[0024] A preparation method of a polyvinylidene fluoride modified composite membrane, comprising the steps of:
[0025] a) Graphene oxide (GO) was prepared by an improved Hummer's chemical method;
[0026] b) Preparation of aminated graphene oxide (NGO): performing amination modification on the graphene oxide obtained in step a) to obtain aminated graphene oxide;
[0027] c) Preparation of amino-functionalized graphene oxide/zinc oxide (NGO-ZnO) composite photocatalyst; dissolving the aminated graphene oxide obtained in step b) in absolute ethanol, ultrasonically dispersing, adding zinc acetate dihydrate, and heating to dihydrate After the zinc acetate is completely dissolved, add the ethanol solution of potassium hydroxide, then place it in the reaction kettle for reaction, wash and dry to obtain the NGO-ZnO composite photocatalyst;
[0028] d) Preparation of polyvinylidene fluoride modified composite membrane (PVDF/NGO-ZnO), as follows:
[0029] d1) After ultrasonically dispersing the NGO-ZnO composite photocatalyst obtained in step c) in a polyethylene glycol (PEG) dimethylformamide solution (DMF), add PVDF, and under constant temperature conditions, stir until the PVDF is completely dissolved and then stand still Degassing until no bubbles are produced to obtain the casting solution;
[0030] d2) Add the casting liquid onto a dry glass plate dropwise, scrape the film, and quickly immerse the obtained film in a pure water coagulation bath. After the film is formed, wash it with pure water to obtain a PVDF/NGO-ZnO composite film.
[0031] When zinc oxide (ZnO) is used as an n-type semiconductor oxide in the process of photocatalytic degradation of pollutants, there are the following problems: (1) post-treatment for catalyst removal is required; (2) agglomerates are easily formed in the solution, reducing the effective surface area ; (3) It is difficult to realize the complete recovery of the catalyst; (4) The photogenerated electrons and holes recombine in a short time. As an excellent carrier and electron transport material, nitrogen-doped graphene (NGO) has a large surface area and excellent electrical conductivity and mechanical properties. NGO modified ZnO can effectively inhibit the recombination of photogenerated electrons. Compared with zinc oxide itself As a photocatalyst, the photocatalytic performance is improved, but there is still the problem that the photocatalyst is not easy to recycle.
[0032] As a membrane material, polyvinylidene fluoride (PVDF) is widely used in the treatment of organic pollutants due to its good chemical stability, high mechanical strength, and excellent anti-aging performance. PVDF reprocessing process is required.
[0033] Therefore, the embodiment of the present invention combines PVDF as a carrier with an NGO-ZnO composite photocatalyst, and proposes a method for preparing a PVDF/NGO-ZnO composite film. The NGO-ZnO composite photocatalyst is loaded on a PVDF carrier to form a composite film with The composite membrane with high catalytic degradation performance can not only effectively solve the problem of catalyst recovery, but also degrade the organic matter that pollutes PVDF, realize the self-cleaning function of the composite membrane, and at the same time have a good catalytic degradation effect.
[0034] Further, in step c), the concentration of aminated graphene oxide in absolute ethanol is 0.1-15 mg/ml; the concentration of zinc acetate dihydrate is 0.1-15 mg/ml; the concentration of aminated graphene oxide and zinc acetate dihydrate The mass ratio is 1:1-1:100.
[0035] Further, in step c), the reaction temperature in the reactor is 80-150°C, and the reaction time is 3-12h.
[0036] Further, in step c), the ethanol solution of potassium hydroxide is prepared by ultrasonically dissolving 0.5-3 g of potassium hydroxide in 1-10 ml of absolute ethanol.
[0037] In one embodiment of the present invention, in step d1), the amount of amino-functionalized graphene oxide/zinc oxide composite photocatalyst accounts for 0.1-1wt% of the dimethylformamide solution; specifically, it can be 0.1wt%, 0.2wt%, 0.4 wt%, 0.5wt%, 0.8wt%, 1wt%. Within this range, with the increase in the amount of NGO-ZnO composite photocatalyst, the catalytic degradation ability of the composite film gradually increases, but if the amount of NGO-ZnO composite photocatalyst is too much, it will cause photocatalyst aggregation, reduce the light utilization rate, and affect the catalytic performance. Degradation performance, while the catalyst is not easy to recycle. Preferably, the amount of the NGO-ZnO composite photocatalyst accounts for 0.5 wt% of the dimethylformamide solution. The catalytic effect of the composite membrane at this ratio is the best.
[0038] Further, in step d1), the amount of PVDF accounted for dimethylformamide solution can be 2-20wt%; preferably, the amount of PVDF accounted for dimethylformamide solution 16-20wt%, specifically can be 16wt%, 18wt% %, 20wt%. Excessive use of PVDF will reduce the self-cleaning performance of the composite membrane.
[0039] Further, in step d1), the mass ratio of NGO-ZnO composite photocatalyst to PVDF is 1:1-40. Preferably, the mass ratio of NGO-ZnO composite photocatalyst to PVDF is 1:20-32. The appropriate ratio of NGO-ZnO composite photocatalyst to PVDF is beneficial to the uniform loading of the composite photocatalyst on PVDF, thereby improving the catalytic performance.
[0040] Further, in step d1), the constant temperature is 20-80°C; preferably, the constant temperature is 55-65°C; more preferably, the constant temperature is 60°C. This temperature range is conducive to better dissolution of PVDF, which is beneficial to the loading of NGO-ZnO photocatalyst.
[0041] Further, in step d1), the concentration of polyethylene glycol can be 2-8wt%; specifically, it can be 2wt%, 4wt%, 6wt%, 8wt%, etc.
[0042] Further, in step d1), the standing time for defoaming can be 1-24h. Specifically, it can be 10h, 12h, 15h, etc., for example, the standing defoaming time is 12h. Stand for defoaming until no bubbles are produced in the casting solution.
[0043] Further, in step d2), the temperature of the coagulation bath may be 10-60°C. Specifically, it may be 20°C, 25°C, or 30°C. For example, the temperature of the coagulation bath may be 25°C. The temperature of the coagulation bath has an important influence on the forming effect of the composite membrane. Too low or too high temperature is not conducive to the forming of the composite membrane.
[0044] Further, in step d2), the film scraping rod used in the scraping film may have a thickness of 100-300 μm; specifically, it may be 100 μm, 200 μm, 300 μm, etc.
[0045] In a preferred embodiment of the present invention, the amount of the amino-functionalized graphene oxide/zinc oxide composite photocatalyst accounts for 0.5 wt% of the dimethylformamide solution, and the amount of PVDF accounts for 16-20 wt% of the dimethylformamide solution.
[0046] In one embodiment of the present invention, step a) utilizes improved Hummer's chemical method to prepare graphene oxide (GO), specifically can be:
[0047] Add 5-20g of pretreated graphite powder and 1-10g of sodium nitrate into a reactor containing 100-500ml of concentrated sulfuric acid, stir in an ice-water bath for 0.5-5h, then slowly add 10-50g of potassium permanganate and continue stirring 1-5h; then raise the temperature of the reaction system to 10-50°C, continue the reaction for 1-5h, slowly add 100-500ml of deionized water, raise the temperature of the reaction system to 50-150°C and stir for 5-30min; then add to the system Slowly add 200-1000ml of deionized water, stir for 1-10min, then add 10-50ml of 30wt% hydrogen peroxide to terminate the reaction, the color of the solution changes from black to bright yellow, continue to stir for 10-30min, then pickle the product, Washed with water to pH ≈ 7, suction filtered and freeze-dried to obtain graphene oxide (GO), ready for use.
[0048] In an embodiment of the present invention, step b) prepares aminated graphene oxide (NGO), which may specifically be:
[0049] Weigh 30-50 mg of GO obtained in step a) and disperse it in a beaker containing N,N methyl-formamide (DMF), cool the GO solution to 0 °C, and then add 3-8 mmol 1-( 3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and 3-8 mmol N-hydroxysuccinimide (NHS). After the mixture was activated at 0° C. for 0.5-5 h, 6-15 mmol of diethylenetriamine was added to the solution and stirred overnight at room temperature. The product was centrifuged, washed three times with acetone and water respectively, and freeze-dried to obtain aminated graphene oxide (NGO), which was ready for use.
[0050] In one embodiment of the present invention, step c) prepares amino-functionalized graphene oxide/zinc oxide composite photocatalyst (NGO-ZnO), which may specifically be:
[0051] Weigh 0.5-3g of potassium hydroxide (KOH) and ultrasonically dissolve it in 1-10ml of absolute ethanol for use. Dissolve 1-100mg of the aminated graphene oxide (NGO) obtained in step b) in 10-100mL of absolute ethanol, disperse it ultrasonically, and add 10-500mg of zinc acetate dihydrate to the solution, and raise the temperature in an oil bath to 50 -100°C, after the zinc acetate dihydrate is completely dissolved, quickly add 1-3ml of KOH ethanol solution and let it react for 3-10min, then transfer the above liquid to a tetrafluoroethylene-lined reactor and raise the temperature to 80-150°C and Keep for 3-12h. Finally, wash with deionized water three times, wash with absolute ethanol once, and dry at 25-80°C. This is also reported in related literature (Dongdong Zhang, Yiping Zhao, et al. "Fabrication and characterization of amino-grafted graphene oxide modified ZnO with high photocatalytic activity." Applied Surface Science 458(2018):638–647.).
