Preparation method and application of a bimetallic site MOF

Abstract

This invention discloses a method for preparing bimetallic site-regulated metal-organic framework adsorbents and their application in capturing low-concentration toluene. The method uses MIL-101(Cr) as the substrate material and employs a solvothermal method to introduce Al in situ during the synthesis process. 3+ By regulating Al 3+ With Cr 3+ A bimetallic coordination structure was constructed using a specific molar ratio to obtain an Al-MIL-101(Cr) dual-site modified material. This material retains its original crystal framework structure and incorporates Al-O coordination structures and polymorphic porous structures within the framework, increasing the number of Lewis acid active sites. The material prepared in this invention is suitable for the adsorption of volatile organic compounds (VOCs) in the concentration range of 0-1000 ppm, and is particularly suitable for the adsorption treatment of low concentrations of toluene. This invention achieves multi-site synergistic regulation of MOF materials through a combination of metal ion doping and structural modulation, providing a new technical approach for the design of adsorption materials for low-concentration organic pollutants.

Description

Technical Field

[0001] This invention belongs to the field of novel functional materials, specifically relating to a method for preparing a metal-organic framework material for the efficient adsorption and removal of toluene in low-concentration VOCs environments. Background Technology

[0002] Toluene (C7H8) is a typical volatile organic compound (VOC) widely used in pharmaceutical synthesis, coating resin production, dye manufacturing, and industrial applications such as explosives and pesticides. With the accelerating pace of industrialization, toluene emissions have been continuously increasing, becoming a significant source of air pollution. Toluene is characterized by its high volatility, high chemical stability, and ease of migration and accumulation in the environment. Long-term exposure to low concentrations of toluene may cause damage to the nervous system, cardiovascular disease, and even increase the risk of cancer. Therefore, developing efficient, stable, and sustainable toluene removal technologies is of great importance.

[0003] Currently, the main methods for treating toluene pollution include condensation, combustion, biodegradation, and adsorption. Among these, adsorption is promising for industrial applications due to its advantages such as simple operation, low energy consumption, recyclability, and applicability to low-concentration (50-2000 ppm) organic waste gas treatment. Regarding adsorption materials, traditional materials such as activated carbon, zeolite, and hypercrosslinked polymers, while possessing certain adsorption capacity, suffer from insufficient moisture resistance, poor high-temperature stability, or limited adsorption efficiency for low-concentration toluene. Metal-organic frameworks (MOFs) are a class of porous crystalline materials constructed from metal ions or metal clusters and organic ligands through coordination. They possess advantages such as high specific surface area, tunable pore structure, and abundant active sites, exhibiting excellent performance in gas storage and separation.

[0004] MIL-101(Cr) is a typical three-dimensional porous MOF material, composed of Cr 3+ Formed by self-assembly with H2BDC ligands, it possesses an ultra-large specific surface area and abundant unsaturated metal Lewis acid sites, showing great potential for application in the field of gas adsorption. Under low concentration toluene (approximately 500 ppm) conditions, traditional single-metal MIL-101(Cr) materials mainly rely on van der Waals forces and pore-based physical adsorption mechanisms, with weak host-guest interactions, and there is still room for improvement in adsorption capacity.

[0005] Recent studies have shown that constructing bimetallic sites through metal ion doping can regulate the electronic structure, pore structure, and number of Lewis acid sites in MOF materials, thereby enhancing the adsorption capacity of these materials for aromatic hydrocarbon molecules. Aluminum ions (Al...) 3 +Al has a small ionic radius and strong Lewis acidity; its unoccupied 3s and 3p orbitals can interact with the π electrons of the aromatic ring. 3+ Introducing it into the MIL-101(Cr) framework is expected to form new Lewis acid sites and regulate the pore structure, thereby enhancing the adsorption performance for low concentrations of toluene.

[0006] Currently, there is considerable research on the adsorption of toluene by single-metal MOF materials, but systematic studies on the enhanced adsorption of low-concentration toluene by bimetallic MOFs are still relatively limited. Therefore, it is necessary to develop a structurally stable, site-tunable, and significantly enhanced adsorption capacity for low-concentration toluene dual-site MOF material. Summary of the Invention

[0007] To address the shortcomings in current research on adsorption site construction and pore structure regulation of low-concentration VOCs adsorption materials, this invention provides a method for preparing MOFs dual-site modified materials and their applications. Based on a metal ion doping strategy to construct bimetallic coordination structures, it achieves the construction of dual Lewis acid active sites and polymorphic pore structures in the material for the adsorption of low-concentration VOCs. The technology of this invention is achieved through the following technical solutions: A method for preparing a MOF-modified toluene adsorbent material with dual-site modification includes the following steps: (1) Dispersion / mixing of precursor solution: In the solvent system, Cr(NO3)3·9H2O is dissolved in deionized water, and then H2BDC is added. Under the conditions of alternating stirring and sonication, it is dispersed evenly. Then hydrofluoric acid is added and Al(NO3)3·9H2O is introduced to obtain a mixed solution. (2) Synthesis of materials: The mixed solution from step (1) was transferred to a reaction vessel and reacted at 180-240 °C for 6-10 h for a solvothermal reaction. Then the temperature was lowered to room temperature, and after centrifugation, it was washed and dried to obtain the dual-site modified material Al-MIL-101(Cr).

[0008] In this invention, Cr(NO3)3·9H2O is the metal source, H2BDC is the organic ligand, Al(NO3)3·9H2O is the doped metal source, hydrofluoric acid is the mineralizing agent, deionized water is the solvent, and DMF and anhydrous ethanol are used for material washing treatment.

[0009] As a preferred technical solution, the molar ratio of Cr(NO3)3·9H2O to H2BDC in step (1) is 1:0.5-2.

[0010] As a preferred technical solution, the molar ratio of Al(NO3)3·9H2O to Cr(NO3)3·9H2O in step (1) is 0.05-0.12.

[0011] As a preferred technical solution, the amount of deionized water used in step (1) is 2.4-9.6 L per mole of Cr(NO3)3·9H2O.

[0012] As a preferred technical solution, the amount of hydrofluoric acid added in step (1) is 0.01-0.04 mL / mmol Cr(NO3)3·9H2O.

[0013] As a preferred technical solution, the centrifugation conditions in step (2) are 6000-10000 rpm and the time is 5-10 min.

[0014] As a preferred technical solution, in step (2), the material is washed with DMF and anhydrous ethanol in sequence.

[0015] As a preferred technical solution, the vacuum drying time in step (2) is 10-15 h.

[0016] The MOFs dual-site modified material prepared by this invention maintains the original crystal framework structure of MIL-101(Cr) while introducing Al-O coordination structure into the material framework, forming a bimetallic coordination structure and polymorphic channel structure, thereby constructing a metal-organic framework material with dual Lewis acid active sites.

[0017] The MOFs dual-site modified material of the present invention can be applied to the adsorption and separation of VOCs in the concentration range of 0-1000 ppm, and is especially suitable for the adsorption treatment of low concentration toluene.

[0018] The principle of this invention: This invention addresses the problems of insufficient adsorption sites and limited pore structure control during the adsorption of low-concentration toluene. It proposes a metal ion doping modification strategy based on dual-site modification of MIL-101(Cr) material. This is achieved by introducing Al during the synthesis of MIL-101(Cr). 3+ , making part of Al 3+ Replace some Cr 3+ Stable coordination bonds are formed, creating an Al-O coordination structure within the material framework while maintaining the original crystal framework structure, and constructing a bimetallic coordination structure. This bimetallic coordination structure alters the original pore structure of the material, resulting in a polymorphic pore structure and increasing the number of Lewis acid active sites. Simultaneously, Al… 3+ The introduction of [the substance] did not disrupt the original crystal structure of MIL-101(Cr), and the modified material retained its original crystal framework characteristics. Based on the above structural changes, the material achieved pore structure regulation and increased active sites while maintaining the stability of the original framework, thus providing a material basis for the adsorption of low concentrations of toluene.

[0019] Compared with the prior art, the advantages of this invention are: (1) The MOFs dual-site modified materials prepared in this invention are produced by a solvothermal method, by introducing Al during the synthesis of MIL-101(Cr). 3+ It is obtained that a bimetallic coordination structure is formed while maintaining the original crystal framework structure.

[0020] (2) The MOFs dual-site modified material prepared in this invention forms an Al-O coordination structure in the material framework and increases the number of Lewis acid active sites, which is beneficial to the adsorption of low concentration toluene.

[0021] (3) The MOFs dual-site modified materials prepared in this invention in Al 3+ The doping process did not damage the original crystal structure of MIL-101(Cr), and the modified material still retained the octahedral morphology and the original crystal framework characteristics.

[0022] (4) The MOFs dual-site modified material prepared in this invention is obtained through Al 3+ The introduction of this technology alters the original pore structure of the material, creating a polymorphic pore structure, thus enabling the control of the material's pore structure.

[0023] (5) The MOFs dual-site modified material prepared by the present invention can be applied to the adsorption treatment of low concentration toluene, providing a new material for the adsorption of low concentration VOCs.

[0024] (6) The preparation method of the present invention is simple and easy to operate, and the solvothermal method used can realize the preparation of materials. Attached Figure Description

[0025] Figure 1 It is MIL-101(Cr) and different Al 3+ Scanning electron microscope (SEM) images of Al-MIL-101(Cr) doped materials, where (a) is MIL-101(Cr), (b) is Al(5%)-MIL-101(Cr), and (c) is Al(10%)-MIL-101(Cr).

[0026] Figure 2 It is MIL-101(Cr) and different Al 3+ X-ray diffraction (XRD) pattern of Al-MIL-101(Cr) material with varying doping ratio.

[0027] Figure 3 It is MIL-101(Cr) and different Al 3+Pore ​​structure characterization diagrams of Al-MIL-101(Cr) doped with specific ratios, where (a) is the N2 adsorption-desorption isotherm diagram and (b) is the pore size distribution curve.

[0028] Figure 4 It is MIL-101(Cr) and different Al 3+ Toluene adsorption isotherms of Al-MIL-101(Cr) doped materials, where (a) is... P / P The isothermal adsorption curves of toluene under the conditions of 0 = 0-0.8 are shown in (b). P / P Isothermal adsorption curves of toluene under the conditions of 0 = 0-0.05. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the scope of protection of the embodiments. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0030] Comparative Example 1 A method for preparing a single-metal adsorbent material MIL-101(Cr) includes the following steps: MIL-101(Cr) was synthesized using a solvothermal method: (1) Dissolve 5 mmol of Cr(NO3)3·9H2O in 24 mL of deionized water, and then slowly add 5 mmol of H2BDC to the solution. During this process, stir magnetically at 500 rpm for 30 min. If the mixture is not fully mixed, alternate with sonication to ensure that the mixture is homogeneous.

[0031] (2) Add 89 μL of hydrofluoric acid as a crystallizing agent, transfer it to a high-pressure reactor, set the oven temperature program to a heating rate of 2 °C per minute, heat to 220 °C, and react at 220 °C for 8 h. After cooling the reactor to room temperature, centrifuge the resulting mixture (8000 rpm, 6 min).

[0032] (3) Then, the product was washed three times with DMF and anhydrous ethanol, first by heating in a water bath for a period of time and then by centrifugation (8000 rpm, 6 min), and then dried in a 70 ℃ oven to extract the crude product.

[0033] (4) Finally, MIL-101(Cr) was obtained by vacuum drying at a pressure below 2 Pa for 12 h.

[0034] Example 1 A method for preparing a bimetallic adsorbent material Al-MIL-101(Cr) includes the following steps: Al-MIL-101(Cr) was synthesized using a solvothermal method: (1) Add 0.25 mmol Al(NO3)3·9H2O to the mixed solution formed by 4.75 mmol Cr(NO3)3·9H2O and H2BDC. Stir magnetically at 500 rpm for 30 min. If the mixing is not sufficient, alternate with sonication to make it evenly mixed.

[0035] (2) Add 89 μL of hydrofluoric acid as a crystallizing agent, transfer it to a high-pressure reactor, set the oven temperature program to a heating rate of 2 °C per minute, heat to 220 °C, and react at 220 °C for 8 h. After cooling the reactor to room temperature, centrifuge the resulting mixture (8000 rpm, 6 min). (3) Then, the product was washed three times with DMF and anhydrous ethanol, first by heating in a water bath for a period of time and then by centrifugation (8000 rpm, 6 min), and then dried in a 70 ℃ oven to extract the crude product.

[0036] (4) Finally, Al(5%)-MIL-101(Cr) was obtained by vacuum drying for 12 h at a pressure below 2 Pa.

[0037] Example 2 A method for preparing bimetallic adsorbent Al-MIL-101(Cr) with different proportions includes the following steps: Al-MIL-101(Cr) was synthesized using a solvothermal method: (1) Add 0.5 mmol Al(NO3)3·9H2O to the mixed solution formed by 4.5 mmol Cr(NO3)3·9H2O and H2BDC. Stir magnetically at 500 rpm for 30 min. If the mixture is not fully mixed, alternate with sonication to make it evenly mixed.

[0038] (2) Add 89 μL of hydrofluoric acid as a crystallizing agent, transfer it to a high-pressure reactor, set the oven temperature program to a heating rate of 2 °C per minute, heat to 220 °C, and react at 220 °C for 8 h. After cooling the reactor to room temperature, centrifuge the resulting mixture (8000 rpm, 6 min). (3) Then, the product was washed three times with DMF and anhydrous ethanol, first by heating in a water bath for a period of time and then by centrifugation (8000 rpm, 6 min), and then dried in a 70 ℃ oven to extract the crude product.

[0039] (4) Finally, Al(10%)-MIL-101(Cr) was obtained by vacuum drying for 12 h at a pressure below 2 Pa.

[0040] Material performance testing The products prepared in Comparative Example 1 and Examples 1-2 of this invention were subjected to structural and performance characterization analysis.

[0041] (I) Scanning Electron Microscopy (SEM) Analysis The microstructure of Al(5%)-MIL-101(Cr) and Al(10%)-MIL-101(Cr) prepared in Comparative Example 1 and Examples 1-2 of this invention was characterized using a Hitachi SU8020 scanning electron microscope (SEM). Figure 1 As shown. Figure 1 (a) is a scanning electron microscope image of Comparative Example 1. Figure 1 (b) Al doped in Example 1 3+ Scanning electron microscope image of Al(5%)-MIL-101(Cr). Figure 1 (c) Al doped in Example 1 3+ Scanning electron microscope image of Al(10%)-MIL-101(Cr). Figure 1 (a) shows that MIL-101(Cr) is a standard octahedral morphology with clear edges, a smooth surface, no impurities, and relatively large particle size. Figure 1 (b) and Figure 3-1 The sample in (c) is an Al-doped sample. 3+ MOF in Al 3+ Despite the influence of Al, the material still maintains a uniform and regular octahedral shape. 3+ This alters the apparent structure, causing slight deformations in MIL-101(Cr), including blurred crystal edges and reduced grain size. (The text abruptly ends here, likely due to an incomplete translation or missing information.) 3+ The modified MOF framework does not significantly alter the external geometry of the crystal, but the integration process affects the internal structure of the MOF, causing defects around the coordination material.

[0042] (II) X-ray diffraction (XRD) analysis The XRD patterns of Comparative Example 1 and Examples 1-2 are as follows: Figure 2As shown in (a). The XRD patterns of Comparative Example 1 and Examples 1-2 are consistent with those reported in the literature, indicating the successful preparation of MIL-101(Cr), Al(5%)-MIL-101(Cr), and Al(10%)-MIL-101(Cr). Furthermore, no additional peaks were observed below 10° in any of the samples, indicating that the synthesized MIL-101(Cr) and Al-MIL-101(Cr) series samples have high purity. Figure 2 (a) It can be seen that Al 3+ The different proportions do not change the position of the diffraction peaks and have no effect on the crystal coordination of MIL-101(Cr). No new diffraction peaks appearing on the Al coordination planes in the XRD patterns of Al(5%)-MIL-101(Cr) and Al(10%)-MIL-101(Cr) are observed because Al... 3+ Only replaces part of Cr 3+ No independent coordination structure was formed. Furthermore, the peak intensity of the modified material was not significantly weaker than that of the raw material, indicating that aluminum ion doping does not alter the crystallinity of MIL-101(Cr).

[0043] (III) Fourier Transform Infrared Spectroscopy (FT-IR) The chemical properties of all materials were investigated using Fourier transform infrared spectroscopy, and the results are as follows: Figure 2 As shown in (b). The three materials at 1629 cm -1 and 1396 cm -1 Strong absorption peaks were observed at all locations, corresponding to the symmetric and asymmetric extensions of the dicarboxylic acid OC=O ligand, respectively. Furthermore, a strong absorption peak was observed at 10¹⁸ cm⁻¹. -1 and 752 cm -1 A weak and narrow peak was observed at 588 cm⁻¹, which is due to the δ(CH₂) and γ(CH₂) vibrations of the benzene ring in the ligand. -1 The characteristic peak with moderate intensity is caused by the Cr-O stretching vibration, indicating that the synthesis of MIL-101(Cr) was successful.

[0044] Al(5%)-MIL-101(Cr) and Al(10%)-MIL-101(Cr) materials at 513 cm⁻¹ -1 and 1049 cm -1 The nearby infrared absorption peaks are related to the bending or octahedral coordination vibrations of the Al-O bonds. The appearance of these two sets of peaks is due to the partial Al... 3+ Replaced part of Cr 3+ Stable coordinate bonds were formed, indicating that Al 3+ Successfully embedded in the framework structure of MIL-101(Cr).

[0045] Further analysis revealed that Al3+ The proportion of Al is significantly correlated with the infrared signal intensity. 3+ When the molar ratio of the organic ligand to the ligand is increased from 5% to 10%, 513 cm -1 and 1049 cm -1 The peak intensity at that point is significantly enhanced, indicating that the vibrational signal of the Al-O bond in the material increases with the change in Al intensity. 3+ The effect is enhanced by increasing the doping amount.

[0046] (iv) N2 adsorption and pore structure analysis Figure 3 (a) is the N2 isothermal adsorption-desorption curve of Comparative Example 1 and Examples 1-2 at -196 °C. Figure 3 (a) It can be seen that the adsorption-desorption lines of Comparative Example 1 and Examples 1-2 are both Type I isotherms. P / P At a concentration of 0 < 0.25, the adsorption capacity increases significantly, indicating that MIL-101(Cr) and the two modified materials exhibit typical microporous structures. At low concentrations ( P / P (0 < 0.08), the N2 adsorption capacity of the two modified materials is slightly greater than that of MIL-101(Cr). In P / P The N2 adsorption capacity of MIL-101(Cr) at 0 = 0.10-0.90 is greater than that of Al(5%)-MIL-101(Cr) and Al(10%)-MIL-101(Cr).

[0047] Figure 3 (b) shows the pore size distribution of MIL-101(Cr) and the modified material. As can be seen from the figure, the peak at 12.0 Å shifts, and a new pore size distribution appears in the 9.6 Å-11.5 Å range, proving that Al... 3+ The introduction of [a substance] affects the original pore structure of MIL-101(Cr). Simultaneously, the appearance of new peaks or shoulders in the curve morphology at 15-30 Å indicates that Al [is present]. 3+ Doping reduces the proportion of mesopores and thus enhances the contribution of micropores by regulating the pore size distribution of materials.

[0048] As shown in Table 1, the specific surface area of ​​the Al-MIL-101(Cr) series modified materials is lower than that of MIL-101(Cr). This is because the Al-MIL-101(Cr) modified materials are modified by Al-MIL-101(Cr). 3+ The pore structure changed after modification. As the specific surface area decreased, the total pore volume of Al(5%)-MIL-101(Cr) decreased to 1.35 cm³. 3While the total pore volume remained unchanged, the proportion of micropores in the total pore volume increased. This is because the number of new micropores appearing in the 9.6-11.5 Å region decreased, resulting in intergranular pores. The specific surface area of ​​the Al(10%)-MIL-101(Cr) material was significantly lower than that of MIL-101(Cr), far below that of the original material. This is because excessive Al doping caused partial pore collapse, reducing the specific surface area. The micropore volume data shows that the total pore volume of both modified materials was significantly lower than that of the original material. However, the reduced micropore size brought the micropore dimensions closer to the size of toluene molecules, enhancing the toluene adsorption force and improving selective adsorption. Simultaneously, the smaller micropore volume shortened the diffusion path of toluene molecules within the micropores, accelerating the adsorption kinetics. Under low pressure, the diffusion rate of molecules is relatively slow; shortening the diffusion path reduces the time for molecules to reach the adsorption site, improving adsorption efficiency and making it more suitable for toluene adsorption under low pressure.

[0049]

[0050]

[0051] (v) Analysis of the adsorption line of toluene isotherm Figure 4 (a) Comparative Example 1 and Examples 1-2 were tested at 298K. P / P The toluene isotherm adsorption curves under conditions of 0 = 0-0.8 are shown in the figure. As can be seen from the figure, the isotherm adsorption curves of MIL-101(Cr), Al(5%)-MIL-101(Cr), and Al(10%)-MIL-101(Cr) for low-concentration toluene are Type I. When the relative pressure is less than 0.1, the adsorption capacity of MIL-101(Cr), Al(5%)-MIL-101(Cr), and Al(10%)-MIL-101(Cr) for toluene increases vertically because microporous adsorption occurs in all materials. In the relative pressure range of 0.1 to 0.8, the performance of Examples 1-2 is inferior to that of Comparative Example 1. Analysis of the data in Table 1 shows that the decrease in saturated adsorption capacity is mainly due to the decrease in the specific surface area of ​​the materials.

[0052] Figure 4 (b) For the modified materials of the MIL-101(Cr) and Al-MIL-101(Cr) series, in P / P The toluene isotherm adsorption curve is 0-0.05. As shown in the figure, the toluene adsorption capacity of both modified materials is higher than that of the original material in the range of 100-1000 ppm, and the toluene adsorption capacity is 2.1 times that of the original material at 500 ppm. The adsorption performance of the modified materials is higher than that of the original material in the range of 0-1000 ppm, indicating that Al... 3+Although the introduction of Al reduces the specific surface area of ​​the material, it results in a larger adsorption capacity, significantly improving its adsorption capacity in the low-pressure region. This is because Al doping... 3+ The subsequent development of MIL-101(Cr) optimized the microporous structure, added adsorption sites, and enhanced the adsorption of low concentrations of toluene. 3+ Partially replaces Cr 3+ Subsequently, more exposed Al-O cluster metal sites are formed, which have stronger Lewis acidity than the original Cr sites. The π electrons of the benzene ring of toluene interact with Al. 3+ Empty orbitals form strong coordination interactions, effectively capturing toluene molecules under low-pressure conditions. The material relies solely on micropores for adsorption in the relatively low-pressure region, while mesoporous adsorption dominates in the relatively high-pressure region. Therefore, Al(5%)-MIL-101(Cr) exhibits the best adsorption performance for low concentrations of toluene.

[0053] The examples provided in this invention are not intended to limit the implementation of the invention. Those skilled in the art will recognize that various variations and modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of the claims.

Claims

1. A method for preparing a MOFs dual-site modified toluene adsorbent material, characterized in that, Includes the following steps: (1) Dispersion and mixing of precursor solution: Dissolve Cr(NO3)3·9H2O in deionized water, then add terephthalic acid (H2BDC), and disperse it evenly under alternating stirring and sonication. Then add mineralizing agent hydrofluoric acid and aluminum source Al(NO3)3·9H2O to obtain a mixed solution. (2) Solvent thermal reaction and post-treatment: The mixed solution obtained in step (1) was transferred to a reaction vessel and reacted at 180-230 °C for 6-10 h. After the reaction was completed, the temperature was lowered to room temperature. After centrifugation, the solution was washed with N,N-dimethylformamide (DMF) and anhydrous ethanol in sequence, and then vacuum dried for 10-15 h to obtain the bimetallic MOF material Al-MIL-101(Cr).

2. The preparation method according to claim 1, characterized in that: In step (1), the molar ratio of Cr(NO3)3·9H2O to H2BDC is 1:0.5-2.

3. The preparation method according to claim 1, characterized in that: In step (1), the molar ratio of Al(NO3)3·9H2O to Cr(NO3)3·9H2O is 0.02-0.

25.

4. The preparation method according to claim 1, characterized in that: In step (1), the amount of deionized water used is 2-10 L / mol per mole of Cr(NO3)3·9H2O.

5. The preparation method according to claim 1, characterized in that: In step (1), the amount of hydrofluoric acid added is 0.01-0.04 mL / mmol Cr(NO3)3·9H2O.

6. The preparation method according to claim 1, characterized in that: In step (2), the centrifugation conditions are 6000-10000 rpm and the time is 5-10 min.

7. The preparation method according to claim 1, characterized in that: In step (2), the washing process involves washing with N,N-dimethylformamide and anhydrous ethanol 2-5 times each, combined with heat treatment.

8. The preparation method according to claim 1, characterized in that: In step (1), magnetic stirring and ultrasonication are performed alternately to ensure uniform mixing.

9. The MOFs dual-site modified material prepared by the method according to any one of claims 1 to 8, characterized in that: While maintaining the crystal framework structure of MIL-101(Cr), this material introduces an Al-O coordination structure to form a bimetallic coordination structure and a polymorphic channel structure, thereby constructing a metal-organic framework material with dual Lewis acid active sites.

10. The application of the MOFs dual-site modified material as described in claim 9, characterized in that: Application of the material in the adsorption and separation of VOCs in the concentration range of 0-1000ppm.

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