MOF composite nanosheet photocatalytic materials with sandwich structure, their preparation methods and applications

Abstract

This invention discloses a MOF composite nanosheet photocatalytic material with a sandwich structure, its preparation method, and its application. A ZIF-8 / Ti3C2MXene / ZIF-8-X catalyst was prepared by calcining two-dimensional conductive nanosheets with a metal-organic framework material in a tube furnace under air atmosphere, improving the material's activity and stability. This material achieved a photocatalytic bactericidal efficiency of 6.63 log₂O₃ against *E. coli* within 90 minutes under simulated sunlight. 10 CFU mL ‑1 The present invention further prepared a photocatalytic sterilization membrane based on ZIF-8 / Ti3C2MXene / ZIF-8-X and applied it to a flowing photocatalytic drinking water disinfection system. The membrane filter has the advantages of high photocatalytic sterilization efficiency, low metal ion residue, and good long-term cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials technology, specifically relating to a MOFs composite nanosheet photocatalytic material with a sandwich structure, its preparation method and application. Background Technology

[0002] With rapid societal development, effectively eliminating waterborne pathogens in drinking water is an urgent issue to reduce the prevalence of infectious diseases and eliminate harm to global health. Photocatalytic solar water purification systems are among the most effective methods for sterilizing drinking water. However, common nano-photocatalysts are limited by their surface area and catalytic sites, resulting in insufficient efficiency in adsorbing and capturing bacteria, leading to low reactive oxygen species (ROS) production and limiting their application in sterilization. Therefore, researching ultrathin two-dimensional (2D) materials with abundant catalytic sites and contact surface area to capture and kill bacteria is of great significance.

[0003] Metal-organic frameworks (MOFs) are synthesized through coordination interactions between metal ions / clusters and organic ligands, and have attracted widespread attention in fields such as photocatalytic hydrogen evolution, photocatalytic CO2 reduction, and photocatalytic sterilization. However, most MOFs (such as ZIF-8) have wide band gaps and low light utilization, resulting in less than ideal photocatalytic activity. Combining MOF photocatalysts with two-dimensional conductive nanosheets (such as Ti3C2 MXene) is an effective strategy to promote electron conduction and charge separation. This primarily improves sterilization performance by influencing the formation and accumulation pathways of reactive oxygen species (ROS) on the photocatalyst surface and the electrostatic attraction between the positively charged photocatalyst and the negatively charged bacteria.

[0004] This study prepared a series of sandwich-structured composite nanosheet materials (ZIF-8 / MXene / ZIF-8) based on ZIF-8 and Ti3C2MXene; after optimization of the nanosheet materials, a ZIF-8 / MXene / ZIF-8-300 bactericidal membrane was prepared. Escherichia coli was used as a model bacterium, and the materials were used as photocatalysts for photocatalytic sterilization experiments. Summary of the Invention

[0005] This invention provides a MOF composite nanosheet photocatalytic material with a sandwich structure, its preparation method, and its application. This invention combines two-dimensional conductive nanosheets with a metal-organic framework material, and prepares a (ZIF-8 / MXene / ZIF-8-300) catalyst through a low-temperature calcination activation strategy. Furthermore, the process parameters and raw material types are selected and optimized during the preparation process, solving the problems of low light energy utilization and low catalytic performance of traditional photocatalytic materials.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a MOF composite nanosheet photocatalytic material with a sandwich structure includes the following steps:

[0008] (1) Preparation of Ti3C2MXene

[0009] LiF was dissolved in HCl solution to obtain LiF solution; Ti3AlC2 was immersed in LiF solution, stirred, washed with ultrapure water, ultrasonically separated and centrifuged to obtain Ti3C2 MXene nanosheets;

[0010] The above preparation process can be carried out in a Teflon bottle;

[0011] HCl solution concentration 9M;

[0012] The mass-to-volume ratio of LiF to HCl solution is 0.8-1.2:15-30, g / mL; preferably 1:20, g / mL.

[0013] The mass ratio of LiF to Ti3AlC2 is 0.8-1.2:0.5-2, preferably 1:1;

[0014] Specifically, Ti3AlC2 was immersed in LiF solution and stirred at 400-600 rpm for 20-30 h at room temperature. Then, it was repeatedly centrifuged and washed with ultrapure water at 2000-4000 rpm until the pH of the supernatant was neutral. After that, it was sonicated for 2 h under nitrogen atmosphere, centrifuged at 5000-8000 rpm for 30 min, and the lower solid was collected to obtain ultrathin Ti3C2 MXene nanosheets.

[0015] (2) Preparation of ZIF-8 / MXene / ZIF-8-X

[0016] An aqueous dispersion of Ti3C2MXene nanosheets was added to a methanol solution of 2-methylimidazole, followed by a methanol solution of zinc nitrate hexahydrate. The mixture was stirred at room temperature for 1-3 hours and then post-treated to obtain ZIF-8 / MXene / ZIF-8.

[0017] The preferred concentrations are: Ti3C2MXene nanosheet aqueous dispersion 4 mg / mL, 2-methylimidazole methanol solution 0.8 M, and zinc nitrate hexahydrate methanol solution 0.8 M.

[0018] The volume ratio of the aqueous dispersion of Ti3C2MXene nanosheets, the methanol solution of 2-methylimidazole, and the methanol solution of zinc nitrate hexahydrate is 1-5:1-5:1-5, preferably 1:1:1;

[0019] The specific post-processing method is as follows: After the reaction is completed, the reaction solution is centrifuged to remove the supernatant, washed with anhydrous ethanol and ultrapure water by centrifugation respectively, and finally freeze-dried to obtain ZIF-8 / MXene / ZIF-8.

[0020] (3) Place ZIF-8 / MXene / ZIF-8 in a tube furnace and calcine it at 200-550℃ for 1-3 hours in an air atmosphere to obtain the MOFs composite nanosheet photocatalytic material with sandwich structure, denoted as: ZIF-8 / MXene / ZIF-8-X, where X represents the calcination temperature;

[0021] The preferred heating rate is 5℃ / min;

[0022] The preferred method is to calcine at 300℃ for 2 hours to obtain ZIF-8 / MXene / ZIF-8-300.

[0023] This invention relates to MOFs composite nanosheet photocatalytic materials with a sandwich structure prepared by the above-described method.

[0024] The present invention also relates to a bactericidal membrane, the preparation method of which is as follows: using a microporous filter membrane as a substrate, an aqueous dispersion of ZIF-8 / MXene / ZIF-8-X is filtered, and the membrane obtained by filtration is post-treated to obtain a bactericidal membrane;

[0025] The microporous filtration membrane is a CA-CN water-mixed fiber microporous filtration membrane with a pore size of 0.45μm;

[0026] The preferred concentration of the aqueous dispersion of ZIF-8 / MXene / ZIF-8-X is 0.05 mg / mL;

[0027] The post-processing method is as follows: the filtered membrane is vacuum dried at 40-80℃ (preferably 60℃) for 1 hour.

[0028] The MOFs composite nanosheet photocatalytic material with a sandwich structure and its bactericidal membrane described in this invention can be used for photocatalytic sterilization.

[0029] The technical principles and beneficial effects of this invention include:

[0030] This invention combines two-dimensional conductive nanosheets with metal-organic framework materials and calcines them in a tube furnace under an air atmosphere to prepare a (ZIF-8 / Ti3C2 MXene / ZIF-8-300) catalyst, which improves the activity and stability of the material.

[0031] This invention employs a low-temperature calcination activation strategy to reconstruct the crystal structure of the granular ZIF-8 layer on the surface of Ti3C2MXene, resulting in a continuous, conformal ZIF-8 ultrathin layer. This layer is anchored to the Ti3C2MXene surface via Ti-O-Zn bonds, effectively preventing ZIF-8 surface detachment. The resulting composite nanosheets exhibit an expanded light absorption range, improved photothermal conversion efficiency, and increased local photogenerated holes and singlet oxygen accumulation, further enhancing photocatalytic bactericidal activity. In other words, this strategy improves the light transmittance and thermal insulation of the ZIF-8 layer, and also benefits the electronic conductivity and photothermal conversion of MXene, further improving photocatalytic bactericidal activity, stability, and recyclability. The material of this invention exhibits a photocatalytic bactericidal efficiency of 6.63 log [missing value] against Escherichia coli within 90 minutes under simulated sunlight. 10 CFU mL -1 .

[0032] This invention further prepared a photocatalytic sterilization membrane based on ZIF-8 / MXene / ZIF-8-300 and applied it to a flowing photocatalytic drinking water disinfection system. The membrane filter has advantages such as high photocatalytic sterilization efficiency, low metal ion residue, and good long-term cycle stability. Moreover, the preparation method is simple, easy to implement, and low in cost, and can be mass-produced. Attached Figure Description

[0033] Figure 1 Scanning electron microscope images of samples 1-5 in Examples 1-5; (a) Ti3C2MXene, (b) ZIF-8 / MXene / ZIF-8, (c) ZIF-8 / MXene / ZIF-8-300, (d) ZIF-8 / MXene / ZIF-8-300 membrane before drinking water disinfection experiment, (e) ZIF-8 / MXene / ZIF-8-300 membrane after drinking water disinfection experiment.

[0034] Figure 2 XRD patterns of sample 1 (Ti3C2MXene), sample 2 (ZIF-8 / MXene / ZIF-8), and sample 3 (ZIF-8 / MXene / ZIF-8-300).

[0035] Figure 3 Comparison of sterilization effects of samples 2 and 3 under simulated sunlight and darkness for 90 minutes (left) and sterilization curve under sunlight for 90 minutes (right).

[0036] Figure 4 Photocatalytic cyclic sterilization diagrams of samples 4 and 5; (a) Schematic diagram of a flow photocatalytic system for drinking water disinfection; (b) Drinking water disinfection performance of the ZIF-8 / MXene / ZIF-8-300 membrane in a simulated cyclic photocatalytic system for three consecutive cycles. Detailed Implementation

[0037] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0038] Example 1:

[0039] Weigh 1 g of LiF and disperse it in 20 mL of HCl solution (9 M) in a Teflon bottle. After the LiF is completely dissolved in the HCl solution, slowly immerse 1 g of Ti3AlC2 into the mixed solution at room temperature. Stir at 500 rpm for 24 h and wash repeatedly with ultrapure water (3500 rpm, 5 min) until the pH of the supernatant is close to neutral. Sonicate the resulting multilayer MXene suspension under a nitrogen atmosphere for 2 h to separate the layers. Finally, collect the suspension after centrifugation at 7500 rpm for 30 min to obtain sample 1.

[0040] Example 2:

[0041] Weigh 2 mL of the aqueous dispersion of Sample 1 from Example 1 (4 mg / mL) and add it directly to 2 mL of 2-methylimidazolium methanol solution (0.8 M). Then, add 2 mL of Zn(NO3)2·6H2O methanol solution (0.8 M), stir slowly at room temperature for 2 h, centrifuge to remove the supernatant, wash with anhydrous ethanol and ultrapure water respectively, and finally freeze-dry to obtain Sample 2.

[0042] Example 3:

[0043] Sample 2 from Example 2, after drying, was further calcined in a tube furnace at 300°C in an air atmosphere at a heating rate of 5°C / min for 2 hours to obtain Sample 3.

[0044] Example 4:

[0045] A CA-CN water-mixed fiber microporous filter membrane (50 mm in diameter) with a pore size of 0.45 μm was used to vacuum filter an aqueous dispersion (0.05 mg / mL) of sample 3 from Example 3 containing 5 mg. The filtered membrane was then vacuum dried at 60 °C for 1 h to obtain sample 4.

[0046] Example 5:

[0047] Sample 4 from Example 4 was used in a flow photocatalytic drinking water disinfection system experiment for 60 minutes under simulated sunlight to obtain sample 5.

[0048] Figure 1The images are scanning electron microscope (SEM) images of samples 1-5 in Examples 1-5. Sample 1 (Ti3C2MXene) is observed to be a nanosheet structure. Sample 2 (ZIF-8 / MXene / ZIF-8) is formed by the in-situ growth of ZIF-8 nanoparticles on the surface of Ti3C2MXene, resulting in granular ZIF-8 deposition. Sample 3 (ZIF-8 / MXene / ZIF-8-300) is a smooth, continuous sandwich-structured nanosheet structure. Samples 4 and 5 (ZIF-8 / MXene / ZIF-8-300 bactericidal film before and after the drinking water disinfection experiment) show green-marked inactivated Escherichia coli, proving that the bactericidal film can effectively capture bacteria without changing its morphology.

[0049] Figure 2 The XRD patterns of samples 1, 2, and 3 show that these materials were successfully prepared.

[0050] Figure 3 The sterilization effects of samples 2 and 3 under simulated sunlight and in darkness are compared. The control experiment shows that, in the absence of synthesized samples, light alone and the addition of the photocatalyst ZIF-8 alone have little effect on the sterilization effect of *E. coli*. The ZIF-8 / MXene / ZIF-8-300 system obtained through a low-temperature calcination activation strategy exhibits the highest sterilization efficiency, with the bacterial concentration decreasing to 6.63 log₂O₅ after 90 minutes of photocatalysis. 10 CFU mL -1 .

[0051] Figure 4 Schematic diagrams of the flow photocatalytic drinking water disinfection system for samples 4 and 5, and a photocatalytic cyclic sterilization diagram. As shown in the diagrams, after the bacterial solution is introduced into the flow device, it is separated by the ZIF-8 / MXene / ZIF-8-300 membrane, and the remaining bacteria are counted using a collector. Within 30 minutes of cyclic reaction, the ZIF-8 / MXene / ZIF-8-300 sterilization membrane almost completely eliminates E. coli, and the membrane maintains excellent sterilization activity after three consecutive cycles, demonstrating long-term cyclic stability.

[0052] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. All experimental and technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a MOFs composite nanosheet photocatalytic material with a sandwich structure, characterized in that, Includes the following steps: (1) Preparation of Ti3C2 MXene LiF was dissolved in HCl solution to obtain LiF solution; Ti3AlC2 was immersed in LiF solution, stirred, washed with ultrapure water, ultrasonically separated and centrifuged to obtain Ti3C2 MXene nanosheets; (2) Preparation of ZIF-8 / MXene / ZIF-8 An aqueous dispersion of Ti3C2 MXene nanosheets was added to a methanol solution of 2-methylimidazole, followed by a methanol solution of zinc nitrate hexahydrate. The mixture was stirred at room temperature for 1-3 h, and then post-treated to obtain ZIF-8 / MXene / ZIF-8. (3) Place ZIF-8 / MXene / ZIF-8 in a tube furnace and calcine it at 300 °C for 1-3 h in an air atmosphere to obtain the MOFs composite nanosheet photocatalytic material with sandwich structure, denoted as ZIF-8 / MXene / ZIF-8-X, where X represents the calcination temperature.

2. The method for preparing the MOFs composite nanosheet photocatalytic material with a sandwich structure as described in claim 1, characterized in that, In step (1), the concentration of HCl solution is 9M, and the mass-to-volume ratio of LiF to HCl solution is 0.8-1.2:15-30, g / mL.

3. The method for preparing the MOFs composite nanosheet photocatalytic material with a sandwich structure as described in claim 1, characterized in that, In step (1), the mass ratio of LiF to Ti3AlC2 is 0.8-1.2:0.5-2.

4. The method for preparing the MOFs composite nanosheet photocatalytic material with a sandwich structure as described in claim 1, characterized in that, Step (1) Immerse Ti3AlC2 in LiF solution and stir at 400-600 rpm for 20-30 h at room temperature. Then, repeatedly centrifuge and wash with ultrapure water at 2000-4000 rpm until the pH of the supernatant is neutral. Then, sonicate the layers under nitrogen atmosphere for 2 h, centrifuge at 5000-8000 rpm for 30 min, and collect the lower solid layer to obtain ultrathin Ti3C2 MXene nanosheets.

5. The method for preparing the MOFs composite nanosheet photocatalytic material with a sandwich structure as described in claim 1, characterized in that, In step (2), the concentration of the aqueous dispersion of Ti3C2 MXene nanosheets is 4 mg / mL, the concentration of the methanol solution of 2-methylimidazole is 0.8 M, and the concentration of the methanol solution of zinc nitrate hexahydrate is 0.8 M.

6. The method for preparing the MOFs composite nanosheet photocatalytic material with a sandwich structure as described in claim 1, characterized in that, In step (2), the volume ratio of the aqueous dispersion of Ti3C2 MXene nanosheets, the methanol solution of 2-methylimidazole, and the methanol solution of zinc nitrate hexahydrate is 1-5:1-5:1-5.

7. The method for preparing the MOFs composite nanosheet photocatalytic material with a sandwich structure as described in claim 1, characterized in that, In step (3), the heating rate is 5 ℃ / min, and the calcination is carried out at 300 ℃ for 2 h.

8. The MOFs composite nanosheet photocatalytic material with a sandwich structure prepared by the preparation method according to any one of claims 1 to 7.

9. A bactericidal film, characterized in that, The preparation method is as follows: using a microporous filtration membrane as a substrate, the aqueous dispersion of ZIF-8 / MXene / ZIF-8-X is filtered, and the resulting membrane is post-treated to obtain a bactericidal membrane; The ZIF-8 / MXene / ZIF-8-X is prepared by the preparation method described in any one of claims 1 to 7.

10. The application of the MOFs composite nanosheet photocatalytic material with a sandwich structure as described in claim 8 or the bactericidal membrane as described in claim 9 in photocatalytic sterilization.

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