Nanofiltration two-dimensional channel membrane as well as preparation method and application thereof

Abstract

The invention provides a nanofiltration two-dimensional channel membrane as well as a preparation method and application thereof, and belongs to the technical field of membrane separation. The nanofiltration two-dimensional channel membrane provided by the invention comprises a basement membrane, and digested graphene oxide and zirconium phosphate which are loaded on the basement membrane, the basement membrane is a cellulose membrane; the digested graphene oxide is of an ordered layered structure with sub-nanometer size channels; the zirconium phosphate is distributed in the sub-nanometer size channel of the digested graphene oxide. The digested graphene oxide in the nanofiltration two-dimensional channel membrane provided by the invention can interact with strontium ions and provide a water flow channel, so that the rejection rate and the water flux are effectively improved, and meanwhile, zirconium phosphate further improves the rejection rate of the strontium ions by utilizing the excellent adsorption performance of the zirconium phosphate. The result of the embodiment shows that the rejection rate of the nanofiltration two-dimensional channel membrane provided by the invention on strontium ions can be up to 100%, and the water flux can be up to 780.14 L.m <-2 >. H <-1 >. Bar <-1 >.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane separation, and in particular to a nanofiltration two-dimensional channel membrane, a preparation method thereof, and an application thereof. Background Art

[0002] Traditional methods for treating radioactive wastewater include chemical precipitation, membrane filtration, ion exchange, and adsorption. Among them, the chemical precipitation method is simple and has a wide range of applicable elements, but it has the disadvantages of difficult solid-liquid separation and a large sludge yield, and the sludge needs to be further treated; when using ion exchange to treat sewage, ion exchange resins are used, and their regeneration requires the participation of chemical reagents, which will cause irreparable secondary pollution; using the adsorption method to treat sewage is simple and flexible, but the adsorption process is usually reversible, and the adsorbent needs a suitable desorption method for regeneration, and the type of adsorbent will affect the adsorption effect. Membrane filtration technology is a newly developed technology that uses driving forces such as pressure difference, temperature difference, and potential difference to separate and concentrate radioactive nuclides in wastewater, and has the advantages of environmental protection, low pollution, and excellent nanofiltration performance. Currently, membrane separation methods are commonly used to treat radioactive wastewater. For example, the prior art provides a nanofiltration membrane with a strontium rejection rate of 80% and a water flux that can reach 75L·m -2 ·h -1 ·bar -1 ; however, its rejection rate and water flux still cannot meet the requirements of practical applications. Summary of the Invention

[0003] The purpose of the present invention is to provide a nanofiltration two-dimensional channel membrane, a preparation method thereof, and an application thereof. The nanofiltration two-dimensional channel membrane provided by the present invention has a high rejection rate and a high water flux.

[0004] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions: The present invention provides a nanofiltration two-dimensional channel membrane, including a substrate membrane and exfoliated graphene oxide and zirconium phosphate loaded on the substrate membrane; the substrate membrane is a cellulose membrane; The exfoliated graphene oxide has an ordered layered structure with sub-nanometer-sized channels; the zirconium phosphate is distributed in the sub-nanometer-sized channels of the exfoliated graphene oxide; The total loading amount of the exfoliated graphene oxide and zirconium phosphate is 1-5mg / cm 2 .

[0005] Preferably, the total loading amount of the exfoliated graphene oxide and zirconium phosphate is 2-3mg / cm 2 .

[0006] The present invention also provides a preparation method of the nanofiltration two-dimensional channel membrane according to the above technical solution, including the following steps: (1) Mix graphene oxide, nitric acid, hydrofluoric acid with water and carry out a digestion reaction to obtain a digested graphene oxide suspension; (2) Mix the digested graphene oxide suspension obtained in step (1) with zirconium oxychloride for adsorption to obtain a zirconium oxychloride - digested graphene oxide suspension; (3) Mix the zirconium oxychloride - digested graphene oxide suspension obtained in step (2) with hydrofluoric acid and phosphoric acid and carry out a cross - linking reaction to obtain a zirconium phosphate - digested graphene oxide suspension; (4) Form a film of the zirconium phosphate - digested graphene oxide suspension obtained in step (3) on a substrate membrane to obtain a nanofiltration two - dimensional channel membrane.

[0007] Preferably, in step (1), the mass ratio of graphene oxide, the volume of nitric acid and the volume of hydrofluoric acid is 1 mg:(0.01 - 0.02) mL:(0.1 - 0.2) mL; the concentration of graphene oxide in the mixed solution of graphene oxide, nitric acid, hydrofluoric acid and water is 5 - 6 mg / mL; the mass concentration of the nitric acid is 65 - 68%; the mass concentration of the hydrofluoric acid is 35 - 40%.

[0008] Preferably, in step (1), the temperature of the digestion reaction is 145 - 165 °C, and the time of the digestion reaction is 2 - 4 h.

[0009] Preferably, in step (2), the mass ratio of digested graphene oxide to zirconium oxychloride in the digested graphene oxide suspension is (10 - 30):(3000 - 3500).

[0010] Preferably, in step (2), the temperature of the adsorption is 75 - 85 °C, and the time of the adsorption is 0.5 - 1.2 h.

[0011] Preferably, in step (3), the volume ratio of hydrofluoric acid and phosphoric acid to the digested graphene oxide suspension in step (2) is (1 - 3):(0.2 - 1.5):(10 - 30); the mass concentration of the hydrofluoric acid is 35 - 40%; the mass concentration of the phosphoric acid is ≥85%.

[0012] Preferably, in step (3), the temperature of the cross - linking reaction is 75 - 85 °C, and the time of the cross - linking reaction is 0.5 - 1 h.

[0013] The present invention also provides the application of the nanofiltration two - dimensional channel membrane described in the above technical solution or the nanofiltration two - dimensional channel membrane obtained by the preparation method described in the above technical solution in removing strontium ions in water.

[0014] The present invention provides a nanofiltration two-dimensional channel membrane, which comprises a substrate membrane and exfoliated graphene oxide and zirconium phosphate loaded on the substrate membrane; the substrate membrane is a mixed cellulose membrane; the exfoliated graphene oxide has an ordered layered structure with sub-nanometer-sized channels; the zirconium phosphate is distributed in the sub-nanometer-sized channels of the exfoliated graphene oxide; the total loading amount of the exfoliated graphene oxide and zirconium phosphate is 1-5 mg / cm 2 In the nanofiltration two-dimensional channel membrane of the present invention, the exfoliated graphene oxide has an ordered layered structure with sub-nanometer-sized channels, which can have cation-π interaction and electrostatic interaction with strontium ions in water, so as to achieve the interception of strontium ions and effectively improve the interception rate; and the two-dimensional channels formed by this layered structure enable water molecules to pass through smoothly, effectively improving the water flux; at the same time, the zirconium phosphate loaded in the two-dimensional channels of the exfoliated graphene oxide itself has excellent adsorption performance for strontium ions, which can effectively prevent strontium ions from passing through the channel membrane, achieving the effect of separating strontium ions in an aqueous solution; and when the strontium ions adsorbed by the zirconium phosphate are sufficient, it can generate a charge repulsion effect on subsequent strontium ions, further improving the interception rate of the nanofiltration two-dimensional channel membrane. The results of the examples show that the nanofiltration two-dimensional channel membrane provided by the present invention can have an interception rate of strontium ions as high as 100%, and the water flux can be as high as 780.14 L·m -2 ·h -1 ·bar -1 。 Description of the Drawings

[0015] Figure 1 is the SEM image of the surface of the nanofiltration two-dimensional channel membrane of Example 1; Figure 2 is the SEM image of the cross-section of the nanofiltration two-dimensional channel membrane of Example 1; Figure 3 is the XRD pattern of the nanofiltration two-dimensional channel membrane of Example 1; Figure 4 is the bar chart of the interception rate and water flux of the nanofiltration two-dimensional channel membrane of Example 1 for strontium ion solutions with different concentrations; Figure 5 is the bar chart of the interception rate and water flux of the nanofiltration two-dimensional channel membrane of Example 1 used for different times; Figure 6 is the bar chart of the interception rate and water flux of the nanofiltration two-dimensional channel membranes of Examples 1-4; Figure 7 is the bar chart of the interception rate and water flux of the nanofiltration two-dimensional channel membranes of Example 1 and Examples 5-8; Figure 8 is the bar chart of the interception rate and water flux of the nanofiltration two-dimensional channel membrane of Example 1, a commercially available graphene oxide solution membrane and zirconium phosphate. Detailed Embodiments

[0016] The present invention provides a nanofiltration two-dimensional channel membrane, comprising a substrate membrane and exfoliated graphene oxide and zirconium phosphate loaded on the substrate membrane; the substrate membrane is a cellulose membrane; The exfoliated graphene oxide has an ordered layered structure with sub-nanometer-sized channels; the zirconium phosphate is distributed in the sub-nanometer-sized channels of the exfoliated graphene oxide; The total loading amount of the exfoliated graphene oxide and zirconium phosphate is 1-5 mg / cm 2 .

[0017] As an embodiment of the present invention, the substrate membrane is a cellulose membrane; the cellulose membrane can be a commercially available mixed cellulose filter membrane; the pore size of the substrate membrane can be 0.1-0.4 μm, or can be 0.2 μm.

[0018] As an embodiment of the present invention, the total loading amount of the exfoliated graphene oxide and zirconium phosphate is 1-5 mg / cm 2 , can be 2-4 mg / cm 2 , or can be 3-3.5 mg / cm 2 ; the mass ratio of the exfoliated graphene oxide to zirconium phosphate can be (0.5-1.5):(10-70), or can be (0.8-1.4):(20-60), or can also be (1.0-1.2):(30-50). In the present invention, by limiting the loading amounts of the exfoliated graphene oxide and zirconium phosphate, the functions of both are fully exerted, and the rejection rate is further improved.

[0019] The exfoliated graphene oxide of the nanofiltration two-dimensional channel membrane provided by the present invention has an ordered layered structure with sub-nanometer-sized channels, which can interact with strontium ions in water to achieve the rejection of strontium ions; at the same time, the two-dimensional channels formed by this layered structure allow water molecules to pass through smoothly, effectively improving the water flux; and zirconium phosphate with excellent adsorption performance for strontium ions is loaded in the sub-nanometer-sized channels of the exfoliated graphene oxide, further improving the rejection rate.

[0020] The present invention also provides a preparation method of the nanofiltration two-dimensional channel membrane according to the above technical solution, comprising the following steps: (1) Mix graphene oxide, nitric acid, hydrofluoric acid and water and carry out an exfoliation reaction to obtain an exfoliated graphene oxide suspension; (2) Mix the exfoliated graphene oxide suspension obtained in step (1) with zirconium oxychloride for adsorption to obtain a zirconium oxychloride-exfoliated graphene oxide suspension; (3) Mix the zirconium oxychloride-exfoliated graphene oxide suspension obtained in step (2) with hydrofluoric acid and phosphoric acid and carry out a crosslinking reaction to obtain a zirconium phosphate-exfoliated graphene oxide suspension; (4) Form a film of the zirconium phosphate-digested graphene oxide suspension obtained in the step (3) on a substrate membrane to obtain a nanofiltration two-dimensional channel membrane.

[0021] In the present invention, graphene oxide, nitric acid, hydrofluoric acid and water are mixed and then subjected to a digestion reaction to obtain a digested graphene oxide suspension.

[0022] As an embodiment of the present invention, the graphene oxide can be graphene oxide prepared by the improved Hummer method.

[0023] As an embodiment of the present invention, the mixing of the graphene oxide, nitric acid, hydrofluoric acid and water is preferably carried out under the conditions of stirring and ultrasonic treatment; the stirring rate can be 900-1200 rpm, or 950-1150 rpm, or 1000-1100 rpm; the stirring time can be 10-20 min, or 12-18 min, or 15-16 min; the power of the ultrasonic treatment can be 20-40 KHz, or 25-35 KHz, or 28-30 KHz; the ultrasonic treatment time can be 10-20 min, or 12-18 min, or 15-16 min. In the present invention, by defining the process parameters of stirring and ultrasonic treatment, the reaction raw materials are ensured to be mixed evenly.

[0024] As an embodiment of the present invention, the ratio of the mass of the graphene oxide, the volume of the nitric acid and the volume of the hydrofluoric acid can be 1 mg: (0.01-0.02) mL: (0.1-0.2) mL, or 1 mg: 0.01 mL: 0.13 mL; the concentration of the graphene oxide can be 5-6 mg / mL, or 5.2-5.8 mg / mL, or 5.5-5.6 mg / mL; the mass concentration of the nitric acid can be 65-68%, or 66-67%; the mass concentration of the hydrofluoric acid can be 35-40%, or 36-39%, or 37-38%. In the present invention, by defining the dosage and concentration of each reaction raw material, the reaction raw materials are fully contacted and reacted to ensure the obtained digested graphene oxide suspension.

[0025] As an embodiment of the present invention, the temperature of the digestion reaction can be 145-165 °C, or 150-162 °C, or 155-160 °C; the time of the digestion reaction can be 2-4 h, or 2.5-3.5 h, or 3-3.2 h. In the present invention, the structure of graphene oxide is destroyed at high temperature, laying a foundation for the subsequent combination with zirconium phosphate; by defining the process parameters of the digestion reaction, the full reaction between the reaction raw materials is realized.

[0026] As an embodiment of the present invention, centrifugation, washing, and resuspension can be sequentially performed after the digestion reaction.

[0027] As an embodiment of the present invention, the centrifugation rate can be 8000 - 15000 rpm, or 9000 - 13000 rpm, or 10000 - 12000 rpm; the centrifugation time can be 10 - 20 min, or 12 - 18 min, or 15 - 16 min; the detergent for washing can be water; the number of times of centrifugation and washing can independently be 2 - 5 times, or 3 - 4 times, or 3 times; the solvent for resuspension can be water.

[0028] The present invention has no special limitation on the operations of washing and resuspension, and the operations of washing and resuspension commonly used by those skilled in the art can be adopted.

[0029] As an embodiment of the present invention, the concentration of digested graphene oxide in the digested graphene oxide suspension can be 1 - 2 mg / mL, or 1.2 - 1.5 mg / L, or 1.25 mg / L. In the present invention, by limiting the process parameters of the centrifugation operation after the digestion reaction and the concentration of the digestion reaction product, it is beneficial to remove the unreacted raw materials in the digestion reaction, and at the same time ensure that there is sufficient digested graphene oxide in the obtained suspension for subsequent reactions.

[0030] After obtaining the digested graphene oxide suspension, the present invention mixes the digested graphene oxide suspension with zirconium oxychloride for adsorption to obtain a zirconium oxychloride - digested graphene oxide suspension.

[0031] As an embodiment of the present invention, the mass ratio of digested graphene oxide to zirconium oxychloride in the digested graphene oxide suspension can be (10 - 30):(3000 - 3500), or (15 - 25):(3100 - 3400), or (18 - 20):(3200 - 3300). In the present invention, by limiting the dosage ratio of the reaction raw materials, the sufficient contact reaction between the reaction raw materials is ensured.

[0032] As an embodiment of the present invention, the adsorption temperature can be 75 - 85 °C, or 76 - 82 °C, or 78 - 80 °C; the adsorption time can be 0.5 - 1.2 h, or 0.8 - 1 h. In the present invention, during the contact process of the reaction raw materials, zirconium oxychloride is adsorbed on the digested graphene oxide; by limiting the process parameters of the adsorption process, the sufficient adsorption of zirconium oxychloride is ensured.

[0033] As an embodiment of the present invention, stirring can be carried out during the adsorption; the present invention has no special limitation on the operation of the stirring, and the stirring operation adopted by those skilled in the art can be used.

[0034] As an embodiment of the present invention, dilute ammonia water can also be added during the adsorption process; the mass concentration of the dilute ammonia water can be 2.5 - 2.8%, or can be 2.6 - 2.7%; the volume ratio of the dilute ammonia water to the suspension of exfoliated graphene oxide can be (0.2 - 4):20, or can be (0.5 - 3):20, or can also be (1 - 2):20. In the present invention, by adding dilute ammonia water during the adsorption process, the full dispersion of exfoliated graphene oxide can be realized, which is beneficial to the full contact between exfoliated graphene oxide and zirconium oxychloride.

[0035] After obtaining the zirconium oxychloride - exfoliated graphene oxide suspension, the present invention mixes the zirconium oxychloride - exfoliated graphene oxide suspension with hydrofluoric acid and phosphoric acid and then carries out a cross - linking reaction to obtain a zirconium phosphate - exfoliated graphene oxide suspension.

[0036] As an embodiment of the present invention, the volume ratio of the hydrofluoric acid and phosphoric acid to the suspension of exfoliated graphene oxide can be (1 - 3):(0.2 - 1.5):(10 - 30), or can be (1.5 - 2.8):(0.5 - 1.2):(15 - 28), or can also be (2 - 2.5):(0.8 - 1):(20 - 25); the mass concentration of the hydrofluoric acid can be 35 - 40%, or can be 36 - 39%, or can also be 37 - 38%; the mass concentration of the phosphoric acid can be ≥85%, or can be ≥87%, or can also be ≥90%. In the present invention, by limiting the dosage and concentration of the reaction raw materials, the full reaction between the reaction raw materials is ensured, and the phosphorylation of zirconium oxychloride is fully realized.

[0037] As an embodiment of the present invention, the temperature of the cross - linking reaction can be 75 - 85°C, or can be 76 - 82°C, or can also be 78 - 80°C; the time of the cross - linking reaction can be 0.5 - 1 h, or can be 0.6 - 0.9 h, or can also be 0.7 - 0.8 h. In the present invention, hydrofluoric acid can make F - form a zirconium fluoride complex ion with Zr 4+ , reducing the concentration of zirconium ions in the solution and avoiding the precipitation of Zr 4+ as an inactive solid, controlling the generation rate of zirconium phosphate in the system, and realizing the formation of zirconium phosphate; at the same time, it undergoes a cross - linking reaction with exfoliated graphene oxide to form a new two - dimensional channel; by controlling the process parameters of the cross - linking reaction, the progress of the reaction is further controlled.

[0038] As an embodiment of the present invention, stirring can be carried out simultaneously during the cross-linking reaction; the present invention has no special limitation on the operation of the stirring, and the common stirring used by those skilled in the art can be adopted.

[0039] As an embodiment of the present invention, after the cross-linking reaction, centrifugation and resuspension can be carried out in sequence to obtain a zirconium phosphate-digested graphene oxide suspension.

[0040] As an embodiment of the present invention, the centrifugation rate can be 8000-15000 rpm, or 9000-13000 rpm, or 10000-12000 rpm; the centrifugation time can be 10-20 min, or 12-18 min, or 15-16 min; the number of centrifugation times can be 2-5 times, or 3 times; the resuspension solvent can be water; the concentration of the zirconium phosphate-digested graphene oxide suspension after resuspension can be 4-23 mg / mL, or 5-20 mg / mL, or 10-15 mg / mL. In the present invention, by performing centrifugation and resuspension treatments after the cross-linking reaction, unreacted raw materials are fully removed to avoid their influence on the retention performance and water flux of the membrane material.

[0041] After obtaining the zirconium phosphate-digested graphene oxide suspension, the present invention forms a film of the zirconium phosphate-digested graphene oxide suspension on a substrate membrane to obtain a nanofiltration two-dimensional channel membrane.

[0042] As an embodiment of the present invention, the film-forming method can be pressure filtration or suction filtration; the suction filtration pressure can be 0.01-0.1 MPa, or 0.02-0.08 MPa, or 0.05-0.06 MPa. In the present invention, by limiting the process parameters of the suction filtration operation, the zirconium phosphate-digested graphene oxide suspension can form a better film, further improving the performance of the membrane material.

[0043] As an embodiment of the present invention, the volume ratio of the zirconium phosphate-digested graphene oxide suspension to the area of the nanofiltration two-dimensional channel membrane can be (1-6) mL:(11-12) cm 2 , or (1-3) mL:(11-11.5) cm 2 , or (2-2.5) mL:(11.2-11.34) cm 2 . In the present invention, by limiting the dosage of the suspension and the volume of the membrane material, the uniform distribution of digested graphene oxide and zirconium phosphate is ensured, further improving the retention rate.

[0044] The present invention has no special limitation on the operation of the pressure filtration, and the common pressure filtration used by those skilled in the art can be adopted.

[0045] As an embodiment of the present invention, the position of film formation can be on the side of the small-hole surface of the base film. In the present invention, by defining the film formation position, the full combination of the base film with exfoliated graphene oxide and zirconium phosphate is realized, further improving the performance of the nanofiltration two-dimensional channel membrane.

[0046] The preparation method provided by the present invention realizes the preparation of exfoliated graphene oxide and zirconium phosphate and the combination of the two with the base film, which is beneficial to giving full play to the roles of the two and effectively improving the rejection rate and water flux of the nanofiltration two-dimensional channel membrane.

[0047] The present invention also provides the application of the nanofiltration two-dimensional channel membrane described in the above technical solution or the nanofiltration two-dimensional channel membrane obtained by the preparation method described in the above technical solution in removing strontium ions in water.

[0048] As an embodiment of the present invention, the concentration of strontium ions in the water can be 0.1 - 200 mg / L, or can also be 1 - 10 mg / L.

[0049] In order to further illustrate the present invention, the following describes in detail the nanofiltration two-dimensional channel membrane provided by the present invention, its preparation method and application in combination with examples, but they cannot be understood as limiting the protection scope of the present invention.

[0050] Example 1 A nanofiltration two-dimensional channel membrane is composed of a commercially available mixed cellulose filter membrane and exfoliated graphene oxide and zirconium phosphate loaded on the commercially available mixed cellulose membrane; the pore size of the commercially available mixed cellulose filter membrane is 0.2 μm, and the area is 1.13×10 -3 m 2 ; The exfoliated graphene oxide has an ordered layered structure with sub-nanometer-sized channels; the zirconium phosphate is distributed in the sub-nanometer-sized channels of the exfoliated graphene oxide; The total loading amount of the exfoliated graphene oxide and zirconium phosphate is 2.12 mg / cm 2 ; among which the mass ratio of exfoliated graphene oxide to zirconium phosphate is 1:23; The preparation method of the nanofiltration two-dimensional channel membrane is specifically as follows: (1) Mix 25 mg of graphene oxide with 20 mL of water, stir for 15 min and then sonicate at 40 KHz for 15 min. Then add 0.25 mL of 65% nitric acid and 3.25 mL of 40% hydrofluoric acid, stir for 15 min and sonicate at 40 KHz for 15 min. Carry out a digestion reaction at 160 °C for 4 h. After the reaction, centrifuge at 10,000 rpm to obtain digested graphene oxide, and wash it 3 times; then resuspend it with deionized water to obtain a digested graphene oxide suspension with a concentration of 1 mg / mL; the mass ratio of graphene oxide, the volume of nitric acid, and the volume of hydrofluoric acid is 1 mg:0.01 mL:0.13 mL; The preparation method of graphene oxide is as follows: Add 3 g of natural graphite powder, 2.5 g of P 2 O 5 and 2.5 g of K 2 S 2 O 8 to 12 mL of 98% H 2 SO 4 . After sonication at 40 KHz, stir for 2 h; filter, vacuum dry the filter cake at 60 °C for 12 h to obtain a pre-oxidized product. Mix the pre-oxidized product with 120 mL of 98% H 2 SO 4 and stir at 5 °C for 6 h. Then add 15 g of KMnO 4 to the mixture at 60 °C for oxidation; after oxidation, dilute with 1 L of deionized water and use 20 mL of H 2 O 2 to further oxidize the product at 80 °C; centrifuge and wash the oxidized product with HCl and deionized water, and finally dilute it to 1 L with deionized water to obtain a graphene oxide solution; (2) Mix 20 mL of the digested graphene oxide suspension obtained in step (1) with 3.3 g of zirconium oxychloride, then add 0.2 mL of dilute ammonia water with a mass concentration of 2.8%, and carry out adsorption at 850 rpm and 80 °C for 60 min to obtain a zirconium oxychloride-digested graphene oxide suspension; the mass ratio of digested graphene oxide to zirconium oxychloride in the digested graphene oxide suspension is 20:3300; the volume ratio of the dilute ammonia water to the digested graphene oxide suspension is 0.2:20; (3) Mix the zirconium oxychloride-digested graphene oxide suspension obtained in step (2) with 2 mL of hydrofluoric acid with a mass concentration of 40% and 0.3 mL of phosphoric acid with a mass concentration of 85%, and carry out a cross-linking reaction at 850 rpm and 80 °C for 45 min. After the cross-linking reaction is completed, centrifuge at 12,000 rpm for 15 min, repeat the washing 3 times, and resuspend with deionized water to 50 mL to obtain a zirconium phosphate-digested graphene oxide suspension; the volume ratio of hydrofluoric acid and phosphoric acid to the digested graphene oxide suspension in step (2) is 2:0.3:20; (4) Dilute 3 mL of the zirconium phosphate-digested graphene oxide suspension obtained in step (3) to 42.5 mL, and then dry it into a film on the small-hole side of a mixed cellulose membrane (pore size: 0.2 μm, surface area: 1.13×10 -3 m 2 ) under 0.1 MPa to obtain a nanofiltration two-dimensional channel membrane.

[0051] After drying the nanofiltration two-dimensional channel membrane obtained in Example 1 at 60 °C for 12 h, use a scanning electron microscope to detect the surface and cross-section of the nanofiltration two-dimensional channel membrane obtained in Example 1, and the results are as shown in Figure 1 and Figure 2 shown. It can be seen from Figure 1 that the surface of the nanofiltration two-dimensional channel membrane is intact, rough, uneven and has wrinkles but no large pores or obvious defects; it can be seen from Figure 2 that the membrane is a tightly stacked layered structure.

[0052] Use an X-ray diffractometer to detect the dried nanofiltration two-dimensional channel membrane obtained in Example 1, and the results are as shown in Figure 3 shown. It can be seen from Figure 3 that the interlayer spacing of the membrane is 0.98 nm.

[0053] Example 2 The difference between Example 2 and Example 1 is only that in step (4) of the preparation method of the nanofiltration two-dimensional channel membrane, 1.5 mL of the zirconium phosphate-digested graphene oxide suspension obtained in step (3) is diluted to 42.5 mL and then formed into a membrane, and the loading amount of digested graphene oxide and zirconium phosphate is 1.06 mg / cm 2 ; others are the same as in Example 1.

[0054] Example 3 The difference between Example 3 and Example 1 is only that in step (4) of the preparation method of the nanofiltration two-dimensional channel membrane, 4.5 mL of the zirconium phosphate-digested graphene oxide suspension obtained in step (3) is diluted to 42.5 mL and then formed into a membrane, and the loading amount of digested graphene oxide and zirconium phosphate is 3.17 mg / cm 2; wherein the mass ratio of exfoliated graphene oxide to zirconium phosphate is 1.5:34.5, and the others are the same as in Example 1.

[0055] Example 4 The difference between Example 4 and Example 1 is only that in step (4) of the preparation method of the nanofiltration two-dimensional channel membrane, 6 mL of the zirconium phosphate-exfoliated graphene oxide suspension obtained in step (3) is diluted to 42.5 mL and then formed into a membrane, and the loading amount of exfoliated graphene oxide and zirconium phosphate is 4.23 mg / cm 2 ; the others are the same as in Example 1.

[0056] Example 5 The difference between Example 5 and Example 1 is only that in step (3) of the preparation method of the nanofiltration two-dimensional channel membrane, the volume ratio of hydrofluoric acid and phosphoric acid to the exfoliated graphene oxide suspension in step (2) is 2:0.2:20, and the rest is the same as in Example 1.

[0057] Example 6 The difference between Example 6 and Example 1 is only that in step (3) of the preparation method of the nanofiltration two-dimensional channel membrane, the volume ratio of hydrofluoric acid and phosphoric acid to the exfoliated graphene oxide suspension in step (2) is 2:0.5:20, and the rest is the same as in Example 1.

[0058] Example 7 The difference between Example 7 and Example 1 is only that in step (3) of the preparation method of the nanofiltration two-dimensional channel membrane, the volume ratio of hydrofluoric acid and phosphoric acid to the exfoliated graphene oxide suspension in step (2) is 2:1.0:20, and the rest is the same as in Example 1.

[0059] Example 8 The difference between Example 8 and Example 1 is only that in step (3) of the preparation method of the nanofiltration two-dimensional channel membrane, the volume ratio of hydrofluoric acid and phosphoric acid to the exfoliated graphene oxide suspension in step (2) is 2:1.5:20, and the rest is the same as in Example 1.

[0060] Application Example 1 Use the nanofiltration two-dimensional channel membrane of Example 1 to conduct retention experiments on strontium ion solutions of 1 mg / L, 10 mg / L, 50 mg / L, and 200 mg / L respectively; the specific steps are as follows: Pour the strontium ion solutions of 1 mg / L, 10 mg / L, 50 mg / L, and 200 mg / L into the feed side of the filtration device respectively, use the nanofiltration two-dimensional channel membrane of Example 1 as the filter membrane, conduct suction filtration under a pressure of 0.1 MPa, and record the time required for the same volume of suction filtration; Water flux ( ) calculation formula:

[0061] In the formula, A is the effective membrane area (m 2 ), ∆t is the permeation time (h), P is the filtration pressure (bar); Collect the filtrate at the end of the filtration device; by inductively coupled plasma-optical emission spectrometry (ICP-OES, iCAP 7400, Thermo Fisher Scientific, Dreieich, Germany), detect the activity concentration of strontium ions in the initial aqueous strontium ion solution (denoted as C 1 ), and the activity concentration of strontium ions in the filtrate (denoted as C 2 ); The calculation formula for the rejection rate of strontium ions ( %) is:

[0062] Repeat the experiment three times, and the obtained results are shown in Table 1 and Figure 4 as follows; Table 1 Record table of water flux and rejection rate of the nanofiltration two-dimensional channel membrane in Example 1

[0063] As can be seen from Table 1 and Figure 4 the nanofiltration two-dimensional channel membrane provided by the present invention has a high rejection rate and a high water flux; especially in a solution with a low strontium ion concentration, the rejection rate of the nanofiltration two-dimensional channel membrane in Example 1 can be as high as 99.88%.

[0064] Application Example 2 Use the nanofiltration two-dimensional channel membrane of Example 1 to conduct a rejection experiment on a 10 mg / L strontium ion solution; the specific steps are as follows: Pour the 10 mg / L strontium ion solution into the feed side of the filtration device respectively, use the nanofiltration two-dimensional channel membrane of Example 1 as the filter membrane, conduct suction filtration at a pressure of 0.1 MPa for 5 h, take the filtrate every 0.5 h, and record the time required for the same volume of suction filtration; Repeat the experiment three times, and the obtained results are shown in Table 2 and Figure 5 as follows; Table 2 Record table of water flux and rejection rate of the nanofiltration two-dimensional channel membrane in Example 1

[0065] As can be seen from Table 2 and Figure 5It can be seen that the nanofiltration two-dimensional channel membrane provided by the present invention can still maintain an extremely high rejection rate and water flux for strontium ion solution under long-term retention, indicating the good stability of the nanofiltration two-dimensional channel membrane.

[0066] Application Example 3 The nanofiltration two-dimensional channel membranes of Examples 1 to 4 were respectively used to conduct a retention experiment on a 10 mg / L strontium ion solution; the specific steps are as follows: The 10 mg / L strontium ion solution was respectively poured into the feed side of the filtration device, and the nanofiltration two-dimensional channel membranes of Examples 1 to 4 were respectively used as the filter membranes, and suction filtration was carried out under a pressure of 0.1 MPa, and the time required for suction filtration of the same volume was recorded; The experiment was repeated three times, and the results obtained are shown in Table 3 and Figure 6 as follows; Table 3 Record table of water flux and rejection rate of nanofiltration two-dimensional channel membranes of Examples 1 to 4

[0067] It can be seen from Table 3 and Figure 6 that the nanofiltration two-dimensional channel membrane provided by the present invention has a high rejection rate and high water flux; and as the loading amount of exfoliated graphene oxide and zirconium phosphate increases, the rejection rate of the nanofiltration two-dimensional channel membrane also increases, and the highest can reach 99.99%, having excellent strontium rejection rate.

[0068] Application Example 4 The nanofiltration two-dimensional channel membranes of Examples 1 and 5 to 8 were respectively used to conduct a retention experiment on a 10 mg / L strontium ion solution; the specific steps are as follows: The 10 mg / L strontium ion solution was respectively poured into the feed side of the filtration device, and the nanofiltration two-dimensional channel membranes of Examples 1 and 5 to 8 were respectively used as the filter membranes, and suction filtration was carried out under a pressure of 0.1 MPa, and the time required for suction filtration of the same volume was recorded; The experiment was repeated three times, and the results obtained are shown in Table 4 and Figure 7 as follows; Table 4 Record table of water flux and rejection rate of nanofiltration two-dimensional channel membranes of Examples 1 and 5 to 8

[0069] It can be seen from Table 4 and Figure 7 that changing the dosage of phosphoric acid will affect the formation of zirconium phosphate and the performance of the membrane material by affecting its complexation with zirconium ions; the nanofiltration two-dimensional channel membrane provided by the present invention has a high rejection rate and high water flux.

[0070] Comparative Application Example 1 Perform a retention experiment on a 10 mg / L strontium ion solution using a commercially available graphene oxide solution membrane, zirconium phosphate, and the nanofiltration two-dimensional channel membrane of Example 1. The specific steps are as follows: Pour the 10 mg / L strontium ion solution into the feed side of the filtration device respectively. Use the commercially available graphene oxide solution membrane, zirconium phosphate, and the nanofiltration two-dimensional channel membrane of Example 1 as the filter membranes respectively. Perform suction filtration under a pressure of 0.1 MPa, and record the time required for the same volume of suction filtration. Repeat the experiment three times, and the results obtained are shown in Table 5 and Figure 8 as follows; Table 5 Record table of water flux and retention rate of the nanofiltration two-dimensional channel membranes of Example 1, commercially available graphene oxide solution membrane, and zirconium phosphate

[0071] As can be seen from Table 5 and Figure 8 it can be seen that the nanofiltration two-dimensional channel membrane provided by the present invention has excellent performance in terms of water flux and retention rate.

[0072] In summary, the nanofiltration two-dimensional channel membrane provided by the present invention has a high retention rate and a high water flux, and the membrane material has stable performance and can fully retain strontium ions in water.

[0073] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A nanofiltration two-dimensional channel membrane, characterized in that: It comprises a base film and digested graphene oxide and zirconium phosphate loaded on the base film; the base film is a cellulose film; The decomposed graphene oxide has an ordered layered structure with sub-nanometer-sized channels; the zirconium phosphate is distributed in the sub-nanometer-sized channels of the decomposed graphene oxide; The total loading amount of the digested graphene oxide and zirconium phosphate is 1-5 mg / cm 2 .

2. The nanofiltration two-dimensional channel membrane according to claim 1, characterized in that: The total loading amount of the digested graphene oxide and zirconium phosphate is 2-3 mg / cm 2 .

3. The method for preparing the nanofiltration two-dimensional channel membrane according to claim 1 or 2, characterized in that: The following steps are involved: (1) mixing graphene oxide, nitric acid and hydrofluoric acid with water and performing a digestion reaction to obtain a digested graphene oxide suspension; (2) mixing the degraded graphene oxide suspension obtained in step (1) with zirconium oxychloride for adsorption to obtain a zirconium oxychloride-degraded graphene oxide suspension; (3) mixing the zirconium oxychloride-digested graphene oxide suspension obtained in step (2) with hydrofluoric acid and phosphoric acid, and performing a cross-linking reaction to obtain a zirconium phosphate-digested graphene oxide suspension; (4) Forming a film of the zirconium phosphate-digested graphene oxide suspension obtained in step (3) on a substrate membrane to obtain a nanofiltration two-dimensional channel membrane.

4. The preparation method according to claim 3, characterized in that: In the step (1), the ratio of the mass of graphene oxide, the volume of nitric acid and the volume of hydrofluoric acid is 1 mg:(0.01-0.02) mL:(0.1-0.2) mL; the concentration of graphene oxide in the mixed solution of graphene oxide, nitric acid, hydrofluoric acid and water is 5-6 mg / mL; the mass concentration of nitric acid is 65-68%; and the mass concentration of hydrofluoric acid is 35-40%.

5. The preparation method according to claim 3, characterized in that: The temperature of the digestion reaction in step (1) is 145-165° C., and the time of the digestion reaction is 2-4 hours.

6. The preparation method according to claim 3, characterized in that: The mass ratio of the digested graphene oxide to the zirconium oxychloride in the digested graphene oxide suspension in step (2) is (10-30):(3000-3500).

7. The preparation method according to claim 3, characterized in that: The adsorption temperature in step (2) is 75-85° C., and the adsorption time is 0.5-1.2 h.

8. The preparation method according to claim 3, characterized in that: The volume ratio of hydrofluoric acid and phosphoric acid in step (3) to the graphene oxide digestion suspension in step (2) is (1-3):(0.2-1.5):(10-30); the mass concentration of the hydrofluoric acid is 35-40%; the mass concentration of the phosphoric acid is ≥85%.

9. The preparation method according to claim 3, characterized in that: The temperature of the cross-linking reaction in step (3) is 75-85° C., and the time of the cross-linking reaction is 0.5-1 h.

10. Use of the nanofiltration two-dimensional channel membrane according to claim 1 or 2 or the nanofiltration two-dimensional channel membrane obtained by the preparation method according to any one of claims 3 to 9 in removing strontium ions from water.

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