Preparation method and application of tannic acid-mediated LDH@PVDF membrane

Abstract

The present invention belongs to the technical field of preparation of environmental functional materials, and provides a preparation method and application of a tannic acid-mediated LDH@PVDF membrane. First, a casting solution is prepared; then the membrane is scraped and phase inversion is performed, followed by water washing; finally, the membrane is immersed in a tannic acid solution for modification to obtain a tannic acid-mediated LDH@PVDF membrane. The morphology and underwater oleophobic water properties of the tannic acid-mediated LDH@PVDF membrane are revealed by a variety of characterization methods, and the catalytic properties are discussed using methylene blue as an example. This simple preparation process of a multifunctional membrane with superior performance has great application potential in wastewater treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of environmental functional materials, and relates to a preparation method of a tannic acid-mediated LDH@PVDF membrane and application thereof. Background Art

[0002] In recent years, a variety of pollutants have been detected in water, such as antibiotics, dyes, and insoluble oils. These pollutants not only destroy the ecological balance, but also have potential hazards to human health, so it is crucial to remove these pollutants. For insoluble oil pollution, common technologies such as mesh filtration, adsorption, centrifugation, and biodegradation are often used, but there are problems such as low separation efficiency and secondary pollution. In order to overcome these difficulties, pressure-driven membrane technology (including microfiltration, nanofiltration, ultrafiltration, and reverse osmosis) came into being. It has been widely studied because of its simple operation, small footprint, high effluent quality, and sustainable water treatment. Among them, microfiltration membranes are widely used in the separation of oil-water emulsions. However, a serious problem that is overlooked in the actual separation process is that other organic pollutants cannot be effectively removed, such as antibiotics, dyes, etc. In addition, pollutants can cause membrane fouling, thereby reducing separation efficiency and flux. Membrane fouling is one of the main problems in water treatment using membrane technology.

[0003] As a natural biomass material, tannic acid (TA) is often used to prepare hydrogels for water treatment, such as oil-water separation, removal of metal ions, detection of metal ions, catalysis, etc. Therefore, hydrogels have attracted widespread attention due to their excellent surface properties such as hydrophilicity and stability. Hydrogels can also effectively adsorb metal ions, form complexes to remove metal ions, and can also reduce the loss of metal ions during the catalytic process. Therefore, it is necessary to invent a simple and effective method for preparing low-cost super-hydrophilic / underwater super-oleophobic catalytic membrane materials. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a tannic acid-mediated LDH@PVDF membrane, which utilizes the following advantages of tannic acid: (1) it has abundant phenolic hydroxyl groups and exhibits excellent hydrophilic properties; (2) a large number of hydroxyl groups promote the catalytic process; (3) it is easy to cross-link with metal ions, improve the stability of LDH, and reduce the loss of metal ions during the catalytic process. First, a casting solution is prepared; then the membrane is scraped and phase inverted, followed by water washing; finally, it is immersed in a tannic acid solution for modification to obtain a tannic acid-mediated LDH@PVDF membrane. And through a variety of characterization methods, the morphology and underwater oleophobic water properties of the tannic acid-mediated LDH@PVDF membrane are revealed, and the catalytic performance is discussed using methylene blue as an example. This simple preparation process of a multifunctional membrane with superior performance has great application potential in wastewater treatment.

[0005] The technical solution adopted by the present invention is:

[0006] The preparation method of tannic acid-mediated LDH@PVDF membrane is carried out according to the following steps:

[0007] Step 1: Prepare the casting solution:

[0008] The iron nitrate, cobalt nitrate, PVDF and polyvinyl pyrrolidone are stirred and dissolved in a solvent to prepare a film casting solution;

[0009] Step 2: Scrape the membrane, perform phase inversion, and then wash with water:

[0010] After the casting solution is cooled, remove the bubbles, use a scraper to evenly spread the casting solution on the glass plate, and quickly immerse it in NaOH and Na 2 CO 3 In the coagulation bath of the mixed solution, the generation and phase transformation of LDH are completed, and after washing with water until neutral, the LDH@PVDF membrane can be obtained;

[0011] Step 3: Immerse in tannic acid solution for modification:

[0012] The TA-mediated LDH@PVDF membrane was obtained by immersing the LDH@PVDF membrane in TA solution and washing it with water several times.

[0013] Specifically:

[0014] In step 1, the molar ratio of ferric nitrate to cobalt nitrate is 1:1;

[0015] In step 1, the usage ratio of ferric nitrate, cobalt nitrate, PVDF, polyvinyl pyrrolidone and solvent is 0.05-0.5 mol: 0.05-0.5 mol: 2.5-4.5 g: 0.1-1 g: 30 mL.

[0016] The solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone;

[0017] In step 1, the temperature for stirring and dissolving is 30-80°C, and the stirring time is 2-24h;

[0018] In step 2, the gap of the scraper is 50-320μm,

[0019] In step 2, NaOH and Na 2 CO 3 In the mixed solution, NaOH and Na 2 CO 3 The molar concentration ratio is 2:1, wherein the concentration of NaOH is 0.05-1 mol / L, and the mixture is immersed in the coagulation bath for 1-30 min;

[0020] In step 3, the concentration of the TA solution is 0.05-2wt%, and the soaking time is 1-30min.

[0021] The prepared tannic acid-mediated LDH@PVDF membrane is used for oil-water emulsion separation or degradation of pollutants in water.

[0022] Beneficial effects of the present invention:

[0023] (1) The tannic acid used in the present invention is a natural green substance with abundant sources and low price.

[0024] (2) The prepared tannic acid-mediated LDH@PVDF membrane has stable oil-water separation.

[0025] (3) The prepared tannic acid-mediated LDH@PVDF membrane has excellent properties such as degradation of pollutants in water.

[0026] (4) Given the excellent performance of the tannic acid-mediated LDH@PVDF membrane, it can be widely used in the fields of oil-water separation and wastewater treatment.

[0027] (5) The preparation method of the present invention is simple and easy to implement, has a short process, and is easy to operate and control, and is suitable for popularization and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the contact angle of TA-mediated LDH@PVDF membrane.

[0029] Figure 2 Emulsion flux (a) and separation efficiency (b) for oil-water separation.

[0030] Figure 3 The degradation effect of TA-mediated LDH@PVDF membrane on pollutants in water: (a) degradation of MB (b) degradation of TC. DETAILED DESCRIPTION

[0031] 1. The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0032] Embodiment 1:

[0033] First, 0.05mol of ferric nitrate and 0.05mol of cobalt nitrate, 2.5g of PVDF powder and 0.1g of polyvinyl pyrrolidone were dissolved in 30ml of N,N-dimethylacetamide at 30℃ and stirred for 24h; then, after the casting liquid was cooled, the bubbles were removed and the casting solution was evenly spread on the glass plate using a scraper with a gap of 50μm. Then, it was quickly immersed in 0.05mol / LNaOH and 0.025mol / L Na 2 CO 3The mixed solution was used as a coagulation bath for 10 min. After washing with water until neutral, the LDH@PVDF membrane was obtained; the LDH@PVDF membrane was immersed in a 0.2wt% TA solution for 10 min and washed with water again for several times. The TA-mediated LDH@PVDF membrane was obtained.

[0034] Figure 1 is the contact angle of TA-mediated LDH@PVDF membrane. Figure 1 a is the contact angle of water in air, which is obviously 0°; Figure 1 b is the underwater oil contact angle, which is 154.2°, which fully demonstrates that the TA-mediated LDH@PVDF membrane has the properties of superhydrophilicity and underwater superoleophobicity.

[0035] Figure 2 is the emulsion flux and separation efficiency of oil-water separation. Figure 2 a is the emulsion flux of TA-mediated LDH@PVDF membrane for oil-water separation. For different types of oil-water emulsions, the flux exceeds 500 L m -2 h -1 bar -1 ; Figure 2 b is the separation efficiency of different types of oil-water emulsions. It can be clearly seen that they are all above 95%, which fully demonstrates that the TA-mediated LDH@PVDF membrane has excellent oil-water separation performance.

[0036] Figure 3 The degradation effect of TA-mediated LDH@PVDF membrane on pollutants in water. Figure 3 a is the change of MB residual amount with time. It can be seen that MB is completely degraded in about 6 minutes; similarly, for TC, 11 minutes is the time for complete degradation of TC.

[0037] Embodiment 2:

[0038] First, 0.1mol iron nitrate and 0.1mol cobalt nitrate, 4g PVDF powder and 0.4g polyvinyl pyrrolidone were dissolved in 30ml N,N-dimethylacetamide at 80℃ and stirred for 2h; then, after the casting liquid was cooled, the bubbles were removed and the casting solution was evenly spread on the glass plate using a scraper with a gap of 320μm. Then, it was quickly immersed in 1mol / L NaOH and 0.5mol / L Na 2 CO 3 The mixed solution was used as a coagulation bath for 5 minutes. After washing with water until neutral, the LDH@PVDF membrane was obtained; the LDH@PVDF membrane was immersed in a 0.2wt% TA solution for 30 minutes and washed with water again for several times. The TA-mediated LDH@PVDF membrane was obtained.

[0039] Embodiment 3:

[0040] First, 0.5 mol of ferric nitrate and 0.5 mol of cobalt nitrate, 3 g of PVDF powder and 0.1 g of polyvinyl pyrrolidone were dissolved in 30 ml of N,N-dimethylformamide at 80 °C under a magnetic field and stirred for 2 h. Then, after the casting liquid was cooled, the bubbles were removed and the casting solution was evenly spread on the glass plate using a scraper with a gap of 200 μm. The casting solution was quickly immersed in 0.05 mol / L NaOH and 0.025 mol / L Na 2 CO 3 The mixed solution was used as a coagulation bath for 30 minutes. After washing with water until neutral, the LDH@PVDF membrane was obtained; the LDH@PVDF membrane was immersed in a 2wt% TA solution for 1 minute and washed with water again for several times. The TA-mediated LDH@PVDF membrane was obtained.

[0041] Embodiment 4:

[0042] First, 0.2 mol of ferric nitrate and 0.2 mol of cobalt nitrate, 4.5 g of PVDF powder and 1 g of polyvinyl pyrrolidone were dissolved in 30 ml of N-methylpyrrolidone at 70 °C and stirred for 5 h. Then, after the casting liquid was cooled, the bubbles were removed and the casting solution was evenly spread on the glass plate using a scraper with a gap of 200 μm. The casting solution was quickly immersed in 0.05 mol / L NaOH and 0.025 mol / L Na 2 CO 3 The mixed solution was used as a coagulation bath for 30 minutes. After washing with water until neutral, the LDH@PVDF membrane was obtained; the LDH@PVDF membrane was immersed in a 0.05wt% TA solution for 30 minutes and washed with water again for several times. The TA-mediated LDH@PVDF membrane was obtained.

[0043] 2. The present invention is further described below in conjunction with performance tests:

[0044] (1) Oil-water separation performance

[0045] First, an emulsion of hexane, petroleum ether, toluene, soybean oil, etc. with a volume content of 0.5-5% was prepared by stirring and ultrasonication; dead-end filtration or cross-flow filtration was performed at a pressure of 0.01-0.1MPa to explore the oil-water separation performance test. The separation efficiency was calculated by ultraviolet absorption spectroscopy. The flux was calculated by the following formula:

[0046]

[0047] J is the flux (L·m-2h-1Bar-1), and V is the volume of filtrate within a certain time (T, h) at a certain pressure (P, Bar).

[0048] (2) Degradation performance

[0049] Taking dye methylene blue (MB) and antibiotic tetracycline (TC) as examples, the degradation performance of TA-mediated LDH@PVDF membrane was explored. First, a certain concentration of MB and TC aqueous solution was prepared; then an oxidant solution such as potassium persulfate, potassium hydrogen sulfate, potassium persulfate, etc. was prepared; finally, the TA-mediated LDH@PVDF membrane was immersed in the above pollutant and oxidant mixed solution to conduct a degradation experiment.

Claims

1. A method for preparing a tannic acid-mediated LDH@PVDF membrane, characterized in that: Follow the steps below: Step 1: Prepare the casting solution: The iron nitrate, cobalt nitrate, PVDF and polyvinyl pyrrolidone are stirred and dissolved in a solvent to prepare a film casting solution; Step 2: Scrape the membrane, perform phase inversion, and then wash with water: After the casting liquid is cooled, the bubbles are removed, and the casting solution is evenly spread on the glass plate with a scraper, and then quickly immersed in a coagulation bath of a mixed solution of NaOH and Na2CO3 to complete the generation and phase transformation of LDH. After washing with water until neutral, the LDH@PVDF membrane can be obtained; Among them, in the mixed solution of NaOH and Na2CO3, the molar concentration ratio of NaOH and Na2CO3 is 2:

1. The concentration of NaOH is 0.05-1 mol / L, and the mixture is immersed in the coagulation bath for 1-30 min; Step 3: Immerse in tannic acid solution for modification: The TA-mediated LDH@PVDF membrane was obtained by immersing the LDH@PVDF membrane in TA solution and washing it with water several times.

2. The method for preparing tannic acid-mediated LDH@PVDF membrane according to claim 1, characterized in that: In step 1, the molar ratio of ferric nitrate to cobalt nitrate is 1:1; the dosage ratio of ferric nitrate, cobalt nitrate, PVDF, polyvinyl pyrrolidone and solvent is 0.05-0.5 mol: 0.05-0.5 mol: 2.5-4.5 g: 0.1-1 g: 30 mL.

3. The method for preparing tannic acid-mediated LDH@PVDF membrane according to claim 1, characterized in that: In step 1, the solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

4. The method for preparing tannic acid-mediated LDH@PVDF membrane according to claim 1, characterized in that: In step 1, the temperature for stirring and dissolving is 30-80° C., and the stirring time is 2-24 h.

5. The method for preparing tannic acid-mediated LDH@PVDF membrane according to claim 1, characterized in that: In step 2, the gap of the scraper is 50-320 μm.

6. The method for preparing tannic acid-mediated LDH@PVDF membrane according to claim 1, characterized in that: In step 3, the concentration of the TA solution is 0.05-2wt%, and the soaking time is 1-30min.

7. Use of the tannic acid-mediated LDH@PVDF membrane prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The prepared tannic acid-mediated LDH@PVDF membrane is used for oil-water emulsion separation or degradation of pollutants in water.

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