages of this kind of nanoporous carbon materials which are different from ordinary activated carbon materials. Compared with activated carbon materials with wider pore size distribution, MOF-derived porous carbon materials avoid the decrease in adsorption selectivity caused by too large pore size on the one hand, and avoid the difficulty of entering radioactive gas molecules due to too small pore size on the other hand. The resulting nanoporous carbon material has a high specific surface area and a large micropore distribution matching the molecular size of the target radioactive gas.

(2) The MOF-derived carbon material of the present invention can quickly adsorb radioactive radon in the environment, and the adsorption efficiency can reach more than 90% within 30 minutes. Due to the orderliness of the metal-organic framework structure of the precursor and the subsequent regulation of the high-temperature pyrolysis temperature, the performance of the obtained nanoporous carbon material is greatly improved compared with the original metal-organic framework material and traditional activated carbon material. In addition to the large specific surface area and special pore structure of such materials, radioactive radon gas molecules are physically adsorbed on the surface, and the heteroatoms in the precursor MOF, such as N atoms, are also used as doping materials during the in-situ pyrolysis process of derived carbon materials Atoms are dispersed in the pore structure, and as heteroatoms that increase the polarizability of the carbon skeleton, the interaction force between the carbon skeleton and the target gas molecule is improved, and the adsorption selectivity to the target gas molecule is further improved.

(3) The MOF-derived carbon material of the present invention inherits the inherent network connection of the precursor MOFs material. Compared with the traditional activated carbon material, it has the characteristics of adjustable pore structure, which greatly improves the adsorption selectivity of the radioactive gas radon . At the same time, high-temperature carbonization through a suitable path increases the effective pore volume of the material, improves the adsorption capacity of the material for radon, and improves the adsorption efficiency of the material.

(4) The MOF-derived carbon material of the present invention utilizes the pore size screening characteristics of ZIFs materials to realize separation, and can realize the increase of pore volume at high temperature and improve the adsorption capacity. At the same time, the thermal stability of the carbon material can be used to realize High temperature operation. In the invention, the ZIFs material is subjected to high-temperature treatment through a suitable path, and is used for the adsorption of radioactive gas radon, and the results show that this type of material shows good adsorption selectivity and adsorption efficiency.

Description of drawings

In order to make the content of the present invention more easily understood, the present invention will be described in further detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

Figure 1 is a scanning electron microscope image of the derived carbon material prepared in Example 1-2 of the present invention; wherein, (a) is ZIF-11-850, and (b) is ZIF-11-950.

Fig. 2 is a scanning electron micrograph of the derived carbon material prepared in Example 3-4 of the present invention; wherein, (a) is ZIF-8-850, and (b) is ZIF-8-950.

Fig. 3 is the N ₂ adsorption curve of the derived carbon material prepared in Example 1-2 of the present invention; wherein, (a) is the N ₂ adsorption isotherm, and (b) is the pore size distribution.

Fig. 4 is the N ₂ adsorption curve of the derived carbon material prepared in Example 3-4 of the present invention; wherein, (a) is the N ₂ adsorption isotherm, and (b) is the pore size distribution.

Fig. 5 is the penetration curve of the derived carbon material prepared by Example 1-2 of the present invention; wherein, (a) is the penetration curve of ZIF-11-850 to Rn, (b) is the penetration curve of ZIF-11-950 to Rn Penetrate the curve.

Fig. 6 is the penetration curve of the derivative carbon material prepared by the embodiment of the present invention 3-4; Wherein, (a) is the penetration curve of ZIF-8-850 to Rn, (b) is the penetration curve of ZIF-8-950 to Rn Penetrate the curve.

Fig. 7 is the penetration curve of comparative example 1-3 material of the present invention; Wherein, (a) is the penetration curve of ZIF-8 to Rn, (b) is the penetration curve of ZIF-11 to Rn, (c) is Breakthrough curve of coconut shell activated carbon for Rn.

Fig. 8 is a comparison chart of the adsorption efficiency of radon by the materials of Examples 1-4 of the present invention and materials of Comparative Examples 1-3.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and implement it, but the examples given are not intended to limit the present invention.

Example 1

A method for preparing a metal-organic framework-derived carbon material, comprising the steps of:

0.24 g of benzimidazole was dissolved in 6.4 g of anhydrous methanol solvent, and a mixed solution of 9.2 g of toluene and 2.4 g of ammonia was added at room temperature under mechanical stirring. Then, 0.22g of zinc acetate dihydrate was dissolved in 3.2g of anhydrous methanol solvent, and then quickly added to the above mixture at room temperature and under mechanical stirring, and the stirring was continued for 5 minutes. The obtained product was washed three times with anhydrous methanol and dried to obtain ZIF-11. The synthesized ZIF-11 was transferred to a high-temperature tube furnace, heated to 850 °C at a heating rate of 5 °C/min under the protection of _N2 , kept for 2 h, and cooled to room temperature naturally. The obtained carbon material was subjected to activation treatment at 130° C. and packed into a column.

Example 2

A method for preparing a metal-organic framework-derived carbon material, comprising the steps of:

0.24 g of benzimidazole was dissolved in 6.4 g of anhydrous methanol solvent, and a mixed solution of 9.2 g of toluene and 2.4 g of ammonia was added at room temperature under mechanical stirring. Then, 0.22g of zinc acetate dihydrate was dissolved in 3.2g of anhydrous methanol solvent, and then quickly added to the above mixture at room temperature and under mechanical stirring, and the stirring was continued for 5 minutes. The obtained product was washed three times with anhydrous methanol and dried to obtain ZIF-11. The synthesized ZIF-11 was transferred to a high-temperature tube furnace, heated to 950 °C at a heating rate of 5 °C/min under the protection of _N2 , kept for 2 h, and cooled to room temperature naturally. The obtained carbon material was subjected to activation treatment at 130° C. and packed into a column.

Example 3

A method for preparing a metal-organic framework-derived carbon material, comprising the steps of:

0.59g of zinc nitrate hexahydrate and 0.65g of 2-methylimidazole were mixed and dissolved in 80mL of anhydrous methanol, stirred for 2h, and then allowed to stand at room temperature for 24h. The resulting product was washed three times with anhydrous methanol and dried to obtain ZIF-8. The synthesized ZIF-8 was transferred to a high-temperature tube furnace, heated to 850 °C at a heating rate of 5 °C/min under the protection of _N2 , kept for 2 h, and cooled to room temperature naturally. The obtained carbon material was subjected to activation treatment at 130° C. and packed into a column.

Example 4

A method for preparing a metal-organic framework-derived carbon material, comprising the steps of:

0.59g of zinc nitrate hexahydrate and 0.65g of 2-methylimidazole were mixed and dissolved in 80mL of anhydrous methanol, stirred for 2h, and then allowed to stand at room temperature for 24h. The resulting product was washed three times with anhydrous methanol and dried to obtain ZIF-8. The synthesized ZIF-8 was transferred to a high-temperature tube furnace, heated to 950 °C at a heating rate of 5 °C/min and kept for 2 h under the protection of _N2 , and then naturally cooled to room temperature. The obtained carbon material was subjected to activation treatment at 130° C. and packed into a column.

Tests show that the ZIF-8-950 derived carbon material prepared in this example has a micropore volume as high as 0.289 cm ³ /g, and the dynamic adsorption coefficient of Rn can reach 9.47 L/g at 25°C and 5% humidity. g, the adsorption efficiency is 100%, and the half-breakthrough time is 91 minutes.

Comparative example 1

Mix and dissolve 0.59g of zinc nitrate hexahydrate and 0.65g of 2-methylimidazole in 80mL of anhydrous methanol, stir for 2h, and then let stand at room temperature for 24h. The resulting product was washed three times with anhydrous methanol and dried to obtain ZIF-8.

Comparative example 2

0.24 g of benzimidazole was dissolved in 6.4 g of anhydrous methanol solvent, and a mixed solution of 9.2 g of toluene and 2.4 g of ammonia was added at room temperature under mechanical stirring. Then, 0.22g of zinc acetate dihydrate was dissolved in 3.2g of anhydrous methanol solvent, and then quickly added to the above mixture at room temperature and under mechanical stirring, and the stirring was continued for 5 minutes. The obtained product was washed three times with anhydrous methanol and dried to obtain ZIF-11.

Comparative example 3

Traditional coconut shell activated carbon material.

test case

Performance characterization or testing was performed on the materials of Examples 1-4 of the present invention and Comparative Examples 1-3.

(1) SEM analysis

Fig. 1-2 is the scanning electron micrograph of two ZIF-11 and ZIF-8 that embodiment 1-4 is selected respectively, it can be seen that the carbon material after high-temperature pyrolysis basically keeps the appearance of precursor material, and this and The irregular morphology of traditional coconut shell activated carbon materials is in sharp contrast, indicating that this kind of high-temperature pyrolysis can make our derived carbon materials have a high specific surface area of the precursor MOF, and due to the stability of the precursor itself, it can be used during the pyrolysis process. The middle frame will not completely collapse due to high temperature, and basically retains a large microporous structure, which is beneficial to the material's adsorption of radon gas.

(2) Structural characterization

The material was characterized by BET specific surface area analyzer, and the micropore volume is shown in Table 1. Figures 3-4 are the _N2 adsorption curves and pore size distribution diagrams of the two ZIF-11 and ZIF-8 selected in Examples 1-4, respectively. It can be seen that the carbon material after high-temperature pyrolysis has a high _N2 adsorption capacity , which further proves that the derived carbon materials have high specific surface area and pore volume. The pore size distribution of the surface-derived carbon material is mainly micropores of about 0.5nm, which can better match the dynamic size of radon atoms, avoiding the fact that radon atoms cannot enter the pores because the pore size is too small, and also avoid Because the pore size is too large, the material lacks adsorption selectivity for radon atoms.

(3) Penetration experiment of Rn

First, all test samples were degassed and activated under vacuum (10Pa) conditions for 12 hours in an oil bath at 130 ° C, N ₂ purging for 2 hours. Then, 1 g of each activated sample was weighed in a vacuum glove box, and loaded into a Ф12.8 mm×115.1 mm loading column respectively.

Before sample loading, in order to ensure that radon chamber concentration and temperature no longer change and measure the average concentration of radon (the material of embodiment 1-2, comparative example 2 is to carry out under 10% humidity condition; Embodiment 3-4, comparative example The materials in 1 and 3 are carried out under the condition of 5% humidity), we first connect the RAD7 to the cycle, and test the radon concentration change of the cycle system every 10 minutes. About 3 hours later, under the premise of ensuring the stability of the instrument test, we put the material into the drying column, and recorded the dynamic adsorption data of radon by the test material through RAD7, and plotted with the measured radon concentration change as the ordinate and time as the abscissa Dynamic adsorption curve.

Adsorption capacity: Q=∫∫(c _t ×F×t)dcdt/m (F is the gas flow rate controlled in the test procedure (mL/min); m is the mass of the adsorbed sample (g); t is the adsorption time (min) ; c _t is the radon concentration (Bq/m ³ ) measured at time t; Q is the adsorption capacity (Bq/g) of the material calculated for the integral concentration-time, which reflects the adsorption capacity of the material to radon) .

Dynamic adsorption coefficient: k _d =Q/c ₀ (k _d is the dynamic adsorption coefficient (L/g), which normalizes the test influencing factors such as initial concentration, mass and gas flow, and reflects the adsorption of radon gas by the material ability).

Adsorption efficiency: η=(c _t /c ₀ )×100% (η is the adsorption efficiency (%), this amount refers to the concentration of radon detected at the outlet when the adsorption reaches the lowest equilibrium point and the concentration detected at the outlet after the final adsorption is saturated The ratio of the radon concentration obtained can also be understood as the maximum depth that can remove radon gas under the same conditions. The larger the value, the stronger the adsorption capacity of the material for radon, which is a parameter that reflects the adsorption and binding capacity of the material for radon) .

Half-penetration time: τ=k _d ×m/F (τ is the half-penetration time (min), which refers to the time when the material absorbs radon from the beginning of the air flow through the adsorption material to the penetration of the 50% saturation point. Time is also a parameter reflecting the material's ability to absorb radon).

Table 1 shows the relevant parameters of the final measured material:

Table 1

It can be seen from Table 1 that under the same conditions of controlled ambient temperature and humidity, the dynamic adsorption coefficients of ZIF-11-derived carbon materials and ZIF-8-derived carbon materials prepared by high-temperature pyrolysis are much higher than those of their corresponding precursors. materials, indicating that high-temperature pyrolysis significantly improves the adsorption capacity of such materials for radioactive radon, and under the same environmental conditions, the dynamic adsorption coefficient of ZIF-8 derived carbon materials pyrolyzed at 950°C is as high as 9.47L/g, which is a high Its precursor material is more than 40 times, and the environmental concentration of 3000Bq/m3 radon is reduced to the lower detection limit of RAD7 instrument (3.7Bq/m ³ ), and the half-penetration time is as long as 91min. The most widely used coconut shell activated carbon material on the market has a dynamic adsorption coefficient of only 6.06L/g under the same environmental conditions, an adsorption efficiency of 64.29%, and a half-breakthrough time of 40 minutes. Therefore, in terms of the adsorption of radon, the radioactive gas in the environment, it is feasible for the zeolite imidazole framework derivative carbon material prepared by the invention to be used in areas with high radon concentration in special environments to reduce radon concentration.

Figures 5-7 are the penetration test curves of ZIF-11-derived carbon, ZIF-8-derived carbon and their precursors, and traditional coconut shell activated carbon to radon, respectively. It can be seen from the results that ZIF-11-derived carbon and ZIF-8-derived carbon materials have obvious removal depth of radon concentration, indicating that the materials have strong interaction with radon atoms and high selectivity, compared with the precursors ZIF-11 and ZIF-8 The adsorption effect on radon is extremely obvious, and the removal depth of radon concentration is deeper than that of traditional coconut shell activated carbon materials. This further confirms that the derived carbon material has a stronger adsorption capacity for radon gas. At the same time, it can be seen from the integral area of the curve that the integral area of ZIF-11 derived carbon and ZIF-8 derived carbon materials for the reduction of radon concentration reflects that this type of material has a very large adsorption capacity for radon, which is different from the special pores of this type of material. The structure is related to the narrow pore size distribution, which is why this type of material has a better adsorption effect on radon than traditional activated carbon materials.

Figure 8 shows the adsorption efficiency of ZIF-11-derived carbon, ZIF-8-derived carbon and their precursors and traditional coconut shell activated carbon on radioactive radon obtained in parallel experiments. It can be seen that the adsorption efficiencies of ZIF-11-derived carbon and ZIF-8-derived carbon for radioactive radon gas are both over 90%, much higher than their corresponding precursor materials and traditional coconut shell activated carbon materials.

Apparently, the above-mentioned embodiments are only examples for clear description, and are not intended to limit the implementation. For those of ordinary skill in the art, on the basis of the above description, other changes or changes in various forms can also be made. It is not necessary and impossible to exhaustively list all the implementation manners here. However, the obvious changes or changes derived therefrom are still within the scope of protection of the present invention.

Claims (10)

1. A method for preparing a metal-organic framework-derived carbon material, comprising the steps of:

   The zeolite imidazole framework precursor is heated and carbonized in an inert gas environment to obtain the metal organic framework derived carbon material; the zeolite imidazole framework precursor is ZIF-7, ZIF-8, ZIF-11, ZIF-12 and One or more of ZIF-67.
2. The method for preparing metal-organic framework-derived carbon materials according to claim 1, wherein the zeolite imidazole framework precursor is synthesized by a solvothermal synthesis method.
3. The method for preparing metal-organic framework-derived carbon materials according to claim 1, wherein the inert gas is nitrogen or argon, and the gas flow rate is 50-100mL/min.
4. The method for preparing metal-organic framework-derived carbon materials according to claim 1, wherein the heating rate is 2-5° C./min.
5. The method for preparing metal-organic framework-derived carbon materials according to claim 1, wherein the carbonization is carbonization at 750-950° C. for 2-4 hours.
6. The method for preparing metal-organic framework-derived carbon materials according to claim 1, characterized in that, after heating up carbonization, cooling treatment is also included, and the temperature after cooling is 20-40°C.
7. A metal-organic framework-derived carbon material prepared by the preparation method described in any one of claims 1-6.
8. An application of the metal-organic framework-derived carbon material described in claim 7 in the adsorption of radioactive gas radon.
9. The application of the metal-organic framework-derived carbon material in the adsorption of radioactive gases according to claim 8, characterized in that the radioactive gas radon is ²²² Rn.
10. The application of the metal-organic framework-derived carbon material in the adsorption of radioactive gases according to claim 8, characterized in that the concentration of the radioactive gas radon is ≥300Bq/m ³ .

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