A hybrid composite membrane and its preparation method

Abstract

The present invention belongs to the technical field of membrane separation, and particularly relates to a hybrid composite membrane and a preparation method thereof. In the present invention, modified graphene powder and modified hydrotalcite powder are used as inorganic particles and added to the hybrid composite membrane, so that the nano-inorganic particles are uniformly hybridized into the polyvinylidene fluoride base film, and the prepared hybrid composite membrane has a high water flux; the modification of graphene oxide powder and the addition of piperazine can increase the hydrophilicity of the hybrid composite membrane, thereby increasing the hydrophilic sites on the surface of the hybrid composite membrane, improving the anti-fouling ability of the hybrid membrane layer, effectively reducing the flux attenuation of the hybrid composite membrane, and prolonging the service life of the hybrid composite membrane.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and particularly relates to a hybrid composite membrane and a preparation method thereof. Background Art

[0002] Membrane technology has a very broad application prospect in the field of water treatment. It has the characteristics of low cost, small floor area, good treatment effect and little environmental pollution, and can effectively solve problems such as resources and the environment.

[0003] Solvent-resistant nanofiltration is based on nanofiltration. By screening the membrane-making materials, the prepared nanofiltration membrane can be applied in high-temperature and strongly polar solutions. However, the large-scale application process of solvent-resistant nanofiltration is still less. The main problem is that the current solvent-resistant nanofiltration membrane flux is still relatively low, and it is difficult to maintain a stable permeation flux and selectivity in strongly polar organic solvents for a long time. Developing a solvent-resistant nanofiltration membrane with high flux and high solvent resistance is a research hotspot.

[0004] Polyvinylidene fluoride has high water separation efficiency and strong toughness. It has good chemical stability, heat resistance and mechanical stability. It can be dissolved in some strongly polar organic solvents at a lower temperature and is easy to form a membrane by the phase inversion method. However, the surface energy of the polyvinylidene fluoride membrane is extremely low, with strong hydrophobicity, and it is easy to adsorb grease and block the membrane pores, resulting in a lower water flux after film formation, serious adsorption of pollutants when separating sewage, rapid flux decay, and a shorter membrane life. Therefore, an improved method for increasing the flux and life of polyvinylidene fluoride is needed.

[0005] The patent application document with the publication number CN103657446A discloses a polyvinylidene fluoride hollow fiber membrane, which is prepared from polyvinylidene fluoride, sodium dodecyl sulfate, ethylene glycol monostearate, silicon dioxide, dimethyl sulfoxide, polyvinylpyrrolidone, triethyl phosphate, calcium carbonate, sodium dodecylbenzenesulfonate, polyethylene glycol, dimethylacetamide, sodium dodecylaminopropionate, deionized water, polyvinyl alcohol, methylcellulose, dimethylformamide, cetyltrimethylammonium bromide, fatty amine polyoxyethylene ether, and polyethylene oxide. This polyvinylidene fluoride hollow fiber membrane has relatively high compressive and tensile strength, relatively high flux and flexibility, but it does not solve the technical problem of short life caused by polyvinylidene fluoride adsorbing pollutants.

[0006] The patent application document with the publication number CN117563428A discloses a preparation method of a high-pressure-resistant and high-flux polyvinylidene fluoride nanofiltration membrane. A polyvinylidene fluoride composite nanofiltration membrane is prepared by a phase inversion method, an in-situ growth method, and interfacial polymerization. The hydrophilic property of the polyvinylidene fluoride membrane is improved by adding hydrophilic inorganic nanoparticles. A layer of iron hydroxide nanoparticles is prepared by in-situ growth on the surface of the blend membrane to enhance the stability and permeation performance of the nanofiltration separation layer obtained by subsequent interfacial polymerization. However, this polyvinylidene fluoride nanofiltration membrane does not increase the flux of the polyvinylidene fluoride nanofiltration membrane. Summary of the Invention

[0007] In order to solve the technical problems such as the fast flux decay and short lifespan of polyvinylidene fluoride nanofiltration membranes in related technologies, the object of the present invention is to provide a hybrid composite membrane and a preparation method thereof.

[0008] In order to achieve the above object, the technical solution of the present invention is as follows:

[0009] A preparation method of a hybrid composite membrane, comprising the following steps:

[0010] S1: Mix polyvinylidene fluoride powder, nanoparticles, and N,N-dimethylformamide, and perform ultrasonic dispersion to obtain a dispersion;

[0011] S2: Add piperazine and polyethylene glycol to the dispersion obtained in step S1, stir, heat, and then stand for defoaming to obtain a casting solution;

[0012] S3: Pour the casting solution obtained in step S2 onto a glass plate, scrape it into a film with a doctor blade, and then immerse it in a pure water coagulation bath for phase inversion to obtain a hybrid composite membrane;

[0013] The nanoparticles are composed of modified graphene oxide powder and modified hydrotalcite powder in a mass ratio of 7-11:3-5.

[0014] In the present invention, modified graphene oxide powder and modified hydrotalcite powder are used as inorganic particles and added to the hybrid composite membrane, so that the nano-inorganic particles are uniformly hybridized into the polyvinylidene fluoride base film, making the obtained hybrid composite membrane have a high water flux and improving the service life of the hybrid composite membrane. Piperazine is incorporated into the casting solution to increase the hydrophilicity of the hybrid composite membrane, making the surface of the obtained hybrid composite membrane rich in the aqueous monomer piperazine. The hybrid composite membrane is prepared by in-situ polymerization, which not only solves the problem of poor surface wettability of the polyvinylidene fluoride membrane, slows down the flux decay of the polyvinylidene fluoride membrane, but also improves the stability of the hybrid composite membrane.

[0015] Further, the preparation method of the modified graphene oxide powder is as follows: Graphene oxide is mixed evenly with deionized water, then tartaric acid and bromoacetic acid are added, followed by ultrasonic treatment, centrifugal separation. The precipitate at the lower layer is taken, washed with deionized water until neutral, dried, and ground to obtain the modified graphene oxide powder.

[0016] Graphene oxide has a two-dimensional layered structure and is rich in oxygen-containing functional groups in its structure. It has excellent dispersibility, good chemical stability, and a high specific surface area in water or most polar solvents, and can effectively increase the flux of the hybrid composite membrane. However, it cannot solve the flux decay of the hybrid composite membrane. In the present invention, graphene oxide is modified in tartaric acid and bromoacetic acid, so that the number of oxygen-containing functional groups rich in graphene oxide increases, thereby increasing the hydrophilic sites on the surface of the hybrid composite membrane, improving the anti-fouling ability of the hybrid membrane layer, effectively reducing the flux decay of the hybrid composite membrane, and increasing the lifespan of the hybrid composite membrane.

[0017] Furthermore, in the preparation method of the modified graphene, the mass ratio of the graphene oxide, tartaric acid, and bromoacetic acid is 1:13 - 15:6 - 9; the frequency of the ultrasonic treatment is 200 - 300 kHz, and the ultrasonic time is 3.5 - 4 h; the drying temperature is 55 - 60 °C.

[0018] Further, the preparation method of the modified hydrotalcite powder is as follows: (1) Bamboo powder is placed in a tube furnace, heated, pyrolyzed, cooled and sieved. The powder passed through a 400-mesh sieve is soaked in a mixed solution of nitric acid solution and sulfuric acid solution, taken out, washed with deionized water until neutral, dried, and ground to obtain carbon powder; (2) The carbon powder, hydrotalcite powder, cobalt nitrate solution, and nickel nitrate solution prepared in step (1) are mixed, heated, stirred, and ammonia water is added dropwise to adjust the pH value to 10 - 11, cooled, centrifugally separated, and the precipitate at the lower layer is vacuum dried and ground to obtain the modified hydrotalcite powder.

[0019] Hydrotalcite has a layered structure, a large specific surface area, and high reaction activity. Adding it to the hybrid composite membrane can increase the flux of the hybrid composite membrane. However, it is prone to aggregation during the reaction process, reducing the active sites. Research has found that modifying hydrotalcite with oxidized biochar can effectively improve the dispersibility of hydrotalcite, obtain a larger interlayer spacing through the bound water between the metal hydroxide layers, and further increase the flux of the hybrid composite membrane.

[0020] Further, in step (1) of the preparation method of the modified hydrotalcite powder, the temperature for heating up is 800 - 900 °C, the heating rate is 5 - 10 °C / min, and the pyrolysis time is 4 - 4.5 h; in the mixed solution of the nitric acid solution and the sulfuric acid solution, the volume ratio of the nitric acid solution to the sulfuric acid solution is 1:1, the volume fraction of the nitric acid solution is 65% - 70%, and the volume fraction of the sulfuric acid solution is 70% - 75%; the soaking time is 1 - 2 h, the drying temperature is 60 - 65 °C, and the drying time is 24 - 28 h; it is ground until the particle size of the powder is 600 - 800 nm.

[0021] Further, in step (2) of the preparation method of the modified hydrotalcite powder, the mixed mass ratio of the carbon powder, hydrotalcite powder, cobalt nitrate solution and nickel nitrate solution is 2 - 5:7 - 11:18 - 22:20 - 23, and the concentrations of the cobalt nitrate solution and the nickel nitrate solution are 0.5 - 0.7 mol / L; the temperature for heating up is 70 - 75 °C, and the stirring time is 45 - 60 min; the mass fraction of the ammonia water is 25% - 30%; the vacuum drying temperature is 80 - 85 °C, and the vacuum drying time is 24 - 28 h.

[0022] Further, in step S1 of the preparation method of the hybrid composite membrane, the mixed mass ratio of the polyvinylidene fluoride powder, nanoparticles and N,N - dimethylformamide is 8 - 12:3 - 6:19 - 23.

[0023] Further, in step S1 of the preparation method of the hybrid composite membrane, the ultrasonic frequency for ultrasonic dispersion is 200 - 300 kHz, and the ultrasonic dispersion time is 4.5 - 5 h.

[0024] Further, in step S2 of the preparation method of the hybrid composite membrane, the mass parts of each component are: 30 - 35 parts of the dispersion liquid, 10 - 14 parts of piperazine, and 8 - 12 parts of polyethylene glycol; the polyethylene glycol is polyethylene glycol 1000.

[0025] Further, in step S2 of the preparation method of the hybrid composite membrane, the stirring time is 3.5 - 4 h, the heating temperature is 90 - 100 °C, and the static defoaming time is 2.5 - 3 h.

[0026] Further, in step S3 of the preparation method of the hybrid composite membrane, the blade thickness is 300 μm, the phase inversion time is 48 - 52 h, and pure water is changed every 6 h.

[0027] The present invention also provides a hybrid composite membrane prepared by using the above - mentioned preparation method of the hybrid composite membrane.

[0028] Compared with the prior art, the hybrid composite membrane and its preparation method provided by the present invention have the following technical advantages:

[0029] (1) In the present invention, modified graphene oxide powder and modified hydrotalcite powder are added to polyvinylidene fluoride, and a hybrid composite membrane is prepared by an in-situ polymerization method, which has a high water flux.

[0030] (2) In the present invention, by modifying graphene oxide and incorporating piperazine into the casting solution, the prepared hybrid composite membrane has good anti-fouling ability, can effectively slow down the flux decay caused by the adsorption of pollutants, and has a long service life.

[0031] (3) The raw materials of the hybrid composite membrane provided by the present invention are easily available, and the preparation process is simple, which is conducive to realizing industrial production. Detailed implementation manners

[0032] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. The specific embodiments described are only part of the embodiments of the present invention, rather than a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present invention.

[0033] Example 1

[0034] A preparation method of a hybrid composite membrane includes the following steps:

[0035] S1: Mix polyvinylidene fluoride powder, nanoparticles and N,N-dimethylformamide according to a mass ratio of 11:5:21, and ultrasonically disperse for 4.8 h at 280 kHz to obtain a dispersion; the nanoparticles are composed of modified graphene oxide powder and modified hydrotalcite powder according to a mass ratio of 9:4.

[0036] S2: Take 33 parts of the dispersion prepared in step S1, add 12 parts of piperazine and 10 parts of polyethylene glycol 1000, stir for 3.8 h, heat to 95 °C and then stand for defoaming for 2.8 h to obtain a casting solution.

[0037] S3: Set the blade thickness to 300 μm, pour the casting solution prepared in step S2 onto a clean glass plate, and stay in the air for 20 s, then immerse the glass plate in a pure water coagulation bath and soak for 50 h for phase inversion, and change the pure water every 6 h to obtain a hybrid composite membrane.

[0038] The preparation method of the modified graphene oxide powder is as follows: Mix 1 part of graphene oxide with 20 parts of deionized water evenly, then add 14 parts of tartaric acid and 8 parts of bromoacetic acid, ultrasonically disperse at 250 kHz for 3.8 h, centrifuge and separate, take the lower layer precipitate, wash it with deionized water until neutral, dry it at 58 °C, and grind it to a particle size of 750 nm to obtain the modified graphene oxide powder.

[0039] The preparation method of the modified hydrotalcite powder is as follows: (1) Place bamboo powder in a tube furnace, heat it to 850 °C at a rate of 8 °C / min, pyrolyze for 4.2 h, cool and screen. Put the powder passing through a 400-mesh sieve into a mixed solution of nitric acid solution (volume fraction 68%) and sulfuric acid solution (volume fraction 73%) with a volume ratio of 1:1, soak for 1.5 h, take it out, wash it with deionized water until neutral, dry at 63 °C for 26 h, and grind to obtain carbon powder; (2) Mix the carbon powder, hydrotalcite powder, cobalt nitrate solution (0.6 mol / L), and nickel nitrate solution (0.6 mol / L) prepared in step (1) according to a mass ratio of 4:9:20:21, heat up to 73 °C, stir for 50 min, add ammonia water (mass fraction 28%) to adjust the pH value to 11, cool, centrifuge, take the lower layer precipitate, vacuum dry at 83 °C for 27 h, and grind to a particle size of 700 nm to obtain the modified hydrotalcite powder.

[0040] Example 2

[0041] A preparation method of a hybrid composite membrane includes the following steps:

[0042] S1: Mix polyvinylidene fluoride powder, nanoparticles, and N,N-dimethylformamide according to a mass ratio of 8:3:19, and ultrasonically disperse for 5 h at 200 kHz to obtain a dispersion; the nanoparticles are composed of modified graphene oxide powder and modified hydrotalcite powder according to a mass ratio of 7:3;

[0043] S2: Take 30 parts of the dispersion prepared in step S1, add 10 parts of piperazine and 8 parts of polyethylene glycol 1000, stir for 3.5 h, heat to 90 °C, and then stand for 3 h to remove bubbles to obtain a casting solution;

[0044] S3: Set the blade thickness to 300 μm, pour the casting solution prepared in step S2 onto a clean glass plate, and stay in the air for 20 s, then immerse the glass plate in a pure water coagulation bath and soak for 48 h for phase inversion, changing the pure water every 6 h to obtain a hybrid composite membrane.

[0045] The preparation method of the modified graphene oxide powder is as follows: Mix 1 part of graphene oxide with 20 parts of deionized water evenly, then add 13 parts of tartaric acid and 6 parts of bromoacetic acid, ultrasonically treat at 200 kHz for 4 h, centrifuge, take the lower layer precipitate, wash it with deionized water until neutral, dry at 55 °C, and grind to a particle size of 700 nm to obtain the modified graphene oxide powder.

[0046] The preparation method of the modified hydrotalcite powder is as follows: (1) Place bamboo powder in a tube furnace, heat it to 800 °C at a rate of 5 °C / min, pyrolyze for 4.5 h, cool and screen. Put the powder passing through a 400-mesh sieve into a mixed solution of nitric acid solution (volume fraction of 65%) and sulfuric acid solution (volume fraction of 70%) with a volume ratio of 1:1, soak for 1 h, take it out, wash it with deionized water until neutral, dry it at 60 °C for 28 h, and grind to obtain carbon powder; (2) Mix the carbon powder, hydrotalcite powder, cobalt nitrate solution (0.5 mol / L), and nickel nitrate solution (0.7 mol / L) prepared in step (1) according to a mass ratio of 2:7:18:20, heat it to 70 °C, stir for 45 min, add ammonia water (mass fraction of 25%) to adjust the pH value to 10, cool, centrifuge and separate, take the lower layer precipitate, vacuum dry it at 80 °C for 28 h, and grind it to a particle size of 600 nm to obtain the modified hydrotalcite powder.

[0047] Example 3

[0048] A preparation method of a hybrid composite membrane includes the following steps:

[0049] S1: Mix polyvinylidene fluoride powder, nanoparticles, and N,N-dimethylformamide according to a mass ratio of 12:6:23, and ultrasonically disperse for 4.5 h at 300 kHz to obtain a dispersion; the nanoparticles are composed of modified graphene oxide powder and modified hydrotalcite powder according to a mass ratio of 11:5;

[0050] S2: Take 35 parts of the dispersion prepared in step S1, add 14 parts of piperazine and 12 parts of polyethylene glycol 1000, stir for 4 h, heat to 100 °C, and then stand for defoaming for 2.5 h to obtain a casting solution;

[0051] S3: Set the blade thickness to 300 μm, pour the casting solution prepared in step S2 onto a clean glass plate, and let it stay in the air for 20 s, then immerse the glass plate in a pure water coagulation bath and soak for 52 h for phase inversion, changing the pure water every 6 h to obtain the hybrid composite membrane.

[0052] The preparation method of the modified graphene oxide powder is as follows: Mix 1 part of graphene oxide with 20 parts of deionized water evenly, then add 15 parts of tartaric acid and 9 parts of bromoacetic acid, ultrasonically disperse at 300 kHz for 3.5 h, centrifuge and separate, take the lower layer precipitate, wash it with deionized water until neutral, dry it at 60 °C, and grind it to a particle size of 800 nm to obtain the modified graphene oxide powder.

[0053] The preparation method of the modified hydrotalcite powder is as follows: (1) Place bamboo powder in a tube furnace, heat it to 900 °C at a rate of 10 °C / min, pyrolyze for 4 h, cool and screen. Put the powder passing through a 400-mesh sieve into a mixed solution of nitric acid solution (volume fraction of 70%) and sulfuric acid solution (volume fraction of 75%) with a volume ratio of 1:1, soak for 2 h, take it out, wash it with deionized water until neutral, dry it at 65 °C for 24 h, and grind to obtain carbon powder; (2) Mix the carbon powder, hydrotalcite powder, cobalt nitrate solution (0.7 mol / L), and nickel nitrate solution (0.5 mol / L) prepared in step (1) according to a mass ratio of 5:11:22:23, heat it to 75 °C, stir for 60 min, add ammonia water (mass fraction of 30%) dropwise to adjust the pH value to 11, cool, centrifuge, take the lower layer precipitate, vacuum dry it at 85 °C for 24 h, and grind it to a particle size of 800 nm to obtain the modified hydrotalcite powder.

[0054] Comparative Example 1

[0055] The preparation method of the hybrid composite film in this comparative example is similar to that in Example 1. The difference between this comparative example and Example 1 is that all the nanoparticles in this comparative example are modified graphene oxide powder.

[0056] Comparative Example 2

[0057] The preparation method of the hybrid composite film in this comparative example is similar to that in Example 1. The difference between this comparative example and Example 1 is that all the nanoparticles in this comparative example are modified hydrotalcite powder.

[0058] Comparative Example 3

[0059] The preparation method of the hybrid composite film in this comparative example is similar to that in Example 1. The difference between this comparative example and Example 1 is that in step S2 of the preparation method of the hybrid composite film in this comparative example, an equal amount of deionized water is used to replace piperazine.

[0060] Comparative Example 4

[0061] The preparation method of the hybrid composite film in this comparative example is similar to that in Example 1. The difference between this comparative example and Example 1 is that the nanoparticles in this comparative example are composed of modified graphene oxide powder and modified hydrotalcite powder according to a mass ratio of 4:9.

[0062] Comparative Example 5

[0063] The preparation method of the hybrid composite film in this comparative example is similar to that in Example 1. The difference between this comparative example and Example 1 is that in the preparation method of the modified graphene oxide in this comparative example, an equal amount of bromoacetic acid is used to replace tartaric acid.

[0064] Comparative Example 6

[0065] The preparation method of the hybrid composite membrane described in this comparative example is similar to that of Example 1. The difference between this comparative example and Example 1 is that in this comparative example, an equal amount of hydrotalcite powder is used instead of the modified hydrotalcite powder.

[0066] Test Example

[0067] Membrane surface wettability test: The water contact angles (WCAs) of the membranes prepared in Examples 1 - 3 and Comparative Examples 1 - 4 were measured by a semiconductor contact angle and surface tension measuring instrument using the static sessile drop method.

[0068] Flux test: The fluxes of the hybrid composite membranes prepared in Examples 1 - 3 and Comparative Examples 1 - 6 were tested using a dead-end filtration device with an effective filtration area of 10.18 cm 2 . Specifically:

[0069] (1) Pure water flux test: Under an operating pressure of 0.15 MPa, pure water was pressurized through the hybrid composite membrane for 30 min until the system was stable, and then the operating pressure was switched to 0.10 MPa and filtration continued for 2 h. Pure water was collected every 10 min and its volume was recorded. The calculation formula for the pure water flux is: J0 = V / St, where V is the volume of pure water passing through the membrane, S is the effective area through which water passes, and t is the time for each water sampling.

[0070] (2) Oil solution flux test: The test process for the oil solution flux was similar to that for the pure water flux (filtering a 400 mg / L n - hexadecane emulsion with the membrane). The oil content in the aqueous solution before and after membrane filtration was tested using a total organic carbon analyzer (Shimadzu TOC - L CPH, Japan) to calculate and evaluate the reversible fouling degree (RFR) and relative flux decline rate (RFD) of the hybrid composite membrane. The calculation formulas for RFR and RFD are respectively: RFR = J w / J0 × 100%, RFD = (J0 - J c ) / J0 × 100%, where J w is the pure water recovery flux measured after membrane rinsing, J c is the permeation flux after 120 min of operation in the feed liquid, and J0 is the pure water flux.

[0071] Test results: The test results are shown in Table 1.

[0072] Table 1 Test results of hybrid composite membranes

[0073]

[0074] As can be seen from Table 1, the water contact angles of the hybrid composite membranes prepared in Examples 1 - 3 of the present invention are 38.9 - 45.1°, indicating that the hybrid composite membranes have good wetting properties; the pure water fluxes are 1152.78 - 1215.93 L / (m2 ·h), the reversible fouling degree is 84.21% - 87.64%, and the relative flux decline rate is 20.10% - 23.24%. This indicates that the hybrid composite membrane has good flux, low flux decline, and a long service life. Among them, the hybrid composite membrane prepared in Example 1 has the best wettability and flux, and is the best embodiment of the present invention.

[0075] Compared with Example 1, in Comparative Example 1, all the nanoparticles are modified graphene oxide powder, but the water contact angle and pure water flux of the prepared hybrid composite membrane decrease. This shows that the modified graphene oxide powder can improve the hydrophilic property of the hybrid composite membrane, and the modified graphene oxide and modified hydrotalcite powder can act synergistically as inorganic nanoparticles to effectively increase the pure water flux of the hybrid composite membrane; in Comparative Example 2, all the nanoparticles are modified hydrotalcite powder, but the water contact angle of the prepared hybrid composite membrane increases, the pure water flux and reversible fouling degree decrease, and the relative flux decline rate increases. This shows that the addition of the modified graphene oxide powder can improve the hydrophilic property of the hybrid composite membrane, reduce the flux decline, and can act together with the modified hydrotalcite powder to increase the pure water flux of the hybrid composite membrane; in Comparative Example 3, an equal amount of deionized water is used to replace piperazine, but the water contact angle and relative flux decline rate of the prepared hybrid composite membrane increase significantly. This shows that the addition of piperazine can solve the problem of poor surface wettability of the polyvinylidene fluoride membrane and slow down the flux decline of the hybrid composite membrane; in Comparative Example 4, the mass ratio of the modified graphene oxide powder and the modified hydrotalcite powder is changed, but the wettability and flux of the prepared hybrid composite membrane are affected to varying degrees. This shows that the mass ratio of the modified graphene oxide powder and the modified hydrotalcite powder in the present invention has reached optimization; in Comparative Example 5, an equal amount of bromoacetic acid is used to replace tartaric acid, but the relative flux decline rate of the prepared hybrid composite membrane increases. This shows that tartaric acid and bromoacetic acid act together during the preparation of the modified graphene oxide to effectively increase the active sites on the surface of graphene oxide, thereby improving the anti-fouling ability of the hybrid composite membrane; in Comparative Example 6, an equal amount of hydrotalcite powder is used to replace the modified hydrotalcite powder, but the flux and reversible fouling degree of the prepared hybrid composite membrane decrease significantly, and the relative flux decline rate increases. This shows that the use of oxidized biochar to modify the hydrotalcite powder in the present invention can effectively improve the dispersion ability of the hydrotalcite powder, obtain a larger interlayer spacing, and increase the flux of the hybrid composite membrane.

[0076] The above embodiments are only preferred embodiments of the present invention, and are not limitations of the present invention. Any person skilled in this technology shall not modify the above embodiments without departing from the spirit and scope of the present invention. Therefore, any modifications, equivalent replacements, and improvements made by those skilled in the art under the technical idea of the present invention are still covered by the claims of the present invention.

Claims

1. A method for preparing a hybrid composite membrane, characterized in that: The following steps are involved: S1: mixing polyvinylidene fluoride powder, nanoparticles and N,N-dimethylformamide, and performing ultrasonic dispersion to obtain a dispersion; S2: adding piperazine and polyethylene glycol to the dispersion obtained in step S1, stirring, heating and then standing to degas, to obtain a casting solution; S3: pouring the casting solution obtained in step S2 onto a glass plate, scraping it with a scraper to form a film, and then immersing it in a pure water coagulation bath for phase inversion to obtain a hybrid composite membrane; The nanoparticles are composed of modified graphene oxide powder and modified hydrotalcite powder in a mass ratio of 7-11:3-5; The preparation method of the modified graphene oxide powder is as follows: graphene oxide and deionized water are uniformly mixed, then tartaric acid and bromoacetic acid are added, ultrasonication is performed, centrifugation is performed, a lower precipitate is taken out, the lower precipitate is washed with deionized water until it is neutral, drying is performed, and grinding is performed to obtain the modified graphene oxide powder; The preparation method of the modified hydrotalcite powder is as follows: (1) placing bamboo powder in a tube furnace, heating, pyrolyzing, cooling and sieving, placing the powder after passing through a 400-mesh sieve into a mixed solution of a nitric acid solution and a sulfuric acid solution, soaking it, taking it out and washing it with deionized water until it is neutral, drying it, grinding it, and obtaining carbon powder; (2) mixing the carbon powder, hydrotalcite powder, cobalt nitrate solution and nickel nitrate solution obtained in step (1), heating it, stirring it, adding ammonia water dropwise to adjust the pH value to 10-11, cooling it, centrifuging it, removing the lower layer of precipitate, vacuum drying it, and grinding it to obtain modified hydrotalcite powder.

2. The method for preparing a hybrid composite membrane according to claim 1, characterized in that: The mass ratio of graphene oxide to tartaric acid and bromoacetic acid is 1:13-15:6-9; the frequency of ultrasound is 200-300kHz, and the time of ultrasound is 3.5-4h; and the temperature of drying is 55-60°C.

3. The method for preparing a hybrid composite membrane according to claim 1, characterized in that: The heating temperature in step (1) is 800-900° C., the heating rate is 5-10° C. / min, and the pyrolysis time is 4-4.5 h. The volume ratio of the nitric acid solution to the sulfuric acid solution in the mixed solution of the nitric acid solution and the sulfuric acid solution is 1:1, the volume fraction of the nitric acid solution is 65%-70%, and the volume fraction of the sulfuric acid solution is 70%-75%. The soaking time is 1-2 h, the drying temperature is 60-65° C., and the drying time is 24-28 h. The powder is ground to a particle size of 600-800 nm.

4. The method for preparing a hybrid composite membrane according to claim 1, characterized in that: The mixing mass ratio of the carbon powder, hydrotalcite powder, cobalt nitrate solution and nickel nitrate solution in step (2) is 2-5:7-11:18-22:20-23, the concentration of the cobalt nitrate solution and the nickel nitrate solution is 0.5-0.7 mol / L; the heating temperature is 70-75°C, and the stirring time is 45-60 min; the mass fraction of the ammonia water is 25%-30%; the vacuum drying temperature is 80-85°C, and the vacuum drying time is 24-28 h.

5. The method for preparing a hybrid composite membrane according to claim 1, characterized in that: In step S1, the mixing mass ratio of the polyvinylidene fluoride powder, nanoparticles and N,N-dimethylformamide is 8-12:3-6:19-23; the ultrasonic frequency of ultrasonic dispersion is 200-300 kHz, and the ultrasonic dispersion time is 4.5-5 hours.

6. The method for preparing a hybrid composite membrane according to claim 1, characterized in that: The mass fractions of the components in step S2 are: 30-35 parts of dispersion, 10-14 parts of piperazine, and 8-12 parts of polyethylene glycol; the polyethylene glycol is polyethylene glycol 1000; the stirring time is 3.5-4 hours, the heating temperature is 90-100° C., and the standing degassing time is 2.5-3 hours.

7. The method for preparing a hybrid composite membrane according to claim 1, characterized in that: In step S3, the thickness of the scraper is 300 μm, the phase inversion time is 48-52 hours, and the pure water is replaced every 6 hours.

8. A hybrid composite membrane prepared according to the method for preparing a hybrid composite membrane according to any one of claims 1 to 7.

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