Preparation method of hollow single crystal MOF-801

Abstract

The invention discloses a preparation method of single crystal MOF-801 with a hollow structure, and the method comprises the following steps: firstly, synthesizing UiO-66 particles with a uniform size; then, synthesizing a single crystal U iO-66 (at) MOF-801 with a core-shell structure by taking the U iO-66 particles as a template; and then formic acid and excessive MOF-801 ligands are added in the etching process through a ligand protection strategy to etch the single crystal U iO-66 and protect an MOF-801 shell layer, so that the single crystal hollow MOF-801 is prepared. The defect-free and chemically stable hollow MOF-801 is constructed by changing the dissolution equilibrium of the core-shell MOF. The method comprises the following steps: firstly, taking UiO-66 which is not matched with MOF-801 crystal lattice as a template for epitaxial growth to construct a core-shell structure; furthermore, in order to protect the shell structure from being affected while removing the template, excessive MOF-801 ligands are added in the template removal process to change the dissolution equilibrium of the shell MOF so as to enable the shell MOF to be well preserved, and the core MOF is selectively and completely etched away so as to form the single-crystal hollow MOF-801. The preparation method has universality, and can greatly enrich the types of the hollow MOF.

Description

Technical Field

[0001] The invention relates to the technical field of porous materials, and in particular to a method for preparing a hollow single crystal MOF-801 with high chemical stability. Background Art

[0002] Metal-organic frameworks (MOFs) are a class of inorganic-organic hybrid porous materials that have attracted extensive attention in recent years due to their inherent properties such as high porosity, high structural regularity, and highly diverse structural / compositional designability. Through clear metal / ligand selection and clever structural design, MOF materials have shown great promise in many applications. Recently, constructing MOFs with characteristic hierarchical pores, especially hollow structures, has been demonstrated to be a practical strategy to further expand their applications in catalysis, batteries, supercapacitors, sensing, and gas separation. This is because the hollow MOFs allow guest molecules to diffuse faster and enter the nanopores of the MOFs more easily while maintaining all the characteristics of the nanopores.

[0003] At present, the construction of hollow MOFs usually adopts the sacrificial template method. In this typical method, MOF is first grown on the surface of the sacrificial template and then removed by chemical etching. The challenge of this method is that the sacrificial template needs to be stable enough to withstand the solvothermal synthesis conditions of the MOF shell, and at the same time be unstable enough to be removed later without damaging the MOF. It is for this reason that the hollow MOFs reported so far are mainly limited to ZIF-8, MOF-74 and UMOM-2. Most of these are acid unstable, which also limits the application of these hollow MOFs in many harsh chemical environments. It is worth mentioning that due to the interfacial incompatibility between MOFs and templates, most of the hollow MOFs reported so far are polycrystalline MOF shells. Compared with the single crystal shell, the crystal arrangement in the polycrystalline shell is loose, which introduces grain boundaries and defects into its structure. These defects and gaps will weaken the mechanical properties of the hollow structure on the one hand, and on the other hand, the presence of defects will greatly reduce the molecular sieving effect of MOFs materials, which is very unfavorable for the application of hollow MOFs materials in the fields of separation and catalysis.

[0004] In view of this, the existing technology still needs to be improved. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing a hollow single crystal MOF-801 with high chemical stability, so as to solve the problem of poor stability of single crystal hollow MOF in the prior art, promote the application of hollow MOF materials in harsh chemical environments, and expand the preparation method of single crystal hollow MOF.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for preparing a single-crystalline MOF-801 having a hollow structure, wherein the method comprises:

[0008] Synthesize UiO-66 particles with uniform size;

[0009] Using the UiO-66 particles as a template, synthesizing single crystal UiO-66@MOF-801 having a core-shell structure;

[0010] Through the ligand protection strategy, formic acid and excess MOF-801 ligand were added during the etching process to etch single-crystalline UiO-66 and protect the MOF-801 shell, thereby preparing single-crystalline hollow MOF-801.

[0011] The method for preparing the single-crystalline MOF-801 having a hollow structure, wherein the synthesis of UiO-66 particles having uniform size specifically comprises:

[0012] ZrCl 4 , terephthalic acid is dissolved in N,N-dimethylformamide solution, and glacial acetic acid is added; the container is sealed and covered and placed at 80-140° C. for 12-48 hours to obtain UiO-66 particles with uniform size.

[0013] The preparation method of the single-crystalline MOF-801 having a hollow structure, wherein the synthesis of the single-crystalline UiO-66@MOF-801 having a core-shell structure specifically comprises:

[0014] The pre-synthesized UiO-66 particles were dispersed in a ZrCl 4 and fumaric acid in N,N-dimethylformamide solution, stirring the mixture for 5-10 minutes, and then adding formic acid; then, heating the mixture in an oven at 80-140° C. for 2-12 hours to obtain single-crystalline UiO-66@MOF-801 particles with uniform size.

[0015] The method for preparing the single-crystalline MOF-801 having a hollow structure, wherein the ligand protection etching strategy specifically includes:

[0016] UiO-66@MOF-801 particles were added into a mixed solution of fumaric acid and formic acid to obtain single-crystalline MOF-801 with a hollow structure.

[0017] The preparation method of the single-crystalline MOF-801 with a hollow structure, wherein the size of the UiO-66 particles is 0.2 to 1.5 μm; the mass ratio of N,N-dimethylformamide and ZrCl4 in the UiO-66 synthesis reaction solvent is 100 to 400; the molar ratio of terephthalic acid and ZrCl4 in the UiO-66 synthesis precursor is 1 to 3; the UiO-66 synthesis temperature is 80 to 140° C.; and the UiO-66 synthesis time is 12 to 48 hours.

[0018] The preparation method of the single-crystalline MOF-801 with a hollow structure, wherein the single-crystalline core-shell UiO-66@MOF-801 particles are prepared by UiO-66, ZrCl 4 The mass ratio of formic acid to fumaric acid is: 0.5-3:1:1; the molar ratio of formic acid to fumaric acid in the preparation of the single crystal core-shell UiO-66@MOF-801 particles is 92:368; the reaction solvent in the preparation of the single crystal core-shell particles is N,N-dimethylformamide, and the mass ratio of N,N-dimethylformamide to UiO-66 is 100:800; the synthesis temperature of the single crystal core-shell UiO-66@MOF-801 particles is 80-140°C, and the synthesis time is 12-48 hours.

[0019] The method for preparing the single-crystal MOF-801 with a hollow structure, wherein the MOF-801 ligand is fumaric acid.

[0020] The preparation method of the single-crystalline MOF-801 with a hollow structure, wherein the mass ratio of UiO-66@MOF-801 and fumaric acid in the ligand protection etching strategy is 2:10; the mass ratio of formic acid and fumaric acid in the ligand protection etching strategy is 10:100; the synthesis temperature in the ligand protection etching strategy is 80-140°C, and the synthesis time is 2-48 hours.

[0021] Compared with the prior art, the preparation method of the single crystal MOF-801 with a hollow structure provided by the present invention is mainly to construct a defect-free and chemically stable hollow MOF-801 by changing the dissolution equilibrium of the core-shell MOF. The method first uses UiO-66, which does not match the MOF-801 lattice, as a template for epitaxial growth to construct a core-shell structure. Furthermore, in order to protect the shell structure from being affected while removing the template, an excess of MOF-801 ligands is added during the template removal process to change the dissolution equilibrium of the shell MOF so that it is well preserved, and the shell MOF is selectively and completely etched away to form a single crystal hollow MOF-801. This preparation method is universal and can greatly enrich the types of hollow MOFs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Shown are SEM (A) and TEM (B) images of UiO-66 synthesized in the present invention.

[0023] Figure 2 The SEM (A) and TEM (B) images of UiO-66@MOF-801 with a core-shell structure synthesized according to the present invention are shown.

[0024] Figure 3 Shown are the PXRD spectra of UiO-66, UiO-66@MOF-801, MOF-801(h), simulated MOF-801 and UiO-66 synthesized in the present invention.

[0025] Figure 4 Shown are SEM (A) and TEM (B) images of the hollow MOF-801 synthesized in the present invention.

[0026] Figure 5 Shown are the infrared spectra of UiO-66, UiO-66@MOF-801, and MOF-801(h) synthesized in the present invention.

[0027] Figure 6 Shown is the TEM single crystal diffraction spectrum of the hollow MOF-801 synthesized in the present invention.

[0028] Figure 7 The N of UiO-66, UiO-66@MOF-801 and MOF-801(h) synthesized by the present invention is shown in FIG. 2 Adsorption isotherms (A) and pore size distribution diagrams (B).

[0029] Figure 8 Shown are TEM and SEM images of MOF-801 (h) after treatment with 1 M HCl (A), concentrated HCl (B), and boiling water (C) in the present invention.

[0030] Fig. 9 Shown is a schematic flow chart of a method for preparing a single-crystalline MOF-801 having a hollow structure provided by the present invention. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the technical solution of the present disclosure, and to fully understand and implement how the present disclosure applies technical means to solve technical problems and achieve the corresponding technical effects, the technical solution in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only embodiments of a part of the present disclosure, not all of the embodiments. The embodiments of the present disclosure and the various features in the embodiments can be combined with each other without conflict, and the technical solutions formed are all within the scope of protection of the present disclosure. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of the present disclosure.

[0032] It should be noted that the terms "first", "second", etc. in the specification and claims of the present disclosure and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present disclosure described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, device, product or equipment that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0033] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those generally understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, according to the grasp of the prior art by those skilled in the art and the record of the present invention, any methods, equipment, and materials of the prior art similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention can also be used to realize the present invention.

[0034] In the prior art, the construction of hollow MOFs usually adopts the sacrificial template method. In this typical method, MOF is first grown on the surface of the sacrificial template and then removed by chemical etching. The challenge of this method is that the sacrificial template needs to be stable enough to withstand the solvent thermal synthesis conditions of the MOF shell, and at the same time be unstable enough to be removed later without damaging the MOF. It is for this reason that the hollow MOFs reported so far are mainly limited to ZIF-8, MOF-74 and UMOM-2. Most of these are acid unstable, which also limits the application of these hollow MOFs in many harsh chemical environments. And most of them are polycrystalline structures, and the crystals in the polycrystalline shell are arranged loosely, which introduces grain boundaries and defects into their structure. On the one hand, these defects and gaps will weaken the mechanical properties of the hollow structure. On the other hand, the presence of defects will greatly reduce the molecular sieving effect of MOFs materials, which is very unfavorable for the application of hollow MOFs materials in the fields of separation and catalysis.

[0035] Therefore, the present invention provides a method for preparing a chemically stable but defect-free hollow single crystal MOF-801. Fig. 9 As shown, the method includes:

[0036] S100, synthesis of UiO-66 particles with uniform size;

[0037] S200, using the UiO-66 particles as a template to synthesize single crystal UiO-66@MOF-801 with a core-shell structure;

[0038] S300, adding formic acid and excess MOF-801 ligand during the etching process through a ligand protection strategy to etch single crystal UiO-66 and protect the MOF-801 shell, thereby preparing single crystal hollow MOF-801.

[0039] In a specific embodiment, the reactant in step S100 is ZrCl 4 and terephthalic acid; the reaction solution is N,N-dimethylformamide, and the regulator is glacial acetic acid; the size of the UiO-66 particles is 0.2 to 1.5 μm; the UiO-66 synthesis reaction solvent is N,N-dimethylformamide and ZrCl 4 The mass ratio is 100-400; the molar ratio of terephthalic acid and ZrCl4, the UiO-66 synthesis precursors, is 1-3; the UiO-66 synthesis temperature is 80-140°C; the UiO-66 synthesis time is 12-48.

[0040] In a specific embodiment, the reactants in step S200 are UiO-66, ZrCl4 and fumaric acid synthesized in advance; the reaction solution is N,N-dimethylformamide, the regulator is formic acid; the reaction temperature is 80-140°C; and the reaction time is 12-48 hours. In the preparation of the single-crystalline core-shell UiO-66@MOF-801 particles, the mass ratio of UiO-66, ZrCl4 and fumaric acid is 0.5-3:1:1; in the preparation of the single-crystalline core-shell UiO-66@MOF-801 particles, the molar ratio of formic acid to fumaric acid is 92-368; in the preparation of the single-crystalline core-shell particles, the reaction solvent is N,N-dimethylformamide, and the mass ratio of N,N-dimethylformamide to UiO-66 is 100-800.

[0041] In a specific embodiment, the mass ratio of UiO-66@MOF-801 and fumaric acid in the ligand protection etching strategy in step S300 is 2 to 10; the mass ratio of formic acid and fumaric acid in the ligand protection etching strategy is 10 to 100; the synthesis temperature in the ligand protection etching strategy is 80 to 140° C., and the synthesis time is 2 to 48 hours.

[0042] The technical solution and technical effects of the present application are further explained below through specific implementation methods.

[0043] Example 1

[0044] This example is the preparation of UiO-66.

[0045] In this embodiment, UiO-66 particles are prepared by the following preparation method: ZrCl 4 (0.349 g, 1.5 mmol), H 2 BDC (0.249 g, 1.5 mmol) was dissolved in 100 ml of DMF solution, and 9.2 mL (0.16 mol) of glacial acetic acid was added. The container was sealed and placed at 120 ° C for 12 hours. After the reaction, the crystals were collected by centrifugation, washed twice with DMF, washed three times with methanol, and soaked in methanol. Finally, monodispersed UiO-66 particles with uniform size and an average particle size of 410 ± 30 nm were synthesized. The corresponding scanning electron microscope (SEM) and transmission electron microscope (TEM) images are shown in Figure 2. Figure 1 The powder X-ray diffraction (PXRD) pattern is shown in Figure 3 shown.

[0046] Example 2

[0047] This example is the preparation of single crystal core-shell UiO-66@MOF-801 (abbreviated as 66@801)

[0048] Preparation of UiO-66@MOF-801: 2.5 mg UiO-66 was added to 0.5 mL fumaric acid (30 mM) DMF solution under ultrasound. After mixing, 0.5 mL ZrCl 4 (30 mM) DMF solution was stirred for 10 minutes. Then, 52 μL of formic acid was added to the solution. The mixture was heated in an oven at 120°C for 120 minutes. After cooling to room temperature, the product was collected by centrifugation and washed three times with DMF and anhydrous methanol respectively. Figure 2 As shown, a layer of ~34nm dense, smooth single-crystalline MOF-801 shell is successfully wrapped on the surface of UiO-66. The powder X-ray diffraction (PXRD) spectrum shows that the characteristic peaks of UiO-66 and MOF-801 overlap, indicating that the crystallinity of both phases is very good ( Figure 3 ).

[0049] Example 3

[0050] This example is the preparation of single-crystalline hollow MOF-801 with core-shell structure

[0051] The synthesized UiO-66@MOF-801 was redispersed in 1.25 mL DMF containing 260 μL formic acid under ultrasound. After mixing, the mixture was heated in an oven at 120 °C for 4 h. TEM images showed the formation of well-defined hollow MOF-801 particles ( Figure 4 ). The average shell thickness is ~90nm, which is significantly thicker than the MOF-801 layer of the core-shell structure UiO-66@MOF-801. This may be because the Zr dissolved from UiO-66 is used for the continued growth of the MOF-801 shell. The presence of fumaric acid promotes the growth of MOF-801, which will cause the MOF-801 shell to grow again when it is dissolved. When the recrystallization rate exceeds the dissolution rate, the shell is retained.

[0052] On the other hand, UiO-66 cannot recrystallize in the presence of fumaric acid due to the mismatch in ligand length. Therefore, it will continue to dissolve in the presence of formic acid. SEM images show that hollow MOF-801 exhibits an octahedral morphology with a smooth surface ( Figure 4 ). PXRD patterns and Fourier transform infrared (FT-IR) spectroscopy also confirmed the complete removal of the UiO-66 sacrificial template and the retention of the MOF-801 crystalline form ( Figure 3 and Figure 5 ). In addition, electron diffraction (SAED) experiments were performed on MOF-801(h) crystals. The SAED pattern of MOF-801 single crystal has the same hexagonal diffraction point array as the

[110] band axis, indicating that MOF-801(h) is indeed a single crystal ( Figure 6 ).

[0053] This observation proves that UiO-66 promotes the oriented growth of MOF-801 crystallites, which eventually merge into a single crystalline shell. The BET surface area of ​​UiO-66 was calculated to be 1230 m 2 ·g -1 , higher than MOF-801 (680m 2 ·g -1 ). The BET surface area of ​​66@801 is 914 m 2 ·g -1 , lower than UiO-66, but higher than MOF-801. The nitrogen adsorption isotherm of 66@801 is also between MOF-801 and UiO-66. After etching, MOF-801(h) shows the same performance as MOF-801(680m 2 ·g -1 ) similar nitrogen adsorption isotherms and BET surface areas (677 m 2 ·g -1 At the same time, analysis of pore size distribution also revealed that both MOF-801(h) and MOF-801 have pores of 0.6 to 0.7 nm, while UiO-66 has a larger pore size (0.8 nm). These results well demonstrate that MOF-801(h) is highly crystalline ( Figure 7 ).

[0054] Example 3

[0055] Chemical stability test of single crystal hollow MOF-801 in this example

[0056] We further studied the chemical stability of MOF-801(h). To test its acid stability, MOF-801(h) was soaked in 1M HCl or concentrated HCl (~12M) for 1 hour. To test its hydrothermal stability, MOF-801(h) was boiled in water for 3 hours. After treatment, the hollow structure of MOF-801(h) was still intact, with no visible defects ( Figure 8 ).

[0057] In summary, the present invention provides a method for preparing a single-crystalline MOF-801 with a hollow structure, the method comprising: first, synthesizing UiO-66 particles with uniform size; then using the UiO-66 particles as a template to synthesize a single-crystalline UiO-66@MOF-801 with a core-shell structure; then adding formic acid and an excess of MOF-801 ligands during the etching process through a ligand protection strategy to etch the single-crystalline UiO-66 and protect the MOF-801 shell, thereby preparing a single-crystalline hollow MOF-801. It constructs a defect-free and chemically stable hollow MOF-801 by changing the dissolution equilibrium of the core MOF. The method first uses UiO-66, which does not match the MOF-801 lattice, as a template for epitaxial growth to construct a core-shell structure. Furthermore, in order to protect the shell structure from being affected while removing the template, an excess of MOF-801 ligands is added during the template removal process to change the dissolution equilibrium of the shell MOF so that it is well preserved, while the core MOF is selectively and completely etched away to form a single crystalline hollow MOF-801. This preparation method is universal and can greatly enrich the types of hollow MOFs.

[0058] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all these changes or substitutions should fall within the protection scope of the claims attached to the present invention.

Claims

1. A method for preparing a single-crystal MOF-801 having a hollow structure, characterized in that: The method comprises: Synthesize UiO-66 particles with uniform size; Using the UiO-66 particles as a template, synthesizing single crystal UiO-66@MOF-801 having a core-shell structure; Through the ligand protection strategy, formic acid and excess MOF-801 ligand were added during the etching process to etch single-crystalline UiO-66 and protect the MOF-801 shell, thereby preparing single-crystalline hollow MOF-801.

2. The method for preparing the single-crystalline MOF-801 having a hollow structure according to claim 1, characterized in that: The synthesis of UiO-66 particles with uniform size specifically comprises: Dissolve ZrCl4 and terephthalic acid in N,N-dimethylformamide solution, and add glacial acetic acid; seal the container and place it at 80-140°C for 12-48 hours to obtain UiO-66 particles with uniform size.

3. The method for preparing the single-crystalline MOF-801 having a hollow structure according to claim 1, characterized in that: The synthesis of single crystal UiO-66@MOF-801 with a core-shell structure specifically includes: The pre-synthesized UiO-66 particles were dispersed in an N,N-dimethylformamide solution containing ZrCl4 and fumaric acid. After stirring the mixture for 5-10 minutes, formic acid was added. Then, the mixture was heated in an oven at 80-140°C for 2-12 hours to obtain single-crystalline UiO-66@MOF-801 particles with uniform size.

4. The method for preparing the single-crystalline MOF-801 having a hollow structure according to claim 1, characterized in that: The ligand protection etching strategy specifically includes: UiO-66@MOF-801 particles were added into a mixed solution of fumaric acid and formic acid to obtain single-crystalline MOF-801 with a hollow structure.

5. The method for preparing the single-crystalline MOF-801 having a hollow structure according to claim 1, characterized in that: The size of the UiO-66 particles is 0.2 to 1.5 μm; the mass ratio of N,N-dimethylformamide and ZrCl4 in the UiO-66 synthesis reaction solvent is 100 to 400; the molar ratio of terephthalic acid and ZrCl4 in the UiO-66 synthesis precursor is 1 to 3; the UiO-66 synthesis temperature is 80 to 140° C.; and the UiO-66 synthesis time is 12 to 48 hours.

6. The method for preparing the single-crystalline MOF-801 having a hollow structure according to claim 1, characterized in that: In the preparation of the single crystal core-shell UiO-66@MOF-801 particles, the mass ratio of UiO-66, ZrCl4 and fumaric acid is: 0.5-3:1:1; in the preparation of the single crystal core-shell UiO-66@MOF-801 particles, the molar ratio of formic acid and fumaric acid is 92:368; in the preparation of the single crystal core-shell particles, the reaction solvent is N,N-dimethylformamide, and the mass ratio of N,N-dimethylformamide and UiO-66 is 100:800; the synthesis temperature of the single crystal core-shell UiO-66@MOF-801 particles is 80-140°C, and the synthesis time is 12-48 hours.

7. The method for preparing the single-crystalline MOF-801 having a hollow structure according to claim 1, characterized in that: The MOF-801 ligand is fumaric acid.

8. The method for preparing the single-crystalline MOF-801 having a hollow structure according to claim 7, characterized in that: The mass ratio of UiO-66@MOF-801 and fumaric acid in the ligand protection etching strategy is 2:10; the mass ratio of formic acid and fumaric acid in the ligand protection etching strategy is 10:100; the synthesis temperature in the ligand protection etching strategy is 80-140° C., and the synthesis time is 2-48 hours.

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