A nanofiltration two-dimensional channel membrane, its preparation method and application

Abstract

The present invention provides a nanofiltration two-dimensional channel membrane, a preparation method and an application thereof, belonging to the technical field of membrane separation. The nanofiltration two-dimensional channel membrane provided by the present invention comprises 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 exfoliated graphene oxide in the nanofiltration two-dimensional channel membrane provided by the present invention can interact with strontium ions and provide a water flow channel, effectively improving the rejection rate and water flux. At the same time, zirconium phosphate further improves the rejection rate of strontium ions by virtue of its excellent adsorption performance. The results of the examples show that the nanofiltration two-dimensional channel membrane provided by the present invention can have a rejection rate of strontium ions as high as 100% and a water flux as high as 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 radioactive wastewater treatment methods include chemical precipitation, membrane filtration, ion exchange, adsorption, etc. 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 production, and the sludge needs to be further treated; the use of ion exchange to treat sewage will use ion exchange resin, and its regeneration requires the participation of chemical reagents, which will cause irreparable secondary pollution; the use of 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:

[0005] 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;

[0006] 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;

[0007] The total loading amount of the exfoliated graphene oxide and zirconium phosphate is 1-5mg / cm 2 .

[0008] Preferably, the total loading amount of the exfoliated graphene oxide and zirconium phosphate is 2-3mg / cm 2 .

[0009] 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:

[0010] (1) Mix graphene oxide, nitric acid, hydrofluoric acid with water and carry out a digestion reaction to obtain a digested graphene oxide suspension;

[0011] (2) Mix the digested graphene oxide suspension obtained in the step (1) with zirconium oxychloride for adsorption to obtain a zirconium oxychloride-digested graphene oxide suspension;

[0012] (3) Mix the zirconium oxychloride-digested graphene oxide suspension obtained in the step (2) with hydrofluoric acid and phosphoric acid and carry out a crosslinking reaction to obtain a zirconium phosphate-digested graphene oxide suspension;

[0013] (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.

[0014] Preferably, in the 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%.

[0015] Preferably, in the step (1), the temperature of the digestion reaction is 145 - 165 °C and the time of the digestion reaction is 2 - 4 h.

[0016] Preferably, in the step (2), the mass ratio of digested graphene oxide to zirconium oxychloride in the digested graphene oxide suspension is (10 - 30):(3000 - 3500).

[0017] Preferably, in the step (2), the temperature of the adsorption is 75 - 85 °C and the time of the adsorption is 0.5 - 1.2 h.

[0018] Preferably, in the step (3), the volume ratio of hydrofluoric acid and phosphoric acid to the digested graphene oxide suspension in the 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 ≥ 85%.

[0019] Preferably, in the step (3), the temperature of the crosslinking reaction is 75 - 85 °C and the time of the crosslinking reaction is 0.5 - 1 h.

[0020] 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.

[0021] 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 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 undergo cation-π interaction and electrostatic interaction with strontium ions in water, achieving the interception of strontium ions and effectively improving the interception rate; moreover, the two-dimensional channels formed by this layered structure enable water molecules to pass through smoothly, effectively increasing 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, a charge repulsion effect can be generated on the 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 up to 100% for strontium ions and a water flux of up to 780.14 L·m -2 ·h -1 ·bar -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 SEM image of the surface of the nanofiltration two-dimensional channel membrane of Example 1;

[0023] Figure 2 SEM image of the cross-section of the nanofiltration two-dimensional channel membrane of Example 1;

[0024] Figure 3 XRD pattern of the nanofiltration two-dimensional channel membrane of Example 1;

[0025] Figure 4 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;

[0026] Figure 5 Bar chart of the interception rate and water flux of the nanofiltration two-dimensional channel membrane of Example 1 used for different times;

[0027] Figure 6 Bar chart of the interception rate and water flux of the nanofiltration two-dimensional channel membranes of Examples 1-4;

[0028] Figure 7 Bar chart of the interception rate and water flux of the nanofiltration two-dimensional channel membranes of Example 1 and Examples 5-8;

[0029] Figure 8 Bar graph of the rejection rate and water flux of the nanofiltration two-dimensional channel membrane of Example 1, the commercially available graphene oxide solution membrane, and zirconium phosphate. Detailed implementation mode

[0030] 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;

[0031] 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;

[0032] The total loading amount of the exfoliated graphene oxide and zirconium phosphate is 1-5 mg / cm 2 .

[0033] As an implementation mode 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.

[0034] As an implementation mode 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 the two are fully exerted, and the rejection rate is further improved.

[0035] 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 enable 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.

[0036] The present invention also provides a preparation method of the nanofiltration two-dimensional channel membrane described in the above technical solution, including the following steps:

[0037] (1) Mix graphene oxide, nitric acid, hydrofluoric acid and water, and then carry out a digestion reaction to obtain an exfoliated graphene oxide suspension;

[0038] (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;

[0039] (3) Mix the zirconium oxychloride-digested graphene oxide suspension obtained in step (2) with hydrofluoric acid and phosphoric acid, and then carry out a cross-linking reaction to obtain a zirconium phosphate-digested graphene oxide suspension;

[0040] (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.

[0041] 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.

[0042] As an embodiment of the present invention, the graphene oxide may be graphene oxide prepared by the improved Hummer method.

[0043] 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 may be 900-1200 rpm, or 950-1150 rpm, or 1000-1100 rpm; the stirring time may be 10-20 min, or 12-18 min, or 15-16 min; the power of the ultrasonic treatment may be 20-40 KHz, or 25-35 KHz, or 28-30 KHz; the time of the ultrasonic treatment may be 10-20 min, or 12-18 min, or 15-16 min. In the present invention, by limiting the process parameters of stirring and ultrasonic treatment, the reaction raw materials are ensured to be mixed evenly.

[0044] 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 may 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 may 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 may be 65-68%, or 66-67%; the mass concentration of the hydrofluoric acid may be 35-40%, or 36-39%, or 37-38%. In the present invention, by limiting the amounts and concentrations of the reaction raw materials, the reaction raw materials are fully contacted and reacted to ensure the obtained digested graphene oxide suspension.

[0045] 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 limiting the process parameters of the digestion reaction, sufficient reaction between the reaction raw materials is achieved.

[0046] As an embodiment of the present invention, after the digestion reaction, centrifugation, washing and resuspension can be carried out in sequence.

[0047] 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.

[0048] 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.

[0049] 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 enough digested graphene oxide in the obtained suspension for subsequent reactions.

[0050] 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.

[0051] 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, sufficient contact reaction between the reaction raw materials is ensured.

[0052] 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 exfoliated graphene oxide; by defining the process parameters of the adsorption process, the full adsorption of zirconium oxychloride is ensured.

[0053] 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.

[0054] 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 2.6 - 2.7%; the volume ratio of the dilute ammonia water to the exfoliated graphene oxide suspension can be (0.2 - 4):20, or (0.5 - 3):20, or (1 - 2):20. In the present invention, by adding dilute ammonia water during the adsorption process, the full dispersion of the exfoliated graphene oxide can be achieved, which is beneficial to the full contact between the exfoliated graphene oxide and zirconium oxychloride.

[0055] 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.

[0056] As an embodiment of the present invention, the volume ratio of the hydrofluoric acid, phosphoric acid to the exfoliated graphene oxide suspension can be (1 - 3):(0.2 - 1.5):(10 - 30), or (1.5 - 2.8):(0.5 - 1.2):(15 - 28), or (2 - 2.5):(0.8 - 1):(20 - 25); the mass concentration of the hydrofluoric acid can be 35 - 40%, or 36 - 39%, or 37 - 38%; the mass concentration of the phosphoric acid can be ≥85%, or ≥87%, or ≥90%. In the present invention, by defining 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.

[0057] As an embodiment of the present invention, the temperature of the cross - linking reaction can be 75 - 85°C, or 76 - 82°C, or 78 - 80°C; the time of the cross - linking reaction can be 0.5 - 1 h, or 0.6 - 0.9 h, or 0.7 - 0.8 h. In the present invention, hydrofluoric acid can make F - react with Zr 4+Form zirconium fluoride complex ions, reducing the concentration of zirconium ions in the solution and avoiding Zr 4+ Form a precipitate with inactive solids to control the formation rate of zirconium phosphate in the system and achieve the formation of zirconium phosphate; at the same time, cross-link with the digested graphene oxide to form new two-dimensional channels; by controlling the process parameters of the cross-linking reaction, further control the progress of the reaction.

[0058] As an embodiment of the present invention, stirring can be carried out during the cross-linking reaction; the present invention has no special limitation on the operation of the stirring, and the stirring commonly used by those skilled in the art can be adopted.

[0059] As an embodiment of the present invention, centrifugation and resuspension can be carried out in sequence after the cross-linking reaction to obtain a zirconium phosphate-digested graphene oxide suspension.

[0060] 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 carrying out 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.

[0061] 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.

[0062] As an embodiment of the present invention, the film-forming method can be pressure filtration or suction filtration; the pressure of the suction filtration can be 0.01 - 0.1 MPa, or 0.02 - 0.08 MPa, or 0.05 - 0.06 MPa. In the present invention, by defining 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.

[0063] 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 2It can also be (2 to 2.5) mL : (11.2 to 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 the digested graphene oxide and zirconium phosphate is ensured, and the rejection rate is further improved.

[0064] 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.

[0065] As an embodiment of the present invention, the film-forming position can be on the side of the small-hole surface of the base membrane. In the present invention, by limiting the film-forming position, the full combination of the base membrane with the digested graphene oxide and zirconium phosphate is realized, and the performance of the nanofiltration two-dimensional channel membrane is further improved.

[0066] The preparation method provided by the present invention realizes the preparation of the digested graphene oxide and zirconium phosphate and the combination of the two with the base membrane, 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.

[0067] 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.

[0068] As an embodiment of the present invention, the concentration of strontium ions in the water can be 0.1 to 200 mg / L, or can also be 1 to 10 mg / L.

[0069] In order to further illustrate the present invention, the following examples are used to describe in detail the nanofiltration two-dimensional channel membrane provided by the present invention, its preparation method and application, but they cannot be understood as limiting the protection scope of the present invention.

[0070] Example 1

[0071] A nanofiltration two-dimensional channel membrane is composed of a commercially available mixed cellulose filter membrane and digested 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 ;

[0072] The digested 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 digested graphene oxide;

[0073] The total loading amount of the digested graphene oxide and zirconium phosphate is 2.12 mg / cm 2 ; wherein the mass ratio of the digested graphene oxide to zirconium phosphate is 1:23;

[0074] The preparation method of the nanofiltration two-dimensional channel membrane is as follows:

[0075] (1) Mix 25 mg of graphene oxide with 20 mL of water, stir for 15 min and then ultrasonicate 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 ultrasonicate 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 redisperse 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.

[0076] The preparation method of graphene oxide is as follows:

[0077] Add 3 g of natural graphite powder, 2.5 g of P2O5, and 2.5 g of K2S2O8 to 12 mL of 98% H2SO4, ultrasonicate at 40 kHz and then stir for 2 h. Filter, vacuum dry the filter cake at 60 °C for 12 h to obtain a pre-oxidized product. Stir the pre-oxidized product with 120 mL of 98% H2SO4 at 5 °C for 6 h, and then add 15 g of KMnO4 to the mixture at 60 °C for oxidation. After oxidation, dilute with 1 L of deionized water and further oxidize the product with 20 mL of H2O2 at 80 °C. Centrifuge and wash the oxidized product with HCl and deionized water, and finally dilute it with deionized water to 1 L to obtain a graphene oxide solution.

[0078] (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 2.8% dilute ammonia water, 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.

[0079] (3) Mix the zirconium oxychloride-digested graphene oxide suspension obtained in step (2) with 2 mL of 40% hydrofluoric acid and 0.3 mL of 85% phosphoric acid, 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 redisperse 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.

[0080] (4) Dilute 3 mL of the zirconium phosphate-digested graphene oxide suspension obtained in step (3) to 42.5 mL, and then dry it to form a film on the side of the small hole surface of a mixed cellulose membrane (pore size 0.2 μm, surface area 1.13×10 -3 m 2 ) under a vacuum of 0.1 MPa to obtain a nanofiltration two-dimensional channel membrane.

[0081] After drying the nanofiltration two-dimensional channel membrane obtained in Example 1 at 60 °C for 12 h, the surface and cross-section of the nanofiltration two-dimensional channel membrane obtained in Example 1 were detected using a scanning electron microscope, and the results are as shown in Figure 1 and Figure 2 . It can be seen from Figure 1 that the surface of the nanofiltration two-dimensional channel membrane is intact, rough, uneven and wrinkled but without large pores or obvious defects; it can be seen from Figure 2 that the membrane is a closely stacked layered structure.

[0082] The dried nanofiltration two-dimensional channel membrane obtained in Example 1 was detected using an X-ray diffractometer, and the results are as shown in Figure 3 . It can be seen from Figure 3 that the interlayer spacing of the membrane is 0.98 nm.

[0083] Example 2

[0084] 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 film, and the loading amount of the digested graphene oxide and zirconium phosphate is 1.06 mg / cm 2 ; other conditions are the same as in Example 1.

[0085] Example 3

[0086] 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 film, and the loading amount of the digested graphene oxide and zirconium phosphate is 3.17 mg / cm 2 ; the mass ratio of the digested graphene oxide to zirconium phosphate is 1.5:34.5, and other conditions are the same as in Example 1.

[0087] Example 4

[0088] Example 4 is only different from Example 1 in that in step (4) of the preparation method of the nanofiltration two-dimensional channel membrane, 6 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 amounts of the digested graphene oxide and zirconium phosphate are 4.23 mg / cm 2 ; others are the same as in Example 1.

[0089] Example 5

[0090] Example 5 is only different from Example 1 in 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 digested graphene oxide suspension in step (2) is 2:0.2:20, and the rest is the same as in Example 1.

[0091] Example 6

[0092] Example 6 is only different from Example 1 in 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 digested graphene oxide suspension in step (2) is 2:0.5:20, and the rest is the same as in Example 1.

[0093] Example 7

[0094] Example 7 is only different from Example 1 in 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 digested graphene oxide suspension in step (2) is 2:1.0:20, and the rest is the same as in Example 1.

[0095] Example 8

[0096] Example 8 is only different from Example 1 in 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 digested graphene oxide suspension in step (2) is 2:1.5:20, and the rest is the same as in Example 1.

[0097] Application Example 1

[0098] The nanofiltration two-dimensional channel membrane of Example 1 was used to conduct retention experiments on strontium ion solutions with concentrations of 1 mg / L, 10 mg / L, 50 mg / L, and 200 mg / L respectively; the specific steps are as follows:

[0099] The strontium ion solutions with concentrations of 1 mg / L, 10 mg / L, 50 mg / L, and 200 mg / L were respectively poured into the feed side of the filtration device, and the nanofiltration two-dimensional channel membrane of Example 1 was used as the filter membrane, 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;

[0100] Water flux ( ) calculation formula:

[0101]

[0102] Wherein, A is the effective membrane area (m 2 ), ∆t is the permeation time (h), P is the filtration pressure (bar);

[0103] Collect the filtrate at the terminal 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 strontium ion aqueous solution (denoted as C 1 ), and the activity concentration of strontium ions in the filtrate (denoted as C 2 );

[0104] The calculation formula for the rejection rate of strontium ions ( %) is:

[0105]

[0106] Repeat the experiment three times, and the obtained results are shown in Table 1 and Figure 4 as shown;

[0107] Table 1 Record table of water flux and rejection rate of the nanofiltration two-dimensional channel membrane in Example 1

[0108]

[0109] It can be seen from Table 1 and Figure 4 that 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%.

[0110] Application Example 2

[0111] 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:

[0112] 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, perform 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 suction filtration of the same volume;

[0113] Repeat the experiment three times, and the obtained results are shown in Table 2 and Figure 5 as shown;

[0114] Table 2 Record Table of Water Flux and Retention Rate of Nanofiltration Two-Dimensional Channel Membrane in Example 1

[0115]

[0116] As can be seen from Table 2 and Figure 5 it can be seen that the nanofiltration two-dimensional channel membrane provided by the present invention can still maintain an extremely high retention rate and water flux for strontium ion solution under long-term retention, indicating the good stability of the nanofiltration two-dimensional channel membrane.

[0117] Application Example 3

[0118] 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:

[0119] 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 used as filter membranes respectively, 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;

[0120] The experiment was repeated three times, and the results obtained are shown in Table 3 and Figure 6 as follows;

[0121] Table 3 Record Table of Water Flux and Retention Rate of Nanofiltration Two-Dimensional Channel Membranes of Examples 1 to 4

[0122]

[0123] As can be seen from Table 3 and Figure 6 it can be seen that the nanofiltration two-dimensional channel membrane provided by the present invention has a high retention rate and high water flux; and as the loading amount of exfoliated graphene oxide and zirconium phosphate increases, the retention rate of the nanofiltration two-dimensional channel membrane also increases, and the highest can reach 99.99%, having excellent strontium retention rate.

[0124] Application Example 4

[0125] The nanofiltration two-dimensional channel membranes of Example 1 and Examples 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:

[0126] 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 Example 1 and Examples 5 to 8 were used as filter membranes respectively, 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;

[0127] The experiment was repeated three times, and the results obtained are shown in Table 4 and Figure 7 as follows;

[0128] Table 4 Records of water flux and rejection rate of nanofiltration two-dimensional channel membranes in Example 1 and Examples 5 - 8

[0129]

[0130] As can be seen from Table 4 and Figure 7 it can be seen that changing the dosage of phosphoric acid will affect the formation of zirconium phosphate and the performance of the membrane material by influencing its complexation with zirconium ions; the nanofiltration two-dimensional channel membrane provided by the present invention has a high rejection rate and a high water flux.

[0131] Comparative Application Example 1

[0132] A retention experiment was carried out 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:

[0133] The 10 mg / L strontium ion solution was respectively poured into the feed side of the filtration device, and a commercially available graphene oxide solution membrane, zirconium phosphate, and the nanofiltration two-dimensional channel membrane of Example 1 were used as 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;

[0134] The experiment was repeated three times, and the results obtained are shown in Table 5 and Figure 8 as follows;

[0135] Table 5 Records of water flux and rejection rate of nanofiltration two-dimensional channel membranes of Example 1, commercially available graphene oxide solution membrane, and zirconium phosphate

[0136]

[0137] 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 both water flux and rejection rate.

[0138] In summary, the nanofiltration two-dimensional channel membrane provided by the present invention has a high rejection rate and a high water flux, and the performance of this membrane material is stable and can fully retain strontium ions in water.

[0139] 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 includes a base membrane and exfoliated graphene oxide and zirconium phosphate loaded on the base membrane; the base 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 ; The method for preparing the nanofiltration two-dimensional channel membrane includes the following steps: (1) Mix graphene oxide, nitric acid, hydrofluoric acid and water, and then 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 then carry out a cross-linking reaction to obtain a zirconium phosphate-exfoliated graphene oxide suspension; (4) Form a film of the zirconium phosphate-exfoliated graphene oxide suspension obtained in step (3) on the base membrane to obtain a nanofiltration two-dimensional channel membrane.

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

3. The preparation method of the nanofiltration two-dimensional channel membrane according to claim 1 or 2, characterized in that, It includes the following steps: (1) Mix graphene oxide, nitric acid, hydrofluoric acid and water, and then 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 then carry out a cross-linking reaction to obtain a zirconium phosphate-exfoliated graphene oxide suspension; (4) Form a film of the zirconium phosphate-exfoliated graphene oxide suspension obtained in step (3) on the base membrane to obtain a nanofiltration two-dimensional channel membrane.

4. The preparation method according to claim 3, characterized in that, In 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 the nitric acid is 65 - 68%; the mass concentration of the hydrofluoric acid is 35 - 40%.

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

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

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

8. The preparation method according to claim 3, characterized in that, In step (3), the volume ratio of hydrofluoric acid and phosphoric acid to the exfoliated 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 ≥ 85%.

9. The preparation method according to claim 3, characterized in that 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.

10. Application 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 - 9 in removing strontium ions from water.

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