PYRAZOLE COBALT-BASED METAL-ORGANIC FRAMEWORK MATERIAL WITH DYNAMIC PORE SIZE, METHOD FOR MAKING THE SAME, AND USE IN SULFUR HEXAFLUORIDE CAPTURE

Abstract

The present disclosure provides a pyrazole cobalt-based metal-organic framework material, a chemical formula of the pyrazole cobalt-based metal-organic framework material is CoC.sub.12H.sub.8N.sub.4, and the pyrazole cobalt-based metal-organic framework material is named Co-DPB; a ligand of the Co-DPB is 1,3-Di (1-H-pyrazolyl) benzene H.sub.2DPB, and a structural formula is

##STR00001##

and the Co-DPB is prepared by a solvothermal reaction of an organic ligand H.sub.2DPB and a cobalt source; and the Co-DPB is a purple bulk crystal material.

Claims

1-18. (canceled)

19. Use of a Co (II)-based metal-organic framework material constructed with a pyrazole ligand in SF.sub.6/N.sub.2 separation, wherein: the metal-organic framework material is a purple bulk crystal material prepared by a solvothermal reaction of an organic ligand H.sub.2DPB and a cobalt source, with a chemical formula of CoC.sub.12H.sub.8N.sub.4 and named Co-DPB, wherein H.sub.2DPB is 1,3-di (1H-pyrazol-4-yl) benzene with a molecular formula of C.sub.12H.sub.10N.sub.4; wherein from a perspective of a crystal structure, the Co-DPB belongs to a tetragonal crystal system, a space group is 14.sub.1/amd, a unit cell parameter is V=6546.9(3) .sup.3, a=22.9279(5) , b=22.9279(5) , c=12.4539(3) , =90, =90 and =90; wherein in a framework of the Co-DPB, each cobalt atom is coordinated with four nitrogen atoms in a tetrahedral configuration, those coordinated nitrogen atoms are from pyrazole groups of four different ligands, each nitrogen atom on two pyrazoles of each ligand in the framework of the Co-DPB is involved in coordination, a zigzag metal chain-like secondary building unit (SBU) is formed by adjacent metal atoms through a bridged pyrazole group, and a three-dimensional framework structure is formed by an alternating connection of the ligand and the zigzag metal chain-like SBU; wherein the Co-DPB is provided with a pore channel, a size of the pore channel changes dynamically and ranges from 4 to 8 ; wherein the SF.sub.6/N.sub.2 separation is carried out under a condition of a relative humidity ranging from 0 to 90%; and wherein the Co-DPB adsorbed with SF.sub.6 is desorbed by helium purge for reuse.

20. The use of the Co (II)-based metal-organic framework material constructed with the pyrazole ligand in SF.sub.6/N.sub.2 separation of claim 19, wherein a synthesis method of Co-DPB comprises: step (1): dissolving the organic ligand H.sub.2DPB and Co(CH.sub.3COO).sub.2 in a mixed solvent of N,N-dimethylformamide (DMF), acetic acid and water, to obtain a mixed solution; and step (2): ultrasonic shaking and stirring of the mixed solution in the step (1), then performing the solvothermal reaction to obtain a bulk single crystal; and then washing the bulk single crystal with DMF and methanol successively.

21. The use of the Co (II)-based metal-organic framework material constructed with the pyrazole ligand in SF.sub.6/N.sub.2 separation of claim 20, wherein a temperature of the solvothermal reaction is in a range of 130 C. to 160 C., and a reaction time is in a range of 8 hours to 16 hours.

22. The use of the Co (II)-based metal-organic framework material constructed with the pyrazole ligand in SF.sub.6/N.sub.2 separation of claim 19, wherein the Co-DPB is used to adsorb SF.sub.6.

23. The use of the Co (II)-based metal-organic framework material constructed with the pyrazole ligand in SF.sub.6/N.sub.2 separation of claim 22, wherein after the Co-DPB is washed by DMF and is solvent exchanged with methanol, and then is heated in vacuum at 120 C. to remove solvent molecules, the Co-DPB is used to adsorb SF.sub.6.

24. The use of the Co (II)-based metal-organic framework material constructed with the pyrazole ligand in SF.sub.6/N.sub.2 separation of claim 19, wherein the separation is carried out at room temperature and under a pressure ranging from 0.1 bar to 1.0 bar.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0034] FIG. 1 is a schematic view of a dynamic pore channel of a CO-DPB material obtained in Example 1 and a pore channel after adsorbing sulfur hexafluoride molecules.

[0035] FIG. 2 is a thermal analysis diagram of the CO-DPB material obtained in Example 1.

[0036] FIG. 3 is a powder diffraction pattern of a fresh synthetic sample of the CO-DPB material obtained in Example 1 and a sample after an adsorption/breakthrough test.

[0037] FIG. 4 is an adsorption isotherm diagram of sulfur hexafluoride and a nitrogen gas of the CO-DPB material obtained in Example 1 at room temperature.

[0038] FIG. 5 is adsorption isotherms of an SF.sub.6/N.sub.2 selectivity of the CO-DPB material obtained in Example 1 and an SF.sub.6/N.sub.2 gas mixture (1:9) predicted by an ideal adsorption solution theory (IAST).

[0039] FIG. 6A is two types of adsorption sites in a crystal structure of SF.sub.6@CO-DPB.

[0040] FIG. 6B is an FH interaction at an SF.sub.6 binding site (site I) in a cavity of a wall structure of a pore channel.

[0041] FIG. 6C is an FH interaction at a secondary SF.sub.6 binding site (site II) in the pore channel.

[0042] FIG. 7A is a breakthrough curve of the CO-DPB material and a purity of SF.sub.6 calculated from desorption.

[0043] FIG. 7B is a breakthrough separation result diagram of an SF.sub.6/N.sub.2 (10/90 and 1:99) gas mixture.

[0044] FIG. 7C is breakthrough separation results of five cycles of the SF.sub.6/N.sub.2 (10/90) gas mixture at 90% relative humidity (RH).

[0045] FIG. 8A is water vapor adsorption/desorption isotherms of the CO-DPB material.

[0046] FIG. 8B is a kinetic adsorption curve of SF.sub.6 of the CO-DPB material.

[0047] FIG. 8C is a kinetic adsorption curve of H.sub.2O of the CO-DPB material.

[0048] FIG. 8D is fitting of diffusion time constants for SF.sub.6/H.sub.2O kinetic selectivity calculation.

[0049] FIG. 9A is an SEM image of a CO-DPB sample before a breakthrough experiment under a humid condition.

[0050] FIG. 9B is an SEM image of the CO-DPB sample after the breakthrough experiment under the humid condition.

DESCRIPTION OF EMBODIMENTS

[0051] The present disclosure is described clearly below in conjunction with embodiments, apparently, the present disclosure is not limited to the following embodiments.

Example 1

[0052] Dissolving H.sub.2DPB (0.14 mmol, 30 mg) and Co(OAc).sub.2.Math.4H.sub.2O (0.24 mmol, 60 mg) in 10 mL DMF, then placing in a 20 mL glass vial, and dissolving under ultrasound, to obtain a mixture. Then, adding 0.10 mL acetic acid and 8.0 mL deionized water to the mixture. Sealing the glass vial, and then stirring for another 30 minutes under ultrasound, to obtain a suspension. Heating the suspension at 150 C. for 12 hours. Cooling to room temperature, then filtering to obtain blue-purple crystals, and washing the blue-purple crystals with DMF and methanol to remove amorphous solids. Collecting crystals by filtration, and drying under vacuum at 80 C. for 6 hours.

Example 2

[0053] Dissolving H.sub.2DPB (0.14 mmol, 30 mg) and Co(OAc).sub.2.Math.4H.sub.2O (0.28 mmol,70 mg) in 10 mL DMF, then placing in a 20 mL glass vial, and dissolving under ultrasound, to obtain a mixture. Then, adding 0.30 mL acetic acid and 9.0 mL deionized water to the mixture. Sealing the glass vial, and then stirring for another 30 minutes under ultrasound, to obtain a suspension. Heating the suspension at 160 C. for 8 hours. Cooling to room temperature, then filtering to obtain blue-purple crystals, and washing the blue-purple crystals with DMF and methanol to remove amorphous solids. Collecting crystals by filtration, and drying under vacuum at 80 C. for 6 hours.

Example 3

[0054] Dissolving H.sub.2DPB (0.14 mmol, 30 mg) and Co(OAc).sub.2.Math.4H.sub.2O (0.28 mmol, 35 mg) in 10 mL DMF, then placing in a 20 mL glass vial, and dissolving under ultrasound, to obtain a mixture. Then, adding 0.20 mL acetic acid and 8.0 mL deionized water to the mixture. Sealing the glass vial, and then stirring for another 30 minutes under ultrasound, to obtain a suspension. Heating the suspension at 130 C. for 16 hours. Cooling to room temperature, then filtering to obtain blue-purple crystals, and washing the blue-purple crystals with DMF and methanol to remove amorphous solids. Collecting crystals by filtration, and drying under vacuum at 80 C. for 6 hours.

[0055] An elemental analysis on Co-DPB obtained in Example 1 is performed, and results are: C.sub.12H.sub.8N.sub.4Co(267.15 g/mmol). Calculated value (%): C, 53.93; H, 3.00; N, 20.97; and actual measurement value: C, 52.63; H, 3.41; N, 20.01.

[0056] Crystal data of the Co-DPB obtained in Example 1 are shown in following Table 1:

TABLE-US-00001 TABLE 1 Empirical formula C.sub.12H.sub.8N.sub.4Co Measurement temperature 294.15 Crystal system Tetragonal Space group I4.sub.1/amd a() 22.9279(5) b() 22.9279(5) c() 12.4539(3) () 90 () 90 () 90 Volume(.sup.3) 6546.9(3) Z 16 Calculated density(g/cm.sup.3) 1.082 Independent reflections(I > 2(I)) 1736 [R.sub.int = 0.0547] Reflections collected 15528 Goodness-of-fit on F.sup.2 1.084 R.sub.1.sup.a, wR.sub.2.sup.b[I > 2(I)] R.sub.1 = 0.0681, wR.sub.2 = 0.1799 R.sub.1.sup.a, wR.sub.2.sup.b (all data) R.sub.1 = 0.0733, wR.sub.2 = 0.1835 Largest diff. peak and hole(e/.sup.3) 0.29/0.34

[0057] FIG.1 is a schematic view of a dynamic pore channel of a metal-organic framework material prepared in Example 1 and a pore channel after adsorbing sulfur hexafluoride molecules. In a structure of the Co-DPB, a one-dimensional pore channel with a square shape is provided along a c-axis, and a cavity is provided on a wall of the one-dimensional pore channel, dynamic properties of the framework are introduced by a swinging motion of a phenyl ring in the H.sub.2DPB ligand, and a minimum distance observed from a disordered position thereof is 2.97 . Flexibility of the ligand allows a pore channel size to change from about 4 to 8 , thereby facilitating an accommodation of guest molecules of different sizes. Specifically, after SF.sub.6 is adsorbed, the pore channel size is fixed at about 7 , and the ligand does not have any disorder.

[0058] FIG. 2 is a thermal analysis diagram of an activated metal-organic framework material, which proves that the Co-DPB has high thermal stability, and no obvious collapse of an MOF framework structure is observed before 570 C. A mass loss before 200 C. is speculated to be a removal of the guest molecules in the pore channel.

[0059] FIG. 3 is a powder diffraction pattern of the metal-organic framework material, showing that the structure of the Co-DPB has excellent stability and still maintains excellent crystallinity after an adsorption/penetration test, and the structure does not collapse significantly.

Example 4: A Gas Adsorption Performance Test

[0060] A porosity of the Co-DPB is evaluated by a nitrogen gas adsorption experiment at 77 K. A specific surface area calculated by a Brunauer-Emmett-Teller (BET) method is 866 m.sub.2/g, single component adsorption isotherms of the Co-DPB at 298K and 273K show significant SF.sub.6 adsorption capacity thereof, while adsorption of N.sub.2 is almost negligible, as shown in FIG. 4. At 298K, the SF.sub.6 adsorption capacity of the Co-DPB at 0.1 bar is 2.82 mmol/g, and 3.55 mmol/g at 1 bar. In contrast, the adsorption of N.sub.2 by the Co-DPB at 298K is negligible (0.262 mmol/g).

[0061] In addition, based on the single component adsorption isotherms, a selectivity of SF.sub.6/N.sub.2 is evaluated using an ideal adsorption solution theory (IAST). Simulated mixed adsorption isotherms of the SF.sub.6/N.sub.2 gas mixture (1:9) in FIG. 5 show that as a pressure increases, the adsorption capacity of SF.sub.6 gradually increases, while the adsorption capacity of N.sub.2 remains very low throughout an entire pressure range. Therefore, an IAST selectivity gradually increases and reaches a maximum value of 2485 at 1 bar (SF.sub.6/N.sub.2=10:90). The selectivity significantly exceeds selectivities of all porous materials reported so far, thereby making the CO-DPB a highly potential material for directly recovering high-purity SF.sub.6 through desorption, and specific results are shown in Table 2.

TABLE-US-00002 TABLE 2 Comparison of SF.sub.6/N.sub.2 separation performance between BUT- 53 and other reported porous adsorbents at 298 K and 1 bar. SF.sub.6/N.sub.2 Qst Qst SF.sub.6 N.sub.2 selec- for for uptake uptake tivity SF.sub.6 N.sub.2 at 0.1 bar at 1 bar (v/v, (kJ/ (kJ/ Adsorbents (mmol/g) (mmol/g) 10/90) mol) mol) Ref. BUT-53 2.82 0.26 2484.8 23.8 20.4 This work Ni(NDC)(TED).sub.0.5 2.73 0.27 750 34.1 13.1 16 Cu-MOF-NH.sub.2 3.39 0.28 266.2 55.2 19.1 17 Ni(adc)(dabco).sub.0.5 2.23 0.30 948.2 47.6 19.4 18 Ga-TCPB 2.26 0.32 418.5 30.44 19 V-TCPB 2.29 0.40 360.7 30.48 19 Zn(TMBDC) 2.51 0.33 239 45.2 24.6 20 (DABCO).sub.0.5 Ni(ina).sub.2 2.39 0.54 375.1 33.4 16.1 21 HKUST-1 1.12 70.4 9.5 22

[0062] As shown in FIG. 6A, there are two SF.sub.6 binding sites in the CO-DPB structure. As shown in FIG. 6B, a main adsorption site of SF.sub.6 (site I) is located in the cavity of the wall structure of the pore channel, at the site, a plurality of FH interactions are mainly formed through hydrogen atoms on the benzene ring and pyrazole ring of four DPB.sup.2 ligands and six fluorine atoms of SF.sub.6, to achieve the capture of SF.sub.6, and an occupancy rate of the site is relatively high. Specifically, strong FH interactions (FH distance: 2.65-2.89 ) are formed at the site by two axial fluorine atoms of an SF.sub.6 molecule with six hydrogen atoms, while relatively weak FH interactions (FH distance is about 3.15 ) are formed by four equatorial fluorine atoms. In addition, the one-dimensional pore channel of the CO-DPB framework is a secondary binding site (site II) (FIG. 6C), at the site, only the two axial fluorine atoms of the SF.sub.6 molecule participate in the plurality of FH interactions (FH distance: 2.63-3.18 ), therefore, an occupancy rate of the site is relatively low.

Example 5: Research on the Dynamic Separation Performance of the CO-DPB Under a Condition Simulating Actual Applications

[0063] A column breakthrough separation experiment is carried out using the SF.sub.6/N.sub.2 gas mixture. Specific operations are as follows: a gas separation experiment is carried out using a fixed-bed breakthrough device. A CO-DPB sample is added into a quartz glass column, and an SF.sub.6/N.sub.2 gas mixture with a volume ratio of 10:90 is flowed through the quartz glass column at a total flow rate of 10 mL min.sup.1.

[0064] As shown in FIG. 7A, N.sub.2 passes through the quartz glass column quickly, while a breakthrough time of SF.sub.6 is 23 min/g, indicating that the CO-DPB has a higher selective adsorption capacity for SF.sub.6 than N.sub.2, thereby confirming an efficient separation ability of the CO-DPB for the SF.sub.6/N.sub.2 gas mixture. After the column breakthrough separation experiment, a desorption experiment of the CO-DPB is carried out by helium purge at 100 C., in an initial stage of desorption, the concentration of SF.sub.6 remains at a high level (49-58 min), and then the concentration of SF.sub.6decreases rapidly (FIG. 7A). This step-wise desorption behavior is attributed to a rapid desorption of weakly bound SF.sub.6 molecules, and followed by a slow desorption of strongly bound SF.sub.6 molecules.

[0065] Quantitative analysis of a desorption curve shows that SF.sub.6 with a purity greater than or equal to 99.9% can be obtained, and a yield is 8.4 mL/g. This is the first time that SF.sub.6 with such high purity is obtained through the adsorption separation, thereby indicating the high selectivity of the CO-DPB. After an adsorbent is fully activated, a breakthrough curve shows consistent performance in at least five cycle tests without significant degradation, and the separation performance and structural stability of the CO-DPB remain unchanged, thereby fully verifying excellent cyclic regeneration ability thereof.

[0066] In addition, the CO-DPB still performs excellently in capturing trace amounts of SF.sub.6. A breakthrough experiment is carried out using an SF.sub.6/N.sub.2 gas mixture with a volume ratio of 99:1, a breakthrough time of SF.sub.6 is as long as 152 min/g, thereby obtaining a high-purity nitrogen gas (>99.99%) (FIG. 7B).

[0067] As shown in FIG. 7C, under a condition of a relative humidity (RH) of 90%, the separation performance of the CO-DPB is almost identical to that under dry conditions. In addition, in five cycle breakthrough experiments carried out by the CO-DPB under the condition of RH=90%, the SF.sub.6/N.sub.2 separation efficiency remains consistent, further proving the stability of the separation performance of the CO-DPB in a humid environment.

[0068] FIG. 8A is a water vapor adsorption isotherm of the CO-DPB, showing that before a relative pressure (P/PO) reaches 0.62, an adsorption amount of water is very small, indicating that an affinity for water is low thereof, which is in sharp contrast to an adsorption isotherm of SF.sub.6, the adsorption isotherm of SF.sub.6 shows significant adsorption even at a low pressure. In addition, adsorption kinetics of water and SF.sub.6 are studied, and results are shown in FIGS. 8b and 8c, an adsorption rate of SF.sub.6 under a condition of 90% relative humidity (RH) is significantly higher than an adsorption rate of water. A kinetic selectivity of SF.sub.6/water reaching 545 is concluded through fitting the diffusion time constants, referring to FIG. 8D, a co-adsorption of water throughout a separation process is effectively reduced by slow water-adsorption kinetics combined with a high kinetic selectivity of SF.sub.6/water.

[0069] In order to evaluate a retention situation of the structure after the breakthrough experiment, a plurality of characterization analyses such as SEM and PXRD are carried out. SEM measurements show that a crystal morphology remains substantially intact after the breakthrough experiment carried out under a humid condition (FIG. 9A and FIG. 9B). A PXRD spectrum shows that the sample still maintains excellent crystallinity even after the breakthrough experiment. N.sub.2 adsorption and BET surface area of the CO-DPB sample at 77 K show almost no change after adsorption and breakthrough experiments (FIG. 3). These results show that the CO-DPB sample can maintain structural integrity even after repeated exposure to a high-humidity environment, further demonstrating the excellent stability thereof.

[0070] The present disclosure uses a process of a pyrazole-based metal-organic framework (MOF) CO-DPB for recovering greenhouse gas SF.sub.6 from the SF.sub.6/N.sub.2 gas mixture, the CO-DPB can achieve SF.sub.6 purity recovery exceeding 99.9%, and this result is attributed to a high SF.sub.6/N.sub.2 selectivity of up to 2485 thereof. Superior performances of the CO-DPB are attributed to an excellent SF.sub.6 capture capacity thereof, resulting from the one-dimensional pore channel with the square shape and the cavity provided on the wall of the one-dimensional pore channel of the structure therein, which can optimally accommodate SF.sub.6 molecules. In addition, the CO-DPB exhibits excellent moisture resistance ability and stability after a plurality of cycles in a dynamic breakthrough experiment, which is due to a high SF.sub.6/H.sub.2O kinetic selectivity of the CO-DPB and inherent hydrophobicity of a pore surface of the CO-DPB.