Preparation method of MOFs (Metal-Organic Frameworks) material with hindered Lewis acid-base para-sites

Abstract

The invention discloses a preparation method of an MOFs material with hindered Lewis acid-base para sites, and relates to the technical field of metal organic porous materials, and the preparation method comprises the following steps: forming a Zr-MOFs (OH) material with-OH groups through competitive coordination of H2O molecules and organic ligands in a solvothermal process; and subsequently, carrying out photoactivation to prepare the hollow Zr-MOFs (OH-OV) material with hindered Lewis acid-base sites. In the synthesis process of the Zr-MOFs material, H2O molecules and organic ligands compete for coordination together, so that Zr-MOFs (OH) with a large amount of OH is obtained, the Zr-MOFs (OH) is further converted into hindered Lewis acid-base para sites (OH-OV) under illumination, the Lewis acid-base sites in the Zr-MOFs adsorb CO2 in a bridge mode, efficient adsorption and activation of CO2 are achieved, the method has the advantages of being simple, convenient and easy to operate, good in repeatability and the like, and the method is suitable for industrial production. The catalyst has a potential application prospect in the aspect of catalytic conversion of CO2.

Description

Technical Field

[0001] The invention relates to the technical field of metal organic porous materials, and more specifically to a method for preparing a MOFs material with hindered Lewis acid-base pairing sites. Background Art

[0002] CO2 is the most abundant and cheapest carbon resource and also an important component of greenhouse gases. How to efficiently and selectively catalytically convert CO2 into more valuable carbon products is a hot topic of current research. Metal-Organic Frameworks (MOFs) are a class of porous crystalline materials with a periodic network structure formed by self-assembly of transition metals and nitrogen / oxygen-containing organic ligands. Due to their ultra-high specific surface area and porosity, controllable morphology and active sites, MOFs materials have great application potential in gas storage and separation, catalytic sensing, etc. However, conventional MOFs materials only expose a small number of active sites, resulting in low activity in the re-catalytic process of MOFs materials alone. At present, in order to improve the catalytic activity of MOFs materials, defect sites are usually introduced into the material to expose a large number of active sites and improve its catalytic activity.

[0003] Li's team reported that different ligands were introduced into the synthesis of Ni-MOF to prepare materials with unsaturated metal sites and accelerate the structural transformation to metal hydroxide oxides, which showed higher catalytic activity compared with defect-free MOF materials (Ding, J., Guo, D., Wang, N., Wang, HF, Yang, X., Shen, K., Chen, L., Li, Y. Defect engineered metal-organic framework with accelerated structural transformation for efficient oxygen evolution reaction. Angewandte Chemie International Edition, 2023 62, e202311909). In addition, He et al. reported that an appropriate amount of acetic acid was added during the synthesis of UiO-66-NH2, thereby exposing abundant defect sites and forming hindered Lewis acid-base pairs (FLPs) Zr 3+-OH MOF catalyst, thereby improving its catalytic activity (He, Y., Li, C., Chen, X. B., Shi, Z., Feng, S. Visible-light-responsive UiO-66(Zr) with defects efficiently promoting photocatalytic CO2 reduction. ACSapplied materials &

[0004] In summary, although some research progress has been made in the application of MOFs-based materials in the catalytic conversion of CO2, there is still no substantial breakthrough in the efficient adsorption, activation, and conversion of CO2, resulting in no essential improvement in its catalytic performance. Recently, compared with single-site catalysts that linearly adsorb CO2, many studies have reported that hindered Lewis acid-base sites can effectively improve the conversion efficiency by bridging adsorption and activation of CO2 (Wang, X., Lu, L., Wang, B., et al. Frustrated lewis pairs accelerating CO2 reduction onoxyhydroxide photocatalysts with surface lattice hydroxyls as a solid-state proton donor, Advanced Functional Materials, 2018, 28, 1804191; Zhong, L., Liao, X., Cui, H., et al. Hydrogenation of α, β-unsaturated aldehydes over defective UiO-66 with Frustrated Lewis Pairs: Modulation of densities of defect sites viatailoring ligand-vacancies, Applied Catalysis B:Environmental,2024,342,123421; Liang,X.,Wang,X.,Zhang,X.,et al.Frustrated lewis pairs on In(OH) 3–xfacilitate photocatalytic CO2 reduction.ACS Catalysis, 2023, 13, 6214-6221). Therefore, the preparation of MOFs materials with abundant hindered Lewis acid-base pair sites through simple and easy synthesis methods and steps remains to be studied. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a MOFs material having hindered Lewis acid-base pair sites.

[0006] In order to solve the above technical problems, the present invention provides a method for preparing a MOFs material having hindered Lewis acid-base pair sites, comprising the following steps:

[0007] (4) dissolving the metal salt, deionized water, organic ligand and acetic acid in N,N-dimethylformamide solvent, stirring and dissolving to obtain a mixed solution;

[0008] (5) heating the mixed solution obtained in step (1) under stirring conditions for crystallization; after cooling, washing, drying, and activating in a vacuum oven, obtaining a Zr-MOFs (OH) material in which H2O and an organic ligand are competitively coordinated;

[0009] The material obtained in step (2) was activated under vacuum conditions and irradiated with a 300W xenon lamp to obtain Zr-MOFs (OH-O V )Material.

[0010] The present invention.

[0011] Preferably, in step (1), the metal salt is ZrCl4.

[0012] Preferably, in step (1), the H2O is deionized water or ultrapure water.

[0013] Preferably, in step (1), the organic ligand is terephthalic acid or 2-aminoterephthalic acid.

[0014] Preferably, in step (1), the molar concentration of the Zr salt in the mixed solvent is 0.01-0.04 mol / L; the volume of the deionized water in the mixed solvent is 100-1000 μL; the molar concentration of the organic ligand in the mixed solvent is 0.01-0.04 mol / L; and the volume of the formic acid in the mixed solvent is 1-10 mL.

[0015] Preferably, the stirring and dissolving time in step (1) is 5-30 min.

[0016] Preferably, the temperature of the heating crystallization in step (2) is 110-150° C., the stirring speed is 300-800 rpm, and the time of the heating crystallization is 24-48 h.

[0017] Preferably, the activation temperature of the vacuum oven in step (2) is 120-180° C., and the activation time is 12-24 h.

[0018] Preferably, the light irradiation time in step (3) is 1-5 h.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The preparation method of the present invention is a simple water and organic ligand competition method, which uses H2O and organic competitive coordination method to prepare Zr-MOFs (OH-O V ) material synthesis mechanism is novel. In the synthesis process of Zr-MOFs materials, H2O molecules compete with organic ligands for coordination, thereby obtaining Zr-MOFs (OH) with a large amount of OH, which is further converted into hindered Lewis acid-base sites (OH-O) under light. V ).

[0021] 2. In the process of synthesizing Zr-MOFs materials, the present invention constructs a hindered Lewis acid-base pair site structure. The Lewis acid-base sites are highly stable and can be recycled, which is conducive to the efficient adsorption and conversion of CO2 and has potential practical application value.

[0022] 3. The Zr-MOFs material with Lewis acid-base pair sites prepared by the present invention is used for CO2 reduction conversion to prepare other fuel gases. Under the condition of using pure light and without adding any sacrificial agent, the CO yield can reach 33.1 μmol g -1 h -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The hollow UiO-66-NH2(OH-O V )’s X-ray diffraction (XRD) spectrum;

[0024] Figure 2 The hollow UiO-66-NH2(OH-O V ) transmission electron microscope (TEM) image;

[0025] Figure 3 The hollow UiO-66-NH2(OH-O V ) of nitrogen adsorption;

[0026] Figure 4 The hollow UiO-66-NH2(OH-O V )’s infrared spectrum;

[0027] Figure 5 The hollow UiO-66-NH2(OH-O V ) of ammonia temperature programmed desorption;

[0028] Figure 6 TEM image of solid UiO-66-NH2 prepared in Comparative Example 1 of the present invention;

[0029] Figure 7 The hollow UiO-66-NH2 (OH-O V ) and UiO-66-NH2 materials for photocatalytic reduction of CO2 to produce CO product performance evaluation diagram. DETAILED DESCRIPTION

[0030] To facilitate those skilled in the art to understand the technical solution of the present invention, the technical solution of the present invention is further described in conjunction with the accompanying drawings.

[0031] Example 1

[0032] This embodiment discloses a UiO-66-NH2(OH-O V ) material preparation method, comprising the following steps:

[0033] (1) 0.6 mmol of ZrCl4 and 0.6 mmol of 2-aminoterephthalic acid were dissolved in N,N-dimethylformamide solvent (40 mL), acetic acid (5 mL) and water solvent (500 μL), and ultrasonically dissolved for 30 min to obtain a mixed solution;

[0034] (2) The mixed solution obtained in step (1) was transferred to a Shrek reaction bottle, heated to 120°C, and maintained for 24 hours; after cooling to room temperature, filtered, washed once with N,N-dimethylformamide, then washed three times with anhydrous ethanol, and dried at 60°C for 12 hours to obtain a hollow UiO-66-NH2 material with OH, recorded as hollow UiO-66-NH2(OH);

[0035] (3) The material obtained in step (2) was activated for 3 h under vacuum conditions and irradiated with a 300 W xenon lamp to obtain UiO-66-NH2 (OH-O V ).

[0036] Figure 1The hollow UiO-66-NH2(OH-O V )’s X-ray diffraction (XRD) spectrum.

[0037] UiO-66-NH2(OH-O V ) has good crystallinity, and the material exhibits strong X-ray diffraction. In addition, the diffraction peak at 3.6° belongs to

[0038] UiO-66-NH2(OH-O V )The absence of Zr secondary structural units in the crystal.

[0039] Figure 2 The hollow UiO-66-NH2(OH-O V ) transmission electron microscope (TEM) image, from Figure 2 It can be seen that the UiO-66-NH2(OH-O V ) has a hollow structure.

[0040] Figure 3 The hollow UiO-66-NH2(OH-O V ) of nitrogen absorption and desorption, from Figure 3 It can be seen that the hollow UiO-66-NH2(OH-O V ) materials have micropores and mesopores, indicating that the synthesized hollow UiO-66-NH2(OH-O V )The material forms a multi-level pore structure.

[0041] Figure 4 The hollow UiO-66-NH2(OH-O V ) infrared spectrum, from Figure 4 It can be seen that the hollow UiO-66-NH2(OH-O V ) materials have abundant -OH groups, indicating that the synthesized hollow UiO-66-NH2(OH-O V ) materials are conducive to the formation of hindered Lewis acid-base pairs.

[0042] Figure 5 The ammonia temperature-programmed desorption diagram of the hollow UiO-66-NH2(OH) prepared in Example 1 is shown in FIG. Figure 5 It can be seen that the hollow UiO-66-NH2(OH) material prepared in Example 1 contains more acid sites (higher area for desorption of ammonia) than the UiO-66-NH2 prepared in Comparative Example 1, indicating that part of the -OH is oxidized to oxygen vacancies by photogenerated electrons, further proving that the synthesized hollow UiO-66-NH2(OH-V ) materials tend to form hindered Lewis acid-base pairs.

[0043] Comparative Example 1

[0044] The traditional preparation method of UiO-66-NH2 includes the following steps:

[0045] (1) 0.6 mmol ZrCl4, 0.6 mmol 2-aminoterephthalic acid and 5 mL acetic acid were ultrasonically dispersed in 40 mL N,N-dimethylformamide to obtain a suspension;

[0046] (2) The suspension in step (1) was heated and crystallized at a temperature of 120° C. for 24 h; after cooling, it was filtered, washed, and dried to obtain UiO-66-NH2

[0047] Figure 6 TEM image of UiO-66-NH2 prepared in Comparative Example 1. Figure 6 It can be seen that the material has a solid structure. The hollow UiO-66-NH2(OH-O V ) Compared with the UiO-66-NH2 prepared by the comparative example 1, the preparation process is simple, the material mass transfer resistance is small, and the active sites are abundant.

[0048] Example 2

[0049] In 10 mg of the hollow UiO-66-NH2 (OH-O V ) was added with 1 mL of n-hexane and ultrasonically dispersed for 10 min. 10 mg of hollow UiO-66-NH2(OH-O V ) is evenly applied to the bottom of the photothermal reaction bottle and dried for later use. 0.1MPa of CO2 is charged into the reactor. The photoreaction is carried out for 4 hours under full spectrum illumination. The gas products are detected by gas chromatography every 1 hour. Figure 7 The hollow UiO-66-NH2(OH-O V ) and UiO-66-NH2 materials for photocatalytic CO2 reduction to produce CO products. The yields of methanol were 33.1 and 1.6 μmol g -1 h -1 , indicating that the hollow UiO-66-NH2(OH-O V ) material has an ultra-high yield for reducing CO2 to produce CO products. It further illustrates that the hollow UiO-66-NH2(OH-O V ) is beneficial to improving the catalytic performance of the material.

[0050] In summary, the preparation method of the present invention is a simple water and organic ligand competition method, which uses H2O and organic competitive coordination method to prepare Zr-MOFs (OH-O V ) material synthesis mechanism is novel. In the synthesis process of Zr-MOFs materials, H2O molecules compete with organic ligands for coordination, thereby obtaining Zr-MOFs (OH) with a large amount of OH, which is further converted into hindered Lewis acid-base sites (OH-O) under light. V ). In the process of synthesizing the Zr-MOFs material, the present invention constructs a hindered Lewis acid-base pair site structure, and the Lewis acid-base site has strong stability and can be recycled, which is conducive to the efficient adsorption and conversion of CO2 and has potential practical application value.

[0051] The embodiments of the present invention disclose preferred embodiments, but are not limited thereto. A person skilled in the art can easily understand the spirit of the present invention based on the above embodiments and make different extensions and changes. However, as long as they do not deviate from the spirit of the present invention, they are all within the protection scope of the present invention.

Claims

1. A method for preparing a MOFs material having hindered Lewis acid-base pairing sites, characterized in that: The following steps are involved: (1) dissolving a metal salt, H2O, an organic ligand and acetic acid in an N,N-dimethylformamide solvent, and stirring to dissolve to obtain a mixed solution; (2) heating the mixed solution obtained in step (1) under stirring conditions for crystallization; after cooling, washing, drying, and activating in a vacuum oven, obtaining a Zr-MOFs (OH) material in which H2O and an organic ligand are competitively coordinated; (3) Activating the material obtained in step (2) under vacuum conditions and irradiation with a 300W xenon lamp to obtain Zr-MOFs (OH-O V )Material.

2. The method for preparing the MOFs material having hindered Lewis acid-base pairing sites according to claim 1, characterized in that: In step (1), the metal salt is ZrCl4.

3. The method for preparing the MOFs material having hindered Lewis acid-base pairing sites according to claim 1, characterized in that: In step (1), the H2O is deionized water or ultrapure water.

4. The method for preparing the MOFs material having hindered Lewis acid-base pairing sites according to claim 1, characterized in that: In step (1), the organic ligand is terephthalic acid or 2-aminoterephthalic acid.

5. The method for preparing the MOFs material having hindered Lewis acid-base pairing sites according to claim 1, characterized in that: In step (1), the molar concentration of the Zr salt in the mixed solvent is 0.01-0.04 mol / L; the volume of the deionized water in the mixed solvent is 100-1000 μL; the molar concentration of the organic ligand in the mixed solvent is 0.01-0.04 mol / L; and the volume of the formic acid in the mixed solvent is 1-10 mL.

6. The method for preparing the MOFs material having hindered Lewis acid-base pairing sites according to claim 1, characterized in that: The stirring and dissolving time in step (1) is 5-30 minutes.

7. The method for preparing the MOFs material having hindered Lewis acid-base pairing sites according to claim 1, characterized in that: The temperature of the heating crystallization in step (2) is 110-150° C., the stirring speed is 300-800 rpm, and the time of the heating crystallization is 24-48 h.

8. The method for preparing the MOFs material having hindered Lewis acid-base pairing sites according to claim 1, characterized in that: The activation temperature of the vacuum oven in step (2) is 120-180° C., and the activation time is 12-24 hours.

9. The method for preparing the MOFs material having hindered Lewis acid-base pairing sites according to claim 1, characterized in that: The light irradiation time in step (3) is 1-5h.

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