Metal-organic framework composite loaded with metal monatomic atom and preparation method and application thereof

Abstract

This invention belongs to the field of selective adsorption and recovery technology of VOCs, specifically relating to a metal-organic framework composite material loaded with metal single atoms, its preparation method, and its application. The metal-organic framework composite material loaded with metal single atoms is prepared by first mixing the metal source used to prepare MIL-100(Fe) with a modified transition metal source to form a precursor, and then reacting it with an organic ligand. This method enables the transition metal to be uniformly dispersed on MIL-100(Fe) in the form of single atoms. With almost no reduction in the specific surface area of ​​MIL-100(Fe) itself, it enhances the adsorption capacity and selectivity of the resulting composite material for volatile organic compounds with extremely low loading, significantly improving the utilization rate of the transition metal and providing a new reference scheme for the design of efficient selective adsorption of VOCs.

Description

Technical Field

[0001] This invention belongs to the field of selective adsorption and recovery technology of VOCs. More specifically, it relates to a metal-organic framework composite material loaded with metal single atoms, its preparation method, and its application. Background Technology

[0002] Volatile organic compounds (VOCs) are classified as known or probable human carcinogens, irritants, and toxins. Their main sources include the chemical industry, oil refineries, and fuel combustion plants. They also cause serious environmental problems such as photochemical smog and particulate matter, and are one of the main contributors to air pollution. Since the vast majority of VOCs in industrial emissions are often usable, and separation during VOC emission is difficult, there is a need to develop adsorbents capable of efficiently adsorbing and desorbing VOCs to achieve effective VOC separation.

[0003] Metal-organic frameworks (MOFs) are porous framework materials with a metal as the central ion, linked by chemical bonds between the metal and organic ligands. They possess advantages such as large specific surface area, high porosity, structural stability, and surface modifiability, and have shown broad application prospects in energy storage, gas-liquid separation, and heterogeneous catalysis. Furthermore, the porosity of MOFs facilitates contact and interaction between the substrate and adsorbent. Based on these structural characteristics, MOF materials can not only serve as adsorbents for high-density storage of VOCs emitted from industry, but also exhibit differential interactions with different types of VOC molecules, achieving economical and energy-saving VOC separation and recovery. Therefore, they have enormous application potential in the field of gas adsorption and separation.

[0004] Generally, pure metal-organic frameworks (MOFs) exhibit poor adsorption performance and typically require modification to improve their adsorption capacity, such as by adding transition metals. For example, a study (Kim SI, Kim AR, Bae HJ, et al. Cu(I)-incorporation strategy for develostyrene selective adsorbents[J]. Chemical Engineering Journal, 2021, 425: 130601.) successfully loaded Cu(I) ions into mesoporous MOFs using redox-active Fe(II) sites. The resulting material exhibited the best adsorption performance at a copper ion loading of 22.78 wt%. However, in this method, copper is ionicly loaded into the MOF material, which blocks the micropores of the MOF, significantly reducing its specific surface area. When the copper ion loading reached 22.78 wt%, the specific surface area of ​​the resulting composite material decreased from 2347 m² to 1288 m².2 / g, which is reduced by 45%, and a high loading of copper ions is required to achieve a good adsorption effect. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of existing commonly used MOF adsorbent materials, which require a lot of transition metal modification, resulting in high cost, uneven dispersion of transition metals after modification, and easy clogging of micropores. The present invention provides a method for preparing metal-organic framework composite materials loaded with transition metal single atoms.

[0006] The purpose of this invention is to provide a metal-organic framework composite material loaded with transition metal single atoms prepared by the aforementioned preparation method.

[0007] Another object of the present invention is to provide the application of the metal-organic framework composite material with the load of transition metal single atoms.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution:

[0009] This invention protects a method for preparing a metal-organic framework composite material loaded with transition metal single atoms, comprising the following steps:

[0010] S1. Mix the Fe source solution and the transition metal source solution thoroughly at 40-80℃, cool to room temperature, adjust the pH to 7.5-8.5, allow the reaction to complete, and then perform post-processing to obtain the precursor.

[0011] S2. Add the precursor and pyromellitic acid obtained in step S1 to a mixed solution composed of water, glacial acetic acid and polar organic solvent, mix thoroughly, and react completely at 80-200℃. After post-treatment, the transition metal single atom@MIL-100(Fe) (metal-organic framework composite material loaded with transition metal single atoms) is obtained.

[0012] The transition metal source is selected from one or more of Au, Cu, Ag, Pt, or Pd.

[0013] Modifying MOF materials with transition metals is a common modification strategy. However, in existing technologies, the metals used for modification are generally distributed in the form of metal nanoparticles or ions within the MOF framework. The particle size of these metal nanoparticles or ions is relatively large, and they are particularly prone to spontaneous aggregation, leading to poor modification effects. The inventors have creatively discovered that by first mixing the metal source used to prepare MIL-100(Fe) with a modified transition metal source to form a precursor, the transition metal is reduced to single atoms during this process. The resulting precursor is then reacted with an organic ligand. During the formation of MIL-100(Fe) from the precursor and organic ligand, the single-atom form of transition metal is uniformly dispersed on MIL-100(Fe). The resulting composite material does not experience transition metal agglomeration, and due to the small particle size, it does not significantly clog the micropores of the MOF. The specific surface area shows only a small change compared to pure MIL-100(Fe).

[0014] Preferably, the Fe source is selected from one or more of ferric nitrate, ferric chloride, and ferric sulfate.

[0015] Preferably, the molar ratio of Fe in the Fe source to the transition metal in the transition metal source is (30-250):1.

[0016] Preferably, the molar ratio of the precursor to pyromellitic acid is 1:(1-20).

[0017] Preferably, the polar organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0018] Preferably, the volume ratio of water, glacial acetic acid and polar organic solvent is 1:(10-200):(20-200).

[0019] Preferably, the mass-to-volume ratio of the precursor to the mixed solution is 1:(100-200)g / mL.

[0020] Preferably, the Au in the transition metal source is selected from chloroauric acid and / or gold trichloride.

[0021] Preferably, the Cu in the transition metal is selected from one or more of copper nitrate, copper chloride, and copper sulfate.

[0022] Preferably, the Ag in the transition metal is selected from silver nitrate.

[0023] Preferably, the Pt in the transition metal is selected from platinum chloride and / or platinum nitrate.

[0024] Preferably, the Pd in ​​the transition metal is selected from palladium chloride and / or palladium nitrate.

[0025] Preferably, the transition metal in the transition metal source is selected from Au.

[0026] Preferably, the pH is adjusted to 8.0-8.5.

[0027] Preferably, the alkaline reagent for adjusting the pH is sodium carbonate or sodium hydroxide. Adjusting the pH to alkaline conditions yields iron oxide.

[0028] Further, in step S1, the thorough mixing at 40-80°C involves mixing the Fe source solution and the transition metal source solution, heating the mixture to 40-80°C under stirring conditions, increasing the stirring speed, and continuing to stir to achieve thorough mixing.

[0029] Furthermore, the stirring speed is 200-300 r / min, the stirring speed is increased to 400-500 r / min, and the stirring time is 20-50 min.

[0030] Furthermore, in steps S1 and S2, the post-processing includes centrifugation, washing, and drying.

[0031] Furthermore, the washing is performed using anhydrous ethanol or deionized water at 50–60°C.

[0032] Preferably, in step S2, the heating rate for the reaction to complete is 0.1–10 °C / min.

[0033] Preferably, in step S1, the reaction takes 1 to 2 hours to complete.

[0034] Preferably, in step S2, the reaction takes 10 to 40 hours to complete.

[0035] As a preferred embodiment, the method for preparing the metal-organic framework composite material loaded with transition metal single atoms includes the following steps:

[0036] S1. Mix the Fe source solution and Au source solution thoroughly at 40-80℃, cool to room temperature, adjust the pH to 8.0-8.5, allow the reaction to complete, and then perform post-processing to obtain the Au@Fe2O3 precursor.

[0037] S2. The Au@Fe2O3 precursor obtained in step S1 and pyromellitic acid are added to a mixed solution composed of water, glacial acetic acid and polar organic solvent and mixed thoroughly. The reaction is carried out at 80-200℃ until complete. After post-treatment, the metal-organic framework composite material Au@MIL-100(Fe) loaded with Au single atoms is obtained.

[0038] This invention also protects a metal-organic framework composite material loaded with single atoms of a transition metal, prepared by the above-described preparation method. The metal-organic framework composite material is obtained by dispersing a transition metal in the form of single atoms on a metal-organic framework material MIL-100(Fe).

[0039] The metal-organic framework composite material obtained by this invention consists of transition metals uniformly dispersed in the form of single atoms on the metal-organic framework material MIL-100(Fe). The atomic particle size is very small, so it will not easily agglomerate like nanoparticles, nor will it clog the micropores of MIL-100(Fe) like metals existing in the form of nanoparticles or ions, which would lead to a significant decrease in its specific surface area. The metal-organic framework composite material obtained by this invention enables MIL-100(Fe) to have better adsorption activity while maintaining its original large specific surface area. Only a small number of metal atoms are loaded to improve the adsorption capacity and adsorption selectivity of MIL-100(Fe) for VOCs, realizing efficient treatment of VOCs and significantly improving the utilization rate of transition metals.

[0040] The mechanism by which the metal-organic framework composite material loaded with metal single atoms of the present invention can improve the adsorption performance is as follows: the aforementioned transition metal has the structural characteristic of centrally coordinated unsaturated structure, which is conducive to π coordination with VOCs containing unsaturated coordination and double bonds, allowing them to be preferentially adsorbed on the metal surface and improving adsorption selectivity; the transition metal single atoms have small particle size and are highly dispersed on the support, resulting in strong interaction with the support, which is particularly conducive to the adsorption of VOCs with more unsaturated bonds. Metal-organic framework materials have the advantages of large specific surface area, high porosity, structural stability and surface modification, and can adsorb volatile organic compounds. However, the adsorption capacity and selectivity of pure metal-organic frameworks are usually low. Therefore, by combining metal single atoms with metal-organic framework materials, the single-atom metal is highly dispersed on the metal-organic framework, which can effectively improve the adsorption performance of the composite material with a low loading, enabling the adsorption of a large number of VOCs and improving adsorption selectivity, thus achieving efficient treatment of VOCs.

[0041] This invention also protects the application of the metal-organic framework composite material loaded with transition metal single atoms in the adsorption of volatile organic compounds.

[0042] Furthermore, the volatile organic compounds are one or more of the following: benzene compounds, aldehydes, esters, ketones, alkanes, halogenated hydrocarbons, and alkenes.

[0043] Preferably, the benzene compound is one or more of styrene, benzene, toluene, ethylbenzene, and xylene.

[0044] More preferably, the benzene compound is styrene and / or ethylbenzene.

[0045] Preferably, the aldehyde is formaldehyde and / or acetaldehyde.

[0046] Preferably, the ester is ethyl acetate and / or butyl acetate.

[0047] Preferably, the ketone is acetone and / or isobutyl ketone.

[0048] Preferably, the alkane is cyclohexane, n-hexane, or n-pentane.

[0049] Preferably, the halohydrocarbon is dichloromethane and / or trichloromethane.

[0050] Preferably, the olefin is cyclohexene, ethylene, or propylene.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] The metal-organic framework composite material loaded with single metal atoms described in this invention is prepared by first mixing the metal source used to prepare MIL-100(Fe) with a modified transition metal source to form a precursor, and then reacting it with an organic ligand. This method enables the transition metal to be uniformly dispersed on MIL-100(Fe) in the form of single atoms. With almost no reduction in the specific surface area of ​​MIL-100(Fe) itself, the adsorption capacity and selectivity of the resulting composite material for volatile organic compounds are enhanced with extremely low loading, significantly improving the utilization rate of the transition metal and providing a new reference scheme for the selective adsorption design of highly efficient VOCs. Attached Figure Description

[0053] Figure 1 This is a TEM image of Au@MIL-100(Fe) prepared in Example 1.

[0054] Figure 2 The image shows the HAADF-STEM image of Au@MIL-100(Fe) prepared in Example 1.

[0055] Figure 3 The chart shows the statistical data of the single-component adsorption performance of Au@MIL-100(Fe) prepared in Example 1 and MIL-100(Fe) prepared in Comparative Example 1 on ethylbenzene and styrene.

[0056] Figure 4 The chart shows the adsorption performance data of Au@MIL-100(Fe) prepared in Example 1 and MIL-100(Fe) prepared in Comparative Example 1 on styrene / ethylbenzene mixed gas.

[0057] Figure 5 A statistical chart showing the VOCs concentration data at the outlet of the styrene / ethylbenzene mixture prepared by Au@MIL-100(Fe) in Example 1 and MIL-100(Fe) in Comparative Example 1. Detailed Implementation

[0058] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0059] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0060] Example 1: A metal-organic framework composite material loaded with metal single atoms

[0061] A metal-organic framework composite material loaded with metal single atoms, specifically comprising the following steps:

[0062] S1. Dissolve 2.02 g of Fe(NO3)3·9H2O in 50 mL of deionized water to obtain a Fe(NO3)3·9H2O solution. Disperse 16 mg of HAuCl4·3H2O in 1.6 mL of deionized water to obtain a HAuCl4·3H2O solution. Mix the Fe(NO3)3·9H2O solution and the HAuCl4·3H2O solution to obtain an Au@Fe2O3 precursor solution. Heat the obtained Au@Fe2O3 precursor solution to 50 °C under mechanical stirring at 300 r / min, increase the stirring speed to 400 r / min, and stir vigorously for 30 min. After the mixture cools to room temperature, add 0.25 mol / L Na2CO3 solution dropwise over 30 min until the pH reaches 8. Then let it stand for 1 h with continuous stirring at 300 r / min. The Au@Fe2O3 precursor solution was centrifuged, and the precipitated material was washed with deionized water at 60°C. Finally, the washed material was dried in a vacuum drying oven at 60°C to obtain Au@Fe2O3.

[0063] S2. Mix 0.7880g H3btc, 21.75mL DMF, 0.435mL deionized water, and 34.32mL acetic acid and sonicate for 30min. Add 0.3g Au@Fe2O3 obtained in step S1, stir and mix evenly, then transfer to a 100mL polytetrafluoroethylene reactor and react at 100℃ for 24h. After the solution cools to room temperature, collect the solid product by centrifugation, wash three times with anhydrous ethanol, and dry overnight in a drying oven at 60℃. The result is Au@MIL-100(Fe) metal-organic framework composite material loaded with metal single atoms, where Au is 0.45wt% of Au@MIL-100(Fe).

[0064] Example 2: A metal-organic framework composite material loaded with metal single atoms

[0065] A metal-organic framework composite material loaded with metal single atoms, specifically comprising the following steps:

[0066] S1. Dissolve 2.02 g of Fe(NO3)3·9H2O in 50 mL of deionized water to obtain a Fe(NO3)3·9H2O solution. Disperse 8 mg of HAuCl4·3H2O in 0.8 mL of deionized water to obtain a HAuCl4·3H2O solution. Mix the Fe(NO3)3·9H2O solution and the HAuCl4·3H2O solution to obtain an Au@Fe2O3 precursor solution. Heat the obtained Au@Fe2O3 precursor solution to 50 °C under mechanical stirring at 300 r / min, increase the stirring speed to 400 r / min, and stir vigorously for 30 min. After the mixture cools to room temperature, add 0.25 mol / L Na2CO3 solution dropwise over 30 min until the pH reaches 8. Then let it stand for 1 h with continuous stirring at 300 r / min. The Au@Fe2O3 precursor solution was centrifuged, and the precipitated material was washed with deionized water at 60°C. Finally, the washed material was dried in a vacuum drying oven at 60°C to obtain Au@Fe2O3.

[0067] S2. Mix 0.7880g H3btc, 21.75mL DMF, 0.435mL deionized water, and 34.32mL acetic acid and sonicate for 30min. Add 0.3g Au@Fe2O3 obtained in step S1, stir and mix evenly, then transfer to a 100mL polytetrafluoroethylene reactor and react at 100℃ for 24h. After the solution cools to room temperature, collect the solid product by centrifugation, wash three times with anhydrous ethanol, and dry overnight in a drying oven at 60℃. The result is Au@MIL-100(Fe) metal-organic framework composite material loaded with metal single atoms, where Au is 0.3wt% of Au@MIL-100(Fe).

[0068] Example 3: A metal-organic framework composite material loaded with metal single atoms

[0069] A metal-organic framework composite material loaded with metal single atoms, specifically comprising the following steps:

[0070] S1. Dissolve 2.02 g of Fe(NO3)3·9H2O in 50 mL of deionized water to obtain a Fe(NO3)3·9H2O solution. Disperse 32 mg of HAuCl4·3H2O in 3.2 mL of deionized water to obtain a HAuCl4·3H2O solution. Mix the Fe(NO3)3·9H2O solution and the HAuCl4·3H2O solution to obtain an Au@Fe2O3 precursor solution. Heat the obtained Au@Fe2O3 precursor solution to 50 °C under mechanical stirring at 300 r / min, increase the stirring speed to 400 r / min, and stir vigorously for 30 min. After the mixture cools to room temperature, add 0.25 mol / L Na2CO3 solution dropwise over 30 min until the pH reaches 8. Then let it stand for 1 h with continuous stirring at 300 r / min. The Au@Fe2O3 precursor solution was centrifuged, and the precipitated material was washed with deionized water at 60°C. Finally, the washed material was dried in a vacuum drying oven at 60°C to obtain Au@Fe2O3.

[0071] S2. Mix 0.7880g H3btc, 21.75mL DMF, 0.435mL deionized water, and 34.32mL acetic acid and sonicate for 30min. Add 0.3g Au@Fe2O3 obtained in step S1, stir and mix evenly, then transfer to a 100mL polytetrafluoroethylene reactor and react at 100℃ for 24h. After the solution cools to room temperature, collect the solid product by centrifugation, wash three times with anhydrous ethanol, and dry overnight in a drying oven at 60℃. The result is Au@MIL-100(Fe) metal-organic framework composite material loaded with metal single atoms, where Au is 0.85wt% of Au@MIL-100(Fe).

[0072] Example 4: A metal-organic framework composite material loaded with metal single atoms

[0073] A metal-organic framework composite material loaded with metal single atoms, specifically comprising the following steps:

[0074] S1. Dissolve 2.02 g of Fe(NO3)3·9H2O in 50 mL of deionized water to obtain a Fe(NO3)3·9H2O solution. Disperse 48 mg of HAuCl4·3H2O in 4.8 mL of deionized water to obtain a HAuCl4·3H2O solution. Mix the Fe(NO3)3·9H2O solution and the HAuCl4·3H2O solution to obtain an Au@Fe2O3 precursor solution. Heat the obtained Au@Fe2O3 precursor solution to 50 °C under mechanical stirring at 300 r / min, increase the stirring speed to 400 r / min, and stir vigorously for 30 min. After the mixture cools to room temperature, add 0.25 mol / L Na2CO3 solution dropwise over 30 min until the pH reaches 8. Then let it stand for 1 h with continuous stirring at 300 r / min. The Au@Fe2O3 precursor solution was centrifuged, and the precipitated material was washed with deionized water at 60°C. Finally, the washed material was dried in a vacuum drying oven at 60°C to obtain Au@Fe2O3.

[0075] S2. Mix 0.7880g H3btc, 21.75mL DMF, 0.435mL deionized water, and 34.32mL acetic acid and sonicate for 30min. Add 0.3g Au@Fe2O3 obtained in step S1, stir and mix evenly, then transfer to a 100mL polytetrafluoroethylene reactor and react at 100℃ for 24h. After the solution cools to room temperature, collect the solid product by centrifugation, wash three times with anhydrous ethanol, and dry overnight in a drying oven at 60℃. The result is Au@MIL-100(Fe) metal-organic framework composite material loaded with metal single atoms, where Au is 0.98wt% of Au@MIL-100(Fe).

[0076] Example 5: A metal-organic framework composite material loaded with metal single atoms

[0077] A metal-organic framework composite material loaded with metal single atoms, specifically comprising the following steps:

[0078] S1. Dissolve 2.02 g of Fe(NO3)3·9H2O in 50 mL of deionized water to obtain a Fe(NO3)3·9H2O solution. Disperse 64 mg of HAuCl4·3H2O in 6.4 mL of deionized water to obtain a HAuCl4·3H2O solution. Mix the Fe(NO3)3·9H2O solution and the HAuCl4·3H2O solution to obtain an Au@Fe2O3 precursor solution. Heat the obtained Au@Fe2O3 precursor solution to 50 °C under mechanical stirring at 300 r / min, increase the stirring speed to 400 r / min, and stir vigorously for 30 min. After the mixture cools to room temperature, add 0.25 mol / L Na2CO3 solution dropwise over 30 min until the pH reaches 8. Then let it stand for 1 h with continuous stirring at 300 r / min. The Au@Fe2O3 precursor solution was centrifuged, and the precipitated material was washed with deionized water at 60°C. Finally, the washed material was dried in a vacuum drying oven at 60°C to obtain Au@Fe2O3.

[0079] S2. Mix 0.7880g H3btc, 21.75mL DMF, 0.435mL deionized water, and 34.32mL acetic acid and sonicate for 30min. Add 0.3g Au@Fe2O3 obtained in step S1, stir and mix evenly, then transfer to a 100mL polytetrafluoroethylene reactor and react at 100℃ for 24h. After the solution cools to room temperature, collect the solid product by centrifugation, wash three times with anhydrous ethanol, and dry overnight in a drying oven at 60℃. The result is Au@MIL-100(Fe) metal-organic framework composite material loaded with metal single atoms, wherein Au is 1.37%wt% of Au@MIL-100(Fe).

[0080] Preparation of Comparative Example 1 MIL-100 (Fe)

[0081] The preparation method of the metal-organic framework material MIL-100(Fe) specifically includes the following steps:

[0082] S1. Dissolve 2.02 g of Fe(NO3)3·9H2O in 50 mL of deionized water to obtain a Fe(NO3)3·9H2O solution. Heat the solution to 50 °C with mechanical stirring at 300 r / min, then increase the stirring speed to 400 r / min and stir vigorously for 30 min. After the system cools to room temperature, add 0.25 mol / L Na2CO3 solution dropwise until the pH reaches 8. Then let it stand for 1 h with continuous stirring at 300 r / min to obtain a Fe2O3 precursor solution. Centrifuge the Fe2O3 precursor solution, wash the precipitated material with deionized water at 60 °C, and finally dry the washed material in a vacuum drying oven at 60 °C to obtain Fe2O3.

[0083] S2. Mix 0.7880g H3btc, 21.75mL DMF, 0.435mL deionized water, and 34.32mL acetic acid and sonicate for 30min. Add 0.3g of Fe2O3 obtained in step S1, stir and mix evenly, then transfer to a 100mL polytetrafluoroethylene reactor and react at 100℃ for 24h. After the solution cools to room temperature, collect the solid product by centrifugation, wash three times with anhydrous ethanol, and dry overnight in a drying oven at 60℃. The result is pure material MIL-100(Fe).

[0084] Experimental Example 1: Morphology Test

[0085] The morphology of Au@MIL-100(Fe) obtained in Example 1 was measured, and the results are as follows: Figures 1-2 As shown, where Figure 1 TEM image of Au@MIL-100(Fe) Figure 2 HAADF-STEM image of Au@MIL-100(Fe). From Figure 1 As can be seen, the metal-organic frameworks synthesized by this method maintain structural stability, exhibiting an octahedral structure and good crystallinity; from Figure 1 No particles were visible. Further observation of the Au distribution using spherical aberration electron microscopy yielded the following results: Figure 2 As shown, the loaded Au is uniformly dispersed on MIL-100(Fe) in the form of single atoms (the circled white particles are gold atoms).

[0086] Experiment Example 2: Adsorption and Desorption Performance Experiment

[0087] 1. Experimental Methods

[0088] In single-component adsorption / desorption experiments, ethylbenzene (EB) and styrene (ST) were selected as typical volatile organic compounds (VOCs), and the adsorption and photothermal desorption properties of MIL-100(Fe) and Au@MIL-100(Fe) nanocomposites were investigated. Before the adsorption reaction, the adsorbent was activated under vacuum at 120℃ for 12 hours. Then, 0.05 g of adsorbent was packed into a fixed-bed cubic quartz reactor and purged with nitrogen for 4 hours at 120℃ to remove adsorbed impurities. After the adsorbent cooled to 30℃, the inlet gas of the reactor was switched to VOCs gas with a nitrogen balance of 200 ppm. The gas flow rate was controlled at 30 mL / min using a mass flow meter. The entire adsorption process was carried out in darkness, and the VOCs concentration before and after adsorption was continuously monitored using a GC-9800 gas chromatograph equipped with a flame ionization detector.

[0089] After the adsorbent reached equilibrium with VOCs adsorption, a photothermal desorption experiment was conducted. The inlet gas of the reactor was switched to nitrogen at a flow rate of 30 mL / min, and a xenon lamp (300 W) was used as the light source for the photothermal desorption experiment. The reactor was placed 10 cm directly below the light source. The concentration of VOCs released by the adsorbent was detected by gas chromatography.

[0090] In the two-component selective adsorption separation experiment of styrene, styrene and ethylbenzene were mixed at a ratio of 1:1, with a total flow rate of 30 mL / min. The activation conditions and adsorption performance tests of the adsorbent were consistent with those of the single-component method.

[0091] 2. Experimental Results

[0092] The adsorption capacities and desorption rates of Au@MIL-100(Fe) obtained in Example 1 and MIL-100(Fe) obtained in Comparative Example 1 for ethylbenzene and styrene, respectively, were obtained by the above method (Table 1). Figure 3 ) and the adsorption performance diagram of styrene / ethylbenzene mixed gas ( Figure 4 The results showed that the adsorption capacity of Au@MIL-100(Fe) obtained in Example 1 for single-component styrene and ethylbenzene, as well as the styrene / ethylbenzene mixture, was higher than that of MIL-100(Fe) in Comparative Example 1. Furthermore, the adsorbent material modified with Au atoms not only further increased the adsorption capacity for single-component styrene and ethylbenzene, but also significantly improved the desorption capacity for ethylbenzene, resulting in excellent desorption capacity for both ethylbenzene and styrene.

[0093] Furthermore, in the adsorption experiment of MIL-100(Fe) from Comparative Example 1 and the composite material Au@MIL-100(Fe) from Example 1 in an ethylene / ethylbenzene mixed gas, the concentration ratio of VOCs at the test outlet was measured. The greater the time difference between the detection of the two gases at the outlet, the better the adsorption selectivity. The results are as follows: Figure 5 As shown in Table 2, the results indicate that pure material MIL-100(Fe) was detected at 164 minutes, at which point styrene was not detected. Styrene was detected at 192 minutes, and only ethylbenzene was detected at the outlet during these 28 minutes. In contrast, the composite material Au@MIL-100(Fe) from Example 1 showed ethylbenzene detection at 330 minutes and styrene detection at 430 minutes, with only ethylbenzene detected at the outlet during these 100 minutes. These results confirm that compared to pure material MIL-100(Fe), the composite material Au@MIL-100(Fe) has a stronger adsorption capacity for ethylbenzene and styrene, and also exhibits better styrene adsorption selectivity.

[0094] Table 1. Adsorption capacity and desorption rate of the adsorbent material for single-component ethylbenzene and styrene, respectively.

[0095]

[0096] Table 2 Results of outlet detection time of ethylbenzene and styrene in styrene / ethylbenzene mixture by adsorption material

[0097]

[0098]

[0099] Experimental Example 3: Specific Surface Area Determination

[0100] 1. Experimental Methods

[0101] Specific surface area testing method: The adsorption-desorption isotherm of nitrogen was obtained at 77 K using a BELSORP-max (MicrotracBEL Corp) analyzer. The specific surface area of ​​the sample was evaluated using a multi-point BET (Brunauer-Emmett-Teller) model.

[0102] 2. Experimental Results

[0103] The results are shown in Table 3.

[0104] Table 3 Au loading and specific surface area results of the adsorbent materials

[0105] Comparative Example 1 - MIL-100(Fe) 0 1232.60 Example 1 - Au@MIL-100(Fe) 0.45 1213.50 Example 5 - Au@MIL-100(Fe) 1.37 1186.60

[0106] As shown in Table 3, the Au in Au@MIL-100(Fe) obtained in this invention is distributed as single atoms within the framework of MIL-100(Fe), which basically does not block the micropores of MIL-100(Fe) and does not cause a significant decrease in the specific surface area of ​​MIL-100(Fe). This allows Au@MIL-100(Fe) modified with Au atoms to still retain the large specific surface area of ​​the original MIL-100(Fe).

[0107] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A metal-organic framework composite material loaded with transition metal single atoms, characterized in that, The preparation process includes the following steps: S1. Mix the Fe source solution and the transition metal source solution thoroughly at 40~80 ℃, cool to room temperature, adjust the pH to 7.5~8.5, allow the reaction to be complete, and then perform post-processing to obtain the Au@Fe2O3 precursor. S2. Add the precursor obtained in step S1 and pyromellitic acid to a mixed solution composed of water, glacial acetic acid and polar organic solvent, mix thoroughly, and react completely at 80~200 °C. After post-treatment, the transition metal single atom @MIL-100(Fe) is obtained. The transition metal source is chloroauric acid; The molar ratio of Fe in the Fe source to the transition metal in the transition metal source is (30~250):1; The polar organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; In step S1, the thorough mixing at 40~80℃ means mixing the Fe source solution and the transition metal source solution, heating them to 40~80℃ under stirring conditions, and increasing the stirring speed to continue stirring. The stirring conditions are as follows: the stirring speed is 200~300 r / min, the stirring speed is increased to 400~500 r / min, and the stirring time is 20~50 min. In steps S1 and S2, the post-processing includes centrifugation, washing, and drying; In step S1, the drying is performed under vacuum at 60 °C; In step S2, the drying process involves drying at 60 °C overnight. The Fe source is selected from one or more of ferric nitrate and ferric chloride.

2. The metal-organic framework composite material with transition metal single atoms according to claim 1, characterized in that, The molar ratio of the precursor to pyromellitic acid is 1:(1~20).

3. The metal-organic framework composite material with a transition metal single atom loaded according to claim 1, characterized in that, The volume ratio of water, glacial acetic acid and polar organic solvent is 1:(10~200):(20~200).

4. The metal-organic framework composite material with transition metal single atoms according to claim 1, characterized in that, The mass-to-volume ratio of the precursor to the mixed solution is 1:(100~200)g / mL.

5. The metal-organic framework composite material with a transition metal single atom loaded according to claim 1, characterized in that, The loading of transition metals is 0.2~1.5wt%.

6. The application of the metal-organic framework composite material with transition metal single atoms as described in any one of claims 1 to 5 in the adsorption of volatile organic compounds; The volatile organic compounds are styrene and / or ethylbenzene.

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