Graphene composite nanofiltration membrane, preparation method and application thereof

Abstract

The application relates to a graphene composite nanofiltration membrane and a preparation method and application thereof, the graphene composite nanofiltration membrane comprises graphene oxide sheet layers, wrinkled graphene balls and a substrate; the wrinkled graphene balls and the graphene oxide sheet layers are jointly loaded on the surface of the substrate to form a multi-dimensional nanochannel structure. The graphene composite nanofiltration membrane breaks through the performance limitation of a traditional single-structure membrane, and the hot-pressing process in the preparation method ensures that the functional layer and the substrate are not peeled off, and the long-term stability of the membrane is improved; under high salt concentration, the rejection rates of four kinds of salts are greatly improved, and meanwhile, high flux is maintained.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of nanofiltration membrane materials, and particularly relates to a graphene composite nanofiltration membrane and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of economy and industry in China, the application demand of nanofiltration membrane technology in the fields of high-salinity wastewater treatment and hard water softening is increasing. Traditional nanofiltration membranes generally have problems of poor structural stability, insufficient molecular channel regulation, and low rejection efficiency due to the limitation of the preparation process. Although polyacrylonitrile (PAN) has good thermal stability and chemical inertness, its mechanical properties limit its application in high-pressure separation scenarios. Graphene oxide (GO) has become a research hotspot for nanofiltration membrane modification due to its excellent hydrophilicity, high specific surface area, and mechanical strength. The existing technology such as patent CN109046041B introduces multiple GO layers (such as four layers) through LB self-assembly technology, which to some extent improves the separation performance of the membrane, but still faces the bottleneck of single nanochannel and limited anti-fouling capacity.

[0003] In recent years, researchers have optimized membrane performance by compounding nanomaterials or constructing multi-dimensional structures, but it is still challenging to precisely regulate molecular-level channels and synergistically improve permeability and rejection rate. SUMMARY

[0004] The technical problem to be solved by the application is to provide a graphene composite nanofiltration membrane and a preparation method and application thereof, which solve the technical problems of single molecular channel, low separation efficiency, and poor stability of existing nanofiltration membranes.

[0005] The application provides a graphene composite nanofiltration membrane, which comprises graphene oxide layers, wrinkled graphene spheres, and a substrate; the wrinkled graphene spheres and the graphene oxide layers are jointly loaded on the surface of the substrate to form a multi-dimensional nanochannel structure.

[0006] Preferably, the substrate is a polyacrylonitrile nanofiber membrane with a thickness of 100-800 pm and a porosity of 10%-40%.

[0007] Preferably, the graphene oxide layers have 1-10 layers of modification, and the thickness of a single layer is 1.0-10 nm; the wrinkled graphene spheres have 1-4 layers of modification, and the thickness of a single layer is 1.0-10 pm.

[0008] Preferably, the multi-dimensional nanochannel has a diameter of 0.5-1.2 nm.

[0009] The application provides a preparation method of the graphene composite nanofiltration membrane, which comprises the following steps:

[0010] S1. Preparing a wrinkled graphene sphere film by Langmuir-Blodgett (LB) technology and transferring the film to a substrate;

[0011] S2. Re-dipping and pulling, and repeating the step to obtain a wrinkled graphene sphere modified nanofiltration membrane;

[0012] S3. Preparing an oxidized graphene sheet film by Langmuir-Blodgett technology and transferring the film to the wrinkled graphene sphere modified nanofiltration membrane;

[0013] S4. Re-dipping and pulling, and repeating the step to obtain an oxidized graphene modified composite nanofiltration membrane;

[0014] S5. Performing heat pressing treatment to enhance the interface bonding to obtain a graphene composite nanofiltration membrane.

[0015] Preferably, the Langmuir-Blodgett technology in step S1 is specifically as follows: a wrinkled graphene sphere spreading solution is injected into water surface, and after standing, a compact wrinkled graphene sphere film is formed by compression of a slide barrier, and then the film is transferred to a substrate by a film pulling machine; and the Langmuir-Blodgett technology in step S3 is specifically as follows: an oxidized graphene spreading solution is injected into water surface, and after standing, a compact oxidized graphene film is formed by compression of a slide barrier, and then the film is transferred to the wrinkled graphene sphere modified nanofiltration membrane by a film pulling machine.

[0016] Preferably, the concentration of the wrinkled graphene sphere spreading solution or the oxidized graphene spreading solution is 0.05-1.0 mg / mL; the spreading solvent is a mixed solvent of methanol and deionized water, and the volume ratio of methanol to deionized water is 1:3-1:8.

[0017] Preferably, the dipping speed in step S2 or step S4 is 8-15 mm / min, and the depth of the single dipping liquid surface is 3-5 cm; and the pulling speed is 0.3-0.8 mm / min.

[0018] Preferably, the heat pressing treatment temperature in step S5 is 70-90℃, and the pressure is 0.4-0.6 MPa.

[0019] The preparation of the composite nanofiltration membrane by Langmuir-Blodgett technology is specifically as follows:

[0020] (1) Preparation of wrinkled graphene sphere spreading solution and spreading on water surface monolayer: the wrinkled graphene sphere spreading solution is carefully spread on the water surface by a syringe to obtain sparse monolayer of wrinkled graphene spheres floating on the water surface, the water surface area is reduced by a compression slide barrier, the wrinkled graphene spheres on the water surface are compressed to form a dense film, and a monolayer of wrinkled graphene sphere film floating on the water surface is obtained; the dense wrinkled graphene sphere film floating on the water surface is transferred to the substrate of the electrospun polyacrylonitrile nanofiber membrane by a film pulling machine using LB technology, and a wrinkled graphene sphere-coated polyacrylonitrile nanofiltration membrane is obtained; the above steps are repeated to obtain a wrinkled graphene sphere-coated polyacrylonitrile nanofiltration membrane containing 2 layers;

[0021] (2) Preparation of graphene oxide spreading solution and spreading on water surface monolayer: the graphene oxide spreading solution is carefully spread on the water surface by a syringe to obtain sparse monolayer of graphene oxide floating on the water surface, the water surface area is reduced by a compression slide barrier, the graphene oxide on the water surface is compressed to form a dense film, and a monolayer of graphene oxide film floating on the water surface is obtained; the dense graphene oxide film floating on the water surface is transferred to the wrinkled graphene sphere-coated polyacrylonitrile nanofiltration membrane containing 2 layers by a film pulling machine using LB technology, and a single-layer graphene oxide-coated composite nanofiltration membrane of the application is obtained; the above steps are repeated to obtain a composite nanofiltration membrane sample containing 4 layers of graphene oxide;

[0022] (3) Post-processing: heat pressing (80℃, 0.5MPa) to enhance the interface bonding and ensure that the functional layer is not peeled off from the substrate, and the graphene composite nanofiltration membrane is obtained.

[0023] The application also provides an application of the above graphene composite nanofiltration membrane in a desalination process.

[0024] Preferably, the salt includes one or more of Na2SO4, MgSO4, NaCl and MgCl2, and the concentration of the salt solution is 1.0-3.0mg / mL.

[0025] The present application solves the technical problems of single molecular channel, low separation efficiency and poor stability of the existing nanofiltration membrane by combining the graphene oxide (GO) sheet with the wrinkled graphene ball (rGO), using the Langmuir-Blodgett (LB) self-assembly technology to step by step control the membrane structure. Compared with the traditional single GO sheet structure (such as the four-layer design of patent CN109046041B), the present application forms a multi-dimensional nanochannel by introducing a wrinkled graphene ball, synergistically optimizes the permeation flux and rejection performance of the membrane, and simultaneously uses the three-dimensional structure of rGO to enhance the mechanical support of the substrate, significantly improving the anti-pollution ability and long-term operation stability. In particular, the present application increases the salt solution test concentration to 2.0 mg / mL, breaking through the performance bottleneck of traditional membranes under high salt concentration, and providing an efficient solution for industrial high-salinity wastewater treatment.

[0026] Advantages

[0027] (1) The present application realizes the synergistic loading of rGO and GO by step-by-step LB technology, forms a multi-dimensional nanochannel, and breaks through the performance limitations of traditional single structure membranes;

[0028] (2) The hot pressing process in the present application ensures that the functional layer and the substrate are not peeled off, improving the long-term stability of the membrane;

[0029] (3) The graphene composite nanofiltration membrane in the present application has a greater improvement in the rejection rate of four kinds of salts under high salt concentration (2.0 mg / mL), while maintaining a high flux;

[0030] (4) The preparation process of the present application is simple, the conditions are mild, the thickness of the functional layer can be precisely controlled to the nanometer level, and it is suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The figure is a comparison of the nanofiltration performance of the graphene composite nanofiltration membrane prepared in Example 1 of the present application and the prior art on salt.

[0032] Figure 2 The figure is the nanofiltration performance and flux of the nanofiltration membrane prepared in Example 1 of the present application on NaCl.

[0033] Figure 3 The figure is the nanofiltration performance and flux of the nanofiltration membrane prepared in Example 1 of the present application on Na2SO4.

[0034] Figure 4 The figure is the nanofiltration performance and flux of the nanofiltration membrane prepared in Example 1 of the present application on MgCl2.

[0035] Figure 5 The figure is the nanofiltration performance and flux of the nanofiltration membrane prepared in Example 1 of the present application on MgSO4.

[0036] Figure 6A comparison chart of nanofiltration performance of the nanofiltration membrane prepared for Example 1 of the present application on different salts. DETAILED DESCRIPTION

[0037] The application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and not used to limit the scope of the present application. Furthermore, it should be understood that after reading the content of the present application, those skilled in the art can make various modifications or changes to the present application, and these equivalent forms also fall within the scope of the appended claims of the present application.

[0038] Example 1

[0039] The preparation of the graphene composite nanofiltration membrane in the present embodiment includes the following steps:

[0040] Step 1: First, 3.0 mL of a 1.0 mg / mL aqueous solution of wrinkled graphene ball (rGO) is prepared, then 15.0 mL of methanol is added to the above solution, stirred for 20 min, and a graphene oxide spreading solution with a final concentration of 0.167 mg / mL is obtained.

[0041] Step 2: Take 10.0 mL of the above rGO spreading solution, carefully spread it drop by drop on the water surface in the LB water tank with a syringe, the water tank area is 10*20 cm, stand for 20 minutes, after the methanol on the water surface is completely volatilized, move the slide barrier, the speed is 0.8 cm / min, stop moving when the distance moved to the slide barrier is 1 cm, stand, and wait for the self-assembly of the monolayer rGO film to form.

[0042] Step 3: Cut the polyacrylonitrile nanofiltration membrane into a sample with a size of 5 cm*2.5 cm, immerse the polyacrylonitrile nanofiber in the LB water tank by controlling the parameters of the film pulling machine, setting the immersion speed to 10 mm / min, the length immersed below the liquid surface is 4.0 cm, after waiting for 20 minutes for the liquid surface to stabilize, pull the polyacrylonitrile nanofiber at a pulling speed of 0.5 mm / min, to realize the transfer of the monolayer rGO on the water surface to the surface of the polyacrylonitrile nanofiber membrane.

[0043] Step 4: Repeat Step 3 to obtain a nanofiltration membrane coated with two layers of rGO, named PAN-2rGO.

[0044] Step 5: Take 10.0 mL of the above GO spreading solution, carefully spread it drop by drop on the water surface in the LB water tank with a syringe, the water tank area is 10*20 cm, stand for 20 minutes, after the methanol on the water surface is completely volatilized, move the slide barrier, the speed is 0.8 cm / min, stop moving when the distance moved to the slide barrier is 1 cm, stand, and wait for the self-assembly of the monolayer GO film to form.

[0045] Step 6: The blank polyacrylonitrile nanofiltration membrane was immersed in the LB water tank by controlling the membrane drawing machine parameters, setting the immersion speed to 10 mm / min, the immersion length below the liquid surface was 4.0 cm, after waiting for 20 minutes for the liquid surface to be stable, the nanofiltration membrane was pulled up at a pulling speed of 0.5 mm / min, and the monolayer GO on the water surface was transferred to the blank polyacrylonitrile membrane to obtain a single-layer GO-coated polyacrylonitrile nanofiltration membrane.

[0046] Step 7: Step 6 was repeated three times to obtain a four-layer GO-coated nanofiltration membrane, which was named PAN-4GO.

[0047] Step 8: The rGO-coated nanofiltration membrane (PAN-2rGO) obtained in step 4 was immersed in the LB water tank by controlling the membrane drawing machine parameters, setting the immersion speed to 10 mm / min, the immersion depth below the liquid surface was 4.0 cm, after waiting for 20 minutes for the liquid surface to be stable, the nanofiltration membrane was pulled up at a pulling speed of 0.5 mm / min, and the monolayer GO on the water surface was transferred to the PAN-2rGO nanofiltration membrane surface to obtain a single-layer GO-coated PAN-2rGO nanofiltration membrane.

[0048] Step 9: Step 8 was repeated three times to obtain a four-layer GO-coated PAN-2rGO nanofiltration membrane, which was named PAN-2rGO-4GO, which was the graphene composite nanofiltration membrane sample of the application.

[0049] Example 2

[0050] Four kinds of salt solutions were prepared:

[0051] Four kinds of N a2 SO4, MgSO4, NaCl, MgCl2 salt solutions 1.0 g were accurately measured, stirred constantly until completely dissolved, and then added to 500 mL volumetric flasks, respectively, and then diluted to volume, and stored at room temperature for standby use. The concentrations of the four salt solutions were all 2.0 mg / ml.

[0052] The nanofiltration performance of the test nanofiltration membrane on salt was tested at room temperature, and the specific nanofiltration experiment steps are as follows:

[0053] Step 1: Pre-pressing: Fix the sample on the filtration device, keep the rotation speed of the peristaltic pump at 5 rpm, and press the membrane with deionized water until the water flux reaches a stable state.

[0054] Step 2: Pure water flux determination: Test the flux J of deionized water, i.e. record the volume of the permeated liquid, and terminate the test after stabilization.

[0055] Step 3: Determination of feed liquid retention: Replace the salt solution and test again, and sample test both the permeated solution and the raw material solution.

[0056] Step 4: The rejection performance of the nanofiltration membrane is evaluated by using the rejection rate R, and the calculation formula is as follows:

[0057] R = (1 - C p / Cf)

[0058] In the above formula, R is the rejection rate (%) of the GO / PAN nanofiltration membrane to the four salts, C p is the solute concentration in the permeate, and C f is the solute concentration in the four salts.

[0059] Step 5: Determination of C p and C f of the four salts: The conductivity of the permeate solution and the original salt solution of the four salt solutions is tested by a DDS-11C conductivity meter, and the rejection rate of the four salts is calculated by the formula.

[0060] Figures 2-5 The nanofiltration performance and flux of the PAN, PAN-2rGO, PAN-4GO and PAN-2rGO-4GO nanofiltration membranes to NaCl, Na2SO4, MgCl2 and MgSO4 are sequentially, Figure 6 as shown in Figure 4, which is a comparison diagram of the nanofiltration performance of the nanofiltration membranes to the four salts. It can be seen from Figure 6 that among the four salts, the desalination rate of the nanofiltration membranes with different layers of graphene oxide to Na2SO4 is the highest, and when the graphene oxide reaches four layers, the rejection rate of Na2SO4 is more than 80%; in addition, the rejection rate of the composite nanofiltration membrane (PAN-2rGO-4GO) of the application to the four salts is significantly better than that of other samples, and the rejection rate to Na2SO4 is the highest, reaching more than 90%. Compared with the graphene oxide-containing membrane (PAN-4GO), the introduction of the rGO composite structure further improves the rejection performance, indicating that the design of the multi-dimensional nanochannel effectively enhances the molecular sieving effect.

[0061] Meanwhile, the nanofiltration performance of the nanofiltration membrane of the application to the salt is compared and analyzed with the prior art, and it can be seen from Figure 1 that the flux of the composite nanofiltration membrane prepared in the application to the four salts Na2SO4, MgSO4, NaCl and MgCl2 is much higher than that in the related literature, but the rejection rate to the four salts is comparable to that in the literature; compared with the patent CN109046041B, the flux is comparable, but the rejection rate to the four salts is greatly improved, and it remains stable at high salt concentration (2.0 mg / mL). This breakthrough not only verifies the synergistic effect of the rGO / GO composite structure, but also provides an efficient solution with high flux, high rejection rate and long-term stability for industrial high-salinity wastewater treatment.

[0062] Example 3

[0063] The bovine serum albumin (BSA) aqueous solution was used as a simulated dye system to evaluate the anti-fouling performance of the nanofiltration membrane.

[0064] The BSA solution was prepared as follows: 1000 mg of BSA was accurately weighed, then deionized water was added, and the mixture was stirred until the BSA was dissolved. The resulting solution was then placed in a 1000 mL volumetric flask, and the volume was made up with deionized water to obtain a BSA aqueous solution with a concentration of 1000 mg / L, which was stored at room temperature for later use.

[0065] The main steps for evaluating the anti-fouling performance of the composite nanofiltration membrane were as follows:

[0066] (1) Pre-pressing: The sample was fixed on the filtration device, and the rotation speed of the peristaltic pump was kept at 5 r / min. Deionized water was used to press the membrane for 20 min until the water flux reached a stable state.

[0067] (2) Pure water flux determination: The flux J of deionized water was tested, i.e., the volume of the permeated liquid was recorded, and the water flux J was tested w1 until the test was terminated.

[0068] (3) BSA aqueous solution determination: The BSA aqueous solution was used instead of deionized water for testing, and the flux of the solution was measured as J p .

[0069] (4) Cleaning of the nanofiltration membrane sample: The BSA solution was poured out, and then deionized water was added for cleaning for 15 min.

[0070] (5) Second test of water flux: The washed solution was poured out, and deionized water was added again for testing the second pure water flux J w2 .

[0071] Four parameters for evaluating the anti-fouling performance of the GO / PAN nanofiber membrane were introduced, including the flux recovery rate (FRR) after water cleaning, the flux decay rate (R t ), the reversible flux decay rate (R r ), and the irreversible flux decay rate (R ir ). The calculation formulas were as follows:

[0072] FRR (%) = J w2 / J w1 × 100%

[0073] R t (%) = (1 - J p / J w1 ) × 100%

[0074] R r (%) = (J w2 - J p ) / J w1 × 100%

[0075] R ir (%) = (1 - J w2 / J w1 ) x 100%

[0076] Table 1. Anti-fouling index of the nanofiltration membrane

[0077]

[0078] As shown in Table 1, the graphene composite nanofiltration membrane prepared in the application has excellent anti-fouling performance and can be practically applied to desalination treatment of wastewater.

Claims

1. A graphene composite nanofiltration membrane, characterized by, The graphene composite nanofiltration membrane comprises graphene oxide sheet, corrugated graphene ball and substrate; the corrugated graphene ball and the graphene oxide sheet are jointly loaded on the surface of the substrate to form a multi-dimensional nanochannel structure with a diameter of 0.5-1.2 nm; the modified layer number of the graphene oxide sheet is 1-10 layers, and the single-layer thickness is 1.0-10 nm; the modified layer number of the corrugated graphene ball is 1-4 layers, and the single-layer thickness is 1.0-10 μm; The preparation method of the graphene composite nanofiltration membrane comprises the following steps: S1. A corrugated graphene ball film is prepared by using the Langmuir-Blodgett technology and is transferred to the substrate; S2. The immersion and pulling are repeated to obtain a corrugated graphene ball modified nanofiltration membrane; S3. A graphene oxide sheet film is prepared by using the Langmuir-Blodgett technology and is transferred to the corrugated graphene ball modified nanofiltration membrane; S4. The immersion and pulling are repeated to obtain a graphene oxide modified composite nanofiltration membrane; S5. The interface bonding is enhanced by hot-pressing treatment under the conditions of a temperature of 70-90 ℃ and a pressure of 0.4-0.6 Mpa to obtain the graphene composite nanofiltration membrane.

2. The graphene composite nanofiltration membrane according to claim 1, wherein, The substrate is a polyacrylonitrile nanofiber membrane with a thickness of 100-800 μm and a porosity of 10%-40%.

3. The graphene composite nanofiltration membrane according to claim 1, wherein, In step S1, the Langmuir-Blodgett technology is specifically as follows: the corrugated graphene ball spreading solution is injected into the water surface, and after standing, the dense corrugated graphene ball film is formed by compressing the slide barrier, and then the film is transferred to the substrate by using a film pulling machine; in step S3, the Langmuir-Blodgett technology is specifically as follows: the graphene oxide spreading solution is injected into the water surface, and after standing, the dense graphene oxide film is formed by compressing the slide barrier, and then the film is transferred to the corrugated graphene ball modified nanofiltration membrane by using a film pulling machine.

4. The graphene composite nanofiltration membrane according to claim 3, wherein, The concentration of the corrugated graphene ball spreading solution or the graphene oxide spreading solution is 0.05-1.0 mg / mL; the spreading solvent is a mixed solvent of methanol and deionized water, and the volume ratio of methanol to deionized water is 1:3-1:

8.

5. The graphene composite nanofiltration membrane according to claim 1, wherein, In step S2 or step S4, the immersion speed is 8-15 mm / min, and the single immersion liquid surface below the depth is 3-5 cm; the pulling speed is 0.3-0.8 mm / min.

6. The graphene composite nanofiltration membrane in claim 1 is applied in a desalination process.

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