CN109400891B - Cadmium-based metal organic framework and preparation method and application thereof - Google Patents

Abstract

The invention relates to a cadmium-based metal organic framework and a preparation method and application thereof. The novel porous three-dimensional cadmium-based metal organic framework is synthesized by self-assembling cadmium salt and a planar aromatic ligand containing a tetracarboxylic acid functional group, in the structure, each cadmium ion is coordinated with four carboxyl groups from different ligands, and the four carboxyl groups of each ligand are respectively coordinated with four cadmium ions, so that a one-dimensional rhombic channel along a c-axis is constructed, and the three-dimensional framework is further formed. The cadmium-based metal organic framework is a (4,4) -connected pts three-dimensional network topological structure, and has the advantages of large specific surface area, high porosity, large conjugate center and the like, so that the cadmium-based metal organic framework is applied to CO₂Can be enhanced with CO through large conjugated centers thereof in the adsorption process₂The interaction force between the two components is further shown to be towards CO₂High selective adsorption performance and large adsorption capacity. Meanwhile, the material has the advantages of simple synthesis method, strong thermal stability and strong chemical stability, and is expected to be applied to the fields of carbon dioxide capture, clean energy storage and the like.

Description

Cadmium-based metal organic framework and preparation method and application thereof

Technical Field

The invention relates to the field of functional materials, in particular to a cadmium-based metal organic framework and a preparation method and application thereof.

Background

The Metal Organic Frameworks (MOFs) are composed of metal ions/clustersAnd organic ligand self-assembly, and is widely applied to gas adsorption, storage and separation due to the characteristics of chemical stability, large surface area and high porosity. In recent years, CO is used₂The large amount of emissions causes global warming to pose a serious threat to human survival, and many researchers have been working on research and synthesis of selective CO₂MOFs with adsorption properties. To increase CO₂Various strategies have been proposed including: 1. selecting a suitable ligand; 2. nitrogen-containing or other polarization groups are introduced to carry out reasonable decoration in the pores; 3. the pore size is reduced by increasing the diversity of organic ligands, changing the size or length of the ligands, designing the coordination mode of metal ions in the MOFs structure, and the like. However, existing strategies may result in the surface area and CO of MOFs₂The adsorption capacity is lowered to hinder its practical use. Therefore, CO with both large adsorption capacity and high selectivity is designed and synthesized₂The material of the adsorption capacity is of critical importance.

Disclosure of Invention

Based on the above, the invention aims to provide a cadmium-based metal organic framework, a preparation method and an application thereof, wherein the cadmium-based metal organic framework is used for treating CO₂Has high selective adsorption capacity.

The purpose of the invention is realized by the following technical scheme: a cadmium-based metal organic framework, which is synthesized by self-assembly of cadmium salt and a planar aromatic ligand containing tetracarboxylate functional groups; the planar aromatic ligand containing the tetracarboxylic acid functional group is 1,3,6, 8-tetracarboxypyrene, and has the following structure:

each cadmium ion is coordinated with four carboxyl groups from different ligands, and the four carboxyl groups of each ligand are respectively coordinated with four cadmium ions.

Compared with the prior art, the cadmium-doped zinc oxide material is prepared by cadmium salt and 1,3,6, 8-tetracarboxypyrene (H)₄PTC) ligand self-assembly synthesis of novel porous three-dimensional cadmium-based metal organicFramework (Cd-PTC), which is a (4,4) -connected pts three-dimensional network topology, the points of which

Symbol is (4)²·8⁴) Due to its advantages of large specific surface area, high porosity and large conjugation center, in CO₂Can be enhanced with CO through large conjugated centers thereof in the adsorption process₂The interaction force between the two components is further shown to be towards CO₂High selective adsorption performance and large adsorption capacity.

A preparation method of a cadmium-based metal organic framework comprises the following steps:

s1: dissolving 1,3,6, 8-tetrabromopyrene and copper cyanide in quinoline, heating and stirring to obtain 1,3,6, 8-tetracyanopyrene;

s2: dissolving the 1,3,6, 8-tetracyanopyrene in a mixed solvent of a NaOH solution and absolute ethyl alcohol, and heating and refluxing to obtain 1,3,6, 8-tetracarboxypyrene;

s3: and dissolving the 1,3,6, 8-tetracarboxypyrene and the cadmium salt in a mixed solvent of nitric acid, dimethylformamide and water, and sealing and heating to obtain the cadmium-based metal organic framework.

In step S1, the molar ratio of 1,3,6, 8-tetrabromopyrene to copper cyanide is 1 (30-35).

Further, step S1 is: dissolving 1,3,6, 8-tetrabromopyrene and copper cyanide in quinoline, heating at 95-105 ℃ for 0.5-1 h, and then heating and stirring at 225-235 ℃ for 45-50 h; then cooling to room temperature, adding absolute ethyl alcohol, and heating and stirring at 80-90 ℃ for 0.8-1.2 h; then filtering, and washing and filtering the obtained product by using nitric acid and absolute ethyl alcohol in sequence to obtain the 1,3,6, 8-tetracyanopyrene.

Further, in step S2, the volume ratio of the NaOH solution to the absolute ethyl alcohol is 1 (1.5-1.8).

Further, step S2 is: dissolving the 1,3,6, 8-tetracyanopyrene in a mixed solvent of NaOH solution and absolute ethyl alcohol, and heating and refluxing for 20-28 h at 105-115 ℃; subsequently cooling to room temperature and acidifying to pH 1 with hydrochloric acid; then filtering, washing the obtained product by water and absolute ethyl alcohol, and obtaining the 1,3,6, 8-tetracarboxypyrene.

In step S3, the molar ratio of the 1,3,6, 8-tetracarboxypyrene to the cadmium salt is 1 (0.9-1.1).

Further, in step S3, the volume ratio of the nitric acid to the dimethylformamide to the water is 1 (65-70) to (30-35).

Further, step S3 is: dissolving the 1,3,6, 8-tetracarboxypyrene and cadmium salt in a mixed solvent of nitric acid, dimethylformamide and water, and sealing and heating for 66-78 h at the temperature of 95-105 ℃; then cooling to room temperature, filtering, and washing and filtering the obtained product by using dimethylformamide to obtain the cadmium-based metal organic framework.

The cadmium-based metal organic frame is a CO frame₂Use in adsorption and separation of cadmium-based metal organic frameworks with CO₂Has strong interaction force and can be separated from CO₂/N₂And CO₂/CH₄High-selectivity CO adsorption in mixture₂。

For a better understanding and practice, the invention is described below with reference to the accompanying drawings and examples.

Drawings

FIG. 1 is H₄Scheme for synthesis of PTC ligands.

FIG. 2 shows Cd in Cd-PTC²⁺Schematic representation of coordination mode of central metal ion.

FIG. 3 is a deprotonated ligand PTC^4-Schematic representation of the coordination mode of (a).

FIG. 4 is a three-dimensional frame polyhedral view of Cd-PTC from [100] direction.

FIG. 5 is a three-dimensional frame polyhedral view of Cd-PTC from [001] direction.

FIG. 6 is a space-filling view of a porous three-dimensional framework of Cd-PTC with one-dimensional diamond-shaped channels along the c-axis.

Fig. 7 is a view of a (4,4) connected pts network topology for Cd-PTC.

FIG. 8 is a TGA plot of crude Cd-PTC and desolvated Cd-PTC.

FIG. 9 is a PXRD pattern of crude Cd-PTC and desolvated Cd-PTC.

FIG. 10 is a nitrogen adsorption/desorption curve of desolvated Cd-PTC at 77K.

FIG. 11 shows desolvated Cd-PTC towards CO at 273K and 298K, respectively₂，CH₄And N₂The gas adsorption isotherm of (1).

FIG. 12 shows desolvated Cd-PTC versus mixed gas CO calculated by IAST method₂/N₂(volume ratio 15/85) and CO₂/CH₂(50/50 volume ratio).

FIG. 13 shows desolvated Cd-PTC versus mixed gas CO at 298K₂/N₂Dynamic breakthrough adsorption curve (volume ratio 15/85).

FIG. 14 shows desolvated Cd-PTC vs. mixed gas CO at 298K₂/CH₄Dynamic breakthrough adsorption curve (volume ratio 50/50).

Detailed Description

The invention provides a cadmium-based metal organic framework, which is synthesized by self-assembling cadmium salt and a planar aromatic ligand containing a tetracarboxylic acid functional group; the planar aromatic ligand containing the tetracarboxylic acid functional group is 1,3,6, 8-tetracarboxypyrene, and has the following structure:

each cadmium ion is coordinated with four carboxyl groups from different ligands, and the four carboxyl groups of each ligand are respectively coordinated with four cadmium ions. The cadmium salt can be cadmium nitrate, cadmium chloride or cadmium sulfate.

The invention also provides a preparation method of the cadmium-based metal organic framework, which comprises the following steps:

(1) dissolving 1,3,6, 8-tetrabromopyrene and copper cyanide in a molar ratio of 1 (30-35) in quinoline, heating at 95-105 ℃ for 0.5-1 h, and then heating at 225-235 ℃ and stirring for 45-50 h; then cooling to room temperature, adding absolute ethyl alcohol, and heating and stirring at 80-90 ℃ for 0.8-1.2 h; then filtering, and washing and filtering the obtained product by using nitric acid and absolute ethyl alcohol in sequence to obtain the 1,3,6, 8-tetracyanopyrene.

(2) Dissolving the 1,3,6, 8-tetracyanopyrene in a mixed solvent with the volume ratio of NaOH solution to absolute ethyl alcohol being 1 (1.5-1.8), and heating and refluxing for 20-28 h at 105-115 ℃; subsequently cooling to room temperature and acidifying to pH 1 with hydrochloric acid; then filtering, washing the obtained product by water and absolute ethyl alcohol, and obtaining the 1,3,6, 8-tetracarboxypyrene.

(3) Dissolving the 1,3,6, 8-tetracarboxypyrene and the cadmium salt in a molar ratio of 1 (0.9-1.1) in a mixed solvent of nitric acid, dimethylformamide and water in a volume ratio of 1 (65-70) to (30-35), and sealing and heating at 95-105 ℃ for 66-78 hours; followed by cooling to room temperature, filtration, and washing the filtered product with dimethylformamide to obtain cadmium-based metal organic framework (Me)₂NH₂)₂[Cd(PTC)]·2H₂O。

The following is further illustrated by specific examples.

Example 1

The preparation method of the cadmium-based metal organic framework of the embodiment comprises the following steps:

(1) 1,3,6, 8-tetrabromopyrene (12g, 23.4mmol) as a starting material was reacted with copper cyanide Cu (CN)₂(90g, 0.78mol) in 120mL of quinoline solvent, and heating the mixed solution at 100 ℃ for 0.5h, followed by stirring at 230 ℃ for 48 h; then cooling to room temperature, adding absolute ethyl alcohol, and heating and stirring at 85 ℃ for 1 h; and then filtering, washing the obtained product with nitric acid with the mass fraction of 30% to remove copper residues, and repeatedly washing with absolute ethyl alcohol to obtain the 1,3,6, 8-tetracyanopyrene.

(2) Dissolving the 1,3,6, 8-tetracyanopyrene (2.26g, 7.5mmol) in a mixed solvent of aqueous NaOH (10M, 60mL) and absolute ethanol (EtOH, 90mL), placing in a 250mL round-bottom flask, and heating under reflux at 105 ℃ for 24 h; subsequently cooling to room temperature, acidifying with 37% by mass hydrochloric acid to pH 1 to acidify the carboxylate ligands formed during reflux, so that the salt is converted back to the carboxylic acid and excess NaOH is removed from the solution; then filtering, washing the obtained product with water and absolute ethyl alcohol to obtain 1,3,6, 8-tetracarboxypyrene ligand (H)₄PTC) was added to the reaction solution, and the mass was 1.84g, the yield was 62.5%. H₄The scheme for synthesis of the PTC ligands is shown in FIG. 1.

(3) Subjecting said H to₄PTC ligand (19mg, 0.05mmol), Cd (NO)₃)₂·4H₂O (15mg, 0.05mmol) was dissolved in a mixed solvent of nitric acid (5M, 60. mu.L), dimethylformamide (DMF, 4mL) and water (2mL), sealed and placed in a 10mL glass reaction flask, and heated at 100 ℃ for 72 h; cooling to room temperature at a rate of 5 deg.C/min, filtering, washing the obtained product with DMF, and air drying to obtain cadmium-based metal organic framework (Me)₂NH₂)₂[Cd(PTC)]·2H₂O, i.e. C₂₄H₂₆N₂O₁₀Cd (hereinafter abbreviated to Cd-PTC) was obtained at a yield of 43% (based on the amount of ligand).

Elemental analysis

Elemental analysis was obtained by a Perkin-Elmer 240 elemental analyzer. C₂₄H₂₆N₂O₁₀Analyzing Cd element: calculated values: c46.88, H4.26, N4.56%; measured value: c46.69, H4.20, N4.58%.

Structural analysis

X-ray diffraction test by Bruker APEX II diffractometer using graphite monochromatic Mo-Ka rays

At 296K. Empirical absorption correction values are used to correct for diffraction. Absorption correction and space group determination are performed by the multi-scan method using SADABS and XPREP in APEX2, respectively. The structure was solved by direct method using the SHELXL program (SHELXTL-2014), and using F²The full matrix least squares refines the structure. In the final cycle, the theoretical position of the organic hydrogen atom will be calculated using the isotropic displacement parameters of the organic hydrogen atom. Due to [ Me₂NH₂]⁺The cation and free solvent molecules are highly disordered in the structure, interference of scattering thereof is eliminated by the SQUEEZE program of PLATON, and the final result is used for determination of the structure. The crystal parameters, data collection and refinement are summarized in Table 1The transformed data; table 2 lists the selected bond lengths and the structure is shown in fig. 2.

TABLE 1 Cd-PTC fine structure crystal data

TABLE 2 bond Length of Cd-PTC

The structural analysis shows that the Cd-PTC has monoclinic C2/C space group. In the structure of Cd-PTC, each Cd²⁺The central metal ion coordinates four bidentate chelated carboxylic acid functional groups from four different ligands, as shown in fig. 2; each deprotonated PTC^4-Ligand-linked four Cd²⁺An ion, all four of whose carboxyl groups participate in coordination, as shown in FIG. 3; thereby forming a novel three-dimensional metal-organic framework along the a-axis, as shown in fig. 4. Carboxyl group and Cd of each ligand²⁺The coordinated small building blocks are connected together by the pyrene ring in the ligand to form a one-dimensional rhombohedral channel, as shown in FIGS. 5 and 6, the framework being oriented along [001]]And [100]]Oriented with one-dimensional diamond-shaped channels of dimensions

Solvent contactable volume calculated by PLATON as

(volume per unit cell of

) The porosity is as high as 53.5%. To better understand the intrinsic structure, topological analysis of Cd-PTC was performed using TOPOS 4.0 program, with each ligand and each Cd²⁺Ions can be regarded as 4-connected nodes respectively, so the whole framework can be regarded as a pts network topology of double-node (4,4) connection

Symbol is (4)²·8⁴) As shown in fig. 7.

Thermogravimetric analysis

Thermogravimetric analysis (TGA) was performed on a Netzsch Thermo Microbalance TG 209F 3 Tarsus under a nitrogen flow at a ramp rate of 5 ℃/min from room temperature to 80 ℃.

The thermogravimetric analysis curves of the crude Cd-PTC and desolvated Cd-PTC are shown in FIG. 8. The first weight loss of Cd-PTC crude was 5.39%, corresponding to a loss of 5.85% of DMF molecules as solvent (calculated value); subsequently, when the temperature is higher than 250 ℃, a drastic weight loss of the entire frame occurs, which is attributed to the decomposition of the frame.

X-ray powder diffractograms (PXRD) were measured on a Bruker D8 Advance diffractometer with a Cu target tube and a graphite monochromator at 40kV and 40mA, as shown in fig. 9, a good match of diffraction peaks between the Cd-PTC product and the simulated product from the single crystal analysis results, confirming the phase purity of the Cd-PTC product.

Adsorption analysis

And (3) measuring an adsorption isotherm by using a Quantachrome Autosorb-iQ-MP gas adsorption analyzer. To measure the pore characteristics of Cd-PTC, nitrogen adsorption experiments were performed. And heating the prepared product at 80 ℃ for 4h under vacuum to remove all guest water molecules to obtain desolvated Cd-PTC. Further TGA and PXRD tests showed that the desolvated Cd-PTC retained its framework intact and retained its original crystallinity after removal of all water molecules (as shown in fig. 8 and 9). At 77K, 1.0atm, the nitrogen adsorption/desorption isotherm of the desolvated Cd-PTC sharply increases at the beginning as a typical type I curve, as shown in FIG. 10, N₂The adsorption capacity reaches 302.4cm³And/g, showing that it has microporous characteristics. The Brunauer-Emmett-Teller (BET) specific surface area is 965m²In terms of/g, total pore volume of 0.57cm³/g。

To better measure porosity, desolvated Cd-PTC was subjected to CO at 273K and 298K, respectively₂、CH₄And N₂And (4) adsorption measurement. As shown in FIG. 11, Cd-PTC is on CO at 273K₂Having a width of 80cm³Good adsorption capacity in g, at 298K on CO₂Having a width of 58cm³Adsorption amount per g. However, Cd-PTC pairs of CH under the same conditions₄And N₂Very small adsorption amounts of (C) at 273K and 298K for CH₄Respectively has an adsorption capacity of 9.2cm³G and 6.7cm³In terms of N,/g₂Respectively, the adsorption amounts of (A) and (B) were 2.8cm³G and 1.9cm³(ii) in terms of/g. Obviously, relative CH₄And N₂Cd-PTC pair CO₂Has higher adsorption capacity, and the phenomenon can be attributed to CO₂Larger quadrupole moment (-1.4X 10)^-39cm²) Can produce specific interaction with the main framework of the Cd-PTC body.

In order to better test the adsorption selectivity and separation performance of Cd-PTC, the Ideal Adsorption Solution Theory (IAST) is used to calculate that Cd-PTC is applied to CO when the pressure is up to 100kPa₂And N₂Mixed gas (volume ratio: 15/85), CO₂And CH₄Separation selectivity of mixed gas (volume ratio 50/50). As shown in FIG. 12, Cd-PTC vs CO with increasing pressure₂/N₂(volume ratio 15/85) selectivity factor (adsorbed CO)₂Volume and adsorbed N₂Volume ratio) gradually decreases from 175 to 106. Cd-PTC pair CO₂/CH₄(volume ratio 50/50) selectivity factor (adsorbed CO)₂Volume and adsorbed CH₄Volume ratio) from 31 to 19. These results show that relative to N₂And CH₄Cd-PTC pair CO₂Has a higher selection coefficient, so that it is to CO₂Has stronger adsorption capacity.

To further determine the specific separation and purification performance, dynamic breakthrough adsorption experiments were also performed. As shown in FIG. 13, at 298K, before the adsorption column penetratesIntroduction of CO into₂/N₂The gases were mixed at a volume ratio of 15/85, and dynamic breakthrough adsorption showed CO₂Can successfully separate dynamic CO from the mixture₂The adsorption capacity is 0.78mmol/g, which is equivalent to the performance of HKUST-1 and IRMOF-74, and the adsorption capacity is 0.45 mmol/g and 0.8mmol/g respectively. As shown in fig. 14 for CO₂/CH₄(volume ratio 50/50), since the separation ratio of the mixed gas is relatively low, the breakthrough phenomenon can be observed in a short time.

Compared with the prior art, the cadmium-doped zinc oxide material is prepared by cadmium salt and 1,3,6, 8-tetracarboxypyrene (H)₄PTC) ligand self-assembly to synthesize a novel porous three-dimensional cadmium-based metal organic framework (Cd-PTC) with a (4,4) connected pts three-dimensional network topological structure, wherein the framework has porosity and a large conjugate center, and gas adsorption tests show that desolvated Cd-PTC and CO₂Has strong interaction force and can be separated from CO₂/N₂And CO₂/CH₄High-selectivity CO adsorption in mixture₂。

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.

Claims (9)

1. A cadmium-based metal organic framework, comprising: the cadmium complex is synthesized by self-assembly of cadmium salt and a planar aromatic ligand containing a tetracarboxylate function; the planar aromatic ligand containing the tetracarboxylic acid functional group is 1,3,6, 8-tetracarboxypyrene, and has the following structure:

each cadmium ion is coordinated with four carboxyl groups from different ligands, and the four carboxyl groups of each ligand are respectively coordinated with four cadmium ions;

the preparation method of the cadmium-based metal organic framework comprises the following steps: dissolving 1,3,6, 8-tetracarboxypyrene and cadmium salt in a molar ratio of 1 (0.9-1.1) in a mixed solvent of nitric acid, dimethylformamide and water, and sealing and heating to obtain the cadmium-based metal organic framework.

2. The method of preparing a cadmium-based metal organic framework of claim 1, wherein: the method comprises the following steps:

s1: dissolving 1,3,6, 8-tetrabromopyrene and copper cyanide in quinoline, heating and stirring to obtain 1,3,6, 8-tetracyanopyrene;

s2: dissolving the 1,3,6, 8-tetracyanopyrene in a mixed solvent of a NaOH solution and absolute ethyl alcohol, and heating and refluxing to obtain 1,3,6, 8-tetracarboxypyrene;

s3: dissolving the 1,3,6, 8-tetracarboxypyrene and the cadmium salt in a molar ratio of 1 (0.9-1.1) in a mixed solvent of nitric acid, dimethylformamide and water, and sealing and heating to obtain the cadmium-based metal organic framework.

3. The method of preparing a cadmium-based metal organic framework as claimed in claim 2, wherein: in the step S1, the molar ratio of the 1,3,6, 8-tetrabromopyrene to the copper cyanide is 1 (30-35).

4. The method of preparing a cadmium-based metal organic framework as claimed in claim 3 wherein: step S1 is: dissolving 1,3,6, 8-tetrabromopyrene and copper cyanide in quinoline, heating at 95-105 ℃ for 0.5-1 h, and then heating and stirring at 225-235 ℃ for 45-50 h; then cooling to room temperature, adding absolute ethyl alcohol, and heating and stirring at 80-90 ℃ for 0.8-1.2 h; then filtering, and washing and filtering the obtained product by using nitric acid and absolute ethyl alcohol in sequence to obtain the 1,3,6, 8-tetracyanopyrene.

5. The method of preparing a cadmium-based metal organic framework as claimed in claim 2, wherein: in step S2, the volume ratio of the NaOH solution to the absolute ethyl alcohol is 1 (1.5-1.8).

6. The method of preparing a cadmium-based metal organic framework as claimed in claim 5, wherein: step S2 is: dissolving the 1,3,6, 8-tetracyanopyrene in a mixed solvent of NaOH solution and absolute ethyl alcohol, and heating and refluxing for 20-28 h at 105-115 ℃; subsequently cooling to room temperature and acidifying to pH 1 with hydrochloric acid; then filtering, washing the obtained product by water and absolute ethyl alcohol, and obtaining the 1,3,6, 8-tetracarboxypyrene.

7. The method of preparing a cadmium-based metal organic framework as claimed in claim 2, wherein: in step S3, the volume ratio of the nitric acid to the dimethylformamide to the water is 1 (65-70) to (30-35).

8. The method of preparing a cadmium-based metal organic framework as claimed in claim 7, wherein: step S3 is: dissolving the 1,3,6, 8-tetracarboxypyrene and cadmium salt in a mixed solvent of nitric acid, dimethylformamide and water, and sealing and heating for 66-78 h at the temperature of 95-105 ℃; then cooling to room temperature, filtering, and washing and filtering the obtained product by using dimethylformamide to obtain the cadmium-based metal organic framework.

9. The cadmium-based metal-organic framework of claim 1, in CO₂Use in adsorption and separation.

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