Method for preparing mncs@rfs reticular composite material by mechanical ball milling and catalytic application thereof

Abstract

The application discloses a method for preparing MNCs@RFs reticular composite materials by mechanical ball milling and catalytic application thereof. Firstly, in the presence of an auxiliary solvent, seed crystals of a framework are constructed by using partial metal precursors, and then MNCs and metal precursors are introduced without the auxiliary solvent. The catalyst preparation method is simple and efficient, can avoid high temperature, greatly reduce the use of solvents, so as to break the temperature and solvent incompatibility between MNCs and the framework material, protect the structure of MNCs, improve the catalyst activity, and be more suitable for industrialization.

Description

Technical Field

[0001] This invention relates to a method for preparing MNCs@RFs network composite materials by mechanical ball milling and its catalytic application, belonging to the field of metal nanoclusters. Background Technology

[0002] Constructing precisely controllable composite materials helps in understanding host-guest interactions within materials, facilitating the precise design and performance optimization of composites at the molecular level. Atomically precise microstructures (MNCs) and network chemical materials (RFs), including MOFs, COFs, and HOFs, possess well-defined and tunable structures. Combining these two approaches leverages their synergistic advantages and enables the construction of composite materials with precise structures. Compared to conventional surface adsorption methods, introducing MNCs into the framework allows for complete encapsulation of the MNCs within the outer three-dimensional framework material, endowing them with strong spatial confinement to enhance their stability, accessibility, and selectivity. Notably, the network framework provides MNCs with a well-defined pore structure and a tunable internal surface environment, aiding in elucidating and optimizing the synergistic interactions between the loaded MNCs and the framework.

[0003] Several methods exist for incorporating microcrystalline chromatographs (MNCs) into network chemical materials, such as post-synthetic methods that immerse MNC particles in the channels of MOFs. However, these methods are limited by the pore size of the support material; only MOFs with sufficient pore size to accommodate the MNCs can meet this requirement. In-situ formation of a network chemical material around the MNCs is another effective strategy. This method does not require specific support porosity and typically fixes the MNCs within the support in the form of crystal defects, often significantly improving the stability and even the catalytic performance of the MNCs. Fischer's group incorporating Pt12 clusters into ZIF-8 demonstrated that the ZIF shell can prevent Pt aggregation, even after ligand removal. Professor Jiang Hailong's group at the University of Science and Technology of China successfully optimized the valence state and catalytic performance of Au25 clusters by embedding them into different UiO-66-R supports. Professor Yuan Ruo of Southwest University demonstrated that the ZIF shell can restrict the vibration of ligands in Au clusters, thereby improving their fluorescence performance tenfold. Numerous studies have demonstrated the application potential of MNCs and network chemistry materials in various fields; however, the diversity of these nanocomposites remains limited, hindering the selectivity and tunability of the composites. This limitation is primarily due to the fact that traditional framework synthesis conditions, such as high temperatures and solvents, can destroy the structure of MNCs. Therefore, there is an urgent need to develop novel construction strategies to expand the variety of MNCs@RF. Mechanochemical methods for constructing network chemistry materials have been used in various fields, such as nanoparticle encapsulation, drug delivery, gas separation, and bioenzyme encapsulation. This strategy provides a solid-state, rapid, and mild method for synthesizing network chemistry materials, allowing the structure of MNCs to be preserved during framework formation. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a method for preparing MNCs@RFs mesh composite materials via mechanical ball milling and its catalytic applications. The catalyst preparation method of this invention is simple and efficient, avoiding high temperatures and significantly reducing solvent usage. This overcomes the temperature and solvent incompatibility between MNCs and the framework material, while also protecting the structure of the MNCs, improving catalyst activity, and facilitating industrialization.

[0005] This invention discloses a method for preparing MNCs@RFs mesh composite materials by mechanical ball milling. The method employs a two-step synthesis: first, seed crystals of the framework are constructed using a portion of a metal precursor in the presence of an auxiliary solvent; then, MNCs and the metal precursor are introduced without an auxiliary solvent. Specifically, the method includes the following steps: Step 1: Add some metal precursors and some ligands to a ball mill jar, add grinding balls and auxiliary solvent, and ball mill until the auxiliary solvent has completely evaporated.

[0006] Step 2: Add the remaining metal precursors and ligands to the ball mill jar, then add MNCs, continue ball milling, and after ball milling, clean the obtained material with solvent and vacuum dry at room temperature to obtain the MNCs@RFs mesh composite material.

[0007] The metal precursor is nano zinc oxide.

[0008] The ligand is 2-methylimidazole.

[0009] The auxiliary solvent is ethanol.

[0010] In step 1, the mass of a portion of the metal precursor is half of the total mass of the metal precursor; the mass of a portion of the ligand is half of the total mass of the ligand.

[0011] In step 2, the MNCs are Ag 44 Nanoclusters. The Ag 44 The chemical formula of the nanoclusters is [Ag] 44 (p-MBA) 30 ] 4− Its ligand is p-mercaptobenzoic acid.

[0012] The Ag 44 The preparation method of nanoclusters includes the following steps: (1) An aqueous solution of AgNO3 combines with excess ethanol p-MBA to form an insoluble Ag(I)-p-MBA precursor. The pH is then adjusted to 9 with CsOH to solubilize the precursor, and further adjusted to 12 to stabilize the final cluster compound; (2) Then add NaBH4 aqueous solution, stirring dropwise while stirring for one hour. The final dark red solution produces Ag. 44 (p-MBA) 30 The product, in which the carboxylate is an alkali metal salt; (3) The clusters were separated from the reaction mixture by DMF precipitation. Then, the carboxylate was protonated with acetate until the clusters were completely dissolved in DMF, producing stoichiometric amounts of Ag. 44 (p-MBA) 30 The final product is separated by precipitation.

[0013] For specific methods, please refer to the literature: Ultrastable silver nanoparticles, doi:10.1038 / nature12523.

[0014] The grinding jar and grinding balls of this invention are made of zirconium oxide; the total grinding time is 5 minutes (taking 5 minutes as an example, the first step of grinding is 3 minutes and the second step of grinding is 2 minutes), the frequency is 8 Hz, and the ball-to-material ratio is 1:12.

[0015] In the MNCs@RFs mesh composite material, the mass of the metal nanoclusters is 2% of the mass of the metal-organic framework.

[0016] In this invention, ZIF-8 is used as a model RFs, and models including MOFs, COFs, and HOFs are also studied.

[0017] The application of the MNCs@RFs network composite material prepared in this invention in the catalytic cycloaddition reaction of propyneamine with CO2.

[0018] Propyleneamine undergoes cycloaddition reaction with CO2: 0.8 mmol propyleneamine, 0.2% mmol catalyst (as Ag) 44 (Based on) and 0.08 mmol of 1,8-diazobicyclo[5.4.0]undec-7-ene (DBU) were added to a Schlenk reaction flask containing 3 mL of acetonitrile, the air was purged and CO2 gas was introduced, and the mixture was stirred at room temperature for 12 hours.

[0019] After the reaction was completed, the catalyst was washed with n-hexane for recovery, dried under vacuum overnight at room temperature, and then directly used in the next round of reaction to determine its cycle performance.

[0020] Compared with the prior art, the beneficial effects of the present invention are reflected in: 1. This invention employs mechanical ball milling to prepare metal nanomaterials and network framework composites. High-energy mechanical milling induces strong interactions between the metal nanoclusters, metal precursors, and related ligands. The inherent incompatibility between the network chemical materials and MNCs, including the destructive effects of solvents, temperature, and precursors on the MNCs, can be addressed through a mild and solid-state mechanochemical encapsulation process. The framework shell not only provides a specific microenvironment for the immobilized MNCs but also spatially restricts their structural perturbations, significantly improving the stability of the MNCs under harsh conditions, including chemical / thermal treatment, solvent molecule removal, and various organic reaction conditions.

[0021] 2. The method of this invention provides a way to diversify the selection of frame carriers and MNC species in MNCs@RFs assemblies, and promotes the on-demand construction and performance adjustment of structurally defined composite materials.

[0022] 3. The catalyst preparation method of this invention is simple, mild, fast and efficient, suitable for large-scale preparation and has excellent prospects for industrial application. Attached Figure Description

[0023] Figure 1 Pure ZIF-8 and Ag were obtained through mechanochemistry. 44The (a) SAXS and (b) PXRD spectra of @ZIF-8, (c, d) Ag 44 XPS graph of @ZIF-8.

[0024] Figure 2 Pure ZIF-8 and Ag were obtained through mechanochemistry. 44 (a) Infrared spectrum and (b) thermogravimetric curve of @ZIF-8.

[0025] Figure 3 For (a) Ag 44 Clusters and (b) Ag 44 Transmission electron microscopy image of @ZIF-8.

[0026] Figure 4 For Ag 44 (a) UV spectrum and (b) spherical aberration electron microscopy image of @ZIF-8.

[0027] Figure 5 For Ag 44 (a) Nitrogen adsorption curves and (b) pore distribution of ZIF-8 and pure ZIF-8.

[0028] Figure 6 For (a) Ag 44 @ZIF-8、Ag 44 -on-ZIF-8 and homogeneous Ag 44 The cycle performance diagram. (b) Ag 44 @ZIF-8 and homogeneous Ag 44 UV spectra before and after the reaction. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these specific embodiments. Any person skilled in the art, within the scope of the technology disclosed in this invention, should be covered by the protection scope of this invention if they make equivalents or substitutions to the technical solutions and inventive concepts of this invention. Example 1:

[0030] ZIF-8 was synthesized by a mechanochemical method: 0.5 mmol of nano-zinc oxide and 1.0 mmol of 2-methylimidazole were weighed into a zirconium oxide grinding jar, and 3 g of zirconium oxide microspheres and 60 μL of ethanol solution were added. The mixture was then ground at 8 Hz for 5 minutes to obtain a white powder. The ZIF-8 solid was washed three times with ethanol and dried under vacuum overnight at room temperature.

[0031] The mechanochemical synthesis of UiO-66, MOF-74, HKUST-1, COF-TpPa and HOF-101 (PCF-1) was performed with reference to relevant literature. Example 2:

[0032] Mechanochemical synthesis of Ag44@ZIF-8: This encapsulation method involves two steps to avoid damage to MNCs from trace amounts of ethanol. Step 1: Weigh 0.25 mmol of nano-zinc oxide and 0.5 mmol of 2-methylimidazole into a zirconia mortar, add 3 g of zirconia microspheres and 60 μL of ethanol solution. Then grind at 8 Hz for 3 minutes until the ethanol is completely evaporated. Step 2: Add the remaining precursors (0.25 mmol of nano-zinc oxide and 0.5 mmol of 2-methylimidazole) to a zirconia container, followed by 100 μL of Ag44 in DMF solution, and grind for 2 minutes to obtain a purplish-red powder. The resulting Ag44@ZIF-8 powder is washed three times with DMF and carefully dried.

[0033] Catalytic Example:

[0034] Propyleneamine undergoes cycloaddition reaction with CO2: 0.8 mmol propyleneamine, 0.2% mmol catalyst (as Ag) 44 (Based on) and 0.08 mmol of 1,8-diazobicyclo[5.4.0]undec-7-ene (DBU) were added to a Schlenk flask containing 3 mL of acetonitrile. Air was purged and CO2 gas was introduced, and the mixture was stirred at room temperature for 12 hours. The catalyst was recovered by washing with n-hexane, dried under vacuum overnight at room temperature, and then used directly in the next round of reaction to determine its cycle performance.

[0035] Ag 44 @ZIF-8、Ag 44 -on-ZIF-8 (impregnation method composite) and homogeneous Ag 44 As catalysts for the propyne amine cyclization reaction, their recyclability was studied in detail. All catalysts exhibited excellent catalytic performance, with Ag being the most effective. 44 @ZIF-8 exhibited superior cycling performance. In five-cycle testing, Ag... 44 @ZIF-8 did not show a significant decrease in catalytic performance, porosity, or crystallinity. However, for homogeneous Ag... 44 For the cluster, it loses more than 90% of its catalytic activity after three cycles of reaction. 44 -on-ZIF-8 also loses more than half of its catalytic activity after five cycles. This is mainly because the alkaline conditions in the reaction cause cluster aggregation and deactivation. After being placed under the reaction conditions, homogeneous clusters significantly aggregate or decompose, while the Ag composite material... 44 @ZIF-8 can maintain the cluster structure and activity of its loaded clusters.

[0036] The table below shows the cycloaddition reaction of propyneamine with CO2:

[0037] As can be seen from the above embodiments, the technical solution provided by the present invention involves adding metal nanoclusters, metal precursors, and ligands, along with related auxiliary agents, to a ball mill jar, adding grinding balls, and finally placing the ball mill jar in a ball mill. After ball milling, the mixture is centrifuged, washed, and dried to obtain the MNCs@RFs composite catalyst. This combination method provides a pathway for the diversified selection of framework supports and MNC species in MNCs@RFs assemblies, promoting the on-demand construction and performance tuning of structurally well-defined composite materials. This results in catalysts with higher catalytic activity.

[0038] The contents described in this specification are merely illustrative examples of how the inventive concept can be implemented, and the scope of protection of this invention should not be considered as limited to the specific forms described in the embodiments.

Claims

1. The application of MNCs@RFs mesh composite material in the catalytic cycloaddition reaction of propyneamine with CO2, characterized in that: The MNCs@RFs mesh composite material is obtained by seeding the framework with a portion of the metal precursor in the presence of an auxiliary solvent, and then introducing MNCs and the metal precursor without an auxiliary solvent, including the following steps: Step 1: Add some metal precursors and some ligands to a ball mill jar, add grinding balls and auxiliary solvent, and ball mill until the auxiliary solvent has completely evaporated; Step 2: Add the remaining metal precursors and ligands to the ball mill jar, then add MNCs, continue ball milling, clean the obtained material with solvent after ball milling, and vacuum dry at room temperature to obtain MNCs@RFs mesh composite material; In step 2, the MNCs are Ag 44 Nanoclusters, the Ag 44 The chemical formula of the nanoclusters is [Ag] 44 (p-MBA) 30 ] 4− Its ligand is p-mercaptobenzoic acid; The RFs are MOF materials; The metal precursor is nano zinc oxide.

2. The application according to claim 1, characterized in that: The ligand is 2-methylimidazole.

3. The application according to claim 1, characterized in that: The auxiliary solvent is ethanol.

4. The application according to claim 1, characterized in that: In step 1, the mass of a portion of the metal precursor is half of the total mass of the metal precursor; the mass of a portion of the ligand is half of the total mass of the ligand.

5. The application according to claim 1, characterized in that: The total grinding time was 5 minutes, the frequency was 8 Hz, and the ball-to-material ratio was 1:

12.

6. The application according to claim 1, characterized in that: In the MNCs@RFs mesh composite material, the mass of the metal nanoclusters is 2% of the mass of the metal-organic framework.

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