CN117986610B - A porous cobalt complex with a "pillar-layer" structure and its preparation method and application - Google Patents

Abstract

The invention discloses a porous cobalt complex with a column-layer structure, a preparation method and application thereof, belonging to the technical field of adsorbents, wherein the porous cobalt complex has the structural formula: [ Co ₂(ABTC)(TPP)₂]_n; wherein the ABTC is a group obtained by removing protons on-COOH of 3,3', 5' -azobenzene tetracarboxylic acid; the TPP is 1,2,4, 5-tetra (4-pyridyl) benzene. The preparation method comprises the following steps: cobalt chloride hexahydrate, 3', 5' -azobenzene tetracarboxylic acid and 1,2,4, 5-tetra (4-pyridyl) benzene are dissolved in a mixed solvent, and then the mixture is heated and reacted under the sealing condition, so that the porous cobalt complex is obtained. The porous cobalt complex has good selective adsorption performance on SF ₆ gas small molecules, and can realize low-energy consumption and low-cost storage, purification, recovery and reutilization of SF ₆ gas.

Description

A porous cobalt complex with a "pillar-layer" structure and its preparation method and application

Technical Field

The invention belongs to the technical field of adsorbents, and in particular relates to a porous cobalt complex with a "column-layer" structure and a preparation method and application thereof.

Background technique

Sulfur hexafluoride (SF ₆ ) gas is a fluorine-containing inert gas that is non-toxic, non-flammable, has high dielectric strength, good insulation and solitary extinguishing properties. Therefore, it is widely used in various industries such as electricity, semiconductors, and medical instruments. However, SF ₆ is also a greenhouse gas with extremely serious impacts, and the greenhouse effect it can cause is much higher than that of carbon dioxide (CO ₂ ). According to relevant research, compared with the same volume of CO ₂ , the emission of the same amount of SF ₆ will produce a greenhouse effect 23,900 times greater, and the life span of SF ₆ in the atmosphere is also longer (3200 years). Therefore, in order to protect the ecological environment on which we depend for survival, it is crucial to explore effective SF ₆ adsorption and separation technology.

At present, the separation treatment is mainly carried out by low-temperature distillation, solution absorption, membrane separation and adsorption separation. Among these methods, adsorption separation has the advantages of low investment cost, simple operation and energy saving, and is widely used in the field of gas separation. Metal organic framework materials (MOFs) are a class of porous materials formed by self-assembly of metal ions and organic ligands through coordination bonds. Due to their high porosity, large specific surface area and adjustable pore surface structure, they have been very important in the field of gas adsorption separation.

Therefore, how to provide a metal organic framework material that can achieve the adsorption of small molecules of _SF6 gas and the efficient separation of _SF6 / _N2 mixed gas is a technical problem that those skilled in the art need to solve urgently.

Summary of the invention

In order to solve the above technical problems, the present invention proposes a porous cobalt complex with a "pillar-layer" structure and a preparation method and application thereof.

To achieve the above object, the present invention provides the following technical solutions:

A porous cobalt complex with a "pillar-layer" structure, wherein the molecular formula of the porous cobalt complex is: [Co ₂ (ABTC)(TPP) ₂ ] _n ;

Wherein, the ABTC removes 3,3',5,5'-azobenzenetetracarboxylic acid from the four -COOH protons;

The TPP is 1,2,4,5-tetrakis(4-pyridyl)benzene;

Among them, the crystal structure is a long-range periodic arrangement of basic units, and n in the molecular formula has no specific value.

Preferably, the porous cobalt complex crystallizes in the triclinic system, P-1 space group, with unit cell parameters a=13.6, b=16.4, c=16.6, α=98.9, β=105.2, γ=106.5.

Beneficial effects: The present invention synthesizes a novel metal-organic complex with a "column-layer" structure through two ligand mixing strategies. The complex has a porous structure and is water-stable, and is a potential industrial adsorbent.

A method for preparing a porous cobalt complex with a "pillar-layer" structure comprises the following steps:

Cobalt chloride hexahydrate, 3,3',5,5'-azobenzenetetracarboxylic acid and 1,2,4,5-tetra(4-pyridyl)benzene are dissolved in a mixed solvent and then heated to react under sealing conditions to obtain the porous cobalt complex.

Beneficial effects: The present invention adopts a solution thermal synthesis method, which is simple and highly feasible.

Preferably, the molar ratio of the cobalt chloride hexahydrate, 3,3',5,5'-azobenzenetetracarboxylic acid and 1,2,4,5-tetra(4-pyridyl)benzene is (2-1.5):(1-1.2):(2-3).

Preferably, the mixed solvent is tetrafluoroboric acid, N,N-dimethylformamide, ethanol and water in a volume ratio of 0.1:(3-5):(1.5-2):(0.5-1).

Preferably, the heating reaction is carried out at a temperature of 140-150° C. and for a period of 3-6 days.

A porous cobalt complex with a "pillar-layer" structure is used for adsorption and/or separation of small gas molecules.

Preferably, the gas small molecules are SF ₆ , N ₂ or a SF ₆ /N ₂ mixed gas.

Beneficial effects: The water-stable complex has selective adsorption properties for _SF6 , and has preferential adsorption for _SF6 , which can realize the storage of small molecules _{of SF6} gas, and can realize the separation of _SF6 / _N2 , thereby realizing the purification of _SF6 gas.

More preferably, the adsorption and/or separation of small gas molecules specifically comprises the following steps:

The porous cobalt complex is first soaked in a low-boiling point solvent acetonitrile for 2-3 days, during which the acetonitrile is replaced 3-6 times a day, and then treated at 80°C-100°C in vacuum for 10-16 hours to obtain a pretreated porous cobalt complex, and then the pretreated porous cobalt complex is subjected to an adsorption test on gas small molecules, or the pretreated porous cobalt complex is loaded into a separation column to perform a penetration separation experiment on gas small molecules.

Compared with the prior art, the present invention has the following advantages and technical effects:

The present invention uses 3,3',5,5'-azobenzenetetracarboxylic acid ( _H4ABTC ) and 2,4,6-tri(4-pyridyl)pyridine (TPP) mixed ligands to synthesize a stable porous cobalt complex with a "column layer" structure. The porous cobalt complex obtained by the present invention has good selective adsorption performance for _SF6 gas small molecules, can not only be used as a material for _SF6 gas storage, but also has good separation performance for mixed gas _SF6 / _N2 , and can realize low-energy consumption and low-cost storage, purification, recovery and reuse of _SF6 gas.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

FIG1 is a schematic diagram of the structure of ligands, metal clusters, two-dimensional layers and three-dimensional frameworks in the porous cobalt complex prepared in Example 1 of the present invention;

Among them, (a) is a metal cluster; (b) is an ABTC ligand; (c) is a two-dimensional layer; (d) is a three-dimensional framework; (e) is the л-л stacking effect of the TPP ligand;

FIG2 is a graph of the simulated peaks, experimental peaks, and peaks of the porous cobalt complex prepared in Example 1 by powder X-ray diffraction after immersion in water and at different pH values;

FIG3 is a thermogravimetric diagram of the porous cobalt complex prepared in Example 1 of the present invention;

FIG4 is a graph of N ₂ adsorption of the porous cobalt complex prepared in Example 1 of the present invention at 77K and 1atm;

FIG5 is a graph showing the adsorption of small molecules of SF ₆ and N ₂ gases at 273K and 1atm for the porous cobalt complex prepared in Example 1 of the present invention;

FIG6 is a graph showing the adsorption of small molecules of SF ₆ and N ₂ gases at 298K and 1atm for the porous cobalt complex prepared in Example 1 of the present invention;

FIG7 is a diagram showing the adsorption enthalpy of SF ₆ by the porous cobalt complex prepared in Example 1 of the present invention;

FIG8 is a diagram of the adsorption enthalpy of N ₂ of the porous cobalt complex prepared in Example 1 of the present invention;

FIG9 is a graph showing the separation ratio of the porous cobalt complex prepared in Example 1 of the present invention in a SF ₆ /N ₂ mixed gas at 273K;

FIG10 is a graph showing the separation ratio of the porous cobalt complex prepared in Example 1 of the present invention in a SF ₆ /N ₂ mixed gas at 298K;

FIG. 11 is a separation diagram of the breakthrough curve of SF ₆ /N ₂ of the porous cobalt complex prepared in Example 1 of the present invention at 298K and 1atm.

Detailed ways

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

The embodiment of the present invention discloses a porous cobalt complex with a "pillar-layer" structure, wherein the molecular formula of the porous cobalt complex is: [Co ₂ (ABTC)(TPP) ₂ ] _n ;

Wherein, the ABTC removes 3,3',5,5'-azobenzenetetracarboxylic acid from the four -COOH protons;

The TPP is 1,2,4,5-tetrakis(4-pyridyl)benzene;

In a preferred embodiment, the porous cobalt complex crystallizes in the triclinic system, P-1 space group, with unit cell parameters a=13.6, b=16.4, c=16.6, α=98.9, β=105.2, γ=106.5.

The embodiment of the present invention also discloses a method for preparing a porous cobalt complex with a "pillar-layer" structure, comprising the following steps:

Cobalt chloride hexahydrate, 3,3',5,5'-azobenzenetetracarboxylic acid and 1,2,4,5-tetra(4-pyridyl)benzene are dissolved in a mixed solvent and then heated to react under sealing conditions to obtain the porous cobalt complex.

In a preferred embodiment, the molar ratio of the cobalt chloride hexahydrate, 3,3',5,5'-azobenzenetetracarboxylic acid and 1,2,4,5-tetra(4-pyridyl)benzene is (2-1.5):(1-1.2):(2-3).

In a preferred embodiment, the mixed solvent is tetrafluoroboric acid, N,N-dimethylformamide, ethanol and water in a volume ratio of 0.1:(3-5):(1.5-2):(0.5-1).

In a preferred embodiment, the heating reaction is carried out at a temperature of 140-150° C. and for a period of 3-6 days.

The embodiment of the present invention also discloses the use of a porous cobalt complex with a "column-layer" structure in the adsorption and/or separation of small gas molecules.

In a preferred embodiment, the gas small molecules are SF ₆ , N ₂ or a SF ₆ /N ₂ mixed gas.

In a more preferred embodiment, the adsorption and/or separation of small gas molecules specifically comprises the following steps:

The porous cobalt complex is first soaked in a low boiling point solvent acetonitrile for 2-3 days, during which the acetonitrile is replaced 3-6 times a day, and then treated at 80°C-100°C in vacuum for 10-16 hours to obtain a pretreated porous cobalt complex, and then the pretreated porous cobalt complex adsorbs small gas molecules, or the pretreated porous cobalt complex is loaded into a separation column to separate small gas molecules.

Example 1

A method for preparing a porous cobalt complex with a "pillar-layer" structure comprises the following steps:

To a 25 mL polytetrafluoroethylene liner were added cobalt chloride hexahydrate (0.035 g, 0.15 mmol), H ₄ ABTC (3,3',5,5'-azobenzenetetracarboxylic acid) (0.036 g, 0.075 mmol) and TPP (1,2,4,5-tetrakis(4-pyridyl)benzene) (0.062 g, 0.15 mmol), and then 5.1 mL of a mixture of tetrafluoroboric acid, N,N-dimethylformamide, ethanol and water in a volume ratio of 0.1:3:2:1 was added. After stirring evenly, the mixture was sealed and allowed to react at a constant temperature of 140°C for 4 days to obtain a porous cobalt complex with a structure of [Co ₂ (ABTC)(TPP) ₂ ] _n .

Technical effects:

The structures of the ligands, metal clusters, two-dimensional layers and three-dimensional framework of the porous cobalt complex obtained in Example 1 are shown in FIG1 . Through single crystal-X-ray testing, it can be seen that the prepared complex crystallizes in the triclinic system, P-1 space group, and the unit cell parameters are a=13.6, b=16.4, c=16.6, α=98.9, β=105.2, γ=106.5. It is a two-dimensional layer structure formed by the cross-linking of binuclear metal cobalt clusters [Co ₂ (COO) ₃ N ₂ ] and ABTC, and the two-dimensional layer is supported and connected by the two terminal N atoms of the TPP ligand to form a three-dimensional porous structure. This structure has a The one-dimensional pore structure (measured by the distance between atoms) of the TPP was used to calculate the porosity of 30.6% using the _N2 dynamic radius probe in the PLATON software. It is worth noting that the polyaromatic ring ligands of TPP, which have a conjugated system, are nearly parallel to each other, and there is a π-π stacking effect. The stacking distance between the aromatic rings of different TPP ligands is in The existence of this π-π stacking effect enhances the stability of the overall framework of the complex (Figure 1). The simulated peak and experimental peak of the complex are basically consistent through powder X-ray diffraction, indicating that it has good purity. By immersing the complex in water and solutions of different pH values, it is determined that it has good water stability (Figure 2). The thermal stability of the compound can reach above 380°C through thermogravimetric testing (Figure 3).

Example 2

A method for preparing a porous cobalt complex with a "pillar-layer" structure comprises the following steps:

To a 25 mL polytetrafluoroethylene liner, cobalt chloride hexahydrate (0.048 g, 0.2 mmol), H ₄ ABTC (3,3',5,5'-azobenzenetetracarboxylic acid) (0.036 g, 0.1 mmol) and TPP (1,2,4,5-tetrakis(4-pyridyl)benzene) (0.077 g, 0.2 mmol) were added, and then 15 mL of a mixture of tetrafluoroboric acid, N,N-dimethylformamide, ethanol and water in a volume ratio of 0.1:3:2:1 was added. After stirring evenly, the mixture was sealed and allowed to react at a constant temperature of 145°C for 5 days to obtain a porous cobalt complex with a structure of [Co ₂ (ABTC)(TPP) ₂ ] _n .

Example 3

A method for preparing a porous cobalt complex with a "pillar-layer" structure comprises the following steps:

To a 25 mL polytetrafluoroethylene liner, cobalt chloride hexahydrate (35.7 mg, 0.15 mmol), H ₄ ABTC (3,3',5,5'-azobenzenetetracarboxylic acid) (35.8 mg, 0.10 mmol) and TPP (1,2,4,5-tetrakis(4-pyridyl)benzene) (115.8 mg, 0.30 mmol) were added, and then 18 mL of a mixture of tetrafluoroboric acid, N,N-dimethylformamide, ethanol and water in a volume ratio of 0.1:4:2:1 was added. After stirring evenly, the mixture was sealed and allowed to react at a constant temperature of 140°C for 4 days to obtain a porous cobalt complex with a structure of [Co ₂ (ABTC)(TPP) ₂ ] _n .

Application Examples

1. Using porous cobalt complexes to adsorb small gas molecules:

The porous cobalt complex obtained in Example 1 was soaked in acetonitrile for 2 days, during which the acetonitrile was replaced 3 times a day with an interval of 8 hours each time. After the soaking, it was vacuum degassed at 80°C for 12 hours, and its specific surface area, pore size and adsorption capacity of SF ₆ and N ₂ small molecule gases were tested using a Micromeritics 3-Flex gas adsorption instrument.

The specific surface area and pore size test conditions are N ₂ tests at a temperature of 77 K, and the temperature is mainly controlled by liquid nitrogen. As shown in Figure 4, through the N ₂ test, the BET and Langmuir specific surface areas of the complex are 714m ² /g and 1039m ² /g, respectively, and the pore size is 0.77nm.

The adsorption of N ₂ and SF ₆ at different temperatures is mainly achieved by reflux of ethanol in an external temperature control device, and the two temperature conditions of 273K and 298K are mainly tested. As shown in Figure 5, under the conditions of 273K and 1 atmosphere, the adsorption of N ₂ and SF ₆ can reach 5.4cm ³ /g and 75.0cm ³ /g respectively. As shown in Figure 6, under the conditions of 298K and 1 atmosphere, the adsorption of N ₂ and SF ₆ can reach 3.3cm ³ /g and 64.0cm ³ /g respectively.

In summary, under the conditions of 298K and 1 atmosphere, the porous cobalt complex obtained in Example 1 has good adsorption performance for small molecule _SF6 gas, and its adsorption capacity for _SF6 is much greater than that for _N2 , indicating that the complex can be used as a storage material for _SF6 gas, and also has great potential for separation of _SF6 / _N2 mixed gas.

2. Adsorption enthalpy is an important parameter to measure the strength of the interaction between the adsorbent and the gas molecules during the adsorption process. It determines the energy required in the gas desorption process and the adsorption selectivity of various gases. In order to have a deeper understanding of the interaction between the complex and the gas, the isosteric adsorption heat (-Q _st ) is used to illustrate. The Virial equation is used to fit the single-component gas isothermal adsorption curves at 273K, 283K and 298K to obtain the adsorption enthalpy (-Q _st ). The results are shown in Figures 7 and 8. It can be seen that the adsorption enthalpies of the porous cobalt complex obtained in Example 1 for SF ₆ and N ₂ at the initial 0 atmosphere are 22.8 and 14.0 kJ/mol, respectively.

3. The separation of mixed gases under static conditions was simulated using the adsorption isotherms of single-component gases and the ideal adsorption solution theory (IAST), and the Langmuir-Freundlich (LF) model was used to fit the isothermal adsorption curves to obtain relevant parameters. The results are shown in Figures 9 and 10. It can be seen that the fitting curves of each component gas at different temperatures are basically consistent with the experimental values. Under the conditions of 298K and 1 atm, the separation ratio of the porous cobalt complex obtained in Example 1 for SF ₆ /N ₂ (volume ratio of 1:9) can reach 66.1.

4. In order to further evaluate the separation effect of the porous cobalt complex obtained in Example 1 on the SF ₆ /N ₂ mixed gas under actual industrial conditions, a mixed two-component test was carried out under 298K and 1.0bar. The experimental device used a stainless steel cylinder and the density of the packed bed sample was 1.089g/cm ^3. The flow rate of the mixed gas was controlled by a mass flow controller. Before the experiment, other gases in the device were purged by using high-purity helium at high temperature, and then the SF ₆ /N ₂ (volume ratio of 1:9) mixed gas was sent to the fixed adsorption bed at a flow rate of 1mL/min, and the outlet mixed gas concentration was detected in real time by a gas chromatograph. In terms of material regeneration, high-purity helium was used for purging at room temperature, and then the next cycle experiment was prepared. The results are shown in Figure 11. It can be seen that the porous cobalt complex obtained by the present invention can achieve efficient separation of SF ₆ /N ₂ (volume ratio of 1:9) mixed gas.

The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims (8)

1. A porous cobalt complex with a "pillar-layer" structure, characterized in that the molecular formula of the porous cobalt complex is: [Co ₂ (ABTC)(TPP) ₂ ] _n ; Wherein, the ABTC is a group obtained by removing the proton on -COOH from 3,3',5,5'-azobenzenetetracarboxylic acid; and the TPP is 1,2,4,5-tetrakis(4-pyridyl)benzene. 2. A porous cobalt complex with a "column-layer" structure according to claim 1, characterized in that the porous cobalt complex crystallizes in triclinic system, P-1 space group, unit cell parameters a=13.6, b=16.4, c=16.6, α=98.9, β=105.2, γ=106.5. 3. The method for preparing a porous cobalt complex with a "pillar-layer" structure according to claim 1, characterized in that it comprises the following steps: Cobalt chloride hexahydrate, 3,3',5,5'-azobenzenetetracarboxylic acid and 1,2,4,5-tetra(4-pyridyl)benzene are dissolved in a mixed solvent and then heated to react under sealing conditions to obtain the porous cobalt complex. 4. The method for preparing a porous cobalt complex with a "pillar-layer" structure according to claim 3, characterized in that the molar ratio of cobalt chloride hexahydrate, 3,3',5,5'-azobenzenetetracarboxylic acid and 1,2,4,5-tetra(4-pyridyl)benzene is (2-1.5):(1-1.2):(2-3). 5. The method for preparing a porous cobalt complex with a "column-layer" structure according to claim 3, characterized in that the mixed solvent is tetrafluoroboric acid, N,N-dimethylformamide, ethanol and water mixed in a volume ratio of 0.1:(3-5):(1.5-2):(0.5-1). 6. The method for preparing a porous cobalt complex with a "pillar-layer" structure according to claim 3, characterized in that the heating reaction temperature is 140-150°C and the time is 3-6 days. 7. Use of the porous cobalt complex with a "column-layer" structure as claimed in claim 1 in the adsorption and/or separation of small gas molecules. 8. The use according to claim 7, characterized in that the gas small molecules are _SF6 and _N2 gases.