Metal-organic framework materials, methods of making and using the same

Abstract

The application relates to the field of catalytic material preparation, and discloses a metal organic framework material and a preparation method and application thereof. The metal organic framework material has a morphology of a regular octahedron aggregate, the edge length of the regular octahedron aggregate is 0.5-2 mu m, the regular octahedron aggregate is obtained by aggregation of microspheres, and the diameter of the microspheres is 20-100 nm. The material has a high polyester conversion rate.

Description

Technical Field

[0001] This invention relates to the field of catalytic material preparation, specifically to a metal-organic framework material, its preparation method, and its application. Background Technology

[0002] Metal-organic frameworks (MOFs) are a class of crystalline porous materials with a periodic network structure formed by the self-assembly of metal ions and organic ligands. They have advantages such as high crystallinity, high specific surface area, high porosity, high stability, and strong modifiability, and have wide applications in adsorption, catalysis, separation, and sensing.

[0003] Metal-organic frameworks (MOFs) are multinuclear metal nodes and are widely used in catalysis. The morphology, grain size, and pore structure of MOFs significantly affect catalytic activity, catalytic selectivity, and mass transfer performance.

[0004] The literature [Yufang Wu et al., Angewandte Chemie International Edition, 2022, 61, 24, e202117528] reports a UiO-66 metal-organic framework material for polyester degradation. This material has a smooth octahedral morphology with an edge length of 2.5 μm. Under argon atmosphere, at 1 atm pressure and 260 °C, the material achieves an 81% conversion rate of polyethylene terephthalate after 24 h of reaction.

[0005] The literature [Guoqiang Li et al., Journal of Solid State Chemistry, 2020, 285, 121245] reports a method for preparing MIL-101(Fe) metal-organic framework material. This method involves mixing FeCl3, terephthalic acid, and N,N-dimethylformamide, then heating at 110 °C. The product is then centrifuged and washed to obtain MIL-101(Fe). This material exhibits a smooth, flat octahedral morphology with a grain size of 300–500 nm. The high electron density of the Fe metal clusters, low activation energy, and increased NH bond formation contribute to MIL-101(Fe) exhibiting a photocatalytic nitrogen fixation efficiency of 50.355 μmol·L⁻¹. -1 ·h -1 The activity.

[0006] The two metal-organic framework materials mentioned above have fully coordinated surface sites and smooth surface structures, which prevents the active sites from being fully exposed, hindering the generation of photogenerated carriers and the adsorption and conversion of reactants.

[0007] CN115069219A discloses a method for preparing MIL-101(Fe) metal-organic framework material. The method involves mixing FeCl3, N,N-dimethylformamide, terephthalic acid, and acetic acid, followed by a hydrothermal reaction. The resulting product system is then separated to obtain an intermediate product. This intermediate product is mixed with methanol and then subjected to a hydrothermal reaction to obtain MIL-101(Fe). The MIL-101(Fe) material prepared using this invention possesses tunable pore size, multiple pore structures, and specific active sites. The exposed active sites enable the material to resist NO3-. - The adsorption capacity reached 14.10 mg / g.

[0008] Therefore, there is an urgent need to develop metal-organic framework materials with fully exposed surface active sites. Summary of the Invention

[0009] The purpose of this invention is to overcome the problems of insufficient exposure of surface active sites, low polyester conversion rate, and low photocatalytic ammonia synthesis yield in existing metal-organic framework materials, and to provide a metal-organic framework material, its preparation method, and its applications. This material exhibits high polyester conversion rate and high photocatalytic ammonia synthesis yield.

[0010] During their research, the inventors of this invention discovered that the metal active sites of metal-organic frameworks (MOFs) attract electrons from oxygen atoms via coordination with carbonyl oxygen, thereby increasing the electropositivity of the carbonyl carbon. Some MOFs are photosensitive semiconductors; under illumination, these materials can generate photogenerated electrons and holes, collectively referred to as photogenerated charge carriers. These photogenerated charge carriers migrate to the active sites of the catalyst and react with substances such as water or alcohols to generate reactive free radicals such as hydroxyl radicals and superoxide radicals. These reactive free radicals attack the carbonyl groups in polyester, thus achieving polyester degradation. The inventors further discovered that MOFs with an octahedral aggregate morphology, composed of microspheres, can significantly promote the generation of photogenerated charge carriers and increase the contact area between the catalyst and the polyester raw material during the reaction, thereby improving the polyester conversion rate. When applied to photocatalytic nitrogen fixation, the surface microspheres of the MOFs increase the incident light absorption area, enhancing the generation of photogenerated charge carriers and improving the yield of photocatalytic ammonia synthesis.

[0011] To achieve the above objectives, the first aspect of the present invention provides a metal-organic framework material having an octahedral aggregate morphology, wherein the edge length of the octahedral aggregate is 0.5 to 2 μm, and the octahedral aggregate is obtained by aggregating microspheres, wherein the diameter of the microspheres is 20 to 100 nm.

[0012] Preferably, Fe is present in the metal-organic framework material. II and Fe IIITwo forms, of which Fe II Fe III The ratio is 1:100 to 100:1, preferably 1:4 to 4:1, and more preferably 1:2 to 2:1.

[0013] A second aspect of the present invention provides a method for preparing the metal-organic framework material described in the first aspect, the method comprising the following steps:

[0014] (1) Mix alcohol compounds with organic solvents at a volume ratio of 1:8 to 100 to obtain a mixed solvent;

[0015] (2) The mixed solvent is mixed with the organic ligand and the metal precursor to obtain a precursor solution;

[0016] (3) Crystallize the precursor solution.

[0017] The third aspect of this invention provides the application of the metal-organic framework material described in the first aspect in polyester degradation or photocatalytic nitrogen fixation.

[0018] The metal-organic framework (MOF) material provided by this invention possesses a unique morphology and exhibits strong catalytic performance in polyester degradation or photocatalytic nitrogen fixation reactions. Existing MOF materials suffer from problems such as fully coordinated surface sites and smooth surface structures, leading to insufficient exposure of active sites. This hinders the generation of photogenerated carriers and the adsorption and conversion of reactants, thus affecting polyester degradation efficiency. The MOF material of this invention has an octahedral aggregate morphology, and these aggregates are formed by the aggregation of microspheres. This special structure can greatly promote the generation of photogenerated carriers and increase the contact area between the MOF material and the polyester raw material during the reaction, thereby effectively improving polyester conversion rate. Compared with existing materials that suffer from insufficient exposure of active sites, it exhibits better performance in polyester degradation applications.

[0019] The metal-organic framework material of this invention has a surface microsphere structure that increases the incident light absorption area, thereby enhancing the generation of photogenerated carriers and improving the photocatalytic ammonia synthesis yield. This overcomes the problem of low ammonia synthesis yield caused by insufficient exposure of active sites in existing related materials during photocatalytic nitrogen fixation, making it more advantageous in photocatalytic nitrogen fixation applications. For example, when applied to polyester degradation, the surface microspheres of the metal-organic framework material can expose a large number of active sites, increasing the contact area between the active sites and the polyester, resulting in a polyester conversion rate of 85.9%. When applied to photocatalytic nitrogen fixation, the surface microspheres of the metal-organic framework material increase the incident light absorption area, enhancing the generation of photogenerated carriers and achieving a photocatalytic ammonia synthesis yield of 182 μmol g. -1 h -1 .

[0020] Overall, this invention, through its unique material structure design and corresponding preparation method, solves the problems of low polyester conversion rate and low photocatalytic ammonia yield caused by insufficient exposure of surface active sites in existing metal-organic framework materials in polyester degradation and photocatalytic nitrogen fixation applications. It broadens the performance improvement space of metal-organic framework materials in these two applications, making them more valuable in related fields. Attached Figure Description

[0021] Figure 1 These are scanning electron microscope (SEM) images of the metal-organic framework material in Example 1;

[0022] Figure 2 The image shows the X-ray diffraction (XRD) curve of the metal-organic framework material in Example 1. Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] In this invention, unless otherwise stated, room temperature or normal temperature refers to 25±2℃.

[0025] In this invention, unless otherwise stated, all pressures are gauge pressures.

[0026] The first aspect of the present invention provides a metal-organic framework material having an octahedral aggregate morphology, wherein the edge length of the octahedral aggregate is 0.5 to 2 μm, and the octahedral aggregate is obtained by the aggregation of microspheres, wherein the diameter of the microspheres is 20 to 100 nm.

[0027] Preferably, the edge length of the regular octahedral aggregate is 1 to 1.5 μm, and more preferably 1 to 1.2 μm.

[0028] Preferably, the diameter of the microspheres is 40–80 nm, and more preferably 50–60 nm.

[0029] The metal-organic framework material provided by this invention not only possesses an octahedral morphology, but the octahedral aggregates are also formed by the aggregation of microspheres. The microsphere morphology of the metal-organic framework material exposes more active sites, increasing the contact area between the active sites and reactants, enhancing reactant adsorption. Furthermore, under illumination, the metal-organic framework material generates photogenerated charge carriers, which react with the solvent to generate active free radicals. These active free radicals attack the carbonyl groups in the polyester, thereby achieving polyester degradation and improving polyester conversion efficiency.

[0030] In this invention, the term "regular octahedron" has a broad meaning, including both regular octahedrons and quasi-regular octahedrons.

[0031] In this invention, the term "octahedral aggregate obtained by microsphere aggregation" has a broad meaning, and it is not required that all primary particles be microspheres. A scheme in which more than 90% of the primary particles are microspheres is also within the scope of protection of this invention.

[0032] In this invention, the octahedral aggregate obtained by microsphere aggregation means that the metal-organic framework material has secondary particles formed by the aggregation of primary microsphere particles, and the secondary particles are in the shape of octahedrons.

[0033] In this invention, the morphology of the metal-organic framework material, the edge length of the octahedral aggregates, and the diameter of the microspheres are obtained by SEM characterization. Specifically, the edge length of the octahedral aggregates and the diameter of the microspheres in 50 different regions of the material are statistically analyzed using 20 SEM images, and then the average value is calculated.

[0034] According to a preferred embodiment of the present invention, the metal in the metal-organic framework material is Fe.

[0035] The present invention allows for a wide range of selections of organic ligands in the metal-organic framework material. Preferably, the organic ligands in the metal-organic framework material are selected from at least one of terephthalic acid, 2-aminoterephthalic acid, 2,4-diaminoterephthalic acid, 2-hydroxyterephthalic acid, 2,4-dihydroxyterephthalic acid, 2-carboxyterephthalic acid, and 2,4-dicarboxyterephthalic acid. More preferably, at least one of terephthalic acid, 2-aminoterephthalic acid, and 2,4-diaminoterephthalic acid is selected, and more preferably, terephthalic acid and / or 2-aminoterephthalic acid is selected.

[0036] According to a preferred embodiment of the present invention, the metal-organic framework material is at least one of MIL-101(Fe), MIL-53(Fe), and MIL-88(Fe). The above-mentioned structure of the metal-organic framework material can be confirmed by XRD. The confirmation of the structures of MIL-101(Fe), MIL-53(Fe), and MIL-88(Fe) is well known to those skilled in the art and will not be described in detail here.

[0037] According to a preferred embodiment of the present invention, Fe is present in the metal-organic framework material. II and Fe III Two forms, of which Fe II Fe III The ratio is 1:100 to 100:1, preferably 1:4 to 4:1, and more preferably 1:2 to 2:1. This preferred embodiment is more conducive to the exposure of active sites and the stability of the framework structure.

[0038] In this invention, Fe II This refers to ferrous iron, Fe. III This refers to ferric iron (Fe3+). II and Fe III The presence and ratio of Fe2p were determined by XPS characterization; specifically, Fe2p orbitals in high-resolution Fe2p orbital XPS spectra were detected using X-ray photoelectron spectroscopy. 1 / 2 and Fe 2p 3 / 2 The presence of the peak proves that Fe II and Fe III The presence of Fe; calculated in high-resolution Fe 2p orbital XPS spectra. II and Fe III The corresponding peak area S FeII and S FeIII Calculate S FeII / S FeIII Fe II and Fe III The ratio of .

[0039] According to the present invention, preferably, the specific surface area of ​​the metal-organic framework material is 50-500 cm². 2 / g, preferably 300-500cm 2 / g, more preferably 400-500cm 2 / g. The specific surface area described in this invention was obtained by nitrogen adsorption-desorption experiment. The method for testing specific surface area is well known to those skilled in the art, and will not be described in detail here.

[0040] The present invention does not impose any particular limitation on the preparation method of the metal-organic framework material, as long as the product with the above-described morphology can be prepared.

[0041] A second aspect of the present invention provides a method for preparing the metal-organic framework material described in the first aspect, the method comprising the following steps:

[0042] (1) Mix alcohol compounds with organic solvents at a volume ratio of 1:8 to 100 to obtain a mixed solvent;

[0043] (2) The mixed solvent is mixed with the organic ligand and the metal precursor to obtain a precursor solution;

[0044] (3) Crystallize the precursor solution.

[0045] The inventors of this invention accidentally discovered during their research that mixing alcohol compounds with organic solvents in a specific volume ratio, and then adding organic ligands and metal precursors, could prepare metal-organic framework materials with specific morphologies.

[0046] In this invention, the organic solvent refers to various organic solvents conventionally used in the synthesis of metal-organic framework materials, excluding alcohols. Preferably, the organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and N,N-diethylacetamide, and more preferably N,N-dimethylformamide.

[0047] This invention allows for a wide range of selection of alcohol compounds. Preferably, the alcohol compounds are selected from C1-C5 alcohols. The alcohols can be monohydric or dihydric. According to a preferred embodiment of the invention, the alcohol compounds are selected from at least one of methanol, ethanol, ethylene glycol, and isopropanol, preferably methanol and / or ethylene glycol, and more preferably ethylene glycol. This preferred embodiment is more conducive to the competitive adsorption of alcohol compounds and organic ligands, thereby forming octahedral aggregates.

[0048] According to the present invention, preferably, the volume ratio of the alcohol compound to the organic solvent is 1:25 to 3:50. Using the volume ratio of the alcohol compound to the organic solvent within the above-preferred range is more conducive to preparing metal-organic framework materials with better catalytic performance.

[0049] Preferably, the mixing conditions in step (1) include: a mixing temperature of 10-80°C, preferably 20-30°C, more preferably 25-30°C; and a mixing time of 10-120 min, preferably 20-40 min, more preferably 15-25 min.

[0050] The present invention does not have any particular limitation on the specific mixing method of the mixed solvent, organic ligand and metal precursor in step (2), as long as the three are mixed evenly. In order to further improve the catalytic performance of the prepared material, preferably, step (2) includes: mixing the mixed solvent and organic ligand in a first mixing to obtain an organic ligand solution; and then mixing the organic ligand solution with the metal precursor in a second mixing to obtain the precursor solution.

[0051] The present invention allows for a wide range of choices regarding the amount of organic ligands and metal precursors to be added, and those skilled in the art can make adaptive choices based on specific needs to prepare metal-organic framework materials.

[0052] Preferably, the concentration of the organic ligand in the organic ligand solution is 3-15 g / L, more preferably 3.6-14.5 g / L, and most preferably 10.2-12.5 g / L.

[0053] Preferably, the concentration of the metal precursor in the precursor solution is 3-40 g / L, more preferably 3.3-38.9 g / L, and most preferably 20.5-25.5 g / L.

[0054] Preferably, the metal precursor is selected from at least one of anhydrous ferric chloride, ferric chloride hexahydrate, and ferric nitrate nonahydrate.

[0055] The present invention has a wide range of choices for the organic ligands. Preferably, the organic ligand is selected from at least one of terephthalic acid, 2-aminoterephthalic acid, 2,4-diaminoterephthalic acid, 2-hydroxyterephthalic acid, 2,4-dihydroxyterephthalic acid, 2-carboxyterephthalic acid, and 2,4-dicarboxyterephthalic acid, and more preferably at least one of terephthalic acid, 2-aminoterephthalic acid, and 2,4-diaminoterephthalic acid.

[0056] The first mixing in this invention only requires that the organic ligand dissolves in the mixed solvent. Preferably, the conditions for the first mixing include: a mixing temperature of 10–80°C, more preferably 20–30°C, and more preferably 25–30°C; and a mixing time of 10–120 min, more preferably 20–40 min, and more preferably 15–25 min.

[0057] In the method provided by this invention, the range of organic ligands selected is the same as that described in the first aspect above, and will not be repeated here.

[0058] The second mixing in this invention only requires that the metal precursor and the organic ligand solution be mixed uniformly. Preferably, the conditions for the second mixing include: a mixing temperature of 10–80°C, more preferably 20–30°C, and more preferably 25–30°C; and a mixing time of 10–120 min, more preferably 50–100 min, and more preferably 50–70 min.

[0059] The crystallization step (3) of this invention allows the metal precursor to react with the organic ligand to prepare a metal-organic framework material. The crystallization conditions are designed to produce the product with the aforementioned morphology. Preferably, the crystallization conditions include: a crystallization temperature of 120–180°C, more preferably 140–160°C, and even more preferably 145–155°C; and a crystallization time of 4–72 h, more preferably 10–48 h, and even more preferably 12–24 h.

[0060] According to a specific embodiment of the present invention, the method further includes a separation and drying step after crystallization in step (3), wherein the separation and drying can be carried out using conventional techniques in the art. Preferably, the separation is centrifugal separation, the centrifugation speed is preferably 4000-10000 r / min, more preferably 8000-12000 r / min; the centrifugation time is preferably 1-20 min, more preferably 5-10 min. The drying temperature is preferably 60-120℃, more preferably 90-110℃; the drying time is preferably 3-30 h, more preferably 20-24 h.

[0061] The third aspect of this invention provides the application of the metal-organic framework material described in the first aspect in polyester degradation or photocatalytic nitrogen fixation.

[0062] The metal-organic framework material provided by this invention exhibits excellent catalytic performance in polyester degradation or photocatalytic nitrogen fixation. It has the advantage of high polyester conversion rate in polyester degradation and high ammonia synthesis yield in photocatalytic nitrogen fixation.

[0063] This invention does not impose any particular limitations on the specific application methods and conditions for polyester degradation or photocatalytic nitrogen fixation, and can be carried out in accordance with conventional technical means in this field.

[0064] Preferably, the polyester degradation is either thermocatalytic degradation or photocatalytic degradation, more preferably photocatalytic degradation. The material provided by this invention is more suitable for the photocatalytic degradation of polyester.

[0065] The present invention will be described in detail below through embodiments. In the following embodiments, the characterization methods of XRD, SEM, and XPS are as described above and will not be repeated here.

[0066] Example 1

[0067] (1) Under stirring conditions, 2.5 mL of ethylene glycol and 42.5 mL of N,N-dimethylformamide were added to a glass and stirred at 25°C for 20 min.

[0068] (2) Add 0.498 g of terephthalic acid to the above mixed solvent and continue stirring at 25°C for 20 min.

[0069] (3) Add 0.973 g of anhydrous ferric chloride to the above solution and continue stirring at 25 °C for 60 min. Then transfer the stirred solution to a reaction vessel and heat at 150 °C for 24 h. Centrifuge the product at 10000 r / min for 8 min. Dry the obtained solid product at 100 °C for 24 h.

[0070] SEM images of the prepared metal-organic framework materials are shown below. Figure 1 XRD pattern can be found Figure 2.from Figure 1 As can be seen, the metal-organic framework material prepared in this embodiment has an octahedral aggregate morphology, and the octahedral aggregates are formed by the aggregation of microspheres. The morphological characteristics of the metal-organic framework material and the morphology of Fe obtained by SEM characterization are listed in Table 1. Figure 2 It can be seen that the metal-organic framework material prepared in this embodiment is MIL-101(Fe).

[0071] Example 2

[0072] Metal-organic framework materials were prepared according to the method of Example 1, except that the volume of ethylene glycol added in step (1) was 2 mL. The morphological characteristics of the metal-organic framework materials and the morphology of Fe obtained by SEM characterization are listed in Table 1.

[0073] Example 3

[0074] Metal-organic framework materials were prepared according to the method of Example 1, except that in step (1), ethylene glycol was replaced with an equal volume of methanol. The morphological characteristics of the metal-organic framework materials obtained by SEM characterization are listed in Table 1.

[0075] Example 4

[0076] Metal-organic framework materials were prepared according to the method of Example 1, except that the mass of terephthalic acid added in step (2) was 0.597 g. The morphological characteristics of the metal-organic framework materials and the morphology of Fe obtained by SEM characterization are listed in Table 1.

[0077] Example 5

[0078] Metal-organic framework materials were prepared according to the method of Example 1, except that the solvothermal temperature (crystallization temperature) in step (3) was 130°C. The morphological characteristics of the metal-organic framework materials obtained by SEM characterization and the morphology of Fe are listed in Table 1.

[0079] Example 6

[0080] Metal-organic framework materials were prepared according to the method of Example 1, except that in step (2), terephthalic acid was replaced with 0.543 g of 2-amino-terephthalic acid. The morphological characteristics of the metal-organic framework materials and the morphology of Fe obtained by SEM characterization are listed in Table 1.

[0081] Example 7

[0082] The method of Example 1 was followed, except that in step (1), the amount of N,N-dimethylformamide used was 37.5 mL. The morphological characteristics of the metal-organic framework material and the morphology of Fe obtained by SEM characterization are listed in Table 1.

[0083] Example 8

[0084] The method of Example 1 was followed, except that the amount of terephthalic acid added in step (2) was 0.675 g, and the amount of anhydrous ferric chloride added in step (3) was 1.8 g. The morphological characteristics of the metal-organic framework material and the morphology of Fe obtained by SEM characterization are listed in Table 1.

[0085] Comparative Example 1

[0086] The catalyst was prepared according to the method of Example 1, except that ethylene glycol was not added in step (1) and zirconium chloride was added in step (3). The metal-organic framework material prepared was UiO-66. The morphology of the metal-organic framework material obtained by SEM characterization was octahedral, with a smooth surface and no microsphere structure. The parameters of other metal-organic framework materials are shown in Table 1.

[0087] Comparative Example 2

[0088] The catalyst was prepared according to the method of Example 1, except that the solvothermal temperature in step (3) was 110°C. The metal-organic framework material prepared was MIL-101. The morphology of the metal-organic framework material obtained by SEM characterization was octahedral, with a smooth surface and no microsphere structure. The morphology of Fe and other parameters of the metal-organic framework material are shown in Table 1.

[0089] Comparative Example 3

[0090] The catalyst was prepared according to the method of Example 1, except that in step (1), only 42.5 mL of N,N-dimethylformamide was added and no alcohol compound was added; and in step (3), after anhydrous ferric chloride was stirred evenly, 2.5 mL of ethylene glycol was added, and stirring was continued at 25 °C for 60 min. The metal-organic framework material prepared in this way was MIL-101(Fe). The morphology of the metal-organic framework material obtained by SEM characterization was a spindle-shaped morphology with a major axis dimension of 2 μm and a minor axis dimension of 0.5 μm. The surface was smooth and there was no microsphere structure. The morphology of Fe and the parameters of other metal-organic framework materials are shown in Table 1.

[0091] Comparative Example 4

[0092] The catalyst was prepared according to the method of Example 1, except that ethylene glycol was not added in step (1). The metal-organic framework material prepared was MIL-101(Fe). The morphology of the metal-organic framework material obtained by SEM characterization was octahedral, with a smooth surface and no microsphere structure. The morphology of Fe and the parameters of other metal-organic framework materials are shown in Table 1.

[0093] Comparative Example 5

[0094] The catalyst was prepared according to the method of Example 1, except that in step (1), ethylene glycol was replaced with an equal amount of acetic acid, and the metal-organic framework material prepared was MIL-101(Fe). The morphological characteristics of the metal-organic framework material and the morphology of Fe, as well as the parameters of other metal-organic framework materials, obtained by SEM characterization are shown in Table 1.

[0095] Table 1

[0096]

[0097]

[0098] Note: Fe in Table 1 of this invention II Fe III A value of 0 indicates that the catalyst contains only Fe. III In Table 1 of this invention, " / " indicates that the catalyst does not contain this feature.

[0099] Test Example 1

[0100] This test example uses a temperature-controlled reactor to determine the polyester conversion rate of the catalysts prepared in the above examples and comparative examples. The reactor consists of a heating platform, reaction vessel, thermometer, pressure control valve, circulating water jacket, xenon lamp head, and xenon lamp power supply. The reaction vessel is made of stainless steel and has a sapphire skylight at the top, with a thickness of 1 cm. The polyester reaction evaluation method is as follows: 2g of polyester, 0.2g of catalyst, and 100g of water are added to the reaction vessel; stirring is started and the stirring speed is increased to 300 rpm; then the system temperature is increased to 25°C; and the system pressure is increased to 1 MPa. The xenon lamp power supply is turned on, and the xenon lamp head is directed at the skylight of the reaction vessel, with a xenon lamp density of 750 mW / cm³. 2 (mW / cm³), the light source was full-spectrum light with wavelengths of 200-800nm. After reacting for 2 hours, the reaction solution was collected, filtered using Ф7 medium-speed qualitative filter paper, washed and filtered with 50g / L sodium hydroxide solution, and then washed and filtered with deionized water. The filtered product was dried in an oven at 100℃ for 24 hours, and finally the mass of the solid product was weighed. The polyester conversion rate was calculated using the following formula:

[0101]

[0102] Where, m A m represents the total mass of the catalyst and polyester before the reaction. B This represents the total mass of the dried catalyst and polyester after the reaction. The reaction results are listed in Table 2 below.

[0103] Table 2

[0104]

[0105]

[0106] Test Example 2

[0107] This test example uses a temperature-controlled reactor to determine the ammonia synthesis yield of the catalysts prepared in the examples and comparative examples. The reactor consists of a heating platform, reaction vessel, thermometer, pressure control valve, circulating water jacket, xenon lamp head, and xenon lamp power supply. The reaction vessel is made of stainless steel and has a sapphire skylight at the top, with a thickness of 1 cm. The nitrogen fixation reaction evaluation method is as follows: 0.2 g of catalyst and 100 g of water are added to the reaction vessel, nitrogen gas is introduced, and the system pressure is increased to 1 MPa using nitrogen gas. The stirring speed is increased to 300 r / min; then the system temperature is increased to 25°C. The xenon lamp power supply is turned on, and the xenon lamp head is directed towards the skylight of the reaction vessel, with a xenon lamp density of 750 mW / cm³. 2 (mW / cm³), the light source is full-spectrum light with wavelengths of 200-800nm. After reacting for 2 hours, the reaction solution is collected and filtered using a 0.22μm water-based syringe filter. The catalyst-removed reaction solution is then analyzed by ion chromatography, and the ammonia production is calculated by calculating the peak area. The ammonia synthesis yield is calculated using the following formula:

[0108]

[0109] Where, n NH3 The figure represents the amount of ammonia produced, m represents the mass of catalyst added, and t represents the reaction time. The reaction results are listed in Table 3 below.

[0110] Table 3

[0111] Example number <![CDATA[Synthesis ammonia yield, μmol g -1 h -1 > Example 1 182 Example 2 173 Example 3 156 Example 4 142 Example 5 139 Comparative Example 1 56 Comparative Example 2 42

[0112] The results in the table above show that, compared with the comparative examples, the polyester conversion rate and ammonia synthesis yield are higher in the examples using the metal-organic framework material provided by this invention. This indicates that the metal-organic framework material prepared by this invention, which has an octahedral aggregate morphology and whose aggregates are composed of microspheres, can greatly promote the generation of photogenerated carriers and increase the contact area between the catalyst and the polyester raw material during the reaction. When applied to photocatalytic nitrogen fixation, the surface microspheres of the metal-organic framework material increase the incident light absorption area, enhance the generation of photogenerated carriers, and improve the photocatalytic ammonia synthesis yield. This solves the problems of insufficient exposure of surface active sites of metal-organic framework materials, low polyester conversion rate, and high photocatalytic ammonia synthesis yield.

[0113] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A metal-organic framework material, characterized in that, The metal-organic framework material has an octahedral aggregate morphology, the edge length of the octahedral aggregate is 0.5 to 2 μm, the octahedral aggregate is obtained by the aggregation of microspheres, and the diameter of the microspheres is 20 to 100 nm.

2. The metal-organic framework material according to claim 1, wherein, The edge length of the octahedral aggregate is 1 to 1.5 μm, preferably 1 to 1.2 μm; And / or, the diameter of the microspheres is 40-80 nm, preferably 50-60 nm.

3. The metal-organic framework material according to claim 1 or 2, wherein, The metal in the metal-organic framework material is Fe; The organic ligand in the metal-organic framework material is selected from at least one of terephthalic acid, 2-aminoterephthalic acid, 2,4-diaminoterephthalic acid, 2-hydroxyterephthalic acid, 2,4-dihydroxyterephthalic acid, 2-carboxyterephthalic acid, and 2,4-dicarboxyterephthalic acid, preferably at least one of terephthalic acid, 2-aminoterephthalic acid, and 2,4-diaminoterephthalic acid; Preferably, the metal-organic framework material is at least one of MIL-101(Fe), MIL-53(Fe), and MIL-88(Fe).

4. The metal-organic framework material according to any one of claims 1-3, wherein, The metal-organic framework material contains Fe. II and Fe III Two forms, of which Fe II Fe III The ratio is 1:100 to 100:1, preferably 1:4 to 4:1, and more preferably 1:2 to 2:

1.

5. The metal-organic framework material according to any one of claims 1-4, wherein, The specific surface area of ​​the metal-organic framework material is 50–500 cm². 2 / g, preferably 300-500cm 2 / g.

6. A method for preparing the metal-organic framework material according to any one of claims 1-5, the method comprising the following steps: (1) Mix alcohol compounds with organic solvents at a volume ratio of 1:8 to 100 to obtain a mixed solvent; (2) The mixed solvent is mixed with the organic ligand and the metal precursor to obtain a precursor solution; (3) Crystallize the precursor solution.

7. The preparation method according to claim 6, wherein, The alcohol compound is selected from C1-C5 alcohols, preferably selected from at least one of methanol, ethanol, ethylene glycol and isopropanol, more preferably methanol and / or ethylene glycol, and most preferably ethylene glycol; And / or, the organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide and N,N-diethylacetamide, preferably N,N-dimethylformamide; Preferably, the volume ratio of the alcohol compound to the organic solvent is 1:25 to 3:50; Preferably, the mixing conditions in step (1) include: a mixing temperature of 10-80°C, preferably 20-30°C, more preferably 25-30°C; and a mixing time of 10-120 min, preferably 20-40 min, more preferably 15-25 min.

8. The preparation method according to claim 6, wherein, Step (2) includes: first mixing the mixed solvent with the organic ligand to obtain an organic ligand solution; then second mixing the organic ligand solution with the metal precursor to obtain the precursor solution; Preferably, the concentration of the organic ligand in the organic ligand solution is 3–15 g / L; Preferably, the concentration of the metal precursor in the precursor solution is 3-40 g / L; Preferably, the metal precursor is selected from at least one of anhydrous ferric chloride, ferric chloride hexahydrate, and ferric nitrate nonahydrate; Preferably, the organic ligand is selected from at least one of terephthalic acid, 2-aminoterephthalic acid, 2,4-diaminoterephthalic acid, 2-hydroxyterephthalic acid, 2,4-dihydroxyterephthalic acid, 2-carboxyterephthalic acid, and 2,4-dicarboxyterephthalic acid, and more preferably at least one of terephthalic acid, 2-aminoterephthalic acid, and 2,4-diaminoterephthalic acid; Preferably, the conditions for the first mixing include: a mixing temperature of 10–80°C and a mixing time of 10–120 min; Preferably, the conditions for the second mixing include: a mixing temperature of 10–80°C and a mixing time of 10–120 min.

9. The preparation method according to any one of claims 6-8, wherein, The crystallization conditions include: a crystallization temperature of 120–180°C and a crystallization time of 4–72 h.

10. The application of the metal-organic framework material according to any one of claims 1-5 in polyester degradation, preferably photocatalytic degradation of polyester or photocatalytic nitrogen fixation.

Images