High-stability iron-based metal-organic framework material, and preparation method and application thereof

Abstract

This invention relates to a highly stable iron-based metal-organic framework material, its preparation method, and its applications, belonging to the field of photochemical energy conversion and photocatalytic degradation. The invention addresses the corrosion problem of photocatalysts in photo-Fenton reactions by surface modification of artificial photosynthetic photocatalytic materials. The method involves dissolving ferric chloride hexahydrate and 2-aminoterephthalic acid in N,N-dimethylformamide, stirring thoroughly until dissolved, transferring the solution to a reaction vessel for a solvothermal reaction, cooling to room temperature, washing thoroughly with ethanol, and drying the product under vacuum to obtain MIL-101(Fe)-NH 2 Solid powder. MIL-101(Fe)-NH 2 The product was dispersed in a mixed solution of tetraethyl orthosilicate, anhydrous ethanol, and sodium hydroxide, and ultrasonically vibrated. The mixture was then stirred at room temperature until the tetraethyl orthosilicate was completely hydrolyzed and the solution evaporated. The precipitate was dried under vacuum to obtain SiO₂. x H@MIL-101(Fe)-NH 2 Solid powder.

Description

A highly stable iron-based metal-organic framework material, its preparation method and application Technical Field

[0001] This invention belongs to the field of photochemical energy conversion and photocatalytic degradation. Background Technology

[0002] Since 1972, when Japanese scientists Akira Fujishima and Kenichi Honda first reported that TiO2 electrodes could decompose water to produce hydrogen and oxygen, this discovery opened up research in the field of photocatalysis, and since then, the research on highly efficient photocatalytic materials has attracted much attention. Besides traditional semiconductor materials, metal-organic frameworks (MOFs) have also garnered significant interest. MOFs are porous crystalline materials composed of organic ligands and metal nodes. Compared with traditional photocatalytic materials, they possess many advantages such as high porosity, large specific surface area, and tunable structure and function, making them promising candidates for photocatalysis. Most MOFs exhibit semiconductor-like properties. Under photon excitation with energy greater than or equal to their band gap, electrons located in the highest occupied molecular orbital (HOMO) will jump to the lowest unoccupied molecular orbital (LUMO), leaving holes in the HOMO. Subsequently, electrons or holes migrate to the MOF surface and undergo reduction or oxidation reactions, respectively. Compared with traditional semiconductor photocatalytic materials, MOFs have the following advantages in improving the generation, separation and utilization of electron-hole pairs: (1) MOF materials can enhance the absorption of light energy by introducing broad-spectrum absorbing groups as organic ligands, thereby increasing the number of electron-hole pairs generated under illumination; (2) The high porosity of MOF materials determines that more active sites will be exposed, which is conducive to the transfer and utilization of photogenerated electrons, thereby reducing the recombination rate of electrons and holes; (3) The well-defined and customizable structural characteristics of MOF materials make them an ideal model for studying the structure-activity relationship of photocatalysis. Although MOFs have shown great potential in many aspects, their instability remains a challenge. For example, water molecules may break the metal-ligand bonds in MOFs, leading to structural collapse; organic ligands may decompose at high temperatures; and their structure may also be destroyed in chemical environments such as acids and alkalis.

[0003] In summary, this invention proposes a highly stable iron-based metal-organic framework material, its preparation method, and its applications. The method employs a simple and mild tetrabutyl silicate self-hydrolysis process to coat amorphous silicon hydroxide (SiO2) onto iron-based MOF (MIL-101(Fe)-NH2) grains. xH) Protective layer, to prepare and synthesize SiO₂ with high stability even under extremely strong oxidizing photo-Fenton reaction environment. x H@MIL-101(Fe)-NH2 catalyst. Unlike conventional MIL-101(Fe)-NH2 catalysts that lose stability and decompose in strong oxidizing environments, the amorphous surface-modified catalyst presented in this invention maintains high catalytic activity and cycle stability under the synergistic effect of strong oxidation in photocatalysis and Fenton reaction. Furthermore, the method of this invention is convenient, efficient, and more environmentally friendly and energy-saving, aligning with the low-carbon and low-energy consumption development strategy. Summary of the Invention

[0004] This invention relates to solving the problem of easy self-decomposition and deactivation of highly active iron-based MOF catalysts under strong oxidative Fenton reaction conditions, and proposes a mild, simple and rapid silicon-based hydroxide amorphous layer surface modification and protection strategy. To solve the above problems, a highly stable iron-based metal-organic framework material and its preparation method in this invention are completed through the following steps.

[0005] Step 1: Dissolve ferric chloride hexahydrate and 2-aminoterephthalic acid in N,N-dimethylformamide, stir thoroughly to dissolve, transfer to a reaction vessel for solvothermal reaction, cool to room temperature, wash thoroughly with ethanol, and dry the product under vacuum to obtain MIL-101(Fe)-NH2 solid powder.

[0006] Step 2: Disperse MIL-101(Fe)-NH2 in a mixed solution of tetraethyl orthosilicate, anhydrous ethanol, and sodium hydroxide, and sonicate. Stir at room temperature until the tetraethyl orthosilicate is completely hydrolyzed and the solution evaporates. Dry the precipitate under vacuum to obtain SiO2. x H@MIL-101(Fe)-NH2 solid powder.

[0007] Further specifying, in step one, 1-1.5g of ferric chloride hexahydrate and 0.2-0.7g of 2-aminoterephthalic acid are dissolved in 50-80mL of N,N-dimethylformamide and stirred thoroughly for 30min.

[0008] Further specify that the solvothermal reaction in step one uses a 100mL reactor with a filling degree of 50% to 80%, a reaction temperature of 90 to 120℃, and a reaction time of 8 to 14 hours.

[0009] Further specify that in step one, drying is carried out in a vacuum drying oven at 60°C for 12 hours.

[0010] Further specifying, in step two, the amount of MIL-101(Fe)-NH2 solid powder used is 500-700 mg, and the mixed solution consists of 1-2 mL of tetraethyl orthosilicate, 35-50 mL of anhydrous ethanol, and 12-16 mL of 0.1 M sodium hydroxide.

[0011] Further specifying, the ultrasonic oscillation time in step two is 30 minutes.

[0012] Further specifying, the stirring time at room temperature in step two is 20–28 hours.

[0013] Further specifying, in step two, drying is performed in a vacuum drying oven at 60°C for 12 hours.

[0014] The catalyst prepared by the method of this invention is amorphous SiO2, a product of room temperature hydrolysis of tetraethyl orthosilicate. x MIL-101(Fe)-NH2 with H-layer surface modification. This invention provides a simple, low-temperature, rapid, and atmospheric pressure preparation technique for highly stable iron-based metal-organic framework materials coated with an amorphous silicon-based hydride layer. This technique is suitable for the modification and protection of unstable and easily deactivated catalysts, and has the effect of significantly improving catalyst stability and continuously supplying catalytic activity. Attached Figure Description

[0015] Figure 1 shows SiO x XRD patterns of H@MIL-101(Fe)-NH2 and MIL-101(Fe)-NH2; Figure 2 shows the XRD patterns of SiO2. x Scanning electron microscope image of H@MIL-101(Fe)-NH2 and its energy dispersive spectroscopy (EDS) analysis; Figure 3 shows SiO2. x XPS spectra of H@MIL-101(Fe)-NH2 and MIL-101(Fe)-NH2; Figure 4 shows the SiO2. x The photo-Fenton degradation curves of H@MIL-101(Fe)-NH2 and MIL-101(Fe)-NH2 on RhB indicator over time are shown in the upper right inset, which is a comparison of catalyst stability after one degradation experiment, and the lower left inset is a comparison of three degradation cycles. Detailed Implementation

[0016] Example 1: The use of MIL-101(Fe)-NH2 nano-octahedral crystals in this example was carried out according to the following steps: 1.35g of ferric chloride hexahydrate and 0.45g of 2-aminoterephthalic acid were dissolved in 60mL of N,N-dimethylformamide. After stirring and dissolving for 30min, the solution was transferred to a 100mL reaction vessel. The solvothermal reaction was carried out at 110℃ for 12h. After cooling to room temperature, the solution was washed 5 times with ethanol and then vacuum dried at 60℃ for 12h to obtain MIL-101(Fe)-NH2 solid powder.

[0017] The method for preparing a highly stable iron-based metal-organic framework material in this embodiment is accomplished through the following steps:

[0018] 600 mg of MIL-101(Fe)-NH2 was dispersed in a mixed solution of 1.5 mL tetraethyl orthosilicate, 40 mL anhydrous ethanol, and 15 mL 0.1 M sodium hydroxide. The solution was ultrasonically vibrated for 30 min and then stirred at room temperature for 24 h to allow complete hydrolysis of the tetraethyl orthosilicate until the solution evaporated. The precipitate was dried in a vacuum drying oven at 60 °C for 12 h to obtain an amorphous silicon hydroxide-modified iron-based metal-organic framework material, SiO2. x H@MIL-101(Fe)-NH2.

[0019] The photocatalytic oxidation degradation of Rhodamine B solution was performed using a 300W xenon lamp to simulate sunlight. 10 mg of the catalyst, 600 μL of hydrogen peroxide, and 150 mL of 8 mg / L Rhodamine B solution were placed in a 250 mL beaker. The beaker was fixed 5 cm in front of the light source, and the reaction was continuously stirred magnetically at a constant speed. The absorbance of the reaction solution was measured at equal time intervals, and the concentration of the reaction solution was calculated. A curve showing the degradation rate versus illumination time was plotted to analyze and compare the photocatalytic activity of the samples, as shown in Figure 4.

[0020] As can be seen from Figure 4, in the high-oxidizing photo-Fenton reaction of this invention, the unmodified MIL-101(Fe)-NH2 catalyst is completely oxidized and decomposed after one Fenton experiment, while the SiO2 catalyst modified with the amorphous layer surface is completely oxidized and decomposed. x H@MIL-101(Fe)-NH2 not only exhibits good stability but also considerable cyclic degradation activity, as shown in the upper right inset. For a more intuitive comparison, the lower left inset shows a comparative experiment of pollutant cyclic degradation with the hydrogen peroxide dosage changed to 100 μL. The figure clearly shows that the stability of the unmodified MIL-101(Fe)-NH2 catalyst decreases significantly, while the stability of the SiO2 catalyst modified with an amorphous layer decreases considerably. x The H@MIL-101(Fe)-NH2 catalyst exhibits stable reaction activity.

Claims

1. A method for preparing a highly stable iron-based metal-organic framework material, characterized in that... The preparation method is completed through the following steps: Step 1: Ferric chloride hexahydrate and 2-aminoterephthalic acid are dissolved in N,N-dimethylformamide. After thorough stirring and dissolution, the solution is transferred to a reaction vessel for solvothermal reaction. After cooling to room temperature, the solution is thoroughly washed with ethanol and dried under vacuum to obtain MIL-101(Fe)-NH2 solid powder; Step 2: MIL-101(Fe)-NH2 is dispersed in a mixed solution of tetraethyl orthosilicate, anhydrous ethanol, and sodium hydroxide, and ultrasonically vibrated. The solution is stirred at room temperature until the tetraethyl orthosilicate is completely hydrolyzed until the solution evaporates. The precipitated product is dried under vacuum to obtain SiOxH@MIL-101(Fe)-NH2 solid powder; Step 1 is specifically performed as follows: 1-1.5 g of ferric chloride hexahydrate and 0.2-0.7 g of 2-aminoterephthalic acid are dissolved in 50-80 mL of N,N-dimethylformamide; the temperature of the solvothermal reaction is 90-120℃.

2. The method according to claim 1, characterized in that... Stir thoroughly for 30 minutes during step one to dissolve.

3. The method according to claim 1, characterized in that... In step one, the solvothermal reaction is carried out in a 100mL reactor with a filling degree of 50% to 80% and a reaction time of 8 to 14 hours.

4. The method according to claim 1, characterized in that... In step one, the vacuum drying operation is carried out at a temperature of 60℃ for 12 hours.

5. The method according to claim 1, characterized in that... In step two, the amount of MIL-101(Fe)-NH2 solid powder used is 500-700 mg, and the mixed solution consists of 1-2 mL of tetraethyl orthosilicate, 35-50 mL of anhydrous ethanol, and 12-16 mL of 0.1 M sodium hydroxide.

6. The method according to claim 1, characterized in that... In step two, the ultrasonic oscillation time is 30 minutes.

7. The method according to claim 1, characterized in that... In step two, the stirring time at room temperature is 20–28 hours.

8. The method according to claim 1, characterized in that... In step two, the vacuum drying operation is carried out at a temperature of 60℃ for 12 hours.

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