A mesoporous conductive ZnO / ZIF-8 composite material and its preparation method and application

Abstract

The present invention discloses a mesoporous conductive ZnO / ZIF-8 composite material and its preparation method and application. The preparation method comprises the following steps: dissolving an amphiphilic block copolymer in an organic solvent and stirring to obtain solution A; dissolving 2-methylimidazole in deionized water and stirring to obtain a homogeneous solution B; dissolving a zinc-containing metal salt in deionized water and stirring to obtain a homogeneous solution C; mixing solution A with solution B and stirring to obtain a homogeneous solution D; then mixing solution C with solution D to obtain a homogeneous solution E, and continuously stirring; centrifuging the stirred solution E, washing product F with methanol, and stirring and soaking product F in an organic solvent to obtain product G; partially oxidizing the surface of product G in an air environment. The present invention also discloses the composite material and its application in nitrogen dioxide gas sensors, photocatalysis, and photoelectric detection. The material obtained by the present invention has a high specific surface area, controllable pore size, high crystallinity, and uniform crystallization.

Description

Technical Field

[0001] The invention relates to a composite material and a preparation method and application thereof, in particular to a mesoporous conductive ZnO / ZIF-8 composite material and a preparation method and application thereof. Background Art

[0002] With the further development of science, technology, the economy, and society, the demand for high-performance sensors is increasing. Gas sensors, in particular, show strong promise in health monitoring, the Internet of Things, smart homes, and smart city development, and have garnered close attention from researchers. Mesoporous materials, due to their advantages such as high porosity and high specific surface area, are widely used in gas sensing, adsorption separation, catalysis, and other fields. Metal-organic frameworks (MOFs) hold broad application prospects in catalysis and sensing due to their highly ordered pore structure, ultra-high specific surface area, rigid structure with sufficient mechanical strength, and chemical modifiability.

[0003] However, most MOFs materials have poor inherent electrical conductivity, which greatly limits their application. On the other hand, MOFs materials have a microporous structure with a pore size of less than 2 nm, which is not conducive to the large-scale diffusion of external molecules (such as gases) participating in the reaction within the MOFs material, thereby affecting the contact between the reaction molecules and more active sites within the MOFs material, limiting the further improvement of the performance of MOFs materials.

[0004] ZIF-8 is a common low-conductivity MOFs material. Composite ZIF-8 with conductive materials is an effective method to improve the conductivity of ZIF-8. However, it has the disadvantages of phase separation, insufficient interface composite, and complex mass transfer paths caused by polycrystalline structure, which cannot effectively improve the conductivity and performance of MOFs. Summary of the Invention

[0005] Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing a mesoporous conductive ZnO / ZIF-8 composite material with readily available raw materials and simple operation. Another purpose of the present invention is to provide a mesoporous conductive ZnO / ZIF-8 composite material with high specific surface area, controllable pore size, high crystallinity, uniform crystallization, and high carrier mobility. A further purpose of the present invention is to provide an application of a mesoporous conductive ZnO / ZIF-8 composite material in nitrogen dioxide gas sensors, photocatalysis, and photoelectric detection.

[0006] Technical solution: The method for preparing a mesoporous conductive ZnO / ZIF-8 composite material according to the present invention comprises the following steps:

[0007] Step 1: dissolving the amphiphilic block copolymer in an organic solvent and stirring uniformly to obtain a solution A; dissolving 2-methylimidazole in deionized water and stirring uniformly to obtain a homogeneous solution B; dissolving a zinc-containing metal salt in deionized water and stirring uniformly to obtain a homogeneous solution C;

[0008] Step 2: Mix solution A and solution B, stir to obtain a homogeneous solution D, then mix solution C and solution D to obtain a homogeneous solution E, and continue stirring;

[0009] Step 3, centrifuging the stirred solution E, washing the product F with methanol, and stirring and soaking the product F in an organic solvent to obtain product G;

[0010] Step 4: Partially oxidize the surface of product G in an air environment to obtain a mesoporous conductive ZnO-based composite material.

[0011] Furthermore, in step 1, the amphiphilic block copolymer is one or more of polystyrene-polyethylene oxide (PS-b-PEO), polyethylene oxide-polymethyl methacrylate (PEO-b-PMMA), and polystyrene-poly-4-vinylpyridine (PS-b-P4VP). The hydrophilic segment of the amphiphilic block copolymer has a molecular weight of 1,000 to 9,000 g / mol, and the hydrophobic segment has a molecular weight of 1,000 to 40,000 g / mol.

[0012] Furthermore, the organic solvent is one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), dimethyl sulfoxide (DMSO), pyridine, and tetrahydrofuran (THF).

[0013] Furthermore, the zinc-containing metal salt is one or more of zinc nitrate, zinc chloride, zinc acetate, and zinc sulfate.

[0014] Furthermore, the concentration ratio of the amphiphilic block copolymer, 2-methylimidazole, and zinc-containing metal salt is 0.5-20:1:0.2-5.

[0015] Furthermore, in step 2, the stirring speed is 20-600 rpm, and the stirring time is 6-12 h.

[0016] Furthermore, in step three, the temperature for stirring and soaking is 20-60° C., and the stirring and soaking time is 20 min-24 h.

[0017] Furthermore, in step 4, the surface is partially oxidized by heating the temperature to 260-450°C at a heating rate of 2-10°C / min and keeping the temperature for 1-6 hours.

[0018] The mesoporous conductive ZnO / ZIF-8 composite material obtained by the preparation method of the mesoporous conductive ZnO / ZIF-8 composite material of the present invention is a rhombic dodecahedron with an average pore diameter of 10-50 nm.

[0019] The invention relates to the application of a mesoporous conductive ZnO / ZIF-8 composite material in nitrogen dioxide gas sensors, photocatalysis, and photoelectric detection.

[0020] Preparation principle: Since direct synthesis of mesoporous ZIF-8 materials is very difficult, the present invention uses amphiphilic block copolymers as templates, zinc salts as zinc sources, and 2-methylimidazole as organic ligands. The hydrophobic segments of the amphiphilic block copolymers aggregate in the solvent to form spherical micelles with the hydrophobic segments as cores and the hydrophilic segments as shells. The organic ligands are adsorbed to the hydrophilic segments of the amphiphilic block copolymers through electrostatic attraction. After adding zinc salt solution, zinc and organic ligands grow around the micelles through coordination to form a ZIF-8 / template complex. The template is removed by stirring and soaking to obtain a mesoporous conductive ZnO / ZIF-8 composite material.

[0021] The surface partial oxidation process of mesoporous ZIF-8 in air environment can make the residual sp 2 The template for hybridizing carbon-carbon double bonds generates an amorphous carbon skeleton to maintain the mesoporous structure during oxidation. Further oxidation removes excess carbon, yielding a pure mesoporous conductive ZnO / ZIF-8 composite. This invention provides a new method for preparing MOFs with both a highly open structure and excellent conductivity, expanding the application range of MOFs.

[0022] Because block copolymer molecular weight and oxidation temperature significantly influence the pore size and crystallinity of mesoporous ZIF-8 materials, respectively, this method, combined with appropriate block copolymer molecular weight and oxidation temperature control, yields mesoporous ZIF-8 materials with pore sizes ranging from 10 to 50 nm and high crystallinity. By varying the lengths of the hydrophobic and hydrophilic segments of the amphiphilic block copolymer, mesoporous conductive ZnO / ZIF-8 composites with varying pore sizes and specific surface areas can be synthesized. By controlling the lengths of the hydrophobic and hydrophilic segments of the amphiphilic block copolymer and the ratio of zinc metal salt to organic ligand, ZIF-8 with varying pore order and size can be synthesized. By controlling the rotational speed, the mesoporous ZIF-8 can be synthesized; by controlling the stirring temperature and soaking time of the organic solvent, the mesoporous ZIF-8 can be synthesized. By controlling the heating rate, oxidation temperature, and holding time, mesoporous conductive ZnO / ZIF-8 composites with varying compositions, structures, and crystallinities can be synthesized. Advantageous Effects: Compared with existing technologies, this invention exhibits the following significant advantages:

[0023] 1. The resulting mesoporous ZIF-8 material has the characteristics of high specific surface area, controllable pore size, high crystallinity, uniform crystallinity and high carrier mobility, and has great application prospects in photocatalysis, photoelectric detection, gas sensing and other aspects;

[0024] 2. It solves the conductivity problem of MOFs with poor conductivity and the problem of insufficient performance utilization caused by the inherent microporous structure of MOFs;

[0025] 3. The two-step method for synthesizing mesoporous conductive ZnO / ZIF-8 composite materials has readily available raw materials, simple preparation method, easy to repeat, and suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a SEM image of the mesoporous ZIF-8 material prepared in Example 1 of the present invention;

[0027] Figure 2 is a SEM image of the mesoporous conductive ZnO / ZIF-8 composite material prepared in Example 1 of the present invention;

[0028] Figure 3 is an XRD pattern of the mesoporous conductive ZnO / ZIF-8 composite material prepared in Example 1 of the present invention;

[0029] Figure 4 2 are NO2 gas sensing performance graphs of different materials, wherein (a) is a response-recovery curve graph of the mesoporous conductive ZnO / ZIF-8 composite material obtained in Example 1 to 10 ppm NO2, (b) is a response-recovery curve graph of the non-mesoporous conductive ZIF-8 material obtained in Comparative Example 1 to 10 ppm NO2, (c) is a response-recovery curve graph of the mesoporous ZIF-8 material obtained in Comparative Example 2 to 10 ppm NO2, and (d) is a response graph of the mesoporous conductive ZnO / ZIF-8 composite material obtained in Example 1 to different types of gases;

[0030] Figure 5 This is the SEM image of the product obtained in Comparative Example 3;

[0031] Figure 6 This is the SEM image of the product obtained in Comparative Example 4;

[0032] Figure 7 This is the SEM image of the product obtained in Comparative Example 6. DETAILED DESCRIPTION

[0033] Unless otherwise specified, the materials, reagents, and instruments used in the following examples are commercially available. Experimental methods not specified in the examples were generally performed under conventional conditions or according to the manufacturer's recommendations. Zinc nitrate, 2-methylimidazole, and tetrahydrofuran (THF) were purchased from Aladdin Reagents (Shanghai) Co., Ltd. The amphiphilic block copolymer polystyrene-polyethylene oxide (PS-b-PEO) was purchased from Polymer Source.

[0034] Example 1

[0035] A method for preparing a mesoporous conductive ZnO / ZIF-8 composite material comprises the following steps:

[0036] (1) Dissolve 10 mg of polystyrene-polyethylene oxide (PS-b-PEO) in 0.2 mL of tetrahydrofuran (THF) and stir to obtain a transparent solution A. The molecular weight of the hydrophilic segment of polystyrene-polyethylene oxide (PS-b-PEO) is 2150 g / mol, and the molecular weight of the hydrophobic segment is 6300 g / mol. Dissolve 19.7 mg of 2-methylimidazole in 2 mL of deionized water and stir to obtain a homogeneous solution B. Dissolve 100 mg of zinc nitrate in 2 mL of deionized water and stir to obtain a homogeneous solution C.

[0037] (2) Solution A and solution B were mixed and stirred at 500 rpm for 1 h to obtain a homogeneous solution D.

[0038] (3) While stirring, mix solution C with solution D to obtain a homogeneous solution E, and continue stirring at the original speed for 12 h.

[0039] (4) The stirred solution E was centrifuged, and the product F (ZIF-8 / template composite material) was washed three times with methanol. The product F was stirred and soaked in tetrahydrofuran (THF) at 50 °C for 1 h to obtain product G (mesoporous ZIF-8).

[0040] (5) The surface of product G was partially oxidized in an air environment, that is, the temperature was raised to 300 °C at a heating rate of 5 °C / min and kept at this temperature for 1 h to obtain a mesoporous conductive ZnO-based composite material.

[0041] The mesoporous ZIF-8 material prepared in this example was analyzed by scanning electron microscopy. Figure 1 As shown. Figure 1 It can be seen that the ZIF-8 material prepared in this example has a rhombic dodecahedron structure, and the polyhedrons are distributed with a mesoporous structure, with uniform pore size and an average pore size of about 10 nm.

[0042] The mesoporous conductive ZnO / ZIF-8 composite material prepared in this example was analyzed by scanning electron microscopy. Figure 2 As shown. Figure 2 It can be seen that the mesoporous conductive ZnO / ZIF-8 composite material prepared in this example basically completely retains the rhombic dodecahedron structure and mesoporous structure of the mesoporous ZIF-8 material, indicating that oxidation does not destroy the structure of the original mesoporous MOFs material.

[0043] The mesoporous conductive ZnO / ZIF-8 composite material prepared in this example was subjected to XRD analysis. Figure 3 As shown. Figure 3 It can be seen that the mesoporous conductive ZnO / ZIF-8 composite material prepared in this example mainly shows the characteristic peak of ZIF-8, while the characteristic peak of ZnO is very weak, indicating that a mesoporous conductive ZnO / ZIF-8 composite material with a high degree of crystallinity is obtained.

[0044] Example 2

[0045] A method for preparing a mesoporous conductive ZnO / ZIF-8 composite material comprises the following steps:

[0046] (1) Dissolve 10 mg of amphiphilic block copolymer polyethylene oxide-polymethyl methacrylate (PEO-b-PMMA) in 0.2 mL of N,N-dimethylformamide (DMF) and stir to obtain a transparent solution A. The molecular weight of the hydrophilic segment of polyethylene oxide-polymethyl methacrylate (PEO-b-PMMA) is 1000 g / mol, and the molecular weight of the hydrophobic segment is 1000 g / mol. Dissolve 19.7 mg of 2-methylimidazole in 0.5 mL of deionized water and stir to obtain a homogeneous solution B. Dissolve 10 mg of zinc chloride in 0.5 mL of deionized water and stir to obtain a homogeneous solution C.

[0047] (2) Solution A and solution B were mixed and stirred at 20 rpm for 1 h to obtain a homogeneous solution D.

[0048] (3) While stirring, mix solution C with solution D to obtain a homogeneous solution E, and continue stirring at the original speed for 6 h.

[0049] (4) The stirred solution E was centrifuged, and the product F (ZIF-8 / template composite material) was washed three times with methanol. The product F was stirred and soaked in N,N-dimethylformamide (DMF) at 20 °C for 20 min to obtain product G (mesoporous ZIF-8).

[0050] (5) The surface of product G was partially oxidized in an air environment, that is, the temperature was raised to 260°C at a heating rate of 2°C / min and kept at this temperature for 6 h to obtain a mesoporous conductive ZnO-based composite material with a pore size of about 10 nm.

[0051] Example 3

[0052] A method for preparing a mesoporous conductive ZnO / ZIF-8 composite material comprises the following steps:

[0053] (1) Dissolve 10 mg of the amphiphilic block copolymer polystyrene-poly-4-vinylpyridine (PS-b-P4VP) in 0.2 mL of dimethyl sulfoxide (DMSO) and stir to obtain a transparent solution A. The molecular weight of the hydrophilic segment of polystyrene-poly-4-vinylpyridine (PS-b-P4VP) is 9000 g / mol, and the molecular weight of the hydrophobic segment is 40000 g / mol. Dissolve 19.7 mg of 2-methylimidazole in 5 mL of deionized water and stir to obtain a homogeneous solution B. Dissolve 150 mg of zinc acetate in 5 mL of deionized water and stir to obtain a homogeneous solution C.

[0054] (2) Solution A and solution B were mixed and stirred at 600 rpm for 1 h to obtain a homogeneous solution D.

[0055] (3) While stirring, mix solution C with solution D to obtain a homogeneous solution E, and continue stirring at the original speed for 10 h.

[0056] (4) The stirred solution E was centrifuged, and the product F (ZIF-8 / template composite material) was washed three times with methanol. The product F was stirred and soaked in dimethyl sulfoxide (DMSO) at 60 °C for 24 h to obtain product G (mesoporous ZIF-8).

[0057] (5) The surface of product G was partially oxidized in an air environment, that is, the temperature was raised to 450°C at a heating rate of 10°C / min and kept at this temperature for 2 h to obtain a mesoporous conductive ZnO-based composite material with a pore size of about 50 nm.

[0058] Example 4

[0059] A method for preparing a mesoporous conductive ZnO / ZIF-8 composite material comprises the following steps:

[0060] (1) Dissolve 10 mg of amphiphilic block copolymer polystyrene-polyethylene oxide (PS-b-PEO) in 0.2 mL of pyridine and stir to obtain a transparent solution A. The molecular weight of the hydrophilic segment of polystyrene-polyethylene oxide (PS-b-PEO) is 5000 g / mol, and the molecular weight of the hydrophobic segment is 240000 g / mol. Dissolve 19.7 mg of 2-methylimidazole in 2 mL of deionized water and stir to obtain a homogeneous solution B. Dissolve 80 mg of zinc sulfate in 2 mL of deionized water and stir to obtain a homogeneous solution C.

[0061] (2) Solution A and solution B were mixed and stirred at 450 rpm for 1 h to obtain a homogeneous solution D.

[0062] (3) While stirring, solution C and solution D were mixed to obtain a homogeneous solution E, and stirring was continued at the original speed for 8 h.

[0063] (4) The stirred solution E was centrifuged, and the product F (ZIF-8 / template composite material) was washed three times with methanol. The product F was stirred and soaked in pyridine at 30 °C for 12 h to obtain product G (mesoporous ZIF-8).

[0064] (5) The surface of product G was partially oxidized in an air environment, that is, the temperature was raised to 300 °C at a heating rate of 6 °C / min and kept at this temperature for 4 h to obtain a mesoporous conductive ZnO-based composite material with a pore size of about 30 nm.

[0065] Example 5

[0066] A method for preparing a mesoporous conductive ZnO / ZIF-8 composite material comprises the following steps:

[0067] (1) Dissolve 10 mg of amphiphilic block copolymer polyethylene oxide-polymethyl methacrylate (PEO-b-PMMA) in 0.2 mL of N,N-dimethylacetamide (DMA) and stir to obtain a transparent solution A. The molecular weight of the hydrophilic segment of polyethylene oxide-polymethyl methacrylate (PEO-b-PMMA) is 3000 g / mol, and the molecular weight of the hydrophobic segment is 30000 g / mol. Dissolve 19.7 mg of 2-methylimidazole in 3 mL of deionized water and stir to obtain a homogeneous solution B. Dissolve 90 mg of zinc chloride in 3 mL of deionized water and stir to obtain a homogeneous solution C.

[0068] (2) Solution A and solution B were mixed and stirred at 550 rpm for 1 h to obtain a homogeneous solution D.

[0069] (3) While stirring, solution C and solution D were mixed to obtain a homogeneous solution E, and stirring was continued at the original speed for 9 h.

[0070] (4) The stirred solution E was centrifuged, and the product F (ZIF-8 / template composite material) was washed three times with methanol. The product F was stirred and soaked in N,N-dimethylacetamide (DMA) at 40 °C for 6 h to obtain product G (mesoporous ZIF-8).

[0071] (5) The surface of product G was partially oxidized in an air environment, that is, the temperature was raised to 400 °C at a heating rate of 8 °C / min and kept at this temperature for 3 h to obtain a mesoporous conductive ZnO-based composite material with a pore size of about 20 nm.

[0072] Comparative Example 1

[0073] A method for preparing a non-mesoporous conductive ZIF-8 material comprises the following steps:

[0074] (1) Dissolve 2-methylimidazole in 2 mL of deionized water and stir to obtain a homogeneous solution A; dissolve zinc nitrate in 2 mL of deionized water and stir to obtain a homogeneous solution B.

[0075] (2) Solution A and solution B were mixed to obtain solution C, and the mixture was stirred for 12 h.

[0076] (3) The stirred solution C was centrifuged to obtain the non-mesoporous ZIF-8 material (D), and the product D was then washed three times with methanol.

[0077] (4) The surface of product D was partially oxidized in an air environment and kept at a certain temperature for 1 h to obtain a non-mesoporous conductive ZIF-8 material.

[0078] Comparative Example 2

[0079] A method for preparing a mesoporous ZIF-8 material comprises the following steps:

[0080] (1) The amphiphilic block copolymer polystyrene-polyethylene oxide (PS-b-PEO) was dissolved in 0.2 mL of tetrahydrofuran (THF) and stirred with a magnetic stirrer to obtain a transparent solution A. 2-Methylimidazole was dissolved in 2 mL of deionized water and stirred to obtain a homogeneous solution B. Zinc nitrate was dissolved in 2 mL of deionized water and stirred to obtain a homogeneous solution C.

[0081] (2) Solution A and solution B were mixed and stirred for 1 h to obtain solution D.

[0082] (3) While stirring, solution C and solution D were mixed to obtain solution E and the stirring was continued at the original speed for 12 h;

[0083] (4) The stirred solution E was centrifuged to obtain a ZIF-8 / template composite material (F), which was then washed three times with methanol and stirred and soaked in tetrahydrofuran (THF) to obtain mesoporous ZIF-8.

[0084] Application comparison

[0085] The materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 were used to manufacture semiconductor gas sensors, and their comprehensive gas sensing performance was tested. Specifically, the gas sensing material was placed on a Pt electrode and placed in a 1.8 L test chamber. The Xiaoyu Electronics M2.0 gas-sensitive testing instrument automatically recorded the real-time changes in the resistance of the gas sensing material. At the beginning of the test, a syringe was used to inject dry NO2 gas of several concentrations (2 ppm, 4 ppm, 6 ppm, 8 ppm, 10 ppm), and the resistance began to change. When the resistance stabilized, the lid was opened, the gas sensing material was exposed to the air, and the resistance returned to its initial value. In this test, the sensitivity (responsivity) of the gas sensing material is defined as S = (R a -R g ) / R a , where R a and R g are the resistance values ​​of the gas sensing material in air and test gas respectively. The results are as follows Figure 4 shown.

[0086] Figure 4 These are test graphs of the NO2 gas sensing performance of the materials prepared in Example 1, Comparative Example 1, and Comparative Example 2, wherein (a) is a response-recovery curve of the mesoporous conductive ZnO / ZIF-8 composite material obtained in Example 1 to 10 ppm NO2, (b) is a response-recovery curve of the non-mesoporous conductive ZIF-8 material obtained in Comparative Example 1 to 10 ppm NO2, (c) is a response-recovery curve of the mesoporous ZIF-8 material obtained in Comparative Example 2 to 10 ppm NO2, and (d) is a response graph of the mesoporous conductive ZnO / ZIF-8 composite material obtained in Example 1 to different types of gases (nitrogen dioxide (10 ppm), hydrogen (500 ppm), methanol (50 ppm), ethanol (50 ppm), acetone (20 ppm), formaldehyde (20 ppm), ammonia (20 ppm), benzene (20 ppm), styrene (20 ppm), and hydrogen sulfide (20 ppm)).

[0087] Depend on Figure 4(a)–(c) It can be seen that compared with the non-mesoporous conductive ZIF–8 material and mesoporous ZIF–8 material prepared in Comparative Examples 1 and 2, the mesoporous conductive ZnO / ZIF–8 composite material prepared in Example 1 has a better response to 10 ppm NO2. Although the mesoporous ZIF–8 has an increased specific surface area, it does not show a response to the gas due to its poor electrical conductivity. This indicates that this method successfully improves the electrical properties of the ZIF–8 material, which is conducive to expanding its application range.

[0088] Depend on Figure 4 (d) It can be seen that the sensitivity of the mesoporous conductive ZnO / ZIF-8 composite material sensor prepared in Example 1 to 10 ppm NO2 is much higher than that of other gases, especially methanol and ethanol, indicating that the sensor has extremely high selectivity for NO2.

[0089] Comparative Example 3

[0090] This comparative example aims to explore the effects of the lengths of the hydrophobic and hydrophilic segments of the amphiphilic block copolymers and the ratio of zinc-containing metal salts to organic ligands on the pore order and size of the synthesized materials.

[0091] The remaining steps of this comparative example are the same as those of Example 1, with the only difference being that the molecular weight of the hydrophilic segment of polystyrene-polyethylene oxide (PS-b-PEO) is replaced with 500 g / mol and 10,000 g / mol, and the molecular weight of the hydrophobic segment is replaced with 500 g / mol and 50,000 g / mol, respectively. Figure 5 The results showed that when the molecular weight of the block copolymer was too small, ZIF-8 had no obvious mesoporous structure; when the molecular weight of the block copolymer was too large, disordered pores or even no pores were generated on the surface of ZIF-8.

[0092] Comparative Example 4

[0093] This comparative example aims to explore the effect of stirring speed on the pore structure of the synthesized material.

[0094] The remaining steps of this comparative example are the same as those of Example 1, except that the stirring speed is changed to 300 rpm and 700 rpm respectively. Figure 6 The results showed that: on the one hand, low rotation speed can make MOFs grow uniformly, and on the other hand, it can also ensure the interaction between the template and the MOFs precursor, so that ZIF-8 can grow along the periphery of the template, thus forming a mesoporous structure; when the rotation speed is high, the template and the MOFs precursor cannot effectively interact with each other, resulting in phase separation of MOFs and the template, and thus ZIF-8 with a mesoporous morphology cannot be synthesized.

[0095] Comparative Example 5

[0096] This comparative example aims to explore the effects of stirring immersion temperature and time on the pore structure of the synthetic material.

[0097] The remaining steps of this comparative example were the same as those of Example 1, with the only difference being that the stirring and immersion in step (4) was replaced by stirring and immersing at 70°C for 10 min and at 10°C for 30 h. SEM characterization revealed that when the immersion temperature and immersion time were short, the template in the ZIF-8 mesopores could not be effectively removed, resulting in a less distinct mesoporous structure. When the immersion temperature and immersion time were too long, the mesoporous structure was destroyed by the action of solvent molecules.

[0098] Comparative Example 6

[0099] This comparative example aims to explore the effects of heating rate, oxidation temperature and holding time on the pore structure of the synthetic material.

[0100] The remaining steps of this comparative example are the same as those of Example 1, except that step (5) is replaced by ① heating to 500°C at a heating rate of 1°C / min and holding for 0.5h; ② heating to 200°C at a heating rate of 12°C / min and holding for 8h. Figure 7 The results showed that when the temperature is too high or the holding time is too long, ZIF-8 will be completely oxidized into ZnO, the original structure will be destroyed under the action of high temperature, and agglomeration will occur; when the holding time is too short, a sufficient ZnO conductive layer cannot be produced on the surface of ZIF-8, thereby failing to effectively improve the conductivity of ZIF-8.

Claims

1. A method for preparing a mesoporous conductive ZnO / ZIF-8 composite material, characterized by: The following steps are involved: Step 1, dissolving the amphiphilic block copolymer in an organic solvent and stirring uniformly to obtain a solution A; Dissolve 2-methylimidazole in deionized water and stir evenly to obtain a homogeneous solution B; dissolve a zinc-containing metal salt in deionized water and stir evenly to obtain a homogeneous solution C; Step 2: Mix solution A and solution B, stir to obtain a homogeneous solution D, then mix solution C and solution D to obtain a homogeneous solution E, and continue stirring; Step 3, centrifuging the stirred solution E, washing the product F with methanol, and stirring and soaking the product F in an organic solvent to obtain product G; Step 4: partially oxidizing the surface of the product G in an air environment to obtain a mesoporous conductive ZnO-based composite material; In the step 1, the amphiphilic block copolymer is one or more of polystyrene-polyethylene oxide, polyethylene oxide-polymethyl methacrylate, and polystyrene-poly-4-vinylpyridine; the molecular weight of the hydrophilic segment of the amphiphilic block copolymer is 1000-9000 g / mol, and the molecular weight of the hydrophobic segment is 1000-40000 g / mol; the concentration ratio of the amphiphilic block copolymer, 2-methylimidazole, and zinc-containing metal salt is 0.5-20:1:0.2-5; In the step 2, the stirring speed is 20-600 rpm and the stirring time is 1-12 h; In step 3, the stirring and soaking temperature is 20-60°C, and the stirring and soaking time is 20 min-24 h; In the step 4, the surface is partially oxidized by heating the temperature to 260-450°C at a heating rate of 2-10°C / min and keeping the temperature for 1-6 hours.

2. The method for preparing a mesoporous conductive ZnO / ZIF-8 composite material according to claim 1, wherein: The organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, pyridine, and tetrahydrofuran.

3. The method for preparing a mesoporous conductive ZnO / ZIF-8 composite material according to claim 1, wherein: In the step 1, the zinc-containing metal salt is one or more of zinc nitrate, zinc chloride, zinc acetate, and zinc sulfate.

4. The mesoporous conductive ZnO / ZIF-8 composite material obtained by the preparation method of the mesoporous conductive ZnO / ZIF-8 composite material according to any one of claims 1 to 3, characterized in that: The mesoporous conductive ZnO / ZIF-8 composite material is a rhombic dodecahedron with an average pore diameter of 10-50 nm.

5. Use of the mesoporous conductive ZnO / ZIF-8 composite material according to claim 4 in nitrogen dioxide gas sensors, photocatalysis, and photoelectric detection.

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