A high-strength anti-pollution graphene composite separation membrane and preparation method

Abstract

The application discloses a high-strength anti-pollution graphene composite separation membrane and a preparation method thereof. The preparation method comprises the following steps: firstly, preparing a rigid polymer solution; secondly, bonding nano-titanium dioxide particles and graphene oxide with the rigid polymer to obtain a rigid polymer product uniformly bonded with the nano-titanium dioxide particles and the graphene oxide; and thirdly, gradually adding a separation membrane polymer and a pore forming agent into the rigid polymer solution prepared from the rigid polymer product to obtain a nano-titanium dioxide particle and graphene composite separation membrane. The polymer separation membrane prepared by the application can effectively avoid the attenuation of the anti-pollution performance of the membrane and the loss of the nano-particles and the graphene oxide during use, so that the anti-pollution performance and the mechanical strength of the membrane are permanently improved. The application does not involve toxic reagents, and no complex reactions such as coating and grafting occur, so that the process is simple, the application is environment-friendly, and the application has a good industrialization prospect.

Description

Technical Field

[0001] The present invention relates to the field of polymer separation membrane preparation technology, and specifically to a high-strength, pollution-resistant graphene composite separation membrane and a preparation method thereof. The method is suitable for the preparation and production of pollution-resistant graphene polymer separation membranes. Background Art

[0002] Ultrafiltration membrane separation technology is widely used in sewage reuse, wastewater treatment, municipal water supply, and other fields due to its advantages such as simple operation, low energy consumption, small footprint, and no secondary pollution. However, the polymer materials used in current ultrafiltration membranes have poor hydrophilicity. In other words, their hydrophobicity makes them prone to adsorbing organic matter, colloids, bacteria, and other substances during the separation process, leading to membrane fouling, necessitating frequent chemical cleaning, and resulting in high operating costs for membrane separation systems. On the other hand, polymer materials have low mechanical properties and are prone to breakage and damage during long-term use, which is not conducive to their application in practical engineering. Therefore, the preparation of a high-strength, anti-fouling polymer ultrafiltration membrane is of great significance for expanding the application of ultrafiltration membranes.

[0003] Currently, membranes with composite separation membranes made of nanoparticles such as titanium oxide and zinc oxide are commonly used to improve their anti-fouling properties. The antibacterial properties of these nanoparticles prevent the growth of bacteria and other microorganisms on the membrane surface, significantly slowing down membrane surface fouling. Currently, the use of graphene composite separation membranes to improve the strength and anti-fouling properties of polymer separation membranes is also attracting increasing attention from separation membrane researchers and manufacturers.

[0004] Graphene is a novel material composed of tightly packed, sp2-linked carbon atoms forming a single-layer, two-dimensional honeycomb lattice. Graphene possesses excellent optical, electrical, and mechanical properties, and holds significant application potential in materials science, micro- and nanofabrication, energy, biomedicine, and drug delivery. It is considered a revolutionary material of the future. However, pure graphene is difficult to disperse uniformly in other media. Therefore, graphene oxide, which has a layered structure very similar to graphene, has attracted considerable attention from researchers. Graphene oxide not only shares a similar structure with graphene but also boasts a rich surface richness of reactive groups such as hydroxyl, epoxy, and carboxyl groups. Its large surface area and layered structure contribute to its high ion exchange capacity. The abundance of oxygen-containing groups on the layered surface allows for its uniform dispersion in water. Hydrophilic molecules and polymers can intercalate into the graphene oxide interlayers through hydrogen, ionic, and covalent bonding, forming intercalation compounds. This material holds great potential and promise for applications in the field of separation materials.

[0005] There are currently many problems with combining nanoparticles such as titanium oxide and zinc oxide with graphene in separation membranes. For example, the nanoparticles and graphene aggregate, preventing uniform distribution within the membrane. Furthermore, the composite nanoparticles and graphene fail to form a strong bond with the membrane material and gradually dissipate during use.

[0006] Therefore, how to overcome the defects of poor dispersion of existing nanoparticles and graphene in separation membranes and easy separation of nanoparticles and graphene from the separation membranes is a problem that needs to be solved in this field. Summary of the Invention

[0007] To address the problems of poor dispersion and easy detachment of existing nanoparticles and graphene within separation membranes, the present invention provides a high-strength, anti-fouling graphene composite separation membrane and its preparation method. This membrane can produce a polymer separation membrane with permanent anti-fouling strength. This membrane can delay membrane fouling, prevent fraying, and damage in sewage / water treatment projects, thereby reducing membrane cleaning frequency, extending membrane service life, lowering membrane operating costs, and expanding the membrane's application areas.

[0008] The present invention provides a method for preparing a high-strength anti-pollution graphene composite separation membrane, comprising the following preparation steps:

[0009] Step 1: Preparation of rigid polymer solution

[0010] Add phenylenediamine and an aniline compound with a side group in a molar ratio of 5 / 100 to 100 / 5 to a 1M acid solution, and stir rapidly with a magnetic stirrer for 0.4-2 hours to form a monomer solution;

[0011] preparing an oxidant solution in the acid solution at a monomer / oxidant molar ratio of 5 / 1 to 1 / 5;

[0012] The oxidant solution is added dropwise to the monomer solution to react, and the dropwise addition rate of the oxidant solution is controlled at 0.05-0.2 ml / min; the reaction process is carried out in a constant temperature water bath at a temperature of -20°C to 0°C, and the reaction time is 5-48 hours;

[0013] After the reaction is completed, the reaction solution is stirred while being heated to 25° C. to obtain the rigid polymer solution, a phenylenediamine polymer solution with side groups, whose degree of polymerization (n+m) is in the range of 200-1000;

[0014] Step 2: Bonding nano-titanium dioxide particles and graphene oxide to the rigid polymer

[0015] adding graphene oxide and nano-titanium dioxide particles into pure water and ultrasonically treating the water to obtain a suspension of the nano-titanium dioxide particles and the graphene oxide;

[0016] slowly adding the suspension into the rigid polymer solution, stirring thoroughly for 2-10h, so that the carboxyl and hydroxyl groups on the graphene oxide and nano-titanium dioxide form hydrogen bond with the N on the rigid polymer chain, obtaining a polymer solution in which the nano-titanium dioxide particles and graphene oxide are bonded with the rigid polymer;

[0017] The polymer solution is suction filtered and washed with distilled water until the filtrate is colorless; the polymer is treated with 0.2M ammonia water, and after magnetic stirring for 10-30h, it is suction filtered and washed until the filtrate is colorless and the product is dried, obtaining a rigid polymer product in which the nano-titanium dioxide particles and graphene oxide are bonded with the rigid polymer; wherein:

[0018] The rigid polymer: graphene oxide: nano-titanium dioxide particles = (50%-80%):(5%-20%):(5%-20%), in terms of mass percentage;

[0019] Step 3, preparation of the separation membrane

[0020] The rigid polymer product is added into a solvent, dispersed with ultrasonic waves for 0.5-5h, and kept at a temperature of 20-80℃, obtaining a rigid polymer solution;

[0021] The separation membrane polymer, pore-forming agent are gradually added into the rigid polymer solution, and stirred and dissolved to obtain a casting solution;

[0022] The casting solution is placed on a glass plate to scrape the film, the glass plate with the scraped film is immersed in a gel water bath at 0-65℃ to phase separate and form a film, and after soaking in pure water for 1-3 days, it is taken out and air dried, obtaining a nano-titanium dioxide particle and graphene composite flat plate separation membrane;

[0023] Alternatively,

[0024] The obtained casting solution is transferred to a feeding kettle and transported to a spinneret by pressure to form a hollow fiber membrane, which is immersed in a gel water bath at 0-65℃ to phase separate and form a film, and after soaking in pure water for 1-3 days, it is taken out and air dried, obtaining a nano-titanium dioxide particle and graphene composite hollow fiber separation membrane.

[0025] The rigid polymer product: separation membrane polymer: pore-forming agent: solvent = (0.1%-10%):(10%-30%):(5%-25%):(35%-85%), in terms of mass percentage.

[0026] Preferably, the phenylenediamine is one of m-phenylenediamine, o-phenylenediamine or p-phenylenediamine.

[0027] Preferably, the side group is an aliphatic group or an alkoxy group.

[0028] Preferably, the acid solution is one of HCl, H2SO4 or HNO3.

[0029] Preferably, the oxidizing agent is one of (NH4)2S2O8, K2S2O8, Na2S2O8, K2Cr2O7 or FeCl3.

[0030] Preferably, the solvent is one of dimethylacetamide, dimethylformamide, dimethyl sulfoxide or N-methyl pyrrolidone.

[0031] Preferably, the separation membrane polymer is one of PVDF, PVC, PAN, PES or PS; and the pore-forming agent is PEG and PVP.

[0032] The application also provides a high-strength anti-pollution graphene composite separation membrane prepared by the preparation method, which comprises a dense layer and a porous support layer.

[0033] Preferably, the rigid polymer chain is a straight polymer chain uniformly fixed with graphene oxide and nano-titanium dioxide particles.

[0034] Preferably, the separation membrane is a flat plate type separation membrane composed of the dense layer and the porous support layer.

[0035] Preferably, the flat plate type separation membrane has a thickness of 50 to 200 μm.

[0036] Preferably, the separation membrane is a hollow fiber separation membrane composed of the dense layer and the porous support layer.

[0037] Preferably, the dense layer of the hollow fiber separation membrane is on the outer circle and the porous support layer is on the inner circle.

[0038] Preferably, the hollow fiber filter membrane has a wall thickness of 50 to 500 μm.

[0039] Compared with the prior art, the application has the following beneficial effects:

[0040] 1. The carboxyl and hydroxyl groups on graphene oxide and nano-titanium dioxide are combined with the N-containing groups on the side of the polymer through hydrogen bonds, so that the nanoscale graphene oxide and antibacterial titanium dioxide particles are fixed on the polymer chain, which is beneficial to the dispersion of graphene oxide and nano-particles in the separation membrane, solves the problem that nanoscale particles are easy to agglomerate and cannot be uniformly dispersed, and can fully exert the excellent mechanical strength of graphene oxide and the antibacterial performance of nano-antibacterial particles.

[0041] 2, the rigid polymer chain is introduced into the polymer separation membrane, the introduced polymer chain is not wound, and the straight state is maintained, which is beneficial to the winding of the polymer chain of the separation membrane on the rigid polymer chain, the rigid polymer chain bonded with graphene and nanoparticles is completely integrated with the separation membrane, and the rigid polymer chain bonded with graphene and nanoparticles is not lost during use. Moreover, due to the large bonding force of the hydrogen bond, the graphene and nanoparticles are not easy to separate, and the loss of the effective component during use is avoided.

[0042] 3, in the application, the graphene oxide and the nano antibacterial particles are uniformly dispersed in the separation membrane, forming a nanoscale phase separation microstructure, which is equivalent to introducing countless nano cores in the membrane phase separation process, so that the membrane pore size can be effectively reduced, the membrane pore size distribution can be narrowed, and the membrane porosity can be improved. Macroscopically, the pore size is small, the water flux is large, and the mechanical strength of the membrane is improved. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 The rigid polymer chain polymerization molecular formula structure shown in the application is shown in the figure;

[0044] Figure 2 The rigid polymer chain molecular formula structure of the hydrogen bond bonding graphene oxide and nano titanium dioxide particles of the application is shown in the figure;

[0045] Figure 3 The rigid polymer chain molecular formula structure of the hydrogen bond bonding graphene oxide and nano titanium dioxide particles of the application is shown in the figure;

[0046] Figure 4 The flat plate type separation membrane of the application is shown in the figure;

[0047] Figure 5 The hollow fiber separation membrane of the application is shown in the figure.

[0048] In the figure, 1 is a dense layer, 2 is a porous support layer, and 3 is a rigid molecular chain. DETAILED DESCRIPTION

[0049] The application will be further described below in combination with examples and drawings.

[0050] Example 1:

[0051] 1, preparation of rigid polymer solution

[0052] The molar ratio of m-phenylenediamine and o-butyl aniline is 50 / 50, which is added to a 1M HCl solution, and is quickly magnetically stirred for 1 hour to form a monomer solution.

[0053] The oxidant K2S2O8 solution is configured in the HCl solution according to the molar ratio of monomer / oxidant 1 / 1.

[0054] Add the oxidant K2S2O8 solution dropwise to the monomer solution, and control the oxidant dropping rate at about 0.05 ml / min.

[0055] The above reaction process was carried out in a constant temperature water bath at -20°C for 12 h.

[0056] After the reaction is completed, the reaction solution is stirred while being heated to 25°C to obtain the rigid polymer solution - a copolymer solution of m-phenylenediamine and aniline with butyl groups, the degree of polymerization (n+m) of which is in the range of 200-1000. The molecular structure of the polymer is as follows: Figure 1 shown.

[0057] 2. Bonding nano-titanium dioxide particles and graphene oxide to rigid polymers

[0058] Graphene oxide and nano-titanium dioxide particles were added to pure water and ultrasonically treated for 2 h to obtain a suspension of nano-titanium dioxide particles and graphene oxide.

[0059] The suspension is slowly added to the rigid polymer solution and fully stirred for 8 hours, so that the carboxyl groups and hydroxyl groups on the graphene oxide and nano-titanium dioxide form hydrogen bonds with the N on the rigid polymer chain to obtain a rigid polymer solution.

[0060] Among them, the rigid polymer: graphene oxide: nano-titanium dioxide particles = 70:20:10, which are mass percentages.

[0061] The bonding solution was filtered and washed with distilled water until the filtrate was colorless. The polymer was treated with 0.2M ammonia water, magnetically stirred for 15 hours, filtered and washed until the filtrate was colorless. The product was transferred to a glass watch glass and dried to obtain a rigid polymer product in which nano-titanium dioxide particles and graphene oxide were bonded to the rigid polymer. The molecular formula of the rigid polymer product is as follows: Figure 2 shown.

[0062] 3. Preparation of separation membrane

[0063] 2 g of the rigid polymer product was added to 65 g of dimethylformamide solvent, and dispersed by ultrasonic wave for 5 h while maintaining the temperature at 60° C. to obtain a rigid polymer solution.

[0064] The raw materials of the separation membrane: PVDF 16 g, PEG 10 g, and PVP 7 g were gradually added to the mixed solution and mechanically stirred for 15 h to dissolve to obtain a casting solution.

[0065] The obtained casting solution was placed on a glass plate and scraped, and the scraped glass plate was immersed in a 40°C gel water bath to separate the phases and form a membrane. The membrane was then soaked in pure water for 3 days and then taken out and dried to obtain a nano-titanium dioxide particle and graphene composite flat plate separation membrane. Figure 4 shown.

[0066] The present invention utilizes a rigid polymer chain whose main chain is an aromatic benzene ring to maintain a linear chain state in a solvent (such as Figure 3 As shown, the groups on the nanoparticles form hydrogen bonds with the carboxyl and hydroxyl groups on titanium dioxide and graphene oxide, effectively dispersing and securing the nanoparticles and graphene oxide around the rigid polymer chains. The fully dispersed nanoparticles and graphene oxide are then evenly dispersed into the polymer membrane. Because the rigid polymer chains of sufficient length are not easily curled, they can be dispersed within the polymer chains of the separation membrane and become entangled with them. As a result, during the formation of the separation membrane, the nanoparticles and graphene oxide, secured by hydrogen bonds, are molecularly fixed to the membrane, ensuring that they do not leave the membrane during use. This fully utilizes the high strength and physical advantages of the large lamellar structure of graphene oxide, as well as the bactericidal properties of the antibacterial nanoparticles.

[0067] Example 2:

[0068] The preparation method of this embodiment is basically the same as that of embodiment 1, except that in the preparation of the separation membrane in step 3, the mass of the rigid polymer product is 5 g, which is added to 62 g of dimethylformamide solvent.

[0069] Example 3:

[0070] The preparation method of this embodiment is basically the same as that of embodiment 1, except that in the preparation of the separation membrane in step 3, the mass of the rigid polymer product is 8 g, which is added to 59 g of dimethylformamide solvent.

[0071] Example 4:

[0072] The preparation method of this embodiment is basically the same as that of embodiment 1, except that in the preparation of the separation membrane in step 3, the mass of the rigid polymer product is 10 g, which is added to 57 g of dimethylformamide solvent.

[0073] Comparative Example 1:

[0074] The preparation method of Comparative Example 1 is basically the same as that of Example 1, except that in the preparation of the separation membrane in step 3, no rigid polymer product is added. Instead, the separation membrane raw materials: 16 g of PVDF, 10 g of PEG, and 7 g of PVP are gradually added to 67 g of dimethylformamide solvent, and then mechanically stirred for 15 hours to dissolve to obtain a casting solution.

[0075] The present invention detects the pure water flux of planar membranes and hollow fiber membranes according to GB / T 32360-2015 "Ultrafiltration Membrane Test Method".

[0076] The anti-fouling performance of the separation membrane is characterized by the pure water flux attenuation rate ΔZ of the separation membrane. The test steps are as follows:

[0077] Test the pure water flux Q1 of the cleaned separation membrane;

[0078] The tested separation membrane was immersed in a water bath for 30 days. The immersion conditions were: tap water, exposed to air, and constant temperature of 25°C.

[0079] Test the pure water flux Q2 of the soaked separation membrane;

[0080] The flux attenuation rate ΔZ is calculated as (Q1-Q2) / Q1. The smaller ΔZ is, the better the anti-fouling performance of the membrane is.

[0081] The present invention detects the tensile strength of the hollow fiber membrane according to Q / HBJ03.167-2016 "Test method for tensile strength of hollow fiber membrane".

[0082] The sample preparation for the flat film tensile strength test is as follows:

[0083] The membrane was cut into 2*6 cm test samples using scissors, and then the test method was the same as that of the hollow fiber membrane.

[0084] The planar separation membranes prepared in Examples 1 to 4 and Comparative Example 1 were tested. The test results are shown in Table 1:

[0085] Table 1

[0086]

[0087] The results show that the composite membrane provided by the present invention has comparable pure water flux to the uncomposite membrane in Comparative Example 1. Since the anti-pollution performance of a separation membrane is characterized by the pure water flux decay rate ΔZ of the separation membrane, i.e., the smaller the ΔZ, the better the membrane's anti-pollution performance. Therefore, the composite membrane provided by the present invention has both improved anti-pollution performance and tensile strength to a certain extent. Furthermore, the low flux decay rate after one month of immersion indicates that the titanium dioxide nanoparticles and graphene oxide have a strong bond with the membrane material and do not fall off or leak, thus maintaining good anti-pollution and high strength properties.

[0088] Example 5:

[0089] 1. Preparation of rigid polymer solution

[0090] p-phenylenediamine and o-propoxyaniline in a molar ratio of 75 / 25 were added to a 1M H2NO3 solution and rapidly stirred with a magnetic stirrer for 0.5 hours to form a monomer solution.

[0091] The oxidant K2Cr2O7 solution was prepared in the H2NO3 solution at a monomer / oxidant molar ratio of 3 / 5.

[0092] Add the oxidant K2Cr2O7 solution dropwise to the monomer solution, and control the oxidant dropping rate at about 0.1 ml / min.

[0093] The above reaction process was carried out in a constant temperature water bath at -10°C for 20 h.

[0094] After the reaction is completed, the reaction solution is stirred while being heated to 25°C to obtain the rigid polymer solution - a copolymer solution of p-phenylenediamine and aniline with propoxy groups, the degree of polymerization (n+m) of which is in the range of 200-1000. The molecular structure of the polymer is as follows: Figure 1 shown.

[0095] 2. Bonding nano-titanium dioxide particles and graphene oxide to rigid polymers

[0096] Graphene oxide and nano-titanium dioxide particles were added to pure water and ultrasonically treated for 2 h to obtain a suspension of nano-titanium dioxide particles and graphene oxide.

[0097] The suspension is slowly added to the rigid polymer solution and fully stirred for 12 hours, so that the carboxyl groups and hydroxyl groups on the graphene oxide and nano-titanium dioxide form hydrogen bonds with the N on the rigid polymer chain to obtain a rigid polymer solution.

[0098] Among them, the rigid polymer: graphene oxide: nano-titanium dioxide particles = 75:15:10, which are mass percentages.

[0099] The bonding solution was filtered and washed with distilled water until the filtrate was colorless. The polymer was treated with 0.2M ammonia water, magnetically stirred for 20 hours, filtered and washed until the filtrate was colorless. The product was transferred to a glass watch glass and dried to obtain a rigid polymer product in which nano-titanium dioxide particles and graphene oxide were bonded to the rigid polymer. The molecular formula of the rigid polymer product is as follows: Figure 2 shown.

[0100] 3. Preparation of separation membrane

[0101] 100 g of the rigid polymer product was added to 7100 g of N-methylpyrrolidone solvent, and dispersed by ultrasonication for 5 h while maintaining the temperature at 60° C. to obtain a mixed solution.

[0102] The raw materials of the separation membrane: PES 1500 g, PEG 500 g, and PVP 800 g were gradually added to the mixed solution, and mechanically stirred for 20 h to dissolve to obtain a casting solution.

[0103] The obtained casting solution is transferred to a pressurized feeding kettle and transported to the spinneret by pressure to form a hollow fiber membrane. The membrane is then immersed in a 65°C gel water bath for phase separation and membrane formation. The hollow fiber membrane is then soaked in pure water for 3 days, taken out, and air-dried to obtain a nanoparticle and graphene composite hollow fiber separation membrane. Figure 5 shown.

[0104] Example 6:

[0105] The preparation method of this embodiment is basically the same as that of embodiment 5, except that in the preparation of the separation membrane in step 3, 300 g of the rigid polymer product is added to 6900 g of N-methylpyrrolidone solvent.

[0106] Example 7:

[0107] The preparation method of this embodiment is basically the same as that of embodiment 5, except that in the preparation of the separation membrane in step 3, the mass of the rigid polymer product is 600 g, which is added to 6600 g of N-methylpyrrolidone solvent.

[0108] Example 8:

[0109] The preparation method of this embodiment is basically the same as that of embodiment 5, except that in the preparation of the separation membrane in step 3, 900 g of the rigid polymer product is added to 6300 g of N-methylpyrrolidone solvent.

[0110] Comparative Example 2:

[0111] The preparation method for Comparative Example 2 was essentially the same as that for Example 5, except that no rigid polymer was added to the separation membrane in Step 3, and 7200 g of N-methylpyrrolidone was used as the solvent. The separation membrane raw materials (1500 g of PES, 500 g of PEG, and 800 g of PVP) were gradually added to the mixture and mechanically stirred for 20 hours to dissolve and obtain a casting solution.

[0112] The hollow fiber separation membranes prepared in Examples 5 to 8 and Comparative Example 2 were tested. The test results are shown in Table 2:

[0113] Table 2

[0114]

[0115] The results show that the composite membrane provided by the present invention has comparable pure water flux to that of an uncomposite membrane. However, both anti-fouling performance and tensile strength are improved to a certain extent. Furthermore, after one month of immersion, the flux decay rate is minimal, indicating that the titanium dioxide nanoparticles and graphene oxide have a strong bond with the membrane material and do not fall off or leak, thus maintaining good anti-fouling and high strength properties.

[0116] Example 9:

[0117] 1. Preparation of rigid polymer solution

[0118] Add o-phenylenediamine and o-ethoxyaniline with molar ratio of 90 / 15 into 1M H2SO4 solution, and stir rapidly with magnetic force for 0.8 hours to form monomer solution.

[0119] Prepare oxidant (NH4)2S2O8 solution in the H2SO4 solution according to the monomer / oxidant ratio of 5 / 4.

[0120] Drop the oxidant (NH4)2S2O8 solution into the monomer solution, and control the dropping speed of the oxidant at about 0.08ml / min.

[0121] The above reaction process is carried out in a constant temperature water bath, and the water bath temperature is -15℃, and the reaction time is 24h.

[0122] After the reaction is completed, the reaction solution is stirred while being heated to 25℃ to obtain the rigid polymer solution, i.e. o-phenylenediamine and aniline copolymer solution with ethoxy group, and the polymerization degree (n+m) is in the range of 200-1000. The molecular formula structure of the polymer is shown in Figure 1 .

[0123] 2. Bonding of nano titanium dioxide particles and graphene oxide with rigid polymer

[0124] Add graphene oxide and nano titanium dioxide particles into pure water, and ultrasonically treat for 2.5h to obtain nano titanium dioxide particle and graphene oxide suspension.

[0125] Slowly add the suspension into the rigid polymer solution, and fully stir for 12h to make the carboxyl and hydroxyl groups on the graphene oxide and nano titanium dioxide form hydrogen bond with N on the rigid polymer chain to obtain bonding solution.

[0126] Among them, the rigid polymer: graphene oxide: nano titanium dioxide particle = 75: 15: 10, which is mass percentage.

[0127] Extract the bonding solution and wash with distilled water until the filtrate is colorless polymer; treat the polymer with 0.2M ammonia water, and extract and wash until the filtrate is colorless product after magnetic stirring for 20 hours; move the product into a glass surface dish to dry to obtain the rigid polymer product bonded with nano titanium dioxide particles and graphene oxide. The molecular formula structure of the rigid polymer product is shown in Figure 2 .

[0128] 3. Preparation of separation membrane

[0129] 50 g of the rigid polymer product was added to 6350 g of dimethylacetamide solvent, and dispersed by ultrasonic wave for 6 h while maintaining the temperature at 80° C. to obtain a rigid polymer solution.

[0130] The raw materials of the separation membrane: PVDF 2000 g, PEG 400 g, and PVP 1200 g were gradually added to the solution, and mechanically stirred for 24 hours to dissolve to obtain a casting solution.

[0131] The obtained casting liquid is transferred to a pressurized feeding kettle and transported to the spinneret by pressure to form a hollow fiber membrane, which is then immersed in a 50°C gel water bath for phase separation and membrane formation. The hollow fiber membrane is then soaked in pure water for 3 days, taken out, and dried to obtain a nanoparticle and graphene composite hollow fiber separation membrane.

[0132] Example 10:

[0133] The preparation method of this embodiment is basically the same as that of Example 9, except that in the preparation of the separation membrane in step 3, 300 g of the rigid polymer product is added to 6300 g of dimethylacetamide solvent.

[0134] Example 11:

[0135] The preparation method of this embodiment is basically the same as that of Example 9, except that in the preparation of the separation membrane in step 3, 400 g of the rigid polymer product is added to 6000 g of dimethylacetamide solvent.

[0136] Example 12:

[0137] The preparation method of this embodiment is basically the same as that of embodiment 9, except that in the preparation of the separation membrane in step 3, 700 g of the rigid polymer product is added to 5700 g of dimethylacetamide solvent.

[0138] Example 13:

[0139] The preparation method of this embodiment is basically the same as that of Example 9, except that in the preparation of the separation membrane in step 3, 1000 g of the rigid polymer product is added to 5400 g of dimethylacetamide solvent.

[0140] Comparative Example 3:

[0141] The preparation method of Comparative Example 3 was essentially the same as that of Example 9, except that no rigid polymer product was added to the separation membrane in step 3, and 6400 g of dimethylacetamide was used as the solvent. Separation membrane raw materials: 2000 g of PVDF, 400 g of PEG, and 1200 g of PVP were gradually added to the mixture and mechanically stirred for 20 hours to dissolve and obtain a casting solution.

[0142] In Examples 1 to 13 provided by the present invention, the ratio of the raw materials used to prepare the composite separation membrane is: rigid polymer product: separation membrane polymer: pore former: solvent = (0.1%-10%): (10%-30%): (5%-25%): (35%-85%), which are mass percentages.

[0143] The hollow fiber separation membranes prepared in Examples 9 to 13 and Comparative Example 3 were tested. The test results are shown in Table 3:

[0144] Table 3

[0145]

[0146] The results show that the composite membrane provided by the present invention has comparable pure water flux to that of an uncomposite membrane. However, both anti-fouling performance and tensile strength are improved to a certain extent. Furthermore, after one month of immersion, the flux decay rate is minimal, indicating that the titanium dioxide nanoparticles and graphene oxide have a strong bond with the membrane material and do not fall off or leak, thus maintaining good anti-fouling and high strength properties.

[0147] like Figure 3 、 4 As shown in Figures 5 and 6, the present invention also provides a high-strength, anti-pollution graphene composite separation membrane prepared by the preparation method, comprising a dense layer 1 and a porous support layer 2. The separation membrane is composited with rigid polymer chains 3 containing graphene oxide and nano-titanium dioxide particles. The rigid polymer chains are linear polymer chains uniformly fixed with graphene oxide and nano-titanium dioxide particles. The separation membrane can be prepared as a flat-plate separation membrane consisting of a dense layer 1 and a porous support layer 2. The thickness of the flat-plate separation membrane is 50 to 200 μm. The separation membrane can also be prepared as a hollow fiber separation membrane consisting of a dense layer 1 and a porous support layer 2. The dense layer 1 of the hollow fiber separation membrane is on the outer circle and the porous support layer 2 is on the inner circle. The wall thickness of the hollow fiber filter membrane is 50 to 500 μm.

[0148] The polymer separation membrane prepared by this method effectively prevents degradation of the membrane's anti-fouling properties and loss of nanoparticles and graphene oxide during use, thereby permanently improving the membrane's anti-fouling performance and mechanical strength. The method involves no toxic reagents and avoids complex reactions such as coating and grafting. The process is simple, environmentally friendly, and has promising prospects for industrialization.

[0149] The above descriptions are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a high-strength anti-pollution graphene composite separation membrane, characterized in that: The method comprises the following preparation steps: Step 1: Preparation of rigid polymer solution Add phenylenediamine and an aniline compound with a side group in a molar ratio of 5:100 to 100:5 to a 1M acid solution and stir rapidly with a magnetic stirrer for 0.4-2 hours to form a monomer solution; preparing an oxidant solution in the acid solution at a molar ratio of monomer to oxidant ranging from 5:1 to 1:5; The oxidant solution is added dropwise to the monomer solution to react, and the dropwise addition rate of the oxidant solution is controlled at 0.05-0.2 ml / min; the reaction process is carried out in a constant temperature water bath at a temperature of -20°C to 0°C, and the reaction time is 5-48 hours; After the reaction is completed, the reaction solution is stirred while being heated to 25° C. to obtain the rigid polymer solution, which is a phenylenediamine polymer solution with side groups and a degree of polymerization ranging from 200 to 1000; Step 2: Bonding nano-titanium dioxide particles and graphene oxide to the rigid polymer adding graphene oxide and nano-titanium dioxide particles into pure water and ultrasonically treating the water to obtain a suspension of the nano-titanium dioxide particles and the graphene oxide; Slowly adding the suspension to the rigid polymer solution and stirring for 2-10 hours, so that the carboxyl and hydroxyl groups on the graphene oxide and nano-titanium dioxide form hydrogen bonds with the nitrogen on the rigid polymer chain, thereby obtaining a polymer solution in which nano-titanium dioxide particles and graphene oxide are bonded to the rigid polymer; The polymer solution is filtered and washed with distilled water until the filtrate is colorless; the polymer is treated with 0.2M ammonia water, magnetically stirred for 10-30 hours, filtered and washed until the filtrate is colorless, and then dried to obtain a rigid polymer product in which nano-titanium dioxide particles and graphene oxide are bonded to the rigid polymer; wherein: The rigid polymer: graphene oxide: nano-titanium dioxide particles = (50%-80%): (5%-20%): (5%-20%), which are percentages by mass; Step 3: Preparation of separation membrane Add the rigid polymer product to a solvent, disperse it with ultrasound for 0.5-5 hours, and maintain the temperature at 20-80° C. to obtain a rigid polymer solution; gradually adding a separation membrane polymer and a pore-forming agent into the rigid polymer solution, stirring and dissolving the solution to obtain a casting solution; The casting solution is placed on a glass plate and scraped, and the glass plate with the scraped film is immersed in a gel water bath at 0-65° C. to separate the phases and form a membrane, and then soaked in pure water for 1-3 days, taken out, and dried to obtain a nano-titanium dioxide particle and graphene composite flat plate separation membrane; or, The obtained casting solution is transferred to a feeding kettle and conveyed to a spinneret under pressure to form a hollow fiber membrane, which is then immersed in a gel water bath at 0-65°C for phase separation and membrane formation. The hollow fiber membrane is then soaked in pure water for 1-3 days, taken out, and air-dried to obtain a nano-titanium dioxide particle and graphene composite hollow fiber separation membrane; Among them, the rigid polymer product: separation membrane polymer: pore former: solvent = (0.1%-10%): (10%-30%): (5%-25%): (35%-85%), which are mass percentages.

2. The preparation method according to claim 1, wherein The phenylenediamine is one of m-phenylenediamine, o-phenylenediamine or p-phenylenediamine; and the side group is an aliphatic group or an alkoxy group.

3. The preparation method according to claim 1, wherein The acid solution is one of HCl, H2SO4 or HNO3; the oxidant is one of (NH4)2S2O8, K2S2O8, Na2S2O8, K2Cr2O7 or FeCl3.

4. The preparation method according to claim 1, wherein The solvent is one of dimethylacetamide, dimethylformamide, dimethyl sulfoxide or N-methylpyrrolidone.

5. The preparation method according to claim 1, wherein The separation membrane polymer is one of PVDF, PVC, PAN, PES or PS; the pore-forming agent is PEG and PVP.

6. A high-strength anti-pollution graphene composite separation membrane prepared by the preparation method according to claim 1, characterized in that: The separation membrane comprises a dense layer and a porous support layer. The separation membrane is compounded with a rigid polymer chain containing graphene oxide and nano-titanium dioxide particles.

7. The composite separation membrane according to claim 6, wherein The rigid polymer chain is a linear polymer chain in which graphene oxide and nano-titanium dioxide particles are uniformly fixed.

8. The composite separation membrane according to claim 6, wherein The separation membrane is a flat-plate separation membrane composed of a dense layer and a porous support layer.

9. The composite separation membrane according to claim 8, wherein The flat-plate separation membrane has a thickness of 50 to 200 μm.

10. The composite separation membrane according to claim 6, wherein The separation membrane is a hollow fiber separation membrane composed of a dense layer and a porous support layer.

11. The composite separation membrane according to claim 10, wherein The dense layer of the hollow fiber separation membrane is on the outer circle and the porous support layer is on the inner circle; the wall thickness of the hollow fiber filter membrane is 50 to 500 μm.

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