A C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane and its preparation method

Abstract

The present application discloses a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane and a preparation method thereof. The microporous membrane comprises a PTFE microporous membrane and a ZIF-67 photocatalyst assembled on the PTFE microporous membrane. The ZIF-67 photocatalyst is prepared by a seed-mediated method, specifically, using C-ZnO as seeds, introducing the seeds into the PTFE microporous membrane, and enabling ZIF-67 to grow in-situ on the membrane surface. The average particle size of the C-ZnO is 50-100 nm. The photocatalytic PTFE microporous membrane of the present application has strong photocatalytic degradation performance, excellent self-cleaning ability, and is stable and durable, and can be reused.

Description

Technical Field

[0001] This application relates to the field of photocatalytic membranes, and particularly to a preparation method of a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane. Background Art

[0002] Photocatalytic oxidation technology is a technology that uses semiconductor materials as catalysts to convert the absorbed light energy into chemical energy, generating photo-generated electron-hole pairs with strong oxidation and reduction properties to degrade pollutants and produce small inorganic molecules such as water and carbon dioxide. Metal-organic framework materials (MOFs) are photocatalytic materials with porous frameworks, which are constructed by metal ions or ion clusters and organic ligands through coordination. Due to the high specific surface area and porosity of MOFs themselves, and the flexible adjustability of pore size and pore surface properties, they have potential application values in the fields of energy storage, adsorption separation, catalysis, etc. Zinc oxide derived from ZIF-8 has been widely used in the photocatalytic degradation of dyes and other pollutants. By doping elements such as N, C, and S in zinc oxide, the recombination rate of photo-generated electrons and holes can be effectively reduced, its response spectrum can be extended, visible light response can be achieved, and the photocatalytic degradation efficiency can be significantly improved.

[0003] The photocatalytic Fenton system (photo-Fenton) is a new technology that combines photocatalytic oxidation and Fenton reaction. Under light illumination conditions, the photo-Fenton system degrades refractory organic substances by generating hydroxyl radicals or superoxide radicals. In the prior art, photocatalysts are usually added to the photo-Fenton system in the form of powder particles. On the one hand, effective recycling cannot be achieved, increasing the sludge production in water; on the other hand, the degradation efficiency of existing photocatalysts still needs to be improved. Summary of the Invention

[0004] To solve the problems that the photocatalyst in the photo-Fenton system cannot be effectively recycled and the photocatalytic degradation efficiency is low, this application provides a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane and its preparation method.

[0005] In a first aspect, this application provides a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane. The microporous membrane includes a PTFE microporous membrane and a ZIF-67 photocatalyst assembled on the PTFE microporous membrane. The ZIF-67 photocatalyst is prepared by a seed-mediated method, specifically by using C-ZnO as a seed, introducing the seed into the PTFE microporous membrane, and enabling ZIF-67 to grow in-situ on the membrane surface; the particle size of the C-ZnO is 50 - 100 nm.

[0006] This application combines C-ZnO (carbon-doped zinc oxide) with ZIF-67 to obtain a photocatalytic PTFE microporous membrane with a ZIF-67 metal-organic framework structure on its surface. On the one hand, this microporous membrane has a light-responsive property, and a large number of hydroxyl radicals and superoxide radicals with oxidative degradation effects are generated in the system under light irradiation. On the other hand, the metal-organic framework structure on the membrane surface endows it with strong adsorption ability, which can achieve good adsorption effects on Fenton reagents and organic substances, enabling free radicals and molecular active oxygen to capture and degrade organic substances more efficiently. For conventional photocatalysts, they only have light-responsive properties and do not have adsorption ability, so the reaction degradation efficiency is relatively low.

[0007] The photocatalytic PTFE microporous membrane of this application has excellent synergistic effects with PMS in the Fenton reagent. ZIF-67 activates persulfate under light irradiation to generate molecular active oxygen (ROSs) and sulfate radicals. Among them, sulfate radicals have a relatively high redox potential and a long half-life, and the degradation efficiency is high. In addition, in the degradation system of C-ZnO / ZIF-67 with a high carbon content and a large specific surface area, both free radical and non-free radical paths coexist. Although the free radical path has a prominent degradation effect, excessive anions and too high an oxidation potential will become obstacles to the further degradation of organic substances. In the non-free radical path, the electron transfer between the valence band and the conduction band makes the conduction band have an oxidation effect, which can effectively overcome the defects of the free radical path and realize an efficient and low-consumption organic matter degradation process.

[0008] In addition, the PTFE microporous membrane used in this application has strong hydrophobicity and strong self-cleaning ability. The organic substances attached to its surface can be removed under light irradiation, so it can be effectively recycled. At the same time, the extremely inert PTFE microporous membrane as a catalyst substrate can ensure the high efficiency, stability and durability of the catalyst.

[0009] It should be noted that due to the hydrophobicity of the PTFE microporous membrane, the metal salt organic ligand solution cannot effectively wet the PTFE membrane, resulting in difficulty in the growth of ZIF-67 on the membrane surface. Therefore, this application adopts a seed-mediated method to disperse C-ZnO in the PTFE microporous membrane as the growth site of ZIF-67 to achieve uniform growth of ZIF-67 on the membrane surface. Further, the C-ZnO used in this application has a particle size in the range of 50-100 nm, and the crystal seed particle size is relatively small. After ZIF-67 grows, the obtained photocatalyst particles present a multi-core core-shell structure, that is, a ternary catalytic system with multiple (≥2) C-ZnO as the core layer and ZIF-67 as the shell layer. In this system, there are rich Z-type heterojunctions between different materials such as C-ZnO and between C-ZnO and ZIF-67, which can provide catalytic degradation effects for the non-free radical path and improve the degradation efficiency of the system.

[0010] Preferably, the method for the seeds to penetrate into the PTFE microporous membrane is to mix, gelatinize, calender, and stretch the resin mixture. The resin mixture comprises raw materials in the following parts by mass:

[0011] 200 parts of PTFE dispersion resin;

[0012] 40 - 80 parts of lubricant;

[0013] 2 - 5 parts of surfactant;

[0014] 10 - 40 parts of C-ZnO.

[0015] Preferably, the pore size of the PTFE microporous membrane is 300 - 1000 nm, the porosity is 20% - 60%, and the thickness is 100 - 700 nm.

[0016] Preferably, the surfactant is a mixture of non-ionic surfactant and anionic surfactant with a mass ratio of 1:(1 - 2).

[0017] Preferably, the mass ratio of C-ZnO to PTFE dispersion resin is 1:8 - 15.

[0018] Preferably, the lubricant is a combined mixture of at least two of naphthenic mineral oil, poly-α-olefin synthetic oil, and naphtha.

[0019] By incorporating C-ZnO into the PTFE dispersion resin and going through processes such as mixing, gelatinizing, calendering, and stretching, a PTFE microporous membrane with uniformly distributed C-ZnO can be obtained, ensuring the in-situ growth of ZIF-67. Adding lubricating oil and surfactant can promote the dispersion of C-ZnO and reduce agglomeration. On the basis of ensuring the dispersion effect and reducing the agglomeration phenomenon, the photocatalytic PTFE microporous membrane obtained when the mass ratio of C-ZnO to PTFE dispersion resin is within the range of 1:8 - 15 has a relatively prominent catalytic degradation effect. Particularly, the use of a compound of non-ionic surfactant and anionic surfactant in the mixed resin achieves a more prominent effect. The reason may be that the mixing of non-ionic and anionic surfactants can increase the exposure opportunity of C-ZnO on the membrane surface, improve the ZIF-67 loading rate, and enhance the catalytic performance.

[0020] Preferably, the preparation method of the C-ZnO is as follows:

[0021] Mix the zinc salt methanol solution and 2-methylimidazole methanol solution, stir and react, carry out suction filtration, wash three times with ethanol, and then dry under vacuum to obtain ZIF-8;

[0022] Grind the obtained ZIF-8 in a mortar, heat it to 450 - 550 °C in an air atmosphere for pyrolysis for 3 - 5 h, and then cool it down naturally to obtain the product.

[0023] Preferably, the zinc salt in the zinc salt methanol solution is selected from any one of zinc acetate and zinc nitrate hexahydrate;

[0024] Preferably, the heating rate during pyrolysis is 1-10 °C / min, that is, it is heated from room temperature to 450-550 °C at a rate of 1-10 °C / min.

[0025] Preferably, the mass ratio of the zinc salt to methanol is 1:(24-30).

[0026] ZIF-8 has a metal-organic framework and cannot be directly used as a seed crystal. Pyrolyzing ZIF-8 at high temperature gives a derivative of carbon-doped zinc oxide, which has a large specific surface area (average particle size of 50-100 nm), a high doping ratio, and shows excellent light response effect and photocatalytic performance. In addition, carbon-doped zinc oxide has a more stable structure than ZIF-8 and can withstand the high temperature during the stretching process.

[0027] It should be emphasized that when the C-ZnO of the present application intervenes in the PTFE microporous membrane, it only needs to satisfy that its average particle size is 50-100 nm, and its preparation method is not limited to the method provided above.

[0028] In a second aspect, the present application provides a method for preparing a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane, comprising the following steps:

[0029] Take PTFE dispersion resin, lubricant, surfactant and C-ZnO and mix them evenly, and obtain a gelatinized mixture through gelatinization;

[0030] Compact the gelatinized mixture, extrude and calender the blank to obtain a PTFE strip-shaped base material;

[0031] Perform longitudinal stretching and transverse stretching on the PTFE strip-shaped base material, and shape it to obtain a C-ZnO-intervened PTFE microporous membrane;

[0032] Mix the cobalt salt methanol solution and the 2-methylimidazole methanol solution evenly to obtain a cobalt salt-organic ligand mixed solution;

[0033] Immerse the C-ZnO-intervened PTFE microporous membrane in the cobalt salt-organic ligand mixed solution, stir and react, and after the reaction is completed, dry it under vacuum to obtain a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane;

[0034] Preferably, the gelatinization temperature is 60-70 °C and the gelatinization time is 20-24 h;

[0035] Preferably, the longitudinal stretching temperature is 160-240 °C and the transverse stretching temperature is 50-150 °C;

[0036] Preferably, the stirring reaction time is 18 - 20 h;

[0037] Preferably, the vacuum drying temperature is 50 - 70 °C;

[0038] Preferably, during the preparation of the gelatinized reactant, a high-speed mechanical stirrer is used with a stirring speed of 1000 - 2000 rmp; or a magnetic stirrer is used with a stirring speed of 100 - 500 rpm.

[0039] Preferably, the longitudinal stretching ratio is 1.5 - 3.5, and the transverse stretching ratio is 3 - 7.

[0040] Preferably, the cobalt salt methanol solution is a mixed solution of cobalt salt and methanol, and the mass ratio of the cobalt salt to methanol is 1:(20 - 25).

[0041] By controlling parameters such as the gelatinization temperature, stretching ratio, and raw material ratio during the preparation of the PTFE microporous membrane, the present invention obtains a microporous membrane material with a porosity within a specific range, exposes the active sites on the membrane surface, and obtains a thin film material with excellent mechanical properties, having an average breaking strength of 60 - 85 N and an average elongation at break of 50% - 65%; in addition, the original chemical stability of the PTFE substrate improves the durability of the photocatalytic material. Therefore, the present application provides a photocatalytic PTFE microporous membrane material with strong photocatalytic performance, excellent self-cleaning ability, and stability and durability.

[0042] In a third aspect, the present application provides an application of a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane, specifically forming a Fenton-like catalytic system with persulfate (PMS) as the oxidant and the C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane as the photocatalyst.

[0043] In summary, the present application has the following beneficial effects:

[0044] 1. The present application uses the seed-mediated method to obtain a C-ZnO / ZIF-67 ternary degradation system on an inert PTFE substrate. This system can cooperate with the PMS Fenton system. On the one hand, it has an efficient free radical degradation path and can achieve the degradation of organic matter through strong adsorption and light response performance; on the other hand, through the Z-scheme heterojunction formed in the ternary degradation system, it provides a good non-free radical reaction path, improves the degradation efficiency, and can make up for the defect that excessive anions and too high oxidation potential in the free radical path of the system cause degradation hindrance.

[0045] 2. After pyrolysis, the metal organic framework of ZIF-8 collapses and the particle size decreases, resulting in C-ZnO with a high specific surface area. As a seed for the growth of ZIF-67, a photocatalyst with a multi-core core-shell structure can be obtained, which is beneficial to increase the content of Z-type heterojunction in the photocatalyst and improve the degradation performance based on the non-radical pathway. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is an electron microscope image of the photocatalytic PTFE microporous membrane of Example 1 of the present application;

[0047] Figure 2 is the XRD spectrum of the photocatalytic PTFE microporous membrane of Example 1 of the present application;

[0048] Figure 3 It is a photocatalytic degradation effect diagram of dyes of the photocatalytic PTFE microporous membranes of the examples and comparative examples of the present application. DETAILED DESCRIPTION Example

[0049] The raw materials selection of the following examples:

[0050] The PTFE dispersion resin model is DuPont Teflon601A, the anionic surfactant is sodium dodecylbenzene sulfonate, and the nonionic surfactant is octadecyl polyoxyethylene ether.

[0051] Example 1

[0052] A C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane is prepared according to the following steps:

[0053] (1) Mix a solution of zinc nitrate (19.82 g) in methanol (500 ml) and a solution of 2-methylimidazole (20.54 g) in methanol (500 ml), stir and react for 24 hours, filter, wash three times with ethanol and dry in vacuum to obtain ZIF-8.

[0054] (2) The ZIF-8 obtained in step (1) was ground in a mortar, heated to 500° C. in an air atmosphere for pyrolysis for 4 h, and naturally cooled to obtain ZIF-8-derived oxide C-ZnO (average particle size of 50-100 nm).

[0055] (3) PTFE dispersion resin (2000 g), lubricant (500 g), surfactant (20 g) and C-ZnO (200 g) obtained in step (2) are fully mixed and gelatinized at 70°C for 24 h to obtain a gelatinized mixture. The lubricant is a cycloalkyl mineral oil and a polyalphaolefin synthetic oil in a mass ratio of 2:1; the surface active agent is a nonionic surfactant.

[0056] (4) The gelatinized mixture obtained in step (3) is pressed into a green sheet, and the green sheet is extruded and calendered to obtain a PTFE tape-shaped base material.

[0057] (5) The PTFE tape-shaped base material obtained in step (4) is first longitudinally stretched and then transversely stretched to obtain a C-ZnO-interposed PTFE microporous membrane; wherein the longitudinal stretching ratio is 3 and the longitudinal stretching temperature is 200°C; the transverse stretching ratio is 5 times and the transverse stretching temperature is 120°C.

[0058] (6) A solution of cobalt nitrate (23.68 g) in methanol (400 ml) is mixed with a solution of 2-methylimidazole (24.64 g) in methanol (400 ml) to obtain a cobalt salt-organic ligand mixed solution.

[0059] (7) The C-ZnO-interposed PTFE microporous membrane obtained in step (5) is fixed to the edge of the membrane with a bracket, and the membrane is horizontally supported and immersed in the cobalt salt-organic ligand mixed solution obtained in step (6), stirred for 20 hours, and vacuum dried at 60°C to obtain a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane with a pore size of 400-800 nm, a porosity of 45%, and a thickness of 300 nm.

[0060] Example 2

[0061] A C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane is prepared according to the following steps:

[0062] (1) Mix a solution of zinc nitrate (19.82 g) in methanol (500 ml) and a solution of 2-methylimidazole (20.54 g) in methanol (500 ml), stir and react for 24 hours, filter, wash three times with ethanol and dry in vacuum to obtain ZIF-8.

[0063] (2) The ZIF-8 obtained in step (1) was ground in a mortar, heated to 550° C. in an air atmosphere for pyrolysis for 3 h, and naturally cooled to obtain a ZIF-8-derived oxide C-ZnO (average particle size of 50-100 nm).

[0064] (3) PTFE dispersion resin (2000 g), lubricant (400 g), surfactant (40 g) and C-ZnO (150 g) obtained in step (2) were fully mixed and gelatinized at 60° C. for 24 h to obtain a gelatinized mixture. The lubricant was a cycloalkyl mineral oil and a polyalphaolefin synthetic oil in a mass ratio of 2:1; the surface active agent was an anionic surfactant.

[0065] (4) The gelatinized mixture obtained in step (3) is pressed into a green sheet, and the green sheet is extruded and calendered to obtain a PTFE tape-shaped base material.

[0066] (5) The PTFE strip base material obtained in step (4) is first longitudinally stretched, then transversely stretched, and shaped to obtain a C-ZnO-intervened PTFE microporous membrane; the longitudinal stretching ratio is 1.5, and the longitudinal stretching temperature is 180 °C; the transverse stretching ratio is 3, and the transverse stretching temperature is 100 °C.

[0067] (6) A cobalt salt-organic ligand mixed solution is obtained by mixing a cobalt nitrate (23.68 g) methanol (400 ml) solution with a 2-methylimidazole (24.64 g) methanol (400 ml) solution.

[0068] (7) The edge of the C-ZnO-intervened PTFE microporous membrane obtained in step (5) is fixed with a bracket, horizontally supported and immersed in the cobalt salt-organic ligand mixed solution obtained in step (6), stirred for 20 h, and vacuum dried at 50 °C to obtain a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane with a pore size of 500-1000 nm, a porosity of 30%, and a thickness of 600 nm.

[0069] Example 3

[0070] A C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane is prepared according to the following steps:

[0071] (1) A zinc nitrate (19.82 g) methanol (500 ml) solution is mixed with a 2-methylimidazole (20.54 g) methanol (500 ml) solution, stirred and reacted for 24 hours, filtered by suction, washed three times with ethanol, and then vacuum dried to obtain ZIF-8.

[0072] (2) The ZIF-8 obtained in step (1) is ground in a mortar, pyrolyzed at 480 °C for 3 h in an air atmosphere, and naturally cooled to obtain a ZIF-8-derived oxide C-ZnO (average particle size of 50-100 nm).

[0073] (3) The PTFE dispersion resin (2000 g), lubricant (700 g), surfactant (40 g) and the C-ZnO (250 g) obtained in step (2) are fully mixed, and gelatinized at 70 °C for 20 h to obtain a gelatinized mixture. Among them, the lubricant uses naphthenic mineral oil and poly-α-olefin synthetic oil with a mass ratio of 2:1; the surfactant uses a non-ionic surfactant.

[0074] (4) The gelatinized mixture obtained in step (3) is compacted, and the blank is extruded and calendered to obtain a PTFE strip base material.

[0075] (5) The PTFE strip base material obtained in step (4) is first longitudinally stretched, then transversely stretched, and shaped to obtain a C-ZnO-intervened PTFE microporous membrane; the longitudinal stretching ratio is 3, and the longitudinal stretching temperature is 180 °C; the transverse stretching ratio is 6 times, and the transverse stretching temperature is 100 °C.

[0076] (6) A cobalt salt-organic ligand mixed solution is obtained by mixing a cobalt nitrate (23.68 g) methanol (400 ml) solution with a 2-methylimidazole (24.64 g) methanol (400 ml) solution.

[0077] (7) The edge of the C-ZnO-intervened PTFE microporous membrane obtained in step (5) is fixed with a bracket, horizontally supported and immersed in the cobalt salt-organic ligand mixed solution obtained in step (6), stirred for 20 h, and vacuum dried at 50 °C to obtain a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane with a pore size of 300 - 600 nm, a porosity of 50%, and a thickness of 200 nm.

[0078] Example 4

[0079] A C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane, different from Example 1 in that the amount of C-ZnO used in step (3) is 300 g, and other conditions are the same as those in Example 1. Finally, a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane with a pore size of 400 - 800 nm, a porosity of 42%, and a thickness of 300 nm is obtained.

[0080] Example 5

[0081] A C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane, different from Example 1 in that the amount of C-ZnO used in step (3) is 100 g, and other conditions are the same as those in Example 1. Finally, a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane with a pore size of 400 - 800 nm, a porosity of 47%, and a thickness of 300 nm is obtained.

[0082] Example 6

[0083] A C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane, different from Example 1 in that the surfactant in step (3) is replaced with an equal amount of anionic surfactant instead of non-ionic surfactant. Finally, a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane with a pore size of 400 - 800 nm, a porosity of 45%, and a thickness of 300 nm is obtained.

[0084] Example 7

[0085] A C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane, which is different from Example 1 in that the surfactant in step (3) uses an anionic surfactant and a nonionic surfactant in a mass ratio of 1:1. Finally, a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane with a pore size of 400 to 800 nm, a porosity of 49%, and a thickness of 300 nm is obtained.

[0086] Comparative Example

[0087] Comparative Example 1

[0088] A ZnO / ZIF-67 photocatalytic PTFE microporous membrane, which is different from Example 1 in that ZnO with an average particle size of 50 to 100 nm is used in step (3) to replace C-ZnO with an average particle size of 50 to 100 nm. Finally, a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane with a pore size of 500 to 800 nm, a porosity of 50%, and a thickness of 300 nm is obtained.

[0089] Comparative Example 2

[0090] A C-ZnO photocatalytic PTFE microporous membrane is prepared according to the operations of steps (1) to (5) in Example 1.

[0091] Comparative Example 3

[0092] A ZIF-67 photocatalytic PTFE microporous membrane is prepared according to the following steps:

[0093] (1) PTFE dispersion resin (2000 g), lubricant (500 g), and surfactant (20 g) were fully mixed and gelatinized at 70°C for 24 h to obtain a gelatinized mixture. The lubricant was a cycloalkyl mineral oil and a polyalphaolefin synthetic oil in a mass ratio of 2:1; the surfactant was a nonionic surfactant.

[0094] (2) The gelatinized mixture obtained in step (1) is pressed into a green sheet, and the green sheet is extruded and calendered to obtain a PTFE tape-shaped base material.

[0095] (3) The PTFE tape-shaped base material obtained in step (2) is first longitudinally stretched and then transversely stretched to obtain a PTFE microporous membrane; wherein the longitudinal stretching ratio is 3 and the longitudinal stretching temperature is 200°C; the transverse stretching ratio is 5 times and the transverse stretching temperature is 120°C.

[0096] (4) A solution of cobalt nitrate (23.68 g) in methanol (400 ml) was mixed with a solution of 2-methylimidazole (24.64 g) in methanol (400 ml) to obtain a cobalt salt-organic ligand mixed solution.

[0097] (5) Fix the edge of the PTFE microporous membrane obtained in step (4) with a bracket, horizontally support and immerse it in the cobalt salt-organic ligand mixed solution obtained in step (4), stir for 20 h, and dry it under vacuum at 60 °C to obtain a ZIF-67 photocatalytic PTFE microporous membrane with a pore size of 400-900 nm, a porosity of 40%, and a thickness of 300 nm.

[0098] Performance detection test

[0099] 1. Dye degradation effect test

[0100] The photocatalytic performance of the C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane was evaluated by degrading the dye rhodamine B (Rh B). First, the C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane (10 g) was placed in the dark with a 20 mg / L dye solution (100 ml) for 10 min. After reaching the absorption-desorption equilibrium, PMS (20 mg) was added, and the solution was placed under a visible xenon lamp to trigger the photocatalytic process. The dye solution was extracted at different time points, separated by a 0.22 μm microfilter, and then the concentration of the dye was measured by ultraviolet-visible adsorption. Finally, the dye removal rate of the corresponding microporous membrane was calculated by formula (1):

[0101]

[0102] Among them, A represents the dye removal rate of the membrane; C0 represents the initial concentration of the dye; C represents the dye concentration at different times.

[0103] Table 1. Results of the dye degradation effect test

[0104]

[0105] 2. Mechanical property test of the photocatalytic PTFE microporous membrane

[0106] The tensile properties of the photocatalytic PTFE microporous membrane in the present invention were tested according to the method in "GB / T 1040.3-2006 Plastics - Determination of tensile properties". The width of the test sample was 20 mm, the length was 100 mm, the clamping distance was 50 mm, the tensile speed was 100 mm / min, and each group of samples was tested five times and the average value was taken.

[0107] Table 2. Results of the mechanical property test of the photocatalytic PTFE microporous membrane

[0108]

[0109] Analysis of test results:

[0110] (1) By combining Examples 1-7 and Comparative Examples 1-3 and referring to Table 1, it can be seen that the C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane of the present application has excellent catalytic degradation effect on organic matter in the Fenton-like system. Specifically, by analyzing Example 1 and Comparative Example 1, it can be known that when ZnO is used to replace C-ZnO as the intervention seed, the catalytic performance decreases significantly. The reason may be that for the undoped ZnO material compared with the C-ZnO / ZIF-67 ternary system material, the Z-type heterojunction is significantly reduced, the band gap is increased, and the light utilization rate is decreased, resulting in the reduction of catalytic performance.

[0111] (2) By analyzing Example 1 and Comparative Example 2, it can be known that for the PTFE membrane with in-situ grown ZIF-67 and only containing C-ZnO, the catalytic performance decreases significantly. The reason may be that in the Fenton-like system, Co 2+ has outstanding catalytic performance compared with Zn 2+ . Without the ZIF-67 layer, the catalytic performance decreases significantly, and the metal-organic framework structure has a strong adsorption effect on dyes, adsorbing first and then degrading, showing a synergistic effect. Therefore, the absence of ZIF-67 will greatly reduce the catalytic performance.

[0112] (3) By analyzing Example 1 and Comparative Example 3, it can be known that without the intervention of C-ZnO, the catalytic performance of the PTFE microporous membrane decreases by about 75%. The reason may be that the pure PTFE microporous membrane is a hydrophobic material, and the amount of ZIF-67 that can grow autonomously on the surface is extremely small, so both the adsorption and degradation performance are significantly reduced.

[0113] (4) By analyzing Example 1 and Examples 4-5, it can be known that the more C-ZnO is intervened, the worse the strength of the membrane is. About 200 g is the optimal value, with the best catalytic performance and little impact on the mechanical properties of the membrane. When the dosage is less than 200 g, the catalytic performance is poor; when the dosage is more than 200 g, it is easy to agglomerate, the increase in binding sites is not much, and the strength loss of the membrane is large.

[0114] (5) By analyzing Example 1 and Examples 6-7, it can be known that in the raw materials for preparing the PTFE membrane, the compounding of an anionic surfactant and a non-ionic surfactant can effectively improve the photocatalytic degradation efficiency. The reason may be that the mixing of non-ionic and anionic surfactants can increase the exposure opportunity of C-ZnO on the membrane surface, increase the growth sites of ZIF-67, and improve the ZIF-67 loading rate, thereby enhancing the catalytic performance.

[0115] This specific embodiment is only an explanation of the present application and does not limit the present application. After reading this specification, those skilled in the art can make modifications without creative contributions to this embodiment as needed, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane, characterized in that, It includes a PTFE microporous membrane and a ZIF-67 photocatalyst assembled on the PTFE microporous membrane. The ZIF-67 photocatalyst is prepared by a seed-mediated method, specifically, using C-ZnO as the seed, introducing the seed into the PTFE microporous membrane, and enabling the in-situ growth of ZIF-67 on the membrane surface; the average particle size of the C-ZnO is 50 - 100 nm; the method of introducing the seed into the PTFE microporous membrane is to mix, gelatinize, calender, and stretch a resin mixture, and the resin mixture includes the following raw materials in parts by mass: 200 parts of PTFE dispersion resin, 40 - 80 parts of lubricant, 2 - 5 parts of surfactant, and 10 - 40 parts of C-ZnO.

2. The C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane according to claim 1, wherein The pore size of the PTFE microporous membrane is 300 - 1000 nm, the porosity is 20% - 60%, and the thickness is 100 - 700 nm.

3. The C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane according to claim 1, wherein The surfactant is a mixture of a non-ionic surfactant and an anionic surfactant with a mass ratio of 1:(1 - 2).

4. The C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane according to claim 1, wherein The mass ratio of the C-ZnO to the PTFE dispersion resin is 1:8 - 15.

5. The C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane according to claim 1, characterized in that, The preparation method of the C-ZnO is as follows: Mix a zinc salt methanol solution and a 2-methylimidazole methanol solution, stir and react, filter by suction, wash three times with ethanol, and then dry in vacuum to obtain ZIF-8; Grind the obtained ZIF-8 with a mortar, pyrolyze it at 450 - 550 °C for 3 - 5 h in an air atmosphere, and cool it down naturally to obtain the product; The zinc salt in the zinc salt methanol solution is selected from any one of zinc acetate and zinc nitrate hexahydrate; The heating rate during pyrolysis is 1 - 10 °C / min; The mass ratio of the zinc salt to methanol is 1:(24 - 30).

6. The C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane according to claim 1, wherein The lubricant is a combined mixture of at least two of naphthenic mineral oil, polyalphaolefin synthetic oil, and naphtha.

7. The preparation method of the C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane according to any one of claims 1 to 6, characterized in that, It includes the following steps: Take PTFE dispersion resin, lubricant, surfactant, and C-ZnO, mix them evenly, and gelatinize to obtain a gelatinized mixture; Press the gelatinized mixture, extrude and calender the blank to obtain a PTFE strip-shaped base material; Stretch the PTFE strip-shaped base material longitudinally and transversely, and shape it to obtain a C-ZnO-introduced PTFE microporous membrane; Mix a cobalt salt methanol solution and a 2-methylimidazole methanol solution evenly to obtain a cobalt salt-organic ligand mixed solution; Immerse the C-ZnO-introduced PTFE microporous membrane in the cobalt salt-organic ligand mixed solution, stir and react for 18 - 20 h, and after the reaction is completed, dry it in vacuum at a temperature of 50 - 70 °C to obtain a C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane; The temperature of gelatinization is 60 - 70 °C, and the time of gelatinization is 20 - 24 h; The temperature of longitudinal stretching is 160 - 240 °C, and the temperature of transverse stretching is 50 - 150 °C.

8. The preparation method of the C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane according to claim 7, characterized in that, The longitudinal stretching ratio is 1.5 - 3.5, and the transverse stretching ratio is 3 - 7.

9. The preparation method of the C-ZnO / ZIF-67 photocatalytic PTFE microporous membrane according to claim 7, characterized in that, The cobalt salt methanol solution is a mixed solution of cobalt salt and methanol, and the mass ratio of the cobalt salt to methanol is 1:(20 - 25).

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