A composite membrane capable of purifying dye wastewater and a preparation method thereof

Abstract

The present application relates to a kind of purifiable dye wastewater composite membrane and its preparation method, purifiable dye wastewater composite membrane is composed of graphene oxide and polyacrylonitrile fiber;Graphene oxide is inserted between staggered polyacrylonitrile fiber, and forms three-dimensional network support structure;The porosity of purifiable dye wastewater composite membrane is 18%~27%, and water flux is 330~850L / m 2 h, specific surface area is 15~400m 2 / g;Preparation method is: the inorganic dispersion liquid of graphene oxide and polyacrylonitrile solution are conjugated electrospinning, namely purifiable dye wastewater composite membrane.The method of the present application is simple, suitable for large-scale production;The product of the present application has good adsorption, and removal rate is high.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sewage treatment materials, and relates to a dye wastewater purifying composite membrane and a preparation method thereof. BACKGROUND

[0002] With the acceleration of globalization, the industry has developed rapidly, while the environmental pollution has also become more and more serious. The random discharge of industrial wastewater and domestic sewage has further exacerbated the water shortage situation. There are many harmful substances in wastewater, the most common of which are various dyes, heavy metals that cause poisoning of plants and animals, and organic substances that cause eutrophication of water, etc. If these substances are not treated or treated imperfectly, they will cause serious water pollution once they enter the water body. Therefore, whether it is domestic sewage or industrial wastewater, the harmful substances in the water must be strictly treated before being discharged.

[0003] Membrane separation technology is a simple, efficient and convenient water treatment method, but the diversification of water pollutants also leads to the increasing demand for new membrane materials. At present, high molecular nanofiber membrane materials are attracting much attention, and the nanofiber membrane prepared by electrospinning technology has obvious advantages in water purification due to its large specific surface area and convenient preparation. Polyacrylonitrile is a commonly used nanofiber membrane substrate in electrospinning, and the prepared nanofiber membrane has the characteristics of porosity, softness and chemical resistance.

[0004] At present, there are many ways to treat wastewater. Generally, the method of coating or modifying the surface of the membrane is used to improve the efficiency of wastewater treatment. Graphene oxide is a new type of high-efficiency adsorption material with ultra-high specific surface area and a large number of active groups, and is also quite widely used in water treatment and other applications. The benzene ring structure and active groups contained therein can achieve the purpose of adsorbing or intercepting dyes through electrostatic interaction, π-π interaction, hydrogen bond interaction or Lewis acid interaction.

[0005] Document 1 (Mixed Dye Removal Efficiency of Electrospun Polyacrylonitrile-Graphene Oxide Composite Membranes. Polymers, 2020.) uses cetyltrimethylammonium chloride (CTAC) surfactant to modify the exfoliated graphene oxide (GO) and then electrospins the mixture to form GO-PAN composite nanofibers. However, the removal rate of the prepared composite fibers for methyl blue is only about 30%.

[0006] Document 2 (Design of durable and efficient poly(arylene ether nitrile) / bioinspired polydopamine coated graphene oxide nanofibrous composite membrane for anionic dyes separation. Chemical Engineering Journal, 2017.) prepared arylene ether nitrile nanofiber felt by electrospinning technology and hot pressing treatment, then assembled graphene oxide nanosheet on the arylene ether nitrile nanofiber felt through vacuum suction method, finally, the obtained arylene ether nitrile / graphene oxide nanofiber composite membrane was further modified by bio-inspired polydopamine coating to form arylene ether nitrile / graphene oxide-polydopamine nanofiber composite membrane, but the above preparation method is too complicated and is not suitable for large-scale production.

[0007] Document 3 (Polyacrylonitrile nanofiber membranes incorporated with largereduced graphene oxide content in situ. Journal of Materials Science, 2021.) used cationic surfactant to simply modify the surface of graphene oxide, prepared composite nanofiber, then converted it into film type sheet through heating and pressure treatment, but the obtained composite membrane has long dye filtration time and low efficiency.

[0008] Therefore, the current method for preparing composite membrane using graphene oxide is complicated, the prepared composite membrane has low removal rate and long dye filtration time, the performance of the existing dye adsorption membrane material still cannot meet the use requirement, and it cannot meet the conditions of simple preparation process, suitable for large-scale production, high removal rate and high adsorption capacity for dyes, and non-toxic and non-polluting at the same time.

[0009] Therefore, it is of great significance to develop a dye wastewater purifying composite membrane and a preparation method thereof to solve the above problems. SUMMARY

[0010] The purpose of the present application is to solve the problems in the prior art and provide a dye wastewater purifying composite membrane and a preparation method thereof.

[0011] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0012] A composite membrane capable of purifying dye wastewater, the composite membrane is composed of graphene oxide and polyacrylonitrile fibers; the graphene oxide is interlaced between the staggered stacked polyacrylonitrile fibers to form a three-dimensional network support structure;

[0013] The composite membrane of the present application has the characteristics of polyacrylonitrile fiber membrane and the high adsorption performance of most graphene oxide, and has high water flux and high dye removal efficiency, and can be used for adsorption research of dyes and heavy metals in wastewater;

[0014] The three-dimensional network dense structure formed between the graphene oxide and the polyacrylonitrile fibers in the composite membrane makes the composite membrane have many voids (i.e. high porosity), and the hydrophilic property of the composite membrane is better than that of pure polyacrylonitrile membrane, which is easy to combine with dyes and heavy metals with good hydrophilic property and increase the adsorption capacity;

[0015] Both polyacrylonitrile fibers and graphene oxide have a large specific surface area, and the large specific surface area and many adsorption sites increase the adsorption capacity of dyes and heavy metal ions;

[0016] The porosity of the composite membrane is 18% to 27%, the water flux is 330 to 850 L / m 2 h, and the specific surface area is 15 to 400 m 2 / g;

[0017] The prior art has inorganic spinning solution and polymer fiber conjugate spinning, but the inorganic material is not a sheet structure, has no sheet structure support, and cannot form a three-dimensional network support structure to achieve the technical effects of high flux, high removal rate and high adsorption capacity.

[0018] Document 4 (Preparation and Performance Research of Polyacrylonitrile / Graphene Oxide Composite Nanofiber, Polymer Bulletin, 2019) uses an electrospinning method to prepare polyacrylonitrile / graphene oxide composite nanofibers with different mass fractions, and the results show that the PAN nanofiber becomes thinner and the mechanical properties are better than those of the PAN nanofiber after adding graphene oxide, but as the content of graphene oxide increases, the PAN nanofiber will appear beading phenomenon, which directly reduces its fiber-forming property, and the uniformity of the fiber thickness decreases, affecting the continuity between the fibers and reducing the mechanical properties of the fibers. The reason is that the document does not form the three-dimensional support network structure of the present application, and cannot effectively improve the loading capacity of graphene oxide, so that the morphology of the fiber changes and the performance decreases.

[0019] As a preferred technical solution:

[0020] A composite membrane for purifying dye wastewater as described above, the removal rate of malachite green dye of the composite membrane is 78% to 94.5%, and the adsorption capacity is 9.0 to 18.0 mg / g; the removal rate of methylene blue dye of the composite membrane is 70 to 98%, and the adsorption capacity is 7.8 to 13.0 mg / g; after being reused for 4 times, the removal rate of malachite green dye or methylene blue dye of the composite membrane remains at 65% to 91%.

[0021] A composite membrane for purifying dye wastewater as described above, the breaking strength of the composite membrane is 1.28139 to 1.44552 N, and the elongation at break is 19.69 to 23.56%; the single-layer rigid structure of graphene oxide plays a reinforcing role in the orientation degree of structural units in the fiber during the fiber drafting process, increases the force between the surface fibers, and makes the composite membrane have greater breaking strength and deformation capacity than the pure polyacrylonitrile membrane.

[0022] A composite membrane for purifying dye wastewater as described above, the diameter of the polyacrylonitrile fiber is 0.3 to 0.5 μm; and the thickness of the composite membrane is 0.028 to 0.049 mm.

[0023] A composite membrane for purifying dye wastewater as described above, the content of graphene oxide in the composite membrane is 1.25 to 6.25 wt.%, and the content of the loaded graphene oxide in the composite membrane can also be adjusted by adjusting the process.

[0024] The application also provides a preparation method of the composite membrane for purifying dye wastewater as described above, and the inorganic dispersion solution of graphene oxide and the polyacrylonitrile solution are conjugated electrospun to obtain the composite membrane for purifying dye wastewater.

[0025] The application adds an injection pump for spraying the inorganic dispersion solution of graphene oxide on the original electrospun equipment, the spinning device comprises two spinnerets and two high-voltage power supplies with opposite polarities, the high-voltage power supplies are connected to the two spinnerets; an aluminum foil is covered on the metal roller for receiving nanofibers, and the roller is connected to the ground wire; in the process of building the composite membrane, one spinneret electrospins to build nanofibers, and the other spinneret electrospays to spray two-dimensional materials; the two opposite single-axis spinnerets spray different components, and the components gather in the middle position of the two spinnerets by virtue of electrostatic attraction, and finally form a composite membrane.

[0026] The needle of the graphene oxide injection pump in the spinning device is connected to the same high-voltage as the needle of the polyacrylonitrile to perform conjugated spinning together, this method not only utilizes the adhesion between the fibers before the solvent is completely volatilized, but also utilizes the electrostatic effect between the two beams of nanofibers, and can effectively avoid the repulsion between charges, mutual diffusion of spinning solutions and low spinning efficiency.

[0027] As a preferred technical solution:

[0028] The preparation method as described above, the process parameters include: the volume of the syringe is 3-5ml, the distance from the needle spinneret to the roller is 8-10cm, the rotating speed of the roller is 40-60rpm, the working voltage is 15-20Kv, and the advancing rate of the injection pump is 1-2ml / h; wherein the electrospinning process parameters of the inorganic dispersion liquid of graphene oxide and the polyacrylonitrile solution are the same.

[0029] The preparation method as described above, after the inorganic dispersion liquid of graphene oxide and the polyacrylonitrile solution are configured, they are stirred uniformly at room temperature.

[0030] The preparation method as described above, before the polyacrylonitrile solution is configured, the polyacrylonitrile (powder) is placed in a thermostat at 70℃ for 24 hours to keep dry.

[0031] The preparation method as described above, the concentration of the polyacrylonitrile solution is 0.08-1g / ml, and the solvent of the polyacrylonitrile solution is N,N-dimethylformamide; the stirring is magnetic stirring, and the stirring time is 5-8h.

[0032] The preparation method as described above, the concentration of the inorganic dispersion liquid of graphene oxide is 1-5mg / ml, the solvent of the inorganic dispersion liquid of graphene oxide is water, the stirring is magnetic stirring, and the time is 2h.

[0033] After the conjugate electrospinning, the composite film is vacuum dried at 37℃ for 12h, and then is stored in a vacuum drying box at 24℃; the main purpose of vacuum drying is to remove the water in the fiber film, and it will not affect the morphology of the composite film.

[0034] Beneficial effects

[0035] (1) The method has the advantages of simple operation, non-toxic and non-polluting experimental process, and mild preparation conditions, and is suitable for large-scale batch production.

[0036] (2) The composite film prepared by the method has a large specific surface area, can play the high-efficiency adsorption characteristics of graphene oxide, and can be applied to the purification treatment of dyes in wastewater.

[0037] (3) The composite film prepared by the method has high removal efficiency for dyes, and the adsorption capacity of dyes is much higher than that of the blank film, so it has wide application prospect and great use value. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 The optical and SEM images of the composite film containing different mass fractions of graphene oxide.

[0039] Figure 2 Figure for comparison of mechanical properties of composite film prepared in Example 1 and polyacrylonitrile film prepared in Comparative Example 1;

[0040] Figure 3 Figure for porosity of composite film containing different mass fractions of graphene oxide;

[0041] Figure 4 Figure for water flux of composite film containing different mass fractions of graphene oxide;

[0042] Figure 5 Removal rate of malachite green by composite film containing different mass fractions of graphene oxide;

[0043] Figure 6 Adsorption amount of malachite green by composite film containing different mass fractions of graphene oxide;

[0044] Figure 7 Removal rate of methylene blue by composite film containing different mass fractions of graphene oxide;

[0045] Figure 8 Adsorption amount of methylene blue by composite film containing different mass fractions of graphene oxide;

[0046] Figure 9 Removal rate of composite film containing different mass fractions of graphene oxide after filtration for four cycles;

[0047] Figure 10 Self-made water flux testing device;

[0048] Figure 11 Schematic diagram of self-made composite film separation device for dye solution.DETAILED DESCRIPTION

[0049] The application will be further described below in connection with specific examples. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application. Furthermore, it should be understood that those skilled in the art can make various modifications or changes to the application after reading the content of the application, and these equivalent forms also fall within the scope of the appended claims.

[0050] The test methods of the parameters involved in the following examples and comparative examples are as follows:

[0051] 1. Mechanical property test

[0052] The products prepared in the examples and the products prepared in the comparative examples were used as test samples, and the specific test steps were as follows:

[0053] (1) After the sample is left to stand for 24 h in a room temperature environment, it is cut into a test sample with a length of 40 mm, a width of 10 mm, and an effective length of 20 mm;

[0054] (2) The breaking strength and breaking elongation of the test sample are determined using a computerized tensile and compressive force testing machine (manufacturer: Shanghai Hengyuan Instrument Co., Ltd., model: HY-940FS), and the test parameters are as follows: tensile rate of 3 mm / min, maximum tensile force of 100 N.

[0055] 2. Test of porosity

[0056] The products prepared in the examples and the products prepared in the comparative examples are used as test samples, and the specific steps for testing the porosity are as follows:

[0057] (1) The test sample of a certain size of film area (a circle with a diameter of 30 mm) is cut with scissors and placed in a constant temperature drying oven at 37°C for 24 h;

[0058] (2) The test sample after being kept in the oven in step (1) is placed in a culture dish containing deionized water, and after being fully soaked in the deionized water, the film sheet is taken out, the water on the surface of the film sheet is wiped off with filter paper, and the weight of the wet film is measured;

[0059] (3) After the measurement, the film sheet is placed in a constant temperature drying oven at 50°C for 5 h, and then the weight of the dry film is measured, and the porosity is calculated;

[0060] The calculation formula of the porosity is as follows:

[0061]

[0062] Wherein, ρ: density of water, g / ml; S: film area, cm 2 ; d: dry film thickness, cm; m w : weight of wet film, g; m d : weight of dry film, g.

[0063] 3. Test of water flux

[0064] The products prepared in the examples and the products prepared in the comparative examples are used as test samples, and the specific steps for testing the water flux are as follows:

[0065] (1) First, the sample film to be measured is cut into a circular film sheet with a diameter of 15 mm, and the film sheet is installed in a micro-separator of a membrane device, and conduits are connected to both ends of the separator of the membrane device, and an electronic pressure gauge is connected to one end of the water inlet;

[0066] Specifically, the micro-separator of the membrane device is a self-made device, as shown in Figure 10As shown, including a hollow circular dish upper part; membrane is attached to the hollow circular dish upper part, the membrane is connected to the water inlet above, the membrane is connected to the small funnel below to receive water, the lower end of the funnel is connected to the water outlet conduit, the water outlet water enters the conical flask for receiving;

[0067] (2) Water is transported by a constant flow pump, and the constant flow pump rate is set to 1 r / min. After pre-pressing for 20 min, the flux is stabilized, and the test is started. Three measurements are taken, and the average value is taken;

[0068] The calculation formula of the water flux of the sample membrane is:

[0069] In the formula, J: water flux (L / m 2 ) ; V: water volume (L) ; S: effective test area (m 2 ) ; t: test time (h).

[0070] 4. Test of removal rate of malachite green / methylene blue dye

[0071] The products prepared in the examples and the products prepared in the comparative examples are used as samples, and adsorption experiments are performed on malachite green / methylene blue. The removal rate of malachite green / methylene blue dye is tested, and the specific steps are as follows:

[0072] (1) The products prepared in the examples and the products prepared in the comparative examples are cut into circular membranes with a diameter of about 30 mm, and the membranes are placed in a separation device. Then 5 ml of malachite green dye solution / methylene blue dye with a concentration of 40 ppm is added to the container above the membrane. Under the action of gravity, the dye solution will gradually wet the membrane and flow into the receiving device below through the gap between the fibers of the membrane;

[0073] The separation device is a self-made device, as shown in Figure 11 , including a 20 ml syringe and a 500 ml conical flask. The circular membrane is clamped between the syringe and the conical flask;

[0074] (2) After the solution completely permeates the membrane, the lower solution collection container is removed, and the concentration of the filtrate is tested by a UV spectrophotometer. The removal rate is calculated;

[0075] The calculation formula of the removal rate is:

[0076]

[0077] In the formula, R is the removal rate, C f is the original solution concentration, and C p is the concentration of the filtrate.

[0078] 5. Test of malachite green / methylene blue adsorption capacity

[0079] The products prepared in the examples and the products prepared in the comparative examples are used as samples to test the adsorption amount of malachite green / methylene blue, and the specific steps are as follows:

[0080] (1) 0.02 mg of the membrane sample is accurately weighed by an electronic balance and placed in a transparent storage glass bottle with a volume of 40 ml, and 30 ml of dye solution with a concentration of 65 ppm is added into the bottle, and the glass bottle is placed in a constant temperature water bath at a temperature of 37°C and shaken at a shaking rate of 60 rpm;

[0081] (2) Every 10 min, 2 ml of the sample is taken out, and the concentration of the solution at this time point is tested by an ultraviolet spectrophotometer, and the shaking is stopped until the concentration of the solution no longer changes with time, and the solution is taken out;

[0082] The calculation formula of the adsorption amount of malachite green / methylene blue is as follows:

[0083]

[0084] In the formula, C0 is the original solution concentration (i.e. 65 ppm), C1 is the final solution concentration when the shaking is stopped, V is the original solution volume (i.e. 40 ml), and m is the mass of the membrane.

[0085] 6. After being used for 4 times, the removal rate of malachite green dye / methylene blue dye

[0086] (1) The products prepared in the examples and the products prepared in the comparative examples are cut into circular membrane pieces with a diameter of about 30 mm, and the membrane pieces are placed on a self-made separation device, and then 5 ml of malachite green dye solution / methylene blue dye with a concentration of 40 ppm is added into the container above the membrane pieces, and so on, 5 ml each time, a total of 20 ml (i.e. tested for 4 times), and the interval time is 250 min (i.e. 250 min is needed for each test); under the action of gravity, the dye solution will gradually wet the membrane pieces and flow into the lower receiving device through the gaps between the fibers of the membrane;

[0087] The separation device used is the same as that used in the test of the removal rate of malachite green dye / methylene blue dye;

[0088] (2) After the solution completely permeates the membrane, the lower solution collection container is taken out, and the concentration of the filtrate is tested by an ultraviolet spectrophotometer, and the removal rate is calculated; the calculation method is the same as the removal rate formula described above.

[0089] The manufacturer of graphene oxide in the raw material preparation of each of the following embodiments is Hangzhou Gaoene Technology Co., Ltd., and the model is Gx-GO-1, with a single-layer rate of more than 99%. The manufacturer of polyacrylonitrile is Shanghai Maikelin Biotechnology Co., Ltd., with a weight average molecular weight of 85,000.

[0090] Example 1

[0091] A preparation method of a dye wastewater purifiable composite membrane, and the specific steps are as follows:

[0092] (1) Preparation of raw materials;

[0093] Polyacrylonitrile solution: polyacrylonitrile was placed in a constant temperature box at 70°C for 24 hours, and then added to N,N-dimethylformamide. At 25°C, magnetic stirring was used for 8 hours to prepare a polyacrylonitrile solution with a concentration of 1 g / ml;

[0094] Inorganic dispersion liquid: graphene oxide was added to water, and then stirred at 25°C for 2 hours by magnetic stirring to prepare an inorganic dispersion liquid with a concentration of 5 mg / ml;

[0095] (2) The inorganic dispersion liquid of step (1) and the polyacrylonitrile solution of step (1) were subjected to conjugate electrospinning, thereby obtaining a dye wastewater purifiable composite membrane. Finally, the composite membrane was vacuum dried at 37°C for 12 hours, and then stored in a 24°C vacuum drying box;

[0096] The process parameters of conjugate electrospinning are as follows: the volume of the syringe is 5 ml, the distance from the needle jet to the roller is 10 cm, the roller speed is 60 rpm, the working voltage is 20 Kv, and the injection pump advancing rate is 2 ml / h. The electrospinning process parameters of the inorganic dispersion liquid and the polyacrylonitrile solution are the same.

[0097] The finally prepared dye wastewater purifiable composite membrane is composed of graphene oxide and polyacrylonitrile fibers. The content of graphene oxide in the composite membrane is 6.25 wt.%. The diameter of the polyacrylonitrile fibers is 0.5 μm. The thickness of the composite membrane is 0.049 mm. The graphene oxide is interpenetrated between the interlaced and stacked polyacrylonitrile fibers to form a three-dimensional network support structure. The porosity of the composite membrane is 18%, the water flux is 330 L / m 2 h, and the specific surface area is 400 m 2 / g. The removal rate of the composite membrane for malachite green dye is 94.5%, and the adsorption capacity is 18 mg / g. The removal rate of the composite membrane for methylene blue dye is 98%, and the adsorption capacity is 13 mg / g. After being reused for 4 times, the removal rate of the composite membrane for malachite green dye remains at 91%, and the removal rate of the composite membrane for methylene blue dye remains at 91%. For example, Figure 2The breaking strength of the composite membrane was 1.44552 N and the elongation at break was 23.56%.

[0098] Comparative Example 1

[0099] A method for preparing a dye wastewater purifiable polyacrylonitrile membrane was substantially the same as in Example 1, except that no inorganic dispersion liquid was prepared in Comparative Example 1, and only the polyacrylonitrile solution was electrospun in step (2).

[0100] The porosity of the finally prepared dye wastewater purifiable polyacrylonitrile membrane was 28%, and the water flux was 850 L / m 2 h, the specific surface area was 15 m 2 The removal rate of the membrane for malachite green dye was 58%, and the adsorption capacity was 8 mg / g; the removal rate of the membrane for methylene blue dye was 20%, and the adsorption capacity was 2.8 mg / g; after being reused for 4 times, the removal rate of the membrane for malachite green dye remained at 18%, and the removal rate of the membrane for methylene blue dye remained at 18%; as Figure 2 The breaking strength of the membrane was 1.28139 N, and the elongation at break was 19.69%.

[0101] Compared with Comparative Example 1, the porosity of the composite film of Example 1 is worse than that of Comparative Example 1, because the film of Comparative Example 1 is prepared by electrospinning, so the porosity of the film is very high, when the graphene oxide is added, it will be attached to the fiber, blocking the gap between the fibers, making the composite film more dense, so that the porosity of the composite film decreases; the water flux of the composite film of Example 1 is lower than that of Comparative Example 1, because when the content of GO increases, the GO sheets are scattered in the whole film, and the permeability of the film also decreases, so the flux naturally decreases; the specific surface area of the composite film of Example 1 is higher than that of Comparative Example 1, because the addition of GO sheets increases the gap of the fiber network, and this porous structure increases the specific surface area; the removal rate and adsorption capacity of the composite film of Example 1 for malachite green dye are greater than those of Comparative Example 1 for methylene blue dye, because the composite film containing graphene oxide has strong filtering and adsorbing performance for dyes, because the graphene oxide sheets are randomly arranged and dispersed between the fibers, which leaves a large number of gaps, so that the dye molecules can be quickly adsorbed, and the more the content of graphene oxide, the higher the removal rate and adsorption capacity of the dye; after being reused for 4 times, the removal rate of the composite film of Example 1 for malachite green dye and for methylene blue dye is higher than that of Comparative Example 1, because after the film of Comparative Example 1 is combined with the dye, the permeability decreases rapidly, so the adsorption performance is not as good as the initial state, so the removal rate decreases obviously with the increase of the cycle number, while the composite film containing graphene oxide can better contact with the dye molecules to capture and adsorb the dye molecules, and the intermolecular forces between the dye molecules and GO are adsorbed, so that the composite film still maintains good permeability and dye adsorption performance; the breaking strength and elongation at break of the composite film of Example 1 are greater than those of Example 1, because the graphene oxide increases the force between the surface fibers, so that the composite film has greater breaking strength and deformation capacity than the pure polyacrylonitrile film.

[0102] Example 2

[0103] A method for preparing a composite film for purifying dye wastewater, which is basically the same as Example 1, except that the concentration of the inorganic dispersion liquid in Example 2 is different, so that the content of graphene oxide in the prepared composite film is 2.5wt.%.

[0104] The finally prepared composite film for purifying dye wastewater is composed of graphene oxide and polyacrylonitrile fibers; the diameter of the polyacrylonitrile fibers is 0.4μm; the thickness of the composite film is 0.037mm; the graphene oxide is inserted between the interlaced and stacked polyacrylonitrile fibers to form a three-dimensional network support structure; the porosity of the composite film is 26.5%, the water flux is 530L / m 2 h, and the specific surface area is 370m 2The removal rate of the composite membrane for malachite green dye is 86%, and the adsorption capacity is 13 mg / g; the removal rate of the composite membrane for methylene blue dye is 80%, and the adsorption capacity is 11.4 mg / g; after being reused for 4 times, the removal rate of the composite membrane for malachite green dye remains at 75%, and the removal rate of the composite membrane for methylene blue dye remains at 75%; the breaking strength of the composite membrane is 1.37139 N, and the breaking elongation is 22.42%.

[0105] Example 3

[0106] A preparation method of a dye wastewater purifiable composite membrane, which is basically the same as that in Example 1, except that the concentration of the inorganic dispersion liquid in Example 3 is different, so that the content of graphene oxide in the prepared composite membrane is 1.25 wt.%.

[0107] The finally prepared dye wastewater purifiable composite membrane is composed of graphene oxide and polyacrylonitrile fibers; the diameter of the polyacrylonitrile fibers is 0.35 μm; the thickness of the composite membrane is 0.032 mm; the graphene oxide is interpenetrated between the staggered and stacked polyacrylonitrile fibers to form a three-dimensional network support structure; the porosity of the composite membrane is 27%, the water flux is 780 L / m 2 h, and the specific surface area is 150 m 2 / g; the removal rate of the composite membrane for malachite green dye is 78%, and the adsorption capacity is 9 mg / g; the removal rate of the composite membrane for methylene blue dye is 70%, and the adsorption capacity is 7.8 mg / g; after being reused for 4 times, the removal rate of the composite membrane for malachite green dye remains at 65%, and the removal rate of the composite membrane for methylene blue dye remains at 65%; the breaking strength of the composite membrane is 1.30176 N, and the breaking elongation is 20.65%.

[0108] As Figure 1 shown in the figures, figures a-d are optical diagrams of Comparative Example 1, Example 3, Example 2 and Example 1 respectively, figures e and i are SEM diagrams of Comparative Example 1, figures f and j are SEM diagrams of Example 3, figures g and k are SEM diagrams of Example 2, and figures h and I are SEM diagrams of Example 1; from the optical diagrams, it can be seen that the polyacrylonitrile membrane of Comparative Example 1 is white, and the color of the composite membrane gradually deepens from light brown to dark brown with the increase of the content of graphene oxide; from the SEM pictures, it can be seen that the surface of the polyacrylonitrile membrane of Comparative Example 1 is formed by the staggered and stacked interlaced single fibers with uniform diameter, while the polyacrylonitrile / graphene oxide composite membrane is interlaced with many graphene oxide layers between the single fibers, and the graphene oxide is fixed by the fibers to form a more dense composite membrane than the pure polyacrylonitrile membrane.

[0109] As Figure 3As shown, compared with Comparative Example 1 and Examples 1-3, the porosity of the composite membrane decreases as the graphene oxide content increases.

[0110] like Figure 4 As shown, compared with Comparative Example 1 and Examples 1-3, when the content of graphene oxide increases, the porosity of the membrane decreases, which makes the permeability of the composite membrane worse and the water flux of the composite membrane decreases.

[0111] like Figures 5 to 8 As shown, the composite membranes of Examples 1-3 showed greater removal rates and adsorption capacities for malachite green and methylene blue dyes than Comparative Example 1. Furthermore, the removal rates and adsorption capacities for malachite green and methylene blue dyes increased with the increase of graphene oxide content. Therefore, it can be concluded that the graphene oxide content can improve the removal rates and adsorption capacities for malachite green and methylene blue dyes.

[0112] like Figure 9 As shown, after repeating the experiment 4 times, the composite membranes of Examples 1 to 3 still had a good removal effect on malachite green dye. Among them, the composite membrane of Example 1 still maintained a removal rate of more than 91% for malachite green dye even after filtering 20ml (4 filtrations, 5ml added each time).

Claims

1. A method for preparing a composite membrane capable of purifying dye wastewater, characterized in that, A composite membrane capable of purifying dye wastewater is obtained by conjugating an inorganic dispersion of graphene oxide and a polyacrylonitrile solution into electrospinning. The composite membrane is composed of graphene oxide and polyacrylonitrile fibers; the graphene oxide is interwoven between the staggered polyacrylonitrile fibers to form a three-dimensional network support structure; the graphene oxide content in the composite membrane is 1.25~6.25 wt%; the porosity of the composite membrane is 18%~27%, and the water flux is 330~850 L / m³. 2 h, specific surface area is 15~400m² 2 / g; the tensile strength of the composite membrane is 1.28139~1.44552N, and the elongation at break is 19.69~23.56%.

2. The method for preparing a composite membrane capable of purifying dye wastewater according to claim 1, characterized in that, The process parameters include: the syringe volume is 3~5ml, the distance from the needle nozzle to the roller is 8~10cm, the roller speed is 40~60rpm, the working voltage is 15~20kV, and the injection pump push rate is 1~2ml / h.

3. The method for preparing a composite membrane capable of purifying dye wastewater according to claim 1, characterized in that, The concentration of the polyacrylonitrile solution is 0.08~1.0 g / ml.

4. The method for preparing a composite membrane capable of purifying dye wastewater according to claim 1, characterized in that, The concentration of the inorganic dispersion of graphene oxide is 1~5 mg / ml.

5. The method for preparing a composite membrane capable of purifying dye wastewater according to claim 1, characterized in that, The composite membrane has a removal rate of 78%~94.5% for malachite green dye and an adsorption capacity of 9.0~18.0 mg / g; the composite membrane has a removal rate of 70~98% for methylene blue dye and an adsorption capacity of 7.8~13.0 mg / g; after being reused 4 times, the removal rate of the composite membrane for malachite green dye or methylene blue dye remains at 65%~91%.

6. The method for preparing a composite membrane capable of purifying dye wastewater according to claim 1, characterized in that, The diameter of the polyacrylonitrile fiber is 0.3~0.5μm; the thickness of the composite film is 0.028~0.049mm.

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