Iron-based porous coordination polymer as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of crystal materials, and particularly relates to an iron-based porous coordination polymer as well as a preparation method and application thereof. One repeating unit in the crystal structure of the iron-based porous coordination polymer is composed of Fe3O4 (DMTD) 3 (TPP), and ligands are 3, 4-dimethyl (2, 3-B) thiophene-2, 5-dicarboxylic acid and 2, 4, 6-tri-(4-pyridyl) pyridine; the iron-based porous coordination polymer has high crystallinity, high purity and a three-dimensional frame structure. The iron-based porous coordination polymer can realize separation of acetylene and ethylene mixed gas and ethane and ethylene mixed gas; the catalyst can be used for electrocatalytic oxygen evolution reaction, and OER crossing point location is 260 mV.

Description

Technical Field

[0001] The present invention belongs to the technical field of crystal materials, and particularly relates to an iron-based porous coordination polymer, a preparation method thereof, and an application thereof. Background Art

[0002] Porous coordination polymers are porous crystal materials formed by connecting metal ions or clusters with organic ligands through coordination bonds. Due to their high specific surface area, adjustable pore structure, and diverse functional characteristics, porous coordination polymers have shown broad application prospects in the fields of gas adsorption and separation, catalysis, sensing, and energy storage. In recent years, iron-based porous coordination polymers based on transition metals (such as iron, copper, zinc, etc.) have received extensive attention due to their unique electronic structure and catalytic activity.

[0003] Unsaturated light hydrocarbons are widely used in industry. For example, ethylene is one of the main raw materials for the three major synthetic materials of plastics, synthetic rubber, and synthetic fibers; acetylene can be used in the synthesis of acrylic acid, vinyl chloride, polyurethane, and polyester plastics. During the production of ethylene, impurity gases such as ethane, acetylene, and carbon dioxide are often generated, and during the production of acetylene, impurity gases such as carbon dioxide are also generated. Therefore, in order to meet the requirements of downstream industries for the purity of olefins and alkynes, these impurity gases must be removed. Currently, cryogenic distillation is the main method for purifying these gases, but this method has high energy consumption and large equipment investment. Therefore, developing efficient and energy-saving methods is of great significance in industry.

[0004] Electrocatalytic oxygen evolution reaction plays an important role in energy conversion and storage devices, such as water splitting systems and metal-air batteries. The oxygen evolution reaction (OER) is an essential process in these applications, but its slow kinetics limits its practical feasibility. High-efficiency OER electrocatalysts containing noble metals (RuO2, IrO2, and Ir / C) need to be replaced by low-cost non-noble metal electrocatalysts. Designing and developing these non-noble metal catalysts remains a huge challenge. Exploring new catalytic materials, such as non-noble metal-based catalysts, metal-organic frameworks (MOFs), etc., provides the possibility for realizing the economy and scalable application of electrocatalysts. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention provides an iron-based porous coordination polymer, a preparation method thereof, and an application thereof.

[0006] The present invention is realized through the following technical solutions: A kind of iron-based porous coordination polymer, the composition of a repeating unit in the crystal structure of the iron-based porous coordination polymer is Fe3O(DMTD)3(TPP), the ligands are 3,4-dimethyl(2,3-B)benzo[b]thiophene-2,5-dicarboxylic acid H2DMTD, 2,4,6-tris(4-pyridyl)pyridine TPP; DMTD 2- is the deprotonated form of 3,4-dimethyl(2,3-B)benzo[b]thiophene-2,5-dicarboxylic acid.

[0007] The iron-based porous coordination polymer has a three-dimensional framework structure, including [Fe3(μ3-O)(CO2)6] trinuclear iron clusters. In the [Fe3(μ3-O)(CO2)6] trinuclear iron clusters, three iron ions Fe 3+ are bridged by a central oxygen atom μ3-O to form a triangular structure, and two adjacent iron ions are connected by two carboxyl groups; each Fe 3+ is coordinated with 5 O atoms and 1 N atom to form an octahedral coordination geometry, where 4 O atoms come from 4 DMTD 2- anionic ligands, one O atom is the μ3-O atom, and 1 N atom comes from the TPP ligand; Each [Fe3(μ3-O)(CO2)6] trinuclear iron cluster connects 6 DMTD 2- anionic ligands and three TPP neutral ligands. Each TPP neutral ligand connects three [Fe3(μ3-O)(CO2)6] trinuclear iron clusters, and each DMTD 2- anionic ligand connects two [Fe3(μ3-O)(CO2)6] trinuclear iron clusters. Through the above connection method, it extends infinitely in space to form a three-dimensional framework structure.

[0008] Furthermore, the crystal structure of the iron-based porous coordination polymer belongs to the hexagonal crystal system, the space group is P63 / mmc, and the unit cell parameters are as follows: a = 16.907 Å, b = 16.907 Å, c = 19.538 Å, α = 90 °, β = 90°, γ = 120°, and the unit cell volume is 4836.7 Å 3 .

[0009] Furthermore, mix the inorganic salt of Fe, H2DMTD ligand, and TPP ligand in a 20 mL glass bottle; add DMF and hydrofluoric acid to it, stir well at room temperature to fully mix the reactants; then seal the glass bottle and put it into a heating device at 120 °C, react for 96 hours, then naturally cool to room temperature, remove the mother liquor, add DMF to it, filter to obtain a solid product, exchange the obtained solid product with methanol 3 - 5 times to fully exchange the DMF molecules in the pores, and place it in a vacuum drying oven at 60 °C for 48 hours to remove the methanol molecules in the pores to obtain an activated iron-based porous coordination polymer.

[0010] Furthermore, the inorganic salt of Fe is one of nitrate or halide of Fe. The molar ratio of the inorganic salt of Fe, H2DMTD ligand and TPP ligand is 2:1:1. The addition amount of DMF is limited to 5 mL of DMF corresponding to every 0.1 mmol of H2DMTD ligand; the addition amount of hydrofluoric acid is limited to 0.2 mL of hydrofluoric acid corresponding to every 0.1 mmol of H2DMTD ligand.

[0011] The present invention also provides an application of the iron-based porous coordination polymer in the separation of C2H2 / C2H4, C2H6 / C2H4 and C2H4 / CO2 binary mixed gases.

[0012] The present invention also provides an application of the iron-based porous coordination polymer in electrocatalytic oxygen evolution.

[0013] The beneficial technical effects of the present invention: The present invention provides an iron-based porous coordination polymer with high stability, which is a microporous material with high crystallinity, high purity and three-dimensional framework structure. The crystal material can realize the separation and purification of ethylene from the mixed gas of acetylene and ethylene and the mixed gas of ethane and ethylene; it can be used for electrocatalytic oxygen evolution reaction, and the OER overpotential is 260 mV. Description of the drawings

[0014] Figure 1 It is a three-dimensional framework structure diagram of the iron-based porous coordination polymer; Figure 2 It is a comparison diagram of the powder X-ray diffraction (XRD) pattern of the iron-based porous coordination polymer and the theoretical simulated XRD; Figure 3 It is a thermogravimetric analysis diagram of the iron-based porous coordination polymer; Figure 4 It is an adsorption and desorption curve diagram of N2 of the iron-based porous coordination polymer; Figure 5 It is a pore size distribution diagram of the iron-based porous coordination polymer; Figure 6 It is a single-component adsorption isotherm diagram of C2H2, C2H4, C2H6 and CO2 of the iron-based porous coordination polymer at 273K; Figure 7 It is a single-component adsorption isotherm diagram of C2H2, C2H4, C2H6 and CO2 of the iron-based porous coordination polymer at 298K; Figure 8 It is a separation selectivity result diagram of the iron-based porous coordination polymer for C2H2 / C2H4, C2H6 / C2H4 and C2H2 / CO2 binary mixed gases; Figure 9Adsorption enthalpy results of a Fe-based porous coordination polymer for C2H2, C2H6, C2H4 and CO2; Figure 10 It is the LSV curve of the oxygen evolution reaction of the Fe-based porous coordination polymer. Specific implementation mode

[0015] The present invention will be further described below in conjunction with the accompanying drawings and embodiments, and the embodiments do not limit the present invention in any form.

[0016] The present invention uses an inorganic salt of Fe, H2DMTD ligand and TPP ligand in N,N-dimethylformamide solvent, and uses hydrofluoric acid as a template agent and regulator to synthesize a Fe-based porous coordination polymer, wherein the molar ratio of the inorganic salt of Fe, H2DMTD ligand and TPP ligand is 2:1:1, and the addition amount of N,N-dimethylformamide is limited to 5 mL of N,N-dimethylformamide per 0.1 mmol of H2DMTD ligand; the addition amount of hydrofluoric acid is limited to 0.2 mL of hydrofluoric acid per 0.1 mmol of H2DMTD ligand. At this ratio, the Fe-based porous coordination polymer can be successfully synthesized.

[0017] Example 1 Preparation of Fe-based porous coordination polymer Mix Fe(NO3)9H2O (0.2 mmol), H2DMTD ligand (0.1 mmol), and TPP (0.1 mmol) in a 20 mL glass bottle; add 5 mL of DMF and 0.2 mL of hydrofluoric acid thereto, and stir well at room temperature to fully mix the reactants; then seal the glass bottle and place it in a heating device at 120 °C for 96 hours, and then naturally cool to room temperature, remove the mother liquor, add fresh DMF thereto, filter to obtain a solid product, exchange the solid product with methanol 3-5 times to fully exchange the DMF molecules in the pores, and place it in a vacuum drying oven at 60 °C for 48 hours to remove the methanol molecules in the pores, and obtain an activated Fe-based porous coordination polymer.

[0018] Example 2 Preparation of Fe-based porous coordination polymer The difference between Example 2 and Example 1 is that the iron salt is FeCl 3， The remaining conditions are exactly the same.

[0019] Structure characterization of Fe-based porous coordination polymer The crystal structures of the materials obtained in Examples 1-2 are the same.

[0020] At room temperature, single crystal diffraction data of Fe-MOF was collected on a Bruker Apex II diffractometer, and the X-ray used was MoKα ray ( λ= 0.71073 Å), and after the data was reduced, the crystal structure was solved by the direct method. The structure was refined using the SHELXL program, and the hydrogen atoms on the carbon atoms were obtained by theoretical hydrogenation.

[0021] The iron-based porous coordination polymer has a three-dimensional framework structure ( Figure 1 ), including [Fe3(μ3-O)(CO2)6] trinuclear iron clusters. In the [Fe3(μ3-O)(CO2)6] trinuclear iron clusters, three iron ions Fe 3+ are bridged by a central oxygen atom μ3-O to form a triangular structure, and two adjacent iron ions are connected by two carboxyl groups; each Fe 3+ is coordinated with 5 O atoms and 1 N atom to form an octahedral coordination geometry, where 4 O atoms come from 4 DMTD 2- anionic ligands, one O atom is the μ3-O atom, and 1 N atom comes from the TPP ligand; Each [Fe3(μ3-O)(CO2)6] trinuclear iron cluster connects 6 DMTD 2- anionic ligands and three TPP neutral ligands. Each TPP neutral ligand connects three [Fe3(μ3-O)(CO2)6] trinuclear iron clusters, and each DMTD 2- anionic ligand connects two [Fe3(μ3-O)(CO2)6] trinuclear iron clusters. Through the above connection method, it extends infinitely in space to form a three-dimensional framework structure.

[0022] Characterization of the phase and stability of the iron-based porous coordination polymer crystal material Figure 2 is a comparison diagram of the powder X-ray diffraction (XRD) pattern of the iron-based porous coordination polymer and the theoretical simulated XRD. It can be seen from the figure that the synthesized iron-based porous coordination polymer has good crystallinity and high purity. After methanol exchange and gas adsorption, the XRD was tested, and the results showed that the iron-based porous coordination polymer still remained consistent with the theoretical simulation results, indicating that the material has good stability.

[0023] To determine the thermal stability of the iron-based porous coordination polymer synthesized in Example 1, thermogravimetric analysis (TG) was used to characterize its thermal stability. The sample was heated from room temperature to 700 °C at a heating rate of 5 °C / minute, and the results are as Figure 3 shown. All the solvent molecules in the pores of the original synthesized sample were lost before 200 °C, and then a plateau appeared; for the sample after methanol exchange, all the solvent molecules were lost before 90 °C, and the framework began to collapse until 350 °C, indicating that the synthesized iron-based porous coordination polymer has good thermal stability.

[0024] Specific surface area and pore size test of the iron-based porous coordination polymer To test the specific surface area and pore size of the prepared iron-based porous coordination polymer, the sample was subjected to an isothermal adsorption test of N2 at 77 K, and the test results are as follows: Figure 4 As shown, the specific surface area of the iron-based porous coordination polymer is 1373.6 m 2 / g, and the pore size is 0.8 nm ( Figure 5 as shown).

[0025] Example 3 To characterize the single-component adsorption performance of the prepared iron-based porous coordination polymer for C2H2, C2H4, C2H6, and CO2 at 273 K and 298 K, the single-component adsorption isotherms of these gases at these two temperatures were tested, as shown in Figure 6 and Figure 7 . As can be seen from Figure 6 , at 273 K and 1 bar, the adsorption amounts of the iron-based porous coordination polymer for C2H2, C2H4, C2H6, and CO2 are 164.3 mL / g, 140.5 mL / g, 144.2 mL / g, and 110.3 mL / g, respectively. At 298 K and 1 bar, the adsorption amounts of Fe-MOF for C2H2, C2H4, C2H6, and CO2 are 119.3 mL / g, 107.2 mL / g, 118.5 mL / g, and 56.0 mL / g, respectively.

[0026] To further determine the separation performance of the prepared iron-based porous coordination polymer for C2H2 / C2H4, C2H6 / C2H4, and C2H2 / CO2 mixed gases, the separation selectivity of the binary gas mixtures of C2H2 / C2H4, C2H6 / C2H4, and C2H2 / CO2 at a molar ratio of 1:1 was predicted by the Ideal Adsorbed Solution Theory (IAST), and the adsorption enthalpies of the four gases were also calculated ( Figure 9 ). As can be seen from Figure 8 , at 298 K and 1 bar, the separation ratios of the C2H2 / C2H4, C2H6 / C2H4, and C2H2 / CO2 mixed gases are 1.0, 1.6, and 2.8, respectively, indicating that the synthesized iron-based porous coordination polymer has good separation and purification ability for ethylene and acetylene. As can be seen from Figure 9 , in the low adsorption amount region, the adsorption enthalpies of C2H2, C2H6, C2H4, and CO2 are 27.6 kJ / mol, 24.0 J / mol, 23.5 J / mol, and 21.3 J / mol, respectively.

[0027] Example 4 Electrocatalytic oxygen evolution reaction test of iron-based porous coordination polymer (1)Configuration of electrode materials: Take 3.0 mg of the prepared iron-based porous coordination polymer and disperse it into 300 μL of a mixed solution of isopropanol and water (volume ratio 1:1). Add 2 drops of Nafion ionomer to the mixed solution and ultrasonicate the mixed solution for 15 - 20 min to obtain a homogeneous ink.

[0028] (2)Preparation of electrodes and electrolyte: Prepare a 1.0 mol / L potassium hydroxide solution (for the oxygen evolution reaction OER at the cathode), and then measure 250 mL of the electrolyte and pour it into a beaker as the electrolyte for the following tests. Drop the catalyst material prepared in step 1 evenly onto the nickel foam electrode and connect it to the rotating disk electrode as the working electrode, the Ag / AgCl electrode as the reference electrode, and the graphite rod as the counter electrode, and connect them to the electrochemical workstation.

[0029] (3)After confirming that all parameter settings are correct, start the experiment. Set the electrochemical workstation to perform potential scanning or apply current according to the set parameters, and each set of data should be tested multiple times until the data is stable.

[0030] Figure 10 It is the linear sweep voltammetry (LSV) curve of the oxygen evolution reaction of the prepared iron-based porous coordination polymer. It can be seen from the figure that the OER performance of the material is as follows: when the current density is 100 mA / cm 2 ², it is 1.58 V, that is, the OER overpotential is 260 mV, which is 220 mV lower than that of the empty nickel foam electrode material, indicating that the prepared iron-based porous coordination polymer exhibits excellent catalytic performance in the OER reaction, with a lower overpotential and a higher current density, and is more effective in promoting the reaction of water decomposition to produce oxygen.

Claims

1. A kind of iron-based porous coordination polymer, characterized in that: The composition of a repeating unit in the crystal structure of the iron-based porous coordination polymer is Fe3O(DMTD)3(TPP). The ligands of the iron-based porous coordination polymer are 3,4-dimethyl(2,3-B)benzo[b]thiophene-2,5-dicarboxylic acid H2DMTD and 2,4,6-tris(4-pyridyl)pyridine TPP. The iron-based porous coordination polymer has a three-dimensional framework structure, including a [Fe3(μ3-O)(CO2)6] trinuclear iron cluster. In the [Fe3(μ3-O)(CO2)6] trinuclear iron cluster, three iron ions Fe 3+ are bridged by a central oxygen atom μ3-O to form a triangular structure, and two adjacent iron ions are connected by two carboxyl groups; each Fe 3+ is coordinated with 5 O atoms and 1 N atom to form an octahedral coordination geometry, where 4 O atoms come from 4 DMTD 2- anion ligands, one O atom is the μ3-O atom, and 1 N atom comes from the TPP ligand; Each [Fe3(μ3-O)(CO2)6] trinuclear iron cluster is connected to six DMTD 2- anionic ligands, and three TPP neutral ligands. Each TPP neutral ligand is connected to three [Fe3(μ3-O)(CO2)6] trinuclear iron clusters. Each DMTD 2- anionic ligand is connected to two [Fe3(μ3-O)(CO2)6] trinuclear iron clusters. Through the above connection method, an infinite spatial extension is carried out to form a three-dimensional framework structure.

2. The iron-based porous coordination polymer according to claim 1, wherein: The crystal structure of the iron-based porous coordination polymer belongs to the hexagonal crystal system, and the space group is P63 / mmc. The unit cell parameters are as follows: a = 16.907 Å, b = 16.907 Å, c = 19.538 Å, α = 90 °, β = 90°, γ = 120°, and the unit cell volume is 4836.7 Å 3 .

3. The iron-based porous coordination polymer according to claim 1, wherein: Mix the inorganic salt of Fe, the H2DMTD ligand, and the TPP ligand in a 20 mL glass bottle. Add DMF and hydrofluoric acid to it and stir well at room temperature to fully mix the reactants. Then seal the glass bottle and place it in a heating device at 120 °C for 96 hours, and then naturally cool to room temperature. Remove the mother liquor, add DMF to it, and filter to obtain a solid product. Exchange the obtained solid product with methanol for 3 - 5 times to fully exchange the DMF molecules in the pores. Place it in a vacuum drying oven at 60 °C for 48 hours to remove the methanol molecules in the pores and obtain the activated iron-based porous coordination polymer.

4. The iron-based porous coordination polymer according to claim 1, wherein: The inorganic salt of Fe is one of the nitrate or halide of Fe. The molar ratio of the inorganic salt of Fe, the H2DMTD ligand, and the TPP ligand is 2:1:

1. The addition amount of DMF is limited to 5 mL of DMF corresponding to every 0.1 mmol of the H2DMTD ligand. The addition amount of hydrofluoric acid is limited to 0.2 mL of hydrofluoric acid corresponding to every 0.1 mmol of the H2DMTD ligand.

5. Application of an iron-based porous coordination polymer according to any one of claims 1 - 4 in the separation of C2H2 / C2H4, C2H6 / C2H4, and C2H4 / CO2 binary mixed gases.

6. Application of an iron-based porous coordination polymer according to any one of claims 1 - 4 in electrocatalytic oxygen evolution.

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