KR20200121085A - ZIF modified with amine groups by post-synthetic modification and use thereof - Google Patents

Abstract

The present invention relates to a method for producing zeolitic imidazolate frameworks (ZIFs) into which an amine group is introduced by ligand substitution at a predetermined conversion rate by activating ZIFs having a neutral microporous structure based on zeolitic sodalite (SOD) topology and by being put into contact with an aromatic ring containing at least one nitrogen as a hetero element and having a structure similar to a ligand 2-methylimidazole, and a compound containing at least one amine group substituted on the ring. The present invention also relates to a use of ZIFs produced thereby.

Description

ZIF modified with amine groups by post-synthetic modification and use thereof {ZIF modified with amine groups by post-synthetic modification and use thereof}

The present invention activates zeolitic imidazolate frameworks (ZIFs) having a neutral microporous structure based on a zeolitic sodalite (SOD) topology, and a structure similar to the ligand 2-methylimidazole A method of preparing ZIF in which an amine group is introduced by ligand substitution at a predetermined conversion rate by contacting a compound containing an aromatic ring containing at least one nitrogen as a hetero element and at least one amine group substituted on the ring, and accordingly It relates to the use of the prepared ZIF.

The removal of carbon dioxide (CO ₂ ) from gaseous mixtures, due to its role in the greenhouse effect and its acidic and/or corrosive properties, creates a vast and ever-growing market. As a method of removing CO ₂ , there are several methods, such as a method of absorbing in a liquid phase or a method of adsorption to a highly porous material along with a membrane separation method and a liquefied distillation method. . In particular, methods using ionic liquids (ILs) are useful for the separation of CO ₂ from other gases. An ionic liquid is a solvent composed entirely of ions, exhibits an extremely low vapor pressure, has high chemical stability and inherent electrical conductivity. For these ionic liquids most gases such as nitrogen, oxygen and hydrogen, etc. exhibit very poor solubility, while CO ₂ is quite soluble. However, since the use of ionic liquids still requires high cost, it has a disadvantage of low economical efficiency, and it is difficult to secure physical property data according to the combination of cations and anions, so that the possibility of industrial use is low.

Zeolitic imidazolate frameworks (ZIFs) are a sub-concept of metal organic frameworks (MOFs) that can be applied to a wide range of applications, including catalytic reaction, molecular detection, gas storage and gas or solvent separation. It is attracting considerable attention. Among a wide range of ZIFs families, synthesis methods, adsorption mechanisms, and various potential applications for ZIF-8 including tetrahedral coordination building units having a neutral microporous structure based on a zeolitic sodalite (SOD) topology have been studied. have. However, the inherently weak adsorption site located on its pore surface results in insufficient adsorption uptake for permanent gases including H ₂ , N ₂ , CO ₂ , and O ₂ . Research to improve the equilibrium adsorption of ZIF-8 has focused on the modification of the prototype framework, especially the use of various ligand linkers and metal ions.

Functionalization of ZIF-8 is considered an essential step toward improving versatility and performance. One example is the introduction of an amine moiety within ZIF-8. In particular, the presence of an uncoordinated amine in ZIF-8 regulates its hydrophobicity, and can provide strong binding power to various molecules including CO ₂ , H ₂ O, NO ₂ , and the like. Zhang et al. successfully disclosed a direct solvothermal synthesis method for MAF-7, that is, a ZIF crystal containing a Lewis base active site having an SOD topology using 3-methyl-1,2,4-triazole as a ligand. This shows a significantly increased adsorption capacity compared to ZIF-8 for polar adsorbates containing CO ₂ and H ₂ O due to the advantage of the circular ZIF-8 porous structure according to the additional Lewis base active site (not coordinated Secondary amine). In addition, the presence of an uncoordinated amine site in ZIF-8 may allow for further chemical modification to modulate its intrinsic properties. However, MAF-7 synthesized by direct synthesis because of insufficient active sites for CO ₂ and the chemical interactions have still limited in excess of CO ₂ adsorption.

Postsynthetic modification (PSM) through metathesis of organic linkers is a new method for functionalization of MOF while maintaining structural integrity and high porosity. To date, the PSM approach is an essential tool necessary to overcome many of the critical issues of MOFs, enhancing the stability of MOFs and modulating the properties of MOFs, as well as enabling the reaction of MOFs previously unattainable. Finally, PSM will gradually become a promising method for the modification of MOFs.

The present inventors, while maintaining the crystal structure and size of the parent ZIF, through the introduction of an amine group, selectively improves adsorption capacity for CO ₂ , and discovers a method for producing ZIF that provides a reactive functional group capable of additional modification. As a result of intensive research efforts, a compound having a structure similar to that of a ligand through the synthesis and post-synthesis modification of activated ZIF and containing at least one nitrogen as a hetero element and at least one amine group substituted on the ring In the case of introducing an amine group by ligand exchange, it was confirmed that the adsorption capacity for CO ₂ was improved and the synthesis of a substance having novel properties was possible by additional chemical modification through the amine group, and the present invention was completed.

The first aspect of the present invention is a first step of activating zeolitic imidazolate frameworks (ZIFs) having a neutral microporous structure based on a zeolitic sodalite (SOD) topology; And an aromatic ring containing at least one nitrogen as a hetero element and at least one amine group substituted on the ring having a similar structure to the activated zeolite imidazolate skeleton, which is a ligand constituting it, 2-methylimidazole. A method for producing ZIF in which an amine group is introduced by ligand substitution, comprising a second step of contacting a compound containing, wherein the ZIF into which the amine group is introduced is ligand substituted at a conversion rate of 10 to 65% with respect to the total ligand, It maintains the same crystal structure as ZIF prior to the introduction of the amine group, but the selective adsorption capacity of CO ₂ to N ₂ or CH ₄ is improved, providing a manufacturing method.

In a second aspect of the present invention, activated ZIF has a structure similar to 2-methylimidazole, a ligand constituting it, and an aromatic ring containing at least one nitrogen as a hetero element and at least one amine group substituted on the ring. It provides a composition for adsorption of CO ₂ comprising ZIF into which an amine group is introduced by ligand substitution, prepared by contacting the containing compound.

In a third aspect of the present invention, a gas mixture containing CO ₂ and N ₂ , CH ₄ or both has a structure similar to 2-methylimidazole, a ligand constituting the activated ZIF, and nitrogen as a hetero element. Including the step of contacting ZIF into which an amine group is introduced by ligand substitution, prepared by contacting an aromatic ring containing at least one and a compound containing at least one amine group substituted on the ring, CO ₂ and N ₂ , A method of removing CO ₂ from a gas mixture containing CH ₄ or both is provided.

Hereinafter, the present invention will be described in more detail.

In the present invention, in ZIF, which is a kind of metal-organic framework (MOF) containing imidazolate as a ligand, its physical properties and/or catalytic activity are improved through modification to a functional group while maintaining the parental skeleton. It is based on the finding that the modification in the desired manner can be achieved through postsynthetic modification (PSM) by ligand substitution with a compound of similar size and structure to the ligand contained in the parent. In particular, it was confirmed that it is applicable to selective gas separation by improving the adsorption ability with specific gas molecules, such as CO ₂ , through PSM as a compound containing an amine group.

The present invention relates to a first step of activating zeolitic imidazolate frameworks (ZIFs) having a neutral microporous structure based on a zeolitic sodalite (SOD) topology; And an aromatic ring containing at least one nitrogen as a hetero element and at least one amine group substituted on the ring having a similar structure to the activated zeolite imidazolate skeleton, which is a ligand constituting it, 2-methylimidazole. It provides a method for producing ZIF into which an amine group is introduced by ligand substitution, including a second step of contacting the containing compound. Through this, the same crystal structure as the ZIF before the introduction of the amine group is maintained, but the selective adsorption capacity of CO ₂ to N ₂ or CH ₄ is improved, and the amine group introduced ZIF can be provided.

In the manufacturing method of the present invention, the first step may be performed by maintaining the dried ZIF under reduced pressure at 160 to 200° C. for 6 to 24 hours, but is not limited thereto, and conventional ZIF activation known in the art The method can be used as it is, or it can be appropriately changed and used.

In the production method of the present invention, the second step is a step performed to introduce a desired functional group, that is, an amine group, to the group synthesized ZIF through ligand substitution, and a C _1-4 alcohol solution in which ZIF to be introduced with an amine group is dispersed. It can be carried out by adding a compound having a structure similar to that of 2-methylimidazole and containing an aromatic ring containing at least one nitrogen as a hetero element and at least one amine group substituted on the ring.

In this case, the second step may be performed for 0.5 to 36 hours.

As described above, by adjusting the execution time of the second step, the amine group introduction rate, that is, the ligand constituting ZIF, that is, the aromatic ring containing at least one nitrogen as a hetero element of 2-methylimidazole, and on the ring The rate of substitution with a compound containing one or more substituted amine groups may be adjusted.

For example, the second step may be performed at 40 to 60° C., but is not limited thereto, and may be performed under reaction conditions for ligand substitution known in the art.

The ZIF to be introduced into the amine group by applying the manufacturing method of the present invention may be ZIF-8, but is not limited thereto.

Further, as a compound having a similar structure to the 2-methylimidazole, an aromatic ring containing at least one nitrogen as a hetero element and at least one amine group substituted on the ring, 3-amino-1,2, 4-triazole may be used, but is not limited thereto.

ZIF to which the amine group is introduced synthesized by the production method of the present invention has a reduced pore volume compared to ZIF before the introduction of the amine group. Due to such a reduced pore volume, the selective adsorption capacity for some gas particles may be reduced. For example, the selective adsorption capacity of C ₃ H ₆ to C ₃ H ₈ shows a tendency to decrease compared to before the modification due to the modification. In addition, adsorption capacity to N ₂ and CH ₄ may also decrease as the conversion rate of the ligand increases.

In addition, the present invention has a structure similar to that of 2-methylimidazole, a ligand constituting the activated ZIF, and includes an aromatic ring containing at least one nitrogen as a hetero element and at least one amine group substituted on the ring. It provides a composition for adsorption of CO ₂ comprising ZIF into which an amine group is introduced by ligand substitution, prepared by contacting a compound.

ZIF into which an amine group is introduced by substitution of the ligand contained in the composition for adsorbing CO ₂ of the present invention may be prepared according to the first aspect of the present invention described above.

In addition, the present invention has a gas mixture containing CO ₂ and N ₂ , CH ₄ or both, has a structure similar to 2-methylimidazole, a ligand constituting the activated ZIF, and one nitrogen as a hetero element. Including the step of contacting with ZIF into which an amine group is introduced by ligand substitution, prepared by contacting an aromatic ring containing the above and a compound containing at least one amine group substituted on the ring, CO ₂ and N ₂ , CH ₄ or it provides a method of removing CO ₂ from a gas mixture containing both.

ZIF into which an amine group is introduced by the ligand substitution used in the CO ₂ removal method of the present invention may be prepared according to the first aspect of the present invention described above.

In a specific embodiment of the present invention, as a compound containing an aromatic ring containing at least one nitrogen as a hetero element and at least one amine group substituted on the ring,

The production method of the present invention can provide ZIF with improved physical properties and/or catalytic activity by introducing a desired functional group at a predetermined conversion rate while maintaining the skeleton structure of the parent ZIF by using post-synthesis modification. ZIF into which the amine group has been introduced exhibits a specifically increased adsorption capacity for CO ₂ , so selective adsorption and/or separation thereof from the mixed gas is possible, and thus can be applied to a mixed substrate membrane for gas separation.

1 is a diagram showing a synthesis method of ZIF8-A by (A) direct synthesis method and (B) post synthesis modification method.
2 is a diagram showing (A) representative FE-SEM images of ZIF-8 and ZIF8-A synthesized by a direct solvate reaction and (B) an XRD pattern according to the Atz molar ratio to mim. (A1) is ZIF-8 (Atz/mim = 0/10), (A2) is ZIF8-A (Atz/mim = 2/8), (A3) is ZIF8-A (Atz/mim = 4/6) , (A4) is ZIF8-A(Atz/mim = 6/4), (A5) is ZIF8-A(Atz/mim = 8/2), (A6) is ZIF8-A(Atz/mim = 10/0) )to be.
Figure 3 shows (A) ¹ H NMR spectrum of ZIF-8 and ZIF8-A prepared according to a direct synthesis method while adjusting the ligand ratio between Atz and mim from 0/10 to 10/0 and (B) the synthesis of ZIF8-A. It is a diagram showing the relationship of the Atz content in the skeleton of the reaction product according to the Atz amount in the solution for.
Figure 4 shows A) ¹ H NMR spectra in H ₂ SO ₄ /CD ₃ OD (10/90 v/v) solutions of ZIF-8 and ZIF8-A with different Atz conversions and (B) ZIF-8 at room temperature. , ZIF8-A15%, ZIF8-A37%, ZIF8-A61%, and ZIF8-A74% FT-IR spectrum.
Figure 5 shows the TGA curves of ZIF-8, ZIF8-A15%, ZIF8-A37%, ZIF8-A61%, and ZIF8-A74% measured at a flow rate of 10° C./min under N ₂ atmosphere. Is also.
6 is a diagram showing (A) representative FE-SEM images of ZIF-8 and ZIF8-A and (B) XRD patterns according to Atz conversion rates. (A1) to (A5) are ZIF-8, ZIF8-A15%, ZIF8-A37%, ZIF8-A61%, and ZIF8-A74%, respectively.
7 is a diagram showing the gas selectivity according to the Atz conversion and sorption isotherms at 35° C. for various gases of ZIF-8 and ZIF8-A having different Atz conversion rates. (A) to (C) are respectively in CO ₂ , N ₂ , and CH ₄ Is the curve for (solid line was optimized by Langmuir model). (D) shows the CO ₂ /N ₂ and CO ₂ /CH ₄ selectivity at 1 bar and 35° C. as a function of Atz conversion (solid line aids visual identification). (E1) and (E2) are C ₃ H ₆ and C ₃ H ₈ adsorption isotherms at 35° C. in ZIF-8, ZIF8-A37%, and ZIF8-A74%, respectively (solid lines were optimized by Langmuir model). .
8 is a diagram showing the pore-size distribution of (A) isotherms of N ₂ adsorption (closed figure)/desorption (open figure) and (B) ZIF-8 and ZIF8-A having different Atz conversion rates.
9 is a diagram showing the charge density (unit e/Å ³ ) on the gate surfaces of (A) ZIF-8 and (B) ZIF8-A and CC and CN distances defining the gate size by DFT calculation. The white dotted line guides the CC distance in ZIF-8 and the CN distance in ZIF8-A. The purple circles in the center of the image represent these gate sizes.
Figure 10 shows (A) a method for synthesizing ZIF-8 (ZIF8-vinyl) functionalized with vinyl and (B) XRD patterns of ZIF-8, ZIF8-A57%, ZIF8-MA17%, and ZIF8-MH13%, and (C ) ¹ H NMR spectrum (H ₂ SO ₄ /CD ₃ OD = 10/90 v/v solution) is a diagram showing.
11 is a diagram showing representative FE-SEM images of (A) ZIF8-A57%, (B) ZIF8-MA17%, and (C) ZIF8-MH13%.
12 is a diagram showing ¹³ C NMR spectra of ZIF-8, ZIF8-A57%, ZIF8-MA17%, and ZIF8-MH13% (H ₂ SO ₄ /CD ₃ OD = 10/90 v/v solution).
Figure 13 shows the pores determined by (A) N ₂ adsorption/desorption isotherms and (B) Horvath-Kawazoe (HK) models for ZIF8-A57%, ZIF8-MA17%, and ZIF8-MH13%. -It is a diagram showing the size distribution.

Hereinafter, the present invention will be described in more detail through examples. These examples are for explaining the present invention more specifically, and the scope of the present invention is not limited by these examples.

<material>

Zinc nitrate hexahydrate (98%), 2-methylimidazole (mim, 99%), 3-amino-1,2,4-triazole (3-amino-1,2) ,4-triazole; Atz, ≥95%), methacrylic anhydride (MAA, 94%), trimethylamine (≥99%), glycidyl methacrylate (GMA, 97%) ), chloroform (99.5%), N-methyl-2-pyrrolidone (NMP, 99.5%), tetrahydrofuran (THF, ≥99%), and methanol ( methanol, 99.9%) was purchased from Sigma Aldrich and Daejeong Chemical, and was used without further purification.

Manufacturing example One: ZIF Synthesis of -8

Zinc nitrate hexahydrate (Zn(NO ₃ ) ₂ ·6H ₂ O, 2.9 g, 9.7 mmol, solution A ) and 2-methylimidazole (mim, 6.9 g, 84 mmol, solution ) prepared by dissolving each in 100 mL methanol The two solutions of B ) were mixed to synthesize ZIF-8. Specifically, mim solution B was rapidly poured into solution A, and stirred at 30° C. for 2 hours to cause a reaction. Centrifuged and washed with methanol to obtain a white solid of ZIF-8. The above purification process was repeated 3 times. The obtained ZIF-8 was dried at 70° C. overnight and activated at 180° C. for 12 hours under reduced pressure.

Comparative example 1: direct Solvent heat Synthetically ZIF8 Synthesis of -A

By applying a direct solvothermal method, ZIF8-A was synthesized using a methanol solution containing a mixture of mim and Atz as a mixed ligand and Zn(NO ₃ ) ₂ ·6H ₂ O as a metal ion. The molar ratio of metal and ligand was maintained at 1:8 in all reactions. The molar ratio between min and Atz of the prepared ligand mixture was 2/8, 4/6, 6/4, and 8/2 (mim/Atz). The same reaction procedure as used for the synthesis of ZIF-8 in Example 1 was applied. Briefly, 10 mL of a methanol solution of the ligand mixture was rapidly poured into 10 mL of a methanol solution of Zn(NO ₃ ) ₂ ·6H ₂ O (0.29 g, 0.97 mmol), and stirred at 30° C. for 2 hours to react. The precipitate was separated from the reaction solution by centrifugation and washed with methanol. The centrifugation and washing process were repeated three times. Subsequently, the product obtained for activation was dried in an oven at 70° C. under reduced pressure for 3 days.

Example One: After synthesis By modification method ZIF8 Synthesis of -A

ZIF8-A was synthesized using a postsynthetic modification (PSM) method. Activated ZIF-8 (200 mg, 0.88 mmol) prepared according to Preparation Example 1 was sonicated in a water bath for 30 minutes to be dispersed in 100 mL methanol, and Atz (585 mg, 6.96 mmol) in the ZIF-8 dispersion Was added. PSM reactions were performed at 50° C. for a set time for Atz conversion (1 hour, 8 hours, 24 hours, and 48 hours for 15%, 37%, 61%, and 74%, respectively). For purification, centrifugation and washing were repeated 3 times similar to the process of synthesizing ZIF-8 of Example 1. The white precipitate obtained was dried at 70° C. for 3 days under reduced pressure. For mass production, the amount of all reagents and solvents used was increased to 5 times the amount used in the small scale ZIF8-A synthesis reaction, and reacted for 24 hours to obtain ZIF8-A with 57% Atz conversion.

Example 2: additional chemistry To reform by ZIF8 -vinyl: ZIF8 -MA synthesis

ZIF8-MA containing a methacrylate (MA) group was synthesized by a nucleophilic substitution reaction using an amino group in ZIF8-A. In a typical reaction procedure, ZIF8-A (eg, ZIF8-A57%, 100 mg, 0.44 mmol) was dispersed in 50 mL of dry CHCl ₃ solvent by sonication for 20 minutes. Triethylamine (0.30 mL, 2.18 mmol) was added to the ZIF8-A dispersion, and then MAA (0.32 mL, 2.18 mmol) was slowly added to the dispersion under an argon atmosphere. The reaction was stirred at 30° C. for 24 hours. The obtained product was purified by centrifugation and washed with methanol. After repeating the purification process 3 times, ZIF8-MA obtained by gentle sonication for 5 minutes was dispersed in THF, filtered and dried under vacuum at 40° C. for 2 days to obtain ZIF8-MA powder.

Example 3: additional chemistry To reform by ZIF8 -vinyl: ZIF8 - MH Produce

ZIF8-MH containing a methacrylate and hydroxide (MH) group was synthesized by a nucleophilic substitution reaction. In a typical reaction process, ZIF8-A (eg, ZIF8-A57%, 100 mg, 0.44 mmol) was dispersed in 10 mL of dry toluene by sonication for 20 minutes, and GMA (1.15 mL, 8.71 mmol) was dissolved in an argon atmosphere. It was slowly added to the dispersion. The reaction was stirred at 80° C. for 24 hours. The obtained product was purified by centrifugation and washed with methanol. After repeating the purification process 3 times, ZIF8-MH obtained by gentle sonication for 5 minutes was dispersed in THF, filtered and dried under vacuum at 40° C. for 2 days to obtain ZIF8-MA powder.

Experimental example 1: computer calculation method

Density functional theory (DFT) was performed using the Vienna ab initio simulation package. The exchange correlation function was described by the PBE (Perdew-Burke-Ernzerhof) function with a generalized gradient approximation (GGA). A pseudopotential based on the projector-augmented wave (PAW) method was created. The cut-off energy for the planewave basis was set to 500 eV, and the structure was optimized within the force criteria 0.01 eV/Å. The lattice parameter of unit cell was set to 16.97×16.97×16.97 Å ³ based on the experimental XRD results. The DFT-D3 method with Becke-Jonson damping was applied to include van der Waals interactions. The structure of the obtained ZIF-8 and ZIF8-A including the charge density obtained from the theoretical calculation was derived using the VESTA code.

Experimental example 2: Theory and evaluation of gas isothermal adsorption

The sorption isotherms of gas penetrants in porous materials with a finite number of adsorption sites are described by the Langmuir adsorption model:

(방정식 S1)

(Equation S1)

Where C _i is the concentration of the permeate _i in the porous molecular sieve, p _i is the partial pressure of the permeate _i in equilibrium, and C _H, i'is the Langmuir capacity constant (mmol/g) And b _i is the Langmuir affinity constant (atm ^-1 ). All samples were dried for 12 hours at 35° C. under vacuum prior to each experiment and tested for various gas permeates including CO ₂ , N ₂ , CH ₄ , C ₃ H ₆ , and C ₃ H ₈ . Langmuir sorption capacity for N ₂ , CH ₄ , C ₃ H ₆ and C ₃ H ₈ , C _H,i ', is due to a decrease in the number of Langmuir adsorption sites, as the Atz conversion rate increases. While decreasing monotonically, the value for CO ₂ increased to 61% with increasing Atz conversion due to improved chemisorptions with uncoordinated primary and secondary amines (Table 1).

sample BET Langmuir model variables Pore volume
(cm ³ /g) Surface area
(m ² /g) CO ₂ N ₂ CH ₄ C _H '
(mmol/g) b
(atm ^-1 ) C _H '
(mmol/g) b
(atm ^-1 ) C _H '
(mmol/g) b
(atm ^-1 ) ZIF-8 1.48 1848 3.02±0.19 0.21±0.02 1.49±0.08 0.11±0.00 1.92±0.12 0.16±0.01 ZIF8-A15% 0.93 1525 4.49±0.26 0.33±0.04 1.31±0.12 0.11±0.00 1.79±0.14 0.15±0.01 ZIF8-A37% 0.85 1251 4.95±.023 0.41±0.03 1.29±0.09 0.10±0.00 1.35±0.04 0.15±0.01 ZIF8-A61% 0.70 882 5.28±0.37 0.45±0.02 1.21±0.07 0.10±0.00 1.28±0.05 0.12±0.01 ZIF8-A74% 0.17 183 3.18±0.31 0.25±0.02 1.13±0.08 0.10±0.00 1.23±0.04 0.10±0.01 ZIF8-A57% 0.74 1036 N/A N/A N/A N/A N/A N/A ZIF8-MA17% 0.73 1016 N/A N/A N/A N/A N/A N/A ZIF8-MH13% 0.73 1022 N/A N/A N/A N/A N/A N/A

Experimental example 3: Characterization

¹ H NMR spectra in H ₂ SO ₄ (10/90 v/v) diluted with CD ₃ OD were obtained on a Bruker FT NMR (400 MHz) spectrometer at 25°C. The thermal stability of the ZIF particles was evaluated by thermogravimetric analysis (TGA, TA instrument TGA Q-50) at a flow rate of 10°C/min in a nitrogen atmosphere. Fourier-transform infrared spectroscopy (FT-IR) spectra were collected on a Nicolet IS10 spectrophotometer (Thermo Scientific) with the sample after activation. The X-ray diffraction (XRD) pattern is a Rigaku diffractometer running at 45 kV and 40 mA with CuKα radiation (λ = 1.5406 Å) using a diffracted beam monochromator ( Rigaku Smart Lab, Rigaku Co., Japan). Data were collected at 0.01° intervals between 2θ = 5° and 45°. The morphology and shape of ZIF-8, ZIF8-A, and ZIF8-MA were analyzed by field-emission scanning electron microscopy (FE-SEM, Inspect F50). The Brunauer-Emmett-Teller (BET) pore volume and surface area of each sample were evaluated by BELSORB-max (Japan) at 77K under N ₂ atmosphere. Each sample was pretreated on a BELPREP-vac II instrument under vacuum at 120° C. for 2 hours. Equilibrium sorption isotherms of CO ₂ , N ₂ , CH ₄ , C ₃ H ₆ and C ₃ H ₈ gases in ZIF-8 and ZIF8-A nanoparticles were performed using the pressure decay method. And carried out at 35°C. Single gas permeation of propylene (C ₃ H ₆ ) and propane (C ₃ H ₈ ) of ZIF-8 was analyzed at 2 atm, 35° C. using a standard isochoric technique.

<Results and Discussion>

For ZIF8-A, a direct solvent heat synthesis method was attempted by reacting Zn ^{2 +} in a methanol solvent containing Atz or Atz and mim mixture (molar ratio from 2:8 to 8:2) (FIG. 1). However, none of these showed the high crystal structure and morphology seen in ZIF-8 (Fig. 2). XRD patterns and FE-SEM images for ZIF8-A of different conversion rates showed amorphous morphologies and broad diffraction peaks, significantly different from that in ZIF-8 (FIGS. 2A and 2B, respectively). The reaction with the Atz-mim ligand mixture formed an Atz-driven product of 87 mol% or more even in the reaction with a minimum Atz concentration of 20 mol% (Fig. 3). The failure of direct synthesis for ZIF8-A synthesis may be due to the kinetic fast metal-chelating functionalization of Atz and the stronger Brønsted-base nature of the mim in the backbone.

The PSM method may be a promising alternative approach to introducing specific moieties into ZIFs while maintaining the basic structure. In the PSM reaction of ZIFs, the pKa value of the N-heterocyclic ligand is an important variable determining the equilibrium constant of ligand exchange. For example, Erkartal et al. reported that a lower pKa value at the NH binding to the daughter ligand compared to the value for the parent ligand when the molecules are similar in size can promote the PSM reaction. Taking this into account, the PSM response of Atz and ZIF-8 as daughter ligands can be triggered by the pKa difference between mim (ca. 14.2) versus Atz (ca. 10.3). ZIF-8 nanocrystals were synthesized for the first time by reacting for 2 hours at room temperature using a methanol solution containing Zn(NO ₃ ) ₂ ·6H ₂ O and mim (Fig. 1B). Then, PSM was performed for a predetermined time according to the Atz conversion rate at 50° C. for the synthesized ethanol solution of ZIF-8 and Atz (1/8 molar ratio) (FIG. 1B).

¹ H NMR spectrum of ZIF-8 showed peaks corresponding to the methyl and methine groups of mim at (a) 2.7 ppm and (b,b') 7.4 ppm, respectively (FIG. 6A). The increase in Atz conversion resulted in an increase in peak intensity at (c) 8.1 ppm corresponding to the methine peak of Atz. ^{In 1} H NMR, the reaction conversion rate of Atz in ZIF8-A was determined using the intensity ratio of the methine peak between b and c (Fig. 4A), and from 15% (1 hour) to 74 using different time durations. % (48 hours). Furthermore, the FT-IR spectrum of ZIF8-A is shown at 3430 cm ^-1 , 3370 cm ^{- 1} and 1623 cm ^-1 and 3210 cm ^{- 1} and 1052 cm ^-1 , respectively, in Atz (d) -NH ₂ and ( e) demonstrated an increase in the conversion rate Atz according to the peak intensity increases that corresponds to the -NH (Fig. 6 B). In addition, other strong signal peaks of (f) C=N-NH, (g) C-NH ₂ , and (h) NC-NH at 1545 cm ^-1 , 1518 cm ^-1 , and 1212 cm ^-1 , respectively, are Atz It grew with an increase in conversion, indicating that the Atz component of ZIR8-A can be systematically controlled.

The TGA curves of ZIF-8 and ZIF8-A with different Atz conversions showed a decrease in thermal degradation points with increasing Atz conversion (FIG. 5). This may be because the binding strength of the ZIF8-A nanoparticles decreases as the Atz conversion rate increases due to the presence of strong electron donating groups (eg, NH and -NH ₂ ). The XRD pattern and FE-SEM images of ZIF8-A with different Atz conversions all showed that all ZIF8-A nanoparticles prepared by PSM maintained the high crystallinity and morphology of the mother ZIF-8 regardless of the conversion rate ( Fig. 6). This property of ZIF8-A indicates that the PSM-based ligand metathesis of ZIF-8 with Atz is in fact a suitable method for the synthesis of ZIF8-A.

Isothermal adsorption of ZIF-8 and ZIF8-A with different Atz conversions to CO ₂ , N ₂ , and CH ₄ was performed at 35° C. (FIG. 7 ). As shown in Figures 7A-7C, all adsorption behaviors were depicted with a Langmuir mode adsorption model (equation S1). The CO ₂ isothermal adsorption line for ZIF-8 showed a continuous increase in the CO ₂ sorption uptake (Figure 7A), whereas the N ₂ and CH ₄ adsorption uptakes for ZIF8-A both showed Atz conversion up to 61%. It was continuously decreased with the increase of (Figs. 9B and 9C), and both CO ₂ /N ₂ and CO ₂ /CH ₄ selectivity were improved (Fig. 7D). More specifically, a stronger decrease was observed in CH ₄ adsorption uptake compared to the results for N ₂ , which is a larger kinetic diameter and higher condensability (diameter 3.80 Å vs. 3.64 Å; critical) of CH ₄ This can be attributed to the critical temperature (T _c ) 190.6K versus 126.2K. This sustained decrease in both the N ₂ and CH ₄ adsorption uptake of ZIF8-A with increasing Atz conversion may be due to a decrease in pore volume and surface area, as shown by Brunauer-Emmett-Teller (BET) analysis ( 8B and Table 1).

In contrast to the N ₂ and CH ₄ adsorption behavior, there was a substantial increase in CO ₂ adsorption uptake in the ZIF8-A sample with Atz conversion of up to 61%, which was introduced by the PSM process, which was not coordinated with CO _2. It can be due to chemical interactions between primary and secondary amines. At 2 bar, the uptake of CO ₂ adsorption of ZIF8-A61% was almost 2.5 times higher than that of ZIF-8 (2.51 mmol/g vs. 0.99 mmol/g). The CO ₂ adsorption uptake of ZIF-8 was in close agreement with the values reported by Koros et al. (1.0 mmol/g at 308K and 2 bar). For comparison, Zhang et al. designed amine functionalized ZIF-8 (ED-ZIF-8) using ethylenediamine in order to improve CO ₂ uptake, which is the result for ZIF8-A61% (2.51) according to the present invention. mmol/g) still lower, at 308K and 2.5 bar, a value of 1.48 mmol/g. The CO ₂ adsorption uptake of ZIF8-A was further compared with other values for previously reported ZIFs and modified ZIFs, which supported that the ZIF8-A61% of the present invention had a high level of CO ₂ uptake capacity (Table 2). ).

Entry Modification method Measuring conditions CO ₂ intake
(mmol/g) CO ₂ intake
(cm ³ /g) Reference
literature ZIF-8 - 308K, 2 bar 0.99 12.5 The present invention ZIF8-A15% ZIF-8 PSM by HAtz 308K, 2 bar 1.95 24.6 ZIF8-A37% ZIF-8 PSM by HAtz 308K, 2 bar 2.23 28.1 ZIF8-A61% ZIF-8 PSM by HAtz 308K, 2 bar 2.51 31.6 ZIF8-A74% ZIF-8 PSM by HAtz 308K, 2 bar 1.03 13.0 ZIF-67 - 273K, 1 atm - 28.7 5 ZIF-68 - 273K, 0.08 MPa 2.60 - 6 ZIF-69 - 273K, 0.08 MPa 2.70 - 6 ZIF-7 - 303K, 100 kPa 2.25 - 7 ZIF-78 - 298K, 1 atm - 51 8 ZIF-79 - 298K, 1 atm - 34 8 ZIF-8 - 308K, 2 bar 1.00 - 2 ZIF-81 - 298K, 1 atm - 39 8 ZIF-82 - 298K, 1 atm - 51 8 ZIF-93 - 298K, 1 atm 1.7 - 9 ZIF-94 - 298K, 1 atm 2.4 - 9 ZIF-8-NH ₂ ^a By simulation
Modification of the ZIF-8 structure 298K, 5 bar 3.10 - 10 ZIF-8-(NH ₂ ) ₂ ^a 298K, 5 bar 4.50 - 10 ED-ZIF-8 ^b To ethylenediamine
ZIF-8 PSM 308K, 2.5 bar 1.48 - 11 ZIF-8-90-(50) ZIF-8 to 2-amBzIm
in situ substitution 308.15K, 200 kPa 2.50 - 12 ZIF-7-NH ₂ (70) Of ZIF-7 to 2-amBzIm
in situ substitution 308K, 250 kPa - 32 4 Zn40-ZIF-67 Zn-doped on ZIF-67 273K, 1 atm - 26.6 5 ZIF-7/8
(10% bIm) ZIF-8 PSM to bIm 273K, 100 kPa 1.5 - 13 ZIF-7/8
(44% bIm) ZIF-8 PSM to bIm 273K, 100 kPa 2.5 - 13 Zn/Co-ZIF 2-mim and
Mixing with Zn and Co salts 273K, 1 bar - 34.16 14 LeZIF8-NO ₂ Im _168h ^c With NO ₂ Im
Solvent-assisted ligand exchange 273K, 900 mmHg - 76 15 LeZIF8-SHBzIm _72h ^d With SHBzIm
Solvent-assisted ligand exchange 273K, 900 mmHg - 77 15 LeZIF8-NH ₂ BzIm _168h ^e NH _{2 with} BzIm
Solvent-assisted ligand exchange 273K, 900 mmHg - 38.5 15 LeZIF8-PhIm _168h ^f PhIm
Solvent-assisted ligand exchange 273K, 900 mmHg - 43 15

a: derived from theoretical calculation

b: The mim linker of ZIF-8 is partially substituted by ethylene diamine (ED)

c: a mixed ligand of NO ₂ Im and mim is present in the ligand exchanged (Le) ZIF-8 in a molar ratio of 66.6:33.4

d: The mixed ligand of SHBzIm and mim is present in LeZIF-8 in a molar ratio of 12:88

e: The mixed ligand of NH ₂ BzIm and mim is present in LeZIF-8 in a molar ratio of 16:84

f: The mixed ligand of PhIm and mim is present in LeZIF-8 in a molar ratio of 10:90

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Langmuir-mode, including Langmuir capacity constant (CH') and Langmuir affinity constant (b), for CO ₂ , N ₂ , and CH ₄ by the Langmuir mode adsorption model. Calculate the adsorption variable (equation S1), it is shown in Table 1. Although this ZIF8-A sample of the C _H of the CO ₂ 'increases monotonously with the increase of Atz conversion by the CO ₂ chemisorption to 61%, the values for the N ₂ and CH ₄ is significantly due to a decrease of the Langmuir adsorption sites It is worth noting that it has decreased significantly (Table 1). In addition, the b value of the ZIF8-A sample for CO ₂ continuously increased with an increase in Atz conversion up to 61% by improved chemical interaction (Table 2). ZIF8-A74% still showed a somewhat higher CO ₂ absorption uptake compared to ZIF-8, but showed a decrease in CO ₂ absorption uptake compared to the results for other ZIF8-A crystals (FIG. 7A). This is due to a substantial reduction in both the pore volume and surface area of about 90% for ZIF-8, despite the highest concentration of amine (Table 1).

Analyzing the C ₃ H ₆ and C ₃ H ₈ isothermal adsorption properties of different ZIF crystals (ZIF-8, ZIF8-A37%, and ZIF8-A74%) to add gate size changes of ZIF-8 induced by Atz functionalization. It was confirmed as (Fig. 7E). Considering that the effective gate sizes of ZIF-8 are 4.0 and 4.2 Å, the change in C ₃ H ₆ /C ₃ H ₈ adsorption properties can be a good criterion for evaluating the Atz-induced change in the gate size of ZIF-8. have. Again, the C ₃ H ₆ and C ₃ H ₈ isothermal adsorption were depicted by the Langmuir mode adsorption model, and the Langmuir parameters of ZIF-8 calculated for the two adsorbates were consistent with the previously reported values (Table 3). The adsorption intake of C ₃ H ₆ (4.0 Å) and C ₃ H ₈ (4.2 Å) decreased monotonically with increasing Atz conversion. A more specific analysis showed that C ₃ H ₈ adsorption intake was further reduced compared to C ₃ H ₆ (Fig. 7E And Table 3), which may be evidence for gate size reduction due to the introduction of Atz into ZIF-8.

Entry Langmuir model variables C ₃ H ₆ C ₃ H ₈ references C _H '
(mmol/g) b
(atm ^-1 ) C _H '
(mmol/g) b
(atm ^-1 ) ZIF-8 6.19±0.06 1.97±0.06 5.40±0.09 2.88±0.19 The present invention ZIF8-A37% 4.27±0.09 1.67±0.23 3.47±0.07 1.40±0.07 The present invention ZIF8-A74% 2.98±0.14 1.45±0.08 3.16±0.20 1.08±0.16 The present invention ZIF-8 6.36 1.72 5.65 2.58 2

ref 2: J. Phys. Chem. Lett., 2012, 3, 2130-2134.

Experimental observations of BET, gas adsorption and gas separation supported the reduction of the gate size of ZIF-8 by the substitution of mim by the Atz ligand. In order to further verify this observation, a theoretical calculation based on the density functional theory (DFT) was performed. After optimizing the structures of ZIF-8 and ZIF8-A, the charge distribution and distance between the nearest neighboring atoms (C-C and C-N) in different ligands surrounding the pore were calculated, and the results are shown in FIG. 9. This distance is very important in evaluating the change in the ZIF-8 gate size by PSM. Introduction of the amino electron donating group in the ZIF-8 structure shortened the C-N distance from 4.98 Å (ZIF-8) to 4.73 Å (ZIF8-A50%, 3 Atz substitutions in the 6-membered ring) (FIG. 9 ). In addition, the charge distribution images of ZIF-8 and ZIF8-A showed that the internal pore size of ZIF8-A was slightly reduced compared to ZIF-8 (FIG. 9). Similarly, Zhang et al. also disclosed that the gate size of ZIF-8 decreases upon substitution of the ligand with amino-containing imidazole based on computer calculations. They suggested that the presence of an electron donating group in the imidazole ligand induces electrostatically repulsive interaction between the ligands, thereby reducing the gate size. Therefore, the computer calculation results of the present invention are in good agreement with the previously reported calculations based on ZIF-8 ligand modification by PSM (Fig. 9).

Expanded application of ZIF-8 can be achieved by control of the structure and introduction of new functional groups into ZIF-8. Further chemical modification with the amino group of ZIF8-A may allow the introduction of vinyl groups as other functional groups (FIG. 10A). Vinyl groups are widely used as reactive sites for many reactions such as Michael addition, thiol-ene click and radical polymerizations. The first scale-up synthesis (5x) of ZIF8-A was performed on an increased scale using the same process applied to the synthesis of ZIF8-A61%. The increased scale synthesis showed almost the same Atz conversion (57%), morphology, and crystal structure as in ZIF8-A61% prepared on a small scale. Reaction with methacrylic anhydride (MAA) or glycidyl methacrylate (GMA) for 24 hours to react at the amino site in ZIF8-A57%, respectively, as a new functional group, methacrylamide. amide; MA) or methacryl hydroxide (MH) was introduced vinyl functionalized ZIF-8 was synthesized (Fig. 10A). The morphology and crystal structure of the obtained ZIF8-MA or -MH (ZIF8-vinyl) were confirmed by FESEM and XRD, respectively, and it was demonstrated that they had the same or similar structural topology as ZIF8-A57% having various sizes (Fig. 10B And Fig. 11).

In order to confirm the chemical structure and conversion rate, ¹ H NMR spectrum of ZIF8-vinyl was used. The reaction of MAA with ZIF8-A led to the formation of (d) new ¹ H NMR peaks at 5.6 and 6.0 ppm derived from vinyl groups and (e) the formation of other peaks at 1.9 ppm corresponding to methyl groups (Fig. ). Introduction of MA into ZIF8-A, with methylene peaks at (f) 3.6 ppm and (g,h) 4.2 ppm, due to ring opening of the glycidyl group, (d') 5.6 ppm and (e') 6.0 A typical ¹ H NMR peak including a methacrylate peak in ppm was shown (FIG. 12C ). The ¹ H NMR spectrum showed a relatively broad peak due to the network form due to an additional reaction between the produced secondary amine and the hydroxyl group of the introduced MA. The ¹ H NMR spectrum of ZIF8-vinyl can be used for quantification of the MA- and MH-terminated triazole content in ZIF8-vinyl, showing 17% and 13% fractions, respectively (mim/Atz/MA = 52 %/31%/17% and mim/Atz/MH = 51%/36%/13%). Furthermore, ¹³ C NMR spectra for ZIF-8, ZIF8-A57%, ZIF8-MA17%, and ZIF8-MH13% were also used to confirm the chemical structure of the ligands in ZIF8-MA and ZIF8-MH. The successful synthesis of ZIF8-MA and ZIF8-MH was confirmed from the assignment of all peaks observed in the ¹³ C NMR spectrum (Fig. 12). The N ₂ adsorption/desorption isotherm of ZIF8-vinyl was shown to have almost the same surface area and pore volume as that of ZIF8-A57% (1036.22 m ² /g and 0.74 cm ³ /g, Table 1). This indicates that ZIF8-vinyl maintains the structural integrity and high porosity of the mother ZIF8-A well (FIG. 13 and Table 1). Through these various characterizations, it was confirmed that the amino group introduced into ZIF8-A having the same SOD topology is accessible for additional chemical modification so that it can impart new properties to ZIF-8. Thus, chemical modification of ZIF8-A may be a promising material for synthesizing versatile ZIFs with tailored properties for various applications such as catalysis, molecular detection, gas storage and gas separation.

<Conclusion>

The inventors have confirmed that PSM is a scalable and straightforward approach to functionalizing ZIF-8 with Atz under moderate conditions. The ZIF8-A obtained by PSM in this way was (1) enhanced CO ₂ selective adsorption by gate tuning effect and chemical interaction, (2) free of ZIF-8 for further application ( versatile) was tested for two special purposes: whether to enable chemical modification. ZIF8-A61% prepared according to the present invention significantly improved the selectivity of CO ₂ /N ₂ (ca. 3.4 times) and CO ₂ /CH ₄ (ca. 4.7 times) compared to ZIF-8. The substantial improvement in CO ₂ selective adsorption resulted from the combination of controlled gate size and chemical interactions by Atz introduction. The precise control of the gate size according to the present invention was confirmed by C ₃ H ₆ /C ₃ H ₈ separation performance as well as DFT-based computer calculation. Furthermore, ZIF8-A is a combination of methacryl amide (MA) or methacrylic hydroxide (MH), which imparts new properties to ZIF-8 and can enable many other reactions by further chemical modification through vinyl groups. It was possible to introduce a new functional group. As such, the amine functionalized ZIF-8 of the present invention, ZIF8-A, can serve as a versatile platform for designing ZIF-based materials with special functional groups and properties for extended potential applications.

Claims (13)

A first step of activating zeolitic imidazolate frameworks (ZIFs) having a neutral microporous structure based on a zeolitic sodalite (SOD) topology; And
The activated zeolite imidazolate skeleton has a structure similar to 2-methylimidazole, a ligand constituting it, and includes an aromatic ring containing at least one nitrogen as a hetero element and at least one amine group substituted on the ring As a method for producing ZIF into which an amine group is introduced by ligand substitution, comprising a second step of contacting the compound
The ZIF into which the amine group is introduced is a ligand-substituted with a conversion rate of 10 to 65% with respect to the total ligand, and maintains the same crystal structure as the ZIF before the introduction of the amine group, but has a selective adsorption capacity of CO ₂ to N ₂ or CH ₄ It is improved, the manufacturing method.
The method of claim 1,
The first step is to be carried out by maintaining the dried ZIF at 160 to 200 °C for 6 to 24 hours under reduced pressure.
The method of claim 1,
The second step has a structure similar to 2-methylimidazole in a C _1-4 alcohol solution in which ZIF to be introduced into an amine group is dispersed, and is substituted on the ring and an aromatic ring containing at least one nitrogen as a hetero element. To be carried out by adding a compound containing at least one amine group, the manufacturing method.
The method of claim 1,
The second step is to be performed for 0.5 to 36 hours, the manufacturing method.
The method of claim 4,
By controlling the execution time of the second step, the amine group introduction rate is controlled.
The method of claim 1,
The second step is to be carried out at 40 to 60 ℃, the manufacturing method.
The method of claim 1,
The ZIF is ZIF-8.
The method of claim 1,
Compounds having a structure similar to that of 2-methylimidazole and containing at least one nitrogen as a hetero element and at least one amine group substituted on the ring are 3-amino-1,2,4-tria That is sol, the manufacturing method.
The method of claim 1,
ZIF into which the amine group is introduced has a reduced pore volume compared to ZIF before the introduction of the amine group.
Prepared by contacting activated ZIF with a compound having a structure similar to 2-methylimidazole, a ligand constituting it, and containing an aromatic ring containing at least one nitrogen as a hetero element and at least one amine group substituted on the ring One, a composition for CO ₂ adsorption comprising ZIF into which an amine group is introduced by ligand substitution.
The method of claim 10,
ZIF into which an amine group is introduced by the ligand substitution is prepared by the method of any one of claims 1 to 9, wherein the composition for CO ₂ adsorption.
A gas mixture containing CO ₂ and N ₂ , CH ₄ or both has a structure similar to 2-methylimidazole, a ligand constituting the activated ZIF, and an aromatic ring containing at least one nitrogen as a hetero element And contacting with ZIF into which an amine group has been introduced by ligand substitution, prepared by contacting a compound containing at least one amine group substituted on the ring.
A method of removing CO ₂ from a gas mixture containing CO ₂ and N ₂ , CH ₄ or both.
The method of claim 12,
ZIF into which the amine group is introduced by the ligand substitution is prepared by the method of any one of claims 1 to 9, CO ₂ removal method.

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